Exploiting an Efficient and Stable Catalyst for the Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran by Incorporating Vanadium in the Framework of Hydroxyapatite

Hydroxyapatite displays immense potential in catalysis because of its properties to form doped single and multiphasic systems. In the present study, vanadium-incorporated hydroxyapatite was investigated for aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran. The amount of vanadium precursor and the pH in catalyst synthesis were significant factors in defining the catalytic properties of V-HAP. The morphologies and structures of the catalysts were well studied. Field emission scanning electron microscopy revealed different morphologies of the catalyst with varying amounts of vanadium and pH, suggesting that both these factors play a critical role in determining the catalytic properties. Through X-ray diffraction spectra, the incorporation of vanadium ions into the HAP framework by replacing phosphate ions was confirmed by the augmentation of lattice parameters and unit cell volume. The vanadium amount corresponding to x = 3 and pH 11 for the synthesis of the catalyst displayed good catalytic efficiency for HMF conversion. To further enhance the performance of the synthesized catalyst, the reaction parameters such as the temperature of reaction and catalyst loading were optimized. Under optimum reaction conditions, 78% HMF conversion with 63 and 81% DFF yield and selectivity, respectively, was observed. V-HAP (x = 3) was highly stable in nature and did not show a decrease in activity during experimental cycles, thereby showing that the incorporated vanadium did not leach out and that the catalyst was recyclable, which was also confirmed by energy-dispersive X-ray spectroscopy results. V-HAP (x = 3) was also compared with V₂O₅-HAP and was found to have superior catalytic properties as compared to the latter. This study contributes to the development of green and stable catalysts for biomass conversion.