Catalytic science daniel duprez, fabrizio cavani (eds ) handbook of advanced methods and processes in oxidation catalysis from laboratory to industry (2014, imperial college press)

HANDBOOK OF ADVANCED
METHODS AND PROCESSES IN

OXIDATION
CATA LYSIS

From Laboratory to Industry

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HANDBOOK OF ADVANCED
METHODS AND PROCESSES IN

OXIDATION
CATA LYSIS

From Laboratory to Industry

Editors

Daniel Duprez
University of Poitiers, France

Fabrizio Cavani
University of Bologna, Italy

ICP

P791_9781848167506_tp.indd 2

Imperial College Press

26/6/14 12:11 pm


Published by
Imperial College Press
57 Shelton Street
Covent Garden
London WC2H 9HE
Distributed by
World Scientific Publishing Co. Pte. Ltd.
5 Toh Tuck Link, Singapore 596224
USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601
UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE

Library of Congress Cataloging-in-Publication Data
Duprez, Daniel, 1945–
Handbook of advanced methods and processes in oxidation catalysis : from laboratory to industry / Daniel
Duprez, University of Poitiers, France, Fabrizio Cavani, Universita di Bologna, Italy.
pages cm
Includes bibliographical references and index.
ISBN 978-1-84816-750-6 (hardcover : alk. paper)
1. Oxidation. 2. Catalysis. 3. Chemistry, Organic. I. Cavani, Fabrizio. II. Title.
QD281.O9D87 2014
660'.28443--dc23
2014017262


British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.

Copyright © 2014 by Imperial College Press
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Advanced Methods and Processes in Oxidation Catalysis

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Preface
Advanced Methods and Processes in Oxidation Catalysis
From Laboratory to Industry
edited by Daniel Duprez (University of Poitiers, France) &
Fabrizio Cavani (Universit`a di Bologna, Italy)

Since the discovery by Humphry Davy in 1817 of the flameless combustion of
coal gas over Pt wires, tremendous progress has been made in the understanding
of complex phenomena occurring in oxidation catalysis. In parallel, advanced technologies were developed to make these processes more efficient and safer. In the
nineteenth century, researchers observed that hydrocarbon oxidation could lead to
organic intermediates on noble metals. The huge demand from the chemical industry for new compounds prompted them to take advantage of the selective oxidation
to synthesize oxygenated chemicals. Synthesis of new compounds required specific
oxide catalysts much more selective than noble metals. Considerable progress was
made during the twentieth century while the development of cleaner, greener and
safer catalytic processes remains a permanent objective of the chemical industry
today.

This book offers a comprehensive overview of the most recent developments
in both total oxidation and combustion and also in selective oxidation. For each
topic, fundamental aspects are paralleled with industrial applications. The book
covers oxidation catalysis, one of the major areas of industrial chemistry, outlining
recent achievements, current challenges and future opportunities. One distinguishing feature of the book is the selection of arguments which are emblematic of
current trends in the chemical industry, such as miniaturization, use of alternative,
greener oxidants, and innovative systems for pollutant abatement. Topics outlined
are described in terms of both catalyst and reaction chemistry, and also reactor and
process technology.
The book is presented in two volumes. The first ten chapters are devoted to total
oxidation while the next eighteen chapters deal with selective oxidation.
v


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Preface

Different aspects of total oxidation processes are reviewed in the first part of
the book: hydrocarbon oxidation (Chapter 1) and soot oxidation (Chapter 2) for

mobile applications while oxidation of volatile organic compounds (VOC) is treated
in the next five chapters. Chapter 3 provides a general overview of VOC oxidation
while chlorinated VOCs are specifically discussed in Chapter 4 and persistent VOC
in Chapter 5. Plasma catalysis processes for VOC abatement are reviewed in Chapter
6. Finally, Chapter 7 gives the point of view of industry for the development and
applications of catalysis for air depollution technologies. Total oxidation is also used
for energy production by combustion processes exemplified in Chapter 8. The last
two chapters are devoted to oxidation processes in liquid media by electrochemical
techniques (Chapter 9) or more generally as "advanced oxidation processes" for
water depollution (Chapter 10).
The part devoted to selective oxidation includes chapters aimed at providing an
overview of oxidation technologies from an industrial perspective, with contributions from chemical companies such as eni SpA, Radici Chimica, Polynt, Sabic,
DSM, and Clariant (Chapters 11–16). Then, Chapters 17–19 gives an updated view
of experimental tools and techniques aimed at the understanding of catalyst features and interactions between catalysts and reactants/products. Chapters 20–23 are
focussed on specific classes of homogenous and heterogeneous catalysts, such as
vanadyl pyrophosphate, polyoxometalates, supported metals and metal complexes.
Finally, Chapters 24–28 deal with classes of reactions, reactor configurations and
process technologies used in selective oxidation, again offering a perspective on
recent developments and new trends, such as oxidation of alkanes, oxidations under
supercritical conditions, use of non-conventional oxidants, membrane and structured
reactors.
Daniel Duprez and Fabrizio Cavani


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Contents

Preface

v

1.

1

Oxidation of CO and Hydrocarbons in Exhaust Gas Treatments
Jacques Barbier Jr and Daniel Duprez
1.1. Introduction . . . . . . . . . . . .
1.2. The Pioneer Works (1970–1990) .
1.3. Recent Investigations (After 1990)
1.4. Conclusions . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . .

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Soot Oxidation in Particulate Filter Regeneration
Junko Uchisawa, Akira Obuchi and Tetsuya Nanba

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2.1.
2.2.

