Catalytic Conversion of Carbohydrates to Initial Platform Chemicals: Chemistry and Sustainability

Simultaneous Coproduction of Xylonic Acid and Xylitol: Leveraging In Situ Hydrogen Generation and Utilization from Xylose

Pentose oxidation and reduction, processes yielding value-added sugar-derived acids and alcohols, typically involve separate procedures necessitating distinct reaction conditions. In this study, a novel one-pot reaction for the concurrent production of xylonic acid and xylitol from xylose is proposed. This reaction was executed at ambient temperature in the presence of a base, eliminating the need for external gases, by leveraging Pt-supported catalysts. Initial experiments using commercially available metal-supported carbon catalysts validated the superior activity of Pt. However, a notable decline in recycling performance was observed in Pt/C, which is attributed to the sintering of Pt nanoparticles. In contrast, the synthesized Pt-supported ZrO2 catalysts exhibited enhanced recycling performance because of the strong metal-support interaction between Pt and the ZrO2 support. Furthermore, mechanistic insights and density functional theory calculations show that product desorption involves a significantly higher energy barrier compared to substrate adsorption and hydrogenation, highlighting an efficient transfer hydrogenation mechanism leading to equivalent yields of both xylonic acid and xylitol. This study introduces a promising approach for the simultaneous production of sugar-derived acids and alcohols, with implications for sustainable catalysis and process optimization.

Model-Assisted Optimization of Xylose, Arabinose, Glucose, Mannose, Galactose and Real Hemicellulose Streams Dehydration To (Hydroxymethyl)Furfural and Levulinic Acid

Conversion of hemicellulose streams and the constituent monosaccharides, xylose, arabinose, glucose, mannose, and galactose, was conducted to produce value-added chemicals, including furfural, hydroxymethylfurfural (HMF), levulinic acid and anhydrosugars. The study aimed at developing a kinetic model relevant for direct post-Organosolv hemicellulose conversion. Monosaccharides served as a tool to in detail describe the kinetic behavior and segregate contribution of hydrothermal decomposition and acid catalyzed dehydration at the temperature range of 120-190 °C. Catalyst free aqueous media demonstrated enhanced formation of furanics, while elevated temperatures led to significant saccharide isomerization. The introduction of sulfuric and formic acids maximized furfural yield and significantly reduced HMF concentration by facilitating its rehydration into levulinic acid (46 mol%). Formic acid additionally substantially enhanced formation of anhydrosaccharides. An excellent correlation between modeled and experimental data enabled process optimization to maximize furanic yield in two distinct hemicellulose streams. Sulfuric acid-containing hemicellulose stream achieved the highest furfural yield after 30 minutes at 238 °C, primarily due to the high Ea for pentose dehydration (150-160 kJ mol-1). Contrarily, formic acid-containing hemicellulose stream enabled maximal furfural yield at more moderate temperature and extended reaction time due to its lower Ea for the same reaction step (115-125 kJ mol-1).

Carbon-carbon bond formation using aromatics from biomass

The transition to a circular economy requires that we adapt currently used chemical processes to the structurally diverse and often highly oxygenated precursors that are accessible from biomass. In this review, we highlight different examples of carbon-carbon bond formation using aromatics derived from bio-based sources, reported during 2015-2024. Examples of sustainable biomass building blocks include heterocycles such as furfural and hydroxymethylfurfural, obtained from carbohydrates, as well as lignin-based aromatics such as vanillin and eugenol. These have subsequently been applied in a variety of different types of carbon-carbon bond formation, including more classical methods such as aldol condensation and Morita-Baylis-Hillman reactions, but also employing transition metal catalysis, electrochemistry or photochemistry to create new C-C bonds.

Phase transition induced hydrogen activation for enhanced furfural reductive amination over a CoCu bimetallic catalyst

The synthesis of primary amines from renewable biomass and its derivatives through reductive amination has garnered significant attention. How to construct efficient non-noble-metal catalysts that enable low-temperature catalysis still remains challenging. Herein, we report a Cu-doped Co@CoO x heterostructure catalyst that features structural Co-CoCuO x bifunctional sites, which enable room temperature reductive amination of various aldehydes with 1.57-45 times higher efficiency than Co@CoO x , outperforming many reported non-noble and even noble metal catalysts. Experiments and DFT calculations indicate that Cu doping leads to a phase transition of Co from hcp to fcc, while electrons are transferred from Cu to Co, forming a dual active site with electron-rich Co closely interacting with CoCuO x . These electron-rich Co sites demonstrate excellent activity in the activation and dissociation of hydrogen, while the CuO x component facilitates hydrogen spillover at the CoCuO x interface, thus resulting in a highly efficient cooperative effect for the furfural (FAL) reductive amination. This work provides general guidance for the rational design of high-performance reductive amination catalysts for biomass upgrading.

Conversion of Sugars to Lactic Acid using Homogeneous Niobium-Substituted Polyoxometalate Catalysts

The catalytic conversion of biomass into high-value chemicals is an increasing field of research. This study uniquely investigates the use of various Keggin-type heteropoly salts (HPS) for the chemical conversion of sugars into lactic acid under mild conditions of 160 °C and 20 bar N2. In the first phase, Nb- and V-substituted HPSs were employed to synthesize lactic acid from dihydroxyacetone, an intermediate in the conversion of sugars to lactic acid. Results indicated that increasing the Nb content within the Keggin structure enhances the yield of lactic acid while reducing the formation of the byproduct acetaldehyde. A correlation was established between the redox activity of the HPS and the catalytic performance. The most active catalyst, Na5[PNb2Mo10O40], (NaNb2) achieved a lactic acid yield of 20.9 % after 1 h of reaction. In the second phase of the study, NaNb2 was applied for the conversion of different sugars including glucose, fructose, mannose, sucrose, xylose, and cellobiose. It was demonstrated that the catalyst remains active for complex hexoses, achieving lactic acid yields of up to 12 %. Post-mortem analysis using infrared (IR) and Raman spectroscopy, nuclear magnetic resonance (NMR), and inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed the stability of NaNb2.

Photochemical reactions of biomass derived platform chemicals

Platform chemicals obtained from biomass will play an important role in chemical industry. Already existing compounds or not yet established chemicals are produced from this renewable feedstock. Using photochemical reactions as sustainable method for the conversion of matter furthermore permits to develop processes that are interesting from the ecological and economical point of view. Furans or levoglucosenone are thus obtained from carbohydrate containing biomass. Photochemical rearrangements, photooxygenation reactions or photocatalytic radical reactions can be carried out with such compounds. Also, sugars such pentoses or hexoses can be more easily transformed into heterocyclic target compounds when such photochemical reactions are used. Lignin is an important source for aromatic compounds such as vanillin. Photocycloaddition of these compounds with alkenes or the use light supported multicomponent reactions yield interesting target molecules. Dyes, surfactants or compounds possessing a high degree of molecular diversity and complexity have been synthesized with photochemical key steps. Alkenes as platform chemicals are also produced by fermentation processes, for example, with cyanobacteria using biological photosynthesis. Such alkenes as well as terpenes may further be transformed in photochemical reactions yielding, for example, precursors of jet fuels.

