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 CoO_x–Ag/CeO₂ catalysts where Ag⁺–O_v–Ce³⁺ interfacial sites are generated. For the first time, a mono-noble metal Ag catalyst, namely, CoO_x–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 O_v–Ce³⁺ sites during the rate-determining step: the Ag⁺ site facilitates cleavage of the C–H bond, and the O_v–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.