A core-shell structured alumina material and its preparation method

Abstract

The present invention discloses a core-shell structured alumina material and a preparation method thereof. The alumina material is spherical, the core phase is an aggregate of granular small crystal alumina, the shell layer is an aggregate of flaky large crystal alumina, and the shell layer thickness is 0.3r - 0.7r. For the flaky large crystal alumina, the sum of the areas of the (100) crystal plane and the (111) crystal plane and the proportion thereof are 30% - 40%. The preparation method is as follows: (1) mixing pseudoboehmite with a physical pore former, and performing rolling ball forming to obtain a spherical precursor S1; (2) mixing γ-phase alumina powder with an aqueous propylene oxide solution, and then performing sealed heat treatment to obtain a flaky large crystal pseudoboehmite material W1; (3) mixing the material W1 with the spherical precursor S1, performing rolling ball forming, and then drying and calcining to obtain the core-shell structured alumina material. The alumina material of the present invention can be used for preparing catalysts for macromolecular multiphase reactions, and has broad application prospects in reaction processes such as adsorption, separation, and catalysis.

Description

Technical Field

[0001] The present invention belongs to the field of material synthesis, and particularly relates to an alumina material with a core-shell structure and a preparation method thereof. Background Art

[0002] Alumina is an important chemical raw material and is widely used in fields such as ceramics, medicine, adsorbent materials, catalysts, and catalyst carriers. So far, at least eight or more forms of alumina have been found, and their respective macroscopic structural properties are also different. γ-Al2O3, known as "activated alumina", has become the most widely used catalyst or catalyst carrier in the chemical and petroleum industries due to its adjustable pore structure, large specific surface area, good adsorption performance, acidic surface, and good thermal stability. For example, it plays an important role in reaction processes such as petroleum hydrocracking, hydrofining, hydroreforming, dehydrogenation reaction, and automotive exhaust purification.

[0003] Adjusting the pore structure of alumina according to the size of reactant molecules has always been a key research direction in this field. For example, in the conversion process of inferior heavy oil, the pore channels of traditional alumina carriers are relatively small and cannot meet the reaction requirements. The voids formed by the accumulation of alumina grains in the catalyst provide the pore channels for the mass transfer and diffusion of reactants and products; while the surface of alumina grains is the place where the reaction occurs, and the crystal plane characteristics of alumina grains directly affect the type and structure of the active phase of the catalyst. With the in-depth research, it has been found that the surface crystal plane characteristics (crystal plane type and proportion) of alumina carrier materials are also one of the key factors affecting the catalytic performance of the catalyst. For example, Yukio Sakashita et al. (Applied Catalysis A: General 2001, 215: 101-110) studied the influence of the crystal grain morphology and crystal plane orientation of alumina carriers on the catalytic activity of molybdenum sulfide catalysts.

[0004] CN107913691A discloses an alumina carrier containing macropores and a preparation method thereof. First, pseudoboehmite powder and sesbania powder are added to a kneader and mixed evenly. Then, a styrene-butadiene rubber emulsion with a particle size of 10-500 nm is prepared, and an organic acid or inorganic acid is added thereto. Then, the acid solution containing the styrene-butadiene rubber emulsion is added to the pseudoboehmite powder and sesbania powder and kneaded evenly. After extrusion, forming, drying, and calcination, an alumina carrier containing macropores is obtained. The pore diameter distribution of the alumina carrier prepared by this method is 60-400 nm. However, the preparation process of the pore-expanding agent styrene-butadiene rubber emulsion in this method is relatively complex. In addition, the pore channels of the carrier are relatively large, resulting in unsatisfactory strength of the carrier.

[0005] CN104646008A discloses a hydrodesulfurization and demetallization catalyst for inferior heavy oil and its preparation method. The catalyst uses alumina as the carrier and elements of Group VIII and VIB, especially Ni-Mo, as the active components. The pore volume of the catalyst is 0.61 - 0.70 mL / g, the specific surface area is 155 - 200 m 2 / g, and the average pore diameter is 13.0 - 18.0 nm. The preparation method of this catalyst is to treat the shaped and calcined carrier particles with acid solutions of continuously increasing concentrations, so that the average pore diameter of the final catalyst gradually increases from the center to the outer surface along the radial direction of the catalyst particles.

