Lysine functional heteropolyacid nanospheres as bifunctional acid-base catalysts for cascade conversion of glucose to levulinic acid

Abstract Acid–base bifunctional heteropolyacid (HPA) nanospheres (C 6 H 15 O 2 N 2 ) 3 − x H x PW 12 O 40 (abbreviated as Ly 3 − x H x PW) have been evaluated in cascade isomerization/dehydration of glucose to 5-hydroxymethylfurfural (HMF) or levulinic acid (LA) in choline chloride (ChCl) based on deep eutectic solvent system. Compared to other heterogeneous catalysts, the dehydration of glucose catalyzed by Ly 0.5 H 2.5 PW gave almost the best efficiency (75.1% conversion and 52.6% LA yield) within very short time (30 min) at 130 °C using ChCl as solvent. The main reason was its unique property of double Bronsted acidity and base property, while the base sites were main candidate for isomerization of glucose to fructose; in addition, the Bronsted acidity might promote the conversion of glucose to product LA rather than HMF. Moreover, this catalyst was suitable for high concentrated glucose (up to 66.7 wt.%) conversion which was obtained after the additive of ChCl. Ly 0.5 H 2.5 PW was easily recovered and recycled by simple washing treatment.