Impact of Thermal Treatment of Nb2O5 on Its Performance in Glucose Dehydration to 5-Hydroxymethylfurfural in Water

Abstract

The cascade dehydration of glucose to 5-hydroxymethylfurfural (HMF) was carried out in water over a series of Nb2O5 catalysts, which were derived from the thermal treatment of niobic acid at 300 and 550 °C, under air or inert atmosphere. Amorphous niobic acid showed high surface area (366 m2/g) and large acidity (2.35 mmol/g). With increasing the temperature of the thermal treatment up to 550 °C, the amorphous Nb2O5 was gradually transformed into a pseudohexagonal phase, resulting in a decrease in surface area (27–39 m2/g) and total acidity (0.05–0.19 mmol/g). The catalysts’ performance in cascade dehydration of glucose realized in pure water was strongly influenced by the total acidity of these materials. A remarkable yield of 37% HMF in one-pot reaction in water was achieved using mesoporous amorphous niobium oxide prepared by thermal treatment of niobic acid at 300 °C in air. The best-performing catalyst displayed a total acidity lower than niobic acid (1.69 mmol/g) which afforded a correct balance between a high glucose conversion and limited further conversion of the target product to numerous polymers and humins. On the other hand, the treatment of niobic acid at 550 °C, independently of the atmosphere used during the sample preparation (i.e., air or N2), resulted in Nb2O5 catalysts with a high ratio of Lewis to Brønsted acid sites and poor total acidity. These materials excelled at catalyzing the isomerization step in the tandem process.

Niobium Oxide Nanorods Obtained by Hydrothermal Synthesis—Structure, Morphology, and Electrochemical Detection of Oxygen Via Oxygen Reduction Reaction

“…Other authors [41] report that nitrogen insertion into the crystal structure of niobium is already possible between 500 and 600 • C in N 2 . Still, XRD signals corresponding to the formation of Nb x N y appeared at temperatures of 800, 1000, and 1100 • C. In other work [42], similar XRD patterns were found for Nb 2 O 5 samples annealed in air and N 2 atmosphere; the authors did not attribute any signal to Nb x N y . Nb 4 N 5 was synthesized by the heat treatment of Nb 2 O 5 in a mixture of NH 3 and N 2 atmosphere at temperatures between 700 and 900 • C.…”

Investigation of Nb2O5 and Its Polymorphs as Catalyst Supports for Pyrolysis Oil Upgrading through Hydrodeoxygenation

“…In the acid catalyzed reactions such as dehydration of sugars, an adequate total acidity seems to improve the catalyst performance. According to Eblagon et al, niobic acid was highly active in fructose dehydration at short reaction times, due to its highest acidity between polymorphs. Nonetheless, it enhanced condensation and polymerization reactions to form humins at long reaction times.…”

“…In account of the differing polymorph properties, their activity and suitability have been evaluated for several reactions such as dehydration of sugars (i.e., glucose and furfuryl alcohol), , hydrodeoxygenation of vanillin and 1,6-hexanediol , ), methane oxidation to formaldehyde, and esterification of fatty acids . In these studies, the polymorphs were obtained via thermal treatment at different temperatures of niobic acid (Nb 2 O 5 · n H 2 O), ,, commercial Nb 2 O 5, and hydrothermally synthesized Nb 2 O 5. …”

Niobium-Modified HZSM-5 Zeolite Catalyzes Low-Energy Regeneration of CO2-Captured Amine Solution

“…49 This structural complexity with two types of abundant acid sites endows Nb oxides being promising solid acid catalysts for CO 2 regeneration. 50 In this work, an efficient solid acid catalyst, niobium-modified HZSM-5 (Nb/HZ), was synthesized by the impregnation method. HZSM-5 was employed as the support of Nb due to its advantages including low cost, large surface areas, and activity for amine regeneration.…”

“…As niobic acid has a high acid strength (H 0 ≤ −5.6) comparable to over 70% H 2 SO 4 , Nb 2 O 5 is a popular acid catalyst that can provide stable and strong surface acid sites for various acid-catalyzed reactions such as hydrolysis of sucrose. , In the niobium-based catalysts, the surface −OH groups over the distorted polyhedrons of Nb 2 O 5 or the slightly distorted NbO 6 provide Bro̷nsted acid sites, while the highly distorted octahedral and tetrahedra sites on the surface of NbO 6 provide Lewis acid sites . This structural complexity with two types of abundant acid sites endows Nb oxides being promising solid acid catalysts for CO 2 regeneration . In this work, an efficient solid acid catalyst, niobium-modified HZSM-5 (Nb/HZ), was synthesized by the impregnation method.…”