Preparation method and application of a catalyst for synthesizing dimethyl carbonate from carbon dioxide and methanol

Abstract

The application relates to the technical field of catalyst materials, in particular to a preparation method and application of a catalyst for synthesizing dimethyl carbonate from carbon dioxide and methanol; the method comprises the following steps: A, poloxamer is configured into a solution, HAc, NaClO4 and 1,3,5-trimethylbenzene are added into the solution and uniformly mixed to obtain a mixture; B, (NH4)2Ce(NO3)6 and H2BDC are added into the mixed solution in step A, the obtained solid after reaction is centrifugally separated, washed, soaked and dried to obtain a primary product, and finally the catalyst is obtained through calcination; in the application, HF-UiO-66 is synthesized by taking F127 as a template agent and taking 1,3,5-trimethylbenzene (TMB) as an expanding agent; the derivative HF-CeO2 catalyst with different TMB adding amounts is prepared through calcination; the adding of the expanding agent greatly increases the specific surface area of the catalyst, the CeO2 crystal grains generated through calcination are small, the number of acid-base sites is greatly increased, and therefore the catalyst has the largest catalytic activity, and the DMC yield reaches 12.02 mmol DMC / g cat .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst materials, in particular to a preparation method and application of a catalyst for synthesizing dimethyl carbonate from carbon dioxide and methanol. BACKGROUND

[0002] Carbon dioxide (CO2) is one of the most important greenhouse gases, and its massive emission has caused increasingly serious environmental problems such as global warming and ocean acidification. Countries are facing great challenges in CO2 emission reduction. However, CO2 is also a C1 resource with low cost and abundant reserves, and it is of great significance to convert it into high-value chemicals and liquid fuels through chemical catalytic technology. This not only helps to reduce greenhouse gas emissions, but also realizes the resource utilization of CO2.

[0003] The reaction process of directly synthesizing DMC from CO2 and methanol is not only economical, green and sustainable, but also an ideal synthesis path. However, the yield of DMC is low, and the reaction has not been industrialized. This is mainly caused by two reasons. One is the limitation of reaction kinetics, and the other is the inertness of CO2 (C=O bond energy is 806 KJ mol -1 ) which makes it difficult to activate and requires a large amount of energy input. Therefore, the catalytic activity and high pressure and high temperature are necessary to reduce the reaction energy barrier, so the selection and design of the catalyst are particularly critical.

[0004] At present, the activity and yield of the CeO2-based catalyst in the reaction of directly synthesizing DMC from CO2 and methanol need to be further improved. SUMMARY

[0005] In order to solve the above technical problems, the embodiments of the present application provide a preparation method and application of a catalyst for synthesizing dimethyl carbonate from carbon dioxide and methanol.

[0006] In order to achieve the above purpose, the embodiments of the present application adopt the following technical solutions:

[0007] On the one hand, the present application provides a preparation method of a catalyst for synthesizing dimethyl carbonate from carbon dioxide and methanol, comprising the following steps:

[0008] A. Poloxamer is configured into a solution, HAc, NaClO4 and 1,3,5-trimethylbenzene are added thereto and uniformly mixed to obtain a mixture;

[0009] B. (NH4)2Ce(NO3)6 and H2BDC are added to the mixed solution of step A, and the obtained solid after reaction is centrifuged, washed, soaked and dried to obtain a primary product, and finally calcined to obtain the catalyst.

[0010] In some embodiments, in step A, the molar ratio of the mass of the poloxamer to HAc is 2g:102mmol.

[0011] In some embodiments, in step A, the molar ratio of the HAc to NaClO4 is 51:35.

[0012] In some embodiments, in step A, the molar ratio of the volume of 1,3,5-trimethylbenzene to NaClO4 is (1~5)mL:70mmol.

[0013] In some embodiments, in step A, the molar ratio of the volume of 1,3,5-trimethylbenzene to NaClO4 is (3~5)mL:70mmol.

[0014] In some embodiments, in step B, the molar ratio of (NH4)2Ce(NO3)6 to H2BDC is 1:1.

[0015] In some embodiments, in step B, the molar ratio of HAc to H2BDC in step A is 51:10.

[0016] In some embodiments, in step B, the reaction temperature is 60℃, the reaction time is 20min, and the drying temperature is 60℃.

[0017] In some embodiments, in step B, the calcination temperature is 400~650℃, and the time is 2h.

