Oxygen-rich defective two-dimensional MOF catalyst, preparation method and application

Abstract

The present application provides an oxygen-rich defect two-dimensional MOF catalyst, a preparation method and an application, and belongs to the technical field of green chemistry and efficient utilization of carbon resources.The present application forms an oxygen-rich defect two-dimensional MOF through heteropoly acid etching, designs a catalytic site by using the super-high specific surface area of the two-dimensional MOF, and realizes the synthesis of dimethyl carbonate by methanol carbonylation.The prepared oxygen-rich defect two-dimensional POMs / MOF catalyst has a "yin-yang composite vacancy cluster" composed of "oxygen vacancies" and "zirconium vacancies".The cluster is no longer a single active site, but a powerful "multi-active site center", which can work synergistically, greatly improving the efficiency of activating inert CO2 and reacting it with methanol to generate dimethyl carbonate, thereby solving the bottleneck problem of insufficient activity of traditional catalysts.

Description

Technical Field

[0001] This invention belongs to the field of green chemistry and efficient utilization of carbon resources, specifically relating to an oxygen-rich defect-based two-dimensional MOF catalyst, its preparation method, and its application. Background Technology

[0002] The efficient conversion and utilization of carbon dioxide has become a key technological direction for solving carbon emission problems and achieving resource recycling. CO2, as an abundant C1 raw material, can be converted into high-value-added fine chemicals, reducing atmospheric CO2 concentration and creating significant economic benefits, making it a current research hotspot in the chemical engineering field. Dimethyl carbonate (DMC), as a green, environmentally friendly, and economically valuable chemical, possesses colorless, transparent, low-toxicity, and volatile physical properties, and is widely used in industry. The carbonyl, methyl, and methoxy groups in the DMC molecular structure endow it with excellent reactivity, making it an ideal substitute for highly toxic phosgene and dimethyl sulfate. It plays an important role in lithium battery electrolytes, high-oxygen fuel additives, and polycarbonate synthesis; especially in the pharmaceutical and pesticide industries, DMC is a key intermediate for producing low-toxicity, high-efficiency products such as carbaryl and ciprofloxacin, with continuously growing market demand. Traditional DMC synthesis mainly relies on the phosgene method, which not only uses highly toxic raw materials but also produces corrosive byproducts, failing to meet the trend of green chemical development and gradually facing elimination. The process of directly synthesizing DMC from CO2 and methanol (CH3OH) (reaction formula: 2CH3OH + CO2 → (CH3O)2CO + H2O) boasts 100% atom economy, emits no toxic substances, and converts the greenhouse gas CO2 into a high-value-added product, directly aligning with the goal of carbon neutrality. Therefore, developing efficient and stable DMC preparation methods has broad application prospects and enormous market potential in the fields of new energy development and green chemical engineering.

[0003] Although the direct synthesis of DMC from CO2 and CH3OH has significant advantages in terms of high atom economy, it still faces many technical bottlenecks in its industrialization process, mainly in the following aspects: The reaction is limited by thermodynamic equilibrium, and the CO2 molecule has extremely high thermodynamic stability and chemical inertness, requiring the activation process to overcome a high energy barrier, making the reaction difficult to carry out efficiently and seriously hindering industrial application. Zr-based catalysts exhibit low catalytic activity in the synthesis of dimethyl carbonate from methanol carbonylation; traditional efficient methods for DMC synthesis rely excessively on single oxygen vacancies (V0.05). o Furthermore, the single oxygen vacancy in the Zr-based catalyst may simultaneously and strongly adsorb both the reactant CO2 and the activation product of methanol, leading to competitive adsorption and thus inhibiting the reaction. Summary of the Invention

[0004] Existing Zr-based catalysts used for the direct synthesis of DMC from CO2 and CH3OH exhibit low catalytic activity, and their single oxygen vacancy may adsorb activation products of CO2 and methanol, leading to competitive adsorption and inhibiting the DMC synthesis reaction. To address this issue, this invention provides an oxygen-rich defect-laden two-dimensional MOF catalyst, its preparation method, and its application.

