An imidazole ligand zirconium-based MOF catalyst, and a preparation method and application thereof

Abstract

The application provides a kind of imidazole ligand zirconium-based MOF catalyst and its preparation method and application, belong to catalyst preparation technical field;1H-imidazole-4-carboxylic acid is introduced as unit carboxylic acid ligand into UiO-66 in the application, so as to realize the modification of zirconium-based MOF catalyst, obtain imidazole ligand zirconium-based MOF catalyst;The imidazole ligand zirconium-based MOF catalyst increases the acid-base site of UiO-66 by introducing imidazole ligand, and then improves the catalytic effect of zirconium-based MOF;The imidazole ligand zirconium-based MOF catalyst has very good application in catalyzing carbon dioxide and methanol to directly synthesize dimethyl carbonate.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to an imidazole ligand zirconium-based MOF catalyst, its preparation method, and its application. Background Technology

[0002] Dimethyl carbonate (DMC) possesses low toxicity, high solubility, and excellent environmental performance, making it a promising candidate for applications in chemical products. Currently, the main synthetic routes for DMC include methanol phosgenation, methanol oxidative carbonylation, and direct synthesis from urea. However, these routes suffer from drawbacks such as toxic raw materials and the generation of byproducts. Therefore, a new, safe, and pollution-free synthetic route for DMC is needed.

[0003] Carbon dioxide is an abundant, colorless, non-toxic, and harmless source of C1, but its excessive emissions contribute to global warming. Therefore, it is necessary to convert carbon dioxide into valuable chemical products to reduce emissions and thus purify the environment. Direct synthesis of dimethyl methyl ether (DMC) from CO2 and methanol is a safe and pollution-free process with water as the only byproduct. With the addition of a dehydrating agent, the selectivity for DMC can be considered 100%, reducing CO2 emissions while increasing its added value. However, CO2 has high chemical inertness, making the reaction difficult to carry out. Improving the yield of DMC requires research into kinetics and breaking thermodynamic equilibrium. Catalysis is central to green chemistry and plays a crucial role in the future development of processes.

[0004] Zirconium-based metal-organic frameworks (UiO-66) exhibit good acid resistance and thermal stability, and are easily functionalized, making them widely used in the catalysis of carbon dioxide. However, UiO-66 has relatively few acid-base sites, making it difficult to improve the efficiency of the direct synthesis of dimethyl carbonate from carbon dioxide and methanol. Therefore, there is a need to develop a catalytic method to enhance the efficiency of this reaction. Summary of the Invention

[0005] To address some shortcomings in existing technologies, this invention provides an imidazole-ligand-based zirconium-based MOF catalyst, its preparation method, and its applications. This invention introduces 1H-imidazolium-4-carboxylic acid as a single carboxylic acid ligand into UiO-66, thereby modifying the zirconium-based MOF catalyst to obtain an imidazole-ligand-based zirconium-based MOF catalyst. The imidazole-ligand-based zirconium-based MOF catalyst increases the acid-base sites of UiO-66 by introducing imidazole ligands, thus improving the catalytic effect of the zirconium-based MOF. This imidazole-ligand-based zirconium-based MOF catalyst has excellent applications in the direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0006] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0007] The present invention first provides an imidazole ligand zirconium-based MOF catalyst, wherein the imidazole ligand zirconium-based MOF catalyst is in the form of a slender rod; the imidazole ligand zirconium-based MOF catalyst is obtained by introducing an imidazole ligand to replace part of the terephthalic acid ligand on a regular octahedron UiO-66; the proportion of the imidazole ligand in the imidazole ligand zirconium-based MOF catalyst is not more than 50%.

[0008] Preferably, the imidazole ligand zirconium-based MOF catalyst uses soluble zirconium salt as a precursor of metallic zirconium and terephthalic acid and 1H-imidazol-4-carboxylic acid as ligands.

[0009] This invention also provides a method for preparing the above-mentioned imidazole ligand zirconium-based MOF catalyst, specifically comprising:

[0010] Soluble zirconium salt was dissolved in a polar amide solvent, and 1H-imidazolium-4-carboxylic acid and terephthalic acid were added and stirred until completely dissolved. Then, acetic acid was added as a modifier and stirred to obtain a uniform mixture. The mixture was subjected to a solvothermal reaction. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the imidazolium ligand zirconium-based MOF catalyst.

