Search Results (10)

The catalytic production of lactic acid from carbohydrates was considered a green way to efficiently utilize renewable biomass resources. In this study, an easy post-synthesis method was used to prepare a Sn-Beta catalyst for the production of lactic acid from glucose at 180 °C, 2 MPa, and 30 min. With optimized reaction time, temperature, pressure, and the ratio of raw material to catalyst, the yield of lactic acid reached an astonishingly high level of 76.0%. In addition, the catalyst characterizations were performed in-depth, revealing the intrinsic relationship between catalyst performance and structure, proving that the 2 wt% Sn was uniformly dispersed in the skeleton of Beta zeolite, which significantly increased the density of Lewis acid. Thus, the enhanced isomerization and retro-aldol condensation processes over the Lewis acid sites led to the high yield of lactic acid. This catalytic system kept stable after five cycles at mild conditions, showing high potential for industrial biomass utilization. Full article

Using computational methods, we examine if the presence of H₂S can tame the unruly formose reaction by generating a free energy map of the reaction thermodynamics and kinetics of sulfur analogs within the core cycle. With mercaptoaldehyde as the linchpin C₂ species, and feeding the cycle with CH₂O, selected aldol additions and enolizations are kinetically more favorable. Thione formation is thermodynamically less favored compared to aldehydes and ketones, but all these species can be connected by enolization reactions. In some sulfur analogs, the retroaldol transformation of a C4 species back into linchpin species is thermodynamically favorable, and we have found one route incorporating where incorporating sulfur selects for a specific pathway over others. However, as CH₂O diminishes, the aldol addition of larger species is less favorable for the sulfur analogs. Our results also suggest that competing Cannizzaro side reactions are kinetically less favored and thermodynamically disfavored when H₂S is abundant. Full article

The bioconversion of cellulose and the transformation of glycerol can yield various diols, aligning with environmental sustainability goals by reducing dependence on fossil fuels, lowering raw material costs, and promoting sustainable development. However, in the selective hydrogenolysis of glycerol to ethylene glycol (EG) and 1,2-propylene glycol (1,2-PG), challenges such as low selectivity of catalytic systems, poor stability, limited renewability, and stringent reaction conditions remain. The production of diols from cellulose involves multiple reaction steps, including hydrolysis, isomerization, retro-aldol condensation, hydrogenation, and dehydration. Consequently, the design of highly efficient catalysts with multifunctional active sites tailored to these specific reaction steps remains a significant challenge. This review aims to provide a comprehensive overview of the selective regulation of catalysts for producing EG and 1,2-PG from cellulose and glycerol. It discusses the reaction pathways, process methodologies, catalytic systems, and the performance of catalysts, focusing on active site characteristics. By summarizing the latest research in this field, we aim to offer a detailed understanding of the state-of-the-art in glycerol and cellulose conversion to diols and provide valuable guidance for future research and industrial applications. Through this review, we seek to clarify the current advancements and selective control strategies in diol production from glycerol or cellulose, thereby offering critical insights for future investigations and industrial scale-up. Full article

The catalytic transformation of sugars into lactic acid has shown great potential for the scalable utilization of renewable biomass. Herein, RuO_x/MoS₂ catalysts were synthesized with the assistance of CaO for the one-pot conversion of glucose to lactic acid. Under the reaction conditions of 120 °C and 1 MPa O₂, a 96.6% glucose conversion and a 54.3% lactic acid selectivity were realized in the one-pot catalytic reaction, with relatively high stability after four successive cycles. This catalytic system was also effective for the conversion of many other carbohydrate substrates, such as fructose, xylose and cellulose (selectivity 68.9%, 78.2% and 50.6%, respectively). According to catalyst characterizations and conditional experiments, the highly dispersed RuO_x species on the surface of MoS₂, together with OH⁻, promoted isomerization, retro-aldol condensation, dehydration and hydration reactions, resulting in a relatively high lactic acid yield for sugar conversions. Full article

