MgAl2O4 carrier as well as preparation method and application thereof

Abstract

The invention provides an MgAl2O4 carrier as well as a preparation method and application thereof, and relates to the technical field of catalysts. The preparation method comprises the following steps: mixing urea, soluble aluminum salt, soluble magnesium salt, polydiene dimethyl ammonium chloride and water, and carrying out a hydrothermal reaction to obtain a precipitate; the molar ratio of the urea to the aluminum element in the soluble aluminum salt to the magnesium element in the soluble magnesium salt to the polydiene dimethyl ammonium chloride is 4.5: 2: 1: (1-2); and sequentially drying and calcining the precipitate, so as to obtain the MgAl2O4 carrier. The prepared MgAl2O4 carrier is used as a catalyst carrier to be used in a high-temperature and high-pressure methane and carbon dioxide dry reforming reaction, excellent stability is shown, and the MgAl2O4 carrier is evaluated for 230 h under the high-temperature and high-pressure conditions of 850 DEG C and 2 MPa, has no obvious difference in morphology before and after the reaction, has small change in specific surface area, and shows excellent mechanical strength and chemical stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a MgAl2O4 carrier, a preparation method and application thereof. BACKGROUND

[0002] Methane-carbon dioxide reforming (dry reforming, DRM) technology is to produce synthesis gas (CO and H2) by using two kinds of greenhouse gases, methane and carbon dioxide, as raw materials. The synthesis gas can be further used for the production of low molecular alcohols and ethers. DRM technology effectively reduces the emission of greenhouse gases and provides a new idea for the clean production of hydrogen.

[0003] The methane-carbon dioxide reforming reaction is an endothermic reaction, which usually needs to be carried out under high temperature and high pressure (such as 850℃, 2MPa). With the increase of pressure, the stability, thermal stability and carbon deposition resistance of the catalyst become key problems to be solved. The commonly used catalyst carriers include Al2O3, SiO2, TiO2, ZrO2, activated carbon, carbon nanotubes and molecular sieves, etc. Although these materials have certain catalytic activity in the reaction, they usually face the problems of carbon deposition accumulation and poor thermal stability, which makes the service life of the catalyst shorter.

[0004] Magnesium aluminate spinel (MgAl2O4) as a catalyst carrier has excellent thermal stability and carbon deposition resistance, which meets the conditions of high temperature and high pressure of DRM reaction. MgAl2O4 also has a large specific surface area and a suitable pore structure, which can effectively load active metal Ni and improve the dispersion of the catalyst, showing high catalytic activity. Compared with traditional catalysts such as MgO and Al2O3, it has better structural stability and will not react with quartz tube (SiO2) to cause impure mixed gas.

[0005] At present, the industrial synthesis method of MgAl2O4 carrier is mainly ammonia precipitation method. The ammonia precipitation method has low cost and simple operation, but its shortcomings are also obvious. The structure of magnesium aluminate spinel synthesized by ammonia precipitation is difficult to control, and the stability is poor, which affects the catalytic performance. The hydrothermal method promotes the formation of metal hydroxide by using water as a solvent in a sealed container. The main advantage of the hydrothermal method is that it can react under mild conditions, so that the structure of the obtained magnesium aluminate spinel is controllable, the particle size is uniform, and a more stable and higher performance catalyst can be obtained. However, the stability of the MgAl2O4 carrier synthesized by the hydrothermal method in the methane-carbon dioxide reforming reaction under high temperature and high pressure still needs to be improved. SUMMARY

[0006] Therefore, the application aims to provide a MgAl2O4 carrier, a preparation method and application thereof.

[0007] In order to achieve the above-mentioned application purposes, the application provides the following technical solutions. The application provides a preparation method of a MgAl2O4 carrier, comprising the following steps. Urea, a soluble aluminum salt, a soluble magnesium salt, polydiene dimethyl ammonium chloride and water are mixed to perform a hydrothermal reaction to obtain a precipitate; the molar ratio of the urea, aluminum in the soluble aluminum salt, magnesium in the soluble magnesium salt and polydiene dimethyl ammonium chloride is 4.5:2:1:(1-2); The precipitate is sequentially dried and calcined to obtain the MgAl2O4 carrier.

