High-activity catalyst for synthesizing dimethyl carbonate from methanol and carbon dioxide by direct method

Abstract

This invention relates to the field of heterogeneous catalysis technology in chemical engineering, specifically to a highly active catalyst for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. The catalyst is CeO2 derived from Ce-MOF, with a Taylor ratio of 0.15-0.35. Using acidic Ce-MOFs as a cerium precursor, this catalyst leverages their ordered pore structure, large specific surface area, and superior adsorption capacity to achieve the resorption of metal ions (CeO2, MgO, MgO, MgO, MgO) by... 3+ Ce 4+ The high dispersion of the catalyst in Ce-MOF, and the addition of appropriate hydroxides can reduce the adsorption of non-reactive substances, thereby significantly improving the catalytic activity of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of heterogeneous catalysis technology in chemical engineering, specifically to a highly active catalyst for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Background Technology

[0002] Dimethyl carbonate (DMC) is a promising green and environmentally friendly chemical that can replace toxic and harmful raw materials in many fields such as carbonylation, methylation, and transesterification (MAPacheco; CL Marshall. Review of dimethylcarbonate (DMC) manufacture and its characteristics as a fuel additive. Energy & Fuels. 1997, 11(1): 2-29.). Meanwhile, DMC is widely used in pesticides, fuels, oil additives, and dyes (Y. Ono. Dimethyl carbonate for environmentally benign reactions. Catalysis Today. 1997, 35(1): 15-25.). The synthesis of DMC using carbon dioxide (CO2) and methanol as raw materials conforms to the basic principles of green chemistry and can also effectively catalyze the conversion of CO2, alleviating the environmental problems caused by excessive CO2 emissions. Therefore, the efficient utilization of CO2 and the efficient synthesis of DMC make this process route of profound social significance.

[0003] Compared to the problems of separation, recovery, and reuse of homogeneous catalysts, heterogeneous catalysts can greatly simplify the process and reduce energy consumption, and are therefore widely used in the direct synthesis of DMC. These catalysts include transition metal oxides, heteropolyacids, and supported catalysts.

[0004] CeO2 is a multifunctional catalyst that exhibits good catalytic activity in batch reactors and is a widely recognized catalyst for the synthesis of dimethyl carbonate. It contains three types of surface active sites: redox sites, Lewis acid sites, and Lewis basic sites (oxygen vacancies: redox sites; Ce atoms adjacent to oxygen vacancies and their neighboring oxygen atoms: Lewis acid-base sites). These three different surface active sites can catalyze certain chemical reactions individually or synergistically catalyze complex reaction processes to obtain a wide variety of reaction products. Staudt et al. used DFT calculations to find that oxygen vacancies on the cerium oxide surface participate in the CO2 activation process (T. Staudt; Y. Lykhach; N. Tsud, et al. Ceria reoxidation by CO2: A modelstudy. Journal of Catalysis. 2010, 275(1):181-185.), and surface oxygen vacancies can be regarded as "active sites" for oxygen atom activation. The dissociation and adsorption of methanol on the CeO2 surface to form methoxy species requires a cation / anion pair (i.e., a Lewis acid-base pair) (BADRI A, BINET C, LAVALLEY J C. Use of Methanol as an IR Molecular Probe to Study the surface of Polycrystalline Ceria[J]. Journal of the Chemical Society, 1997, 93: 1159-1168.), and the formed methoxy species depend on the coordination environment of the Ce sites on the surface and the presence of oxygen vacancies.

[0005] The catalytic activity of CeO2 still needs to be improved. Summary of the Invention

[0006] This invention provides a highly active catalyst for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. This catalyst uses acidic Ce-MOFs as a cerium precursor and leverages their ordered pore structure, large specific surface area, and strong adsorption capacity to achieve the adsorption of metal ions (Ce... 3+ Ce 4+ The high dispersion of the catalyst in Ce-MOF, and the addition of appropriate hydroxides can reduce the adsorption of non-reactive substances, thereby significantly improving the catalytic activity of the catalyst.

[0007] A catalyst, which is CeO2 derived from Ce-MOF, having a Taylor ratio of 0.15-0.35.

