Atomic Scale Engineering of Multivalence‐State Palladium Photocatalyst for Transfer Hydrogenation with Water as a Proton Source

Abstract Hydrogenation reactions are fundamental in the fine chemical, pharmaceutical, and petrochemical industries, however heavily relying on H 2 gas at high temperatures and pressures, incurring large energy and carbon costs. Photocatalytic transfer hydrogenation, using water as a proton source, offers a greener alternative, but existing photocatalysts often suffer from modest yields, limited selectivity, and narrow substrate scope. Additionally, they often require co‐activation, such as Mg‐activated water or non‐sustainable hydrogen feeds. Here, a photocatalyst is introduced that offers high yields and selectivities across a broad spectrum of organic compounds. The developed photocatalyst is a multivalence palladium superstructure with ultrasmall Pd 0 nanoparticles enveloped by isolated Pd 2+ /Pd 4+ atoms within a carbon‐nitride matrix. Mechanistic studies reveal that the redox‐flexible Pd single atoms, with triethylamine as an electronic modulator, attract photogenerated holes for water oxidation, while Pd 0 nanoparticles facilitate hydrogen transfer to the unsaturated bonds of the organic molecules. The cooperative and dynamic behavior of Pd centers during catalysis, involving transitions among Pd +2 , Pd +3 , and Pd +4 states, is validated using operando electron paramagnetic resonance spectroscopy. This multivalent palladium catalyst represents a conceptual advance in photocatalytic transfer hydrogenation with water as a hydrogen source, holding promise for sustainable hydrogenation processes in the chemical industry.