Catalytic Isomerization of Biomass-Derived Aldoses: A Review

Enhanced catalytic activity of carbonate buffer for isomerization of D-galactose into D-tagatose

D-tagatose (Tag) is a rare monosaccharide with health benefits. In this work, catalytic activity of CAPS (pH 10.4), carbonate (pH 10.4), triethylamine (pH 11.2), quinuclidine (pH 11.5), and L-arginine (pH 12.5) was examined for isomerization of D-galactose (Gal) to Tag. The maximum yields of Tag were 15.0 % with CAPS, 15.2 % with carbonate, 19.3 % with triethylamine, 19.6 % with quinuclidine, and 18.1 % with L-arginine. Despite identical pH, the Tag formation rate with carbonate buffer was 3-8 times higher than with CAPS. For carbonate buffer, the reaction orders for hydroxide and carbonate anions were ∼ 1 and ∼ 0, respectively. Operando NMR studies of Gal-1-13C isomerization in carbonate and CAPS buffers indicate similar tautomeric distributions of the substrate in both buffers. The deuterium kinetic isotope effect demonstrated that carbonate facilitates isomerization through a proton transfer mechanism, with hydroxide anions acting as the catalytically active species whereas carbonate anions stabilize the enediolate anion and/or the transition state.

Preparation of 5-hydroxymethylfurfural from cellulose catalyzed by silicon-based composite solid acids

In order to improve the efficiency of solid acid catalyzed cellulose preparation of 5-hydroxymethylfurfural (HMF), this study prepared a silica-based solid acid with dual acid sites comprising both Lewis and Brønsted acids. Firstly, SiO2 microspheres prepared by reverse microemulsion method were used as the carrier, and the surface was modified with -SO3H and -NH2, and finally Cr3+ was loaded on to SiO2 to prepare the composite solid acid catalyst Cr-SiO2-SO3H, and its characterization and catalytic performance were determined. The experimental results showed that in the two-phase reaction system composed of [BMIM]Cl and THF, using microcrystalline cellulose (MCC) as the substrate, when the reaction temperature was 160 °C, the reaction time was 4 h, the addition amount of Cr-SiO2-SO3H was 1 g/g (cellulose), and the volume ratio of [BMIM]Cl to THF was 1:3, the maximum yield of HMF could reach 54.8%, which was 1.49 and 1.34 times the maximum yield of SiO2-SO3H and Cr-SiO2, respectively.

Enzymatic Upgrading of Biomass-Derived Aldoses to Rare Deoxy Ketoses Catalyzed by Transketolase Variants

A sustainable, convenient, scalable, one-step method for the two-carbon chain elongation of cheap and biomass-derived pentoses (l-arabinose, and 2-deoxy-d-ribose) and hexose l-rhamnose was developed to produce Cn+2 deoxy ketoses (C-7 and C-8) using transketolase, an enzyme catalyzing the quasi-irreversible transfer of a ketol group from an α-keto acid to an aldehyde. Deoxygenated ketoses - commonly obtained by chemical synthesis - were afforded through a suitable combination of both nucleophile and electrophile substrates in the presence of rationally designed TK variants. Pyruvate as nucleophile with pentose l-arabinose (C-5) as electrophile gave 1-deoxy-L-gluco-heptulose (C-7), while ß-hydroxypyruvate (HPA) as nucleophile with acceptors 2-deoxy-d-ribose (C-5) and 6-deoxy-l-mannose (l-rhamnose) (C-6) led to formation of 4-deoxy-d-altro-heptulose (C-7) and 8-deoxy-l-glycero-l-galacto-octulose (C-8), respectively. These three deoxy ketoses were easily obtained with efficient TK variants under mild conditions with complete or high substrate conversions, good to excellent yields and high diastereoselectivities. This strategy offers interesting prospects to study the biological activities of these three rare and valuable deoxy ketoses on various cellular targets.

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.

Phase Effects in Zirconia Catalysed Glucose Conversion to 5-(Hydroxymethyl)furfural

5-(hydroxymethyl)furfural (HMF) is a key biomass derived platform chemical used to produce fuel precursors or additives and value-added chemicals, synthesised by the cascade isomerisation of glucose and subsequent dehydration of reactively formed fructose to HMF over Lewis and Bronsted acid catalysts, respectively. Zirconia is a promising catalyst for such reactions; however, the impact of acid properties of different zirconia phases is poorly understood. In this work, we unravel the role of the zirconia crystalline phase in glucose isomerisation and fructose dehydration to HMF. The Lewis acidic monoclinic phase of zirconia is revealed to preferentially facilitate glucose isomerisation, while the nanoparticulate tetragonal phase possesses Brønsted acid sites which favour fructose dehydration. Synergy between both zirconia phases facilitates cascade HMF production, with both catalysts investigated as physical mixtures in batch and flow reactor configurations. Using a physical mixture of only 15 wt % m-ZrO2 with 85 wt % t-ZrO2 in either batch or packed bed reactor configuration is sufficient to reach equilibrium conversion of glucose for subsequent dehydration by the t-ZrO2 component. Under continuous flow, a six-fold increase in HMF production was obtained when operating with a physical mixture of m- and t-ZrO2 compared to that from a single bed of t-ZrO2.

