Macroporous alumina and preparation method thereof

Abstract

The present invention relates to the technical field of inorganic materials, and in particular to a macroporous alumina and a preparation method thereof. The raw materials for synthesizing the macroporous alumina include the following components: potassium carbonate, ethyl acetate, low-carbon alcohol, urea / carboxyl surfactant conjugate, aluminum salt, triethylamine, triethoxysilane, sucrose and water; the urea / carboxyl surfactant conjugate is synthesized by coupling a carboxyl surfactant with urea through EDC / NHS. The present invention prepares macroporous alumina with high specific surface area and excellent pore distribution through the joint action of key components of potassium carbonate, ethyl acetate and urea / carboxyl surfactant conjugate, and the preparation method is simple in process, suitable for large-scale production, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic materials, and in particular to macroporous alumina and a preparation method thereof. Background Art

[0002] Macroporous alumina is an aluminum oxide material with a large pore structure, with pore sizes typically ranging from 50 nanometers to several micrometers. By controlling the pore size and porosity, this material can significantly increase the specific surface area and permeability of the material while maintaining excellent mechanical strength and chemical stability.

[0003] Due to its high specific surface area and good pore distribution, macroporous alumina is widely used in catalysis, adsorption, filtration, sensing and other fields. As a catalyst carrier, it can improve the mass transfer efficiency and catalytic activity of reactants in the fields of petrochemicals, environmental protection, etc. In terms of adsorption materials, it can effectively adsorb pollutants such as organic molecules and heavy metals, and is used in scenarios such as water treatment and air purification. In addition, due to its high temperature resistance and corrosion resistance, macroporous alumina is also an ideal choice for high-temperature filter materials and gas sensors, especially because it can maintain the stability of its structure and performance under extreme conditions.

[0004] The pore structure of macroporous alumina can be precisely controlled through techniques such as template method, sol-gel method, and bio-template method to form a complex porous network. However, the existing technology still has some shortcomings in its preparation process. For example, it is difficult to precisely control the pore structure, especially when it comes to ensuring a multi-level pore structure while maintaining the structural properties of the material. In addition, the preparation process is complex and costly, which limits the economic feasibility of its large-scale application. In addition, high-temperature calcination can easily lead to the collapse or deformation of the pore structure, reduce the specific surface area, and ultimately weaken its catalytic or adsorption effect. Therefore, the development of more efficient synthesis technology remains a major challenge facing current technology. Summary of the Invention

[0005] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a macroporous alumina and a preparation method thereof.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: The present invention proposes a macroporous alumina, and the raw materials for synthesizing the macroporous alumina include the following components: potassium carbonate, ethyl acetate, low-carbon alcohol, urea / carboxyl surfactant conjugate, aluminum salt, triethylamine, triethoxysilane, sucrose and water.

[0007] Preferably, the method for preparing the urea / carboxyl surfactant conjugate comprises the following steps:

[0008] A1. Dissolve 0.1 mol of urea in 100 mL of anhydrous ethanol and stir until completely dissolved. Add 0.12 mol of acetic anhydride and 0.6 mL of anhydrous pyridine. Stir and react at room temperature for 2-4 hours. After the reaction is complete, pour the reaction mixture into 0°C diethyl ether solution, centrifuge, collect the precipitate, and wash with diethyl ether to obtain acetylated urea.

[0009] A2. Add 0.1 mol of a carboxyl surfactant to 100 mL of ethanol and stir until completely dissolved. Then add 0.11 mol of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and stir at 500 rpm for 3 h. After the reaction, add 0.11 mol of N-hydroxysuccinimide (NHS) and stir at 500 rpm for 3 h to obtain an activated solution.

[0010] A3. Dissolve the acetylated urea prepared in step A1 in 100 mL of deionized water, heat in a water bath at 50°C with stirring for 4 h, cool to room temperature, and then slowly add the solution to the activation solution prepared in step A2. Stir the mixture at 400-600 rpm at 30-35°C for 6-12 h. After completion of the reaction, the product is obtained. Extract the product with dichloromethane, and then place the product in a rotary evaporator to evaporate the dichloromethane. After complete evaporation, a urea / carboxyl surfactant conjugate is obtained.

