Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 39: Heterogeneous Catalysis

O 39.2: Poster

Dienstag, 17. März 2015, 18:15–21:00, Poster A

Adsorption and Diffusion of Oxygen in Silver — •Regina Wyrwich, Hendrik Schlomberg, Christian Maak, Florian Rott, Lars Bulthaupt, Linh Nguyen Thuy, and Joost Wintterlin — Ludwig-Maximilians-Universität, München, Germany

The heterogeneously catalyzed selective oxidation of ethylene over silver is a large scale industrial process. Many studies have investigated the oxygen adsorption on silver surfaces to identify the active species for this reaction. A central issue has been the question about a possible role of oxygen atoms on subsurface positions or dissolved in the bulk. We report about a study in which we have investigated exchange processes between surface and bulk oxygen. A home-built reactor system has been used to load polycrystalline silver foils or an Ag(111) single crystal with oxygen at pressures of up to 800 mbar. The sample was then analyzed by TDS. In addition, an UHV apparatus equipped with XPS and LEED was used to investigate the sample surface after loading with oxygen. Depending on the loading parameters, two oxygen species were detected and selectively prepared, the so-called 'electrophilic oxygen' with a desorption temperature of 720 K and an XPS O 1s binding energy of 530.2 eV and the so-called 'O-gamma' with a desorption temperature of >870 K and an XPS O 1s binding energy of 529.3 eV. The species could be located at the surface (electrophilic oxygen) and in the bulk (O-gamma). It was found that the two species do not grow independently from one another, but that the formation of the 530.2 eV-species depends on the amount of O-gamma present.