Phosphate enrichment of niobium-based catalytic surfaces in relation to reactions of carbohydrate biomass conversion: The case studies of inulin hydrolysis and fructose dehydration

Abstract

In this work, some physical mixtures of Nb2 O5·nH2 O and NbOPO4 were prepared to study the role of phosphate groups in the total acidity of samples and in two reactions involv-ing carbohydrate biomass: hydrolysis of polyfructane and dehydration of fructose/glucose to 5-hydroxymethylfurfural (HMF). The acid and catalytic properties of the mixtures were dominated by the phosphate group enrichment. Lewis and Brønsted acid sites were detected by FT-IR experiments with pyridine adsorption/desorption under dry and wet conditions. Lewis acidity decreased with NbP in the composition, while total acidity of the samples, measured by titrations with phenylethy-lamine in cyclohexane (~3.5 µeq m−2 ) and water (~2.7 µeq m−2 ), maintained almost the same values. Inulin conversion took advantage of the presence of surfaces rich in Brønsted sites, and NbOPO4 showed the best hydrolysis activity with glucose/fructose formation. The catalyst with a more phosphated surface showed less deactivation during the dehydration of fructose/glucose into HMF.