[0005] This invention prepares an oxygen-rich defect-laden two-dimensional MOF catalyst by etching a two-dimensional MOF with a heteropolyacid possessing both acidic sites and variable valence metals. This catalyst is used for the carbonylation of methanol to synthesize dimethyl carbonate. The ultra-high specific surface area of ​​the two-dimensional MOF is utilized to construct catalytic sites composed of "oxygen vacancies" and "zirconium vacancies" as "anionic-ionic composite vacancy clusters," achieving the carbonylation of methanol to synthesize dimethyl carbonate. This invention's preparation method, through innovative catalyst design and reaction process optimization, overcomes the thermodynamic equilibrium limitations in traditional CO2 conversion, providing an efficient and environmentally friendly solution for the resource utilization of CO2.

[0006] A method for preparing an oxygen-rich defective two-dimensional MOF catalyst includes the following steps:

[0007] Step 1: Add sodium molybdate solution and disodium hydrogen phosphate solution to sodium metavanadate solution. Acidify the resulting mixed solution with sulfuric acid. Then add hydrazine sulfuric acid and stir for a period of time. Add KCl and stir until completely dissolved. Finally, filter the solution and let the filtrate stand at room temperature to obtain phosphomolybdate-vanadium heteropolyacid.

[0008] Step 2: Thoroughly mix and stir the phosphomolybdenum vanadium heteropolyacid obtained in Step 1, along with zirconium salt, 1,3,5-tris(4-carboxyphenyl)benzene, terminator, N,N-dimethylformamide, and water. Then, place the mixture into a hydrothermal reactor and heat it for hydrothermal reaction. After the reaction is complete, wash the resulting reaction solution with deionized water until neutral, and then collect the precipitate obtained by centrifugation. The precipitate is then washed with dichloromethane and methanol sequentially at room temperature and dried in a vacuum drying oven to form a highly crystalline white solid. The white solid is the oxygen-rich defect two-dimensional MOF catalyst (POMs / MOF).

[0009] Furthermore, in step one:

[0010] Dissolve 2-14 g of sodium metavanadate in 50-70 mL of deionized water at 70℃ or above to obtain a sodium metavanadate solution, and then cool to room temperature.

[0011] At room temperature, dissolve 5-50 g of sodium molybdate in 70-90 mL of deionized water to obtain a sodium molybdate solution;

[0012] At room temperature, dissolve 0.8-2 g of disodium hydrogen phosphate in 10-15 mL of deionized water to obtain a disodium hydrogen phosphate solution;

[0013] The mass ratio of sodium metavanadate, sodium molybdate, disodium hydrogen phosphate, hydrazine sulfate and KCl is (2-14):(5-50):(0.8-2)(0.6-3):(2-4).

[0014] Furthermore, in step one, the stirring time for adding hydrazine sulfate is 3 hours.

[0015] Furthermore, in step one, concentrated sulfuric acid is added to acidify the mixed solution to pH 2-5.

[0016] Furthermore, in step two, the ratio of the amount of phosphomolybdic vanadium heteropolyacid, zirconium salt, 1,3,5-tris(4-carboxyphenyl)benzene, terminator, N,N-dimethylformamide and water is (25-100 mg): (100-400 mg): (150-450 mg): (9-36 mL): (20-80 mL): (2-8 mL).

[0017] Furthermore, in step two, the hydrothermal reaction temperature is 100-140℃, and the reaction time is 40-50 h;

[0018] Furthermore, in step two, the vacuum drying temperature is 80-120℃, and the drying time is 12-24 h.

[0019] Furthermore, in step two, the zirconium salt is one of zirconium dichloride hydrate, zirconium tetrachloride, zirconium oxynitrate hydrate, and zirconium sulfate hydrate;

[0020] Furthermore, in step two, the terminating agent is one of formic acid, acetic acid, or phosphoric acid.

[0021] The oxygen-rich defective two-dimensional MOF catalyst POMs / MOF prepared by the above method can be used for the catalytic oxidation of CO2 and the carbonylation of CH3OH to synthesize DMC. The method is as follows: CH3OH and the oxygen-rich defective two-dimensional MOF catalyst POMs / MOF are added to a high-pressure reactor, CO2 gas at a certain pressure is introduced, and the reaction is started after the temperature rises to the set reaction temperature.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) The ultra-high specific surface area of ​​two-dimensional MOFs can be used to construct a large number of active sites. In this invention, a heteropolyacid with acidic sites and variable valence metals was prepared. The heteropolyacid was used to prepare an oxygen-rich defect two-dimensional MOF catalyst by etching during the growth of MOF, and a "cation-anion composite vacancy cluster" composed of "oxygen vacancy" and "zirconium vacancy" was successfully constructed.

