A fin-shaped ceria@molecular sieve membrane reactor is constructed and used for carbon dioxide and methanol to dimethyl carbonate

Abstract

This invention belongs to the field of catalyst preparation technology, specifically relating to the construction of a finned cerium dioxide@molecular sieve membrane reactor and its application in the synthesis of dimethyl carbonate from carbon dioxide and methanol. The finned cerium dioxide has a rod-like structure, with cerium dioxide particles uniformly and densely covering the surface of the rod-like structure, forming a unique finned cerium dioxide. Then, the finned cerium dioxide is loaded onto a molecular sieve membrane to construct an integrated catalytic-separation finned cerium dioxide@molecular sieve membrane reactor. This catalyst is used in the synthesis of dimethyl carbonate from carbon dioxide and methanol. Under reaction temperatures of 80–200 °C and reaction pressures of 0.1–5.0 MPa, it achieves efficient and green synthesis of dimethyl carbonate with a conversion rate greater than 4% and a selectivity greater than 94%, exhibiting excellent stability and showing promising industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to the construction of a fin-shaped cerium dioxide@molecular sieve membrane reactor and its application in the production of dimethyl carbonate from carbon dioxide and methanol. Background Technology

[0002] Dimethyl carbonate (DMC) is an environmentally friendly chemical in the emerging field of "green chemistry." DMC molecules contain numerous organic functional groups, including methoxy, carbonyl, and methyl groups, making them a preferred building block for methylation and carbonylation reactions, replacing toxic precursors such as dimethyl sulfate (DMS) and phosgene. Furthermore, DMC is used as a potential fuel additive due to its high octane number and high oxygen content. Battery-grade DMC can be used as a lithium-ion carrier in lithium-ion battery electrolytes, improving battery stability and power density. Based on these excellent properties, the demand for DMC is continuously increasing, and its application prospects are broad.

[0003] The main methods for synthesizing dimethyl carbonate (DMC) include the phosgene method, transesterification, urea alcoholysis, liquid-phase methanol oxidative carbonylation, methanol and carbon dioxide synthesis, dimethyl oxalate decarbonylation, and nitrite carbonylation. The phosgene method uses toxic phosgene, and the generated HCl corrodes equipment, therefore this process is gradually being phased out. The urea alcoholysis method mostly uses homogeneous catalysts, which makes catalyst-product separation difficult. The liquid-phase methanol oxidative carbonylation method suffers from drawbacks such as chlorine loss, difficulty in separating the catalyst from DMC, and the risk of oxygen explosion. The dimethyl oxalate decarbonylation method suffers from catalyst deactivation.

[0004] The direct synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO2) and methanol (CH3OH) is one of the most promising synthetic routes, but this process is still in its early stages in the laboratory. Catalysts for the synthesis of DMC from methanol and CO2 mainly include alkoxy catalysts, supported catalysts, and metal oxide catalysts. Alkoxy catalysts are poisoned by the water produced in the reaction, accelerating catalyst deactivation. Supported catalysts are mainly Cu / Ni bimetallic catalysts. Supported metal catalysts have a large specific surface area and many exposed active sites, resulting in good methanol conversion, but their catalytic performance is greatly affected by the support, and the selectivity for DMC needs further improvement. Metal oxides are used for the synthesis of DMC from CO2 and methanol due to their suitable acid-base sites and oxygen vacancies, with CeO2 catalysts being the most widely used. However, metal oxide catalysts suffer from problems such as small specific surface area and low oxygen vacancy content, and the synthesis of DMC from CO2 and methanol is limited by thermodynamic equilibrium, as the equilibrium constant of this reaction is extremely small (usually around 10). -5 ~10 -3(On the order of magnitude), the single-pass conversion rate of carbon dioxide is less than 1%. The synthesis of dimethyl carbonate from methanol and carbon dioxide relies heavily on a highly efficient catalyst. However, because the synthesis of dimethyl carbonate is a severely thermodynamically constrained reaction, existing research systems often require the addition of chemical dehydrating agents to remove the byproduct water, thereby shifting the equilibrium towards the positive side. Common dehydrating agents include 2-cyanopyridine and methyl trichloroacetate. While chemical dehydrating agents can improve the conversion rate, they often suffer from high costs and difficulty in regenerating.

