Transition metal substituted supported polyacid metal organic framework catalyst as well as preparation method and application thereof
By introducing transition metals into Keggin polyacids and encapsulating them in UIO-66, a loaded polyacid metal organic frame catalyst was prepared, which solved the problem that complex lignin structures were difficult to efficiently utilize, achieved efficient yields of lignin degradation, and had good recycling characteristics and green chemical properties.
Patent Information
- Application Number
- CN202510330839.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-20
- Publication Date
- 2025-06-20
AI Technical Summary
The stubborn and complex structure of lignin makes it difficult to use efficiently, especially in efficient depolymerization technology, which makes it difficult for existing catalysts to effectively break the C-O bonds on the aryl ether and avoid recondensation.
The supported polyacid metal organic frame catalyst replaced by transition metal is used to adjust the Lewis acidity and B acidity of the catalyst by introducing the transition metal into the Keggin polyacid and encapsulating it in UIO-66, thereby improving the degradation yield of the lignin degradation product.
This catalyst significantly improves the degradation yield of lignin degradation products, and has good recycling characteristics, meets green chemistry requirements, is mild in conditions and is simple in operation.
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Figure CN120169439A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, a preparation method thereof, and an application thereof. Background Art
[0002] The depletion of fossil resources and climate change have promoted the rapid development of the bio-based economy, which aims to obtain fuels, platform chemicals, and material precursors from renewable biomass raw materials. In the past decade, the use of clean and sustainable energy has increased significantly to meet the growing energy demand while reducing greenhouse gas emissions and air pollution.
[0003] Lignocellulose is the most renewable resource with the highest hydrocarbon content in biomass. It consists of three main components: cellulose, hemicellulose, and lignin, and is considered the most promising alternative to fossil energy. Among them, the conversion of lignin into high-value products is of great significance for improving the utilization rate, economic feasibility, and environmental sustainability of plant fiber raw materials in the biorefinery process using lignin as a raw material. Moreover, the three aspects of biorefinery technology, namely lignocellulose fractionation, lignin depolymerization, and upgrading to target chemicals, will determine whether lignin can be converted into valuable final products. In addition, due to the rich oxygen-containing active groups (such as phenolic hydroxyl groups) in the lignin side chain, it can also be combined with other chemical substances to prepare lignin-based polymer materials.
[0004] However, the stubborn and complex structure of lignin makes its efficient utilization very difficult. The key to efficient depolymerization technology is to effectively and selectively break the C-O bond on the aryl ether, and then avoid the recondensation of lignin caused by the coupling of C-C bonds after the C-O bond is broken, to obtain highly selective lignin monomers, and then realize their utilization. In this process, the design of efficient catalysts and depolymerization systems has become a hot topic in lignin catalytic depolymerization. Summary of the Invention
[0005] To solve the above technical problems, the present invention proposes a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, a preparation method thereof, and an application thereof.
[0006] To achieve the above object, the present invention provides the following technical solutions:
[0007] A preparation method of a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, which introduces a transition metal into a Keggin-type polyoxometalate by an ion exchange method to synthesize a transition metal-substituted heteropolyacid, and then uses an impregnation method to encapsulate the transition metal-substituted heteropolyacid in UIO-66 to obtain the transition metal-substituted supported polyoxometalate metal-organic framework catalyst.
[0008] Beneficial effects: By introducing transition metals Ni / Co and adding Zr atoms to UIO-66, the Lewis acidity of the catalyst is adjusted. Coupled with the strong Brønsted acidity of the Keggin-type polyoxometalate itself, it synergistically affects the reaction activity of the catalyst, thereby increasing the degradation yield of lignin degradation products. In addition, UIO-66 endows the catalyst with good recycling characteristics, which conforms to the essence of green chemistry. From the perspective of possible mechanisms, first, the appropriate Lewis acidity carried by the POMs themselves and the Zr ions in the MOF framework jointly promote the dissolution of lignin in methanol / water. Then, the efficient combination of methanol radicals and lignin molecular fragments under the action of PMo@MOF not only stabilizes the reaction intermediates but also regulates the selective formation of the final products. Finally, the excellent heterogeneity of MOF ensures the reuse of the catalyst. The present invention provides a new potential idea for the design of heterogeneous catalysts with multiple active sites in the lignin oxidative depolymerization system. This method has mild conditions and simple operation methods, which is of positive significance for increasing the yield of lignin degradation products.