2.3.
2.4.
2.5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . .
Method for Evaluation of Catalytic Soot Oxidation Activity
Classification of PM Oxidation Catalyst . . . . . . . . . .
Mechanisms and Examples of each Catalyst Type . . . . .
Practical Application and Improvement of Soot
Oxidation Catalysts . . . . . . . . . . . . . . . . . . . . .
2.6. Concluding Remarks and Outlook . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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The Catalytic Oxidation of Hydrocarbon Volatile Organic Compounds
Tomas Garcia, Benjamin Solsona and Stuart H. Taylor

51

3.1.
3.2.
3.3.

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82
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Introduction . . . . . . . . . . . . . . . . . .
Technology Options for VOC Abatement . . .
Operational Parameters Affecting the Catalytic
Combustion of VOCs . . . . . . . . . . . . .
3.4. Review of VOC Oxidation Catalysts . . . . .
3.5. Conclusions . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . .

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viii

4.

Advanced Methods and Processes in Oxidation Catalysis

Contents

Catalytic Oxidation of Volatile Organic Compounds:
Chlorinated Hydrocarbons
Juan R. Gonz´alez-Velasco, Asier Aranzabal, Be˜nat Pereda-Ayo,
M. Pilar Gonz´alez-Marcos, and Jos´e A. Gonz´alez-Marcos

91

4.1.
4.2.
4.3.
4.4.

Introduction . . . . . . . . . . . . . . . . . . . . . . . .
Catalysts for Chlorinated VOC Oxidation . . . . . . . . .
Kinetic Studies . . . . . . . . . . . . . . . . . . . . . . .
Influence of Water Vapour and Co-Pollutants
in Feed Streams . . . . . . . . . . . . . . . . . . . . . .

4.5. Chlorinated VOC Catalyst Deactivation and Regeneration
4.6. Outlook and Conclusions . . . . . . . . . . . . . . . . .
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.

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Introduction . . . . . . . . . . . . . . . . . . . . .
Preliminary Study on POP Precursors . . . . . . . .
Advanced Study: Oxidation of PAHs in the Presence
of a Complex Pollutants Matrix . . . . . . . . . . .
5.4. Conclusion . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . .

132

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138

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145
149
150

Plasma Catalysis for Volatile Organic Compounds Abatement
J. Christopher Whitehead
6.1.
6.2.
6.3.
6.4.
6.5.

91
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98

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. 124

Zeolites as Alternative Catalysts for the Oxidation of Persistent
Organic Pollutants
St´ephane Marie-Rose, Mihaela Taralunga, Xavier Chaucherie,
Fran¸cois Nicol, Emmanuel Fiani, Thomas Belin,
Patrick Magnoux and J´erˆome Mijoin
5.1.
5.2.
5.3.

6.

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Introduction . . . . . . . . . . . . . . . . . . . . . .
Plasma Catalyst Interactions . . . . . . . . . . . . . .
Plasma Catalysis for the Abatement of Halomethanes
Plasma Catalysis for the Abatement of Hydrocarbons
The Role of Ozone in Plasma Catalysis for VOC
Abatement . . . . . . . . . . . . . . . . . . . . . . .
6.6. Cycled Systems for Plasma Catalytic Remediation . .
6.7. Conclusions . . . . . . . . . . . . . . . . . . . . . .
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . .

155
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7.

ix

Catalytic Abatement of Volatile Organic Compounds:
Some Industrial Applications
Pascaline Tran, James M. Chen and Robert J. Farrauto

173

7.1.
7.2.
7.3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . .
Case #1: Catalytic Oxidation of Purified Terephthalic Acid
Case #2: Oxidation of Nitrogen-Containing VOCs:
Precious Metal Catalysts vs Base Metal Catalysts . . . .
7.4. Case #3: Regenerative Catalytic Oxidation Catalysts . . .
7.5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.

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Hydrocarbon Processing: Catalytic Combustion and Partial
Oxidation to Syngas
Unni Olsbye
8.1. Introduction . . . . . . . . . . . . . . . . . . . . . .
8.2. Catalytic Partial Oxidation of Hydrocarbons to Syngas
8.3. Catalytic Combustion . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . .

9.

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Oxygen Activation for Fuel Cell and Electrochemical
Process Applications
Christophe Coutanceau and St`eve Baranton
9.1. Introduction . . . . . . . . . . . . . . . . . . . . . .
9.2. Thermodynamics . . . . . . . . . . . . . . . . . . . .
9.3. Molecular Oxygen Electroreduction . . . . . . . . . .
9.4. Atomic Oxygen Activation: Alcohol Electro-Oxidation
9.5. Conclusion . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . .

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10. Advanced Oxidation Processes in Water Treatment
Gabriele Centi and Siglinda Perathoner

11.

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10.1. Advanced Oxidation Processes . . . . . . . . . . . . . . . . .
10.2. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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283

Selective Oxidation at SABIC: Innovative Catalysts and Technologies
Edouard Mamedov and Khalid Karim

291

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

301

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Contents

Development of Selective Oxidation Catalysts at Clariant
Gerhard Mestl
12.1. Introduction . . . . . . . . . .
12.2. Research in Oxidation Catalysis
Acknowledgements . . . . . . . . . .
References . . . . . . . . . . . . . . .

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13. The Industrial Oxidation of KA Oil to Adipic Acid
Stefano Alini and Pierpaolo Babini
13.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . .
13.2. Nitric Acid Oxidation of a Cyclohexanol/Cyclohexanone
Mixture to Produce Adipic Acid . . . . . . . . . . . . . .
13.3. Development of Reactors for Adipic Acid Synthesis . . .
13.4. Safety Aspects . . . . . . . . . . . . . . . . . . . . . . .
13.5. Materials . . . . . . . . . . . . . . . . . . . . . . . . . .
13.6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.

15.