The Formation of γ-Valerolactone from Renewable Levulinic Acid over Ni-Cu Fly Ash Zeolite Catalysts

Zeolites with different structures (P1, sodalite, and X) were synthesized from coal fly ash by applying ultrasonically assisted hydrothermal and fusion-hydrothermal synthesis. Bimetallic catalysts, containing 5 wt.% Ni and 2.5 wt.% Cu, supported on the zeolites, were prepared by a post-synthesis incipient wetness impregnation method. The catalysts were characterized by X-ray powder diffraction (XRPD), N2 physisorption, transmission electron microscopy (TEM), Mössbauer and X-ray photoelectron spectroscopies (XPS), and H2-temperature-programmed reduction (H2-TPR) analyses. The XRPD results showed that crystalline Cu0 and NixCuy intermetallic nanoparticles were formed in the reduced catalysts. The presence of the intermetallic phase affected the reducibility of the nickel by shifting it to a lower temperature, as confirmed by the H2-TPR curves. Based on the Mössbauer spectroscopic results, it was established that the iron contamination of the coal fly ash zeolites (CFAZs) was distributed in ionic positions of the zeolite lattice and as a finely dispersed iron oxide phase on the external surface of the supports. The formation of the NiFe alloy, not detectable by XRPD, was also evidenced on the impregnated samples. The catalysts were studied in the upgrading of levulinic acid (LA), derived from lignocellulosic biomass, to γ-valerolactone (GVL), in a batch reactor under 30 bar H2 pressure at 150 and 200 °C, applying water as a solvent. The NiCu/SOD and NiCu/X catalysts showed total LA conversion and a high GVL yield (>75%) at a reaction temperature of 200 °C. It was found that the textural parameters of the catalysts have less influence on the catalytic activity, but rather the stable dispersion of metals during the reaction. The characterization of the spent catalyst found the rearrangement of the support structure. The high LA conversion and GVL yield can be attributed to the weak acidic character of the support and the moderate hydrogenation activity of the Ni-Cu sites with high dispersion.

One-Pot Catalytic Cascade for the Depolymerization of the Lignin β-O-4 Motif to Non-phenolic Dealkylated Aromatics

Aromatic monomers obtained by selective depolymerization of the lignin β-O-4 motif are typically phenolic and contain (oxygenated) alkyl substitutions. This work reveals the potential of a one-pot catalytic lignin β-O-4 depolymerization cascade strategy that yields a uniform set of methoxylated aromatics without alkyl side-chains. This cascade consists of the selective acceptorless dehydrogenation of the γ-hydroxy group, a subsequent retro-aldol reaction that cleaves the Cα-Cβ bond, followed by in situ acceptorless decarbonylation of the formed aldehydes. This three-step cascade reaction, catalyzed by an iridium(I)-BINAP complex, resulted in 75 % selectivity for 1,2-dimethoxybenzene from G-type lignin dimers, alongside syngas (CO : H2≈1.4 : 1). Applying this method to a synthetic G-type polymer, 11 wt % 1,2-dimethoxybenzene was obtained. This versatile compound can be easily transformed into 3,4-dimethoxyphenol, a valuable precursor for pharmaceutical synthesis, through an enzymatic catalytic approach. Moreover, the hydrodeoxygenation potential of 1,2-dimethoxybenzene offers a pathway to produce valuable cyclohexane or benzene derivatives, presenting enticing opportunities for sustainable chemical transformations without the necessity for phenolic mixture upgrading via dealkylation.

Carbon chain elongation characterizations of electrode-biofilm microbes in electro-fermentation

The higher efficiency of electro-fermentation in synthesizing medium-chain fatty acids (MCFAs) compared to traditional fermentation has been acknowledged. However, the functional mechanisms of electrode-biofilm enhancing MCFAs synthesis remain research gaps. To address this, this study proposed a continuous flow electrode-biofilm reactor for chain elongation (CE). After 225 days of operation, stable electrode-biofilms formed and notably improved caproate yield by more than 38 %. The electrode-biofilm was enriched with more CE microorganisms and electroactive bacteria compared to the suspended sludge microorganisms, including Caproicibacterium, Oscillibacter and Pseudoramibacter. Besides, the upregulated CE pathways were evaluated by metagenomic analysis, and the results indicated that the pathways such as acetyl-CoA and malonyl-[acp] formation, reverse beta-oxidation, and fatty acid biosynthesis pathway were all markedly enhanced in cathodic biofilm, more than anodic biofilm and suspended microorganisms. Moreover, microbial community regulated processes like bacterial chemotaxis, flagellar assembly and quorum sensing, crucial for electrode-biofilm formation. Electron transfer, energy metabolism, and microbial interactions were found to be prominently upregulated in the cathodic biofilm, surpassing levels observed in anodic biofilm and suspended sludge microorganisms, which further enhanced CE efficiency. In addition, the statistical analyses further highlighted key microbial functions and interactions within the cathodic biofilm. Oscillospiraceae_bacterium was identified to be the most active microbe, alongside pivotal roles played by Caproiciproducens_sp._NJN-50, Clostridiales_bacterium, Prevotella_sp. and Pseudoclavibacter_caeni. Eventually, the proposed microbial collaboration mechanisms of cathodic biofilm were ascertained. Overall, this study uncovered the biological effects of the electrode-biofilm on MCFAs electrosynthesis, thereby advancing biochemicals production and filling the knowledge gaps in CE electroactive biofilm reactors.

Advancing Lignocellulosic Biomass Fractionation through Molten Salt Hydrates: Catalyst-Enhanced Pretreatment for Sustainable Biorefineries

Developing a process that performs the lignocellulosic biomass fractionation under milder conditions simultaneously with the depolymerization and/or the upgrading of all fractions is fundamental for the economic viability of future lignin-first biorefineries. The molten salt hydrates (MSH) with homogeneous or heterogeneous catalysts are a potential alternative to biomass pretreatment that promotes cellulose's dissolution and its conversion to different platform molecules while keeping the lignin reactivity. This review investigates the fractionation of lignocellulosic biomass using MSH to produce chemicals and fuels. First, the MSH properties and applications are discussed. In particular, the use of MSH in cellulose dissolution and hydrolysis for producing high-value chemicals and fuels is presented. Then, the biomass treatment with MSH is discussed. Different strategies for preventing sugar degradation, such as biphasic media, adsorbents, and precipitation, are contrasted. The potential for valorizing isolated lignin from the pretreatment with MSH is debated. Finally, challenges and limitations in utilizing MSH for biomass valorization are discussed, and future developments are presented.

Nickel-Catalyzed α-selective Hydroalkylation of Vinylarenes

C(sp3) centers adjacent to (hetero) aryl groups are widely present in physiologically active molecules. Metal-hydride-catalyzed hydroalkylation of alkenes represents an efficient means of forging C(sp3)-C(sp3) bonds, boasting advantages as a wide source of substrates, mild reaction conditions, and facile selectivity manipulation. Nevertheless, the hydroalkylation of vinylarenes encounters constraints in terms of substrate scope, necessitating the employment of activated alkyl halides or alkenes containing chelating groups, remains a challenge. In this context, we report a general nickel-hydride-catalyzed hydroalkylation protocol for vinylarenes. Remarkably, this system enables α-selective hydroalkylation of both aryl and heteroaryl alkenes under an extra ligand-free condition, demonstrating excellent coupling efficiency and selectivity. Furthermore, through the incorporation of chiral bisoxazoline ligands, we have achieved regio- and enantioselective hydroalkylation of vinylpyrroles, thereby facilitating the synthesis of α-branched alkylated pyrrole derivatives.

