Preparation method of high-performance alumina material, alumina material and application thereof

Abstract

The application discloses a preparation method of high-performance alumina material, the alumina material and application thereof, and the preparation method comprises the following steps: (1) immersing a pretreated alumina matrix in an aluminum-based inorganic salt solution; (2) calcining the immersed alumina matrix at high temperature to obtain the high-performance alumina material. In the application, the alumina matrix raw material is pretreated to remove impurities on the surface and in the pores of the matrix, then the pretreated alumina matrix is immersed in the aluminum-based inorganic salt solution, so that aluminum ions fill the atomic vacancies in the matrix, and then the aluminum-based inorganic salt permeated into the pores of the matrix is converted into aluminum-based oxide through calcination to fill the pores, so that the obtained alumina material has increased compactness and obviously improved mechanical strength. Meanwhile, small alumina particles are formed on the surface of the alumina material to form physical isolation between active sites, and reduction of catalyst performance caused by aggregation of noble metal particles at high temperature is reduced.

Description

Technical Field

[0001] This invention belongs to the technical field of alumina materials, specifically, it relates to a method for preparing high-performance alumina materials, alumina materials and their applications. Background Technology

[0002] Alumina materials possess high strength, high hardness, and good wear resistance, making them widely used as catalyst supports for aerospace catalysts and in-situ preparation of Mars propellants. However, the abundant porous structure and atomic vacancies in the alumina matrix generally result in low mechanical strength. Poor mechanical strength can lead to catalyst breakage, thus affecting the overall performance of the catalyst. Especially for aerospace catalysts used in harsh environments such as those found in operational spacecraft, the thermal stress generated by rapid heating and cooling can cause damage or even catastrophic failures. Therefore, alumina matrices with high mechanical strength and high thermal shock resistance are of great significance for the development of aerospace catalysts and catalysts for in-situ preparation of Mars propellants.

[0003] Currently, the main substances used to impregnate alumina materials are aluminum-based complexes and aluminum sols. The synthesis process of aluminum-based complexes is complex and requires specific conditions, making large-scale preparation inconvenient. Furthermore, the large size of aluminum-based complexes makes it difficult for them to penetrate the smaller pores of alumina during impregnation, resulting in a limited strength improvement. Alumina sols, on the other hand, consist of alumina nanoparticles. Due to their relatively large size, similar to aluminum-based complexes, these nanoparticles also struggle to penetrate the smaller pores of the alumina matrix, leading to a limited strength improvement in the alumina material.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing high-performance alumina materials. The method involves pretreating the alumina matrix raw material to remove impurities from the matrix surface and pores, then immersing it in an aluminum-based inorganic salt solution to allow aluminum ions to fill the atomic vacancies in the matrix. The aluminum-based inorganic salt that has penetrated into the matrix pores is then converted into aluminum-based oxides through calcination, which fill the pores and reduce the proportion of macropores. The resulting alumina material has increased density and significantly improved mechanical strength.

[0006] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a high-performance alumina material includes the following steps:

[0008] (1) The pretreated alumina matrix is ​​immersed in an aluminum-based inorganic salt solution;

[0009] (2) The impregnated alumina matrix is ​​calcined at high temperature to obtain high-performance alumina material;

[0010] Preferably, in step (1), the mass ratio of the pretreated alumina matrix to the aluminum-based inorganic salt in the aluminum-based inorganic salt solution is 1:(1-10).

[0011] Furthermore, the mass ratio of the pretreated alumina matrix to the aluminum-based inorganic salt in the aluminum-based inorganic salt solution is 1:(3-5), preferably 1:3.

[0012] In the above scheme, by reasonably setting the mass ratio of alumina matrix to aluminum-based inorganic salt, the aluminum-based inorganic salt can be more effectively filled into the pores of the matrix. If there is too little alumina matrix, the aluminum-based inorganic salt will be coated too much on the surface of the alumina matrix, covering the original active sites on the alumina surface and affecting its performance as a catalyst carrier. At the same time, it will also waste the aluminum-based inorganic salt solution and increase the cost. If there is too much alumina matrix, it will reduce the filling rate of the matrix pores and affect the improvement effect of the mechanical strength of the prepared alumina material.

[0013] Furthermore, in step (1), the pretreated alumina matrix is ​​dispersed in an aluminum-based inorganic salt solution to form a mixed solution, and the mixed solution is placed in a container to complete the impregnation of the alumina matrix in the aluminum-based inorganic salt solution.

[0014] The immersion temperature is 0–50°C, and the time is 0.1–20 h.

[0015] Preferably, the impregnation temperature is 25-35°C and the time is 2-10 hours.

[0016] More preferably, the impregnation temperature is 30°C and the time is 2 hours.

[0017] In the above scheme, the alumina matrix raw material is pretreated to remove impurities from the matrix surface and pores, preventing impurities from clogging the pores and affecting the filling rate of the pores by the subsequent aluminum-based inorganic salt; then the pretreated alumina matrix is ​​immersed in an aluminum-based inorganic salt solution, where aluminum ions fill the atomic vacancies in the matrix, and the aluminum-based inorganic salt fills the pores of the matrix, reducing the proportion of macropores.

