Electrochemical Activation of Catalysis. Promotion, Electrochemical Promotion, and Metal-Support Interactions

Electrochemical Activation of Catalysis. Promotion, Electrochemical Promotion, and Metal-Support Interactions




This book describes the phenomenology, theory and potential applications of the phenomenon of electrochemical promotion, where electrochemically induced ion spillover activates and controls heterogeneous catalysis. The origin of electrochemical promotion is discussed in light of a plethora of surface spectroscopic and electrochemical techniques. Electrochemical and classical promotion are compared, their common rules are identified and promotional kinetics are rigorously modeled and compared with experiment.



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Published 01 January 2002
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EAN13 0306475510
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Chapter 1 Introduction, Brief History and Basic Concepts 1.1The Phenomenon of Electrochemical Promotion 1.2Basic Concepts and Terminology 1.3Structure of This Book
Chapter 2 Promotion in Heterogeneous Catalysis 2.1Introduction 2.1.1Catalysis, Chemical and Electrochemical Promotion: An Example 2.2Chemisorption and Catalytic Kinetics 2.3Catalytic Kinetics and Promoters 2.4Interactions of Adsorbates Acting as Promoters or Poisons with Catalyst Surfaces 2.4.1Definitions 2.4.2Electropositive (Electron Donor) and Electronegative (Electron Acceptor) Promoters 2.4.3Electropositive Promoters: Alkali Metals 2.4.4Electronegative Promoters Structure of the Adsorbed Adatom Layer and Adatom Induced Surface Reconstruction 2.5Adsorption on Surfaces Modified by Electropositive or Electro negative Promoters 2.5.1Adsorption of Gases on Surfaces Modified by Alkali Promoters CO Adsorption
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23 23
23 24 30
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CONTENTS Effect on the CO Molecular Chemisorption Effect on the CO Dissociative Chemisorption Adsorption NO Adsorption Effect on the NO Molecular Chemisorption Effect on the NO Dissociative Chemisorption Oxygen Adsorption Hydrogen Adsorption Nitrogen Adsorption of Organic Compounds of Ethylene of Methanol 2.5.2Adsorption of Gases on Surfaces Modified by Electronega tive Adatoms CO Adsorption NO Adsorption Modifiers Effect on the Molecular NO Chemisorption. Modifiers Effect on the Dissociative NO Adsorption. Adsorption Adsorption Adsorption of Organic Compounds Adsorption of Ethylene Adsorption of Methanol Catalytic Activity on Surfaces Modified by Promoters or Poisons 2.6.1CO Oxidation on Lidoped Pt(111) Surfaces 2.6.2Ethylene Epoxidation 2.6.3Synthesis Gas Conversion Reactions Effect of Alkali Promoters of Electronegative Additives Summarizing Comments and Rules
Chapter 3 Solid Electrolytes, Catalysis and Spillover 3.1Solid Electrolytes 3.2Solid Electrolyte Potentiometry (SEP) 3.3Solid Electrolyte CellsElectrocatalytic Operation of
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45 46 48 50 52 52 55
56 56 62
64 64 67 68 68 70 72 73 74 77 79 81 82
91 94 96
Spilloverbackspillover Phenomena101 3.4.1Phenomenology101 3.4.2Acceptor PhasesMechanisms: Donor and 101 3.4.3Thermodynamics and Kinetics of SpilloverBackspillover Between a Solid Electrolyte and a Metal CatalystElectrode104
Chapter 4 Electrochemical Promotion of Catalytic Reactions 4.1Experimental Setup 4.1.1The Reactor and the Gas Analysis System 4.1.2The Catalyst Film General Features Catalyst Preparation 4.1.3Counter and Reference Electrodes 4.1.4Quasireference Electrodes 4.2CatalystElectrode Film Characterization 4.2.1Catalytic Characterization: Measurement of the Metal/Gas Interface Area 4.2.2Electrochemical Characterization: Measurement of the CatalystSolid Electrolyte Exchange Current 4.3A NEMCA Experiment: Galvanostatic and Potentiostatic Transients 4.3.1ConductorsElectrochemical Promotion Using 4.3.2ConductorsElectrochemical Promotion Using CO Oxidation on NO Reduction by on 4.3.3General Features and Comparisons 4.4Catalyst Work Function Variation with Potential in Solid Electrolyte Cells 4.5ElectroDefinitions, Phenomenology and Key Aspects of chemical Promotion 4.5.1NEMCA Time Constant 4.5.2Enhancement Factor or Faradaic Efficiency 4.5.3Rate Enhancement Ratio 4.5.4Promotion Index 4.5.5Electrophobic and Electrophilic Reactions 4.5.6Dependence of Catalytic Rates and Activation Energies on Catalyst Potential and Work Function Rate Dependence on and Local and Global r vs Dependence 4.5.7Activation Energy and Preexponential Factor Dependence on Work Function
