Application of laser-generated Au-Ag/Al2O3 nanoparticle catalysts for the selective catalytic oxidation of 5-(Hydroxymethyl) furfural to 2,5-Furan-dicarboxylic acid

Abstract

Conversion of lignocellulosic biomass-derived 5-(Hydroxymethyl) furfural (HMF) into 2,5-Furandicarboxylic acid (FDCA) has a high potential to replace petroleum-based feedstocks for the production of plastics. In this study, a green synthesis strategy for the selective oxidation of HMF to FDCA is reported by using laser-generated and specifically designed bimetallic AuAg nanoparticle catalysts supported on Al2O3 using molecular oxygen as oxidant and water as a solvent. Although supported AuAg catalysts are already known as good catalysts for this reaction, the optimal reaction conditions (type of base, reaction temperature, oxygen pressure), Au:Ag composition, role of metal-support effects and origin of the active site still remain under debate. Interestingly, an Au9Ag1/Al2O3 catalyst exhibited the highest activity with a FDCA yield of up to 66% at 80% HMF conversion. Hereby, NaHCO3 (instead of NaOH) as a smoother base in 2:1 base:HMF ratio, low oxygen pressures of 5 bar, and a mild temperature of 150°C were found optimal. The yield remained fairly stable on reuse of the catalyst for 3 cycles without hints of catalyst sintering or leaching. The titration of surficial hydroxyls on the AuxAgy/Al2O3 surface showed the highest density of acidic hydroxyls for the most active Au9Ag1/Al2O3 catalyst.