[0006] CN107304060A discloses a flaky nano-γ-Al2O3 crystal grain and its preparation method. The crystal grain size and morphology of this alumina are uniform, and it has a three-dimensional morphology of a parallelepiped. The opposite surfaces of the parallelepiped are used as a group of surfaces. One group of surfaces is a parallelogram with an interior angle of 67.0 - 74.5°, and the exposed is the (110) crystal plane family. The other two groups of surfaces are rectangles, and the exposed is the (111) crystal plane family.

[0007] There is little research on how to balance the pore structure and crystal plane characteristics to make alumina materials play a better role in reactions. Summary of the Invention

[0008] In view of the deficiencies in the prior art, the present invention provides a core-shell structured alumina material and its preparation method. The alumina material of the present invention has a high macropore content, and the (100) crystal plane and (111) crystal plane of the alumina constituting the macropores account for a high proportion. This alumina material can be used to prepare catalysts for macromolecular multiphase reactions and has broad application prospects in reaction processes such as adsorption, separation, and catalysis.

[0009] The core-shell structured alumina material of the present invention is spherical. The core phase is an aggregate of granular small crystal grains of alumina, and the shell layer is an aggregate of flaky large crystal grains of alumina. The crystal grain size of the granular small crystal grains of alumina is 20 - 100 nm, and the crystal grain size of the flaky large crystal grains of alumina is 100 - 500 nm. The shell layer thickness is 0.3r - 0.7r, where r is the radius of the alumina material, that is, the straight-line distance from the center of the sphere to the outer surface.

[0010] The diameter of the core-shell structured alumina material of the present invention is 3 mm - 8 mm.

[0011] Flaky large-grained alumina, with the grain surface exposing (110) crystal plane, (100) crystal plane and (111) crystal plane, where the proportion of the area of the (110) crystal plane is 60%-70%, and the rest are (100) crystal plane and (111) crystal plane, and the sum of the areas and the proportion of the two crystal planes are 30%-40%. For the alumina material of the present invention, the most probable pore diameter is 15-25 nm, and the pore volume of pores with a pore diameter greater than 15 nm accounts for 55%-75% of the total pore volume.

[0012] The specific surface area of the alumina material of the present invention is 180-320 m 2 / g, and the pore volume is 0.7-1.5 mL / g.

[0013] The preparation method of the core-shell structured alumina material of the present invention includes the following contents:

[0014] (1) Mix pseudoboehmite with a physical pore former, and obtain spherical precursor S1 through rolling ball forming.

[0015] (2) Mix γ-phase alumina powder with an aqueous propylene oxide solution, and then conduct sealed heat treatment to obtain

[0016] flaky large-grained pseudoboehmite material W1.

[0017] (3) Mix material W1 with spherical precursor S1, conduct rolling ball forming, and then dry and calcine to obtain the core-shell structured alumina material.

[0018] In the method of the present invention, the particle morphology of the pseudoboehmite described in step (1) is granular, which can be a commercially available product or pseudoboehmite prepared by methods such as acid precipitation method, alkali precipitation method, and alcohol aluminum hydrolysis method. Preferably, it is pseudoboehmite with a most probable pore diameter greater than 10 nm.

[0019] In the method of the present invention, the physical pore former described in step (1) can be inorganic substances such as activated carbon, wood chips, and carbon black, or organic substances such as urea, propylene glycol glycerol, triethylene glycol, and melamine, or water-soluble organic polymers such as polyethylene glycol, polyethylene oxide, methyl cellulose, polyethylene oxide, polyacrylamide, and starch. Preferably, it is carbon black. The mass ratio of the physical pore former to pseudoboehmite is 3:100-1:10.

[0020] In the method of the present invention, the ball rolling forming in step (1) is carried out in a rotary table forming machine. The operating conditions for the rotation of the rotary table forming machine are as follows: the inclination angle of the rotary table is 40-70º, the rotation speed of the rotary table is 10-30 rpm; the forming time of the material in the rotary table is 5-120 min. The radius of the spherical precursor S1 is 0.3r - 0.7r, where r is the radius of the final spherical alumina material, that is, the straight-line distance from the center of the sphere to the outer surface. During the forming process, an aqueous solution containing a gelling solvent is sprayed into the material; the aqueous solution containing a gelling solvent is one or a mixture of aqueous solutions of nitric acid, phosphoric acid, oxalic acid, and acetic acid, and the mass concentration of the solution is 1% - 3%, preferably an aqueous solution of acetic acid.