[0024] (2) The ultra-large specific surface area of ​​two-dimensional MOFs allows for the construction of multiple atomically adjacent active sites on their surface, facilitating the activation of CO2 through oxygen vacancies. Simultaneously, it lowers the energy barrier for CO2 to decompose into CH3OCO after combining with *CH3O to form the key intermediate (CH3OC(O)2). This enables a stable and continuous high-efficiency catalysis for the methanol carbonylation synthesis of dimethyl carbonate, avoiding the decomposition of intermediate products due to low catalytic activity.

[0025] (3) The oxygen-rich defective two-dimensional MOF catalyst POMs / MOF prepared by the present invention has good reusability, and the preparation process is simple, easy to operate, and suitable for industrial production. Attached Figure Description

[0026] Figure 1 Transmission electron microscopy images of the two-dimensional MOF prepared in Example 1 and the oxygen-rich defect two-dimensional MOF catalysts in Examples 1-4.

[0027] Figure 2 The X-ray diffraction patterns are those of the two-dimensional MOF in Example 1 and the oxygen-rich defective two-dimensional MOF catalyst POMs / MOF.

[0028] Figure 3 The electron paramagnetic resonance spectra of the two-dimensional MOF in Example 1 and the oxygen-rich defect two-dimensional MOF catalyst POMs / MOF are shown.

[0029] Figure 4 This is an atomic force microscopy image of the oxygen-rich defective two-dimensional MOF catalyst POMs / MOF in Example 1.

[0030] Figure 5 The N2 adsorption-desorption curves and pore size distribution diagrams of the two-dimensional MOF and the oxygen-rich defective two-dimensional MOF catalyst POMs / MOF in Example 1 are shown.

[0031] Figure 6 XPS spectra of the two-dimensional MOF and the oxygen-rich defective two-dimensional MOF catalyst POMs / MOF in Example 1.

[0032] Figure 7 The figures show the performance test results of the two-dimensional MOFs in Examples 1-4 and the four oxygen-enriched defect two-dimensional MOF catalysts. Detailed Implementation

[0033] The technical solution of the present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0034] Example 1:

[0035] 1. Preparation of two-dimensional MOF catalysts POMs / MOF with oxygen-rich defects: The preparation steps are as follows:

[0036] (1) Dissolve 2.6 g of sodium metavanadate in 50 mL of deionized water at 70 °C and cool to room temperature. Add sodium molybdate solution (6 g of sodium molybdate dissolved in 70 mL of deionized water) and disodium hydrogen phosphate solution (0.93 g of disodium hydrogen phosphate dissolved in 10 mL of deionized water) dissolved at room temperature. Acidify the mixture with concentrated sulfuric acid to pH=2, then add 2 g of hydrazine sulfate and stir for 3 h. Then add 3 g of KCl and stir until completely dissolved. Finally, filter the solution and let the filtrate stand at room temperature to obtain phosphomolybdate-vanadium heteropolyacid (H5PMo). 10 V2O 40 ).

[0037] (2) Add 0.05 g H5PMo 10 V2O 40 0.20 g ZrCl4, 0.25 g 1,3,5-tris(4-carboxyphenyl)benzene, 17.5 mL formic acid, 41 mL N,N-dimethylformamide and 3 mL water were thoroughly mixed and stirred for 10 min. Then, the mixture was placed in a 100 mL hydrothermal reactor and heated in an oven at 120 °C for 48 h. After centrifugation, a highly crystalline white solid was obtained. The solid was washed with dichloromethane and methanol sequentially at room temperature until neutral and then dried under vacuum at 100 °C for 12 h to obtain the oxygen-rich defective two-dimensional MOF catalyst POMs / MOF.

[0038] Preparation of two-dimensional MOF catalyst (for comparison, without heteropolyacid etching): 0.20 g ZrCl4, 0.25 g 1,3,5-tris(4-carboxyphenyl)benzene, 17.5 mL formic acid, 41 mL N,N-dimethylformamide and 3 mL water were thoroughly mixed and stirred for 10 min. Then, the mixture was placed in a hydrothermal reactor and heated in an oven at 120 °C for 48 h. After the reaction was completed, the resulting reaction solution was washed with deionized water until neutral. Then, the precipitate obtained by centrifugation was collected. The precipitate was washed with dichloromethane and methanol successively until neutral at room temperature, and then dried under vacuum at 100 °C for 12 h to obtain a white solid as the two-dimensional MOF catalyst.

