Catalysis and Automotive Pollution Control (Studies in Surface Science and Catalysis)

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Studies in Surface Science and Catalysis 30 CATALYSIS AND AUTOMOTIVE POLLUTION CONTROL

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Studies in Surface Science and Catalysis Advisory Editors: B. Delman and J.T. Yates

Vol. 30

CATALYSIS AND AUTOMOTIVE POLLUTION CONTROL Proceedings of the First International Symposium (CAPOC I), Brussels, September 8-11, 1986

Ed itors

A. Crucq and A. Frennet Unite de Recherche sur la Catalyse, Universite libre de Bruxelles, Brussels, Belgium

ELSEVIER

Amsterdam - Oxford - New York - Tokyo 1987

ELSEVIERSCIENCEPUBLISHERS B. V Sara Burgerhartstraat 25 P.O Box 211, 1000 AE Amsterdam, The Netherlands Distriburors for the United States and Canada.

ELSEVIER SCIENCE PUBLISHING COMPANY INC. 52, Vanderbilt Avenue New York, NY 10017, U.S.A.

ISBN 0-444-42778-3 (Vol. 30) ISBN 0-444-41801-6 (Series)

© Elsevier Science Publishers B.V., 1987 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier SCIence Publishers B.V./ Science & Technology Division, P.O. Box 330, 1000 AH Amsterdam, The Netherlands. Special regulations for readers in the USA - This publication has been registered with the Copyright Clearance Center Inc. (CeCL Salem, Massachusetts. Information can be obtained from the cee about conditions under which photocopies of parts of this publication may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred to the copyright owner, Elsevier Science Publishers B.V., unless otherwise specified. Printed in The Netherlands

CONTENTS

- Studies in Surface Science and Catalysis (other volumes in the series)

IX

- Foreword

Xl

- Acknowledgements

XII

- Financial Support

XIII

- List of Participants

XIV

- Scientific Papers General introduction to the problem of exhaust gas pollution - "Effect ofMotor Vehicle Pollutants on Health" , M. Chiron - "AutomotiveTraffic. Risksforthe Environment", R. Impens

11

- "Catalysis in Modern Petroleum Refining", J. Grootjans

31

- "The Point ofView ofthe AutomobileIndustry. Prevention is better than cure", C.Gerryn

39

- "Control ofDiesel Particulate Emissions in Europe", M.P. Walsh

51

- "The Problems involvedin Preparing and Upholding Uniform Exhaust-Gas Standards within the Common Market", H. Henssler

_

- "The Marketfor Car Exhaust Catalysts in Western Europe. A ReviewofTrends and Developments", W. Groenendaal

69

81

General introduction to the role of catalysis in exhaust gas control - "Automobile Catalytic Converters", K.C. Taylor (General lecture) - "Aspects ofAutomotiveCatalyst Preparation, Performance and Durability", BJ. Cooper, W.D.J. Evans and B. Harrison (General lecture)

.. ~ _

--~

97

117

VI

Reaction Mechanisms and Surface States - "Titrations ofCarbon Monoxide and Oxygen on a Platinum on Silica Catalyst", CO. Bennett, L.M. Laporta and M.B. Cutlip _ ~ ~ _ _ _

143

- "The AlF Window with Three-Way Catalyst. Kinetic and Surface Investigations", E.KobersteinandG. Wannemacher _ ~ _ . _ _ _ _ _ _ _ _

155

- "Elemental Steps during the Catalytic Decomposition ofNO over Stepped Single Crystal Surfaces ofPt and Ru", N. Kruse and J.H. Block ~______

173

- "Periodic Operation Effects on AutomotiveNoble Metal Catalysts. Reaction Analysis ofBinary Gas Systems", H. Shinjoh, H. Muraki and Y. Fujitani

187

- "The Role ofResearch in the Development ofNew Generation AutomotiveCatalysts", H.S. Gandhi and M. Shelef (Extended paper) - - - - - - - -

199

- "Mechanisms ofthe Carbon Monoxide Oxidation and Nitric Oxide Reduction Reactions over Single Crystal and Supported Rhodium Catalysts: High Pressure Rates Explained using Ultrahigh Vacuum Surface Science", G.B. Fischer, Se H. Oh, J.E. Carpenter, cr, DiMaggio, SJ. Schmieg, D.W. Goodman, T.W. Root, S.B. Schwartz and L.D. Schmidt (Extended paper) 215 - "Electronic State of Cerium-Based Catalysts Studied by Spectroscopic Methods (XPS, XAS)", F.Le Normand, P.Bemhardt, L.Hilaire, K.Kili, G.Krill and G.Maire - "An AESInvestigation ofthe Reactivity ofPt, Rh and Various Pt-Rh AlloySurfaces towards 02> NO, CO and H 2 " , F.e.M.J. M.Van Delft, G.H. Vurens, M.e. Angevaare-Gruter and B.E. Nieuwenhuys

__ 221

__ 229

- "Reactivity Studies ofAutomobileExhaust Catalysts in Presence ofOxidising or Reducing Conditions", G. Meunier, F. Garin, l.L. Schmitt, G. Maire and R. R o c h e - 243 - "The Effect ofWeight Loading and Reduction Temperature on Rh/Silica Catalysts for NO Reduction by CO", W.e. Hecker and R.B. Breneman

---- 257

- "Reactivation ofLead-Poisoned Pt/ Al20J Catalysts by Sulfur Dioxide", l.W.A. Sachtler, I. Onal and R.E. Marinangeli -- ---- 267

Support - "Alumina Carriers for AutomotivePollution Control", P. Nortier and M. Soustelle (General lecture) _ ~ ~ _

275

VII

- "Advances in AutomotiveCatalysts Supports", John S. Howitt - - -

30 I

- "Structural Consideration with respect to the Thermal Stability ofa New Platinum Supported Lanthanum-Alumina Catalyst", F. Oudet, E. Bordes, P. Courtine, G. Maxant, e. Lambert and J.P. Guerlet--

313

- "Influence ofthe Porous Structure ofAlumina Pellets and the Internal Convective Flow on the Effective DiffusivityofExhaust Gas Catalyst", S. Cheng, A. Zoulalian and J.P. Brunelle

323

- "The Effect ofthe Chemical Nature ofthe Wash-Coat on the Catalytic Performance of co Oxydation Catalysts ofMonolith type", L.B. Larsson, L.O. Lowendahl and J.E. Otterstedt

333

Metal-Support Interaction - "The Promotion of PtlSi02 Catalysts by W03 for the NO-CO Reaction", J.R. Regalbuto and E.E. Wolf

__ - 345

- "Surface Diffusion ofOxygen in RhlAl203 and PtlAl203 Catalysts", H. Abderrahim and D. Duprez ----~--- ---

359

- "Rhodium-Support Interactions in AutomotiveExhaust Catalysts", cz, Wan and J.e. Dettling

369

Base Metal Catalysts - "Development ofa Copper Chromite Catalyst for Carbon Monoxide AutomobileEmission Control", J. Laine, A. Albomoz, J. Brito, O. Carias, G. Castro, F. Severino and D. Valera

387

- "Development ofNon-Noble Metal Catalysts for the Purification of AutomotiveExhaust Gas", Lin Peiyan, Wang Min, Shan Shaochun, Huang Minmin, Rong Jingfang, Yu Shomin, Yang Heng Xiang and Wang Qiwu 395 - "Improving the S02 Resistance ofPerovskite Type Oxidation Catalyst", Li Wan, Huang Qing, Zhang Wan-Jing, Lin Bing-Xiung and Lu Guang-Lie - "Tungsten Carbide and Tungsten-MolybdenumCarbides as AutomobileExhaust Catalysts", L. Leclercq, M. Prigent, F. Daubrege, L. Gengembre and G. Leclercq

- 405

A17

VIII

Practical Studies - "Dynamic Behavior ofAutomotiveThree- Way Emission Control Systems", R. K. Herz (Extended paper) _ _ _ _ _ _ _ _ _ _ _ _ - "Effect ofLead on Vehicle Catalyst Systemsin the European Environment", M. Kilpin, A. Deakin and H.S. Gandhi

~

427

- - 445

- "ALaboratory Methodfor Determining the Activityof Diesel Particulate Combustion Catalysts", R.E. Marinangeli, E.H. Homeier and ES. Molinaro -

457

Fuels and Additives - "Synthesis ofHigher Alcohols on Low-Temperature Methanol Catalysts", G. Fomasari, S. Gusi, T.M.G. La Torretta, E Trifiro' and A. Vaccari - "An AlkeneIsomerization Catalyst for Motor Fuel Synthesis", E.G. Baker and N.J. Clark

469 .

483

IX STUDIES IN SURFACE SCIENCE AND CATALYSIS Advisory Editors: B. Delmon, Unlversite Catholique de Louvain, Louvain-Ia-Neuve, Belgium J.T. Yates, University of Pittsburgh, Pittsburgh, PA, U.S.A. Volume 1

Volume 2

Volume 3

Volume 4

Volume 5

Volume 6

Volume 7

Volume 8 Volume 9

Volume 10

Volume 11

Volume 12

Volume 13 Volume 14

Preparation of Catalysts I. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the First International Symposium held at the Solvay Research Centre, Brussels, October 14-17, 1975 edited by B. Delmon, P.A. Jacobs and G. Poncelet The Control of the Reactivity of Solids. A Critical Survey of the Factors that Influence the Reactivity of Solids, with Special Emphasis on the Control of the Chemical Processes in Relation to Practical Applications by V.V. Boldyrev, M. Bulens and B. Delmon Preparation of Catalysts II. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Second International Symposium, Louvain-Ia-Neuve, September 4-7, 1978 edited by B. Delmon, P. Grange, P. Jacobs and G. Poncelet Growth and Properties of Metal Clusters. Applications to Catalysis and the Photograph ic Process. Proceedings of the 32nd International Meeting of the Societe de Chimie Physique, Villeurbanne, September 24-28, 1979 edited by J. Bourdon Catalysis by Zeolites. Proceedings of an International Symposium organized by the Institut de Recherches sur la Catalyse - CNRS - Villeurbanne and sponsored by the Centre National de la Recherche Scientifique, Ecully (Lyon), September 9-11, 1980 edited by B. Imelik, C. Naccache, Y. Ben Taarit, J.C. Vedrine, G. Coudurier and H. Praliaud Catalyst Deactivation. Proceedings of the International Symposium, Antwerp, October 13-15, 1980 edited by B. Delmon and G.F. Froment New Horizons in Catalysis. Proceedings of the 7th International Congress on Catalysis, Tokyo, June 30-July 4,1980. Parts A and B edited by T. Seiyama and K. Tanabe Catalysis by Supported Complexes by Yu.1. Yermakov, B.N. Kuznetsov and V.A. Zakharov Physics of Solid Surfaces. Proceedings of the Symposium held in Bechyne, September 29-0ctober 3, 1980 edited by M. Laznicka Adsorption at the Gas-5olid and Liquid-5olid Interface. Proceedings of an International Symposium held in Alx-en-Provence, September 21-23, 1981 edited by J. Rouquerol and K.S.W. Sing Metal-Support and Metai·Additive Effects in Catalysis. Proceedings of an International Symposium organized by the Institut de Recherches sur la Catalyse - CNRS Villeurbanne and sponsored by the Centre National de la Recherche Scientifique, Ecully (Lvonl.Beprember 14-16, 1982 edited by B. Imelik, C. Naccache, G. Couduriar, H. Praliaud, P. Meriaudeau, P. Gallezot, G.A. Martin and J.C. Vedrine Metal Microstructures in Zeolites. Preparation - Properties - Applications. Proceedings of a Workshop, Bremen, September 22-24,1982 edited by P.A. Jacobs, N.!. Jaeger, P. Jir(l and G. Schulz·Ekloff Adsorption on Metal Surfaces. An Integrated Approach edited by J. Benard Vibrations at Surfaces. Proceedings of the Third International Conference, Asilomar, CA, September 1-4, 1982 edited by C.R. Brundle and H. Morawitz

x Volume 15 Volume 16

Volume 17

Volume 18

Volume 19

Volume 20

Volume 21

Volume 22 Volume 23 Volume 24

Volume 25

Volume 26

Volume 27 Volume 28

Volume 29 Volume 30

Heterogeneous Catalytic Reactions Involving Molecular Oxygen by G.I. Golodets Preparation of Catalysts III. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Third International Symposium, Louvain-Ia-Neuve, September 6-9, 1982 edited by G. Poncelet, P. Grange and P.A. Jacobs Spillover of Adsorbed Species. Proceedings of the International Symposium, Lyon-Villeurbanne, September 12-16,1983 edited by G.M. Pajonk, S.J. Teichner and J.E. Germain Structure and Reactivity of Modified Zeolites. Proceedings of an International Conference, Prague, July 9-13, 1984 edited by P.A. Jacobs, N.I. Jaeger, P. Jiru, V.B. Kazansky and G. Schulz-Ekloff Catalysis on the Energy Scene. Proceedings of the 9th Canadian Symposium on Catalysis, Quebec, P.Q., September 30-0ctober 3, 1984 edited by S. Kaliaguine and A. Mahay Catalysis by Acids and Bases. Proceedings of an International Symposium organized by the Institut de Recherches sur la Catalyse-CNRS-Villeurbanne and sponsored by the Centre National de la Recherche Scientifique, Villeurbanne (Lyon), September 25-27, 1984 edited by B. Imelik, C. Naccache, G. Coudurier, V. Ben Taarit and J.C. Vedrine Adsorption and Catalysis on Oxide Surfaces. Proceedings of a Symposium, Brunei University, Uxbridge, June 28-29, 1984 edited by M. Che and G.C. Bond Unsteady Processes in Catalytic Reactors by Vu.Sh. Matros Physics of Solid Surfaces 1984 edited by J. Koukal Zeolites: Synthesis, Structure, Technology and Application. Proceedings of the International Symposium, Portoroz-Pcrtorose, September 3-8, 1984 edited by B. Drzaj, S. HoCevar and S. Pejovnik Catalytic Polymerization of OIefins. Proceedings of the International Symposium on Future Aspects of Olefin Polymerization, Tokyo, July 4-6,1985 edited by T. Keii and K. Soga Vibrations at Surfaces 1985. Proceedings of the Fourth International Conference, Bowness-on-Windermere, September 15-19, 1985 edited by D.A. King, N.V. Richardson and S. Holloway Catalvtic Hvdrogenation edited by L. Cerveny New Developments in Zeolite Science and Technology. Proceedings of the 7th International Zeolite Conference, Tokyo, August 17-22, 1986 edited by V. Murakami, A. lijima and J.W. Ward Metal Clusters in Catalysis. edited by B.C. Gates, L. Guczi and H. Knozinger Catalysis and Automotive Pollution Control. Proceedings of the First International Symposium (CAPaC I), Brussels, September 8-11, 1986 edited by A. Crucq and A. Frennet

XI

FOREWORD

In June 1984 the EEC Commission proposed new standards of permissible exhaust gas from motor vehicles to be introduced in Europe; these standards were approved by the Ministers of the Environment one year later. As the control of automotive pollution is at present mainly a catalytic problem, we thought this was a good opportunity to organize an International Symposium on the subject and an organizing committee composed of people engaged in catalytic research in the different Belgian Universities was constituted. As the symposium was the first one to be organized at international level in this otherwise very restricted scientific field, this decision may have initially appeared somewhat risky, but was justified by the success of the four-day symposium, with 177 people attending. Most participants came from the EEe countries, with large delegations from Belgium (33), France (32), West Germany (26), the United Kingdom (16) and the Netherlands (10) but we must note the size of the U.S. (20) and Swedish (10) delegations and the interest shown by people coming from Australia, China, Finland, Hungary, Japan, Switzerland and Venezuela. About 60% of the participants came from industry, mainly from the car and oil industries and catalyst manufacturers. The number of abstracts submitted was not very large (38) but as noted by the Paper Selection Committee and as the reader of the Proceedings will be able to judge for himself, the quality and the scientific interest of the papers presented are exceptional, and this was also true of the discussions following the presentation; unfortunately these discussions are not published. The introduction of the new EEC standards raised some controversy in the industries concerned as well as in public opinion. That is why the organizers chose to devote the first day of the conference to a general introduction to the problem of pollution by exhaust gas. Seven invited lectures were presented and are published in these Proceedings, dealing with the effects of exhaust gas on human health and the environment, with the economical and legislative problems associated with the new EEC standards, and with the points of view of the oil and motor industries. The first day ended with a round table, with the participation of W.D.J. Evans, C. Gerryn, W. Groenendaal, H.Henssler, K. Taylor and M. Walsh; the ensuing general discussion, which is unfortunately not published, was very stimulating. The topics to be dealt with during the catalytic sessions included not only the catalytic converters, but also such problems as specific pollution control of diesel engines, synthesis of adequate fuels, and additives adapted to catalytic converters. Surprisingly, very few papers (3) were submitted and presented on these subjects, whereas 24 papers were devoted to fundamental and applied studies on catalytic converters, support preparation and base metal catalysts. Finally the organizers have been strongly encouraged by many participants to hold a follow-up symposium in a not-too-short delay of 2 to 3 years. We hope the CAPOC II Conference will generate the same interest as CAPOC I, the Proceedings of which are contained in this volume.

XII

ACKNOWLEDGEMENTS The Organizing Committee is greatly indebted to Mr Ducarme, "Ministre de l'Environnement de l'Executif Regional Wallen", for his support and interest to this symposium and who accepted to give the opening address. The organizers also greatly appreciated the cooperation of the members of the organizing committee. In this respect, we are particularly grateful to W. Hecq, E. Cadron, M. Campinne and E. Derouane for the active part they have taken in the organization. The suggestions and advices of A. Derouane, G. Froment, A. Germain, G. Poncelet were very helpful. Special thanks are due to the members of the paper selection committee for their important contribution in selecting the proposed papers with conscientiousness (W.DJ. Evans, G. Leclercq, G. Maire, A. Pentenero, V. Ponec, M. Prigent). The Organizing Committee is indebted to all the authors of the lectures delivered during the introductory session who analyzed various points of view related to the general problem of pollution by motor vehicles exhaust gases : health, environment, economics. It is a pleasure to acknowledge the stimulating action of C. Gerryn as well in the organization of the symposium as in the introductory session. We also are grateful to K. Taylor for her outstanding general introductory lecture on the problem of exhaust catalysts. Special thanks to W.DJ. Evans for his active part in the paper selection committee and the scientific advisory board and who gave a remarkable general lecture on the exhaust catalyst. The Organizing Committee acknowledges the authors who presented papers, the Chairmen and all the participants who made the symposium fruitful. The Organizing Committee wants to associate with these acknowledgements the members of the "Unite de Recherche sur la Catalyse" of the "Universite Libre de Bruxelles" who contributed in various degrees to the success of this symposium: J.-M.Bastin, M.Cogniaux, L.Degols, J.-P.Demiddeleer, P.Moisin, B.Parmentier, G. Thiry, M.-N. Zauwen. We are indebted to the authorities of the "Universite Libre de Bruxelles'' who agreed that this meeting could be held in the facilities of the "Institut de Sociologie". The organizers,

AFRENNET Chairman of the Organizing Committee

ACRUCQ Secretary of the Organizing Committee

XIII

THE ORGANIZING COMMITTEE ACKNOWLEDGES THE FINANCIAL SUPPORT OF :

Minlstere de I'Environnement de l'Executif Regional Wallon Federation BeIge des Industries de l'AutomobiIe et du Cycle (FEBlAC)

Solvay & Cie S.A. Societe Chimique de Belgique Banque Bruxelles Lambert

XIV

LIST OF PARTICIPANTS

A.

FULL CONGRESS Andersson, Lennart

Univ. Chalmers Goteborg Sweden

Andersson, Soren

EKANobelAB Sweden

Ashworth, Richard

T.!. Cheswick Silencers United Kingdom

Baker, RG.

Univ. Flinders Australia

Baresel, D.

Rob. Bosch West Germany

Bauwens, Jean

Cockerill Materials Ind. Belgium

Bennett, C.O.

Univ. Connecticut

U.S.A. Berndt, Malte

Doduco K.G. West Germany

Blanchard, G.

Rhone- Poulenc France

Block, Jochen

Fritz Haber Inst. West Germany

Bordes, Elisabeth

Univ. Compiegne France

Boulhol, Olivier

Ag. Qual. Air France

Boulinguiez (Mrs)

Elf France

Bradt, Willy

Clayton Belgium

Brandt, Gerhard

Ethyl Mineral Additives West Germany

xv Cairns, J.

UKAEA Harwell United Kingdom

Campinne, M.

Ecole Royale Militaire, Brussels Belgium

Chapelet Letourneux, Gilbert

ElfSolaize France

Cheng San


Chiron, Mireille

INRETS France

Colbourne, D.

Shell West Germany

Collette, Herve

FNDP, Namur Belgium

Cooper, Barry 1.

J ohoson Matthey USA

Courtine, Pierre


Crucq, Andre

ULB, Brussels Belgium

Darville

FNDP, Namur Belgium

Davies, MJ.


Deakin, Alan

Ford United Kingdom

Degols,Luc


Delmon, Bernard

UCL, Louvain La Neuve Belgium

Dettling,1.e.

Engelhard USA

XVI

Donnelly, Richard G.

W.R. Grace & Co USA

Douglas. J.M.K.

Johnson Matthey United Kingdom

Doziere, Richard

IFP France

Druart, Guy

Soc. Bel. Gaz Petrole Belgium

Dubas, Henri

Ciba-Geigy Switzerland

Duprez,D.

Univ. Poitiers France

Durand. Daniel

IFP France

Engler

Degussa West Germany

Evans, W.DJ.


Finck, Francois

Univ. L. Pasteur, Strasbourg France

Fisher Galen B.

General Motors USA

Fitch, Frank

Laporte Inorganics United Kingdom

Fitoussi

Rhone Poulenc France

Foster, Al

BP United Kingdom

Fougere

UTAC France

Frennet, Alfred


XVII

Frestad, Arne

EKANobelAB Sweden

Froment, G.

Univ. Gent Belgium

GandhiH.S.

Ford USA

Garin, F.


Garreau

Rhone-Poulenc France

GermainA.

Univ. Liege Belgium

Gerryn, Claude

Ford Belgium

Girard, Philippe

ElfSolaise France

Gonzalez-Velasco, Juan R.

Univ. Pais Vasco Bilbao Spain

Gottberg, Ingemar

Volvo Sweden

Gould David, G.

Ford United Kingdom

Groenendaal, Willem

Strategic Analysis Europe The Netherlands

Grootjans, J.

Labofina Belgium

Haas, Jurgen

Dornier West Germany

Hammer, Hans

Brennstoffchemie West Germany

Harrison, Brian


XVIII

Havil

Univ. Paris 6 France

Hawker, P.N.


Hecker, William C.

Univ. Brigham Young, Provo USA

Hecq, Walter


Hegedus, L. Louis

W.R. Grace & Co USA

Held, Wolfgang

Volkswagen West Germany

Henssler, H.

EEC

Herz, Richard

Univ. California San Diego USA

Hickey, C. (Mrs)

Esso Petroleum United Kingdom

Howitt, John S.

Coming Glass Works USA

Imai, Tamotsu

Signal USA

Impens,R.

Fac. Agronomique, Gembloux Belgium

Ing,Hok

UTAC France

Jacobs, Peter

KUL,Leuven Belgium

Jagel, Kenneth I.

Engelhard USA

Johansen, Keld

Topsee Denmark

XIX

Jourde, Jean-Pierre

Renault France

Joustra, A.H.

Shell The Netherlands

Kaczmarec

Rhone Poulenc France

Kapsteyn, F.

Univ. Amsterdam, The Netherlands

Kilpin, Michael

Ford United Kingdom

Koberstein, E.

Degussa West Germany

Kruger

Hoechst West Germany

Kruse, Norbert

Fritz Haber Institute West Germany

Kuijpers, E.G.M.

VEG The Netherlands

Laine. J.

Inst. Ven. Invest. Cientificas Venezuela

Le Normand, F.


Leclercq, Ginette

Univ. Lille France

Leclercq, Lucien

Univ. Lille France

Lehmann, Ulrich

Condea Chemie West Germany

Lester, George R.

Signal USA

Li Wan (Mrs)

Univ. Beijing China

Lienard, Georges


xx Lin Peyian (Mrs)

Univ. Hefei China

Lowendahl, L.

Univ. Chalmers Goteborg Sweden

Mabilon

IFP France

Maire, G.


Maret, Dominique

Peugeot France

Marinangeli, Richard E.

Signal USA

MarseII, Lars

Saab-Scania AB Sweden

Mathieu, Veronique

FNDP,Namur Belgium

Maxant, Genevieve (Mrs)

Comptoir Lyon Alemand Louyot France

Merian, Ernest

Journalist Chemosphere/IAEACISAGUF Switzerland

Mesters.C,

Shell The Netherlands

Meunier, Guillaume


Moles,P.J.

Magnesium Elektron United Kingdom

Mottier, Michel Henri

Consultant Switzerland

Murphy, Michael

General Motors Eur. Techn. Center G.D. Luxembourg

Naudin, Thierry

Peugeot France

XXI

Niemantsverdriet, J.W.

Fritz Haber Institute West Germany

Nieuwenhuys, B.E.

Univ, Leiden The Netherlands

Nortier, P.

Rhone-Poulenc France

Odenbrand, I.

Univ. Lund Sweden

Otterstedt, I.A.

Univ. Chalmers, Goteborg Sweden

Oudet, Francois

Univ, Compiegne France

Pentenero, Andre

Dniy. Nancy France

Pernicone, Nicolas

Institute G. Donegani Italy

Poncelet, G.

DCL, Louvain La Neuve Belgium

Ponec, V.

Dniy. Leiden The Netherlands

Praliaud, Helene (Mrs)

IRC, Villeurbanne France

Prigent, Michel

IFP France

Questiaux, Daniel

Labofina Belgium

Rinckel, Francis

Peugeot France

Roche.Rene

PSA-ER France

Salanne, Simo

KemiraOy Finland

Schay, Zoltan

Inst. Isotopes, Budapest Hungary

XXII

Schwaller


Seip, Ulrike (Mrs)

MAN West Germany

Senamaud, Jean Michel

Renault France

Shelef, Mordecai

Ford USA

Shinjoh, H.

Toyota Japan

Singoredjo, L.

Univ. Amsterdam, The Netherlands

Skoldheden, Per

Volvo Sweden

Slater, Hawes

AC Spark Plug USA

Smailes, R.


Soustelle, M.

Ecole des Mines, St Etienne France

Sposini, Mario

Ecofuel Italy

Stohr,H.

Grace GmbH West Germany

Tauzin

PSA-ER France

Taylor,

x.c

General Motors USA

Tsuchitani, Kazuo

Shokubai Kagaku Japan

Tuenter,G.

Neth. Energy Res. Found. The Netherlands

Umehara,K.

NGKEurope West Germany

XXIII

B.

Vaccari, Angelo

Univ. Bologna Italy

Van Delft, F.C.MJ.M.

Univ. Leiden The Netherlands

Vandervoort, Philippe

Toyota Motor Corp. Belgium

Virta Pirrko (Mrs)

KemiraOy Finland

Walsh Michael P.

Consultant USA

Wan, C.Z.

Engelhard USA

Weber, Kurt H.

Volvo Sweden

Wolf, Eduardo

Univ. Notre Dame USA

Wolsing, Wilhelm

Engelhard Kali Chemie Autocat. West Germany

Yamazaki Takayuki

Nissan Motor Co Ltd Belgium

Zhao, Jiusheng

Univ. Tianjin China

Zink, Uwe

Coming Keramik West Germany

1ST DAY INTRODUCTORY SESSION ONLY Crate

Volvo Car Corporation Belgium

De Nil, A.

Analis Belgium

Jensen, Bent

CEFIC Belgium

Luck, Lucien

General Motors Continental Belgium

XXIV

Machej

UCL, Louvain-La-Neuve Belgium

MacKinley

EEC

Norcross, Geoffrey

Intern. Prof. Assoc. Envir. Affairs Belgium

Rasson, Andre

Austin Rover Distribution Belgium

WiIlems,H.

Johnson Matthey Belgium

Evans,P.W.

Molycorp SARL France

Yonehara Kiyoshi

Nippon Shokubai Kagaku Co. Japan

Searles R.A

Johnson Matthey Chemicals, Div. Autocatalysts United Kingdom

Maegerlein

Degussa AG Dpt AC/GKA West Germany

Brunoli, Joseph A

Signal Automotive Products Norplex Europa West Germany

Hulsmann

Ford Werke AG. West Germany

Maegerlein

Degussa AG Dpt AC/GKA West Germany

Ogata,Hideo

Mitsubishi Motor Corp. West Germany

Schneider, Dietrich

Ford Werke AG. West Germany

von Salmuth, H.D.

Ford Werke A.G. West Germany

A. Crucq and A. Frennet (Editors), Catalysis and AutomotivePollution Control 1987 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

1

EFFECTS OF MOTOR VEHICLE POLLUTANTS ON HEALTH M.CHIRON INRETS,I09

Av.Salvadn~

Allende BP 75,69b72 BRON Cedex France

INTRODUCTION

The characteristic feature of pollution due to road traffic is its wide sp:eading such that the whole population is affected, including children,

invalids, old people and pregnant women. On the

other hand,the durations

within wide

li~its.

Thus

the

of exposure may

vary

traffic can be continuous

in

some areas and very intermittent in others while the displacement of people can vary to a great extent.

The pollutants can also be prevented from dispersing

because of local configurations or unfavourable weather conditions.

Further-

more it should be noted how certain pollutants can accumulate in the body in the absence of the long periods free from exposure that are required for them to be eliminated and how it is impossible to protect people suffering from some particular sensitivity or illness from the effects of pollution. All this must be borne in mind when considering the effects of motor vehicle pollutants on health. There is also the obvious difference between the evaluation of the effect of a pollutant dispersed in the environment as a whole and one that is dispersed in an industrial area where both the level of pollution and the duration of exposure are known, where the total duration of exposure cannot in any case exceed 45 years and where an individual can be withdrawn from the risk at any time. For pollutants in the form of a gas the dispersion is very rapid for the usual weather conditions and the exposure decreases with distance from the vehicle exhaust systems.