[0021] In the method of the present invention, the γ-phase alumina powder described in step (2) can be a commercially purchased product or can be prepared according to the prior art. Generally, a pseudo-boehmite precursor purchased commercially or prepared by oneself according to the prior art is used as the raw material, and is calcined to obtain the γ-phase alumina powder; the calcination temperature is 400 - 600°C, and the calcination time is 4 - 8 hours.

[0022] In the method of the present invention, the mass percentage concentration of the aqueous propylene oxide solution described in step (2) is 2.5% - 12%, preferably 4% - 8%. The mass ratio of the amount of the aqueous propylene oxide solution used to the mass of the γ-phase alumina powder is 3:1 - 10:1, preferably 4:1 - 8:1. In the present invention, the γ-phase alumina powder can also be mixed with propylene oxide first and then with water, or the γ-phase alumina powder can be mixed with water first and then with propylene oxide. Preferably, polyethylene glycol 2000 - 20000 is added to the aqueous propylene oxide solution at the same time, and the addition amount of polyethylene glycol 2000 - 20000 and the mass ratio of the γ-phase alumina powder is 0.01:1 - 0.05:1.

[0023] In the method of the present invention, the sealed heat treatment described in step (2) is carried out in a sealed container. The sealed container is preferably an autoclave. The treatment temperature is 110 - 180°C, preferably 120 - 160°C, and the treatment time is 4 - 8 hours. The pressure in the sealed container during the heat treatment is the self-generated pressure.

[0024] In the method of the present invention, the flaky large-grained pseudo-boehmite described in step (2) has the following properties: the grain size is 100-500 nm, preferably 200-300 nm, 1.0 < P1 ≤ 1.5, 1.5 < P2 ≤ 1.8, P1 = D(120) / D(031), P2 = D(120) / D(020); the D(120) represents the grain size of the crystal plane corresponding to the (120) peak in the XRD spectrum of the pseudo-boehmite grains; D(031) represents the grain size of the crystal plane corresponding to the (031) peak in the XRD spectrum of the pseudo-boehmite grains; D(020) represents the grain size of the crystal plane corresponding to the (020) peak in the XRD spectrum of the pseudo-boehmite grains; the 120 peak refers to the characteristic peak with 2θ of 25.5-29.9º in the XRD spectrum; the 031 peak refers to the characteristic peak with 2θ of 36.3-40.5º in the XRD spectrum; the 020 peak refers to the characteristic peak with 2θ of 12.0-16.2º in the XRD spectrum, D = Kλ / (Bcosθ), where K is the Scherrer constant, λ is the diffraction wavelength of the target, B is the full width at half maximum of the diffraction peak, and θ is the diffraction angle.

[0025] In the method of the present invention, the flaky large-grained pseudo-boehmite described in step (2) is transformed into flaky γ-aluminum oxide after calcination at 450-650 °C. The grain size of this aluminum oxide is 100-500 nm, preferably 200-300 nm, and the crystal planes exposed on the surface are (110) crystal plane, (100) crystal plane, and (111) crystal plane. Among them, the proportion of the area of the (110) crystal plane is 60%-70%, and the sum of the areas of the (100) crystal plane and the (111) crystal plane accounts for 30%-40%. The area ratio of each crystal plane is calculated by the following method: randomly observe 100 complete aluminum oxide grains through an electron microscope, measure the grain size of each aluminum oxide grain and calculate the area of each crystal plane and the total grain area in each grain, sum up the measurement results of all grains, and the ratio of the total area of each crystal plane to the total grain area is the area ratio of each crystal plane.

[0026] In the method of the present invention, the ball rolling forming described in step (3) is carried out in a rotary forming machine. The operating conditions for the rotation of the rotary forming machine are: the inclination angle of the turntable is 40-70º, the rotation speed of the turntable is 10-30 rpm; the forming time of the material in the turntable is 10-60 min, and the final sphere diameter is 3-8 mm. During the forming process, an aqueous solution containing a gelling solvent is sprayed into the material; the aqueous solution containing a gelling solvent is one or a mixture of aqueous solutions of nitric acid, phosphoric acid, oxalic acid, and acetic acid, and the mass concentration of the solution is 1%-3%, preferably an aqueous solution of acetic acid.

