Hydrogenation Of Xylose Research Articles

Efficient corn stover-derived metal-supported biochar catalyst for hydrogenation of xylose to xylitol

Xylitol, one of the top twelve chemical building blocks, is commercially synthesized through the xylose hydrogenation reaction using a metal catalyst. Biochar has emerged as an eco-efficient catalyst support material. In this study, biochar derived from corn stover (BCS) was first used as a metal catalyst support material for xylose hydrogenation into xylitol. The catalyst was prepared by carbonizing corn stover (CS), impregnating the resulting biochar with metal, and reducing the metal-impregnated BCS. The catalyst characteristics were comprehensively explored. The Ru/BCS catalyst was employed in xylose conversion to xylitol at different process temperatures (100 – 160 °C), retention times (3 – 12 h), H2 pressures (2 – 5 MPa), and Ru contents (1 – 5 %). The highest xylitol yield (87.0 wt.%) and selectivity (91.6 %) were derived at 120 °C for 6 h under 4 MPa H2 using 5 % Ru. Interestingly, the Ru/BCS catalyst showed high stability under the promising process condition. Additionally, xylitol production from hydrolysates enriched with CS xylose was subsequently explored. On the other hand, the catalyst characterization results revealed that the superior catalytic efficiency of 5Ru/BCS was mainly due to the metal nanoparticles embedded in the biochar. Additionally, BCS proved to be an outstanding support material for a bimetallic hydrogenation catalyst (Ru-Ni/BCS). Therefore, these results indicate that BCS can be a competitive support material for metal hydrogenation catalysts, enhancing environmental friendliness and potentially being employed in industrial-scale xylitol production.

Supported Ruthenium Phosphide as a Promising Catalyst for Selective Hydrogenation of Sugars

AbstractThis work demonstrates that supported ruthenium phosphides (RuP2) are attractive catalysts for selective production of alditols by sugar hydrogenation. In our studies, carbon supported RuP2 with a ruthenium content of 5 wt.– % led to the highest activity in xylose hydrogenation and to nearly 100 % yield for xylitol. ICP‐OES and XRD measurements revealed the stability of this novel RuP2/C catalyst under typical hydrogenation conditions (50 barH2, 120 °C) in aqueous phase. Furthermore, STEM‐EDX illustrated the close proximity of ruthenium and phosphorous on the catalyst site and the formation of nanoparticles in the size of 2–4 nm. The catalyst system was successfully applied for the selective hydrogenation of further sugar substrates, including glucose, fructose, and disaccharides, such as cellobiose and sucrose. Here, the RuP2/C revealed its bifunctional acidic/metallic character, enabling in a tandem reaction the hydrolysis of disaccharides, directly followed by a selective hydrogenation to form sugar alcohols in high yield.

Ruthenium supported on silicate and aluminosilicate mesoporous materials applied to selective sugar hydrogenation: Xylose to xylitol

A series of ruthenium-based catalysts supported on a set of silicate and aluminosilicate mesoporous molecular sieves was synthesized and tested in xylose hydrogenation. The materials were characterized in terms of morphology, textural properties, acidity, as well as ruthenium loading, dispersion, and oxidation state. In general, the aluminosilicates-based catalysts displayed a higher activity compared to their respective silicate supports, which can be ascribed to a higher Ru content and dispersion, enhanced by a higher acidity. The most active synthesized catalyst (Ru/Al-MCM-4) displayed an improved performance compared to a commercial Ru/C catalyst due to a better xylitol selectivity. Two modelling approaches were implemented to describe the kinetic rate. The first model was based on the hypothesis that xylose molecules and hydrogen are adsorbed in different active sites on the catalyst surface, while the second model supposes the formation of an intermediate on the catalyst surface that reacts to form xylitol. Both models gave a very good description of the experimental data.

XylR Overexpression in Escherichia coli Alleviated Transcriptional Repression by Arabinose and Enhanced Xylitol Bioproduction from Xylose Mother Liquor.