[0011] Preferably, the soluble zirconium salt includes one of ZrCl4, ZrOCl2·8H2O or Zr(NO3)4·5H2O;

[0012] The polar amide solvent includes one of N,N-dimethylformamide, N,N-diethylformamide, or N,N-dimethylacetamide.

[0013] Preferably, the soluble zirconium salt is ZrCl4;

[0014] The polar amide solvent is N,N-dimethylformamide.

[0015] Preferably, the molar ratio of the soluble zirconium salt to the total amount of the two ligand compounds is 1:1 to 1.1.5;

[0016] The two ligand compounds are 1H-imidazol-4-carboxylic acid and terephthalic acid, and the molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:19 to 7:3.

[0017] Preferably, the molar ratio of the soluble zirconium salt to the total amount of the two ligand compounds is 1:1.1;

[0018] The molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:9 to 1:1;

[0019] The volume ratio of the acetic acid to the N,N-dimethylformamide is 1:1 to 9.

[0020] Preferably, the molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:4;

[0021] The volume ratio of the acetic acid to the N,N-dimethylformamide is 1:9.

[0022] Preferably, the solvothermal reaction is carried out at 100–160°C for 20–40 h.

[0023] Preferably, the solvothermal reaction is carried out at 120°C for 24 hours.

[0024] This invention also provides the application of the above-mentioned imidazole ligand zirconium-based MOF catalyst in the direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0025] The present invention also provides a method for synthesizing dimethyl carbonate, comprising:

[0026] Methanol, a dehydrating agent, the above-mentioned imidazole ligand-zirconium-based MOF, and carbon dioxide were heated and stirred at high temperature to react. After the reaction was completed, the mixture was centrifuged to obtain the synthesized dimethyl carbonate.

[0027] Preferably, the volume ratio of methanol to dehydrating agent is 10:1 to 2:1.

[0028] Preferably, the volume ratio of methanol to dehydrating agent is 5:2.

[0029] Preferably, the amount of the imidazole ligand zirconium-based MOF catalyst is 0.1 g, and the amount of carbon dioxide is 3.5 MPa.

[0030] Preferably, the dehydrating agent includes one of trimethyl orthoformate, 2-cyanopyridine, or anhydrous calcium chloride.

[0031] Preferably, the dehydrating agent is trimethyl orthoformate.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The catalytic mechanism of the direct synthesis of dimethyl carbonate from carbon dioxide and methanol in this invention relies on the acid-base sites of the catalyst. Methanol is activated at acidic and basic positions to form methyl and methoxy groups, respectively. Carbon dioxide adsorbed on the basic center reacts with the methoxy group to form a methoxy bicarbonate anion, which then reacts with the methyl cation to generate dimethyl carbonate. In the zirconium-based metal-organic framework UiO-66, unsaturated metals or metal clusters can generate Lewis acid centers, and unsaturated oxygen can generate Lewis base centers. This invention uses 1H-imidazolium-4-carboxylic acid to replace part of the terephthalic acid ligand, which exposes more active sites, and the incorporation of imidazolium can also act as a basic site, thereby improving the catalytic effect of the zirconium-based MOF.

[0034] The imidazole ligand-based zirconium MOF catalyst UiO-66-Im-X (where X is the ratio of imidazole ligand to total ligands) prepared in this invention exhibits the best catalytic performance in the form of UiO-66-Im-0.2, with a catalytic yield of 0.9335% and a catalytic efficiency of 0.7211 mmol·g. - 1·h -1 , with UiO-66 (0.3236%, 0.2499 mmol·g) - 1·h -1 Compared to the previous method, its catalytic yield increased by 2.88 times. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the synthesis of imidazole ligand-zirconium-based MOF catalyst.

[0036] Figure 2 The XRD pattern of the imidazole ligand-zirconium-based MOF catalyst is shown.

[0037] Figure 3 SEM images of UiO-66 (a,b) and imidazole ligand-zirconium-based MOF catalyst (c,d); where a and c have a size of 1 μm, and b and d have a size of 1 nm.