[0008] Preferably, the soluble aluminum salt comprises Al(NO3)3, and the soluble magnesium salt comprises Mg(CH3COO)2.

[0009] Preferably, the weight average molecular weight of the polydiene dimethyl ammonium chloride is 450000±50000.

[0010] Preferably, the temperature of the hydrothermal reaction is 120-150℃, and the time is 12-14h.

[0011] Preferably, after the hydrothermal reaction, the obtained reaction liquid is cooled to room temperature and then is allowed to stand; the standing time is 3-6h.

[0012] Preferably, the temperature of the drying is 90-110℃.

[0013] Preferably, the temperature of the calcination is 680-710℃, the holding time is 5.5-6h, and the temperature rising rate from room temperature to the temperature of the calcination is 2℃ / min.

[0014] The application provides a MgAl2O4 carrier prepared by the preparation method.

[0015] The application provides an application of the MgAl2O4 carrier as a catalyst carrier in a dry reforming reaction of methane and carbon dioxide.

[0016] Preferably, the temperature of the dry reforming reaction of methane and carbon dioxide is 700-900℃, and the pressure is 0.1-2MPa.

[0017] The application provides a preparation method of a MgAl2O4 carrier, comprising the following steps: mixing urea, a soluble aluminum salt, a soluble magnesium salt, polydiallyldimethylammonium chloride and water to perform a hydrothermal reaction, so as to obtain a precipitate; the molar ratio of the urea, aluminum in the soluble aluminum salt, magnesium in the soluble magnesium salt and polydiallyldimethylammonium chloride is 4.5:2:1:(1-2); and the precipitate is sequentially dried and calcined, so as to obtain the MgAl2O4 carrier. The MgAl2O4 carrier is prepared by using a hydrothermal method, and polydiallyldimethylammonium chloride is introduced into the reaction system, which can be combined with aluminum and magnesium metal ions as a high-molecular chelating agent, a large molecular chain of which forms a physical barrier around the ions, so that the dispersity of aluminum and magnesium ions in a precursor solution is improved, the mutual approaching and agglomeration of the ions in the precipitation process are effectively inhibited, and the precursor is promoted to form uniform and fine particles; in the subsequent hydrothermal reaction process, the polydiallyldimethylammonium chloride guides the ordered growth of crystals, and constructs a spinel phase with a more compact structure and a more complete morphology, so that the mechanical strength of the carrier itself is significantly enhanced. The MgAl2O4 carrier prepared by the application is applied to a high-temperature and high-pressure methane and carbon dioxide dry reforming reaction as a catalyst carrier, and excellent stability is exhibited. The results of the examples show that, for a methane-carbon dioxide reforming reaction, under the high-temperature and high-pressure conditions of 850 DEG C and 2 MPa, the MgAl2O4 carrier is evaluated for 230 h, and the morphology of the MgAl2O4 carrier before and after the reaction has no obvious difference, and the specific surface area changes little, which shows excellent mechanical strength and chemical stability, while the MgAl2O4 carrier prepared by the hydrothermal method without adding polydiallyldimethylammonium chloride has a large degree of fragmentation in the morphology. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 XRD patterns of the MgAl2O4 carriers obtained in Comparative Examples 1 and 2 with different urea ratios and the MgAl2O4 carrier prepared by the ammonia precipitation method in Comparative Example 5; Figure 2 XRD patterns of the MgAl2O4 carriers obtained in Example 1, Comparative Example 1, Comparative Example 3 and Comparative Example 5; Figure 3 BET curves of the MgAl2O4 carriers prepared in the examples and the comparative examples, Figure 3BET curves of MgAl204support prepared under the molar ratio of CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA of 4:2:1:1, (b) BET curves of MgAl204support prepared under the molar ratio of CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA of 4.5:2:1:2, (c) BET curves of MgAl204support prepared under the molar ratio of CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA of 4.5:2:1:1, (d) BET curves of MgAl204support prepared by ammonia precipitation; Figure 4 SEM images of MgAl204supports prepared for examples and comparative examples at 1 μm, Figure 4 In (a), SEM images of MgAl204supports prepared under the molar ratio of CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA of 4.5:2:1:0.5, (b) SEM images of MgAl204supports prepared under the molar ratio of CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA of 4.5:2:1:1, (c) SEM images of MgAl204supports prepared under the molar ratio of CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O of 4.5:2:1:2, (d) SEM images of MgAl204supports prepared under the molar ratio of CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O of 4.5:2:1, (e) SEM images of MgAl204supports prepared by ammonia precipitation; Figure 5 SEM images of MgAl204supports prepared for examples and comparative examples at 200-500 nm, Figure 5Fig. 1 is a SEM image of a MgAl204 carrier prepared according to the method of the present application, wherein (a) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:2; (b) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:1; (c) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:0.5; (d) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O molar ratio of 4.5:2:1; (e) corresponds to a MgAl204 carrier prepared by an ammonia precipitation method. Figure 6 Fig. 2 is a SEM image of a MgAl204 carrier after a test at 850℃, 2MPa for 230h, wherein (a) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:2; (b) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:1; (c) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:0.5; (d) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O molar ratio of 4.5:2:1; (e) corresponds to a MgAl204 carrier prepared by an ammonia precipitation method. Figure 6 Fig. 1 is a SEM image of a MgAl204 carrier prepared according to the method of the present application, wherein (a) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:2; (b) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:1; (c) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:0.5; (d) corresponds to a MgAl204 carrier with a CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O molar ratio of 4.5:2:1; (e) corresponds to a MgAl204 carrier prepared by an ammonia precipitation method. DETAILED DESCRIPTION

