MgAl2O4 carrier, and preparation method and application thereof

Abstract

The application provides a MgAl2O4 carrier and a preparation method and application thereof, and relates to the technical field of catalysts. Urea, a soluble aluminum salt, a soluble magnesium salt, polydiallyldimethylammonium chloride and water are mixed to carry out a hydrothermal reaction to obtain a precipitate; the molar ratio of the urea, aluminum elements in the soluble aluminum salt, magnesium elements in the soluble magnesium salt and the polydiallyldimethylammonium chloride is 4.5:2:1:(1-2); the precipitate is sequentially dried and calcined to obtain the MgAl2O4 carrier. The prepared MgAl2O4 carrier is used as a catalyst carrier in a high-temperature and high-pressure dry reforming reaction of methane and carbon dioxide, and excellent stability is exhibited; under high-temperature and high-pressure conditions of 850 DEG C and 2 MPa, the MgAl2O4 carrier is evaluated for 230 hours, and the morphology of the MgAl2O4 carrier before and after the reaction has no obvious difference, the specific surface area changes little, and excellent mechanical strength and chemical stability are shown.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a MgAl2O4 support, its preparation method, and its application. Background Technology

[0002] Methane-carbon dioxide reforming (dry reforming, DRM) technology uses two greenhouse gases—methane and carbon dioxide—as feedstock to produce syngas (CO and H2). This syngas can then be further used to produce low-molecular-weight alcohols and ethers. DRM technology effectively reduces greenhouse gas emissions and provides a new approach for the clean production of hydrogen.

[0003] The methane-carbon dioxide reforming reaction is an endothermic reaction, typically requiring high temperature and high pressure (e.g., 850℃, 2MPa). With increasing pressure, the stability, thermal stability, and resistance to carbon deposition of the catalyst become critical issues that urgently need to be addressed. Currently, commonly used catalyst supports include Al₂O₃, SiO₂, TiO₂, ZrO₂, activated carbon, carbon nanotubes, and molecular sieves. Although these materials exhibit certain catalytic activity in the reaction, they often face problems such as carbon buildup and poor thermal stability, resulting in a relatively short catalyst lifespan.

[0004] Magnesium aluminum spinel (MgAl2O4) exhibits excellent thermal stability and resistance to carbon deposition as a catalyst support, meeting the high-temperature and high-pressure conditions required for the DRM reaction. MgAl2O4 also possesses a large specific surface area and suitable pore structure, effectively supporting the active metal Ni and improving catalyst dispersion, thus demonstrating high catalytic activity. Compared to traditional catalysts such as MgO and Al2O3, it exhibits better structural stability and will not react with quartz tubes (SiO2) to avoid impurities in the gas mixture.

[0005] Currently, the main industrial synthesis method for MgAl2O4 supports is the ammonia precipitation method. While the ammonia precipitation method is low-cost and simple to operate, it also has significant drawbacks. The structure of the MgAl spinel synthesized via ammonia precipitation is difficult to control, resulting in poor stability and thus affecting catalytic performance. The hydrothermal method, using water as a solvent in a closed container, promotes the formation of hydroxides from metal ions. The main advantage of the hydrothermal method is that it allows for reaction under mild conditions, resulting in MgAl spinel with controllable structure and uniform particle size, leading to more stable and higher-performance catalysts. However, the stability of MgAl2O4 supports synthesized via the hydrothermal method in the high-temperature, high-pressure methane-carbon dioxide reforming reaction still needs improvement. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a MgAl2O4 support, its preparation method, and its application. The MgAl2O4 support prepared by this invention exhibits excellent stability in the high-temperature and high-pressure methane-carbon dioxide reforming reaction.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a MgAl2O4 support, comprising the following steps:

[0009] Urea, soluble aluminum salt, soluble magnesium salt, polydienedimethylammonium chloride and water are mixed and subjected to a hydrothermal reaction to obtain a precipitate; the molar ratio of aluminum in urea, aluminum in soluble aluminum salt, magnesium in soluble magnesium salt and polydienedimethylammonium chloride is 4.5:2:1:(1~2);

[0010] The precipitate was dried and calcined sequentially to obtain the MgAl2O4 support.

[0011] Preferably, the soluble aluminum salt includes Al(NO3)3, and the soluble magnesium salt includes Mg(CH3COO)2.

[0012] Preferably, the weight-average molecular weight of the polydiene dimethyl ammonium chloride is 450,000 ± 50,000.

[0013] Preferably, the hydrothermal reaction is carried out at a temperature of 120-150°C for 12-14 hours.

[0014] Preferably, after the hydrothermal reaction, the resulting reaction solution is cooled to room temperature and then allowed to stand for 3 to 6 hours.

[0015] Preferably, the drying temperature is 90~110℃.

[0016] Preferably, the calcination temperature is 680~710℃, the holding time is 5.5~6h, and the heating rate from room temperature to the calcination temperature is 2℃ / min.

[0017] This invention provides a MgAl2O4 support prepared by the preparation method described above.

[0018] This invention provides the application of the MgAl2O4 support described above as a catalyst support in the dry reforming reaction of methane and carbon dioxide.

[0019] Preferably, the temperature of the dry reforming reaction of methane and carbon dioxide is 700~900℃ and the pressure is 0.1~2MPa.

[0020] This invention provides a method for preparing a MgAl2O4 support, comprising the following steps: mixing urea, soluble aluminum salt, soluble magnesium salt, polydienedimethylammonium chloride and water for a hydrothermal reaction to obtain a precipitate; wherein the molar ratio of aluminum in urea, aluminum in soluble aluminum salt, magnesium in soluble magnesium salt and polydienedimethylammonium chloride is 4.5:2:1:(1~2); and sequentially drying and calcining the precipitate to obtain the MgAl2O4 support. This invention employs a hydrothermal method to prepare a MgAl₂O₄ support and introduces polydiallyldimethylammonium chloride (PDMC) into the reaction system. PDMC acts as a high-molecular-weight chelating agent, capable of complexing with aluminum and magnesium metal ions. Its large molecular chains form a physical barrier around the ions, improving the dispersion of aluminum and magnesium ions in the precursor solution and effectively inhibiting their approach and aggregation during precipitation, thus promoting the formation of uniform and fine precursor particles. In the subsequent hydrothermal reaction, PDMC guides the orderly growth of crystals, constructing a more dense and morphologically complete spinel phase, thereby significantly enhancing the mechanical strength of the support itself. The MgAl₂O₄ support prepared in this invention, when used as a catalyst support in the high-temperature, high-pressure dry reforming reaction of methane and carbon dioxide, exhibits excellent stability. The results of the examples show that, when used in the methane-carbon dioxide reforming reaction, the MgAl2O4 support exhibits no significant difference in morphology before and after the reaction under high temperature and high pressure conditions of 850℃ and 2MPa for 230h, and the specific surface area does not change much, demonstrating excellent mechanical strength and chemical stability. In contrast, the MgAl2O4 support prepared by hydrothermal method without the addition of polydiene dimethyl ammonium chloride shows a greater degree of morphological breakage. Attached Figure Description

[0021] Figure 1 The XRD patterns are of MgAl2O4 supports obtained under different urea ratios in Comparative Examples 1-2 and MgAl2O4 supports prepared by ammonia precipitation in Comparative Example 5.

[0022] Figure 2 The XRD patterns of the MgAl2O4 supports obtained in Example 1, Comparative Example 1, Comparative Example 3 and Comparative Example 5 are shown.

[0023] Figure 3 The BET curves of the MgAl2O4 supports prepared in the examples and comparative examples are shown. Figure 3(a) is the BET curve of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4:2:1:1; (b) is the BET curve of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:2; (c) is the BET curve of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1; and (d) is the BET curve of MgAl2O4 support obtained by ammonia precipitation.

[0024] Figure 4 The images shown are SEM images of the MgAl2O4 supports prepared in the examples and comparative examples at 1 μm. Figure 4 In the image, (a) is a SEM image of the MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:0.5; (b) is a SEM image of the MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:1; and (c) is a SEM image of the C... SEM images of MgAl2O4 support with a molar ratio of O(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1:2; (d) SEM image of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1; (e) SEM image of MgAl2O4 support prepared by ammonia precipitation method.

[0025] Figure 5 The images shown are SEM images of the MgAl2O4 supports prepared in the examples and comparative examples at 200-500 nm. Figure 5(a) is a SEM image of the MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:2; (b) is a SEM image of the MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1; (c) is a SEM image of CO(NH2)2·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1. 2: SEM image of MgAl2O4 support with a molar ratio of Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:0.5; (d) SEM image of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1; (e) SEM image of MgAl2O4 support prepared by ammonia precipitation method;

[0026] Figure 6 The image shows a SEM image of the MgAl2O4 support after 230 hours of testing at 850℃ and 2MPa. Figure 6 (a) MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:2; (b) MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:1; (c) MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:1. (d) MgAl2O4 support with a molar ratio of NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:0.5; (e) MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1; (f) MgAl2O4 support prepared by ammonia precipitation method. Detailed Implementation

[0027] This invention provides a method for preparing a MgAl2O4 support, comprising the following steps:

[0028] Urea, soluble aluminum salt, soluble magnesium salt, polydienedimethylammonium chloride and water are mixed and subjected to a hydrothermal reaction to obtain a precipitate; the molar ratio of aluminum in urea, aluminum in soluble aluminum salt, magnesium in soluble magnesium salt and polydienedimethylammonium chloride is 4.5:2:1:(1~2);

[0029] The precipitate was dried and calcined sequentially to obtain the MgAl2O4 support.

[0030] Unless otherwise specified, all raw materials involved in this invention are commercially available products in the field.

[0031] This invention involves mixing urea, soluble aluminum salt, soluble magnesium salt, polydimethylammonium chloride, and water and carrying out a hydrothermal reaction to obtain a precipitate.

[0032] In this invention, the soluble aluminum salt preferably includes Al(NO3)3 (aluminum nitrate), and the soluble magnesium salt preferably includes Mg(CH3COO)2 (magnesium acetate). In embodiments of this invention, Al(NO3)3 is added in the form of Al(NO3)3·9H2O, and Mg(CH3COO)2 is added in the form of Mg(CH3COO)2·4H2O. The weight-average molecular weight of the polydienedimethylammonium chloride (PDDA, CAS: 26062-79-3) is preferably 450,000 ± 50,000. In embodiments of this invention, the polydienedimethylammonium chloride is added in the form of a polydienedimethylammonium chloride solution. The water is preferably deionized water.

[0033] In this invention, the molar ratio of urea (CO(NH2)2), aluminum in the soluble aluminum salt, magnesium in the soluble magnesium salt, and polydienedimethylammonium chloride is 4.5:2:1:(1~2), which can be 4.5:2:1:1 or 4.5:2:1:2; the molar ratio of urea to water is preferably 1:(340~360), which can be 1:350. In an embodiment of this invention, the polydienedimethylammonium chloride is added in the form of a 20wt% aqueous solution, and the molar amount of the polydienedimethylammonium chloride is calculated by dividing the mass of the polydienedimethylammonium chloride aqueous solution by the average relative molecular mass of the polydienedimethylammonium chloride aqueous solution, wherein the average relative molecular mass is 491.06. In this embodiment of the invention, the performance of MgAl2O4 support prepared under the condition of a molar ratio of urea, aluminum in soluble aluminum salt, magnesium in soluble magnesium salt, and polydienedimethylammonium chloride of 4.5:2:1:0.5 was compared. The results showed that after high temperature and high pressure (850℃, 2MPa, 230h) methane-carbon dioxide reforming reaction, the morphology of MgAl2O4 support was significantly broken, while the morphology of MgAl2O4 support obtained under the condition of a molar ratio of urea, aluminum in soluble aluminum salt, magnesium in soluble magnesium salt, and polydienedimethylammonium chloride of 4.5:2:1:(1~2) did not show significant changes, exhibiting excellent stability.

[0034] In this invention, the preferred method for mixing urea, soluble aluminum salt, soluble magnesium salt, polydiallyldimethylammonium chloride, and water is as follows: water is added to the soluble aluminum salt, soluble magnesium salt, and polydiallyldimethylammonium chloride for a first stirring and mixing, followed by adding urea and water to the resulting mixture for a second stirring and mixing. In this invention, the first stirring and mixing time is preferably 1 hour, ensuring uniform mixing of Al and Mg ions; the second stirring and mixing time is preferably 2 hours, ensuring thorough homogenization of the solution. In this embodiment of the invention, the mixture obtained by mixing urea, soluble aluminum salt, soluble magnesium salt, polydiallyldimethylammonium chloride, and water is referred to as the precursor solution.

[0035] In this invention, the preferred temperature for the hydrothermal reaction is 120-150°C, which can be 120, 130, 140, or 150°C, and the preferred time is 12-14 hours, which can be 12, 13, or 14 hours. Preferably, the precursor solution is transferred to a polytetrafluoroethylene liner and sealed in a stainless steel high-pressure reactor for the hydrothermal reaction. During the hydrothermal reaction, urea is decomposed by hot water, releasing hydroxide ions that combine with aluminum and magnesium ions in the system. Simultaneously, polydiallyldimethylammonium chloride acts as a structure-directing agent, regulating the precipitation rate and crystal nucleation growth, inducing the formation of a hydroxide precursor with regular morphology and uniform particle size, laying the structural foundation for subsequent calcination to obtain a high-performance spinel carrier.

[0036] After the hydrothermal reaction, the present invention preferably cools the resulting reaction solution to room temperature and then allows it to stand; the standing time is preferably 3-6 hours, which can be 3, 4, 5 or 6 hours. In the present invention, the purpose of the standing is to promote the uniform growth of crystal nuclei.

[0037] After settling, the reaction product is preferably subjected to solid-liquid separation and water washing in sequence to obtain the precipitate. In this invention, the solid-liquid separation can be performed by vacuum filtration, and the water washing is preferably performed multiple times with deionized water to remove residual impurities.

[0038] After obtaining the precipitate, the present invention sequentially dries and calcines the precipitate to obtain the MgAl2O4 support.

[0039] In this invention, the drying temperature is preferably 90~110℃, and can be 100℃, and the drying time is preferably 24h; in this invention, the precipitate is preferably transferred to a petri dish and placed in an oven for drying.

[0040] In this invention, the calcination temperature is preferably 680~710℃, and can be 700℃; the holding time is preferably 5.5~6h; and the heating rate from room temperature to the calcination temperature is preferably 2℃ / min. The calcination is carried out in an air atmosphere. Preferably, the dried precipitate is ground into a uniform powder using a ball mill, transferred to a silicon carbide crucible, and calcined in a muffle furnace. During the calcination process, residual moisture and polydienedimethylammonium chloride volatilize, decompose, and oxidize upon heating, forming an initial porous structure. As the temperature rises, amorphous hydroxides and salt intermediates decompose into active MgO and Al2O3 components. Finally, during the set high-temperature holding stage, the two components achieve ion interdiffusion through a solid-phase reaction, successfully constructing a long-range ordered, perfectly crystalline spinel structure. After calcination, a high-purity MgAl2O4 support is obtained, which is then naturally cooled to room temperature with the furnace.

[0041] The reaction formulas involved in the preparation of the MgAl2O4 support in this invention are as follows:

[0042] .

[0043] This invention provides a MgAl2O4 support prepared by the preparation method described above.

[0044] This invention provides the application of the MgAl2O4 support described above as a catalyst support in the dry reforming reaction of methane and carbon dioxide.

[0045] In this invention, the preferred temperature for the dry reforming reaction of methane and carbon dioxide is 700-900℃, which can be 850℃; the preferred pressure is 0.1 (atmospheric pressure) to 2 MPa; and the preferred volume ratio of methane to carbon dioxide is 1:1. In application, Ni is loaded onto the MgAl2O4 support. This invention does not have particular requirements on the amount of Ni loaded or the method of loading Ni; loading amounts and methods well known to those skilled in the art can be used. The MgAl2O4 support provided by this invention exhibits excellent mechanical strength and chemical stability under harsh reaction conditions of high temperature and high pressure.

[0046] To further illustrate the present invention, the MgAl2O4 support, its preparation method, and its application provided by the present invention are described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0047] The raw material information used in the examples and comparative examples is shown in Table 1.

[0048] Table 1. Raw material information used in the examples and comparative examples.

[0049]

[0050] Example 1 (molar ratio CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA=4.5:2:1:1)

[0051] Accurately weigh 1.9192 g of urea, 5.3276 g of Al(NO3)3·9H2O, 1.5228 g of Mg(CH3COO)2·4H2O, and 3.4584 g of PDDA solution. First, transfer the Al(NO3)3·9H2O, Mg(CH3COO)2·4H2O, and PDDA solution to a beaker and add 100 mL of deionized water. Stir continuously with a magnetic stirrer for 1 hour to ensure uniform mixing of Al and Mg ions. Then add urea and 100 mL of deionized water, and stir continuously with a magnetic stirrer for 2 hours to fully homogenize the precursor solution, obtaining the precursor solution. Transfer the precursor solution to a 500 mL polytetrafluoroethylene-lined container and seal it in a 316L stainless steel high-pressure reactor. Perform a hydrothermal reaction at 150°C for 14 hours. After the reaction, allow it to cool naturally to room temperature and then let it stand for 6 hours to promote uniform growth of crystal nuclei.

[0052] After vacuum filtration, the reaction products were washed multiple times with deionized water to remove residual impurities. The filter cake was transferred to a petri dish and dried in an oven at 100°C for 24 hours. Subsequently, the dried solid was ground into a uniform powder using a ball mill and transferred to a silicon carbide (SiC) crucible. The powder was then calcined in a muffle furnace at a heating rate of 2°C / min to 700°C and held at that temperature for 6 hours. Finally, the furnace was allowed to cool naturally to room temperature to obtain a high-purity MgAl2O4 support.

[0053] Example 2 (molar ratio CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA=4.5:2:1:2)

[0054] Accurately weigh 1.9192 g of urea, 5.3276 g of Al(NO3)3·9H2O, 1.5228 g of Mg(CH3COO)2·4H2O, and 6.9168 g of PDDA solution. First, transfer the Al(NO3)3·9H2O, Mg(CH3COO)2·4H2O, and PDDA solution to a beaker and add 100 mL of deionized water. Stir continuously with a magnetic stirrer for 1 hour to ensure uniform mixing of Al and Mg ions. Then add urea and 100 mL of deionized water, and stir continuously with a magnetic stirrer for 2 hours to fully homogenize the precursor solution, obtaining the precursor solution. Transfer the precursor solution to a 500 mL polytetrafluoroethylene-lined container and seal it in a 316L stainless steel high-pressure reactor. Perform a hydrothermal reaction at 150°C for 14 hours. After the reaction, allow it to cool naturally to room temperature and then let it stand for 6 hours to promote uniform growth of crystal nuclei.

[0055] After vacuum filtration, the reaction products were washed multiple times with deionized water to remove residual impurities. The filter cake was transferred to a petri dish and dried in an oven at 100°C for 24 hours. Subsequently, the dried solid was ground into a uniform powder using a ball mill and transferred to a silicon carbide (SiC) crucible. The powder was then calcined in a muffle furnace at a heating rate of 2°C / min to 700°C and held at that temperature for 6 hours. Finally, the furnace was allowed to cool naturally to room temperature to obtain a high-purity MgAl2O4 support.

[0056] Comparative Example 1 (molar ratio CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O = 4.5:2:1)

[0057] Accurately weigh 1.9192 g of urea (CO(NH2)2), 5.3276 g of Al(NO3)3·9H2O, and 1.5228 g of Mg(CH3COO)2·4H2O. First, transfer Al(NO3)3·9H2O and Mg(CH3COO)2·4H2O to a beaker and add 100 mL of deionized water. Stir continuously with a magnetic stirrer for 1 hour to ensure uniform mixing of Al and Mg ions. Then add urea and 100 mL of deionized water, and stir continuously with a magnetic stirrer for 2 hours to fully homogenize the precursor solution, obtaining the precursor solution. Transfer the precursor solution to a 500 mL polytetrafluoroethylene-lined reactor and seal it in a 316L stainless steel high-pressure reactor. Perform a hydrothermal reaction at 150°C for 14 hours. After the reaction, allow it to cool naturally to room temperature, and then let it stand for 6 hours to promote uniform growth of crystal nuclei.

[0058] After vacuum filtration, the reaction products were washed multiple times with deionized water to remove residual impurities. The filter cake was transferred to a petri dish and dried in an oven at 100°C for 24 hours. Subsequently, the dried solid was ground into a uniform powder using a ball mill and transferred to a silicon carbide (SiC) crucible. The powder was then calcined in a muffle furnace at a heating rate of 2°C / min to 700°C and held at that temperature for 6 hours. Finally, the furnace was allowed to cool naturally to room temperature to obtain a high-purity MgAl2O4 support.

[0059] Comparative Example 2

[0060] The molar ratios CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O were adjusted to 8:2:1, 6:2:1, 5.5:2:1, 5:2:1, 4:2:1, 3.5:2:1, and 3:2:1, respectively, while the rest remained the same as in Comparative Example 1.

[0061] Comparative Example 3

[0062] The molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA was adjusted to 4:2:1:1, and the rest was the same as in Example 1.

[0063] Comparative Example 4 (molar ratio CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA=4.5:2:1:0.5)

[0064] Accurately weigh 1.9192 g of urea, 5.3276 g of Al(NO3)3·9H2O, 1.5228 g of Mg(CH3COO)2·4H2O, and 1.7292 g of PDDA solution. First, transfer the Al(NO3)3·9H2O, Mg(CH3COO)2·4H2O, and PDDA solution to a beaker and add 100 mL of deionized water. Stir continuously with a magnetic stirrer for 1 hour to ensure uniform mixing of Al and Mg ions. Then add urea and 100 mL of deionized water, and stir continuously with a magnetic stirrer for 2 hours to fully homogenize the precursor solution, obtaining the precursor solution. Transfer the precursor solution to a 500 mL polytetrafluoroethylene-lined container and seal it in a 316L stainless steel high-pressure reactor. Perform a hydrothermal reaction at 150°C for 14 hours. After the reaction, allow it to cool naturally to room temperature and then let it stand for 6 hours to promote uniform growth of crystal nuclei.

[0065] After vacuum filtration, the reaction products were washed multiple times with deionized water to remove residual impurities. The filter cake was transferred to a petri dish and dried in an oven at 100°C for 24 hours. Subsequently, the dried solid was ground into a uniform powder using a ball mill and transferred to a silicon carbide (SiC) crucible. The powder was then calcined in a muffle furnace at a heating rate of 2°C / min to 700°C and held at that temperature for 6 hours. Finally, the furnace was allowed to cool naturally to room temperature to obtain a high-purity MgAl2O4 support.

[0066] Comparative Example 5: Preparation of MgAl2O4 Support by Ammonia Precipitation

[0067] Accurately weigh 5.3276 g of Al(NO3)3·9H2O and 1.5228 g of Mg(CH3COO)2·4H2O, add them to 100 mL of deionized water and mix. Then, add ammonia water dropwise to the mixture to maintain the pH value at 9.5±0.2. At this time, the precipitate will continuously precipitate. After the precipitate stops precipitating after adding ammonia water, stir and continue aging for 12 h. Then, wash, filter, and dry at 120℃ for 15 h. Then, place the precursor powder in an alumina crucible, transfer it to a muffle furnace and calcine at 800℃ for 8 h. After naturally cooling to room temperature, MgAl2O4 support is obtained.

[0068] The MgAl2O4 supports prepared in the examples and comparative examples were characterized by XRD, SEM, and BET analysis, as detailed below:

[0069] XRD: The crystal form of the catalyst was determined by X-ray, 40kW, 100mA, λ=1.54178Å, test speed 1° / min, angle range 2θ=10~80°;

[0070] SEM: Field emission scanning electron microscopy was used to observe the morphological features of the catalyst's microscopic surface and compare the morphological changes of the samples before and after pressure.

[0071] BET: By quantifying the amount of monolayer adsorption, the specific surface area of ​​a material can be accurately determined.

[0072] Figure 1 The images show the XRD patterns of the MgAl2O4 supports obtained under different urea ratios in Comparative Examples 1 and 2, and the MgAl2O4 support prepared by the ammonia precipitation method in Comparative Example 5. Figure 2 The images show the XRD patterns of the MgAl2O4 supports obtained in Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 5. Figures 1-2 It can be seen that when the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O is 4.5:2:1, the MgAl2O4 spinel support structure is simple and free of other impurities (PDF#97-005-4062 2θ=19.001,31.274,36.85,38.552,44.815,49.088,55.661,59.363,65.242,68.639,69.749). As the proportion of urea increases, the diffraction peak of MgO (PDF#97-006-4930) becomes more and more obvious. This is because with the increase of urea, the pH value gradually increases, causing Al2O3 to transform into HAlO2 under high pH conditions and be washed out and filtered out. The XRD pattern of MgAl2O4 remained unchanged after the addition of the chelating agent PDDA, consistent with that before the addition.

[0073] Nitrogen adsorption tests were performed on the MgAl2O4 supports prepared in the examples and comparative examples, and the adsorption capacity was measured. The results are as follows: Figure 3 As shown, Figure 3(a) is the BET curve of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4:2:1:1; (b) is the BET curve of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:2; (c) is the BET curve of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1; and (d) is the BET curve of MgAl2O4 support obtained by ammonia precipitation. Calculations show that the specific surface area of ​​the MgAl2O4 support is 204.7800 m² when the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA is 4:2:1:1. 2 The specific surface area of ​​the MgAl2O4 support is 204.9231 m² / g when the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA is 4.5:2:1:2. 2 / g; with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1, the specific surface area of ​​the MgAl2O4 support is 215.9870 m². 2 / g; The specific surface area of ​​the MgAl2O4 support prepared by the ammonia precipitation method is 106.4563 m² / g. 2 / g, by comparison, the specific surface area of ​​MgAl2O4 prepared by the hydrothermal method is larger than that prepared by the ammonia precipitation method.

[0074] Figure 4 The images shown are SEM images of the MgAl2O4 supports prepared in the examples and comparative examples at 1 μm. Figure 4In the image, (a) is a SEM image of the MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:0.5; (b) is a SEM image of the MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:1; and (c) is a SEM image of the C... SEM images of MgAl2O4 support with a molar ratio of O(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1:2 are shown in (d); SEM image of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1 is shown in (e); SEM image of MgAl2O4 support prepared by ammonia precipitation method is shown in (e). All samples exhibit obvious spherical and plate-like morphological characteristics. The sheet-like structures are more compact when the molar ratios of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA are 4.5:2:1:1 and 4.5:2:1:2, and the most loose structure is when the molar ratio of Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O is 4.5:2:1. The structure with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:0.5 is more compact than the structure without PDDA, but not as compact as the structure with a higher PDDA concentration. The sheet-like structures of the samples prepared by the ammonia precipitation method are not obviously stacked. Figure 4 The results show that changing the concentration of the chelating agent does not alter the basic shape of the MgAl2O4 support, which primarily exhibits a combination of spherical and plate-like structures. This structural characteristic indicates that changes in the concentration of the chelating agent have no significant impact on the macroscopic morphology of the MgAl2O4 support. Under different concentrations of chelating agent, the spherical and plate-like structures of the particles are preserved, with only slight variations in particle aggregation observed in individual regions.

[0075] Figure 5 The images shown are SEM images of the MgAl2O4 supports prepared in the examples and comparative examples at 200-500 nm. Figure 5(a) is a SEM image of the MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:2; (b) is a SEM image of the MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1; (c) is a SEM image of CO(NH2)2·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1. 2. SEM images of MgAl2O4 support with a molar ratio of Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:0.5; (d) SEM image of MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1; (e) SEM image of MgAl2O4 support prepared by ammonia precipitation. It can be seen that the samples treated with different amounts of the chelating agent PDDA showed a significant increase in particle size. This may be due to the interaction between the chelating agent and metal ions, which promotes particle aggregation or grain growth, resulting in increased particle size and a more compact structure. The sample prepared by ammonia precipitation exhibits a plateau structure and a high degree of dispersion. This phenomenon indicates that the addition of the chelating agent may affect the crystallization process of MgAl2O4 material, further altering its microstructural characteristics.

[0076] The MgAl2O4 support prepared in the examples and comparative examples was used for dry reforming reaction of methane and carbon dioxide. It was tested under high temperature and high pressure for 230 h at 850 °C, 2 MPa, and a methane:carbon dioxide volume ratio of 1:1 (total gas flow rate of methane and carbon dioxide was 101 mL / min), and compared with the unaged sample.

[0077] Figure 6 The image shows a SEM image of the MgAl2O4 support after 230 hours of testing at 850℃ and 2MPa. Figure 6(a) MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:2; (b) MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:1; (c) MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:1. (d) MgAl2O4 support with a CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratio of 4.5:2:1:0.5; (e) MgAl2O4 support prepared by ammonia precipitation method. After 230 h of testing at 850 °C and 2 MPa, the morphology of the MgAl2O4 supports with CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratios of 4.5:2:1:1 and 4.5:2:1:2 did not show significant changes. Scanning electron microscopy (SEM) images showed that the particle morphology, size distribution, and overall structure of the material remained stable, with no obvious particle aggregation or morphological damage. This indicates that under the tested high-temperature and high-pressure environment, the material exhibits good structural stability after the appropriate addition of PDDA, and can resist morphological degradation or damage under long-term conditions. In contrast, the morphology of the MgAl2O4 support under CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA molar ratios of 4.5:2:1:0 and 4.5:2:1:0.5 showed significant fragmentation, while the morphology of the material obtained by ammonia precipitation was almost completely disrupted.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a MgAl204 support, characterized in that, The method comprises the following steps: mixing urea, a soluble aluminum salt, a soluble magnesium salt, polydiallyldimethylammonium chloride and water to perform a hydrothermal reaction to obtain a precipitate; a molar ratio of the urea, aluminum in the soluble aluminum salt, magnesium in the soluble magnesium salt and the polydiallyldimethylammonium chloride is 4.5:2:1:(1-2); the hydrothermal reaction is performed at a temperature of 150°C for 12-14 hours; drying and calcining the precipitate in sequence to obtain the MgAl2O4 carrier; the calcination is performed at a temperature of 680-710°C for 5.5-6 hours, and a temperature rising rate from room temperature to the calcination temperature is 2°C / min.

2. The production method according to claim 1, characterized by, The soluble aluminum salt comprises Al(NO3)3, and the soluble magnesium salt comprises Mg(CH3COO)2.

3. The preparation method according to claim 1, characterized in that, The polydiallyldimethylammonium chloride has a weight average molecular weight of 450000±50000.

4. The production method according to claim 1, characterized by, After the hydrothermal reaction, the obtained reaction liquid is cooled to room temperature and then is allowed to stand; the standing time is 3-6 hours.

5. The preparation method according to claim 1, characterized in that, The drying is performed at a temperature of 90-110°C.

6. The MgAl2O4 carrier prepared by the preparation method in any one of claims 1-5.

7. Application of the MgAl2O4 carrier in claim 6 as a catalyst carrier in a dry reforming reaction of methane and carbon dioxide.

8. Use according to claim 7, characterized in that, The dry reforming reaction of methane and carbon dioxide is performed at a temperature of 700-900°C and a pressure of 0.1-2 MPa.

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