Efficient glucose dehydration to HMF onto Nb-BEA catalysts

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.

Combination of deep eutectic solvent and functionalized metal-organic frameworks as a green process for the production of 5-hydroxymethylfurfural and furfural from sugars

Biomass is an abundant and sustainable resource that can be converted into energy and chemicals. Therefore, the development of efficient methods for the conversion of biomass into platform intermediates is crucial. In this study, the one-pot conversion of sugars into 5-hydroxymethylfurfural (HMF) and furfural was achieved using the metal-organic framework combined with metal ions [MIL-101(Cr)] as a high-activity catalyst, and a deep eutectic solvent (choline chloride and lactic acid) as a green solvent. The optimal temperature, time, amount of catalyst used, and amount of deep eutectic solvent used were all determined. The highest HMF yield of 49.74% and furfural yield of 55.90% were obtained. The recyclability of the catalysts and deep eutectic solvent was also investigated. After three reaction runs, the HMF yield was still nearly 30.00%. Finally, the MIL-101(Cr) catalytic system was selected to study the kinetic mechanism underlying the conversion of glucose into HMF.

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

The valorization of non-grain biomass feedstocks to value-added chemicals, polymers and alternative fuels is a crucial route for the utilization of renewable resources. Inulin belongs to a type of fructans, which is a pivotal platform bridging upstream fructose-rich biomass feedstocks typically represented by Jerusalem artichoke and downstream platform molecules such as alcohols, aldehydes and acids. Fructose can be directly obtained from the inulin hydrolysis and further converted into various platform chemicals, which is a more environmentally economical route than the conventional catalytic upgrading of cellulose. Nevertheless, most perspectives over the last decade have focused on the valorization of cellulose-derived carbohydrates, without much emphasis on the practical importance of one-pot transformation of inulin. In this review, we aim to demonstrate an efficient one-pot tandem transformation system of the inulin as fructose-rich platform towards 5-hydroxymethylfurfural (HMF). Core concerns are placed on elucidating the contributing roles of acid sites and solvents in enhancing the overall catalytic performance. The perspectives presented in this review may contribute to the innovation in the catalytic refining of fructose-rich non-grain biomass and the development of a greener biomass-based energy system.

Niobium: The Focus on Catalytic Application in the Conversion of Biomass and Biomass Derivatives

The world scenario regarding consumption and demand for products based on fossil fuels has demonstrated the imperative need to develop new technologies capable of using renewable resources. In this context, the use of biomass to obtain chemical intermediates and fuels has emerged as an important area of research in recent years, since it is a renewable source of carbon in great abundance. It has the benefit of not contributing to the additional emission of greenhouse gases since the CO2 released during the energy conversion process is consumed by it through photosynthesis. In the presented review, the authors provide an update of the literature in the field of biomass transformation with the use of niobium-containing catalysts, emphasizing the versatility of niobium compounds for the conversion of different types of biomass.

Microflow chemistry and its electrification for sustainable chemical manufacturing

Sustainability is vital in solving global societal problems. Still, it requires a holistic view by considering renewable energy and carbon sources, recycling waste streams, environmentally friendly resource extraction and handling, and green manufacturing. Flow chemistry at the microscale can enable continuous sustainable manufacturing by opening up new operating windows, precise residence time control, enhanced mixing and transport, improved yield and productivity, and inherent safety. Furthermore, integrating microfluidic systems with alternative energy sources, such as microwaves and plasmas, offers tremendous promise for electrifying and intensifying modular and distributed chemical processing. This review provides an overview of microflow chemistry, electrification, their integration toward sustainable manufacturing, and their application to biomass upgrade (a select number of other processes are also touched upon). Finally, we identify critical areas for future research, such as matching technology to the scale of the application, techno-economic analysis, and life cycle assessment.

Glucose Conversion into 5-Hydroxymethylfurfural over Niobium Oxides Supported on Natural Rubber-Derived Carbon/Silica Nanocomposite

