Method for catalyzing isomerization of xylose into lyxose, arabinose and ribose by using carbon-based molybdenum catalyst

Abstract

The invention provides a preparation method of lyxose, arabinose and ribose, which is characterized in that xylose is used as a raw material, carbon-based molybdenum is used as a catalyst, and the lyxose, the arabinose and the ribose are obtained through catalytic conversion. The invention also provides a preparation method of the carbon-based molybdenum catalyst, biomass carbon-based chitosan is taken as a carbon source and is combined with ammonium molybdate to prepare the carbon-based molybdenum catalyst, and the catalyst is a heterogeneous catalyst and is easy to separate in a reaction system, so that the common problem of product pollution in homogeneous catalysis is effectively avoided. According to the method disclosed by the invention, xylose is taken as a reaction substrate, the use of strong corrosive substances is avoided through a mild reaction system, and the requirement on the corrosion resistance of equipment is remarkably reduced, so that the investment and maintenance cost of the equipment is effectively reduced. Compared with a traditional process, the method has the advantages that high-valued sugars such as lyxose are efficiently prepared, and the yield of the lyxose product is remarkably increased and can reach 34.1%; the yield of arabinose can reach 29.7%, and the yield of ribose can reach 17.8%. The method has the advantages of high yield of lyxose, simple reaction process, short time and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of high-value biomass, and in particular to a method for preparing a carbon-based molybdenum catalyst and its application in xylose isomerization. Background Art

[0002] Biomass catalytic conversion technology has become a research hotspot due to its broad application prospects in the fields of sustainable energy and fine chemicals. Xylose, the second most abundant monosaccharide in lignocellulosic biomass after glucose, has become a key precursor for the production of a variety of high-value-added products through chemical or biological conversion pathways, thanks to its renewable nature and multiple conversion pathways. The development of efficient catalytic conversion systems for this pentose resource is driving technological innovation and research progress in the biorefining field.

[0003] D-lyxose is an aldopentose. As an endogenous metabolite, it participates in metabolic pathways within organisms and serves as a precursor for the synthesis of other rare sugars. However, lyxose is a non-natural rare sugar that requires chemical synthesis or biotransformation, making it relatively expensive. Arabinose, a key component of plant hemicellulose, can be converted from xylose via microbial enzymes. In the food industry, arabinose is used as a low-calorie sweetener, particularly for diabetic patients. Its fermentation potential to produce ethanol is also being widely studied in the biofuel sector. Ribose can be used in the production of antiviral drugs and nutritional supplements. Its synthesis relies on bioengineering techniques or chemical methods, resulting in a high market price. Multi-stage isomerization of biomass-based xylose can synthesize a variety of value-added monosaccharides, such as lyxose, arabinose, and ribose. These high-value monosaccharides serve as precursors for a variety of pharmaceuticals and high-value-added chemicals.

[0004] Heterogeneous catalysts are less corrosive and easily recyclable from the reaction system. Chitosan and sucrose, due to their unique properties, have emerged as strong contenders as carbon sources for catalytic reactions, thus combining with molybdate to form heterogeneous catalysts. For chitosan-based systems, the abundant amino and hydroxyl groups in its molecular backbone strongly coordinate with the molybdenum metal precursor, thereby ensuring uniform dispersion and fixation of the metal atoms during catalyst preparation. This helps prevent metal agglomeration during the catalytic reaction, thereby improving the catalyst's catalytic performance and resulting in excellent activity and cyclic stability. Notably, the nitrogen-doped carbon skeleton formed after chitosan carbonization not only enhances the support's conductivity, but its residual basic sites also optimize reactant adsorption, creating a more efficient "metal-support" synergistic catalytic interface. For sucrose systems, its relatively stable molecular structure makes it less susceptible to unwanted side reactions in various catalytic systems, thus ensuring the purity and stability of the catalyst. At the same time, its good solubility in common solvents and biological systems helps to evenly distribute the carbon source in the reaction system, facilitating interaction with the active centers of the catalyst, thereby achieving efficient carbon source transfer and utilization. Furthermore, sucrose is widely available in nature and has low production costs, which makes research using sucrose as a carbon source significantly advantageous in terms of scalability and cost-effectiveness.