[0011] Preferably, the carboxyl surfactant in step A2 is any one of stearic acid, oleic acid, palmitic acid, capric acid and sodium laurate.

[0012] Preferably, the low-carbon alcohol is any one of methanol, ethanol, n-propanol and isopropanol.

[0013] Preferably, the aluminum salt is any one of aluminum chloride, aluminum nitrate and aluminum sulfate.

[0014] The present invention also provides a method for preparing macroporous alumina, which specifically comprises the following steps:

[0015] S1. Weigh 100-200 mg of urea / carboxyl surfactant conjugate and add it to 10 mL of water. Stir until completely dissolved to obtain a surfactant solution. Weigh aluminum salt and add it to water. Dissolve evenly to prepare a 1-2 mol / L aluminum salt solution.

[0016] S2. Add 1-2 g potassium carbonate, 5-10 mL low-carbon alcohol, 10-20 mL ethyl acetate, 0.5-2 g sucrose, and 90-100 mL water to a 150 mL container, stir and disperse evenly, and continue to add the surfactant solution prepared in step S1, stir and disperse evenly to obtain a mixed solution;

[0017] S3. Add 40 mL of aluminum salt solution dropwise to the mixed solution prepared in step S2, stir at 400-600 rpm for 3-6 hours to form a uniform emulsion, then add 4-6 mL of triethylamine and 2-5 mL of triethoxysilane, continue stirring for 30-60 minutes, and after the reaction is completed, let it stand for 6-12 hours to obtain a sol solution;

[0018] S4, placing the sol solution prepared in step S3 in an oven at 60°C for 4-6 hours, then heating to 80°C for drying until the sol solution is completely free of moisture to obtain a solid precursor;

[0019] S5. Place the solid precursor obtained in step S4 in a muffle furnace, and heat it to 500-700°C at a heating rate of 5-10°C / min under the protection of a nitrogen flow at a flow rate of 1 L / min, maintain it for 3-5 hours, and naturally cool it to room temperature to obtain a product. Wash the product three times with water and ethanol alternately, and obtain macroporous alumina after drying.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention significantly improves the pore structure and performance of macroporous alumina by innovatively using potassium carbonate, urea / carboxyl surfactant conjugate, triethoxysilane and ethyl acetate as key components for synthesizing macroporous alumina. Specifically, ethyl acetate plays a key role as a mixed solvent. Its solvent properties disrupt the uniformity of the solution during the mixing process, forming a unique structural grid. This grid structure not only helps to form preliminary pores, but also works together with the surfactant to ensure the formation of larger pores in the solid precursor. This method effectively optimizes the size and distribution of pores by regulating the interaction between the solvent and the surfactant.

[0022] In addition, the conjugate of urea and carboxyl surfactant plays an important role in the high-temperature calcination process. When heated, urea decomposes to produce ammonia and carbon dioxide. These gases generate pressure in the solid precursor, thereby further expanding the pore size. The decomposition of urea, combined with the action of the surfactant, enhances the pore expansion effect, ensuring the porosity and pore size uniformity of the final material. The addition of potassium carbonate further enhances the pore size expansion. During the high-temperature calcination process, potassium carbonate decomposes to release potassium vapor and carbon dioxide. These gases generate pressure inside the solid precursor, effectively promoting the expansion of pores. This process not only enhances the formation of pore size, but also optimizes the pore distribution and structural stability. Large porosity and high specific surface area provide more active sites for catalytic reactions, while increasing the contact time of reactants and improving the catalytic conversion rate. For heterogeneous catalysts, a large specific surface area can accommodate more catalytic active centers, thereby enhancing the catalytic effect. Due to the effect of potassium carbonate, the distribution and structure of the pores are optimized, and the structural stability of the material is also enhanced; especially when the catalytic reaction is carried out at high temperature, the pore structure of the catalyst can be effectively prevented from collapsing, thereby extending the life of the catalyst. The present invention introduces triethoxysilane modification to form a protective layer through the hydrolysis and condensation of silicon oxide, thereby improving the catalytic performance of macroporous alumina, especially the selectivity and stability in acid-base catalytic reactions. By optimizing the pore structure and surface chemical properties, the addition of triethoxysilane can effectively enhance the reaction efficiency and life of the catalyst. The present invention introduces a small amount of carbon source material sucrose into the precursor solution, removes the carbon source by calcination to produce additional pore structure, and further expands the porosity and specific surface area; at the same time, the gas generated by the decomposition of the carbon source contributes to pore formation and increases the mechanical strength of the material.

