Preparation method of unit cell distorted pseudo-boehmite and preparation method of alumina carrier with pore channels in gradient distribution

Abstract

The invention provides a preparation method of unit cell distorted pseudo-boehmite and a preparation method of an alumina carrier with pores in gradient distribution, and the preparation method of the unit cell distorted pseudo-boehmite comprises the following steps: placing aluminum nitrate in a crucible, and carrying out first roasting to obtain an amorphous aluminum oxide compound; crushing the prepared amorphous aluminum oxide, putting the crushed amorphous aluminum oxide into a high-pressure kettle, adding a urea solution into the high-pressure kettle, and uniformly mixing through magnetic stirring; sealing the high-pressure kettle, and sequentially carrying out primary hydrothermal treatment and secondary hydrothermal treatment on the high-pressure kettle; cooling the autoclave in cold water to obtain a solid material, then filtering and washing the solid material, and carrying out first drying to obtain the unit cell distortion pseudo-boehmite; the preparation method is simple, industrial production is facilitated, unit cells are distorted to be in a petal cluster shape, the structure is novel and regular, the form is uniform, and rich macroporous channels are contained. The method is suitable for the technical field of inorganic material preparation.

Description

Technical Field

[0001] The present application relates to the field of inorganic material preparation, and in particular to a method for preparing unit cell distorted pseudo-boehmite and a method for preparing an alumina carrier with gradient pore distribution. Background Art

[0002] Pseudoboehmite, also known as monohydrated aluminum oxide, has a chemical formula of AlOOH·nH2O, where n=0.08-0.62. It is a non-toxic, tasteless, and odorless white colloid (wet product) or powder (dry product). Pseudoboehmite has high crystalline purity, good peptization properties, a high specific surface area, and a large pore volume. Its hydrated state forms a thixotropic gel. Pseudoboehmite can be used as a catalyst support, activated alumina, and other aluminum salt raw materials.

[0003] Alumina supports, which are white powdered or formed solids, are the most widely used catalyst carrier, accounting for approximately 70% of supported catalysts in industry. Alumina has high hardness and chemical stability and is widely used in bioceramics, precision ceramics, rare earth tri-color phosphors, aviation light source devices, chemical catalysts, integrated circuit chips, and other fields.

[0004] The properties of pseudo-boehmite directly determine the selectivity, stability, and activity of catalysts. Current research on pseudo-boehmite primarily focuses on the influence of synthesis conditions on its morphology, pore structure, surface properties, and peptization properties. Limited research has been conducted on pseudo-boehmite with distorted unit cells, and few technical literature or methods exist for synthesizing pseudo-boehmite containing distorted unit cells.

[0005] Patent publication number CN104646008A discloses a catalyst for the hydrodesulfurization and demetallization of low-quality heavy oil and its preparation method. This method involves treating alumina support particles with an acid solution of continuously increasing concentration to improve the pore structure on the catalyst surface and within the catalyst. The catalyst prepared by this method exhibits a low content of macropores on the surface and poor pore openness.

[0006] The patent application number CN202311751864.2 discloses a gradient pore distribution alumina carrier and its preparation method. This method uses elliptical lamellar pseudo-boehmite as the raw material for the "shell layer" of the alumina carrier. The preparation process of the elliptical lamellar pseudo-boehmite is relatively complicated. In addition, the pores formed by the accumulation of elliptical lamellar particles are relatively hollow, which is not conducive to the sufficient reaction of the reactants on the surface.

[0007] Alumina is widely used as a catalyst or catalyst support in the petrochemical industry due to its excellent physical and chemical properties. Defects in alumina refer to structural incompleteness or missing portions within the alumina crystals, which significantly affect the physical and chemical properties of alumina. Alumina supports prepared using existing technologies lack sufficient surface defects, which impairs their activity. Summary of the Invention

[0008] In order to solve one of the above technical defects, the present application provides a method for preparing unit cell distorted pseudo-boehmite and a method for preparing an alumina carrier with gradient pore distribution.

[0009] According to a first aspect of the present application, a method for preparing unit cell distorted pseudo-boehmite is provided, comprising: calcining aluminum nitrate to obtain an amorphous aluminum oxide compound; The prepared amorphous aluminum oxide compound is crushed and placed in an autoclave, and a urea solution is added to the autoclave, with the mass ratio of the amorphous aluminum oxide compound to the urea solution being 1:2 to 1:10; and then stirred evenly; The autoclave is sealed, and then the autoclave is subjected to a first hydrothermal treatment and a second hydrothermal treatment in sequence; The autoclave is placed in cold water to cool to obtain a solid material, and then the solid material is filtered, washed, and subjected to a first drying to obtain the unit cell distorted pseudo-boehmite.