[0005] Molecular sieve membranes, with their excellent molecular sieving performance and high stability, have become a research hotspot in the field of separation. Currently, commercially available molecular sieve membranes are mainly used for the efficient separation of aqueous azeotropes, such as the successful separation of ethanol / water, isopropanol / water, and ethyl acetate / water systems using LTA-type molecular sieve membranes. The direct synthesis of DMC from CO2 and methanol is severely limited by thermodynamic equilibrium. If a molecular sieve catalytic membrane reactor integrating catalysis and separation functions can be constructed, and the in-situ, continuous removal of product water can be achieved using a molecular sieve membrane, it is expected that the Le Chatelier principle will be applied to shift the reaction equilibrium to the right, thereby overcoming the equilibrium limitation of this reaction and significantly improving the reaction efficiency.

[0006] Therefore, developing efficient catalysts for the synthesis of dimethyl carbonate and loading them onto molecular sieve membranes to construct integrated catalytic-separation finned cerium dioxide@molecular sieve membrane reactors is of great practical significance for promoting the development of process routes for the direct synthesis of dimethyl carbonate from carbon dioxide and methanol. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a method for preparing a finned cerium dioxide@molecular sieve membrane reactor with high stability, high methanol conversion rate, and high DMC selectivity, and in particular, to provide a high-performance catalyst for the high-pressure gas-solid phase continuous synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: The construction of a finned cerium dioxide@molecular sieve membrane reactor and its application in the synthesis of dimethyl carbonate from carbon dioxide and methanol are disclosed. The reactor is characterized by first preparing finned cerium dioxide with a high specific surface area and abundant oxygen vacancy concentration, then loading the finned cerium dioxide onto a molecular sieve membrane to construct an integrated catalytic-separation finned cerium dioxide@molecular sieve membrane reactor. This reactor exhibits excellent catalytic performance in the synthesis of dimethyl carbonate from carbon dioxide and methanol. The process uses carbon dioxide and methanol as raw materials and can continuously and efficiently synthesize dimethyl carbonate. The reaction temperature is 80–200 °C, and the reaction pressure is 0.1–5.0 MPa. The finned cerium dioxide@molecular sieve membrane reactor mainly consists of finned cerium dioxide and a molecular sieve membrane, wherein the specific surface area of ​​the finned cerium dioxide is 20–400 m². 2 / g, with a pore size of 1~100 nm, and the loading of finned cerium dioxide on the molecular sieve membrane is 1%~10%; the preparation method of the finned cerium dioxide@molecular sieve membrane reactor includes the following steps: 1) Synthesis of finned cerium dioxide: The cerium precursor is dissolved in solvent A and mixed evenly to obtain a cerium precursor solution. Then, the first key ligand is dissolved in solvent B and mixed evenly to obtain a first key ligand solution. The cerium precursor solution and the first key ligand solution are then mixed evenly to obtain a mixed solution. The second key ligand is then added to the mixed solution and mixed evenly. The mixture is then transferred to a polytetrafluoroethylene-lined crystallization vessel and allowed to stand in an oven at 100-180 °C for 1-24 hours. After filtration and washing until neutral, the mixture is dried in an oven at 25-150 °C for 1-48 hours. Finally, it is calcined in a muffle furnace at 200-800 °C for 0.5-24 hours to obtain a finned cerium dioxide catalyst. 2) Preparation of finned cerium dioxide@molecular sieve membrane: The finned cerium dioxide catalyst from step 1) is dispersed in solvent C to form a finned cerium dioxide suspension. The two ends of the molecular sieve membrane are plugged, and then the molecular sieve membrane is vertically immersed in the finned cerium dioxide suspension using a pull-up method. After holding for a period of time, it is pulled out at a uniform rate. After drying and curing, the molecular sieve membrane is immersed in the finned cerium dioxide suspension again. The immersion, drying, and curing process is repeated until the loading of finned cerium dioxide on the molecular sieve membrane reaches 1%~10%, and finally the finned cerium dioxide@molecular sieve membrane reactor is obtained.

[0009] As a preferred embodiment, the construction of the finned cerium dioxide@molecular sieve membrane reactor and its application in the production of dimethyl carbonate from carbon dioxide and methanol is characterized in that the cerium precursor used in step 1) can be one or a combination of several of cerium nitrate, cerium sulfate, cerium carbonate, cerium tetrafluoride, cerium phosphate, cerium chloride, cerium perchlorate and cerium ammonium nitrate.

[0010] As a preferred embodiment, the construction of the finned cerium dioxide@molecular sieve membrane reactor and its application in the production of dimethyl carbonate from carbon dioxide and methanol is characterized in that the first key ligand used in step 1) is one or a combination of several of 2-aminoterephthalic acid, benzoic acid, succinic acid, alanine, ammonium hydroxide, ammonium nitrate and ammonium chloride, and the second key ligand used in step 1) is one or a combination of several of benzoic acid, phenylacetic acid, acetic acid, ethyl acetate and formic acid.

