Mullite carrier with large specific surface area and preparation method thereof

Abstract

The invention discloses a mullite carrier with a large specific surface area and a preparation method thereof. The preparation method of the mullite carrier comprises the following steps: (1) mixing silicate ester, a C1-4 alcohol solvent and water to obtain a silicon-containing solution; (2) mixing a template agent, water and aluminum salt to obtain an aluminum salt-containing solution; (3) mixing the silicon-containing solution in the step (1) with the aluminum salt-containing solution in the step (2) to obtain a mixed solution 1; (4) filtering the mixed solution 1, and drying a filter cake to obtain Al / Si xerogel; and (5) carrying out roasting treatment on the Al / Si xerogel: adopting a gradient heating form, heating from room temperature to 900-1200 DEG C for the first time, preserving heat for 10-140 minutes, heating to 1250-1500 DEG C for the second time, and preserving heat for 1-10 hours to obtain the mullite carrier. The prepared mullite carrier is good in heat resistance, large in specific surface area, simple in process and easy for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic technology and relates to a mullite support with a large specific surface area and a preparation method thereof. Background Art

[0002] Mullite (3Al 2 O 3 ·2SiO 2 ) is one of the important aluminosilicate ceramics. Due to its characteristics of high temperature resistance, low thermal expansion coefficient, high mechanical strength, excellent erosion resistance and creep resistance, it is widely used as a material for traditional and advanced ceramics in applications such as heat insulation, high-temperature filters, and sensor materials.

[0003] There is charge compensation caused by the coupled substitution of Si 4+ and Al 3+ in the mullite crystal structure. Therefore, a large number of oxygen defects (vacancies) in mullite can provide abundant anchoring sites for loading active metals. In addition, good thermal stability and a special crystal structure make mullite theoretically promising as a catalyst support. However, there is less research on mullite supports, mainly focusing on improving the mechanical properties and structure of the ceramic structure of mullite, such as heat conduction and strength.

[0004] Traditional mullite synthesis commonly uses the solid-phase sintering method. According to the theoretical chemical stoichiometric composition of mullite, alumina and silica are solid-phase diffused by high-temperature calcination (>1400 °C), and the aluminum and silicon components are recombined and crystallized to form a mullite structure. However, for the mullite material synthesized by the solid-phase sintering method, alumina and silica impurities are easily precipitated after high-temperature roasting, and the specific surface area is relatively small (5 - 20 m 2 / g). As reported in the literature (Yang Jianlin, et al. Preparation and performance study of mullite-corundum catalyst support [J]. Chinese Journal of Process Engineering, 2022, 22(01): 79-88.), mullite support was prepared by the combined acid-base method using high-aluminum fly ash as raw material. During its synthesis process, after high-temperature calcination, not only mullite crystal phase was formed, but also impurity alumina crystal phase appeared. Therefore, its thermal stability is poor. Due to the low specific surface area of mullite after high-temperature calcination, it is difficult to load a high loading of highly dispersed active metal. Therefore, in practical applications, other supports with high specific surface area need to be introduced to assist in loading the active metal. For example, Chinese invention patent CN110605114A publicly reported using mullite honeycomb ceramic support to load Pd catalyst. During its preparation process, it is necessary to coat the surface of the mullite honeycomb ceramic support with high specific surface area oxides many times to load the active metal. However, during actual use, the high-temperature environment easily causes the phase transformation (γ-alumina transforms to θ-alumina and further transforms to α-alumina) or recombination (multi-component oxides recombine into spinel structure) of the coated oxide metal, resulting in the weakening of the interaction between the loaded active metal and the support, so that the active metal agglomerates and precipitates or volatilizes, ultimately leading to irreversible deactivation of the catalyst. Therefore, the low porosity caused by the low specific surface area limits the application of mullite as a catalyst support.

