(666e) Direct Propylene Epoxidation Via Water Activation over Electrocatalysts

Current propylene oxide production relies on highly energy-intensive and hazardous oxidants, such as chlorine and peroxides. While direct oxidation of propylene using molecular oxygen has been explored as an alternative solution, achieving high selectivity for propylene oxide is challenging due to the allylic hydrogen stripping in propylene and consequent further oxidation. In this regard, a selective direct propylene epoxidation pathway using water as a cleaner and easily accessible oxygen source would present a compelling alternative to the current epoxidation methods. In this work, we developed an oxidized palladium-platinum alloy catalyst, which enables efficient oxygen-atom transfer from water to propylene without using mediators. This catalyst reaches a Faradaic efficiency of 66±5% toward propylene epoxidation at 50 mA/cm² at ambient temperature and pressure, outperforming previously reported electrocatalysts for direct epoxidation. Embedding platinum into the palladium oxide crystal structure stabilized oxidized platinum species, resulting in improved catalyst performance. The reaction mechanism was investigated using a multi-faceted approach including kinetic rate measurements, probe substrate analysis, and substrate-based descriptor assessment. The reaction kinetics suggest that epoxidation on this catalyst proceeds through the electrophilic attack by metal-bound peroxo intermediates. This work demonstrates an effective strategy for selective electrochemical oxygen-atom transfer from water, without mediators, for diverse oxygenation reactions.