[0011] As a preferred embodiment, the construction of the finned cerium dioxide@molecular sieve membrane reactor and its application in the production of dimethyl carbonate from carbon dioxide and methanol is characterized in that, in step 1), solvent A is one or a combination of water, methanol, ethanol, ethylenediamine, isopropanol and ethylene glycol, and solvent B is one or a combination of water, methanol, ethanol, isopropanol, acetone, benzyl alcohol, ethylene glycol and N,N-dimethylformamide.

[0012] As a preferred embodiment, the construction of the finned cerium dioxide@molecular sieve membrane reactor and its application in the production of dimethyl carbonate from carbon dioxide and methanol is characterized in that the solvent C used in step 2) can be one or a combination of several of water, methanol, ethanol, isopropanol, acetone, and toluene.

[0013] As a preferred embodiment, the construction of the finned cerium dioxide@molecular sieve membrane reactor and its application in the production of dimethyl carbonate from carbon dioxide and methanol is characterized in that the molecular sieve membrane used in step 2) is one of LTA, FAU, and MFI membranes.

[0014] As a preferred embodiment, the construction of the finned cerium dioxide@molecular sieve membrane reactor and its application in the production of dimethyl carbonate from carbon dioxide and methanol is characterized in that the drying temperature in step 2) is 20~150 ℃ and the curing temperature is 120~600 ℃.

[0015] Compared with the prior art, the construction of the finned cerium dioxide@molecular sieve membrane reactor of the present invention and its application in the production of dimethyl carbonate from carbon dioxide and methanol have the following significant features: (1) The finned cerium dioxide@molecular sieve membrane reactor solves the problems of carbon dioxide being difficult to activate and thermodynamic equilibrium limitation in the process of synthesizing dimethyl carbonate from carbon dioxide and methanol. Finned cerium dioxide can efficiently catalyze the synthesis of dimethyl carbonate from carbon dioxide and methanol. The molecular membrane can continuously remove the by-product water, promote the forward movement of the reaction, and significantly improve the conversion rate. Compared with the problems of toxic raw materials and environmental pollution in the traditional synthesis of dimethyl carbonate, this process has the advantages of being green and environmentally friendly and having high atom economy, and has potential application prospects.

[0016] (2) During the preparation process, the surface area of ​​the finned cerium dioxide catalyst is increased by the dense and uniform distribution of finned particles, thereby increasing the concentration of acid and base sites and oxygen vacancies in the catalyst, so that more carbon dioxide can be effectively activated. The acidic and base sites can activate both methanol and carbon dioxide. In addition, the catalyst preparation process is simple and the structure is stable, and the active components are not easily lost. Therefore, the finned cerium dioxide catalyst exhibits high activity and high stability.

[0017] (3) Molecular sieve membranes have excellent molecular sieving performance and high stability. Molecular sieve membranes can achieve in-situ and continuous removal of by-product water. Based on the Le Chatelier principle, it is expected to drive the reaction equilibrium to the right, thereby breaking through the thermodynamic equilibrium limitation of the reaction and significantly improving the reaction efficiency. Attached Figure Description

[0018] Figure 1 The image shows a SEM image of the catalyst prepared in Example 1. Figure 2 The XRD pattern of the catalyst prepared in Example 1 is shown below. Figure 3 The image shows a TEM image of the catalyst prepared in Example 1. Figure 4 Image of the CeO2@LTA membrane on which the catalyst prepared in Example 1 is supported; Figure 5 The image shows a SEM image of the catalyst prepared in Example 2. Figure 6 The XRD pattern of the catalyst prepared in Example 2 is shown below. Figure 7 The image shows a TEM image of the catalyst prepared in Example 2. Figure 8 The image shows the CeO2@FAU membrane on which the catalyst prepared in Example 2 is supported; Figure 9 The image shows a SEM image of the catalyst prepared in Example 3. Figure 10 The XRD pattern of the catalyst prepared in Example 3 is shown below. Figure 11 The image shows a TEM image of the catalyst prepared in Example 3. Figure 12 Here is a SEM image of the catalyst prepared in Example 4; Figure 13 The XRD pattern of the catalyst prepared in Example 4 is shown below. Figure 14 The image shows a TEM image of the catalyst prepared in Example 4. Figure 15 The image shows a SEM image of the catalyst prepared in Example 5. Figure 16 The XRD pattern of the catalyst prepared in Example 5 is shown below. Figure 17 The image shows a TEM image of the catalyst prepared in Example 5. Figure 18 The image shows a SEM image of the catalyst prepared in Example 6. Figure 19 The XRD pattern of the catalyst prepared in Example 6 is shown below. Figure 20 The image shows a TEM image of the catalyst prepared in Example 6. Figure 21 The stability test diagram is shown in Example 1. Figure 22 This is a schematic diagram of the structure of fin-shaped cerium dioxide. Detailed Implementation

