Catalysis by Metals and Alloys

745 Pages·1995·31.6 MB·English

by  Vladimir Ponec and Geoffrey C. Bond (Eds.)

Studies in Surface Science and Catalysis 95
CATALYSIS BY METALS AND ALLOYS
TThhiiss PPaaggee IInntteennttiioonnaallllyy LLeefftt BBllaannkk
Studies in Surface Science and Catalysis
Advisory Editors: B. Delmon and J.T. Yates
Vol. 95
C ATA LY S I S
BY METALS
AND ALLOYS
Vladimir Ponec
Leiden Institute of Chemistry, Leiden University, Leiden, The Nether~ands
Geoffrey C. Bond
Department of Chemistry, Brunel University, London, United Kingdom
ELSEVIER
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First printing: 1995
Second impression: 1998
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1995, ELSEVIER SCIENCE B.V. All rights reserved.
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Contents
PROLOGUE
Chapter 1
STRUCTURE AND PROPERTIES OF METALS AND ALLOYS 7
1.1 A microscopic theory of solids 7
1.1.1 The quantum theory of pure metals 7
1.1.2 Pauling's theory of pure metals 19
1.1.3 The Engel-Brewer theory of metals and alloys 23
1.1.4 The Miedema theory of stability of alloys 25
1.1.5 The quantum theory of alloys 26
1.2 Some results of the theory of chemisorption on
metals and alloys 35
1.2.1 General features of chemisorption 35
1.2.1.1 Chemisorption of atoms 35
1.2.1.2 Chemisorption of undissociated molecules 41
1.2.1.3 Adsorption of molecular fragments 46
1.2.1.4 Semi-empirical approach to the problem
of chemisorption 48
1.3 Adsorption of molecules and radicals which are intermediates
in catalytic reactions 50
1.3.1 Hydrocarbons 50
1.3.2 Other molecules 53
1.4 Macroscopic thermodynamic theory of alloys 54
1.4.1 A short introduction to the statistical thermodynamic
description of alloys, as random solutions 55
1.4.2 Phase composition of some catalytically interesting alloys 59
Chapter 2
EXPERIMENTAL TECHNIQUES OF SOLID STATE PHYSICS,
RELEVANT TO RESEARCH ON ALLOYS 73
2.1 Photoelectron Spectroscopy (PES) 74
2.1.1 Instrumentation 74
2.1.2 Basic principles and phenomena in PES 76
2.1.2.1 Ionization and relaxation effects on
the binding energy of electrons in atoms
and molecules 77
2.1.2.2 Relaxation effects in solids, particularly metals 80
2.1.2.3 Relaxation effects in adsorbed atoms
and molecules 81
2.1.2.4 Theoretical and semi-empirical calculation
of binding energies in atoms, molecules,
metals and alloys 84
2.1.2.5 Integrated and angle-resolved spectra of
valence band electrons in metals and alloys 94
vi Contents
2.1.2.6 Quantitative analysis by XPS 98
2.2 Auger spectroscopy 102
2.2.1 Basic principles 102
2.2.2 Quantitative analysis by AES 106
2.3 Other methods 113
2.3.1 Ion scattering techniques (LEIS) 113
2.3.2 Medium and high energy ion scattering 115
2.3.3 Ion neutralisation spectroscopy (INS) by slow ions 117
2.3.4 Secondary Ion Mass Spectroscopy (SIMS) 118
2.3.5 High-Field Emission Techniques 119
2.3.6 Microscopes with atomic resolution 122
2.3.7 Work function measurements 124
2.3.8 Extended X-ray Absorption Fine Structure (EXAFS) 127
Chapter 3
THE ELECTRONIC STRUCTURE OF ALLOYS;
EXPERIMENTAL RESULTS 143
3.1 Magnetic measurements 143
3.2 The M~Jssbauer effect 148
3.3 Photoemission Spectroscopy (PES) 150
3.4 Soft X-ray emission and absorption 167
3.5 Conclusions 169
Chapter 4
SURFACE COMPOSITION OF ALLOYS 175
4.1 General remarks on surfaces of metals 175
4.2 Binary systems with surface segregation 181
4.2.1 Chemical approach, kinetic and thermodynamic
description of equilibrium 181
4.2.2 Simple thermodynamics of segregation 183
4.2.3 Broken-bond model of alloy surfaces 184
4.2.4 Regular solution model for systems with components
of different molar volume 192
4.2.5 Monte-Carlo calculations on surface segregation 194
4.2.6 Metal-on-metal layers 196
4.3 Surface segregation in catalytically interesting alloys 202
4.3.1 Nickel-copper alloys 202
4.3.2 Palladium alloys 206
4.3.3 Platinum alloys 208
Chapter 5
PHYSICAL PROPERTIES AND STRUCTURES OF SMALL
METAL AND ALLOY PARTICLES 219
5.1 The electronic structure of small free metal particles 219
5.2 Equilibrium shape and thermal properties of small
metal particles 224
Contents vii
5.3 Adsorption sites on small metal particles 227
5.4 Reactivity of small metal particles 229
5.5 Polarization and charging of small metal particles
by a support 234
Chapter 6
THE CATALYTIC CYCLE 247
6.1 Prelude 247
6.2 The role of reaction mechanism in catalytic research 248
6.3 Methods of investigating catalysed reactions 250
6.3.1 Heat transfer and mass-transport limitation 250
6.3.2 Methods for conducting reactions in gas-solid systems 253
6.3.3 Transient kinetics and temporal analysis of products (TAP) 258
6.3.4 Ways of performing reactions in gas-liquid-solid systems 261