[0027] In the method of the present invention, the drying time in step (3) is 1 to 8 hours, preferably 2 to 6 hours, the drying temperature is 60°C to 180°C, preferably 80°C to 150°C; the calcination temperature is 350 to 800°C, preferably 500 to 650°C, and the calcination time is 2 to 6 hours, preferably 2 to 4 hours.

[0028] The present invention also provides a hydrogenation catalyst, which catalyst comprises the above-mentioned alumina material with a core-shell structure.

[0029] Application of the alumina material with a core-shell structure of the present invention in reaction processes such as adsorption, separation, and catalysis.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] For the alumina material with a core-shell structure of the present invention, the shell layer is formed by the accumulation of large-grained flaky alumina, making the surface pores of the material larger, and the pores formed by the accumulation of flaky particles have good openness, reducing or avoiding the formation of "ink bottle" - shaped pores, improving the penetration of the pores on the carrier surface. This structure is beneficial to the mass transfer and diffusion of macromolecular reactants. For conventional γ-phase alumina grains, the (110) crystal plane, (100) crystal plane, and (111) crystal plane are exposed on the grain surface, among which the area ratio of the (110) crystal plane is about 65% - 75%, and the rest are the (100) crystal plane and (111) crystal plane. The (100) crystal plane and (111) crystal plane among the three crystal planes of alumina are high-activity crystal planes. The shell-layer alumina of the alumina material with a core-shell structure of the present invention improves the proportion of the (100) crystal plane and (111) crystal plane in the shell-layer alumina grains by adjusting the particle morphology of the alumina grains. The alumina material prepared by this method organically combines the pore structure characteristics with the crystal plane structure characteristics of the alumina grains, making it easier for macromolecular reactants to contact the surface of alumina grains with high catalyst activity, and strengthening the mass transfer, diffusion, and reaction effects. Description of the Drawings

[0032] Figure 1 is the SEM image of the flaky large-grained pseudo-boehmite W 1-1 prepared in Example 1.

[0033] Figure 2 is the XRD spectrum of the flaky large-grained pseudo-boehmite W 1-1 prepared in Example 1.

[0034] Figure 3 is the SEM image of the cross-section of the core phase of the alumina material with a core-shell structure prepared in Example 5.

[0035] Figure 4 is the SEM image of the cross-section of the shell layer of the alumina material with a core-shell structure prepared in Example 5. Detailed Embodiments

[0036] The technical solutions and effects of the present invention will be further described below in conjunction with embodiments, but are not limited to the following embodiments. Among them, in the present invention, wt% represents mass fraction.

[0037] BET method: The pore structures of the carriers in the examples and comparative examples were characterized by N2 physical adsorption - desorption. The specific operations are as follows: The pore structure of the sample was characterized using an ASAP - 2420 type N2 physical adsorption - desorption instrument. A small amount of the sample was vacuum - treated at 300 °C for 3 - 4 hours, and finally the product was placed under liquid nitrogen low - temperature (-200 °C) conditions for nitrogen adsorption - desorption testing. The specific surface area was obtained according to the BET equation, and the distribution rate of the pore volume and pore diameter below 30 nm was obtained according to the BJH model.

[0038] The microstructure of the alumina carrier was characterized by scanning electron microscopy. The specific operations are as follows: The microstructure of the carrier was characterized using a JSM - 7500F scanning electron microscope, with an acceleration voltage of 5 KV, an acceleration current of 20 µA, and a working distance of 8 mm.

[0039] X - ray diffraction (XRD) analysis was carried out on a D / max - 2500 type full - automatic rotating - target X - ray diffractometer produced by Rigaku Corporation of Japan. A Cu target, Kα radiation source, graphite monochromator were used, with a tube voltage of 40 kV and a tube current of 80 mA.

[0040] The crystal plane of alumina was characterized. The crystal plane characteristics of alumina grains were measured using a JEM - 2200FS type transmission electron microscope, and the measurement method was referred to (the relationship between the surface acidity and microstructure of γ - Al2O3 carriers in industrial applications, Petroleum Processing and Petrochemicals, 2015, (46) 10) for measurement.

[0041] Determination of the most probable pore diameter: Taking the pore diameter of the material as the abscissa and the change rate of the pore volume with the pore diameter as the ordinate, the pore diameter differential distribution curve was obtained, and the peak value in the curve was the most probable pore diameter.

