JP3332817B2 - Mesoporous silica and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a mesoporous silica having a porous structure having a uniform pore diameter and useful for a catalyst carrier, an adsorbent, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Porous silica is utilized as a material separating agent, a catalyst carrier, an immobilizing carrier for enzymes and functional organic compounds, etc. by utilizing its porous structure. In these applications, porous silica having a uniform pore diameter and a high specific surface area has been developed and put to practical use in order to effectively exert the action caused by the pore structure.

Conventionally, as a technique for producing a porous silica material called mesoporous silica, the following two methods are known according to the type of silica source. The first method uses a layered silicate as a starting silica source, and is reported by T. Yanagisawa [Bu
Ll.Chem.Soc.Jpn., to Vol.63,988-992 (1990)], which is one of the layered silicate kanemite _{(NaHSi 3 O 5 · 3H 2} O) and an alkyl trimethyl ammonium (hereinafter referred to as "ATMA" And the like, and a method for obtaining mesoporous silica by synthesizing the composite and calcining the composite to remove organic substances has been proposed. The second method uses amorphous silica powder or an aqueous solution of alkali silicate as a starting silica source,
JSBeck et al. (J. Am. Chem. Soc., Vol. 114, 10834-10
843 (1992)] describes synthesis examples from various silica sources. As an example of the synthesis, for example, a mixture of precipitated silica and an aqueous solution of tetramethylammonium silicate is used for A
A method in which TMA is reacted at a temperature of 150 ° C. to form a composite, or a method in which silica gel obtained by neutralizing sodium silicate with sulfuric acid is reacted with ATMA at a temperature of 100 ° C. for 6 days to form a composite, is proposed. Have been.

However, in the first method, it is necessary to prepare kanemite as a starting material, and since a large amount of Na is present in the reaction system, the Na component destroys the silica structure during calcination of the composite, and the porous structure is destroyed. Has the drawback of reducing the surface area. Further, Na becomes a catalyst poison in applications such as a catalyst, and causes a reduction in catalytic activity. On the other hand, when the amorphous silica powder is used as a raw material in the second method, heating and heating of an autoclave at 100 ° C. or more are required, so that energy costs and equipment costs increase, and tetramethylammonium silicate contains an alkali metal. Although it is a preferable reaction material because it is an aqueous alkali silicate solution, it is expensive, and requires a water treatment because all the tetramethylammonium in the raw material is contained in the wastewater. In addition, the method of obtaining silica gel by neutralizing sodium silicate with sulfuric acid requires a long aging operation at 100 ° C. or more for 6 days, and the heat resistance of porous silica due to the presence of a large amount of Na in the reaction system. There are drawbacks such as a decrease in performance. In addition, Japanese Patent Publication No. 5-503499 discloses a method for producing mesoporous silica in which the silica sol or a quaternary ammonium silicate and precipitated silica or silica sol are used as a silica source. For example, a commercially available silica sol has a primary particle diameter of 10 nm.
The above dense silica polymer having a specific surface area of 300
m ² / g or less, the degree of polymerization of SiO ₂ is 10,000 or more, whereas mesoporous silica has a specific surface area of 800 to 1400.
m ² / g, which is estimated to be from 2 to 4 SiO _{2 in} the thickness direction of the wall of the mesopore skeleton estimated from this,
In order to form a mesopore structure from SiO ₂ particles of silica sol, it is essential to use a large amount of heat energy and a large amount of an alkali agent. In addition, the precipitated silica can be considered as aggregate particles in which the silica sol is continuous, but when such aggregate particles are used as a silica source, the aggregate structure is cut, and further the mesoporous silica is converted from fragmentary sol particles. Due to the need to reconstruct the backbone arrangement, a higher thermal energy is required than silica sol. In this reconstitution, the silica molecules detached from the particles due to the partial dissolution of the sol particles form a mesoporous skeleton, but in the dissolution step, a very limited fixed amount of an alkaline component must be present. At this time, the excess alkali amount is stable in the fused silica state and does not contribute to the skeletal structure, so that a long treatment and a high temperature state are required to complete the reaction with a limited alkalinity, and industrially, A high temperature and high pressure device such as an autoclave will be used. The use of quaternary ammonium silicate alone results in an excessively large ratio of quaternary ammonia / silica released upon dissociation and an excessive amount of alkali stabilizes silica, contributing to the formation of a mesopore skeleton. It cannot be used as a single source of silica because it will no longer be used, and must be used in combination with precipitated silica or silica sol. Considering that the reaction conditions require a long time at high temperature and pressure, and the production process of quaternary ammonium silicate is taken into consideration. Then, it is rather disadvantageous industrially. As described above, it is difficult to obtain mesoporous silica having a low Na content and a uniform pore diameter using the silica source according to the conventional technique.