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Selective Oxidation Reactions in Polynt: An Overview
of Processes and Catalysts for Maleic Anhydride
Mario Novelli, Maurizio Leonardi and Carlotta Cortelli
14.1. Introduction . . . . . . . . . . . . . . . . . . . . . . .
14.2. Maleic Anhydride Market Trends and Production . . . .
14.3. The Most Consolidated Gas-Phase Selective Oxidation
Process for Maleic Anhydride Production:
The Oxidation of Benzene . . . . . . . . . . . . . . . .
14.4. Selective Oxidation of n-Butane for Maleic
Anhydride Production . . . . . . . . . . . . . . . . . .
14.5. Gas-Phase Selective Oxidation of n-Butane
to Maleic Anhydride: The ALMA Process . . . . . . .

14.6. Some Recent Developments in the Fixed-Bed Process
for Gas-Phase Selective Oxidation of n-Butane
to Maleic Anhydride . . . . . . . . . . . . . . . . . . .
14.7. Conclusions . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Selective Oxidations at Eni
353
Roberto Buzzoni, Marco Ricci, Stefano Rossini and Carlo Perego
15.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 353


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15.2. TS-1 and Related Materials: A Materialized Dream . .
15.3. Selective Oxidation with Hydrogen Peroxide by TS-1
and Related Materials . . . . . . . . . . . . . . . . .
15.4. Hydrogen Peroxide Production . . . . . . . . . . . .

15.5. Other Oxidations . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.

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Selective Oxidation in DSM: Innovative Catalysts and Technologies
Paul L. Alsters, Jean-Marie Aubry, Werner Bonrath,
Corinne Daguenet, Michael Hans, Walther Jary, Ulla Letinois,
V´eronique Nardello-Rataj, Thomas Netscher, Rudy Parton,
Jan Sch¨utz, Jaap Van Soolingen, Johan Tinge
and Bettina W¨ustenberg
16.1. Polyhydroxy Compounds: Ascorbic Acid . . . . . . . . . . .
16.2. Aromatic Oxidations . . . . . . . . . . . . . . . . . . . . . .
16.3. Oxidations in Monoterpene Chemistry . . . . . . . . . . . .
16.4. Vitamin B5 : Ketopantolactone . . . . . . . . . . . . . . . . .
16.5. Cyclohexane Oxidation . . . . . . . . . . . . . . . . . . . .
16.6. Toluene Side-Chain Oxidation . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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In Situ and Operando Raman Spectroscopy of Oxidation Catalysts
Israel E. Wachs and Miguel Ba˜nares
17.1. Introduction . . . . . . . . . . . . . . . . . . . . . . .
17.2. Methanol Oxidation to Formaldehyde . . . . . . . . . .
17.3. Methane Oxidation to Formaldehyde . . . . . . . . . .
17.4. Ethane Oxidative Dehydrogenation (ODH) to Ethylene
17.5. Ethylene Oxidation to Ethylene Epoxide . . . . . . . .
17.6. Propane Oxidative Dehydrogenation to Propylene . . .
17.7. Propylene Oxidation and Ammoxidation . . . . . . . .
17.8. Propane Oxidation and Ammoxidation . . . . . . . . .
17.9. Butane Oxidation to Maleic Anhydride . . . . . . . . .
17.10. Isobutane Oxidation . . . . . . . . . . . . . . . . . . .
17.11. o-Xylene Oxidation to Phthalic Anhydride . . . . . . .
17.12. SO2 oxidation to SO3 . . . . . . . . . . . . . . . . . .
17.13. Conclusions and Outlook . . . . . . . . . . . . . . . .
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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18.

Advanced Methods and Processes in Oxidation Catalysis

Contents

Infrared Spectroscopy in Oxidation Catalysis
Guido Busca

447

18.1. Introduction . . . . . . . . . . . . . . . . . . . . . . .
18.2. Experimental Techniques . . . . . . . . . . . . . . . .
18.3. The Bulk Characterisation of Solid Oxidation
Catalysts by IR . . . . . . . . . . . . . . . . . . . . . .
18.4. Surface Characterisation of Oxidation Catalysts
by IR Spectroscopy . . . . . . . . . . . . . . . . . . .
18.5. Studies of Oxidation Reactions Over Solid Catalysts:
Methodologies . . . . . . . . . . . . . . . . . . . . . .
18.6. IR Spectroscopy Studies of Heterogeneously Catalyzed
Oxidations: Case Studies . . . . . . . . . . . . . . . .
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.

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485
485

In Situ Non-Vibrational Characterization Techniques to Analyse
Oxidation Catalysts and Mechanisms
Angelika Br¨uckner, Evgenii Kondratenko, Vita Kondratenko,
J¨org Radnik and Matthias Schneider
19.1.

19.2.
19.3.
19.4.

Introduction . . . . . . . . . . . . . . . . . . . .
Electronic (Resonance) Techniques . . . . . . . .
X-ray Techniques . . . . . . . . . . . . . . . . .
Temperature-programmed Reduction, Oxidation
and Reaction Spectroscopy (TPR, TPO and TPRS)
19.5. Transient Techniques . . . . . . . . . . . . . . . .
19.6. Concluding Remarks . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . .

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20. Vanadium-Phosphorus Oxide Catalyst for n-Butane Selective
Oxidation: From Catalyst Synthesis to the Industrial Process
Elisabeth Bordes-Richards, Ali Shekari and Gregory S. Patience
20.1. Introduction . . . . . . . . . . . . . . . . . . . . .
20.2. Portrait of a Selective Oxidation Catalyst . . . . . .
20.3. Application to VPO Catalysts in n-butane Oxidation
to Maleic Anhydride . . . . . . . . . . . . . . . . .
20.4. Transient Regimes . . . . . . . . . . . . . . . . . .
20.5. Experiments in Alternative Reactors . . . . . . . . .
20.6. Conclusions . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . .

549

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549
551

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569
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Advanced Methods and Processes in Oxidation Catalysis

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Contents

21.

xiii

Polyoxometalates Catalysts for Sustainable Oxidations
and Energy Applications

586

Mauro Carraro, Giulia Fiorani, Andrea Sartorel
and Marcella Bonchio
21.1. Polyoxometalates . . . . . . . . . . . . . . . .