[0010] Preferably, the morphology of the obtained unit cell distorted pseudo-boehmite is a petal cluster with a size of 3 to 6 μm; the petal cluster is composed of multiple lamellae clusters, the size of the lamellae is 0.3 to 0.8 μm, the ratio of the length to the width of the lamellae is 3:1 to 6:1, and the thickness of the lamellae is 25 to 45 nm.

[0011] Preferably, the concentration of urea in the urea solution is 11.5-18.5 wt %.

[0012] Preferably, the temperature of the first hydrothermal treatment is 90-130° C., and the time of the first hydrothermal treatment is 1-4 hours.

[0013] More preferably, the temperature of the second hydrothermal treatment is 150-200° C., and the time of the second hydrothermal treatment is 10-16 h.

[0014] Preferably, the particle size of the amorphous aluminum oxide compound after pulverization is less than 20 μm.

[0015] Preferably, the first calcination temperature is 450-600° C., and the first calcination time is 4-8 hours.

[0016] Preferably, the first drying temperature is 100-160° C., and the first drying time is 6-10 hours.

[0017] According to a second aspect of the present application, a method for preparing an alumina support having a gradient pore distribution is provided, comprising: Weigh the pseudo-boehmite A and the unit cell distorted pseudo-boehmite prepared by any of the above methods for preparing the unit cell distorted pseudo-boehmite; The unit cell distorted pseudo-boehmite and pseudo-boehmite A are mixed in a mass ratio of 20% to 40%, and the mixture is subjected to a first ball rolling process to obtain a spherical alumina support precursor; The spherical alumina carrier precursor is mixed with the unit cell distorted pseudo-boehmite in a mass ratio of 1:10 to 1:20, subjected to a second ball rolling process, and then subjected to a second drying and a second calcination process to prepare the alumina carrier.

[0018] Preferably, the most probable pore diameter of the pseudo-boehmite A is 10-30 nm, and the proportion of the most probable pore diameter of the pseudo-boehmite A to the total pore diameter is greater than 45%.

[0019] The beneficial effects of this application are: The preparation method provided in this application is simple and convenient for industrial production. The morphology of the prepared unit cell distorted pseudo-boehmite is a petal cluster with a size of 3-6 μm; the petal cluster is composed of multiple lamellae, the size of the lamellae is 0.3-0.8 μm, the ratio of the length to the width of the lamellae is 3:1-6:1, and the thickness of the lamellae is 25-45 nm. The structure is novel and regular, the morphology is uniform, the (202) crystal plane spacing is smaller than that of SB powder, the specific surface area is large, and it contains abundant open macropores of 50-100 nm. The unit cell distorted pseudo-boehmite can be used as an alumina precursor in a wide range of applications in wear-resistant polishing liquids, pearlescent pigments, inorganic fillers, cosmetics, functional coatings, chemicals, environmental protection, adsorption, catalysis and other fields.

[0020] Other features and advantages of the present application will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present application. The purpose and other advantages of the present application can be realized and obtained by the contents indicated in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 This is a SEM image of the amorphous aluminum oxide compound provided in Example 1 of the present application; Figure 2 This is an SEM image of the unit cell distorted pseudo-boehmite provided in Example 1 of the present application; Figure 3 This is an SEM image of pseudo-boehmite provided in Comparative Example 1 of this application; Figure 4 This is an SEM image of pseudo-boehmite provided in Comparative Example 2 of this application; Figure 5 This is an SEM image of pseudo-boehmite provided in Comparative Example 3 of this application; Figure 6 The XRD spectrum of the amorphous aluminum oxide compound provided in Example 1 of the present application; Figure 7 SB powder, XRD spectrum of the unit cell distorted pseudo-boehmite provided in Example 1 of the present application; Figure 8 This is an SEM image of the unit cell distorted pseudo-boehmite provided in Example 5 of the present application; Figure 9 This is the XRD spectrum of SB powder and the unit cell distorted pseudo-boehmite provided in Example 5 of the present application. DETAILED DESCRIPTION

[0022] In order to make the technical solutions and advantages of the embodiments of the present application more clearly understood, the exemplary embodiments of the present application are further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, and are not an exhaustive list of all the embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other unless they conflict.