[0019] To facilitate understanding of the present invention, the following detailed description will be provided through embodiments. These embodiments are merely illustrative and not intended to limit the scope of the invention. Since the present invention can also be described and explained through other solutions that do not depart from its technical features, modifications within the scope of the present invention or its equivalents should be considered within the protection scope of the present invention.

[0020] The present invention will be further illustrated below with reference to embodiments, comparative examples, and application examples.

[0021] Example 1 1) Synthesis of finned cerium dioxide: Cerium sulfate was dissolved in deionized water and mixed evenly to obtain a cerium precursor solution. Then, benzoic acid ligand was dissolved in N,N-dimethylformamide and mixed evenly to obtain a first key ligand solution. The cerium precursor solution and the first key ligand solution were then mixed evenly to obtain a mixed solution. Acetic acid ligand was then added to the mixed solution and mixed evenly. The mixture was then transferred to a stainless steel crystallization kettle lined with polytetrafluoroethylene and allowed to stand in an oven at 180 °C for 6 hours. After filtration and washing until neutral, the mixture was dried in an oven at 60 °C for 4 hours. Finally, it was calcined in a muffle furnace at 500 °C for 4 hours to obtain a finned cerium dioxide catalyst. 2) Preparation of finned cerium dioxide@molecular sieve membrane: The finned cerium dioxide catalyst from step 1) was dispersed in an aqueous solvent to form a finned cerium dioxide suspension. The two ends of the LTA molecular sieve membrane were plugged, and then the molecular sieve membrane was vertically immersed in the finned cerium dioxide suspension using a pull-up method. After holding for 0.1 minutes, it was pulled out at a uniform rate, dried at 20 ℃, and cured at 120 ℃. The molecular sieve membrane was then immersed in the finned cerium dioxide suspension again. The immersion, drying, and curing were repeated until the loading of finned cerium dioxide on the molecular sieve membrane reached 1%, and finally the finned cerium dioxide@molecular sieve membrane reactor was obtained.

[0022] Figure 1 This is a SEM image of the catalyst prepared in Example 1. The catalyst exhibits a rod-like structure with densely distributed fin-like particles. The rod-like structure has a size of 200 nm to 2000 nm, and the fin-like particles have a size of 20 nm to 50 nm. Figure 2 The image shows the XRD pattern of the catalyst prepared in Example 1. It can be seen that the catalyst has high crystallinity and exhibits the characteristic peak of CeO2. Figure 3 This is a TEM image of the catalyst prepared in Example 1, showing that the catalyst fin structure grows densely and uniformly on the rod structure. Figure 4 The image shows the finned CeO2@LTA membrane on which the catalyst prepared in Example 1 is supported. It can be seen that the finned CeO2 is uniformly coated on the molecular sieve membrane.

[0023] Example 2 1) Synthesis of finned cerium dioxide: Cerium carbonate was dissolved in deionized water and mixed evenly to obtain a cerium precursor solution. Then, alanine ligand was dissolved in methanol and mixed evenly to obtain a first key ligand solution. The cerium precursor solution and the first key ligand solution were then mixed and stirred evenly to obtain a mixed solution. Formic acid ligand was added to the mixed solution and mixed evenly. The mixture was then transferred to a stainless steel crystallization kettle lined with polytetrafluoroethylene and allowed to stand in an oven at 150 °C for 10 hours. After filtration and washing until neutral, the mixture was dried in an oven at 70 °C for 6 hours. Finally, it was calcined in a muffle furnace at 800 °C for 3 hours to obtain a finned cerium dioxide catalyst.