[0038] Figure 4 The image shows the nitrogen adsorption isotherm spectrum of the imidazole ligand-zirconium-based MOF catalyst. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0040] Example 1: Preparation of imidazole ligand zirconium-based MOF catalyst UiO-66-Im-0.1

[0041] Figure 1 A schematic diagram of the synthesis of imidazole ligand-zirconium-based MOF catalysts. This example is based on... Figure 1 The imidazole ligand-zirconium-based MOF catalyst is prepared via the indicated pathway, with the specific steps as follows:

[0042] 1.1651 g ZrCl4 was dissolved in 60 mL N,N-dimethylformamide, and 0.0561 g 1H-imidazolium-4-carboxylic acid and 0.7476 g terephthalic acid were added and stirred until completely dissolved. Then, 6 mL acetic acid was added and stirred until homogeneous to obtain a mixture. The mixture was transferred to a 100 mL high-pressure reactor with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 120 °C for 24 h. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the imidazolium ligand zirconium-based MOF catalyst, denoted as UiO-66-Im-0.1.

[0043] Figure 2 The image shows the XRD pattern of the imidazole ligand-zirconium-based MOF catalyst. As can be seen from the figure, UiO-66 exhibits obvious diffraction peaks at 2θ of 7.3° and 8.4°. However, no significant changes occurred after introducing a certain proportion of imidazole ligand, indicating that the introduction of imidazole ligand did not alter the crystal structure of UiO-66. However, when the amount of imidazole ligand added was 0.5%, the crystal structure collapsed.

[0044] Figure 3 The image shows the SEM pattern of the imidazole ligand-zirconium-based MOF catalyst. It can be seen from the image that UiO-66 has a regular octahedral morphology, but after the introduction of the imidazole ligand, the morphology changes and it becomes a slender rod shape.

[0045] Example 2: Preparation of imidazole ligand zirconium-based MOF catalyst UiO-66-Im-0.2

[0046] 1.1651 g ZrCl4 was dissolved in 60 ml N,N-dimethylformamide. 0.1121 g 1H-imidazolium-4-carboxylic acid and 0.6645 g terephthalic acid were added and stirred until completely dissolved. Then, 6 ml acetic acid was added and stirred until homogeneous to obtain a mixture. The mixture was transferred to a 100 mL high-pressure reactor with a polytetrafluoroethylene liner. The reactor was subjected to reaction at 120 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and dried to obtain the imidazolium ligand zirconium-based MOF catalyst, denoted as UiO-66-Im-0.2.

[0047] Figure 4 The figure shows the nitrogen adsorption isotherm spectrum of the imidazole ligand-zirconium-based MOF catalyst. It can be seen from the figure that the introduction of imidazole ligand increases the specific surface area of ​​UiO-66, with UiO-66-Im-0.2 being the optimal value. Further increasing the proportion of imidazole ligand decreases the specific surface area.

[0048] Example 3: Preparation of imidazole ligand zirconium-based MOF catalyst UiO-66-Im-0.3

[0049] 1.1651 g ZrCl4 was dissolved in 60 ml N,N-dimethylformamide. 0.1682 g 1H-imidazolium-4-carboxylic acid and 0.5815 g terephthalic acid were added and stirred until completely dissolved. Then, 6 ml acetic acid was added and stirred until homogeneous to obtain a mixture. The mixture was then transferred to a 100 mL high-pressure reactor with a polytetrafluoroethylene liner. The reactor was reacted at 120 °C for 24 h. After the reaction, the mixture was cooled to room temperature, centrifuged, washed, and dried to obtain the imidazolium ligand zirconium-based MOF catalyst, denoted as UiO-66-Im-0.3.

[0050] Example 4: Preparation of imidazole ligand zirconium-based MOF catalyst UiO-66-Im-0.4

[0051] 1.1651 g ZrCl4 was dissolved in 60 ml N,N-dimethylformamide. 0.2242 g 1H-imidazolium-4-carboxylic acid and 0.4984 g terephthalic acid were added and stirred until completely dissolved. Then, 6 ml acetic acid was added and stirred until homogeneous to obtain a mixture. The mixture was transferred to a 100 mL high-pressure reactor with a polytetrafluoroethylene liner. The reactor was reacted at 120 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and dried to obtain the imidazolium ligand zirconium-based MOF catalyst, denoted as UiO-66-Im-0.4.

