Homogeneous silver catalyst for propylene electrooxidation to propylene glycol

Electrically-powered synthesis provides a sustainable approach for propylene oxidation to propylene oxide and propylene glycol in aqueous medium using water as the oxygen source, which can substitute conventional energy-intensive process that relies on hazardous oxidants. However, current electrosynthesis is suffering from expensive catalysts, low current density and Faradaic efficiency. Herein, guided by accidental finding of Ag⁺ showing activity for propylene electrooxidation to propylene glycol and following mechanistic understanding, we report 1,2,3-triazole-chelated Ag catalyst with improved current density (15.8 mA/cm²) and Faradaic efficiency (62.5%), comparable with heterogeneous Pt and Pd catalysts using 30-fold less expensive metal. We experimentally and theoretically demonstrate that triazole coordination modulates the oxidative ability of the in-situ formed Ag-oxo species, suppressing overoxidation and oxygen evolution. Furthermore, by employing a high-pressure electrolyzer, we strengthen propylene mass transfer and attain an enhanced current density of 61.1 mA/cm² with Faradaic efficiency of 73.4%. By circulating electro-deposition/dissolution of Ag, the catalyst shows reusability in 10 cycles. This work demonstrates the potential of using cost-effective homogeneous catalyst for propylene electrooxidation.