[0008] Specifically, the Taylor ratio of the catalyst is 0.15, 0.18, 0.25, 0.27 or 0.35.

[0009] MOF (metal-organic framework) structures can increase the surface area of ​​CeO2, reducing the possibility of CeO2 agglomeration and collapse that prevents internal active sites from activating. At the same time, acidic MOFs can bind to Lewis basic sites on the surface of cerium dioxide, shielding Lewis basic sites and reducing the adsorption rate of carbon dioxide on Lewis basic sites.

[0010] Based on extensive research, this invention has determined that for Ce-MOF-derived CeO2, the MOF topology provides the optimal Taylor ratio (TR) for expanding the surface area of ​​cerium dioxide. This catalyst effectively combines the adsorption and reaction of CO2 and methanol, thereby further enhancing its reactivity.

[0011] Taylor ratio (TR): The ratio of the area of ​​active sites on the catalyst surface to the total surface area of ​​the catalyst.

[0012] Specifically, the catalyst is prepared by calcining Ce-MOF.

[0013] Specifically, the Ce-MOF is prepared by reacting pyromellitic acid, a cerium metal salt, and a soluble hydroxide in the presence of a solvent.

[0014] This invention obtains the optimal Taylor ratio for a highly active catalyst (i.e., CeO2 derived from Ce-MOF) that promotes the direct synthesis of dimethyl carbonate by adjusting the amount of soluble hydroxide (alkali) added.

[0015] The present invention also provides a method for preparing the above-mentioned catalyst, comprising:

[0016] 1) Ce-MOF is prepared by reacting pyromellitic acid (BTC), a cerium metal salt and a soluble hydroxide in the presence of an organic solvent;

[0017] 2) Ce-MOF is calcined to obtain Ce-MOF-derived CeO2, which is the catalyst.

[0018] Specifically, in step (1) above, the cerium metal salt is selected from at least one of cerium nitrate, cerium sulfate, cerium chloride, or cerium acetate.

[0019] Specifically, in step (1) above, the molar ratio of cerium ions to pyromellitic acid is 1:(1-5).

[0020] Specifically, in step (1) above, the organic solvent is at least one of anhydrous methanol, anhydrous ethanol, acetone, etc.

[0021] Specifically, in step (1) above, the reaction is carried out in a mixed solution of organic solvent and water, for example, the organic solvent and water are in equal volume ratio.

[0022] Specifically, in step (1) above, the soluble hydroxide is an alkali metal hydroxide, an alkaline earth metal hydroxide, or a transition element hydroxide.

[0023] Specifically, in step (1) above, the soluble hydroxide is one or more of KOH and NaOH.

[0024] Specifically, the reaction temperature in step (1) above is 70-100℃. Optionally, the reaction is carried out under stirring conditions for 60-120 min.

[0025] Specifically, in step (1) above, the concentration of the soluble hydroxide in the reaction system is 0.5-2 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L.

[0026] Specifically, in step (2) above, the heating rate of the calcination is 3-5℃ / min, the calcination temperature is 460-480℃, and the calcination time is 3-5h. The preferred heating rate is 3℃ / min, the preferred calcination temperature is 460℃, and the preferred calcination time is 3h.

[0027] Specifically, the preparation method of the above catalyst includes the following steps:

[0028] (1) Dissolve a certain amount of pyromellitic acid in a mixed solution of an equal volume of organic solvent A and deionized water, add a certain amount of cerium metal salt solution, stir for a period of time under water bath heating, accurately weigh a certain amount of soluble hydroxide and add it to the above solution, continue to stir for a period of time under water bath heating, centrifuge to separate, wash the product three times with water and ethanol respectively, and dry for 10h to obtain Ce-MOF sample;

[0029] (2) The obtained Ce-MOF sample is placed in a muffle furnace and heated to a certain temperature at a certain rate. After calcination for a certain time, CeO2 derived from Ce-MOF can be obtained.

[0030] In step (1) above, the water bath temperature is 70-100℃ and the stirring time is 60-120min, with the two stirring times being the same.

[0031] The temperature of the constant temperature drying oven used in step (1) above is 80℃-120℃.

[0032] In step (1) above, the concentration of hydroxide in the final mixed solution is 0.5-2 mol / L.

