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 Nb2O5·nH2O 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 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 phenylethylamine 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.

One‐Pot Tandem Transformation of Inulin as Fructose‐Rich Platform Towards 5‐Hydroxymethylfurfural: Feedstock Advantages, Acid‐Site Regulation and Solvent Effects

“…These results emphasized the important role of Brønsted acid compared to Lewis acid in promoting inulin hydrolysis and fructose dehydration. Also, similar conclusions were found in other cases [20] . Meanwhile, the decisive contribution from Brønsted acid was further confirmed by the work of Chen et al [39] .…”

“…Also, similar conclusions were found in other cases. [20] Meanwhile, the decisive contribution from Brønsted acid was further confirmed by the work of Chen et al [39] in which the sulfonic acid-functionalized Metal-Organic Frameworks (MOF) was employed for the dehydration of fructose to HMF, and the corresponding synthetic pathways and theoretical structures could be found in Figure 6b and 6c. It was found that the contribution of Brønsted acidity towards fructose dehydration was strongly correlated with the À SO 3 H grafting rate of the MOF-SO 3 H. Both fructose conversion and HMF selectivity were found to correlate positively and linearly with the density of sulfonic acid sites (acid density and S content) in MOF-SO 3 H, as shown in Figure 6d and 6e.…”

“…In the presence of an acid catalyst, the glycosidic bonds of inulin are rapidly cleaved to generate fructose in a relatively rapid manner, as shown in Figure 1c. [20] Jian Xiong obtained her master's degree at the China West Normal University, P. R. China, in 2012. She is currently employed as an associate professor at the School of Science, Tibet University, P. R. China.…”

“…Both acid‐catalyzed hydrolysis and enzymatic hydrolysis have been reported to readily obtain fructose from inulin, [21] where acid‐promoted hydrolysis is currently considered to be the most common approach. In the presence of an acid catalyst, the glycosidic bonds of inulin are rapidly cleaved to generate fructose in a relatively rapid manner, as shown in Figure 1c [20] . Without an acid catalyst, high temperature conditions can also trigger the depolymerization of inulin, although this is usually accompanied by the formation of large amounts of humins.…”