KR20040015418A - Mesoporous alumina molecular sieve, and process for preparing the same - Google Patents

Abstract

PURPOSE: Provided is a method for preparing a meso-porous alumina molecular sieve having a high surface area and excellent thermal stability under a mild reaction condition without using any additives except for a surfactant. CONSTITUTION: The method for preparing a meso-porous alumina molecular sieve comprises the steps of: (a-1) mixing a surfactant and an alumina precursor in an organic solvent to form a mixture; (a-2) adding water to the mixture; (a-3) hydrothermally synthesizing the mixture added with water; and (a-4) removing the residual amount of the surfactant by drying and baking. In particular, the mole ratio of the alumina precursor : water is 1 : 0.1-10.

Description

Mesoporous alumina molecular sieve, and process for preparing the same

The present invention relates to a mesoporous alumina molecular sieve using a surfactant and a method for producing the same, and provides a mesoporous alumina molecular sieve having a high surface area and excellent thermal stability, and is easily prepared as compared to the conventional method. do.

In general, alumina has been used as an important catalyst and support in industrial processes. The alumina has a uniform surface of mesopores and has a high surface area and has chemical and thermal stability. The synthesis of eggplant alumina is becoming increasingly important.

The preparation of alumina with mesopores has been produced using various surfactants (cationic, anionic, nonionic) so far, especially nonionic surfactants, sodium dodecyl sulfate, and long chain carboxyl. Case studies have been made of producing alumina having high surface area mesopores using acid.

However, the greatest difficulty in the synthesis of mesoporous alumina molecular sieves using cationic surfactants is the very fast hydrolysis of aluminum cations in aqueous solution, and hydrated hydroxide in the form of lamellar in the presence of surfactants. mesoporous alumina molecular sieves have been synthesized by inhibiting rapid hydrolysis by using additives such as triethanolamine as hydrolysis inhibitors because they cause the formation of hydroxides).

Therefore, there is a need for a method for producing the molecular sieve in a higher surface area, excellent thermal stability, and a simpler process.

The technical problem to be achieved by the present invention is to provide a mesoporous alumina molecular sieve having a high surface area and excellent thermal stability under mild reaction conditions without using any additives other than a surfactant, and a method for preparing the same.

1 is a TEM photograph of a mesoporous alumina molecular sieve according to Example 5 of the present invention.

2 is a graph showing an X-ray diffraction pattern of the mesoporous alumina molecular sieve according to Example 4 of the present invention.

The present invention to achieve the above technical problem,

(a-1) mixing a surfactant and an alumina precursor in an organic solvent to form a mixture;

(a-2) adding water to the mixture;

(a-3) hydrothermally synthesizing the mixture to which water has been added; And

(A-4) provides a method for producing a mesoporous alumina molecular sieve comprising the step of removing the residual surfactant through the drying and calcining process.

In the method of preparing the molecular sieve, the molar ratio of alumina precursor to water is preferably 1: 0.1 to 10.

In the method for producing the molecular sieve, the molar ratio of alumina precursor: water is more preferably 1: 1 to 3.

In the method for preparing the molecular sieve, the molar ratio of the alumina precursor to the surfactant is preferably 1: 0.1 to 10.

It is preferable that surfactant used in the manufacturing method of the said molecular sieve is a cationic surfactant.

The cationic surfactant is preferably a compound of the formula (1).

[Formula 1]

Wherein R ₁ to R ₃ represent a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, R ₄ represents a substituted or unsubstituted alkyl group having 8 to 22 carbon atoms, and X represents a halogen atom, acetate, or phosphate , Nitrate, or methyl sulfate)

As an alumina precursor used by the manufacturing method of the said molecular sieve, an aluminum alkoxide is preferable, For example, aluminum tri-sec- butoxide, aluminum isopropoxide, etc. can be used.

As the organic solvent used in the method for producing the molecular sieve, an alcohol-based organic solvent is preferable, and for example, 1-butanol, 2-butanol, 1-propanol, 2-propanol and the like can be used.

In the method of preparing the molecular sieve, the hydrothermal synthesis process is preferably performed for a reaction time of 10 to 100 hours at a reaction temperature of 0 to 200 ° C.

The present invention also provides mesoporous alumina molecular sieve prepared by the above method.

Hereinafter, the present invention will be described in more detail.

The present invention provides a process for producing mesoporous alumina molecular sieves using surfactants and alumina precursors under milder conditions.

