Selective Aerobic Oxidation of C–H Bond over C–C Bond on Pd ₁ /Mn ₂ O ₃ Single-Atom Catalysts

Aerobic oxidation of the C–H bond is a fundamental transformation in heterogeneous catalysis, yet achieving high selectivity remains challenging because the oxidation products are often more reactive than the starting hydrocarbons. Herein, we demonstrate that a Mn2O3-supported Pd single-atom catalyst (Pd1/Mn2O3) enables selective aerobic oxidation of the benzylic C–H bond to ketones while suppressing undesired overoxidation via C–C bond cleavage. Other SAC systems, including Au1/Mn2O3, Ru1/Mn2O3, and Pd1/TiO2, exhibit similar selectivity trends, supporting the generality of the mechanistic insight. Combined experimental and DFT studies reveal that single atoms are intrinsically inactive toward further oxidation of ketones due to their inability to promote keto–enol transformation, thereby preventing C–C bond cleavage and overcoming the conventional activity–selectivity trade-off. This work provides a mechanistic understanding of selective C–H activation in heterogeneous catalysis.