Surface Oxygen Dynamics Govern Photocatalytic Glycolaldehyde Synthesis from Ethylene on SnO ₂

Glycolaldehyde (GA) is an important C2 oxygenate and a versatile building block for the synthesis of pharmaceuticals, polymers, and fine chemicals. However, conventional GA production routes, including biomass pyrolysis and catalytic transformations, typically suffer from low selectivity, harsh reaction conditions, and limited scalability. Here, we demonstrate a photocatalytic route to GA from ethylene, driven by lattice oxygen exchange over SnO 2 under oxidative aqueous conditions. This strategy achieves a GA yield of 4017 μmol·g −1 with 75% liquid-phase selectivity at ambient temperature and moderate pressure. We investigated the reaction mechanism by density functional theory (DFT) calculation, in synergy with experimental analysis. The formation of C2 oxygenates proceeds through a radical-mediated oxidation mechanism involving • OH and lattice oxygen. During the reaction, product desorption generates oxygen vacancies that are efficiently replenished under light irradiation through catalyst regeneration by molecular oxygen. These findings highlight the role of mobile lattice oxygen in steering selective photocatalytic oxidation and provide insights for the design of catalysts for selective alkene oxidation and oxygenate synthesis.