Sunlight-Driven Olefin Epoxidation via a Bromide Radical-Mediated Process

Epoxides have been widely used in the daily chemical and plastics industries. However, as a mainstream epoxide production approach, the direct oxidation of olefins with O₂ often suffers from extensive energy consumption and excessive CO₂ emission. Here, we provide an olefin epoxidation strategy via a photodriven Br-mediated pathway, which exhibits a broad range of extension to olefin substrates, including linear alkenes, cyclic olefins, and aromatic olefins. Employing ethylene epoxidation as a model reaction, a high ethylene oxide yield rate of 7.19 mmol g⁻¹ h⁻¹ with a selectivity of 90.3% was achieved over Pd3.91Au0.50/TiO₂ under simulated sunlight. After a 5-day (40 h) outdoor experiment, 862.9 mg of ethylene oxide was obtained by natural sunlight irradiation. Mechanism investigations confirmed that the photogenerated holes oxidized Br⁻ into high-activity Br radicals over Pd3.91Au0.50/TiO₂ that initiated the reaction. The alloying of Au and Pd modulated the adsorption capacity of Br and C₂H₄ species on Pd3.91Au0.50/TiO₂ to promote 2-bromoethanol intermediate production, which further underwent spontaneous cyclization into ethylene oxide under NaOH supply.