Hydrolysis–Dehydration of Cellulose: Efficiency of NbZr Catalysts under Batch and Flow Conditions

Abstract

Niobium oxide supported on ZrO2 and mixed oxide of NbOx-ZrO2 was prepared and characterized. Mechanical treatment was followed by the microwave heating procedure of catalysts with more advanced textural parameters. The amount of Lewis (LAS) and Brønsted (BAS) acid sites rose with the increasing Nb content in the catalysts. The catalytic properties of samples of niobia-zirconia (NbZr samples, NbZr catalysts) were studied in a cellulose hydrolysis–dehydration reaction at 453 K under an inert Ar atmosphere in a batch reactor. Glucose and 5-hydroxumethylfurfural (5-HMF) were the major products. The initial reaction rate could be tuned by the density of acid sites on the surface of solid. At a low density of acid sites (0.1–0.3 µmol·m−2), the initial reaction rate had a pronounced inverse correlation. Increasing the LAS/BAS from 0.3 to 2.5 slightly stimulated the formation of the target products. The catalytic properties of NbZr catalysts prepared by microwave treatment were studied in cellulose transformation in a flow set-up. Glucose was found to be the major product. The maximum yield of glucose was observed in the presence of the sample of 17%Nb/ZrO2. Increasing Nb content resulted in the formation of Nb-associated acid centers and, in turn, increasing catalyst acidity and activity.