[0018] In another aspect, the application also provides a use of the catalyst prepared by the above preparation method in synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0019] Compared with the prior art, the application has the beneficial effects that:

[0020] The application adopts a hydrothermal synthesis method, synthesizes HF-UiO-66 by taking F127 as a template agent and 1,3,5-trimethylbenzene (TMB) as an expanding agent, and prepares derivative HF-CeO2-X catalysts with different TMB addition amounts by calcination. 2 / g of F-CeO2-450 is increased to 135 cm 2 / g, the pore distribution was enlarged from 0-100 nm of F-CeO2-450 to 0-200 nm of HF-CeO2-450, and the grain size was reduced from 8.1 nm of F-CeO2-450 to 7.2 nm of HF-CeO2-450. The catalytic activity of MOFs calcined at various temperatures after adding TMB was improved, and the yield of HF-CeO2-450 was increased to 12.02 mmol DMC / g cat This is because the addition of TMB further optimizes the pore structure of MOFs derivatives, improves the accessibility of reactants, increases the exposed active sites, and generates smaller CeO2grains.

[0021] HF-Ce-UiO-66 calcined at 450℃ and TMB addition amount of 4 mL, the MOFs derivative has the largest specific surface area, oxygen vacancy concentration and acid-base site number, so it shows the optimal catalytic activity. The reaction conditions are optimized: when the amount of methanol is 15 mL, the amount of catalyst is 0.1 g, the reaction temperature is 140℃, the reaction pressure is 3 MPa, and the reaction time is 4 h, the methanol conversion rate reaches 0.64%, the DMC selectivity reaches 100%, and the DMC space-time yield reaches 2.95 mmol·g -1 ·h -1 , the yield reaches 12.02 mmol DMC / g cat . BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 XRD patterns (a) and N2physical adsorption-desorption isotherms (b) of HF-Ce-UiO-66-Y with different TMB addition amounts;

[0023] Figure 2 XRD patterns of HF-CeO2-Y with different TMB addition amounts;

[0024] Figure 3 N2adsorption-desorption isotherms (a) and pore size distribution curves (b) of HF-CeO2-Y with different TMB addition amounts;

[0025] Figure 4 SEM images of HF-CeO2-Y with different TMB addition amounts: 0 mL (a), 1 mL (b), 2 mL (c), 3 mL (d), 4 mL (e), 5 mL (f);

[0026] Figure 5 NH3-TPD (a) and CO2-TPD (b) spectra of HF-CeO2-Y with different TMB addition amounts;

[0027] Figure 6 Ce 3d XPS (a) and O 1S (b) spectra of HF-CeO2-Y for different TMB addition amounts;

[0028] Figure 7 Effect of calcination temperature (a) and TMB addition amount (b) on the catalytic activity of HF-CeO2-Y;

[0029] Figure 8 Effect of catalyst dosage (a), reaction temperature (b), and reaction time (c) on the catalytic activity of HF-CeO2-4;

[0030] Figure 9 Cyclic stability of HF-CeO2-4. DETAILED DESCRIPTION

[0031] The technical solutions in some embodiments of the present disclosure will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments provided by the present disclosure, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present disclosure.

[0032] XRD characterization

[0033] XRD (X-Ray Powder Diffraction) characterization was tested on a DX-2700BH X-ray diffractometer produced by Dandong Haoyuan Instrument Co., Ltd., using a Cu K a Scanning was performed at a working voltage of 40 kV and a working current of 40 mA, with a scanning speed of 1° / min, a scanning step of 0.02° / min, and a scanning range of 5°~80°.

[0034] N2 physical adsorption and desorption characterization

[0035] N2 physical adsorption and desorption characterization was tested on an SSA-4000 pore size and specific surface area analyzer instrument of Beijing Aude Electronic Technology Co., Ltd. First, the sample was degassed at 120℃~180℃ for 12 h, and then N2 adsorption and desorption testing was performed. The specific surface area was calculated using the BET method, the pore size distribution was calculated using the BJH adsorption method, and the pore volume was calculated using the N2 adsorption amount at P / P0=0.98.

[0036] FT-IR characterization

[0037] FT-IR (Fourier Transform infrared spectroscopy) characterization was tested on Thermo Scientific FTIR-Nicolet iS50 spectrometer in USA. The background value was tested before sample testing, so as to deduct the subsequent background value. Under the magnesium light, the sample was taken: KBr was mixed and ground in the ratio of 1:100, and then pressed into a transparent sheet to place the sample cell for testing. The scanning range was 400 cm -1 4000 cm -1 , and the scanning number was 80.