[0005] The invention patent CN201410375939.6 discloses a method for preparing lyxose. This method for preparing lyxose by selective isomerization of xylose uses ammonium molybdate as a catalyst and boric acid, chloride, and citric acid as co-catalysts. However, the reaction is complex and takes a long time. The catalyst used is a homogeneous catalyst and is not easy to separate from the reaction system. In addition, no arabinose and ribose are produced in this system. Summary of the Invention

[0006] The objective of the present invention is to provide a carbon-based molybdenum catalyst, which has a simple preparation method and can efficiently thermally catalyze the isomerization of xylose into lyxose, arabinose and ribose.

[0007] In order to achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a carbon-based molybdenum catalyst, comprising the following steps:

[0008] (1) dissolving a substance containing a carbon source into a molybdate solution and stirring to obtain a mixed solution;

[0009] (2) drying the mixed solution to obtain a solid;

[0010] (3) The solid was ground and calcined.

[0011] Furthermore, the molybdate is ammonium molybdate tetrahydrate, and the substance containing the carbon source is biomass carbon-based chitosan / sucrose.

[0012] Furthermore, the added carbon-containing source material has an atomic number Mo / C of 3.5 to 3.8, the stirring time is 15 to 20 minutes, and the rotation speed is 300 to 400 rpm.

[0013] Furthermore, the drying temperature in step (2) is 120-140° C., and the drying time is 12-24 hours.

[0014] Furthermore, the calcination in step (3) is carried out by hydrogen calcination at 500° C. in a tubular furnace for 8 to 10 hours.

[0015] A carbon-based molybdenum catalyst is used to add the carbon-based molybdenum catalyst to a xylose aqueous solution and heat to catalyze the isomerization of the xylose to produce lyxose, arabinose, and ribose. The xylose aqueous ethanol solution has a concentration of 5 to 30 g / L, the catalyst is heated at a temperature of 80 to 160°C, the ethanol aqueous solution has a mass concentration of 20 to 90 wt%, and the added mass of the catalyst is 30 to 50 mg.

[0016] Furthermore, the short-term high catalytic temperature of 80°C for 1 hour is conducive to the rapid production of lyxose, with a yield of 34.1%; high temperature or longer reaction time is conducive to the production of arabinose and ribose, and 140°C for 2 hours is the optimal production condition for arabinose and ribose, with yields of 29.7% and 17.8%, respectively.

[0017] Beneficial effects

[0018] This study successfully prepared a carbon-based molybdenum catalyst, Mo@CC, by leveraging the abundant amino and hydroxyl functional groups in chitosan molecules and the strong coordination of metallic Mo in ammonium molybdate. Furthermore, the relative stability of sucrose molecules was utilized to combine with ammonium molybdate to successfully prepare a carbon-based molybdenum catalyst, Mo@CS, of high purity and stability. The performance of these two carbon-based molybdenum catalysts prepared by combining these two different carbon sources with ammonium molybdate was evaluated. Furthermore, the highly efficient thermal catalytic isomerization of xylose into lyxose, arabinose, and ribose was achieved, providing a new synthetic pathway for the efficient catalytic synthesis of high-value monosaccharides, including lyxose, arabinose, and ribose, from xylose.