Xylitol is a polyol widely used in food, pharmaceuticals, and light industries. It is currently produced through the chemical catalytic hydrogenation of xylose and generates xylose mother liquor as a substantial byproduct in the procedure of xylose extraction. If xylose mother liquor could also be efficiently bioconverted to xylitol, the greenness and atom economy of xylitol production would be largely improved. However, xylose mother liquor contains a mixture of glucose, xylose, and arabinose, raising the issue of carbon catabolic repression in its utilization by microbial conversion. Targeting this challenge, the transcriptional activator XylR was overexpressed in a previously constructed xylitol-producing E. coli strain CPH. The resulting strain CPHR produced 16.61g/L of xylitol in shake-flask cultures from the mixture of corn cob hydrolysate and xylose mother liquor (1:1, v/v) with a xylose conversion rate of 90.1%, which were 2.23 and 2.15 times higher than the starting strain, respectively. Furthermore, XylR overexpression upregulated the expression levels of xylE, xylF, xylG, and xylH genes by 2.08-2.72 times in arabinose-containing medium, suggesting the alleviation of transcriptional repression of xylose transport genes by arabinose. This work lays the foundation for xylitol bioproduction from xylose mother liquor.

Xylose Hydrogenation Promoted by Ru/SiO2 Sol–Gel Catalyst: From Batch to Continuous Operation

Xylose is nowadays converted into xylitol, a popular special chemical sweetener. Xylitol can be used not only in the pharmaceutical and food industries, but also in cosmetics and synthetic resins because of its countless properties. Conventionally, xylitol is produced by slurry reactors operating in batch with dispersed or supported catalysts. Hydrogen is continuously fed to maintain a constant pressure. In this work, the kinetics of the reaction were investigated to find the optimal operating conditions to minimize the by-products obtained. Given the great performances shown by the new Ru/SiO2 sol–gel derived catalyst in glucose hydrogenation, in this work the mentioned catalyst was tested in the hydrogenation of xylose to xylitol both in batch and in continuous production to prove its stability and activity.

XYLITOL PRODUCTION FROM XYLOSE OVER ZIRCONIA-DOPED SILICA SBA-15 SUPPORTED RUTHENIUM CATALYSTS

Xylitol is an important product of xylan valorization — the main hemicellulose of birch and aspen wood. Xylitol is obtained by direct hydrogenation of xylose. In present study, the xylose was obtained by acid hydrolysis of birch wood xylan. The industrial catalyst for the xylitol production process is Raney nickel. Pyrophoricity, tendency to sintering, Ni leaching and contamination of the product are actual problems of its use. We have developed new supported ruthenium catalysts based on mesoporous silicate SBA-15 doped with zirconia. The proposed method of modification of SBA-15 by doping with zirconia improves the hydrothermal stability. The deposited Ru is present in the form of highly dispersed RuO2 particles and is distributed evenly. The catalysts are stable, safe and environmentally friendly. Their high catalytic activity allows the process to be carried out in very mild conditions – in pure water at 70 °C and a pressure of 5.5 MPa H2. While the catalysts provide 96-99% selectivity for xylitol. The introduction of the developed catalysts into the xylitol production might reduce the product purification cost of and the process energy consumption, thereby improving ecological and economic indicators of deep chemical processing of plant raw materials.

Kinetic studies of solid foam catalysts for the production of sugar alcohols: Xylitol from biomass resources

Structured catalysts, such as solid foams, represent a very promising technology for continuous and stable production of high-value compounds derived from biomass, traditionally produced with batch and semibatch technologies using suspended catalysts. However, the synthesis of structured catalysts presents additional challenges related to their structure and the generation of porous coatings with suitable properties for dispersing the catalytically active phase on the support.This work was focused on synthesizing a Ru/C solid foam catalyst and investigating its activity in the selective hydrogenation of xylose to xylitol under different operational conditions. The carbon coating, the key step of preparation, was based on the formation and pyrolysis of poly(furfuryl alcohol) in the presence of different amounts of poly(ethylene glycol) (PEG; M = 8 kDa) as a pore former, which enabled tuning the support porosity. Thus, the catalyst prepared with 5 wt% PEG presented a micro-to-mesopores volume ratio of 1, and a good dispersion of Ru nanoparticles, as well as a better stability compared to the catalyst prepared without PEG.The extensive kinetic data collected in this work were mathematically modelled using three different approaches to elucidate the reactant adsorption mode: a non-competitive adsorption model, a non-competitive adsorption model considering the effect of temperature, and a semi-competitive adsorption model. The non-competitive temperature-dependent model displayed better performance in terms of fitting and reliability of the estimated parameters and predicted the adsorption of xylose as an endothermic process. On the other hand, the semi-competitive model gave similar results in terms of fitting and a value for the competitiveness factor of 0.74, which matches the hypothesis that the larger molecules, sugars, can occupy most of the active sites, while some interstitial sites remain accessible for hydrogen adsorption. The modelling results revealed a complex mode of sugar adsorption on the catalyst surface. This modelling concept can be applied to any system in which the molecule sizes are very different.

