A pseudo-boehmite and a method for producing the same

Abstract

The application relates to the field of inorganic material preparation, and particularly discloses a pseudo-boehmite and a preparation method thereof. The preparation method of the pseudo-boehmite comprises the following steps: (1) mixing an aluminum salt solution and an aluminate solution, adding a crystal form regulator, stirring and reacting to obtain a sol system; the crystal form regulator is ZnS quantum dots modified by mercaptopropionic acid; (2) adding a pore size directing agent to the sol system and aging for 6-8 hours; the pore size directing agent is a compound of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer and sodium citrate; and (3) performing solid-liquid separation on the aged sol system, washing and drying the obtained solid to obtain the pseudo-boehmite. The pseudo-boehmite prepared by the preparation method has a pore ratio of 5-10 nm of more than 90%, can meet the pore distribution requirements of the pseudo-boehmite for fine catalytic reactions, and is beneficial to realizing high-efficiency catalytic reactions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of inorganic material preparation, and more particularly, to a pseudo-boehmite and a preparation method thereof. BACKGROUND

[0002] Alumina is used as a carrier material in various chemical industries due to its excellent physicochemical properties, especially in the field of hydrogenation catalysts in petroleum processing. The main raw material for producing alumina carriers is pseudo-boehmite (AlOOH·nH2O, n=0.08-0.62), also known as pseudo-boehmite, which is a type of aluminum hydroxide with uncertain composition, incomplete crystallization, and thin wrinkled lamellae. It has high specific surface area and large pore volume. The performance of alumina carriers is mainly determined by the properties of their precursor pseudo-boehmite, especially the pore structure of pseudo-boehmite, which basically determines the pore structure of alumina carriers. Therefore, to prepare high-performance alumina carriers, high-performance pseudo-boehmite bodies must first be prepared. The main methods for preparing pseudo-boehmite in industry are neutralization, seeding, and aluminum alcohol. Among them, the neutralization method is the commonly used production method in China, which can be further divided into aluminum nitrate method, aluminum sulfate method, carbonization method, double aluminum method, and pH swing method.

[0003] In related technologies, patent CN116253344B discloses a kind of pseudo-boehmite and its preparation method and the alumina prepared by it, and the preparation of pseudo-boehmite in the scheme adopts double aluminum method, i.e. mixing aluminum salt solution and aluminate solution containing inorganic additives to make it nucleate and age to obtain pseudo-boehmite. The pore volume of the prepared pseudo-boehmite can reach 0.5-2.0cm 3 / g, but the pore size mainly concentrates in 15-32nm. Although the pseudo-boehmite prepared by this method has certain advantages in pore volume and specific surface area, the pore size distribution range is wide and mainly concentrates in the mesoporous region.

[0004] However, since the pore size of the pseudo-boehmite is mainly concentrated in 15-32 nm, for the pseudo-boehmite used as a catalytic carrier in the reactions such as olefin epoxidation and aromatic hydroxylation in the fine chemical field, since the reactants are mostly small-molecule organic compounds such as propylene and phenol, the molecular dynamics diameter is about 0.3-0.8 nm, and the reaction needs to be carried out on the active center of the catalyst for rapid adsorption and conversion, the wide pore size distribution range and the excessively large pore size will lead to the decrease of the dispersion degree of the active component, and at the same time, increase the invalid consumption of the diffusion path of the reactants, and reduce the catalytic efficiency. Therefore, for the pseudo-boehmite used as a catalytic carrier in the reactions such as olefin epoxidation and aromatic hydroxylation, it is required that the mesopore pore size distribution of the pseudo-boehmite is as concentrated as possible, especially the proportion of the pores with a size of 5-10 nm is required to be more than 90%, so that the dispersion of the active component and the diffusion selectivity of the reactants can be maintained in the application of the catalyst. However, the pseudo-boehmite in the related art has a large pore size and a dispersed distribution, which cannot meet the above requirements, and the carrier performance is limited in the fine catalytic reaction, and high-efficiency catalysis is difficult to achieve. SUMMARY

[0005] In order to prepare the pseudo-boehmite with the proportion of the pores with a size of 5-10 nm being more than 90%, so as to meet the pore distribution requirements of the pseudo-boehmite in the fine catalytic reaction and achieve high-efficiency catalysis, the application provides a pseudo-boehmite and a preparation method thereof.