The method for producing the mesoporous alumina molecular sieve of the present invention is a hydrolysis rate of the alumina precursor using only a surfactant and stoichiometric water on an alcohol-based organic solvent without using additives such as triethanolamine that have been used in the conventional method. Since it is possible to control the formation of hydrated hydroxides (hydrated hydroxides) due to the rapid hydrolysis can be suppressed to the maximum. It is also possible to control the size and distribution of the mesopores of the alumina molecular sieve formed by adjusting the synthesis conditions and the length of the tail portion of the surfactant.

More specifically, the mesoporous alumina molecular sieve of the present invention is a mixture of a surfactant and an alumina precursor in an organic solvent to form a mixture, and then slowly added water to the hydrothermal synthesis, and then the residual interface through the drying and calcining process It can be prepared by removing the active agent.

The surfactant used in the method of preparing the molecular sieve may be used without particular limitation as long as it is used in the art, but it is preferable to use a cationic surfactant, and more preferably the compound of Formula 1 as the cationic surfactant Can be used.

<Formula 1>

Wherein R ₁ to R ₃ represent a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, R ₄ represents a substituted or unsubstituted alkyl group having 8 to 22 carbon atoms, and X represents a halogen atom, acetate, or phosphate , Nitrate, or methyl sulfate) In particular, examples of the cationic surfactant of Formula 1 include CH ₃ (CH ₂ ) _n-1 N (CH ₃ ) ₃ Br, wherein n represents 12, 14, 16 or 18. And CH ₃ (CH ₂ ) _n-1 N (CH ₃ ) ₃ Cl (wherein n represents 12, 14, 16 or 18). Since the size of the mesopores can be adjusted according to the length of the tail portion of the cationic surfactant can be used to select a cationic surfactant having an appropriate tail length according to the size of the desired mesopores.

Such a surfactant is preferably used in a molar ratio of about 0.1 to 10 moles with respect to 1 mole of the alumina precursor used. If the content of the surfactant is less than 0.1 molar ratio, it is difficult to form an effective micelle (micelle) structure of the surfactant, when the content exceeds 10 molar ratio is not preferable because the excessive amount of the surfactant is not economical.

The alumina precursor used in the method of preparing the molecular sieve may be used without particular limitation as long as it is commonly used in the art, but aluminum alkoxide is preferable, for example, aluminum tri-sec-butoxide, aluminum isopropoxide, Etc. can be used.

In the case of such an alumina precursor, for example, aluminum alkoxide, hydrolysis occurs at a very high rate to form a hydrated hydroxide, so that conventional hydrolysis is suppressed by using an additive or the like. By using the stoichiometric ratio of water corresponding to the content of the alumina precursor, it becomes possible to suppress the rate of hydrolysis.

The water added for hydrolysis is preferably added only in the content of stoichiometric ratio in accordance with the content of the alumina precursor, and is preferably added dropwise to the mixed solution in which the alumina precursor and the surfactant are previously mixed with the organic solvent. The content of water in the stoichiometric ratio is preferably a molar ratio of about 0.1 to 10 moles with respect to 1 mole of the alumina precursor, and more preferably about 1 to 3 moles. If the water content is less than 0.1 molar ratio, hydrolysis with the aluminum precursor is difficult to occur effectively, and if the water content exceeds 10 molar ratio, hydrolysis occurs rapidly due to a large amount of water, which is not preferable because of the problem of formation of uniform mesopores. .

As the organic solvent used in the method for producing the molecular sieve, an alcohol-based organic solvent is preferable, and for example, 1-butanol, 2-butanol, 1-propanol, 2-propanol and the like can be used.

In the method for preparing the molecular sieve, water is added to a mixed solution of a surfactant and an alumina precursor mixed with an organic solvent, followed by hydrothermal synthesis. Such hydrothermal synthesis is a dehydration reaction in a complex of an alumina precursor, a surfactant, and water. It is carried out for the purpose of forming a precursor of the alumina mesoporous material through, typically, the hydrothermal synthesis process is preferably carried out for a reaction time of 10 to 100 hours at a reaction temperature of 0 to 200 ℃.

After the hydrothermal synthesis process, the drying and calcining process can produce the desired mesoporous alumina molecular sieve. The drying process is preferably carried out at room temperature or at a high enough temperature to remove the unreacted water and the organic solvent, it can be variously adjusted according to the content of the water and the organic solvent used. The firing step is carried out to remove the residual surfactant, it is preferably carried out for about 1 to 10 hours at a high temperature of 200 to 800 ℃ in an inert atmosphere or air atmosphere.