[0019] The present application provides a preparation method of a MgAl204 carrier, comprising the following steps: mixing urea, a soluble aluminum salt, a soluble magnesium salt, poly diallyl dimethyl ammonium chloride and water to perform a hydrothermal reaction, to obtain a precipitate; a molar ratio of the urea, aluminum element in the soluble aluminum salt, magnesium element in the soluble magnesium salt and poly diallyl dimethyl ammonium chloride is 4.5:2:1:(1~2); drying and calcining the precipitate in sequence to obtain the MgAl204 carrier.

[0020] In the present application, the raw materials involved are all commercially available in the art, unless otherwise specified.

[0021] The urea, the soluble aluminum salt, the soluble magnesium salt, the polydiallyldimethylammonium chloride and water are mixed to carry out a hydrothermal reaction to obtain a precipitate.

[0022] In the present application, the soluble aluminum salt preferably includes Al(NO3)3 (aluminum nitrate), and the soluble magnesium salt preferably includes Mg(CH3COO)2 (magnesium acetate). In the embodiments of the present application, the Al(NO3)3 is added in the form of Al(NO3)3·9H2O, and the Mg(CH3COO)2 is added in the form of Mg(CH3COO)2·4H2O. The weight average molecular weight of the polydiallyldimethylammonium chloride (PDDA, CAS: 26062-79-3) is preferably 450000±50000. In the embodiments of the present application, the polydiallyldimethylammonium chloride is added in the form of a polydiallyldimethylammonium chloride solution. The water is preferably deionized water.

[0023] In the present application, the molar ratio of the urea (‌CO(NH2)2), the aluminum element in the soluble aluminum salt, the magnesium element in the soluble magnesium salt and the polydiallyldimethylammonium 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 the urea and the water is preferably 1:(340~360), which can be 1:350. In the embodiments of the present application, the polydiallyldimethylammonium chloride is added in the form of a 20wt% aqueous solution. The molar amount of the polydiallyldimethylammonium chloride is calculated by dividing the mass of the polydiallyldimethylammonium chloride aqueous solution by the average relative molecular mass of the polydiallyldimethylammonium chloride aqueous solution, wherein the average relative molecular mass is taken as 491.06. In the embodiments of the present application, the performance of the MgAl2O4 carrier prepared under the condition that the molar ratio of the urea, the aluminum element in the soluble aluminum salt, the magnesium element in the soluble magnesium salt and the polydiallyldimethylammonium chloride is 4.5:2:1:0.5 is compared. The results show that after the methane-carbon dioxide reforming reaction under high temperature and high pressure (850℃, 2MPa, 230h), the morphology of the MgAl2O4 carrier is greatly broken, while the morphology of the MgAl2O4 carrier obtained under the condition that the molar ratio of the urea, the aluminum element in the soluble aluminum salt, the magnesium element in the soluble magnesium salt and the polydiallyldimethylammonium chloride is 4.5:2:1:(1~2) does not change obviously, showing excellent stability.

