Ordered mesoporous Nb-W oxides for the conversion of glucose to fructose, mannose and 5-hydroxymethylfurfural

A series of ordered mesoporous NbxW(8-x) oxides with tunable Nb/W ratio were successfully synthesized by evaporation-induced self-assembly method. The mesoporous structure, morphologies, surface chemical state, and acidic properties of these catalysts were fully characterized by low-temperature sorption of N-2, small-angle and wide-angle XRD, TEM, Raman, XPS, and Py-IR. It was shown that the NbxW(8-x) oxides created large amounts of Lewis as well as Brensted acid sites, which promoted the isomerization of glucose to fructose followed its dehydration to 5-hydroxymethylfurfural (HMF). Mannose was also. formed via the epimerization of glucose. Of them, the mesoporous Nb4W4 exhibited the best catalytic activity with a comparatively low Ea about 90.2 kJ/mol and good stability in aqueous medium. The kinetic behavior revealed that Lewis acid sites facilitated to glucose-to-fructose isomerization while Brensted acid sites promoted the dehydration of fructose to form HMF. (C) 2016 Elsevier B.V. All rights reserved.