In conclusion, we have developed a novel photocatalytic system based on a molecular cobaloxime catalyst for the semi-hydrogenation of acetylene to ethylene, under visible light irradiation and at room temperature. In homogenous conditions, at dilute catalyst conditions, the system achieves TON >1,000 after 20 hours of illumination with >99.9% selectivity for ethylene vs. ethane. At concentrated catalyst conditions, the system produces 63 μmol C2H4 after four hours of irradiation with a quantum yield (QY) of 1.0%, a 10-and 50-fold improvement over our recently investigated Co-porphyrin or Co-PCN-222 system, respectively. Furthermore, the cobaloximebased system completely reduces the acetylene in a dilute acetylene co-feed with ethylene (the industrially relevant conditions) without any detectable over-hydrogenation to ethane in just 50 minutes, which represents a more than 30-and 100-fold improvement over our recently investigated Co-porphyrin systems, respectively. The production efficiency of our system is ∼13 L g -1 h -1 , which exceeds the industrial demand of >10 L g -1 h -1 . We note, however, that comparing the present system with other thermo-and electro-catalytic routes is challenging due to dissimilar conditions (amount and state of catalysts, proton sources, etc.) and that the present system still requires the use of sacrificial electron donors, which ultimately increases its cost.