[0005]

Accordingly, an object of the present invention is to provide a uniform and sharp pore distribution, a high specific surface area, an extremely low Na content, and a relative vapor pressure of 0.5.
An object of the present invention is to provide mesoporous silica having an extremely high benzene adsorption amount and excellent crystallinity, and a method for producing the same.

[0006]

Under such circumstances, the present inventors have made intensive studies and as a result, have dissolved sodium silicate and a cationic surfactant once in an alkaline region, and then deposited silica under a specific condition. The mesoporous silica obtained by performing the reaction below has a high specific surface area and a high benzene adsorption amount at a relative vapor pressure of 0.5, and particularly has a very low Na content and a uniform Further, they have found that they have a sharp pore distribution, and have completed the present invention.

That is, according to the present invention, the average pore diameter is 20 to
Silica having a porous structure of 100 angstroms, having a nitrogen adsorption specific surface area of 1000 m ² / g or more, a Na content of 0.1% by weight or less, and a relative vapor pressure of 0.
05, the benzene adsorption at a relative vapor pressure of 0.5 was 60 g / 10
An object of the present invention is to provide mesoporous silica having property characteristics of 0 g or more.

In the present invention, sodium silicate and a cationic surfactant are dissolved in an alkaline region, and the pH is adjusted with an acid.
7 to 12 to precipitate silica and then 90 ° C
The first step of reacting under the above heating to form a complex of the silica and the cationic surfactant, the second step of washing the complex and removing Na, and then the removing Na An object of the present invention is to provide a method for producing the above mesoporous silica, which sequentially performs a third step of firing the composite.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The mesoporous silica of the present invention comprises:
The porous structure has a uniform and sharp pore distribution of micropores or mesopores having an average pore diameter of 20 to 100 Å, and a nitrogen adsorption specific surface area of 1 according to the BET method.
It has an extremely large surface area of 000 m ² / g or more and a Na content of 0.1% by weight or less, which is significantly smaller than that of a conventional porous silica material. The benzene adsorption at a relative vapor pressure of 0.05 is 8 g / 100 g or less, and the benzene adsorption at a relative vapor pressure of 0.5 is 60 g / 100 g.
It has the above adsorption characteristics. Further, among the above characteristics of the mesoporous silica, the average pore diameter is 30 to 50.
Angstrom is preferred, and the nitrogen adsorption specific surface area by the BET method is preferably 1,000 or more and 1200 m ² / g or less,
The Na content is preferably 0.05% by weight or less, and the amount of benzene adsorbed at a relative vapor pressure of 0.05 is 7.5 g / 100.
g or less, and the benzene adsorption amount at a relative vapor pressure of 0.5 is preferably 65 g / 100 g or more.

[0010] In the present invention, the average pore diameter was measured spacing d100 of hexagonal structure (100) plane of the powder method X-ray diffraction pattern, obtained from the equation of an average pore diameter = 2d ₁₀₀ / √3 from this value. The specific surface area is determined from a nitrogen adsorption isotherm by a known BET method.

The relative vapor pressure 0.05 is 5 to 100 n
The pore radius determined by the following Kelvin equation effective for measuring the pore radius of m corresponds to a pore diameter of 14 Å. Therefore, in the present invention, the fact that the benzene adsorption amount at a relative vapor pressure of 0.05 is 8 g / 100 g or less indicates the pore characteristics that pores having a pore diameter of 14 Å or less substantially do not exist.

In (P / P ₀ ) = − 2V COS θ / r _k RT In the formula, V indicates a molar volume of the adsorbate, θ indicates a contact angle (usually 0), and R is a gas constant. the shows, T represents the absolute temperature, r _k denotes the radius of the capillary condensation (pore), P /
P ₀ indicates the relative vapor pressure.