Thus the people exposed to the greatest levels of

pollution are first of all the drivers of the motor vehicles, then those making use of two-wheeled vehicles and finally the pedestrians. Pollutants in the form of particles on the other hand settle very quickly and the level of atmospheric pollution falls very rapidly on moving away from the vehicles.

However the particles land on the ground and in water and can

accordingly find their way into food, this giving rise to pollution at a distance which can even affect people living in country areas. CARBON MONOXIDE This is the pollutant for which the effects on the human organism are the most well understood.

2

The carbon monoxide in the atmosphere originates to a large extent from motor vehicles and is almost completely due to them in the vicinity of streets. In some

very polluted and poorly ventilated areas carbon monoxide

concentrations of 50 to 100 ppm can persist for several hours and the individuals that are obliged to remain in such areas because of their work are exposed to high levels of pollution solely because of motor vehicle traffic. It can be assumed that daily averages of 30 ppm apply for an individual travelling

by

car in town and exceptionally of 80 ppm for someone

standing

at a heavily polluted point (not taking _into account the inside of a tunnel). The action in the human organism is well understood:

the carbon monoxide

replaces the oxygen on attaching itself to the normal haemoglobin.

Thus it

inhibits the normal respiratory function of the haemoglobin which is to transport the oxygen contained in the air to the body tissues. The affinity of carbon monoxide for haemoglobin is 250 times greater than that of oxygen.

A permanent balance is established between the carbon monoxide

in the atmosphere and that in the blood;

there is no accumulation in the

organism and the carbon monoxide is completely rejected on expiring air when the atmospheric concentration is zero.

The speed of attachment or rejection

of the carbon monoxide depends in particular on the level of pulmonary ventilation.

Curves have been produced showing how the concentration of carbon

monoxide in the blood (in terms of the proportion of carboxyhaemoglobin) varies with that in the atmosphere, the duration of

eA~osure

and the pulmonary

ventilation (curves produced on referring to Coburn and Forster's equation). See Ref.l and figures

1

&2

3

The consequences of hypoxia (reduction in the transport of oxygen to the tissues) can be classified into three different categories: a)

For fairly high concentrations of carbon monoxide (greater than 50 ppm)

persisting for several hours, functional but unspecific disorders can be observed, mainly headaches, asthenia, giddiness and nausea. b)

For lower concentrations, of the order of those normally experienced by

town dwellers, the hypoxia can be sufficient to give rise to an hypoxia attack in the case of subjects already suffering from ischaemic arteriopathy.

These

subjects cannot compensate for the reduction in the carriage of oxygen by an increased flow of air. distal region.

Such attacks can occur in the coronary, cerebral or

A critical level of 2.5 per cent of carboxyhaemoglobin has been

established by the W.H.O. for this type of attack, corresponding to a long duration carbon monoxide concentration of about 13 ppm. c)

The third effect, again in the case of low carbon monoxide concentrations,

is to accelerate the formation of atheroma plaques corresponding to a premature ageing of the arteries.

It has not been possible to define a limiting concen-

tration for this effect since the accumulation of cholesterol in the arteries falls when the supply of oxygen is greater than normal.

Thus any increase in

the supply of oxygen is beneficial. NITROGEN OXIDES , OZONE AND OXIDIZING PHOTOCHEMICAL DERIVATIVES The nitrogen

oxides concentrations in towns can amount to about 1 ppm

during peak traffic hours.

Under the action of solar radiation the N02

dissociates into NO and atomic oxygen which gives rise to the formation of ozone 03'

The organic molecules react with the ozone

to form free

radicals which in turn act as a catalyst for the oxidation of the NO and the hydrocarbons.

Thus the irradiated exhaust gases are "biologically more active",

that is to say the total oxidising power is increased as well as the concentration of irritant aldehydes. The nitrogen

oxides

together with the photo-oxidising fog, the action

of which is similar to that of the ozone as the pulmonary aveola are concerned.

,act as irritating agents so far The active surface agent is oxidised

and there is an inflammatory reaction. A certain adaptation of the organism has been observed in the case of short duration exposures. The oxidising agents favour the onset of pulmonary infections and the induction of respiratory allergies. For people in good health, the results of epidemiological studies have indicated that the average concentration of N02 over a 24 hour period should not exceed 0.05 ppm.

.... HbC a

.s f t t Lng

b ,walking c ,working

50 ppn

- - - -0.08

~

~---===

0.06

-

'-------~

---

'- ...

~ "W"

0.04 10 pf'T1

10

2

FIG.l

HbeO-for a

male,versus

athmos~heric

pulmonary ventilation. (Ref. 2)

CO,duration

of exposure,

11

12

t

(hours)

co

HbCO

ppm

v..

tue

r 80

- -,

wed

- -

o thu

"ri

sat

I - - I - - I -- I

ambientCO

sun

mon

I

\: ~~~p

o.

smoker 70

60

50

40

FIG. 2 : HbCO for a saleswoman,frolll actual CO contents on her workplace (Ref.2)

0'

6

It should be noted however that in the case of more sensitive individuals, particularly those suffering of asUuna,this value is to high bu t there is a lack of data foY' the establishment of a more suitable value .

The peak concentrations, given the results of studies for this type of pollution, should amount to 0.25 ppm of ':02 two to three times a week for a period of one hour. HYIJROCARBONS

A large number of hydrocarbon compounds are emitted by the vehicles either as a result of a simple evaporation before combustion or of an incomplete combustion Some studies have been concerned with particular elements or a group of compounds and others with the petrol vapour as a whole. In all cases the studies have revealed evidence of mutagenic or carcinogenic action, eii::her on bacteria,on cell cultures or on living animals The responsible products are mainly benzene and its homologues and the aromatic polycyclic hydrocarbons. For the amounts encountered in the environment it is impossible to quantify the effects of the different carcinogenic agents that are present. The limiting exposure is often expressed in the f'o rm of a maximum amount that may be inhaled during a lifetime, as in the case of radiation.

This

amount is then converted to a maximum acceptable concentration. For example, the maximum amount of a-B.P. (a-Benzo Pyrene) that may be inhaled is 12 to 16 rug corresponding to a maximum acceptable concentration of O.1 5/, g/ m3.

Of the different aromatic hydrocarbons a-B.P. has been the subject of most

studies but is not the most carcinogenic. It should be noted however that the subject of chemical carcinogenesis is

still not well understood and there are multiple interactions between the different pollutants whether they

are of

alimentary, domestic or environ-

mental nature. Just as the combined effects of alcohol and tobacco are much greater than the sum of their individual effects,

it is likely that there are a number of

interactions between carcinogenic chemicals. Thus it does not make much sense to establish limiting values for each chemical given the fact that they have a combined effect. It should also be pointed out here that significant inhalations of hydrocarbons are possible in the vicinity of petrol filling stations.

7 DIESEL EXHAUST PARTICLES These particles when viewed under an electron microscope are in the form of clusters of smaller round sub-particles formed during combustion that subsequently have sticked together. The average diameter of the particles lies between 0.2 to 0.3 microns. They each have a nucleus of pratically pure carbon surrounded by adsorbed hydrocarbons. The particles, due to their small diameter, penetrate deep into the lungs as far as the alveoli. Some 80 per cent of the inhaled particles are retained in the lungs for long, almost indefinite, periods of time. Thus the lungs fill up with "dust". The diesel exhaust particles, as well as the hydrocarbons that are extracted from them, have a mutagenic effect in the laboratory but it has not been possible to quantify this effect as a result of epidemiological studies.

HEAVY METALS (excluding lead) Motor vehicles emit a number of metals: chromium, manganese, barium, vanadium,

iron,

aluminium,

cadmium,

nickel,aso.

However it is difficult to determine the contribution of the motor vehicles to this type of pollution. Many of these metals are toxic as it has been recognised in industrial medicine. In particular cadmium, nickel and chromium are carcinogenic while manganese is toxic so far as the nervous system is concerned. However it is

unlikely that any of these elements have any detec-

table effect when considered separately.

LEAD Lead pollution so far as man is concerned is of purely artificial origin. Lead additives pollute the atmosphere, the ground, water, vegetatim and finally animals and msn. In the vicinity of roads the pollutim, extends for sane hundred of meters. Beymd that distance, the levels are 10 to 30 times less than the levels in urban areas but are nevertheless still mainly due to the transfer over short or long distances of pollutants due to the motor vehicles. The fact that additives are responsible for most of the lead cmtent in the air, in dust and even in most of our food has allowed to estimate, as a result of a study of the intake by the mrren organism, that at least fJJ per cent of the lead in the body comes fran lead alkyls. Other food or food related sources (timed foods, capsules, filters, water pipes) playa much less important role than is generally believed. In areas where the traffic is important the contribution of the motor vehicle can account for

8

80 per cent of the lead in the human body. Lead, at the observed levels of exposure is acting on the proto-

porphyrin of the red corpuscles, whose increase in number is an indication of a restriction on the synthesis of haemoglobin.

Such an increase can be detect-

ed for lead concentrations in the blood as low as about 1 5 ~ g / d l ,

r g/dl or less is considered

a frequently

I

observed value ( a concentration of 35

as

normal)

However this effect, although detectable, cannot be regarded as a pathological one in the absence of any anemia. The most important effect, so far as public health is concerned, is the insidious one on the development of childrens' brains, with particular consequences for their intelligence (in terms of

I~'s)

and behaviour.

It is common for children to ingest lead in a particular way - on raising dirty hands and objects to their mouths likely to be contaminated with high lead content dust in areas where the

traffic is important.

100

90

80

~

70

~

i

'" ~ ~

a......

60

50

40

'" ... ;l:

!c ...

30

~

~

o

20

10

50

60

70

60

90

_

00

=

=

_

VERBAl LO.

fig.1.Cumulative frequency distributions of verbal 10 scores in high and low lead subjects(ref.3)

9

AIJ)EHYIJES These irritate the upper respiratory tracts and eyes.

The aldehyde

content in the exhaust of petrol engined vehicles give rise to concentrations in the atmosphere that are already at the limit established for irritant effects (0.1 ppm). Formaldehyde is classed as a mutagenic substance.

The limiting concen-

tration must accordingly be set very low and this is the emission which is of most concern to the public health specialists when considering the use of alcoholic fuels. ALCOHOLS:

ETHANOL AND METHANOL

Ethanol, when inhaled in the small concentrations in the atmosphere that could arise in the case of the use of partially alcoholised fuels, does not appear to constitute a public health risk. Nethanol on the other hand is very toxic as was recognised quite recently in connection with the adulteration of wines (the ingestion of only a few millilitres can be fatal). lung~

or skin.

Nethanol can penetrate into the organism via the

It accumulates in the body and the maximum acceptable con-

centrations in the absence of periods of non-exposure for the elimination of the poison, is very low (3ppm). The methanol is oxidised within the organism into formaldehyde and then into formic acid and these substances are the real poisons.

Ethanol is destroyed by

the same enzymes thai: a t t.ack the methanol.Thus the presence of ethanol can inhibit the formation of formaldehyde and formic acid and can therefore be regarded as an antidote. Nethanol (and its metabolic waste products) for low rates of exposure can cause irritation and damage to the eyes (optic nerve) while chronic exposure can lead to a permanent decrease in visual acuity. CONCLUSIONS On

considering the possibility of decreasing the emission of pollutants as

a result of catalytic action we can class the substances emitted by motor vehicles into three categories: a)

The concentrations of carbon monoxide, nitrogen monoxide and oxidizing

derivatives are, under normal conditions, at the limit of any detectable effects on health.

An appreciable reduction in the emission of these substances would

result in negligible concentrations for the general public (not counting professional exposures). b)

Lead is not eliminated from the enviTonment nor fTom the human

organism and its insidious action on the development of childrens' brains calls

10

for a cautious approach. Even if lead additives are eliminated, lead will remain in people's blood for a long time, to a large extent as a result of it being already present in the environment and in living beings as a result of previous motor vehicle emissions. c)

In the case of mutagenic or carcinogenic pollutants it is impossible to

establish a safe level of concentration" their combined action. pollution in general.

as we know almost nothing about

Some 80 per cent of cancers have been attributed to

There is probably some cell repairing activity for very

low concentrations but we have no precise knowledge of this.

The best that we

can do in these circumstances is to ensure that the total amount of carcinogenic pollutants in the environment, i.e. of benzene, aromatic polycyclic hydrocarbons, diesel exhaust particles and formaldehyde is kept as low as possible. Coburn R.F. ,Forster R.E.,Kane P.B. ,Considerations of the physiological variables that determine the blood carboxyhemoglobin concentration in man ,J. of clinical invest igat ions: vol 44,11, p , 1899-191 ('-; 1965 2Joumard R.,Chiron M.,Vidon R.,La fixation du monoxyde de carbone sur l'hemoglobine et ses effets sur l'homme,Institut de Recherche des Transports,Bron.France.Oct 1983 3 Needleman B.L.,Leviton L.A.,Bellinger D.,Lead associated intellectual deficit.,New England J.Med.,306:367 ,1982

A. Crucq and A. Frennet (Editors), Catalysis and AutomotivePollution Control 1987 Elsevier Science Puhl-shers B.V., Amsterdam - Printed in The Netherlands

AUTOMOTIVE TRAFFIC Risks for the Environment by R. IMPENS Departernent de Biologie vegetale, Faculte des Sciences Agronomiques de l'Etat, Gemboux (Belgique)

ABSTRACT Automotive traffic generates a lot of air pollutants, some metallic contaminants and causes troubles, not only for the roadside environment but also for the terrestrial and aquatic ecosystems. The exhaust gases of vehicle's engines contain mainly carbon monoxide and dioxide, nitrogen oxides, a few sulfur dioxide, a great number of hydrocarbons, or organic carbon derivates, and some heavy metals particulates. Some of these compounds are directly toxic for living organisms, when they occur in a closed environment such as inside the car, tunnels, subterranean car parks, or rooms; but they are harmless when emitted in open space, when natural diffusion conditions are sufficient to prevent high concentrations in the air. Other emitted gases will interact with oxidants (e.g. 03) to form new labile compounds, which have a high phytotoxic activity at low concentrations (p.A.N.,and photochemical smogs). These oxidants, obtained by photochemical reactions in the atmosphere, may be involved in the widespread dieback and decline of forests in both Europe and North America. The 03 and photooxidants theory, and its influence on acid deposition, will be shortly presented and discussed. Heavy metals contamination of soil, water and plant materials, near highways is well known, and there's a trend to accelerate the reduction of lead addition in the fuels. The vicinity of heavy traffic roads, is a source for important troubles to terrestrial and aquatic ecosystems. Some examples of these will be discussed for their direct or indirect effects on animal, microbiological or plant lifes. The regular use of deicing salts, essentially sodium and calcium chlorides, in winter period, affects the resistance to drought stress of trees and crops, and increases the sensitivity of plants to parasitic diseases. The compaction of soils near the road is involved in anaerobic conditions near the roots of trees, which will be followed by an important dieback. The risks for environment alterations could be prevented and reduced by clean motors, with a drastic reduction of gaseous pollutants. The lead problem will be progressively resolved by the new European standards of lead addition to fuels; but the lead already present in soils will remain a threat for some sensitive crops and forages. A passive protection of roadside contamination could be obtained by green

11

12

screens, containing resistant and rustic shrubs and trees, which will filter the air and act as efficient sinks for dust and heavy metals particles. Due to aerial long distance transport and photochemical reactions, prevention of damages to forests request more attention. The solution is reduced emissions of the precursors of lethal compounds: clean motors are wanted... Other risks for the roadside environment (chlorides, asphyxic conditions, etc.) are not directly involved with air pollutants emissions: disastrous landscape modifications by speedways construction are more fundamental.

1. INTRODUCTION Automotive traffic generates a lot of gaseous air pollutants,.some metallic contaminants, asbestos, and causes troubles not only to the roadside environment but also for the terrestrial and aquatic ecosystems. Three major pollutions emanate from the highway: smog, noise and dust. Effects of noise have ominous portent for the enjoyment of life by the human race, and are already affecting our health. The exhaust gases of vehicle's engines contain mainly carbon monoxide (CO) and dioxide (Cod, nitrogen oxides (NO,), a great number of hydrocarbons (HC), or organic carbonaceous derivates, a few sulphur dioxide, particles and soot (Table 1).

Table 1 Average exhaust gas composition of an Otto test engine Compound

co2 H20 02

NO,

% by Volume

12.8 10.5 1.o

0.5

Compound

co N2 H2 Hydrocarbons

% by Volume

2.3 76.0 0.4 0.1

(in V.D.I. Richtlinic 2282)

The emitted quantities are correlated to the traffic density. Estimations are made with different criteria: the total amount of emitted pollutants (Table 2) or the relative importance of traffic pollution in the global pollution pattern (Table 3).

13

I

Table 2 Estimation of the emissions due to automotive traffic in Belgium (year 1977) Type of fuel

Number of vehicles

Gasoline 3.0 x 106 Diesel 0.5 x 106

co 1 400 43

(CW, NO,

109 11

90 39

SO2

3.8 13.0

Pb++ Br-

1.8 0.9

CI-

0.7

Results given in Id T. (from Hecq and empoux 980)

Table 3 Estimation of the emissions of SO2 and NO, in France (year 1982) Pollutant

Industry 1157 KT (48.7%) 254 KT (19.0%)

Transport 57.5 KT (2.4%) 648.0 KT (52.0%)

Power plants 933.3 240.0

Domestic use

KT 230.1 KT (39.2%) (9.7%) KT 140.0 KT (18.0%) (11.0%)

Results given in 1@T. (or %) - (from CITEPA 1983)

The conditions of these emissions are well known, an important literature is devoted to correlate the pollutions with the type of engine, type of fuel, the speed of the car, the driving cycle, etc. (Sibenuler1972). Other parameters of the pollutions are :

- the type of traffic, and the emissions level of each vehicle - the traffic capacity - the wind velocity - the wind direction - the atmospheric stability - the type of site

- the distance from the source ( J o m r d and Vidon1970). 2. DESCRIPTION OF THE EMITTED POLLUTANTS

Carbon oxides (COX) Carbon monoxide is one of the three most common products of fuel combustion, carbon dioxide and water vapor are the other two. Most of the CO in the atmosphere results from incomplete combustion of carbonaceous materials.

2.1.

14

Carbon monoxide is quite stable in the atomosphere and is probably converted to C02, but the rate of this conversion (not known exactly) is low. Its a poisonous inhalent and no other toxic gaseous air pollutant is found at such relatively high concentrations in the urban atmosphere. Carbon monoxide is dangerous because it has a strong affinity for hemoglobin. The major risks for human or animal health are when CO is emitted in confined or enclosed spaces (inside the car, in tunnels or subterranean car-parks, etc.) where it will accumulate and reach the toxic levels. There are few data on eventual risks for plants. Fluckiger (1979) reports an increase of peroxydase activity and of ethylen synthesis by birches (Betula pendula) growing near highways. An early abscission ofleaves is observed too. Carbon dioxide is a normal component of air, it is an important material for plant life - emitted by all living organisms during the respiration and fixed in photosynthesis by green plants. Normal concentrations in the air are ranging from 300 to 380 ppm. Concentrations, which could be toxic are rarely observed (a volcanic emission, occurred recently in Cameroun, contradicts this optimistic opinion).

2.2.

Nitrogen oxides (NOx) Oxides of nitrogen are an important group of air contaminants, produced during the high temperature combustion of gasoline in the engine. The combustion fixes atmospheric nitrogen to produce first nitrogen monoxide (NO), which will be converted in nitrogen dioxide (N02)' This oxidation is rather rapid at high concentration, the rate is much slower at low concentrations. In sunlight, especially in presence of organic material (hydrocarbons), this conversion is greatly accelerated. By gasoline powered engines, NO x emissions increase with average speed (Pearce, 1986 -Joumard, 1986). The hazards associated with nitrogen oxides are: - a direct noxious effect on the health and well being of people; - a direct phytotoxic effect on plant communities. The measure NO x concentrations in the air, are generally always low, and don't cause plant damages, except when they are associated with other gaseous air pollutants as sulfur dioxide or ozone; - an indirect effect : due to photochemical oxidation of organic material, with an abundant production of toxic compounds.

2.3.

Hydrocarbons An analysis of hydrocarbons and other organic compounds emitted in exhaust gas of a four cylinder otto engine is listed in Table 4 (Becker KH. et al, 1985). The composition of car exhaust and of the organic fraction, is "in the road" condition quite variable and strongly dependant on the mode of driving. Among the substances responsible for photochemical air pollution are

15

insaturated hydrocarbons (faster reactors), saturated hydrocarbons (slower reactors), aromatics and aldehydes. Automobile exhaust is the major source; however hydrocarbons and other organic gases are also expelled during the production, refining and handling of gasoline.

2.4.

Oxidants The general terms "oxidants" and "photochemical air pollutants" include a large number of trace compounds, results of reactions between primary pollutants (NO, N02 and hydrocarbons) under the action of sunlight. Important reaction products (or secondary pollutants) are ozone (03), peroxyacetyl nitrate (p.A.N.), higher oxides of nitrogen, aldehydes and ketones, as well as several gaseous and/or particle-bound inorganic and organic acids. The effects of photochemical pollutants are mainly: - Plant damage: with a definite economic significance, because the damages to crops and forests. Some cultivated species are very susceptible to ozone and P.A.N (ex. tobacco and grape). There is considerable evidence that chronic exposure of a variety of plants to concentrations below these that cause irreversible damage, adversely affects plant growth, and decreases the resistance of plants to climatic stresses and parasitic diseases, and finally induces a progressive dieback. - deterioration of materials: ex. fast cracking of stretched rubber products. - eye irritation and health hazards. - decrease in visibility.

These oxidants could be involved in the forest dieback; this theory will be later discussed.

2.5.

Particles A large number of extremely fine particles are emitted from automobile exhaust systems, with approximately 70 percent in the size range of 0,02 to 0,06 micron. These particles consist of the both inorganic and organic compounds of high molecular weight. The quantity of solid and droplet material produced in the exhaust amounts to a few milligrams per gram of gasoline burned (Rose 1962).

16

Table 4 Volatile organic emissions of an Otto engine (Dulson 1981) Compound

% by m a s of total

Compound

Methane Ethine Ethene Ethane Propene Propane Acetaldehyde n-Butane Butenes Acetonitrilite Acetone Isopentane n-Pentane

7.0 10.9 15.7 1.6 0.2 1.1 0.7 1.8 0.7 1.3 0.9 5.2 1.4

% by mass of total

organic emissions

organic emissions

2-Methylpentane 3-Methylpentane n-Hexane Benzene 2-Methylhexane 3-Ethylpentane n-Heptane Toluene 1,l-Dimethylhexane Ethylbenzene m-, p-Xylene 0-Xylene Trimethylbenzenes

1.1 0.8 1.o 12.7 0.7 0.6 0.4 18.9 0.3 2.1 6.1

1.8 4.0

I

Most gasoline contain lead additives, which provide the antiknock characteristics that are required by present-day high compression engines. The most common additives contain tetra-ethyl lead or tetra-methyl lead together with organic chlorides and bromides. Lead as a pollutant in the air,on plants and in soils has elicited increasing attention during the last twenty years. The dispersion of this heavy metal in the terrestrial and aquatic ecosystems is well known, and the hazards, associated to increasing concentrations of lead in water, crops, forages and soils are well known. Legislative measures (quality standards of fuels) and regulations will progressively prohibit the use of alkyl-lead additions in fuels, and reduce the risks of lead contamination of the food-chain, but there will still remain an important problem of soil, sediments and water contamination by lead. Other heavy metals: Fe, Cu, Cd, Zn and Cr, are emitted by automotive traffic, due to panelbody alterations, tyres, brakes systems etc. Asbestos dusts could be released by brake-linings or clutch facings .

3.

EXAMPLES OF POLLUTIONS DUE TO AUTOMOTIVE TRAFFIC

Gaseous air compounds acting as primary pollutants. In 1974, a National Commission for Environment near Highways was created under leading of Dr E. MANNAERT. The first objectives were to measure air pollution, dust deposition and lead contamination, due to automotive traffic near motorways. The research was performed by our colleagues of the BECEWA (Rijks

3.1.

17

University Gent) in association with our laboratory (Gembloux). Six different sampling sites were choiced along the heavy loaded "OstendBrussels-Liege" highway. The sites differ by the traffic density and the road profile, all of them were in rural areas. Four gaseous air pollutants were measured at increasing distances from the motorway: CO, NO x, light and heavy hydrocarbons. Additional but sporadic measurements of 3-4 benzopyrene were made in only one sampling site (10 Km Wof Brussels). Deposited dusts, and soots were collected too. The results of these researches were published in a confidential report (1. Vandenbossche et al, 1976). As an example, we compare NO x distribution in the air, in flat country - near Gent with an average traffic density of ± 10 000 cars and ± 3 000 lorries during a 7h period (Fig. 1) and near Liege (traffic density ± 3 000 cars, ± 1 100 lorries during the same period) (Fig.2). The major influences on air pollutants dispersion are traffic capacity, wind direction, type of site and the distance from the source.

3.2.

Lead contamination.

A research collaboration between the "Green project" and the Plant Biology Department of Gembloux Faculty started in 1972. The aims of this research were to collect informations about lead emission by exhaust gases of cars, and to survey the fallout of lead particles near highways and prevent any contamination of the food chain. A survey of lead deposition on vegetation gives a lot of information on the level of contamination and on the various factors affecting the dust deposition patterns.

3.2.1.

Techniques

More than 20 sites were located near Belgian highways, in rural areas, some other sites were chosen in Brussels (parks and avenues). During five years, every month (every fortnight during the summer period), samples of soil, grass, tree leaves and vegetables were collected. Ten years ago, we started a programme of sampling (soil and grasses) to survey the efficiency of a windbreak. Vaselinated plates were placed: before, in- and behind windbreaks to follow the deposition of lead particles and dust. After being dried and extracted with a 1/1 HCI03 - HN03 solution, the samples are analysed for their heavy metals content. In all samples. Pb, Zn and Cd are determined by pulse polarography (Delcarte et aI1973) or by flame spectrometric atomic absorption. All the results, in the following tables and figures, are given in p.p.m. (mg/kg dry weight). Our sampling sites are located in a map (see Fig.3). A rural site, chosen far away from any road, serves as a control area, where samples are collected to measure the background levels of the studied heavy metals.

18

ppb

NO x

160

/'

....-

-.

"1\

\

/

140

/

I

120

"",,_

I

/

/

I

100

I

/

/

.......

~_-~\

''',,,

'"

1\ \, \ \

/

/ /.-'-'~.

..........

~.

195°C

64.0 - 80.0 29.0 - 17.0 6.6. - 2.5 0.3 - 0.5

G 2 E 70 E 23 E 5

ipecific Gravity d c

0.71 - 0.74

0.74 - 0.75

[ON dON

89.0 - 94.0 78.0 - 80.0

96.3 - 97.3 81.0- 81.5

36

In a second processing step, the depropanized effluent of the zeolitic conversion is etherified with methanol on a cationic resin. Table 2 summarizes the global material balances, and again gives the comparison with the phosphoric acid process.

Table 2 : Overall material balances after etherification

Labofina combination process wt %

vol%

Phosphoric acid on Kieselguhr wt%

vol%

IN: I + N-Butane N-Bu tenes Methanol Total

50.0 50.0 4.3

50.0 50.0 3.2

50.0 50.0

50.0 50.0

104.3

103.2

100.0

100.0

OUT Light ends Propylene I + N-Butane N-Butenes MTBE TAME Heavy ethers Olefinic gasoline Total

0.9 8.3 50.0 5.0

50.0 5.0

50.0 5.0

2.0 2.3 30.3

9.6 50.0 5.0 4.4 1.6 1.9 24.4

45.0

36.1

104.3

96.9

100.0

91.1

5.5

Table 3 gives the analysis of the final etherified gasoline. Emphasis is given on the blend octane numbers since these reflect how this component will perform in the gasoline pool. For a complex refinery with alkylation and a phosphoric acid oligomerization process, the linear programming simulation selects the combination process while shutting down the phosphoric acid oligomerization unit. The alkylation remains at full capacity.


.\. Cruce and A. Fren net (Editors), Catalysis and AutomotivePollution Control 1987 Elsevier Science Publishers B.Y., Amsterdam - Printed in The Netherlands

THE POINT OF VIEW OF THE AUTOMOBILE INDUSTRY Prevention is better than cure by Claude GERRYN

FORD of Europe Inc, 2 Boulevard de la Woluwe, 1150 Brussels, Belgium,

ABSTRACT Emphasizing on the fact that prevention is better than cure, it is shown that the development of engines such as the lean bum engine, that produce only low levels of polluting gases and thus requires only simple oxidation catalytic converters or even no catalytic converter at all, appears much more promising, from an economical viewpoint - lower buying price, cheaper maintenance, lower fuel consumption-, than the complex technology of the 3-way catalytic converters. The new EEC standards are criticized because their introduction in a too short delay gives at best a half hearted support to- and at worse results in a slowing down of- the development, still under way, of the lean bum technology. Finally attention is also drawn on the fact that the use of 3-way catalytic converters may result in substituting some forms of pollution by others not necessarily less harmful: examples of such substitution are given.

THANK YOU and good afternoon Mr President, Ladies and Gentlemen! Let me first tell you how honoured and pleased I am to be with you today: - honoured to have the privilege of addressing such a select group of experts and decision-makers - pleased to be able to present our views on a topic of such pressing importance to us all. After reading the impressive list of outstanding papers and knowing most authors present, prepared to share their expertise with us, I am sure a better understanding of the differences and disagreements on this -international debate will evolve at the end of this symposium: and I wish, therefore, to thank and congratulate the Universite Libre de Bruxelles for taking this initiative.