[0039] 2. Catalytic activity test:

[0040] 0.1 g of POMs / MOF was weighed and dispersed in 20 mL of methanol. CO2 was then introduced into the reactor at a pressure of 3 MPa. The reaction system was carried out at 140 °C for 3 h at a rotation speed of 600 rpm. The resulting liquid product was analyzed by gas chromatography with a flame ionization detector. The liquid product was filtered through a 0.2 μm polytetrafluoroethylene (PTFE) membrane. 1 mL of the liquid was taken, and 89 μl of 1-propanol was added as an internal standard. High-purity N2 was used as the carrier gas. The detection conditions were: vaporization chamber temperature 220 °C, detector temperature 250 °C, column inlet pressure 0.06 MPa, and column temperature 80 °C. A microsyringe was used for injection, ensuring that each injection volume was 0.4 μL. The standard curve for DMC was y = 3.4276x + 0.0012 (where y represents the mass ratio of DMC to 1-propanol, and x represents the peak area ratio of DMC to 1-propanol). Calculation results show that the product DMC can achieve a high yield, with a DMC yield of 3.12 mmol / g after 3 h of reaction.

[0041] 3. Regeneration performance test:

[0042] The prepared oxygen-rich defective two-dimensional MOF catalyst POMs / MOF can be obtained by centrifugation, separation, and drying. The recovered catalyst was re-introduced into the above catalytic activity experiments to test its catalytic effect; four regeneration experiments were conducted using this method. The detection method and experimental conditions for the obtained liquid products were the same as those for the above catalytic activity experiments. The results show that the catalyst activity loss during regeneration is low; during the first to fifth regeneration experiments, the selectivity of DMC decreased from 99.9% to 96.3%.

[0043] Example 2:

[0044] 1. Preparation of 25-POMs / MOF, a two-dimensional MOF catalyst with oxygen-rich defects, using the following steps:

[0045] (1) Dissolve 2.6 g of sodium metavanadate in 50 mL of deionized water at 70 °C and cool to room temperature. Add sodium molybdate solution (6 g of sodium molybdate dissolved in 70 mL of deionized water) and disodium hydrogen phosphate solution (0.93 g of disodium hydrogen phosphate dissolved in 10 mL of deionized water) dissolved at room temperature. Acidify the mixture with concentrated sulfuric acid to pH=2, then add 2 g of hydrazine sulfuric acid and stir for 3 h. Then add 3 g of KCl and stir until completely dissolved. Finally, filter the solution and let the filtrate stand at room temperature to obtain phosphomolybdate-vanadium heteropolyacid (H5PMo). 10 V2O 40 ).

[0046] (2) Add 0.025g H5PMo 10 V2O 400.25 g ZrO(NO3)2·2H2O, 0.25 g 1,3,5-tris(4-carboxyphenyl)benzene, 16 mL acetic acid, 41 mL N,N-dimethylformamide and 3 mL water were thoroughly mixed and stirred for 10 min. Subsequently, the mixture was heated in a 100 mL hydrothermal reactor in an oven at 120 °C for 48 h. After centrifugation, a highly crystalline white solid was obtained. The solid was washed with dichloromethane and methanol sequentially at room temperature until neutral, and then dried under vacuum at 100 °C for 12 h to obtain the oxygen-rich defective two-dimensional MOF catalyst 25-POMs / MOF.

[0047] 2. Catalytic performance test:

[0048] 0.15 g of 25-POMs / MOF was weighed and dispersed in 25 mL of methanol. CO2 was then introduced into the reactor at a pressure of 2 MPa. The reaction system was carried out at 135 °C for 4 h at a rotation speed of 600 rpm. The resulting liquid product was analyzed by gas chromatography with a flame ionization detector. The liquid product was filtered through a 0.2 μm polytetrafluoroethylene (PTFE) membrane. 1 mL of the liquid was taken, and 89 μl of 1-propanol was added as an internal standard. High-purity N2 was used as the carrier gas. The detection conditions were: vaporization chamber temperature 220 °C, detector temperature 250 °C, column inlet pressure 0.06 MPa, and column temperature 80 °C. A microsyringe was used for injection, ensuring that each injection volume was 0.4 μL. The standard curve for DMC was y = 3.4276x + 0.0012 (where y represents the mass ratio of DMC to 1-propanol, and x represents the peak area ratio of DMC to 1-propanol). The calculation results show that the product DMC can achieve a high yield, with a DMC yield of 2.63 mmol / g after 4 h of reaction.

