2015 03-25 Rideal Berlin Philip R Davies

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Cardiff Catalysis Institute, Surface Science & Catalysis GroupSurface Science & Catalysis Group
Cardiff Catalysis Institute
Low Energy Pathways and Precursor States in the
Catalytic Oxidation of Water and Carbon Dioxide at
Metal Surfaces and Comparisons with Ammonia
Oxidation
Phil Davies
Cardiff Catalysis Institute
Cardiff University

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Cardiff Catalysis Institute, Surface Science & Catalysis Group

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O2(g) O2(s) O-(s) O-(a) O2-(a)
Theme:
The Reactivity of Transient Complexes

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CO3(a)
C0(a)
Cd-(a)
280 285 290 295 300
Al(111) 80K
O2(g) O2(s) O-(s) O-(a) O2-(a)
CO(g) CO(s) qCO ~0
CO(g) + O2(g) CO3(a)
A. F. Carley, M. W. Roberts (1987) Chem Comm 355
Oxygen-Induced Dissociation of Carbon-Monoxide at an
sp-Metal Surface
O2-(a) + CO(g) No reaction
Al(111) + CO(g) No reaction

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Role of Oxygen Transients in …. O2/NH3 coadsorption
Zn(0001)
M. W. Roberts et al.
Faraday Trans 86 (1990) 2701
O2/Zn(0001)
Sticking probability: 10-3
O2(g) O2(s) O-(s) O-(a) O2-(a)
O=O
NH3

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H2O
The development of a new concept: the role of oxygen transients,
defect and precursor states in surface reactions
NH3
Pyridine
C3H6
CO
O2(g) O2(s) O-(s) O-(a) O2-(a)
M. W. Roberts et al.
Catalysis Letters 80 (2002) 25

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The case for H2O/O2 coadsorption
‘…… adsorbed water plays a vital part in the hydrogenation process’’
Boswell, 1922
‘‘The great difficulties of proving this (Boswell’s hypothesis)— seems to have
led it to receiving little attention’’.
Otto Beeck 1935
‘‘The exact role of water in heterogeneous (reactions) catalysis has been a
subject of speculation for over 50 years’.
Wyn Roberts 1981
“Water was an obvious system to follow on from ammonia but with some
experimental disadvantages compared with ammonia, …”
Wyn Roberts, Catalysis Letters 2014

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H2O/O2 coadsorption
HREELS & XPS studies of
•Zn (0001)
O2 & H2O unreactive
•Ag(111)
O2 & H2O unreactive
•Cu(110) & Cu(111)
H2O unreactive

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Zn(0001) / H2O HREELS
x104
80 K
1 L H2O
160 K
H2O(g) H2O(s)

10
(d)
2250 L
Binding energy /eV
Binding energy /eV
Zn(0001)/ H2O/O2 1:1 mixture at 180 K
XPS
180 K

11
80K 1 L H2O
130 K
160 K
Ag(111) /H2O
HREELS
H2O(g) H2O(s)

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H2O /O2 Coadsorption on Ag(111)
XPS
130 K,
1 L H2O
130 K,
765 L O2
534.3
532.2
530.2 290 K
160 K
220 K
534.3
532.2
530.2

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HREELS

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Water-Oxygen Interactions at Surfaces
220 K
530.2
320
3640
H
O
Virtually pure OH monolayer at 220 K

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Cu(110): H2O /O2 32:1
160 K
H
O
XPS

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Carley et al. App. Surf. Sci. 81 (1994) 265
12 L
160 K
36 L
160 K
190 K
H
O
HREELS
XPS
Cu(111): H2O /O2 Coadsorption
52:1 160 K

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Coadsorption and surface order
Surface reactions under dynamic conditions tend to
be associated with:
• Higher selectivity
• Higher surface concentrations
• Increased surface order

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The Chemisorption of Nitric Oxide and the Oxidation of Ammonia at Cu(110)
Surfaces
Roberts et al. Topics in Catalysis 14, (2000) 101
O(a) /NH3(g)
550 K
O(a) /NH3(g)
300 K
3.3x1014 cm-2
< 2x1014 cm-2
396.5 396.5
Preadsorption Co-adsorption
6.7x1014 cm-2
O2(g) /NH3(g)
475 K
O2(g) /NH3(g)
295 K
2.4x1014 cm-2
N(a)
NH(a)NH/NH2(a)
N(a)

