Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 4: Heterogeneous catalysis I

O 4.5: Vortrag

Montag, 22. März 2010, 12:15–12:30, H33

Mechanisms of CO oxidation at nanoporous gold: combined TPD and XPS study — •Sarah Röhe, Tobias Becker, Andreas Schaefer, Arne Wittstock, Volkmar Zielasek, and Marcus Bäumer — Universität Bremen, Institut für Angewandte und Physikalische Chemie, Leobener Str. NW2, 28359 Bremen

Unsupported nanoporous gold (NPG) shows high catalytic activity for CO oxidation with molecular oxygen even below room temperature [1]. So far, the mechanisms of how the surface of NPG catalyzes this reaction have been somehow puzzling. In particular, several experiments on various low-index single crystal gold surfaces had demonstrated that the rate of O₂ dissociation at pure gold is negligible - even at higher temperatures and even if the surface had been roughened on the atomic scale by Ar sputtering.

Based on a combined TPD and XPS study in ultrahigh vacuum at NPG we will provide evidence for residual silver in the NPG surface playing a major role for the activation of molecular oxygen for CO oxidation. Since NPG is produced by leaching of silver from Au-Ag alloy, rest silver with total concentrations of 1-5% and up to 20% at the surface remains in the material and was speculated on as an active ingredient in the CO oxidation, before. Our data indicate that at temperatures above 200 K O₂ is dissociated at silver sites and atomic oxygen probably binds at silver but also spills over to gold surrounding silver islands.

[1] V. Zielasek, B. Jürgens, C. Schulz, J. Biener, M.M. Biener, A.V. Hamza, M. Bäumer, Angew. Chem. Int. Ed. 45 (2006) 8241.