[0038] NH3-TPD characterization

[0039] NH3-TPD (NH3 temperature programmed desorption) characterization was tested on Peterco PCA-1200 chemisorption instrument. 0.1 g of catalyst was placed in a U-shaped quartz tube, purged under He atmosphere with a gas flow of 30 mL / min, and the temperature was increased to 300℃ at a heating rate of 10℃ / min, and kept for 30 min. After stopping heating, when the temperature decreased to 50℃, 3% NH3 / N2 adsorption with a gas flow of 30 mL / min was carried out for 30 min. Finally, the atmosphere was switched to He, and the temperature was increased to 900℃ at a heating rate of 10℃ / min to desorb the adsorbed NH3, and the change of signal was recorded by TCD detector.

[0040] CO2-TPD characterization

[0041] CO2-TPD (CO2 temperature programmed desorption) characterization was tested on Peterco PCA-1200 chemisorption instrument. 0.1 g of catalyst was placed in a U-shaped quartz tube, purged under He atmosphere with a gas flow of 30 mL / min, and the temperature was increased to 300℃ at a heating rate of 10℃ / min, and kept for 30 min. After stopping heating, when the temperature decreased to 50℃, 3% NH3 / N2 adsorption with a gas flow of 30 mL / min was carried out for 30 min. Finally, the atmosphere was switched to He, and the temperature was increased to 900℃ at a heating rate of 10℃ / min to desorb the adsorbed NH3, and the change of signal was recorded by TCD detector.

[0042] SEM characterization

[0043] SEM (Scanning Electron Microscopy) was tested by German ZEISS Sigama300 field emission scanning electron microscope, and the acceleration voltage was 3 kV.

[0044] XPS characterization

[0045] XPS (X-ray Photoelectron Spectroscopy) characterization was tested on the American ThermoScientific K-Alpha X-ray photoelectron spectrometer. The excitation source was Al Ka ray with a wavelength of 1486.6 eV, the working voltage was 12 kV, the energy resolution was 0.1 eV, and the charge correction was carried out with C 1s binding energy (284.8 eV).

[0046] Catalyst performance evaluation

[0047] Catalyst performance evaluation was carried out in a 100 mL magnetic high-pressure reaction kettle produced by Xi'an Taikang Biotechnology Co., Ltd. After the catalyst and 15 mL of methanol were placed in the reaction kettle, CO2 was introduced to replace the air in the reaction kettle, and after three times, 3.0 MPa of CO2 was introduced, and the pressure in the kettle was stable, and the reaction was carried out at 300 rpm and 140℃ for 4 h. After the reaction was completed, the mixture in the kettle was cooled to room temperature, and the solid-liquid separation was carried out, and the upper liquid phase product was collected for gas phase analysis.

[0048] Product analysis

[0049] Product analysis was carried out by GC-9790 gas chromatograph of Zhejiang Fulai Analysis Instrument Co., Ltd. The carrier gas was Ar, the product was separated by KB-1 capillary chromatographic column, and the product was analyzed by FID detector. The experimental data was processed by internal standard method, and the internal standard was ethanol. The gas chromatography conditions were: detector temperature 180℃, column oven temperature 40℃, and vaporization temperature 240℃. The conversion rate of methanol (C MeOH ), the selectivity of dimethyl carbonate (S DMC ), the space-time yield of dimethyl carbonate (STY DMC ), and the yield of dimethyl carbonate (Y DMC ) were calculated according to the following formula:

[0050] (2-1)

[0051] (2-2)

[0052] (2-3)

[0053] (2-4)

[0054] wherein n is the amount of substance of added methanol; n DMC , n MeOH is the amount of substance of methanol and DMC in the product; m cat is the mass of catalyst; t is the reaction time.

[0055] Example 1

[0056] 2 g of poloxamer (F127) was dissolved in 120 mL of deionized water, then HAc (102 mmol), NaClO4(70 mmol) and TMB (1,3,5-trimethylbenzene, 1 mL) were added, and after mixing well, (NH4)2Ce(NO3)6(20 mmol) and H2BDC (terephthalic acid, 20 mmol) were added. After stirring at 60 °C for 20 min, the resulting solid was separated by centrifugation and washed with deionized water and DMF twice, and then soaked in ethanol at 60 °C for two days, during which the ethanol was replaced every day. Finally, the product was dried at 60 °C under vacuum overnight to obtain the initial product, which was recorded as HF-Ce-UiO-66-1. After calcining HF-Ce-UiO-66-1 in a muffle furnace at 450 °C for 2 h, the catalyst was obtained, which was recorded as HF-CeO2-450 or HF-CeO2-1.

