Influence of Support Properties and Particle Size on the Gold-Catalyzed Base-Free Aerobic Oxidation of 5-Hydroxymethylfurfural

Selective oxidation of biomass platform molecule 5-hydroxymethylfurfural (HMF) into valuable bio-monomer 2,5-furandicarboxylic acid (FDCA) is an important biorefinery process. In our work, the structure-activity relationship of Au nanoparticles supported on the composite of hydrotalcite and activated carbon (HT-AC) toward selective oxidation of HMF to FDCA without a base was studied with a focus on the influence of support property and Au particles size. The initial conversion rate of substrates and the intrinsic selectivity of products were investigated. Various physicochemical techniques including XRD, Raman, XPS, CO2-TPD and TEM were used to characterize the HT-AC supports and the Au/HT-AC catalysts. Synergistic support effect was observed when HT and AC were combined to show the features of both basic sites and oxygen-containing functional groups attached to the catalyst surface, which eventually promoted the adsorption of HMF and the formation of FDCA. The Au NPs were found in metallic state and highly dispersed with a mean size of 2.5 nm, which was favored to efficiently convert HMF to FDCA. It was disclosed that both the support effect and Au size effect could promote FDCA production through accelerating the conversion rate of HMF and HMFCA, and the rate-determining step was determined in HMFCA transformation.