[0024] In the present application, the method for mixing the urea, the soluble aluminum salt, the soluble magnesium salt, the polydialkyldimethylammonium chloride and the water is preferably: adding the water into the soluble aluminum salt, the soluble magnesium salt and the polydialkyldimethylammonium chloride, carrying out the first stirring and mixing, adding the urea and the water into the obtained mixed solution, and carrying out the second stirring and mixing. In the present application, the time for the first stirring and mixing is preferably 1 h, and the Al and Mg ions are mixed uniformly through the first stirring and mixing; the time for the second stirring and mixing is preferably 2 h, and the solution is fully homogenized through the second stirring and mixing. In the embodiment of the present application, the mixed solution obtained by mixing the urea, the soluble aluminum salt, the soluble magnesium salt, the polydialkyldimethylammonium chloride and the water is referred to as a precursor solution.

[0025] In the present application, the temperature for the hydrothermal reaction is preferably 120-150℃, which can be 120℃, 130℃, 140℃ or 150℃, and the time is preferably 12-14 h, which can be 12 h, 13 h or 14 h. The precursor solution is preferably transferred into a polytetrafluoroethylene liner and sealed in a stainless steel high-pressure reaction kettle for the hydrothermal reaction. In the process of the hydrothermal reaction, the urea is hydrolyzed to release hydroxyl ions under heating, which combine with the aluminum and magnesium ions in the system; at the same time, the polydialkyldimethylammonium chloride acts as a structure-directing agent to control the precipitation rate and the crystal nucleation and growth, and induce the formation of a hydroxide precursor with regular morphology and uniform particle size, which lays a structural foundation for obtaining a high-performance spinel carrier by subsequent calcination.

[0026] After the hydrothermal reaction, the obtained reaction solution is preferably cooled to room temperature and then allowed to stand. The standing time is preferably 3-6 h, which can be 3 h, 4 h, 5 h or 6 h. In the present application, the standing promotes the uniform growth of the crystal nucleus.

[0027] After the standing, the reaction product after the standing is preferably subjected to solid-liquid separation and water washing in sequence to obtain the precipitate. In the present application, the solid-liquid separation can be vacuum filtration, and the water washing preferably uses deionized water for multiple times to remove residual impurities.

[0028] After obtaining the precipitate, the precipitate is subjected to drying and calcination in sequence to obtain the MgAl2O4 carrier.

[0029] In the present application, the temperature for the drying is preferably 90-110℃, which can be 100℃, and the time is preferably 24 h. The precipitate is preferably transferred into a surface dish and placed in an oven for the drying.

[0030] In the present application, the calcination temperature is preferably 680-710℃, and can be 700℃, the holding time is preferably 5.5-6h, the heating rate from room temperature to the calcination temperature is preferably 2℃ / min; the calcination is carried out in an air atmosphere. In the present application, the dried precipitate is preferably ground into uniform powder by a ball mill, and then transferred into a silicon carbide crucible for the calcination in a muffle furnace. In the process of the calcination, the residual moisture and polydiene dimethyl ammonium chloride are volatilized, decomposed and oxidized to form an initial pore structure, with the increase of the temperature, the amorphous hydroxide and salt intermediates are decomposed into active MgO and Al2O3 components, finally, through the ion interdiffusion by solid phase reaction, a long-range ordered and crystalline perfect spinel structure is successfully constructed. After the completion of the calcination, a high-purity MgAl2O4 carrier is obtained, and then the furnace is naturally cooled to room temperature.