[0023] In response to the above problems, the present application provides a method for preparing unit cell distorted pseudo-boehmite, comprising: Aluminum nitrate is placed in a crucible and subjected to a first calcination to obtain an amorphous aluminum oxide compound (i.e., amorphous aluminum oxide); the first calcination temperature is 450-600° C., and the first calcination time is 4-8 hours; The prepared amorphous aluminum oxide compound was crushed, and 10 g of the amorphous aluminum oxide compound was placed in a 150 ml autoclave. The amorphous aluminum oxide compound was crushed to a particle size of less than 20 μm. A urea solution was added to the autoclave, and then magnetic stirring was performed for 10 minutes to ensure uniform mixing. The amount of urea added was 2 / 3 of the height of the autoclave lining, or the mass ratio of the amorphous aluminum oxide compound to the urea solution was 1:2 to 1:10. The concentration of urea in the urea solution was 11.5 to 18.5 wt%. The autoclave is sealed, and then the autoclave is subjected to a first hydrothermal treatment and a second hydrothermal treatment in sequence; the temperature of the first hydrothermal treatment is 90-130°C, and the time of the first hydrothermal treatment is 1-4 hours; the temperature of the second hydrothermal treatment is 150-200°C, and the time of the second hydrothermal treatment is 10-16 hours; during the first hydrothermal treatment, the treatment temperature is low and the time is short, and the amorphous aluminum oxide compound first slowly forms unit cell distorted pseudo-boehmite nuclei in the system; during the second hydrothermal treatment, the unit cell distorted pseudo-boehmite nuclei continue to grow with the amorphous aluminum oxide as a raw material, facilitating the subsequent formation of the final unit cell distorted pseudo-boehmite; the morphology of the prepared unit cell distorted pseudo-boehmite is petal-like clusters with abundant macropore channels; The autoclave is placed in cold water to cool to obtain a solid material, and then the solid material is filtered, washed, and subjected to a first drying to obtain the unit cell distorted pseudo-boehmite; the first drying temperature is 100-160° C., and the first drying time is 6-10 hours.

[0024] The preparation method provided in this application is simple and convenient for industrial production. The morphology of the prepared unit cell distorted pseudo-boehmite is a petal cluster with a size of 3-6 μm; the petal cluster is composed of multiple lamellae, the size of the lamellae is 0.3-0.8 μm, the ratio of the length to the width of the lamellae is 3:1-6:1, and the thickness of the lamellae is 25-45 nm. The structure is novel and regular, the morphology is uniform, the (202) crystal plane spacing is smaller than that of SB powder, the specific surface area is large, and it contains abundant open macropores of 50-100 nm. The unit cell distorted pseudo-boehmite can be used as an alumina precursor in a wide range of applications in wear-resistant polishing liquids, pearlescent pigments, inorganic fillers, cosmetics, functional coatings, chemicals, environmental protection, adsorption, catalysis and other fields.

[0025] To demonstrate the beneficial effects of the method for preparing a unit cell-distorted pseudo-boehmite provided herein, this application provides Examples 1 through 4, Comparative Examples 1 through 3, and a blank control. The blank control is high-quality, high-purity pseudo-boehmite developed by Sasol, Germany, produced using high-purity aluminum and higher alcohols as raw materials. Hereinafter referred to as SB (Sasol boehmite) powder. The raw material ratios and preparation conditions for the Examples and Comparative Examples are shown in Table 1.

[0026] In this application, scanning electron microscopy is used to characterize the microstructure of the products obtained in the examples, comparative examples and blank controls, and corresponding scanning electron microscope images (SEM images) can be obtained. For the purpose of simplicity, this application takes Example 1 as an example and provides SEM images of the amorphous aluminum oxide compound and the unit cell distorted pseudo-boehmite prepared in Example 1, which are respectively Figure 1 and Figure 2Provides SEM images of pseudo-boehmite prepared in Comparative Example 1 to Comparative Example 3, respectively Figure 3 、 Figure 4 、 Figure 5 .