[0023] In summary, the present invention innovatively improves the pore structure of macroporous alumina by combining the combined effects of ethyl acetate, urea / carboxyl surfactant conjugate, triethoxysilane and potassium carbonate. This method not only effectively expands the pore size, but also ensures the uniform distribution of pores and the structural properties of the material, providing a new technical path for the preparation of macroporous alumina. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 is a scanning electron microscope image of the macroporous alumina prepared in Example 1 of the present invention;

[0026] Figure 2is a scanning electron microscope image of the macroporous alumina prepared in Example 2 of the present invention;

[0027] Figure 3 is a scanning electron microscope image of the macroporous alumina prepared in Example 3 of the present invention;

[0028] Figure 4 is a scanning electron microscope image of the macroporous alumina prepared in Comparative Example 1 of the present invention;

[0029] Figure 5 is a scanning electron microscope image of the macroporous alumina prepared in Comparative Example 2 of the present invention;

[0030] Figure 6 is a scanning electron microscope image of the macroporous alumina prepared in Comparative Example 3 of the present invention;

[0031] Figure 7 This is the XRD pattern of the macroporous alumina prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. It should be noted that unless otherwise specified, the raw materials involved in the present invention were purchased through conventional commercial channels.

[0033] Example 1: This example proposes a macroporous alumina, wherein the raw materials for synthesizing the macroporous alumina include the following components: potassium carbonate, ethyl acetate, ethanol, urea / sodium laurate conjugate, aluminum chloride, triethylamine and water.

[0034] The preparation method of the urea / sodium laurate conjugate comprises the following steps:

[0035] A1. Dissolve 0.1 mol of urea in 100 mL of anhydrous ethanol and stir until completely dissolved. Add 0.12 mol of acetic anhydride and 0.6 mL of anhydrous pyridine. Stir and react at room temperature for 2-4 hours. After the reaction is complete, pour the reaction mixture into 0°C diethyl ether solution, centrifuge, collect the precipitate, and wash with diethyl ether to obtain acetylated urea.

[0036] A2. Add 0.1 mol of sodium laurate to 100 mL of ethanol and stir until completely dissolved. Then add 0.11 mol of EDC and stir at 500 rpm for 3 h. After the reaction, add 0.11 mol of NHS and stir at 500 rpm for 3 h to obtain an activated solution.

[0037] A3. Dissolve the acetylated urea prepared in step A1 in 100 mL of deionized water, heat in a water bath at 50°C with stirring for 4 h, cool to room temperature, and then slowly add the solution to the activation solution prepared in step A2. Stir the mixture at 400-600 rpm at 30-35°C for 6-12 h. After completion of the reaction, the product is obtained. Extract the product with dichloromethane, and then place the product in a rotary evaporator to evaporate the dichloromethane. After complete evaporation, urea / sodium laurate conjugate is obtained.

[0038] This embodiment also provides a method for preparing macroporous alumina, which specifically includes the following steps:

[0039] S1. Weigh 200 mg of urea / sodium laurate conjugate and add it to 10 mL of water. Stir until completely dissolved to obtain a surfactant solution. Weigh aluminum chloride and add it to water. Dissolve evenly to prepare a 2 mol / L aluminum chloride solution.

[0040] S2. Add 2 g of potassium carbonate, 10 mL of ethanol, 15 mL of ethyl acetate, 2 g of sucrose, and 100 mL of water to a 150 mL container, stir and disperse them evenly, and continue to add the surfactant solution prepared in step S1, stir and disperse them evenly to obtain a mixed solution;

[0041] S3. Add 40 mL of aluminum chloride solution dropwise to the mixed solution prepared in step S2, and stir at 400 rpm for 6 h to form a uniform emulsion. Then, add 6 mL of triethylamine and 5 mL of triethoxysilane, and continue stirring for 60 min. After the reaction is completed, let it stand for 12 h to obtain a sol solution.