[0005] In high-temperature catalytic reaction systems such as low-carbon alkane oxidation, automotive exhaust purification, N 2 O decomposition or decomposition catalysts for non-toxic unit propellants such as AND, the actual use temperature ranges from 800°C to 1500°C. Therefore, extremely high requirements are placed on the thermal stability of the catalyst and the support. For this reason, it is necessary to develop a mullite support with a large specific surface area. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to reduce the pore collapse during the preparation of mullite, resulting in a reduction in the specific surface area of the support at high temperature, and at the same time avoid the appearance of impurity phases in the synthesized mullite, and develop a mullite support with a large specific surface area and its preparation method; this mullite support has good heat resistance, a large specific surface area, a simple preparation process, and is easy to scale up production.

[0007] The present invention solves the above technical problems through the following technical solutions.

[0008] The present invention provides a preparation method of a mullite support, which includes the following steps:

[0009] (1) Mix silicate ester, C 1-4 alcohol solvent and water to obtain a silicon-containing solution;

[0010] The silicate ester is selected from one or more of methyl silicate, ethyl silicate, propyl silicate and butyl silicate;

[0011] (2) Mix the template agent, water, and aluminum salt to obtain an aluminum salt-containing solution;

[0012] The aluminum salt is an organoaluminum salt or an inorganic aluminum salt;

[0013] The organoaluminum salt is selected from one or more of aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide, and aluminum sec-butoxide;

[0014] The inorganic aluminum salt is selected from one or more of aluminum nitrate, aluminum chloride, and aluminum sulfate;

[0015] (3) Mix the silicon-containing solution in step (1) with the aluminum salt-containing solution in step (2) to obtain a mixed solution 1;

[0016] (4) Filter the mixed solution 1, and dry the filter cake to obtain an Al / Si xerogel;

[0017] (5) Calcinate the Al / Si xerogel: In a form of gradient heating, first heat from room temperature to 900 - 1200 °C for 10 - 140 min, and then heat to 1250 - 1500 °C for 1 - 10 h to obtain a mullite support.

[0018] In a certain embodiment, in step (1), the water is pure water, deionized water, or ultrapure water; for example, deionized water.

[0019] In step (1), the mixing time of the silicon-containing solution is such that the silicon-containing solution forms a homogeneous solution. In a certain embodiment, the mixing time is 10 - 120 min, for example, 30 min.

[0020] In a certain embodiment, in step (1), the molar ratio of the silicate ester to the water is 1:(1 - 5), for example, 1:4.

[0021] In a certain embodiment, in step (1), the silicate ester and the C 1-4 molar volume ratio of the alcohol solvent is (0.5 - 2) mol / L, for example, 0.98 mol / L or 1.6 mol / L.

[0022] In a certain embodiment, in step (1), the silicate ester is methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, isopropyl orthosilicate, or butyl orthosilicate; for example, methyl orthosilicate or ethyl orthosilicate.

[0023] In a certain embodiment, in step (1), the C 1-4 alcohol solvent is methanol, ethanol, propanol, isopropanol, or butanol, for example, ethanol or butanol.

[0024] In one embodiment, in step (2), preferably, an aluminum salt is added to a mixed solution of a template agent and water to obtain a solution containing the aluminum salt after mixing.

[0025] In one embodiment, in step (2), the aluminum salt is selected from one or two of aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide, and aluminum sec-butoxide; preferably, it is aluminum isopropoxide.

[0026] In step (2), the mixing time is such that the raw materials are mixed evenly, and from the appearance, the color is uniform and there is no precipitation or stratification. In one embodiment, the mixing time is 5 - 70 min, such as 60 min.

[0027] In one embodiment, in step (2), the dosage of the template agent is 3 - 15 wt%, preferably 3 - 5 wt%, such as 3.5 wt%; wt% refers to the percentage of the mass of the template agent in the mass of the solution containing the aluminum salt.

