Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 35: Heterogeneous catalysis II

O 35.2: Talk

Tuesday, March 23, 2010, 15:15–15:30, H33

Steps to detect catalytic ethylene oxide formation on single crystals — •Sebastian Böcklein, Sebastian Günther, Robert Reichelt, Markus Seibald, Andreas Preimesser, Martin Ehrensberger, Gergely Rozsa, and Joost Wintterlin — Ludwig-Maximilians-Universität, 81377 München, Germany

As part of a project to bridge the "pressure gap" for the catalytic synthesis of ethylene oxide (EtO) on Ag surfaces we have undertaken extensive studies in a model reactor. The investigations aimed at finding conditions under which the production of EtO can be unambiguously and quantitatively detected on single crystal Ag surfaces, a challenging task because of the extremely low ethylene-to-EtO reaction probability. The experiments were performed in a specially designed reactor, and they involved the variation of partial pressures, temperature, and type of Ag samples (powders and polycrystalline sheets), and great effort was expended for proper background subtraction. We find that for the sheets an essential ingredient is an activation treatment by annealing in oxygen, which raises the activity by more than one order of magnitude. There are indications that subsurface O atoms are created by this pretreatment. The maximum values obtained for activity, selectivity, yield, and reaction probability allow us to predict that EtO produced on a single Ag crystal can indeed be detected under flow conditions in a UHV chamber. Experiments on the deactivation show that sintering plays an important role for the dispersed samples, but that there is an additional deactivation process for the sheets that is not caused by sintering or poisoning.