Visible-Light Driven Acetylene Semi-Hydrogenation to Ethylene With a Copper Photosensitizer and a Cobaloxime Catalyst

The purification of ethylene streams from acetylene impurities remains a key industrial challenge, for which light-powered strategies are emerging as sustainable alternatives to conventional approaches. Recent studies have shown that hydrogen atom transfer (HAT) pathways enable highly selective acetylene semi-hydrogenation by ensuring rapid and controlled hydrogen delivery while suppressing over-hydrogenation or H2 evolution. Here, we report a fully noble-metal-free homogenous photocatalytic system in which a molecular cobaloxime catalyst [Co(dmgH)2(Im)Cl] (dmg = dimethylglyoxime, Im = imidazole) operates in tandem with a Cu-based photosensitizer [Cu(N^N)(P^P)]+ to drive the selective transfer hydrogenation from acetylene to ethylene under visible light irradiation. Under a pure C2H2 atmosphere, our system converts acetylene to ethylene with a turnover number (TON) of 670 after 48 h of visible-light irradiation with 99.6% selectivity, while under ethylene-rich conditions, acetylene impurities are completely removed with 99.3% selectivity. Mechanistic studies reveal that catalysis proceeds via a CoIII─H intermediate. Overall, this work demonstrates that rational pairing of cobaloxime catalysts with earth-abundant Cu-based photosensitizers provides an efficient and sustainable strategy for photocatalytic acetylene semi-hydrogenation and ethylene purification.