[0028] The template agent is a conventional template agent in the art. In one embodiment, in step (2), the template agent is selected from one or more of hexadecyltrimethylammonium bromide (CTAB), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (EO 20 PO 70 EO 20 , P123), and poly(oxyethylene oxypropylene) triblock copolymer (Pluronic F-127, F127); preferably, it is CTAB, P123, or F127, such as CTAB or P123.

[0029] In one embodiment, in step (2), the molar ratio of the aluminum salt to the water is 1:(10 - 50), such as 1:20.

[0030] In one embodiment, in step (3), the molar ratio of the silicate ester in the silicon-containing solution to the aluminum salt in the solution containing the aluminum salt is 1:(2 - 10), preferably 1:(2 - 6), such as 1:3 or 1:5.

[0031] In one embodiment, step (3) is to add the silicon-containing solution of step (1) to the solution containing the aluminum salt of step (2) for mixing.

[0032] In one embodiment, in step (3), the mixing time is 9 - 48 h, such as 12 h.

[0033] In one embodiment, in step (4), the filtration is vacuum filtration.

[0034] In one embodiment, in step (4), during the filtration, it is washed with water until the pH value of the filtrate is 6.8 - 7.2, preferably 7.0 - 7.2, such as 7.0.

[0035] In one embodiment, in step (4), the drying time is until constant weight.

[0036] In one embodiment, in step (4), the drying temperature is 80 - 140 °C, such as 100 °C.

[0037] In one embodiment, in step (4), the drying method is vacuum drying.

[0038] In one embodiment, in step (5), the first temperature increase is to 950 - 1150 °C; preferably 1000 °C or 1100 °C.

[0039] In one embodiment, in step (5), the second temperature increase is to 1250 - 1450 °C, such as 1300 °C or 1400 °C.

[0040] In one embodiment, in step (5), the heat preservation time after the first temperature increase is 20 - 130 min, such as 30 min or 120 min.

[0041] In one embodiment, in step (5), the heat preservation time after the second temperature increase is 1 - 9 h, such as 2 h or 8 h.

[0042] In one embodiment, in step (5), the temperature increase is carried out under flowing gas, and the gas is preferably air, and more preferably high-purity air.

[0043] In one embodiment, in step (5), the flow rate of the air is 400 - 800 mL / min, such as 600 mL / min.

[0044] In one embodiment, in step (5), the air is heated at a heating rate of 4 - 6 °C / min, such as a heating rate of 5 °C / min.

[0045] In one embodiment, in step (5), after the second heat preservation is completed, it is cooled to obtain mullite, and the cooling method is preferably natural cooling.

[0046] In one embodiment, the preparation method includes the following steps:

[0047] (1) Mix a silicate ester, C 1-4 an alcohol solvent and water to obtain a silicon-containing solution;

[0048] The silicate ester is methyl orthosilicate or ethyl orthosilicate;

[0049] (2) Mix the template agent, water and aluminum salt to obtain an aluminum salt-containing solution;

[0050] The aluminum salt is aluminum isopropoxide;

[0051] (3) Mix the silicon-containing solution in step (1) with the aluminum salt-containing solution in step (2) to obtain mixed solution 1;

[0052] (4) Filter the mixed solution 1, wash it with water until the pH value of the filtrate is neutral to obtain an Al / Si wet gel; dry the Al / Si wet gel to constant weight to obtain an Al / Si dry gel;

[0053] (5) Under an air atmosphere, perform a calcination treatment on the Al / Si dry gel: in a form of gradient heating, first heat from room temperature to 1000 - 1100 °C for 30 - 120 min, then heat to 1300 - 1400 °C for 2 - 8 h, and obtain a mullite support after cooling.

[0054] In a certain embodiment, in the preparation method, the materials are composed of the silicate ester as described above, C 1-4 alcohol solvent, the template agent as described above, the aluminum salt as described above and water.