[0018] By properly setting the impregnation temperature and time, the filling rate of aluminum-based inorganic salts in the pores can be improved. If the impregnation time is too short, the amount of aluminum-based inorganic salts entering the pores of the alumina matrix will be too small, affecting the improvement of the strength of the alumina material. If the impregnation time is too long, the aluminum-based inorganic salts will cover too much of the original surface of the alumina matrix, affecting the subsequent metal loading and thus affecting the catalytic performance.

[0019] Since the movement of aluminum ions requires a certain temperature, if the impregnation temperature is too low, the movement of aluminum ions is slow, which affects the subsequent filling of the pores in the alumina matrix by aluminum-based inorganic salts; if the temperature is too high, the movement of aluminum ions is too vigorous, which also affects the subsequent filling of the pores in the alumina matrix by aluminum-based inorganic salts, thereby affecting the improvement of the strength of the alumina material.

[0020] Furthermore, in step (2), the roasting temperature is 400-1200℃ and the time is 0.1-7h.

[0021] Preferably, the roasting temperature is 800-1200℃ and the time is 4-6 hours.

[0022] Preferably, the roasting temperature varies in a stepwise manner.

[0023] Preferably, the calcination heating rate is 10℃ / min, and the temperature is maintained at 400℃ for 2 hours, at 800℃ for 2 hours, and at 1200℃ for 2 hours.

[0024] In the above scheme, calcination at high temperature transforms the aluminum-based inorganic salts filling the matrix channels into aluminum-based oxides, improving the density and mechanical strength of the alumina material. Simultaneously, by forming small alumina particles on the surface of the alumina material from the aluminum-based inorganic salts at high temperature, the surface of the prepared alumina material becomes rougher, creating physical isolation between active sites and preventing the degradation of catalyst performance due to the aggregation of noble metal particles at high temperatures. However, if the calcination temperature is too low, it affects the transformation of the aluminum-based inorganic salts into aluminum-based oxides, thus impacting the strength of the alumina material. Conversely, if the calcination temperature is too high, it reduces the number of active sites on the alumina material surface used to stabilize metals, affecting the subsequent metal loading and consequently impacting catalytic performance.

[0025] By varying the calcination temperature in a stepwise manner and maintaining it at a suitable temperature for a period of time, it is beneficial for the transformation of aluminum-based inorganic salts into aluminum-based oxides, thereby improving the conversion rate and the stability of the transformation process.

[0026] Repeating steps (1) and (2) 1 to 6 times, preferably repeating steps (1) and (2) 3 times, can effectively improve the filling rate of aluminum-based inorganic salts in the pores of the alumina matrix, as well as the conversion rate of aluminum-based inorganic salts into aluminum-based oxides during the calcination process, thereby further improving the density and mechanical strength of the alumina material.

[0027] Furthermore, in step (1), the pretreatment includes: immersing the alumina matrix raw material in a pretreatment solution, washing it with high-purity water, and then drying it at low temperature;

[0028] Preferably, the pretreatment solution is a hydrochloric acid solution with a mass concentration of 1-36%, more preferably a hydrochloric acid solution with a mass concentration of 20-32%, and even more preferably a hydrochloric acid solution with a mass concentration of 27%.

[0029] Preferably, the soaking time is 10 to 60 minutes; the low-temperature drying temperature is 30 to 120°C, and the time is 1 to 24 hours.

[0030] In the above scheme, the pretreatment solution can be an inorganic acid or water. The inorganic acid includes hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, etc., with hydrochloric acid being preferred because it can dissolve impurities that are not soluble in water, such as small transition metal particles. Furthermore, hydrochloric acid has high volatility and can be removed by drying at 90°C. Additionally, the small amount of residual chloride ions guides the subsequent filling of aluminum-based inorganic salts into the matrix pores, effectively improving the filling rate. It also assists in the conversion of aluminum-based inorganic salts into aluminum-based oxides, increasing the conversion rate of aluminum-based inorganic salts, thereby improving the density and mechanical strength of the alumina material, exhibiting a synergistic effect. However, if the concentration of hydrochloric acid is too low, it will not effectively remove impurities; if the concentration is too high, it will damage the alumina matrix raw material.

[0031] Similarly, soaking the alumina matrix raw material in the pretreatment solution not only effectively removes impurities from the pores and surface of the alumina matrix raw material, but also facilitates the entry and uniform dispersion of residual chloride ions in the hydrochloric acid solution into the pores and on the matrix surface. This provides a good auxiliary effect for guiding aluminum-based inorganic salts to fill the matrix pores and for dispersing alumina particles on the material surface. If the soaking time is insufficient, it will not effectively remove impurities; if the soaking time is too long, it will damage the alumina matrix raw material.

