Fundamental Concepts in Heterogeneous Catalysis

This book is based on a graduate course and suitable as a primer for any newcomer to the field, this book is a detailed introduction to the experimental and computational methods that are used to study how solid surfaces act as catalysts.

• First comprehensive description of modern theory of heterogeneous catalysis
• Basis for understanding and designing experiments in the field  
• Allows reader to understand catalyst design principles
• Introduction to important elements of energy transformation technology
• Test driven at Stanford University over several semesters

Jens K. Nørskov, PhD, is the Leland T. Edwards Professor of Engineering at Stanford University. He is the founding director of the SUNCAT Center for Interface Science and Catalysis at Stanford University and SLAC National Accelerator Laboratory. He has pioneered the development of a set of concepts allowing a molecular level understanding of surface chemical processes and heterogeneous catalysis.

Felix Studt, PhD, is a Staff Scientist at the SLAC National Accelerator Laboratory. His SUNCAT research group focuses on understanding catalytic processes for efficient energy conversion and using this as a basis for design of new catalysts.

Frank Abild-Pedersen, PhD, is a Staff Scientist at the SUNCAT Center at SLAC National Accelerator Laboratory where his group focuses on the development of theoretical models of molecule surface interactions and models describing ultrafast surface processes measured in x-ray free electron lasers.

Thomas Bligaard, PhD, is a Senior Staff Scientist at at SLAC National Accelerator Laboratory and the deputy director for theory at the SUNCAT Center. His research group focuses on the development of electronic structure methods, kinetics tools, and data mining in catalysis.

Preface viii

1 Heterogeneous Catalysis and a Sustainable Future 1

2 The Potential Energy Diagram 6

2.1 Adsorption 7

2.2 Surface Reactions 11

2.3 Diffusion 13

2.4 Adsorbate–Adsorbate Interactions 15

2.5 Structure Dependence 17

2.6 Quantum and Thermal Corrections to the Ground-State Potential Energy 20

3 Surface Equilibria 26

3.1 Chemical Equilibria in Gases Solids and Solutions 26

3.2 The Adsorption Entropy 31

3.3 Adsorption Equilibria: Adsorption Isotherms 34

3.4 Free Energy Diagrams for Surface Chemical Reactions 40

Appendix 3.1 The Law of Mass Action and the Equilibrium Constant 42

Appendix 3.2 Counting the Number of Adsorbate Configurations 44

Appendix 3.3 Configurational Entropy of Adsorbates 44

4 Rate Constants 47

4.1 The Timescale Problem in Simulating Rare Events 48

4.2 Transition State Theory 49

4.3 Recrossings and Variational Transition State Theory 59

4.4 Harmonic Transition State Theory 61

5 Kinetics 68

5.1 Microkinetic Modeling 68

5.2 Microkinetics of Elementary Surface Processes 69

5.3 The Microkinetics of Several Coupled Elementary Surface Processes 74

5.4 Ammonia Synthesis 79

6 Energy Trends in Catalysis 85

6.1 Energy Correlations for Physisorbed Systems 85

6.2 Chemisorption Energy Scaling Relations 87

6.3 Transition State Energy Scaling Relations in Heterogeneous Catalysis 90

6.4 Universality of Transition State Scaling Relations 93

7 Activity and Selectivity Maps 97

7.1 Dissociation Rate-Determined Model 97

7.2 Variations in the Activity Maximum with Reaction Conditions 101

7.3 Sabatier Analysis 103

7.4 Examples of Activity Maps for Important Catalytic Reactions 105

7.4.1 Ammonia Synthesis 105

7.4.2 The Methanation Reaction 107

7.5 Selectivity Maps 112

8 The Electronic Factor in Heterogeneous Catalysis 114

8.1 The d-Band Model of Chemical Bonding at Transition Metal Surfaces 114

8.2 Changing the d-Band Center: Ligand Effects 125

8.3 Ensemble Effects in Adsorption 130

8.4 Trends in Activation Energies 131

8.5 Ligand Effects for Transition Metal Oxides 134

9 Catalyst Structure: Nature of the Active Site 138

9.1 Structure of Real Catalysts 138

9.2 Intrinsic Structure Dependence 139

9.3 The Active Site in High Surface Area Catalysts 143

9.4 Support and Structural Promoter Effects 146

10 Poisoning and Promotion of Catalysts 150

11 Surface Electrocatalysis 155

11.1 The Electrified Solid–Electrolyte Interface 156

11.2 Electron Transfer Processes at Surfaces 158

11.3 The Hydrogen Electrode 161

11.4 Adsorption Equilibria at the Electrified Surface–Electrolyte Interface 161

11.5 Activation Energies in Surface Electron Transfer Reactions 162

11.6 The Potential Dependence of the Rate 164

11.7 The Overpotential in Electrocatalytic Processes 167

11.8 Trends in Electrocatalytic Activity: The Limiting Potential Map 169

12 Relation of Activity to Surface Electronic Structure 175

12.1 Electronic Structure of Solids 175

12.2 The Band Structure of Solids 179

12.3 The Newns–Anderson Model 184

12.4 Bond-Energy Trends 186

12.5 Binding Energies Using the Newns–Anderson Model 193

Index 195

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