Photocatalytic Partial Water Dissociation by Protonated Carbon Nitride for Hydrogenation Reactions

: Catalytic hydrogenation using pressurized hydrogen at elevated temperature is of utmost importance in refinery and fine chemical industries, but heavily relies on the hydrocarbon reforming industry. Photocatalytic water dissociation provides a sustainable solution for hydrogenation; however, the strong O─H bond and instant recombination of generated hydrogen atoms and hydroxyl radicals need to be solved. Here, we demonstrate efficient hydrogenation of unsaturated aromatics using water by a protonated graphitic carbon nitride photocatalyst with dioxane as a hydroxyl radical trap under mild conditions. The dissociation energy of the H─O bond is reduced from 5.15 to only 1.48 eV, enabling the formation of H atoms and surface adsorbed hydroxyl radicals (•OHads) under visible light. The •OHads reacts with dioxane, yielding value-added dioxane-2-ol and prolonging the lifetime of hydrogen atoms for hydrogenation. A high quantum efficiency of ∼6% can be realized under visible light irradiation for the selective hydrogenation of aromatic bromides and aldehydes with high conversion. This approach is scalable in a flow system, revealing financial and environmental potential for hydrogenation and deuteration at a practical level.