[0032] This invention employs low-temperature drying to dry the pretreated alumina matrix. Low-temperature drying facilitates the slow removal of the pretreatment solution, promotes the dispersion of residual chloride ions, and further facilitates the uniform filling of aluminum-based inorganic salts into the matrix channels and the uniform dispersion of alumina particles on the material surface. This results in a uniform improvement in the overall mechanical strength of the prepared alumina material, and the uniform dispersion of the physical isolation formed between the active sites of alumina particles provides excellent isolation. Furthermore, low-temperature drying does not adversely affect the subsequent calcination process.

[0033] Furthermore, before step (1), the method further includes: stirring and dissolving the aluminum-based inorganic salt in a solvent to obtain a uniformly dispersed aluminum-based inorganic salt solution, wherein the mass ratio of the aluminum-based inorganic salt to the solvent is 1:(0.5~10);

[0034] Preferably, the temperature of the dissolution process is 0–50°C and the time is 0.1–20 h.

[0035] In the above scheme, by reasonably setting the mass ratio of aluminum-based inorganic salt to solvent, the temperature and time of the dissolution process, and by promoting the dissolution of aluminum-based inorganic salt through stirring, a fully dissolved and uniformly dispersed aluminum-based inorganic salt solution is obtained, which is beneficial to improving the subsequent impregnation effect on the alumina matrix. The setting of the dissolution temperature is the same as the impregnation temperature, which enables aluminum ions to move and better fill the pores of the alumina matrix.

[0036] Furthermore, the aluminum-based inorganic salt is selected from one or a combination of several of aluminum phosphate, aluminum nitrate, aluminum acetate, aluminum chloride, aluminum bromide, and aluminum sulfate.

[0037] The solvent is selected from one or a combination of several of the following: water, ethanol, propanol, butanol, isopropanol, and N,N-dimethylformamide.

[0038] In the above schemes, aluminum-based inorganic salts are preferably aluminum nitrate, aluminum acetate, or aluminum chloride, and more preferably aluminum chloride, because aluminum chloride and the hydrochloric acid solution of the pretreatment solution both contain chloride ions, which can play a synergistic role and have an auxiliary effect on filling the aluminum-based inorganic salt into the matrix channels and transforming the aluminum-based inorganic salt into aluminum-based oxides.

[0039] The preferred solvent is ethanol, isopropanol, or N,N-dimethylformamide, with ethanol being more preferred because ethanol is volatile, easy to process, readily available, and low in cost. Furthermore, the aluminum-based inorganic salt solution prepared with ethanol exhibits better solubility and dispersibility, which facilitates the uniform filling of the aluminum-based inorganic salt into the pores of the alumina matrix and the uniform dispersion of alumina particles on the surface of the alumina material. This results in a uniform overall improvement in the mechanical strength of the prepared alumina material, and the uniform dispersion of the physical isolation formed between the active sites by the alumina particles provides excellent isolation.

[0040] Furthermore, the alumina matrix is ​​spherical or cylindrical, with a diameter of 0.1–5 mm and a specific surface area of ​​50–300 m². 2 / g.

[0041] In the above scheme, the alumina matrix has a small size and a large specific surface area, which can fully contact the pretreatment solution, improve the dispersibility in the aluminum-based inorganic salt solution, enable the aluminum-based inorganic salt to effectively and uniformly fill the channels of the alumina matrix, and provide more active sites. Furthermore, the alumina particles loaded on the material surface form physical isolation between the active sites, preventing the reduction of catalyst performance caused by the aggregation of noble metal particles at high temperatures.

[0042] It should be noted that the pores on the alumina matrix include macropores and micropores. The aluminum-based inorganic salt fills the macropores. Therefore, the remaining micropores can increase the loading rate of noble metal active sites when the alumina material is used as a catalyst support. The increase in active sites improves the catalytic performance.

[0043] An alumina material is prepared by the method described above for preparing a high-performance alumina material, wherein the mechanical strength of the alumina material is 35-51 MPa.

[0044] An application of an alumina material, wherein the alumina material described above is used as a catalyst carrier in at least the following applications: catalyst for aerospace propellant conversion reaction, catalyst for in-situ preparation of Mars propellant, catalyst for alkane dehydrogenation reaction, catalyst for n- and para-hydrogen conversion, and catalyst for water-gas conversion reaction.

[0045] Preferably, alumina materials are used as catalyst carriers in catalysts for aerospace propellant conversion reactions or in-situ preparation of Mars propellants.

[0046] It should be noted that when the alumina material with high mechanical strength prepared in this invention is used as a catalyst carrier in the application of catalysts for aerospace propellant conversion reactions and in-situ preparation of Mars propellants, the resulting catalysts can withstand ambient temperatures as high as 800-1200℃ during application, and the catalysts can be used normally with a low breakage rate.

[0047] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0048] 1. This invention pretreats the alumina matrix with a pretreatment solution, effectively removing impurities from the matrix surface and matrix pores, preventing impurities from clogging the matrix pores, and facilitating better filling of the alumina matrix pores by subsequent aluminum-based inorganic salts.