21.2. Oxidation Catalysis by POMs . . . . . . . . . .
21.3. Heterogeneous Polyoxometalate-Based Systems
21.4. Conclusions . . . . . . . . . . . . . . . . . . .
Acknowledgments . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . .
22.

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Supported Metal Nanoparticles in Liquid-Phase Oxidation Reactions

586
589
615
618
619
619
631

Nikolaos Dimitratos, Jose A. Lopez-Sanchez
and Graham J. Hutchings
22.1. Introduction . . . . . . . . . . . . . . . . .
22.2. Oxidation of Alcohols and Aldehydes using
Molecular Oxygen . . . . . . . . . . . . . .
22.3. Selective Oxidation of Hydrocarbons . . . .
22.4. Other Selective Oxidation Reactions . . . .
22.5. Conclusions and Final Remarks . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . .
23.

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631

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632
656
666
668
669

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Sustainability Trends in Homogeneous Catalytic Oxidations

679

Alessandro Scarso and Giorgio Strukul
23.1. Introduction . . . . . . . . . . . . . . . . . . . . .
23.2. Use of Oxygen and Hydrogen Peroxide . . . . . . .
23.3. Enantioselective Oxidations . . . . . . . . . . . . .
23.4. Water as the Reaction Medium . . . . . . . . . . .
23.5. The Use of Less Toxic Metals as Active Ingredients
23.6. Heterogenization of Homogeneous Systems . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . .
24.

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Light Alkanes Oxidation: Targets Reached and Current Challenges

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679
681
681
719
732
738
755
767

Francisco Ivars and Jos´e M. L´opez Nieto
24.1.
24.2.
24.3.
24.4.

Introduction . . . . . . . . . . . . . . . . . . . . . . .
Oxidative Dehydrogenation of Light Alkanes to Olefins
Partial Oxidation of C2 –C4 Alkanes . . . . . . . . . . .
Selective Oxidative Activation of Methane . . . . . . .

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. 767
. 789
. 792
. 809


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xiv

25.

Contents

24.5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

814
815

Opportunities for Oxidation Reactions under Supercritical Conditions
Udo Armbruster and Andreas Martin

835

25.1.
25.2.
25.3.
25.4.

. . . . . . . . .
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. . . . . . . . .

835
845
851

. . . . . . . . .
. . . . . . . . .
. . . . . . . . .

863
864
865

Introduction . . . . . . . . . . . . . . . . . .
Oxidation in Supercritical Carbon Dioxide . .
Oxidation in Supercritical Water . . . . . . . .
Heterogeneously Catalysed Oxidation in Other
Supercritical Fluids . . . . . . . . . . . . . .
25.5. Summary and Outlook . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . .
26.

b1675-fm

Unconventional Oxidants for Gas-Phase Oxidations
Patricio Ruiz, Alejandro Karelovic and Vicente Cort´es Corber´an

877

26.1. Nitrous oxide (N2 O) . . . . . . . . . . . . . . . . . . . . . . . 877
26.2. Carbon dioxide (CO2 ) . . . . . . . . . . . . . . . . . . . . . . 894
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914
27.

Membrane Reactors as Tools for Improved Catalytic
Oxidation Processes
Miguel Men´endez
27.1. Introduction . . . .

27.2. Dense Membranes .
27.3. Porous Membranes .
27.4. Conclusions . . . .
References . . . . . . . . .

28.

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921
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Structured Catalytic Reactors for Selective Oxidations
Gianpiero Groppi, Alessandra Beretta and Enrico Tronconi
28.1. General Considerations on Structured Catalysts . . . . .
28.2. Applications of Structured Catalysts in Short Contact

Time Processes . . . . . . . . . . . . . . . . . . . . . .
28.3. Applications of Monolithic Catalysts Based on Low
Pressure Drop Characteristics . . . . . . . . . . . . . .
28.4. Applications of Structured Catalysts Based on Enhanced
Heat Exchange . . . . . . . . . . . . . . . . . . . . . .
28.5. Summary and Conclusions . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Index

921
922
925
933
934
943

. . . .

943

. . . .

951

. . . .

965

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. . . .
. . . .

970
989
990
999


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Chapter 1
Oxidation of CO and Hydrocarbons in Exhaust Gas Treatments
Jacques BARBIER Jr and Daniel DUPREZ∗
The present chapter aims to describe the kinetics and mechanisms of CO and HC
oxidation in exhaust gas treatments. Attention will be paid to reactions carried out
on noble metal catalysts (Pt, Pd, Rh) usually employed in three-way catalysts (spark
ignition engines) around stoichiometry. The effect of ceria, usually employed as
an oxygen storage material, will also be reviewed.

1.1.

Introduction

Since 1972 in the United States and 1989 in Europe, regulations have been imposed
on the automobile industry to limit air pollution emitted by vehicles. Since these
dates, legislation has been regularly reinforced with more and more severe regulations concerning four categories of pollutants: carbon monoxide, hydrocarbons
(and other organics), nitrogen oxides (NO and NO2 ) and soot particulates.1–3 To
achieve abatement of these pollutants, automotive catalytic converters were implemented on new cars to eliminate CO, HC and NOx, while particulate filters are
intended to be mounted in the exhaust gas pipe of diesel engines. Oxidation of
CO and hydrocarbons is an important process occurring over three-way catalysts.
These catalysts are currently employed in the catalytic converters of gasoline engines
(close-looped engines) while similar formulations are used in diesel oxidation converters. Three-way (TW) catalysts contain Pt, Pd and Rh deposited on a mixed oxide
made typically of doped alumina (La, Ca, . . .) and an oxygen storage capacity component (Cex Zr1−x O2 binary oxides or CeZrXOy ternary oxides, X being another
rare earth element).4–7 The term “oxygen storage capacity” was introduced by Yao
and Yu Yao to qualify the ability of the catalyst to work in cycling conditions: the
solid stores oxygen during the lean phases and releases it during the rich ones.8
With this method, the noble metals continue to be fed with O species when the O2
concentration significantly decreases in the gas phase.
∗ Laboratoire de Catalyse en Chimie Organique, UMR 6503 CNRS-Universit´e de Poitiers, 40 avenue du Recteur
Pineau, 86022 Poitiers cedex. France.