[0042] S4, placing the sol solution prepared in step S3 in an oven at 60° C. and drying for 6 h, then heating to 80° C. and drying until the sol solution is completely free of moisture to obtain a solid precursor;

[0043] S5. Place the solid precursor obtained in step S4 in a muffle furnace, and heat it to 700°C at a heating rate of 10°C / min under the protection of a nitrogen flow at a flow rate of 1 L / min, maintain it for 3 hours, and naturally cool it to room temperature to obtain a product. Wash the product three times with water and ethanol alternately, and obtain macroporous alumina after drying.

[0044] Example 2: This example proposes a macroporous alumina, wherein the raw materials for synthesizing the macroporous alumina include the following components: potassium carbonate, ethyl acetate, methanol, urea / oleic acid conjugate, aluminum nitrate, triethylamine, and water.

[0045] The preparation method of the urea / oleic acid conjugate comprises the following steps:

[0046] A1. Dissolve 0.1 mol of urea in 100 mL of anhydrous ethanol and stir until completely dissolved. Add 0.12 mol of acetic anhydride and 0.6 mL of anhydrous pyridine. Stir and react at room temperature for 2-4 hours. After the reaction is complete, pour the reaction mixture into 0°C diethyl ether solution, centrifuge, collect the precipitate, and wash with diethyl ether to obtain acetylated urea.

[0047] A2. Add 0.1 mol of oleic acid to 100 mL of ethanol and stir until completely dissolved. Then add 0.11 mol of EDC and stir at 500 rpm for 3 h. After the reaction, add 0.11 mol of NHS and stir at 500 rpm for 3 h to obtain an activated solution.

[0048] A3. Dissolve the acetylated urea prepared in step A1 in 100 mL of deionized water, heat in a water bath at 50°C with stirring for 4 h, cool to room temperature, and then slowly add the solution to the activation solution prepared in step A2. Stir the mixture at 400-600 rpm at 30-35°C for 6-12 h. After completion of the reaction, the product is obtained. Extract the product with dichloromethane, and then place the product in a rotary evaporator to evaporate the dichloromethane. After complete evaporation, the urea / oleic acid conjugate is obtained.

[0049] This embodiment also provides a method for preparing macroporous alumina, which specifically includes the following steps:

[0050] S1. Weigh 150 mg of urea / oleic acid conjugate and add it to 10 mL of water. Stir until completely dissolved to obtain a surfactant solution. Weigh aluminum nitrate and add it to water. Dissolve evenly to prepare a 1.5 mol / L aluminum nitrate solution.

[0051] S2. Add 1 g of potassium carbonate, 8 mL of methanol, 20 mL of ethyl acetate, 0.5 g of sucrose, and 90 mL of water to a 150 mL container, stir and disperse them evenly, and continue to add the surfactant solution prepared in step S1, stir and disperse them evenly to obtain a mixed solution;

[0052] S3. Add 40 mL of aluminum nitrate solution dropwise to the mixed solution prepared in step S2, and stir at 600 rpm for 3 h to form a uniform emulsion. Then, add 4 mL of triethylamine and 2 mL of triethoxysilane, and continue stirring for 40 min. After the reaction is completed, let it stand for 6 h to obtain a sol solution.

[0053] S4, placing the sol solution prepared in step S3 in an oven at 60° C. and drying for 4 h, then heating to 80° C. and drying until the sol solution is completely free of moisture to obtain a solid precursor;

[0054] S5. Place the solid precursor obtained in step S4 in a muffle furnace, and heat it to 500°C at a heating rate of 5°C / min under the protection of a nitrogen flow at a flow rate of 1 L / min, maintain it for 4 hours, and naturally cool it to room temperature to obtain a product. Wash the product three times with water and ethanol alternately, and obtain macroporous alumina after drying.

[0055] Example 3: This example proposes a macroporous alumina, wherein the raw materials for synthesizing the macroporous alumina include the following components: potassium carbonate, ethyl acetate, n-propanol, urea / stearic acid conjugate, aluminum sulfate, triethylamine and water.