[0024] 2) Preparation of finned cerium dioxide@molecular sieve membrane: The finned cerium dioxide catalyst from step 1) was dispersed in an ethanol solvent to form a finned cerium dioxide suspension. The two ends of the FAU molecular sieve membrane were plugged, and then the molecular sieve membrane was vertically immersed in the finned cerium dioxide suspension using a pull-up method. After holding for 10 minutes, it was pulled out at a uniform rate, dried at 25 ℃, and cured at 150 ℃. The molecular sieve membrane was then immersed in the finned cerium dioxide suspension again. The immersion, drying, and curing were repeated until the loading of finned cerium dioxide on the molecular sieve membrane reached 2%, and finally the finned cerium dioxide@molecular sieve membrane reactor was obtained. Figure 5 This is a SEM image of the catalyst prepared in Example 2. It can be seen that the catalyst morphology exhibits a rod-like structure with densely distributed fin-like particles on the rod-like structure. Figure 6 The image shows the XRD pattern of the catalyst prepared in Example 2. It can be seen that the catalyst has high crystallinity and exhibits the characteristic peak of CeO2. Figure 7 This is a TEM image of the catalyst prepared in Example 2, showing that the catalyst fin structure grows densely and uniformly on the rod structure. Figure 8 The image shows the CeO2@FAU membrane on which the catalyst prepared in Example 2 is supported. It can be seen that the fin-shaped CeO2 is uniformly coated on the molecular sieve membrane.

[0025] Example 3 1) Synthesis of finned cerium dioxide: Cerium nitrate was dissolved in ethylene glycol and mixed evenly to obtain a cerium precursor solution. Then, succinic acid ligand was dissolved in ethanol and mixed evenly to obtain a first key ligand solution. The cerium precursor solution and the first key ligand solution were then mixed and stirred evenly to obtain a mixed solution. Phenylacetic acid was added to the mixed solution and mixed evenly. The mixture was then transferred to a stainless steel crystallization kettle lined with polytetrafluoroethylene and allowed to stand in an oven at 180 °C for 6 hours. After filtration and washing until neutral, the mixture was dried in an oven at 100 °C for 8 hours. Finally, it was calcined in a muffle furnace at 600 °C for 4 hours to obtain a finned cerium dioxide catalyst.

[0026] 2) Preparation of finned cerium dioxide@molecular sieve membrane: The finned cerium dioxide catalyst from step 1) was dispersed in methanol solvent to form a finned cerium dioxide suspension. The two ends of the MFI molecular sieve membrane were plugged, and then the molecular sieve membrane was vertically immersed in the finned cerium dioxide suspension using the dip-lift method. After holding for 3 minutes, it was pulled out at a uniform rate, dried at 30 °C, and cured at 140 °C. The molecular sieve membrane was then immersed in the finned cerium dioxide suspension again. The immersion, drying, and curing were repeated until the loading of finned cerium dioxide on the molecular sieve membrane reached 4%, and finally the finned cerium dioxide@molecular sieve membrane reactor was obtained.

[0027] Figure 9 This is a SEM image of the catalyst prepared in Example 3. It can be seen that the catalyst morphology exhibits a rod-like structure with densely distributed fin-like particles on the rod-like structure. Figure 10 The image shows the XRD pattern of the catalyst prepared in Example 3. It can be seen that the catalyst has high crystallinity and exhibits the characteristic peak of CeO2. Figure 11 This is a TEM image of the catalyst prepared in Example 3, showing that the catalyst fin structure grows densely and uniformly on the rod structure.

[0028] Example 4 1) Synthesis of finned cerium dioxide: Cerium ammonium nitrate was dissolved in isopropanol and mixed evenly to obtain a cerium precursor solution. Then, 2-aminoterephthalic acid ligand was dissolved in isopropanol and mixed evenly to obtain a first key ligand solution. The cerium precursor solution and the first key ligand solution were then mixed and stirred evenly to obtain a mixed solution. Benzoic acid ligand was added to the mixed solution and mixed evenly. The mixture was then transferred to a stainless steel crystallization kettle lined with polytetrafluoroethylene and allowed to stand in an oven at 160 °C for 8 hours. After filtration and washing until neutral, the mixture was dried in an oven at 110 °C for 10 hours. Finally, it was calcined in a muffle furnace at 550 °C for 5 hours to obtain a finned cerium dioxide catalyst.

[0029] 2) Preparation of finned cerium dioxide@molecular sieve membrane: The finned cerium dioxide catalyst from step 1) was dispersed in isopropanol solvent to form a finned cerium dioxide suspension. The two ends of the FAU molecular sieve membrane were plugged, and then the molecular sieve membrane was vertically immersed in the finned cerium dioxide suspension using the dip-lift method. After holding for 8 minutes, it was pulled out at a uniform rate, dried at 40 ℃ and cured at 120 ℃. The molecular sieve membrane was then immersed in the finned cerium dioxide suspension again. The immersion, drying and curing were repeated until the loading of finned cerium dioxide on the molecular sieve membrane reached 6%, and finally the finned cerium dioxide@molecular sieve membrane reactor was obtained.