Catalytic Hydrogenation of Hemicellulosic Sugars: Reaction Kinetics and Influence of Sugar Structure on Reaction Rate**

AbstractHemicelluloses are a major component of lignocellulosic biomass. Different sugars can be obtained from hemicelluloses: xylose, arabinose, galactose, mannose, glucose. Their catalytic hydrogenation produces polyols: xylitol, arabinitol, dulcitol, mannitol, sorbitol, which are valuable chemicals and platform molecules. In this paper, the hydrogenation of sugars was investigated with a Ru/TiO2 catalyst. The influence of temperature, pressure, xylose concentration and catalyst amount was studied for xylose hydrogenation and a Langmuir‐Hinshelwood kinetic model was designed. The comparative study of five hemicellulose sugars showed a strong impact of sugar structure on hydrogenation rate: hexoses (glucose, mannose, galactose) react slower than pentoses (xylose, arabinose).

Xylitol Production from Xylose by Catalytic Hydrogenation over an Efficient Cu–Ni/SiO2 Bimetallic Catalyst

Xylitol is a value-added health product from the hemicellulose component in biomass. In this work, highly efficient Cu–Ni/SiO2 catalysts are developed for the production of xylitol by means of xylose hydrogenation. The bimetallic catalysts exhibit higher activity compared to the corresponding monometallic nickel or copper catalyst and the currently used industrial Raney nickel catalyst. The bimetallic catalyst with a higher ratio of nickel to copper shows a better performance. The 5Cu15Ni/SiO2 catalyst exhibits a xylose conversion of 96% accompanied by higher than 99% selectivity to xylitol under the moderate conditions of 100 °C and 3MPa H2. The bimetallic catalysts show improved performances when they are activated at a low temperature. The apparent activation energies of xylose hydrogenation over the 5Cu15Ni/SiO2 and 20Ni/SiO2 catalysts are 16.6 and 25.2 kJ/mol, respectively. The formation of the Cu–Ni alloy leads to a lower activation energy and thus superior performance for xylose hydrogenation to xylitol.

Tandem conversion xylose to 2-methylfuran with NiCu/C catalyst

Nowadays, 2-methylfuran is urgently needed especially in pharmaceutical manufacture. However, the direct synthesis of 2-methylfuran via the efficient dehydration and hydrogenation of xylose usually requires a multistep reaction. Herein, a route of tandem conversion xylose to 2-methylfuran was developed. The xylose was firstly converted into furfural by Hβ zeolite, followed by the catalysis of furfural to 2-methylfuran over 0.5NiCu/C. Compared with two-step reaction, cascade strategy applied xylose conversion improved the 2-methylfuran yield rate by 41.5%. In general, this work expanded the application of tandem method for the enhancement of xylose effective conversion and provided a new biomass utilization technology.

Selective Xylose Hydrogenation to Xylitol with Cu@C Prepared from Ion Exchange Resin Under Relatively low Hydrogen Pressure

Selective Xylose Hydrogenation to Xylitol with Cu@C Prepared from Ion Exchange Resin Under Relatively low Hydrogen Pressure

Hydrogenation of Xylose to Xylitol in the Presence of Bimetallic Nanoparticles Ni3Fe Catalyst in the Presence of Choline Chloride