[0049] 3. Regeneration performance test:

[0050] The regeneration performance test method was the same as in Example 1. The results showed that the catalyst activity was not significantly lost during the regeneration reaction, and the selectivity of DMC decreased from 99.9% to 95.5% during the first to fifth regeneration experiments.

[0051] Example 3:

[0052] 1. Preparation of 75-POMs / MOF, a two-dimensional MOF catalyst with oxygen-rich defects.

[0053] (1) Dissolve 2.2 g of sodium metavanadate in 50 mL of deionized water at 70 °C and cool to room temperature. Add sodium molybdate solution (48 g of sodium molybdate dissolved in 90 mL of deionized water) and 0.93 g of disodium hydrogen phosphate solution (0.93 g of disodium hydrogen phosphate dissolved in 10 mL of deionized water) dissolved at room temperature. Acidify the mixture with concentrated sulfuric acid to pH=2, then add 2 g of hydrazine sulfuric acid and stir. Then add 3 g of KCl. Finally, filter the solution and let the filtrate stand at room temperature to obtain phosphomolybdate-vanadium heteropolyacid (H4PMo). 11 VO 40 ).

[0054] (2) Add 0.075 g H4PMo 11 VO 40 0.20 g Zr(SO4)2·4H2O, 0.25 g 1,3,5-tris(4-carboxyphenyl)benzene, 17.5 mL formic acid, 41 mL N,N-dimethylformamide and 3 mL water were thoroughly mixed and stirred for 10 min. Then, the mixture was heated in a 100 mL hydrothermal reactor in an oven at 120 °C for 48 h. After centrifugation, a highly crystalline white solid was obtained. The solid was washed with dichloromethane and methanol sequentially at room temperature until neutral, and then dried under vacuum at 100 °C for 12 h to obtain the oxygen-rich defective two-dimensional MOF catalyst 75-POMs / MOF.

[0055] 2. Catalytic performance test:

[0056] 0.2 g of 75-POMs / MOF was weighed and dispersed in 30 mL of methanol. CO2 was then introduced into the reactor at a pressure of 2.5 MPa. The reaction system was carried out at 135 °C for 4 h at a rotation speed of 600 rpm. The resulting liquid product was analyzed by gas chromatography with a flame ionization detector. The liquid product was filtered through a 0.2 μm polytetrafluoroethylene (PTFE) membrane. 1 mL of the liquid was taken, and 89 μl of 1-propanol was added as an internal standard. High-purity N2 was used as the carrier gas. The detection conditions were: vaporization chamber temperature 220 °C, detector temperature 250 °C, column inlet pressure 0.06 MPa, and column temperature 80 °C. A microsyringe was used for injection, ensuring that each injection volume was 0.4 μL. The standard curve for DMC was y = 3.4276x + 0.0012 (where y represents the mass ratio of DMC to 1-propanol, and x represents the peak area ratio of DMC to 1-propanol). The calculation results show that the product DMC can achieve a high yield, with a DMC yield of 2.54 mmol / g after 4 h of reaction.

[0057] 3. Regeneration performance test:

[0058] The regeneration performance test method was the same as in Example 1. The results showed that the catalyst activity was not significantly lost during the regeneration reaction, and the selectivity of DMC decreased from 99.9% to 95.8% during the first to fifth regeneration experiments.

[0059] Example 4:

[0060] 1. Preparation of 100-POMs / MOF, a two-dimensional MOF catalyst with oxygen-rich defects.