[0055] In a certain embodiment, the preparation method comprises the following steps:

[0056] (1) Mix the silicate ester, C 1-4 alcohol solvent and water to obtain a silicon-containing solution;

[0057] The silicate ester is methyl orthosilicate or ethyl orthosilicate;

[0058] (2) Mix the template agent, water and aluminum salt to obtain an aluminum salt-containing solution;

[0059] The aluminum salt is aluminum isopropoxide;

[0060] (3) Mix the silicon-containing solution in step (1) with the aluminum salt-containing solution in step (2) to obtain mixed solution 1;

[0061] (4) Filter the mixed solution 1, wash it with water until the pH value of the filtrate is neutral to obtain an Al / Si wet gel; dry the Al / Si wet gel to constant weight to obtain an Al / Si dry gel;

[0062] (5) Under an air atmosphere, the Al / Si xerogel is calcined: in a form of gradient heating, it is first heated from room temperature to 1000 - 1100 °C and held for 30 - 120 min, then heated to 1300 - 1400 °C and held for 2 - 8 h, and a mullite support is obtained after cooling.

[0063] The present invention also provides a mullite support prepared by the above preparation method.

[0064] In a certain embodiment, the molar ratio of Al to Si of the mullite support is (2 - 10):1, preferably (2 - 6):1, such as 3:1 or 5:1.

[0065] In a certain embodiment, the specific surface area of the mullite support is 40 - 60 m 2 / g, such as 44.2 m 2 / g, 45 m 2 / g or 53 m 2 / g.

[0066] The present invention also provides a mullite support with a molar ratio of Al to Si of (2 - 10):1 and a specific surface area of 40 - 60 m 2 / g.

[0067] In a certain embodiment, the molar ratio of Al to Si of the mullite support is (2 - 6):1, such as 3:1 or 5:1.

[0068] In a certain embodiment, the specific surface area of the mullite support is 44.2 m 2 / g, 45 m 2 / g or 53 m 2 / g.

[0069] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be arbitrarily combined to obtain various preferred examples of the present invention.

[0070] The reagents and raw materials used in the present invention are all commercially available.

[0071] The positive and progressive effects of the present invention are as follows: the present invention utilizes the sol - gel combined with template agent assisted pore - forming method, and through the hydrolysis process of aluminum isopropoxide and tetraalkyl orthosilicate precursors, Al(OH) 3 and Si(OH) 4Species polymerization and polycondensation reactions crosslink it into silicon-aluminum species, and at the same time self-assemble with the template agent in the system to form a mullite precursor. During the calcination process, the template agent is demolded to form pores, and at the same time, the pore collapse in the mullite precursor is delayed. Finally, a mesoporous mullite support with a high specific surface area and thermal stability is synthesized. The prepared mullite support has good heat resistance, a simple process, is easy to scale up, and can be prepared in kilograms in batches. It can be used as a heat-resistant catalyst support for loading high-load active metals. It broadens the application prospects of mullite and lays a good foundation for the application of mullite as a catalyst support. Description of the Drawings

[0072] Figure 1 XRD patterns of mullite for Example 1 and Test Example 1

[0073] Figure 2 Nitrogen adsorption-desorption isotherms of mullite for Example 1 and Test Example 1

[0074] Figure 3 XRD patterns of mullite for Example 2 and Test Example 2

[0075] Figure 4 Nitrogen adsorption-desorption isotherm diagrams of mullite for Example 2 and Test Example 2

[0076] Figure 5 XRD patterns of mullite for Example 3 and Test Example 3

[0077] Figure 6 Nitrogen adsorption-desorption isotherm diagrams of mullite for Example 3 and Test Example 3 Detailed Description of the Invention

[0078] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions in the following examples are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0079] Example 1