The mesoporous alumina molecular sieve obtained by such a manufacturing method can easily adjust the size and distribution of the pores, unlike the conventional method, and is obtained in a more homogeneous form because the formation of hydrated hydroxide is suppressed because the rate of hydrolysis is not fast. The use of additives makes it possible to manufacture more economically.

In the radical definition of the present invention, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms includes a straight or branched radical, wherein at least one hydrogen atom of the radical is a halogen atom, a hydroxyl group, a carboxyl group, a cyano group, an amino group And the like can be substituted. Preferred examples of such radicals are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl and the like.

In the radical definition of the present invention, a substituted or unsubstituted alkyl group having 1 to 22 carbon atoms includes a straight or branched radical, wherein at least one hydrogen atom of the radical is a halogen atom, a hydroxyl group, a carboxyl group, a cyano group, an amino group And the like can be substituted. Preferred examples of such radicals are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, isoamyl, hexyl, octyl, isooctyl, nonyl, lauryl, myri Steel, cetyl, stearyl and the like.

In the radical definition of the present invention, a substituted or unsubstituted alkyl group having 8 to 22 carbon atoms includes a straight or branched radical, and at least one hydrogen atom in the radical is a halogen atom, a hydroxyl group, a carboxyl group, a cyano group, an amino group And the like can be substituted. Preferred examples of such radicals are octyl, isooctyl, nonyl, lauryl, myristyl, cetyl, stearyl and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

<Examples 1 to 5>

The method for synthesizing mesoporous alumina molecular sieve is as follows.

As shown in Table 1 below, CH ₃ (CH ₂ ) _n-1 N (CH ₃ ) ₃ -Br (where n = 12, 14, or 16) as the cationic surfactant and aluminum tri-sec-butoxide as the alumina precursor The side was mixed with 70 ml of 1-butanol, stirred to a uniform solution, and distilled water was added slowly. The molar composition of the homogeneous mixture thus prepared was made to be surfactant: aluminum tri-sec-butoxide: distilled water 0.5: 1: 1. After stirring to obtain a homogeneous mixture, the formed gelled mixture was transferred to a teflon-lined autoclave container, followed by a 24-hour hydrothermal process at various temperatures shown in Table 1 below. Rough The product thus obtained was washed several times with ethanol, and then dried at room temperature for 16 hours and again at 110 ° C. for 5 hours. Mesoporous alumina molecular sieve was obtained by removing the remaining surfactant through a calcination process in an air atmosphere at a temperature of 500 ℃ for 4 hours. The specific surface area and pore distribution according to the synthetic conditions are shown in Table 1 below. In addition, the TEM image of the mesoporous alumina molecular sieve of Example 5 thus prepared is shown in FIG. 1. It can be seen from FIG. 1 that the relatively uniform mesopores have a structure similar to a worm-hole in which they are distributed.

TABLE 1

division Surfactant (CH ₃ (CH ₂ ) _n-1 N (CH ₃ ) ₃ -Br) Temperature (℃) Time (h) BET specific surface area (m ² / g) BJH pore size (nm) Example 1 n = 12 100 24 429 1.8 Example 2 n = 14 100 24 241 6.5 Example 3 n = 16 RT 24 310 7.2 Example 4 n = 16 100 24 337 6.7 Example 5 n = 16 150 24 401 4.8

As shown in Table 1, the surface area of the mesoporous alumina molecular sieve obtained in Examples 1 to 5 was 241 to 429 m ² / g. In the dependence of the BET surface area and BJH pore size distribution obtained from the nitrogen isothermal adsorption test on the synthesis temperature and the tail length of the surfactant in the molecular sieve, the pore size increases as the synthesis temperature increases from room temperature to 423 K It decreased from 7.2nm to 4.8nm, and the distribution of pores was even narrower. It was also found that the pore size increased with the length of the tail of the surfactant. From these results, it can be seen that the pore size can be controlled to some extent according to the conditions of the synthesis.