[0061] (1) Dissolve 13.4 g of sodium metavanadate in 70 mL of deionized water at 70 °C and cool to room temperature. Add 21.8 g of sodium molybdate solution (21.8 g of sodium molybdate dissolved in 85 mL of deionized water) and 0.93 g of disodium hydrogen phosphate solution (0.93 g of disodium hydrogen phosphate dissolved in 10 mL of deionized water) dissolved at room temperature. Acidify the mixture with concentrated sulfuric acid to pH=2, then add 2 g of hydrazine sulfuric acid and stir. Then add 3 g of KCl. Finally, filter the solution and let the filtrate stand at room temperature to obtain phosphomolybdate-vanadium heteropolyacid (H6PMo9V3O). 40 ).

[0062] (2) Add 0.1 g of H6PMo9V3O 40 0.30 g ZrOCl2·8H2O, 0.25 g 1,3,5-tris(4-carboxyphenyl)benzene, 16 mL acetic acid, 41 mL N,N-dimethylformamide and 3 mL water were thoroughly mixed and stirred for 10 min. Then, the mixture was heated in a 100 mL hydrothermal reactor in an oven at 120 °C for 48 h. After centrifugation, a highly crystalline white solid was obtained. The solid was washed with dichloromethane and methanol sequentially at room temperature until neutral, and then dried under vacuum at 100 °C for 12 h to obtain the oxygen-rich defective two-dimensional MOF catalyst 100-POMs / MOF.

[0063] 2. Catalytic performance test:

[0064] 0.1 g of 100-POMs / MOF was weighed and dispersed in 20 mL of methanol. CO2 was then introduced into the reactor at a pressure of 2 MPa. The reaction system was carried out at 145 °C for 4 h at a rotation speed of 600 rpm. The resulting liquid product was analyzed by gas chromatography with a flame ionization detector. The liquid product was filtered through a 0.2 μm polytetrafluoroethylene (PTFE) membrane. 1 mL of the liquid was taken, and 89 μl of 1-propanol was added as an internal standard. High-purity N2 was used as the carrier gas. The detection conditions were: vaporization chamber temperature 220 °C, detector temperature 250 °C, column inlet pressure 0.06 MPa, and column temperature 80 °C. A microsyringe was used for injection, ensuring that each injection volume was 0.4 μL. The standard curve for DMC was y = 3.4276x + 0.0012 (where y represents the mass ratio of DMC to 1-propanol, and x represents the peak area ratio of DMC to 1-propanol). The calculation results show that the product DMC can achieve a high yield, with a DMC yield of 2.75 mmol / g after 4 h of reaction.

[0065] 3. Regeneration performance test:

[0066] The regeneration performance test method was the same as in Example 1. The results showed that the catalyst activity was not significantly lost during the regeneration reaction, and the selectivity of DMC decreased from 99.9% to 96.2% during the first to fifth regeneration experiments.

[0067] Figure 1 Transmission electron microscopy (TEM) images of the two-dimensional MOF catalysts and oxygen-rich defective two-dimensional MOF catalysts POMs / MOFs prepared in Examples 1-4. Figure 1 Image A in the image is a transmission electron microscope (TEM) image of the two-dimensional MOF material prepared in Example 1. Figure 1 B, C, D, and E are the oxygen-rich defective two-dimensional MOF catalysts prepared in Examples 1-4, respectively.

[0068] From transmission electron microscopy images ( Figure 1 As can be seen in (A), the two-dimensional MOF material has an ultrathin sheet-like structure, and the modified oxygen-rich defect two-dimensional MOF catalyst ( Figure 1 In samples B, C, D, and E, while exhibiting an ultrathin sheet-like structure, heteropolyacid etching traces can be observed on the MOF surface. The etching degree varies with different heteropolyacid contents. Transmission electron microscopy images confirm that the prepared samples are ultrathin sheet-like structures with a large specific surface area. Furthermore, the surface area is further increased by heteropolyacid etching, providing more active sites.

[0069] Figure 2 The images show the X-ray diffraction patterns of the two-dimensional MOF catalyst in Example 1 and the oxygen-rich defect-laden two-dimensional MOF catalyst POMs / MOF. Figure 2X-ray diffraction patterns show that the prepared oxygen-rich defect-laden two-dimensional MOF catalyst POMs / MOF still exhibits the basic MOF structure, indicating that the heteropolyacid etching did not affect the MOF structure. Furthermore, no characteristic diffraction peaks of the heteropolyacid were observed in the XRD pattern, suggesting that the heteropolyacid was almost completely washed away.

