Silver catalysts find wide industrial application for ethylene oxidation because of its uniquely high selectivity towards ethylene oxide (EO). The nature of the selective oxygen species on/in silver is been extensively debated in the literature because of the scarcity of molecular level measurements and computational calculations. The reactions of ethylene with the oxygen species on/in Ag powder and Ag/α-Al2O3 are chemically probed with integration of in situ Raman spectroscopy and Temperature Programmed Surface Reaction (TPSR) spectroscopy. Although multiple oxygen species are present on/in Ag (surface, subsurface and bulk), the oxygen species that give rise to a Raman band at ~ 820 cm-1 are associated with selective formation of ethylene oxide. The Raman band at ~820 cm-1 is found to selectively exchange under mild conditions (T &lt; 100 oC) with C18O2 indicating that this oxygen species is present on the surface of Ag. X-Ray Photoelectron Spectroscopy (XPS) studies indicate the oxygen species with binding energy at ~532 eV is consumed by reacting with ethylene. Density Functional Theory (DFT) calculations bring insights into the detailed structures of the corresponding oxygen species. The methodologies and insights developed are widely applicable to the understanding of a wide range of catalytic oxidation reactions.

Unraveling the reactivity of ethylene with oxygen species on/in silver catalysts

ACS Spring Meeting 2021

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