[0052] Example 5: Preparation of imidazole ligand zirconium-based MOF catalyst UiO-66-Im-0.5

[0053] 1.1651 g ZrCl4 was dissolved in 60 ml N,N-dimethylformamide. 0.2803 g 1H-imidazolium-4-carboxylic acid and 0.4253 g terephthalic acid were added and stirred until completely dissolved. Then, 6 ml acetic acid was added and stirred until homogeneous to obtain a mixture. The mixture was transferred to a 100 mL high-pressure reactor with a polytetrafluoroethylene liner. The reactor was subjected to reaction at 120 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and dried to obtain the imidazolium ligand zirconium-based MOF catalyst, denoted as UiO-66-Im-0.5.

[0054] Comparative Example 1: Preparation of Zirconium-based MOF catalyst UiO-66

[0055] 1.1651 g ZrCl4 was dissolved in 60 ml N,N-dimethylformamide, and 0.8307 g terephthalic acid was added and stirred until completely dissolved. Then, 6 ml acetic acid was added and stirred until homogeneous to obtain a mixture. The mixture was then transferred to a 100 mL autoclave with a polytetrafluoroethylene liner and reacted at 120 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and dried to obtain the imidazole ligand zirconium-based MOF catalyst, denoted as UiO-66.

[0056] The present invention also uses the catalysts prepared in Examples 1-5 and Comparative Example 1 to catalyze the direct synthesis of dimethyl carbonate from carbon dioxide and methanol. The specific steps are as follows:

[0057] In a 50 mL stainless steel high-pressure reactor, 5 mL of methanol, 1.5 mL of dehydrating agent, and 0.1 g of catalyst were added. The gas inside the reactor was displaced under 0.2 MPa carbon dioxide, and then the pressure was increased to 3.5 MPa. After reacting at 140 °C for 8 h, the yield and formation rate of dimethyl carbonate were obtained by gas chromatography. The dehydrating agent was selected from one of trimethyl orthoformate, 2-cyanopyridine, or anhydrous calcium chloride. The yield and formation rate are shown in Table 1.

[0058] Table 1. Yields and formation rates of dimethyl carbonate synthesized from carbon dioxide and methanol using different catalysts

[0059] catalyst Dehydrating agent DMC Yield (%) <![CDATA[DMC formation rate (mmol·g-1·h -1 )]]> Comparative Example 1 UiO-66 TMM 0.3236 0.2499 Example 1 UiO-66-Im-0.1 TMM 0.6531 0.5045 Example 2 UiO-66-Im-0.2 TMM 0.9335 0.7211 Example 3 UiO-66-Im-0.3 TMM 0.7364 0.5698 Example 4 UiO-66-Im-0.4 TMM 0.5939 0.4588 Example 5 UiO-66-Im-0.5 TMM 0.4289 0.3313

[0060] Table 1 shows the yield and formation rate of different catalysts in the synthesis of dimethyl carbonate from carbon dioxide and methanol. As can be seen from Table 1, the catalyst with the introduction of imidazole ligand has a higher catalytic yield and catalytic efficiency than UiO-66. The best catalytic effect is achieved when the proportion of imidazole ligand added, X = 0.2, is 0.9335%, which is 2.88 times higher than that of UiO-66 (0.3236%).

[0061] In summary, this invention uses 1H-imidazolium-4-carboxylic acid to replace part of the terephthalic acid ligand, which exposes more active sites and the imidazolium incorporation can also act as a basic site, thereby improving the catalytic effect of zirconium-based MOFs. The imidazolium-ligand zirconium-based MOF catalyst has excellent applications in the catalytic synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0062] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. The application of an imidazole ligand zirconium-based MOF catalyst in the direct synthesis of dimethyl carbonate from carbon dioxide and methanol, wherein the preparation method of the imidazole ligand zirconium-based MOF catalyst includes the following steps: Soluble zirconium salt was dissolved in a polar amide solvent, and 1H-imidazolium-4-carboxylic acid and terephthalic acid were added and stirred until completely dissolved. Then, acetic acid was added and stirred until homogeneous to obtain a mixture. The mixture was subjected to a solvothermal reaction. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the imidazolium ligand zirconium-based MOF catalyst. The molar ratio of the soluble zirconium salt to the total amount of the two ligand compounds is 1:1 to 1.1.5; The two ligand compounds are 1H-imidazol-4-carboxylic acid and terephthalic acid, and the molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:19 to 7:

3. The volume ratio of the acetic acid to the N,N-dimethylformamide is 1:1~9; The conditions for the solvothermal reaction are: reaction at 100~160℃ for 20~40h; The imidazole ligand zirconium-based MOF catalyst is in the form of a slender rod; the imidazole ligand zirconium-based MOF catalyst is obtained by introducing imidazole ligands to replace part of the terephthalic acid ligands on a regular octahedron UiO-66; the proportion of imidazole ligands in the imidazole ligand zirconium-based MOF catalyst does not exceed 50%.