Evaluation of cross-linkers in the design of immobilized multi isomerase cascade for the preparation of rare sugars

The cascade of sugar isomerases is one of the most practical methods for producing rare sugars, and enzyme immobilization endows it with high economic efficiency, operational convenience and reusability. However, the most employed cross-linker glutaraldehyde (GA) has the disadvantages of enzyme deactivation and limitation of substrate binding. Herein, three compounds, glyoxal, GA, and 2,5-furandicarboxaldehyde (DFF) were evaluated within a previously developed cascade comprising ribose-5-phosphate isomerase and D-tagatose-3-epimerase to prepare D-ribulose form D-xylose. Analyses of surface morphology, element and chemical bond revealed that all compounds effectively cross-linked the isomerases. High concentration of the cross-linkers was generally beneficial for binding protein and preventing enzyme leak during reusing cycles. Glyoxal performed the highest immobilization rate, though it hadn't been employed as a cross-linker for enzyme immobilization. DFF mediated cross-linking revealed the highest activity recovery, substrate conversion and residual activity after reusing cycles, suggesting better biocompatibility than glyoxal and GA. After 8 rounds of recycling, the residual activity of enzyme immobilized by DFF was 61.4 %, ∼30 % higher than that of GA. This study proved a potential alternative cross-linker DFF for the immobilization of enzyme cascade with high activity recovery and reusability, which could promote the efficient production of high value-added products from biomass monosaccharides.

From sugars to aliphatic amines: as sweet as it sounds? Production and applications of bio-based aliphatic amines

Aliphatic amines encompass a diverse group of amines that include alkylamines, alkyl polyamines, alkanolamines and aliphatic heterocyclic amines. Their structural diversity and distinctive characteristics position them as indispensable components across multiple industrial domains, ranging from chemistry and technology to agriculture and medicine. Currently, the industrial production of aliphatic amines is facing pressing sustainability, health and safety issues which all arise due to the strong dependency on fossil feedstock. Interestingly, these issues can be fundamentally resolved by shifting toward biomass as the feedstock. In this regard, cellulose and hemicellulose, the carbohydrate fraction of lignocellulose, emerge as promising feedstock for the production of aliphatic amines as they are available in abundance, safe to use and their aliphatic backbone is susceptible to chemical transformations. Consequently, the academic interest in bio-based aliphatic amines via the catalytic reductive amination of (hemi)cellulose-derived substrates has systematically increased over the past years. From an industrial perspective, however, the production of bio-based aliphatic amines will only be the middle part of a larger, ideally circular, value chain. This value chain additionally includes, as the first part, the refinery of the biomass feedstock to suitable substrates and, as the final part, the implementation of these aliphatic amines in various applications. Each part of the bio-based aliphatic amine value chain will be covered in this Review. Applying a holistic perspective enables one to acknowledge the requirements and limitations of each part and to efficiently spot and potentially bridge knowledge gaps between the different parts.

Iron-Modified Acid Carbons for the Conversion of Fructose to 5-Hydroxymethylfurfural under Microwave Heating

Carbons with Brønsted acidic sites and iron oxide modifications were prepared through hydrothermal carbonization and glycerol pyrolysis in the presence of sulfuric acid, magnetite, and iron(III) nitrate. The solids were tested as catalysts in converting fructose to 5-hydroxymethylfurfural (5-HMF). Characterization techniques revealed a uniform presence of 4.89 mmol g-1 total acidic groups, including up to 1.87 mmol g-1 sulfonic and carboxylic groups. Combined with a reduced surface area, the Brønsted and Lewis acidity enabled the conversion of 94% of fructose with selectivity values as high as 95% for 5-HMF in just 10 min at 140 °C, using microwave heating and dimethyl sulfoxide (DMSO) as the solvent. This performance was attributed to the selective heating of the catalyst surface by the microwave absorption capacity of the acidic groups and iron oxide, leading to the formation of "hot spots." The catalyst obtained by hydrothermal carbonization in the presence of Fe3O4, HCC-20% Fe3O4, demonstrated stability when reused for up to four consecutive cycles. A slight reduction in conversion and selectivity was observed after the first use, attributed to the presence of acid species not incorporated into the solid during the synthesis process.

Interfacial Thermoconvection and Atomic Relay Catalysis Enable Equilibrium Shifting and Rapid Glucose-to-Fructose Isomerization

The aqueous glucose-to-fructose isomerization is controlled by thermodynamics to an equilibrium limit of ~50 % fructose yield. However, here we report an in situ fructose removal strategy enabled by an interfacial local photothermal effect in combination with relay catalysis of geminal and isolated potassium single atoms (K SAs) on graphene-type carbon (Ksg/GT) to effectively bypass the equilibrium limit and markedly speed up glucose-to-fructose isomerization. At 25 °C, an unprecedented fructose yield of 68.2 % was obtained over Ksg/GT in an aqueous solution without any additives under 30-min solar-like irradiation. Mechanistic studies expounded that the interfacial thermoconvection caused by the local photothermal effect of the graphene-type carbon and preferable glucose adsorption on single-atom K could facilitate the release of in situ formed fructose. The geminal K SAs were prone to form a stable metal-glucose complex via bidentate coordination, and could significantly reduce the C-H bond electron density by light-driven electron transfer toward K. This facilitated the hydride shift rate-determining step and expedited glucose isomerization. In addition, isolated K SAs favored the subsequent protonation and ring-closure process to furnish fructose. The integration of the interfacial thermoconvection-enhanced in situ removal protocol and tailored atomic catalysis opens a prospective avenue for boosting equilibrium-limited reactions under mild conditions.