[0042] Preparation of flaky large - grain pseudo - boehmite material W1:

[0043] Example 1

[0044] 500 grams of pseudo - boehmite (prepared by the aluminum sulfate - sodium meta - aluminate method, with a dry - basis weight content of 73%) was weighed and calcined at 450 °C for 6 hours to obtain γ - phase alumina.

[0045] 100 grams of the above - mentioned γ - phase alumina was weighed, 540 grams of a 6.2% propylene oxide solution by mass concentration was added, and magnetic stirring was carried out for 30 minutes. Then the mixed material was transferred into an autoclave, sealed, and heated at 135 °C for 6.5 hours. After cooling, the solid material was filtered, washed, and dried at 110 °C for 6 hours to obtain flaky large - grain pseudo - boehmite material W 1-1 , the properties of the pseudo - boehmite are shown in Table 1, and the scanning electron microscope image of this pseudo - boehmite is shown inFigure 1 , the XRD pattern is shown in Figure 2 . After the pseudo-boehmite is calcined at 600 °C for 6 hours, it is transformed into γ-phase alumina, and the proportion of the (100) crystal plane and (111) crystal plane of γ-phase alumina is 36%.

[0046] Example 2

[0047] Same as Example 1, except that the calcination temperature of the pseudo-boehmite is 550 °C. The amount of the propylene oxide solution used is 430 g, and the mass concentration of the solution is 7.6%. The heat treatment temperature is 150 °C, and the treatment time is 5.5 hours to obtain the flaky large-grain pseudo-boehmite material W 1-2 , the properties of the pseudo-boehmite are shown in Table 1. After the pseudo-boehmite is calcined at 600 °C for 6 hours, it is transformed into γ-phase alumina, and the proportion of the (100) crystal plane and (111) crystal plane of γ-phase alumina is 38%.

[0048] Example 3

[0049] Same as Example 1, except that the amount of the propylene oxide solution used is 740 g, and the mass concentration of the solution is 4.3%. The heat treatment temperature is 160 °C, and the treatment time is 4.5 hours to obtain the flaky large-grain pseudo-boehmite material W 1-3 , the properties of the pseudo-boehmite are shown in Table 1. After the pseudo-boehmite is calcined at 600 °C for 6 hours, it is transformed into γ-phase alumina, and the proportion of the (100) crystal plane and (111) crystal plane of γ-phase alumina is 34%.

[0050] Example 4

[0051] Same as Example 1, except that the amount of the propylene oxide solution used is 630 g, the mass concentration of the solution is 5.5%, and an appropriate amount of polyethylene glycol-10000 is added to the mixed material. The addition amount of polyethylene glycol-10000 is 1.5 g. The heat treatment temperature is 125 °C, and the treatment time is 7 hours to obtain the flaky large-grain pseudo-boehmite material W 1-4 , the properties of the pseudo-boehmite are shown in Table 1. After the pseudo-boehmite is calcined at 600 °C for 6 hours, it is transformed into γ-phase alumina, and the proportion of the (100) crystal plane and (111) crystal plane of γ-phase alumina is 39%.

[0052] Comparative Example 1

[0053] Same as Example 1, except that the propylene oxide is replaced with the same amount of ethylene oxide to obtain the comparative rehydrated pseudo-boehmite W5. The properties of the pseudo-boehmite are shown in Table 1. After the pseudo-boehmite is calcined at 600 °C for 6 hours, it is transformed into γ-phase alumina, and the proportion of the (100) crystal plane and (111) crystal plane of γ-phase alumina is 28%.

[0054] Comparative Example 2

[0055] Same as Example 1, except that propylene oxide was replaced with the same amount of distilled water to prepare the comparative rehydrated pseudoboehmite W6. The properties of the pseudoboehmite are shown in Table 1. After calcination at 600 °C for 6 hours, this pseudoboehmite was transformed into γ-phase alumina, and the proportion of the (100) crystal plane and (111) crystal plane of the γ-phase alumina was 31%.