[0019] The carbon-based molybdenum catalyst prepared with chitosan as the carbon source in this invention has significant advantages due to its unique molecular structure and rich functional groups. The amino and hydroxyl functional groups of chitosan form strong coordination with molybdenum ions, effectively inhibiting the aggregation of catalyst particles. The Mo@CC catalyst using chitosan as the carbon source has a smaller particle size and a higher specific surface area. In addition, the "N" element in the chitosan-derived carbon carrier provides The acid sites work synergistically with the Lewis acid sites of molybdenum to significantly improve the catalytic efficiency of Mo@CC; while the Mo@CS catalyst prepared with sucrose as the carbon source exhibits excellent structural stability and cyclic performance. The solubility of sucrose enables it to form a uniform and dense carbon layer after carbonization, with a complete crystal structure and few surface defects. After five cycles, no obvious crystal phase change occurs, indicating strong stability.

[0020] By comparing chitosan and sucrose, two carbon carriers, this paper reveals the differential effects of carbon carrier characteristics on catalyst performance. Chitosan-based catalysts, due to their rich functional groups and acid-base synergistic effects, perform outstandingly in product selectivity regulation; sucrose-based catalysts, due to their structural stability and high degree of graphitization, are suitable for scenarios requiring high cycle times or harsh reaction conditions. The research results provide a theoretical and technical basis for the targeted conversion of biomass sugars into high-value chemicals, and also provide a new paradigm for the "support-active site co-optimization" strategy in the design of heterogeneous catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a scanning electron microscope image of the carbon-based molybdenum catalyst prepared in Example 4;

[0022] Figure 2 is a BET diagram of the carbon-based molybdenum catalyst prepared in Example 4;

[0023] Figure 3 FT-IR image of the carbon-based molybdenum catalyst prepared in Example 4;

[0024] Figure 4 is the XPS graph of the carbon-based molybdenum catalyst prepared in Example 4;

[0025] Figure 5 is the XRD pattern of the carbon-based molybdenum catalyst prepared in Example 4;

[0026] Figure 6 HRTEM image of the carbon-based molybdenum catalyst prepared in Example 4;

[0027] Figure 7 is the EDS image of the carbon-based molybdenum catalyst prepared in Example 4;

[0028] Figure 8 This is a graph showing the catalytic efficiency of the carbon-based molybdenum catalyst prepared in Example 4 when catalyzing xylose at 80°C to 160°C for 1 hour. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below with reference to specific embodiments.

[0030] Example 1

[0031] The preparation method of the carbon-based molybdenum catalyst of the present embodiment comprises the following steps:

[0032] 1. Dissolve 15 g of ammonium molybdate tetrahydrate in 85 g of deionized water to prepare a 15 wt% ammonium molybdate solution, add an appropriate amount of sucrose so that the atomic number of the raw material added Mo / C is 3.5-3.8, and stir with magnetic stirring at 300-400 r / min for 15-20 min to obtain a mixed solution.

[0033] 2. Add the mixed solution into a polytetrafluoroethylene-lined reactor and dry it in a vacuum drying oven at 120-140°C overnight.

[0034] 3. After the dried solid is ground, it is activated with hydrogen in a tube furnace at 500°C for 8 to 10 hours, wherein the gas contains 5% hydrogen and 95% argon.

[0035] 4. Place 4 mL of 10 g / L xylose solution into a 10 mL microreactor lined with polytetrafluoroethylene, add 30-50 mg of carbon-based molybdenum catalyst to the xylose solution, and place the microreactor in an oil bath at 80°C to 160°C to heat and catalyze the isomerization of xylose to obtain lyxose, arabinose, and ribose.

[0036] Example 2

[0037] The preparation method of the carbon-based molybdenum catalyst of the present embodiment comprises the following steps:

[0038] 1. Dissolve 15 g of ammonium molybdate tetrahydrate in 85 g of deionized water to prepare a 15 wt% ammonium molybdate solution, add an appropriate amount of sucrose so that the atomic number of the raw material added Mo / C is 3.5-3.8, and stir with magnetic stirring at 300-400 r / min for 15-20 min to obtain a mixed solution.

[0039] 2. Add the mixed solution into a polytetrafluoroethylene-lined reactor and dry it in a vacuum drying oven at 120-140°C overnight.

[0040] 3. Grind the dried solid and perform oxygen activation in a tube furnace at 500°C for 8 to 10 hours.

