Ag-based electrocatalysts for ethylene epoxidation

Ethylene oxide (EO) is industrially produced by epoxidation of ethylene on Ag-based heterogeneous cata-lysts. Electrophilic oxygen species are assumed to be active key species in the EO production. This study explores the possibility to electrochemically produced these oxygen species in a solid oxide electrochem-ical cell. Two series of Ag based cermet electrodes were prepared either with Yttria Stabilized Zirconia (YSZ), a pure oxygen ionic conductor, or with Gadolinia-Doped Ceria (GDC), a mixed ionic and electronic conductor. Ag/YSZ cermet layers were deposited on planar and tubular YSZ dense substrates by using a conventional chemical method while Ag/GDC cermets were coated on GDC dense pellets by reactive magnetron sputtering. We evidenced a self-redispersion of Ag in the ethylene/oxygen mixture in Ag/YSZ cermet layers leading to the formation of small Ag clusters in close interaction with YSZ which are selec-tive for epoxidation. However, the sintering process of these small Ag clusters is too fast even at 260 degrees C to maintain the EO selectivity. On the other hand, the selectivity towards EO and the ethylene conversion of Ag/GDC cermet coatings were found to linearly increase with the applied current, demonstrating for the first time, the direct electrooxidation of ethylene into EO. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study investigates the possibility of electrochemically producing active oxygen species on Ag-based ceramic electrodes in a solid oxide electrochemical cell. It was found that small Ag clusters formed in Ag/YSZ cermet layers were selective for epoxidation, but the sintering process happened too quickly to maintain EO selectivity. On the other hand, Ag/GDC cermet coatings demonstrated a linear increase in selectivity towards EO and ethylene conversion with applied current, indicating the direct electrooxidation of ethylene into EO.