[0056] Table 1 Properties of Pseudoboehmite

[0057]

[0058] Preparation of core-shell structured alumina material:

[0059] Example 5

[0060] (1) 11 g of carbon black powder was mixed evenly with 200 g of pseudoboehmite. The mixed material was placed in a rotary table molding machine and mixed thoroughly. The inclination angle of the rotary table was adjusted to 45º, and the rotation speed of the rotary table was 15 rpm. An aqueous acetic acid solution with a mass concentration of 1.5% was sprayed onto the material in the rotary table through a sprayer. After mixing and contacting, the forming time of the material in the rotary table was 45 min, and spherical precursor S1 with a diameter of 2.5 - 3.5 mm was obtained;

[0061] (2) The flaky large-grained pseudoboehmite material W prepared in Example (1) and the spherical precursor S1 prepared in step (1) were placed in a rotary table molding machine and mixed thoroughly. The inclination angle of the rotary table was adjusted to 40º, and the rotation speed of the rotary table was 10 rpm. An aqueous acetic acid solution with a mass concentration of 1.5% was sprayed onto the material in the rotary table through a sprayer. After mixing and contacting, the forming time of the material in the rotary table was 45 min, and spherical material with a diameter of 4 - 6 mm was obtained. The obtained spherical material was dried at 120 °C for 4 h and calcined at 600 °C for 4 h to obtain core-shell structured alumina material S-1. The properties of the carrier are shown in Table 2. The scanning electron micrograph of the core-phase alumina particles of this core-shell structured alumina material is shown in

[0062] (2) The flaky large-grained pseudoboehmite material W 1-1 prepared in step (1) were placed in a rotary table molding machine and mixed thoroughly. The inclination angle of the rotary table was adjusted to 40º, and the rotation speed of the rotary table was 10 rpm. An aqueous acetic acid solution with a mass concentration of 1.5% was sprayed onto the material in the rotary table through a sprayer. After mixing and contacting, the forming time of the material in the rotary table was 45 min, and spherical material with a diameter of 4 - 6 mm was obtained. The obtained spherical material was dried at 120 °C for 4 h and calcined at 600 °C for 4 h to obtain core-shell structured alumina material S-1. The properties of the carrier are shown in Table 2. The scanning electron micrograph of the core-phase alumina particles of this core-shell structured alumina material is shown in Figure 3 and the scanning electron micrograph of the shell-layer alumina particles is shown in Figure 4 .

[0063] Example 6

[0064] Same as Example 5, except that in step (1), the addition amount of carbon black powder was 15 g and the forming time was 55 min; in step (2), the flaky large-grained pseudoboehmite material W 1-1 was replaced with material W 1-2 and the forming time was 35 min to obtain core-shell structured alumina material S-2. The properties of the carrier are shown in Table 2.

[0065] Example 7

[0066] Same as Example 5, except that the addition amount of carbon black powder in step (1) is 7 g and the forming time is 60 min; in step (2), the flaky large-crystalline pseudo-boehmite material W 1-1 is replaced with material W 1-3 , the forming time is 25 min, and the core-shell structured alumina material S-3 is obtained. The properties of the carrier are shown in Table 2.

[0067] Example 8

[0068] Same as Example 5, except that the addition amount of carbon black powder in step (1) is 18 g and the forming time is 35 min; in step (2), the flaky large-crystalline pseudo-boehmite material W 1-1 is replaced with material W 1-4 , the forming time is 55 min, and the core-shell structured alumina material S-4 is obtained. The properties of the carrier are shown in Table 2.

[0069] Comparative Example 3

[0070] Same as Example 5, except that in step (2), the flaky large-crystalline pseudo-boehmite material W 1-1 is replaced with the pseudo-boehmite W5 prepared in Comparative Example 1, and the comparative core-shell structured alumina material S-5 is prepared. The properties of the carrier are shown in Table 2.

[0071] Comparative Example 4

[0072] Same as Example 5, except that in step (2), the flaky large-crystalline pseudo-boehmite material W 1-1 is replaced with the pseudo-boehmite W6 prepared in Comparative Example 2, and the comparative core-shell structured alumina material S-6 is prepared. The properties of the carrier are shown in Table 2.

