Oxygen Insertion-Driven Aerobic Oxidation of Diols over Pd Atomic Layers on Au Decahedra

The aerobic oxidation of aliphatic diols to lactones, such as 1,4-butanediol (BDO) to γ-butyrolactone (GBL), is of great interest but challenging in terms of catalytic efficiency and selectivity. While Pd–Au-based catalysts have been extensively investigated, research to date has largely focused on enhancing catalytic activity by lowering the activation barrier for C–H bond cleavage and increasing the number of sites available for O2 activation. Herein, we report that a Pd–Au/TiO2 catalyst featuring Pd atomic layers supported on Au decahedra delivers 96.0% GBL selectivity at 98.7% BDO conversion in aerobic oxidation. The turnover frequency (TOF) over 30Pd–Au/TiO2 reaches 22038 h–1, a value markedly higher than those reported previously for either Pd or Au catalysts. An abnormal 18O2 KIE effect and the generation of singly 18O-labeled 2-hydroxytetrahydrofuran (2-HTHF, 53.4%) and GBL (58.0%) over Pd–Au/TiO2, combined with in situ FTIR and DFT simulations, point to a mechanism involving insertion of oxygen species into the α-C–H bond to generate a COO* intermediate. Subsequent cleavage of the C–O bond within the COO* to yield an absorbed carbonyl, followed by intramolecular cyclization, constitutes the rate-determining step.