HMF Selectivity Research Articles

Boosting the Formation of Brønsted Acids on Flame-made WOx/ZrO2 for Glucose Conversion.

WOx/ZrO2with ahigher concentrationof Brønsted acid sites (BAS) and a bigger ratio of Brønsted to Lewis acid sites (B/L) than achievable by conventional impregnation (IM)were synthesized usingflame spray pyrolysis (FSP). The rapid quenching and short residence time inherent to FSP prevent the accumulation of W atoms on the ZrO2 support and thus provide an excellent surface dispersion of WOx species. As a result, FSP-made WOx/ZrO2 (FSP-WOx/ZrO2) has a much higher surface concentration of three-dimensional Zr-WOx clusters than corresponding materials prepared by conventional impregnation (IM-WOx/ZrO2). The coordination of W-OH to the unsaturated Zr4+ sites in these clusters results in a remarkable decrease of the concentration of Lewis acid sites (LAS) on the surface of ZrO2 and promotes the formation of bridging W-O(H)-Zr hydroxyl groups acting as BAS. FSP-WOx/ZrO2 possesses ~80% of BAS and a B/L ratio of around 4, while IM-WOx/ZrO2 exhibits ~50% BAS and a B/L ratio of around 1. These catalysts were evaluated in the dehydration of glucose to HMF. The catalytic study demonstrated that B/L ratio plays a crucial role in glucose conversion. The best catalyst, FSP-WOx/ZrO2 with a W/Zr ratio of 1/10 affords nearly 100% glucose conversion and an HMF selectivity of 56-69%.

Highly selective oxidation of 5-HMF to HMFCA via a facile Pt-Ag co-catalytic strategy

5-Hydroxymethyl-2-furancarboxylic acid (HMFCA) is an important feedstock in chemical and pharmaceutical industries. Its production through aerobic conversion of 5-hydroxymethylfurfural (5-HMF) has promising prospects but is challenged by the over-oxidation. In this work, we develop a refined Pt-Ag co-catalytic strategy to tailor the selectivity of 5-HMF’s aerobic oxidation. By simple in situ addition of AgNO3 to the thermal catalytic system of Pt nanoparticles, the main products of 5-HMF oxidation could be shifted from 2,5-furandicarboxylic acid (FDCA) to HMFCA with an ultrahigh selectivity of over 99 %. Density functional theory calculations demonstrate that such strategy could alter the HMFCA adsorption sites from Pt to Ag sites and prevent the oxidation of hydroxymethyl group. In addition, this strategy can be extended to other Ag species, such as AgCl, Ag2O and AgO. This work provides insights into the Pt-Ag synergistic catalysis and opens up a simple avenue to control the product selectivity for biomass refinement.

Zeolite-catalyzed one-pot sucrose-to-HMF transformation: Ge outperforms Sn, Zr, and Al sites

The conversion of renewable compounds to versatile platform molecules over environmentally friendly heterogeneous catalysts is a major challenge. Zeolites stand as active, selective, and reusable solid catalysts for various acid-catalyzed reactions involved in the one-pot cascade transformation of polysaccharides to 5-hydroxymethylfurfural (HMF), a platform molecule opening the way to various valuable chemicals. However, the acidity-performance relationships of zeolite catalysts in HMF synthesis have not been fully elucidated. Here, we have addressed the effect of acid site nature in zeolite catalysts for sucrose-to-HMF transformation by comparing the performance of conventional Al-substituted IWW zeolite with that of Sn-, Zr-, and Ge-containing zeolite catalysts of the same structure. Ge-associated acid sites were found to exhibit superior HMF selectivity compared to Sn, Zr, and Al acid centers, while experiencing evolution into Brønsted acid centers during the catalytic run. The conversion of sucrose over germanosilicate zeolites enhances with increasing catalyst pore diameter or decreasing crystal size. Specifically, the extra-large pore Ge-UTL catalyst, featuring intersecting 14- and 12-ring pores (crystal size 10 × 20 × <1 μm), and large-pore Ge-IWW with 12-, 10- and 8-ring pores (crystal sizes of 1 μm) showed a yield of targeted HMF comparable to or even exceeding the values previously reported for homogeneous or heterogeneous catalysis (54 % after 3 h at 120 °C). Ge-IWW catalyst demonstrated reusability across a minimum of 3 catalytic runs, while in situ structural transformation precluded stable performance of Ge-UTL catalyst in the repetitive catalytic cycles. The results of this study highlight zeolites with uncharacteristic chemical compositions as active, selective, and reusable catalysts for highly demanding applications in biomass valorization.