1


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Advanced Methods and Processes in Oxidation Catalysis

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Jacques Barbier Jr and Daniel Duprez

Oxidation of CO and hydrocarbons in conditions of exhaust gas conversion
(concentrations around 1% for CO and less for HCs) has been widely studied since
the implementation of catalytic converters. Yu Yao was one of the first authors to
publish a systematic study of these reactions over Pt, Pd and Rh catalysts in O2
excess.9, 10 Moreover, the effect of ceria was also investigated, making Yao and
Yu Yao’s reports a source of important information. Their results will be analyzed
and summarized in the first part of this chapter. In the second part, more recent
studies will be reviewed with special attention paid to investigation under cycling
conditions.

1.2. The Pioneer Works (1970–1990)
In TW catalysis, an optimal conversion of all the pollutants (reducers like CO and
HC, and oxidants like NO and NO2 ) is achieved for an S ratio (defined by Schlatter)11
close to unity. The S ratio is given in Eq. 1.1, in which chemical formulae represent
the volume percentages of the gases.
S=

2O2 + NO + 2NO2
CO + H2 + 3nCn H2n + (3n + 1)Cn H2n+1

(1.1)

The numerator represents the number of O atoms available in the oxidants

(O2 and NOx) while the denominator represents the number of O atoms required
for a total oxidation of the reducers: CO, HC (alkenes and alkanes) and H2 . The
Schlatter equation may easily be extended to other HC (aromatics for instance) or
oxygenated compounds. However, other gases such as H2 O and CO2 are not supposed to react with pollutants, which is not always observed (see Section 1.4). Yu
Yao investigated CO and HC oxidation in O2 excess (S = 2). Oxidation reactions
were carried out over Pd, Pt and Rh catalysts of different metal loading and dispersions and at different temperatures. In the publications of Yu Yao,9, 10 the reactions
were carried out over bulk metals (wires), alumina-supported catalysts and finally
over metals supported on ceria-alumina. Specific rates (per gram of catalyst) were
reported as well as activation energies, metal dispersions of supported catalysts
or metal area of bulk catalysts. From this information it was possible to calculate
turnover frequencies (TOF) extrapolated at a given temperature (the same for every
metal catalyst).12 Metal catalysts are compared on the basis of their TOF.

1.2.1.

Oxidation of carbon monoxide

1.2.1.1. Effect of metal particle size
Oxidation of carbon monoxide (Eq. 1.2) is a reaction which can be catalyzed by all
the noble metals usually employed in TW converters but also by many oxides or


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Oxidation of CO and Hydrocarbons in Exhaust Gas Treatments

b1675-ch01

3

Table 1.1. Intrinsic activity of Pd, Pt and Rh for CO oxidation
at 250◦ C (s−1 ). Metal dispersion (%) is given in parentheses.
Metal

Pd

Pt

Rh

Unsupported

4.6

0.31

10.1

2.9 (41%)
0.9 (67%)

0.24 (7%)
0.10 (87%)

1.8 (57%)
0.4 (69%)

Supported on Al2 O3

mixed oxides.13
CO + 1/2O2 → CO2

(1.2)

Table 1.1 compares the turnover frequencies extrapolated at 250◦ C for
S = 2(0.5%CO + 0.5%O2 ).
The three metals show a moderate sensitivity to the metal particle size, large
particles having the highest turnover frequency. Platinum exhibits the lowest structure sensitivity while rhodium appears to have the highest sensitivity to metal
dispersion. Oh et al. confirmed that rhodium was more active than platinum in
O2 excess.14, 15 However, Rh is more sensitive than Pt to the presence of NO,14
or a hydrocarbon.15 For instance, in a 0.5%CO + 0.5%O2 + 500 ppm NO or a
0.1%CO + 1%O2 + 0.2%CH4 , Pt appears to be more active than Rh. Although
the reaction was carried out in conditions far from those encountered in catalytic
converters (silica support), the study by Cant et al. gives useful information about
the reaction of the stoichiometry (1.3%CO + 0.65%O2 ).16 The results are given in
terms of TOF (molecule CO2 per metal atom per hour). At 127◦ C, the following
ranking is observed: Ru; 250 > Pt; 30 > Rh; 23 > Pd; 4 > Ir; 0.4 while at 177◦ C, the
same metal/silica catalysts exhibit the following activity: Ru; 5900 > Rh; 900 > Pt;
150 > Pd; 110 > Ir; 12. The changes between 127 and 177◦ C are due to the lowest
activation energy of Pt (58 kJ mol1 ) instead of 100 kJ mol1 for the other metals. The
very good behavior of Ru in CO oxidation is also observed in many other reactions involved in TW catalysts. Unfortunately, the volatility of Ru tetroxide made
impossible the use of this metal in automotive converters.17

1.2.1.2. Effect of ceria

In O2 excess, ceria (20% in alumina) changes the activity of Pt and Pd very little
but significantly increases that of Rh.10 By contrast, the influence of ceria is much
more marked around the stoichiometry (S = 1) at least for Pt and Rh.18, 19 It is clear
that the beneficial effect of ceria can be observed mainly at low O2 concentration
and most probably in cycling conditions.