[0080] Dissolve 17 g of tetraethyl orthosilicate (TEOS) and 5.8 g of deionized water in 50 ml of anhydrous ethanol solution and stir magnetically for 30 min. According to the molar ratio of Al to Si being 3, weigh 50 g of aluminum isopropoxide (AIP) powder, and in a 250 mL beaker according to AIP:H 2O = 1:20 (molar ratio). Weigh 88.23 g of deionized water and then weigh 5 g of cetyltrimethylammonium bromide (CTAB). After mixing CTAB and deionized water evenly and stirring for 1 h, mix the weighed AIP with the CTAB aqueous solution. At the same time, slowly drip the evenly stirred TEOS / ethanol / aqueous solution into the AIP / CTAB aqueous solution through a constant pressure funnel while magnetically stirring, and keep magnetic stirring for 12 h.

[0081] Use a Buchner funnel to carry out vacuum filtration on the wet gel, wash it with deionized water until the filtrate is neutral (pH = 7), then place it in a petri dish for vacuum drying, and vacuum dry at 100 °C until constant weight to obtain a dry gel. Put the dried dry gel into a corundum crucible, in the furnace tube of a high-temperature furnace, pass high-purity air with a flow rate of 600 mL / min, and the calcination program is heated at 5 °C / min, rising from room temperature to 1000 °C and holding for 30 min, then rising from 1000 °C to 1300 °C and holding for 120 min, and naturally cool down after the calcination ends to obtain mullite. Figure 1 It is the XRD pattern of mullite, which shows a high-purity mullite structure; Figure 2 For mullite N 2 isothermal adsorption and desorption curve graph. The specific surface area of the synthesized mullite support is 45 m 2 / g, Figure 2 showing a typical H3-type hysteresis loop. The addition of the template agent improves the porosity of mullite.

[0082] Example 2

[0083] Dissolve 17 g of TEOS and 5.8 g of deionized water in 50 ml of anhydrous ethanol solution and magnetically stir for 30 min. According to the molar ratio of Al to Si being 3, weigh 50 g of AIP powder. In a 250 mL beaker, according to AIP:H 2 O = 1:20 (molar ratio), weigh 88.23 g of deionized water, mix 5 g of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (P123) with deionized water evenly and stir for 1 h, then mix the weighed AIP with the P123 aqueous solution. At the same time, drip the evenly stirred TEOS / ethanol / aqueous solution into the AIP / P123 aqueous solution through a constant pressure funnel while magnetically stirring, and keep magnetic stirring for 12 h.

[0084] Use a Buchner funnel to carry out vacuum filtration on the wet gel, wash it with deionized water until the filtrate is neutral, then place it in a petri dish for vacuum drying, and vacuum dry at 100 °C until constant weight. Put the dried dry gel into a corundum crucible, in the furnace tube of a high-temperature furnace, pass high-purity air with a flow rate of 600 mL / min, and the calcination program is heated at 5 °C / min, rising from room temperature to 1000 °C and holding for 30 min, then rising from 1000 °C to 1300 °C and holding for 120 min, and naturally cool down after the calcination ends. Figure 3XRD pattern of mullite, showing a high-purity mullite structure; Figure 4 For mullite N 2 isothermal adsorption and desorption curve. The specific surface area of the synthesized mullite support is 53 m 2 / g, showing a typical H3-type hysteresis loop mesoporous structure.