[0049] 2. This invention effectively fills the pores of the alumina matrix by immersing it in an aluminum-based inorganic salt solution, reduces the number of atomic vacancies in the alumina matrix, increases the density of the alumina material, reduces the nucleation and propagation of micro-thermal shock cracks, and gives the resulting alumina material high mechanical strength and high-temperature thermal shock resistance.

[0050] 3. This invention modifies the pore structure of the alumina matrix with aluminum-based inorganic salts, reduces the proportion of macropores, increases the density of the alumina material, and avoids breakage caused by propellant entering the catalyst and reacting inside.

[0051] 4. This invention forms small alumina particles on the surface of alumina materials by causing aluminum-based inorganic salts at high temperatures, thereby stabilizing the loaded noble metal active sites and forming physical isolation between the active sites, preventing the reduction of catalyst performance caused by the aggregation of noble metal particles at high temperatures.

[0052] 5. This invention provides an optimization method for the mechanical strength and high-temperature thermal shock resistance of alumina materials, which solves the problems of low catalyst support strength and poor high-temperature thermal shock resistance, effectively improving the mechanical strength and high-temperature thermal shock resistance of alumina materials. At the same time, this method also has the advantages of simple operation, low cost, and easy large-scale preparation.

[0053] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0054] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0055] Figure 1 This is an SEM characterization image of sample a obtained by constant-temperature calcination of the untreated alumina matrix raw material at 500°C in this invention.

[0056] Figure 2 This is the SEM characterization image of sample b obtained by calcining the pretreated alumina matrix at 500°C in this invention.

[0057] Figure 3 This is a SEM characterization image of sample c prepared in Comparative Example 10 of the present invention;

[0058] Figure 4 This is a SEM characterization image of sample d prepared in Comparative Example 20 of the present invention;

[0059] Figure 5 These are the XRD characterization spectra of three different samples, b, c, and d, in this invention;

[0060] Figure 6 This is the BET characterization spectrum of sample b in this invention;

[0061] Figure 7 This is the BET characterization spectrum of sample c in this invention;

[0062] Figure 8 This is the BET characterization spectrum of sample d in this invention.

[0063] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below with reference to some embodiments. Those skilled in the art will understand that the following embodiments are only used to explain the technical principles of this invention and are not intended to limit the scope of protection of this invention. For example, although this application describes the steps of the method of this invention in a specific order, these orders are not restrictive. Those skilled in the art can perform the steps in different orders without departing from the basic principles of this invention.

[0065] It should be noted that:

[0066] (1) Test method for the mechanical strength of alumina materials: First, measure the particle diameter of each alumina material using vernier calipers and calculate the cross-sectional area. Second, place the alumina material vertically in a mechanical strength tester and test the maximum pressure value that each alumina material can withstand. Finally, combine the cross-sectional area of ​​each alumina material with the maximum pressure it can withstand to calculate the maximum pressure value that each alumina material can withstand. Each type of alumina material is tested twenty times. After removing the two maximum values ​​and two minimum values, the average value of the remaining sixteen tests is taken as the mechanical strength test value of that type of alumina material.

[0067] (2) Test method for the bulk density of alumina: First, weigh a certain amount of alumina material using a balance. Place the weighed alumina material into a suitable clean graduated cylinder and secure the cylinder to the base of the tapped density meter using clips. Second, turn on the power switch of the tapped density meter, set the vibration frequency, and begin vibration. After vibration, record the reading on the graduated cylinder as the volume of the alumina material. Finally, calculate the bulk density of the alumina material by combining its weight and volume. Each type of alumina material is tested ten times. The maximum and minimum values ​​are removed, and the average of the remaining eight tests is taken as the bulk density test value for that type of alumina material.

[0068] Example 1

[0069] (1) Using aluminum chloride as the aluminum-based inorganic salt and ethanol as the solvent, mix them at a mass ratio of 1:3 and stir at 30°C for 2 hours to prepare an aluminum-based inorganic salt solution.

[0070] (2) Using spherical alumina matrix particles as raw material, the alumina matrix particles have a diameter of 2 mm and a specific surface area of ​​200 m².2 / g; The matrix was placed in a 27% HCl solution and soaked at 30°C for 2 hours. After being washed with ultrapure water, it was dried in air at 120°C for 5 hours.

[0071] (3) With a mass ratio of 1:3 between the alumina matrix and the aluminum-based inorganic salt in the aluminum-based inorganic salt solution, the dried alumina matrix is ​​uniformly dispersed in the aluminum-based inorganic salt solution and impregnated. It is kept at 30°C for 2 hours, filtered, and then calcined at high temperature in a muffle furnace. The calcination conditions are: heating rate of 10°C / min, temperature kept at 400°C for 2 hours, temperature kept at 800°C for 2 hours, temperature kept at 1200°C for 2 hours. The impregnation and calcination process is repeated 3 times to obtain the alumina material.

[0072] Comparative Example 1

[0073] Based on Example 1, the aluminum-based inorganic salt solution was replaced with aluminum sol, while other conditions remained unchanged. The performance parameters of the resulting alumina material are shown in Table 1.