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.

Statistically driven automated method for catalytic glucose conversion optimisation

A statistically driven, automated approach to optimize glucose transformations to platform chemicals, methyl lactate and levulinic acid, is reported. The combination of a robotic synthesis platform with design of experiments methods enabled efficient and precise modelling of glucose conversion catalysed by SnCl4·5H2O with 0-100% H2O and methanol as a cosolvent. Using this strategy, optimal reaction conditions within the available reaction space were identified in 58 runs, showcasing the excellent efficiency of this method in producing high yields of methyl lactate (75.9%) and levulinic acid (64.5%) in independent reactions via distinct retro-aldol condensation and dehydration pathways, respectively.

Gluconic Acid Production by Using Recombinant Escherichia coli Waksman pqq+ Cells with a Novel Approach from Biomass Sources

Gluconic acid (GA) is widely used in the pharmaceutical, food, detergent, textile, leather, and concrete industries. However, cost-effective and high-yield production of GA remains a challenge. Due to currently high raw material inputs of GA, various alternative carbohydrate sources are being investigated. Sucrose is one of the cost-effective biomass sources that can be used as feedstock. The most common industrial production of GA is based on wild-type bacteria and fungi, but there are many problems with this production. This study aimed to optimize the production of GA from glucose produced by hydrolysis of sucrose using recombinant E. coli Waksman (W) pqq+ strain. After sucrose was enzymatically hydrolyzed, significant medium components for GA production were determined as glucose, calcium carbonate (CaCO3), peptone, and ammonium phosphate ((NH4)3PO4) using Placket-Burman Design (PBD). Detailed optimization of the medium components that are significant in GA production was carried out using central composite design (CCD), and optimum values of the independent variables examined in maximum GA production (93.5 ± 2.95 g/L) were determined as glucose 95, CaCO3 25, peptone 2, and (NH4)3PO4 1.13 (g/L). Using results obtained in the Erlenmeyer experiments, GA production in the bioreactor was investigated by CCD. The maximum GA efficiency (3.20 ± 0.15 g/L. h) was obtained under conditions where the air supply rate was 10.82 L/min, stirring speed was 656.87 rpm, and CaCO3 concentration was 16.90 g/L. In conclusion, it has been shown that GA can be produced with a high yield with this novel approach using a recombinant strain for GA production from sucrose.

Characterization and Application of Cyrene as a Biomass-Based Solvent for Homogeneous Heck-Coupling Reaction

Cyrene, a renewable, non-toxic substance having negligible vapor pressure, even at high temperatures, was proposed as a reaction medium for homogeneous Pd-catalyzed Heck-coupling reactions. It was first characterized by its temperature-dependent physicochemical properties, i. e., vapor pressure, density, surface tension, heat capacity, and viscosity, the key parameters of its reaction and process chemistry. Its refractive indices in the function of temperature were also determined. Hereafter, the effect of reaction parameters (Pd source, nature of the base, the water content of the reaction mixture, leaving group (-I, -Br, -Cl, and -OTf of aromatic substrates) on Pd-catalyzed Heck-coupling reaction was investigated using iodobenzene and styrene as model substrates. Subsequently, 4-substituted iodobenzene and styrene derivatives were applied to investigate the effect of electronic parameters on the reaction efficiency and functional group tolerance. To demonstrate the applicability of the system, thirteen stilbene derivatives were isolated with good to high yields and purity (>95 %) using 0.2 mol % of Pd, 1.5 eq. of Et3N as a base, in 1 mL of Cyrene for 2 h at 100 °C.

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.

Catalytic Transformation of Biomass into Sustainable Carbocycles: Recent Advances, Prospects, and Challenges

Organic compounds bearing one or more carbocycles in their molecular structure have a discernible presence in all major classes of organic products of industrial significance. However, sourcing carbocyclic compounds from exhaustible, anthropogenic carbon (e. g., petroleum) raises serious concerns about sustainability in the chemical industries. This review discusses recent advances in the renewable synthesis of carbocyclic compounds from biomass components following catalytic pathways. The mechanistic insights, process optimizations, green metrics, and alternative synthetic strategies of carbocyclic compounds have been detailed. Moreover, the renewable syntheses of carbocycles have been assessed against their existing synthetic routes from petroleum for better perspectives on their sustainability and technological preparedness. This work will assist the researchers in acquiring updated information on the sustainable synthesis of carbocyclic compounds from various biomass components, comprehending the research gaps, and developing superior synthetic processes for their commercial production.

Benzenoid Aromatics from Renewable Resources

In this Review, all known chemical methods for the conversion of renewable resources into benzenoid aromatics are summarized. The raw materials that were taken into consideration are CO2; lignocellulose and its constituents cellulose, hemicellulose, and lignin; carbohydrates, mostly glucose, fructose, and xylose; chitin; fats and oils; terpenes; and materials that are easily obtained via fermentation, such as biogas, bioethanol, acetone, and many more. There are roughly two directions. One much used method is catalytic fast pyrolysis carried out at high temperatures (between 300 and 700 °C depending on the raw material), which leads to the formation of biochar; gases, such as CO, CO2, H2, and CH4; and an oil which is a mixture of hydrocarbons, mostly aromatics. The carbon selectivities of this method can be reasonably high when defined small molecules such as methanol or hexane are used but are rather low when highly oxygenated compounds such as lignocellulose are used. The other direction is largely based on the multistep conversion of platform chemicals obtained from lignocellulose, cellulose, or sugars and a limited number of fats and terpenes. Much research has focused on furan compounds such as furfural, 5-hydroxymethylfurfural, and 5-chloromethylfurfural. The conversion of lignocellulose to xylene via 5-chloromethylfurfural and dimethylfuran has led to the construction of two large-scale plants, one of which has been operational since 2023.

Enhancing 5-Hydroxymethylfurfural Production from Fructose Using Triethylbenzylammonium Chloride-Based Acidic Deep Eutectic Solvents: Optimization and Acidity Impact

5-Hydroxymethylfurfural (5-HMF) is an important biomass-based platform compound that links biomass feedstocks with petrochemical refinery products. In this work, we developed a novel approach using triethylbenzylammonium chloride (TEBAC)-based acidic deep eutectic solvents (ADESs) to synthesize 5-HMF through the dehydration of fructose. Our approach demonstrates significant improvements in both 5-HMF yield and process efficiency compared to conventional solvent systems. Under optimal experimental conditions (90 °C, 4.5 h), a maximum 5-HMF yield of 97.77±3.20 % was achieved at a TEBAC:acetic acid ratio of 2 : 3 with 1 wt % fructose loading, which represents a notable advancement over other methods. Notably, our system inhibits the formation of by-products such as levulinic acid (LA) and formic acid (FA), which are commonly detected in other dehydration processes. Additionally, higher 5-HMF yields of 76.67±0.33 % and 73.51±1.14 % were achieved with 10 wt % and 20 wt % fructose loadings, respectively, further highlighting the scalability of the process. The acidity of ADESs was found to significantly affect the dehydration rate and yield, as demonstrated through Hammett's acidity function analysis. The key innovation of our study lies in the strategic selection of hydrogen bond donors and acceptors in the DES, enabling both high efficiency and selectivity in 5-HMF production. These findings provide a promising pathway for large-scale biomass conversion with reduced by-product formation.