Unveiling kinetics post rate-determining step in Brønsted acid-catalyzed reactions of fructose: A strategy for 5-hydroxymethylfurfural production from concentrated feedstock

The development of high-yielding catalytic systems is pivotal in biomass upgrading. However, the investigation of kinetics in these complex reaction systems is often highly challenging, especially when reactions leading to byproduct formation are obscured by a preceding, slow rate-determining step. In this work, we introduce a unique approach to kinetic analysis that enables the investigation of reactions occurring post rate-determining step. The technique was applied to the conversion of sugars to 5-hydroxymethylfurfural (HMF), an important platform molecule for sustainable chemical production. First, screening experiments were carried out to identify a catalytic solvent system that achieves a balance between solvent stability, HMF yield, and cost-effectiveness. Our kinetic analysis on the identified system reveals that the fructose reactant undergoes a rate-determining dehydration step to form an unstable reactive intermediate. This intermediate further reacts competitively with other reactive species, such as the hexose reactants or the HMF product, ultimately lowering the HMF selectivity. The calculated relative activation energies of these reactions post rate-determining step provide intuitive insights into the effects of temperature, co-existing reactive species, as well as the previously unexplained effect of feed concentration on HMF selectivity. Additionally, we propose a novel reaction strategy that significantly enhances HMF yield when compared to a traditional batch synthesis. Notably, a high HMF yield of 74 % was achieved with an extreme 55 wt% fructose loading on an aqueous basis (20 wt% loading on a total weight basis) in a low-boiling 80 wt% dioxane/water mixture using an HCl catalyst at 393 K.

Photothermal dependence on catalytic activity and selectivity of HMF and benzyl alcohol oxidation over Pd/1D‐TiO2 nanotubes

AbstractBACKGROUNDPhotothermal catalytic oxidation technology for synthesis of high value‐added chemicals has become a hot topic of research at home and abroad. As a special structure, titania (TiO2) nanotubes (Ti‐NTs) possess larger specific surface area and adsorption capacity, which have shown great application prospects in photothermal catalytic oxidation.RESULTSIn this work, high‐performance palladium (Pd‐Ti‐NTs catalyst were prepared and applied to the photothermal catalytic oxidation of 5‐hydroxymethyl (HMF) and benzyl alcohol. The photothermal dependence on catalytic activity and selectivity of HMF and benzyl alcohol oxidation was studied in detail. The results revealed that compared with thermal catalytic oxidation, the catalysts showed significantly higher conversions of both benzyl alcohol and HMF under light. in particular, HMF conversion increase from 55.6% to 99.7%. Aldehyde oxidation is inhibited by alcohol and can be dramatically promoted by light radiation. This is probably because alcohol can inhibit the adsorption of aldehyde, and this inhibiting effect is weakened through light radiation, thus promoting the oxidation of aldehydes. Therefore, the selectivity of the final products 2,5‐furandicarboxylic acid (FDCA) and benzoic acid were dramatically increased in both systems under light radiation, and the selectivity for FDCA was obviously increased from 5.8% to 61.3%, and the yield reached 61.0%, which is higher than that of most of the reported Pd‐TiO2‐based catalysts for FDCA.CONCLUSIONSIn this paper, we verify that Pd‐Ti‐NTs could preferentially promote the conversion of aldehydes to acids in the presence of light, and obtained catalysts with high catalytic performance and high stability for benzyl alcohol and HMF oxidation. © 2024 Society of Chemical Industry (SCI).