[0056] The preparation method of the urea / stearic acid conjugate comprises the following steps:

[0057] A1. Dissolve 0.1 mol of urea in 100 mL of anhydrous ethanol and stir until completely dissolved. Add 0.12 mol of acetic anhydride and 0.6 mL of anhydrous pyridine. Stir and react at room temperature for 2-4 hours. After the reaction is complete, pour the reaction mixture into 0°C diethyl ether solution, centrifuge, collect the precipitate, and wash with diethyl ether to obtain acetylated urea.

[0058] A2. Add 0.1 mol of stearic acid to 100 mL of ethanol and stir until completely dissolved. Then add 0.11 mol of EDC and stir at 500 rpm for 3 h. After the reaction, add 0.11 mol of NHS and stir at 500 rpm for 3 h to obtain an activated solution.

[0059] A3. Dissolve the acetylated urea prepared in step A1 in 100 mL of deionized water, heat in a water bath at 50°C with stirring for 4 h, cool to room temperature, and then slowly add the solution to the activation solution prepared in step A2. Stir the mixture at 400-600 rpm at 30-35°C for 6-12 h. After completion of the reaction, the product is obtained. Extract the product with dichloromethane, and then place the product in a rotary evaporator to evaporate the dichloromethane. After complete evaporation, the urea / stearic acid conjugate is obtained.

[0060] This embodiment also provides a method for preparing macroporous alumina, which specifically includes the following steps:

[0061] S1. Weigh 100 mg of urea / stearic acid conjugate and add it to 10 mL of water. Stir until completely dissolved to obtain a surfactant solution. Weigh aluminum sulfate and add it to water. Dissolve evenly to prepare a 1 mol / L aluminum sulfate solution.

[0062] S2. Add 1.5 g of potassium carbonate, 5 mL of n-propanol, 10 mL of ethyl acetate, 1.5 g of sucrose, and 95 mL of water to a 150 mL container, stir and disperse them evenly, and continue to add the surfactant solution prepared in step S1, stir and disperse them evenly to obtain a mixed solution;

[0063] S3. Add 40 mL of aluminum sulfate solution dropwise to the mixed solution prepared in step S2, stir at 500 rpm for 4 h to form a uniform emulsion, then add 5 mL of triethylamine and 4 mL of triethoxysilane, continue stirring for 30 min, and after the reaction is completed, let it stand for 8 h to obtain a sol solution;

[0064] S4, placing the sol solution prepared in step S3 in an oven at 60°C for 5 h, then heating to 80°C for drying until the sol solution is completely free of moisture to obtain a solid precursor;

[0065] S5. Place the solid precursor obtained in step S4 in a muffle furnace, and heat it to 600°C at a heating rate of 8°C / min under the protection of a nitrogen flow at a flow rate of 1 L / min, maintain it for 5 hours, and obtain the product after natural cooling to room temperature. Wash the product three times with water and ethanol alternately, and obtain macroporous alumina after drying.

[0066] Comparative Example 1: This comparative example proposes a macroporous alumina, which differs from Example 1 only in that potassium carbonate is not added, and the remaining components, component contents, and experimental steps are the same as those of Example 1.

[0067] Comparative Example 2: This comparative example proposes a macroporous alumina, which differs from Example 1 only in that ethyl acetate is not added, and the remaining components, component contents, and experimental steps are the same as those in Example 1.

[0068] Comparative Example 3: This comparative example proposes a macroporous alumina, which differs from Example 1 only in that urea is not added.

[0069] Comparative Example 4: This comparative example proposes a macroporous alumina, which differs from Example 1 only in that it is not modified with triethoxysilane.

[0070] Test Example 1: The microscopic morphology of the macroporous alumina prepared in Examples 1-3 of the present invention and Comparative Examples 1-3 was observed using a scanning electron microscope.