Hydrogenation of sugars to sugars alcohols is of prime interest for food applications for instance. Xylose obtained from the hemicellulose fraction of lignocellulosic biomass can be hydrogenated to xylitol. Herein, we conducted catalytic hydrogenation reactions in a non-conventional media approach by using choline chloride, a non-toxic naturally occurring organic compound that can form a deep eutectic solvent with xylose. Acknowledging the benefits of cost-effective transition metal-based alloys, Ni3Fe1 bimetallic nanoparticles were utilized as a hetero-catalyst. Under optimized reaction conditions (110 °C, 3 h and 30 bar H2), a highly concentrated feed of xylose (76 wt.%) was converted to 80% of xylitol, showing the benefit of using choline chloride. Overall, the catalytic conversion activity and the product selectivity in the substrate-assisted DES media are relatively high but, the recyclability of the catalyst should be improved in the presence of such media.

Intelligent self-control of carbon metabolic flux in SecY-engineered Escherichia coli for xylitol biosynthesis from xylose-glucose mixtures.

Xylitol is a salutary sugar substitute that has been widely used in the food, pharmaceutical, and chemical industries. Co-fermentation of xylose and glucose by metabolically engineered cell factories is a promising alternative to chemical hydrogenation of xylose for commercial production of xylitol. Here, we engineered a mutant of SecY protein-translocation channel (SecY [ΔP]) in xylitol-producing Escherichia coli JM109 (DE3) as a passageway for xylose uptake. It was found that SecY (ΔP) channel could rapidly transport xylose without being interfered by XylB-catalyzed synthesis of xylitol-phosphate, which is impossible for native XylFGH and XylE transporters. More importantly, with the coaction of SecY (ΔP) channel and carbon catabolite repression (CCR), the flux of xylose to the pentose phosphate (PP) pathway and the xylitol synthesis pathway in E. coli could be automatically controlled in response to glucose, thereby ensuring that the mutant cells were able to fully utilize sugars with high xylitol yields. The E. coli cell factory developed in this study has been proven to be applicable to a broad range of xylose-glucose mixtures, which is conducive to simplifying the mixed-sugar fermentation process for efficient and economical production of xylitol.

Scaling up xylitol bioproduction: Challenges to achieve a profitable bioprocess

Xylitol is a GRAS (Generally Recognized as Safe) polyol commonly used in the food industry and able to promote several benefits to the health. In addition, it can also be used as a building block molecule for the manufacture of different high-value chemicals. Currently, the commercial production of xylitol occurs by chemical route through the catalytic hydrogenation of xylose from lignocellulosic biomass. Since this is an expensive process due to the severe reactional conditions employed, the biotechnological route for xylitol production, which comprises the biological conversion of xylose into xylitol, emerges as a potential lower-cost alternative to obtain this polyol due to the milder process conditions required. However, the biotechnological route still presents important bottlenecks and challenges that impairs the process scaling up. Modern strategies and technologies that can potentially improve xylitol bioproduction include adaptive evolution of microbial strains to enhance their tolerance to inhibitors and the xylose uptake rate during the fermentation step; development of engineered microorganisms to result in higher xylose-to-xylitol bioconversion yields; as well as xylitol purification techniques to improve the recovery yields. Moreover, techno-economic analysis of the overall production chain is essential to identify the process viability for large-scale implementation as well as the steps requiring improvements. These are some key factors discussed in this review, which aims to provide insights for the development of a more economically competitive, less energy demanding and scalable new technology for xylitol production.

Production of xylitol from acidic hydrolysates of lignocellulosic biomass by catalytic hydrogenation over a Ni–Ru/C catalyst

Acid hydrolysis and hydrogenation reactions were capable to convert xylose obtained from biomass materials using heterogeneous catalysts based on Ni and Ru. Xylose was extracted from sugar cane bagasse using dilute acid sulfuric solutions, and then xylitol was obtained through xylose catalytic hydrogenation. A bimetallic catalyst (Ni 10.0 wt.% and Ru 1.0 wt.%) was prepared by the wet impregnation method, supporting the metallic phase in activated carbon. Sugarcane bagasse was delignified in a three-step pretreatment (acid, basic and organic extractions, respectively), allowing effective hydrolysis of the resulting holocellulose. The acid hydrolysis process for xylose extraction was more effective at the highest concentration of sulfuric acid in the study (2.5% v/v), obtaining a xylose-rich hydrolysate with concentration over 10 g L−1. For the xylose hydrogenation process, conversion of xylose and selectivity to xylitol was near 90 % after 1 h of reaction. Kinetic evolutions were evaluated through a mathematical model in terms of operating time and temperature, providing hydrogenation activation energy values of the order of 40.76 kJ mol−1.