[0070] Figure 3 The images show the electron paramagnetic resonance spectra of the two-dimensional MOF catalyst in Example 1 and the oxygen-rich defect-laden two-dimensional MOF catalyst POMs / MOF. Figure 3 The electron paramagnetic resonance spectrum shows that the peak intensity of POMs / MOF is higher than that of MOF alone, indicating that the prepared catalyst POMs / MOF has more oxygen vacancies, which is beneficial for the adsorption and activation of CO2.

[0071] Figure 4 This is an atomic force microscopy (AFM) image of the oxygen-rich defect-laden two-dimensional MOF catalyst POMs / MOF in Example 1. The AFM image of POMs / MOF shows that the prepared catalyst has a thickness of 4-6 nm, making it an ultrathin MOF material.

[0072] Figure 5 The N in the two-dimensional MOF catalyst of Example 1 and the oxygen-rich defect two-dimensional MOF catalyst POMs / MOF 2 Adsorption-desorption curves and pore size distribution diagrams; where (A) represents N 2 Adsorption-desorption curves, (B) is the pore size distribution diagram. Figure 5 Nitrogen adsorption-desorption curves and pore size distribution diagrams show that, compared with pure MOF, the specific surface area of ​​the prepared oxygen-rich defect-laden two-dimensional MOF catalyst POMs / MOF is significantly higher, increasing from 473 m². 2 / g increased to 658 m 2 / g, pore volume from 0.09 cm³ 3 / g increased to 0.34cm 3 The change from a pore size distribution of 2-4 nm to a pore size distribution range of 4-8 nm indicates that the catalyst has a larger specific surface area and a better pore structure, forming more active sites, which is beneficial for the adsorption and activation of substrates and reaction intermediates, thereby improving the catalytic activity.

[0073] Figure 6XPS spectra of the two-dimensional MOF and the oxygen-rich defect-laden two-dimensional MOF catalyst POMs / MOF in Example 1 are shown below; (a) is a high-resolution spectrum of the C1s region, (b) is a high-resolution spectrum of the O1s region, (c) is a high-resolution spectrum of the Zr 3d region, (d) is a high-resolution spectrum of the P 2p region, (e) is a high-resolution spectrum of the Mo 3d region, and (f) is a high-resolution spectrum of the V 2p region. Figure 6 XPS spectra of two-dimensional MOFs and oxygen-rich defect-laden two-dimensional MOF catalysts POMs / MOFs show the presence of O1s, Zr 3d, C 1s, and Mo 3d signal peaks, with very low Mo content. This indicates that the heteropolyacids were almost completely washed away, but a small amount of Mo was incorporated into the MOF. The O 1s (B) and Zr 3d (C) spectra show partial reduction of Zr. 3+ Zr 3+ The formation of O indicates the formation of both oxygen and zirconium defects. Furthermore, O v With Zr 3+ The close correlation indicates that Mo doping further increases the oxygen and zirconium defect content. In addition, the increased peak intensity of O 1s and Zr 3d in POMs / MOF can be observed, which indicates that the MOF surface changes from a dense structure to a porous / rough structure, increasing the atomic exposure surface and improving the active sites. This shows that the number of defects can be controlled by adjusting the type and content of heteropolyacids.

[0074] Figure 7 The figures show the performance test results of the two-dimensional MOFs in Examples 1-4 and four types of oxygen-rich defective two-dimensional MOF catalysts. It can be seen that compared to the defect-free MOF catalyst, the catalytic performance of the defective MOF catalyst is significantly improved. However, more defects do not necessarily mean better performance. Generally, the more heteropolyacids added, the more defects are formed. Introducing appropriate amounts of ordered, well-defined defects can create advantageous active sites without sacrificing the integrity, stability, and porosity of the structure. Too many defects can lead to material instability, deactivation, loss of selectivity, and loss of repeatability, degenerating a high-performance catalytic material into a disordered, fragile, and unreliable porous solid.

[0075] This invention utilizes defect engineering design during MOF (metal-organic framework) formation to create an "anodic-anionic composite vacancy cluster" composed of both "oxygen vacancies" and "zirconium vacancies." The presence of zirconium vacancies promotes the rapid binding of the intermediate methoxy group (*CH3O) with activated CO2. This cluster is no longer a single active site but a powerful "multi-active site center" that can work synergistically to greatly improve the efficiency of activating inert CO2 and reacting it with methanol to produce dimethyl carbonate, thereby solving the bottleneck problem of insufficient activity in traditional catalysts.