[0057] Example 2

[0058] Example 2 was the same as Example 1, except that the amount of 1,3,5-trimethylbenzene added was 2 mL, and the initial product was recorded as HF-Ce-UiO-66-2, and the catalyst obtained was recorded as HF-CeO2-2.

[0059] Example 3

[0060] Example 3 was the same as Example 1, except that the amount of 1,3,5-trimethylbenzene added was 3 mL, and the initial product was recorded as HF-Ce-UiO-66-3, and the catalyst obtained was recorded as HF-CeO2-3.

[0061] Example 4

[0062] Example 4 was the same as Example 1, except that the amount of 1,3,5-trimethylbenzene added was 4 mL, and the initial product was recorded as HF-Ce-UiO-66-4, and the catalyst obtained was recorded as HF-CeO2-4.

[0063] Example 5

[0064] Example 5 is the same as Example 1, except that the amount of 1,3,5-trimethylbenzene added is 5 mL, and the initial product is designated HF-Ce-UiO-66-5, and the catalyst obtained is designated HF-CeO2-5.

[0065] Example 6

[0066] Example 6 is the same as Example 1, except that the calcination temperature is 400°C.

[0067] Example 7

[0068] Example 7 is the same as Example 1, except that the calcination temperature is 500°C.

[0069] Example 8

[0070] Example 8 is the same as Example 1, except that the calcination temperature is 550°C.

[0071] Example 9

[0072] Example 9 is the same as Example 1, except that the calcination temperature is 600°C.

[0073] Example 10

[0074] Example 10 is the same as Example 1, except that the calcination temperature is 650°C.

[0075] Comparative Example 1

[0076] Comparative Example 1 is the same as Example 1, except that no 1,3,5- trimethylbenzene is added, and the initial product is designated F-Ce-UiO-66, and the catalyst obtained is designated F-CeO2.

[0077] Comparative Example 2

[0078] Comparative Example 2 is the same as Comparative Example 1, except that the calcination temperature is 400°C.

[0079] Comparative Example 3

[0080] Comparative Example 3 is the same as Comparative Example 1, except that the calcination temperature is 500°C.

[0081] Comparative Example 4

[0082] Comparative Example 4 is the same as Comparative Example 1, except that the calcination temperature is 550°C.

[0083] Comparative Example 5

[0084] Comparative Example 5 is the same as Comparative Example 1, except that the calcination temperature is 600°C.

[0085] Comparative Example 6

[0086] Comparative Example 6 is the same as Comparative Example 1, except that the calcination temperature is 650°C.

[0087] 1. Characterization of HF-Ce-UiO-66

[0088] The XRD pattern of HF-Ce-UiO-66-Y (Y represents the volume of 1,3,5-trimethylbenzene added) is shown in FIG. (a) of Figure 1 The XRD pattern of HF-Ce-UiO-66-Y is consistent with the calculated Ce-UiO-66 with face-centered cubic topology, indicating the successful synthesis of MOFs. The peak intensity of HF-Ce-UiO-66 greatly increases after the addition of TMB, and the peak intensity becomes higher as the amount of TMB added increases, which indicates that the addition of TMB increases the crystallinity of MOFs. Among them, the two peaks at 17.4° and 28° are particularly high, which shows a high-angle oriented crystal framework.

[0089] The N2 adsorption-desorption curve of HF-Ce-UiO-66-Y is shown in FIG. (b) of Figure 1 All the curves do not show obvious N2 adsorption at P / P0 < 0.05, which indicates that the MOFs structure does not contain microporous structure, which is related to the directional guidance of F127 as a template agent for MOFs crystallization. The presence of hysteresis loops cannot be observed in the curve, which indicates that the template agent F127 and the swelling agent TMB do not block the pore structure.

[0090] 2. Characterization of HF-CeO2

[0091] The XRD pattern of HF-CeO2-Y (Y represents the volume of 1,3,5-trimethylbenzene added) is shown in FIG. Figure 2 The characteristic peaks all belong to CeO2 with cubic fluorite structure, indicating that the addition of F127 and TMB does not affect the conversion of MOFs to CeO2 during calcination, and the prepared catalyst is CeO2 without other impurities.