Intramolecular interaction induced C-C cleavages in fructose conversion in polar aprotic solvents-origin of the formation of excess formic acid and oligomers.

Understanding the mechanism of excess formic acid formation in the dehydration of fructose to HMF would be beneficial to improve HMF selectivity and carbon efficiency. The production of formic acid from keto-D-fructose in polar aprotic solvents, such as THF, DIO, and MTHF, and MIBK solvents without a catalyst was investigated via DFT calculations. It was found that in THF, DIO and MTHF solvents, fructose tended to generate formic acid directly with the catalysis of the intramolecular hydroxyls, especially C6-OH (terminal hydroxyl), while in MIBK, the solvent molecule could react with the intermediates produced in the process, making the barrier of production of acetic acid lower than that of formic acid. Molecular dynamics simulations showed that the lower dielectric polar aprotic solvents (THF, DIO and MTHF) could not destroy the intramolecular H-bonds of hydroxyls in fructose, which could promote the keto-enol tautomerization and hydration steps, facilitating the formation of six-member-ring transition states, which reduced the ring tension and decreased the activation energy greatly, leading to the overproduction of formic acid and oligomers. ETS-NOCV analysis further indicated that the donated electrons from C-O σ-bonds on the carbon chain of fructose made the intramolecular hydroxyls more basic, which could catalyse keto-enol tautomerization with a lower energy barrier than water molecules. To obtain more target products, such as HMF, suitable reaction environments, such as a higher polar aprotic solvent with a low boiling point or restriction of the activity of hydroxyls of fructose, might be selected to destroy the intramolecular interaction and then reduce the overproduction of formic acid and the formation of oligomers.

Computational insights into selective glucose to 5-hydroxymethylfurfural (HMF) conversion by reducing humins formation in aqueous media under Brønsted acid-catalyzed conditions.

5-Hydroxymethylfurfural (HMF) is known for its potential in biofuel production and as a platform chemical for many commercially important molecules. The cost-effective large-scale production of HMF from glucose is hampered by its poor yield in aqueous media due to the formation of polymeric side products known as humins. Thus, reducing humins formation is a strategy for the efficient conversion of glucose to HMF. However, the origin of humins formation and their structures are elusive. In this regard, we investigated the polymerization mechanism and the structure of humins formed during the Brønsted-acid-catalyzed dehydration of glucose to HMF in an aqueous medium by employing density functional theory-based calculations and microkinetic analyses. Notably, the results of this work indicate that humins formation occurs only after the formation of HMF in the reaction mixture and the major part of the humins structure (about 60%) is composed of furanic rings. Furthermore, based on the knowledge gained from in-depth mechanistic and microkinetic studies, potential strategies to reduce humins formation and thereby enhance HMF selectivity are proposed here.

Incorporation of tin oxide nanoparticles on sulfonated carbon microspheres as a bifunctional catalyst for efficient conversion of biomass-derived monosaccharides to 5-Hydroxymethylfurfural and furfural

Effective production of versatile platform molecules 5-Hydroxymethylfurfural (HMF) and furfural (FF) from biomass-derived carbohydrates is of great importance to synthesis of high-value-added bio-based chemicals and fuels. In order to highly efficient synthesis of HMF and FF, in this work, by integrating tin oxide nanoparticles with sulfonated carbon microspheres, a novel solid acid catalyst (SnOx-NPs@SC) with tunable Lewis/Brønsted acidity was developed for the conversion of glucose and xylose to HMF and FF, respectively. Characterization and experiment revealed that optimization of Sn precursor dosage and pyrolysis temperature was beneficial to the integration of SnOx with sulfonated carbon microspheres and formation of appropriate acid strength and balanced Lewis/Brønsted acid, which could enhance the selective conversion of glucose and xylose to HMF and FF. In the H2O/THF biphasic solvent system with 1.5 mol/L NaCl, the optimized catalyst (0.35-SnOx-NPs@SC-500) exhibited excellent catalytic performance by achieving 90.2% selectivity of HMF at 180 ℃ for 2 h and 85.4% selectivity of FF at 170 ℃ for 2 h, and displayed relatively high stability in five consecutive experimental cycles. The mechanism was discussed based on the physicochemical properties of the catalyst and reaction system. The results of this work provide an effective strategy for designing a bifunctional solid acid catalyst for the one-pot production of highly value-added biomass intermediates.

