Base-Free Aerobic Oxidation of 5-Hydroxymethyl-furfural to 2,5-Furandicarboxylic Acid in Water Catalyzed by Functionalized Carbon Nanotube-Supported Au–Pd Alloy Nanoparticles

The aerobic oxidation of 5-hydroxymethylfurfural (HMF), a key platform compound in cellulose transformation, into 2,5-furandicarboxylic acid (FDCA), a promising renewable alternative to petroleum-derived terephthalic acid, is one of the most attractive reactions for establishing biomass-based sustainable chemical processes. Supported Au catalysts have shown encouraging performance for this reaction, but the need of an excess amount of base additives makes the process less green and less cost-effective. Here, we report a stable and efficient carbon nanotube (CNT)-supported Au–Pd alloy catalyst for the aerobic oxidation of HMF to FDCA in water without any bases. The functionalization of CNT surfaces is crucial for FDCA formation. We have clarified that the CNT containing more carbonyl/quinone and less carboxyl groups favors FDCA formation by enhancing the adsorption of the reactant and reaction intermediates. Significant synergistic effects exist between Au and Pd in the alloy for the base-free oxidation of HMF to FDCA through three tandem steps. The present work provides understanding of the support-enhanced adsorption effect and the alloying effect for supported Au-based bimetallic catalysts, and this knowledge may help develop efficient catalysts for the aerobic oxidation of relatively complicated organic compounds with different functional groups in water.