[0033] The preferred heating rate in step (2) above is 3℃ / min, the preferred calcination temperature is 460℃, and the preferred calcination time is 3h.

[0034] The present invention also includes catalysts prepared by the above method (i.e. Ce-MOF-derived CeO2).

[0035] The present invention also includes the application of the above-mentioned catalyst in the direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol.

[0036] Specifically, the method for directly synthesizing dimethyl carbonate from CO2 and methanol involves a catalytic reaction in a 100-250 ml high-pressure reactor. 0.01-1.5 g of catalyst is placed in the reactor, followed by 6-72 g of methanol. CO2 gas is then introduced at 0.2-5 MPa. The reactor is sealed, and excess gas is purged 3-10 times. The mixture is allowed to stand for 3-5 minutes, and under a carbon dioxide atmosphere, the stirring speed is maintained at 100-600 r / min for 1-15 hours at a temperature of 100-200℃. CO2 and methanol react directly with the catalyst to produce dimethyl carbonate.

[0037] This invention is the first to propose using a highly active catalyst derived from Ce-MOFs at an optimal Taylor ratio for the direct reaction of CO2 and methanol to produce dimethyl carbonate. Effectively combining feedstock adsorption with subsequent reactions further enhances the catalyst's reactivity.

[0038] Ce-MOF's high specific surface area, ordered pore structure, and strong adsorption capacity enable Ce to achieve... 3+ With Ce 4+ The catalyst exhibits high dispersion on CeO2. It effectively combines the adsorption of the raw materials with subsequent reactions, thus avoiding the phenomenon where the acid-base active sites and oxygen vacancies on the CeO2 surface are difficult to activate due to agglomeration and collapse. The catalyst preparation method of this invention is simple, resulting in a significant improvement in catalytic efficiency. Detailed Implementation

[0039] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0040] Example 1

[0041] A certain amount of pyromellitic acid was dissolved in a mixed solution of 70 mL deionized water and 70 mL ethanol. A certain amount of Ce(NO3)3·6H2O was dissolved in 315 mL deionized water, making the molar ratio of cerium ions to pyromellitic acid 1:1. The two solutions were mixed and stirred for 1 h in a water bath (70℃). A certain amount of KOH was accurately weighed and added to the solution to make the alkali concentration 0.5 mol / L. The mixture was stirred for another 1 h in a water bath (70℃), centrifuged, and the product was washed three times with water and three times with anhydrous ethanol, and dried at 80℃ for 10 h to obtain the Ce-MOF sample. The obtained Ce-MOF sample was placed in a muffle furnace and heated to 460℃ at a rate of 3℃ / min, and calcined for 3 h to obtain CeO2 derived from Ce-MOF, which was sample #1. The Taylor ratio was measured to be 0.15.

[0042] Example 2

[0043] A certain amount of trimellitic acid was dissolved in a mixed solution of 10 mL deionized water and 10 mL ethanol. A certain amount of cerium chloride (CeCl3) was dissolved in 45 mL deionized water, making the molar ratio of cerium ions to trimellitic acid 1:2. The two solutions were mixed and stirred in a water bath (70℃) for 1 h. A certain amount of NaOH was accurately weighed and added to the solution to make the alkali concentration in the solution 0.8 mol / L. The mixture was stirred in a water bath (70℃) for another 1 h, centrifuged, and the product was washed three times with water and three times with ethanol, and dried at 90℃ for 10 h to obtain the Ce-MOF sample. The obtained Ce-MOF sample was placed in a muffle furnace and heated to 460℃ at a rate of 3℃ / min, and calcined for 3 h to obtain Ce-MOF-derived CeO2, which is sample #2. The Taylor ratio was measured to be 0.18.