[0031] The reaction formula involved in the preparation of the MgAl2O4 carrier in the present application is as follows: .

[0032] The present application provides the MgAl2O4 carrier prepared by the preparation method in the above technical solution.

[0033] The present application provides the application of the MgAl2O4 carrier in the above technical solution as a catalyst carrier in the dry reforming reaction of methane and carbon dioxide.

[0034] In the present application, the temperature of the dry reforming reaction of methane and carbon dioxide is preferably 700-900℃, and can be 850℃, the pressure is preferably 0.1 (i.e. normal pressure)-2MPa, and the volume ratio of methane to carbon dioxide is preferably 1:1. In the application, the MgAl2O4 carrier is loaded with Ni, and the present application does not have special requirements for the loading amount of Ni and the method of loading Ni, and the loading amount and loading method known to those skilled in the art can be used. The MgAl2O4 carrier provided in the present application shows excellent mechanical strength and chemical stability under harsh reaction conditions of high temperature and high pressure.

[0035] In order to further illustrate the present application, the MgAl2O4 carrier, the preparation method and the application thereof provided in the present application are described in detail below with examples, but they should not be understood as limiting the scope of protection of the present application.

[0036] The information of raw materials used in the examples and comparative examples is shown in Table 1.

[0037] Table 1 Information of raw materials used in the examples and comparative examples

[0038] Example 1 (molar ratio CO(NH2)2: Al(NO3)3.9H2O: Mg(CH3COO)2.4H2O: PDDA = 4.5:2:1:1) Urea 1.9192 g, Al(NO3)3.9H2O 5.3276 g, Mg(CH3COO)2.4H2O 1.5228 g, PDDA solution 3.4584 g were accurately weighed. Al(NO3)3.9H2O, Mg(CH3COO)2.4H2O, PDDA solution were first transferred to a beaker with 100 mL of deionized water, continuously stirred with a magnetic stirrer for 1 h to ensure uniform mixing of Al, Mg ions, then urea and 100 mL of deionized water were added, and the precursor solution was fully homogenized by continuously stirring with a magnetic stirrer for 2 h. The precursor solution was transferred to a 500 mL polytetrafluoroethylene liner and sealed in a 316L stainless steel high-pressure reaction kettle, and hydrothermal reaction was carried out at 150°C for 14 h. After the reaction was completed, it was naturally cooled to room temperature, and then left to stand for 6 h to promote uniform growth of the crystal nucleus.

[0039] After the reaction product was separated by vacuum filtration, it was washed several times with deionized water to remove residual impurities. The filter cake was transferred to a watch glass and dried in a 100°C oven for 24 h. Then, the dried solid was ground into a uniform powder using a ball mill and transferred to a silicon carbide (SiC) crucible. The calcination process was carried out in a muffle furnace at a heating rate of 2°C / min to 700°C and held for 6 h, and finally the furnace was naturally cooled to room temperature. A high-purity MgAl2O4 carrier was obtained.

[0040] Example 2 (molar ratio CO(NH2)2: Al(NO3)3.9H2O: Mg(CH3COO)2.4H2O: PDDA = 4.5:2:1:2) Urea 1.9192 g, Al(NO3)3.9H2O 5.3276 g, Mg(CH3COO)2.4H2O 1.5228 g, PDDA solution 3.4584 g were accurately weighed. Al(NO3)3.9H2O, Mg(CH3COO)2.4H2O, PDDA solution were first transferred to a beaker with 100 mL of deionized water, continuously stirred with a magnetic stirrer for 1 h to ensure uniform mixing of Al, Mg ions, then urea and 100 mL of deionized water were added, and the precursor solution was fully homogenized by continuously stirring with a magnetic stirrer for 2 h. The precursor solution was transferred to a 500 mL polytetrafluoroethylene liner and sealed in a 316L stainless steel high-pressure reaction kettle, and hydrothermal reaction was carried out at 150°C for 14 h. After the reaction was completed, it was naturally cooled to room temperature, and then left to stand for 6 h to promote uniform growth of the crystal nucleus.