[0030] Figure 12 This is a SEM image of the catalyst prepared in Example 4. The catalyst exhibits a rod-like structure with densely distributed fin-like particles. The rod-like structure has a size of 200 nm to 2000 nm, and the fin-like particles have a size of 20 nm to 50 nm. Figure 13 The image shows the XRD pattern of the catalyst prepared in Example 4. It can be seen that the catalyst has high crystallinity and exhibits the characteristic peak of CeO2. Figure 14 This is a TEM image of the catalyst prepared in Example 4, showing that the catalyst fin structure grows densely and uniformly on the rod structure.

[0031] Example 5 1) Synthesis of finned cerium dioxide: Cerium phosphate was dissolved in ethylenediamine solvent and mixed evenly to obtain a cerium precursor solution. Then, alanine ligand was dissolved in acetone and mixed evenly to obtain a first key ligand solution. The cerium precursor solution and the first key ligand solution were then mixed and stirred evenly to obtain a mixed solution. Ethyl acetate ligand was added to the mixed solution and mixed evenly. The mixture was then transferred to a stainless steel crystallization kettle lined with polytetrafluoroethylene and allowed to stand in an oven at 140 °C for 10 hours. After filtration and washing until neutral, the mixture was dried in an oven at 120 °C for 10 hours. Finally, it was calcined in a muffle furnace at 600 °C for 4 hours to obtain a finned cerium dioxide catalyst.

[0032] 2) Preparation of finned cerium dioxide@molecular sieve membrane: The finned cerium dioxide catalyst from step 1) was dispersed in methanol solvent to form a finned cerium dioxide suspension. The two ends of the LTA molecular sieve membrane were plugged, and then the molecular sieve membrane was vertically immersed in the finned cerium dioxide suspension using the dip-lift method. After holding for 0.5 minutes, it was pulled out at a uniform rate, dried at 50 ℃, and cured at 130 ℃. The molecular sieve membrane was then immersed in the finned cerium dioxide suspension again. The immersion, drying, and curing were repeated until the loading of finned cerium dioxide on the molecular sieve membrane reached 8%, and finally the finned cerium dioxide@molecular sieve membrane reactor was obtained.

[0033] Figure 15 This is a SEM image of the catalyst prepared in Example 5. The catalyst exhibits a rod-like structure with densely distributed fin-like particles. The rod-like structure has a size of 200 nm to 2000 nm, and the fin-like particles have a size of 20 nm to 50 nm. Figure 16 The image shows the XRD pattern of the catalyst prepared in Example 5. It can be seen that the catalyst has high crystallinity and exhibits the characteristic peak of CeO2. Figure 17 This is a TEM image of the catalyst prepared in Example 5, showing that the catalyst fin structure grows densely and uniformly on the rod structure.

[0034] Example 6 1) Synthesis of finned cerium dioxide: Cerium perchlorate was dissolved in ethanol and mixed evenly to obtain a cerium precursor solution. Then, ammonium chloride ligand was dissolved in benzyl alcohol and mixed evenly to obtain a first key ligand solution. The cerium precursor solution and the first key ligand solution were then mixed and stirred evenly to obtain a mixed solution. Acetic acid ligand was added to the mixed solution and mixed evenly. The mixture was then transferred to a stainless steel crystallization kettle lined with polytetrafluoroethylene and allowed to stand in an oven at 100 °C for 3 hours. After filtration and washing until neutral, the mixture was dried in an oven at 150 °C for 2 hours. Finally, it was calcined in a muffle furnace at 600 °C for 8 hours to obtain a finned cerium dioxide catalyst.

[0035] 2) Preparation of finned cerium dioxide@molecular sieve membrane: The finned cerium dioxide catalyst from step 1) was dispersed in isopropanol solvent to form a finned cerium dioxide suspension. The two ends of the MFI molecular sieve membrane were plugged, and then the molecular sieve membrane was vertically immersed in the finned cerium dioxide suspension using the dip-lift method. After holding for 2 minutes, it was pulled out at a uniform rate, dried at 40 ℃ and cured at 110 ℃. The molecular sieve membrane was then immersed in the finned cerium dioxide suspension again. The immersion, drying and curing were repeated until the loading of finned cerium dioxide on the molecular sieve membrane reached 3%, and finally the finned cerium dioxide@molecular sieve membrane reactor was obtained.