:39

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Let me quote our Vice-Chairman Walter Hayes in his key-note speech during the FIA Round Table in Bournemouth in May this year: and I quote "It would seem to me that anybody who does not want a strong economy, a safe and clean environment and the most efficient possible use of national and international resources is a very strange person indeed. Anybody who does not want sweeter engines, better roads, safer cars, more responsible drivers and happy owners is not really operating on all his mental cylinders." Unquote

However, there is no doubt that a large part of the increasing pressure for action to protect the environment has come about as a result of increasing public awareness of the issues, but unfortunately this is not always based on real facts or it clear understanding of the problem. Public opinion is being more effectively marshalled by pressure groups and this trend is not lost on the politicians. This results all too often in action whose primary function appears to be to satisfy the political need, to be seen to be "doing something". Realistic evaluation and assessment of the potential effectiveness of the "something" and of its benefit is rarely feasible before implementation, and resulting benefits are difficult to identify. It is accepted that governments have an obligation to serve broad national and international needs on complex environmental matters and act as clearing houses for ideas and programmes. Business, for its part, commands managerial and organisational abilities and can mobilise the scientific and technological resources required to solve these problems. It is imperative that these two great segments of society should rest on a firm foundation of knowledge and understanding, especially in the field of "public problem solving". Realism, without any sign of false sentimentality, should be the base for action and it is not so much what can be done which should determine the route to follow but what needs to be done, with the reasons why and when. We do recognise the international dimension of many environmental problems but these .have to be tackled by coordinated action - bilateral as well as multilateral - between industry, governments and their respective international representative bodies, organisations and the public concerned. We are indeed committed to conducting our operations in an environmentally sound manner and to reducing - as far as technically feasible - any undesirable effect of our products on the environment, but at the same time we have to fulfill the imperative of economic growth and have to produce commercially viable motor vehicles. We too are breathing in this world, want to optimise the use of scarce resources, want environmentally favourable energy options. Our professional burden does not immunise us from undesirable effects but... it does tend to sharpen our perceptions and make us more acutely aware if

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compared with our other social partners of the balance of advantages/disadvantages that must be weighed in order to be clear on the value to society of any given control measure. This concern is unfortunately often misinterpreted as obstructiveness. Allow me to remind you briefly of the six commanding ground rules which seem necessary to me to realise within our society sensibly-balanced environmental progress: * First, governments, in a national or international context, should carefully assess, before developing and implementing environmental policies, the need for such policies, the potential methods of achievement, and their impact on industry. * Second, due to the wide range and complexity of problems raised by environmental protection measures, the closest possible contact and consultation between industry and government should be sought. * Third, any environmental protection measures envisaged must be technically sound and economically acceptable, reviewed in a framework of global approach and where at least safety and energy-use are topics to be included in the global appreciation. * Fourth, care must also be taken to avoid substituting one form of pollution for another. * Fifth, the costs of control requirements, with the resulting benefit to the environment, must be part of the decision-making process. These costs, whether absorbed in the first place by the state or by industry itself, must ultimately be borne by the taxpayer or the consumer, i.e. the general public. * Sixth, especially in the case of motor vehicles, to avoid distortion of trade and to enable cost-effective solutions to be found, exhaust emission legislation in Europe should be, if not totally harmonised, at least accepted by all West European governments, including those who are not EC members. However, this cannot mean a global-worldwide-conformity of environmental pollution limits, since each case has to be judged on its own merits, in its own geographical context, within its road infrastructure, existing town-planning and layout, attitude of the population and their pattern of behaviour. Having said this, and to enable us to examine one of the key questions to the motor industry, namely the political dimension and commercial consideration given to the environmental pollution issue in Europe, we should review step by step in how far the basic ground rules have been respected: In view of the combined "political/emotional" dimension in this instance, it is superfluous to dwell on the assessment of need or the government/industry consultation aspects (the two first commanding ground rules). Whereas the EEC Commission for example can be praised for its effort in seeking through its ERGA Committee a common Europe-wide compromise which is technically and economically feasible, individual national governments have, unfortunately, for political considerations or other reasons - such as prospects for additional employment - diluted the effort available for the exploration of those needs and the means to meet them. The ongoing dialogue between industry and government

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is thereby diminished. It was only on June 27/28, 1985 - after about two years of uncoordinated tugof-war - that an agreement could be formulated by the EC Council of Environmental Ministers - with the exception of Denmark - on the basis of an EC Commission proposal specifying the exhaust emission levels and the introduction dates. Though tough, we were lad that a compromise appeared to have been reached, avoiding a division of the common automobile market. However, the continuing reservation more than one year later, of its position by Denmark and the apparent unwillingness so far of Sweden, Switzerland and Austria to recognise the EC proposal - be it only as an alternative to their national legislation - is a cause for concern. Now what compromise is in our view technically sound and economically acceptable? The third commanding rule: In general, requirements must be so framed that they do not prevent innovation; they must not present unrealistic or arbitrary standards. It must be borne in mind that however necessary the control of motor vehicle emissions and noise may be - and no one would deny the necessity - there are other considerations, such as safety, cost, reliability, which also have to be balanced. There are many major legislative requirements affecting the vehicle, and none of these can be handled in total isolation - all have some interaction on the others, there is a "knock-on" effect, so that a "solution" in one area raises a new task in another. Furthermore, there is a balance to be struck between what can be done and how soon it can be done. The greater the pressure on the technical resources, the higher the cost of meeting the requirements. Inevitably, if too much of a manufacturer's engineering capacity is applied to one objective, other perhaps equally desirable objectives may have to be abandoned, or at least postponed. The constraints defining vehicle design are three-fold: - legislative constraints, or what we must do - market demands, what we would like to do - resource constraints, what we are able to do. Regulation on health/safety, construction and use, trade and economic policy, taxation preferences, all come under the general heading of government policy, part of the legislative constraints. Economic factors, styling preferences, pricing, running and maintenance costs, performance, comfort, reliability, durability, quality at large, are key to customer satisfaction, the market demand. Enginnering and manufacturing resources, research and product development, technological development, skilled manpower, production cost and profitability, are some of the indispensable logistics to be looked at in the context of

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resource constraints. All in all, a tremendous job before a final decision can be reached on any new vehicle design. Due to the many different disciplines involved: design, testing, tooling, finance, manufacturing, homologation and marketing, the gestation period for a major new design - engine or vehicle - is some sixty months.

Please allow me for a few minutes to focus on engineering or, to be more precise, on the present technological developments available for immediate application: If we analyse the means to control exhaust emissions, there are two apparent basic ways in which pollution caused by motor vehicles can be further reduced: * by not generating emissions, developing more efficient cleaner-burning engines which control their emission levels inside the combustion chamber (prevention) or * by not letting them escape, uncleansed, into the environment, using "hang on" equipment to treat the exhaust gases after they leave the engine, and which I would call (cure). Prevention being better than cure, how far can one expect to go with the preventive measure and how good is today's cure? In the first case, the aim is to construct the engine and its combustion chamber, and control the combustion process, in such a way that the creation of undesirable components in the exhaust gases - CO, HC and NOx - is minimised, whilst at the same time its economy is improved and adequate power still developed. One of the techniques is known as "HCLB" - high compression lean bum. This development of engines much leaner than stoichiometric is already finding its way into production. Examples are Ford's 1100 Fiesta, 1.6 Emax Sierra, Volkswagen's new Golf, Jaguar's revised V12 and, of course, the recently introduced 1.8 I Sierra, and the 1.41 and 1.6 I Escort and Orion. Under the maxim "consume less, fume less" offering petrol economy improvements of up to 20% over current - 1983/1984 - engines, this route has the capability in the future of reducing NOx by 60% from the uncontrolled situation, and approximately 90% for CO. Thus, the "best of both worlds" appears possible. The "prove out" process has begun. It is to be hoped that the legislators will give us enough time to further work on it and enough confidence to further invest in it. In the second case, the "curing" or "clean up" approach, various techniques have been evolved to reduce the emission: closed crankcase ventilation systems, exhaust afterburning, catalytic converters, etc, whereby the control systems, and the technology, become more complex.

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There is no doubt that a three-way catalyst is extremely effective in reducing emissions: NOx emissions by up to 80% from the uncontrolled levels, and HC and CO by over 95%. However, such techniques inevitably affect the operation of the vehicle, its performance, its fuel consumption, its driveability. They may also demand specific engine operating conditions in order to be effective, such as : - rich mixtures to use after-burning techniques - stoichiometric air/fuel mixture ratios to ensure the functioning of a three-way catalyst. Catalyst systems are complex in themselves, requiring complex control technology and skilled use of expensive equipment to ensure their continued effectiveness, care in fuel and vehicle use, and regular skilled maintenance, which may be beyond the capability of the third and fourth owners. In addition, some further investigation on potential side-effects during its particular use seems needed : concerning potential odour problems caused by sulphurtrioxyde, or the alleged carcinogenic effect, perhaps falsely or unjustly attributed to the active platinum leaving some types of catalysts, fire hazards as recently reported in the German press where in Cologne a fire, caused by a vehicle equipped with a catalytic converter (Audi 100), caused damage to the extent of 70.000 ECUs or 3.150.000 BFr.

Anyhow, how should we now - more specifically - judge the compromise reached at EEC level from a technical and economic viewpoint? The proposed standards have to be regarded as very tough indeed. This is particularly so for large cars. On the basis of vehicle tests carried out by the German government/UBA/, 10% of cars presently available in the US would fail to comply with the new standards. By effectively requiring three-way catalysts, a duplication of effort and expense is imposed, especially on the manufacturers who are furthest advanced on lean-bum. This duplication of investment in product development and manufacturing will add to the industry's costs, at a time when it is least able to afford it. To have one so-called "green vehicle" in each of the car model ranges is costing Ford for even this limited programme some 250 million ECUs or dollars, which is equivalent to BFr 11 billion 250 million, and is involving up to 10% of European research and development manpower. For the "large" cars, over 2.0 litres, the fitting of three-way catalysts will be virtually necessary since this is the only certain way of ensuring compliance with the emission levels required. This means that all these cars will require considerable changes to the floor pan and exhaust system to accomodate the catalyst, plus additional heat protection - both for the occupants, the interior trim and for grass, which may catch fire as mentioned earlier, due to the heat given off by the catalyst - which works in the range of 350 to 800 degrees Celsius. Also required will be either multi-point or

45

central, single-point fuel-injection or an electronically controlled carburettor, plus a microprocessor, and oxygen-lambda-sensor in the exhaust pipe, probably secondary air pumps and other equipment. Catalyst systems will add approximately 850 ECUs/dollars or BFr 40.000 to the pre-tax showroom "customer" price of these over 2.0 litre cars. Indications are that fuel consumption of the car will be up to 5-10% worse, and, although servicing intervals will remain unchanged, they will be very much more expensive. Looking at real world conditions, in Germany a Scorpio 2 I injection in its catalyst version costs 1.340 ECUs or BFr 60.500 more than the one without a catalytic converter. An Orion/Escort 1.080 ECUs or about BFr 50.000 more, and a Sierra 21 only 755 ECUs or BFr 34.000 more. If comparing a 1.6 injection catalyst engine of 66 kW power and with a manual five-speed gearbox with a 1.6 carburettor non-catalyst engine of the same 66 kW power and the same manual five-speed gearbox, the fuel economy for the noncatalyst versus the catalyst engine is just over 10%. It should, however, be mentioned that the catalyst engine runs on 91 RON fuel where the non-catalyst version is tuned to 96.5 RON fuel. The price difference between normal and super grade fuel should be brought into the final cost equation here to the advantage of the vehicle equipped with a catalytic converter. For "medium" cars of 1.4 to 2.0 litre capacity, the standards defined will most probably require the most complex and costly of the possible lean-burn solutions, greatly reducing the incentive to develop this new European technology. The lean-bum technology offers the prospect of a lasting substantially improved environmental impact with improved fuel economy and cost-of-ownership. Ford expects that an oxidation catalyst will be required, with lean-burn engines, either an "open-loop" - without microprocessor control - or "closed-loop" with microprocessor control. Similar floor pan and exhaust system changes as for three-way catalysts will be required, but the engine equipment will vary greatly. Some "medium" cars, which are of relatively light weight compared to the engine cubic capacity, may use a normal carburettor coupled with a simple computerised ignition system, plus "open-loop" oxidation catalyst. The showroom - or customer price effect of this lay-out could be about 350 ECUs or dollars, or BFr 16.000, before taxes. Other "medium" cars, where the power to weight ratio is less favourable, or where other constraints exist, may need similar fuel injection or electronically controlled carburettors and microprocessors to the three-way catalyst. Here the objective would be to maintain the engine in the lean bum air to fuel range of over 18:1, whereas the three-way system maintains it close to 14.7:1. The showroom price effect of such systems will be slightly lower than the three-way systems noted earlier for "large" cars. But for both systems, however, "open-loop" or "closed loop" with leanbum engines, Ford would expect to obtain an improvement in fuel consumption of

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between 12 and 20%. Service intervals may either remain as now or become even less frequent and, for the "open-loop" system, it will remain relatively simple and relatively cheap. "Closed-loop" systems or those involving injection equipment may become more expensive. "Small" cars, of under 1.4 litres capacity, will generally be able to use leanbum technology alone (although for some markets outside the EC, a catalyst solution may be necessary). Showroom price effects will be minimal, possibly in the order of 150 ECUs/dollars/(BFr 8.000) or less, depending on the type of electronic ignition equipment fitted. Servicing is unlikely to be different to today's cars, and fuel consumption may improve by 12% or so. This possible improvement is especially marked in comparison with the fuel consumption penalty associated with three-way catalysts. It is hoped that the second phase for small cars with introduction dates 1992/1993 and for which the emission levels still have to be decided will enable us to continue with the lean-bum technology. The manufacturing investment for one new lean-bum engine at Dagenham, approaching 250 million ECUs or dollars, or BFr 11 billion 250 million, plus a further 60 million ECUs or dollars or BFr 2 billion 700 million for design and development gives an indication of just how great the cost to Ford will be during a period when profitability, to put it mildly, is less than satisfactory.

The complexity of the matter is even more clearly demonstrated if one takes into account the need to avoid substituting one form of pollution for another. It gives further weight to the argument why industry cannot simply agree to any "quick shot" solutions: there are simply no easy answers to complicated questions. For example. it is recognised that an increasing concentration of C02 in the atmosphere causes a warming trend, leading to climatic changes in the next century, of sufficient magnitude to produce major physical, economic and social dislocations on a world-wide scale. Absorbing heat radiation from the earth's surface, trapping it, and preventing it from dissipating into space, plays a critical role in maintaining the earth's heat balance. Since it looks as if the global atmospheric C02 concentrations could double before the middle of next century, an average annual increase in global surface temperatures of about 2-3 degrees Celsius and possibly as much as 7-10 degrees Celsius could occur in the North Polar region during the winter. Changes in rainfall patterns, desertification, higher sea levels, and so forth ...could be expected. On June 23, 1986, the Energy, Research and Technology Committees of the European Parliament adopted Mr Fitzsimon's report on the measures to be taken against

47

increasing C02 concentration in the atmosphere to avoid - as was said - an ecological catastrophe. A catalytic converter oxydising the harmful CO and HC to the so-called harmless C02 is in view of this problem not a benefactor but a producer of a potential hazard to world environment. Taking another example of a possible shift from one form of pollution to another is the major increase in the sales of diesel-powered passenger cars. Due to the uncertainty on the final national legislation and on sufficient availability Europe-wide of unleaded fuel, a vast number of our customers, in an understandable move to be independent of political bargaining, are giving preference to diesel engines. In this case, smoke and particulates which are characteristics of the diesel engine will increasingly need to be controlled in order to avoid another series of concerns. These concerns are recognised however and development of particulate and gaseous emission standards for diesel engined vehicles is already well advanced at the EC Commission, since for both a final proposal for a Council directive was submitted to the Council in the month of June. For the gaseous emissions for heavy commercial diesel vehicles over 3.5 t gross vehicle mass, the proposal is equivalent to the United Nations regulation R 49 but with the levels reduced by 20% for CO and NOx and 30% for HC, and this starting for new engine homologation on April 1, 1988 and for new registrations on October 1, 1990. Concerning the particulates emissions for diesel passenger cars, the proposal is based on the US measurement method, transposed into the European test procedure and intended to be introduced in two stages, first large cars: October 1, 1988 for new models and October 1, 1989 for new registrations, followed by medium and small cars: from October 1991 for new models and 1993 for new registrations. Legislating satisfactory and consistent diesel fuel quality will also enhance the environmental impact of diesel vehicles. Unlike vehicle legislation which would affect only new vehicle designs, attention to fuel quality would also benefit the environmental performance of the existing diesel vehicle park. Please allow me to interject here that changes in diesel or gasoline fuel quality in the recent past, pressures on refiners resulting in more secondary processing, reduction of lead in leaded gasoline, the introduction of unleaded gasoline and the introduction of three-way catalyst systems - all mean that a pan-European specification for both fuels is both timely and appropriate. Methanol. ethanol and other organic or oxygenate compounds added to gasoline to make up for a decrease in lead and thus to improve its anti-knock quality could also create health and environment problems. Aldehydes, polycyclic aromatic compounds, benzene, ethene, organic acids: some of them are known as potential respiratory, eye and skin irritants, others could mutate cells or cause cancer under specific conditions, dependent on concentration of dose... etc. - and, though there is considerable uncertainty as to the

48

magnitude of the health risks, one should take them into account in any final appraisal. Replacement of asbestos by another product able to respond to equal heat and friction characteristics may well result in a similar atmospheric trace pollutant. It is essential that, before any alternative solution is enforced, one should as far as technically possible - be convinced about its advantages and health characteristics, in other words, its benefits to the environment as well as to its performance, durability, and resistance to deterioration which has to be equal or at least similar to the one being replaced, and - it has to be economically acceptable. All the costs for making this wide variety of vehicles and for testing/approving them are to be paid by "the consumer". His ability to pay for complex technology, including periodic replacement or maintenance, has to be taken into account. It is all part of the balance that needs to be kept between the desirable and the inappropriate, the necessary and the ideal. The estimates prepared by the EC Commission that the annual cost to the Community for the emission issue alone could exceed ten billion ECDs is believed to be accurate. Ford would support the view that all of the implications of the use of threeway catalysts - and to some extent oxidation catalysts - have NOT been fully explored. The concentration of the major, non-communist, supply sources for the raw materials in one country - South Africa - is also a cause for some concern, as are the recent reports of a fourfold increase in the price of rhodium, an essential constituent of catalysts. From less than $ 300 an ounce in 1984 to over $ 1.150 an ounce at the beginning of 1985, falling below $ 800 an ounce mid 1985, to climb again to $ 1.100 end 1985. This shows the instability and uncertainty which exist with the much-needed raw material for the present generation catalyst: the noble metal. The capability of meeting the potential automotive demand for rhodium from known reserves is also in doubt. Also platinum - about two grarnmes goes into each catalyst - stood in August at the highest levels since 1980: prices have more than doubled from a low of $ 237 an ounce last year to $ 545 an ounce, after reaching $ 560. New surges to $ 600-700 an ounce are not implausible. If the entire European auto market were to use catalysts, estimates of an additional annual demand of 500.000 ounces of platinum, 150.000 ounces of palladium and 30.000 ounces of rhodium have been put forward, depending on the number of automobiles sold in the EEC in a given year. The increases in total metal requirements from 1985 levels are expected then to be about 19% for platinum and 17% forrhodium. Not being an economist, I would nevertheless tend to predict in those circumstances some rather drastic price increases on the bullion market.

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And, remember, first cost is never the whole story: costs have a nasty habit of coming back and biting the purchaser again and again, by way of increased maintenance, replacement and general operating costs. Finally, allow me to underline the need to avoid any sort of unique "pioneer role" or "cavalier seul" behaviour of an individual government. European harmonisation of the environmental exhaust emission legislation is a basic demand from industry - to improve the general quality standard, through tess complexity and thus fewer line disturbances, and to avoid distortion of competition and trade between the European countries and to create - through excellence and economy of scale - the best possible product for the best possible price. It appears, however, that we are confronted with at least four different emission standards across Europe - 15.04, EC fifth amendment, Swedish A 10, US 1983/1987 - and this is, to say the least, to be deplored. Even those countries who have collectively agreed to go the 83 US route have different dates/procedures/conformity requirements, all of which increase the manufacturer's burden with no environmental benefit. We have had to undertake the radical re-engineering of no fewer than thirtyseven current and future engine applications. The cost of this enterprise is certainly not less than 200 million ECUs or dollars. No manufacturer, or administration for that matter, has a bottomless pot of gold, and the consumer, equally, has to operate within financial constraints. The cleanest, quietest, road vehicle in the world is of no use if few people can afford to buy it, run it, use it. In the end, this all adds up to compromise: The EC compromise might be assessed as giving at best half-hearted support for the new European technology of lean-burn. It is something - and in view of the circumstances - possibly the only political option left. We have an expression in Belgium: "Qui aime bien, chatie bien'V''Een goede vader spaart de roede niet"I"You always hit the child you love the most!" This may after all be the rationale behind it. Should this give us hope for the future? Thank you, Mr President.



CONTROL OF DIESEL PARTICULATE EMISSIONS IN EUROPE by Michael P. Walsh

Formerly Director of the U.S, Environmental Agency's Office of Mobile Source Air Pollution Control, currently an environmental consultant in the motor vehicle pollution field.Address : 2800 N Dinwiddie Street, Arlington, Virginia 22207, U.S.A.

ABSTRACT The greater use of diesel equipped vehicles for private cars and all categories of commercial vehicles is the major trend observed worldwide over the last decade in the motor vehicle field. While the energy advantages of the diesel are unquestioned, concerns began to grow during the 1970's over the environmental consequences of increased dieselization. Although inherently cleaner than gasoline engines from the standpoint of carbon monoxide (CO) and evaporative hydrocarbons (HC), diesels produce more aldehydes, sulfur oxides (because of the higher sulfur content in diesel fuel than in gasoline) and nitrogen oxides. Offensive smoke and odor emissions are also a problem. Most importantly, however, uncontrolled diesels emit significant amounts of particulate. These particles are a direct health concern as well as a serious source of overall environmental degradation. The purpose of this presentation is to review the information regarding adverse health and environmental consequences associated with diesel particulate. In addition, possible control strategies will be summarized.

I. Background

The greater use of diesel equipped vehicles for private cars and all categories of commercial vehicles is the major trend observed worldwide over the last decade in the motor vehicle field. While, for the first three quarters of this century, the gasoline fueled internal combustion engine (ICE) powered the automobile industry to ever greater peaks of prosperity, the dramatic increase in fuel prices spurred by the OPEC oil embargo and reinforced by the later Iranian crisis, sent the world's automotive engineers searching for a more fuel efficient alternative. For the first time a potential market opportunity for an alternative engine was created - one which promised significantly better fuel efficiency than the conventional gasoline fueled, otto cycle powerplant.

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Not surprisingly, almost all eyes focused on the diesel, a powerplant which had been in common usage on trucks for almost as long as the otto cycle was used in cars. It was familiar, reliable, had the nucleus of a fuel distribution system in place, and most importantly had demonstrated advantages in fuel efficiency. Across the full range of driving conditions, diesel fuel economy was at least 25 percent better than gasoline cars of the same weight and size. In stop and go urban traffic, the efficiency advantage rose to 35 or 40 percent. Worldwide diesel car production increased from about 1.3% of the total passenger car market in 1976 to 5.4% in 1983. With commercial vehicles, worldwide penetration in both vehicle categories is continuing to grow. While the energy advantages of the diesel are unquestioned, concerns began to grow during the 1970's over the environmental consequences of increased dieselization. Although inherently cleaner than gasoline engines from the standpoint of carbon monoxide (CO) and evaporative hydrocarbons (He), diesels produce more aldehydes, sulfur oxides (because of the higher sulfur content in diesel fuel than in gasoline) and nitrogen oxides. Offensive smoke and odor emissions are also a problem. Most importantly, however, diesels emit substantial amounts of fine particulate. Because of this, during its 1985 deliberations regarding motor vehicle pollution issues, the European Community Environmental Ministers asked the Commission to develop a proposal to control diesel particulate emissions. Though originally intended by the end of 1985, it was not possible for the Commission to meet this deadline. However, during June, the Commission approved proposals for two new directives aimed at reducing air pollution caused by diesel powered vehicles. Unfortunately, only one, dealing with passenger cars, addressed particulate emissions and even this did little more than maintain the status quo. The purpose of this paper is to review the reasons why control of diesel particulate emissions is urgently needed, especially in Europe, to show that the technology is available to reduce these emissions and to illustrate the potential impact of introducing this technology in Europe.

II. Health and Environmental Concerns with Diesel Particulate Uncontrolled diesels emit approximately 30 to 70 times more particulate than gasoline-fueled engines equipped with catalytic converters and burning unleaded fuel. These particles are a concern from several standpoints:

1. Many areas already experience unhealthy air quality levels for total suspended particulate (TSP) matter. Most TSP comes from stationary sources but diesels

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contribute. These particles in urban air are of concern because a strong correlation between suspended particulate and variations in infant mortality and total mortality rates has been established. Further, clear evidence emerges from the body of epidemiological literature that implicates particles in aggravating disease among bronchitics, asthmatics, cardiovascular patients and people with influenza. Any significant increase in diesel particulate emissions would add to the difficulty of solving this problem. 2. Beyond the overall impact on TSP, diesel particles raise a special health concern because they are very small (averaging about 0.2 microns in size). SmalI particles, which are much more likely to be deposited in the deepest recesses of the lung (alveolar region) and which require much longer periods of time to be cleared from the respiratory tract, have a greater potential to adversely affect human health than larger particles. In addition, when emitted, they remain suspended in the air near the breathing zones of people for long periods of time. For these reasons, the Harvard University Health Effects Project recently concluded that "particulate pollution should be a public health concern because, even at current ambient concentrations, it may be contributing to excess mortality and morbidity. Furthermore, our recent analyses .... indicate that fine particles (FP) and sulfates (S04=) are among the most harmful particles to public health." 3. In addition, diesel particulate has also been singled out as especially hazardous and toxic because of its composition. The U.S. EPA has noted that up to 10,000 chemicals may be adsorbed on the surface of diesel particles and drawn deep into the lung with them. Many of these chemical compounds are known to be mutagenic in short term bioassays, and to be capable of causing cancer in laboratory animals. Based on an exhaustive multiyear program of in vitro and in vivo studies by EPA and others focusing on the comparative potency of diesel particulate with other known human carcinogens, EPA estimated the risk to range from 0.26 x 10-6 to 1.4 x 10-6 lung cancers per person per year due to a constant lifetime exposure to one microgram per cubic meter of diesel particulate. Since total national urban exposure to diesel particulate in the United States was estimated to range from 3 to 5 micrograms per cubic meter by 1995, it is easy to see why this has been a cause of great concern. Two new animal studies, one sponsored by General Motors and another underway at Lovelace Inhalation Toxicology Research Institute laboratories appear to add further evidence of the cancer risk. A recent study conducted by rno found similar problems in Europe. "As a tentative order of magnitude estimate for the mutagenicity of European exhaust, the following emission factors may be assumed:

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Because as noted in the Harvard project "most of the toxic trace metals, organics, or acidic materials emitted from automobiles or fossil fuel combustion arc highly concentrated in the fine particle fraction" and since diesel engine penetration in Europe is much greater than in the United States, the potential cancer risk is also substantially greater. Other epidemiologic studies have tended to reinforce these concerns. For example, a 1983 study of heavy construction workers found positive trends in lung cancer by length of union membership and a higher than expected rate among retirees. Further, a pilot study of U.S. railroad workers, conducted by researchers at Harvard, indicated that the risk ratio for respiratory cancer in diesel exposed subjects relative to unexposed subjects could be as great as 1.42, i.e., the possibility of developing cancer may be 42 percent greater in individuals exposed to diesels than in individuals which are not exposed. The follow up study which has now been completed appears to be equally alarming - "Using multiple logistic regression to adjust for smoking and asbestos exposure, workers age 64 or less at the time of death with lung cancer had increased relative odds (1.2 - 1.4, P less than 0.05) of having worked in diesel exhaust exposed jobs." Clearly, it is prudent to conclude that greatly increased numbers of diesels without substantial particulate controls could result in a significant increase in cancer risks in Europe as well as elsewhere. Further, since the diesel car population in the Community is projected to grow from today's 5.8 million to about 15 million by 1995, without substantial controls the risk will increase tremendously. 4. While health issues have been the cause of most concern, diesel and other particles can also become a nuisance, degrade aesthetics and material usage through soiling and may contribute directly, or in conjunction with other polluants, to structural damage by means of corrosion or erosion. 5. Impairment of visibility has been widely noted as an adverse effect of increased particulates. Diesel particles because of their composition (primarily carbon based) and size (in the size range of 0.2 microns) are very high light absorbers and scatterers and therefore have the potential to be especially harmful to visibility. During late 1985, the results of several new studies were presented which increased concerns regarding adverse health effects from diesel particulate emissions. In particular; 1. Stoeber (Fraunhofer Institute) reported on carcinogenicity in rodents after long term high dose diesel inhalation. On both mice and rats, malignant tumors increased with exposure to diesel exhaust. With the mice, however, gaseous phase

55

emissions seemed most important whereas with the rats the particles seemed to be the main cause. 2. Brightwell (Batelle-Geneva) reported that unfiltered diesel exhaust produced an increase in lung tumor incidence from 19% to 40%; gasoline emissions reportedly showed no effect. 3. In a summary presentation, McClellan (Lovelace) described the issue as no longer whether diesel exhaust is carcinogenic but rather under what conditions and how much.

