Mechanistic insights into CoOx–Ag/CeO2 catalysts for the aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid†
Abstract
Although Ag catalysts have potential for 5-hydroxymethylfurfural (HMF) oxidation to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), further oxidation into 2,5-furandicarboxylic acid (FDCA) remains a severe challenge. Herein, we propose a strategy to synthesize CoOx–Ag/CeO2 catalysts where Ag+–Ov–Ce3+ interfacial sites are generated. For the first time, a mono-noble metal Ag catalyst, namely, CoOx–Ag/CeO2-2, achieves a satisfactory FDCA yield of 92.8%. Even under base-free conditions, a yield of 71.2% could still be obtained. A combination study unveils the harmonious cooperation between Ag+ and Ov–Ce3+ sites during the rate-determining step: the Ag+ site facilitates cleavage of the C–H bond, and the Ov–Ce3+ site enhances the adsorption of reactants and accelerates the dissociation of H2O and the transformation of the adsorbed O2 into superoxide radicals. The present work sheds light on the mechanism study on the HMF oxidation over Ag-based catalysts and may contribute to the rational design of high-performance heterogeneous catalysts.