Green oxidative esterification of furfural over nano-Au supported on highly basic anion exchange resin beads

Au nanoparticles with an average diameter of 3.7 nm supported on the macroporous anion exchange resin beads with cationic –CH 2 N + Me 3 functional groups and OH − as counter anions were first prepared, for catalyzing the oxidative esterification of biomass-derived furfural in methanol using green O 2 as an oxidant. The main product methyl furoate with a high yield of 98% was obtained at 130 °C for 2 h in the absence of soluble alkali additives. The catalyst beads possessed a particle size range of 560∼700 μm inherited from the shaped support, enabling the separation of catalyst and liquid reaction medium by a simple decantation method. Catalyst poisoning experiments demonstrated Au activated superoxide radical O 2 · − and the basic OH − stored in the anion exchange resin are the decisive active components for the oxidative esterification, and the main product methyl furoate with a yield of 20% and a high selectivity of 96% was obtained under N 2 atmosphere revealed the reaction in this catalytic system followed an oxidative dehydrogenation route. In all catalytic cases except for the catalyst poisoning experiments and the cases of low catalyst dosages, the by-product acetal was almost completely suppressed, probably attributed to the presence of the alkaline OH − in the anion exchange resin of the catalyst.