Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 86: Heterogeneous catalysis I
O 86.9: Vortrag
Donnerstag, 17. März 2011, 18:30–18:45, WIL B122
Investigation of the Ethylene Oxide Formation over Ag using 18O2 — •Sebastian Böcklein, Manuel Joas, Christina Hettstedt, Sebastian Günther, and Joost Wintterlin — Ludwig-Maximilians-Universität, München, Germany
As part of an extensive surface science/catalysis project to investigate the reaction mechanism of the partial oxidation of ethylene to ethylene oxide (EtO) over Ag we have performed experiments in a model reactor. Experiments were performed with Ag-foils at pressures in the mbar range and by using 18O2. The findings are in partial disagreement with the existing literature. The reaction probability to give EtO is extremely low, and proper product detection, and quantification are essential. In very careful experiments we have been able to unambiguously detect the product. By changing the reaction parameters we could also deactivate and reactivate the silver catalyst (by heating the catalyst up to 600∘C in Ar) in a controlled way. There are strong hints of a bulk-dissolved oxygen species that desorbs during this procedure. Its role in the reaction was further investigated with 18O2. Depending on whether 18O2 was used in the high temperature/high pressure pretreatment with oxygen or in the reaction gas feed different isotope compositions were found in the EtO and in the total oxidation product (CO2). The isotope used in the O2 in the reaction feed is mainly found in the products but bulk-dissolved oxygen reacts too as well. The reaction is connected with transport processes of oxygen into and out of the Ag bulk. XPS investigations and sputter/heating experiments show large amounts of oxygen at the surface of the active Ag-foils.