Upgraded cellulose and xylan digestions for synergistic enhancements of biomass enzymatic saccharification and bioethanol conversion using engineered Trichoderma reesei strains overproducing mushroom LeGH7 enzyme

Crop straws provide enormous lignocellulose resources transformable for sustainable biofuels and valuable bioproducts. However, lignocellulose recalcitrance basically restricts essential biomass enzymatic saccharification at large scale. In this study, the mushroom-derived cellobiohydrolase (LeGH7) was introduced into Trichoderma reesei (Rut-C30) to generate two desirable strains, namely GH7-5 and GH7-6. Compared to the Rut-C30 strain, both engineered strains exhibited significantly enhanced enzymatic activities, with β-glucosidases, endocellulases, cellobiohydrolases, and xylanase activities increasing by 113 %, 140 %, 241 %, and 196 %, respectively. By performing steam explosion and mild alkali pretreatments with mature straws of five bioenergy crops, diverse lignocellulose substrates were effectively digested by the crude enzymes secreted from the engineered strains, leading to the high-yield hexoses released for bioethanol production. Notably, the LeGH7 enzyme purified from engineered strain enabled to act as multiple cellulases and xylanase at higher activities, interpreting how synergistic enhancement of enzymatic saccharification was achieved for distinct lignocellulose substrates in major bioenergy crops. Therefore, this study has identified a novel enzyme that is active for simultaneous hydrolyses of cellulose and xylan, providing an applicable strategy for high biomass enzymatic saccharification and bioethanol conversion in bioenergy crops.

Boron-doped sulfonated graphitic carbon nitride as a highly efficient catalyst for the production of 5-hydroxymethylfurfural from carbohydrates

The presence of humins during the conversion of concentrated fructose presents a major obstacle in the large-scale production of 5-hydroxymethylfurfural (HMF) from fructose. Herein, we reported a boron-doped graphitic carbon nitride sulfonated (BGCN-SO3H) as an excellent catalyst for the synthesis of HMF from fructose. The BGCN-SO3H catalyst structures were analyzed using various characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), elemental mapping analysis, and Fourier-transform infrared spectroscopy (FT-IR). The BGCN-SO3H catalyst was evaluated for the synthesis of HMF from fructose. We investigated the influence of catalyst performance, including solvent reactions, catalyst loading, substrates, and volume of solvent to optimize reaction conditions. As a result, the yield of HMF was obtained at 88 % within 5 h when using 30 mg of catalyst. The study of catalyst activity involved examining reactions that allowed recovery and reuse. The research findings offer a method for producing HMF with exceptional efficiency using solid catalysts.

High-Efficiency Solar Transformation of Sugars via a Heterogenous Gallium(III) Catalyst

Extremely limited research exploring the photocatalytic potential of main group metals, such as aluminum, gallium, and tin, has been undertaken due to their weak light harvesting properties. This study reports the efficient transformation of sugars to 5-hydroxymethylfurfural (HMF) with high yield employing an original heterogeneous photocatalyst comprising a gallium(III) complex immobilized on an alumina support. Under visible light irradiation, the reaction rate of HMF formation is ~143 times higher than the equivalent thermal reaction performed in the absence of light. The turnover number (TON) of the heterogeneous gallium(III) photocatalyst was as high as 1500, which was ca. two orders of magnitude higher than the TON of the homogeneous gallium(III) system. It is proposed that photoirradiation significantly enhances the Lewis acidity of the catalyst by forming a semi-coordination state between gallium(III) and N-donor ligands, enabling the increased interaction of reactant sugar molecules with gallium(III) active sites. Consistent with this, the photoresponsive coordination of the gallium(III) complex and the abstraction of the hydroxy group by the metal under irradiation with visible light is observed by NMR spectroscopy for the first time. These findings demonstrate that efficient photocatalysts derived from the main group elements can facilitate biomass conversion using visible light.

Electrochemical Hydrodimerization of Lignocellulose-Derived Carbonyls in Aqueous Electrolytes for Biobased Polymer and Long-chained Synfuel Production: A Review

The transformation from fossil resources, crude oil and natural gas to biomass-derived feedstocks is an urgent and major challenge for the chemical industry. The valorization of lignocellulose as renewable resource is a promising pathway offering access to a wide range of platform chemicals, such as vanillin, furfural and 5-HMF. The subsequent conversion of such platform chemicals is one crucial step in the value-added chain. The electrochemical hydrodimerization (EHD) is a sustainable tool for C-C coupling of these chemicals to their corresponding hydrodimers hydrovanilloin, hydrofuroin and 5,5'-bis(hydroxymethyl)hydrofuroin (BHH). This review covers the current state of art concerning the mechanism of the electrochemical reduction of biobased aldehydes and studies targeting the electrochemical production of these hydrodimers in aqueous media. Moreover, the subsequent conversion of these hydrodimers to valuable additives, polymers and long carbon chain synfuels will be summarized offering a broad scope for their application in the chemical industry.

Efficient Conversion of Glucose to Hydroxymethylfurfural: One-pot Brønsted Base and Acid Promoted Selective Isomerization and Dehydration

Development of elegant, selective, and efficient strategies for the production of value-added platform chemicals from renewable feedstocks are in high demand to achieve the future needs and sustainable goals. In this context, an efficient acid-promoted synthesis of highly valuable hydroxymethylfurfural (HMF) has been demonstrated from glucose, a major constituent of lignocellulosic biomass. The major challenge in the conversion of glucose to HMF is the selective isomerization of glucose to ketose, which in the present work has been successfully addressed through the amine-mediated rearrangement of glucose to aminofructose under Amadori rearrangement. Importantly, subsequent dehydration step affords HMF and regenerates the amine employed in the first step, which could be readily recovered. In addition, scale-up and successful integration into one-pot synthesis of HMF proves the efficiency and applicability of the present transformation in large scale application. In addition, the method was also successfully extended to other monosaccharides and disaccharides to produce HMF.

Furandicarboxylic Acid (FDCA): Electrosynthesis and Its Facile Recovery From Polyethylene Furanoate (PEF) via Depolymerization

Replacing fossil fuels with renewable, bio-based alternatives is inevitable for the modern chemical industry, in line with the 12 principles of green chemistry. 2,5-Furandicarboxylic acid (FDCA) is a promising platform molecule that can be derived from 5-hydroxymethyl furfural (HMF) via sustainable electrochemical oxidation. Herein, we demonstrate TEMPO-mediated electrooxidation of HMF to FDCA in ElectraSyn 2.0 using inexpensive commercially available electrodes: graphite anode and stainless-steel cathode, thereby avoiding the often cumbersome electrode preparation. Key parameters such as concentration of HMF, KOH, and catalyst loading were optimized by experimental design. Under the optimized conditions, using only a low amount of TEMPO (5 mol %), high yield and Faradaic efficiency of 96 % were achieved within 2.5 h. Moreover, since FDCA is a monomer of the bio-based poly(ethylene furanoate), PEF, we aimed to investigate its recovery by depolymerization, which could be of paramount importance in the circular economy of the FDCA. For this, a new polar aprotic solvent, methyl sesamol (MeSesamol), was used, allowing the facile depolymerization of PEF at room temperature with high monomer yields (up to 85 %), while the cosolvent MeSesamol was recycled with high efficiency (95-100 %) over five reaction cycles.