[0006] The application provides a pseudo-boehmite and a preparation method thereof, which adopt the following technical scheme:

[0007] The application provides a pseudo-boehmite and a preparation method thereof, which adopt the following technical scheme:

[0008] (1) After the aluminum salt solution and the aluminate solution are mixed, a crystal form regulator is added, the pH of the reaction system is adjusted to 7.5-8.5 by a pH regulator, the reaction temperature is 50-65 ℃, the stirring rate is 200-300 r / min, and after the reaction for 1-2 h, a sol system is obtained; the crystal form regulator is ZnS quantum dots modified by mercaptopropionic acid;

[0009] (2) A pore size directing agent is added to the sol system, and the sol system is aged at 45-55 ℃ for 6-8 h, and inert gas is continuously introduced for protection during the aging process; the pore size directing agent is a complex of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer and sodium citrate;

[0010] (3) The aged sol system is subjected to solid-liquid separation, and the obtained solid is washed and dried to obtain the pseudo-boehmite.

[0011] By adopting the above technical scheme, after the surface of the ZnS quantum dots in the crystal form regulator is modified by mercaptopropionic acid (HS-CH2CH2COOH), the mercapto group (-SH) can be combined with the aluminum ion (Al 3+) to form a coordination bond, and the surface of the quantum dots is oriented and adsorbed to Al by electrostatic action through the negative charge formed by dissociation of the carboxyl group 3+ , inducing the pseudo-boehmite crystal nucleus to preferentially grow along the (001) crystal face. The crystal face is a layered structure, and the interlayer distance is about 0.7-0.8 nm. The mesopore channel formed by the interlayer stacking is exactly in the range of 5-10 nm. Through the coordination of the number of interlayer stacking and the size of the quantum dots, the generation of macropores is limited from the root of the crystal structure, so that the mesopores of the crystal are concentrated in the growth of 5-10 nm. The PEG segment of the PEG-PPG-PEG triblock copolymer in the pore size directing agent can be anchored on the surface of the pseudo-boehmite crystal nucleus through hydrogen bonding to form a "space template" to limit the pore expansion during the lateral growth of the crystal nucleus; the PPG segment (hydrophobic tail chain) repels each other to avoid pore size unevenness caused by template aggregation, thereby facilitating the growth of the mesopores of the crystal to be concentrated in 5-10 nm and continuously grow along the (001) crystal face. Citrate (C6H5O7 3- ) ionized from sodium citrate forms a weak coordination with Al 3+ , and stabilizes the dispersion of the crystal nucleus through electrostatic repulsion to prevent the agglomeration of particles to form macropore defects, while inhibiting the disordered pore structure caused by the rapid hydrolysis of Al 3+ . By controlling the pH of the reaction system in step (1) to be 7.0-8.5 and the reaction temperature to be 50-65℃, the hydrolysis rate of Al 3+ is controlled, so that Al 3+ is slowly generated as AlOOH precursor under weak alkaline conditions to avoid the disorder of the pore structure caused by rapid precipitation; 50-65℃ promotes the coordination reaction between the quantum dots and Al 3+ , and improves the crystal type directing efficiency. In step (2), aging under inert gas protection can prevent the oxidation of the surface groups of the quantum dots by dissolved oxygen in the solution, maintain the coordination activity, and ensure the sustainability of the directional growth of the crystal nucleus. The preparation method of the present application ensures the stability of the pore structure from the root by crystal type regulation, limits the pore size range by using a pore size directing agent, controls the process parameters to avoid impurity interference, and finally realizes the goal of high proportion of concentrated mesopores. The prepared pseudo-boehmite has a pore ratio of 5-10 nm of more than 90%, which can meet the pore distribution requirements of pseudo-boehmite for fine catalytic reactions, and is conducive to realizing high-efficiency catalysis.

[0012] Optionally, the concentration of the aluminum salt solution is 0.8-1.2 mol / L; the aluminum salt solution is any one of aluminum nitrate solution, aluminum chloride solution and aluminum sulfate.

[0013] Optionally, in step (1), the aluminic acid solution is a sodium meta-aluminate solution; the concentration of the sodium meta-aluminate solution is 0.9-1.1 mol / L.

