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

• Application of acid/base bifunctional HPA catalysts in glucose conversion.
• The catalyst gave high yield of LA (52.6%) within 30 min at 130 °C using ChCl as solvent.
• The catalyst performed as a heterogeneous catalyst in ChCl system.
• Easily recycled by simple washing treatment.

Acid–base bifunctional heteropolyacid (HPA) nanospheres (C6H15O2N2)3−xHxPW12O40 (abbreviated as Ly3−xHxPW) 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 Ly0.5H2.5PW 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 Brønsted acidity and base property, while the base sites were main candidate for isomerization of glucose to fructose; in addition, the Brønsted 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. Ly0.5H2.5PW was easily recovered and recycled by simple washing treatment.

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