Regensburg 2000 – wissenschaftliches Programm

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O: Oberflächenphysik

O 17: Oberflächenreaktionen (I)

O 17.9: Vortrag

Dienstag, 28. März 2000, 13:15–13:30, H45

Inverse model catalysts for studies of metal-support interactions: CO hydrogenation on VOx/Rh and V/Rh — •Wolfgang Reichl, Bernhard Kloetzer, and Konrad Hayek — Institut f. Physikalische Chemie, Univ. Innsbruck, Innrain 52A, A-6020 Innsbruck

The kinetics of the reaction of hydrogen and CO was investigated on vanadium and vanadium oxide-modified Rh surfaces ((111) and polycrystalline) in order to understand the promotion of noble metals by reducible oxides and to asses the effect of the metal oxide boundary. Inverse supported catalysts were prepared by UHV deposition of V metal on the metal surface with or without presence of oxygen. After studying the probability of CO dissociation on clean and V-covered surfaces the methanation kinetics was measured in parallel in a molecular beam experiment and in an externally attached high pressure cell. The reaction is promoted by submonolayer quantities of vanadia, but the reaction rates depend strongly on the temperature of hydrogen reduction. At lower reduction temperature this dependence can be related to concomitant changes of the stochiometry and structure of the VOx deposits. However, after reduction above 823 K, vanadia is reduced to V metal, which migrates into near-surface layers. The same subsurface alloy is obtained by UHV deposition of V metal and annealing. It shows peculiar catalytic properties (high catalytic activity, low deactivation). The origin of this promotional effect is discussed.