[0027] Depend on Figure 1 and Figure 2 It can be seen that the amorphous aluminum oxide compound provided in Example 1 of the present application does not produce petal cluster morphology, while the prepared unit cell distorted pseudo-boehmite is in the shape of petal clusters, composed of multiple layer clusters, with a novel and regular structure and uniform morphology; and contains abundant open macropore channels. Figures 3 to 5 It can be seen that the morphology of the products prepared in Comparative Examples 1 to 3 is not petal-like clusters. Therefore, other aluminum salts except aluminum nitrate and other alkaline solutions except urea solution cannot produce petal-like clusters of unit cell-distorted pseudo-boehmite. Other aluminum salts such as aluminum chloride and aluminum sulfate, and other alkaline solutions such as ammonia solution and ammonium carbonate solution cannot produce petal-like clusters of unit cell-distorted pseudo-boehmite.

[0028] In this application, X-ray diffractometer was used to characterize the physical structure of the products obtained in the examples, comparative examples and blank controls, and the corresponding XRD spectra were obtained. For the purpose of simplicity, this application takes Example 1 as an example and provides the XRD spectra of the amorphous aluminum oxide compound prepared in Example 1 (see FIG. Figure 6 As shown), the XRD spectra of SB powder and the unit cell distorted pseudo-boehmite prepared in Example 1 are provided (as shown Figure 7 shown).

[0029] Depend on Figure 7 As shown, the diffraction peak of the unit cell distorted pseudo-boehmite prepared in Example 1 of the present application is shifted and the peak value becomes smaller compared with SB powder, which further proves that the unit cell distorted pseudo-boehmite prepared in the present application has unit cell distortion.

[0030] The (020) interplanar spacing of Examples 1 to 4 is reduced compared to that of the blank control. The percentage reduction of the (020) interplanar spacing of Examples 1 to 4 compared to the blank control is calculated based on the XRD spectra of the unit cell distorted pseudo-boehmite prepared in Examples 1 to 4 and the XRD spectra of the SB powder in the blank control, specifically including: The crystal plane corresponding to the characteristic peak of 11.1°-17.5° at 2θ in the XRD spectrum is the (020) crystal plane; By Bragg's law , , respectively calculate the interplanar spacing of the blank control and the unit cell distorted pseudo-boehmite prepared in Examples 1 to 4 ; Where n represents the diffraction order, n is an integer, λ represents the wavelength of the incident X-ray, and θ represents the diffraction angle, that is, the angle between the incident beam and the (020) crystal plane. represents the (020) interplanar spacing of SB powder, Respectively represent the (020) crystal plane spacing of the unit cell distorted pseudo-boehmite prepared in Example 1 to Example 4; The percentage reduction of the (020) interplanar spacing of Examples 1 to 4 compared to the blank control was calculated using the following formula: , ; Where, Respectively represent the percentage reduction of the (020) interplanar spacing of Examples 1 to 4 compared with the blank control.

[0031] The properties of the products obtained in the examples and comparative examples of the unit cell distorted pseudo-boehmite provided in this application are shown in Table 1 below.

[0032] Table 1 Preparation conditions and product properties of unit cell distorted pseudo-boehmite examples and comparative examples

[0033] As can be seen from Table 1, the unit cell distorted pseudo-boehmite prepared in the examples of the present application has a smaller (020) crystal plane spacing than that of SB powder, with a reduction percentage of 0.6% to 1.9%, and a larger specific surface area; the morphology of the unit cell distorted pseudo-boehmite is a petal cluster with a size of 3 to 6 μm; the petal cluster is composed of multiple lamellae clusters, the size of the lamellae is 0.3 to 0.8 μm, the ratio of the length to the width of the lamellae is 3:1 to 6:1, and the thickness of the lamellae is 25 to 45 nm.