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4

b1675-ch01

Jacques Barbier Jr and Daniel Duprez

Table 1.2. Kinetic orders and activation energies for CO oxidation at 250◦ C over Pd, Pt and Rh
catalysts. From Ref. 10.
Metal

Pd

Pt

Rh

Support

None

Al2 Oa3

CeO2 Al2 O3

None

Al2 Oa3

CeO2 Al2 O3

None

Al2 Oa3

CeO2 Al2 O3

m (O2 )
n (CO)
Ea (kJ mol−1 )

+1.0
−1.0
125

+0.9

−0.9
108–133

0
+1.0
50

+1.0
−1.0
125

+1.0
−0.9
104–125

+0.5
+0.3
84

+1.0
−1.0
117

+1.0
−0.8
92–113

0
+0.2
104

a Metal dispersion on alumina: 16–65% for Pd, 4–87% for Pt and 7–69% for Rh.

1.2.1.3. Kinetics and mechanisms
Kinetic data reported byYuYao10 are summarized in Table 1.2. Rates were expressed
according to the power law equation:
r = ke

E
− RT

m n
PO2
PCO

(1.3)

Kinetic orders (m and n) and activation energies E were determined by varying the
concentrations and the temperature around the conditions given in Table 1.1.
On unsupported metals and on alumina-supported catalysts, the kinetic orders
with respect to O2 are close to +1 while the reaction is auto-inhibited by CO
(orders close to −1). Ceria has a dramatic effect on the reaction, with all the kinetic
orders becoming nil or positive. Activation energies (close to 120 kJ mol−1 on unsupported metals) decrease with the particle size and the presence of ceria.
The mechanism generally proposed for the reaction on unsupported metals and
alumina-supported catalysts is a classical Langmuir–Hinshelwood mechanism with
CO and O2 competing for the same metal sites M.
Adsorption of CO and O2
CO + M ⇔ CO − M:

equilibrium constant Kco

(1.4)

+ M ⇔ O − M:

equilibrium constant Ko

(1.5)

1/2O

2

Surface reaction (determining step)
CO − M + O − M → CO2 + 2M:

rate constant k

(1.6)

which leads to the following rate equation:
1/

r=k

KCO KO PCO PO2
1/

[1 + KCO PCO + KO PO2 ]2

(1.7)


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Oxidation of CO and Hydrocarbons in Exhaust Gas Treatments

5

Although heat of O2 adsorption is higher than that of CO on noble metals, CO
coverage is always higher than that of oxygen (see Section 1.3). Under the conditions
of CO oxidation, CO appears to be more strongly adsorbed than O2 so that: KCO
PCO

1/

1 + KO PO2 . The rate equation Eq. 1.7 may then be simplified as:
1/

KO PO2
r=k
KCO PCO

(1.8)

which explains the order −1 with respect to CO. Orders +1 in oxygen can be obtained
by modifying the mechanism, supposing either that O2 is not dissociatively adsorbed
O 2 + M ⇔ O2 − M

(1.9)

or that the reaction proceeds via a Rideal mechanism between adsorbed CO and
gaseous O2 :
CO − M + O2 → CO2 + O − M

(1.10)

Nevertheless, in the latter case (Rideal mechanism), order in CO should be nil or
slightly positive so that only the LH mechanism with non-dissociated O2 can account
for the experimental orders. Ceria would create new sites for O2 adsorption. As CO
and O2 do not compete for the same sites, positive orders in CO and O2 are observed.

1.2.2.

General trends in hydrocarbon oxidation

The hydrocarbon reactivity depends on numerous factors: chain length, unsaturation,
presence of cycles more or less distorted . . . For instance, Bart et al. showed that
light alkanes and acetylene were particularly refractory to oxidation over a commercial Pt-Rh/CeO2 -Al2 O3 catalyst.20 Table 1.3 gives the light-off temperatures (T50
required to reach a 50% conversion) of some hydrocarbons over this catalyst. In the
alkane series, HC reactivity increases significantly with the chain length, methane
being by far the most refractory hydrocarbon with a T50 above 500◦ C. Alkenes

and aromatics are relatively easy to oxidize, their T50 being comprised between
Table 1.3. Light-off temperatures T50 (50% conversion) for different hydrocarbons and alcohols over a Pt-Rh/CeO2 -Al2 O3 commercial catalyst. The synthetic gas mixture contains 0.15%
HC (in C1 equivalent) + 0.61%CO + 0.2%H2 + 480 ppm NO + 10 CO2 + 10% H2 O. It is at
the stoichiometry (S = 1). Volumic space velocity was 50,000 h−1 . From Ref. 20.
n-Alkanes
Methane : 515◦ C
Ethane : 435◦ C
Propane : 290◦ C
Hexane : 195◦ C

Alkenes, alkyne
Ethylene : 205◦ C
Propene : 185◦ C
Acetylene : 285◦ C

Aromatics
Benzene : 205◦ C
Toluene : 220◦ C
o-Xylene : 225◦ C

Alcohols
Methanol : 195◦ C
Ethanol : 200◦ C
Propanol : 205◦ C
Butanol : 210◦ C


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Advanced Methods and Processes in Oxidation Catalysis

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Jacques Barbier Jr and Daniel Duprez

185 and 225◦ C. Bart et al. also investigated a series of alcohols whose oxidation
seems very easy.
Some of the factors influencing the hydrocarbon reactivity have been recently
reinvestigated on a series of 48 hydrocarbons.21 The main results will be reported
in Section 1.3.

1.2.3.

