Recent catalytic routes for the preparation and the upgrading of biomass derived furfural and 5-hydroxymethylfurfural

Multigram Synthesis of Pure HMF and BHMF

5-Hydroxymethylfurfural (HMF) is a bio-based platform chemical that can be used as a building block to produce several compounds with diverse applications. Even though HMF synthesis holds promise for a greener future, the current state of technology and the high production cost limit its competitiveness on an industrial scale. In this prospect, we have developed a multigram-scale procedure for HMF by reacting d-fructose with Purolite CT275DR—an acidic resin—in a dimethyl carbonate (DMC)/tetraethyl ammonium bromide (TEAB) biphasic system. Reactions performed in an autoclave for 2 h at 110 °C using up to 40 gram of d-fructose resulted in an overall HMF yield of 70%. HMF was purified by a custom-made procedure leading to ca 50% of the pure crystalline product; meanwhile, the residual HMF-rich oil was directly reduced to bis(hydroxymethyl)furan (BHMF). Green metrics and the Ecoscale algorithm were used to evaluate the sustainability of the herein-proposed procedure in comparison with previously reported works.

Synthesis, biological evaluation and molecular modeling studies of novel 1,2,3-triazole-linked menadione-furan derivatives as P2X7 inhibitors

The P2X7 receptor (P2X7R) is an ion channel that promotes the passage of ions through the membrane through brief stimulation once activated by ATP, its endogenous opener. However, prolonged stimulation with ATP, which occurs in pathological processes, opens a nonselective pore in the plasma membrane, allowing the passage of large molecules and leading to cytokine release or even cell death. In this sense, the search for new inhibitors for this receptor has attracted a great deal of attention in recent years. Considering the booming of biomass upgrading reactions in recent years and the continued efforts to synthesize biologically active molecules containing the 1,2,3-triazole ring, in the present work, we aimed to investigate whether triazole-linked menadione-furan derivatives could present P2X7R inhibitory activity. The novel compounds were tested for their inhibitory activity on ATP-induced dye uptake in peritoneal macrophages. Some have shown promising results, having displayed IC₅₀ values lower than that of the P2X7R inhibitor BBG. Molecular docking studies also indicated that the active compounds bind to an allosteric site on P2X7R, presenting potential P2X7R inhibition.

Alloy-Driven Efficient Electrocatalytic Oxidation of Biomass-Derived 5-Hydroxymethylfurfural towards 2,5-Furandicarboxylic Acid: A Review

In recent years, electrocatalysis was progressively developed to facilitate the selective oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) towards the value-added chemical 2,5-furandicarboxylic acid (FDCA). Among reported electrocatalysts, alloy materials have demonstrated superior electrocatalytic properties due to their tunable electronic and geometric properties. However, a specific discussion of the potential impacts of alloy structures on the electrocatalytic HMF oxidation performance has not yet been presented in available Reviews. In this regard, this Review introduces the most recent perspectives on the alloy-driven electrocatalysis for HMF oxidation towards FDCA, including oxidation mechanism, alloy nanostructure modulation, and external conditions control. Particularly, modulation strategies for electronic and geometric structures of alloy electrocatalysts have been discussed. Challenges and suggestions are also provided for the rational design of alloy electrocatalysts. The viewpoints presented herein are anticipated to potentially contribute to a further development of alloy-driven electrocatalytic oxidation of HMF towards FDCA and to help boost a more sustainable and efficient biomass refining system.

A consolidated review of commercial-scale high-value products from lignocellulosic biomass

For decades, lignocellulosic biomass has been introduced to the public as the most important raw material for the environmentally and economically sustainable production of high-valued bioproducts by microorganisms. However, due to the strong recalcitrant structure, the lignocellulosic materials have major limitations to obtain fermentable sugars for transformation into value-added products, e.g., bioethanol, biobutanol, biohydrogen, etc. In this review, we analyzed the recent trends in bioenergy production from pretreated lignocellulose, with special attention to the new strategies for overcoming pretreatment barriers. In addition, persistent challenges in developing for low-cost advanced processing technologies are also pointed out, illustrating new approaches to addressing the global energy crisis and climate change caused by the use of fossil fuels. The insights given in this study will enable a better understanding of current processes and facilitate further development on lignocellulosic bioenergy production.