5-Hydroxymethylfurfural (HMF) is one of the most important lignocellulosic biomass-derived platform molecules for production of renewable fuel additives, liquid hydrocarbon fuels, and value-added chemicals. The present work developed niobium oxides (Nb2O5) supported on mesoporous carbon/silica nanocomposite (MCS), as novel solid base catalyst for synthesis of HMF via one-pot glucose conversion in a biphasic solvent. The MCS material was prepared via carbonization using natural rubber dispersed in hexagonal mesoporous silica (HMS) as a precursor. The Nb2O5 supported on MCS (Nb/MCS) catalyst with an niobium (Nb) loading amount of 10 wt.% (10-Nb/MCS) was characterized by high dispersion, and so tiny crystallites of Nb2O5, on the MCS surface, good textural properties, and the presence of Bronsted and Lewis acid sites with weak-to-medium strength. By varying the Nb loading amount, the crystallite size of Nb2O5 and molar ratio of Bronsted/Lewis acidity could be tuned. When compared to the pure silica HMS-supported Nb catalyst, the Nb/MCS material showed a superior glucose conversion and HMF yield. The highest HMF yield of 57.5% was achieved at 93.2% glucose conversion when using 10-Nb/MCS as catalyst (5 wt.% loading with respect to the mass of glucose) at 190 °C for 1 h. Furthermore, 10-Nb/MCS had excellent catalytic stability, being reused in the reaction for five consecutive cycles during which both the glucose conversion and HMF yield were insignificantly changed. Its superior performance was ascribed to the suitable ratio of Brønsted/Lewis acid sites, and the hydrophobic properties generated from the carbon moieties dispersed in the MCS nanocomposite.

Heterogeneous Catalysts for the Conversion of Glucose into 5-Hydroxymethyl Furfural

Lignocellulosic biomass, a cheap and plentiful resource, could play a key role in the production of sustainable chemicals. The simple sugars contained in the renewable lignocellulosic biomass can be converted into commercially valuable products such as 5-hydroxymethyl furfural (HMF). A platform molecule, HMF can be transformed into numerous chemical products with potential applications in a wide variety of industries. Of the hexoses contained in the lignocellulosic biomass, the successful production of HMF from glucose has been a challenge. Various heterogeneous catalysts have been proposed over the last decade, ranging from zeolites to metal organic frameworks. The reaction conditions vary in the reports in the literature, which makes it difficult to compare catalysts reported in different studies. In addition, the slight variations in the synthesis of the same material in different laboratories may affect the activity results, because the selectivity towards desired products in this transformation strongly depends on the nature of the active sites. This poses another difficulty for the comparison of different reports. Furthermore, over the last decade the new catalytic systems proposed have increased profoundly. In this article, we summarize the heterogeneous catalysts: Metal Organic Frameworks (MOFs), zeolites and conventional supported catalysts, that have been reported in the recent literature and provide an overview of the observed catalytic activity, in order to provide a comparison.

Production of 5-Hydroxymethylfurfural from Direct Conversion of Cellulose Using Heteropolyacid/Nb2O5 as Catalyst

This study aimed to select the best reaction conditions to produce 5-hydroxymethylfurfural (HMF) from cellulose using heterogeneous catalyst based on a heteropolyacid (H3PW12O40—HPW) and Nb2O5. Initially, the influence of the temperature (160 or 200 °C), acetone:water ratio (50:50 or 75:25 v/v), cellulose load (5% or 10% w/v) and catalyst concentration (1% or 5% w/v) on HMF production from cellulose was evaluated through a Taguchi’s L16 screening experimental design. Afterwards, the main variables affecting this process, namely the temperature (160–240 °C) and acetone:water ratio (60:40–90:10 v/v), were optimized using a central composite rotatable design. Next, a kinetic study on HMF production from cellulose was carried out. Finally, HMF production from cellulose obtained from different biomass sources was evaluated. It was found that the reaction conditions able to result in maximum HMF yield, i.e., around 20%, were 200 °C, acetone:water ratio of 75:25 (v/v), 10% w/v of cellulose, and 5% w/v of catalyst concentration. The kinetic study revealed that the Langmuir–Hinshelwood–Hougen–Watson approach fit to the experimental data. Under the optimized conditions, the catalyst HPW/Nb2O5 was also effective in converting different sources of cellulose into HMF.

In Situ Synthesis of Sn-Beta Zeolite Nanocrystals for Glucose to Hydroxymethylfurfural (HMF)

The Sn substituted Beta nanocrystals have been successfully synthesized by in-situ hydrothermal process with the aid of cyclic diquaternary ammonium (CDM) as the structure-directing agent (SDA). This catalyst exhibits a bifunctional catalytic capability for the conversion of glucose to hydroxymethylfurfural (HMF). The incorporated Sn acting as Lewis acid sites can catalyze the isomerization of glucose to fructose. Subsequently, the Brønsted acid function can convert fructose to HMF via dehydration. The effects of Sn amount, zeolite type, reaction time, reaction temperature, and solvent on the catalytic performances of glucose to HMF, were also investigated in the detail. Interestingly, the conversion of glucose and the HMF yield over 0.4 wt% Sn-Beta zeolite nanocrystals using dioxane/water as a solvent at 120 °C for 24 h are 98.4% and 42.0%, respectively. This example illustrates the benefit of the in-situ synthesized Sn-Beta zeolite nanocrystals in the potential application in the field of biomass conversion.