[0085] Example 3

[0086] Dissolve 7.45 g of methyl orthosilicate and 3.53 g of deionized water in 50 ml of butanol solution and stir magnetically for 30 min. According to the molar ratio of Al to Si being 5, weigh 50 g of AIP powder. In a 250 mL beaker, according to AIP:H 2 O = 1:20 (molar ratio), weigh 88.23 g of deionized water. Mix 5 g of cetyltrimethylammonium bromide (CTAB) with deionized water and stir evenly for 1 h, then mix the weighed AIP with the CTAB aqueous solution. At the same time, slowly drip the evenly stirred TEOS / butanol / water solution into the AIP / CTAB aqueous solution through a constant pressure funnel and stir magnetically, maintaining magnetic stirring for 12 h. Filter the wet gel under reduced pressure using a Buchner funnel, wash it with deionized water until the filtrate is neutral, then place it in a petri dish and dry it in vacuo at 100 °C until constant weight. Take the dried gel after drying and put it into a corundum crucible. Pass high-purity air into the furnace tube of the high-temperature furnace at a flow rate of 600 mL / min. The calcination program is to increase the temperature at 5 °C / min, rise from room temperature to 1100 °C and hold for 120 min, then rise from 1100 °C to 1400 °C and hold for 8 hours. After the calcination is completed, let it cool naturally. Figure 5 XRD pattern of mullite, showing a high-purity mullite structure. Figure 6 For mullite N 2 isothermal adsorption and desorption curve. The specific surface area of the synthesized mullite support is 42 m 2 / g, showing a mesoporous hysteresis loop.

[0087] Test Example 1

[0088] Conduct a high-temperature assessment on the mullite support after calcination in Example 1, that is, re-calcine the calcined sample in a tubular furnace at 1300 °C for 6 h. As shown in the XRD spectrum of Figure 1 , no precipitation phases of alumina and silica are seen in the mullite structure. Additionally, as shown in Figure 2 , its BET specific surface area is 41.2 m 2 / g, maintaining a porous structure. The loss of specific surface area is 3.8 m 2 / g. Therefore, the synthesized mullite support has good thermal stability.

[0089] Test Example 2

[0090] The calcined mullite support of Example 2 was subjected to high-temperature assessment, that is, the calcined sample was re-calcined in a tubular furnace at 1300 °C for 6 h. As Figure 3 shown in the XRD pattern, no precipitation phases of alumina and silica were observed in the mullite structure. Additionally, as Figure 4 shown, its BET specific surface area was 47.7 m 2 / g, maintaining a porous structure, and the specific surface area loss rate was 5.3 m 2 / g. Therefore, the synthesized mullite support has good thermal stability.

[0091] Test Example 3

[0092] The calcined mullite support of Example 3 was subjected to high-temperature assessment, that is, the calcined sample was re-calcined in a tubular furnace at 1400 °C for 6 h. As Figure 5 shown in the XRD pattern, no precipitation phases of alumina and silica were observed in the mullite structure. Additionally, as Figure 6 shown, its BET specific surface area was 37.4 m 2 / g, maintaining a porous structure, and the specific surface area loss rate was 4.6 m 2 / g. Therefore, the synthesized mullite support has good thermal stability.

Claims

1. A method for preparing a mullite carrier, characterized in that: It includes the following steps: (1) Silicate, C 1-4 An alcohol solvent and water are mixed to obtain a silicon-containing solution; The silicate is selected from one or more of methyl silicate, ethyl silicate, propyl silicate and butyl silicate; (2) mixing a template, water and an aluminum salt to obtain an aluminum salt solution; The aluminum salt is an organic alcohol aluminum salt or an inorganic aluminum salt; The organic alcohol aluminum salt is selected from one or more of aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide and aluminum sec-butoxide; The inorganic aluminum salt is selected from one or more of aluminum nitrate, aluminum chloride and aluminum sulfate; (3) mixing the silicon-containing solution in step (1) with the aluminum salt solution in step (2) to obtain a mixed solution 1; (4) filtering the mixed solution 1 and drying the filter cake to obtain an Al / Si dry gel; (5) Calcination of the Al / Si dry gel: using a gradient heating method, the temperature is first increased from room temperature to 900-1200°C, and kept at this temperature for 10-140 minutes, and then the temperature is increased to 1250-1500°C for a second time, and kept at this temperature for 1-10 hours to obtain a mullite carrier.