[0009] Preferably, the ion exchange method includes the following steps:
[0010] Under heating conditions, a transition metal salt is added to a solution of a Keggin-type polyoxometalate. After condensation reflux reaction, part of the solvent is evaporated, then acetone is added to precipitate a solid and filtered. The obtained filtrate is evaporated to dryness and the resulting solid is dissolved in water and subjected to ion exchange with a cation exchange resin to obtain the transition metal-substituted heteropolyacid.
[0011] More preferably, the transition metal salt is Ni(NO3)2·6H2O and / or Co(NO3)2·6H2O.
[0012] More preferably, the ion exchange method specifically includes the following steps:
[0013] Add 0.001 mol of Keggin-type polyoxometalate and 20 mL of distilled water to a flask, heat up to 90 °C, add 0.0015 mol of transition metal salt under stirring conditions, carry out a condensation reflux reaction for 1 h, and after the reaction, evaporate the remaining 10 mL of solution in a fume hood. Cool to room temperature, add 50 mL of acetone, filter the precipitate, and repeat adding acetone until no more precipitate is produced. Transfer the filtrate to a beaker, evaporate acetone at 80 °C until there is a small amount of water left, and dry it in an oven at 50 °C to obtain the transition metal-substituted heteropolyacid salt. Weigh 2 g of the transition metal-substituted heteropolyacid salt and dissolve it in 1000 mL of distilled water, and exchange K + with H + to obtain the transition metal-substituted heteropolyacid.
[0014] Preferably, the Keggin-type polyoxometalate is phosphotungstic acid and / or phosphomolybdic acid; and / or,
[0015] The transition metal is Ni or Co.
[0016] Preferably, the impregnation method comprises the following steps:
[0017] ZrCl4, C8H6O4 (terephthalic acid), the transition metal-substituted heteropolyacid, and hydrochloric acid are mixed and dissolved in an organic solvent, and then the obtained precipitate is collected after stirring and heating reaction, and the precipitate is dried after Soxhlet extraction to obtain the transition metal-substituted supported polyacid metal-organic framework catalyst.
[0018] Preferably, the organic solvent is N,N-dimethylformamide.
[0019] Preferably, the mass ratio of ZrCl4, C8H6O4, the transition metal-substituted heteropolyacid, and MoO3 is 23:(16-17):4:295.
[0020] Preferably, the temperature of the heating reaction is 393K and the extraction time is 24h.
[0021] The temperature of the vacuum drying is 363K and the time is 12h.
[0022] Preferably, the solvent for Soxhlet extraction is methanol and the time is 24h.
[0023] A transition metal-substituted supported polyacid metal-organic framework catalyst prepared by the above preparation method.
[0024] An application of a transition metal-substituted supported polyacid metal-organic framework catalyst in lignin conversion.
[0025] Preferably, the lignin is the lignin obtained after removing cellulose and hemicellulose from biomass.
[0026] A lignin conversion method comprises the following steps:
[0027] The lignin and the transition metal-substituted supported polyacid metal-organic framework catalyst are heated and reacted in a solvent, and then after cooling, removing residues and the solvent, extraction is carried out, the organic phase is collected, and after removing the extraction solvent again, a lignin oily product is obtained.
[0028] Preferably, the mass ratio of the lignin to the transition metal-substituted supported polyacid metal-organic framework catalyst is 2:1.
[0029] Preferably, the temperature of the heating reaction is 140-160 °C and the time is 1-3h.
[0030] Preferably, the solvent is methanol and / or water.
[0031] More preferably, the solvent is a methanol solution obtained by mixing methanol and water in a volume ratio of 8:2.
[0032] The solvents used for extraction are dichloromethane and water.