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4.2 nm
<110>
30 nm
An STM-XPS Study of Ammonia Oxidation
Roberts, Carley & Davies Chem. Comm. (1998) 1793
Cu(110) O2/NH3 300 K

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• Closer packed
• Better order
• Larger domains
STM&XPS Studies of the Oxidation of Aniline: Cu(110)
Preadsorbed oxygen Coadsorbed aniline/oxygen
Davies et al. J. Phys. Chem.B 108 (2004) 18630

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Coadsorption and surface order
 Surface reactions under dynamic conditions
tend to be associated with better surface order
 Further support for Wyn’s hypothesis of a
mobile intermediate
OH(a), NH(a), R’RN(a), CH3S(a), CH3O(a),

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What point did Wyn want to make in this paper?
“Surprisingly there has been little attention
given to the possible role of water in chemical
reactivity at metal surfaces and as far as I am
aware, no relevant STM studies.”

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“A Molecular Perspective of Water at Metal Interfaces”
Figure 5 | STM and DFT results
for extended water overlayers
on two different metal surfaces.
Pt(111)
Cu(110)
Javier Carrasco, Andrew Hodgson and Angelos Michaelides
Nature Materials 11 ( 2012) 667

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O2(g) O2(s) O-(s) O-(a) O2-(a)
The Reactivity of Transient Complexes
H2O

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A catalytic cycle proposed for the mechanism of
oxidation catalysis at P450
Cytochromes P450 catalyse the mono-oxygenase reaction:
RH + O2 + NADPH + H+ → ROH + H2O + NADP+
M. W. Roberts
Catal Lett (2011) 141 365–369
Postulated mechanism:
“FeO2” => “–Fe=O” => -Fe-OH
No direct experimental
evidence
for the precursors

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R. A. Marcus et. Al.
JACS 129, (2007) 5492
‘“On Water”: Unique Reactivity of Organic Compounds in Aqueous Suspension’.
K. Barry Sharpless et al. Angewandte Chemie Int 44 (2005) 3275.
On the Theory of Organic Catalysis “on Water

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Hydroxylation of Metal-Supported
Sheet-Like Silica Films
B. Yang, S. Shaikhutdinov, H.-J. Freund et al.
J. Phys. Chem C 117 2013 8336

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Critical Role of Water in the Direct Oxidation of CO and
Hydrocarbons in Diesel Exhaust after Treatment Catalysis
Alexandre Goguet, Christopher Hardacre et al.
App Catal B: 147 (2014) 764

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Summary
M. W. Roberts Catal. Lett (2014) 144 767
O2(g) O2(s) O-(s) O-(a) O2-(a)
 The role that water/oxygen transients can play in
catalytic reactions has been highlighted.
 Coadsorption methods combined with the right
conditions can generate high concentrations of well
ordered surface intermediates.

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The End
30
e-
d- d-
Initial State
O2-(a)
Final State

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Carbon dioxide activation
Al(111) CO2/H2O
CO2
H2O
95 K
295 K
295 K
292 K

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‘Surface Chemistry of Cu in the Presence of CO2 and H2O’.
Miquel Salmeron et al.
‘Surface Chemistry of Cu in the Presence of CO2 and H2O’.
Miquel Salmeron et al.
Langmuir 24, (2008): 9474

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Cu(100): CO2 activation by NH3
NH2
|
C
O O
Cu Cu Cu Cu
Energy loss /cm-1
“Activation of Carbon Dioxide Leading to a Chemisorbed Carbamate Species
at a Cu(100) Surface.”
M. W. Roberts, Carley & Davies Chem. Comm 1989 677

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NH3(g) + O-(g) NH2 (g) + OH-(g)
O2(g) O2
-(s) O-(s) O-(s) NH(s) + H2O(g)
Pathway 1
N
H
HH
Unreactive
Chemisorbed
Oxygen
O2-(a)
Pathway 2
Surface
diffusion
Cu Cu Cu Cu Cu Cu
NH NH NH

2015 03-25 Rideal Berlin Philip R Davies

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