[0014] By using the above technical solutions, the types, concentrations and proportions of the above aluminum salt and aluminic acid salt ensure that Al 3+With AlO2 － The neutralization reaction rate is stable, providing a suitable aluminum ion concentration environment for the crystal form regulator and pore size guide to function, avoiding pore size deviations caused by fluctuations in raw material concentration. The volume ratio of aluminum salt to aluminate can control the Al content. 3+ With AlO2 － The reaction amount is controlled to ensure a stable stoichiometric ratio of AlOOH produced and to avoid excess Al. 3+ or AlO2 － The resulting amorphous impurities ensure the uniformity of crystal nucleus growth, thereby ensuring the stability of mesopore size.

[0015] Optionally, in step (1), the volume ratio of the aluminum salt solution to the aluminate solution is (0.8-1.2):1; the amount of the crystal form regulator added is 2%-4% of the total mass of the aluminum salt solution and the aluminate solution.

[0016] By adopting the above technical solution, the amount of crystal form regulator added can effectively cover the surface of the crystal nucleus of pseudoboehmite, which not only avoids insufficient guidance due to insufficient dosage, but also prevents excessive quantum dots from agglomerating into impurity cores, which is conducive to ensuring the stability of the pore size distribution of pseudoboehmite and the purity of the product.

[0017] Optionally, the crystal form regulator is prepared by the following method:

[0018] A. Mix ZnS quantum dot dispersion with mercaptopropionic acid aqueous solution, add phosphate buffer solution to adjust pH to 7.0-8.0, and shake the reaction at 35-45℃ for 1.5-2.5h to obtain mercaptopropionic acid modified ZnS quantum dot dispersion;

[0019] B. After dialysis purification, the dispersion obtained in step A is freeze-dried to obtain the crystal form regulator.

[0020] By adopting the above technical solution, in step A, by covering the surface of the quantum dots with mercaptopropionic acid, the mercapto groups react with Zn. 2+ The coordination constant is higher than that of the Zn-S bond, enabling surface modification and substitution. The dissociation of the carboxyl group provides a stable negative charge site. Oscillatory reactions promote molecular diffusion, ensuring uniform modification. Dialysis purification removes unreacted mercaptopropionic acid, preventing its reaction with Al. 3+ Non-specific binding interferes with crystal nucleus growth. Through the above preparation method, it is ensured that the ZnS quantum dot surface is sufficiently modified and well dispersed, thereby stably exerting the crystal form guiding effect and avoiding the failure of pore size control due to insufficient quantum dot modification.

[0021] Optionally, the ZnS quantum dot dispersion has a mass concentration of 8%-12%, the mercaptopropionic acid aqueous solution has a mass concentration of 5%-8%, and the mass ratio of the ZnS quantum dot dispersion to the mercaptopropionic acid aqueous solution is 1:(4-6).

[0022] Optionally, in step (2), the mass ratio of the polyethylene glycol-polypropylene glycol-polyethylene glycol tri-block copolymer to sodium citrate in the pore directing agent is (3-5):1; and the pore directing agent is added in an amount of 1.5%-3% of the mass of the sol system.

[0023] Optionally, in step (3), the washing is performed using a mixture of deionized water and ethanol, and the volume ratio of deionized water to ethanol is (2-3):1, and the washing is performed until the conductivity of the filtrate is ≤50 μS / cm; the solid is dried at a temperature of 40-50°C for 10-12 h.

[0024] Optionally, the polyethylene glycol-polypropylene glycol-polyethylene glycol tri-block copolymer has a molecular weight of 2000-3000, and the polyethylene glycol segment accounts for 60%-70%, and the hydroxyl value is 15-10 mg.

[0025] By using the above technical solution, the proportion of pores with a pore size of 5-10 nm is precisely controlled by limiting the compound ratio, molecular weight and segment proportion of the pore directing agent, and the pore size fluctuation caused by a single template agent is avoided.

[0026] The application also provides a pseudo-boehmite prepared by the above preparation method, wherein the proportion of pores with a pore size of 5-10 nm in the pore size distribution of the pseudo-boehmite is >90%, and the pore volume of the pseudo-boehmite is >1.9 cm 3 / g.