Ball billing induced highly dispersed nano-MgO in biochar for glucose isomerization at low temperatures

The isomerization of glucose is a crucial step for biomass valorization to downstream chemicals. Herein, highly dispersed MgO doped biochar (BM-0.5@450) was prepared from rice straw via a solvent-free ball milling pretreatment and pyrolysis under nitrogen conditions. The nano-MgO doped biochar demonstrated enhanced conversion of glucose in water at low temperatures. A 31 % yield of fructose was obtained from glucose over BM-0.5@450 at 50 °C with 80.0 % selectivity. At 60 °C for 140 min, BM-0.5@450 achieved a 32.5 % yield of fructose. Compared to catalyst synthesized from conventional impregnation method (IM@450), the BM-0.5@450 catalyst shows much higher fructose yields (32.5 % vs 25.9 %), which can be attributed to smaller crystallite size of MgO (11.32 nm vs 19.58 nm) and homogenous distribution. The mechanism study shows that the activated MgOH+·OH- group by water facilitated the deprotonation process leading to the formation of key intermediate enediol.

Efficient isomerization of glucose into fructose by MgO-doped lignin-derived ordered mesoporous carbon

The conversion of glucose into fructose can transform cellulose into high-value chemicals. This study introduces an innovative synthesis method for creating an MgO-based ordered mesoporous carbon (MgO@OMC) catalyst, aimed at the efficient isomerization of glucose into fructose. Throughout the synthesis process, lignin serves as the exclusive carbon precursor, while Mg2+ functions as both a crosslinking agent and a metallic active center. This enables a one-step synthesis of MgO@OMC via a solvent-induced evaporation self-assembly (EISA) method. The synthesized MgO@OMCs exhibit an impeccable 2D hexagonal ordered mesoporous structure, in addition to a substantial specific surface area (378.2 m2/g) and small MgO nanoparticles (1.52 nm). Furthermore, this catalyst was shown active, selective, and reusable in the isomerization of glucose to fructose. It yields 41 % fructose with a selectivity of up to 89.3 % at a significant glucose loading of 7 wt% in aqueous solution over MgO0.5@OMC-600. This performance closely rivals the current maximum glucose isomerization yield achieved with solid base catalysts. Additionally, the catalyst retains a fructose selectivity above 60 % even after 4 cycles, a feature attributable to its extended ordered mesoporous structure and the spatial confinement effect of the OMCs, bestowing it with high catalytic efficiency.

Synthesis and Catalytic Applications of Advanced Sn- and Zr-Zeolites Materials

The incorporation of isolated Sn (IV) and Zr (IV) ions into silica frameworks is attracting widespread attention, which exhibits remarkable catalytic performance (conversion, selectivity, and stability) in a broad range of reactions, especially in the field of biomass catalytic conversion. As a representative example, the conversion route of carbohydrates into valuable platform and commodity chemicals such as lactic acid and alkyl lactates, has already been established. The zeotype materials also possess water-tolerant ability and are capable to be served as promising heterogeneous catalysts for aqueous reactions. Therefore, dozens of Sn- and Zr-containing silica materials with various channel systems have been prepared successfully in the past decades, containing 8 membered rings (MR) small pore CHA zeolite, 10-MR medium pore zeolites (FER, MCM-56, MEL, MFI, MWW), 12-MR large pore zeolites (Beta, BEC, FAU, MOR, MSE, MTW), and 14-MR extra-large pore UTL zeolite. This review about Sn- and Zr-containing metallosilicate materials focuses on their synthesis strategy, catalytic applications for diverse reactions, and the effect of zeolite characteristics on their catalytic performances.

Interaction of Organogermanium Compounds with Saccharides in Aqueous Solutions: Promotion of Aldose-to-ketose Isomerization and Its Molecular Mechanism

This review discusses sugar isomerization with organogermanium compounds. Organogermanium compounds markedly increase the aldose-ketose (glucose-fructose or lactose-lactulose) isomerization ratio, double the initial reaction rate, and significantly reduce the base-catalyzed degradation of sugars. 1H-nuclear magnetic resonance analysis reveals that the affinity of organogermanium compounds with a 3-(trihydroxygermyl)propanoic acid (THGP) structure toward ketoses is 20-40 times stronger than that toward aldoses; thus, such organogermanium compounds form complexes more readily with ketoses than with aldoses. Stable ketose complexes, which contain multiple cis-diol structures and high fractions of furanose structures, suppress the reverse ketose-aldose reaction, thereby shifting the equilibrium toward the ketose side. These complexes also protect sugar molecules from alkaline degradation owing to the repulsion between anionic charges. The increased rate of the initial reaction in the alkaline isomerization process results from stabilizing the transition state by forming a complex between THGP and a cis-enediol intermediate. The cyclic pentacoordinate or hexacoordinate THGP structures give rise to a conjugated system of germanium orbitals, which is extended through dπ-pπ interactions, thereby improving the stability of the complex. Based on these results, we have developed a bench-scale lactulose syrup manufacturing plant incorporating a system to separate, recover, and reuse organogermanium poly-trans-[(2-carboxyethyl)germasesquioxane]. This manufacturing plant can be used as a model of an alkaline isomerization accelerator for continuous industrial production.