[0041] The reaction product was separated by vacuum filtration and washed with deionized water several times to remove residual impurities. The filter cake was transferred to a surface dish and dried in a 100°C oven for 24 h. Subsequently, the dried solid was ground into a uniform powder using a ball mill and transferred to a silicon carbide (SiC) crucible. A calcination process was performed in a muffle furnace by increasing the temperature to 700°C at a rate of 2°C / min and maintaining it for 6 h, and finally, the furnace was naturally cooled to room temperature. A high-purity MgAl2O4 carrier was obtained.

[0042] Comparative Example 1 (molar ratio CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O = 4.5:2:1) Urea (CO(NH2)2) 1.9192 g, Al(NO3)3·9H2O 5.3276 g, and Mg(CH3COO)2·4H2O 1.5228 g were accurately weighed. Al(NO3)3·9H2O and Mg(CH3COO)2·4H2O were first transferred to a beaker, 100 mL of deionized water was added, and a magnetic stirrer was continuously stirred for 1 h to ensure uniform mixing of Al and Mg ions. Then, urea and 100 mL of deionized water were added, and the magnetic stirrer was continuously stirred for 2 h to fully homogenize the precursor solution. The precursor solution was transferred to a 500 mL polytetrafluoroethylene liner and sealed in a 316L stainless steel high-pressure reaction kettle. The hydrothermal reaction was carried out at 150°C for 14 h. After the reaction was completed, it was naturally cooled to room temperature, and then left to stand for 6 h to promote uniform growth of the crystal nucleus.

[0043] The reaction product was separated by vacuum filtration and washed with deionized water several times to remove residual impurities. The filter cake was transferred to a surface dish and dried in a 100°C oven for 24 h. Subsequently, the dried solid was ground into a uniform powder using a ball mill and transferred to a silicon carbide (SiC) crucible. A calcination process was performed in a muffle furnace by increasing the temperature to 700°C at a rate of 2°C / min and maintaining it for 6 h, and finally, the furnace was naturally cooled to room temperature. A high-purity MgAl2O4 carrier was obtained.

[0044] Comparative Example 2 The molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O was 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, and the rest was the same as in Comparative Example 1.

[0045] Comparative Example 3 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.

[0046] Comparative Example 4 (molar ratio CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA = 4.5:2:1:0.5) Urea 1.9192 g, Al(NO3)3·9H2O 5.3276 g, Mg(CH3COO)2·4H2O 1.5228 g, PDDA solution 1.7292 g were accurately weighed, and Al(NO3)3·9H2O, Mg(CH3COO)2·4H2O and PDDA solution were first transferred to a beaker and 100 mL of deionized water was added, and the magnetic stirrer was continuously stirred for 1 h to ensure uniform mixing of Al and Mg ions. Then urea and 100 mL of deionized water were added, and the magnetic stirrer was continuously stirred for 2 h to fully homogenize the precursor solution. The precursor solution was transferred to a 500 mL polytetrafluoroethylene liner and sealed in a 316L stainless steel high-pressure reaction kettle, and hydrothermal reaction was carried out at 150°C for 14 h. After the reaction was completed, it was naturally cooled to room temperature, and then left to stand for 6 h to promote uniform growth of the crystal nucleus.

[0047] After the reaction product was separated by vacuum filtration, it was washed several times with deionized water to remove residual impurities. The filter cake was transferred to a watch glass and dried in a 100°C oven for 24 h. Then, the dried solid was ground into a uniform powder using a ball mill and transferred to a silicon carbide (SiC) crucible. The calcination process was carried out in a muffle furnace at a heating rate of 2°C / min to 700°C and held for 6 h, and finally the furnace was cooled to room temperature naturally to obtain a high-purity MgAl2O4 carrier.

