Controlled Oxidant Delivery Uncovers Selectivity Branching in Heterogeneous Epoxidation Catalysis

Heterogeneous catalysis generally features complex speciation of reactive intermediates that limits selectivity control and mechanistic understanding. Olefin epoxidation is a major and highly carbon-intensive process in the chemical industry, yet the molecular origin of selectivity branching causing the competing, CO 2 -emitting combustion reaction remains debated and is obscured by the presence of multiple oxidants on catalyst surfaces. Herein, we selectively generated surface metaloxygen (M–O) species, a commonly proposed intermediate, and discovered clean, O 2 -dependent chemoselectivity: surface M–O alone exhibited up to 100% selectivity toward epoxidation, whereas the co-existence of surface M–O and O 2 could lead to combustion via a novel oxidative C=C cleavage pathway. Further studies uncovered unprecedented insights into selectivity branching, suggesting new strategies for rationally decarbonizing epoxidation catalysis.