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The blocking of the step-mediated indirect channel to hydrogen dissociation by oxygen on Pt(5 3 3)

The blocking of the step-mediated indirect channel to hydrogen dissociation by oxygen on Pt(5 3 3)
The blocking of the step-mediated indirect channel to hydrogen dissociation by oxygen on Pt(5 3 3)
The initial dissociative sticking probability, S-0, of H-2 on clean and oxygen modified Pt(5 3 3) was measured as a function of incident kinetic energy, E-i, surface temperature, T-s, and coverage, ?(H). At low oxygen coverages, where oxygen adsorption leads to oxygen atoms decorating step sites, the indirect channel to hydrogen dissociation operating in the energy regime E-i<150 meV, is blocked. This blocking is shown to be complete when the (1 0 0) step sites are saturated by oxygen at a coverage of ?(O) = 0.12. For this oxygen decorated surface, a second indirect channel, mediated by an accommodated physisorbed precursor on the clean surface at E-i<30 meV, remains intact, as does the higher energy direct dissociation channel characteristic of the (1 1 1) terraces. A similar weak T-s dependence is exhibited for the very low energy indirect channel on the clean and oxygen modified surface. The low energy (physisorbed precursor) indirect channel, and the direct channel, are blocked only as oxygen is atomically adsorbed on the (1 1 1) terraces. The ?(H) dependence measured at various energies on the clean and oxygen decorated surface at ?(O) = 0.12 also indicate the blocking of the step-mediated indirect channel which is characterised by a weak ?(H) dependence. These results are consistent with the conclusion that the indirect channel to hydrogen dissociation operating in the energy regime E-i<150 meV, suggested to involve an unaccommodated precursor, is mediated by step sites. The importance of the poisoning of step sites in reactions involving hydrogen dissociation from a thermalised isotropic gas at 300 K is also considered.
sticking, hydrogen molecule, oxygen, platinum, platinum crystal-surfaces, molecular-beam, sticking probability, exchange-reaction, pt(111) surface, reactant angle, metal-surfaces, h2-d2 exchange, adsorption, h-2
0039-6028
165-172
Gee, A.T.
389d7e86-c0c8-4024-8e75-03a71c9ed1ea
Hayden, B.E.
aea74f68-2264-4487-9d84-5b12ddbbb331
Mormiche, C.
00a2dfb0-7160-453a-9eb1-02808eb60cb4
Nunney, T.S.
d938cca8-dd83-40bd-8ca3-a26269fac2e5
Gee, A.T.
389d7e86-c0c8-4024-8e75-03a71c9ed1ea
Hayden, B.E.
aea74f68-2264-4487-9d84-5b12ddbbb331
Mormiche, C.
00a2dfb0-7160-453a-9eb1-02808eb60cb4
Nunney, T.S.
d938cca8-dd83-40bd-8ca3-a26269fac2e5

Gee, A.T., Hayden, B.E., Mormiche, C. and Nunney, T.S. (2002) The blocking of the step-mediated indirect channel to hydrogen dissociation by oxygen on Pt(5 3 3). Surface Science, 512 (3), 165-172. (doi:10.1016/S0039-6028(02)01733-8).

Record type: Article

Abstract

The initial dissociative sticking probability, S-0, of H-2 on clean and oxygen modified Pt(5 3 3) was measured as a function of incident kinetic energy, E-i, surface temperature, T-s, and coverage, ?(H). At low oxygen coverages, where oxygen adsorption leads to oxygen atoms decorating step sites, the indirect channel to hydrogen dissociation operating in the energy regime E-i<150 meV, is blocked. This blocking is shown to be complete when the (1 0 0) step sites are saturated by oxygen at a coverage of ?(O) = 0.12. For this oxygen decorated surface, a second indirect channel, mediated by an accommodated physisorbed precursor on the clean surface at E-i<30 meV, remains intact, as does the higher energy direct dissociation channel characteristic of the (1 1 1) terraces. A similar weak T-s dependence is exhibited for the very low energy indirect channel on the clean and oxygen modified surface. The low energy (physisorbed precursor) indirect channel, and the direct channel, are blocked only as oxygen is atomically adsorbed on the (1 1 1) terraces. The ?(H) dependence measured at various energies on the clean and oxygen decorated surface at ?(O) = 0.12 also indicate the blocking of the step-mediated indirect channel which is characterised by a weak ?(H) dependence. These results are consistent with the conclusion that the indirect channel to hydrogen dissociation operating in the energy regime E-i<150 meV, suggested to involve an unaccommodated precursor, is mediated by step sites. The importance of the poisoning of step sites in reactions involving hydrogen dissociation from a thermalised isotropic gas at 300 K is also considered.

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More information

Published date: 1 July 2002
Keywords: sticking, hydrogen molecule, oxygen, platinum, platinum crystal-surfaces, molecular-beam, sticking probability, exchange-reaction, pt(111) surface, reactant angle, metal-surfaces, h2-d2 exchange, adsorption, h-2

Identifiers

Local EPrints ID: 19743
URI: http://eprints.soton.ac.uk/id/eprint/19743
ISSN: 0039-6028
PURE UUID: 1559f9b0-1f7c-4803-bbc4-abe0f18a0394
ORCID for B.E. Hayden: ORCID iD orcid.org/0000-0002-7762-1812

Catalogue record

Date deposited: 20 Feb 2006
Last modified: 09 Jan 2022 02:35

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Contributors

Author: A.T. Gee
Author: B.E. Hayden ORCID iD
Author: C. Mormiche
Author: T.S. Nunney

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