Site-defined Cu-O ensembles enable hydrogen-conserving light-driven ethane upgrading

Upgrading light alkanes to value-added olefins is a long-standing challenge, owing to the high stability of C–H bonds and the tendency for overoxidation at elevated temperatures. Here, we introduce a light-driven strategy for ethane dehydrogenation using Cu-doped TiO2, in which atomically dispersed Cu coordinated to bridging oxygen (Obr–Cu) creates well-defined [Cu–O] ensembles that orchestrate site-specific, stepwise C–H activation. Photogenerated holes localize at Obr–Cu sites to initiate the first C–H cleavage, while adjacent Cu centers mediate β–H elimination and H2 evolution. In contrast, minor β–H activation at Obr–Ti sites generates *H species that cannot desorb due to a prohibitive coupling barrier with *H on Obr–Cu, leading to Cu reduction and progressive deactivation. Co-feeding CO2 restores the active Cu coordination environment and suppresses this deactivation process without perturbing the primary reaction pathway. This cooperative design achieves a C2H4 production rate of 21.1 mmol g−1 h−1 with nearly stoichiometric H2 evolution and an apparent quantum efficiency of 6.1% under 365 nm irradiation. These findings establish a site-defined, hydrogen-conserving route for photocatalytic alkane upgrading, offering a general blueprint for selective C–H bond transformations with long-term stability. Converting light alkanes into useful olefins is hard because strong bonds and heat drive overoxidation. This study uses a copper-doped titanium dioxide photocatalyst to steer bond breaking, yielding ethylene and hydrogen.