[0092] The N2 adsorption-desorption isotherm curve of HF-CeO2-Y with different TMB addition amounts is shown in FIG. (a) of Figure 3 All the isotherm curves are type IV, indicating the presence of mesopores. From the pore size distribution curve of HF-CeO2-Y in FIG. (b) Figure 3 It can be seen that the number of mesopores within 10 nm increases with the addition of TMB. It can also be seen in Table 1 that the addition of TMB increases the specific surface area of the catalyst, which indicates that TMB as a swelling agent expands the pore size of the catalyst and enriches the pore structure, which is helpful for the diffusion of reactants, Figure 3 HF-CeO2-0 in FIG. is F-CeO2 in Comparative Example 1.

[0093] SEM images of HF-CeO2-Y are shown below. Figure 4 As shown, when TMB dosage was 0-2 mL, the crystals did not exhibit a clear regular morphology, showing a tendency to form octahedral shapes. When the TMB dosage reached 3 mL, the particles exhibited a clear octahedral morphology. The particle size increased with the addition of TMB, from 1 μm to 1.5 μm, indicating that the oil-water interface formed by TMB addition facilitated the crystallization of Ce-based MOFs, increasing their crystallinity, which is consistent with the XRD results. Furthermore, the mesopore size of the catalyst gradually increased with the addition of TMB, and obvious mesopores were observed at a dosage of 3 mL. This explains the increase in specific surface area, indicating that the addition of TMB enriches the pore structure of the catalyst, providing not only mass transfer channels but also increasing the exposure rate of active sites, thus facilitating the reaction.

[0094] The NH3-TPD and CO2-TPD of HF-CeO2-Y catalysts with different TMB dosages were characterized to determine the catalyst's acidity and basicity. Figure 5 The NH3-TPD spectrum shows that the peak intensity of HF-CeO2-Y at 50-400℃ is significantly increased after adding TMB as a swelling agent, indicating a substantial increase in the number of weak / moderately strong acid sites; Figure 5 The CO2-TPD spectrum shows that, compared with F-CeO2 without TMB, HF-CeO2 exhibits a significantly enhanced desorption signal in the 50-200℃ range, with the strongest signal observed when the TMB dosage is 4 mL. This indicates an increase in the number of basic sites, with HF-CeO2-4 possessing the highest number of basic sites.

[0095] This is likely due to the increased pore size resulting from the addition of TMB, which significantly enriches the internal pore structure of the catalyst. Furthermore, the calcined catalyst retains its pore structure and a larger specific surface area, improving the accessibility of NH3 and CO2 molecules. Previous studies have shown that methanol is activated at the acidic and basic sites of the catalyst to form methyl and methoxy species, respectively. The methoxy species then reacts with carbon dioxide adsorbed at the basic sites of the catalyst to form methoxy carbonate anions, which further react with methyl compounds to generate DMC. Therefore, by introducing hierarchical pores to prepare Ce-MOF derivatives with rich pore structures, the acid and basic sites of the catalyst can be significantly increased, thereby facilitating the reaction.

[0096] XPS characterization was performed on HF-CeO2-Y catalysts with different TMB dosages to observe the surface Ce and O composition of the catalysts. Figure 6As shown, Ce 3D spectrum can be divided into 10 peaks, corresponding to 5 pairs of Ce 3d5 / 2 and Ce 3d3 / 2 spin-orbit, in which 6 peaks are marked as V 0 (880.6 eV), V (881.9 eV), V' (883.9 eV), V'' (888.5 eV), V''' (897.6 eV), corresponding to Ce 4+ 3d 10 4f0. The remaining 4 peaks are marked as U 0 (898.6 eV), U' (901.9 eV), U'' (906.9 eV), U''' (906.1 eV), corresponding to Ce 3+ 3d 10 4f1. The peaks at 529.1 eV and 530.5 eV in O 1s XPS spectrum correspond to lattice oxygen (O lat ) and oxygen vacancy (O vac ), respectively. With the increase of TMB addition amount, the binding energy of O vac and O lat is negatively shifted, which indicates that the increase of electron density and entropy in the catalyst makes O vac and O lat more easily adsorbed and reacted with reactant molecules as active sites. Table 1 summarizes the contents of Ce 3+ and Ovacof HF-CeO2-Y catalysts. As can be seen from the table, the Ce 3+ and O vac concentrations of HF-CeO2-Y first increase and then decrease, and the Ce 3+ and O vac of HF-CeO2-4 reach a maximum of 26.3% and 30.1%, respectively.

