Cs-substituted tungstophosphate-supported ruthenium nanoparticles: An effective catalyst for the aerobic oxidation of 5-hydroxymethylfurfural into 5-hydroxymethyl-2-furancarboxylic acid

In this study, a new method was developed for the oxidation of 5-hydroxymethylfurfural (HMF) into 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) over heterogeneous Ru catalyst. Cs-substituted tungstophosphate (CsPW) was prepared by the exchange of H+ in H3PW12O40 with Cs+, which was then used to immobilize Ru nanoparticles to give the RU/CsPW catalyst. The Ru/CsPW catalyst was well characterized by TEM, XRD, XPS and FT-IR technologies. The physical characterizations clearly indicated that the spherica Ru nanoparticles with an average size of 2.4 nm were homogeneously dispersed on the surface of the CsPW support. The as-prepared catalyst was studied for the oxidation of HMF, and some important parameters were investigated. The reaction solvent showed a great effect on both HMF conversion and the products selectivity. Aromatic solvents were found to be the best reaction medium for the oxidation of HMF into HMFCA. Increasing the reaction temperature and the amount of the Ru/CsPW catalyst accelerated the HMF conversion and HMFCA yield. High HMF conversion of 97.2% and HMFCA yield of 72.9% were obtained after 12 h at 130 degrees C with oxygen flow rate of 20 ml/min. Unfortunately, the Ru/CsPW catalyst was not very stable during the reaction, and a slight loss of its catalytic activity was observed during the recycling experiments. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.