[0033] Compared with the prior art, the present invention has the following advantages and technical effects:
[0034] By introducing transition metals Ni / Co and adding Zr atoms into UIO-66-Zr, the Lewis acidity of the catalyst is adjusted. Coupled with the strong B acidity of the Keggin-type polyacid itself, the reaction activity of the catalyst is synergistically affected, thereby increasing the degradation yield of lignin degradation products. The present invention provides a new catalyst synthesis idea for improving the yield of lignin degradation into aromatic monomers. The lignin degradation process is carried out in a high-pressure reactor under mild conditions and with a simple operation method. Therefore, the present invention has a positive significance for increasing the yield of lignin degradation products, provides a new catalyst synthesis idea for lignin catalytic conversion, and has great significance for the high-value utilization of biomass resources. Description of the Drawings
[0035] The drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation of this application. In the drawings:
[0036] Figure 1 is the GC-MS diagram of lignin degradation under the catalytic conditions of Ni-PMo@UIO-66;
[0037] Figure 2 is the GC-MS diagram of lignin degradation under the catalytic conditions of Co-PW@UIO-66;
[0038] Figure 3 are the SEM scanning photo and TEM scanning photo of the catalyst obtained in Example 2 of the present invention;
[0039] Among them, (a) is the TEM image of Ni-PMo@UIO-66; (b) is the EDS element distribution image of Ni-PMo@UIO-66; (c) and (d) are both HAADF-STEM images; (e) and (f) are TEM images at a higher magnification, showing possible polyoxometalate (PMo) clusters and metal-organic framework (MOF) supports, indicated by yellow and cyan arrows respectively;
[0040] Figure 4 are the XRD patterns of the catalysts obtained from UIO-66, Example 3, Example 5 and Comparative Example 5. Detailed Embodiments
[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0042] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0043] In the embodiments of the present invention, the room temperature refers to 25 ± 2°C.
[0044] The raw materials in the embodiments of the present invention are all obtained through commercial channels;
[0045] Among them, methanol is of analytical purity and the concentration is 99.5%;
[0046] The lignin used in the embodiments of the present invention is pine lignin extracted from pine by the dioxane extraction method. The specific preparation method includes the following steps:
[0047] (1) Ball-mill the crushed pine wood powder for 4 h, and then perform degreasing treatment. The degreasing treatment method is: wrap the birch wood powder with degreasing filter paper and put it into a Soxhlet extractor. Add benzene and ethanol (volume ratio 2:1) to the bottom of the round-bottom flask and place it in an oil bath. Set the temperature to 90°C and extract in a fume hood for 6 h, ensuring that the extraction frequency per hour is 4 - 6 times. After the extraction is completed, dry the pine wood powder for later use.
[0048] (2) The pine lignin was extracted by the organic solvent method, specifically referring to the method of Lan et al. (C.S. Lancefield, O.S. Ojo, F. Tran, N.J.J.A.C. Westwood, Isolation of Functionalized Phenolic Monomers through Selective Oxidation and C O Bond Cleavage of the β-O-4 Linkages in Lignin, 127(1)(2015)260 - 264.): 50 g of the pine powder obtained in step (1) was placed in a three-necked flask, 298 mL of 1,4-dioxane and 8.5 mL of hydrochloric acid (37 wt%) were poured into the three-necked flask and mixed evenly, then the three-necked flask was placed in an oil bath and stirred and heated, while condensing and refluxing for 4 h. After the reaction ended, it was naturally cooled to room temperature. Subsequently, 16.8 g of NaHCO3 was added and stirred for 0.5 h. The solid and liquid were separated by vacuum filtration to retain the mixed liquid. After the separation was completed, the filtrate was distilled under reduced pressure in a water bath at 40 °C until a concentrated solution was formed. Then 150 mL of ethyl acetate was added to dilute the concentrated solution, and it was dropped into 500 mL of n-hexane, and a precipitate appeared. After filtration, finally, 1000 mL of distilled water was added for washing and drying, and the obtained solid product was pine lignin.
[0049] Example 1
[0050] A synthesis method of a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, comprising the following steps:
[0051] (1) Co-H3PMo was prepared by the ion exchange method 12 O 40 : 2.34 g of K7PMo 11 O 39 ·20H2O (0.001 mol) and 20 mL of distilled water were added to the flask, heated to 90 °C, 0.44 g of Co(NO3)2·6H2O (0.0015 mol) was added under stirring conditions, and the reaction was refluxed for 1 h. After the reaction ended, the remaining 10 mL of the solution was evaporated in a fume hood. It was cooled to room temperature, 50 mL of acetone was added, and the precipitate was filtered. Acetone was repeatedly added until no more precipitate was produced. The filtrate was transferred to a beaker, the acetone was evaporated at 80 °C, and a small amount of water remained. It was dried in an oven at 50 °C to obtain a light yellow-green powder K5PMo 11 CoO 39 . Weigh 2 g of K5PMo 11 CoO 39 and dissolve it in 1000 mL of distilled water. The K + was exchanged for H + through a cation exchange resin to obtain Co-H3PMo12 O 40 。
[0052] (2) Dissolve 0.46 g of ZrCl4, 0.33 g of C8H6O4 (BDC), 0.08 g of Co-H3PMo 12 O 40 , and 5 mL of 37% HCl in N,N-dimethylformamide (DMF), stir for 1 h, then heat and react at 393 K for 24 h. After the reaction is completed, cool to room temperature, then filter out the blue precipitate. Use a Soxhlet extractor to extract the obtained blue precipitate with methanol as the solvent for 24 h, and then vacuum dry at 363 K for 12 h to obtain a Co-substituted supported polyoxometalate metal-organic framework catalyst, denoted as Co-PMo@UIO-66.