[0097] 3. Activity evaluation of HF-CeO2

[0098] The catalytic performance of HF-CeO2-X (X represents the calcination temperature) and HF-CeO2-Y catalysts in the direct synthesis of DMC from CO2 and CH3OH was evaluated in a high-pressure reaction kettle, and the results are shown in Figure 7 . Figure 7 The (a) graph in the figure explores the effect of calcination temperature on the catalytic performance of F-CeO2 and HF-CeO2. It can be seen that the activities of the two catalysts show a volcano trend, both first increase and then decrease, and 450°C is the best calcination temperature.

[0099] This is because the catalyst calcined at 450℃ possesses the largest specific surface area, oxygen vacancy concentration, and number of acid-base sites, thus exhibiting optimal catalytic activity; the catalytic activity of MOFs calcined at various temperatures after the addition of TMB is improved to some extent. The yield of F-CeO2-450 is 10.44 mmol. DMC / g cat The yield of HF-CeO2-450 increased to 12.02 mmol. DMC / g cat This is because the addition of TMB increases the crystallinity of the catalyst, optimizes the pore structure of the catalyst, improves the accessibility of reactants, and increases the number of exposed active sites. Figure 7 Figure (b) in the figure explores the effect of TMB dosage on catalytic activity. Figure 7 As shown in Figure (b), the activity of HF-CeO2-Y first increases and then decreases with the addition of TMB, reaching its maximum at an addition volume of 4 mL.

[0100] 4. Characterization of HF-CeO2-Y and its structure-activity relationship

[0101] Table 1 summarizes the physicochemical properties of the HF-CeO2-Y catalyst, including its structural properties, texture properties, and surface chemical composition, to facilitate the establishment of structure-activity relationship with the catalyst's performance. As shown in Table 1, the smallest CeO2 grain size in HF-CeO2-4 is 7.22 nm; the largest specific surface area is 135 cm². 2 / g;Ce 3+ The highest content and oxygen vacancy concentration were observed, at 26.1% and 30.1%, respectively. (Combined) Figure 5 Characterization tests of NH3-TPD and CO2-TPD in and Figure 3 Pore ​​size distribution analysis to determine how TMB addition affects catalytic activity:

[0102] 1. The addition of the expanding agent TMB causes the PPO end of the micelles formed by the template agent to expand, resulting in larger pore size of the HF-CeO2-Y catalyst. The increase in the number of large mesopores and macropores optimizes the pore structure, and the specific surface area also increases due to the abundance of pores, thereby optimizing the texture performance of the catalyst. This can also be observed intuitively in the SEM image.

[0103] 2. The addition of TMB without washing and removal saves on the use of chemical agents and prevents the collapse of the pore structure during high-temperature calcination, while also avoiding the agglomeration of CeO2 due to thermal instability to form large grains.

[0104] 3. The abundant porous structure increases the accessibility of reactant molecules, as well as CH3OH and CO2 molecules. Furthermore, the reduced size of CeO2 crystallites exposes more active sites. This can be observed in the change in the number of acid-base sites.

[0105] 4. The optimization of the above physicochemical properties led to the improvement of Ce on the catalyst surface. 3+ O V Increased content leads to the formation of more Lewis acid-base sites, thereby enhancing CO2 activation; while the increase in acidic sites strengthens the activation of CH3OH. The presence of bifunctional acid-base sites and Ce 3+ O V The presence of both promotes the direct synthesis of DMC from CO2 and CH3OH.

[0106] Table 1. Structural properties, textural properties, and surface chemical composition of HF-CeO2-Y catalysts

[0107]

[0108] 5. Optimization of reaction conditions for HF-CeO2-4

[0109] Based on the evaluation results of the activity of HF-CeO2 based on calcination temperature and TMB addition, the effects of catalyst dosage, reaction temperature, and reaction time on the activity of HF-CeO2-4 catalyst were investigated under the same conditions. Figure 8 As shown in Figure (a), the conversion of HF-CeO2-4 initially increases and then stabilizes with increasing catalyst dosage, which is due to the influence of substrate concentration limitations. The optimal catalyst dosage is 0.1 g, with a conversion rate of 0.64%. Figure 8 As shown in Figure (b), the conversion rate of HF-CeO₂⁻⁴ first increases and then decreases with increasing calcination temperature, exhibiting a volcanic trend, reaching its maximum at 140℃. This is because the reaction rate is slow at low temperatures, limiting the activation and conversion of methanol and CO₂. The Gibbs free energy of the reaction indicates that it is exothermic, and the reactivity decreases slightly with increasing temperature. Figure 8 As shown in Figure (c), the methanol conversion rate gradually increases with increasing reaction time, stabilizing after 4 h. In summary, the optimal reaction conditions for the HF-CeO₂⁻⁴ catalyst are: 15 mL methanol, 0.1 g catalyst, reaction temperature 140℃, reaction pressure 3 MPa, and reaction time 4 h. Under these conditions, the methanol conversion rate is 0.64%, the DMC selectivity is 100%, and the DMC space-time yield is 2.95 mmol·g⁻¹. -1 ·h -1 The yield was 12.02 mmol. DMC / gcat .