FIG. 2 shows the results of X-ray diffraction analysis in a range of representative small and wide angles of the mesoporous alumina molecular sieve of Example 4, which was fired at 773 K to remove the surfactant. Only one peak was observed in the small-angle XRD pattern, which is closely related to the distribution of pores, as is known from the reported mesoporous alumina material, indicating an irregular mesoporous structure. From the results of X-ray diffraction analysis at the wide angle, it can be seen that the synthesized mesoporous alumina molecular sieve coincides with the peaks of the bulk gamma-alumina. This fact indicates that the mesoporous alumina molecular sieve of Example 4 is composed of aluminum oxide or low crystalline aluminum oxyhydroxide.

In the pore structure of the mesoporous alumina molecular sieve obtained in Example 4, no significant continuous structure arrangement of the pore structure was observed, although considerable pore structure uniformity was shown. The pore connection structure of the mesoporous pores is considered to have a wormhole-like or sponge-like structure commonly found in irregular mesoporous silica or alumina. Although a wide range of regular arrangements are not seen, one strong peak is believed to represent a regular distribution of each of the pores, as can be seen from the results of the small angle X-ray diffraction analysis.

Solid state NMR allows a structural explanation of aluminum for the mesoporous alumina molecular sieve formed. ²⁷ Al MAS (Masic angle spinning), CPMAS (Cross Polarization Masic Angle Spinning), MQMAS (Multiple Quantum Masic Angle Spinning) NMR experiments according to tail length of surfactant for the molecular sieves of Examples 1 to 5 synthesized in this experiment The results show two well resolved ²⁷ Al NMR peaks, indicating that there are nonequivalent magnetic Al centers. These two peaks can be interpreted as sites of aluminum having tetrahedral and octahedral structures, respectively. Furthermore, a very weak NMR peak could be observed around 33 ppm, which can be determined by the 5-coordinated aluminum site. ²⁷ Al CPMAS (Cross Polarization Magic Angle Spinning) NMR results show three well resolved NMR peaks at 72, 33 and -1 ppm, which is the center of the 5-coordinated aluminum by the cross polarization effect. Can be seen to increase. In other words, the relative NMR peak of 5-coordinated aluminum is increased by magnetization transfer from protons to aluminum. These 5-coordinated aluminum centers have been reported to act as Lewis acids. Therefore, it can be said that the 5-coordinated aluminum center present in the molecular sieve synthesized using the cationic surfactant also has an electron acceptor functional group.

Therefore, the mesoporous alumina molecular sieves synthesized according to the present invention showed a structure of wormhole-like pores, and exhibited an aluminum site having a high surface area thermal stability and a coordination number different from the conventional one.

The mesoporous alumina molecular sieve prepared according to the present invention is simple and economical in the preparation of mesoporous alumina using cationic surfactants, which can control the size and distribution of pores without using additives that have been used in the past. It is possible to produce a molecular sieve having a high surface area and excellent thermal stability.

Claims (12)

(a-1) mixing a surfactant and an alumina precursor in an organic solvent to form a mixture; (a-2) adding water to the mixture; (a-3) hydrothermally synthesizing the mixture to which water has been added; And (A-4) Method for producing a mesoporous alumina molecular sieve, characterized in that it comprises the step of removing the residual surfactant through the drying and calcining process. The method of claim 1, wherein the molar ratio of the alumina precursor: water is 1: 0.1 to 10. The method of claim 2, wherein the molar ratio of the alumina precursor: water is 1: 1 to 3. The method of claim 1, wherein the molar ratio of the alumina precursor: surfactant is 1: 0.1 to 10. The method of claim 1, wherein the surfactant is a cationic surfactant. The method of claim 5, wherein the cationic surfactant is a compound of Formula 1 below. <Formula 1> Wherein R ₁ to R ₃ represent a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, R ₄ represents a substituted or unsubstituted alkyl group having 8 to 22 carbon atoms, X represents a halogen atom, a halogen atom, Acetate, phosphate, nitrate, or methyl sulfate) The method of claim 1, wherein the alumina precursor is aluminum alkoxide. 8. The method of claim 7, wherein the aluminum alkoxide is aluminum tri-sec-butoxide, or aluminum isopropoxide. The method of claim 1, wherein the organic solvent is an alcohol-based organic solvent. 10. The method of claim 9, wherein the alcohol-based organic solvent is 1-butanol, 2-butanol, 1-propanol, or 2-propanol. The method of claim 1, wherein the hydrothermal synthesis process is performed for a reaction time of 10 to 100 hours at a reaction temperature of 0 to 200 ℃. A mesoporous alumina molecular sieve, which is obtained according to the method of any one of claims 1 to 11.