[0053] Example 2
[0054] A method for synthesizing a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, comprising the following steps:
[0055] (1) Prepare Ni-H3PMo 12 O 40 by the ion exchange method: Add 2.34 g of K7PMo 11 O 39 ·20H2O (0.001 mol) and 20 mL of distilled water to a flask, heat up to 90 °C, add 0.44 g of Ni(NO3)2·6H2O (0.0015 mol) under stirring conditions, carry out a condensation reflux reaction for 1 h. After the reaction is completed, evaporate the remaining 10 mL of the solution in a fume hood. Cool to room temperature, add 50 mL of acetone, filter the precipitate, and repeat adding acetone until no more precipitate is produced. Transfer the filtrate to a beaker, evaporate acetone at 80 °C, leave a small amount of water, and dry in an oven at 50 °C to obtain a light yellowish-green powder K5PMo 11 NiO 39 . Weigh 2 g of K5PMo 11 NiO 39 and dissolve it in 1000 mL of distilled water. Exchange K + for H + through a cation exchange resin to obtain Ni-H3PMo 12 O 40 .
[0056] (2) Dissolve 0.46 g of ZrCl4, 0.33 g of C8H6O4 (BDC), 0.08 g of Ni-H3PMo 12 O 40, and 5 mL of 37% HCl was dissolved in N,N-dimethylformamide (DMF), stirred for 1 h, then heated and reacted at 393 K for 24 h. After the reaction, it was cooled to room temperature, and then the blue precipitate was filtered out. The obtained blue precipitate was extracted with methanol as the solvent using a Soxhlet extractor for 24 h, and then vacuum dried at 363 K for 12 h to obtain a Ni-substituted supported polyoxometalate metal-organic framework catalyst, denoted as Ni-PMo@UIO-66.
[0057] Example 3
[0058] A method for synthesizing a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, comprising the following steps:
[0059] (1) Co-H3PW was prepared by ion exchange method 12 O 40 : Add 3.27 g of K7PW 11 O 39 ·20H2O (0.001 mol) and 20 mL of distilled water to a flask, heat up to 90 °C, add 0.44 g of Co(NO3)2·6H2O (0.0015 mol) under stirring conditions, carry out a reflux reaction for 1 h, and after the reaction, evaporate the remaining 10 mL of the solution in a fume hood. Cool to room temperature, add 50 mL of acetone, filter the precipitate, and repeat adding acetone until no more precipitate is produced. Transfer the filtrate to a beaker, evaporate acetone at 80 °C, leave a small amount of water, and dry it in an oven at 50 °C to obtain a light yellow-green powder K5PW 11 CoO 39 . Weigh 2 g of K5PW 11 CoO 39 and dissolve it in 1000 mL of distilled water. Exchange K + with H + through a cation exchange resin to obtain Co-H3PW 12 O 40 .
[0060] (2) Dissolve 0.46 g of ZrCl4, 0.33 g of C8H6O4 (BDC), 0.08 g of Co-H3PW 12 O 40 , and 5 mL of 37% HCl in N,N-dimethylformamide (DMF), stir for 1 h, then heat and react at 393 K for 24 h. After the reaction, cool to room temperature, filter out the blue precipitate, extract the obtained blue precipitate with methanol as the solvent using a Soxhlet extractor for 24 h, and then vacuum dry at 363 K for 12 h to obtain a Co-substituted supported polyoxometalate metal-organic framework catalyst, denoted as Co-PW@UIO-66.