[0074] Experimental Example 1

[0075] This experiment tested the alumina matrix raw material and the alumina materials prepared in Example 1 and Comparative Example 1. The test results are shown in Table 1:

[0076] Table 1

[0077]

[0078] As shown in Table 1, the alumina matrix raw material was used as a blank control and was not treated in any way. In Example 1, alumina material was prepared according to the method of the present invention. The results showed that the mechanical strength and density of the alumina material prepared in the present invention were significantly improved compared with the untreated alumina matrix raw material.

[0079] This is because the alumina matrix raw material is first pretreated with a pretreatment solution, effectively removing impurities from the matrix surface and pores, preventing impurities from clogging the pores, and facilitating better filling of the pores by subsequent aluminum-based inorganic salts. The invention further utilizes aluminum ions to fill atomic vacancies in the alumina matrix by immersing the pretreated alumina matrix in an aluminum-based inorganic salt solution, reducing the number of atomic defects. Then, through calcination, the aluminum-based inorganic salts that have penetrated into the pores are transformed into aluminum-based oxides, filling the pores, reducing the proportion of macropores, increasing the density of the alumina material, and reducing the nucleation and propagation of microscopic thermal shock cracks, resulting in alumina material with superior properties. Its high mechanical strength and high-temperature thermal shock resistance, when applied to catalysts for in-situ propellant preparation, can effectively prevent breakage caused by propellants and other reactants entering the catalyst interior, thereby reducing the breakage rate of alumina materials and catalysts at high temperatures. The stepwise temperature variation during calcination, maintained at a suitable temperature for a period of time, facilitates the transformation of aluminum-based inorganic salts into aluminum-based oxides, improving the conversion rate and the stability of the transformation process. Furthermore, by forming small alumina particles on the surface of the alumina material at high temperatures, the loaded noble metal active sites are stabilized, and physical isolation is formed between the active sites, preventing the degradation of catalyst performance due to the aggregation of noble metal particles at high temperatures, thus improving the stability of catalytic performance.

[0080] However, in Comparative Example 1, aluminum sol was used to impregnate the alumina matrix. The particles of aluminum sol are alumina nanoparticles. Since the alumina nanoparticles are relatively large, they are difficult to enter the pores of the alumina matrix, resulting in an insignificant improvement in the mechanical strength of the alumina material.

[0081] Experiment Example 2

[0082] Based on Example 1, this experiment changed the mass ratio of alumina matrix to aluminum-based inorganic salt while keeping other conditions unchanged, resulting in Comparative Examples 2 to 4. The properties of the prepared alumina materials were then tested, and the test results are shown in Table 2.

[0083] Table 2

[0084]

[0085] As shown in Table 2, according to the preparation method of the alumina support in this invention, changing the mass ratio of the alumina matrix to the aluminum-based inorganic salt, when the mass ratio of the alumina matrix to the aluminum-based inorganic salt is within the range of 1:(1 to 10) defined in this invention, as the mass of the aluminum-based inorganic salt increases, the aluminum-based inorganic salt can more effectively fill the pores of the matrix, thus gradually increasing the compact strength and mechanical strength of the prepared alumina support. However, if there is too little alumina matrix, the aluminum-based inorganic salt will be coated too much on the surface of the alumina matrix, covering the original active sites on the alumina surface, affecting its performance as a catalyst support, and also wasting the aluminum-based inorganic salt solution, increasing costs. If there is too much alumina matrix, it will reduce the filling rate of the matrix pores, affecting the improvement effect on the mechanical strength of the prepared alumina material. Therefore, considering the need to ensure the performance as a catalyst support and reduce costs while enhancing mechanical strength, the preferred mass ratio of the alumina matrix to the aluminum-based inorganic salt is 1:(3 to 5), more preferably 1:3.

[0086] Experimental Example 3

[0087] Based on Example 1, this experiment changed the immersion time of the alumina matrix in the aluminum-based inorganic salt solution while keeping other conditions unchanged, resulting in Comparative Examples 5 to 8. The properties of the prepared alumina materials were then tested, and the test results are shown in Table 3.

[0088] Table 3

[0089]

[0090] In this invention, a pretreated alumina matrix is ​​immersed in an aluminum-based inorganic salt solution to allow the aluminum-based inorganic salt to enter the pores of the alumina matrix. This experiment varied the immersion time of the alumina matrix in the aluminum-based inorganic salt solution. Experimental results showed that when the immersion time was within the range of 0.1–20 h specified in this invention, the aluminum-based inorganic salt had sufficient time to fill the pores of the alumina matrix, effectively improving the density and mechanical strength of the prepared alumina material. However, if the immersion time was too short, the amount of aluminum-based inorganic salt entering the pores of the alumina matrix was too small, affecting the improvement of the alumina material's strength; if the immersion time was too long, the aluminum-based inorganic salt would excessively cover the original surface of the alumina matrix, affecting the subsequent metal loading and thus the catalytic performance. Therefore, to improve the yield while ensuring the immersion effect and the catalytic performance when prepared as a catalyst, an immersion time of 2–10 h is preferred, more preferably 2 h.

