Auδ−–Ov–Ti3+: Active site of MOx-Au/TiO2 catalysts for the aerobic oxidation of 5-hydroxymethylfurfural

Despite wide applications of noble metal-based catalysts in 5-hydroxymethylfurfural (HMF) oxidation, promoting the catalytic performance at low loading amounts still remains a significant challenge. Herein, a series of metal oxide modified MO x -Au/TiO 2 (M = Fe, Co, Ni) catalysts with low Au loading amount of 0.5 wt% were synthesized. Addition of transition metal oxides promotes electron transfer and generation of the Au δ − –O v –Ti 3+ interface. A combination study reveals that the dual-active site (Au δ − -O v -Ti 3+ ) governs the catalytic performance of the rate-determining step, namely hydroxyl group oxidation. Au δ − site facilitates chemisorption and activation of O 2 molecules. At the same time, O v -Ti 3+ site acts as the role of “killing two birds with one stone”: enhancing adsorption of both reactants, accelerating the activation and dissociation of H 2 O, and facilitating activation of the adsorbed O 2 . Besides, superoxide radicals instead of base is the active oxygen species during the rate-determining step. On this basis, a FDCA yield of 71.2% was achieved under base-free conditions, complying with the “green chemistry” principle. This work provides a new strategy for the transition metal oxides modification of Au-based catalysts, which would be constructive for the rational design of other heterogeneous catalysts.