Efficient production of 5-hydroxymethylfurfural from glucose over the combination of nano-metal oxides and HCl in biphasic methyl isobutyl ketone/H2O–NaCl

5-Hydroxymethylfurfural (HMF) is a versatile biomass-derived platform compound, but its production from glucose and cellulose remains challenging. In this study, several nano-metal oxides (Al₂O₃, TiO₂, ZrO₂, and SnO₂) with distinct Lewis acidities were combined with a trace amount of HCl to catalyze the conversion of glucose to HMF in a methyl isobutyl ketone (MIBK)/H₂O–NaCl biphasic system. Without HCl, fructose was formed and accumulated in the aqueous phase due to insufficient Brønsted acidity, limiting further dehydration to HMF. The addition of HCl effectively overcame this bottleneck, with Al₂O₃ and HCl showing the best synergy. Under optimized conditions, a HMF yield of 69.1 % was achieved at 180 °C, and Al₂O₃ exhibited excellent recyclability. This work demonstrates a promising approach for combining homogeneous and heterogeneous catalysis for efficient conversion of renewable carbohydrates into platform chemicals.