[0027] The pseudo-boehmite prepared by the above preparation method has a proportion of mesopores with a pore size of 5-10 nm ≥90%, and the pore size distribution of 5-10 nm is concentrated, effectively solving the problems of large pore size and dispersed distribution in the prior art. The high proportion of mesopores with a pore size of 5-10 nm can perfectly match the diffusion requirements of small molecule reactants in fine chemical industry, reduce the invalid diffusion path, and significantly improve the dispersion of active components through the pore channel confinement effect, avoiding material agglomeration. In addition, the pseudo-boehmite can still maintain a stable pore structure after calcination, providing a continuous and efficient active environment for catalytic reactions, and is particularly suitable for catalyst carriers for fine chemical reactions such as olefin epoxidation and aromatic hydroxylation, which can significantly improve the selectivity and efficiency of the reaction; and has wide application space in the fields of environmental protection catalysts and new energy materials, and can meet the stringent requirements of different scenarios for the pore structure of the carrier.

[0028] In summary, the application has the following beneficial effects:

[0029] 1、In the preparation of pseudo-boehmite, the application uses ZnS quantum dots modified by mercaptopropionic acid as a crystal type regulator. The mercapto groups on the surface of the ZnS quantum dots form coordinate bonds with aluminum ions, and the negative charges dissociated from the carboxyl groups are adsorbed on the aluminum ions by electrostatic attraction, thereby inducing the crystal nucleus to grow preferentially along the (001) crystal face. The interlayer distance of this crystal face is about 0.7-0.8 nm, and the mesoporous channels formed by the interlayer stacking naturally fall within the range of 5-10 nm, thereby limiting the formation of large pores from the root of the crystal structure. Meanwhile, a pore size directing agent composed of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer and sodium citrate limits the expansion of the pore channels of the crystal nucleus by the "space template" effect and stabilizes the dispersion of the crystal nucleus by electrostatic repulsion, thereby avoiding the agglomeration of particles to form large pore defects. In combination with the synergistic control of process parameters such as pH, temperature, and stirring rate, the proportion of pores with a size of 5-10 nm in the pseudo-boehmite finally reaches more than 90%, thereby solving the problems of large pore size and dispersed distribution in the prior art.

[0030] 2、The high proportion of 5-10 nm mesopores in the pseudo-boehmite prepared by the application can perfectly match the diffusion requirements of small molecule reactants in fine chemical industry, reduce invalid diffusion paths, and significantly improve the dispersion of active components through pore confinement effect, thereby avoiding the agglomeration of substances. In addition, the pseudo-boehmite can still maintain a stable pore structure after calcination, thereby providing a continuously efficient active environment for catalytic reactions. The pseudo-boehmite is particularly suitable for use as a catalyst carrier in fine chemical reactions such as olefin epoxidation and aromatic hydroxylation, and can significantly improve the selectivity and efficiency of the reactions. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Figure for detecting the changes in pore size and pore volume of the pseudo-boehmite of Example 1 of the application;

[0032] Figure 2 Figure for detecting the changes in pore size and pore volume of the pseudo-boehmite of Comparative Example 1 of the application. DETAILED DESCRIPTION

[0033] The application will be further described in detail below in combination with examples.

[0034] Preparation Example of Crystal Type Regulator

[0035] Preparation Example 1

[0036] The crystal type regulator is prepared by the following method:

[0037] A. 1 kg of ZnS quantum dot dispersion with a mass concentration of 8% is mixed with 4 kg of mercaptopropionic acid aqueous solution with a mass concentration of 5%. Phosphate buffer solution is added to adjust the pH to 7.0, and the mixture is oscillated at 35°C for 1.5 h to obtain ZnS quantum dots modified by mercaptopropionic acid.

[0038] B, the dispersion solution obtained in step A is purified by dialysis, dialysis is carried out at 30℃ for 12h using deionized water, the purified solution is freeze-dried to obtain the crystal form regulator.

[0039] Preparation Example 2

[0040] The crystal form regulator is prepared by the following method:

[0041] A, 1kg of ZnS quantum dot dispersion solution with a mass concentration of 10% is mixed with 5kg of mercaptopropionic acid aqueous solution with a mass concentration of 6%, a phosphate buffer solution is added to adjust the pH to 7.5, and the reaction is carried out at 40℃ for 2.0h to obtain a mercaptopropionic acid modified ZnS quantum dot dispersion solution;

[0042] B, the dispersion solution obtained in step A is purified by dialysis, dialysis is carried out at 30℃ for 12h using deionized water, the purified solution is freeze-dried to obtain the crystal form regulator.