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128 128 131 131 134 137
140 140 141 146 148 151
152 152 156
4.6 4.7
CONTENTS Effect 4.5.8Selectivity Modification 4.5.9Promotional Effects on Chemisorption Experimental Results Electrostatic Interactions of Adsorbates in a Double Layer 4.5.10 "Permanent NEMCA" Prediction of the Magnitude of the Faradaic Efficiency Synopsis of the Phenomenology: Reactions Studied so Far
Chapter 5 Origin of NEMCA 5.1Problems and Methods 5.2A Galvanostatic NEMCA Transient Revisited 5.3Analysis of Rate Time Constants During Galvanostatic Transients. 5.3.1Introduction 5.3.2Time constants During Galvanostatic Transients and Faradaic Efficiency 5.3.3Transient Analysis and Promotion Index 5.4Work Function and Electrochemical Promotion 5.4.1Work Function, Fermi Level, Vacuum Level, Galvani and Volta Potentials, Dipole Moments 5.4.2The Work Function of Catalyst Films Deposited on Solid Electrolytes Results Implications of the Experimental Results 5.4.3Catalyst Films Deposited onThe Work Function of Solid Electrolytes: Rationalization of the PotentialWork Function Equivalence 5.4.4Spatial Variations 5.4.5Transients and Measurement of Dipole Moments 5.4.6Deviations from the Equality in the Changes of Extraction Potential and Electrode Potential 5.5Temperature Programmed Desorption (TPD) 5.6Solid Electrolyte Cyclic Voltammetry 5.6.1Adsorbed SpeciesDetection of 5.6.2Potential Programmed Reduction 5.7AC Impedance Spectroscopy 5.7.1General Features 5.7.2Measurement of the tpb Length 5.8XPS Investigations 5.8.1XPS in Catalysis and Solid State Electrochemistry
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175 176 179 181
189 191 198 198
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224 228 233 233 237 237 237 243 244 244
5.9 5.10 5.11 5.12
5.13 5.14
5.8.2XPS Studies of Metals Supported on Conductors UPS Investigations SERS Investigations PEEM Investigations Scanning Tunelling Microscopy 5.12.1Direct Atomic Scale Observation of Electrochemically Controlled Spillover/Backspillover 5.12.2Ordered Promoter Adlattices and Electrochemical Promotion Quantum Mechanical Calculations The Effective Double Layer
Chapter 6 Rules and Modeling of Promotion 6.1Electron Acceptor and Electron Donor Adsorbates 6.2Electrophobic, Electrophilic, Volcano and Inverted Volcano Reactions: Rationalization, Rules, and Predictions 6.2.1Similarities and Differences Between Electrochemical and Classical Promotion 6.2.2Promotional Rules Reactions Electrophilic ReactionsType Reactions Inverted Volcano (Minimum) Type Reactions More Complex Examples 6.2.3and Adsorbate CoverageConnection Between 6.2.4Local Promotional Rules 6.2.5Practical Considerations 6.3the Promotional RulesRationalization of 6.3.1Derivation of the Experimental Local Rules L1 and L2 from the Fundamental Rules F1 and F2 6.3.2Experimental Confirmation and First Principle Rationalization of Rules F1 and F2 6.3.3Summary of Promotion Rules 6.4Mathematical Modellingof Electrochemical Promotion and Classical Promotion 6.4.1Introduction 6.4.2a Double LayerAdsorption in Presence of 6.4.3Adsorption in Absence of Coadsorbing Species 6.4.4Adsorption Isotherms, Nernst Equation and Potential Work Function Equivalence
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264 267 271
283 285 285 288 289 290 293 295 296 298 299
300 302
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Catalytic Kinetics in Presence of a Double Layer
Chapter 7 The Absolute Potential 7.1Introduction 7.2Absolute Potential Scales in Aqueous Electrochemistry 7.3Absolute Potential Scale and Zero Energy Level of Electrons in Solid State Electrochemistry 7.3.1the Effective Double LayerThe Nature of 7.3.2Experimental Establishment of the Absolute Potential Scale 7.4The Work Function of Catalyst Films Deposited on Solid Electrolytes: Rationalization of the Potential Work Function Equivalence 7.5the Absolute Potential Scale inDefinition and Properties of Solid Electrochemistry 7.6Potential Distribution in a Solid Electrolyte Cell 7.7Absolute Potential of Supported Catalysts