Enhanced 5-hydroxymethylfurfural production from cellulose in monophasic molten salt hydrate: Insights into the effect of catalyst acidity on conversion

Production of 5-HMF from cellulose is a promising approach for advanced bio-fuels preparation, but the degradation of active 5-hydroxymethylfurfural (5-HMF) is a critical challenge affecting 5-HMF selectivity. To address this issue, biphasic reaction system consisting of water and organic solvent is generally used to in-situ extract 5-HMF into organic phase to inhibit product degradation. Despite the high 5-HMF selectivity achieved in biphasic system, low product concentration and difficulty in separation restrict its industrial applications. Molten salt hydrate (MSH) is unique in cellulose conversion and 5-HMF preservation. In this work, MSH of LiBr was used as monophasic solvent for cellulose conversion and an acidity tunable solid acid AlSiO-x was used as the catalyst. It was found that a relatively high 5-HMF yield of 44.5% together with carbon balance of 75.0% were obtained at 170 °C for 20 min, which is higher than the results ever reported. Importantly, this work proved that the ratio of total Brønsted to Lewis acid sites on solid acid is the key issue affected 5-HMF yield. After reaction, solid acid can be recycled for more than 5 times without catalytic performance decline, and the dissolved 5-HMF can be sufficiently separated from MSH via hyper cross-linked polymer (HCP) adsorption.

Recent Advances in Zeolites-Catalyzed Biomass Conversion to Hydroxymethylfurfural: The Role of Porosity and Acidity.

Biomass is an attractive raw material for the production of fuel oil and chemical intermediates due to its abundant reserves, low price, easy biodegradability, and renewable use. Hydroxymethylfurfural (5-HMF) is a valuable platform chemically derived from biomass that has gained significant research interest owing to its economic and environmental benefits. In this review, recent advances in biomass catalytic conversion systems for 5-HMF production were examined with a focus on the catalysts selection and feedstocks' impact on the 5-HMF selectivity and yield. Specifically, the potential of zeolite-based catalysts for efficient biomass catalysis was evaluated given their unique pore structure and tunable (Lewis and Brønsted) acidity. The benefits of hierarchical modifications and the interactions between porosity and acidity in zeolites, which are critical factors for the development of green catalytic systems to convert biomass to 5-HMF efficiently, were summarized and assessed. This Review suggests that zeolite-based catalysts hold significant promise in facilitating the sustainable utilization of biomass resources.

Industrially Promising β‐Ni(OH)2 Nanosheets Self‐Supported Electrode for Highly Efficient Electrooxidation of 5‐Hydroxymethylfurfural

AbstractThe electrocatalytic selective oxidation of 5‐hydroxymethylfurfural (HMF) presents a highly efficient and eco‐friendly method for biomass utilization. Herein, we synthesized pure β‐Ni(OH)2 and amorphous Ni(OH)2 on nickel foam (NF) using a facile stepwise electrodeposition technique and evaluated their catalytic performances for the oxidation of HMF to 2,5‐furan dicarboxylic acid (FDCA). The β‐Ni(OH)2 nanosheets‐decorated electrode (β‐NiNS/NF) exhibited excellent interfacial lattice matching with the substrate nickel, resulting in enhanced electron transfer at the catalyst‐substrate interface, as confirmed by electrochemical analysis. Consequently, the β‐NiNS/NF electrode displayed improved intrinsic electrocatalytic activity and interfacial stability. Additionally, it demonstrated effective HMF adsorption capability. These advantageous properties led to enhanced HMF conversion, selectivity, and structural stability. Notably, the β‐NiNS/NF electrode achieved an unprecedented FDCA yield of 80.6 % under relatively large current density galvanostatic electrolysis commonly used in industry. Moreover, our investigation identified a novel possible oxidation pathway during HMF electrocatalysis. This study not only showcases an efficient and scalable synthetic approach but also highlights the potential of the β‐NiNS/NF electrode for industrial HMF electrocatalytic oxidation under conditions involving relatively large applied currents.