To substitute fossil resources, it is necessary to investigate the conversion of biomass into 1,2-propanediol (1,2-PDO) as a high-value-added chemical. The Pt/deAl-Beta@Mg(OH)₂ catalytic system is designed to obtain a higher 1,2-PDO production yield. The optimal yield of 1,2-PDO is 34.1%. The unique shell-core structure of the catalyst demonstrates stability, with a catalytic yield of over 30% after three times of use. The primary process path from glucose to 1,2-PDO, glucose-hexitol-1,2-PDO, is speculated by the experiments of intermediate product selectivity. The alkaline catalytic mechanism of the reaction process is elucidated by studying catalyst characterization and analyzing different time courses of products. The introduction of Mg(OH)₂ improves the target yield by promoting the isomerization from glucose to fructose and retro-aldol condensation (RAC) conversion, with pseudo-yield increases of 76.1% and 42.1%, respectively. By studying the processes of producing lactic acid and 1,2-PDO from glucose, the glucose hydrogenolysis flow chart is improved, which is of great significance for accurately controlling 1,2-PDO production in industrial applications. The metal, acid, and alkali synergistic catalytic system constructed in this paper can provide a theoretical basis and route reference for applying biomass conversion technology in practice. Full article

l-Tryptophan derivatives, such as hydroxylated or halogenated l-tryptophans, are used in therapeutic peptides and agrochemicals and as precursors of bioactive compounds, such as serotonin. l-Tryptophan biosynthesis depends on another proteinogenic amino acid, l-serine, which is condensed with indole-3-glycerophosphate by tryptophan synthase. This enzyme is composed of the α-subunit TrpA, which catalyzes the retro-aldol cleavage of indole-3-glycerol phosphate, yielding glyceraldehyde-3-phosphate and indole, and the β-subunit TrpB that catalyzes the β-substitution reaction between indole and l-serine to water and l-tryptophan. TrpA is reported as an allosteric actuator, and its absence severely attenuates TrpB activity. In this study, however, we showed that Corynebacterium glutamicum TrpB is catalytically active in the absence of TrpA. Overexpression of C. glutamicumtrpB in a trpBA double deletion mutant supported growth in minimal medium only when exogenously added indole was taken up into the cell and condensed with intracellularly synthesized l-serine. The fluorescence reporter gene of an l-serine biosensor, which was based on the endogenous transcriptional activator SerR and its target promoter P_serE, was replaced by trpB. This allowed for l-serine-dependent expression of trpB in an l-serine-producing strain lacking TrpA. Upon feeding of the respective indole derivatives, this strain produced the l-tryptophan derivatives 5-hydroxytryptophan, 7-bromotryptophan, and 5-fluorotryptophan. Full article

Lipid A, the membrane-bound phosphoglycolipid component of bacteria, is held responsible for the clinical syndrome of gram-negative sepsis. In this study, the fragmentation behavior of a set of synthetic lipid A derivatives was studied by electrospray ionization multistage mass spectrometry (ESI-MSⁿ), in conjunction with tandem mass spectrometry (MS/MS), using low-energy collision-induced dissociation (CID). Genealogical insight about the fragmentation pathways of the deprotonated 4’-monophosphoryl lipid A structural analogs led to proposals of a number of alternative dissociation routes that have not been reported previously. Each of the fragment ions was interpreted using various possible mechanisms, consistent with the principles of reactions described in organic chemistry. Specifically, the hypothesized mechanisms are: (i) cleavage of the C-3 primary fatty acid leaves behind an epoxide group attached to the reducing sugar; (ii) cleavage of the C-3’ primary fatty acid (as an acid) generates a cyclic phosphate connected to the nonreducing sugar; (iii) cleavage of the C-2’ secondary fatty acid occurs both in acid and ketene forms; iv) the C-2 and C-2’ primary fatty acids are eliminated as an amide and ketene, respectively; (v) the ^0,2A₂ cross-ring fragment contains a four-membered ring (oxetanose); (vi) the ^0,4A₂ ion is consecutively formed from the ^0,2A₂ ion by retro-aldol, retro-cycloaddition, and transesterification; and (vii) formations of H₂PO₄⁻ and PO₃⁻ are associated with the formation of sugar epoxide. An understanding of the relation between ^0,2A₂ and ^0,4A₂-type sugar fragments and the different cleavage mechanisms of the two ester-linked primary fatty acids is invaluable for distinguishing lipid A isomers with different locations of a single ester-linked fatty acid (i.e., at C-3 or C-3’). Thus, in addition to a better comprehension of lipid A fragmentation processes in mass spectrometers, our observations can be applied for a more precise elucidation of naturally occurring lipid A structures. Full article