Chapter 8 Electrochemical Promotion with Conductors 8.1The Use ofConductors 8.1.1Complete Oxidation Reactions Oxidation on Pt Oxidation on Rh Oxidation on Pd Oxidation on and Mixtures: Equivalence of MetalSupport Interaction and NEMCA Equivalence of MetalSupport Interaction and Electrochemical Promotion Catalyst Film Mass and MetalSolid Electrolyte Capacitance Oxidation on Ethylene Oxidation on on Pt on Pt. on Pt Oxidation on Pt and Pd Oxidation on Ag
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363 363 363 368 373
376 376 377 379 381 382 385 390
8.3 Oxidation on AgPd Alloys and on Au 8.1.2 Partial Oxidation Reactions Agand Epoxidation Oxidation on Pt and Ag Coupling on Ag 8.1.3 Dehydrogenation and Hydrogenation Reactions Dehydrogenation on Ag and Pt on Rh on Pd Hydrogenation on Pd Reforming on Ni Dehydrogenation on Pt 8.1.4. NO Reduction Reactions NO and Reduction by CO on Pd/YSZ Reduction by on Pt/YSZ Reduction by and CO on Rh/YSZ in Presence of Oxygen Electrochemical Promotion of a Classically Promoted Rh Catalyst for NO Reduction by CO in Presence of The Use of Conductors 8.2.1 CO Oxidation on The Use of Mixed Conductors 8.3.1 Oxidation on 8.3.2 Oxidation on
390 393 393 398 402 403 403 406 408 409 410 411 411 411 412
417 420 420 420 420 428
Chapter 9 Electrochemical Promotion with Cationic Conductors 9.1Alkali Ion ConductorsThe Use of 435 9.1.1Ethylene Oxidation on435 9.1.2Ethylene Oxidation on Pt/NASICON440 9.1.3 CO Oxidation on442 9.1.4 Ethylene Epoxidation on445 9.1.5 NO Reduction Studies on446 NO Reduction by on447 NO Reduction by CO on447 Reduction by on449 Reduction by on451 9.1.6 Benzene Hydrogenation on452 9.1.7 Hydrogenation on Pd453 9.1.8 Selective Hydrogenation on and 453
Decomposition on
and on
9.1.10Hydrogen Oxidation on Pt/glass The Use of Conductors 9.2.1Hydrogen Oxidation on Pt/Nafion Galvanostatic TransientState Effect of Open and Closed Circuit Kinetics 9.2.2Isomerization of 1Butene on PdBlack Cathodes/ Nation 117 9.2.3Ethylene Cathodes Hydrogenation on 9.2.4Ammonia Synthesis on Fe Supported on a Proton Conductor 9.2.5Methane Dimerization Using Proton Conductors 9.2.6Oxidation on
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466 467
468 470 470
Chapter 10 NEMCA with Aqueous Electrolytes and Inorganic Melts 10.1Evolution and Aldehyde Oxidation at Ib Metals in Alkaline Solutions475 10.2Hydrogen Oxidation on Pt in Aqeous Alkaline Solutions476 10.3Maleic Acid Hydrogenation on Pt in Aqueous Acidic Solutions.481 10.4Ammonium PolysulfideProduction of 482 10.5MeltsOxidation in 482
Chapter 11 Electrochemical Promotion and MetalSupport Interactions 11.1MetalSupport Interactions 11.2the Mechanistic Equivalence ofExperimental Confirmation of NEMCA and MetalSupport Interactions 11.3Mathematical Modeling: Dimensionless Numbers Governing Electrochemical Promotion and MetalSupport Interactions 11.3.1Modeling Considerations and Kinetics Modeling of Electrochemical Promotion Modeling of MetalSupport Interactions
500 501 501
11.3.2Numerical Examples Promoted Films Supported Catalysts 11.3.3Summary of Modelling Results Interrelation of Promotion, Electrochemical Promotion and MetalSupport Interactions: The DoubleLayer Model of Catalysis
507 507 508 509
Chapter 12 Practical Applications, Summary and Perspectives 12.1Classical Promoter Selection516 12.2Material Cost Minimization: Dispersed and Commercial Catalysts516 12.2.1Electrochemical Promotion with Highly Dispersed Catalysts518 Oxidation on Pt Fully Dispersed on Au Deposited on YSZ518 on Pt Fully Dispersed on C Electrodes in Aqueous Alkaline Solutions520Butene Isomerization on Pd Fully Dispersed on C Electrodes Deposited on Nafion520 12.2.2Electrochemical Promotion of Commercial Catalysts520 IndustrialElectrochemical Promotion of Synthesis Catalyst520 Electrochemical Promotion of an Industrial Oxidation Catalyst521 12.3PromotionBipolar Electrochemical 521 12.3.1Electrochemical Promotion ofOxidation on Pt Using a Bipolar Design521 12.3.2Electrochemical Promotion ofOxidation on Pt Using MultiStripe and MultiDot Bipolar Catalysts523 12.3.3Electrochemical Promotion Using a Bipolar Monolithic Reactor524 12.3.4Electrochemical Promotion of Particulate Matter (Soot) Combustion Using a CeriaGadolinia Solid Electrolyte and a Dispersed Perovskite Catalyst525 12.4Summary and Perspectives528
Appendix A Common Questions about Electrochemical Promotion A.1Questions533 A.2Answers536
Appendix B Materials and Instrumentation for Starting Electrochemical Promotion Experiments B.1CatalystElectrodes, Solid Electrolytes B.2Instrumentation B.3Apparatus B.4Procedures
Appendix C Main Research Groups
543 547 550 553