Improving the catalytic performance of Ag/SiC for ethylene epoxidation via modifying SiC surface using CeO2

Abstract

Ethylene epoxidation over high-loading Ag/α-Al₂O₃ catalysts is an important industrial process to produce ethylene oxide. However, the low specific surface area and poor thermal conductivity of α-Al₂O₃ restrict further improvement of the catalyst’s performance in ethylene epoxidation. In this work, we employed CeO₂-modified SiC as the support of active component Ag for the ethylene epoxidation reaction. Under the condition of 230 °C, 2 MPa, gas hourly space velocity of 3540 h⁻¹, the catalyst achieved good performance without any additives. The conversion, ethylene oxide selectivity, and space–time yields were 5.4 %, 74.3 %, and 66 kg/(m³·h), respectively. The experimental and calculation results showed that oxygen molecules were activated on the Ag catalyst surface to form ¹O₂ and •O₂^– species. These species then migrated onto the SiC with the ethylene adsorbed on the SiC surface. The oxygen vacancies in CeO₂ promote the migration of these oxygen species, and thus enhance the reaction performance.