[0041] 4. Place 4 mL of 10 g / L xylose solution into a 10 mL microreactor lined with polytetrafluoroethylene, add 30-50 mg of carbon-based molybdenum catalyst to the xylose solution, and place the microreactor in an oil bath at 80°C to 160°C to heat and catalyze the isomerization of xylose.

[0042] Example 3

[0043] The preparation method of the carbon-based molybdenum catalyst of the present embodiment comprises the following steps:

[0044] 1. Dissolve 15 g of ammonium molybdate tetrahydrate in 85 g of deionized water to prepare a 15 wt% ammonium molybdate solution, add an appropriate amount of chitosan so that the atomic number of the raw material added is Mo / C = 3.5-3.8, and stir with magnetic stirring at 300-400 r / min for 15-20 min to obtain a mixed solution.

[0045] 2. Add the mixed solution into a polytetrafluoroethylene-lined reactor and dry it in a vacuum drying oven at 120-140°C overnight.

[0046] 3. Grind the dried solid and perform oxygen activation in a tube furnace at 500°C for 8 to 10 hours.

[0047] 4. Place 4 mL of 10 g / L xylose solution into a 10 mL microreactor lined with polytetrafluoroethylene, add 30-50 mg of carbon-based molybdenum catalyst to the xylose solution, and place the microreactor in an oil bath at 80°C to 160°C to heat and catalyze the isomerization of xylose.

[0048] Example 4

[0049] The preparation method of the carbon-based molybdenum catalyst of the present embodiment comprises the following steps:

[0050] 1. Dissolve 15 g of ammonium molybdate tetrahydrate in 85 g of deionized water to prepare a 15 wt% ammonium molybdate solution, add an appropriate amount of chitosan so that the atomic number of the raw material added is Mo / C = 3.5-3.8, and stir with magnetic stirring at 300-400 r / min for 15-20 min to obtain a mixed solution.

[0051] 2. Add the mixed solution into a polytetrafluoroethylene-lined reactor and dry it in a vacuum drying oven at 120-140°C overnight.

[0052] 3. After the dried solid is ground, it is activated with hydrogen in a tube furnace at 500°C for 8 to 10 hours, wherein the gas contains 5% hydrogen and 95% argon.

[0053] 4. Place 4 mL of 10 g / L xylose solution into a 10 mL microreactor lined with polytetrafluoroethylene, add 30-50 mg of carbon-based molybdenum catalyst to the xylose solution, and place the microreactor in an oil bath at 80°C to 160°C to heat and catalyze the isomerization of xylose to obtain lyxose, arabinose, and ribose.

[0054] The scanning electron microscope image of the carbon-based molybdenum catalyst prepared in this example is as follows: Figure 1As shown, (a) and (b) are scanning electron micrographs of Mo@CC at different scales. The images show that the catalyst particles are porous, with a carbon nanolayer uniformly coating the intrinsic material surface. Voids can be observed within the particle layer, indicating that the catalyst possesses a sufficient specific surface area, enhancing the accessibility of catalytic sites and facilitating mass transfer and reaction. Chitosan has a unique molecular structure, with numerous amino and hydroxyl functional groups on its polysaccharide chains, which strongly interact with metal ions and prevent excessive particle growth.

[0055] The BET diagram of the carbon-based molybdenum catalyst prepared in this example is as follows: Figure 2 As shown in the figure, the adsorption-desorption curve of Mo@CC composite material is H3 type, and the specific surface area of ​​Mo@CC composite material is 8.28m 2 / g, the nitrogen in the chitosan molecule is ultimately retained within the carbon structure, forming a nitrogen-containing carbon material. Nitrogen-containing functional groups not only serve as active sites but also influence the electronic structure of the carbon material, thereby affecting its specific surface area. Furthermore, the introduction of nitrogen atoms may distort the carbon skeleton, increasing the probability of pore formation.