Conversion of low-rank coal and sewage sludge into syngas for H2SO4 production and straw hydrolysis

This study investigates the potential of using sewage sludge and low-rank coal for the sustainable production of sulfuric acid, which can then be used for the hydrolysis of straw through ASPEN PLUS simulation. Pyrolysis and gasification processes were used to convert sewage sludge and low-rank coal into syngas, which were then purified and oxidized to produce H2SO4 and NH3 gas. The pyro-gasification enhanced syngas yield. The effects of key process parameters such as temperature, steam-to-biomass ratio, equivalence ratio, and feedstock composition on the yield and composition of syngas and H2SO4 coupled with minor parameters like pressure were investigated. The simulation was conducted over the temperature and pressure range of 400 - 900°°C and 70 - 150 kPa respectively. While the steam-to-biomass ratio and equivalence ratio were respectively varied from 0.66 - 1.65 and 0.14 - 0.35. Part of the 1012.88 kg/h of H2SO4 produced was used to hydrolyze straw, producing glucose as a valuable feedstock for biorefineries. About 3989.10 kg/h of NH3 was produced. Results showed that the use of sewage sludge and low-rank coal as feedstocks for syngas production can be a sustainable and cost-effective alternative to traditional fossil fuels. The resulting H2SO4 can also be used for various other applications, such as in the production of fertilizers and detergents. Overall, this study agrees with the literature, demonstrates the potential of integrating biomass and waste resources for the sustainable production of high-value chemicals and fuels, and contributes to the field of sustainable chemical and energy production while addressing environmental and economic considerations.

Tuning of MgO's base characteristics by blending it with amphoteric ZnO facilitating the selective glucose isomerization to fructose for bioenergy development

Fructose serves as an important intermediate in the preparation of liquid fuel compounds. Herein, we report its selective production via a chemical catalysis method over ZnO/MgO nanocomposite. The blending of an amphoteric ZnO with MgO reduced the latter's unfavorable moderate/strong basic sites that can influence the side reactions in the sugar interconversion, reducing fructose productivity. Of all the ZnO/MgO combinations, a 1 : 1 ratio of ZnO and MgO showed a 20% reduction in moderate/strong basic sites in MgO with ∼2-2.5 times increase in weak basic sites (overall), which is favorable for the reaction. The analytical characterizations affirmed that MgO settles on the surface of ZnO by blocking the pores. The amphoteric ZnO undertakes the neutralization of the strong basic sites and improves the weak basic sites (cumulative) by the Zn-MgO alloy formation. Therefore, the composite afforded as high as 36% fructose yield and 90% selectivity at 90 °C; especially, the improved selectivity can be accounted for by the effect of both basic and acidic sites. The favorable action of acidic sites in controlling the unwanted side reactions was maximum when an aqueous medium contained 1/5^th methanol. However, ZnO's presence regulated the glucose's degradation rate by up to 40% compared to the kinetics of pristine MgO. From the isotopic labelling experiments, the proton transfer pathway (or LdB-AvE mechanism by the formation of 1,2-enediolate) is dominant in the glucose-to-fructose transformation. The composite exhibited a long-lasting ability based on the good recycling efficiency of up to 5 cycles. The insights into the fine-tuning of the physicochemical characteristics of widely available metal oxides would help develop a robust catalyst for sustainable fructose production for biofuel production (via a cascade approach).

Mass Spectrometry Approach for Differentiation of Positional Isomers of Saccharides: Toward Direct Analysis of Rare Sugars

Rare sugars have gained popularity in recent years due to their use in antiaging treatments, their ability to sweeten with few calories, and their ability to heal infections. Rare sugars are found in small quantities in nature, and they exist typically as isomeric forms of traditional sugars, rendering some challenges in their isolation, synthesis, and characterization. In this work, we present the first direct mass spectrometric approach for differentiating structural isomers of sucrose that differ only by their glycosidic linkages. The method employed a noncontact nanoelectrospray (nESI) platform capable of analyzing minuscule volumes (5 μL) of saccharides via the formation of halide adducts ([M+X]-; X = Cl and Br). Tandem mass spectrometry analysis of the five structural isomers of sucrose afforded diagnostic fragment ions that can be used to distinguish each isomer. Detailed mechanisms showcasing the distinct fragmentation pattern for each isomer are discussed. The method was applied to characterize and confirm the presence of all five selected rare sugars in raw honey complex samples. Aside from the five natural α isomers of sucrose, the method was also suitable for differentiating some β isomers of the same glycosidic linkages, provided the monomeric sugar units are different. The halide adduct formation via the noncontact nESI source was also proven to be effective for oligosaccharides such as raffinose, β-cyclodextrin, and maltoheptaose. The results from this study encourage the future development of methods that function with simple operation to enable straightforward characterization of small quantities of rare sugars.