[0071] Figure 1 is a scanning electron microscope image of the macroporous alumina prepared in Example 1 of the present invention, Figure 2 This is a scanning electron microscope image of the macroporous alumina prepared in Example 2 of the present invention. Figure 3This is a scanning electron microscope image of the macroporous alumina prepared in Example 3 of the present invention. As shown in the figure, the surfaces of the alumina prepared in Examples 1-3 are all distributed with significantly larger and uniform pores, with diameters of about 1 to 2 μm, indicating that the macroporous alumina of the present invention was successfully prepared. Figure 4 This is a scanning electron microscope image of the macroporous alumina prepared in Comparative Example 1 of the present invention. Figure 5 This is a scanning electron microscope image of the macroporous alumina prepared in Comparative Example 2 of the present invention. Figure 6 This is a scanning electron microscope image of the macroporous alumina prepared in Comparative Example 3 of the present invention. As shown in the figure, the pore size of the alumina prepared in the comparative example is smaller than that in Example 1, and the void density is smaller, indicating that potassium carbonate, urea / carboxyl surfactant conjugate and ethyl acetate can effectively expand the pore size of the synthetic alumina.

[0072] Test Example 2: The specific surface area and structure of the macroporous alumina prepared in Example 1 were analyzed using BET test and XRD test.

[0073] Figure 7 This is the XRD diagram of the macroporous alumina prepared in Example 1 of the present invention. As shown in the figure, the macroporous alumina prepared in Example 1 has obvious X-ray diffraction peaks, a regular and orderly structure, and the characteristic peaks are consistent with the standard diffraction peaks of γ-alumina, indicating that the macroporous alumina described in the present invention was successfully prepared.

[0074] The specific surface areas of the macroporous aluminas prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were analyzed using BET and XRD tests. The results are shown in Table 1 below.

[0075] Table 1. Specific surface area results of macroporous alumina prepared in Examples and Comparative Examples

[0076]

[0077] Table 1 shows the specific surface area results of the macroporous alumina prepared in Examples 1 to 3 of the present invention and Comparative Examples 1 to 4. The macroporous alumina has a relatively high specific surface area and is successfully prepared.

[0078] Catalytic reaction test: The macroporous alumina samples prepared in Example 1 of the present invention and Comparative Examples 1 to 4 were dried and pretreated at 100° C. for 2 h, 0.5 g of the sample was added with 20 mL of ethyl acetate and 40 mL of water, the reaction temperature was maintained at 70° C., and the mixture was stirred evenly at 400 rpm. The sample was sampled once every 30 minutes. The concentration change of ethyl acetate was detected by high performance liquid chromatography, and the conversion rate was calculated as (initial concentration of ethyl acetate-residual concentration of ethyl acetate) / initial concentration of ethyl acetate × 100%. The conversion rates at 30 min, 60 min, and 120 min were recorded. After the reaction was completed, the catalyst sample was separated from the reaction system, washed three times with water and ethanol, and the catalyst was vacuum dried at 100° C. again. The above reaction process was repeated for three cycles. The results are shown in Table 2.

[0079] Table 2. Macroporous alumina catalytic reaction results

[0080]

[0081] It can be seen from the results in Table 1 above that the macroporous alumina prepared by the present invention has excellent catalytic efficiency and can maintain good catalytic performance in multiple cycle tests; it can be seen from the results of Comparative Example 1 and Example 1 that potassium carbonate plays a role in releasing gas and expanding pores during high-temperature calcination. The lack of potassium carbonate will lead to smaller pore size, uneven pore structure, reduced specific surface area, lower catalytic efficiency, and due to poor stability, the conversion rate decreases significantly in multiple cycle tests; it can be seen from the results of Comparative Example 2 and Example 1 that due to the absence of ethyl acetate, the uniformity in the solution will be significantly improved, resulting in the inability to form a grid structure, thereby affecting the generation of pores, and the pore size finally formed is small and unevenly distributed, the active sites in the catalytic reaction are insufficiently exposed, the reaction efficiency and selectivity will decrease, and the uneven pore distribution causes the reaction efficiency to decrease during multiple cycles; it can be seen from the results of Comparative Example 3 and Example 1 that there is no The decomposition of urea produces gas, and the pore expansion is limited, resulting in a relatively small pore size and a decrease in porosity, which affects the specific surface area of ​​the catalyst and the diffusion channel of the reactants. The gas decomposed by urea synergizes with the gas decomposed by potassium carbonate to form a macroporous structure through internal pressure. In the absence of urea, the synergistic effect fails, resulting in the inability to effectively expand the pore size, and the porosity and reaction efficiency are significantly reduced. It can be seen from the results of Comparative Example 4 and Example 1 that the triethoxysilane coating can effectively enhance the structural stability of the catalyst at high temperatures. The lack of this coating causes the catalyst surface to easily agglomerate at high temperatures. In addition, triethoxysilane synergizes with the pore structure of macroporous alumina to improve the acid-base properties and surface stability of the catalyst. The lack of this synergistic effect leads to a decline in many aspects of catalyst performance, especially the selectivity and stability in acid-base catalytic reactions are significantly reduced, and its service life and stability are significantly affected in multiple cycle tests.