[0073] Table 2 Properties of macroporous alumina carriers

[0074]

Claims

1. A core-shell structured alumina material, characterized in that: The alumina material is spherical. The core phase is an aggregate of granular small-grained alumina, and the shell layer is an aggregate of flaky large-grained alumina. The grain size of the granular small-grained alumina is 20 - 100 nm, and the grain size of the flaky large-grained alumina is 100 - 500 nm. The shell thickness is 0.3r - 0.7r, where r is the radius of the alumina material, that is, the straight-line distance from the center of the sphere to the outer surface. The preparation method of the core-shell structured alumina material includes the following: (1) Mix pseudoboehmite with a physical pore-expanding agent and form into spheres by rolling to obtain a spherical precursor S1. (2) Mix γ-phase alumina powder with an aqueous propylene oxide solution, and then conduct sealed heat treatment to obtain a flaky large-grained pseudoboehmite material W1. (3) Mix the material W1 with the spherical precursor S1, form into spheres by rolling, and then dry and calcine to obtain the core-shell structured alumina material. The sealed heat treatment in step (2) is carried out in a sealed container, the treatment temperature is 110 - 180 °C, the treatment time is 4 - 8 hours, and the pressure in the sealed container during the heat treatment is the autogenous pressure. The flaky large-grained pseudoboehmite in step (2) has the following properties: the grain size is 100 - 500 nm, 1.0 < P1 ≤ 1.5, 1.5 < P2 ≤ 1.8, P1 = D(120) / D(031), P2 = D(120) / D(020). The D(120) represents the grain size of the crystal plane corresponding to the (120) peak in the XRD pattern of the pseudoboehmite grains; D(031) represents the grain size of the crystal plane corresponding to the (031) peak in the XRD pattern of the pseudoboehmite grains; D(020) represents the grain size of the crystal plane corresponding to the (020) peak in the XRD pattern of the pseudoboehmite grains. The 120 peak refers to the characteristic peak with 2θ of 25.5 - 29.9 ° in the XRD pattern; the 031 peak refers to the characteristic peak with 2θ of 36.3 - 40.5 ° in the XRD pattern; the 020 peak refers to the characteristic peak with 2θ of 12.0 - 16.2 ° in the XRD pattern, D = Kλ / (Bcosθ), where K is the Scherrer constant, λ is the diffraction wavelength of the target, B is the half-peak width of the diffraction peak, and θ is the diffraction angle.

2. The alumina material according to claim 1, characterized in that: The diameter of the alumina material is 3 mm - 8 mm.

3. The alumina material according to claim 1, wherein: For the flaky large-grained alumina, the (110), (100), and (111) crystal planes are exposed on the grain surface. Among them, the proportion of the (110) crystal plane area is 60% - 70%, and the sum of the areas of the (100) and (111) crystal planes accounts for 30% - 40%.

4. The alumina material according to claim 1, characterized in that: The most probable pore diameter is 15 - 25 nm, and the pore volume of pores with a pore diameter greater than 15 nm accounts for 55% - 75% of the total pore volume.

5. The alumina material according to claim 1, wherein: The specific surface area is 180 - 320 m 2 / g, and the pore volume is 0.7 - 1.5 mL / g.

6. A method for preparing the alumina material with a core-shell structure according to any one of claims 1 to 5, characterized in that It includes the following steps: (1) mixing pseudo-boehmite with a physical pore former, followed by rolling ball forming to obtain a spherical precursor S1; (2) mixing γ-alumina powder with an aqueous propylene oxide solution, and then performing sealed heat treatment to obtain a flaky large-grained pseudo-boehmite material W1; (3) mixing the material W1 with the spherical precursor S1, performing rolling ball forming, and then drying and calcining to obtain an alumina material with a core-shell structure; the sealed heat treatment in step (2) is carried out in a sealed container, the treatment temperature is 110-180 °C, the treatment time is 4-8 hours, and the pressure in the sealed container during the heat treatment is the autogenous pressure; the flaky large-grained pseudo-boehmite in step (2) has the following properties: the grain size is 100~500 nm, 1.0<P1≤1.5, 1.5<P2≤1.8, P1 = D(120) / D(031), P2 = D(120) / D(020); the D(120) represents the grain size of the crystal plane corresponding to the (120) peak in the XRD pattern of the pseudo-boehmite grains; D(031) represents the grain size of the crystal plane corresponding to the (031) peak in the XRD pattern of the pseudo-boehmite grains; D(020) represents the grain size of the crystal plane corresponding to the (020) peak in the XRD pattern of the pseudo-boehmite grains; the 120 peak refers to the characteristic peak with 2θ of 25.5-29.9º in the XRD pattern; the 031 peak refers to the characteristic peak with 2θ of 36.3-40.5º in the XRD pattern; the 020 peak refers to the characteristic peak with 2θ of 12.0-16.2º in the XRD pattern, D = Kλ / (Bcosθ), where K is the Scherrer constant, λ is the diffraction wavelength of the target, B is the full width at half maximum of the diffraction peak, and θ is the diffraction angle.