Unveiling the mechanism for selective cleavage of C-C bonds in sugar reactions on tungsten trioxide-based catalysts

Conversion of naturally occurring sugars, the most abundant biomass resources on Earth, to fuels and chemicals provides a sustainable and carbon-neutral alternative to the current fossil resource-based processes. Tungsten-based catalysts (e.g., WO3) are efficient for selectively cleaving C-C bonds of sugars to C2,3 oxygenate intermediates (e.g., glycolaldehyde) that can serve as platform molecules with high viability and versatility in the synthesis of various chemicals. Such C-C bond cleavage follows a mechanism distinct from the classical retro-aldol condensation. Kinetic, isotope 13C-labeling, and spectroscopic studies and theoretical calculations, reveal that the reaction proceeds via a surface tridentate complex as the critical intermediate on WO3, formed by chelating both α- and β-hydroxyls of sugars, together with the carbonyl group, with two adjacent tungsten atoms (W-O-W) contributing to the β-C-C bond cleavage. This mechanism provides insights into sugar chemistry and enables the rational design of catalytic sites and reaction pathways toward the efficient utilization of sugar-based feedstocks.

Deep eutectic solvent assisted fabrication of zirconium phytate thin nanosheets for important biomass transformations

Utilization of naturally occurring resources to construct functional catalytic materials is significantly important, and facile and environmental-benign strategies are highly desired to afford the materials having a specific structure and good catalytic activity. Herein, we reported an innovative deep eutectic solvent (DES)-assisted strategy to synthesize zirconium phytate with a thin nanosheet structure (denoted as Zr-Phy-DES) using plant-originated phytic acid (PhyA) as the renewable building block. This strategy was eco-friendly and adjustable owing to the designability of DESs. The Zr-Phy-DES as an acidic catalyst showed high activity on two important biomass transformations, i.e., dehydration of carbohydrates and Meerwein-Ponndorf-Verley reduction of ethyl levulinate. Interestingly, Zr-Phy-DES showed higher catalytic performance than the zirconium phytates prepared in ethylene glycol and N,N-dimethylformamide, confirming the advantage of DESs for preparing functional materials. Notably, the unique feature of this proposed strategy is that renewable catalysts are prepared in an environmental-benign solvent for efficiently catalyzing biomass transformation.

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An eco-friendly strategy for preparing catalytic materials with a specific structure

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The catalytic activity of the prepared materials varied with the type of solvents

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The material prepared in deep eutectic solvent showed better performance

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Catalytic materials from natural resources and green solvents to convert biomass

5-Hydroxymethylfurfural Oxidation to 2,5-Furandicarboxylic Acid on Noble Metal-Free Nanocrystalline Mixed Oxide Catalysts

Noble metal-free catalysts based on earth-abundant and inexpensive mixed oxides are active catalysts of all steps of the reaction cascade leading from 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) using tert-butyl hydroperoxide (TBHP) as oxidation agent. Catalysts covering the whole range of composition in the Cu-Mn and Co-Fe series have been prepared and characterised. The nature and composition of the catalyst strongly affect conversion and selectivity. The distribution of products indicates that radical-type oxygen species, deriving from the activation of TBHP, play a determining role in the reaction. The early steps of reaction mainly follow the pattern expected for heterogeneous Fenton catalysts. Mixed oxide catalysts are the most effective in further oxidation steps, leading to the formation of FDCA, both in the Cu-Mn and Co-Fe systems. This behaviour can be related to the distribution of charge in the mixed oxides, suggesting a possible implication of the lattice oxygen in the last reaction steps. The results provide indications on how to optimize the reaction and minimize the formation of byproducts (humins and oligomers).

Selective Oxidation of Furfural at Room Temperature on a TiO2-Supported Ag Catalyst

The catalytic performance of the Ag/TiO2 catalyst was evaluated in the oxidation of furfural (FF) to furoic acid (FA) in an alkaline aqueous solution under 15 bar of air in a batch reactor. The catalytic activity, yield, and stability of the catalyst were compared as a function of different reaction parameters including temperature (25–110 °C), nature of the atmosphere, base equivalent (nbase/nFF = 0.25–3), and nature of the inorganic bases used (NaOH, NaHCO3, and Na2CO3). Under optimum conditions, the yield of FA (96%) was achieved at room temperature, with an excellent carbon balance (>98%). The recyclability of the catalyst was also studied and the catalytic activity of the Ag/TiO2 catalyst slightly declined due to an increase in particle size as confirmed by TEM studies.