Electrocatalytic water-to-oxygenates conversion: redox-mediated versus direct oxygen transfer

Electrocatalytic oxygenation of hydrocarbons with high selectivity has attracted much attention for its advantages in the sustainable and controllable production of oxygenated compounds with reduced greenhouse gas emissions. Especially when utilizing water as an oxygen source, by constructing a water-to-oxygenates conversion system at the anode, the environment and/or energy costs of producing oxygenated compounds and hydrogen energy can be significantly reduced. There is a broad consensus that the generation and transformation of oxygen species are among the decisive factors determining the overall efficiency of oxygenation reactions. Thus, it is necessary to elucidate the oxygen transfer process to suggest more efficient strategies for electrocatalytic oxygenation. Herein, we introduce oxygen transfer routes through redox-mediated pathways or direct oxygen transfer methods. Especially for the scarcely investigated direct oxygen transfer at the anode, we aim to detail the strategies of catalyst design targeting the efficient oxygen transfer process including activation of organic substrate, generation/adsorption of oxygen species, and transformation of oxygen species for oxygenated compounds. Based on these examples, the significance of balancing the generation and transformation of oxygen species, tuning the states of organic substrates and intermediates, and accelerating electron transfer for organic activation for direct oxygen transfer has been elucidated. Moreover, greener organic synthesis routes through heteroatom transfer and molecular fragment transfer are anticipated beyond oxygen transfer.

Catalytic conversion of chitin-based biomass to nitrogen-containing chemicals

The exploration of renewable alternatives to fossil fuels for chemical production is indispensable to achieve the ultimate goals of sustainable development. Chitin biomass is an abundant platform feedstock that naturally bears both nitrogen and carbon atoms to produce nitrogen-containing chemicals (including organonitrogen ones and inorganic ammonia). The expansion of biobased chemicals toward nitrogen-containing ones can elevate the economic competitiveness and benefit the biorefinery scheme. This review aims to provide an up-to-date summary on the overall advances of the chitin biorefinery for nitrogen-containing chemical production, with an emphasis on the design of the catalytic systems. Catalyst design, solvent selection, parametric effect, and reaction mechanisms have been scrutinized for different transformation strategies. Future prospectives on chitin biorefinery have also been outlined.

Biomass to green surfactants: Microwave-assisted transglycosylation of wheat bran for alkyl glycosides production

Depolymerization of carbohydrate biomass using a long-chain alcohol (transglycosylation) to produce alkyl glycoside-based bio-surfactants has been gaining industrial interest. This study introduces microwave-assisted transglycosylation in transforming wheat bran, a substantial agricultural side stream, into these valuable compounds. Compared to traditional heating, microwave-assisted processing significantly enhances the product yield by 53 % while reducing the reaction time by 72 %, achieving a yield of 29 % within 5 h. This enhancement results from the microwave's capacity to activate intermolecular hydrogen and glycosidic bonds, thereby facilitating transglycosylation. Life-cycle assessment and techno-economic analysis demonstrate the benefits of microwave heating in reducing energy consumption by 42 %, CO2 emissions by 56 %, and equipment, operational and production costs by 44 %, 35 % and 30 %, respectively. The study suggests that microwave heating is a promising approach for efficiently producing bio-surfactants from agricultural wastes, with potential cost reductions and environmental benefits that could enhance industrial biomass conversion processes.

Production of levulinic acid from macroalgae by hydrothermal conversion with ionic resin catalyst

Gracilaria verrucosa is red algae (Rhodophyta) that is particularly significant because of its potential for bioenergy production as a sustainable and environmentally friendly marine bioresource. This study focuses on the production of levulinic acid from G. verrucosa using hydrothermal conversion with an ionic resin Purolite CT269DR as the catalyst. By optimization of the conversion condition, a 30.3 % (22.58 g/L) yield of levulinic acid (LA) (based on carbohydrate content) was obtained at 200 °C for 90 min with 12.5 % biomass and 50 % catalyst loading of biomass quantity. Simultaneously, formic acid yielded 14.0 % (10.42 g/L). The LA yield increased with increasing combined severity (CS) levels under tested ranges. Furthermore, the relationship between CS and LA synthesis was effectively fitted to the nonlinear sigmoidal equation. However, as the yield of sugar decreased, LA yield was linearly increased. Thus, the use of ionic resin as a heterogeneous catalyst presents significant potential for the manufacture of platform chemicals, specifically LA, through the conversion of renewable marine macroalgae.

Production of H2 and Glucaric Acid Using Electrocatalyst Glucose Oxidation by the Ta NiFe LDH Electrode

The slow anodic oxygen evolution reaction (OER) significantly limits electrocatalytic water splitting for hydrogen production. We proposed the electrocatalyst for glucose oxidation by Ta-doping NiFe LDH nanosheets to simultaneously obtain glucaric acid (GRA) and hydrogen gas as a useful byproduct. Superior glucose oxidation reaction (GOR) activity is demonstrated by the optimized Ta-NiFe LDH, which has a low overpotential of 192 mV, allowing for a small Tafel slope of 70 mV dec-1 and a current density of 50 mA cm-2. The Ta NiFe LDH-oxidized glucose to GRA with a 72.94% yield and 64.3% Faradaic efficiency at 1.45 VRHE. Herein, we report the Ta NiFe LDH/NF electrode for the GOR&hydrogen evolution reaction (HER), which exhibits a cell voltage of 1.62 V to reach a current density of 10 mA cm-2, which is 250 mV lower compared to OER&HER (1.87 V). This study reveals that GOR is an energy-efficient and cost-effective method for producing H2 and valorizing biomass.

Indium-Mediated Acyloxyallylation-Based Synthesis of Galacto-Configured Higher-Carbon Sugar Alcohols as Potential Phase Change Materials

Sugar alcohols fulfilling specific structural requirements are a substance class with great potential as organic phase change materials (PCMs). Within this work, we demonstrate the indium-mediated acyloxyallylation (IMA) as a useful strategy for the synthesis of higher-carbon sugar alcohols of the galacto-family featuring all hydroxyl groups in a 1,3-anti-relationship with three major synthetic achievements: first, the dihydroxylation of the IMA-derived allylic sugar derivates was systematically studied in terms of diastereoselectivity, revealing a high degree of substrate control toward anti-addition. Second, we demonstrated the use of a "double Mitsunobu" reaction, inverting the stereochemistry of terminal diols. Third, the IMA toolbox was expanded to accomplish the synthesis of derivatives with up to 10 carbon atoms from particularly unreactive aldoses. Thermal investigations of all synthesized sugar alcohols, including examples with exclusive 1,3-anti- and suboptimal 1,3-syn-relationships as well as even and odd numbers of carbon atoms, were performed. We observed clear trends in melting points and thermal storage densities and discovered limitations of organic substances in this class with melting points above 240 °C as PCMs in terms of thermal stability. With our study, we provide insights into the dependence of thermal properties on structural features, thus contributing to further understanding of organic PCMs for thermal energy storage applications.

