Recent Developments in Heterogeneous Catalyzed Epoxidation of Ethylene to Ethylene Oxide.

Epoxidation of ethylene to produce ethylene oxide (EO) is a vital heterogeneous catalytic chemical process in industry, as EO is an important intermediate for the synthesis of fine chemicals including ethylene glycol, ethoxylates, plastics and polyester. EO is commercially produced by the silver-catalyzed partial oxidation of ethylene with air or oxygen. However, it remains challenging to understand its chemical behavior under reaction conditions. To overcome this challenge, a series of catalysts with well-defined structures have been developed. The present review is devoted to summarizing the recent advances in the exploitation of novel catalytic materials for the epoxidation of ethylene, such as metal nanoparticles, clusters, single atoms, and bimetal. The role of promoters in selectivity enhancement will be discussed. A deep understanding of the active species, oxygen species, active structures, activity-structure relationship, and mechanisms contributing to epoxidation process are highlighted. The integration with other advanced technologies such as electrocatalytic and photocatalytic is also reviewed. Finally, the current challenges and future prospects are provided so as to give guidance for the design of efficient catalysts for heterogeneous epoxidation of ethylene to EO, and to improve the fundamental understanding of the underlying catalytic chemistry.