Highly Porous Niobium-Containing Glasses as Catalysts for Microwave-Assisted Rapid Conversion of Sugars into Hmf

The conversion of sugars into furfurals represents a crucial step towards sustainability in the production of biobased fuels and chemicals. Herein, a series of porous silica-based glasses decorated with niobium oxide was prepared, thoroughly characterized, and employed in the microwave-assisted catalytic conversion of hexoses into 5-hydroxymethylfurfural (HMF) at low temperatures. The glasses were designed by sol-gel synthesis utilizing an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, as a catalytic agent for phase condensation. Decoration with niobium(V) surface oxide performed by wet impregnation at considerably low concentrations followed by thermal treatment is shown to improve metal dispersion toward near single-atom catalysts, consequently changing surface chemistry by creating Lewis and Brønsted acid sites for the selective conversion of fructose into HMF. Lowering niobium loading decreases the amount of Lewis acid sites, resulting in increased HMF selectivity, thus mitigating humin formation. Moreover, the high niobium dispersion delivered superior HMF productivity than those of reference materials.