Phosphate Enrichment of Niobium-Based Catalytic Surfaces in Relation to Reactions of Carbohydrate Biomass Conversion: The Case Studies of Inulin Hydrolysis and Fructose Dehydration

In this work, some physical mixtures of Nb2O5 center dot nH(2)O and NbOPO4 were prepared to study the role of phosphate groups in the total acidity of samples and in two reactions involving 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 Bronsted 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 phenylethylamine in cyclohexane (similar to 5 mu eq m(-2)) and water (similar to 2.7 mu eq m(-2)), maintained almost the same values. Inulin conversion took advantage of the presence of surfaces rich in Bronsted 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.

Automated summary

In this study, physical mixtures of Nb2O5•nH(2)O and NbOPO4 were prepared to investigate the role of phosphate groups in total acidity and two reactions involving carbohydrate biomass. The acid and catalytic properties were influenced by phosphate group enrichment. The presence of Bronsted sites on the surface favored inulin conversion and NbOPO4 exhibited the best hydrolysis activity with glucose/fructose formation. Additionally, a catalyst with a more phosphated surface showed reduced deactivation during the dehydration of fructose/glucose into HMF.