[0043] Preparation Example 3

[0044] The crystal form regulator is prepared by the following method:

[0045] A, 1kg of ZnS quantum dot dispersion solution with a mass concentration of 12% is mixed with 6kg of mercaptopropionic acid aqueous solution with a mass concentration of 8%, a phosphate buffer solution is added to adjust the pH to 8.0, and the reaction is carried out at 45℃ for 2.5h to obtain a mercaptopropionic acid modified ZnS quantum dot dispersion solution;

[0046] B, the dispersion solution obtained in step A is purified by dialysis, dialysis is carried out at 30℃ for 12h using deionized water, the purified solution is freeze-dried to obtain the crystal form regulator.

[0047] Preparation Example 4

[0048] The crystal form regulator is different from that of preparation example 1 in that the mass concentration of the ZnS quantum dot dispersion solution in this preparation example is 20%.

[0049] Example

[0050] Example 1

[0051] A method for preparing a pseudo-boehmite, comprising the following steps:

[0052] (1) 4L of aluminum nitrate solution with a concentration of 0.8mol / L and 5L of sodium metaaluminate solution with a concentration of 0.9mol / L are mixed, then 180g of the crystal form regulator prepared in preparation example 1 is added, the pH of the reaction system is adjusted to 7.5 by a sodium hydroxide solution with a mass concentration of 20%, the reaction temperature is 50℃, the stirring rate is 200r / min, and after 1h of reaction, a sol system is obtained;

[0053] (2) Add 138 g of pore directing agent to the sol system, and age at 45 °C for 6 h, with continuous nitrogen protection during the aging process; the pore directing agent is a compound of mass ratio of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer to sodium citrate of 3:1;

[0054] (3) Centrifuge the aged sol system, and wash the obtained solid with a mixture of deionized water and ethanol, with a volume ratio of deionized water to ethanol of 2:1, until the conductivity of the filtrate is ≤50 μS / cm; then vacuum dry at 40 °C for 10 h to obtain the pseudoboehmite.

[0055] Example 2

[0056] A method for preparing pseudoboehmite, comprising the following steps:

[0057] (1) Mix 5 L of aluminum chloride solution with a concentration of 1.0 mol / L and 5 L of sodium metaaluminate solution with a concentration of 1.0 mol / L, and then add 300 g of the crystal form regulator prepared in Preparation Example 2, adjust the pH of the reaction system to 8.0 with a 20% sodium hydroxide solution, and react at a temperature of 60 °C and a stirring rate of 250 r / min for 1.5 h to obtain a sol system;

[0058] (2) Add 260 g of pore directing agent to the sol system, and age at 50 °C for 7 h, with continuous nitrogen protection during the aging process; the pore directing agent is a compound of mass ratio of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer to sodium citrate of 4:1;

[0059] (3) Centrifuge the aged sol system, and wash the obtained solid with a mixture of deionized water and ethanol, with a volume ratio of deionized water to ethanol of 2.5:1, until the conductivity of the filtrate is ≤50 μS / cm; then vacuum dry at 45 °C for 11 h to obtain the pseudoboehmite.

[0060] Example 3

[0061] A method for preparing pseudoboehmite, comprising the following steps:

[0062] (1) Mix 6 L of aluminum sulfate solution with a concentration of 1.2 mol / L and 5 L of sodium metaaluminate solution with a concentration of 1.1 mol / L, and then add 440 g of the crystal form regulator prepared in Preparation Example 3, adjust the pH of the reaction system to 8.5 with a 20% sodium hydroxide solution, and react at a temperature of 65 °C and a stirring rate of 300 r / min for 2 h to obtain a sol system;

[0063] (2) Add 345 g of pore directing agent to the sol system, and age at 55 °C for 8 h, with nitrogen continuously introduced during the aging process; the pore directing agent is a compound of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer and sodium citrate at a mass ratio of 5:1;

[0064] (3) Centrifugal separation is performed on the aged sol system, and the obtained solid is washed with a mixture of deionized water and ethanol at a volume ratio of 3:1 until the conductivity of the filtrate is ≤50 μS / cm; then vacuum drying is performed at 50 °C for 12 h to obtain pseudoboehmite.

[0065] Example 4

[0066] A method for preparing pseudoboehmite, which differs from Example 1 in that the crystal form regulator used in this example is the crystal form regulator prepared in Preparation Example 4.