III. Diesel Smoke and Particulate Control Outside Europe Because of these various problems associated with diesel smoke and particulate, control programs have been underway for many years. This next section will review the history of these programs to date. In general, one can note that the initial focus was on smoke control because it was clearly visible and a nuisance. As the evidence has grown in recent years regarding the serious health and environmental problems, more attention has focused on control of the particles themselves. Smoke is composed primarily of unburned carbon particles from the fuel and usually results when there is an excess amount of fuel available for combustion. This condition is most likely to occur under high engine load conditions such as acceleration and engine lugging when the engine needs additional fuel for power. Further, a common maintenance error, failure to clean or replace a dirty air cleaner, may produce high smoke emissions because it can choke off available air to the engine resulting in a lower than optimum air-fuel mixture. Vehicle operation can also be important since smoke emissions from diesel engines are minimized by selection of the proper transmission gear to keep the engine operating at the most efficient speeds. Moderate accelerations and lower highway cruising speed changes as well as reduced speed for hill climbing also minimize smoke emissions. United States U.S. emission control requirements for smoke from engines used in heavy duty trucks and buses were first implemented for the 1970 model year. These opacity standards were specified in terms of percent of light allowed to be blocked by the smoke in the diesel exhaust (as determined by a light extinction meter). Heavy duty diesel engines produced during model years 1970 through 1973 were allowed a light extinction of 40 percent during the acceleration phase of the certification test and 20 percent during the lugging portion; 1974 and later model years are subject to smoke opacity standards of 20 percent during acceleration, 15 percent during lugging, and 50 percent at maximum power. It appeared to the EPA during the early 1970's that before very significant

56

pollution controls on trucks and buses could actually be brought about a new test procedure encompassing truly representative modes of usage in urban areas was needed. A multiyear effort to develop such a test was therefore initiated. While this work was underway, EPA became alarmed by the sudden growth in diesel cars which started during the late 1970's. Even though trucks and buses were clearly more important sources of particulate than cars and light trucks at that time, EPA concluded that the latter vehicles were very significant and that it was possible to initiate controls on these vehicles more quickly than on trucks and buses. Accordingly, the first diesel exhaust particulate standards in the world were established for cars and light trucks in an EPA rulemaking published on March 5, 1980. Standards of 0.6 grams per mile (0.37 g/km) were set for all cars and light trucks starting with the 1982 model year dropping to 0.2 grams per mile (0.12 g/km) and 0.26 (0.16) for 1985 model year cars and light trucks, respectively. In early 1984, EPA delayed the second phase of the standards from 1985 to 1987 model year. Almost simultaneously, California decided to adopt its own diesel particulate standards - 0.4 grams per mile (0.25 g/km) in 1985,0.2 (0.12) in 1986 and 1987, and 0.08 (0.05) in 1989. Less than one year later, in January 1981, EPA formally proposed similar particulate standards for trucks and buses. A comprehensive urban truck and bus test procedure had been developed by that time and analysis clearly showed that smoke controls were inadequate to bring about truly significant particulate reductions. A four year delay ensued before final action was taken by EPA. During this time, a new Administration at EPA reevaluated the need for diesel particulate control as well as the newly developed truck test procedure. These reevaluations reached the same fundamental conclusions as the earlier work - truck and bus controls is extremely important because the pollutants involved endanger the public health and environment and trucks are a major contributor to those pollutants; as a result, the first particulate standards for heavy duty diesel engines were promulgated by the U.S. EPA earlier this year. Standards of 0.60 grams per Brake - Horsepower - Hour (g/bhph) (0.80 grams per kilowatt-hour) were adopted for 1988 through 1990 model years, 0.25 (0.34) for 1991 through 1993 model years and 0.10 (0.13) for 1994 and later model years. Because of the special need for bus control in urban areas, the 0.10 (0.13) standard for these vehicles will go into effect in 1991, three years earlier than for heavy duty trucks. These standards are required to be met over the full life of the vehicle or engine, rather than over half the life as is the case with cars. Also, EPA based the standard on the new "transient" test referenced above rather thanon the old "steadystate" test because the transient test is much more representative of the manner in which trucks are driven in cities.

57

Canaan In March of 1985, in parallel with a significant tightening of gaseous emissions standards, Canada adopted the V.S. particulate standards for cars and light trucks (0.2 and 0.26 grams per mile, respectively) to go into effect in the 1988 Model Year. Since then, Canada has initiated a review of truck controls and is considering adoption of V.S. standards for these vehicles as well.

Japan Japan does not currently regulate exhaust particulate emissions from diesel engines. However, smoke standards have applied to both new and in-use vehicles since 1972 and 1975, respectively. The maximum permissible limits for both are 50 percent opacity; however, the new vehicle standard is the more stringent because smoke is measured at full load, while in-use vehicles are required to meet standards under the less severe no-load acceleration test. Smoke standards versus particular standards While smoke standards provide a limited degree of emission control, by not focusing on particulate levels over an average driving cycle and because they are fairly lenient, their effect actually reducing particulate emitted is somewhat limited. It is safe to say that particulate emissions throughout the world outside the U.S. remain virtually uncontrolled at the present time.

IV. The European Response To Date A. Common Market Smoke limits similar to those described above in the United States and Japan have been in effect in Europe for many years. However, recognizing that these requirements are not adequate, during its 1985 deliberations regarding motor vehicle pollution issues, the European Community Environmental Ministers asked the Commission to develop a proposal to control diesel particulate emissions. Specifically, the proposed standards are:

Type approval 1.3 g/test

Conformity of production 1.7 g/test

These standards, which many European produced vehicles are already achieving, are intended to be introduced on the following timetable:

58

I

I Vehicle type New models over 2 000 cm3 2 000 cm3 or less D.I.

Introduction date New cars

October 1988 October 1991 October 1994

October 1989 October 1993 October 1996

Studies conducted by Germany have indicated that the approximate conversion rate between the US and ECE tests is about 3, i.e., 0.2 grams per mile on the US test is roughly equivalent to about 0.6 grams per test on the ECE test. Approximate conversions are summarized below: ~~

Test procedure

us

ECE Gramshest Gramdkilometer

Gramdmile 0.6 0.2 0.08

1.8 0.6 0.24

0.45 0.15 0.06

B. Non Common Market European Countries In stark contrast to the Common Market, several other European countries have been cooperating in moving toward more significant diesel particulate requirements. Sweden has already adopted the US passenger car standard to go into effect in 1989 and Switzerland and Austria are likely to do so in the near future. These countries are also looking hard at more stringent requirements for trucks and buses.

V. Impact of the Commission Proposal On Common Market Emissions Overall diesel car sales increased by 21.3% across Europe from 1984 to 1985.As illustrated below, the increase was even greater in some countries.

Country Belgium-Luxembourg Denmark France Ireland Italy Netherlands Spain United Kingdom West Germany

1985

95 000 10 400 264 800 8 400 438 600 71 300 124 900 66 200 530 800

9% Market 26.4 6.6 15.0 14.2 25.1 14.4 22.6 3.6 22.3

1984

% Change

96 900 10 300 240 400 6 000 425 300 61 000 126 700 45 100 321 800

1984-1985 -1.9 0.2 10.1 41.7 3.1 17.0 -1.4 46.8 64.9

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It is especially ironic that West Germany has encouraged the growth of high particulate emitting diesel cars by allowing them to qualify for "low pollution" tax incentives without any requirement that they meet the same particulate levels as Gennan models exported to the US. In part as a result of these tax incentives, diesel car sales in Germany have accelerated in the last year, as is illustrated in Figure 1. Fortunately, in adopting its low pollution tax policies earlier this year, the Netherlands did not provide similar tax reductions for uncontrolled diesels. Because of the high growth rate for diesel vehicles in Europe and the modest particulate reductions proposed by the Commission, it appears that overall particulate emissions will grow tremendously throughout the next twenty five years. This is illustrated in Figure 2 which plots motor vehicle particulate during this period. This figure shows that emissions from all categories of vehicles will continue to grow under the Commission proposal. Even these projections may be understating the potential problem, however, as concerns have been growing that diesel fuel quality may deteriorate significantly in the future in Europe. Should this happen, particulate emissions will likely rise even further.

VI. What Is Possible Light duty vehicles Fortunately, it is possible to do something about these problems. Two major approaches exist for meeting stringent diesel particulate standards: engine modifications to lower engine out emission levels, and trap-oxidizers and their associated regeneration systems. Engine modifications include changes in combustion chamber design, fuel injection timing and spray pattern, turbocharging, and the use of exhaust gas recirculation. Further particulate controls appear possible through greater use of electronically controlled fuel injection which is currently under rapid development. Using such a system, signals proportional to fuel rate and piston advance position are measured by sensors and are electronically processed by the electronic control system to determine the optimum fuel rate and timing. Exhaust aftertreatment generally consists of a filter or trap to capture the particulate and a regeneration system to convert it to less harmful materials; Trap oxidizer prototype systems have shown themselves capable of 70 to 90 percent reductions from engine out particulate emissions rates and with proper regeneration the ability to achieve these rates for high mileage. Systems have now started to be introduced commercially. Figure 3 shows the distribution of emission results for 1986 model cars in the United States. Compared to an average emission rate of 0.6 grams per mile in 1980, it can be seen that current emissions now average about 0.2 grams per mile. (It

60

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FIG.6

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ESTIMATION OF PARTICULATE EMISSIONS IN EUROPE FROM 1985 TO 2010. COMPARISON BETWEEN ECE COMMISSION PROPOSAL AND U.S. STANDARDS. (SMALL CARS )

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2000

CALENDAR

FIG.7

2005

2010

YEAR

ESTIMATION OF PARTICULATE EMISSIONS IN EUROPE FROM 1985 TO 2010. COMPARISON BETWEEN ECE COMMISSION PROPOSAL AND U.S. STANDARDS. ( LARGE CARS )

E2L1

US

STuOnos

~

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220 200 180

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1990

1995

CALENDAR

FIG.8

2000

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ESTIMATION OF PARTICULATE EMISSIONS IN EUROPE FROM 1985 TO 2010. COMPARISON BETWEEN ECE COMMISSION PROPOSAL AND U.S. STANDARDS. (COMMERCIAL VEHICLES )

66

In addition, member countries which have adopted tax incentives to encourage consumers to purchase low pollution vehicles should either exclude diesels from any tax credits or require them at a minimum to achieve 0.6 grams per test (BCE test) or 0.2 grams per mile (US test) particulate to qualify for low pollution tax credits. IX. References

1. "The Benefits and Costs of Light Duty Diesel Particulate Controls," Michael P. Walsh, SAE #830179 2. "The Benefits and Costs of Light Duty Diesel Particulate Controls II," Michael P. Walsh, SAE, February 1984 3. "The Benefits and Costs of Light Duty Diesel Particulate Controls III - The Urban Bus," Michael P. Walsh, SAE, February 1985 4. "The Benefits and Costs of Light Duty Diesel Particulate Controls IV - The InUse Urban Bus," Michael P. Walsh, SAE, February 1986 5. "Cancer Incidence Among Members of A Heavy Construction Equipment Operators Union With Potential Exposure To Diesel Exhaust Emissions," Submitted to Coordinating Research Council by Environmental Health Associates, 18 April, 1983 6. Mortality Among Members of A Heavy Construction Equipment Operators Union With Potential Exposure To Diesel Exhaust Emissions," Submitted to Coordinating Research Council by Environmental Health Associates, 18 April, 1983 7. "Relation of Air Pollution To Mortality: an Exploration Using Daily Data for 14 London Winters, 1958-1972", Mazumdar, Schimmel, Higgins, Electric Power Research Institute, Palo Alto, 1980 8. "Diesel Cars, Benefits, Risks and Public Policy," National Academy of Sciences, December 1981 9. "Review of Recent Information Regarding Carcinogenicity of Diesel Engine Emissions", Pepelko to Gray, U.S. EPA, June 14, 1985 10. U.S. Environmental Protection Agency, Heavy Duty Diesel Particulate Regulations, Draft Regulatory Analysis, Approved by Michael P. Walsh, December 23, 1980 11. "Impact of Light Duty Diesels On Visibility in California," Trijonis, March 1982 12. "Diesel Exhaust Odor and Irritants: A Review," Nicholas P. Cernansky, Journal of the Air Pollution Control Association, February 1983 13. U.S. Environmental Protection Agency, Control of Air Pollution From New Motor Vehicles and New Motor Vehicle Engines; Gaseous Emission and Particulate Emission Regulations, Federal Register, March 15, 1985 14. "Trap-Oxidizer Technology For Light-Duty Diesel Vehicles: Feasibility, Costs and Present Status," Weaver and Miller, Report to EPA by Energy and Resource Consultants, March 1983 15. "Diesel Technology", National Research Council, Report of the Technology Panel of the Diesel Impacts Study Committee, National Academy of Sciences, 1982 16. "Draft Environmental Guidelines On The Diesel Vehicle," Clavel and Walsh, United Nations Environment Program, March 1983

67

t 7. "Benefits of Reducing Odors From Diesel Vehicles: Results Of A Contingent 18. 19. 20. 21. 22. 23.

24. 25. 26.

Valuation Survey," Prepared for Environmental Protection Agency by Charles River Associates, March 1983 "Diesel Exhaust and Air Pollution," TNO, Netherlands Organization For Applied Scientific Research, January 1986 "Begrenzung der Partikelemission von Dieselfahrzeugen im Rahmen der europaischen Abgasvorschriften", Umweltbundesarnt, October 1985 CCMC Manufacturers' Measurements of Particulates On Diesel Engined Passenger Cars, November 1985 "Health Effects of Airborne Particles," Ozkaynak and Spengler, Health Effects Project Staff, Harvard University, February 1986 OECD, "Road Research Programme, Impact of Heavy Freight Vehicles, Final Report," September 28, 1982 Shenker, Smith, Munoz, Woski, Speizer, "Lung Cancer Among Diesel Exposed Railroad Workers, Results of a Pilot Study," Harvard School of Public Health, 1982 Schenker, Oral Statement, American Lung Association Convention, May 1984 U.S. Environmental Protection Agency, Federal Register, March 5, 1980. Standard for Emission of Particulate, Regulation for Diesel Fueled Light Duty Vehicles and Light Duty Trucks U.S. Environmental Protection Agency, Regulatory Analysis of the Light Duty Diesel Vehicles, U.S. Environmental Protection Agency, February 20,1980



THE PROBLEMS INVOLVED IN PREPARING AND UPHOLDING UNIFORM EXHAUST-GAS STANDARDS WITHIN THE COMMON MARKET by H. Henssler

Commission of the European Communities, Directorate Internal Market and Industrial Affairs 200 rue de la Loi, B-1049 Brussels, Belgium.

ABSTRACT Uniform exhaust emission standards for passenger cars and light duty vehicles exist since 1970 in the Common Market. In June 1985 the Council of Ministers for the Environment agreed by majority a further decisive reduction of these standards. The future European emission standards are based on the principle of equivalence of their environmental effect with that of the current US standards, taking account of the European conditions in particular with regard to the composition of the car fleet and its operating characteristics. Like the preceding steps of the EEC exhaust emission regulations, the new standards refer to the present European test procedure which however at a later stage should be completed by a test cycle representing extraurban driving conditions. The new European emission standards will apply to passenger cars with a maximum mass up to 2,500 kg having not more than 6 seats. The limit values and the effective dates are differentiated according to 3 categories of engine capacity. The presentation describes the aims, the development and the rationale of the EEC exhaust emission regulations and also gives a summary of their legal bases.

THE EEC'S LEGAL BASES AND METHODS OF PROCEDURE 1. In March 1970 the Council of Ministers of the European Communities adopted, as the second separate directive of the EEC type-approval procedure, directive 70/220/EEC "on the approximation of the laws of the Member States relating to measures to be taken against air pollution by gases from positive-ignition engines of motor vehicles". Since this date, uniform exhaust emission standards exist throughout the whole Community for the concerned category of vehicles. 2. The present contribution is intended to describe the aims, development and significance of the European Communities' exhaust-gas standards. It appears suitable, by way of an introduction, first of all to describe the essential aspects of the EEC's legal bases and methods of procedure. 3. A fundamental aim of the 1957 Treaty of Rome establishing the European Economic Community is the creation of a common internal market among the

69

70

Member States! within which cinzens, goods and services may cross borders without let or hindrance. Naturally, if goods are to move freely, first of all customs barriers and then the so-called non-tariff barriers or technical barriers to trade must be removed. The major non-tariff barrier to the cross-frontier trade in motor vehicles is constituted by the Member States' type-approval procedures, together with their various technical requirements and administrative practices. It has for good reasons been impossible simply to do away with each Member State's procedures and to replace them with an EEC type approval procedure which, however, was needed if barriers to trade of this type were to be avoided. 4. Use was therefore made of "optional harmonization" whereby the EEC typeapproval is established in parallel to the Member State procedures, but does not replace them. From this results the possibility of a choice at two levels: - Member States may retain, alongside the EEC provisions which they are bound to introduce, divergent national provisions, and - Manufacturers may, where Member States decide to retain national provisions, choose whether they wish to manufacture their products in accordance with EEC or Member State provisions.

The relevant national authorities must approve vehicle types, permit vehicles to be sold on their territory and to enter service if they comply with EEC provisions. However, they may deliver such approval on the basis of other criteria, such as any national technical requirements already existing. 5. The European Communities issue their technical and administrative standards in the motor vehicle field in the form of "directives". A directive is one of the legal instruments made available to the executive of the Communities under the Treaty of Rome in order that it may perform its function. It is addressed to Member States and for them its aim is binding, while the choice of means of implementation is left open to them. Under normal circumstances four European institutions work together in preparing a directive: the Commission, the European Parliament, the Economic and Social Committee and the Council of Ministers. Their respective functions are laid down in Article 100 of the Treaty of Rome: the Commission has the right of initiative i.e. it proposes directives, while the Parliament and Economic and Social Committee deliver opinions on it and the Council adopts and issues the directive. IThe founder members of the EEC: Belgium, Federal Republic of Germany, France, Italy, Luxembourg and the Netherlands. Subsequent accession of: Denmark, Greece, Ireland, Portugal, Spain and the United Kingdom.

71

LINKS BETWEEN EEC AND ECE STANDARDS 6. Before we go into individual detail on the development of the Community exhaustgas standards, it would seem appropriate to make one or two basic remarks concerning the relationship between the Commission of the European Communities and the United Nations' Economic Commission for Europe (ECE), Geneva as regards vehicle regulations. Under the 1958 Geneva Convention the ECE has adopted a number of such regulations, which, however, are not embedded in a complete type-approval procedure. As signatories to this Convention the majority of the EEC Member States base their national type-approval systems more or less on these regulations. The Commission has therefore been forced to take them into account. The advantages of technically equivalent standards within the Community and in the much wider area covered by the Geneva requirements are obvious. The EEC has thus decided to transpose the technical requirements of the ECE regulations into the corresponding separate directives where these are relevant to its type-approval procedure. DEVELOPMENTS SO FAR AS REGARDS THE EEC'S EXHAUST GAS STANDARDS 7. The need for effective exhaust gas regulations arose on both sides of the Atlantic in the late 60's. This caused the European Community to adopt its Directive 70/220/EEC in 1970. In content, it is equivalent to ECE Regulation 15. Like the American approach the European provisions limited emissions only of carbon monoxide (CO) and unburnt hydrocarbons (HC) for health-policy reasons, or more precisely because of their effects on the quality of the air ingested in large conurbations. Dynamic methods of measurements which were representative of the type of operation which vehicles were subjected to in inner city areas were devised to back-up the relevant approval tests. 8. It is nowadays difficult to quantify the improvement of vehicle emission behaviour intended by this first generation of exhaust gas standards since there has been no statistically reliable study of the preceding period i.e, there has been no basis for reliable comparison. However, it can be taken that these standards correspond to the state of the art at the time and thus on average made a certain improvement to the relevant emissions by the overall vehicle fleet. 9. Later on these standards were tightened up several times in both the United States and Europe. The fact that in the US also the driving cycle and in Europe the sampling and analysis methods were altered makes it difficult to carry out a direct evaluation of the reduction in vehicle emissions thus achieved. It can be said overall

72

that nowadays, following the three reduction stages set out in the EEC Directives in line with amendments 01, 03 and 04 to ECE Regulation 15, the European approval tests require emissions that are 50% lower than the original limit values for CO and He. The corresponding reductions in the United States are about 90%. 10.Initially nitrogen oxide (NO) emissions by vehicles were not covered by European or American legislation. However, they were soon identified in the United States as contributors to the well-known Los Angeles "smog" and were limited from 1973 onwards. Europe reacted somewhat hesitantly, as public health hazards due to climatic conditions of this type were still largely unfamiliar. Admittedly here too, a considerable increase in NOx emissions was recorded, not least as a result of the motor industry's efforts to meet the legal requirements concerning CO and HC emissions, but also to reduce fuel consumption - since the first energy crisis was now in full swing. The relevant state of the art was therefore enshrined in the limit values set out in Directive 77/102/EEC (ECE Regulation 15.02). After two further reductions the European standards lay roughly 30% below the original limit values. In this instance the United States have achieved a cut of 65%. l1.Basically the European approach can be described as progress through continuous adaptation of its legislation to the state of the art achieved by the European motor industry. Conversely American Legislation had from the outset been shaped by political objectives such as Senator Musky's 1970 demand that vehicle emissions be reduced by 90% within ten years.

EEC REACTION TO THE GERMAN STEPS TOWARDS THE INTRODUCTION OF "LOW POLLUTION" VEHICLES - ORIGINS OF THE "LUXEMBOURG COMPROMISE" OF 27 JUNE 1985 12.The steps in Germany towards the introduction of low-pollution vehicles made exhaust gas regulations a political issue in Europe as well. Owing to the legal situation at the start in the EEC this initiative had of necessity to result in a discussion of an appropriate amendment to the exhaust gas directive. The Commission was at pains to place the proposals required of it on an objective basis. It convened the Working Party known as ERGA (Evolution of Regulations, Global Approach) which, as part of its global approach, was first of all made responsible for identifying the relationships between vehicle emissions and air quality, for describing possible technical ways of reducing those emissions and for examining their economic impact. Under a second mandate the Working Party then mapped out strategies for the EEC-wide introduction of unleaded petrol. The know-how which the, in this form certainly unique, Working Party acquired was used by the Commission to form the basis for its June 1984 proposals on the

73

introduction of unleaded gasoline and on the reduction of the permissible exhaust gas emissions from motor vehicles. The latter, moreover, was based on the principle of equivalence with the environmental effect of the current US exhaust gas standards while taking account of European conditions with regard to motor vehicle fleet and its operating characteristics. These proposals received the approval of the majority of the Member States at the meetings of their environment ministers of 20 March and 27 June 1985. However, since Denmark and Greece entered fundamental reservations regarding the future "European exhaust emission standards" agreed by the majority, it has not been possible even now to adopt this directive formally. UNDERLYING ASPECTS OF THE COMMUNITY'S FUTURE EXHAUST GAS STANDARDS 13.We will now go on to the underlying aspects of the exhaust gas standards agreed by the majority. These will apply to passenger cars having a maximum permissible mass of up to 2500 kg, while the limit values and dates of entry into force are divided up into three engine capacity classes. The pollutants covered are carbon monoxide (CO), unburnt hydrocarbons (HC) and nitrogen oxide (N0x)' 14.1t is assumed that vehicles with an engine capacity of more than 2 litres already exist in a US version, or else that the appropriate catalytic converter technology can be applied to them without raising technical and economic problems. The new European standards for this class are based on measurements taken from vehicles for which a US exhaust gas certificate has been issued and are such that basically vehicles of this type can also be issued with EEC type approval. For the approval of new vehicle types the following limit values have been established: CO:25g!test, for the combined emissions of HC and NO x: 6.5g1test, for NO x: 3.5g/test. For the control of production conformity a certain tolerance to these values is granted which results in the following limit values: for CO: 30g/test, for the combined HC and NO x emissions: 8.1g!test and for NO x: 4.4g!test. These limit values will apply to new vehicle types from October 1988 on and to all vehicles registered for the first time from October 1989 on. 15.Essentially the same technology can apply to vehicles having an engine capacity between 1.4 and 2 litres, but it should be possible to provide cheaper

74

alternatives and in particular lean-bum engines having a centralized fuel supply, plus oxidation type catalytic convertors or equivalent. Therefore, and because statistically speaking mid-range vehicles cover a shorter annual distance than topof-the-range vehicles, slightly higher limit values apply to CO and the combined emissions of HC and NO x ' while additional flexibility is gained by dispensing with a separate NOx limit value. For the approval of new vehicle types the following limit values apply: for CO: 30g/test, for the combined emissions of HC and NOx' 8g/test. The corresponding limit values for the control of production conformity are: for CO: 36g/test, for the combined emissions ofHC and NO x' 109/test. These limit values will be implemented as from October 1991 for new vehicle types and as from October 1993 for all vehicles registered for the first time. 16.0wing to a lack of experience by the European motor industry in meeting the US standards where vehicles have an engine capacity of less than 1.4 I, it is not considered possible to lay down equivalent European standards for the moment. For the time being limit values corresponding to the current state of the art will be applied to vehicles in this category. For the approval of new vehicle types these values are: For CO: 45g/test, for the combined emissions of HC and NO x: 15g/test and for NO x: 6g/test. For the control of production conformity the following limit values apply: For CO: 54g/test, for the combined emissions of HC and NOx: 199/test and for NO x: 7.5g/test. These limit values will be implemented as from October 1990 for new vehicle types and as from October 1991 for all vehicle registered for the first time. Before the end of 1987 a fmal European standard for this vehicle class will be laid down which then will apply, from October 1992, to new vehicle types and from October 1993, to all vehicles placed in service for the first time. 17.The limit values referred to are based on the current European urban driving cycle, which is considered by the majority of the Member States basically still to be representative of the traffic conditions in European conurbations. The expansion of the European test procedure by adding driving conditions representative of car operation outside built up areas -considered by most of those involved to be desirably in the longer term - is to be decided upon by the end of 1987.

75

I8.For private cars with an engine capacity of 1.4 litres and more the directive provides, as an alternative to the European test procedure limited in time, for transposition of the relevant parts of the American certification process - basically the FfP-75 driving cycle. The underlying notion here is that manufacturers with vehicle types meeting the US specifications will first of all have to adapt these to European test conditions before they may, on this basis, apply for type approval, while on the other hand it is desirable for environmental protection purposes to offer such vehicles on the European market in the near future. The limit values are those of the 1983 federal "'49 states") standards, i.e.: for CO: 2.llg/km, for HC: 0.25g/km and for NO x: 0.62g/km. These limit values will apply both to typeapproval and to control of production conformity according to the American sampling procedure. 19.As it is aware of the specific problems affecting diesel engines and more particularly the meeting of stringent NOx limit values, the majority of the Member States agreed to the Commission's proposal to apply the limit values for vehicles of between 1.4 and 2 litres engine capacity to all diesel cars larger than l.4litres. This is also intended to secure the necessary flexibility in the subsequent establishment of limit values for particulate emissions from diesel engines for which in the meantime the Commission has presented a proposal. For vehicles equipped with a direct injection diesel-engine of a capacity between 1.4 and 2litres the new European emission standards will only apply from October 1993 (new types) and October 1996 (first registrations) respectively. Thereby the Member States intend to grant an additional lead-time for those manufacturers who are developing such engine concepts in view of a further improvement of fuel economy as well as exhaust emissions of future diesel car generations. 20.Equally, for private cars equipped with automatic transmissions exceptional provisions have been agreed, provided that such cars are derived from models with manual transmissions for which an EEC approval has already been granted. In this case, the automatic transmission version will be approved against limit values which result from the multiplication of the above-mentioned limit values multiplied with a factor of 1.2 for the combined HC and NOx emissions and I.3 for the NOx emissions. 21.With a view to the rapid introduction of unleaded petrol it has also been agreed that all new car types subject to approval which have engines larger than 2 litres must be designed for the exclusive use of such fuels from 1 October 1988 and those with engines of less than 2 litres from 1 October 1989. Moreover, from 1 October 1990, Member States of the Community may in general terms prohibit the approval of new vehicles which are unable to run on unleaded fuel. Where a manufacturer can demonstrate considerable technical difficulty in converting

76

vehicles from leaded to unleaded furl those vehicles will be exempted and the dates decided for the implementation of the new emission standards will apply. 22.As mentioned before, the new European emission standards apply to private cars of not more than 6 seats and a total mass of not more than 2,500kg. It is this category of vehicles - except those cars having an engine capacity of less than 1.4 litres - with which European manufacturers have been able to gain experience of the technology required to meet the US standards. For all other vehicles covered by the scope of the present directive, notably those of category N 1 (Tight duty trucks") it has been agreed to follow an approach analogous to that chosen for the private cars below 1.4 litres i.e. to introduce interim emission standards. These consist of the limit values of Directive 83/351/EEC, the application of which to the concerned vehicles will imply a reduction of their HC and NO x emissions in the order of 25% compared to the present situation. These interim standards will apply from 1 October 1989 to new vehicle types and from 1 October 1990 to all new vehicles put into service. In 1987 the Council will decide, on proposal of the Commission, the definitive European standards which should apply to these vehicles in 1993/1994.

ASSESSMENT OF THE "LUXEMBOURG AGREEMENT" 23.The fact that the majority decisions of March and June 1985 aim at an intrinsic European solution to the environment problems caused by road traffic must be welcomed without reservation in Brussels. 24.For several reasons the - apparently so obvious - direct transposition of the US exhaust gas regulation would quite definitely not have been a feasible solution for the Community as a whole. One thing we can mention here is the completely different legal frameworks of the American and European regulatory systems. For example, options, such as that open to the US approval authority, of suspending the application of stringent exhaust gas standards either in general terms of in respect of individual manufacturers, or, as in the case of the commercial-vehicle exhaust gas standards now proposed of permitting manufacturers to "offset" these is not provided for either in the EEC's type approval procedure or in those of the individual Member States. Secondly, the passenger car market in the USA cannot be compared with that in the Community. For example, vehicles with engines smaller than l.4litres capture an insignificant part of the US market, whereas in Europe their market share is

77

somewhat over 50%. Similarly, diesel cars have virtually disappeared from the US market but currently account for 14% of new registrations in the Community, and the figure is rising. 25.The compromise effected via the "Luxembourg Agreement" takes overall account of European conditions. On one hand it enables motor manufacturers within the Community to back up existing know-how in Europe with proven US technology. On the other hand, it leaves them the option where the greatest turnover is, i.e. in mid-range and small cars, of developing cheaper alternative solutions which offer a considerable reduction in fuel consumption alongside lower emission values, thereby making them particularly attractive to a wide range of customers. The marketing of low-pollution vehicles on a voluntary basis on the German market can be taken a') confirmation that the industry has grasped this opportunity. 26.As a precautionary measure the "Luxembourg Agreement" seems to guarantee achievement of the environmental-protection target. The European CO and HC emission standards for top-of-the-range vehicles are 87% lower, and in the case of NO x emissions 70% lower than the original 1970 limit values. These values are roughly 80%n3% below the original values in the case of mid-range vehicles. In order of magnitude these figures are fully in line with the reduction aimed at by the standards laid down in the United States. In addition, calculations based on the available documents on the vehicle fleet, the mode of operation of the individual vehicle classes and the specific emissions from these show that the overall NOx emissions from the EEC fleet will reach the American level of roughly 1.5 million tonnes per year, when predominantly made up of vehicles meeting the new EEC standards i.e. roughly around the year 2000. EXTENSION OF THE EUROPEAN EMISSIONS REGULATIONS ON OTHER POLLUTANTS AND EACH VEHICLE CATEGORY 27.Pursuant its undertakings at the Environment Councils of 27 June an 28 November 1985 relating to the gaseous emissions of passenger cars and light commercial vehicles covered by Directive 70/220/EEC, the Commission presented on 23 June 1986 two further proposals on motor vehicle emissions to the Council. 28.The first proposal concerns the particulate emissions of diesel engines equipping the motor vehicles covered by the above-mentioned Directive. Particulate emissions are besides smoke - which, since 1972 has been controlled by a Community Directive - a specific problem of diesel engines. The limitation of these emissions appears today the more necessary as the diesel car pare is increasing rapidly and is forecasted to reach about 15 million units in the mid-90's which shall be compared with the present 6 million units.