Microwave-assisted conversion of fructose to 5-HMF using carbonaceous acidic catalysts

Recently, the catalytic conversion of fructose to 5-hydroxymethylfurfural (5-HMF) has attracted much interest. The idea of a low-cost, sustainable, energy-efficient method is critical to obtain excellent yield and selectivity for the target product 5-HMF. In this work, microwave (MW) irradiation was chosen as a heating source for the conversion of fructose to 5-HMF with the presence of various amorphous carbons containing Brønsted acid sites as catalysts in dimethyl sulfoxide (DMSO) as a solvent. The catalysts’ morphology, surface functional groups, thermal stability, and compositions of the obtained solids were examined by scanning electron microscope (SEM), elemental mapping, thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), energy dispersive X-Ray spectroscopy (EDX), Raman spectroscopy and X-ray diffraction (XRD) techniques. The effect of solvent, heating technique, MW power, time, and catalytic loading on the reaction was studied thoroughly. The highest 5-HMF yield of 79.9% and 5-HMF selectivity of 79.7% were achieved with the optimal condition. 5-HMF was easily separated using a liquid-liquid extraction procedure with high purity. Moreover, the catalyst can be quickly recovered and reused. MW irradiation has proved to selectively and efficiently promote the formation of 5-HMF with high yield in a short reaction time. A mechanism for the formation 5-HMF from fructose was also proposed.

Conversion of Cellulose to 5-HMF in the Presence of Silica-Alumina Catalysts Synthesized by Dual Template at Low Temperature

In this study, which incorporates many principles of green chemistry (use of renewable feedstocks, catalysis, improvement of energy efficiency, and harmless solvents and auxiliaries), the single-phase catalytic conversion of cellulose to 5-HMF in over silica-alumina catalysts was investigated. A series of dual-template silica-alumina catalysts with CTAB as the main template and F127 or triethylamine (TEA) as the co-template were synthesized at a low temperature of 60 °C and characterized by XRD, N2 adsorption-desorption technique, FT-IR and pyridine adsorption FT-IR. The surface area is increased by using the second template in silica-alumina catalyst. In addition, the acidity of the surface was changed by using the second template. The cellulose conversion and yield of 5-HMF increased from 36% to 52% and from 3.13% to 4.24%, respectively, due to the properties gained by using the second template. 52% cellulose conversion and 8.13% selectivity of 5-HMF were obtained in aqueous medium, 220 °C and 6 h reaction time with the catalyst using TEA as co-template. Eco-friendly silica catalysts synthesized at low temperatures with a dual template can be considered as a potential alternative for the conversion of cellulose into value-added biobased products.

Determination of the Anticarcinogenic Activity of 5-Hydroxymethyl-2-furfural Produced from Grape Must Under in vitro Conditions

Every year, millions of tons of food and beverage waste are thrown away unused around the world. The carbohydrates found in food waste create a raw material potential for the production of high value-added products that are used in energy, feed and pharmacology. One of these products, 5-Hydroxymethyl-2-furfural (5-HMF), is a by-product of simple dehydration of carbohydrates. It finds wide use in the field of pharmacy due to its anticancer, antifungal and antimicrobial activities. Many studies have stated that the sugar source with the highest conversion rate in 5-HMF production is fructose. For this reason, in this study, it was aimed to realize the production of 5-HMF in autoclave sterilization carried out under high temperature and pressure using grape must waste, which is known to have high fructose content, and determine the anticarcinogenic activity and cytotoxicity of the produced 5-HMF under in vitro conditions. In this study, it was determined that the medium containing DMSO increased the sugar conversion percentage, 5-HMF efficiency and selectivity in the waste grape must more than the medium containing only water. In the production of 5-HMF, the conversion of sugar in the medium saturated with salt, and the efficiency and selectivity of 5-HMF were determined as 97.04%, 68.61% and 70.82%, respectively, when DMSO organic solvent was used. In addition, it has been determined that 5-HMF produced from waste grape must has a toxic effect on both healthy cells and cancer cells and has anticancer properties.

