Efficient Epimerization of Aldoses Using Layered Niobium Molybdates

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.

A new synthesis of d-lyxose from d-arabinose

A new synthesis of rare d-lyxose from easily available d-arabinose is disclosed. The route includes 7 steps with a total 40% yield. Inversion of configuration at C3 promoted by DAST reagent is utilized on trans-2,3-di-hydroxy pentofuranose to provide cis-2,3-di-hydroxy pentofuranose, which is hardly synthesized using normal method.

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

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

Effect of the Wells–Dawson phosphomolybdic heteropolyacid on the conversion of glucose into glycolic acid

The Wells–Dawson phosphomolybdic heteropolyacid had high activity and selectivity in the epimerization of glucose into mannose and the [2 + 4] retro-aldol reaction of glucose/mannose.

Advances in catalytic routes for the production of carboxylic acids from biomass: a step forward for sustainable polymers

Polymers are ubiquitously present in our daily life because they can meet a wide range of needs and fields of applications. This success, based on an irresponsible linear consumption of plastics and the access to cheap oil, is creating serious environmental problems. Two lines of actions are needed to cope with them: to adopt a circular consumption of plastics and to produce renewable carbon-neutral monomers. This review analyses the recent advances in the chemocatalytic processes for producing biomass-derived carboxylic acids. These renewable carboxylic acids are involved in the synthesis of relevant general purpose and specialty polyesters and polyamides; some of them are currently derived from oil, while others can become surrogates of petrochemical polymers due to their excellent performance properties. Polyesters and polyamides are very suitable to be depolymerised to other valuable chemicals or to their constituent monomers, what facilitates the circular reutilisation of these monomers. Different types of carboxylic acids have been included in this review: monocarboxylic acids (like glycolic, lactic, hydroxypropanoic, methyl vinyl glycolic, methyl-4-methoxy-2-hydroxybutanoic, 2,5-dihydroxypent-3-enoic, 2,5,6-trihydroxyhex-3-enoic acids, diphenolic, acrylic and δ-amino levulinic acids), dicarboxylic acids (2,5-furandicarboxylic, maleic, succinic, adipic and terephthalic acids) and sugar acids (like gluconic and glucaric acids). The review evaluates the technology status and the advantages and drawbacks of each route in terms of feedstock, reaction pathways, catalysts and economic and environmental evaluation. The prospects and the new research that should be undertaken to overcome the main problems threatening their economic viability or the weaknesses that prevent their commercial implementation have also been underlined.

H3PMo12O40 Immobilized on Amine Functionalized SBA-15 as a Catalyst for Aldose Epimerization

In this work various amount of phosphomolybdic acid (PMo) were immobilized on amine functionalized SBA-15 and used as heterogeneous catalysts in the epimerization of glucose in aqueous solution. 13.3PMo/NH₂-SBA-15 exhibited the best catalytic performance with a glucose conversion of 34.8% and mannose selectivity of 85.6% within two hours at 120 °C. The activation energy of 80.1 ± 0.1 kJ·mol^-1 was lower than that of 96 kJ·mol^-1 over the homogeneous H₃PMo₁₂O₄₀ catalyst. The catalytic activities of 13.3PMo/NH₂-SBA-15 for the transformation of some other aldoses including mannose, arabinose and xylose were also investigated.

MoOx Nanoparticle Catalysts for d-Glucose Epimerization and Their Electrical Immobilization in a Continuous Flow Reactor

Activity and immobilization of catalysts in liquid-phase reactions seem not to coexist. We report here the excellent activity of an MoO_x nanoparticle (NP) catalyst for d-glucose epimerization to d-mannose and the electrical immobilization of NPs in a flow reaction. Prior to that, a green and one-pot method to synthesize the MoO_x NPs (3.05 nm) via oxidizing metal Mo by hydrogen peroxide was presented. The NPs overwhelmed the reported catalysts including epimerase for d-glucose epimerization, originating from a strong interaction between the NPs and the reactant that was demonstrated by ex situ and in situ characterizations and theoretical calculations. The electrically charged feature of NPs inspired us to find a convenient way to "immobilize" them inside an activated carbon bed, and thereby, a flow reactor was assembled. The continuous epimerization was run under 24 V for 16 days with an almost unchanged activity, and only 3.2% of total Mo was lost.

Rational Design of Metal Oxide Solid Acids for Sugar Conversion

Aqueous-phase acid-catalyzed reactions are essential for the conversion of cellulose-based biomass into chemicals. Brønsted acid and Lewis acid play important roles for these reactions, including hydrolysis of saccharides, isomerization and epimerization of aldoses, conversion of d-glucose into 5-hydroxymethylfurfural, cyclodehydration of sugar alcohols and conversion of trioses into lactic acid. A variety of metal oxide solid acids has been developed and applied for the conversion of sugars so far. The catalytic activity is mainly dependent on the structures and types of solid acids. Amorphous metal oxides possess coordinatively unsaturated metal sites that function as Lewis acid sites while some crystal metal oxides have strong Brønsted acid sites. This review introduces several types of metal oxide solid acids, such as layered metal oxides, metal oxide nanosheet aggregates, mesoporous metal oxides, amorphous metal oxides and supported metal oxides for sugar conversions.

Catalytic use of layered materials for fine chemical syntheses

The present work reviews the catalytic use of layered solid materials for fine chemical syntheses with focus on layered double hydroxides, but including other classes of layered compounds of catalytic relevance.