[0036] Figure 18This is a SEM image of the catalyst prepared in Example 6. The catalyst exhibits a rod-like structure with densely distributed fin-like particles. The rod-like structure has a size of 200 nm to 2000 nm, and the fin-like particles have a size of 20 nm to 50 nm. Figure 19 The image shows the XRD pattern of the catalyst prepared in Example 6. It can be seen that the catalyst has high crystallinity and exhibits the characteristic peak of CeO2. Figure 20 This is a TEM image of the catalyst prepared in Example 6, showing that the catalyst fin structure grows densely and uniformly on the rod structure.

[0037] Comparative Example 1 The finned cerium dioxide prepared in step 1) of Example 1 was used as the catalyst of Comparative Example 1.

[0038] Comparative Example 2 Commercially available cerium dioxide catalyst was used as the catalyst in Comparative Example 2.

[0039] Application examples The finned cerium dioxide@molecular sieve membrane reactors prepared in Examples 1-6 were used to evaluate the synthesis of dimethyl carbonate from carbon dioxide and methanol using a high-pressure continuous flow membrane reactor. The catalysts prepared in Comparative Examples 1 and 2 were used to evaluate the synthesis of dimethyl carbonate from carbon dioxide and methanol using a high-pressure continuous flow fixed-bed reactor (inner diameter = 10 mm). The reaction feed ratio was n. CO2 :n CH3OH =1:2 (molar ratio), airspeed GHSV = 5353 gcat -1 ·h -1 The reaction temperature was 150℃, and the reaction pressure was 3.0 MPa. Circulating water was used to condense the gas, and the product was obtained by offline chromatography. The product included dimethyl carbonate (DMC) as the main product, and dimethyl ether (DME) and dimethoxymethane (DMM) as byproducts. The conversion rate X of methanol (ME) was calculated accordingly. ME Dimethyl carbonate based on methanol selectivity S DMC / ME .

[0040] As shown in Table 1, this invention continuously synthesizes dimethyl carbonate using carbon dioxide and methanol as raw materials. A novel finned cerium dioxide@molecular sieve membrane reactor was designed. Examples 1-6 used membrane reactors, while Comparative Examples 1 and 2 used fixed-bed reactions. The methanol conversion and dimethyl carbonate selectivity of Examples 1-6 were significantly better than those of Comparative Examples 1 and 2. Due to severe thermodynamic equilibrium limitations, the conversion rates of Comparative Examples 1 and 2 were low. However, the use of membrane reactors can rapidly remove the byproduct water from the reaction system, thereby shifting the equilibrium to the right and significantly improving the conversion rates of Examples 1-6.

[0041] Table 1 Catalytic performance of catalysts in Examples 1-6 and Comparative Examples 1 and 2 catalyst <![CDATA[X ME / %]]> <![CDATA[S DMC / ME / %]]> Example 1 5.0 96.0 Example 2 5.3 95.1 Example 3 6.2 95.4 Example 4 4.2 94.5 Example 5 7.3 94.2 Example 6 5.2 94.1 Comparative Example 1 0.2 93.0 Comparative Example 2 0.3 92.9 Figure 21 The image shows the long-term performance test results of the finned cerium dioxide@molecular sieve membrane reactor prepared in Example 1. The catalyst can operate stably for more than 200 hours, and the methanol conversion rate and dimethyl carbonate selectivity remain essentially unchanged. This demonstrates that the catalyst used in the continuous synthesis of dimethyl carbonate from carbon dioxide and methanol according to this invention exhibits high stability.

[0042] The results of the above examples and comparative examples show that the finned cerium dioxide@molecular sieve membrane reactor prepared in this invention is a highly stable and selective catalyst, especially suitable for the continuous gas-solid phase synthesis of dimethyl carbonate from carbon dioxide and methanol.