Erythrose and Threose: Carbonyl Migrations, Epimerizations, Aldol, and Oxidative Fragmentation Reactions under Plausible Prebiotic Conditions

The prebiotic generation of sugars in the context of origins of life studies is of considerable interest. Among the important intramolecular processes of sugars are carbonyl migrations and accompanying epimerizations. Herein we describe the carbonyl migration-epimerization process occurring down the entire carbon chain of chirally pure d-tetroses sugars under mild conditions. Employing chirally pure 1-¹³ C-erythrose, 4-¹³ C-erythrose and 1-¹³ C-threose, we (1) identify all the species formed as the carbonyl migrates down the four-carbon chain and (2) assess the rates associated with the production of each of these species. Competing aldol reactions and oxidative fragmentation processes were also observed. Further observations of self-condensation of glycolaldehyde mainly yielding 2-keto-hexoses (sorbose and tagatose) and tetrulose also provides a basis for understanding the effect of carbonyl migrations on the product distribution in plausible prebiotic scenarios.

A Plausible Prebiotic Path to Nucleosides: Ribosides and Related Aldosides Generated from Ribulose, Fructose, and Similar Abiotic Precursors

The prebiotic origins of ribose, nucleosides, and eventually RNA are enduring questions whose answers are central to the RNA world hypothesis. The abiotic synthesis of sugars was first demonstrated over a century ago, but no known prebiotic reaction produces ribose (an aldose sugar) selectively and in good yield. In contrast, ribulose, and fructose (ketose sugars) and other monosaccharides are formed in high yield by several robust abiotic reactions. It is reported here that ketose sugars - both ketopentoses and ketohexoes - serve as precursors for the formation of ribosides and other aldosides, as demonstrated by glycoside-forming reactions involving barbituric acid, a plausibly prebiotic nucleobase. Moreover, a one-pot reaction of glyceraldehyde and barbituric acid was discovered which under mild conditions, and without special minerals or other catalysts, results in the formation of glycosides. These results reveal that an exclusive or high-yielding generation of free ribose was not required for its incorporation into processes that provided the foundations for life.

Radiosynthesis, Preclinical, and Clinical Positron Emission Tomography Studies of Carbon-11 Labeled Endogenous and Natural Exogenous Compounds

The presence of positron emission tomography (PET) centers at most major hospitals worldwide, along with the improvement of PET scanner sensitivity and the introduction of total body PET systems, has increased the interest in the PET tracer development using the short-lived radionuclides carbon-11. In the last few decades, methodological improvements and fully automated modules have allowed the development of carbon-11 tracers for clinical use. Radiolabeling natural compounds with carbon-11 by substituting one of the backbone carbons with the radionuclide has provided important information on the biochemistry of the authentic compounds and increased the understanding of their in vivo behavior in healthy and diseased states. The number of endogenous and natural compounds essential for human life is staggering, ranging from simple alcohols to vitamins and peptides. This review collates all the carbon-11 radiolabeled endogenous and natural exogenous compounds synthesised to date, including essential information on their radiochemistry methodologies and preclinical and clinical studies in healthy subjects.

Enhanced Catalytic Activity of Modified ZSM-5 Towards Glucose Isomerization to Fructose

The present study focuses on generating mesopores within H-ZSM-5 (H-Z) zeolite via desilication and dealumination to incorporate Lewis acidic metal, such as Sn, into the framework (Sn₄ ZS₁₈₀ A₁₅ ) to catalyse glucose isomerisation. Sn₄ ZS₁₈₀ A₁₅ possesses enhanced surface area (457 m²  g^-1 ), mesopore volume (0.585 cm³  g^-1 ) and a high weak-medium to strong acidic sites ratio, compared to parent H-Z (395 m²  g^-1 ; 0.174 cm³  g^-1 ). DRS-UV-Vis and XPS results corroborate Sn incorporation into the framework of Sn₄ ZS₁₈₀ A₁₅ , based on the absorbance peak around 200-220 nm and peaks appearing at 495.8 and 487.4 eV, respectively. Sn₄ ZS₁₈₀ A₁₅ exhibits higher catalytic activity towards glucose isomerisation in ethanol-water at 110 °C, yielding 44.2 % fructose with 80.0 % selectivity. Conversely, the parent H-Z afforded negligible glucose conversion with a fructose yield of <1 % under identical conditions. Moreover, Sn-incorporated on dealuminated (Sn₄ ZS₀ A₁₅ ) and desilicated (Sn₄ ZS₁₈₀ A₀ ) catalysts give a low yield of fructose (7-10 %), signifying the requirement of the desilication-dealumination process before incorporating Sn into the framework.

Structure–activity relationships of LDH catalysts for the glucose-to-fructose isomerisation in ethanol

Hydrotalcite catalysed liquid phase glucose isomerisation in EtOH.