78

The proposal is based on the presently available though limited knowledge of the performances of the best available diesel technology in the European motor industry as a whole. Furthermore, it takes into account the lack of accuracy and reproductibility which result from the simple transposal, into the European test procedure, of the sampling and analysis method of the current US legislation which is at present the only codified method available. The limit value proposed for the type-approval of new car models, independent of the weight and engine size, is 1.3g per European test as defined in Directive 70/220jEEC. The limit value proposed for conformity of production, or otherwise, that which every new car must meet on its first registration, is 1.7g/test. These limit values are proposed to be implemented at the dates agreed at the Luxembourg Council for the implementation of the new European standards for gaseous emissions. By that means the Commission intends to assure that the motor industry can concentrate its resources on adapting its production to the new Community requrements as a whole and that the administrative procedures related to the type-approval of modified car models will be limited to what is strictly necessary. 29.The second proposal concerns the emissions of gaseous pollutants (CO, HC, NO x) from the diesel engines of commercial vehicles and buses of all weight classes. The contribution of the emission of these vehicles - which until now in Europe are not controlled except for smoke - to the general air pollution becomes more important since the continuing regulatory efforts of the Community to reduce the emissions of light motor vehicles take effect. Here again, the absence of any control of the concerned emissions of heavy vehicles in the Member States results in very little data about the emission performance of big diesel engines and the possibilities of their improvement in this respect. The present proposal is based on a regulation ("R49") of the Economic Commission for Europe of the United Nations, from which it takes over the test procedure. The limit values of this regulation, however, no longer correspond to the state of the art in diesel technology and an across the board reduction for all three pollutants concerned appeared possible. Hence, the proposal contains limit values which for CO and NO x are 20% below those of R49 and for HC 30% below the R49 limit. In absolute figures, the limit values proposed are

11.2 g/kWh for CO 2.4 g/kWh for HC and 14.4 g/kWh for NO x

79

It is proposed that these limit values will have to be complied with both by new vehicle types, at the latest on 1.4.1988, and by all new vehicles from 1.10.1990 onwards.

30.FURTHER DEVELOPMENT This presentation aimed at the explanation of the past developments and the present situation of the Communities' exhaust emission regulations. It needs to be understood that these regulations are in a permanent process of evolution. On the political level, initiatives are being taken to allow the "Luxembourg agreements" to become operational, to adopt the proposed particulate standards and the standards for gaseous emissions of commercial vehicles. On the technical level expert talks are going on about the future test cycle representing extra-urban driving conditions, about the definitive emission standards for passenger cars below 1.4 litres engine capacity and for light duty vehicles as well as about possible European requirements relating to the durability of anti-pollution devices and evaporation losses. These latter discussions should allow the Commission to present, by the end of 1987, appropriate regulatory proposals for the concerned matters to the Member States.


"\. Crucq and A. Frennet (Editors), Catalysis and A utomot ioe Pollution Control 1987 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

THE MARKET FOR CAR EXHAUST CATALYSTS IN WESTERN EUROPE A Review of Trends and Developments by Willem GROENENDAAL

STRATEGIC ANALYSIS-EUROPE, Brussels, Belgium

ABSTRACT The application of catalysts to control the emission of harmful components in the exhaust gases of cars equipped with gasoline engines is an established technology in North America and Japan since the early seventies. In the last year alone, some 14 million catalyst equipped cars were sold. In Western Europe the development started much later and last year major decisions were taken which will determine the shape of the future European market. The paper will discuss the options in pollution abatement technology available under the EC regulations and the major role catalysts are expected to play. Estimates will be presented on the future catalyst demand both in the EC and other West European countries. Cost breakdowns for three way catalyst manufacture will be included. Apart from catalysts manufacturers with an established position in North America a number of new suppliers may well emerge in Western Europe. Announced catalyst and carrier manufacturing capacities will be compared with future market requirements. The demand for lead free gasoline in Western Europe is determined by the size of the catalysts equipped car population and government measures to stimulate the use. The expected demand developments will be discussed and the technology to produce lead free gasoline will be highlighted. INTRODUCTION Car exhaust catalyst systems have been installed in the majority of the new cars in the USA since model year 1975 and on all new gasoline fueld cars since 1981. The use of catalysts in the exhaust system of passenger cars and light duty commercial vehicles is considered the most practical way to comply with emission control standards in the USA and Japan. The technology is considered mature and proven (Ref. 1). In the last year alone some 14 million new catalyst equipped cars were sold and in total some 130 million catalyst cars are now in use in the world. Until 1985 catalyst equipped cars manufactured in Western Europe were exported to the USA and Japan. In 1985 legislation came in force in West Germany and Switzerland which encouraged the sales of cars with low levels of emissions of

81

82

pollutants. Also in that year lead free gasoline started to become available in most Western European countries. In 1985 fifty thousand new catalyst cars were sold in Western Europe. This paper will discuss the options in pollution abatement technology available to meet the EC regulations agreed upon in 1985 and the major role catalysts are expected to play. Estimates will be presented on the future catalyst demand both in the EC and other Western European countries. Cost breakdowns for catalysts will be included, which will show the major impact of the precious metal price and the metal content of the catalyst. Apart from catalyst manufacturers with an established position in North America new suppliers may well emerge in Western Europe. Announced catalyst and carrier manufacturing capacities will be compared with future market requirements. The demand for lead free gasoline in Western Europe is determined by government measures to stimulate its use and the size of the catalyst equipped car population. The expected development of demand will be discussed and the technology to produce lead free gasoline will be highlighted. POLLUTANT EMISSION REGULATIONS AND LEGISLATION The reduction of pollutants in automobile exhaust and in industrial waste and stack gases is of major concern in Western Europe. This was fueled in the last years by the extensive forest die-back caused by acid rain. Government policies are to achieve substantial reductions in the emissions of hydrocarbons (HC's), CO, S02, NO x and particulate matter. Road traffic is one of the major contributors to the man made emissions of HC's, CO and NO x' International and national regulations, legislation and incentives coming into force will substantially reduce these emissions. Since 1970 substantial reductions in emissions of pollutants from passenger cars already were achieved in the countries of the European Community (EC): HC emissions were reduced by 60%, CO by 70% and NO by 30% (2). These reductions were obtained by engine modifications. In the USA and Japan the reductions in emissions have been much higher. This was caused by the stringent legislation which made the use of exhaust catalysts unavoidable. In June 1985 EC regulations were announced which set a timetable for a drastic reduction of pollutants from automobile exhausts in the next ten years. These new standards differ from the US an Japanese standards. In the EC the passenger car fleet has been divided into three engine cylinder volume classes: below 1.4 liter (1), between 1.4 and 21 and above 21. The year in which the new emissions standard has to be met and the level of the emission differ for each class. The so-called Stockholm Group are the other countries in Western Europe,

8:J

that is the Nordic countries, Austria and Switzerland. Within the next years these countries will adopt the US '83 emission standards. However, the timetables are different. Denmark is a member of both groups of countries. The testing procedures used for measuring pollutant levels and the methods checking whether emission standards are achieved differ in the USA, EC and Japan. The EC test, R 15n5, lasts 13 minutes from cold start and the maximum speed is 50 kilometers (km) per hour. The US test, FrP 75, lasts 41 minutes and the maximum speed is 90 km per hour. In the US regulations pollutant levels should be below the legal limit during a period of 50,000 miles with the same catalyst installed. The forthcoming EC directive is summarised in Table 1.

Table 1 EC Car Exhaust Gas Emission Directive Decided on June 28, 1985 Passenger cars for less than 6 persons and a weight below 2,500 kg Engine size

Proposed date for implementation

Proposed emission limits gr/test maximum*

> 2 liter

1.10.88 new models 1.10.89 all new cars

CO NO x

:25.0 3.5 HC+NO x : 6.5

30.0 4.4 8.1


CO NO x

:30.0

36.0

HC +NO x : 8.0

10.0

CO NO x

54.0 7.5 19

(except Diesel) 1.4 - 21iter

< 1.4 liter

Stage 1:


:45.0 6.0 HC +NO x : 15

Stage 2 :

> 2 liter

* EC test R ISn3


Decision in 1987 on limits

for respectively new model approval and productionchecks.

Each member state is free to decide whether and when it will adopt these EC regulations and delays in implementation could occur in some countries. Standards for maximum levels of particulate emissions are being developed and will be decided upon in 1987. Also an EC test cycle with a high speed section is under development.

84

Tax incentives have been created in West Germany and the Netherlands to stimulate the early introduction of low emission cars before the EC regulations become effective. The announced legislation for the Stockholm Group of countries is summarized in Table 2.

Table 2 STOCKHOLM GROUP EMISSION LEGISLATION Country

Date of implementation

Standard

Austria

voluntary + new diesel all new cars> 1.51 all new cars < 1.5 I all new vehicles below 2500 kg 01.10.87 all new vehicles below 3500 kg 01.10.86 voluntary 01.10.88 all new cars similar to Sweden

USA'83 USA'83 USA'83

Switzerland

Sweden Finland, Norway

25.05.86 01.01.87 01.01.88 01.10.86

USA'77 USA'83 USA'83 USA'83

USA '83 regulations, valid in 49 States and from 1.09.87 in Canada, are as follows: Emission limits light duty vehicles; HC: 0.41, CO: 3.4, NOx: 1.0 and particulate 0.20 (in gr/mile).

Comparisons between the US limits and the existing and forthcoming EC limits have been made (Ref. 2). The relation between the two is strongly influenced by the type of exhaust clean up system used. In Table 3 the comparison between the US and EC limits has been expressed according to the EC test method, which results in a wide spread of the US emission limits.

85

Table 3 Comparison between US and EC Standards Engine size

US limits are expressed in EC terms as gr/test EC Pollutant US '83 Current Forthcoming

> 2 liter

CO HC+NO x

15 - 30 4- 9

80 - 100 26 - 29

30 8

104 - 2liter

CO HC+NO x

15 - 30 4- 9

70 - 80 24 - 26

36

CO HC+NO x

15 - 30 4- 9

70 24

54 19

< 104 liter

-

_

.

_

-

_

.

_

-

10

,

.

_

-

-

-

-

-

-

-

-

-

~

-

-

-

-

-

* *

I I I

-

* Stage 1 For the engine class above 21iter the forthcoming EC limits are close to the US standards. For the smaller two classes the EC standards are less stringent. EMISSION REDUCTION CONCEPTS The engine exhaust gas contains the products of the incomplete combustion of LPG, gasoline or diesel fuel. The typical composition of the exhaust gas of a gasoline engine is given in Figure 1. Figure 1 Typical exhaust gas composition from a gasoline engine

NO. HC THREEWAY LEAN BURN CATALYSIS I'l'l

4000 2DOO

3000

t5CO

ZOOO

1000

1 I I

I

U 1•• 7 IS

1,2 I II

I,.

I

20

I 22

86

The current US emission limits for light duty vehicles are achieved for gasoline fueled cars by engines equipped with a controlled threeway catalyst system including an oxygen sensor and fuel injection. For the older engine types dual bed reduction/oxidation catalyst systems are often applied (Ref. 3). Cars with diesel engines meet the standards without exhaust catalysts. Except in California diesel cars meet the particulte emission standards. Soot traps or filters are generally installed in new diesel cars sold in California. In general the less stringent EC emission limits offer the possibility to apply a wider range of emission reduction techniques (Ref. 4). Threeway catalysis controlled and uncontrolled Dual bed reduction/oxidation catalysis Lean burn engine with oxidation catalysis Exhaust gas recycle and oxidation catalysis or thermal oxidation The effectiveness and the costs of the various methods vary greatly. Apart from the reduction in emissions, another advantage of the new lean burn engine technology is a reduction in fuel consumption. However only a small number of car manufacturers have opted for this route. For the three EC engine classes, the following techniques are considered likely to meet the forthcoming emission limits. Cars with above 2 liter gasoline engines The emission limits by model year 1989/1990 are close to the US standards and therefore the same systems can be applied. Controlled threeway monolith type catalysts, predominantly single bed, are the preferred choice (Ref. 5, 6, 7). The catalyst formulations are modified to cope with European driving conditions (Ref.8,9). Cars in the 1.4 - 2 liter engine class For this class of cars the forthcoming emission limits must be met by model year 1992/1994. This class can be divided in two groups:

- Heavy and high performance vehicles. Single bed controlled threeway monolity catalysts with fuel injection or a high performance carburator are the most likely choice. - Light vehicles.Uncontrolled single bed threeway monolith catalysts, internal or external exhaust gas recycle followed by an oxidation catalyst or even thermal oxidation, or a lean burn engine followed by an oxidation catalyst are being considered and/or applied.

87

Cars with engines below 1.4 liter A large number of car types already meet the Stage 1 requirements of the forthcoming EC standards for model year 1990/1991. The current types which do not meet Stage 1 standards are being adapted. Catalysts are expected to play an insignificant role. Stage 2 standards for model year 1993/1994, to be decided in 1987, are anticipated to be comparable or less stringent than those for the 1.4 - 2 liter engine class. Catalysts are expected to play a significant role. However, in view of the increasing costs of Platinum (pt) and particularly Rhodium (Rh), emission reduction systems are likely to be chosen which minimize the use of these precious metals. There are many car manufacturers in Europe and also many importers and each produces a number of engine families. In model year 1984, some 373 different engine families were sold in West Germany (Ref. 10), thus there is a a very wide variety of conditions with which to cope. The solutions selected will be engine specific and chosen from the range of options discussed above. WEST EUROPEAN CAR MARKET The total number of passenger cars manufactured in Western Europe in 1985 was 11.5 million, an increase of 4% compared with 1984; about 0.6 million were exported to the USA. Total worldwide production was 32.7 million cars. Total sales of new cars in the EC in 1985 was 9.5 million, an increase of 3% over the previous year, of which 0.9 million cars were imported from Japan. West Europe in total recorded new car sales of 10.5 million in 1985 of which 10.7% were Japanese imports. Diesel cars represented 17% of sales in the EC and 15.9% of the total cars sales in Western Europe. The distribution of the 1985 and 1990 car sales over the emission classes in the EC is estimated (forecasted) as follows:

I=n' t y~ Gasoline

l

Di,,,,l

Engine size, liter 1985

below 1.4 1.4 - 2 above 2

% of Sales

I

1990

50% 29 4

48% 28 4

17

20

I I

j

The distribution varies from country to country with a very high percentage of small cars in Italy and France and relatively high diesel car populations in West Germany and Italy. Total car sales by 1990 in the EC are expected to exceed 10 million units.

88

CATALYST TECHNOLOGY AND COSTS Catalyst technology Since the introduction of the exhaust emission controls in the US in the midseventies, catalyst technology has developed steadily and the European practice reflects the state of the art. The composition of a typical European catalyst, the operating conditions and performance are given in the following Table 4. ---_._. _..... _ - - - - - - - _ . _ - - - - - -

Table 4 Typical European Threeway Catalyst Composition

Carrier

Cordierite monolith with 400 passages per square inch and a waIl thickness of 0.15 mm.

Washcoat

20% wt. pseudo-boehmite promoted with a.o. lanthanides, to improve the high temperature stability and the adhesion to the carrier.

Metals

Pt + Rh: 35-40 gr/cu ft (1.24-1.41 gr/l), Pt/Rh wt. ration: 5.

Bulk density

0.45 gr/l,

OPERATING CONDITIONS

Temperature

300-900C

Space velocity

100,000 - 200,000 Ill. h

Catalyst to engine cylinder volume ratio:

0.8 - 1.5

PERFORMANCE

Controlled within; A = 0.99 +/- 0.06 Conversion in %: Fresh; HC: above 80%, CO and NO x: above 70% Uncontrolled within: A= 1.05 +/- 0.2 Conversion in %: Fresh; HC: min. 50%, avo 70%; CO min. 20%, avo 55%; NO x min.lO%, avo 50%

89

The precious metal content of a typical threeway catalyst in the USA currently is 20gr/cu ft (Ref. 6). To maintain a catalyst life similar to the US standard of a minimum 50,000 miles at the anticipated much higher remaining lead content (max. 13 mg/l) of European lead free gasolines, the precious metal content will have to be higher. Instead of ceramic monoliths, high temperature Ni metal-based honeycomb carriers are available (Ref. 11, 12). In view of their overall weight and size advantages they are used as pre-catalysts and as retrofits. However on a price per volume basis, including canning, ceramic material currently is 2-3 times less expensive. The continuing price increases (see below) of Pt and particularly Rh, both indispensable components in a threeway catalyst, stimulated renewed R&D efforts to substitute at least in part, both products by less costly metals. To date these efforts have not resulted in a catalyst with equal peformance. Catalyst life in particular was impaired. Catalyst costs The sales price of threeway catalysts is for a major part determined by the precious metal costs, while for the less expensive oxidation catalyst, the impact is far less pronounced. This is illustrated in the following Figures 2 and 3.

Figure 2 Cost build-up for a Typical European Threeway Catalyst 1.3 liter ceramic carrier with 1.24 grlI Pt + Rh (ratio 5) Price: $ 47 per unit (large quantities)

~"""S STOCKS+LOSSES .,1

~3, & \

% OTHER

12,5

%

90

Figure 3 Cost build-up for a Typical European Oxidation Catalyst 1 liter ceramic carrier with 1.24 gr/l Pt + Pd (ratio 8) Price: $ 30 per unit (large quantities)

STDCKS+LDSSES

PLATINUM

3,9%

49,5% PALLADIUM

18, 2

0,7%

%

Because of the smaller size and the much lower price of Pd an oxidation catalyst is about 64% of the cost of a threeway catalyst. The prices for the relevant platinum group metals during the last three years are given in Figure 4, Figure 4 Monthly Average Prices of Platinum, Palladium and Rhodium 1985-1986.(source : Metals Bulletin)

$

per oz 1200....--------------:;-------, 1100 1000 900 m 800 ! ~ 700 ~ 600 1 I 500 II 400 I 300 200 100

o

2 4 1985 •

p l at inum

8 •

10 12

palladium

91

The increased prices of Pt and Rh increased the cost for a typical European threeway catalyst during the last half year by about 40% in US dollars. Worldwide consumption of precious metals in car exhaust catalyst ((Ref. 13) in 1985is given in Table 6.

Table 6 Precious Metals Consum tion in Auto Catalysts 1985 ~housank'~ r o yOunces

Region

-

pt

Pd

Rh

North America Japan Rest of Western World (incl.Europe)

650 175

190 100

96 30 9

Total

875

290

135

31%

11%

54%

Percentage of total demand

50

In 1985 close to 85% of the Pt supply of the Western World originated from South Africa. Based on the catalyst requirements for export models and the expected penetration of catalyst cars in Western Europe the precious metal requirements for auto catalysts is forecast to be 375,000 oz in Europe by 1994 (Ref. 13). CATALYST AND CARRIER MANUFACTURING CAPACITY AND DEMAND The US car industry mainly applies autocatalysts on ceramic monoliths; only GM uses pellets for 30% of its production. The two main manufacturers of ceramic monoliths are Coming, USA and NGK, Japan. The technology was developed by Coming in the early seventies. Four companies manufacture and supply monolith-based catalysts in the USA: Degussa, Engelhard, Johnson Matthey and Allied-Signal (UOP).In Japan and Europe the car industry applies only monolithic type catalysts. The total number of local catalysts manufacturers in Japan is seven; three are subsidiaries of car companies. The total local manufacturing capacity appears more than adequate to supply both existing and future requirements. In Western Europe the industry has been tooling up to meet the rising demand. Total planned catalyst manufacturing capacity is ten million units of which about seven million either exists or is under construction. Degussa and JMC

92

have existing facilities, Engelhard Kali-Chemie has a plant under construction and Allied-Signal has announced the construction of a plant in France. In West Germany Heraeus and Doduco supply catalysts for retrofitting existing cars. Three other firms have indicated their intention to build manufacturing facilities. Both Corning and NGK have cordierite monolith manufacturing facilities under construction in Europe with an initial total capacity of 6.5 million units. The total investment costs for these two plants are DM 140 million The current manufacturing capacity in Western Europe for metal monoliths is around 0.5 million. Future requirements for car exhaust catalysts in Western Europe for the next 5 to 10 years are extremely difficult to forecast as: - Emission limits for cars below 1.4 I stage 2 have not been decided - EC regulations are mandatory and the degree of compliance is not known. Therefore only ranges can be given for the expected future requirements. In Table 7 our forecasts are presented until 1994, the year the EC regulations are expected to become fully effective. Table 7 Demand Forecast for Car Exhaust Catalysts Western Europe: 1986-1994

Year

Minion units

1986 1990 1994

1.5 - 2 2.5 - 3 5.0 - 9

On the basis of this forecast the announced manufacturing capacity in Western Europe is adequate for the anticipated demand, including exports. With an average size of 1.3 liter and a precious metal load of 1.3g/l per unit, 380,000 oz of Pt, Rh and Pd are required for 7 million catalyst units. MOTOR GASOLINE QUALITY REQUIREMENTS The quality of the transport fuels, motor gasoline and diesel fuel in the next 10-15 years will be strongly influenced, apart from market demands, by: - Environmental legislation, directly and indirectly - Whitening of the barrel Critical aspects of gasoline quality for the performance of the engine are

93

octane and volatility. High octane is required for high compression engines with high performance and low fuel consumption. The current premium grade in Western Europe has an average Research Octane Number (RON) of about 97.5, regular is above 91 RON. From the 100 million tonnes of gasoline consumed annually, 25% is regular, but there are large differences in consumption patterns, ranging from 50% regular in West Germany to 95% premium in Italy. The estimated average Western European pool RON without lead additive is about 92.5. The average lead based octane increase is 3 to 3.5. The mounting concern in the last years on the negative health effects of lead in the environment has resulted in the reduction of the gasoline lead content and the promotion of the use of lead free gasoline. The lead content of motor gasolines by January 1, 1987, will be reduced to max. 0.15gr/1 in most European countries, the remaining countries are expected to follow in the early nineties. The EC has agreed on a timetable for the introduction of new cars fueled with lead free gasoline only: - by 1.10.89 all new models - by 1.10.91 all new cars Lead free gasoline has been available on a limited basis in all countries since 1985. The government policies in Western Europe are far from uniform: in some countries tax incentives have resulted in the replacement of regular by lead free regular; other countries promote by tax incentives the use of lead free super and still others only make lead free super and regular available. In the latter case market forces result in virtually no sales of lead free gasoline (the price is higher) which in tum reduces availability. There are doubts in the minds of consumers whether it is wise to buy a catalyst equipped car or even to use lead free gasoline. Given time a more uniform supply pattern will emerge. Two grades of lead free gasoline have been introduced; Euro Super with RON 95 and Regular with RON 90-91. Specifications for both are given below: Property

Regular

Super

Research Octane Number (RON) Motor Octane Number (MON) Density at 15C, g/ml Sulfur content, % wt Benzene content, % vol Lead content, gil

min.900r91 min. 80 or 82.5 0.70- 0.79 Below 0.1 Below 5.0 Below 0.013

min. 95 min. 85 0.70 - 0.79 Below 0.1 Below 5.0 Below 0.013

94

Within the next 10 to 15 years lead compounds will disappear as a gasoline octane improver and some 250 million octane tons per year (6 million octane barrels per day) are required to fill this gap. The current estimated average gasoline composition in Western Europe (Ref. 14) is illustrated in Figure 5 below. The two main blending components are reformate and cat cracked gasoline. By reforming paraffins and naphtenes present in naphtha into isoparaffins and aromatics the octane number is greatly improved. The main product of the conversion of heavy crude oil fractions in a catalytic cracker is gasoline. The light naphtha part in the average gasoline includes raffinate from aromatics extraction. Under the heading high octane light components: alkylate, polygasoline, isomerisate and oxygenates (alcohols and ethers) have been taken combined. Figure 5 Estimated Average Gasoline Composition Western Europe 1986

BUTANE 3.0 % UGHT NAPHTA 8.0 % CAT.CR.GASOLINE 33.0 %

REFORMATE 49.0 % HIGH OCTANE LIGHT COMP. The whitening of the barrel, we anticipate, will continue and will result in a lower percentage of straight run naphtha (derived) components and a higher percentage of cat cracker and hydrocracker derived components in the gasoline (Ref.15). The increase in octane number required to replace lead can be achieved in a number of ways (Ref. 16), all of which increase the manufacturing costs; some require substantial additional investment. At the current state of the art and prices the average cost of an octane-ton is about $ 1.8. The most attractive but limited octane enhancement is obtained by the use of octane boosting catalysts in the cat cracker. The technology to meet the octane level for total lead free gasoline is available and the time schedule leaves sufficient room for refiners to make the required adaptations and investments.

95

REFERENCES

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

M.P. Walsh, Experience in the United States with Automobile Emission Control, Platinum Metals Review, July 1986, vol. 30, n03, 106-115. K.H. Neumann, Emission reduction by modern engine design, VDI-Bericht 531, Duesseldorf 1984. (In German). P. Oeser and W. Brandstetter, Fundamentals of Catalyst Systems for S.l. Engines, MTZ Motortechnische Zeitschrift, vol 45, 5/84, 1-6 (In German). Catalysts - Meeting new challenges in a $ 2.5 billion global business, Chemical Week, vol. 138, n026, June 251986,20-71. H.D. Schuster, J. Abthoff and C. Noller, Concepts of Catalyst Exhaust Emission Control for Europe, SAE paper 852095. W.B. Williamson et al, Durability of Automotive Catalysts for European Applications, SAE paper 852097. W.DJ. Evans and AJJ. Wilkins, Single Bed, Three Way Catalysts in the European Environment, SAE paper 852096. E. Koberstein, B.H. Engler and H. Voelker, Catalytic Automotive Exhaust Purification - The European Situation 1985, SAE paper 852094. BJ. Cooper and TJ. Truex, Operational criteria affecting the design of thermally stable single bed catalysts, SAE paper 850128. Eurosystem Vehicle Registration Report (Germany). November 29,1984. P. Oeser et al, Catalytic control of exhaust emissions by metal supported precious metal catalysts. M. Nonnemann,Metal Supports for Exhaust Gas Catalysts, SAE paper 850131. G.G. Robsom, Platinum 1986, Johnson Matthey pIc. W. Groenendaal, What is new for Fluid Cat Cracking - Outlook in Western Europe - Katalistiks 7th annual symposium, 1986. S. Bernstein, European Automotive Fuels for the 80's and 90's, SAE paper 845047. J.A. Weiszmann et al, Pick your option for higher octane, Hydrocarbon Processing, June 1986,41-45.


,\, Crucq and A, Frennet (Editors), Catalysis and AutomotivePollution Control 1987 Elsevier Science Publishers B,V" Amsterdam -- Printed in The Netherlands

97

AUTOMOBILE CATALYTIC CONVERTERS K. C. TAYLOR Physical Chemistry Dept., General Motors Research Labs, Warrer"

MI (USA)

INTRODUCTION The automobile is identified as one source of emissions of hydrocarbons, carbon monoxide, and nitrogen oxides to the atmosphere. such as conventional power plants are another.

Stationary sources

Concern for the danger of

these substances to public hea lth in urban areas has led to the development of motor vehicle emission regulations by industrialized nations, in general. Current and proposed regulations have been designed to improve air quality by reducing the impact of automobile exhaust on smog formation and on carbon monoxide levels, and more recently to reduce acid deposition. The relationship between automobile exhaust emission levels and stationary pollutant sources and air quality is not a direct one.

Complex mathematical

models have been developed for predicting trends in air quality.

These models

include as input information on vehicle populations, atmospheric chemistry, meteorological variables, and other variables which can impact on the air quality of an urban area.

Predicting the level of control needed to meet air

quality goals is complicated by the multiple inputs to the atmosphere in urban areas. EMISSION CONTROL REQUIREMENTS The emission control needs of countries differ and different emission limits for passenger cars and for trucks have been established throughout the world.

Exhaust emission standards for vehicles for countries where regula-

tions have been set cannot be compared directly because the tests on which the emissions are measured differ; however, the range of control for passenger cars regulated can be viewed by expressing the limits as the intended percent reduction from the uncontrolled level as shown in Table 1.

For example, the

U.S. Federal standards represent a reduction form uncontrolled levels of 96% for hydrocarbons and carbon monoxide and 76% for nitrogen oxides.

Standards

have also been established for gasoline fueled commercial vehicles and for diesel fueled vehicles.

98 TABLE Exhaust emission standards Passenger cars [1 J

--~~"---"-------

Country

Percent Reduction CO

2 U.S. Canada 2,3 Australia

2

1

HC

NO

96

96

76

70

80

24

82

86

24

Japan (10-mode and 11-mode)

95

93

92

Europe (ECE R15.04)4

70

Sweden,

x

50

c; Switzerland~

SWitzerland 5,6

67

72

24

87

88

51

1Percent reductions for U.S., Canada, Australia, Sweden and Switzerland based on 1960 U.S. uncontrolled models. 2Measured on 1975 U.S. FTP. 3Enforced in 1986. 4Standards vary with vehicle weight. 5Measured on 1972 U.S. FTP. 6Standards effective October 1, 1986.

The exhaust emission standards (limits) and the emission test procedures for passenger cars are listed in Tables 2 and 3, respectively.

The current

Federal U.S. standards for passenger cars are 0.41 g/mile hydrocarbons, 3.4 g/mile carbon monoxide, and 1.0 g/mile nitrogen oxides.

