Unraveling Structure Sensitivity in the Photocatalytic Dehydrogenative C-C Coupling of Acetone to 2,5-Hexanedione over Pt/TiO₂ Catalysts

Structure sensitivity is the phenomenon where the activity of each available active site of a catalyst varies depending on its specific structure and coordination environment. Understanding structure sensitivity can assist in the rational design of catalysts, allowing for control over activity and selectivity. Here, we demonstrate that the activity and selectivity of acetone coupling to 2,5-hexanedione (2,5-HDN), an important raw material, via a photocatalytic dehydrogenative route are highly structure sensitive and prove how the size of the supported Pt influences the catalytic performance. Under optimized conditions, the formation rate of 2,5HDN on subnanometer Pt cluster modified anatase-TiO2 (Pt-CL/TiO2) reaches 45.3 mu mol/h, 1.5-9.0 times higher than the Pt NPs and Pt single-atom doped TiO2 photocatalysts. Mechanism studies reveal that water, which is oxidized by the excited hole of the anatase semiconductor, acts as a co-catalyst in the reaction and generates hydroxyl radicals. The formed hydroxyl radicals subsequently assist the cleavage of the sp(3) C-H bond of acetone. The dimerization of the center dot CH2COCH3 radicals delivers 2,5-HDN. The remarkable center dot OH radical formation capability and relatively high H-abstraction activity of the Pt-CL/TiO2 photocatalyst account for its excellent activity and selectivity over other Pt/TiO2 catalysts.