Insights into pathways and solvent effects of fructose dehydration to 5-hydroxymethylfurfural in acetone–water solvent

Preparation of 5-hydroxymethylfurfural (HMF) from fructose is a typical liquid-phase biomass conversion reaction, strongly affected by solvent media and acid catalysts, including fructose reactivity and HMF selectivity. Most works on solvent selection were conducted experimentally, however, lack of theoretical guidance. Herein, we applied experimental and theoretical techniques to investigate solvent effects of acetone–water solvent on HMF production. Factors including product distribution, key intermediate and byproduct identification, reaction pathways, and solvation simulation of solutes were systematically evaluated. The results indicate that water ensures high substrate concentration and assists intermolecular hydrogen transfer to accelerate reaction rate. Various HMF degradation reactions are introduced in the presence of water, however, are significantly inhibited by acetone. Moreover, acetone increases the population of high-reactive fructofuranose isomers, thus improving HMF yield. Therefore, water and acetone play a synergistic role in HMF preparation. Also, our findings provide theoretical insights for solvent selection and methodology for studying solvent effects.

Plasmon resonance enhanced palygorskite-based composite toward the photocatalytic reformation of cellulose biomass under full spectrum

Photo-driven reformation of cellulose biomass is deemed a promising technology to produce value-added chemicals. Herein, the photocatalytic conversion of cellulose to 5-hydroxymethylfurfural (5-HMF) employing a palygorskite (Pal) clay-based composite as a catalyst was reported. Pal modified with phosphoric acid (P-Pal) not only induced the growth of Cu2(PO4)(OH) nanosheets on its surface with high dispersion effectively enhancing light absorption, but also enabled intimate adsorption of catenulate cellulose in the colloidal solution. The in-situ precipitated Cu2(PO4)(OH) owned abundant Lewis acid sites and localized surface plasmon resonance (LSPR) effect, which extended the absorbance range to near-infrared (NIR) light and provided a substrate for local thermal activation. Under simulated solar light irradiation, Bronsted acid provided by P-Pal and the formed hydroxyl radicles (·OH) synergistically facilitated the cleavage of the β-1,4-glycosidic bond of cellulose to produce glucose, while the Lewis acid sites directed the selective glucose isomerization to produce 5-HMF. The 20 wt% Cu2(PO4)(OH)/P-Pal exhibited the highest 5-HMF selectivity of 72% along with remarkable reusability, and the yield of 5-HMF reached 53 mg/L even under NIR irradiation, benefiting from the immobilization and acid sites of the Pal clay.

Production of 5-hydroxymethylfurfural from glucose by recyclable heteropolyacid catalyst in ionic liquid

In this study, heteropolyacid catalyst (SiO 2 -ATS-PTA) was prepared by using silica as a supporter to convert glucose to 5-hydroxymethylfurfural (HMF). The structure and morphology of catalyst was characterized by ESEM, XPS, and Raman. The prepared SiO 2 -ATS-PTA was used in the conversion of glucose into HMF with 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) ionic liquid as solvent via the oil bath. The effect of the reaction time, temperature and catalyst dosage on the glucose conversion, HMF yield, and HMF selectivity was investigated. The highest HMF yield of 74.67% was obtained from glucose at 140 °C, 180 min, and 70 mg of catalyst. Furthermore, the reusability of the SiO 2 -ATS-PTA and ionic liquid was examined for 3 consecutive cycles. The results showed that the glucose conversion, HMF yield, and HMF selectivity only decrease by 4.63%, 4.74%, and 4.85%, respectively, after three times reused. This study puts forward SiO 2 -ATS-PTA as a recyclable heteropolyacid catalyst for the conversion of glucose to HMF, indicating a favorable application in the biorefinery. • HMF is prepared from glucose in [Emim]Cl with phosphotungstic acid solid catalyst . • The morphology and structure of SiO 2 -ATS-PTA was characterized. • The highest HMF yield of 74.67% was obtained from glucose at 140 °C, 180 min, and 70 mg of catalyst. • SiO 2 -ATS-PTA and [Emim]Cl could be reused without a significant loss of catalytic activity.