[0091] Experiment Example 4

[0092] Based on Example 1, this experiment changed the calcination conditions of the impregnated alumina material while keeping other conditions unchanged, resulting in Comparative Examples 9 to 12. The properties of the prepared modified alumina materials were then tested, and the test results are shown in Table 4.

[0093] Table 4

[0094]

[0095] In this invention, the impregnated alumina matrix is ​​calcined at high temperature to convert the aluminum-based inorganic salts that have entered the pores of the alumina matrix into aluminum-based oxides. This experiment changed the calcination conditions. The experimental results show that when the calcination temperature is within the range defined by this invention, such as Comparative Examples 9 to 11, and a constant temperature calcination method is used, the mechanical strength and bulk density of the obtained alumina material gradually increase with increasing temperature. In particular, when the calcination temperature is between 800 and 1200°C, the mechanical strength of the prepared alumina material is significantly improved compared to the alumina matrix raw material.

[0096] However, when the calcination temperature exceeds the limits of this application, if the calcination temperature is too low, it will affect the transformation of aluminum-based inorganic salts into aluminum-based oxides, thus affecting the improvement of the strength of alumina materials; if the calcination temperature is too high, it will reduce the number of active sites on the surface of alumina materials, affecting the subsequent metal loading, and thus affecting the catalytic performance.

[0097] Comparative Example 12 also employed a stepped calcination method, which, compared to isothermal calcination, is more conducive to the conversion of aluminum-based inorganic salts into aluminum-based oxides, improving the conversion rate and the stability of the conversion process. The mechanical strength and bulk density of the prepared alumina material are both improved. As can be seen from the data in the table, the mechanical strength of the alumina material prepared under the calcination conditions in Example 1 is better than that in Comparative Example 12. This is because Example 1 has more temperature steps than Comparative Example 12, and the temperature difference between each temperature step is smaller, which is more conducive to the stability of the conversion of aluminum-based inorganic salts into aluminum-based oxides.

[0098] Experimental Example 5

[0099] Based on Example 1, this experiment changed the type and concentration of the pretreatment solution while keeping other conditions unchanged, resulting in Comparative Examples 13 to 20. The properties of the prepared modified alumina materials were then tested, and the test results are shown in Table 5.

[0100] Table 5

[0101]

[0102] Comparative Example 20 served as a blank control. Based on Example 1, the untreated alumina matrix was directly immersed in an aluminum-based inorganic salt solution, with other conditions remaining unchanged. The performance parameters of the resulting alumina material are shown in Table 5. Because the alumina matrix was not pretreated, impurities blocked the pores, affecting the subsequent filling of the alumina matrix pores with aluminum-based inorganic salts. The surface impurities also seriously affected the loading rate and stability of the noble metal active sites, resulting in no significant improvement in the performance of the alumina material.

[0103] In this invention, a pretreatment solution is used to pretreat the alumina matrix to remove impurities from the matrix surface and pores, preventing impurities from clogging the pores and affecting the filling rate of the pores by the subsequent aluminum-based inorganic salts. This results in improved mechanical strength and density of the prepared alumina material. In particular, when the pretreatment solution is a hydrochloric acid solution with a mass concentration of 20-32%, the mechanical strength and density of the prepared alumina material are significantly improved. For example, in Example 1, when the pretreatment solution is a hydrochloric acid solution with a mass concentration of 27%, the mechanical strength of the prepared alumina material is greatly improved, and the improvement in density is most obvious. Furthermore, as in Examples 1 and Comparative Examples 17 to 19, when the mass concentration of the pretreatment solution is the same, 27%, changing the type of pretreatment solution results in different mechanical properties of the final prepared alumina material. This is because nitric acid, phosphoric acid, and sulfuric acid can only remove impurities, while hydrochloric acid can not only remove impurities, but also guide the subsequent filling of aluminum-based inorganic salts into the matrix pores after drying, effectively improving the filling rate. It can also assist the aluminum-based inorganic salts in transforming into aluminum-based oxides, improving the conversion rate of aluminum-based inorganic salts, thereby improving the density and mechanical strength of the alumina material, and has a synergistic effect.

[0104] Experimental Example 6

[0105] By replacing the aluminum-based inorganic salt solution in Comparative Example 9 with an aluminum-based complex, and keeping other conditions unchanged, Comparative Example 21 was obtained.

[0106] Sample a was obtained by isothermal calcination of untreated alumina matrix raw material at 500℃; sample b was obtained by isothermal calcination of pretreated alumina matrix at 500℃; sample c was prepared in Comparative Example 9; and sample d was prepared in Comparative Example 21. The results of testing the above different samples are shown in Table 6.

[0107] Table 6

[0108] sample Mechanical strength / MPa Bulk density / g / ml a 22 0.73 b 22 0.76 c 35 0.90 d 27 0.80

[0109] The different samples were characterized using SEM, XRD, and BET to obtain... Figures 1 to 8 The characterization results.