A series of Ru-(Mn-M)O_X catalysts (M: Al, Ti, Zr, Zn) prepared by co-precipitation were investigated in the hydrogenolysis of xylitol in water to ethylene glycol, propylene glycol and glycerol at 200 °C and 60 bar of H₂. The catalyst promoted with Al, Ru-(Mn-Al)O_X, showed superior activity (57 h⁻¹) and a high global selectivity to glycols and glycerol of 58% at 80% xylitol conversion. In comparison, the catalyst prepared by loading Ru on (Mn-Al)O_X, Ru/(Mn-Al)O_X was more active (111 h⁻¹) but less selective (37%) than Ru-(Mn-Al)O_X. Characterization of these catalysts by XRD, BET, CO₂-TPD, NH₃-TPD and TEM showed that Ru/(Mn-Al)O_X contained highly dispersed and uniformly distributed Ru particles and fewer basic sites, which favored decarbonylation, epimerization and cascade decarbonylation reactions instead of retro-aldol reactions producing glycols. The hydrothermal stability of Ru-(Mn-Al)O_X was improved by decreasing the xylitol/catalyst ratio, which decreased the formation of carboxylic acids and enabled recycling of the catalyst, with a very low deactivation. Full article

This review discusses principal patterns that govern the processes of lignins’ catalytic oxidation into vanillin (3-methoxy-4-hydroxybenzaldehyde) and syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde). It examines the influence of lignin and oxidant nature, temperature, mass transfer, and of other factors on the yield of the aldehydes and the process selectivity. The review reveals that properly organized processes of catalytic oxidation of various lignins are only insignificantly (10–15%) inferior to oxidation by nitrobenzene in terms of yield and selectivity in vanillin and syringaldehyde. Very high consumption of oxygen (and consequentially, of alkali) in the process—over 10 mol per mol of obtained vanillin—is highlighted as an unresolved and unexplored problem: scientific literature reveals almost no studies devoted to the possibilities of decreasing the consumption of oxygen and alkali. Different hypotheses about the mechanism of lignin oxidation into the aromatic aldehydes are discussed, and the mechanism comprising the steps of single-electron oxidation of phenolate anions, and ending with retroaldol reaction of a substituted coniferyl aldehyde was pointed out as the most convincing one. The possibility and development prospects of single-stage oxidative processing of wood into the aromatic aldehydes and cellulose are analyzed. Full article

Due to the depletion of fossil fuels, biomass-derived sugars have attracted increasing attention in recent years as an alternative carbon source. Although significant advances have been reported in the development of catalysts for the conversion of carbohydrates into key chemicals (e.g., degradation approaches based on the dehydration of hydroxyl groups or cleavage of C-C bonds via retro-aldol reactions), only a limited range of products can be obtained through such processes. Thus, the development of a novel and efficient strategy targeted towards the preparation of a range of compounds from biomass-derived sugars is required. We herein describe the highly-selective cascade syntheses of a range of useful compounds using biomass-derived sugars as carbon nucleophiles. We focus on the upgrade of C2 and C3 oxygenates generated from glucose to yield useful compounds via C-C bond formation. The establishment of this novel synthetic methodology to generate valuable chemical products from monosaccharides and their decomposed oxygenated materials renders carbohydrates a potential alternative carbon resource to fossil fuels. Full article