[0056] The FT-IR image of the carbon-based molybdenum catalyst prepared in this example is as follows: Figure 3 As shown. The material has a clear absorption peak at 3190 cm-1, which originates from the hydroxyl groups on the chitosan surface. The absorption peak at 1400 cm-1 is attributed to the sp2 C=C skeleton vibration after carbonization of the material. The absorption peak at 930 cm-1 is attributed to the symmetric stretching vibration of Mo-O-Mo. At 1630 cm-1, Mo@CC has a clear absorption peak attributed to the stretching vibration of the C=N bond, indicating that nitrogen atoms are introduced during the carbonization process of chitosan to form a pyridine-type structure, which can enhance the surface basic sites of the Mo@CC composite material and promote the adsorption process in the catalytic reaction. It also shows the successful preparation of the Mo@CC composite material.

[0057] The XPS analysis of the carbon-based molybdenum catalyst prepared in this example is as follows: Figure 4 As shown. A small amount of Mo in the Mo 3d spectrum of Mo@CC composite material 6+ (230.3eV) may be due to the insufficient reducing gases (NH3, CO) generated by chitosan carbonization, which results in the incomplete reduction of some molybdates to Mo 4+ Mo@CS's Mo 4+ The peak is more single and the binding energy is slightly lower (231.8eV), indicating that the reducing gases (such as CO and H2) released by sucrose carbonization are more sufficient to promote the formation of MoO4 2-→The complete conversion of MoO2 in this process is also conducive to the formation of a porous structure of sucrose during the carbonization process. The O1s spectrum of Mo@CC has a high proportion of adsorbed oxygen (~533.2eV), which may be related to the abundant oxygen-containing functional groups (such as CO, COOH) on the surface of nitrogen-doped carbon. The O1s spectrum of Mo@CS is mainly Mo-O (530.4eV), indicating that the oxygen mainly comes from the MoO2 lattice and the degree of surface oxidation is low. The CN peak (286.4eV) can be seen in the C1s spectrum of Mo@CC, indicating the formation of nitrogen-doped carbon, which enhances the conductivity and surface active sites of the material. The presence of pyridinic nitrogen (396.9eV) and graphitic nitrogen (401.2eV) in the N1s spectrum of Mo@CC confirms that nitrogen atoms have been successfully incorporated into the carbon skeleton.

[0058] The XRD analysis diagram of the carbon-based molybdenum catalyst prepared in this example is as follows: Figure 5 As shown in the figure. As shown in the figure, the XRD characteristic peaks of the sample are relatively sharp, indicating that the material has good crystallinity. There are no other impurity peaks in the spectrum, indicating that the purity of the synthesized crystal form is high. Significant characteristic peaks of MoO2 were observed in the XRD spectrum of the catalyst, among which the peaks at 26.22°, 37.18°, 53.8°, 66.94°, and 79.14° correspond to the characteristic crystal planes of MoO2 (-111), (111), (-222), (-231), and (040) (PDF#76-1807). The metal oxide molybdenum dioxide (MoO2) belongs to the monoclinic system and has a distorted rutile crystal structure. The O atoms are tightly packed into octahedrons, and the Mo atoms occupy half of the octahedral vacancies and are not in the center of the octahedron.

[0059] The HRTEM image of the carbon-based molybdenum catalyst prepared in this example is as follows: Figure 6 As shown. Figure 6 As shown in (a) and (b), Mo@CC exhibits an irregular block structure with varying particle sizes and a relatively dispersed distribution. This structure is likely due to the porous structure formed by chitosan during the carbonization process. As can be seen from the images, chitosan, as a carbon support, has a well-developed porous structure, which helps increase the specific surface area and active sites of the molybdenum-containing carbon support. The Mo@CC catalyst has smaller particles, resulting in a higher specific surface area, which in turn improves catalytic activity. Its porous structure and good dispersion help increase the contact area between reactants, thereby improving catalytic efficiency.