Different exhaust

emission control standards have been set for the State of California.

The

standards for nitrogen oxides for California are stricter than the Federal standards, optional 0.7 g/mile and a primary standard of 0.4 g/mile.

Start-

ing in 1989 passenger cars must be certified at the primary standard in California.

The current Federal U.S. HC/CO/NO

trucks are 0.80/10/2.3 g/mile, respectively.

requirements for light duty x The light duty truck diesel

eXhaust particulate standard is 0.6 g/mile, dropping to 0.26 g/mile effective in 1987.

Additional requirements apply to heavy duty vehicles.

99 ',ABLE 2 Exhaust

emissio~

Passe~ger

sta~dards

cars [ 1 ]

COU', try

Standard

co

1

U.S. Canada 1,2

(g/km)

HC

NO

2.11

0.62

0.25

15.5

1. 93

1.2

Australia 1

9.3

0.93

1.9

Japan (10-mode) (imported)

2.7

0.39

0.48

Japan (10-mode) (domestic)

2.1

0.25

0.25

x

(ll-mode) (imported)

85.0 g/test

9.50 g/test

6.00 g/test

Japan (11-mode) (domestic)

60.0 g/test

4.4 g/test

7.0 g/test

Europe (ECE R15.04)3

58-110 g/test

Japa~

.

Sweden, SWitzerland

4

Switzerland 1 ,5 8, canada 7, SWitzerland Sweden 9 Saudia Arabia, Israel, Singapore (ECE R15.03)3 6 Korea

x:

19-28 g/test

24.2

2.1

1.9

9.3

0.9

1.2

2.1

0.62

0.25

65-143 g/test

6-9.6 g/test

8.5-13.6 g/test

2.11

0.25

0.62

lMeasured on 1975 U.S. FIP. 2Enforced in 1986. 3Standards vary with vehicle weight. 4Measured on 1972 U.S. FIP. 5Standards effective October 1, 1986. 6Light duty vehicles, effective July, 1987. 7Standards effective September, 1987. 8Standards effective October, 1987 9Standards effective 1989 MY.

HC+NO

100 TABLE 3 Emissio~

test procedures

Passenger cars [1J

Cou'1try

Exhaust Emiss l or.s Evap. Emi ss ions Samplir;g Methods Dri v ir.g Cycle Mettl0ds

U.S.

1975 U.S. FTP

Ca'1ada

19'75 U.S. FTP

Australia

2

Japan

1975 U.S. FTP 10-Mode 11 - t ~ o d e 6-Mode

Europe (International)

6

ECE (R15. 04)

1 Test Fuels

CVS, FlO 3 CVS, FID 3

SHED~

UL,D

Trap

UL,D

CVS, FID 3 CVS, FID3

SHED~

UL,D

Trap 5

UL,D

CVS, FID

UL

CVS, HFID

D

CVS, FID

L,D

ECE (R15.03)

Big Bag, NDIR

L,D

1972 U.S. FTP

CVS, FlO

L,D

Sweden, Switzerland Switzer land 9

1975 U.S. FTP

CVS, FID

Saud i Arab ia

ECE (R15. 03)

Big Bag, NDIR

Israe 1, Singapore 8 Korea

ECE (R15.03)

Big Bag, NDIR CVS, FID 3

1975 U.S. FTP

1UL = unleaded gasoline; L

leaded gasoline; D

UL

diesel.

2Enforced in 1986. 3Heated FID used for diesel vehicles. 4SHED = Sealed Housing for Evaporative Determination. 5Gasoline vehicles only. 6 May b e chassis . or engine dy'1amometer procedure. 7Tr ap measurements accepted. 8Light duty vehicles, effective July, 1987. 9Effective October, 1986.

SHED 4,7

L L

SHED~

UL

101

Because exhaust emissions vary as a function of such factors as the driving mode and the ambient conditions, the exhaust emissions of a vehicle are compared with the standards using an established driving cycle and sampling method.

Like the emission limits these emission test procedures are a key

part of the emission regulations.

While test methods and instrumentation for

sampling the exhaust have been virtually standardized, significant differences exist in the driving cycle schedules required in Europe, Japan, and the United States.

These variations greatly dilute the complex emission control develop-

ment process and require costly triplication of compliance verification. Today's arguments for cycle differences are weak; good progress has been made during the last twenty years in the development of efficient road systems and improvement of traffic flow, both urban and rural.

The growing division with-

in Europe on this sUbject suggests that a fresh look at a harmonized driving cycle is entirely appropriate.

Vehicle speed vs time traces for the driving

cycles for the U.S., Japan, and Europe are shown in Figure 1.

Compared with

the European cycle, the U.S. cycle goes to higher top speeds, has a cold start and hot start, and is a longer test. The third key part of emission regulations is the protocol for evaluating vehicle compliance with the emission standards.

Common to emission regula-

tions world wide is the requirement to give evidence of compliance with emission regUlations and obtain government approval prior to vehicle production. This requirement generally takes the form of sUbmitting descriptive documents and test data on a prototype vehicle which indicates that the vehicle meets the emission regulations.

In the U.S., for example, prototype passenger cars

accumulate mileage using a standardized driving schedule in order to predict the emissions performance of vehicles during the 50,000 mile compliance period.

This procedure is called the AMA durability schedule.

A vehicle

representative of each engine family must be tested. The number of different engine families sold in the U.S. in 1984 was 192; an equivalent categorization showed 119 in Japan, 78 in Australia, and 373 in West Germany [1J.

In the

U.S., Sweden, and Switzerland the governments may run their own verification

tests on vehicles submitted for certification. nesses the testing.

In Japan, the government wit-

In saudi Arabia and Canada the manufacturer's test re-

sults are not required as part of the documentation. All emission regulations specify that the production vehicle must be bUilt to match the preprOduction prototype vehicle for which emission performance was extensively tested and shown to comply with the regulations.

Furthermore,

the emissions of the production vehicles must comply with the regulations. demonstrate compliance of production vehicles, some regulations require

To

102

UNITED STATES 1972 FTP, 1975 FTP

"'0 f------,.,.-----------------'--I

.J)lUS " ' ; ~POOI ) \

u S 1572 FTP o n l y - - - - - - -

~ ~

""'~~~:HOQ ... 400°C.

Cat. 1.

r,.lO' :mdCDIm's]

4.5

3

1.5

0.01

0.02

0.03

0.04 Po,[bil'!

Pco Ib..-J

Fig. 6. Kinetics: reaction c) (CO

+

1/2 02

-. CO ) T < 250°C. Cat. 1. 2

161

P (0: G. G' bar PO z : G.C:bor

-8 -10 900 0 [

JOGO': ,

1.'8 Fig. 7. Kinetics: Arrhenius plot for reoction a).

Reaction b): CO + NO

-

Ca t. 1.

1/2 N

+ CO 2 2 Fig. 8 to 10 present the data measured with reaction b). At high temperatures very

similar curves are found compared with reaction a), which is due to the controlling mass transfer influence (see Fig. 8). There is no difference whether the reaction rate is measured as function of carbon monoxide concentrotion or NO concentration. At low temperotures different kinetics result depending on whether NO or CO is varied, while the other component is kept constant (see Fig. 9).

r, (mol rO/m1sJ

o,ms

o P.o' 0,002 bar

1,500 0 C

" Pco' 0.002 bar

0,1

0.005 i

0,001

Fig. 8. Kinetics: reaction b) (CO

+

0,002

NO

-

0,003

l/? N

2

0,004

+

CO ) T 2

P co [bar]

P 10 Ibor)

> 400°C.

Cat. 1.

162

r, -10' [mol(Olm's] o

3

2 o p '0' 0,002 bar ., p [0 ' 0,G02 bar

T ,24GO(

0,001

Fig. 9. Kinetics: reaction b) (CO

+

0,002

NO

---+

0,003

1/2 N

2

0,004

+

CO

2)

T

p [0 lbcrl P ,o[bor]

< 250°C.

lnr, Prc' 0,005 bar

P MO' G.005 tnr

-8 -10 _12 900 0,8 I,D 0

(

6000C

1,2

5000 (

:OOO(

1,4

1,6

Fig. 10. Kinetics: Arrhenius plat for reaction b).

Cat. 1.

Cat. 1.

The Arrhenius plot (see Fig. 10) is olso cornpor oble and interpreted as for reaction a),

with

the

exception that no homogenous gas phase reaction (step 4) could be

detected.

Combined reactions a) and b) Fig. 11 to 12 show "Arrhenius diagrams" where reaction rates dnCO/dt resp. dnNO/dt under the reaction conditions indicated are plotted against the reciprocal temperature. Parameters are: fresh and aged technical catalyst 1 (Pt /Rh); high-surface (porous) and low-surface (non-porous) catalyst; single precious metals Pt and Rh. In all cases a similar pattern is obtained: When

CO conversion becames boundary layer diffusion

controlled, the reaction rate for NO x canversion begins to drop. The difference between the abso)ute reaction rates for reactian a) and b) is considerably larger for pure platinum cam pared with pure rhodium or Pt/Rh combinations. As could be expected, the curves for the aged catalyst are shifted to higher temperatures. The

pattern described

above

is

most

clearly

shown

with

high-surface (parous)

catalysts, while low-surface (non-porous) catalysts give nearly identical reaction rates on Rh over a large temperature range, resulting in relatively higher NO x conversions. The latter catalyst also gives higher NO x conversions in the lean range, increasing the A/F window width (see Fig. 2). It must be pointed out that the absolute reaction rates per

geometric catalyst surface are of course much greater with the high-surface

catalyst.

Inri/co

CoU

10(101,,"0)

fresh aged

a 0

CO - NO CO -NO

-3

-4 -5

-6

1.0

1.2

1.4

1.6

Fig. 11. Kinetics: Arrhenius plot for combined reactions a) and b); P = 0.01 bar; Po 0.0065 bar; P = 0.001 bar; CO NO 2 Cat. 1: fresh and aged.

164

In rs,co

[01.2 Cot 4

In(10r~oi

o

co • NO

o

CC

.. NO

-]

-4 -5

-6 -7

-8 L---r-----"--.--~-,___---"--.._--'--,_---

1,0

1,4

1.2

1,6

Fig. 12. Kinetics: Arrhenius plot for combined reactions a) and b); = 0.01 bar; Po = 0.0065 bar; P NO = 0.001 bar; P CO Cat. 2 and 4. 2

INFRARED SURFACE SPECTROSCOPY With the equipment described in chapter "infrared spectroscopy" the absorbance of the Pt-CO resp. Rh-CO bands on catalyst 5 re sp, 6 were measured as function of temperature and oxygen partial pressure under running reaction conditions. The OfF value (ratio: oxidant/fuel) was changed either by oxygen or nitrogen oxide variation. The results are shown in Fig. 13 to 17. For reaction a) similar patterns are obtained for Me-CO absorbance as functian of oxygen partial pressure and temperature with metallic (reduced) catalysts 5 and 6 (Pt resp. Rh). With Pt at low temperatures, CO coverage also in the lean range is found, while at higher temperatures and increasing oxygen partial pressures a step function indicating a sudden CO depletion close to stoichiometry was detected. In the case of rhodium the only difference are comparable CO coverages at lower temperatures and a higher density of the step function with regard to oxygen partial pressure. In case of reaction a) the CO absorbance, Le., the CO coverage, is completely reversible. Reaction b) shows a different behavior. While on catalyst 5 (Pt) CO coverage shews a similar pattern as with reaction a), it is not further reversible with increasing temperatures.

Measurements

at

indicate only small absorbances.

lower

temperatures after high temperature exposure

Obviously,

a large part of the surface is now blocked

16.5 by some reaction intermediate which still has to be characterized. On reduced rhodium (catalyst 3) rapid CO depletion is found at lower temperatures and at very low NO partial

pressures,

indicating

a displacement of CO

by

NO or by an

intermediate

product. With increasing temperatures the step function mentioned above is formed again. After heating of catalyst 6 for 4 hours at 800°C in air ("oxidized Rh"), hardly any Me-CO absorbance could be measured. This confirms the reversible poisoning effect of Rh by oxygen measured in integral reactors.

If 'half of the carbon monoxide is replaced by hydrogen in case of reaction a), a considerable shift of the Pt-CO absorbance "step" into the lean range is found (see Fig. 17).

ca- l/Z OZ- CO 2

Absorbonce PI- [·0

Pco ~ 0,02 bor

v~Z100[m"

ZOOO[ I

1.2

0,8

~\

26'lJO( JOOO[

1,0

+--..l-'

+~ ~

J4O"(

0,6 -&=-=--"T-oA ....L..o:::::::::--....

Cot. 5 (PI}

\

ll:I'[~cc

0,4

0,2 0,1

---'4"ii?C-:)\ '--'" 46lJO~

\

0,008

0,009

0,01

0,011

~ :-. \(0,012 0,013 pOllbal

Fig. 13. Infrared: Me-CO absorbance under running reaction conditions for Cat. 5 (Pt); reaction a).

166

Absorbarce

PI-e-o

CO· NO --C0 2 + 1/ 2N2

v,2100cm- 1

P [0

'

0,02 bar

3

150"C

/

[maflmJJ

0.3-r--_ _

eo O ) r - - - _ ~ ~

0.6 0.1

0.4 It-----f0.2 0.1

0.2

0.3 r lmml

0.4

XI

20

J()

40

50

it l ~ m I

Fig. 19. Model calculation: CO and 02 concentration gradients as function of channel radius (different scale for wcsficoct and gas volume) and CO resp. coverages.

°

171

DISCUSSION Kinetic measurements, infrared investigations and the model calculations give a consistent result, which allows one to understand the factors determining the width of A/F windows on the lean side. These factors are the sorption behavior of carbon monoxide, oxygen and nitrogen oxide as function of temperature and partial pressures and mass transfer influences controlled by the porous structures of the washcoat resp. the boundary layer gas diffusion. Looking upon the situation from the point of view of a precious metal cristallite down in the porous )'-alumina structure - or a differential catalyst element - at low temperatures its surface is blocked by CO on Pt and NO or a reaction intermediate on Rh. This explains the kinetics shown in Fig. 6 and 9 (c.q., self-poisoning by CO). With increasing temperature, reaction begins and quickly accelerates until mass transfer phenomena are rate-limiting. This leads to considerable differences between the local concentrations just above the precious metal surface and the concentration in the outer gas volume. This phenomenon causes a shift of the NO x conversion curve in the direction of stoichiometry - i.e., a reduction of A/F window width in the lean range - with integral reactors. As long as the local CO concentration is high enough - which is always the case under rich conditions - CO is adsorbed and reactions a) and b) proceed. A small local surplus of oxygen leads to a rapid depletion of CO (step function) which immediately stops the NO x conversion. The concentration gradients of the reducing agents caused by mass transfer can be flattened by adding a reducing gas with high diffusion coefficient such as hydrogen (Fig. 17). In a monolith or a pellet layer this consideration for a differential catalyst element has to be extended over the whole reactor, where temperatures and concentrations are changing considerably. Thus the influence of hydrogen is hardly to be detected with integral reactors, probably due to the fact that the very high reaction rate leads to a rapid hydrogen consumption at the entrance, leaving no more hydrogen in the following sections. Starting with a rich mixture in the system CO, NO, O residue

inside

the

catalyst,

enabling a

high

CO

2 coverage and

finally leaves a CO thus also an

NO

conversion. In the case of a lean starting mixture a surplus of oxygen remains, leading to an abrupt decrease in coverage around the stoichiometric point which stops NO conversion. This means that only a part of the catalyst is available for NO x conversion when starting with a lean mixture. By lowering the absolute reaction rate (e.q., low temperature) or by reducing the diffusion resistance (non-porous catalyst), the negative influence of mass transfer on the A/F window width can be counterbalanced. For the system studied here it has to be concluded that only a compromise between A/F window width in the lean range and absolute reaction rote can be attained.

172

LEGEND r'

: rate of reaction inside the catalyst

r

: rate of reaction referred to the geometric surface of the catalyst

[ mol/m

: rate of surface

[ s- 1 ]

S

C

R

c

react~on

(Langmuir-Hinshelwood

[ mol/m\ 2s

: radial coordinate in the tube reactor

[m ]

: axial coordinate in the tube reactor

[ m

: concentration

[ mol/m

: radius of the open channel

[m ]

]

w

: gas velocity

[ m/s ]

w

: average gas velocity

[ m/s ] 3/s

V

volume flow

[ m

D

diffusion coefficient

[ m

2/s

3

]

]

[ m2/s ]

D e ff d'

: thickness of the washcoat

[ m

R

: gas constant

[ J/mol . k ]

T

: temperature

[K ]

M

: molecular weight

[ kg/mol

S

: area of 1 mol surface metal atoms

[ assumed value: 4 2/mol 4 . 10 m

B Bv

: surface

a

: sticking probability

c

s

: effective diffusion coefficient in the catalyst

]

coverage

fraction of the vacant sites : surface metal atoms concentration

[ mol/m 3 ]

ACI Pd > Rh. In contrast, Koblinski et al (Ref. 11) showed, in the same reaction system, that the activity sequence was Pd > Pt > Rh > Ru. The discrepancy between these results may be due to the different catalyst supports: the present study used

190

inactive a-Al Z03 while Koblinski et al used active Al Z03.

100

NO-H2

~

°

static.

c 0 (/\ L.

50

Q)

>

c u 0

0

z 0

400

0 Temperature

(OC )

Figure 2. NO conversion data of noble metal catalysts in NO-Hz reaction under static conditions. Otto et al (Ref. 13) studied the NO-Hz reaction over Pt and Rh catalysts and found that, at a given temperature, Pt exceeds Rh in the turnover frequency by two orders of magnitude. They considered this resulted from the different geometrical surface structure of Rh and Pt catalysts. Rh remains oxidized to a large degree under the conditions of these rate measurements and thus displays fewer active reaction sites. The higher affinity of Rh for oxygen has recently been shown (Ref. 12-15). Consistent with this concept is the fact that the amount of NO chemisorbed on an oxidized surface is smaller than that on a reduced one. This explains why Rh is less active than Pt in the NO-Hz reaction. It is also probable that Pd remains more oxidized than Pt, but to a lesser extent than Rh under present experimental conditions. The reaction products detected in the NO-Hz system, Nz, NzO, NH 3' and HzO, were similar to those in previous studies (Ref. 11). The reaction path could be estimated from the amount of consumed reactants ~ C ( N O ) and ~ C ( H z ) , or their ratio R, where R = [ ~ C ( H z ) / ~ C ( N O ) J . occur simultaneously:

That is, the following set of reactions may

191

NO + 0.5 H2 NO + H2 NO + 2.5 H2

-+ -+ -+

0.5 N20 + 0.5 H2O 0.5 N2 + H2O NH 3 + H2O

(A) ( B)

(C)

Thus for NO reduction processes, when reaction (A) occurs alone, the value of R is 0.5. Similarly, for reactions (B) and (C), the values are 1.0 and 2.5 respectively. Figure 3 shows the ratio of consumed reactants, R, as a function of reaction temperature. The behaviour of the three catalysts differed from one another. In the case of Pt and Pd catalysts, the value depended on catalyst bed temperature. However, the opposite was found in the case of Rh. Over Pt and Pd catalysts below 200°C, the value of R was smaller than 1.0. Therefore the main products of NO reduction with H2 might be N20 and N2• On the other hand, over 500°C, the main products might be NH 3 and N2• With increasing temperature, the main reaction paths may change gradually from (A) to (8) and further to (C) in present experimental conditions.

2

NO-H2

0

z

..........-. . . . . . Pt

u

-~'------

"
'1

for a TWC as a function of the air-fuel

having a BET area of

ratio.

80-100 m2/g.

Since the

201 weight of the washcoat is -20-30% of the total weight of the catalyst body the specific BET area for the whole piece is between 16-25 m2/g.

The composition

of the washcoat can vary substantially depending on the desired performance, which will be discussed in the text to follow.

Nevertheless, it is known that

the most abundant ingredient of the washcoat is alumina either in its '"I-phase or in other transitional form such as 8

or

o.

The alumina may contain a

number of stabilizers usually chosen from the oxides of rare-earth metals and/or alkaline earth metals.

Into this "washcoat" there are incorporated

simultaneously either all three of the precious metals Pt, Pd and Rh or only P:· and Rh. It is the Rh that confers on the TWC the ability to selectively reduce nitric oxide in the presence of oxygen in a stoichiometric gas mixture (A-I). In this process the Rh-catalyzed reduction of nitric oxide is largely directed to molecular nitrogen.

One has to emphasize the scarcity of this metal, which

is mined at a ratio of 1/17 with respect to Pt with which it usually appears as a by-product.

This ratio in the present TWC is usually much higher, between

1/3 to 1/10.

This, associated with the much lesser degree of recovery of Rh

from used catalysts emphasizes the utmost desirahility of utilizing the Rh in an optimal fashion.

The Role of Metal-Support Interactions in TWC The interactions we are concerned with are not those usually classified SMSI (Strong-Metal Support Interactions) which are observed after treatment under reducing conditions and lead to oxygen-deficient forms of the insulator supports.

On the contrary, the interactions we refer to are associated with

oxidation of the active component and its interaction with the support by sharing oxygens that ultimately bridge the metal ions in the support and the metal ions of the active component.

An extreme example would be, the well-

known formation of a nickel or cobalt aluminate (spinel) if one would support Ni or Co on 1-A1203 and expose it to high temperatures under oxidizing conditions.

With noble metals more often than not such interactions are

limited to the surface or subsurface region of the insulator support, but not always.

As a rule, the more refractory the support and the more noble the

active metal the less pronounced is the interaction [3]. Of particular interest to the designer of the automotive catalysts are the interactions with supports of Rh on

o~e

hand and of Pt on the other, since they

may determine the availability of the active sites of these metals and the nature of these active sites which in turn determines reactivity. In general, one may expect that the interactions mediated ,by surface oxygen ions of the insulator support will be related to the reactivity of these

202 ions.

This in turn is related to the stability of the crystallographic form of

the supports.

It has been established that Rh begins to penetrate the subsur-

face of ,-A1203 at >600°C by the solid state reaction between Rh203 and ,A1

This is a temperature which is frequently encountered in an operating 203' catalyst. Minimizing the reactivity of the support will slow down this subsurface penetration and loss of active Rh.

Fig. 2 shows this behavior [4].

the surface Rh is measured by CO chemisorption.

Here

The initial dispersion is

quite similar on the different samples, the higher CO uptake on the Rh ,-A120 3 Treatment at high temperatures under

being due to geminal adsorption.

oxidizing conditions causes a large irreversible loss of site on ,-A1203 a small loss on

and virtually no loss on ZrC2 .

~-A1203

The consequence of the disappearance of Rh

e

E .03

....\

.........

"~bb \

from the surface is a

....

drastic loss of activity

8 : ~ ~ ~ , ~ ~ 800

1000

800

1000

800

as shown in Fig. 3a [5J. 1000

Using the data shown in

1200

CALCINATION IN AIR FOR 5 HOURS AT TEMPERATURE, oK

Fig. 2, one can design a

Fig. 2 - The effect of calcination in air on (A) 0.014 wt% Rh/,-A1203'

washcoat where the Rh is

(B) 0.017

protected from direct

wt% Rh/cr-A1203, and (C) 0.010 wt%

contact with ,-A1203'

Rh/Zr02' ---, Samples reduced at

This is shown in Fig 3b,

673°K; ---, samples reduced at 823°K.

where the Rh was

From Ref.

supported on zirconia

[4].

first and the resulting powder was incorporated into ,-A1203 washcoat on a monolithic body.

The

activity of this catalyst remains virtually intact after calcination in air at 1100°C for one hour [6]. A. 130 ppm Rh/y-AI.O. 100

80

i

60

en a:

