LEED-I(V) Structure Analysis of the (7 × √3)rect SO4 Phase on Ag(111): Precursor to the Active Species of the Ag-Catalyzed Ethylene Epoxidation

According to a recently proposed mechanism, the silver-catalyzed industrial synthesis of ethylene oxide (EO) involves adsorbed SO4. The O atoms that are added to the ethylene molecules to give EO originate from SO4, which may solve the long-standing question about the active oxygen species in this reaction. Here, we report a low-energy electron diffraction structure analysis of an ordered phase of SO4 on the Ag(111) surface, forming a (7 × √3)rect structure and containing the oxygen species that before had been spectroscopically identified on the active catalyst. Using I(V) data from a low-energy electron microscope and an input model from density functional theory, the complex structure could be solved. It contains SO4 moieties on a reconstructed Ag(111) surface in which all four O atoms bind to Ag atoms. In the proposed ethylene epoxide reaction model, the structure represents the parent phase from which the active SO4 phase is formed by a lifting of the reconstruction.