[0067] Example 5

[0068] A method for preparing pseudoboehmite, which differs from Example 1 in that the pore directing agent used in this example is a compound of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer and sodium citrate at a mass ratio of 1:1.

[0069] Comparative Example

[0070] Comparative Example 1

[0071] Pseudoboehmite is prepared according to Example 3 in the patent document with the publication number CN116253344B, entitled "Pseudoboehmite and a method for preparing the same and alumina prepared therefrom".

[0072] Comparative Example 2

[0073] A method for preparing pseudoboehmite, which differs from Example 1 in that no crystal form regulator is added in step (1) and no pore directing agent is added in step (2) of this example, and the sol system is directly aged.

[0074] Comparative Example 3

[0075] A method for preparing pseudoboehmite, which differs from Example 1 in that an equal amount of ZnS quantum dots is used instead of the crystal form regulator in step (1) of this example.

[0076] Comparative Example 4

[0077] A method for preparing pseudoboehmite, which differs from Example 1 in that an equal amount of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer is used instead of the pore directing agent in step (2) of this example.

[0078] Performance detection test

[0079] The performance indicators of the pseudoboehmite prepared in Examples 1-5 and Comparative Examples 1-4 were detected, and the results are shown in Table 1.

[0080] Table 1 detection results

[0081]

[0082] As can be seen from Table 1, the specific surface area of the pseudoboehmite prepared in Examples 1-3 is 423-427m 2 / g, and the pore volume is 1.95-1.97cm 3 / g, indicating that the pseudoboehmite prepared in the present application has a high specific surface area and pore volume, a larger specific surface area can provide more active sites for catalytic reactions, and a larger pore volume is conducive to the diffusion and transmission of reactants and products, thereby improving the efficiency of catalytic reactions. Referring to Figure 1 , the peak pore diameter of the pseudoboehmite prepared in Examples 1-3 is 7.2nm, 7.4nm and 7.2nm respectively, all of which are concentrated in the range of 5-10nm and the values are relatively stable. This shows that the preparation method of the present application can effectively control the pore diameter of the pseudoboehmite in the ideal range through the synergistic effect of the crystal type regulator and the pore diameter directing agent, and the precise control of the process parameters; the 5-10nm pore volume ratio is more than 95%. This shows that the preparation method of the present application can make the mesopore of the pseudoboehmite highly concentrated in the 5-10nm interval, which meets the strict requirements of the pseudoboehmite pore distribution in the fine chemical industry such as olefin epoxidation and aromatic hydroxylation, and is conducive to realizing high-efficiency catalysis.

[0083] The peak pore diameter of the pseudoboehmite prepared in Example 4 is 9.5nm, which is still in the range of 5-10nm, but is larger than that of Examples 1-3. This shows that the amount of ZnS quantum dot dispersion liquid has an effect on the performance of the crystal type regulator when preparing the crystal type regulator, so the control of the pore diameter is unstable, which may lead to changes in the interlayer stacking during the crystal nucleus growth process, resulting in an increase in the peak pore diameter.

[0084] The peak pore diameter of the pseudoboehmite prepared in Example 5 is 10.3nm, indicating that the number of mesopores greater than 10nm is relatively large. The 5-10nm pore volume ratio is 87.2%, but is lower than that of Examples 1-3. This shows that the compounding ratio of the directing agent has a significant effect on the 5-10nm pore ratio, further emphasizing the importance of accurately controlling the compounding ratio of the pore diameter directing agent.

[0085] The peak pore size of the pseudoboehmite prepared in Comparative Example 1 is 32.3 nm, which is far greater than the ideal range of 5-10 nm. The pore size of the pseudoboehmite prepared by the method mainly concentrates in 15-32 nm, which cannot meet the requirement of small pore size for fine catalytic reaction. The proportion of pore volume in the range of 5-10 nm is only 35.6%, which is far lower than the level of the embodiments. This fully shows that the pseudoboehmite in the related art is limited in carrier performance in such fine catalytic reaction due to the large pore size and dispersed distribution, and it is difficult to achieve efficient catalysis.

[0086] The proportion of pore volume in the range of 5-10 nm of the pseudoboehmite prepared in Comparative Example 2 is only 42.3%, which is far lower than the embodiments. This shows that the crystal type regulator and the pore size directing agent play a crucial role in controlling the pore size distribution and increasing the proportion of 5-10 nm pores, and are indispensable.

