Solvent- and Base-Free Oxidation of 5-Hydroxymethylfurfural over a PdO/AlPO₄-5 Catalyst under Mild Conditions

Abstract

A solvent-free method was proposed to upgrade the biomass-derived compound 5-hydroxymethylfurfural (HMF). The oxidation of HMF to produce 2,5-furandicarboxylic acid (FDCA) has been examined in the presence of O2 without the addition of solvent and base. Different from the conversion of the aldehyde group on HMF as the initial oxidation step in H2O solvent, the hydroxyl group on HMF was first oxidized and FDCA was finally generated without the addition of solvent. The role of O2 is to replenish the consumption of active oxygen species on the catalyst surface. The oxidation of HMF to FDCA proceeded due to the solvent-free effect. A 83.6% FDCA selectivity at 38.8% HMF conversion was measured with a PdO/AlPO4-5 catalyst at 80 °C for 5 h and the reaction mechanism was proposed.