[0060] The EDS pattern of the carbon-based molybdenum dioxide catalyst prepared in this example is as follows: Figure 7 The surface element distribution of the catalyst Mo@CC was obtained by EDS characterization technology. Figure 7As shown. Element C is the base element of chitosan and sucrose, and elements such as O and Mo are evenly distributed on them, indicating the successful preparation of the composite material, and further illustrating the appropriate firing time and temperature during the preparation process. It can also be seen from the figure that the molybdenum element is evenly distributed on the two catalysts. The uniform distribution of molybdenum in the Mo@CC catalyst is first attributed to the chitosan carrier containing a large number of amino (-NH2) and hydroxyl (-OH) functional groups. When chitosan is mixed with AHM solution, chitosan has a better chelating effect with molybdenum ions, which helps to evenly disperse molybdenum elements on the carbonized carrier. Secondly, during the calcination process, chitosan can form a carbon carrier with more voids and a more uniform carbon layer, which helps to limit the migration of molybdenum particles and prevent agglomeration.

[0061] The catalytic efficiency of the carbon-based molybdenum catalyst prepared in this example at 80°C to 160°C for 1 hour is shown in the figure below: Figure 8 As shown, the lyxose yield reached 34.1% at 80°C. This low energy barrier stems from the fact that xylose isomerization only requires a configurational inversion of the C2 hydroxyl group. At 160°C, the lyxose yield decreased significantly. The formation of arabinose and ribose showed an initial increase followed by a decrease. At 140°C, the arabinose yield rose from 25.2% to 28.7%, and the ribose yield rose from 13.5% to 16.3%. However, above 140°C, the yields of arabinose and ribose decreased to 20.6% and 13.4%, respectively, indicating that high temperatures exacerbate side reactions. Experiments have shown that 140°C is the optimal temperature for arabinose / ribose formation, while 80°C is the optimal condition for efficient lyxose synthesis.

Claims

1. A method for preparing a carbon-based molybdenum catalyst, characterized in that: The following steps are involved: (1) dissolving a substance containing a carbon source into a molybdate solution and stirring to obtain a mixed solution; (2) drying the mixed solution to obtain a solid; (3) The solid was ground and calcined.

2. The method for preparing a carbon-based molybdenum catalyst according to claim 1 or 2, wherein The molybdate is ammonium molybdate tetrahydrate, and the substance containing the carbon source is biomass carbon-based chitosan / sucrose.

3. The method for preparing a carbon-based molybdenum catalyst according to claim 1, wherein An appropriate amount of carbon source material is added to make the atomic number of the raw material added Mo / C = 3.5 to 3.8, the stirring time is 15 to 20 minutes, and the rotation speed is 300 to 400 rpm.

4. The method for preparing a carbon-based molybdenum catalyst according to claim 1, wherein The drying temperature in step (2) is 120-140° C., and the drying time is 12-24 hours.

5. The method for preparing a carbon-based molybdenum catalyst according to claim 1, wherein The calcination in step (3) is carried out in a tubular furnace at 500° C. for 8 to 10 hours in hydrogen.

6. A use of the carbon-based molybdenum catalyst according to claim 1, characterized in that: The carbon-based molybdenum catalyst is added to a xylose aqueous solution and heated to catalyze the isomerization of xylose to produce lyxose, arabinose, and ribose. The xylose concentration is 5 to 30 g / L, the catalytic reaction temperature is 80 to 160°C, the mass fraction of the ethanol aqueous solution is 20 to 90 wt%, and the added mass of the catalyst is 30 to 50 mg.

7. Use of the carbon-based molybdenum catalyst according to claim 1, characterized in that: A short high temperature of 80℃ for 1h is conducive to the rapid production of lyxose, with a yield of 34.1%; high temperature or longer reaction time is conducive to the production of arabinose and ribose, and 140℃ for 2h is the optimal production condition for arabinose and ribose, with yields of 29.7% and 17.8%, respectively.

Images