Mechanistic insights into the preferential CO oxidation in H2-rich gas (PROX) over supported noble metal catalysts [Elektronische Ressource] / Markus Matthias Schubert

Markus Schubert@Scooby

Informations

• Publié par: universitat_ulm
• Publié le: 01 janvier 2000
• Nombre de lectures: 24
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Universität Ulm
Abteilung Oberflächenchemie & Katalyse
Mechanistic Insights into the
Preferential CO Oxidation in H -rich Gas (PROX)2
over Supported Noble Metal Catalysts
Dissertation
vorgelegt von
Markus Matthias Schubert
2000:PaX]Abteilung Oberflächenchemie & Katalyse
Universität Ulm
Mechanistic Insights into the
Preferential CO Oxidation in H -rich Gas (PROX)2
over Supported Noble Metal Catalysts
Dissertation
zur Erlangung des Doktorgrades Dr. rer. nat.
der Fakultät für Naturwissenschaften
der Universität Ulm
vorgelegt von
Markus Matthias Schubert
aus München
Ulm 2000Der experimentelle Teil dieser Arbeit wurde in der Zeit von Oktober 1996 bis September
1999 in der Abteilung Oberflächenchemie und Katalyse der Universität Ulm angefertigt.
Wissenschaftlicher Betreuer: Prof. Dr. R. J. Behm
(Leiter der Abteilung Oberflächenchemie & Katalyse)
Amtierender Dekan: Prof. Dr. O. Marti
1. Gutachter: Prof. Dr. R. J. Behm
2. Gutachter: Prof. Dr. J. Garche
Tag der Promotion: 11. Mai 2000CONTENTS
I. Introduction
1. The selective CO oxidation - reactions..............................................................................1
2. Technical application: PROX............................................................................................3
3. Intention of this work.........................................................................................................5
II. Experimental
1. Setup....................................................................................................................................6
1.1 Reaction gases & mixture facility....................................................................................6
1.2 The plug-flow reactor.......................................................................................................9
1.3 Infrared spectroscopy - DRIFTS.....................................................................................12
1.3.1 DRIFTS-theory.......................................................................................................13
1.3.2 DRIFTS-setup.........................................................................................................15
1.3.3 Processing of DRIFTS spectra...............................................................................17
1.4 On-line GC analysis.......................................................................................................20
1.5 Other methods used........................................................................................................22
1.5.1 XPS.........................................................................................................................22
1.5.2 On-line IMR-MS analysis.......................................................................................22
1.5.3 Isotope studies / pulse experiments.........................................................................23
1.5.4 XRD.........................................................................................................................23
2. Catalyst characterization.................................................................................................24
2.1 Platinum catalysts...........................................................................................................24
2.2 Pt Sn catalyst..................................................................................................................243
2.3 Gold catalysts.................................................................................................................25
iIII. Results & discussion
1. The standard catalyst - Pt/γ-Al O ..................................................................................262 3
1.1 The influence of the CO coverage on the activity / selectivity.......................................27
1.1.1 Selectivity & hydrogen induced rate enhancement.................................................27
1.1.2 Experimental limitations - neglecting the reaction rate.........................................29
1.1.3 Adsorption of CO in pure N ..................................................................................322
1.1.4 Adsorption of CO in H / N ...................................................................................362 2
1.1.5 Coadsorption behaviour of CO and H ..................................................................392
1.2 From idealized to more realistic conditions...................................................................46
1.2.1 Self-poisoning by CO ...........................................................................................46ad
1.2.2 Influence of water...................................................................................................48
1.2.3 Performance in CO -rich gas.................................................................................562
1.3 Other support materials..................................................................................................63
1.3.1. Comparison of activity / selectivity........................................................................63
1.3.2. The water-gas shift - limiting the CO conversion..................................................66
1.4 Summary on platinum catalysts......................................................................................71
2. Improved performance on bimetallic systems - Pt Sn/Vulcan.....................................733
2.1 Low-temperature CO oxidation over Pt Sn/Vulcan.......................................................753
2.1.1 Superior performance on Pt Sn/Vulcan vs Pt/ -Al O ...........................................753 2 3
2.1.2 Alloying effects........................................................................................................78
2.1.3 Coverage dependence of the selectivity..................................................................82
2.1.4 Catalyst state during conditioning & reaction.......................................................84
2.1.5 Mechanistic proposal - avoiding the CO poisoning...............................................89
2.2 Other important characteristics for an application in a PROX-stage.............................93
2.2.1 Long-term stability.................................................................................................93
2.2.2 Performance in more realistic reformates..............................................................99
2.2.3 The water-gas shift activitiy of Pt Sn/Vulcan.......................................................1033
2.3 Summary on bimetallic Pt Sn catalyst..........................................................................1053
ii
g
g3. An alternative for the low temperature conversion - Au/α-Fe O ............................1072 3
3.1 Mechanistic insight into the CO oxidation over gold catalysts....................................109
3.1.1 A short review.......................................................................................................109
3.1.2 The „support-effect“.............................................................................................111
3.1.3 Oxygen supply from the FeO -support (Transient response measurements).......116x
3.1.4 Proposed reaction scheme....................................................................................121
3.2 The influence of structural parameters on the activity / selectivity..............................123
3.2.1 The dependence of the activity on the particle size..............................................123
3.2.2 Influence of the calcination temperature..............................................................129
3.2.3 The dependence of the particle size on the sodium content..................................132
3.3 The CO coverage on Au and its influence on the kinetics...........................................134
.............................................................................................1343.3.1 Kinetic observations
....................1373.3.2 Comparison of the CO coverage on Pt/ -Al O versus Au/ -Fe O2 3 2 3
3.3.3 Temperature dependence......................................................................................143
3.4 Deactivation behaviour.................................................................................................147
3.4.1 „Off-line deactivation“.........................................................................................147
3.4.2 „On-line deactivation“ during CO oxidation......................................................148
a) Irreversible poisoning of more crystalline samples...........................................150
b) Reversible deactivation on amorphous samples................................................155
c) Deactivation model.............................................................................................157
3.5 Effects of CO and H O on the activity / selectivity....................................................1602 2
3.5.1 Selectivity enhancement by water.........................................................................160
3.5.2 Performance in CO -containing mixtures............................................................1632
3.6 Reverse water-gas shift over Au/ -Fe O ....................................................................1702 3
3.7 Other support mate