[0048] Comparative Example 5 Preparation of MgAl2O4 carrier by ammonia precipitation method Al(NO3)3·9H2O 5.3276 g and Mg(CH3COO)2·4H2O 1.5228 g were accurately weighed and added to 100 mL of deionized water. Ammonia was added dropwise to the mixture to maintain a pH of 9.5±0.2. At this time, the precipitate was continuously precipitated. After the ammonia was added, the precipitate no longer precipitated, and the stirring was continued for 12 h of aging treatment. Then, the precursor powder was washed, filtered, and dried at 120°C for 15 h. The precursor powder was then transferred to an alumina crucible and placed in a muffle furnace at 800°C for 8 h. The temperature was then allowed to cool to room temperature naturally to obtain a MgAl2O4 carrier.

[0049] The MgAl2O4 carriers prepared in the examples and comparative examples were characterized by XRD, SEM and BET analysis, as follows: XRD: X-ray was used to determine the crystal form of the catalyst, 40 kW, 100 mA, λ = 1.54178 Å, test speed 1° / min, angle range 2θ = 10-80°; SEM: Field emission scanning electron microscope was used to observe the morphology of the catalyst micro-surface and compare the morphology changes of the samples before and after pressure; BET: By quantifying the monolayer adsorption capacity, the specific surface area of the material can be accurately determined.

[0050] Figure 1 XRD patterns of MgAl2O4 supports obtained in Comparative Examples 1-2 with different urea ratios and Comparative Example 5 prepared by ammonia precipitation. Figure 2 XRD patterns of MgAl2O4 supports obtained in Example 1, Comparative Example 1, Comparative Example 3 and Comparative Example 5. From the XRD patterns of 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 has a single structure and no 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 urea ratio increases, the MgO (PDF #97-006-4930) diffraction peak becomes more and more obvious, because as the amount of urea increases, the pH gradually increases, causing Al2O3 to be washed out under high pH conditions. After adding the chelating agent PDDA, the XRD pattern of MgAl2O4 did not change and remained consistent with that without adding.

[0051] The MgAl2O4 supports prepared in the examples and comparative examples were subjected to nitrogen adsorption test to measure the adsorption capacity, and the results are shown in Figure 3 , Figure 3 In (a), the BET curve of the 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) the BET curve 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, (c) the BET curve 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, and (d) the BET curve of the MgAl2O4 support prepared by ammonia precipitation. By calculation, the specific surface area of the MgAl2O4 support with a molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4:2:1:1 is 204.7800 m2 The specific surface area of the MgAl204 support prepared under the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:2 was 204.9231 m2 / g 2 The specific surface area of the MgAl204 support prepared under the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1 was 215.9870 m2 / g 2 The specific surface area of the MgAl204 support prepared by the ammonia precipitation method was 106.4563 m2 / g 2 Compared with the specific surface area of the MgAl204 support prepared by the ammonia precipitation method, the specific surface area of the MgAl204 support prepared by the hydrothermal method was larger.

[0052] Figure 4 The SEM images of the MgAl204 supports prepared for the examples and comparative examples at 1 μm, Figure 4 In the figure, (a) is the SEM image of the MgAl204 support prepared under the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:0.5; (b) is the SEM image of the MgAl204 support prepared under the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1; (c) is the SEM image of the MgAl204 support prepared under the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1:2; (d) is the SEM image of the MgAl204 support prepared under the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1; and (e) is the SEM image of the MgAl204 support prepared by the ammonia precipitation method. All the samples exhibited obvious spherical and flaky morphological characteristics. The flaky structure was more compact under the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:1 and 4.5:2:1:2, the most loose under the molar ratio of Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O of 4.5:2:1, and the structure under the molar ratio of CO(NH2)2:Al(NO3)3·9H2O:Mg(CH3COO)2·4H2O:PDDA of 4.5:2:1:0.5 was more compact than the structure without PDDA but less compact than the structure with higher PDDA concentration, and the flaky structure of the sample prepared by the ammonia precipitation method was not obvious. Figure 4It is shown that the basic shape of MgAl2O4 support remains consistent by changing the concentration of chelating agent, mainly showing a combination of spherical and flaky structure. This structural feature shows that the concentration change of chelating agent has no significant effect on the macro-morphology of MgAl2O4 support. Under the condition of different concentrations of chelating agent, the spherical flaky structure of the particles is retained, and only the aggregation degree of the particles in the individual area is observed to be different.