[0110] The HF-CeO2-4 catalyst was selected for 5 cycle experiments to evaluate its stability, and the results are shown in Table 2. Figure 9 The HF-CeO2-4 catalyst showed excellent stability, and the methanol conversion rate decreased from 0.64% to 0.43% after 5 cycle experiments.

[0111] The present application synthesizes HF-UiO-66 using F127 as a template agent and 1,3,5-trimethylbenzene (TMB) as an expanding agent, and calcines to prepare a derivative HF-CeO2 catalyst with different TMB addition amounts. The addition of the expanding agent greatly increases the specific surface area of the catalyst, and makes the CeO2 crystal grains generated by calcination smaller, and the number of acid and base sites is also greatly increased, so it has the largest catalytic activity, and the DMC yield reaches 12.02 mmol / g DMC cat .

[0112] As can be seen from Table 2, the CeO2-based catalyst shows more excellent catalytic activity than the ZrO2-based, CaO2-based and TiO2-based catalysts, and can obtain an ideal DMC yield under relatively mild conditions. The activity of the HF-CeO2 in the present application is improved compared with the nano-CeO2 prepared by the precipitation method and the hollow CeO2 with manufacturing defects, which shows that the preparation of the hierarchical pore MOFs derivative catalyst from the MOFs as the precursor has excellent physical and chemical properties such as large specific surface area, small CeO2 particle size, high oxygen vacancy content and high acid-base site content, which reflects more excellent catalytic performance, which embodies the significance and innovation of the present research topic.

[0113] Table 2 Catalyst performance for direct synthesis of DMC from CO2 and methanol

[0114]

[0115] Note: The reaction temperature is 140℃.

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[0118] ​Reference 2: Wang S, Zhao L, Wang W, et al. Morphology control of nanoceria for catalytic conversion of carbon dioxide and methanol[J]. Nanoscale, 2013, 5(12): 5582-5588.

[0119] Reference 3: Zhang J, Huang S, Zhao Y, et al. CeO2 hollow nanospheres catalyze the synthesis of dimethyl carbonate from carbon dioxide and methanol: the effect of cavity on catalytic performance[J]. Asia-Pacific Journal of Chemical Engineering, 2021, 16(1): e2554.

[0120] Reference 1: Jin S, Guan X, Zhang X, et al. CeO2 nanorods with dual-functional oxygen vacancies promote the photocatalytic conversion of CO2 and CH3OH to dimethyl carbonate at low pressure[J]. Journal of Environmental Chemical Engineering, 2023, 11(6): 111374.

[0121] Reference 6: Fu Z, Zhong Y, Yu H, et al. TiO2-doped CeO2 nanorods for direct synthesis of dimethyl carbonate from CO2 and CH3OH: catalytic performance and kinetic study[J]. ACS Omega, 2018, 3(1): 198-207.

[0122] Reference 7: Shi D, Heyte S, Capron M, et al. Direct synthesis of dimethyl carbonate from methanol and CO2 over ZrO2 catalysts combined with a dehydrating agent and a cocatalyst[J]. Catalysts, 2024, 14(10): 657.

[0123] Based on the above, TMB was added as an expanding agent to prepare HF-UiO-66 containing mesoporous structure and hollow structure. By pyrolysis, the ligand, F123, and TMB were removed to obtain HF-UiO-66 derivatives that retain large mesopores and macropores. A series of characterization methods were used to analyze the physicochemical properties of the catalysts, and the effects of TMB addition amount on Ce valence, acid-base sites, and catalytic performance were explored. The structure-activity relationship between the physicochemical properties of HF-UiO-66 derivatives and their catalytic performance was established. The main conclusions are as follows:

[0124] (1) The addition of TMB forms an oil-water interface, increasing the solubility of H2BDC and promoting the crystallization of Ce-UiO-66.

[0125] (2) The addition of appropriate TMB, the introduction of large mesopores and macropores makes the internal pore structure of the catalyst more abundant, increases the specific surface area of the catalyst, improves the accessibility of the internal active sites of the catalyst, greatly increases the content of acid-base sites of the catalyst, and thus promotes the activity of the catalyst.