40

z o

...> z

o

u

20

o

~~~~...l.-l....ad~~ 0.8

1.0

1.2

1.4

1.6

REDOX RATIO, R

1.8 OS

1.0

1.2

1.4

1.6

1.8

2.0

REDOX RATIO, R

Fig. 3 - The steady-state activities of (a) Rh/,-A1203 and (b) A1203 after thermal treatment at 1100°C.in air for Ih.

[Rh/Zr02]/,-

From Ref.

[5].

203 On the other hand in the consideration of interaction of Pt with insulator supports we are often faced with a completely opposite

tas~

i.e. that of trying

to maximize the surface interaction to enhance and maintain high dispersion. The reason for this is the relative instability of Pt oxide and its tendency to decompose at temperatures

Ce02.

Z

0

U

w

z

maintain the high initial dispersion

40

Z o U o 40

u.s.

and West Germany

is 50 mgPb/gallon.

z

o

;!.

But it

should also be noted that the actual contaminant levels in

20

the

u.s

are considerably

lower, 2-3 mg Pb/gallon, that 1.0

1.2

1.4

1.6

is within the range shown for

REDOX RATIO, R

the data on Fig. 9. Fig. 9 - Effect of trace Pb levels on the

Fig 9

shows an extraordinary

steady-state NO activity of 0.22% Pd after

sensitivity of the catalytic

-15,000 simulated miles of pulsator aging at

activity to the lead levels

R - 1.3.

and the experiment resolves

From Ref.

[15].

clearly between minute increments of the lead in the fuel.

While the data in Fig. 9 refer only to the

loss of activity for NO reduction a similar trend is observed for hydrocarbon oxidation [15J.

The sensitivity of Pd to deactivation by traces of lead is thE

main reason why this relatively abundant and cheap noble metal is generally not used extensively in place of Pt, in particular in the first converter of a dual bed system.

210 The experience of automotive catalysis indicates that Rh is only somewhat less susceptible to poisoning by lead traces than Pd while Pt is by far thc most resistant. The use of model systems amenable to detailed surface analysis provides a means for the direct examination of the association of lead wih the surface of noble metals [16].

It immediately becomes apparent that in all the three

supported noble metals the lead is directly associated with the noble metal sites and not with the support material, which in actual catalyst constitutes over 95% of the exposed BET area.

This is shown 0:. Fig. 10 [16J, for Pt

supported on A1203, from the electron probe elemental maps.

The Pt and Pb maps

of samples exposed to simulated exhaust generated from combustion of iso-octane fuel containing 1.5 g Pb/gallon and 0.03 wt%S are exactly superimposed.

The

same obtains whether the support is 1-A1203, Ti02 or Zr02 on one hand or whether the metal is Pt, Rh or Pd.

Fig. 10 - Electron probe elemental map after Pb exposure for 24 h at 700'C for Pt supported on 1-A1203' From Ref.

[16].

211 Nevertheless, Pt is much more resistant than the other noble metals to lead poisoning and the reason for this is largely indirect. amount of sulfur acts as a scavenger for the lead.

Thus the small

To achieve this it is

necessary that the sulfur be in its hexavalent oxidation state to combine with lead oxide to form a stable lead sulfate which in itself is not a site-specific poison.

Only Pt, among the noble metals is a good catalyst for the oxidation

of S02 to S03 [17J and indeed on a Pt catalyst the lead is present as the sulfate as shown in Fig. 11.

It is clear that large amounts of lead sulfate

present in several overlayers will also act as a non site-specific poison by obstructing the access of the

reactants to the surface.

We have established

that in Rh-catalysts the lead is present as an oxide and in the case of Pd catalysts as an intermetallic compound with the Pd [16]. In all cases the association of the lead is

100

specific with the noble metal because the lead-carrying

... o N

:;;

molecules, most probably oxy-

80

halides, decompose on the noble metals sites leaving the lead on the surface.

f--

...

Cf)

0

Z

a. --S: 0"

en

w

'"

f-Z

.Q

0.

40

Table 4 highlights the specificity of this association showing the relative lead counts in microprobe analysis when the same samples of model catalysts of

20

Pt, Pd, Rh supported on A1203' Ti02 or Zr02 are exposed to a combustion gas in which the lead was

28

originally present either as

Fig. 11 - X-ray diffraction pattern of

"motor mix" i.e. tetraethyl

Pt/1-A1203 after Pb exposure for 72 h at

lead with dibromide or

700·C.

dichloride scavengers or, in

From Ref.

[16].

one case, as Pb0 2 vapor in the exhaust. than two orders of magnitude difference in the

There is more

amount of lead deposited on the

noble metal as compared with that deposited on the bare support.

The

difference when the lead-carrying species is the lead oxide is much smaller and may be insignificant.

212

TABLE 4 Pb Affinity for Noble Metals (NM) and Various Supports Pb (counts s-l)a

a

NM

NM/ A1203

NM/Ti02

NM/ Zr02

Pt

758/6

1140/2

980/6

740/l(40/2l)b

895/7

989/1

246/8

Pd

344/10

Rh

896/6

Semiquantitative microprobe analysis: average over 10 areas of 100

~m

x

100Mm size; 20 KV beam energy; 20 s counting time; Pb present in isooctane as TEL Motor Mix (TEL+EDB+EDC scavengers). b

Pb present as Pb0 2 vapor in iso-octane exhaust (EDB and EDC scavengers absent).

The specificity of the association of lead which derives from the gasoline with noble metal sites on the surface of the catalyst is the reason that minute amounts are still quite detrimental as shown most clearly for Pd catalysts in Fig. 9.

CONCLUDING REMARKS The foregoing has made it abundantly clear that the automotive catalyst in itself is a very complex chemical system and becomes even more so when all the subtle interactions with the exhaust environment are taken into account. Relatively minor fuel constituents such as the always present sulfur or small amounts of halides may have a pronounced effect on its overall behavior.

By no

means has the preceding been a complete account of all the possible interactions.

Thus we have omitted the important effects of possible alloy formation

between the active metals [18, 19J and the various deactivating influences deriving from automotive lubricants, the most important being the effect of phosphorus [20].

Further, quite often unexpected contaminants may do severe

harm to the emission hardware [21]. The designer of the automotive catalyst has to take all these into account as well as the expected physical environment, the most important being the driving conditions which will determine the temperature of the device. In an optimal catalyst each precious metal has a specific function to perform, such as Rh for nitric oxide reduction, Pt for the oxidation of

213 salurated hydrocarbons, etc.

In choosing the proper support and its modifiers

for each of the noble metals one has to bear in mind what is the desired dispersion and one has to balance the utilization of the noble metal, that is the proportion available for the surface reaction, versus the probability of the irreversible interaction with the support which results in permanent loss during use.

Further, one has to consider the proper ratios of the noble metals

and the advisability of having them in close contact or separated. Although the development of modern automotive catalysts started about twenty years ago and they have been in use for more than 10 years, there still remains ample room for improvement and better utilization of the scarce noble metals.

This can only be achieved by acquiring more knowledge through well-

directed research. The driving force for this will be on the one hand more strict environmental regulations as now witnessed in California, and on the other, the ever widening environmental concerns in varying parts of the world.

REFERENCES 1 2 3

4 5 6 7 8

9 10 11

12

13 14 15 16

G.P. Gross, W.F. Biller, D.F. Greene and K.K. Kearby, U.S. Patent 3,370,914. J.H. Jones, J.T. Kummer, K. Otto, M. Shelef and E.E. Weaver, Env. Sci. & Tech., 2 (1971) 790-98. H.C. Yao, H.S. Gandhi and M. Shelef, "Metal Support and Metal Additive Effects in Catalysts", B. Imelik (Ed.), ElseVier, Amsterdam, 1982, pp. 159-169. H.C. Yao, H.K. Stepien and H.S. Gandhi, J. of Catalysis, 61 (1980), 54750. H.K. Stepien, W.B. Williamson and H.S. Gandhi, SAE Paper 800843, Dearborn, MI, 1980. H.S. Gandhi, J.T. Kummer, M. Shelef, H.K. Stepien, and H.C. Yao, U.S. Patent 4,233,189. J.E. deVries, H.C. Yao, R.J. Baird, and H.S. Gandhi, J. of Catalysis, 84 (1983), 8-14. H.S. Gandhi, H.C. Yao and H.K. Stepien, Am. Chern. Soc. Symp. Series, No. 178, "Catalysis Under Transient Conditions", A.T. Bell and L.L. Hegedus (Eds), 1982 pp. 143-162. S. Sakellson, G.L. Haller and H.S. Gandhi, personal communication. A.S. Sass, A.V. Kuznetsov, V.A. Shvets, G.A. Savel'eva, N.M. Popova and V.B. Kazanskii, Kinetika i Kataliz, 26 (1985) 1411-15. H.C. Yao, K.M. Adams and H.S. Gandhi in "Frontiers' in Chemical Reaction Engineering", L.K. Doraiswamy and R.A. Mashelkar (Eds.), Wiley Eastern, New Delhi, 1984, pp. 129-141. H.C. Yao and W.G. Rothschild, "Proc. 4th. Int. Conf. on the Chemistry of Molybdenum", H.F. Barry and P.C.H. Mitchell (Eds.), Golden, Colorado, 1982. W.B. Williamson, H.K. Stepien and H.S. Gandhi, Env. Sci. & Technology, 14 (1980), 319-25. H.C. Yao, H.K. Stepien and H.S. Gandhi, J. of Catalysis, 67 (1981), 23136. W.B. Williamson, D. Lewis, J. Perry and H.S. Gandhi, Ind. Eng. Chern., Product R&D, 23 (1984), 531-36. H.S. Gandhi, W.B. Williamson, E.M. Logothetis, J. Tabock, C. Peters, M.D. Hurley and M. Shelef, Surface and Interface Anal., Q (1984) 148-61.

214 17 18 19 20 21

H.S. Gandhi, H.C. Yao, H.K. Stepien and M. Shelef, SAE Paper 780606, Special Publication (SP43l), 1978. W.B. Williamson, H.S. Gandhi, P. Wynblatt, T.J. Truex and R.C. Ku, AICIIE Symposium Series, No. 201, (1980) p. 212. B.M. Joshi, H.S. Gandhi and M. Shelef, Surface Technology, in press, 1986. W.B. Williamson, J. Perry, R.L. Goss, H.S. Gandhi and R.E. Beason, SAE Paper 841406, Baltimore, MD, 1984. H.S. Gandhi, W.B. Williamson, R.L. Goss, L.A. Marcotty and D. Lewis, SAE Paper 860565, Detroit, MI, 1986.


21.5

@)

MECHANISMS OF THE CARBON MONOXIDE OXIDATION AND NITRIC OXIDE REDUCTION REACTIONS OVER SINGLE CRYSTAL AND SUPPORTED RHODIUM CATALYSTS: HIGH PRESSURE RATES EXPLAINED USING ULTRAHIGH VACUUM SURFACE SCIENCE GALEN B. FISHER, SE H. OH,

~OYCE

+

E. CARPENTER, CRAIG L. DiMAGGIO, AND

STEVEN J. SCHMIEG Physical Chemistry Department, General Motors Research Laboratories, Warren, Michigan 48090-9055 (U.S.A.) D. WAYNE GOODMAN Surface Science Division, Sandia National Laboratories, Al buquer que, New Mexico 87185 (U. s. A.) THATCHER W. ROOT*, SCOTT B. SCHWARTZ**, AND LANNY D. SCHMIDT Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (U.S.A.)

ABSTRACT The demonstration that surface parameters obtained in ultrahigh vacuum (UHV) experiments are applicable to high pressure catalytic reactions has long been a goal of catalytic surface science studies. This report summarizes a set of work which has successfully shown, for carbon monoxide oxidation and nitric oxide reduction over rhodium, that high pressure rates can be predicted quantitatively using parameters determined solely under ultrahigh vacuum conditions. One implication of this work is that, for this important class of reactions, the strongly-bound surface species present under the condi tions of UHV studies are the same species reacting at high pressures. INTRODUCTION An effort has been made in this work to evaluate the utility of surface parameters determined in UHV surface science experiments for understanding the high pressure kinetics of certain catalytic reactions.

We have chosen two

test reactions of considerable significance in automotive exhaust catalysis, CO oxidation (2CO rhodium.

+ O ~ 2C0 and NO reduction (2CO + 2 N O ~ 2C0 + N over 2 2) 2) 2 To accomplish this comparison, rate constants for the elementary

steps of both reactions were determined under ultrahigh vacuum conditions. +

Present Address: AC Spark Plug Division, General Motors Corporation, Flint, Michigan 48556. *Present Address: Chemical Engineering Department, University of Wisconsin, Madison, Wisconsin 53706. **Present Address: Sherwin-Williams Co. Research Center, 10909 South Cottage Grove, Chicago, Illinois 60628.

216

Then, steady state rates for each reaction were measured over both single crystal and supported catalysts at realistic, high pressures (1-300 Torr). The use of the UHV-determined parameters in kinetic models based on the surface chemistry studies is successful in predicting quantitatively the rate data taken at high pressures for both reactions. ULTRAHIGH VACUUM AND HIGH PRESSURE SURFACE CHEMISTRY STUDIES To begin wi th, the adsorption properties, activation energies for desorption and dissociation, the orientation, and the binding sites for chemisorbed nitric oxide, carbon monoxide, and oxygen were characterized on the single crystal Rh(111) surface with high resolution electron energy loss spectroscopy (EELS), UPS, XPS, LEED, and temperature programmed reaction spectroscopy (TPRS) [1-6J.

For example, we have found the useful results that the activa-

tion energy for NO dissociation on Rh(111) is 19 ± 1 kcal/mole Rh(100) is 18 ± 1 kcal/mole [6J.

[~J

and on

We've also observed that adsorbed NO and CO

form well-mixed surface layers near reaction temperatures [5J, and that the heat of adsorption for CO on Rh(111) is reduced by 8-10 kcal/mole in the presence of nitrogen atoms [3].

In addition, steady state kinetic studies of -5 -8 -10 Torr)

both reactions on Rh(111) were carried out at low pressures (10 [7,8J and high pressures (1-300iorr).

The high pressure results have been

compared with results over supported Rh catalysts for the same reactions which were measured for the same temperatures and pressures [9J.

Finally, we have

found that rate expressions based on UHV-determined elementary intermediate steps using UHV-determined rate constants quantitatively predict the rates at high pressures for both the CO-0 and supported Rh catalysts.

and NO-CO reactions over single crystal Rh 2 This is the first time we are aware that high

pressure catalytic reaction rates have been predicted solely from UHV-determined experimental parameters.

The success of these predictions based on UHV

work shows, for an important class of reactions, that the strongly-bound species present under the conditions of UHV studies are the same species reacting at high pressures. CARBON MONOXIDE OXIDATION More particularly for the eo-0 reaction, we have measured the reaction 2 rate over Rh(111) for a wide range of pressures around p(eO) ~ P(02) ~ 0.01 a t.m , , pressures similar to those found in automoti ve exhaust, and for temperatures between 450 K and 600 K.

These data are shown in Fig. 1.

is first order in oxygen and negative first order in CO.

The reaction

From 450 K to 600 K

the reaction rate increases by almost four orders of magnitude and is characterized by a single activation energy (29 kcal/mole).

We find excellent

agreement between the specific rates and acti vation energies measured for a

217

1000

Pco

P

:=

02

:=

0.01 atm

• Rh(lll} 1------1 Rh/AI 20 3 ............ Model Q)

'"

100

-C

a::

-,

'" Q)

::J

.. ~

U Q)

\\

o

E

10

\.

N

o

\.

U

'Co ~.

x. ~.

,.,.

i··..

.... Q)

>

o c....

::J

I-

0.1 L-_J--_...L-_..J-_-.L._--'-_--"'_ 1.8 2.0 2.2 1.6 1OOO/T (K- 1)

Fig. 1. Comparisons of the specific rates of the CO-0 reaction measured over 2 Rh(lll) and Rh/A1 at P(CO) = P(02) = 0.01 atm. from Ref. 9. The model 20 prediction fits qUarltitatively with the measured rate data for both catalysts. Rh(111) crystal and a 0.01 wt% Rh/A1

catalyst, an indication of a struc20 3 ture-insensitive reaction. The elementary steps which were used to model the CO oxidation reaction based on the rate constants measured in UHV surface chemistry studies are as follows: CO (g) ;::::' COra) °2 (g)

20(a)

CO(a) As is shown in Fig. 1. we are able to predict the measured absolute rates and activation energies using a kinetic model only employing parameters determined experimentally in UHV studies [9J.

In fact. the same rate expression used

successfully at high pressures predicts the CO-0 pressures (-10

-8

2

reaction rate

~t

much lower

Torr) and at lower temperatures «400 K) where the CO

218

coverage is approximately the same as at high pressures [7].

Because the

reaction rate essentially depends only on reactant surface coverages, our understanding of CO oxidation clearly bridges the "pressure gap". of the CO-0

The picture

reaction which is confirmed by this work is that the Rh surface

2 is predominantly covered by adsorbed CO and the reaction is limited by the

rate of CO desorption (Eq. 1) or, in other words, the rate of creation of a vacant site, where oxygen adsorption (Eq. 2) and subsequent reaction (Eq. 3) can occur. NITRIC OXIDE REDUCTION For the NO-CO reaction over Rh(111) at high pressures, we find that the reaction is positi ve order in NO and surprisingly is zero order in CO.

As is

shown in Fig. 2, from 500 K to 650 K the reaction has an activation energy close to 30 kcal/mole. with nitrogen atoms.

After reaction the Rh(111) surface is nearly covered (The nitrogen atom coverage is also high near the rate

maximum in low pressure studies [8J.)

The elementary steps which were used to

model the NO-CO reaction shown below were also chosen based on the UHV measurements of the rate constants of each step.

-. CO (a) CO(g) 99% conversion) during the laboratory activity tests. There was no change in activity when 5° 2 was introduced. Of course, small changes could not be measured at such high conversions. Figure 6 shows that 2 injection at 350°C causes a sharp drop in CO conversion for a hydrothermally aged catalyst but that the initial activity is recovered after 502 exposure ends. The C3HS conversion for this sample increased with exposure to 2,

5°

5°

5°

The effects of PbBr2 poisoning and reactivation by 2 on CO adsorption were also followed on the model I wt.% Pt/A1 203 sample. Table 3 shows that on a reduced sample, Pb shifts the IR absorption bands of CO on Pt/A1 203 from 2096 to 2025 em-I. Oxidation of the sample causes an increase in band position, as has been observed in the literature (Ref. 7). Reactivation by $02 at 500°C essent i ally restores the ori gi na1 CO absorption band.

274

SUMMARY Reactivation of Pb-poisoned Pt/AI 203 catalysts for C3HS oxidation by exposure to S02 and air has been demonstrated for engine-aged and laboratory PbBr2aged monolithic catalysts using a flow reactor activity test, and in model experiments using PbBr 2-poisoned Pt/A1 203 powder. It has been shown in the model experiments that the reactivation by S02 involves the conversion of Pt-Pb species to Pt and PbS0 4• In the flow reactor activity tests, the C3HS oxidation activity of a Pb-free Pt/A1 203 catalyst was also permanently enhanced by S02' This mechanism may involve sulfate formed on the alumina, but the mechanism of its participation in the C3HS oxidation could not be determined in our experiments. It is possible that the permanent C3H8 oxidation activity increase of the reactivated Pb-poisoned samples observed in the flow-reactor activity tests may have included a contribution from this latter mechanism. In addition to permanent effects, S02 also causes a reversible activation in the activity tests. At temperatures above 500°C, the effects of S02 are not observed. This may be due to the instability of the sulfates and the unfavorable equilibrium of S02 oxidation at high temperatures. S02 exposure reversibly poisons CO oxidation on Pt/A1 203• S02 exposure also converts Pt-Pb species to Pt and PbS0 4• Thus, the net effect is that exposure to S02 has little effect on the activity of Pb-poisoned Pt/A1 203 for CO oxidation. REFERENCES 1.

a) b) c) d)

G. J. M. E.

C. Joy, G. R. Lester and F. S. Molinaro, SAE Paper #790943 (1979). C. Summers and K. Baron, J. Catalysis, 57, 380 (1979). Shelef, K. Otto and N. L. Otto, Adv. C a ~ y s i s , 27, 311 (1978). C. Su, W. R. H. Watkins and H. S. Gandhi, Appl. 8OO°C) which is possible but not abnormal Furthermore, the conversion of the reactants (CO, CnHp, NOx) must be nearly total even though the residence time of gases in the converter is extremely low

276

o

G5

r

,

_r

,.d'I

HYDRARG ILLI TE I.

r..

KHI

--..

~

kApPA

A

r

BAYERITE

L

,

,

_r

1

ETA

--..

P

~

THETA

H

A

r

BoEHM I Tt

AL 0 ((lIn

1

r

J 1

GAIoMA •

ALUIIIIIE "AL2 ~ .

DELTA.

THETA

1--

«(ORIIID. Jl

D£ TRAIlSITION

x

~

()"

hg. I - Different kinds of oxides and hydroxides of ahminum

ALUMINIIM

ALKOXIDE PROCESS

ALUMINA CARRIER

Fig. 2 - Industrial processes providing transition alumina carriers

277 'lost of these problems are sat isfac tori 1y resol ved by using t ransi t ion aluminas as catalyst carrier for the active phases (Pt, Pd, Rh) and promoters (CeO}, NiO, FeO..• ). Among the numerous transition aluminas (as illustrated in Fig.l),gamma, delta illld theta AI ~repared

are the most used. These disordered spinels can be Z03 by dehydration of boehmite. Fig. 2 shows the main ways of producing

such aluminas. The reasons for the choice of alumina are numerous : - Alumina is cheap, partly because the raw materials for special aluminas are GIBBSITE or ALUMINIUM, both of which are available in large amounts at low cost (especially GIBBSITE) derived from bauxite. - The Iso Electric Point of alumina is 9 ; its surface can be electrically charged either positively or negatively and therefore, can selectively adsorb ions. Alumina does not give rise to chemical reaction with the gas feed (except for some poisons). Moreover, since the diffusion of Platinum is very low upon alumina this active metal is stabilised as small clusters with a large surface area. Furthermore, alumina can be shaped with an accurate control of its porosity. This is very important because the catalytic processes of exhaust gas control are most often diffusion limited. From the outset, two kinds of shapes -pellets and monoliths- were developed. They are discussed separately below. Pellets At least four processes are known for making pellets from a powder - PAN PELLETIZING - OIL DROP - EXTRUSION - PILLING or TABLETTING Because of vibrations, edges have to be avoided and only the two first processes are still employed, since they provide spherical particles. The design of the carrier must include the necessity of achieving high efficiency at very low residence times. Consequently the lowest resistance to mass transfer from the gas flow to the catalytic material surface is required, leading to the following characteristics: - A small radius provides a large contact area between the beads and the gas, and lowers the intraparticle distance to the active site,

278

Fig. 3 - Cross section of a pellet type converter --------

-- - - - - - - - -

----------,

pore volume distribution: derivation of p.v.d. cumulat ive s.s.a.

L,

.. 200 ;::'8

'"

8

">e ...'e"

Q,

O.

10 100 PORE DIAMETER

1000 (nm)

fig. 4 - Illustration of bimodality

GOOD

Fig. 5 Shematic showing extremes of micro-macropore distribution

279 TIlis second aim is also the reason for peripheral impregnation of the precious metals, - A high level of macropores (diameter more than 0.1

~m)

facilitates the

intraparticular diffusion, as micropores (diameter less than 20 nm) are necessary to develop a high surface area. This double feature is know as bimodality, illustrated in fig. 4. - Furthermore, poisoning by Zn, Pb and P creates an amorphous, vitreous surface on the bead that clogs the micropores and only leaves the macropores open. Thus the distribution of microand macropores must be well designed as illustrated in Fig. 5. Photographs 6 to 9 show some details of a porosity distribution which is exceptionally well adapted to the automotive exhaust control application. To increase the porous volume by addition of macropores is also an advantage for a cold start efficiency, since this decreases the total heat capacity of the catalytic bed, and enables the catalyst to reach its lightoff temperature more quickly. Thus, the diffusional properties lead us to design very small and porous beads. However mechanical considerations limit this tendency since the crush strength of beads is proportional to the square of their radius and is a decreasing function of their porosity, as illustrated in Fig. 10. Practical considerations with respect to canning and pressure drop through the converter prohibit use of beads smaller than 2 mm diameter. These features as well as the industrial feasibility led to the use of carriers such as those shown in Fig. 11 (1975-1979) and Fig. 12 (since 1979). Monoliths Vibrations can put the beads in motion so that they collide each with other and their surface are abraded. This is the attrition phenomenon which is absent from monolithic structures within which no internal shock can occur. Two types of commercial monolithic substrates are available, made from CERAMICS (fig. 13) or refractory METALS (Fig. 14). The production methods are : ceramic monolith : mixing components, EXTRUSION and reactive calcination - metallic monoliths: wrapping two sheets of metal, one of them being corrugated, and the other flat. Neither of these two materials is suitable for direct impregnation with precious metals, their specific surface area being much too low (less than 2/g) 10 m to allow a good dispersion in a reasonable volume. This explains the need for an alumina coating on the monolithic substrate, this

c~ating

being

"" 00 o

Fig. 6,7,8,9 - S.E.M. photographs of particles exhibiting the chesnut-bur porosity

~

N

N1!P

0

-.0

~

Q13uaJ1S 3u!QsnJ)

~

e e

(J]

c:

o ~

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QJ

...cD

"0

§

(J]

"M

U

U

cD

M

",.. § QJ

u

.c

I

:8

o

rl

281

282

ANAlYSIS CERTIFICATE

SUI 12'3 ! I

ANALYSIS CERTIFICATE 2,IIAII"I'

SCS7g1

OEHSlT£DE IlEl"l'-LI,SAG£

SorrfACE "p[ClnQUE ~':R:.'[

DENSIH

m

24 HUI"H.l, 982" ( &70

RE~PLlIen

z

w

I-

Z

I

.Il

t

25W0 3-SiO Z W0 Olidized

70

65

WO, · · ~ I

3

W0 3

24T 241 42T

041 202 240 40T

60

55

222

I (YELLOW) •I

1

W03

W0 3

WO,

400 140

131 13T

22T 221

50

45

40

001 020 200

WO, WO,

liT III

220 021 20T 201

35

30

DEGREES 28

Fig. 1 XRD diffraction patterns of oxidized (yellow), and partially reduced 25 W03/SiOZ catalysts, and a reduced 1.ZPt/4.7W03/SiOZ catalyst [5).

25

20

TABLE 2. Average crystallite sizes estimated by XRO and CO chemisorption Ca ta lyst

Crysta 11 i te size

Pt loading

Pt/Si0 2

Pt/W0 3-Si02

Pt/WO/Si0 2

XRO

CHEM

1.2P t

600

47.

2.5Pt

500

58.

3.8Pt

385

79.

5.0Pt

260

133.

[A]

CHEM

XRO

CHEM

107

95

394

315

125

95

294

255

154

75

336

115

284

XRO

X-ray photoelectron spectroscopy. The XPS spectrum of three catalysts are shown in Fig.2 [5]. The lower spectrum corresponds to the oxidized 25W0 3/Si0 2 catalysts showing the 14 4f transition corresponding to the +6 state. The upper two spectra corresponding to a reduced low tungsta and high tungsta Pt containing catalyts, show the appearence of shoulders on the low energy binding side which corresponded to the 14+ 5 and 14+4 state respectively. The relative amounts of 14+ 6, 14+ 5, and 14+4 present on each catalyst listed in Table 3, were obtained from spectra like the ones shown in Fig.2. TABLE 3. 6 Extent of reduction of 14+ obtained from deconvolution of the 14 4f spectra. Pt loading

Pt/W0 3/Si02 14+ 6 14+ 5 14+ 4

100

0 Pt 1.2 Pt

70

30

NO

63

37

NO

2.5 Pt

75

25

NO

67

33

NO

3.8 Pt

85

15

NO

42

33

25

40

39

21

5.0 Pt NO

Pt/W0 3-Si02 14+ 6 14+ 5 14+4

not detected

352

>

tCI.)

Z

W

t-

Z

calcined, reduced T< 4O

"";.= 46 E

-'" ...

o

UJ

Cl

o

...J

45

300°C

1.4

1.6 10

Fig 3

3

/

1.8

T

Arrhenius plot of the initial rates of exchange on Rh/A1

203

catalyst.

364

the curves show a break point in the region To = 300-380 0C. Taking account of previous results obtained with the 0.52 % Rh/A1203 catalyst in the equilibrat i on reaction (1602 + 1802 - 2 160180) , the break poi nt at To can be exp1a ined as follows: (i) at T < To, the limiting step of exchange is the adsorption-desorption process on the rhodium particles; the apparent activation energy of this step is in the range 70-80 kJ mol- 1 throughout this series of catalysts; (ii) above To, the rate of exchange is determined by oxygen migration upon the support; in this last instance, the apparent activation energy is relatively low (19-22 kJ mol-I) in accordance with the very nature of the determining step. If this hypothesis holds, the rate of exchange should be proportional to the metal area in the region in which exchange is controlled by adsorption-desorption of 02 on rhodium particles (T6000C) there appears, in the alumina matrix, a diffuse oxide phase (OOP) of rhodium which is difficult to reduce at 5000C (Refs 7,12). Given that threeway catalysts are exposed to extreme of temperature, it was of significant interest to study the influence of the OOP on the rates of exchange and equilibration. The results, reported in Table 5, show that rE decreases in parallel with the degree of reduction at 5000C, whereas the rate of equilibration remains unchanged. This result suggests that oxygen included in the DOP TABLE 5 Influence of the temperature of air calcination on the rates of equilibration at 4000C (sample 5, 1.76 % Rh). TOC calcination

Rhodium reducible at 5000C, %

450 700 900

100 80 50

exchange

and

Exchange Equil i brati on x 1019 at min- 1g- 1 23 19 11

37 36 36

can contribute to the reaction of equilibration. The reason why exchange is relatively adversely affected by the presence of OOP has yet to be clearly elucidated. This could be due either to a decrease of the specific perimeter 10 of the rhodium particles or to a qualitative modification of the support for instance, the coverage of residual hydroxyl groups, which exerts a slight influence on the rate of exchange (Ref 5). Other PM catalysts Exchange was performed on platinum and palladium alumina as with rhodium catalysts.

supported

on the

same

The results, recorded in Table 6, demonstrate that rhodium remains the most active metal in the promotion of oxygen migration on the support. Platinum is approximately four times less active than rhodium, and palladium cannot promote, at a measurable rate, the reaction of exchange at 4000C.

TABLE 6 Comparison of the rates of exchange at 400°C on various PM catalysts. PM

Meta1 loading wt %

Pt Pd Rh

1. 06 0.62 0.52

Dispersion Do %

Rate of exchange 1019 at.min- 1g- 1

65 33 80

4.3 0 18.8

The effect of metal loading is shown on Fig 4. For purposes of comparison, 46 c 0

o

0.6

"iii c 0

~

0.4

LL

0.2 L_...L...._....L._--L_ _L...-_..I.-_....L.....l 14.0 14.2 14.4 14.6 14.8 15.0 15.2

AJF

Fig. 17. Steady-state fractional conversion of CO versus simulated NF predicted by numerical simulation.

100 . - - - - - - - - - - - - - - , 80

60 Oxygen Content (% of max.)

40

20

14.15 14.35 14.55 14.75 14.95 15.15 NF

Fig. 18. Reactive oxygen content of simulated converter at steady-state conditions.

oxygen

445

A. Crucq and A. Frennet (Editors), Catalysis and AutomotivePollution Control © 1987 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

EFFECT OF LEAD ON VEHICLE CATALYST SYSTEMS IN THE EUROPEAN ENVIRONMENT

A Deakin'

M A Kilpin'

H S Gandhi'

'Engine Engineering, Product Development, Ford of Europe 'Research Staff, Ford of USA

ABSTRACT

There

are

two

catalyst

operating

different in Europe to the USA.

parameters

These are the

that could be significantly

average

operating

temperature

and the lead levels in fuel.

A

test

programme

Way Catalyst (TWC) running.

was with

initiated to investigate the effect of lead on Three high

programme

The

temperature was

excursions

completed

in

to

three

simulate stages:

autobahn

Laboratory,

Dynamometer and Vehicle tests.

Testing showed that, depending on owner levels

of

lead,

according

to

usage,

the

effect

of

permissible

DIN standard, in the fuel could significantly

affect the efficiency of the catalyst with extended usage.

INTRODUCTION

Background:The maximum lead level in unleaded fuel has been set at 13 DIN

standard

applicable

applicable

for

6

in

EEC

territories,

months after introduction.

with