Solvation enhanced long-range proton transfer in aqueous phase for glycolaldehyde hydrogenation over Ru/C catalyst

The catalytic hydrogenation of biomass-derived chemicals is essential in chemical industry due to the growing demand for sustainable and renewable energy sources. In this study, we present a comprehensive theoretical investigation regarding the hydrogenation of glycolaldehyde to ethylene glycol over a Ru/C catalyst by employing density functional theory and ab initio molecular dynamics simulations. With inclusion of explicit solvation, we have demonstrated that the glycolaldehyde hydrogenation is significantly improved due to the fast proton transfer through the hydrogen bond network. The enhanced activity could be attributed to the participation of the solvent water as the hydrogen source and the highly positively charged state of a Ru cluster in an aqueous phase, which are critical for the activation of aldehyde groups and proton-assisted hydrogenation. Overall, our findings provide valuable insights into glycolaldehyde hydrogenation over Ru/C catalysts in the aqueous phase, highlighting the importance of solvation effects in the biomass conversion.

Synthesis of Pyrrole-2-Carboxylic Acid from Cellulose- and Chitin-Based Feedstocks Discovered by the Automated Route Search

The shift towards sustainable feedstocks for platform chemicals requires new routes to access functional molecules that contain heteroatoms, but there are limited bio-derived feedstocks that lead to heteroatoms in platform chemicals. Combining renewable molecules of different origins could be a solution to optimize the use of atoms from renewable sources. However, the lack of retrosynthetic tools makes it challenging to examine the extensive reaction networks of various platform molecules focusing on multiple bio-based feedstocks. In this study, a protocol was developed to identify potential transformation pathways that allow for the use of feedstocks from different origins. By analyzing existing knowledge on chemical reactions in large databases, several promising synthetic routes were shortlisted, with the reaction of D-glucosamine and pyruvic acid being the most interesting to make pyrrole-2-carboxylic acid (PCA). The optimized synthetic conditions resulted in 50 % yield of PCA, with insights gained from temperature variant NMR studies. The use of substrates obtained from two different bio-feedstock bases, namely cellulose and chitin, allowed for the establishment of a PCA-based chemical space.

One-pot redox cascade paired electrosynthesis of gamma-butyrolactone from furoic acid

The catalytic valorisation of biomass to afford synthetically useful small molecules is essential for sustainable biorefinery processes. Herein, we present a mild cascaded electrochemical protocol for converting furoic acid, a common biomass-derived feedstock, into a versatile platform chemical, gamma-butyrolactone. In the platinum(+)|nickel(-) electrode paired undivided cell, furoic acid is electrochemically oxidised with 84.2% selectivity to 2(5H)-furanone, the olefin of which is then hydrogenated to yield gamma-butyrolactone with 98.5% selectivity. The final gamma-butyrolactone yield is 69.1% with 38.3% Faradaic efficiency and 80.1% carbon balance when the reaction is performed with 100 mM furoic acid at 80 °C at +2.0 VAg/AgCl. Mechanistic investigation revealed the critical temperature and electrolyte pH conditions that maximise the production and protection of the key intermediate, furan radical, promoting its transition to 2(5H)-furanone rather than self-polymerising. The reaction is scalable, as 2.1 g of 98.1% pure gamma-butyrolactone is isolated through a simple solvent extraction.

Environmental Sustainability of Lighter Fluids

Lighter fluids are consumer products used only at a low-volume scale, representing a realizable goal of fossil fuel replacement by renewables. Physicochemical properties of four fossil-based conventional lighter fluids (Ronsonol, Zippo, Landmann, and Terracotta) and six selected biomass-based chemicals (γ-valerolactone, ethyl-levulinate, ethanol, n-butanol, γ-valerolactone 90% v/v and ethanol 10% v/v, and ethyl-levulinate 90% v/v and ethanol 10% v/v mixtures) as potential biomass-based lighter fluids were assessed. Assessments were carried out in terms of safety, toxicological, and environmental viewpoints, represented by a flash point, boiling point, vapor pressure values, and evaporation rates; oral toxicity measured on rats; and real ethanol equivalent values, respectively. Parameters were collected where available; in the absence of literature data, they were calculated or measured and then analyzed. Finally, multicriteria analysis based on the flash point, boiling point, vapor pressure, toxicity, and ethanol equivalent values revealed γ-valerolactone as a renewable substance, which can be a promising alternative to replace fossil-based lighter fluids because it was awarded as the first in the multicriteria evaluation by obtaining the highest value of the overall scores. In practical usage, however, ignition, combustion experiments, flue gas, and emission analysis are also required to underline its commercial use in the future.

Aluminum ion intercalation in mesoporous multilayer carbocatalysts promotes the conversion of glucose to 5-hydroxymethylfurfural

In this study, an efficient modification strategy was proposed by facile loading of trace aluminum ions and p-toluene sulfonic acid (p-TSA) in carbon materials to improve their catalytic activity. p-TSA is then proven to regulate the carbonization process and promote the formation of mesoporous and multilayer structures. The hexa-coordinated aluminum structure is characterized by 1H-27Al solid-state nuclear magnetic resonance (SSNMR) and X-ray photoelectron spectroscopy, which serves as the Lewis-Brønsted acid site in carbocatalysts. Accordingly, the resulting catalyst facilitates a yield of ∼70% for converting glucose to 5-hydroxymethylfurfural (HMF) with a maximum carbon balance of around 91.4% at 150 °C in 6 h. In situ NMR, electrospray ionization mass spectrometry and isotope labeling analysis reveal that the hexa-coordinated aluminum sites promote the isomerization of glucose, and the sulfonic groups facilitate the subsequent dehydration and rehydration of fructose and levoglucosan intermediates. Kinetic models further indicate the decreased energy barrier for glucose conversion over the Al3+/p-TSA intercalated carbocatalyst. This work provides a promising strategy for engineering waste-derived carbocatalysts toward effectively converting carbohydrates to precursors of biofuels and bioplastics.

Modular Synthesis of Fluoro-Substituted Furan Compounds via Controllable Fluorination of Biomass-Based 5-HMF and Its Derivatives

5-Hydroxymethylfurfural (5-HMF) is regarded as one of the most promising platform feedstocks for producing valuable chemicals, fuels, and materials. In this study, we present a controllable fluorination technique for biomass-based 5-HMF and its oxygenated derivatives. This technique allows us to synthesize mono-fluoromethyl, difluoromethyl, and acylfluoro-substituted furan compounds by adjusting experimental conditions such as different fluorine sources and mole ratio. To gain a deeper understanding the reactivity order, we conducted intermolecular and intramolecular competition experiments. The results revealed that the hydroxyl group exhibited the highest reactivity, followed by the aldehyde group. This finding provides important theoretical support and opens up the possibility of selective fluorination. The reaction offers several advantages, including mild conditions, no need for inert gas protection, and easy operation. Furthermore, the fluoro-substituted furan compounds can be further transformed for the preparation of drug analogs, offering a new route for the high-value utilization of biomass molecules.

