Selective semi-hydrogenation of acetylene using a single-atom cobalt on carbon nitride photocatalyst with water as a proton source

Light-powered strategies for the semi-hydrogenation of acetylene to ethylene are rapidly emerging as sustainable alternatives to the traditional thermochemical processes. The development of a robust, selective, as well as recyclable, non-noble catalyst that can be powered by visible light to accomplish this important reaction using water as the proton source remains a key challenge. Here we report the first demonstration of cobalt single-atom catalysts anchored on carbon-nitride (Co-CN) as an all-in-one photocatalysts for the semi-hydrogenation reaction of acetylene to ethylene using water as the proton source and no organic solvents or hydrogenated organics, offering advantages over current hydrogenation technologies. Carbon nitride is a photoactive support that hosts the individual catalytic active sites of cobalt thus combining photosensitizer and cocatalyst in one unit, in line with first-principles modelling. Under visible light irradiation, Co-CN reduces acetylene to ethylene with stable activity for over 40 days of continuous operation and ≥99.9%, selectivity and provides means for coupling organic upgrading to produce valuable oxidation products. The heterogenous Co-CN can be easily recovered and reused repeatedly without loss of catalytic activity and structural integrity. Thereby, the reported hydrogenation photocatalyst overcomes the need of coupling a separate photosensitiser to a catalyst providing an integrated and recyclable platform, and using noble metal catalysts with an external H2 gas feed. Thanks to these features, together with longevity and semi-hydrogenation selectivity, this system holds potential for practical implementation of light-driven acetylene reduction and for exploration of other non-noble metal single atom heterogenous photocatalysts to achieve this important transformation using water as the proton source.