2. The preparation method according to claim 1, characterized in that: It meets one or more of the following conditions: (1) In step (1), the water is pure water, deionized water or ultrapure water; (2) In step (1), the mixing time of the silicon-containing solution is sufficient to form a homogeneous solution; (3) In step (1), the molar ratio of the silicate to the water is 1:(1-5); (4) In step (1), the silicate and the C 1-4 The molar volume ratio of alcohol solvent is (0.5-2) mol / L; (5) In step (1), the silicate is methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, isopropyl orthosilicate or butyl orthosilicate; (6) In step (1), the C 1-4 The alcohol solvent is methanol, ethanol, propanol, isopropanol or butanol; (7) In step (2), an aluminum salt is added to a mixed solution of a template and water to obtain an aluminum salt solution; (8) In step (2), the aluminum salt is one or two selected from aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide and aluminum sec-butoxide; (9) In step (2), the mixing time is 5-70 min; (10) In step (2), the amount of the template agent used is 3-15 wt %; wt % refers to the percentage of the mass of the template agent to the mass of the aluminum salt solution; (11) In step (2), the template is selected from one or more of hexadecyltrimethylammonium bromide, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer and polyoxyethylene polyoxypropylene ether triblock copolymer; (12) In step (2), the molar ratio of the aluminum salt to the water is 1:(10-50); (13) In step (3), the molar ratio of the silicate in the silicon-containing solution to the aluminum salt in the aluminum salt-containing solution is 1:(2-10); (14) Step (3) is to add the silicon-containing solution of step (1) to the aluminum salt solution of step (2) and mix them; (15) In step (3), the mixing time is 9-48 hours; (16) In step (4), the filtration is vacuum filtration; (17) In step (4), during the filtration, the filtrate is washed with water until the pH value of the filtrate is 6.8-7.2; (18) In step (4), the drying time is until constant weight is reached; (19) In step (4), the drying temperature is 80-140°C; (20) In step (4), the drying method is vacuum drying; (21) In step (5), the first heating is to 950-1150° C.; (22) In step (5), the second heating is to 1250-1450°C; (23) In step (5), the holding time after the first heating is 20-130 min; (24) In step (5), the holding time after the second heating is 1-9 hours; (25) In step (5), the heating is carried out under flowing gas; (26) In step (5), after the second heat preservation is completed, the temperature is lowered to obtain mullite.

3. The preparation method according to claim 2, characterized in that: It meets one or more of the following conditions: (1) In step (1), the water is deionized water; (2) In step (1), the mixing time is 10-120 min; (3) In step (1), the molar ratio of the silicate to the water is 1:4; (4) In step (1), the silicate and the C 1-4 The molar volume ratio of the alcohol solvent is 0.98 mol / L or 1.6 mol / L; (5) In step (1), the silicate is methyl orthosilicate or ethyl orthosilicate; (6) In step (1), the C 1-4 The alcohol solvent is ethanol or butanol; (7) In step (2), the aluminum salt is aluminum isopropoxide; (8) In step (2), the mixing time is 60 min; (9) In step (2), the amount of the template is 3-5wt%; (10) In step (2), the template is CTAB, P123 or F127; (11) In step (2), the molar ratio of the aluminum salt to the water is 1:20; (12) In step (3), the molar ratio of the silicate in the silicon-containing solution to the aluminum salt in the aluminum salt-containing solution is 1:(2-6); (13) In step (3), the mixing time is 12 hours; (14) In step (4), during the filtration, the filtrate is washed with water until the pH value of the filtrate is 7.0-7.2; (15) In step (4), the drying temperature is 100°C; (16) In step (5), the first heating is to 1000° C. or 1100° C.; (17) In step (5), the second heating is to 1300° C. or 1400° C.; (18) In step (5), the first heating time is 30 min or 120 min; (19) In step (5), the second heating time is 2 h or 8 h; (20) In step (5), the heating is carried out under air; (21) In step (5), the cooling method is natural cooling.