Recent Advancements in Electrochemical Hydrogen Production via Hybrid Water Splitting

As one of the most promising approaches to producing high-purity hydrogen (H2 ), electrochemical water splitting powered by the renewable energy sources such as solar, wind, and hydroelectric power has attracted considerable interest over the past decade. However, the water electrolysis process is seriously hampered by the sluggish electrode reaction kinetics, especially the four-electron oxygen evolution reaction at the anode side, which induces a high reaction overpotential. Currently, the emerging hybrid electrochemical water splitting strategy is proposed by integrating thermodynamically favorable electro-oxidation reactions with hydrogen evolution reaction at the cathode, providing a new opportunity for energy-efficient H2 production. To achieve highly efficient and cost-effective hybrid water splitting toward large-scale practical H2 production, much work has been continuously done to exploit the alternative anodic oxidation reactions and cutting-edge electrocatalysts. This review will focus on recent developments on electrochemical H2 production coupled with alternative oxidation reactions, including the choice of anodic substrates, the investigation on electrocatalytic materials, and the deep understanding of the underlying reaction mechanisms. Finally, some insights into the scientific challenges now standing in the way of future advancement of the hybrid water electrolysis technique are shared, in the hope of inspiring further innovative efforts in this rapidly growing field.

Ni-Cu and Ni-Co-Modified Fly Ash Zeolite Catalysts for Hydrodeoxygenation of Levulinic Acid to γ-Valerolactone

Monometallic (Ni, Co, Cu) and bimetallic (Ni-Co, Ni-Cu) 10-20 wt.% metal containing catalysts supported on fly ash zeolite were prepared by post-synthesis impregnation method. The catalysts were characterized by X-ray powder diffraction, N2 physisorption, XPS and H2-TPR methods. Finely dispersed metal oxides and mixed oxides were detected after the decomposition of the impregnating salt on the relevant zeolite support. Via reduction intermetallic, NiCo and NiCu phases were identified in the bimetallic catalysts. The catalysts were studied in hydrodeoxygenation of lignocellulosic biomass-derived levulinic acid to γ-valerolactone (GVL) in a batch system by water as a solvent. Bimetallic, 10 wt.% Ni, and 10 wt.% Cu or Co containing fly ash zeolite catalysts showed higher catalytic activity than monometallic ones. Their selectivity to GVL reached 70-85% at about 100% conversion. The hydrogenation activity of catalysts was found to be stronger compared to their hydration ability; therefore, the reaction proceeds through formation of 4-hydroxy pentanoic acid as the only intermediate compound.

Unraveling the potential-dependent structure evolution in CuO for electrocatalytic biomass valorization

Electrocatalytic oxidation of renewable biomass (such as glucose) into high-value-added chemicals provides an effective approach to achieving carbon neutrality. CuO-derived materials are among the most promising electrocatalysts for biomass electrooxidation, but the identification of their active sites under electrochemical conditions remains elusive. Herein, we report a potential-dependent structure evolution over CuO in the glucose oxidation reaction (GOR). Through systematic electrochemical and spectroscopic characterizations, we unveil that CuO undergoes Cu2+/Cu+ and Cu3+/Cu2+ redox processes at increased potentials with successive generation of Cu(OH)2 and CuOOH as the active phases. In addition, these two structures have distinct activities in the GOR, with Cu(OH)2 being favorable for aldehyde oxidation, and CuOOH showed faster kinetics in carbon-carbon cleavage and alcohol/aldehyde oxidation. This work deepens our understanding of the dynamic reconstruction of Cu-based catalysts under electrochemical conditions and may guide rational material design for biomass valorization.

Synthesis of Levulinic Acids From Muconic Acids in Hot Water

Levulinic acid is a key biorenewable platform molecule. Its current chemical production from sugars is plagued by limited yields, char formation and difficult separations. An alternative and selective route starting from muconic acid via simple heating in water at high temperature (180 °C) has been developed. Muconic acid can be obtained from sugars or catechol fermentation. Chemical oxidation of catechol is another possibility which advantageously can also be applied on substituted catechols, hereby providing substituted muconic acids. When applying the disclosed hydrothermal protocol on these substrates hitherto unknown substituted levulinic acids were accessed. In particular, 3-propyllevulinic acid has been synthesized from 4-propylcatechol, prepared from pine wood. This propylated derivative has been used for the synthesis of a 3-propyllevulinate diester, i.e. butane-1,4-diyl bis(4-oxo-3-propylpentanoate), via esterification with 1,4-butanediol. The diester showed superior performance as plasticizer in comparison to the corresponding levulinate diester in both PVC (polyvinyl chloride) and PLA (polylactic acid). It plasticizes equally effective as the notorious commercial phthalate-based benchmark DEHP (di-2-ethylhexyl phthalate) in PVC.

Efficient conversion of carbohydrates into 5-hydroxymethylfurfural using choline chloride-based deep eutectic solvents

In this study, the conversion of monosaccharides to 5-hydroxymethylfurfural (5-HMF) using different deep eutectic solvents (DESs) was investigated in various conditions. Among all the investigated DESs, [ChCl][trichloroacetic acid], based on choline chloride and trichloroacetic acid with the ratio 1:1, showed the highest catalytic activity. A maximum 5-HMF yield was 82 % for 1 h at 100 °C using [ChCl][trichloroacetic acid] as a catalyst from fructose. [ChCl][trichloroacetic acid] could be recovered and reused three times with a slight loss in activity. Our work demonstrated the low-cost and effective method for the synthesis of 5-HMF from carbohydrates.

Direct and efficient conversion of cellulose to levulinic acid catalyzed by carbon foam-supported heteropolyacid with Brønsted-Lewis dual-acidic sites

This study aimed to produce bio-based levulinic acid (LA) via direct and efficient conversion of cellulose catalyzed by a sustainable solid acid. A carbon foam (CF)-supported aluminotungstic acid (HAlW/CF) catalyst with Brønsted-Lewis dual-acidic sites was creatively engineered by a hydrothermal impregnation method. The activity of the HAlW/CF catalyst was determined via the hydrolysis and conversion of cellulose to prepare LA in aqueous system. The cooperative effect of Brønsted and Lewis acids in HAlW/CF resulted in high cellulose conversion (89.4%) and LA yield (60.9%) at 180 °C for 4 h, which were greater than the combined catalytic efficiencies of single HAlW and CF under the same conditions. The HAlW/CF catalyst in block form exhibited superior catalytic activity, facile separation from reaction system, and favorable reusability. This work offers novel perspectives for the development of recyclable dual-acidic catalysts to achieve one-pot catalytic conversion of biomass to value-added chemicals.

Recent Progress and Opportunity of Metal Single-Atom Catalysts for Biomass Conversion Reactions

The conversion of lignocellulosic biomass into platform chemicals and fuels by metal single atoms is a new domain in solid catalysis research. Unlike the conventional catalysis route, single-atom catalysts (SACs) proliferate maximum utilization efficiency, high catalytic activity, and good selectivity to the desired product with an ultralow loading of the active sites. More strikingly, SACs show a unique cost-effective pathway for the conversion of complex sugar molecules to value-added chemicals in high yield and selectivity, which may be hindered by conventional metal nanoparticles. Primarily, SACs having adjustable active sites could be easily modified using sophisticated synthetic techniques based on their intended reactions. This review covers current research on the use of SACs with a strong emphasis on the fundamentals of catalyst design, and their distinctive activities in each type of reaction (hydrogenation, hydrogenolysis, hydrodeoxygenation, oxidation, and dehydrogenation). Furthermore, the fundamental insights into the superior actions of SACs within the opportunity and prospects for the industrial-scale synthesis of value-added products from the lignocelluloses are covered.

