Thermodynamically stable synthesis of high entropy alloys and efficiently catalyzed oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid under base-free conditions

The high activity and high selectivity in the catalytic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) under non-alkaline conditions has always been a significant challenge in the field of biomass utilization. In this work, a thermodynamically stabilized high-entropy alloy (HEA) structure with relatively low Pt content was synthesized via a simple impregnation-calcination procedure by tuning the mixing enthalpy and the Gibbs free energy of the metal-mixing system. The prepared HEA shows excellent catalytic performance in the aerobic oxidation of HMF into FDCA under base-free conditions. Experiments and DFT calculations revealed that molecular O2 can be easily activated into highly oxidative hydroxyl radicals ((OH)-O-center dot) in the presence of water over the HEA surface, and facilitates the oxidation of HMF to FDCA under base-free conditions. This work provides a valuable reference for similar aerobic oxidation processes in which alkaline promoters and noble metal catalysts are needed. In a completely non-alkaline aqueous system, a high-entropy alloy catalyst composed of FeCoNiCuGaPt activates O2 and H2O molecules to form hydroxyl radicals ((OH)-O-center dot) and efficiently oxidizes 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid.