Regensburg 2013 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 20: Surface Chemical Reactions and Heterogeneous Catalysis II

O 20.11: Vortrag

Montag, 11. März 2013, 18:30–18:45, H33

Ethylene Oxide Formation over Ag(111): Reactivity and Spectroscopy Investigation of the Active Oxygen Species — •Sebastian Böcklein¹, Sebastian Günther², and Joost Wintterlin¹ — ¹Ludwig-Maximilians-Universität München, Germany — ²Technische Universität München, Germany

Despite intensive investigation the ethylene oxide (EtO) formation over Ag catalysts remains an unsolved problem. By applying a special preparation procedure we were able to obtain and characterize the catalytically active oxygen phase on Ag(111). Reactivity experiments of this species with ethylene using temperature-programmed reaction (TPR) show formation of EtO. X-ray photoelectron spectroscopy (XPS) gives an O 1s signal in the range of 530-531 eV. A closer investigation of the XPS data shows that it consists of two distinct oxygen species (O 1s BE 530.2 and 530.7 eV). The ratio depends on the simulataneous presence of the p(4 ×4 )O reconstruction and on the sample temperature. Temperature dependent XPS (TDXPS) measurements show that the 530.2 eV-species increases with temperature, and a quantitative analysis indicates a reversible transformation between the two species. By angle resolved XPS (ARXPS) depth profiles for these species could be evaluated resulting in a model for this system. Using in situ scanning tunneling microscopy (STM) we could follow the reaction of this reactive oxygen phase with ethylene. The reaction is connected with massive changes of the catalyst surface and with the appearance of new ordered structures like a (2 × 2) or a chain-like phase.