Solid Acidic NbO_x/ZrO₂ Catalysts for Transformation of Cellulose to Glucose and 5-Hydroxymethylfurfural in Pure Hot Water

Abstract: Solid acid NbO_x/ZrO₂ catalysts containing 0, 0.5, 1.1 and 2.8 wt.% of Nb were prepared for one–pot hydrolysis-dehydration of mechanically activated cellulose in pure hot water to produce glucose and 5-hydroxymethylfurfural. The catalysts were characterized (XRD, N₂ adsorption, ICP-OES, UV–Vis DRS) and tested in cellulose processing at 453 K. The catalytic activity increased as follows: 0.5%Nb/ZrO₂ < ZrO₂ < < 1.1%Nb/ZrO₂ ~ 2.8%Nb/ZrO₂. This series was accounted for by the acid-basic properties of ZrO₂, by the inhibition of its active sites by monomer niobium species and by the appearance of Brønsted acidity upon the formation of NbO_x-containing polymer structures. The highest glucose and 5-HMF yields (22 and 16 mol%, respectively) were achieved over 2.8%Nb/ZrO₂.