Heterometallic incorporation to promote the catalytic activity of polyoxoniobate toward selective oxidation of 5-hydroxymethylfurfural

Abstract

5-Hydroxymethylfurfural (HMF) serves as a key platform compound for the production of value-added chemicals from biomass. Consequently, its catalytic oxidation to 2,5-furandicarboxylic acid (FDCA), a highly promising renewable monomer substance, is of particular importance. But this process entails a complex dehydroxylation reaction, which can lead to numerous competing side reactions. Therefore, developing highly selective catalysts for this transformation remains a critical challenge. This study pioneers the use of a polyoxoniobate (PONb) incorporating vanadium and copper amine complexes, Nb₁₂V₃Cu, for the catalytic oxidation of HMF. Unlike conventional polyoxometalates (POMs), this PONb-based catalyst exhibits superior stability under alkaline reaction conditions. Comparative experiments reveal that incorporating hetero-metallic components into PONb anions promotes the catalytic centers at the terminal or bridging oxygen atoms. These sites demonstrate enhanced synergistic catalysis towards both the hydroxyl and adjacent methylene groups in HMF, thereby facilitating the dehydrogenation and oxidation processes. Under the optimized conditions, the Nb₁₂V₃Cu catalyst achieved 90.3% HMF conversion with 81.4% FDCA yield, outperforming most reported counterparts, and maintained its activity over five consecutive cycles. This research presents a novel hetero-metallic incorporation approach for the design of polyoxometalate-based catalysts specifically customized for biomass conversion in alkaline media, establishing a robust pathway for cutting-edge research on the selective oxidation of HMF to produce its derived platform chemicals.