Optimized Nb-Based Zeolites as Catalysts for the Synthesis of Succinic Acid and FDCA

Nb(0.05 moles%)-zeolites prepared via a post synthesis methodology (BEA, Y, ZSM-5), or a direct sol-gel method (Silicalite-1) were investigated in the hydroxymethylfurfural (HMF) oxidation by both molecular oxygen, in aqueous phase, and organic peroxides, in acetonitrile. The catalysts prepared through the post synthesis methodology (i.e., Nb-Y5, Nb-ZSM25, Nb-Y30, Nb-BEA12, and Nb-BEA18) displayed a mono-modal mesoporosity and contain residual framework Al-acid sites, extra framework isolated Nb(V)O-H and Nb₂O₅ pore-encapsulated clusters, while Nb-Sil-1, prepared through a direct synthesis procedure, displayed a bimodal micro-mesoporosity and contains only -Nb=O species. These modified zeolites behave as efficient catalysts in both HMF/glucose wet oxidation to succinic acid (SA) and HMF oxidation with organic peroxides to the 2,5-furandicarboxylic acid (FDCA). The catalytic behavior of these catalysts, in terms of conversion and especially the selectivity, mainly depended on the base/acid sites ratio. Thus, the HMF/glucose wet oxidation occurred with a total conversion and a selectivity to SA of 37.7% (from HMF) or 69.1% (from glucose) on the Nb-Y5 catalyst, i.e., the one with the lowest base/acid sites ratio. On the contrary, the catalysts with the highest base/acid sites ratio, i.e., Nb-ZSM25 and Nb-Sil-1, afforded a high catalytic efficiency in HMF oxidation with organic peroxides, in which FDCA was produced with selectivities of 61.3-63.8% for an HMF conversion of 96.7-99.0%.

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

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.

Synthesis and Application of Heterogeneous Catalysts Based on Heteropolyacids for 5-Hydroxymethylfurfural Production from Glucose

This study aimed to evaluate the synthesis and application of heterogeneous catalysts based on heteropolyacids for 5-hydroxymethylfurfural (HMF) production from glucose. Initially, assays were carried out in order to establish the most favorable catalyst synthesis conditions. For such purpose, calcination temperature (300 or 500 °C), type of support (Nb2O5 or Al2O3), and active phase (H3PW12O40—HPW or H3PMo12O40—HPMo) were tested and combined based on Taguchi’s L8 orthogonal array. As a result, HPW-Nb2O5 calcined at 300 °C was selected as it presented optimal HMF production performance (9.5% yield). Subsequently, the reaction conditions capable of maximizing HMF production from glucose using the selected catalyst were established. In these experiments, different temperatures (160 or 200 °C), acetone-to-water ratios (1:1 or 3:1 v/v), glucose concentrations (50 or 100 g/L), and catalyst concentrations (1 or 5% w/v) were evaluated according to a Taguchi’s L16 experimental design. The conditions that resulted in the highest HMF yield (40.8%) consisted of using 50 g/L of glucose at 160 °C, 1:1 (v/v) acetone-to-water ratio, and catalyst concentration of 5% (w/v). Recycling tests revealed that the catalyst can be used in four runs, which results in the same HMF yield (approx. 40%).

Production of 5-Hydroxymethylfurfural from Glucose in Water by Using Transition Metal-Oxide Nanosheet Aggregates

Metal-oxide nanosheet aggregates were prepared by exfoliation and subsequent aggregation of layered metal oxides and used for the conversion of glucose to 5-hydroxymethylfurfural (HMF) in water. Three aggregated nanosheets, HNbWO6, HNb3O8, and HTiNbO5, yielded HMF in water at 393–413 K, whereas ion-exchange resins and H-form zeolites did not. The catalytic activity of the nanosheets decreased in the order HNbWO6 > HNb3O8 > HTiNbO5, which correlates with their acidity. The HNbWO6 nanosheets exhibited higher selectivity for HMF than niobic acid, and the selectivity was improved in the water–toluene biphasic system. The selectivity for HMF over HNbWO6 nanosheets was higher from glucose than from fructose. Kinetic analysis suggested that in addition to fructose, an intermediate species was involved in the reaction pathway of HMF production from glucose.