[0034] Accordingly, the present application provides a method for preparing an alumina carrier having a gradient pore distribution, comprising: S10, weighing pseudo-boehmite A and unit cell distorted pseudo-boehmite; the most probable pore diameter of the pseudo-boehmite A is 10-30 nm, and the proportion of the most probable pore diameter of the pseudo-boehmite A to the total pore diameter is greater than 45%; wherein the pseudo-boehmite A can be prepared by any one of an acid precipitation method, an alkali precipitation method, and an alcohol aluminum hydrolysis method; S20, mixing the unit cell distorted pseudo-boehmite and the pseudo-boehmite A in a mass ratio of 20% to 40%, and performing a first rolling ball forming to obtain a spherical alumina support precursor; the first rolling ball forming adopts a rotary table forming machine, and during the first rolling ball forming process, a 0.5% acetic acid aqueous solution is sprayed onto the material on the turntable to form the rolling balls; during the first rolling ball forming, the inclination angle of the turntable is 30 to 70 degrees, the rotation speed of the turntable is 10 to 30 rpm, and the forming time is 60 to 120 minutes; S30, mixing the spherical alumina carrier precursor and the unit cell distorted pseudo-boehmite in a mass ratio of 1:10 to 1:20, forming the alumina carrier through a second rolling ball, and then performing a second drying and a second calcination. The drying temperature of the second drying is 100 to 160°C, and the drying time of the second drying is 1 to 8 hours; the calcination temperature of the second calcination is 450 to 650°C, and the calcination time of the second calcination is 2 to 8 hours; the second rolling ball forming adopts a rotary table forming machine, and during the second rolling ball forming, the inclination angle of the rotary table is 30 to 70°, the rotation speed of the rotary table is 10 to 30 rpm, and the forming time is 40 to 80 minutes. The present application uses pseudo-boehmite A and unit cell distorted pseudo-boehmite as raw materials to prepare an alumina carrier, which can increase the surface defect content of the alumina carrier and thereby improve the activity of the alumina carrier. In a first ball forming process, a mixture of unit cell distorted pseudo-boehmite and pseudo-boehmite A is used as a raw material to prepare a spherical alumina carrier precursor, and the spherical alumina carrier precursor is used as the inner layer of the alumina carrier, wherein the pore content of 10-30nm is relatively high and the pore content of 50-100nm is relatively low. The spherical alumina carrier precursor and the unit cell distorted pseudo-boehmite are then mixed and subjected to a second ball forming process to obtain the outer layer of the alumina carrier, wherein the pore content of 50-100nm is relatively high.

[0035] The surface defects of the alumina support prepared using the above method exhibit a gradient distribution, with defects higher on the outside and lower on the inside. The outer layer has a high content of macropores and wide, open pores, resulting in a high surface defect content. The inner layer has a high content of mesopores, a certain amount of macropores that facilitate the mass transfer and diffusion of macromolecular reactants, and a certain number of surface defects. This pore structure and surface defect distribution facilitate the diffusion of macromolecular reactants from the support surface to the interior, improving the mass transfer rate and diffusion performance of the reactants. The prepared alumina is particularly suitable for use as a catalyst support material for heavy oil hydroprocessing with high levels of nickel and vanadium metal impurities. This method solves the problems of alumina supports prepared in the prior art, such as low pore content, poor openness, high preparation cost, and poor surface reaction performance of reactants.

[0036] In order to demonstrate the beneficial effects of the method for preparing an alumina support with a gradient pore distribution provided in this application, this application provides Examples 5 to 8 and Comparative Examples 4 to 6. The alumina supports prepared in the Examples and Comparative Examples were measured, and the measurement method is as follows: First, the pore volume, specific surface area, and average pore diameter of the sample are measured using the low-temperature nitrogen adsorption-desorption method (BET). A certain amount of sample is then placed in a catalyst abrasion tester and ground with a certain amount of quartz sand. When the sample particle size is reduced to a certain level, the weight loss is measured and the pore structure is re-evaluated. Based on the relationship that the total pore volume and specific surface area of the sample are equal to the sum of the individual components, the pore volume and specific surface area of the ground-away portion can be calculated, and the average pore diameter can be calculated. The test involves measuring 40-80 samples.

[0037] The present application also provides an SEM image of the unit cell distorted pseudo-boehmite prepared in Example 5 (eg Figure 8 ), also provides SB powder, Example 5 prepared by the unit cell distortion pseudo-boehmite XRD spectrum (as shown Figure 9 ). Figure 8 It can be seen that the unit cell distorted pseudo-boehmite prepared in Example 5 of the present application is in the shape of petals, composed of multiple lamellae, with a novel and regular structure and uniform morphology; and contains abundant open macropores. Figure 9 As shown, the diffraction peak of the unit cell distorted pseudo-boehmite prepared in Example 5 of the present application is shifted and the peak value becomes smaller compared with the SB powder, which further proves that the unit cell distorted pseudo-boehmite prepared in the present application has unit cell distortion and the (020) crystal plane spacing is reduced.

[0038] The addition ratio of each raw material, preparation conditions and measured product properties in the examples and comparative examples of the alumina carrier provided in this application are shown in Table 2 below.