Hierarchical Pores-Confined Ultrasmall Cu Nanoparticles for Efficient Oxidation of 5-Hydroxymethylfurfural

Pyrolysis is one of the most widely utilized protocols for the preparation of nanoconfined metal species for heterogeneous catalysis, but it still suffers from the uncontrollable composition evolution process with undesired metal sintering and porous structure collapse. Herein, a novel and versatile molten salt-assisted pyrolysis strategy was demonstrated for the preparation of ultrasmall transition-metal nanoparticles embedded in hollow hierarchical carbon skeletons. The preparation only involved the fabrication of metal-organic framework templates and subsequent pyrolysis with the addition of KCl-KBr molten salt, which played a crucial role in pore size extending and metal sintering inhibiting. Benefitting from the encapsulation effect, the as-synthesized Cu@HHC materials exhibited remarkable catalytic performance and recycling stability in the selective oxidation of biomass-derived 5-hydroxymethylfurfural into 2,5-diformylfuran under mild reaction conditions.

Tuning the Selectivity of the Hydrogenation/Hydrogenolysis of 5-Hydroxymethylfurfural under Batch Multiphase and Continuous-Flow Conditions

The hydrogenation/hydrogenolysis of 5-hydroxymethylfurfural (HMF) has been carried out either under single (aqueous) phase or batch multiphase (MP) conditions using mutually immiscible aqueous/hydrocarbon phases, 5 % Ru/C as a catalyst, and both with and without the use of trioctylmethyl phosphonium bis-(trifluoro methane) sulfonimide ([P₈₈₈₁ ][NTf₂ ]) as an ionic liquid (IL). Alternatively, the hydrogenation of HMF was explored in the continuous-flow (CF) mode with the same catalyst. By changing reaction parameters, experiments were optimized towards the formation of three products: 2,5-bis(hydroxy methyl)furan (BHMF), 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF), and 1-hydroxyhexane-2,5-dione (HHD), which were obtained in up to 92, 90, and 99 % selectivity, respectively, at quantitative conversion. In particular, the single (aqueous) phase reaction of HMF (0.2 m) carried out for 18 h at 60 °C under 30 bar of H₂ , allowed the exclusive synthesis of BHMF from the partial (carbonyl) hydrogenation of HMF, while the MP reaction run at a higher T and p (100 °C and 50 bar) proved excellent to achieve only HHD derived from a sequence of hydrogenation/hydrogenolysis. It is worth noting that under MP conditions, the catalyst was perfectly segregated in the IL, where it could be recycled without any leaching in the aqueous/hydrocarbon phases. Finally, the hydrogenation of HMF was explored in a H-Cube® flow reactor in the presence of different solvents, such as ethyl acetate, tetrahydrofuran, and ethanol. At 100 °C, 50 bar H₂ , and a flow rate of 0.1 mL min^-1 , the process was optimized towards the formation of the full hydrogenation product BHMTHF. Ethyl acetate proved the best solvent.

Facile Production of 2,5-Furandicarboxylic Acid via Oxidation of Industrially Sourced Crude 5-Hydroxymethylfurfural

The oxidation of 5-hydroxymethylfurfural (HMF) produces value-added chemicals such as 2,5-diformylfuran (DFF) and 2,5-furandicarboxylic acid (FDCA). In this work, FDCA production was achieved by oxidation of crude HMF solution containing around 45 % HMF and unwanted byproducts such as 5,5'-[oxy-bis(methylene)]bis-2-furfural (HMF dimer) and polymers. At optimized reaction conditions similar to the Mid-Century process, homogeneous oxidation of the crude HMF (up to 20 wt% in the feed) by Co/Mn/Br catalyst in acetic acid solution produced FDCA at >95 % yield. The solid FDCA product contained <4000 ppm 5-formyl-2-furancarboxylic acid (FFCA). Such high yields were observed because the impurities in crude HMF were also converted to FDCA, as confirmed by the facile oxidation of HMF dimer to FDCA under reaction conditions. The successful demonstration of crude HMF as feed, obviating the need for HMF purification, suggests potential for cost-effectively producing FDCA in existing terephthalic plants.