6.3.5 Catalysis under UHV conditions 264
6.3.6 Scaling-up 264
6.4 Kinetics of heterogeneously catalysed reactions 266
6.4.1 Ways of expressing the rate of a catalysed reaction 266
6.4.2 Introduction to Langmuir-Hinshelwood kinetics 268
6.4.3 Activation energy 273
6.4.4 The compensation phenomenon 276
6.4.5 Selectivity 277
6.4.6 Epilogue 279
6.5 Structure sensitivity and particle size effects 280
6.5.1 Principles and concepts 280
6.5.2 Hydrogenation of multiple carbon-carbon bonds 283
6.5.3 Hydrogenolysis of the C-C bond 284
6.5.4 Hydrogenation of carbon monoxide 285
6.5.5 Ammonia synthesis 286
6.5.6 Oxidation reactions 288
6.6 Catalytic consequence of metal-support interactions 288
Chapter 7
PREPARATION AND CHARACTERIZATION OF METAL
AND ALLOY CATALYSTS 299
7.1 Macroscopic materials 300
7.1.1 Polycrystalline materials 300
7.1.2 Metal films 303
7.1.3 Other methods of comminution 308
7.1.4 Single crystals 309
7.1.5 Two-dimensional alloys 312
7.1.6 Intermetallic compounds 313
7.1.7 Interstitial alloys 313
7.1.8 Amorphous alloys 314
7.2 Small unsupported metal particles 315
7.2.1 Metal 'blacks' by chemical reduction 315
7.2.2 Colloidal metals 316
viii Contents
7.2.3 Reduction of binary oxides 318
7.2.4 Raney alloys 319
7.3 Supported metal catalysts 320
7.3.0 Introduction 320
7.3.1 Supports 321
7.3.2 Use of precursors in positive oxidation states 330
7.3.3 Use of zero-valent compounds and atoms 344
7.3.4 Methods specific to alloys 348
7.3.5 Reduction to the active form 350
7.4 Characterization of alloy catalysts 356
7.4.0 Introduction 356
7.4.1 Characterization of the physical structure of
supported metal catalysts 357
7.4.2 Physical methods of characterizing small alloy particles 361
7.4.3 Characterization of supported metals and alloys
by selective gas chemisorption 370
Chapter 8
ADSORPTION ON ALLOYS 393
8.1 Ensemble size and composition effects 394
8.2 Ensemble statistics and the extent of adsorption 394
8.3 Adsorption as a probe of active sites on alloys 398
8.4 Adsorption of simple gases on alloys 404
8.4.1 Adsorption of hydrogen 404
8.4.2 Carbon monoxide adsorption as a probe 409
8.4.3 Adsorption of hydrocarbons and of some other gases 424
8.4.4 Adsorption on incomplete layers of alkali metals
on transition metals 430
Chapter 9
CATALYSIS BY ALLOYS - GENERAL FEATURES 437
9.1 Basic problems 437
9.2 Investigation of electronic structure effects by means
of catalytic reactions 441
9.3 Important side effects of alloying 444
Chapter 10
REACTIONS OF HYDROGEN AND ALKANE-DEUTERIUM
EXCHANGE 449
10.1 Reactions involving only hydrogen and its analogues 449
10.1.1 Reactions involving hydrogen atoms 452
10.2 The equilibrium of hydrogen + deuterium and para-
hydrogen conversion 456
10.3 Exchange of alkanes with deuterium 464
Chapter 11
CATALYTIC HYDROGENATION AND DEHYDROGENATION 477
Contents ix
11.1 Hydrogenation of alkenes 477
11.1.1 General principles 477
11.1.2 Carbon deposition 484
11.1.3 Kinetics and mechanism of hydrogenation 486
11.1.4 Hydrogenation of alkenes by alloys 488
11.1.5 Hydrogenation of the cyclopropane ring 490
11.2 Hydrogenation of alkynes and alkadienes 491
11.2.1 General principles 491
11.2.2 Kinetics and mechanism of alkyne hydrogenation 494
11.2.3 Hydrogenation of alkynes by alloys 498
11.2.4 Hydrogenation of alkadienes 500
11.3 Hydrogenation of aromatic compounds 504
11.3.1 General principles 504
11.3.2 Hydrogenation and exchange of aromatics on pure metals 506
11.3.3 Hydrogenation and exchange of aromatics on alloys 508
11.4 Hydrogenation of other unsaturated groups 511
11.4.1 The problem of diffusion limitation 511
11.4.2 Reactions and catalysts 514
11.4.3 Alloy catalysts in liquid-phase hydrogenation 516
11.5 Dehydrogenation 518
11.5.1 Dehydrogenation of alkanes and cycloalkanes 518
11.5.2 Decomposition of formic (methanoic) acid 520
11.5.3 The decomposition of hydrogen peroxide 525
11.5.4 Decomposition of alcohols 526
11.6 Hydrogenation of diatomic molecules: oxygen and nitrogen 527
Chapter 12
OXIDATION REACTIONS 541
12.1 Fundamentals - chemisorption of the reactants 541
12.2 Selected information on simple oxidation reactions on metals 546
12.3 Oxidations on alloys 555
12.3.1 Oxidation of carbon monoxide 555
12.3.2 Oxidation of hydrogen 561
12.3.3 Epoxidation and other reactions of alkenes 564
12.4 Practical applications of oxidation reactions on metals and alloys 568
12.4.1 Three-way catalysts 568
12.4.2 Oxidation of ammonia 571
12.4.30xirane (ethylene oxide, EO) production 572
12.4.4 Electrocatalytic oxidations 573
Chapter 13
REACTIONS OF ALKANES AND REFORMING OF NAPHTHA 583
13.1 Fundamentals 583
13.1.1 Adsorption of hydrocarbons under reaction conditions 583
13.1.2 Kinetics of skeletal reactions 592