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O: Fachverband Oberflächenphysik

O 20: Surface Chemical Reactions and Heterogeneous Catalysis II

O 20.10: Vortrag

Montag, 11. März 2013, 18:15–18:30, H33

Flow-Reactor Investigations of Clean and Cs-promoted Ag foils as Catalysts in the Ethylene Epoxidation Reaction — Gergely Rozsa, •Regina Wyrwich, Sebastian Böcklein, Maximilian Ganiek, and Joost Wintterlin — Department Chemie, Ludwig-Maximilians-Universität München, Germany

The selective epoxidation of ethylene over Ag is a large scale industrial process. Nevertheless the reaction mechanism is still heavily debated. In the commercial process a supported catalyst is used and Cs is added as a promotor to improve the selectivity. Despite intense investigations on model systems the role of Cs remains unclear. Both a site blocking effect as well as an electronic effect are discussed. In the context of an extensive catalytic study we investigated the behaviour of Cs-promoted polycrystalline Ag-foils under reaction conditions. We report about a procedure to reproducibly deposit Cs on sputter-cleaned Ag foils by dip-coating in aqueous CsOH solutions. Based on x-ray photoelectron spectroscopy (XPS) measurements a Langmuir-type behaviour of the deposition process is observed. Evaluation and comparison of the catalytic performance (activity and selectivity) of the Cs-promoted and clean Ag foils is done in a flow-reactor setup with quadrupole mass spectrometry (QMS) for product analysis. A crucial dependency upon the activation procedure (thermal treatment at 500 ^∘C in Ar or O₂) is found in this case. A potential influence of Cs seems to arise at higher pressures of the reactant gases indicating a site blocking effect of Cs.