[0053] Figure 5 SEM images of MgAl2O4 support prepared for examples and comparative examples under 200-500 nm, Figure 5 SEM images of MgAl2O4 support under (a) CO(NH2)2: Al(NO3)3·9H2O: Mg(CH3COO)2·4H2O: PDDA molar ratio of 4.5:2:1:2; (b) CO(NH2)2: Al(NO3)3·9H2O: Mg(CH3COO)2·4H2O: PDDA molar ratio of 4.5:2:1:1; (c) CO(NH2)2: Al(NO3)3·9H2O: Mg(CH3COO)2·4H2O: PDDA molar ratio of 4.5:2:1:0.5; (d) CO(NH2)2: Al(NO3)3·9H2O: Mg(CH3COO)2·4H2O molar ratio of 4.5:2:1; (e) SEM image of MgAl2O4 support prepared by ammonia precipitation method. It can be seen from the comparison that the samples treated with different amounts of chelating agent PDDA show obvious increase in particle size. This may be due to the interaction between the chelating agent and the metal ions, which promotes the aggregation between the particles or the growth of the crystal grains, resulting in the increase of the particle size and the more compact structure. The sample prepared by ammonia precipitation method shows a platform structure with large dispersion. This phenomenon shows that the addition of chelating agent may affect the crystallization process of MgAl2O4 material and further change its microstructure characteristics.

[0054] The MgAl2O4 support prepared in examples and comparative examples was used for dry reforming of methane and carbon dioxide, and was tested at 850℃, 2MPa, methane: carbon dioxide volume ratio of 1:1 (total gas flow of methane and carbon dioxide was 101mL / min) under high temperature and high pressure for 230h, and was compared with the un-aged sample.

[0055] Figure 6 SEM images of MgAl2O4 support after 230h test at 850℃, 2MPa, Figure 6MgAl204 support with CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:2; (b) MgAl204 support with CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:1; (c) MgAl204 support with CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:0.5; (d) MgAl204 support with CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O molar ratio of 4.5:2:1; (e) MgAl204 support prepared by ammonia precipitation method. After 230 h of testing at 850℃ and 2 MPa, the morphology of MgAl204 support with CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:1 and 4.5:2:1:2 did not change significantly. The scanning electron microscope images showed that the particle morphology, size distribution and overall structure of the material remained stable, and there was no obvious particle aggregation or morphology damage. This indicates that, under the high temperature and high pressure environment tested, the appropriate addition of PDDA shows good structural stability and can resist morphology degradation or damage under long-term conditions. The morphology of MgAl204 support with CO(NH2)2:Al(NO3)3.9H2O:Mg(CH3COO)2.4H2O:PDDA molar ratio of 4.5:2:1:0 and 4.5:2:1:0.5 was greatly broken, and the morphology of the ammonia precipitation method was almost completely broken.

[0056] The above only describes the preferred embodiments of the present application, and does not limit the present application in any form. It should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a MgAl2O4 support, characterized in that, Includes the following steps: 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); The precipitate was dried and calcined sequentially to obtain the MgAl2O4 support.

2. The preparation method according to claim 1, characterized in that, The soluble aluminum salt includes Al(NO3)3, and the soluble magnesium salt includes Mg(CH3COO)2.

3. The preparation method according to claim 1, characterized in that, The weight-average molecular weight of the polydiene dimethyl ammonium chloride is 450,000 ± 50,000.

4. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 120-150℃ for 12-14 hours.

5. The preparation method according to claim 1 or 4, characterized in that, After the hydrothermal reaction, the resulting reaction solution is cooled to room temperature and then allowed to stand for 3 to 6 hours.

6. The preparation method according to claim 1, characterized in that, The drying temperature is 90~110℃.

7. The preparation method according to claim 1, characterized in that, 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.

8. The MgAl2O4 support prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the MgAl2O4 support of claim 8 as a catalyst support in the dry reforming reaction of methane and carbon dioxide.

10. The application according to claim 9, characterized in that, The dry reforming reaction of methane and carbon dioxide is carried out at a temperature of 700~900℃ and a pressure of 0.1~2MPa.

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