INSITU RAMAN STUDIES OF ETHYLENE OXIDATION AT AG(111) AND AG(110) UNDER CATALYTIC REACTION CONDITIONS

In this report we present, to our knowledge, the first Raman investigations at single crystalline Ag(111), Ag(110) and microfacetted Ag(110) samples, which were exposed to N2 or N2 + reactive gases (oxygen and ethylene). The pressure and temperature ranges are close to those used for industrial oxidation of ethylene using Ag-catalysts. Depending on the orientation of the Ag-surface and on the history its preparation and temperature cycling (300-900 K), three Raman lines for three Ag-O species were found, assigned to Ag-O(ads.), -Ag-O-Ag- with oxygen located in the sub-surface position and oxygen dissolved in the bulk of silver. The disappearence of the Raman line for sub-surface oxygen in the course of ethylene epoxidation indicates its participation in this reaction.