Regensburg 2000 – scientific programme

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O: Oberflächenphysik

O 11: Postersession (Eröffnung)

O 11.110: Poster

Monday, March 27, 2000, 19:00–22:00, Bereich C

The role VOx and V (sub)surface layers in the dissociation and reaction of CO on Pd (111) and Rh (111) — •Bernhard Kloetzer, Wolfgang Reichl, and Konrad Hayek — Institut f. Physikalische Chemie, Univ. Innsbruck, Innrain 52A, A-6020 Innsbruck

When a noble metal surface is combined with a reducible oxide, metal-support interaction will usually lead to a change of catalytic properties. Oxide submonolayers promote CO hydrogenation while the respective alloy surfaces (e.g. RhxTiy) are much less active. We studied the elementary reaction steps of the CO-H2 reaction on Rh and Pd surfaces modified by submonolayers of vanadium oxide and vanadium metal. Inverse model catalysts were prepared by vapour deposition of V on the single crystal surface with or without presence of oxygen. They were characterised and their catalytic activity was measured in a combined low- and high-flux experiment in the pressure range between 10-10 and 1 mbar. CO dissociation is strongly promoted by the simultaneous presence of vanadia islands and hydrogen on the surface, most likely through the formation of oxygen defect sites at the metal-oxide boundary. On the other hand, vanadium in the metallic state forms a subsurface alloy on Pd and Rh, on which the binding energy of molecular CO is markedly decreased. The catalyst activity in the total reaction may benefit from the combination of these two effects.