[0061] Example 4
[0062] A method for synthesizing a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, comprising the following steps:
[0063] (1) Prepare Ni-H3PW by ion exchange method 12 O 40 : Add 3.27 g of K7PW 11 O 39 ·20H2O (0.001 mol) and 20 mL of distilled water into a flask, heat up to 90 °C, add 0.44 g of Ni(NO3)2·6H2O (0.0015 mol) under stirring conditions, carry out a condensation reflux reaction for 1 h, and after the reaction is completed, evaporate the remaining 10 mL of the solution in a fume hood. Cool to room temperature, add 50 mL of acetone, filter the precipitate, and repeat adding acetone until no more precipitate is produced. Transfer the filtrate to a beaker, evaporate acetone at 80 °C, leave a small amount of water, and dry it in an oven at 50 °C to obtain a light yellow-green powder K5PW 11 NiO 39 . Weigh 2 g of K5PW 11 NiO 39 dissolve it in 1000 mL of distilled water, exchange K + for H + through a cation exchange resin to obtain Ni-H3PW 12 O 40 .
[0064] (2) Dissolve 0.46 g of ZrCl4, 0.33 g of C8H6O4 (BDC), 0.08 g of Ni-H3PW 12 O 40 , and 5 mL of 37% HCl in N,N-dimethylformamide (DMF), stir for 1 h, then heat and react at 393 K for 24 h. After the reaction is completed, cool to room temperature, filter out the blue precipitate, extract the obtained blue precipitate with methanol as the solvent using a Soxhlet extractor for 24 h, and then vacuum dry it at 363 K for 12 h to obtain a Ni-substituted supported polyoxometalate metal-organic framework catalyst, denoted as Ni-PW@UIO-66.
[0065] Example 5
[0066] A method for degrading lignin, comprising the following steps:
[0067] Mix 0.2 g of pine lignin, 0.1 g of Co-PMo@UIO-66 obtained in Example 1, and 10 mL of a methanol solution (methanol and water in a volume ratio of 8:2). React in a high-pressure reactor at 160 °C, 500 rpm, and with 1 MPa of O2 introduced for 3 h. After the reaction, cool for 1 h. Take out the reaction solution and filter to remove the residue in a funnel device. Wash the residual solution in the reactor with the methanol solution. Use a rotary evaporator to perform rotary evaporation to evaporate the methanol, set the temperature to 50 °C. Then, repeatedly extract the evaporated product three times with 20 mL of dichloromethane and 20 mL of distilled water to obtain the organic phase. Add anhydrous magnesium sulfate to the obtained organic phase for drying, and use the rotary evaporator again to perform rotary evaporation at 40 °C to evaporate the dichloromethane and obtain a lignin oily product.
[0068] Example 6
[0069] A method for degrading lignin, comprising the following steps:
[0070] Mix 0.2 g of pine lignin, 0.1 g of Ni-PMo@UIO-66 obtained in Example 2, and 10 mL of a methanol solution (methanol and water in a volume ratio of 8:2). React in a high-pressure reactor at 160 °C, 600 rpm, and with 1 MPa of O2 introduced for 3 h. After the reaction, cool for 1 h. Take out the reaction solution and filter to remove the residue in a funnel device. Wash the residual solution in the reactor with the methanol solution. Use a rotary evaporator to perform rotary evaporation to evaporate the methanol, set the temperature to 50 °C. Then, repeatedly extract the evaporated product three times with 20 mL of dichloromethane and 20 mL of distilled water to obtain the organic phase. Add anhydrous magnesium sulfate to the obtained organic phase for drying, and use the rotary evaporator again to perform rotary evaporation at 40 °C to evaporate the dichloromethane and obtain a lignin oily product.
[0071] Figure 1 The GC-MS diagram of lignin degradation under the catalytic condition of Ni-PMo@UIO-66 shows that the main depolymerization products are vanillin, methyl vanillate, vanillic acid, and 4-hydroxy-3-methoxy-acetophenone. The MS peak values corresponding to its products are higher than those of the Co-PW@UIO-66 catalyst used in Example 7, indicating that the catalytic effect of Ni-PMo@UIO-66 is better than that of Co-PW@UIO-66.
