Niobium phosphates as bifunctional catalysts for the conversion of biomass-derived monosaccharides

Niobium and Zirconium Phosphates as Green and Water-Tolerant Catalysts for the Acid-Catalyzed Valorization of Bio-Based Chemicals and Real Lignocellulosic Biomasses

“…Lastly, higher temperatures were tested (runs 6 and 7, Table 3), showing that these are not appropriate for the HMF synthesis, but rather promoting the consecutive formation of LA (run 7, Table 3). Adopting MW irradiation, it is interesting to note that the highest HMF yield (23.0 mol%), which is comparable to that obtained working in autoclave and higher than those reported in the literature for analogous systems in aqueous phase [1,22,23,28], was reached after only 30 min, highlighting again the efficiency of MW heating. After having identified the optimal temperature for the HMF synthesis (160 • C) adopting MW irradiation, a more thorough investigation of the kinetics was performed, adopting the same glucose/NbPO weight ratio of 1.2 and glucose loading of 5 wt%, and the corresponding results are shown in Figure 3.…”

“…On the other hand, ZrPO, which is characterized by predominant Lewis acidity, led to a slower conversion and higher fructose selectivity in the short reaction time. The achieved catalytic performances indicate commercial NbPO as a suitable system for the production of HMF, reaching the HMF yield of 22.2 mol% after only 3 h of reaction and the highest HMF yield of 24.4 mol% after 6 h; these values are higher than those reported in the literature for analogous systems in aqueous medium [1,22,23,28]. In fact, working in pure water, which leads to a high decomposition of the formed HMF [28], Ordomsky et al obtained HMF yields below 10 mol%, working with the same NbPO system at 135 • C and adopting the glucose loading of 5 wt% [24].…”

“…The achieved catalytic performances indicate commercial NbPO as a suitable system for the production of HMF, reaching the HMF yield of 22.2 mol% after only 3 h of reaction and the highest HMF yield of 24.4 mol% after 6 h; these values are higher than those reported in the literature for analogous systems in aqueous medium [1,22,23,28]. In fact, working in pure water, which leads to a high decomposition of the formed HMF [28], Ordomsky et al obtained HMF yields below 10 mol%, working with the same NbPO system at 135 • C and adopting the glucose loading of 5 wt% [24]. The same authors reached the highest selectivity to HMF equal to 56 mol% at 20 mol% glucose conversion in the presence of a synthesized NbPO with a Brønsted/Lewis acid sites ratio equal to 1 [24], the same acid ratio of the commercial NbPO adopted in our experimental conditions where the maximum HMF selectivity resulted in 62.5 mol% at 11.9 mol% glucose conversion.…”

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

“…Indeed, in both NbO and NbP, the acidity in water is maintained thanks to the formation of NbO 4 -H 2 O adducts, which in part still exhibit Lewis acid character, as proved by Nakajima through Raman and infrared spectroscopy studies of CO adsorption [12]. Actually, taking advantage of this combination of BAS and water-tolerant LAS, NbO and NbP have found successful exploitation in polysaccharidic biomass processing, in particular for hydrolysis and dehydration reactions [13][14][15][16][17][18][19][20][21][22][23][24], albeit with some limitations in terms of resistance to deactivation. Indeed, in these reactions, NbP may easily undergo leaching of phosphate…”

Recent Advances in the Brønsted/Lewis Acid Catalyzed Conversion of Glucose to HMF and Lactic Acid: Pathways toward Bio-Based Plastics

“…However, control of the acidity is even more complicated in this type of materials, due to the strong acidity of the PO 4 − groups. In this sense, Vieira and co-workers [107] reported the use of niobium phosphate in monophasic solvent systems, which is more advantageous than the biphasic systems for industrial application. The authors found an increase of the L/B (Lewis-to-Brønsted) ratio with the decrease of the P/Nb molar ratio.…”