3-3-1 キシロース水素化反応によるキシリトール選択合成を目指した炭素担持銅系触媒の開発

3-3-1 キシロース水素化反応によるキシリトール選択合成を目指した炭素担持銅系触媒の開発

Selective aqueous phase hydrogenation of xylose to xylitol over SiO2-supported Ni and Ni-Fe catalysts: Benefits of promotion by Fe

A monometallic Ni and a bimetallic Ni-Fe catalyst were used in the aqueous phase hydrogenation of xylose in batch conditions (T = 50–150 °C, PH2 = 10–30 bar, xylose mass fraction in water = 3.7–11.0 wt.%) to evidence the benefits of promoting Ni by Fe. The activity of the catalysts increased with temperature, but a temperature of 80 °C allowed minimizing nickel leaching at full conversion. The presence of reduced Fe at the surface of the bimetallic nanoparticles increased both the first-order apparent rate constant and the adsorption constant of xylose. The catalytic activity of Ni/SiO2 strongly declined and no deactivation was found for the Ni-Fe catalyst. A restructuring of the bimetallic nanoparticles took place, as the size of the metal particles and the Fe proportion in the surface layers increased, suggesting a flattening and coalescing of the particles over the silica surface.

Scale-up process for xylose reductase production using rice straw hydrolysate

Xylose reductase (XR), an industrially important enzyme, catalyzes the hydrogenation of xylose into xylitol. Xylitol, a polyol sugar, has tremendous applications in different industries due to its significant properties. XR is mainly produced from yeasts and molds, and limited studies have been reported on bacteria. The present study explores the potential of newly isolated bacteria, i.e., Pseudomonas putida BSX-46 for XR synthesis through process scale-up by tailoring its nutritional and cultural requirements. A simple media containing only four ingredients was designed for the production of XR in a short incubation time of 24 h. A process for pretreatment of rice straw was developed to achieve hydrolysate with a good amount of xylose (140 g/kg of rice straw). The enhanced XR production of 213.14±0.47 IU/mg of cells was achieved at bioreactor level using waste rice straw hydrolysate as compared to 94.26±0.62 IU/mg of cells at flask level. The developed bioprocess using efficient bacterial source and economical raw material would provide a low-cost substitute for XR production from xylose-based agro-waste materials at the industrial level.

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.

Conversion of cyclic xylose into xylitol on Ru, Pt, Pd, Ni, and Rh catalysts: a density functional theory study.

There is currently no theoretical study on the hydrogenation of xylose to xylitol on a catalyst's surface, limiting proper understanding of the reaction mechanisms and the design of effective catalysts. In this study, DFT techniques were used for the first time to investigate the mechanisms of xylose to xylitol conversion on five notable transition metal (TM) surfaces: Ru(0001), Pt(111), Pd(111), Rh(111), and Ni(111). Two transition state (TS) paths were investigated: TS Path A and TS Path B. The TS Path B, which was further subdivided into TS Path B1 and B2, was proposed to be the minimum energy path (MEP) for the reaction process. According to our computational results, the MEP for this reaction begins with the structural rearrangement of cyclic xylose into its acyclic form prior to step-wise hydrogenation. The rate-determining step (RDS) on Ru(0001), Pt(111), Pd(111), and Ni(111) was discovered to be the ring-opening process via C-O bond scission of cyclic xylose. On Rh(111), however, the RDS was found to be the first hydrogenation stage, leading to the hydrogenation intermediate. Furthermore, based on the RDS barrier, our results revealed that the activities of the tested TM surfaces follow the trend: Ru(0001) > Rh(111) ≥ Ni(111) > Pd(111) > Pt(111). This result demonstrates the higher activity of Ru(0001) compared to other surfaces used for xylose hydrogenation. It correlates with experimental trends in relation to Ru(0001) superiority and provides the basis for understanding the theoretical design of economical and more active catalysts for xylitol production.