4. The preparation method according to claim 3, characterized in that: It meets one or more of the following conditions: (1) In step (1), the mixing time is 30 min; (2) In step (2), the amount of the template is 3.5wt%; (3) In step (2), the template is CTAB or P123; (4) In step (3), the molar ratio of the silicate in the silicon-containing solution to the aluminum salt in the aluminum salt-containing solution is 1:3 or 1:5; (5) In step (4), during the filtration, washing with water until the pH value of the filtrate reaches 7.0; (6) In step (5), the heating is carried out under high-purity air; (7) In step (5), the air flow rate is 400-800 mL / min; (8) In step (5), the air is heated at a rate of 4-6°C / min.

5. The preparation method according to claim 4, characterized in that: It meets one or more of the following conditions: (1) In step (5), the air flow rate is 600 mL / min; (2) In step (5), the air is heated at a heating rate of 5°C / min; (3) In the preparation method described above, the material is composed of the silicate, the C 1-4 The invention comprises an alcohol solvent, the template agent, the aluminum salt and water.

6. The preparation method according to any one of claims 1 to 5, characterized in that: It includes the following steps: (1) Silicate, C 1-4 An alcohol solvent and water are mixed to obtain a silicon-containing solution; The silicate is methyl silicate or ethyl silicate; (2) mixing a template, water and an aluminum salt to obtain an aluminum salt solution; The aluminum salt is aluminum isopropoxide; (3) mixing the silicon-containing solution in step (1) with the aluminum salt solution in step (2) to obtain a mixed solution 1; (4) filtering the mixed solution 1, and washing with water until the pH value of the filtrate is neutral, to obtain an Al / Si wet gel; The Al / Si wet gel is dried to a constant weight to obtain the Al / Si dry gel; (5) Calcination of the Al / Si dry gel in an air atmosphere: using a gradient heating method, the temperature is first increased from room temperature to 1000-1100°C, and kept at this temperature for 30-120 min. The temperature is then increased to 1300-1400°C for a second time, and kept at this temperature for 2-8 h. After cooling, a mullite carrier is obtained.

7. The preparation method according to claim 6, characterized in that: It consists of the following steps: (1) Silicate, C 1-4 An alcohol solvent and water are mixed to obtain a silicon-containing solution; The silicate is methyl silicate or ethyl silicate; (2) mixing a template, water and an aluminum salt to obtain an aluminum salt solution; The aluminum salt is aluminum isopropoxide; (3) mixing the silicon-containing solution in step (1) with the aluminum salt solution in step (2) to obtain a mixed solution 1; (4) filtering the mixed solution 1, washing with water until the pH value of the filtrate is neutral, and obtaining an Al / Si wet gel; and drying the Al / Si wet gel to a constant weight to obtain an Al / Si dry gel; (5) Calcination of the Al / Si dry gel in an air atmosphere: using a gradient heating method, the temperature is first increased from room temperature to 1000-1100°C, and kept at this temperature for 30-120 min. The temperature is then increased to 1300-1400°C for a second time, and kept at this temperature for 2-8 h. After cooling, a mullite carrier is obtained.

8. A mullite carrier prepared by the preparation method according to any one of claims 1 to 7.

9. The mullite carrier according to claim 8, characterized in that: It meets one or both of the following conditions: (1) The molar ratio of Al to Si in the mullite carrier is (2-10):1, preferably (2-6):1, for example 3:1 or 5:1; (2) The specific surface area of ​​the mullite carrier is 40-60m 2 / g, for example 44.2 m 2 / g, 45 m 2 / g or 53 m 2 / g.

10. A mullite carrier, characterized in that: The molar ratio of Al to Si is (2-10):1, and its specific surface area is 40-60m 2 / g; Preferably, it satisfies one or both of the following conditions: (1) The molar ratio of Al to Si in the mullite carrier is (2-6):1, for example, 3:1 or 5:1; (2) The specific surface area of ​​the mullite carrier is 44.2 m 2 / g, 45 m 2 / g or 53 m 2 / g.

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