Recent Advances in Reductive Upgrading of 5-Hydroxymethylfurfural via Heterogeneous Thermocatalysis

The catalytic conversion of 5-hydroxymethylfufural (HMF), one of the vital platform chemicals in biomass upgrading, holds great promise for producing highly valuable chemicals through sustainable routes, thereby alleviating the dependence on fossil feedstocks and reducing CO₂ emissions. The reductive upgrading (hydrogenation, hydrogenolysis, ring-opening, ring-rearrangement, amination, etc.) of HMF has exhibited great potential to produce monomers, liquid fuel additives, and other valuable chemicals. Thermocatalytic conversion has a significant advantage over photocatalysis and electrocatalysis in productivity. In this Review, the recent achievements of thermo-reductive transformation of HMF to various chemicals using heterogeneous catalytic systems are presented, including the catalytic systems (catalyst and solvent), reaction conditions, (reaction temperature, pressure, etc.), and reaction mechanisms. The current challenges and future opportunities are discussed as well, aiming at guiding the catalyst design and practical scalable productions.

Advances of Ionic Liquids and Deep Eutectic Solvents in Green Processes of Biomass-Derived 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) is identified as an important bio-based platform chemical to bridge petroleum-based and biomass-based resources. It can be obtained through dehydration of various carbohydrates as well as converted to value-added fuels and chemicals. As designer solvents, ionic liquids (ILs) and deep eutectic solvents (DESs) have been widely used in catalytic transformation of biomass derivatives to various chemicals. This Review summarizes recent progress in experimental and theoretical studies on dehydration of carbohydrates such as fructose, glucose, sucrose, cellobiose, chitosan, cellulose, inulin, and even raw biomass to generate HMF using ILs and DESs as catalysts/cocatalysts and/or solvents/cosolvents. It also gives an overview of IL and DES-involved catalytic transformation of HMF to downstream products via oxidation, reduction, esterification, decarboxylation, and so forth. Challenges and prospects of ILs and DESs are also proposed for further production of HMF and HMF derivatives from biomass in green and sustainable processes.

Insights into the Electrochemical Reduction of 5-Hydroxymethylfurfural at High Current Densities

The electrocatalytic reduction of 5-hydroxymethylfurfural (HMF) is highly selective to 2,5-bishydroxymethylfuran (BHMF) at pH=9.2, diluted HMF solutions, and low current densities. In this work, the electrochemical reduction of 0.05 m HMF solutions was investigated in the 5-50 mA cm^-2 current density range over an AgCu foam electrocatalyst. The selectivity towards the formation of BHMF or the dimerization depended on the current density, likely due to differences in the electrode potential, and on the reaction time. Operating at current densities of 40-50 mA cm^-2 allowed to find a trade-off between HMF and H₂ O activation, achieving 85 % BHMF selectivity and fostering the productivity (0.567 mmol cm^-2  h^-1 ), though co-producing H₂ . The electrochemical characterization by Tafel slopes and electrochemical impedance spectroscopy indicated that the HMF reduction was kinetically favored in comparison to the hydrogen evolution reaction and that the process was limited by charge transfer.

Integrated Cascade Process for the Catalytic Conversion of 5-Hydroxymethylfurfural to Furanic and TetrahydrofuranicDiethers as Potential Biofuels

The depletion of fossil resources is driving the research towards alternative renewable ones. Under this perspective, 5-hydroxymethylfurfural (HMF) represents a key molecule deriving from biomass characterized by remarkable potential as platform chemical. In this work, for the first time, the hydrogenation of HMF in ethanol was selectively addressed towards 2,5-bis(hydroxymethyl)furan (BHMF) or 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) by properly tuning the reaction conditions in the presence of the same commercial catalyst (Ru/C), reaching the highest yields of 80 and 93 mol%, respectively. These diols represent not only interesting monomers but strategic precursors for two scarcely investigated ethoxylated biofuels, 2,5-bis(ethoxymethyl)furan (BEMF) and 2,5-bis(ethoxymethyl)tetrahydrofuran (BEMTHF). Therefore, the etherification with ethanol of pure BHMF and BHMTHF and of crude BHMF, as obtained from hydrogenation step, substrates scarcely investigated in the literature, was performed with several commercial heterogeneous acid catalysts. Among them, the zeolite HZSM-5 (Si/Al=25) was the most promising system, achieving the highest BEMF yield of 74 mol%. In particular, for the first time, the synthesis of the fully hydrogenated diether BEMTHF was thoroughly studied, and a novel cascade process for the tailored conversion of HMF to the diethyl ethers BEMF and BEMTHF was proposed.

