Operando SXRD : a new view on catalysis Ackermann, M.D.

Operando SXRD : a new view on catalysis

Ackermann, M.D.

Citation

Ackermann, M. D. (2007, November 13). Operando SXRD : a new view on catalysis.

Retrieved from https://hdl.handle.net/1887/12493

Version: Not Applicable (or Unknown)

License: Licence agreement concerning inclusion of doctoral thesis in the Institutional Repository of the University of Leiden

O ^PERANDO SXRD:

A N EW V IEW ON C ATALYSIS

iii

O ^PERANDO SXRD:

A N EW V IEW ON C ATALYSIS

P ROEFSCHRIFT

TER VERKRIJGING VAN

DE GRAAD VAN

D

U

L

,

OP GEZAG VAN

R

M

.

. P.F.

H

,

VOLGENS BESLUIT VAN HET

C

P

13

2007,

KLOKKE

16.15

DOOR

M ARCEL D AVID A CKERMANN

GEBOREN TE

C

(F)

IN

1980

Promotiecommissie:

Promotor:

Prof. Dr. Joost W.M. Frenken (Universiteit Leiden)

Referent:

Prof. Dr. Edvin Lundgren (Universiteit Lund, Zweden)

Overige leden van de Commissie:

Prof. Dr. Salvador Ferrer (CELLS, Barcelona, Spanje)

Prof. Dr. Marc T.M. Koper (LIC, Universiteit Leiden)

Prof. Dr. Bernard E. Nieuwenhuys (LIC, Universiteit Leiden en

Technische Universiteit Eindhoven)

Prof. Dr. Elias Vlieg (Radboud Universiteit Nijmegen)

Dr. ir. Sense Jan van der Molen (LION, Universiteit Leiden)

Dr. Alfons M. Molenbroek (Haldor Topsøe, Lyngby, Denemarken)

Operando SXRD: A New View on Catalysis, M.D. Ackermann

ISBN 978-90-9022489-3

A digital version of this thesis is available at

http://www.physics.leidenuniv.nl/sections/cm/ip

The work presented in this Thesis has been made possible by financial support

from the Dutch Foundation for Fundamental Research on Matter (Stichting

FOM) and the European Synchrotron Radiation Facility (ESRF). The work has

been performed at the Leiden Institute of Physics (LION), and the ID03

Beamline of the ESRF

v

vii

TABLE OF CONTENT:

I: INTRODUCTION AND THEORY 11

1.1:INTRODUCTION 12

1.2:HETEROGENEOUS CATALYSIS 14

1.2.1: Catalysts 14

1.2.2: Reaction mechanisms 15

1.3:THE PRESSURE GAP: 19

1.3.1: Surface Science at elevated pressure and temperature 19 1.3.2: Chemical potential: influence on surface structure 19 1.3.3: Kinetic barriers: Low versus high temperature and pressure 21

1.4:THE MATERIALS GAP 23

1.5:TECHNIQUES FOR STUDYING SURFACES UNDER ELEVATED PRESSURE

CONDITIONS 24

1.5.1: The conflict of surface sensitivity and elevated pressures 24

1.5.2: Hard X-Rays 25

1.5.3: (High Pressure) Scanning Tunneling Microscope 26 1.5.4: A short path through the gas phase 27 1.5.5: Polarization (filtering) 27 1.5.6: Density Functional Theory 28 1.6:SURFACES OF METALS ON THE ATOMIC SCALE 29 1.6.1: Unit cells and the bulk structure of crystals 29 1.6.2: Cuts through crystal structures 31 1.6.3: Low index planes 32 1.6.4: Surface reconstructions 33 1.6.5: High index planes 35 1.6.6: Altering surfaces: adsorption and growth 35

1.7:SURFACE X-RAY DIFFRACTION 39

1.7.1: SXRD from perfect crystal surfaces 39 1.7.2: Non perfect crystals and surfaces: CTRs 43 1.7.3: Calculating structures from SXRD 46 II: STRUCTURE AND REACTIVITY OF SURFACE OXIDES ON PT(110)

DURING CATALYTIC CO OXIDATION 51

2.1:INTRODUCTION 52

2.2:CRYSTAL PREPARATION 52

2.3:EXPOSURE TO HIGH PRESSURE OF O₂ 54

2.4:REACTIVITY OF THE PT SURFACE IN CO OXIDATION 58 2.4.1: Reactivity on the PtO₂ surface 59 2.5:SURFACE MORPHOLOGY OF THE -PTO2 SURFACE 63 2.6:SWITCH FROM OXIDE TO METAL INDUCED BY CO PULSE 69 2.6.1: Rate Limiting step on the metallic surface 70 2.7:‘SPONTANEOUS’ SWITCH TO HIGH REACTIVITY 70 2.8:INTERMEDIATE STRUCTURE: COMMENSURATE (1X2) 71 2.8.1: The (1x2)-structure: DFT calculations 73 2.8.2: Mixed coverage and stability of (1x2)-structure 75

2.9:CONCLUSIONS 81

III: INTERACTION BETWEEN PT(111), O2 AND CO AT ELEVATED

PRESSURE AND TEMPERATURE 83

3.1:INTRODUCTION 84

3.2:EXPERIMENTAL 84

3.3:EXPOSURE TO O2 86

3.3.1: Low pressures of O₂ 86 3.3.2: High pressure of O₂ 86

3.3.2.1: Orientation and commensurability 87

3.3.2.2: Thickness 89

3.3.2.3: Growth oscillations 93

3.3.2.4: Beam effect 99

3.4:EXPOSURE OF -PTO2 TO CO 100

3.5:REACTION RATE AND REACTIVITY OF -PTO₂ 104 3.5.1: Pulses “d” and “e” 106 3.5.2: Surface Structure and reactivity at pulse “f” 108

3.6:2X2 COMMENSURATE STRUCTURE 109

3.7:CONCLUSIONS 113

IV: SXRD STUDY OF PD SINGLE CRYSTAL SURFACES AS MODEL CO

OXIDATION CATALYSTS 115

4.1:INTRODUCTION 116

4.2:PD(001) OXIDATION 116 4.2.1: Low pressure structures 117

4.2.2: Bulk-like PdO 119

4.3:REACTIVITY 123

4.4:SWITCHING BEHAVIOR AND SELF SUSTAINED OSCILLATIONS 129 4.5:PD(553): STRUCTURE AND REACTIVITY 131

4.5.1: Introduction 131

ix

4.6:CONCLUSIONS 135

V ATOMIC STEPS AS A MOTOR FOR REACTION OSCILLATIONS 137

5.1:INTRODUCTION 138

5.2:EXPERIMENTAL 139

5.2.1: Surface roughness and the metal-to-oxide transition 139 5.2.2: Switching point: PCO vs. Roughness 143 5.3:SELF-SUSTAINED REACTION OSCILLATIONS:ROUGHNESS MODEL 145 5.3.1: Numerical model 150

5.4CONCLUSIONS: 154

APPENDIX A: INSTRUMENTATION 157

A.1:THE ID03BEAMLINE 158

A.2:THE HIGH PRESSURE /UHVCHAMBER 159

A.3:THE GAS MANIFOLD 162

A.4:6-CIRCLE DIFFRACTOMETER 165

A.5:A NEW SETUP FOR SXRD AT ELEVATED PRESSURE CONDITIONS 165 BIBLIOGRAPHY 171 SUMMARY 179

SAMENVATTING VOOR DE LEEK 180

SUMMARY (LAYMEN’S TERMS) 185