Catalytic production of 1,2-propanediol from sucrose over a functionalized Pt/deAl-beta zeolite catalyst

To eliminate the dependence on fossil fuels and expand the applications of biomass conversion, an efficient Pt/deAl-beta@Mg(OH)₂ catalyst was designed, with dealuminated beta zeolite loaded with Pt as the core and Mg(OH)₂ as the shell. The catalyst was used to produce 1,2-propanediol (1,2-PDO) from sucrose. The preparation and reaction conditions of the catalyst were optimized. The optimal yield of 1,2-PDO was 33.5% when the conditions were 20 h of dealumination, 3.0 wt% Pt loading, 5.0 wt% Mg(OH)₂, 200 mg of catalyst, 10 mL (11.25 mg mL^-1) of sucrose solution, an initial H₂ pressure of 6 MPa, 200 °C, and 3 h. The core-shell structure of the modified beta zeolite shows good stability, yielding more than 30.0% after three cycles of reuse. Firstly, the molecular zeolite can host more acid sites after dealumination by concentrated nitric acid and this can prolong the catalyst's service life. Secondly, the loading of Pt increases the distribution of acid sites and improves the shape selectivity of the catalyst. The introduction of alkali produces many alkaline sites, inhibits the occurrence of side reactions, and increases the product yield. The above modification methods increase the production of 1,2-PDO by promoting isomerization between glucose and fructose from sucrose hydrolysis and the reverse aldol condensation (RAC) reaction. This paper provides a theoretical basis and reference route for applying biomass conversion technology in practical production, which is of great significance for developing biomass resources into high-value-added chemical products.

Novel Challenges on the Catalytic Synthesis of 5-Hydroxymethylfurfural (HMF) from Real Feedstocks

The depletion of fossil resources makes the transition towards renewable ones more urgent. For this purpose, the synthesis of strategic platform-chemicals, such as 5-hydroxymethylfurfural (HMF), represents a fundamental challenge for the development of a feasible bio-refinery. HMF perfectly deals with this necessity, because it can be obtained from the hexose fraction of biomass. Thanks to its high reactivity, it can be exploited for the synthesis of renewable monomers, solvents, and bio-fuels. Sustainable HMF synthesis requires the use of waste biomasses, rather than model compounds such as monosaccharides or polysaccharides, making its production more economically advantageous from an industrial perspective. However, the production of HMF from real feedstocks generally suffers from scarce selectivity, due to their complex chemical composition and HMF instability. On this basis, different strategies have been adopted to maximize the HMF yield. Under this perspective, the properties of the catalytic system, as well as the choice of a suitable solvent and the addition of an eventual pretreatment of the biomass, represent key aspects of the optimization of HMF synthesis. On this basis, the present review summarizes and critically discusses the most recent and attractive strategies for HMF production from real feedstocks, focusing on the smartest catalytic systems and the overall sustainability of the adopted reaction conditions.

Kinetic Salt Effect on Base-Catalyzed Isomerization of d-Glucose into d-Fructose

Isomerization of d-glucose (Glc) into d-fructose (Fru) is of great importance for food sector as well as for valorization of lignocellulosic biomass. Soluble and solid bases exhibit high catalytic activity for the isomerization. Here, we report a salt effect on the base-catalyzed aqueous-phase Glc-Fru isomerization. Addition of soluble salts (Na₂ SO₄ , NaNO₃ , K₂ SO₄ , and NaCl) results in an increased apparent reaction rate (factors of 1.5 to 6). The salt effect was observed both in the presence of soluble base NaOH at constant pH value and solid bases MgO, Li₃ PO₄ , and Mg-Al hydrotalcite. Apparent activation energy and UV absorption spectra were not significantly influenced by addition of salts. Potentiometric titration showed that the acidity constants of the saccharides increase in the presence of electrolytes. Since the rate of the isomerization depends on the thermodynamic acidity constant of Glc, the isomerization is accelerated by the presence of electrolytes.

Novel Recyclable UCST-Type Immobilized Glucose Isomerase Biocatalyst with Excellent Performance for Isomerization of Glucose to Fructose

The development of a suitable immobilization strategy to improve the performance of immobilized glucose isomerase for the isomerization of glucose to fructose is crucial to promoting the industrial production of high-fructose syrup. In this work, a novel recyclable upper critical solution temperature (UCST)-type mVBA-b-P(AAm-co-AN)@glucose isomerase biocatalyst (PVAA@GI) was prepared, and the immobilized glucose isomerase could capture the glucose substrate through the affinity of 4-vinylbenzeneboronic acid (4-VBA) and the glucose substrate, which led to the enhanced substrate affinity and catalytic efficiency of the PVAA@GI. The biocatalyst exhibited excellent stability in pH, thermal, storage, and recycling compared to the free enzyme. The mVBA-b-P(AAm-co-AN)@glucose isomerase biocatalyst displayed reversibly soluble-insoluble characteristics with temperature change, which was in the soluble state during the enzyme reaction process but could be recovered in an insoluble form by lowering the temperature after the reaction. The highest fructose production rate reached 62.79%, which would have potential application in the industrial production of high-fructose syrup.

