AVS 46th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA10
Probing the Metal Sites of a V-oxide/Pd(111) "Inverse Catalyst": Adsorption of CO

Thursday, October 28, 1999, 5:00 pm, Room 607

Session: Adsorption at Surfaces
Presenter: F.P. Netzer, Karl-Franzens-Universität Graz, Austria
Authors: F.P. Leisenberger, Karl-Franzens-Universität Graz, Austria
G. Koller, Karl-Franzens-Universität Graz, Austria
S. Surnev, Karl-Franzens-Universität Graz, Austria
M.G. Ramsey, Karl-Franzens-Universität Graz, Austria
F.P. Netzer, Karl-Franzens-Universität Graz, Austria
Correspondent: Click to Email
A vanadium oxide / Pd(111) "inverse catalyst" system, consisting of V-oxide island structures and bare Pd(111) patches in between, has been prepared by reactive evaporation of V onto Pd(111) at submonolayer to monolayer coverages and has been characterised by STM and high-resolution core level photoelectron spectroscopy. Here we report a study of the adsorption of CO on these "inverse" V@sub 2@O@sub 3@/ Pd(111) catalyst. Since CO does not adsorb on V-oxide at room temperature, this allows to probe the adsorption properties of free Pd(111) sites in the presence of the V-oxide phase boundary. The adsorption of CO has been followed by monitoring the C 1s core level signals as a function of the V-oxide coverage and the CO exposure at room temperature, using high-resolution XPS with synchrotron radiation. The amount of adsorbed CO, as determined quantitatively from the C 1s peak areas, decreases with the V-oxide coverage as a result of the blocking of Pd adsorption sites. The concomitant decrease of the CO saturation exposure, i.e. the CO exposure necessary to reach CO saturation of the various surfaces, indicates, however, that a precursor state exists on the V-oxide surface, from which CO can diffuse over the metal-oxide boundary on to Pd sites. This spill-over effect is also corroborated by the dependence of the initial sticking probability of CO on the V-oxide surface coverage. The difference of the C 1s binding energies of CO adsorbed on pristine and oxide covered Pd(111) suggests that Pd adsorption sites are electronically influenced by the presence of a V-oxide phase boundary. Supported by the Austrian Science Foundation.