[0039] Table 2 Preparation conditions and product properties of alumina carrier examples and comparative examples

[0040] As can be seen from Table 2, the specific surface area of the alumina carrier prepared in this application is large, reaching 212 m 2 / g; the pore volume is relatively large, which can reach 0.93~0.96 mL / g; the pore content of 10~30nm is reduced compared with the comparative example, which is 39.8~46.1v%; the pore content of 50~100nm is significantly increased compared with the comparative example, which is 31.5~34.1; the average pore diameter of the outer layer is relatively large, which is 65~79nm; the average pore diameter of the inner layer is relatively small, which is 38~46nm, and the pore channels are distributed in a gradient, and the average pore diameters of the outer and inner layers of the prepared alumina carrier are larger than the average pore diameters of the alumina carriers prepared in comparative examples four to six, which is beneficial to the diffusion of macromolecular reactants.

[0041] It should be noted that the reaction conditions for the first calcination, first drying, first ball forming, second ball forming, second calcination, and second drying in this application are within the ranges provided above. When the temperature is low, the time is increased accordingly, and when the temperature is high, the time is shortened accordingly. Tables 1 and 2 only provide examples of some data and are not intended to limit the reaction conditions in this application.

[0042] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0043] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0044] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A method for preparing unit cell distorted pseudo-boehmite, characterized in that: include: calcining aluminum nitrate to obtain an amorphous aluminum oxide compound; The prepared amorphous aluminum oxide compound is crushed and placed in an autoclave, and a urea solution is added to the autoclave, with the mass ratio of the amorphous aluminum oxide compound to the urea solution being 1:2 to 1:10; and then stirred evenly; The autoclave is sealed, and then the autoclave is subjected to a first hydrothermal treatment and a second hydrothermal treatment in sequence; The autoclave is placed in cold water to cool to obtain a solid material, and then the solid material is filtered, washed, and subjected to a first drying to obtain the unit cell distorted pseudo-boehmite.

2. The method for preparing unit cell distorted pseudo-boehmite according to claim 1, characterized in that: The morphology of the obtained unit cell distorted pseudo-boehmite is a petal cluster with a size of 3~6μm; the petal cluster is composed of multiple lamellae clusters, the size of the lamellae is 0.3~0.8μm, the ratio of the length to the width of the lamellae is 3:1~6:1, and the thickness of the lamellae is 25~45nm.

3. The method for preparing unit cell distorted pseudo-boehmite according to claim 1, characterized in that: The concentration of urea in the urea solution is 11.5~18.5wt%.

4. The method for preparing unit cell distorted pseudo-boehmite according to claim 1, characterized in that: The temperature of the first hydrothermal treatment is 90~130℃, and the time of the first hydrothermal treatment is 1~4h.

5. The method for preparing unit cell distorted pseudo-boehmite according to claim 4, characterized in that: The temperature of the second hydrothermal treatment is 150~200℃, and the time of the second hydrothermal treatment is 10~16h.

6. The method for preparing unit cell distorted pseudo-boehmite according to claim 1, characterized in that: The particle size of the amorphous aluminum oxide compound after crushing is less than 20 μm.

7. The method for preparing unit cell distorted pseudo-boehmite according to claim 1, characterized in that: The first roasting temperature is 450-600° C., and the first roasting time is 4-8 hours.

8. The method for preparing unit cell distorted pseudo-boehmite according to claim 1, characterized in that: The first drying temperature is 100-160°C, and the first drying time is 6-10 hours.

9. A method for preparing an alumina carrier with gradient pore distribution, characterized in that: include: Weigh the pseudo-boehmite A and the unit cell distorted pseudo-boehmite prepared by the method for preparing the unit cell distorted pseudo-boehmite according to any one of claims 1 to 8; The unit cell distorted pseudo-boehmite and pseudo-boehmite A are mixed in a mass ratio of 20% to 40%, and the mixture is subjected to a first ball rolling process to obtain a spherical alumina support precursor; The spherical alumina carrier precursor is mixed with the unit cell distorted pseudo-boehmite in a mass ratio of 1:10 to 1:20, subjected to a second ball rolling process, and then subjected to a second drying and a second calcination process to prepare the alumina carrier.

10. The method for preparing an alumina carrier with gradient pore distribution according to claim 9, characterized in that: The most probable pore size of the pseudo-boehmite A is 10-30 nm, and the proportion of the most probable pore size of the pseudo-boehmite A to the total pore size is greater than 45%.

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