7. The method according to claim 6, wherein: The pseudo-boehmite particles in step (1) are granular in morphology, and the most probable pore diameter is greater than 10 nm.

8. The method according to claim 6, wherein: The physical pore former in step (1) is one or more of activated carbon, wood chips, carbon black, urea, propylene glycol glycerol, triethylene glycol, melamine, polyethylene glycol, polyethylene oxide, methyl cellulose, polyoxyethylene, polyacrylamide or starch; the mass ratio of the physical pore former to the pseudo-boehmite is 3:100 - 1:

10.

9. The method according to claim 6, wherein: The rolling ball forming in step (1) is carried out in a rotary forming machine, and the operating conditions for the rotation of the rotary forming machine are: the inclination angle of the turntable is 40~70º, the rotation speed of the turntable is 10~30 rpm; the forming time of the material in the turntable is 5~120 min.

10. The method according to claim 6, characterized in that: The radius of the spherical precursor S1 in step (1) is 0.3r - 0.7r, where r is the radius of the final spherical alumina material.

11. The method according to claim 6, characterized in that: During the forming process in step (1), an aqueous solution containing a colloidal solvent is sprayed into the material; the aqueous solution containing the colloidal solvent is a mixture of one or several of the aqueous solutions of nitric acid, phosphoric acid, oxalic acid, and acetic acid, and the mass percentage concentration of the solution is 1%-3%.

12. The method according to claim 6, characterized in that: The mass percentage concentration of the aqueous propylene oxide solution in step (2) is 2.5%-12%, and the mass ratio of the amount of the aqueous propylene oxide solution used to the mass of the γ-alumina powder is 3:1 - 10:

1.

13. The method according to claim 6, wherein: In step (2), the γ-aluminum oxide powder is mixed with propylene oxide and then with water, or the γ-aluminum oxide powder is mixed with water and then with propylene oxide.

14. The method according to claim 6, characterized in that: In step (2), polyethylene glycol 2000 - 20000 is added to the aqueous solution of propylene oxide. The mass ratio of the added amount of polyethylene glycol 2000 - 20000 to the γ-aluminum oxide powder is 0.01:1 - 0.05:

1.

15. The method according to claim 6, characterized in that: The flaky large-crystalline pseudo-boehmite described in step (2) is transformed into flaky γ-aluminum oxide after calcination at 450 - 650 °C. The grain size of this aluminum oxide is 100 - 500 nm, and the exposed crystal planes on the surface are (110) crystal plane, (100) crystal plane, and (111) crystal plane. Among them, the proportion of the (110) crystal plane area is 60% - 70%, and the sum of the areas of the (100) crystal plane and the (111) crystal plane is 30% - 40%.

16. The method according to claim 6, wherein: The ball rolling forming in step (3) is carried out in a rotary forming machine. The operating conditions for the rotation of the rotary forming machine are as follows: the inclination angle of the turntable is 40 - 70 º, the rotation speed of the turntable is 10 - 30 rpm; the forming time of the material in the turntable is 10 - 60 min, and the final sphere diameter is 3 - 8 mm; during the forming process, an aqueous solution containing a gelling solvent is sprayed into the material; the aqueous solution containing the gelling solvent is one or a mixture of aqueous solutions of nitric acid, phosphoric acid, oxalic acid, and acetic acid, and the mass percentage concentration of the solution is 1% - 3%.

17. The method according to claim 6, characterized in that: The drying time described in step (3) is 1 - 8 hours, and the drying temperature is 60 °C - 180 °C; the calcination temperature is 350 - 800 °C, and the calcination time is 2 - 6 hours.

18. A hydrogenation catalyst, characterized in that: This catalyst contains the alumina material with the core-shell structure described in any one of claims 1 - 5.

19. Use of the alumina material with the core-shell structure described in any one of claims 1 - 5 in the processes of adsorption, separation, and catalytic reaction.

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