Production of 5-hydroxymethylfurfural from glucose in water by using transition metal-oxide nanosheet aggregates

Metal-oxide nanosheet aggregates were prepared by exfoliation and subsequent aggregation of layered metal oxides and used for the conversion of glucose to 5-hydroxymethylfurfural (HMF) in water. Three aggregated nanosheets, HNbWO₆, HNb₃O₈, and HTiNbO₅, yielded HMF in water at 393-413 K, whereas ion-exchange resins and H-form zeolites did not. The catalytic activity of the nanosheets decreased in the order HNbWO₆ > HNb₃O₈ > HTiNbO₅, which correlates with their acidity. The HNbWO₆ nanosheets exhibited higher selectivity for HMF than niobic acid, and the selectivity was improved in the water-toluene biphasic system. The selectivity for HMF over HNbWO₆ nanosheets was higher from glucose than from fructose. Kinetic analysis suggested that in addition to fructose, an intermediate species was involved in the reaction pathway of HMF production from glucose.