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

PyridineC3H6

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)

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(d)

2250 L

Binding energy /eVBinding energy /eV

Zn(0001)/ H2O/O2 1:1 mixture at 180 K

XPS

180 K

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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

534.3532.2

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

HREELSXPS

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 OxidationRoberts, 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 FilmsB. 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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SummaryM. 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

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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 2Surface

diffusion

Cu Cu Cu Cu Cu Cu

NH NH NH