[0110] like Figures 1 to 4 The image shown is a SEM characterization image of different samples. Figure 1 Here is the SEM image of sample a. Figure 2 The image shown is the SEM characterization image of sample b. A comparison of the two images clearly shows the difference. Figure 1 Although the surface of the alumina matrix raw material has pores, most of these pores are blocked by impurities. Figure 2 The alumina matrix in the sample is pretreated to remove impurities, and its surface has a rich porous structure. Figure 3 Here is the SEM image of sample c. Figure 4 The image shows the SEM characterization of sample d. It can be seen that the alumina material impregnated with aluminum-based complexes, after calcination, has a relatively smooth surface but many obvious cracks. Furthermore, due to the large volume of the aluminum-based complexes, they are difficult to penetrate the pores of the alumina matrix during impregnation, resulting in a limited improvement in mechanical strength. Moreover, the synthesis process of aluminum-based complexes is complex and requires stringent conditions, making large-scale preparation inconvenient. In contrast, the alumina material impregnated with aluminum-based inorganic salt solutions shows no obvious cracks, indicating that the aluminum-based inorganic salt solution-impregnated alumina material has a better filling effect. The surface of the aluminum-based inorganic salt solution-impregnated alumina material also exhibits a more pronounced rough morphology. This study shows that when alumina material is used as a supported catalyst carrier, the rough surface morphology can physically isolate the supported active metal, preventing its aggregation at high temperatures and improving the stability of the catalyst performance.

[0111] Figure 5 The XRD patterns of three different samples, b, c, and d, are shown. Figure 5 It can be seen that within the diffraction range of 10-90°, the three samples exhibit three relatively broad diffraction peaks at 2θ = 37.2°, 45.7°, and 66.7°. By comparing the characteristic peaks, these three diffraction peaks can be attributed to the characteristic peaks of γ-Al2O3 on the (311), (400), and (440) crystal planes, indicating that the crystal type of the framework of the three samples after calcination at 500℃ is likely to be the γ-Al2O3 crystal phase. However, η-Al2O3 and γ-Al2O3 have similar crystal structures, and their characteristic peaks are quite similar in XRD characterization. Therefore, the crystal type of the framework of the three samples cannot be determined to be the γ-Al2O3 crystal phase solely based on the XRD spectra. However, considering that η-Al2O3 is obtained by calcining pebbles at 230℃, and we calcined all three samples at 500℃, it can be determined that the crystal type of the framework of the three samples is the γ-Al2O3 crystal phase. This also indicates that the impregnation with aluminum-based inorganic salt solutions and aluminum-based complexes has little effect on the crystal type of the calcined alumina matrix. Furthermore, from... Figure 1It can be seen that after sample c was calcined at 500℃, the characteristic peak of γ-Al2O3 was narrower and the peak height was higher. Based on the results of scanning electron microscopy, it can be inferred that this is mainly due to the formation of alumina particles with higher crystallinity and smaller particle size on the surface of the alumina material after impregnation with aluminum-based inorganic salt solution.

[0112] Figure 6 , Figure 7 , Figure 8 The BET characterization spectra of samples b, c, and d show that the specific surface area of ​​sample b is 167 m². 2 / g, the specific surface area of ​​sample c is 97m². 2 / g, the specific surface area of ​​sample d is 53m². 2 / g. Comparison revealed that the specific surface area of ​​the alumina sample impregnated with aluminum-based inorganic salt solution was 44m² higher than that of the alumina sample impregnated with aluminum-based complex. 2 Based on the results of scanning electron microscopy and X-ray diffraction characterization, it can be inferred that this is mainly due to the rough morphology and small particle size of alumina on the surface of the alumina material after impregnation with aluminum-based inorganic salt solution. When alumina material is used as a catalyst support, a higher specific surface area not only facilitates the generation of more active sites, but also significantly promotes the diffusion process of reactants during the catalytic reaction. Therefore, the catalytic performance of alumina samples impregnated with aluminum-based complexes as catalyst supports is not as good as that of alumina samples impregnated with aluminum-based inorganic salt solution as catalyst supports in this application.

[0113] Experimental Example 7

[0114] The alumina material prepared in this invention is used as a catalyst support to prepare a catalyst for aerospace propellant conversion reaction. Under the action of the catalyst, the chemical propellant realizes the conversion of chemical energy into kinetic energy through catalytic decomposition reaction, thereby completing the real-time control of the spacecraft's orbit and attitude. The ambient temperature of the catalyst application environment is simulated, and the mechanical strength of the catalyst after application is tested.

[0115] In this experimental example, the alumina material prepared in Example 1 was used as a catalyst support to prepare a catalyst for aerospace propellant conversion reaction. The catalyst was placed in a simulated ambient temperature of 1200℃ for 12 hours. After that, the mechanical strength of the catalyst was tested and found to be 40 MPa, which is much greater than the mechanical strength of 30 MPa required for aerospace propellant conversion reaction catalyst. Therefore, the alumina material prepared in this invention has high mechanical strength. After being prepared as a catalyst support for aerospace propellant conversion reaction catalyst, it can still maintain high mechanical strength in harsh aerospace environment, preventing catalyst breakage and failure, and ensuring the catalytic effect of the catalyst and the normal operation of aerospace equipment.