[0082] The present invention and its embodiments are described above. Such description is not restrictive. The drawings show only one embodiment of the present invention, and actual applications are not limited thereto. In short, if a person skilled in the art is inspired by the above, and does not deviate from the purpose of the present invention, any method and embodiment similar to the technical solution without creative design shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing macroporous alumina, characterized in that: The macroporous alumina synthesis raw materials include the following components: potassium carbonate, ethyl acetate, low-carbon alcohol, urea / carboxyl surfactant coupling compound, aluminum salt, triethylamine, triethoxysilane, sucrose and water; The preparation method of the urea / carboxyl surfactant conjugate comprises the following steps: A1. Dissolve urea in anhydrous ethanol, stir until completely dissolved, add acetic anhydride and anhydrous pyridine, stir and react at room temperature for 2-4 hours. After the reaction is completed, pour the reaction mixture into an excess of 0°C ether solution, centrifuge, take the precipitate, wash with ether, and obtain acetylated urea; A2. Add the carboxyl surfactant to 100 mL of ethanol, stir to completely dissolve, continue to add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, stir at 500 rpm for 3 h, and after the reaction is completed, continue to add N-hydroxysuccinimide, stir at 500 rpm for 3 h to obtain an activated solution; A3, dissolving the acetylated urea prepared in step A1 into 100 mL of deionized water, heating in a water bath at 50°C with stirring for 24 h, cooling to room temperature, and then slowly adding the solution to the activation solution prepared in step A2, stirring at 400-600 rpm at 30-35°C for 6-12 h, obtaining a product after the reaction is completed, extracting the product with dichloromethane, and then placing the product in a rotary evaporator to evaporate the dichloromethane, and obtaining a urea / carboxyl surfactant conjugate after complete evaporation; The ratio of the amount of urea, anhydrous ethanol, acetic anhydride and anhydrous pyridine used in step A1 is 0.1 mol: 100 mL: 0.12 mol: 0.6 mL; the ratio of the amount of carboxyl surfactant, ethanol, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide used in step A2 is 0.1 mol: 100 mL: 0.11 mol: 0.11 mol; The carboxyl surfactant in step A2 is any one of stearic acid, oleic acid, palmitic acid, capric acid and sodium laurate; The low-carbon alcohol is any one of methanol, ethanol, n-propanol and isopropanol; The aluminum salt is any one of aluminum chloride, aluminum nitrate and aluminum sulfate; The preparation method of the macroporous alumina specifically comprises the following steps: S1, weighing urea / carboxyl surfactant conjugate, adding it to water, stirring until completely dissolved to obtain a surfactant solution, weighing aluminum salt, adding it to water, and dissolving it evenly to obtain an aluminum salt solution; S2, adding potassium carbonate, low-carbon alcohol, ethyl acetate, sucrose and water into a container, stirring and dispersing them evenly, and continuing to add the surfactant solution prepared in step S1, stirring and dispersing them evenly to obtain a mixed solution; S3, adding aluminum salt solution dropwise to the mixed solution prepared in step S2, stirring for 3-6 h to form a uniform emulsion, continuing to add triethylamine and triethoxysilane, continuing to stir for 30-60 min, and standing for 6-12 h after the reaction is completed to obtain a sol solution; S4, drying the sol solution prepared in step S3 at 60° C. for 4-6 h, and then heating to 80° C. for drying until the sol solution is completely free of water to obtain a solid precursor; S5. The solid precursor obtained in step S4 is heated to 500-700°C at a heating rate of 5-10°C / min under the protection of a nitrogen flow, maintained for 3-5 hours, and naturally cooled to room temperature to obtain a product, which is then washed and dried to obtain macroporous alumina.

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