[0044] Example 3

[0045] A certain amount of trimellitic acid was dissolved in a mixed solution of 60 mL deionized water and 60 mL ethanol. A certain amount of cerium chloride (CeCl3) was dissolved in 270 mL deionized water, making the molar ratio of cerium ions to trimellitic acid 1:3. The two solutions were mixed and stirred for 1 h in a water bath (70℃). A certain amount of KOH was accurately weighed and added to the solution to make the alkali concentration 1 mol / L. The mixture was stirred for another 1 h in a water bath (70℃), centrifuged, and the product was washed three times with water and three times with anhydrous ethanol, and dried at 100℃ for 10 h to obtain the Ce-MOF sample. The obtained Ce-MOF sample was placed in a muffle furnace and heated to 460℃ at a rate of 3℃ / min, and calcined for 3 h to obtain CeO2 derived from Ce-MOF, which was sample #3. The Taylor ratio was measured to be 0.25.

[0046] Example 4

[0047] A certain amount of pyromellitic acid was dissolved in a mixed solution of 50 mL deionized water and 50 mL ethanol. A certain amount of cerium acetate (Ce(Ac)3·nH2O) was dissolved in 225 mL deionized water, making the molar ratio of cerium ions to pyromellitic acid 1:4. The two solutions were mixed and stirred for 1 h in a water bath (70℃). A certain amount of KOH was accurately weighed and added to the solution to make the alkali concentration 1.5 mol / L. The mixture was stirred for another 1 h in a water bath (70℃). After centrifugation, the product was washed three times with water and three times with ethanol, and dried at 100℃ for 10 h to obtain the Ce-MOF sample. The obtained Ce-MOF sample was placed in a muffle furnace and heated to 460℃ at a rate of 3℃ / min. After calcination for 3 h, CeO2 derived from Ce-MOF was obtained, which was sample #4. The Taylor ratio was measured to be 0.27.

[0048] Example 5

[0049] A certain amount of pyromellitic acid was dissolved in a mixed solution of 40 mL deionized water and 40 mL ethanol. A certain amount of cerium acetate (Ce(Ac)3·nH2O) was dissolved in 180 mL deionized water, making the molar ratio of cerium ions to pyromellitic acid 1:5. The two solutions were mixed and stirred for 1 h in a water bath (70℃). A certain amount of NaOH was accurately weighed and added to the solution to make the alkali concentration 2 mol / L. The mixture was stirred for another 1 h in a water bath (70℃). After centrifugation, the product was washed three times with water and three times with ethanol, and dried at 100℃ for 10 h to obtain the Ce-MOF sample. The obtained Ce-MOF sample was placed in a muffle furnace and heated to 460℃ at a rate of 3℃ / min. After calcination for 3 h, CeO2 derived from Ce-MOF was obtained, which was sample #5. The Taylor ratio was measured to be 0.35.

[0050] Comparative Example 1

[0051] A certain amount of trimellitic acid was dissolved in 10 mL of deionized water and 10 mL of ethanol, and a certain amount of cerium chloride (CeCl3) was dissolved in 45 mL of deionized water, making the molar ratio of cerium ions to trimellitic acid 1:2. The two solutions were mixed and placed in a water bath and heated to 70 °C, with vigorous stirring for 1 h. The product was separated from the liquid by centrifugation, and then the product was centrifuged with water and ethanol respectively, washed and circulated three times. The product was then dried in an oven at 100 °C for 10 h to obtain Ce-MOF. The obtained Ce-MOF was placed in a muffle furnace and heated to 460 °C at a rate of 3 °C / min, and calcined for 3 h to obtain CeO2 derived from Ce-MOF.

[0052] Test case

[0053] The catalyst particles obtained in Examples 1-5 were applied to the direct synthesis of DMC from CO2 and CH3OH. The specific operation was as follows: 0.01g of catalyst particles 1#, 0.5g of catalyst 2#, 1.5g of catalyst 3#, 1.0g of catalyst 4#, 0.06g of catalyst 5#, and 0.5g of catalyst prepared in Comparative Example 1 were placed in a 100mL high-pressure stirred reactor. 35g of methanol was added, and the reactor was purged with 0.2MPa CO2, allowed to stand for 3min, and then the air was purged. The air was circulated and replaced three times. The pressure was increased to 4.5MPa, the rotation speed was maintained at 300r / min, the temperature was increased to 100-180℃ and the time was 0.5-5h. After the reaction was completed, the reactor was cooled and the pressure was released. Then, 0.1mL of n-propanol was added to the reactor as an internal standard, mixed evenly with a dropper, and the supernatant was collected by centrifugation for gas chromatography analysis.