a

mg/l

waiver

Pb to

in 20

These levels are anticipated to

give a concern of catalyst poisoning if they appear in the

field.

TWC's

particularly affected by lead oxide compound covering the Rhodium sites,

Typical

Pb

level

in

without

European

as

results in Pb

such

levels

are

(2).

fuel generally available in U.S.A. is 0,8 mg/l. TWC's

can contain this level market

the mg!l

concern.

non-dedicated

reaching

the

legal

However

if

unique

conditions

in

tankage, or octane boosting using Pb maximum,

then

following data, there will be a high risk of contamination.

as

shown

by

the

446 It

was

the

possibility

of high lead levels in the pump fuels which led to

the initiation of the extensive test programme described in this paper.

TEST PROGRAM

The test stages were:-.

1.

Laboratory

Pulsator Tests

2.

Dynamometer

Simulated 80K km Ageing

3.

Vehicles

80K km ageing on AMA City Driving Schedule

Two lead levels were used during the test programme. Trace lead (up to 3mg/l) similar to

that

found

currently

in

U.S.A.

pump

fuel. 10mg/1

was

chosen

as

it

was

anticipated that early supplies of unleaded

fuel in Europe could be close to the legal limit.

Each

stage

contributed

data

from

a

aspect

different

advantage of Laboratory and Dynamometer data was that

it

of

ageing.

could

be

The

generated

much quicker than by using 80K km vehicle tests.

Laboratory Pulsator Tests

Catalyst samples were aged in a pulse flame reactor (1).

The

were

as

shown in Fig. 1.

It

included a high temperature mode (1000 deg C) for 25%

of

the

to

take

test

account

simulate

the

modification

cycle

of

and

activity

autobahn

conditions for

driving. found

Europe,

and

duplicates 48km/h steady state temperature

effects

on

measurements

Pb

on

The the

test AMA

procedure City

cycle was

Driving

Cycle,

with

has a nominal space velocity of 40000/hr which vehicle

operation.

To

be

able

to

evaluate

retention another catalyst was aged on a modified

cycle that used only 730 deg C for 6% of the cycle instead of 1000 25% of the cycle.

time

developed to

deg

C

for

447

Catalyst Temperature Cycle:

25% Time: 1000°C

max. with 3% CO excess

75% Time: 500°C

14.45:1 AFR

Activity Measurements:

Pulsator Modulation: 500°C; 40000/hr (Nominal); + 1 AFR at 0.5 Hz;

Final Steady-State:

Fig. 1

550°C; 60000/hr

Pulsator Test Cycle and Activity Measurement Conditions

Reprinted with permission c 1985 Society of Automotive Engineers, Inc

The

ageing

mg/l.Pb

fuels

added.

tetraethyllead

consisted of isooctane with 0.2 mg/l P and either 3 or 10

The (TEL),

source

of

ethylene

Pb

was

in an atomic ratio of Pb:Cl:Br of 1:2:1 injected furnace

with for

catalysts

a

nebulizer

combustion.

were

measured

directly Steady

at

"TEL

Motor

Mix"

containing

dichloride (EDC) and ethylene dibromide (EDB)

550

The into

state deg

Pb

the

containing hot

activities C

and

isooctane

was

portion of the pulsator of

the

40000/hr.

pulsator

A

diagram

aged of the

apparatus and the synthetic gas mixture used is described in reference (3).

Dynamometer Tests

To maximise lead deposition, and to simulate life

doing

Fig. 2, the ageing duration is 300 hrs.

two

vehicle

spends

its

The

cycle

is

summarized

in

This represents 80K km on the road.

catalysts, one aged with 3mg/l fuel and the other with 10mg/l were,

in turn, fitted to an emission test data vehicle, that performance

that

city driving, two catalysts were aged on a dynamometer engine to a

predominantly low temperature, low load cycle.

The

the

using

a

6,4K

km aged catalyst.

were undertaken with both catalysts.

had

a

known

emission

A series of 83US emission tests

448

TWC Ageing

Condition 1

8%

Time Inlet Temp

815 -c

885°C

RPM

84%

8%

14,65 + 0.10

AIF Ratio

Condition III

Condi tion II

465°C 14,65 + 0.10

14,95 + 0.10

3000 - 3500 RPM

Fuel

Ageing Time

Lead:

0.003

or 0.010

gil

Phosphorus:

0.001

gil

Sulphur:

0.225

gil

Fig 2

300 hrs

80,000 km

Ageing Cycle for Dynamometer Tests


Vehicle Durability

A fleet of 5 vehicles were prepared to each complete 80K km to the Driving

Schedule.

Two

vehicle

widen the database generated. from

a

european

types

and

Vehicles 4 and 5 were 49

competitor.

They

AMA

State

Federal

models

were 1985 model year production vehicles

purchased from a franchised dealer in the USA. Vehicles 1 and 2, 4 and paired,

one

running

on

trace

lead

fuel

the

other on 10 mg/l.

assigned as shown in Fig. 3. Vehicle 3 was tested

at

then

mg/1.

run

straight

through

to

80K

km

on

10

0

mile,

the

test

5

were

They were

6,4K

km

and

This was to generate

information as quickly as possible. Knowing data from this to

City

engine capacities were chosen to

car,

modifications

method, and emission test interval, for the other vehicles could

be incorporated if desired. Vehicles 1,2,4, and 5

have

been

emission

to the 83 U.S. test procedure according to the schedule shown on Fig. 4.

tested

449

1

2.0L

10 mg/l

2

2.0L

Trace Lead

3

2.0L

10 mg/l

4

1.8L

5

1.8L

10 mg/l Trace Lead

Engine Size & Lead Levels for 80K km Vehicles

Fig 3

o

6.4

10

30

50

80

1

X

X

x

X

X

X

X

X

X

Vehicle Ident

Fig 4

2

X

X

3

X

X

4

X

X

X

X

X

5

X

X

X

X

X

K km

X

Test Schedule for 80K km Vehicles

The

vehicles

were

all

multi point EFI equipped with HEGO control and full

engine management suitable for 83 U.S. markets. the

Fuel Lead Level

Engine Size

Vehicle Identification

routine

specified

for

the

vehicle

Servicing was carried

plus

out

to

any non scheduled maintenance

required.

DISCUSSION

& RESULTS

Laboratory Pulsator Tests

Increasing residual Pb levels in the fuel from 3 ageing

at

a

maximum

temperature

of

to

10

mg/l

for

pulsator

1000 deg C substantially decreased TWC

performance during pulsator modulation and steady state

conditions.

See Fig 5.

450

% Conversion

Steady State (550°C)

Pulsator (500°C) 14.5 AFR

Simulated Fuel

Mileage Km

mg Pb/l

(OOO'sl

14.3 AFR

14.6 AFR

HC

CO

NOx

HC

CO

NOx

HC

CO

NOx

3

24

63

67

67

95

98

98

66

41

82

10

24

37

33

22

92

95

92

52

45

67

Fig 5

Effect of Fuel Pb levels on Activity of Pulsator-Aged Catalysts


Evaluated

at

500

deg C at an air fuel ratio (AFR) of 14.5:1 + 1 A/F at 0.5

Hz the Nox performance was the most affected dropping from 24K

for

3

mg/l to 22% conversion for 10 mg/l.

efficiency and HC was least affected with rate.

Analysis

of

the

retention on the catalyst

a

26%

catalysts

after

surface.

Therefore

67%

conversion

at

CO suffered a 34% decrease in drop

ageing the

to

with

a 3

37%

conversion

mg/l showed no Pb

threshold

for

retention

occurs above 3 mg/1 but is already highly deleterious by 10 mg/l.

Steady

state

conditions

measured

at

550

deg

respectively shows that at stoichiometry the HC,

CO

and

Nox

is

mg/1 aged catalysts.

3%,

C at AFR 14.5:1 and 14.3:1

conversion

efficiency

loss

for

3% and 6% respectively when comparing 10 mg/1 and 3

However at AFR

rich

of

stoichiometry

the

performance

deterioration is very significant for HC and Nox at 14%, and 15% respectively.

% Conversion (550°C) Max Temp C

Fuel

Simulated

mg/l

km (OOO's)

14.6 AFR

14.3 AFR

HC

CO

Nox

HC

CO

Nox

1000

3

24

95

98

98

66

41

82

730

3

24

96

98

98

32

60

69

Fig 6

Steady State Activity for Catalysts Aged with 730

& 1000 deg C Maxima

451 The cycle was modified to include 6% of the time at 25%

at

1000 deg C.

3 mg/l, at 550 deg C instead

of

66%.

at 1000 deg C. with

3

730

deg

C

instead

of

The results are shown in Fig. 6

for the same Pb level of

14.3

HC

AFR

steady

state,

the

conversion

was

32%

The surface area of the catalyst at 730 deg C was twice that

However as stated previously the Pb retention

mg/l was zero.

and 730 deg C is more

at

1000

deg

C

Therefore the poisoning effect of Pb deposition at 500 significant

than

the

loss

of

50% surface

area

to

catalyst efficiency.

Dynamometer Ageing

A

pair

of catalysts, one dynamometer aged to 80K km on 3 mg/l and the other

10 mg/l Pb was tested in turn on a 1.6L Ford Escort with

~n

history.

83

U.S.

tests

were

conducted.

a

known

emission

The results obtained are shown in

Fig 7.

HC

co

km

0.18

1.18

0.11

80K km

0.26

1.85

0.12

3 mg Pb/l

80K km

0.80

4.52

0.26

10 mg Pb/l

Legal Limit

0.32

2.62

0.77

Assumes 1.3 D.F.

o

Fig 7

NOx

Emission Results with Catalyst Dynamometer Aged (Values in grams/mile)

The maximum temperature reached during This

temperature

the

ageing

cycle

was achieved for only 8% of the cycle.

lead

indicates

deposition that

a

was

typical

high. vehicle

This is

accounts able

to

Pb

level

is

significantly

and

Interpolating

between

3

mg/l.

produces

HC

whereas

10

and

figures

CO

deg

C.

area

but

it

also

for the deactivation, but travel

relatively low temperature, driving and still remain the

885

84% of the cycle was

at 475 deg C which was low enough to maintain high surface meant

was

80K

inside

mg/l

deactivates above

km

legal

the

of

urban,

levels

the legal

if

catalyst level.

these points, assuming linear deactivation against lead

level, up to 5 mg/l could

be

tolerated

before

deactivated to remain inside the legal limits.

the

catalyst

would

be

too

452 To

demonstrate

this,

catalysts were tested on the pulsator rig and results

showed that efficiencies had decreased to 50%, 61% and 47% for These

respectively.

results

compare

and broadly substantiate the assumption

HC,CO

and

Nox

with those at 14.5 AFR shown in Fig 5. that

increasing

lead

levels

reduce

catalyst activity linearly in this range.

sequence

test

This

clearly

indicates

that

conformity at zero mile and 80K km with 3mg/l fuel

a

vehicle

that

deteriorates

has

good

significantly

with lOmg/l Pb fuel.

Vehicle Durability

The

vehicles

used

during this stage of testing are shown in Fig 3. and the

emission test schedule undertaken is shown in Fig. 4.

A summary of the 83 U.S. emission test data, and the

corresponding

catalyst

conversion efficiencies is shown in Fig 8.

Vehicle No

,000 km

Emissions (gms/mile) CO Nox HC

% Conversion HC

CO

Remarks Nox

0.32

2.26

0.77

1

0 6.5 50 80 80

0.285 0.509 1.012 1.260 0.748

2.24 4.32 7.66 6.83 4.14

0.26 0.38 0.41 0.56 0.87

86.4 79.9 71.4 68.6 75.1

80.9 67.7 55.6 54.1 66.3

91.3 89.3 86.3 81.8 73.8

Aged Hego 10 mg Pb/l Aged Hego Fresh Hego

2

0 6.5 50

0.248 0.418 0.479

1.07 2.52 3.92

0.61 0.58 0.45

89.4 83.8 83.03

89.3 77.5 71.93

80.7 84.6 84.8

Aged Hego

3

6.5 80 80

0.152 0.607 0.358

1.36 6.00 2.86

0.62 0.70 1.03

89.2 65.0 76.7

88.7 69.4 79.1

85.4 83.6 76.2

Aged Hego 10 mg Pb/1 Fresh Hego

4

0 6.5 50

0.156 0.358 0.675

1.01 2.24 3.32

0.26 0.63 1.18

90.5 78.3 71.8

89.6 82.0 69.0

88.6 84.2 59.7

Aged Hego

0 6.5 50

0.175 0.184 0.216

0.85 1.16 1.47

0.44 0.70 1.37

88.8 89.8 90.0

86.9 80.4

77.0 52.5

Aged Hego

5

Fig 8

Legal level assuming 1.3 D.F

Trace Pb

10 mg Pb/1

Trace Pb

Summary of Emission Results for 80K km Durability Vehicles

453 Vehicles

1

and

2

were

fitted

higher than ideal emission levels whilst

vehicle

with an early, partly developed, hence the at

2 ran trace Pb fuel.

zero

mile.

Vehicle

the two vehicles and the catalyst efficiency throughout the damaged

was

Sufficient distance had been covered to

performance

characteristic.

catalyst

demonstrates

a

significant

loss

which HC and CO conversions were never above vehicle

2

with

trace

mg/l

test.

Vehicle

2

from

demonstrate

the

progressed.

for

72%

The

vehicle

HC and CO by 10K km after

and

65%

respectively.

On

lead however the HC performance remained constant over

50K km with conversions always occur

10

Fig 9 illustrates the large differences

in catalyst efficiencies that developed as the test 1

used

before 80K km had been reached resulting in the 50K km test being

the last data point. catalyst

1

Fig. 8 shows the emission performance of

above

80%.

For

CO

some

deterioration

did

90% at start of test to 72% at completion, but its performance was

superior to the 10 mg/l catalyst.

':r

-------------2

'-.)

J:

1

60

>
2;

100

0

'-.)

x

0

80

1

2;

60 0 Fig 9.

10

50

Catalyst Efficiencies for Vehicles 1 and 2

The Nox conversion performance of both catalysts deterioration

factor

generated

that of the 10 mg/l catalyst. km

the

80

was

satisfactory

but

the

by the trace lead catalyst is 32% better than

Although vehicle 2 had to be stopped

after

50K

superior performance of the catalyst at this point relative to vehicle

1 is demonstrated by the HC figures of 0.48 g/m against 1.01 of 3.92 g/m against 7.66 g/m.

g/m

and

the

CO

454 The

catalyst

that

had

been

subjected

to

the

suffered 10% to 15% performance loss due to lead. generated

a

fresh

The results

show

improvement

for

10

After

had

a

7%

conversion

efficiency

data

improvement

CO and a 8% deterioration of Nox.

been

this

had

been

HEGO sensor was fitted to vehicle 1 and the test repeated.

a

for

HC,

a

12%

This indicates that it was

controlling the engine leaner than the 80K aged HEGO. there

mg!l fuel has clearly

Therefore

rich drift, and maximum catalyst

with

ageing

conversion potential was

not being used.

The result of vehicle significantly

inside

3 the

at

6,4K

legal

from 85% to 89% on the three gases. HC

and

km

shows

limit,

the

HC,

CO

and

Nox

levels

with conversion efficiencies ranging

At 80K km the

conversion

efficiency

for

CO had dropped to 65% and 69.4% respectively which results in tailpipe

levels of 0.61 g/m and 6.0 g/m.

Both these are

above

the

legal

level.

Nox

conversion however was retained at 84% giving a 0.7 g/m result.

The

results

sufficient to

from

vehicle

3

show

that

the

to achieve legal levels at 80K km.

vehicle

3

showed

the

same

trend

as

rich

during

ageing.

HC 10% for CO and 7% for Nox.

Fitting

activity is almost

a

fresh

HEGO

sensor

vehicle 1. HC and CO efficiencies

increased whilst Nox efficiencies decreased drifted

catalyst

indicating

the

HEGO

sensor

had

The changes observed for vehicle 3 were 10% for This is of

similar

order

to

the

changes

on

vehicle 1.

Vehicles

4

and

5

were

the

competitor

vehicles

as described in Fig. 3.

Vehicle 4 was fuelled with 10 mg/l, vehicle 5 with trace Pb. two

vehicles

is available to 50K km.

the engine settings were found to be and

so

away

from

specification

emission data generated at 0 mile was discarded.

to specification and retested.

Data

for

these

At the 6,4K km test point for vehicle 5

The subsequent poor

significantly,

The engine was reset

Nox

performance

of

this

vehicle has not been explained but is subject to further investigation.

Fig

10

shows

the

catalyst

efficiencies over 50K km and comparing the two

vehicles for HC and CO only, it can retains

a

constant

deterioration. the

test.

conversion

The

performance

be

seen for

that HC,

the and

Catalyst conversion remained between 10mg/l

efficiency

catalyst and

a

efficiency between 70% and 80%.

13%

however loss

has for

trace only

80%

suffered CO,

and

lead

catalyst

exhibits 90%

a

12%

bringing

the

7%

CO

throughout loss

in HC

conversion

455 The

Nox

conversion

efficiencies

of

deterioration over 50K km, indicating a This

fuel.

deterioration

almost 19/m to 1.18g/m. limits

for

HC

and

The

earlier.

CO

mileage

Consequently

progress.

results

the catalyst on vehicle 4 shows a 29% severe

in

effect

from

50K

is

in

the

be

within

legal

km, but Nox must be disregarded as explained

accumulation data

Pb

the tailpipe Nox levels increasing by

Vehicle 5 emission data shows it to at

the

for

not

vehicles

4

and

5

is

still

in

yet available for the BOK km stage, or

for the fitting of a fresh HEGO sensor.

o>
3000

211B

Cu/TH/CR/~LKAL

MOS/~LKAL

r

r

523-673 473-593

5-15

ZNICR/K

710

25.3

5.0

20000

13

CU/ZN/K

560

7.5

0.45

2500-5000

16

Cu/TI/N~

620

6.0

2.0

11000

18

CUIlN/~L!K

555

13.0

0.5

3200

33

Cu/b';~L!~lKAll

0.3-1.9

3000-15000

25

In our recent studies, a characterization of title propert i es and of the cat alyt i c behaviour in the low temperature methanol synthesis of Cu:Zn:Me (Me= Al and/or Cr) catalysts have been reported as a function of the composition (26-28). The aim of this paper was to investigate the possible parameters which influence the selectivity of these catalysts towards the synthesis of H.M.A., with a particular emphasis on reaction conditions. Thus we tested catalysts chosen among the

471

most active and selective in the methanol synthesis, focusing our attention on those obtained from homogeneous hydrotalcite-like precursors (26-28). As previously reported, these phases are characterized by the presence of all the cations in positively charged brucite-like layers (29), thus favouring the interactions among the elements. EXPERIMENTAL The precursors with different composition (see below, Table 2) were obtained by coprecipitation from an aqueous solution of the nitrates of the elements with sodium bicarbonate at constant pH and 333K, under continuous stirring. The resulting precipitates were filtered and washed in vacuo until the complete elimination of the nitrates and until the residual amount of sodium, determined with a Mark II EEL photometer, was less than 0.05% (as Na dried at 363K for 12h, calcined at 623K for 24h

The precipitates were 20). and crushed

to a particle size of 0.250-0.420 mm. The catalysts were impregnated with different percentages of potassium (w/w) using solutions of CH and calcined at 3COOK 623K. K-doped alumina was prepared in the same way using a Y-A1 (Akzo-Chemie, 203 2 grade E) with a surface area of 125 m / g, and the absence of surface acid centers was verified by titration (30). XRO powder patterns were collected with Ni-filtered CUK u radiation (A= 0.15418 nm) using a Philips goniometer equipped with stepping motor and automated by means of a General Automation 16/240 computer. The phase compositions and crystal sizes were determined by a profile fitting method, comparing the observed profiles with the computed ones, calculated according to Allegra and Ronca (31). A Carlo Erba Sorptomatic 1826 apparatus with N adsorption was used to 2 measure the surface area and pore volume. The calcined precursors were reduced in the reactor by hydrogen diluted in nitrogen, with the hydrogen content and temperature being progressively increased (14,23,32). The catalytic tests were performed in a copper

plug flow reac-

tor, operating up to 2.0 MPa and 623K, using 0.3-0.5 g of catalyst, different space velocities and reaction gas mixtures. The reaction products were analyzed on-line without condensation using a Carlo Erba 4300 gas chromatograph equipped with FlO and two columns (1/8-in. diam. x 2.0-m long) fitted with 80-120 Poropack OS. After cooling at 263K, the gases were analyzed by a Carlo Erba 4300 gas chromatograph equipped with TCO and two

472

columns (1/8-in. diam. x 2.0-m long) fitted with Carbosieve 100-120. The chromatographic data were collected and processed by a Perkin-Elmer Sigma 15 Data Station. RESULTS AND DISCUSSION In Table 2, the compositions and the characteristic data of the catalysts examined, after both drying at 363K and calcination at 623K, are summarized, while the XRD powder patterns are reported in Figures la and b, respectively. TABLE 2 Catalyst compositions and characteristic data after drying at 363K and calcination at 623K for 24h.

SAnPLE

Co,~pos

I T I ON

ArOMIC RAT ros

SURFACE ARF.A*

SURFACE AREA:t::t:

CAT

1

CU:ZN:CR

CAT

2

Cu,ZN,AL,CR

CAT

3

Cu:ZN:AL

38,0:38,0:24,0 38,0,38,0,12,0,12,0 38,0,38,0:24,0

106

(RYST III

CuO

ZNO

119

6,5

5,0

138

5,0

~.

72

3,0

11,5

(%)

a

SIZE (rm) SPlflEl-lTKE PHASE

3,0 QlJEoi?~

-AlIORPHOUS

2. . !: !~5!

MlORPHOUS

* AFTER DRYING AT 363K FOR 12H, ** AFTER CALCINATION AT 623K FOR 24H,

In all the precipitates only a hydrotalcite-like phase was present, with lower crystal size for the chromium containing compounds. After calcination, a strong increase of the surface area was observed for all the samples. They also showed pore size distribution curves with a narrow peak centered around the most frequently occurring pore radius (28) and low crystal sizes. Role of the potassium concentration and of catalyst composition The relationship between the catalyst characteristics and the amount of potassium added are shown in Figures 2 and 3. It is possible to observe a decrease of surface area by increasing the amount of promoter added, with this effect being more marked for the chromium containing sample. However, the decrease of surface area did not exceed the 40% of the original values even for the highest amounts of potassium examined.

473

b

Cat 2 Cat 2 C")

0 0

Cat3

2

U

:::l "0 0

6

->:

i

"-

a.

4 2

e, 0

0 0

0.2 K

0.6

0.4

0.8

0

E

1.0

...>...o>

:::l "0 0 "-

a.

percentage (w/w)

Fig. 4. Productivity in methanol (II), H,M.A. ( ~ ) and hydrocarbons (.-) for Cat 1 as a function of the amount of potassium added (T= 553K; P= 1.5 MPa; H 2; GHSV= 1700 h- l).

2/CO=

.....

.....

:J

I

U

:J

I

I

I

U

Cl

....

g

-

2.5 I-

l::l

a:a

I I I I Ol.--....L--...l-----'----'----'---'

1.4 Pressure

1.6

1.8

2.0

(MPaJ

Fig. 8. Pressure effect on productivity in H.M.A. ( ~ , L 1 ) and hydrocarbons (4t,()) for Cat 1 doped with 0.2% of potassium (temperature: 543K (closed symbols), 563K (open symbols); P= 1.5 MPa; H 2; GHSV= 1700 h- l). 2/CO=

479

-

,...

N

0

u

Ol

\

~

..c 5.00

-.

ril

e/

\

s: o c 30 o

60

u

-o

Q>

s:

o c 50

2

OJ

OJ 25

45

l-

o

I

I

1

2

I

Time (hours)

Fig. 3. Isomerization of I-butene/H? at 360°C. Catalyst preconditioned.at 380°C in HZ only, • ; and ln HZ/HZO, o.

e_e_

o

4

(hours I

Fig. 4. Isomerization of I-pentene/H at 300°C. Catalyst preconditio~ed at 380°C in HZ only, • ; and in HZ/HZO, o.

in an argon carrier at 300°C. Low temperature treatment; heated at 300°C in argon (5 min) then I-pentene/argon admitted. High temperature treatment; heated at 450°C in argon, (10 min) cooled to 300°C in argon then I-pentene/argon admitted. The results in table 4 show the initial distributions. In both catalysts activity fell rapidly with time. It is important to note that neither catalyst has been exposed to HZ or HZO in its pretreatment or during the reaction test. The alternative procedure of conditioning in argon then running in HZ/HZO was investigated. In this experiment I-butene was used as the test hydrocarbon and the following pretreatment undertaken on fresh sample of catalyst. Low temperature; air at room temperature then argon at 360°C then I-butene/H Z/H ZO admitted. High temperature; argon heated to 450°C, 15 mins in air at 450°C then

488

cooling to 360°C in argon then I-butene/H admitted. Results are in table Z/H ZO 5. After low temperature treatment the major activity is double bond shift, while after high temperature treatment hydrogenation activity predominates. The effect of the temperature of preconditioning was investigated to test whether shorter times at higher temperatures are effective. Fresh catalyst was heated in HZ/HZO to 450°C for 30 mins and cooled to 300°C then tested for reaction of I-pentene in HZ/HZO at 300°C. The results (table 6) are compared with the previous results obtained after catalyst conditioning at 380°C for Z8 hours. This high temperature activation treatment results initially in rather more disproportionation and hydrogenation. Catalyst life and ultimate product distributions were not adversely affected. Exposure of a conditioned catalyst to air was found to be detrimental, particularly for the butene isomerization. Fresh catalyst was heated in a glass tube at 400°C for 4 hours in HZ/HZO. Upon cooling the catalyst was transferred in air to a reactor tube, heated under HZ/HZO to 360°C and I-butene admitted. Results (table 7) indicate that decreased skeletal isomer is formed and that increased hydrogenation occurs. ISOMERIZATION OF HIGHER ALKENES Reaction of I-hexene (table 8) occurs at lower temperatures and yields higher ratio of branched than pentene. Very high activity for the isomerization of I-hexene was observed at higher temperatures. At 400°C the loading of hexene was increased to 670 mg/g of catalyst with conversion to 50% branched product. With higher molecular weight alkenes a competitive reaction occurs which becomes more dominant as the molecular weight of the alkene increases. This reaction involves cracking the alkene to produce mainly propene, Z-methylpropene or Z-methyl 2-butene. Table 9 shows the product distribution, by carbon number, from the cracking of l-octene: greater than 95% of the products were branched. At Z80°C only 35% of the octene was cracked, mainly to Z-methylpropene and propene. All of the alkenes produced by cracking show very high branched/ straight chain ratios e.g. Z-methylpropene/Z-butene = 4.4 and Z-methyl Z-butene/ Z-pentene = 2.0. At Z80°C the l-octene which was not cracked was highly isomerized but identification of the isomers was not made. When I-dodecene was passed over the catalyst at 300°C the product distribution shown in Fig. 5 was obtained. Within anyone carbon number the ratio of branched chain/straight chain molecules was very high, being about 4:1 for C 4's and 3:1 for C5's. The lifetime of catalysts was substantially reduced by cracking but as the cracking activity decreased the ability of the catalyst to skeletally isomerize without cracking became apparent. Thus, after 21 hours cracking of I-dodecene at 300°C the products from the catalyst consisted almost entirely of branched (but unidentified) dodecenes.

489

TABLE 4

Effect of preconditioning in argon; reaction of 1-pentene/argon at 300°C Product distribution (%) preconditioned preconditioned 450°C, 10 min 300°C, 5 min 2-methyl propene 2-methyl butane pentane 2-methyl I-butene 1-pentene 2-pentene 2-methyl 2-butene

TABLE 5

1.9 4.5 39.7 50.3

10.0 77 .0

13.0

Effect of preconditioning in air/argon; reaction of 1-butene/H 2/H20 at 360°C Product distribution (%) preconditioned preconditioned air at 25°C air at 450°C then Ar at 360°C then Ar at 360°C propene 2-methyl propane butane I-butene 2-butene 2-methyl propene

TABLE 6

2.3 1.3

0.35 0.35 16.8 70.5 11. 9

1.3 0.3 42.0 6.4 28.8 22.0

Effect of precondition conditions with H 2/H 20; reaction of 1-pentene/H 2/H 20 Product distribution (%) preconditioned preconditioned 450°C, 30 min. 380°C, 28 hr. 2-methyl propene 2-methyl butane pentane 2-methyl I-butene 1-pentene 2-pentene 2-methyl 2-butene

6.8 3.9 3.1 1.6 1.6 30.4 52.4

1.6 1.9 37.1 54.5

Total branched isomers

64.7

61.0

3.7 1.2

ISOMERIZATION OF FISCHER-TROPSCH PRODUCT The conditions for operating the tungsten isomerization catalyst are compatible with the composition of the exit streGm from a Fischer-Tropsch reactor. The presence of unreacted hydrogen and water vapour together with CO and CO 2 provides an effective oxygen partial pressure equivalent to that required by the isomerization catalyst.

490

Effect of exposure of conditioned catalyst to air; reaction of 1-butene/H 2/H 20 at 360°C Product distribution ( ) catalyst reduced catalyst reduced then exposed to air on line

TABLE 7

6.1 1.4 19.7 8.1 32.7 31.9

propene 2-methyl propane butane I-butene 2-butene 2-methyl propene

6.8 2.6 0.3 10.0 43.7 36.6

Isomerization of 1-hexene/H /H20, Catalyst preconditioned H 2 / ~ 2 0 at 380°C Product distribution (%) 250°C 320°C

TABLE 8

2-methyl pentane hexane 2-methyl 1-pentene 1-hexene 2-hexene 3-methyl 2-pentene 2,3-dimethyl 2-butene

TABLE 9

3.3 2.3 1.6 7.5 20.6 58.3 6.3

5.6 3.6 2.0 8.2 15.7 58.2 6.8

Products from the cracking and isomerization of at 300°C 1-octene/H 2/H 20 Products numbers C1

C2

C3 4.1

Weight %

C4 39.8

C5 8.0

C6 3.6

C7 2.9

25

-

20 ftZ

W

u 15 0::

w

0..

t:I:

-

10 f-

C>

W ~

5

o

2

~

3

4

5

PRODUCT

FIG. 5.

6

7

CARBON

8

9

10

11

12

NUMBER

Product distribution for reaction of 1-octene/H Z/HZO on 6% WOx/HT-alumina, 300°C.

C8 41.6

C9

491

o Product 25

from F-T catalyst

[1i:l Straight chain} Products from •

Branched

WOx catalyst

!z 20 LlJ '-'

a:

~ '5

5

23456 7 PRODUCT CARBON

FIG. 6.

"

12

Product distribution from an alkene selective Fischer-Tropsch catalyst before and after passage over 6% WOx/HT-alumina isomerization catalyst.

A Fischer-Tropsch catalyst with high selectivity to alkenes has been developed (ref. 9). Product from this reaction was passed over the 6% W0 3/HT-alumina catalyst contained in a separate reactor tube and preconditioned in H2/H The 20. F-T product before and after the isomerization catalyst shown in fig. 6. Alkenes above C6 were cracked to branched alkenes and C4-C 6 alkenes were branched. The resulting ratios of branched/straight chain alkenes were close to equilibrium values. Over a period of Z hours the tungsten catalyst lost its branching activity and produced mainly straight chain Z-alkenes. However it was regenerated when treated with air at 450°C for 5 minutes and resumed its initial activity. The apparatus was later modified so that the products from reactor 1 passed through a cooling coil to trap hydrocarbons greater than CS' The remaining products were passed over the tungsten oxide catalyst in reactor Z. The product distribution was that which would be expected from isomerization alone, with little cracking, and the lifetime of the catalyst was much greater. CATAL1ST REGENERATION The specific conditions for catalyst activity depended in the al kene and on the operating temperature. Diminished activity was observed after various reaction times (see figs. I,Z). Treatments to regenerate isomerization activity were investigated. These involved oxidation followed by reduction. The reaction of I-pentene/H Z/H 20 at 300°C was followed after each of the following treatments on catalysts which had lost activity. A. Heat 450°C in air, 15 min; cool in argon B. Heat 450°C in air, 15 min; cool in HZ/HZO

492

C. D.

Heat 380°C in air, 60 min; cool in argon Heat 380°C in air, 60 min; cool in HZ/HZO The results in table 10 refer to initial catalytic activity 10 mins after addition of the hydrocarbon to the stream. The trend in all cases is for hydrogenation activity to subside with time. The final column contains data from an optimally conditioned catalyst for comparison. It is concluded that in order to minimize pentane production and maximize branched product the catalyst should be exposed to HZ/HZO prior to admission of 1-pentene. at 360°C was tested after the following Reaction of 1-butene/H Z/H ZO regenerations. (a) Increase temperature to 450°C; 15 mins air; decrease to 380°C in argon then Z8 hours in HZ/HZO. (b) Increase temperature to 450°C; 15 mins air; decrease to 360°C in argon and immediately introduce 1-butene/H Z/H ZO. (c) Increase temperature to 450°C; 15 mins air then 30 mins HZ/HZO at 450°C prior to cooling 360°C. The results are shown in figure 7. In case (b) significant quantitites of butane are present in the product stream. It appears that the most effective regeneration is (c) as it is quick and returns the catalyst to excellent isomerization activity. This activity is prolonged as 33% total branched product was observed after ZZ hours. The data in figures 1 and Z indicate that the effective catalyst lifetime for I-butene isomerization is ~ u b s t a n t i a l l y shorter than that of I-pentene. Experiments were designed to investigate whether a catalyst inactive for I-butene isomerization could effectively isomerize 1-pentene and also to determine the level of I-butene isomerization for a catalyst that has been

~ 5 r-

·,,"0

-

Fiq.7. Reaction of at 360°C. I-butene/H z/HzO Comparison of three regeneration procedures (see text).

o~

;l.

- ~o

r-

lc~·-

. ' \ . .___________

~

\

o

101

0-

0_

5. 35 _ _0 -

"0

0"'1 bl

1

g 30-/

(IJ

25

o

I

I

I

I

2

3

Time afler regeneration

I hr s I

493

TABLE 10

Reaction of I-pentene/H Z/H ZO at 300°C on regenerated catalyst Treatment as in text A B C D Fresh catalyst conditioned Hz/HZO 380°C

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