Oxidation of light alkanes

1.2.3.1. Effect of metal particle size
Yu Yao investigated the oxidation of C1–C4 alkanes over Pd, Pt and Rh catalysts9
(Table 1.4). As for CO oxidation, TOF were calculated on the basis of specific
activities and metal dispersions reported by Yu Yao. For each alkane, TOF were
extrapolated to the same temperature (using the activation energy also reported by
Yu Yao), which allowed a direct comparison between the three metals.
It was confirmed that oxidation rates strongly depend on the length of the
molecule. Palladium was the most active metal for methane oxidation, the order
of activity being: Pd Rh > Pt. It is still very active in ethane oxidation with an

inversion between Pt and Rh (Pd > Pt > Rh). For C3–C4 hydrocarbons, platinum is
definitely the most active catalyst (Pt Pd Rh). Whatever the alkane molecule,
all the metals show high structure sensitivity in oxidation: the greater the particle
size, the higher the TOF. As the specific activity Rm (per gram of metal) is proportional to the product D × TOF, there exists a value of the metal dispersion D for
which Rm is maximal. Depending on the hydrocarbon, this optimal dispersion is
between 15 and 40% for Pt, while it is somewhat higher for Pd (about 50%).
Similar size effects were observed by Hicks et al. for methane oxidation
(6.5%CH4 + 15%O2 ) over Pt and Pd catalysts.22, 23 At 350◦ C, TOF of 0.005 s−1
Table 1.4. Oxidation of C1−C4 alkanes over Pd, Pt and Rh catalysts (unsupported or
supported on alumina). From Ref. 9.

Metal

Disp.% ↓

HC →
T◦ C→

CH4
400

C2 H 6
350

C3 H 8
250

C4 H10
225

0.25
0.0072
0.0045

0.19
0.0042
0.0014

Pd
"
"

Unsupported
16
65

5.4
0.31
0.012

3.6
0.093
0.030

Pt
"
"

Unsupported
6

87

0.017
0.0095
—

0.93
0.31
—

Rh
"
"

Unsupported
7
57

0.050
0.017
0.0085

0.16
0.011
0.0095

10.0
1.5
0.16
0.010

0.0006
0.0004

10.4
5.2
1.75
0.0076
0.0004
0.0004


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Oxidation of CO and Hydrocarbons in Exhaust Gas Treatments

7

and 0.008 s−1 were found for well-dispersed and sintered Pt, respectively. They
amounted to 0.02 s−1 and 1.3 s−1 for well-dispersed and sintered Pd catalysts.
The preferential orientation along more active surfaces during sintering has been
employed to interpret these results.24, 25

1.2.3.2. Effect of ceria
Except for Rh, ceria has rather a negative effect in alkane oxidation (Table 1.5).
This is essentially due to the fact that O2 chemisorption is not a limiting factor in
alkane oxidation (see Section 1.2.3.3). Rhodium was also the metal most sensitive
to the presence of ceria for CO oxidation (see Section 1.2.1.2). There is certainly a
specificity to the interaction of this metal with ceria.

1.2.3.3. Kinetics and mechanisms
Kinetic data relative to propane oxidation are reported in Table 1.6. Contrary to what
was observed in CO oxidation, the kinetic orders strongly depend on the nature of
the metal. They are nil or positive for Pd and Rh while, on Pt, a negative order
with respect to O2 and an order of +2 with respect to C3 H8 are recorded. Relative
close orders (around −1 in O2 and +1 in HC) were reported by Yu Yao for methane
oxidation over Pt, which tends to prove that the mechanism of oxidation is similar
for both alkanes.
Table 1.5. Effect of ceria in alkane oxidation. Activity ratio (per
g. of metal) between catalysts supported on 20%CeO2 -Al2 O3 and
catalysts supported on pure alumina (S = 2). From Ref. 9.
Reaction

Pd (0.15%)

Pt (0.22%)

Rh (0.15%)

CH4 + O2
C3 H8 + O2

0.3 (400◦ C)

0.2 (350◦ C)

0.05 (500◦ C)
0.5 (250◦ C)

1 (500◦ C)
3 (400◦ C)

Table 1.6. Oxidation of propane over Pd, Pt and Rh catalysts. Kinetic orders with respect to O2
(m) and to C3 H8 (n) and activation energies. From Ref. 9.
Metal

Pd

Pt

Rh

Support

None

Al2 O3

CeO2 Al2 O3

None

Al2 O3

CeO2 Al2 O3

None

Al2 O3

CeO2 Al2 O3

m (O2 )
n (C3 H8 )
Ea (kJ mol−1 )

0
+0.4
96

+0.1
+0.6
66–96

+0.1
+0.6
63

−1
+1.2
92

−1
+2

84–105

−1
+2
96

+0.1
+0.5
92

0
+0.5
100

+0.1
+0.4
84


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Advanced Methods and Processes in Oxidation Catalysis

8

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Jacques Barbier Jr and Daniel Duprez

The results of Table 1.6 show that oxygen is more strongly bound to the metals
than propane. The difference is much more marked on Pt than on the other two
metals, which leads to a negative order with respect to O2 . There is no mechanism
unanimously accepted for alkane oxidation on Pt. For this reaction an “oxygenolysis” mechanism comparable to that of hydrogenolysis has been proposed with the
following elementary steps:12
Dehydrogenating adsorption of propane:
C3 H8 + Pt → C3 H8−x − Pt + x/2 H2

(1.11)

Dissociative adsorption of O2 :
1/2 O

2

+ Pt ⇔ O − Pt

(1.12)

C−C bond rupture in the adsorbed hydrocarbon species, the decomposition occurring either spontaneously:
C3 H8−x − Pt + Pt → CHy − Pt + CH8−x−y − Pt

(1.13)

or by reaction with O2 :
C3 H8−x − Pt + 2O − Pt → CO − Pt + H2 O − Pt + C2 H6−x − Pt

(1.14)

These reactions are rapidly followed by oxidation of HC fragments and hydrogen.
On Pt, only Eq. 1.14 is able to account for the kinetic observations. If mechanism
Eq. 1.11–Eq. 1.12–Eq. 1.14 occurs, the kinetic derivation leads to the following rate
equation:
r=k

KC KO2 PC PO

(1.15)

1/

[1 + KC PC + KO PO2 ]3

in which PC and PO are the partial pressures in propane and O2 , KC and KO the equilibrium constants of steps Eq. 1.11, Eq. 1.12 and k, the rate constant of step Eq. 1.14,
which is supposed to be the rate-determining step. On Pt (the most active metal for
1/

propane oxidation), oxygen is strongly adsorbed so that: KO PO2
rate equation (Eq. 1.15) can then be simplified:
r=k

KC PC
1/

1 + KC PC . The

(1.16)

KO PO2

As for CO oxidation (Eq. 1.8), order −1 in O2 experimentally observed may
suggest that the O2 molecule could react before it is dissociated.


