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 (O_br-Cu) creates well-defined [Cu-O] ensembles that orchestrate site-specific, stepwise C-H activation. Photogenerated holes localize at O_br-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 O_br-Ti sites generates *H species that cannot desorb due to a prohibitive coupling barrier with *H on O_br-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.