2. The application according to claim 1, characterized in that, The soluble zirconium salt includes one of ZrCl4, ZrOCl2·8H2O or Zr(NO3)4·5H2O; The polar amide solvent includes one of N,N-dimethylformamide, N,N-diethylformamide, or N,N-dimethylacetamide.

3. The application according to claim 2, characterized in that, The soluble zirconium salt is ZrCl4; The polar amide solvent is N,N-dimethylformamide.

4. The application according to claim 3, characterized in that, The molar ratio of the soluble zirconium salt to the total amount of the two ligand compounds is 1:1.1; The molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:9 to 1:1; The volume ratio of the acetic acid to the N,N-dimethylformamide is 1:9; The solvothermal reaction was carried out at 120°C for 24 hours.

5. The application according to claim 4, characterized in that, The molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:

4.

6. A method for synthesizing dimethyl carbonate, characterized in that, include: Methanol, a dehydrating agent, an imidazole ligand zirconium-based MOF catalyst, and carbon dioxide were heated and stirred at high temperature. After the reaction was completed, the mixture was centrifuged to obtain the synthesized dimethyl carbonate. The preparation method of the imidazole ligand zirconium-based MOF catalyst includes the following steps: Soluble zirconium salt was dissolved in a polar amide solvent, and 1H-imidazolium-4-carboxylic acid and terephthalic acid were added and stirred until completely dissolved. Then, acetic acid was added and stirred until homogeneous to obtain a mixture. The mixture was subjected to a solvothermal reaction. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the imidazolium ligand zirconium-based MOF catalyst. The molar ratio of the soluble zirconium salt to the total amount of the two ligand compounds is 1:1 to 1.1.5; The two ligand compounds are 1H-imidazol-4-carboxylic acid and terephthalic acid, and the molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:19 to 7:

3. The volume ratio of the acetic acid to the N,N-dimethylformamide is 1:1~9; The conditions for the solvothermal reaction are: reaction at 100~160℃ for 20~40h; The imidazole ligand zirconium-based MOF catalyst is in the form of a slender rod; the imidazole ligand zirconium-based MOF catalyst is obtained by introducing imidazole ligands to replace part of the terephthalic acid ligands on a regular octahedron UiO-66; the proportion of imidazole ligands in the imidazole ligand zirconium-based MOF catalyst does not exceed 50%.

7. The method for synthesizing dimethyl carbonate according to claim 6, characterized in that, The volume ratio of methanol to dehydrating agent is 10:1 to 2:1; The amount of the imidazole ligand zirconium-based MOF catalyst used is 0.1 g, and the amount of carbon dioxide used is 3.5 MPa; The dehydrating agent includes one of trimethyl orthoformate, 2-cyanopyridine, or anhydrous calcium chloride.

8. The method for synthesizing dimethyl carbonate according to claim 6, characterized in that, The soluble zirconium salt includes one of ZrCl4, ZrOCl2·8H2O or Zr(NO3)4·5H2O; The polar amide solvent includes one of N,N-dimethylformamide, N,N-diethylformamide, or N,N-dimethylacetamide.

9. The method for synthesizing dimethyl carbonate according to claim 8, characterized in that, The soluble zirconium salt is ZrCl4; The polar amide solvent is N,N-dimethylformamide.

10. The method for synthesizing dimethyl carbonate according to claim 6, characterized in that, The molar ratio of the soluble zirconium salt to the total amount of the two ligand compounds is 1:1.1; The molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:9 to 1:1; The volume ratio of the acetic acid to the N,N-dimethylformamide is 1:9; The solvothermal reaction was carried out at 120°C for 24 hours.

11. The method for synthesizing dimethyl carbonate according to claim 10, characterized in that, The molar ratio of 1H-imidazol-4-carboxylic acid to terephthalic acid is 1:4.

Images