[0126] (3) The catalyst activity presents a volcano-type trend with the addition amount of TMB, and the highest catalytic activity is shown in HF-CeO2-4, because TMB is 4, which represents the largest specific surface area, the largest oxygen vacancy concentration, the most acid-base sites and the smallest grain size.

[0127] (4) The reaction conditions are optimized: when the amount of methanol is 15 ml, the amount of catalyst is 0.1 g, the reaction temperature is 120 DEG C, the reaction pressure is 3 Mpa, and the reaction time is 4 h, the methanol conversion rate reaches 0.64%, the DMC selectivity reaches 100%, the DMC space-time yield reaches 2.95 mmol·g -1 ·h -1 , and the DMC yield reaches 12.02 mmol DMC / g cat .

[0128] The present application adopts a hydrothermal synthesis method, uses F127 as a template agent, uses 1,3,5-trimethylbenzene (TMB) as an expanding agent to synthesize HF-UiO-66, and calcines to prepare derivative HF-CeO2-X catalysts with different TMB addition amounts. The characterization results show that: TMB as an expanding agent greatly enriches the pore of the HF-UiO-66 derivative, the specific surface area is increased from 101 cm 2 / g of F-CeO2-450 to 135 cm 2 / g of HF-CeO2-450, the pore distribution is expanded from 0-100 nm of F-CeO2-450 to 0-200 nm of HF-CeO2-450, and the grain size is reduced from 8.1 nm of F-CeO2-450 to 7.2 nm of HF-CeO2-450. The catalytic activity of the MOFs after adding TMB and calcining at various temperatures is improved, and the yield of HF-CeO2-450 is increased to 12.02 mmol DMC / g cat This is because the addition of TMB further optimizes the pore structure of the MOFs derivative, improves the accessibility of the reactants, increases the exposed active sites, and generates smaller CeO2 grain size.

[0129] The MOFs derivative has the largest specific surface area, oxygen vacancy concentration and acid-base site number when the HF-Ce-UiO-66 is calcined at 450 ℃ and the TMB addition amount is 4 mL, so the catalytic activity is the best. The reaction conditions are optimized: when the methanol amount is 15 mL, the catalyst amount is 0.1 g, the reaction temperature is 140 ℃, the reaction pressure is 3 MPa and the reaction time is 4 h, the methanol conversion rate reaches 0.64%, the DMC selectivity reaches 100% and the DMC space-time yield reaches 2.95 mmol·g -1 ·h -1 , the yield reaches 12.02 mmol DMC / g cat .

[0130] In the description of the present specification, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0131] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which 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 catalyst for synthesizing dimethyl carbonate from carbon dioxide and methanol, characterized by, The method comprises the following steps: A. Poloxamer is configured into a solution, HAc, NaClO4 and 1,3,5-trimethylbenzene are added and mixed to obtain a mixture; B. (NH4)2Ce(NO3)6 and H2BDC are added to the mixed solution of step A, and the obtained solid after reaction is centrifuged, washed, soaked and dried to obtain a primary product, and finally calcined to obtain a catalyst.

2. The production method according to claim 1, characterized by, In step A, the mass of the poloxamer and the molar ratio of HAc are 2g:102mmol.

3. The preparation method according to claim 1, characterized in that, In step A, the molar ratio of HAc to NaClO4 is 51:

35.

4. The production method according to claim 1, characterized by, In step A, the volume of 1,3,5-trimethylbenzene and the molar ratio of NaClO4 are (1-5)mL:70mmol.

5. The preparation method according to claim 4, characterized in that, In step A, the volume of 1,3,5-trimethylbenzene and the molar ratio of NaClO4 are (3-5)mL:70mmol.

6. The method of claim 1, wherein, In step B, the molar ratio of (NH4)2Ce(NO3)6 to H2BDC is 1:

1.

7. The preparation method according to claim 1, characterized in that, In step B, the molar ratio of HAc in step A to H2BDC is 51:

10.

8. The method of claim 1, wherein, In step B, the reaction temperature is 60℃, the reaction time is 20min, and the drying temperature is 60℃.

9. The method of claim 1, wherein, In step B, the calcination temperature is 400-650℃, and the time is 2h.

10. The use of a catalyst prepared by the preparation method of any one of claims 1-9 in the synthesis of dimethyl carbonate from carbon dioxide and methanol.

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