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Oxidation of CO and Hydrocarbons in Exhaust Gas Treatments

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Table 1.7. Propene oxidation at 150◦ C: turnover frequencies (s−1 ) of unsupported metals and metals supported on alumina. Metal dispersion is given in
parentheses. Gas composition: 0.1% C3 H6 + 1% O2 + N2 . From Ref. 9.
Metal
Unsupported
Supported on Al2 O3

Pd

Pt

Rh

0.56
0.10 (40%)

0.35
0.016 (13%)
0.20 (87%)

0.95
0.003 (7%)
0.030 (69%)

1.2.4. Alkene oxidation
1.2.4.1. Effect of metal particle size and effect of ceria
Specific activities of Pd, Pt and Rh catalysts in propene oxidation are reported in
Table 1.7. Contrary to what was observed in alkane oxidation, propene oxidation
is not very sensitive to the nature of the metal. Quite similar TOF were measured
over unsupported metals, while Pt and Pd seemed to be slightly more active than Rh
when supported on alumina. Propene oxidation is not very sensitive to metal particle
size. However, intrinsic activity would be rather higher on small particles. As TOF
are higher or much higher on unsupported metals, it seems that alumina could
play a negative role in propene oxidation. The intermediary formation of partially
oxidized compounds (acrolein, alcohols, . . . ) is not excluded. Alumina might store
and stabilize these intermediates, slowing down the total oxidation.
Propene oxidation is much faster than propane oxidation over Pd and Rh. The
reverse tendency would occur over Pt. However, propene is more strongly adsorbed
on Pt than propane, which explains why, in the oxidation of C3 H6 /C3 H8 mixtures,
propene oxidizes first; propane oxidation starts when virtually all the propene is

oxidized.26
Ceria has a moderate effect in propene oxidation. It is rather positive on Pt and
Rh. The presence of 20% ceria in alumina can increase the activity by a factor of
two or three on these metals. For Pd, the effect of ceria seems limited and rather
negative.

1.2.4.2. Kinetics and mechanisms
Kinetic orders are very different to those observed for alkane oxidation (Table 1.8).
They are rather close to those measured in CO oxidation at least for Pd and Pt,
rhodium showing a different behavior.
Propene appears to be more strongly adsorbed than O2 over Pt and Pd: kinetic
orders are definitely positive in O2 and negative in C3 H6 . This inhibiting effect of
propene is not observed on Rh, on which O2 appears to be more strongly adsorbed
than propene.


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Advanced Methods and Processes in Oxidation Catalysis

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Jacques Barbier Jr and Daniel Duprez

Table 1.8. Propene oxidation over Pd, Pt and Rh catalysts. Kinetic orders with respect to O2 (m)
and to C3 H6 (n) and activation energies. From Ref. 9.
Metal

Pd

Pt

Rh

Support

None

Al2 O3

CeO2 Al2 O3

None

Al2 O3

CeO2 Al2 O3

None

Al2 O3

CeO2 Al2 O3

m (O2 )
n (C3 H6 )
Ea (kJ mol−1 )

+1.5
−0.6
125

+1.5
−0.5
63–117

+0.7
−0.3
63

+1.8
−0.8
92

+2.0
−1.0
67–125

+1.5
−0.6
80

−1.3
+1.3

96

−0.8
+0.9
67–92

0
+0.5
92

The mechanism of propene oxidation is undoubtedly different from that of alkanes. Propene adsorption does not require a C-H bond rupture, alkene molecules
being adsorbed on most metals via the π electrons of the C=C double bond. This
adsorption would be strong on Pd and Pt and much weaker on Rh. It is interesting
to note that Rh is the metal most sensitive to the presence of the support, its intrinsic
activity being 30 to 300 times less when it is supported on alumina (Table 1.7).
This suggests that the support could play a role in propene adsorption, tending to
inhibit the reaction on the metal. Oxidation most likely goes further according to
steps similar to those written for propane (Eqs 1.13 and 1.14).
As a rule, activation energies are close to those measured on alkanes. Again,
ceria tends to decrease Ea for Pd and Pt while it is virtually unchanged for Rh.

1.2.5.

Overview of the behavior of Pd, Pt and Rh catalysts in CO
and HC oxidation

Activity of Pd, Pt and Rh catalysts for CO and HC oxidation and corresponding
rate equations depend first on the relative adsorption equilibrium of the reducer and
oxygen on the metals. From the kinetic data reported in Sections 1.2.2 to 1.2.4, the
scheme represented in Fig. 1.1 can be drawn.

This scheme allows us to account for the general behavior of Pd, Pt and Rh
catalysts in oxidation. Reducers whose adsorption constant is higher than that of
O2 (bars on the right of O2 ) are strongly adsorbed and behave as inhibitors of the
reaction (negative orders while that of O2 is positive). Conversely, reducers whose
adsorption constants are lower than that of O2 (bars on the left of O2 ) are weakly
adsorbed: O2 acts as an inhibitor of the reaction (negative orders while those of
the reducers are positive). Ceria significantly changes this picture as it offers new
sites for O2 adsorption. Chlorine has a detrimental effect on propane and propene
oxidation as it blocks hydrocarbon adsorption.26 Fortunately, water produced during oxidation leads to progressive catalyst dechlorination, which helps in restoring
activity.