Electro- and Photocatalytic Oxidative Upgrading of Bio-based 5-Hydroxymethylfurfural

Conversion of biomass into biofuels and high value-added chemicals is a promising strategy to solve the increasingly deteriorating environmental problems caused by fossil energy consumption. The development of efficient technologies and methods is the premise and guarantee to realize the high-value conversion of biomass. 5-Hydroxymethylfurfural (HMF), as a versatile biomass platform compound, is generated via dehydration of hexoses (e. g., fructose and glucose) derived from cellulosic biomass. This Review gives an overview of the advances and challenges of electro- and photocatalytic oxidation of biomass-derived HMF to high-value chemicals such as 2,5-formylfuran (DFF) and 2,5-furandicarboxylic acid (FDCA). These strategies and methods for the preparation of high-value chemicals by electro- and photocatalytic oxidation of HMF, coupled with, for example, hydrogen evolution reaction, organic substrate reduction, CO₂ reduction reaction, or N₂ reduction reaction, were summarized and discussed. Moreover, the catalytic efficiency and mechanism of different types of catalysts were also introduced in these conversion systems.

Thermal Hydroquinone Oxidation on Co/N-doped Carbon Proceeds by a Band-Mediated Electrochemical Mechanism

Molecular metal complexes catalyze aerobic oxidation reactions via redox cycling at the metal center to effect sequential activation of O₂ and the substrate. Metal surfaces can catalyze the same transformations by coupling independent half-reactions for oxygen reduction and substrate oxidation mediated via the exchange of band-electrons. Metal- and nitrogen-doped carbons (MNCs) are promising catalysts for aerobic oxidation that consist of molecule-like active sites embedded in conductive carbon hosts. Owing to their combined molecular and metallic features, it remains unclear whether they catalyze aerobic oxidation via the sequential redox cycling pathways of molecules or band-mediated pathways of metals. Herein, we simultaneously track the potential of the catalyst and the rate of turnover of aerobic hydroquinone oxidation on a cobalt-based MNC catalyst in contact with a carbon electrode. By comparing operando measurements of rate and potential with the current-voltage behavior of each constituent half-reaction under identical conditions, we show that these molecular materials can display the band-mediated reaction mechanisms of extended metallic solids. We show that the action of these band-mediated mechanisms explains the fractional reaction orders in both oxygen and hydroquinone, the time evolution of catalyst potential and rate, and the dependence of rate on the overall reaction free energy. Selective poisoning experiments suggest that oxygen reduction proceeds at cobalt sites, whereas hydroquinone oxidation proceeds at native carbon-oxide defects on the MNC catalyst. These findings highlight that molecule-like active sites can take advantage of band-mediated mechanisms when coupled to conductive hosts.

Recent progress in direct production of furfural from lignocellulosic residues and hemicellulose

Furfural is a vital biomass-derived platform molecule, which can be used to synthesize a wide range of value-added chemicals. Furfural and its derivatives are promising alternatives to conventional petroleum chemicals. However, recent industrial production of furfural existed some thorny problems, including low efficiency, energy waste, and environmental pollution. Therefore, tremendous and continuous efforts have been made by researchers to develop novel furfural production processes with high economic viability, production efficiency, and sustainability. This review summarized the merits and shortcomings of disparate catalytic systems for the synthesis of furfural from biomass and biomass pretreatment hydrolysate on the basis of recently published literature. Furthermore, the suggestions for furfural production research were put forward.

Efficient Electrooxidation of 5-Hydroxymethylfurfural Using Co-Doped Ni3 S2 Catalyst: Promising for H2 Production under Industrial-Level Current Density

Replacing oxygen evolution reaction (OER) by electrooxidations of organic compounds has been considered as a promising approach to enhance the energy conversion efficiency of the electrolytic water splitting proces. Developing efficient electrocatalysts with low potentials and high current densities is crucial for the large-scale productions of H2 and other value-added chemicals. Herein, non-noble metal electrocatalysts Co-doped Ni3 S2 self-supported on a Ni foam (NF) substrate are prepared and used as catalysts for 5-hydroxymethylfurfural (HMF) oxidation reaction (HMFOR) under alkaline aqueous conditions. For HMFOR, the Co0.4 NiS@NF electode achieves an extremely low onset potential of 0.9 V versus reversible hydrogen electrode (RHE) and records a large current density of 497 mA cm-2 at 1.45 V versus RHE for HMFOR. During the HMFOR-assisted H2 production, the yield rates of 2,5-furandicarboxylic acid (FDCA) and H2 in a 10 mL electrolyte containing 10 × 10-3 M HMF are 330.4 µmol cm-2 h-1 and 1000 µmol cm-2 h-1 , respectively. The Co0.4 NiS@NF electrocatalyst displays a good cycling durability toward HMFOR and can be used for the electrooxidation of other biomass-derived chemicals. The findings present a facile route based on heteroatom doping to fabricate high-performance catalyses that can facilitate the industrial-level H2 production by coupling the conventional HER cathodic processes with HMFOR.