An Effective Heterogeneous Catalyst of [BMIM]3 PMo12 O40 for Selective Sugar Epimerization

The development of heterogeneous catalysts for the epimerization of sugars has received much less attention than that for the isomerization of sugars. To date, molybdates are the most effective catalysts for the epimerization of sugars, although they lack stability toward hydrolysis of their active sites in water. To solve the issue of the formation of a highly water-soluble heteropolyblue (PMo_red ) for phosphomolybdates (PMos) in aqueous reaction systems, herein, a 1-butyl-3-methylimidazolium phosphomolybdate ([BMIM]₃ PMo₁₂ O₄₀ ) was synthesized through an ion-exchange method. This catalyst was effective and selective for the C2-epimerization of sugars under mild reaction conditions (<100 °C; 1-2 h) with good water-tolerant properties. The reaction was confirmed to occur in a heterogeneous manner and no leaching of PMo_red was detected by means of UV/Vis spectroscopy. Moreover, the catalyst can be simply separated by filtration and reused for at least eight cycles without a drop in catalytic activity. XRD, FTIR, and X-ray photoelectron spectroscopy measurements indicate that the catalyst is stable under the reaction conditions. In a comparison of the catalytic activity and surface wettability with those of other PMo salts, that is, 1-ethyl-3-methylimidazolium phosphomolybdate ([EMIM]₃ PMo₁₂ O₄₀ ), 1-hexyl-3-methylimidazolium ([HexMIM]₃ PMo₁₂ O₄₀ ), [choline]₃ PMo₁₂ O₄₀ , and cetyltrimethylammonium phosphomolybdate ([CTA]₃ PMo₁₂ O₄₀ ), it is found that [BMIM]₃ PMo₁₂ O₄₀ has more appropriate hydrophobic-hydrophilic balance, which should be responsible for better catalytic activity and stability.

Mechanochemical Decomposition of Crystalline Cellulose in the Presence of Protonated Layered Niobium Molybdate Solid Acid Catalyst

Direct depolymerization of crystalline cellulose into water-soluble sugars by solvent-free ball milling was examined in the presence of a strongly acidic layered metal oxide, HNbMoO₆ , resulting in full conversion with 72 % yield of water-soluble sugars. Measurements by ¹³ C cross-polarization magic angle spinning NMR spectroscopy and X-ray diffraction revealed that amorphization of cellulose occurred rapidly within 10 min. Scanning electron microscopy equipped with an energy dispersive X-ray indicated that the substrate and the catalyst were well mixed during milling. The time course of the product distribution showed that most of the resultant water-soluble sugars were produced not by successive degradation of oligosaccharides but by direct depolymerization of cellulose chains. The products included glucose, mannose, and cello-oligomers, as well as anhydrosugars. Addition of small amounts of polar solvents increased the sugar yield, whereas further addition of water decreased the selectivity to anhydrosugars. Calculations of the mechanical energy required for the ball-milling process showed that 0.02 % was utilized for the chemical transformation under the conditions examined in this study.

Aldose to ketose interconversion: galactose and arabinose isomerization over heterogeneous catalysts

Isomerization of glucose, galactose and arabinose to corresponding keto-sugars was studied in the present work over a range of heterogeneous catalysts.

Catalyst and Process Design for the Continuous Manufacture of Rare Sugar Alcohols by Epimerization-Hydrogenation of Aldoses

Sugar alcohols are applied in the food, pharmaceutical, polymer, and fuel industries and are commonly obtained by reduction of the corresponding saccharides. In view of the rarity of some sugar substrates, epimerization of a readily available monosaccharide has been proposed as a solution, but an efficient catalytic system has not yet been identified. Herein, a molybdenum heteropolyacid-based catalyst is developed to transform glucose, arabinose, and xylose into less-abundant mannose, ribose, and lyxose, respectively. Adsorption of molybdic acid onto activated carbon followed by ion exchange to the cesium form limits leaching of the active phase, which greatly improves the catalyst stability over 24 h on stream. The hydrogenation of mixtures of epimers is studied over ruthenium catalysts, and it is found that the precursor to the desired polyol is advantageously converted with faster kinetics. This is explained by density functional theory on the basis of its more favorable adsorption on the metal surface and the lower energy barrier for the addition of a hydrogen atom to the primary carbon atom. Finally, different designs for a continuous process for the conversion of glucose into mannitol are studied, and it is uncovered that two reactors in series with one containing the epimerization catalyst and the other containing a mixture of the epimerization and hydrogenation catalysts increases the mannitol/sorbitol ratio to 1.5 from 1 for a single mixed-bed reactor. This opens a prospective route to the efficient valorization of renewables to added-value chemicals.

Catalytic Isomerization of Biomass-Derived Aldoses: A Review

Selected aldohexoses (D-glucose, D-mannose, and D-galactose) and aldopentoses (D-xylose, L-arabinose, and D-ribose) are readily available components of biopolymers. Isomerization reactions of these substances are very attractive as carbon-efficient processes to broaden the portfolio of abundant monosaccharides. This review focuses on the chemocatalytic isomerization of aldoses into the corresponding ketoses as well as epimerization of aldoses at C2. Recent advances in the fields of catalysis by bases and Lewis acids are considered. The emphasis is laid on newly uncovered catalytic systems and mechanisms of carbohydrate transformations.