[0054] The product was quantitatively analyzed using the internal standard method. A series of DMC standard solutions of varying concentrations were accurately prepared using n-propanol as the internal standard. These standard solutions were analyzed by gas chromatography to calculate the mass of DMC in the test solution. The DMC yield Y of the reaction was calculated using equation (1). DMC After three repeated tests, the error was 3%–5%. The conversion rate X of methanol was calculated using equations (2) and (3) respectively. M Selectivity of DMC DMC The calculation formula is as follows:

[0055] Y DMC =(2m) DMC ×M methanol ) / (M DMC ×m methanol )×100% (1)

[0056] X M =m DMC / (n M ×M DMC (2) × 100%

[0057] S DMC =m DMC / M DMC / (m DMC / M DMC +n 副产物 )×100% (3)

[0058] Where: m DMC The mass (g) of DMC produced; Y DMC DMC yield (%); M DMC This refers to the molar mass (g / mol) of DMC; m methanol The initial mass (g) of methanol; M methanol The molar mass of methanol (g / mol); mDMC The mass (g) of DMC produced; n M Indicates the number of carbon moles of methanol in the feed; n 副产物 This indicates the number of carbon moles in the byproduct.

[0059] The reaction conditions and results for each Ce-MOF catalyst particle in this experiment are shown in the table below:

[0060] Table 1. Catalytic performance test results of the examples and comparative examples.

[0061]

[0062] Thermodynamic studies show that the direct synthesis of DMC does not proceed spontaneously under standard conditions at 298 K; however, it can proceed spontaneously when the reaction temperature exceeds 333 K and the reaction pressure is in the range of 5-10 MPa. As shown in the table above, the Ce-MOF catalyst prepared by this invention exhibits milder reaction conditions and significantly higher reactant conversion and product yield in the direct synthesis of DMC. The highest methanol conversion reaches 17.6%, the DMC selectivity reaches 100%, and the DMC yield reaches 16.9%. Comparative Example 1 and Example 2 demonstrate that the CeO2 derived from Ce-MOF under optimal Taylor ratio calcination exhibits significantly improved activity.

[0063] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A catalyst for the synthesis of dimethyl carbonate by a direct method from CO2 and methanol, characterized in that it comprises a mixture of a basic catalyst and a Lewis acid catalyst. It is CeO2 derived from Ce-MOF, and the Taylor ratio of the catalyst is 0.15-0.35; The catalyst is prepared by calcining Ce-MOF; the Ce-MOF is prepared by reacting trimesic acid, cerium metal salt and soluble hydroxide in the presence of a solvent, wherein the concentration of soluble hydroxide is 0.5-2 mol / L; The soluble hydroxide is an alkali metal hydroxide or an alkaline earth metal hydroxide.

2. The catalyst for the synthesis of dimethyl carbonate by the direct process from CO2 and methanol according to claim 1, characterized by the fact that, The catalyst has a Taylor ratio of 0.15, 0.18, 0.25, 0.27 or 0.

35.

3. Process for the preparation of the catalyst according to claim 1 or 2, characterized in that, include: 1) Ce-MOF is prepared by reacting pyromellitic acid, a cerium metal salt, and a soluble hydroxide in the presence of an organic solvent, such that the concentration of the soluble hydroxide in the reaction system is 0.5-2 mol / L; 2) Ce-MOF was calcined to obtain Ce-MOF-derived CeO2; The soluble hydroxide is an alkali metal hydroxide or an alkaline earth metal hydroxide.

4. The method of claim 3, wherein, In step (1), the cerium metal salt is selected from at least one of cerium nitrate, cerium sulfate, cerium chloride, or cerium acetate.

5. The method according to claim 3 or 4, characterized in that, In step (1) above, the molar ratio of cerium ions to pyromellitic acid is 1:(1-5).

6. The method of claim 5, wherein, The soluble hydroxide is one or more of KOH and NaOH.

7. The method of claim 3, wherein, In step (1), the concentration of the soluble hydroxide in the reaction system is 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L.

8. The application of the catalyst according to claim 1 or 2 in the direct synthesis of dimethyl carbonate from CO2 and methanol.

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