Study of base-catalyzed isomerization of d-glucose with a focus on reaction kinetics

We explored the isomerization of d-glucose into d-fructose using the simplest possible base catalyst, aqueous NaOH, to maintain a constant pH value during the reaction. Under the applied mild conditions (T 50–90 °C, pH 9.5–11.5), yields of d-fructose of up to 31% were observed. Selectivity-conversion plots were not significantly influenced by variation of the temperature, pH value or substrate concentration. A reaction network for kinetic modelling includes d-glucose-d-fructose interconversion, co-production of d-mannose and d-allulose (also known as d-psicose) as well as decomposition paths after deprotonation of the hexoses. All four hexoses were employed as substrates in the isomerization. Thermodynamic ionization constants of the saccharides were measured by means of potentiometric titration. In the kinetic studies, pH-independent rate constants as well as activation energies were determined. The obtained kinetic and thermodynamic results as well as selectivity-conversion correlations present a useful benchmark for soluble and solid base catalysts.

From cis-Lobeline to trans-Lobeline: Study on the Pharmacodynamics and Isomerization Factors

Lobeline is an alkaloid derived from the leaves of an Indian tobacco plant (Lobelia inflata), which has been prepared by chemical synthesis. It is classified as a partial nicotinic agonist and has a long history of therapeutic usage ranging from emetic and respiratory stimulant to tobacco smoking cessation agent. The presence of both cis and trans isomers in lobeline is well known, and many studies on the relationship between the structure and pharmacological activity of lobeline and its analogs have been reported. However, it is a remarkable fact that no studies have reported the differences in pharmacological activities between the two isomers. In this article, we found that different degrees of isomerization of lobeline injection have significant differences in respiratory excitatory effects in pentobarbital sodium anesthetized rats. Compared with cis-lobeline injections, the respiratory excitatory effect was significantly reduced by 50.2% after administration of injections which contained 36.9% trans-lobeline. The study on the influencing factors of isomerization between two isomers shown that this isomerization was a one-way isomerism and only converted from cis to trans, where temperature was the catalytic factor and pH was the key factor. This study reports a new discovery. Despite the widespread use of ventilators, first-aid medicines such as nikethamide and lobeline has retired to second line, but as a nonselective antagonist with high affinity for a4b2 and a3b2 nicotinic acetylcholine receptors (nAChRs). In recent years, lobeline has shown great promise as a therapeutic drug for mental addiction and nervous system disorders, such as depression, Alzheimer disease and Parkinson disease. Therefore, we suggest that the differences between two isomers should be concerned in subsequent research papers and applications.

Enhanced catalytic activity of layered double hydroxides via in-situ reconstruction for conversion of glucose/food waste to methyl lactate in biorefinery

Conversion of food waste into valuable chemicals under mild conditions has attracted increasing attention. Herein, a series of nano-sized MgAl layered double hydroxides (LDHs) were firstly developed as solid base catalyst for the methyl lactate (MLA) production directly from glucose/food waste. Glucose, which could be easily obtained from cellulose or starch-rich food waste via hydrolysis, was thus selected as the model compound. It is inspiring to find that the metal hydroxide layer in prepared LDHs was highly stable and suitable enlarged interlayer distance was reconstructed owing to in-situ intercalation of formed aromatics during the reaction, which was demonstrated by ²⁷Al magic angle spinning nuclear magnetic resonance and time-of-flight secondary ion mass spectrometry analysis. As a result, in-situ activation of the catalysts along with gradually enhanced catalytic activity was obtained in the recycling runs and the highest MLA yield of 47.6% from glucose was achieved over LDHs (5:1) after 5 runs at 150 °C. Most importantly, the scope was further extended to other typical substrates (e.g. Chinese cabbage and rice) and the results demonstrated the effectiveness of present conversion system for real food waste.

High-Productivity Continuous Conversion of Glucose to α-Hydroxy Esters over Postsynthetic and Hydrothermal Sn-Beta Catalysts

The retro-aldol fragmentation of glucose is a complex reaction of industrial relevance, which provides a potentially sustainable route for the production of α-hydroxyester compounds of relevance to the green polymer industry, such as methyl lactate and methyl vinyl glycolate. Although the zeolite catalyst, Sn-Beta, has shown itself to be a promising catalyst for this process, important information concerning the stability of the catalyst during continuous operation is not yet known, and improvements to its yield of retro-aldol products are also essential. Here, we perform detailed spectroscopic studies of a selection of Sn-Beta catalysts and evaluate their performances for the retro-aldol fragmentation of glucose under continuous processing conditions, with the dual aims of developing new structure-activity-lifetime relationships for the reaction and maximizing the productivity and selectivity of the process. Kinetic studies are performed under both established reaction conditions and in the presence of additional promoters, including water and alkali salts. Generally, this study demonstrates that the reaction conditions and choice of catalyst cannot be optimized in isolation, since each catalyst explored in this study responds differently to each particular process perturbation. However, by evaluating each type of the Sn-Beta catalyst under each set of reaction conditions, we reveal that postsynthetic Sn-Beta catalysts exhibit the best levels of performance when activity, selectivity, and stability are taken into account. Specifically, the best levels of performance are obtained with a postsynthetic Sn-Beta catalyst that is preactivated in a flow of methanol prior to reaction, which provides α-hydroxyester yields over 90% at the early stages of continuous operation and operates at high yield and selectivity for over 60 h on stream. Space-time-yields over two orders of magnitude higher than any previously reported for this reaction are achieved, setting a new benchmark in terms of the retro-aldol fragmentation of glucose.