Pd-Catalyzed Activation of Carbon-Carbon Bonds in Hydroxymethylfurfural Derivatives

Palladium-catalyzed activation of C-C bonds in organic molecules is a powerful tool for the synthesis of value-added compounds. 5-Hydroxymethylfurfural (HMF) derivatives are a promising class of biomass-derived chemicals that have received considerable attention due to their potential applications in the synthesis of biologically active molecules and materials. However, the selective activation of unstrained C-C bonds is a challenging task, mainly due to their relatively high bond dissociation energies. Herein, we report a palladium-catalyzed method for the efficient C-C bond activation of HMF derivatives, enabling their arylation with iodobenzenes. Mechanistic studies, including reaction-profile analysis, competition experiments and head-space IR spectroscopy suggest a decarboxylative mechanism.

Structure investigation of light-colored lignin extracted by Lewis acid-based deep eutectic solvent from softwood

Lignin is the most abundant natural phenolic polymer. However, the severe condensations of industrial lignin resulted in an undesirable apparent morphology and darker color, which hindered its application in the field of daily chemicals. Therefore, a ternary deep eutectic solvent is used to obtain lignin with light-color and low condensations from softwood. The results showed that the brightness value of lignin extracted from aluminum chloride-1,4-butanediol-choline chloride at 100 °C and 1.0 h was 77.9, and the lignin yield was 32.2 ± 0.6%. It is important that 95.8% of β-O-4 linkages (β-O-4 and β-O-4') was retained. Lignin is used to prepare sunscreens and is added to physical sunscreens at 5%, with SPF up to 26.95 ± 4.20. Meanwhile, enzyme hydrolysis experiments and reaction liquid composition tests were also conducted. In conclusion, a systematic understanding of this efficient process could facilitate high-value utilization of lignocellulosic biomass in industrial processes.

Halide Adsorption Enhances Electrochemical Hydrogenolysis of 5-Hydroxymethylfurfural by Suppressing Hydrogenation

Reductive upgrading of 5-hydroxymethylfurfural (HMF), a biomass-derived platform molecule, to 2,5-dimethylfuran (DMF), a biofuel with an energy density 40% greater than that of ethanol, involves hydrogenolysis of both the aldehyde (C═O) and the alcohol (C-OH) groups of HMF. It is known that when hydrogenation of the aldehyde occurs to form 2,5-bis(hydroxymethyl)furan (BHMF), BHMF cannot be further reduced to DMF. Thus, aldehyde hydrogenation must be suppressed to increase the selectivity for DMF production. Previously, it was shown that on a Cu electrode hydrogenolysis occurs mainly through proton-coupled electron transfer (PCET), where a proton from the solution and an electron from the electrode are transferred to the organic species. In contrast, hydrogenation occurs not only through PCET but also through hydrogen atom transfer (HAT), where a surface-adsorbed hydrogen atom (H*) is transferred to the organic species. This study shows that halide adsorption on Cu can effectively suppress HAT by decreasing the steady-state H* coverage on Cu during HMF reduction. As HAT enables only aldehyde hydrogenation, a striking suppression of BHMF is observed, thereby enhancing DMF production. We discuss how the identity and concentration of the halide, along with the reduction conditions (i.e., potential and pH), affect halide adsorption on Cu and identify when optimal halide coverages are achieved to maximize DMF selectivity. Our experimental results are presented alongside computational results that elucidate how halide adsorption affects the adsorption energy of hydrogen and the steady-state H* coverage on Cu, which provide an atomic-level understanding of all experimentally observed effects.

Efficient Synthesis of Novel Biginelli and Hantzsch Products Sourced from Biorenewable Furfurals Using Gluconic Acid Aqueous Solution as the Green Organocatalyst

The Biginelli reaction provides 3,4-dihydropyrimidin-2(1H)-ones (DHPMs), whereas the Hantzsch reaction leads to 1,4-dihydropyridines (DHPs) by the one-pot, multicomponent, and operationally simple transformations starting from readily available starting materials. DHPMs and DHPs are well-established heterocyclic moieties in the synthetic organic chemistry literature and have pronounced pharmacological activities. This work reports the synthesis of novel DHPMs and DHPs from carbohydrate-derived 5-substituted-2-furaldehydes by employing gluconic acid aqueous solution (GAAS) as an efficient, inexpensive, and eco-friendly catalyst. The use of urea (or thiourea) as the reagent led to DHPMs, whereas ammonium acetate produced DHPs, selectively, keeping the other two starting materials (i.e., furfurals and ethyl acetoacetate) and the reaction parameters unaltered. Using the general synthetic protocol under optimized reaction conditions (60 °C, 3-6 h, 25 mol % GAAS cat.), all the DHPM and DHP derivatives were obtained in good to excellent isolated yields.

Engineering of Local Coordination Microenvironment in Single-Atom Catalysts Enabling Sustainable Conversion of Biomass into a Broad Range of Amines

Utilizing renewable biomass as a substitute for fossil resources to produce high-value chemicals with a low carbon footprint is an effective strategy for achieving a carbon-neutral society. Production of chemicals via single-atom catalysis is an attractive proposition due to its remarkable selectivity and high atomic efficiency. In this work, a supramolecular-controlled pyrolysis strategy is employed to fabricate a palladium single-atom (Pd1 /BNC) catalyst with B-doped Pd-Nx atomic configuration. Owing to the meticulously tailored local coordination microenvironment, the as-synthesized Pd1 /BNC catalyst exhibits remarkable conversion capability for a wide range of biomass-derived aldehydes/ketones. Thorough characterizations and density functional theory calculations reveal that the highly polar metal-N-B site, formed between the central Pd single atom and its adjacent N and B atoms, promotes hydrogen activation from the donor (reductants) and hydrogen transfer to the acceptor (C═O group), consequently leading to exceptional selectivity. This system can be further extended to directly synthesize various aromatic and furonic amines from renewable lignocellulosic biomass, with their greenhouse gas emission potentials being negative in comparison to those of fossil-fuel resource-based amines. This research presents a highly effective and sustainable methodology for constructing C─N bonds, enabling the production of a diverse array of amines from carbon-neutral biomass resources.

Effect of morphologies and compositions of silver-based multicomponent heterogeneous nanocrystals on the reduction of 4-nitrophenol

Silver-based nanocrystals have excellent catalytic performance in various reactions, such as the reduction of 4-nitrophenol. The catalytic performance of nanocrystals varies with several parameters, including nanocrystal morphology, composition, and plasmon-induced hot electrons around nanocrystals. Here, highly heterogeneous nanocrystals (Au-Ag and Ag2S-Ag nanocrystals) fabricated on polymer films via a seed-mediated method are used as catalysts for the reduction of 4-nitrophenol, and the effect of the morphology and composition of nanocrystals on the catalytic performance is investigated. These nanocrystals on polymer films exhibit higher reusability (low catalyst loss) in catalytic applications compared to catalysts dispersed freely in the reaction solution. The excellent catalyst performance of these heterogeneous nanocrystals is attributed to their high surface area/volume ratio (flower-like nanocrystals) and strong synergistic effect (cage-like nanocrystals). These nanocrystals with special morphologies and composites showed higher catalytic performance (higher reactivity at lower catalyst contents) than silver-based nanocrystals reported in the literature. Due to the excellent plasmonic properties of Ag nanocrystals, the catalytic performance of these nanocrystals can be further enhanced by generating hot electrons around the nanocrystals under irradiation. These results demonstrated that by carefully controlling the morphology and composition of nanocrystals, it is possible to design and fabricate excellent catalysts for various reactions.