[0072] Example 7
[0073] A method for degrading lignin, comprising the following steps:
[0074] Mix 0.2 g of pine lignin, 0.1 g of Co-PW@UIO-66 obtained in Example 3, and 10 mL of methanol solution (methanol and water in a volume ratio of 8:2), and react in a high-pressure reactor at 150 °C, 500 rpm, and with 1 MPa of O2 introduced for 3 h. After the reaction, cool for 1 h, take out the reaction solution and filter to remove the residue in a funnel device, wash the residual solution in the reactor with methanol solution, perform rotary evaporation using a rotary evaporator to evaporate methanol, set the temperature to 50 °C, then repeatedly extract the evaporated product three times with 20 mL of dichloromethane and 20 mL of distilled water to obtain the organic phase. Then add anhydrous magnesium sulfate to the obtained organic phase for drying, and again perform rotary evaporation at 40 °C using a rotary evaporator to evaporate dichloromethane to obtain a lignin oily product.
[0075] Figure 2 It is the GC-MS diagram of lignin degradation under the catalytic condition of Co-PW@UIO-66. It can be seen that the main depolymerization products are vanillin, methyl vanillate, vanillic acid, and 4-hydroxy-3-methoxy-acetophenone. The catalytic activity of Co-PW@UIO-66 is relatively lower than that of Ni-PMo@UIO-66.
[0076] Example 8
[0077] A method for degrading lignin, comprising the following steps:
[0078] Mix 0.2 g of pine lignin, 0.1 g of Ni-PW@UIO-66 obtained in Example 3, and 10 mL of methanol solution (methanol and water in a volume ratio of 8:2), and react in a high-pressure reactor at 140 °C, 400 rpm, and with 1 MPa of O2 introduced for 3 h. After the reaction, cool for 1 h, take out the reaction solution and filter to remove the residue in a funnel device, wash the residual solution in the reactor with methanol solution, perform rotary evaporation using a rotary evaporator to evaporate methanol, set the temperature to 50 °C, then repeatedly extract the evaporated product three times with 20 mL of dichloromethane and 20 mL of distilled water to obtain the organic phase. Then add anhydrous magnesium sulfate to the obtained organic phase for drying, and again perform rotary evaporation at 40 °C using a rotary evaporator to evaporate dichloromethane to obtain a lignin oily product.
[0079] Comparative Example 1
[0080] A method for degrading lignin, comprising the following steps:
[0081] Mix 0.2 g of pine lignin, 0.1 g of H3PMo 12 O 40, Mix with 10 mL of methanol solution (methanol and water in a volume ratio of 8:2), react in a high-pressure reactor at 140 °C, 400 rpm, and introduce 1 MPa of O₂ for 1 h. After the reaction, cool for 1 h, take out the reaction solution and filter to remove residues in a funnel device, wash the residual solution in the reactor with methanol solution, perform rotary evaporation using a rotary evaporator to evaporate methanol, set the temperature to 50 °C, then repeatedly extract the evaporated product three times with 20 mL of dichloromethane and 20 mL of distilled water to obtain the organic phase. Then add anhydrous magnesium sulfate to the obtained organic phase for drying, and use the rotary evaporator again to perform rotary evaporation at 40 °C to evaporate dichloromethane to obtain a lignin oily product.
[0082] Comparative Example 2
[0083] A method for degrading lignin, comprising the following steps:
[0084] Mix 0.2 g of pine lignin, 0.1 g of H3PW 12 O 40 , and 10 mL of methanol solution (methanol and water in a volume ratio of 8:2), react in a high-pressure reactor at 150 °C, 500 rpm, and introduce 1 MPa of O₂ for 2 h. After the reaction, cool for 1 h, take out the reaction solution and filter to remove residues in a funnel device, wash the residual solution in the reactor with methanol solution, perform rotary evaporation using a rotary evaporator to evaporate methanol, set the temperature to 50 °C, then repeatedly extract the evaporated product three times with 20 mL of dichloromethane and 20 mL of distilled water to obtain the organic phase. Then add anhydrous magnesium sulfate to the obtained organic phase for drying, and use the rotary evaporator again to perform rotary evaporation at 40 °C to evaporate dichloromethane to obtain a lignin oily product.
[0085] Comparative Example 3
[0086] A synthesis method of a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, comprising the following steps:
[0087] Dissolve 0.46 g of ZrCl4, 0.33 g of C8H6O4 (BDC), 0.08 g of H3PMo 12 O 40 , and 37% HCl in N,N-dimethylformamide (DMF), stir for 1 h, then heat and react at 393 K for 24 h. After the reaction, cool to room temperature, then filter out the blue precipitate, extract the obtained blue precipitate using a Soxhlet extractor with methanol as the solvent for 24 h, and then vacuum dry at 363 K for 12 h to obtain an organic framework catalyst, denoted as PMo@UIO-66.
