Dresden 2014 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 62: Posters: Surface Reactions and Dynamics, Nanostructures

O 62.6: Poster

Mittwoch, 2. April 2014, 17:30–21:00, P1

CO oxidation at nanoporous gold: TPD, XPS, and DFT study — Sarah Röhe, Lyudmila Moskaleva, Andreas Schaefer, Arne Wittstock, •Volkmar Zielasek, and Marcus Bäumer — Institut für Angewandte und Physikalische Chemie, Universität Bremen

Nanoporous gold (np-Au) is an efficient catalyst for CO oxidation, even below RT. To gain insight into relevant mechanisms and surface species, we employed TPD and XPS in UHV directly at np-Au catalyst samples which were produced by leaching of silver from AgAu alloy and then activated for CO oxidation in a continuous-flow reactor. Supported by DFT calculations, the experiments indicate that the catalytic activity is based on a complex interplay of gold, silver, CO, and several oxygen species on and within the np-Au surface.

Residual silver is crucial for the ability of np-Au to chemisorb molecular oxygen, resulting in presumably atomic oxygen (Oact) at the surface available for CO oxidation. TPD after exposing np-Au to CO at 105 K shows pronounced CO and CO2 desorption at temperatures above 200 K, indicating an additional, more stable type of CO binding sites on np-Au as compared to pure gold. Only CO at these binding sites is oxidized by Oact. DFT calculations demonstrate that the strong binding of CO to np-Au cannot be explained by the presence of silver residues. It can be conceived, however, that it is induced by the formation of O-Au-CO complexes at low-coordinated surface sites. In fact, besides silver and Oact, we find various resident oxygen species on and within the np-Au surface. Their presence may be as crucial for the catalytic activity of np-Au as residual silver.