Subnanometric Cu clusters on atomically Fe-doped MoO2 for furfural upgrading to aviation biofuels

Single cluster catalysts (SCCs) are considered as versatile boosters in heterogeneous catalysis due to their modifiable single cluster sites and supports. In this work, we report subnanometric Cu clusters dispersed on Fe-doped MoO₂ support for biomass-derived furfural upgrading. Systematical characterizations suggest uniform Cu clusters (composing four Cu atoms in average) are homogeneously immobilized on the atomically Fe-doped ultrafine MoO₂ nanocrystals (Cu₄/Fe_0.3Mo_0.7O₂@C). The atomic doping of Fe into MoO₂ leads to significantly modified electronic structure and consequently charge redistribution inside the supported Cu clusters. The as-prepared Cu₄/Fe_0.3Mo_0.7O₂@C shows superior catalytic performance in the oxidative coupling of furfural with C₃~C₁₀ primary/secondary alcohols to produce C₈~C₁₅ aldehydes/ketones (aviation biofuel intermediates), outperforming the conventionally prepared counterparts. DFT calculations and control experiments are further carried out to interpret the structural and compositional merits of Cu₄/Fe_0.3Mo_0.7O₂@C in the oxidative coupling reaction, and elucidate the reaction pathway and related intermediates.

Sustainable Approaches to Selective Conversion of Cellulose Into 5-Hydroxymethylfurfural Promoted by Heterogeneous Acid Catalysts: A Review

5-Hydroxymethylfurfural (5-HMF) as a triply catalytic product is a value-added refining chemical in industry production. 5-HMF as biomass feedstock enables to be transformed into other high-value industrial compounds, such as 2,5-furandicarboxylic acid (FDCA), 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), 5-formyl-2-furancarboxylic acid (FFCA), 2,5-diformylfuran (DFF), 2,5-bis(aminomethyl)furan (BAMF), and 2,5-dimethylfuran (DMF). Hence, catalytic conversion of biomass into 5-HMF has been given much more attention by chemists. In this review, some latest studies about the conversion of cellulose to 5-HMF have been introduced systematically. Solid acids such as heterogeneous catalysts have been widely applied in the conversion of cellulose into 5-HMF. Therefore, some novel solid acids with Brønsted and/or Lewis acidic sites, such as sulfonated solid acids, carbon-based acids, and zeolite particles employed for biomass conversions are listed.

Preparation of 5-hydroxymethylfurfural using magnetic Fe3O4@SiO2@mSiO2-TaOPO4 catalyst in 2-pentanol

5-Hydroxymethylfurfural (HMF) is one of the most important platform molecules and could be transformed into a variety of fuel additives and high value-added chemicals. Multiple catalyst systems have been developed for the conversion of carbohydrates to HMF, but there are still unavoidable problems, including high temperature and pressure, difficult recovery of solvent, corrosion of equipment, poor catalyst circulation, etc. Herein, a new magnetic Fe3O4@SiO2@mSiO2-TaOPO4 catalyst for the preparation of HMF from fructose in 2-pentanol was developed. The structures of the catalysts were characterized by FT-IR, TSM, EDS, SEM, XRD and VSM. The 2-pentanol solvent is not only conducive to the production of HMF, but also enables the reaction to be carried out at a lower pressure. The highest yield of HMF (85.4%) was obtained using 20 wt% catalyst under 10% substrate concentration (0.5 g of fructose) at 120 °C for 3 h. The catalysts can be easily separated by magnetism. The slight decrease in catalyst activity after 7 cycles was mainly due to the loss of catalyst during the cycle operation. Simultaneously, the total yield of HMF was 51.3% after scale-up to 15 g of fructose, showing the possible industrial application potential of this catalyst system.