[0088] Comparative Example 4
[0089] A method for degrading lignin, comprising the following steps:
[0090] Mix 0.2 g of pine lignin, 0.1 g of PMo@UIO-66 obtained in Comparative Example 3, and 10 mL of a methanol solution (methanol and water in a volume ratio of 8:2), and react in a high-pressure reactor at 160 °C, 600 rpm, and with 1 MPa of O2 introduced for 3 h. After the reaction is completed, cool for 1 h, take out the reaction solution and filter to remove the residue in a funnel device, wash the residual solution in the reactor with the methanol solution, perform rotary evaporation using a rotary evaporator to evaporate the methanol, set the temperature to 50 °C, then repeatedly extract the evaporated product three times with 20 mL of dichloromethane and 20 mL of distilled water to obtain an organic phase, add anhydrous magnesium sulfate to the obtained organic phase for drying, and again perform rotary evaporation at 40 °C using a rotary evaporator to evaporate the dichloromethane to obtain a lignin oily product.
[0091] Comparative Example 5
[0092] A method for synthesizing a transition metal-substituted supported polyoxometalate metal-organic framework catalyst, comprising the following steps:
[0093] Dissolve 0.46 g of ZrCl4, 0.33 g of C8H6O4 (BDC), 0.08 g of H3PW 12 O 40 , and 37% HCl in N,N-dimethylformamide (DMF), stir for 1 h, then heat and react at 393 K for 24 h. After the reaction is completed, cool to room temperature, then filter out the blue precipitate, extract the obtained blue precipitate with methanol as a solvent using a Soxhlet extractor for 24 h, and then vacuum dry at 363 K for 12 h to obtain an organic framework catalyst, denoted as PW@UIO-66.
[0094] Comparative Example 6
[0095] A method for degrading lignin, comprising the following steps:
[0096] Mix 0.2 g of pine lignin, 0.1 g of PW@UIO-66 obtained in Comparative Example 5, and 10 mL of a methanol solution (methanol and water in a volume ratio of 8:2) in a high-pressure reactor at 140 °C, 600 rpm, and with 1 MPa of O2 introduced for 2 h. After the reaction, cool for 1 h. Take out the reaction solution and filter it through a funnel device to remove the residue, and wash the residual solution in the reactor with a methanol solution. Use a rotary evaporator to perform rotary evaporation to evaporate the methanol, set the temperature to 50 °C, and then repeatedly extract the evaporated product three times with 20 mL of dichloromethane and 20 mL of distilled water to obtain an organic phase. Then add anhydrous magnesium sulfate to the obtained organic phase for drying, and use the rotary evaporator again at 40 °C for rotary evaporation to evaporate the dichloromethane to obtain a lignin oily product.
[0097] Technical effect:
[0098] 1. Performance characterization
[0099] Figure 3 These are the SEM scanning photos and TEM scanning photos of the catalyst obtained in Example 2 of the present invention;
[0100] Among them, (a) is the TEM image of Ni-PMo@UIO-66; (b) is the EDS elemental distribution image of Ni-PMo@UIO-66; (c) and (d) are both HAADF-STEM images; (e) and (f) are TEM images at a higher magnification, showing possible polyoxometalate (PMo) clusters and metal-organic framework (MOF) supports, indicated by yellow and cyan arrows respectively;
[0101] The TEM image in Figure (a) shows the morphology of Ni-PMo@UIO-66, presenting a shape between oval and circular, with a particle size range between 100 and 150 nm; the energy-dispersive spectroscopy (EDS) elemental mapping in Figure (b) further confirms the good dispersion of Ni, Mo, and Zr in the NiPMo@UIO-66 sample, which is consistent with the Figure 4 XRD analysis results in. It should be noted that the HAADF-STEM images in Figures (c) and (d) reveal an almost spherical cage-like structure. Inside this structure, there are many regularly distributed linear substances, which may be PMo crystals neatly arranged inside the MOF cage. It is inferred from the TEM images at a higher magnification in Figures (e) and (f) that the yellow circles represent the linear arrangement of PMo clusters, while the cyan part represents the almost circular cage-like structure of the MOF, which wraps the PMo inside. Through the above catalyst characterization of the present invention, the successful preparation of the catalyst is proved.
