Selective visible-light photocatalysis of acetylene to ethylene using a cobalt molecular catalyst and water as a proton source

The acetylene contaminant present in ethylene feeds used to produce polymers is typically removed by thermal hydrogenation. Now, it has been shown that the conversion of acetylene to ethylene at room temperature can be achieved in a visible-light-driven process using an earth-abundant metal (cobalt) catalyst and a water proton source. The production of polymers from ethylene requires the ethylene feed to be sufficiently purified of acetylene contaminant. Accomplishing this task by thermally hydrogenating acetylene requires a high temperature, an external feed of H-2 gas and noble-metal catalysts. It is not only expensive and energy-intensive, but also prone to overhydrogenating to ethane. Here we report a photocatalytic system that reduces acetylene to ethylene with >= 99% selectivity under both non-competitive (no ethylene co-feed) and competitive (ethylene co-feed) conditions, and near 100% conversion under the latter industrially relevant conditions. Our system uses a molecular catalyst based on earth-abundant cobalt operating under ambient conditions and sensitized by either [Ru(bpy)(3)](2+) or an inexpensive organic semiconductor (metal-free mesoporous graphitic carbon nitride) under visible light. These features and the use of water as a proton source offer advantages over current hydrogenation technologies with respect to selectivity and sustainability.