Progress and perspective on the fundamental understanding of structure–activity/selectivity relationships for Ag catalyzed ethylene epoxidation

Abstract

Ethylene oxide (EO) stands among the most pivotal gateway chemicals where Ag-catalyzed ethylene epoxidation is the only viable route in the chemical industry. Academically, it is also one of the most attractive model reactions that involves advancements of multiple disciplines in catalysis science. Over the past decades, a list of classic fundamental questions have emerged that sparked extensive debates regarding i) nature of selective oxygen species; ii) state of the silver surface layer under reaction condition, iii) detailed reaction mechanism of ethylene epoxidation, etc. In this contribution, we critically review what has been achieved to date on the understandings of the molecular structure – activity relationship for silver-catalyzed ethylene oxidation. We first highlight how cutting-edge in situ/operando spectroscopic characterization techniques played a unique role in deciphering the catalytic structure of the silver catalyst under working conditions. Next, we provide a strategic summary on the means of maneuvering the activity and EO selectivity over supported Ag/α-Al₂O₃ catalysts, including particle size manipulation, crystal phase engineering, silver oxidation state and support management. The review ends with a perspective on the computational insights into the kinetics and mechanism of Ag-catalyzed ethylene epoxidation. We hope that the developments and methodologies highlighted in this review will not only help academia and industry to further the fundamental understanding and commercial development of silver-based catalysts for ethylene epoxidation, but also inspire revolutionary breakthroughs in other heterogeneous catalysis applications.