Fabrication of Brønsted acidic ionic liquids functionalized organosilica nanospheres for microwave-assisted fructose valorization

A series of Brønsted acidic ionic liquids (BAILs) functionalized hollow organosilica nanospheres ([C_3/4Im][OTs/OTf]-Si(Et)Si, C_3/4 = Pr/BuSO₃H) were synthesized by two steps. The process involved the preparation of hollow nanosphere supports via a toluene-swollen sol-gel co-condensation of 1,2-bis(trimethoxysilyl)ethane and 3-chloropropyltriethoxysilane in the presence of F127, and followed by a successive quaternary ammonization and protonation with imidazole, 1,3-propane/1,4-butane sultone and trifluoromethane sulfonic acid/p-toluenesulfonic acid. The adjustable acid property, hollow inner diameter (5-15 nm) and shell thickness (5-9 nm) of [C_3/4Im][OTs/OTf]-Si(Et)Si are achieved by introducing different organic acids and controlling toluene concentration, respectively. The [C_3/4Im][OTs/OTf]-Si(Et)Si were applied in selective conversion of fructose to 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF) under microwave heating. Under the optimized conditions, the [C₄Im][OTs]-Si(Et)Si3.0 nanospheres with the largest inner diameter and the smallest shell thickness exhibit the highest HMF yield (79.4%, 15 min) in fructose dehydration. And the [C₃Im][OTf]-Si(Et)Si0.5 nanospheres with the highest acid strength possess the highest EMF yield (70.4%, 30 min) in fructose ethanolysis. The high Brønsted acid-site density and acid strength of [C_3/4Im][OTs/OTf]-Si(Et)Si catalysts accompanied by high microwave heating energy lead to excellent dehydration/ethanolysis activity. The product selectivity strongly depended on the BAILs structures and morphological characteristics of the catalyst. More importantly, the [C_3/4Im][OTs/OTf]-Si(Et)Si can be reused three times without changes in leaching of BAILs, due to strong covalent bond between BAILs and silicon/carbon framework. This work will provide a simple strategy of chemically bonded BAILs on suitable supports as efficient solid acids, and an approach of combining morphology-controlled solid acids with microwave-heating for catalytic conversion of biomass/derivatives to fuels and value-added chemicals.

Boosting the electro-oxidation of 5-hydroxymethyl-furfural on a Co-CoS x heterojunction by intensified spin polarization

The conversion of biomass-derived platform molecules (e.g., 5-hydroxymethyl furfural (HMF)) represents a sustainable route to produce value-added chemicals. Here we report the fabrication of an N-doped carbon nanotube assembled yolk-shell polyhedron with embedded Co-CoS x nanoparticles (NPs) (Y-Co-CoS x @CN) for efficient HMF electrooxidation. DFT calculations demonstrate that the formation of the heterojunction could intensify spin polarization in Co-CoS2, thus achieving effective d-p coupling between the catalyst and reactant/intermediate. As expected, Y-Co-CoS x @CN exhibits excellent HMF electro-oxidation activity at a low applied potential of 1.29 V vs. RHE at 10 mA cm-2 in 0.1 M KOH with 5 mM HMF, affording an FDCA yield of 96% and FE of 93.5%. This work not only sheds light on the catalytic nature of the heterojunction and the underlying mechanisms for the enhancement of HMF electro-oxidation activity, but would also provide a descriptor for the rational design of advanced electro-catalysts.

Use of heterogeneous catalysis in sustainable biofuel production

Biofuel is a sustainable energy source that may use to replace fossil-based carbon dioxide and mitigate the adverse effects of exhaust emissions. Nowadays, we need to replace petroleum fuels with alternatives from environmentally sustainable sources of increasing importance. Biofuels derived from biomass have gained considerable attention, and thus most of the traditional methods that harm the environment and humans have retreated. Developing an active and stable heterogeneous catalyst is a step of utmost importance in the renewable liquid fuel technology. Thus, there is a great interest in developing methods for producing liquid fuels from non-edible sources. It may also be from dry plant tissues such as agricultural waste. Lignocellulosic biomass can be a sustainable source for producing renewable fuels and chemicals, as well as the replacement of petroleum products. Hence, the researchers aspired to synthesize new catalysts using a cheap technology developed to hydrolyze cellulose and then produce bioethanol without needing expensive enzymes, which may ultimately lead to a lower fuel price. In this paper, we will focus on the recent technologies used to produce sustainable biofuels through inexpensive incentives and innocuous to the environment.