[0076] This invention not only synthesizes a high-performance Zr-based MOF catalyst, but more importantly, it provides a catalyst design philosophy: shifting the focus from "single defects" to constructing "multifunctional defect clusters." This approach of solving catalytic challenges through "surface engineering" and "active site regulation" offers valuable insights for designing more efficient zirconium-based catalysts and even other catalytic systems in the future, paving a practical path for the green resource utilization of CO2.

[0077] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention.

Claims

1. A method for preparing an oxygen-rich defect-laden two-dimensional MOF catalyst, characterized in that, Includes the following steps: Step 1: Add sodium molybdate solution and disodium hydrogen phosphate solution to sodium metavanadate solution. Acidify the resulting mixed solution with sulfuric acid. Then add hydrazine sulfuric acid and stir for a period of time. Add KCl and stir until completely dissolved. Finally, filter the solution and let the filtrate stand at room temperature to obtain phosphomolybdate-vanadium heteropolyacid. Step 2: Mix phosphomolybdenum vanadium heteropolyacid, zirconium salt, 1,3,5-tris(4-carboxyphenyl)benzene, terminator, N,N-dimethylformamide and water and stir until homogeneous. Then, put it into a hydrothermal reactor and heat it for hydrothermal reaction. After the reaction is completed, wash the resulting reaction solution with deionized water until neutral, centrifuge, and wash and dry the collected centrifuged precipitate to obtain the oxygen-rich defect two-dimensional MOF catalyst.

2. The preparation method according to claim 1, characterized in that, In step one, the preparation methods for sodium metavanadate solution, sodium molybdate solution, and disodium hydrogen phosphate solution are as follows: Dissolve 2-14 g of sodium metavanadate in 50-70 mL of deionized water at 70℃ or above to obtain a sodium metavanadate solution, and then cool to room temperature. Dissolve 5-50 g of sodium molybdate in 70-90 mL of deionized water to obtain a sodium molybdate solution; Dissolve 0.8-2 g of disodium hydrogen phosphate in 10-15 mL of deionized water to obtain a disodium hydrogen phosphate solution.

3. The preparation method according to claim 2, characterized in that, In step one, the mass ratio of sodium metavanadate, sodium molybdate, disodium hydrogen phosphate, hydrazine sulfate and KCl is (2-14):(5-50):(0.8-2)(0.6-3):(2-4).

4. The preparation method according to claim 3, characterized in that, In step one, the stirring time for adding hydrazine sulfuric acid is 3 hours; concentrated sulfuric acid is added to acidify the mixed solution to pH 2-5.

5. The preparation method according to claim 1, characterized in that, In step two, the ratio of the amount of phosphomolybdic vanadium heteropolyacid, zirconium salt, 1,3,5-tris(4-carboxyphenyl)benzene, terminator, N,N-dimethylformamide and water is (25-100 mg):(100-400 mg):(150-450 mg):(9-36 mL):(20-80 mL):(2-8 mL).

6. The preparation method according to claim 4, characterized in that, In step two, the ratio of the amount of phosphomolybdic vanadium heteropolyacid, zirconium salt, 1,3,5-tris(4-carboxyphenyl)benzene, terminator, N,N-dimethylformamide and water is (25-100 mg):(100-400 mg):(150-450 mg):(9-36 mL):(20-80 mL):(2-8 mL).

7. The preparation method according to claim 1, characterized in that, In step two: The hydrothermal reaction temperature is 100-140℃, and the reaction time is 40-50 h; The temperature for vacuum drying is 80-120℃, and the drying time is 12-24 h.

8. The preparation method according to claim 1, characterized in that, In step two, the zirconium salt is one of zirconium dichloride hydrate, zirconium tetrachloride, zirconium oxynitrate hydrate, or zirconium sulfate hydrate; the terminating agent is one of formic acid, acetic acid, or phosphoric acid.

9. An oxygen-rich defective two-dimensional MOF catalyst prepared by the preparation method according to any one of claims 1-8.

10. The application of the oxygen-rich defective two-dimensional MOF catalyst according to claim 9 in the catalytic oxidation of CO2 and the carbonylation of CH3OH to synthesize DMC.

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