Claims

1. The construction of a finned cerium dioxide@molecular sieve membrane reactor and its application in the production of dimethyl carbonate from carbon dioxide and methanol, characterized in that, First, finned cerium dioxide with high specific surface area and abundant oxygen vacancy concentration was prepared. Then, the finned cerium dioxide was loaded onto a molecular sieve membrane to construct a catalytic-separation integrated cerium dioxide@molecular sieve membrane reactor. This reactor exhibited excellent catalytic performance in the synthesis of dimethyl carbonate from carbon dioxide and methanol. The process uses carbon dioxide and methanol as raw materials and can continuously and efficiently synthesize dimethyl carbonate. The reaction temperature is 80–200 °C, and the reaction pressure is 0.1–5.0 MPa. The finned cerium dioxide@molecular sieve membrane reactor mainly consists of finned cerium dioxide and a molecular sieve membrane, wherein the specific surface area of ​​the finned cerium dioxide is 20–400 m². 2 / g, with a pore size of 1~100 nm, and the loading of finned cerium dioxide on the molecular sieve membrane is 1%~10%; the preparation method of the finned cerium dioxide@molecular sieve membrane reactor includes the following steps: 1) Synthesis of finned cerium dioxide: The cerium precursor is dissolved in solvent A and mixed evenly to obtain a cerium precursor solution. Then, the first key ligand is dissolved in solvent B and mixed evenly to obtain a first key ligand solution. The cerium precursor solution and the first key ligand solution are then mixed evenly to obtain a mixed solution. The second key ligand is then added to the mixed solution and mixed evenly. The mixture is then transferred to a polytetrafluoroethylene-lined crystallization vessel and allowed to stand in an oven at 100-180 °C for 1-24 hours. After filtration and washing until neutral, the mixture is dried in an oven at 25-150 °C for 1-48 hours. Finally, it is calcined in a muffle furnace at 200-800 °C for 0.5-24 hours to obtain a finned cerium dioxide catalyst. 2) Preparation of finned cerium dioxide@molecular sieve membrane: The finned cerium dioxide catalyst from step 1) is dispersed in solvent C to form a finned cerium dioxide suspension. The two ends of the molecular sieve membrane are plugged, and then the molecular sieve membrane is vertically immersed in the finned cerium dioxide suspension using a pull-up method. After holding for 0.1 to 10 minutes, it is pulled out at a uniform rate. After drying and curing, the molecular sieve membrane is immersed in the finned cerium dioxide suspension again. The immersion, drying, and curing process is repeated until the loading of finned cerium dioxide on the molecular sieve membrane reaches 1% to 10%, and finally the finned cerium dioxide@molecular sieve membrane reactor is obtained.

2. The construction of a finned cerium dioxide@molecular sieve membrane reactor according to claim 1 and its application in the production of dimethyl carbonate from carbon dioxide and methanol, characterized in that, The cerium precursor used in step 1) can be one or a combination of several of cerium nitrate, cerium sulfate, cerium carbonate, cerium tetrafluoride, cerium phosphate, cerium chloride, cerium perchlorate, and cerium ammonium nitrate.

3. The construction of a finned cerium dioxide@molecular sieve membrane reactor according to claim 1 and its application in the production of dimethyl carbonate from carbon dioxide and methanol, characterized in that, The first key ligand used in step 1) is one or a combination of several of 2-aminoterephthalic acid, benzoic acid, succinic acid, alanine, ammonium hydroxide, ammonium nitrate and ammonium chloride, and the second key ligand used in step 1) is one or a combination of several of benzoic acid, phenylacetic acid, acetic acid, ethyl acetate and formic acid.

4. The construction of a finned cerium dioxide@molecular sieve membrane reactor according to claim 1 and its application in the production of dimethyl carbonate from carbon dioxide and methanol, characterized in that, The solvent A used in step 1) is one or a combination of water, methanol, ethanol, ethylenediamine, isopropanol and ethylene glycol. The solvent B used in step 1) can be one or a combination of water, methanol, ethanol, isopropanol, acetone, benzyl alcohol, ethylene glycol and N,N-dimethylformamide.

5. The construction of a finned cerium dioxide@molecular sieve membrane reactor according to claim 1 and its application in the production of dimethyl carbonate from carbon dioxide and methanol, characterized in that, The solvent C used in step 2) can be one or a combination of several of the following: water, methanol, ethanol, isopropanol, acetone, and toluene.

6. The construction of a finned cerium dioxide@molecular sieve membrane reactor according to claim 1 and its application in the production of dimethyl carbonate from carbon dioxide and methanol, characterized in that, The molecular sieve membrane used in step 2) is one of LTA, FAU, or MFI membranes.

7. The construction of a finned cerium dioxide@molecular sieve membrane reactor according to claim 1 and its application in the production of dimethyl carbonate from carbon dioxide and methanol, characterized in that, In step 2), the drying temperature is 20~150 ℃ and the curing temperature is 120~600 ℃.

8. The construction of a finned cerium dioxide@molecular sieve membrane reactor according to claim 1 and its application in the production of dimethyl carbonate from carbon dioxide and methanol, characterized in that, The finned cerium dioxide catalyst is used for the continuous gas-solid phase synthesis of dimethyl carbonate from carbon dioxide and methanol.

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