Dehydration of Glucose to 5‐Hydroxymethylfurfural Using Nb‐doped Tungstite

Abstract

Dehydration of glucose to 5‐hydroxymethylfurfural (HMF) remains a significant problem in the context of the valorization of lignocellulosic biomass. Hydrolysis of WCl6 and NbCl5 leads to precipitation of Nb‐containing tungstite (WO3⋅H2O) at low Nb content and mixtures of tungstite and niobic acid at higher Nb content. Tungstite is a promising catalyst for the dehydration of glucose to HMF. Compared with Nb2O5, fewer by‐products are formed because of the low Brønsted acidity of the (mixed) oxides. In water, an optimum yield of HMF was obtained for Nb–W oxides with low Nb content owing to balanced Lewis and Brønsted acidity. In THF/water, the strong Lewis acidity and weak Brønsted acidity caused the reaction to proceed through isomerization to fructose and dehydration of fructose to a partially dehydrated intermediate, which was identified by LC‐ESI‐MS. The addition of HCl to the reaction mixture resulted in rapid dehydration of this intermediate to HMF. The HMF yield obtained in this way was approximately 56 % for all tungstite catalysts. Density functional theory calculations show that the Lewis acid centers on the tungstite surface can isomerize glucose into fructose. Substitution of W by Nb lowers the overall activation barrier for glucose isomerization by stabilizing the deprotonated glucose adsorbate.

Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol with Recyclable Al–Zr@Fe Mixed Oxides

“…[32] For instance, W-Zr mixed oxidesc an efficiently convert cellulose to lactic acid, [33] ethyl lactate can efficiently be obtained from triose sugars over Sn/Al oxide, [34] and glucose can (through fructose) be dehydrated into 5-hydroxymethylfurfural with Nbdoped WO 3 . [35] In our previous work, Al-Zr mixed oxide was confirmed to be an efficient catalystf or the production of GVL from ethyl levulinate, [23] and in continuationo fo ur research on CTH of biomass-derived chemicals, we expecteda lso such catalysts to be active in CTH of FF to FAOL. Solid materials with magnetic properties are highly interesting catalyst supports because they allow easy catalyst separation and recycling from liquid reactionm ixturesb ya pplying an external magnetic field.…”

Early Transition Metal Doped Tungstite as an Effective Catalyst for Glucose Upgrading to 5-Hydroxymethylfurfural

“…5). Previous work shows that doping WO 3 with niobium increased the Brønsted acidity of the material [33]. The exchange of Lewis acidic W VI cations by Nb V species induces a charge defect which is compensated by acidic protons, thus increasing the amount of Brønsted acid sites (BAS).…”

“…These materials are abundant and cheap, and express water-tolerant Lewis acid sites and tunable acid-base properties with promising glucose-upgrading abilities [31,32]. Recently, we have shown that tungstite (WO 3 ·H 2 O) is also a viable contender [33]. The material comprises distorted WO 5 ·H 2 O octahedra, which share 4 equatorial corner oxygens to form a stacked sheet-like material with a low surface area.…”

“…Similarly to TiO 2 and Nb 2 O 5 , it contains water-tolerant Lewis acid functionalities, but its Brønsted acidity is relatively weak, which limits fructose dehydration rates. Doping the material with Nb proved a key factor in enhancing its activity [33].…”

Highly Acidic, Thermal Stable NbPO4@Fullerene Catalyst for Dehydration of Cyclohexanol

“…Dehydration reaction is an important and also challenging reaction for the synthesis of fine chemicals from biomass ,. Dehydration of cyclohexanol retards the rate of hydroalkylation of phenol .…”