[0102] Figure 4XRD patterns of the catalysts obtained from UIO-66, Example 3, Example 5 and Comparative Example 5 show that the parent structure of the polyoxometalate does not change significantly before and after being loaded on UIO-66.
[0103] 2. Add the above lignin oily product to 10 mL of ethyl acetate, store it in a centrifuge tube, filter the reaction solution again using a filtering syringe, and then add the internal standard using a pneumatic air gun. The internal standard is prepared as follows: Dissolve 0.0144 g of 3,5-dimethylphenol in ethyl acetate (chromatographically pure) and make up the volume to 10 mL.
[0104] Perform gas chromatography-mass spectrometry analysis on the obtained solution. The instrument model used is Agilent 6890N / 5973i. The required conditions for detection are as follows: The chromatographic column is an HP-5MS capillary column. The programmed temperature rise is as follows: Initially maintain at 70 °C for 2 min, then rise to 180 °C at a rate of 7 °C / min and maintain for 8 min. Detector: FID (200 °C), internal standard: 3,5-dimethoxyphenol; the carrier gas is helium, the split ratio is 5.01:1, the injection port temperature is 180 °C, and the injection volume is 1 μL.
[0105] The monomer products and yields during lignin degradation are shown in Table 1:
[0106] Table 1 Monomer products and yields during lignin degradation
[0107]
[0108] As can be seen from the above examples, when the reaction time is 3 h, the temperature is 160 °C, and the catalyst is Ni-PMo@UIO-66, the effect is the best. At the same time, it can be seen that the catalyst provided by the present invention can promote lignin degradation and obtain a higher degradation yield, which is beneficial to the development of technologies related to lignin degradation.
[0109] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.
Claims
1. A method for preparing a transition metal-substituted supported polyacid metal organic framework catalyst, characterized in that: The transition metal is introduced into the Keggin type polyacid by an ion exchange method to synthesize a transition metal-substituted heteropolyacid, and then the transition metal-substituted heteropolyacid is encapsulated in UIO-66 by an impregnation method to obtain the transition metal-substituted supported polyacid metal organic framework catalyst.
2. The method for preparing a transition metal-substituted supported polyacid metal organic framework catalyst according to claim 1, characterized in that: The ion exchange method comprises the following steps: Under heating conditions, a transition metal salt is added to a solution of a Keggin-type polyacid, and a portion of the solvent is evaporated after a condensation reflux reaction, and acetone is added to precipitate the precipitate, which is then filtered. The solvent in the obtained filtrate is evaporated and then dried, and the obtained solid is dissolved in water and ion exchanged with a cation exchange resin to obtain the transition metal-substituted heteropolyacid.
3. The method for preparing a transition metal-substituted supported polyacid metal organic framework catalyst according to claim 2, characterized in that: The Keggin type polyacid is phosphotungstic acid and / or phosphomolybdic acid; and / or, The transition metal is Ni or Co.
4. The method for preparing a transition metal-substituted supported polyacid metal organic framework catalyst according to claim 1, characterized in that: The impregnation method comprises the following steps: ZrCl4, terephthalic acid, transition metal-substituted heteropoly acid and hydrochloric acid are mixed and dissolved in an organic solvent, and then the obtained precipitate is collected after stirring and heating reaction, and then the precipitate is extracted by Soxhlet and dried to obtain the transition metal-substituted supported polyacid metal organic framework catalyst.
5. The method for preparing a transition metal-substituted supported polyacid metal organic framework catalyst according to claim 4, characterized in that: The organic solvent is N,N-dimethylformamide.
6. The method for preparing a transition metal-substituted supported polyacid metal organic framework catalyst according to claim 2 or 4, characterized in that: The mass ratio of ZrCl4, C8H6O4, transition metal substituted heteropoly acid and MoO3 is 23:(16-17):4:
295.
7. The method for preparing a transition metal-substituted supported polyacid metal organic framework catalyst according to claim 4, characterized in that: The temperature of the heating reaction is 393K and the extraction time is 24h.
8. The method for preparing a transition metal-substituted supported polyacid metal organic framework catalyst according to claim 4, characterized in that: The solvent of the Soxhlet extraction is methanol, and the extraction time is 24 hours. 9 . The transition metal-substituted supported polyacid metal organic framework catalyst prepared by the preparation method according to claim 1 .
10. Use of the transition metal-substituted supported polyacid metal organic framework catalyst according to claim 9 in lignin conversion.