[0087] The proportion of pore volume in the range of 5-10 nm of the pseudoboehmite prepared in Comparative Example 3 is 65.6%, which is higher than that of Comparative Examples 1 and 2, but far lower than the embodiments. This further proves the importance of mercaptopropionic acid modification of ZnS quantum dots as a crystal type regulator. The use of ZnS quantum dots alone cannot effectively control the mesopore size. Only the quantum dots that are appropriately modified can effectively play a crystal directing role, and then increase the proportion of 5-10 nm pores.

[0088] The proportion of pore volume in the range of 5-10 nm of the pseudoboehmite prepared in Comparative Example 4 is 65.2%, which is similar to that of Comparative Example 3, and far lower than the embodiments. This shows that the compounding of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer and sodium citrate in the pore size directing agent is necessary. The synergistic effect of the two can better achieve precise control of pore size and increase the proportion of 5-10 nm pores.

[0089] The specific embodiments are merely an explanation of the present application, and are not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, and the modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for preparing pseudo-boehmite, characterized by, It comprises the following steps: (1) After mixing the aluminum salt solution and the aluminate solution, a crystal form regulator is added, the pH of the reaction system is adjusted to 7.5-8.5 by a pH regulator, the reaction temperature is 50-65℃, the stirring rate is 200-300r / min, and the sol system is obtained after reacting for 1-2h; The crystal form regulator is ZnS quantum dots modified by mercaptopropionic acid; the concentration of the aluminum salt solution is 0.8-1.2mol / L; the aluminum salt solution is any one of aluminum nitrate solution, aluminum chloride solution and aluminum sulfate solution; the aluminate solution is sodium metaaluminate solution; the concentration of the sodium metaaluminate solution is 0.9-1.1mol / L; the volume ratio of the aluminum salt solution to the aluminate solution is (0.8-1.2):1; the addition amount of the crystal form regulator is 2%-4% of the total mass of the aluminum salt solution and the aluminate solution; (2) The pore size directing agent is added to the sol system, and the sol system is aged at 45-55℃ for 6-8h, and inert gas is continuously introduced for protection during the aging process; the pore size directing agent is a compound of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer and sodium citrate with a mass ratio of (3-5):1; the addition amount of the pore size directing agent is 1.5%-3% of the mass of the sol system; the molecular weight of the polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer is 2000-3000, and the polyethylene glycol segment accounts for 60%-70%, and the hydroxyl value is 15-10mg; (3) The aged sol system is subjected to solid-liquid separation, and the obtained solid is washed and dried to obtain pseudoboehmite.

2. The method of claim 1, wherein the pseudo-boehmite is prepared by the steps of: The crystal form regulator is prepared by the following method: A. The ZnS quantum dot dispersion liquid is mixed with a mercaptopropionic acid aqueous solution, a phosphate buffer solution is added to adjust the pH to 7.0-8.0, and the mixture is oscillated and reacted at 35-45℃ for 1.5-2.5h to obtain a ZnS quantum dot dispersion liquid modified by mercaptopropionic acid; B. The dispersion liquid obtained in step A is purified by dialysis and freeze-dried to obtain the crystal form regulator.

3. A method of preparing pseudo-boehmite according to claim 2, characterized in that: The mass concentration of the ZnS quantum dot dispersion liquid is 8%-12%, the mass concentration of the mercaptopropionic acid aqueous solution is 5%-8%, and the mass ratio of the ZnS quantum dot dispersion liquid to the mercaptopropionic acid aqueous solution is 1:(4-6).

4. The method of claim 1, wherein the pseudo-boehmite is prepared by the steps of: In step (3), deionized water and ethanol are mixed to prepare a washing solution, the volume ratio of deionized water to ethanol is (2-3):1, and the washing is continued until the conductivity of the filtrate is ≤50μS / cm; the solid is dried at a temperature of 40-50℃ for 10-12h.

5. A pseudoboehmite, characterized in that, Prepared by the preparation method of any one of claims 1-4, the pseudoboehmite has a pore size distribution in which the proportion of pores of 5-10 nm is >90%, and the pore volume of the pseudoboehmite is >1.9 cm 3 / g.

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