Highly Efficient and Selective Preparation of 5-Hydroxymethylfurfural from Concentrated Carbohydrates Using Deep Eutectic Solvents

Converting carbohydrates to 5-hydroxymethylfurfural (HMF) is an important goal for biorefinery. Although various deep eutectic solvents (DESs) have been reported for HMF production, the field lacks systematic research on the effect of cations and anions and an effective catalytic system for converting concentrated carbohydrates. Here, 12 kinds of DESs containing four cations and six anions were systematically evaluated and tetraethylammonium bromide (TEAB) was confirmed as the most effective DES, which provided HMF yields of 90 and 76% from fructose and glucose, respectively. The stable bromide-substituted intermediate may explain the positive effect of bromide based on the results of density functional theory calculation. A high concentration substrate has an adverse impact on the selectivity of HMF due to the HMF concentration caused by glucose, CrCl3·6H2O, and concentrated HMF. To inhibit the condensation, a biphasic system of TEAB/THF is developed to convert a highly concentrated glucose of 62.5 wt % (83.3 wt % with respect to TEAB), providing an excellent HMF yield of 72%. This study has revealed the impact of cations and anions of DESs on HMF production, which will serve as a base for designing task-specific DESs. Moreover, an efficient catalytic system to produce HMF from concentrated glucose was also provided.

Chromium Oxide-modified Mesoporous Zirconium Dioxide: Efficient Heterogeneous Catalyst for the Synthesis of 5-Hydroxymethylfurfural.

A highly efficient carbohydrate conversion to 5-hydroxymethylfurfural (5-HMF) is a promising method to achieve green and sustainable development. However, most currently reported strategies are energy consuming, and the 5-HMF yield is relatively lower in the aqueous phase. Herein, a facile method is reported to obtain effective Cr/ZrO2 catalysts with high acidity and their catalytic performances were investigated for catalyzing fructose to 5-HMF at different temperatures and times. With the catalysis of 15 % Cr/ZrO2 catalyst, the highest fructose conversion of 98 %, 5-HMF yield of 48.8 %, and 5-HMF selectivity of 49.8 % are achieved in green solvent with good recyclability. The possible reaction process of the improved catalysis performance is attributed to the highly crystalline and strong acidity of the Cr/ZrO2 catalyst. The Lewis acid sites could increase the overall rate of fructose conversion by promoting side reactions and might suppress fructose to glucose isomerization. In addition, Cr leakage during the reaction might act as the Bronsted acids to catalyze the fructose dehydration to 5-HMF. The reported method of introducing chromium oxides into ZrO2 catalyst will open a new avenue to promote the practical application of biomass and sustainable development in the future.

An aluminum-grafted SBA-15-catalyzed conversion of glucose to 5-hydroxymethylfurfural

Environmentally friendly processes for preparing catalysts and converting glucose into 5-hydroxymethylfurfural (HMF) were studied under water-based conditions. A series of aluminum-grafted SBA-15 mesoporous silica with Si/Al molar ratios of 1.5–20 was prepared by tuning aluminum precursors, solvents, and the pH values in grafting. Among them, the 3Al-S15-w-pH 8 catalyst with high acid capacity and mixed acid sites of Lewis and Brønsted acids was fabricated by adjusting the pH value of the water-soluble aluminum precursor to 8 in a water medium. Thus, it converted 87% of glucose at 160 °C for 5 h in the water medium with 33% HMF selectivity. Moreover, the used 3Al-S15-w-pH 8 catalyst was easily regenerated by calcination in air, which was further used for converting glucose to HMF without losing its performance. Our findings provide new ideas for environmentally friendly catalyst preparation and biomass conversion methods, which can be readily applied to catalysis and bio-refining processes.