Low-energy hemiacetal dehydrogenation pathway：co-production of gluconic acid and green hydrogen via glucose dehydrogenation

Exploring low-energy reaction pathway of catalytic biomass conversion can lead to wider application and the achievement of sustainability objectives. Since glucose dehydrogenation to gluconic acid and H 2 is a cost-effective alternative to glucose oxidation, this study aims to elucidate its mechanism. The detection of lactone as an intermediate indicates that cyclic glucose reacts directly via its hemiacetal group-ring opening is not involved; that is, cyclic glucose is dehydrogenated to lactone, which is further hydrolyzed to gluconic acid. The source of hydrogen is confirmed to be glucose and water by Isotope tracing confirms. Density function theory (DFT) calculations demonstrate that Hemiacetal Dehydrogenation Pathway (this work) is less energy intensive than Ring-opening Oxidation Pathway (previous works). This study provides a new dehydrogenation strategy to produce gluconic acid and H 2 from biomass under mild conditions.

Sustainable Catalytic Synthesis of 2,5-Diformylfuran from Various Carbohydrates

Versatile homogeneous and heterogeneous catalysts that convert carbohydrates to 2,5-diformylfuran (DFF) are essential for the development of sustainable processes for producing high-value chemicals from biomass-derived carbohydrates. An efficient catalytic system consisting of Br−, disulfide, and dimethylsulfoxide (DMSO) promoted the sustainable and selective synthesis of DFF in modest-to-good yields from various carbohydrates, such as fructose, glucose, mannose, galactose, and sucrose. Heterogeneous catalysts containing Br− also facilitated this reaction with recyclable high yields.

N-Doped natural albite mineral as green solid catalyst for efficient isomerization of glucose into fructose in water

A green and effiecient N-doped mineral catalyst (i.e., CS/Ab) prepared by biomass waste and natural albite was explotied for glucose-to-fructose isomerization.

Revealing the contributions of homogeneous and heterogeneous catalysis to isomerization of d-glucose into d-fructose in the presence of basic salts with low solubility

Hydroxide anions are identified as catalytically active species for the isomerization of d-glucose to d-fructose over low soluble basic salts. The highest selectivity for d-fructose was obtained for catalysis by MgCO3.

Functional Phenylboronate Polymers for the Recovery of Diols, Sugar Alcohols, and Saccharides from Aqueous Solution

The ongoing transition from fossil to renewable feedstocks demands new efficient processes for an economically viable production of biomass-derived commodities and fine chemicals. Novel energy- and material-efficient product purification and separation will play a crucial role due to altered product and feed composition. The present study comprises the synthesis and tests of cross-linked p-vinylphenylboronate polymers for the separation of 18 diols, sugar alcohols, and saccharides, which can be obtained during biomass processing. The separation was based on molecular recognition, that is, esterification of the phenylboronate with vicinal diols. A correlation of the molecular complexation constant, the polymer swelling, and the maximum adsorption capacity was found. The adsorption curves over time were recorded. Preliminary results on competitive adsorption of binary mixtures showed a high potential for the separation of substrates with significantly different complexation constants. Desorption tests implied easier desorption of substrates that only adsorb on the outer polymer shell.

Unexpected reactivity related to support effects during xylose hydrogenation over ruthenium catalysts

Xylose is a major component of hemicelluloses. In this paper, its hydrogenation to xylitol in aqueous medium was investigated with two Ru/TiO₂ catalysts prepared with two commercial TiO₂ supports. A strong impact of the support on catalytic performance was evidenced. Ru/TiO₂-R led to fast and selective conversion of xylose (100% conversion in 2 h at 120 °C with 99% selectivity) whereas Ru/TiO₂-A gave a slower and much less selective transformation (58% conversion in 4 h at 120 °C with 17% selectivity) with the formation of several by-products. Detailed characterization of the catalysts with ICP, XRD, FTIR, TEM, H₂ chemisorption, N₂ porosimetry, TPR and acid-base titration was performed to elucidate the role of each support. TiO₂-R has a small specific surface area with large ruthenium nanoparticles in weak interaction with the TiO₂ support and no acidity, whereas TiO₂-A is a mesoporous material with a large specific surface area that is mildly acidic, and bears small ruthenium particles in strong interaction with the TiO₂ support. The former was very active and selective for xylose hydrogenation to xylitol whereas the latter was less active and poorly selective. Moreover, careful analysis of the reaction products also revealed that anatase TiO₂ can catalyze undesired side-reactions such as xylose isomerisation to various pentoses, and therefore the corresponding unexpected polyols (arabitol, ribitol) were produced during xylose conversion by hydrogenation. In a first kinetic approach, a simplified kinetic model was built to compare quantitatively intrinsic reaction rates of both catalysts. The kinetic constant for hydrogenation was 20 times higher for Ru/TiO₂-R at 120 °C.