[0116] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a high-performance alumina material as a catalyst support, characterized in that, Includes the following steps: (1) Immerse the pretreated alumina matrix in an aluminum-based inorganic salt solution; the immersion temperature is 25-35℃ and the time is 2-10h; (2) The impregnated alumina matrix is ​​calcined at high temperature to obtain high-performance alumina material; The pretreatment includes: immersing the alumina matrix raw material in a 27% hydrochloric acid solution, washing it with high-purity water, and then drying it at a low temperature of 30°C. The mass ratio of the pretreated alumina matrix to the aluminum-based inorganic salt in the aluminum-based inorganic salt solution is 1:(3-10); In step (2), the heating rate of the roasting is 10℃ / min, and the temperature is maintained at 400℃ for 2 hours, at 800℃ for 2 hours, and at 1200℃ for 2 hours.

2. The method for preparing a high-performance alumina material as a catalyst support according to claim 1, characterized in that, The mass ratio of the pretreated alumina matrix to the aluminum-based inorganic salt in the aluminum-based inorganic salt solution is 1:(3-5).

3. The method for preparing a high-performance alumina material as a catalyst support according to claim 1, characterized in that, The mass ratio of the pretreated alumina matrix to the aluminum-based inorganic salt in the aluminum-based inorganic salt solution is 1:

3.

4. A method for preparing a high-performance alumina material as a catalyst support according to any one of claims 1-3, characterized in that, In step (1), the pretreated alumina matrix is ​​dispersed in an aluminum-based inorganic salt solution to form a mixed solution. The mixed solution is placed in a container to complete the impregnation of the alumina matrix in the aluminum-based inorganic salt solution.

5. A method for preparing a high-performance alumina material as a catalyst support according to any one of claims 1-3, characterized in that, The alumina matrix is ​​immersed in an aluminum-based inorganic salt solution at a temperature of 30°C for 2 hours.

6. A method for preparing a high-performance alumina material as a catalyst support according to any one of claims 1-3, characterized in that, The alumina matrix raw material is immersed in hydrochloric acid solution for 10 to 60 minutes.

7. A method for preparing a high-performance alumina material as a catalyst support according to any one of claims 1-3, characterized in that, The low-temperature drying process is carried out at a temperature of 30–120°C for 1–24 hours.

8. A method for preparing a high-performance alumina material as a catalyst support according to any one of claims 1-3, characterized in that, Before step (1), the method further includes: stirring and dissolving the aluminum-based inorganic salt in a solvent to obtain a uniformly dispersed aluminum-based inorganic salt solution, wherein the mass ratio of the aluminum-based inorganic salt to the solvent is 1:(0.5~10).

9. The method for preparing a high-performance alumina material as a catalyst support according to claim 8, characterized in that, The dissolution process is carried out at a temperature of 0–50°C for a time of 0.1–20 h.

10. The method for preparing a high-performance alumina material as a catalyst support according to claim 8, characterized in that, The aluminum-based inorganic salt is selected from one or a combination of several of aluminum phosphate, aluminum nitrate, aluminum acetate, aluminum chloride, aluminum bromide, and aluminum sulfate; The solvent is selected from one or a combination of several of the following: water, ethanol, propanol, butanol, isopropanol, and N,N-dimethylformamide.

11. The method for preparing a high-performance alumina material as a catalyst support according to claim 8, characterized in that, The aluminum-based inorganic salt is aluminum nitrate, aluminum acetate, or aluminum chloride.

12. The method for preparing a high-performance alumina material as a catalyst support according to claim 11, characterized in that, The aluminum-based inorganic salt is aluminum chloride.

13. The method for preparing a high-performance alumina material as a catalyst support according to claim 8, characterized in that, The solvent is ethanol, isopropanol, or N,N-dimethylformamide.

14. The method for preparing a high-performance alumina material as a catalyst support according to claim 13, characterized in that, The solvent is ethanol.

15. A method for preparing a high-performance alumina material as a catalyst support according to any one of claims 1-3, characterized in that, The alumina matrix is ​​spherical or cylindrical, with a diameter of 0.1–5 mm and a specific surface area of ​​50–300 m². 2 / g.

16. An alumina material, characterized in that, The alumina material is prepared by the preparation method of any one of claims 1-14, and the mechanical strength of the alumina material is 35-51 MPa.

17. An application of an alumina material, characterized in that, The alumina material as described in claim 16 is used as a catalyst carrier in at least the following applications: catalysts for aerospace propellant conversion reactions, catalysts for in-situ preparation of Mars propellants, catalysts for alkane dehydrogenation reactions, catalysts for n- and para-hydrogen conversion, and catalysts for water-gas conversion reactions.

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