In the present invention, the amount of benzene adsorbed means that a sample is heated and evacuated at 400 ° C. for 1 hour, then a predetermined amount of benzene vapor is introduced at 25 ° C., and the weight and pressure change at that time are measured by In-Situ measurement. It is measured using a possible CAHN-200 balance and determined from the created adsorption isotherm.

Next, the production method of the present invention will be described. The first step of the present invention is to use sodium silicate as a raw material,
This is a step of forming a complex of silica and a cationic surfactant. As the sodium silicate, SiO ₂ /
Na ₂ O having a molar ratio of 2 to 4 can be used.
No. sodium silicate is preferred because it has a relatively low Na content and is inexpensive.

The cationic surfactant is not particularly restricted but includes quaternary ammonium salts and alkylamine salts. The quaternary ammonium salts of the general formula ^{_{[R 1 n (CH 3) 4}} -n N ] ⁺ [X] ^- (1) (wherein, R ¹ represents a straight-chain alkyl group, n 1 An integer of 3 and X represents a halogen atom or a hydroxyl group), and particularly, a general formula [R ¹ (CH ₃ ) ₃ N] ⁺ [X ] ^-
The halide or hydroxide of a quaternary alkyltrimethylammonium represented by the following formula (I) is preferred because it forms a uniform mesoporous silica. In the general formula (1), the number of carbon atoms of the linear alkyl group R ¹ is preferably 8 to 24, particularly preferably 8 to 17. If the carbon number is 25 or more, it is insoluble and difficult to handle. As the halogen atom for X, a chlorine atom and a bromine atom are preferable. Specific compounds of the quaternary alkyltrimethylammonium salt include, for example, octyltrimethylammonium chloride, octyltrimethylammonium bromide, octyltrimethylammonium hydroxide, decyltrimethylammonium chloride, decyltrimethylammonium bromide, decyltrimethylammonium hydroxide, Dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium hydroxide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium hydroxide, octadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, hydroxylic acid Include octadecyl trimethylammonium etc., may be used in combination of one or more of these ammonium salts. Further, in the general formula (1), those in which X is a hydroxyl group are particularly preferably used since the subsequent washing treatment for removing Na is advantageously performed.

The alkylamine salt is represented by the general formula (2): [R ² NH ₃ ] ⁺ [X] ^- (2) (wherein R ² represents a linear alkyl group, and X represents a halogen atom Or a hydroxyl group.). In the general formula (2), a linear alkyl group R
The number of carbon atoms of ¹ is preferably 8 to 24, particularly 8 to 17
Is preferred. If the carbon number is 25 or more, it is insoluble and difficult to handle.
Examples of the halogen atom for X include a chlorine atom and a bromine atom.

Further, in the present invention, the quaternary ammonium salt is preferably used because it has a higher basicity than an alkylamine salt and has excellent reactivity.

In the first step of the method of the present invention, sodium silicate and a cationic surfactant are first dissolved in water in an alkaline region to form a transparent homogeneous solution. The amount of water in the system is preferably in the range of 50 to 300 mol, preferably 70 to 150 mol, per 1 mol of SiO ₂ .
The amount of the cationic surfactant to be added is SiO 2
The molar ratio of ₂ / surfactant is usually 2 to 10, preferably 4 to 5.

The range of the alkaline region is usually pH
12-14. If necessary, caustic soda,
The pH may be adjusted with an alkaline agent such as sodium silicate, sodium aluminate, an alkyl ammonium hydroxide, a quaternary ammonium silicate, and an organic amine so as to be in the above range. In this step, if necessary,
For the purpose of increasing the solubility of sodium silicate in water, the sodium silicate may be dissolved under heating.

Next, an aqueous solution of an alkali silicate containing the cationic surfactant obtained by the above method is acidified to pH 7
The silica is precipitated by adjusting the pH to -12, preferably 7-11, and then reacted under heating to form a complex of silica and a cationic surfactant. As neutralizing acids,
Commonly used mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid, and organic acids such as acetic acid and citric acid can be used, and one or more of these can be used in combination. The acid is gradually added to the aqueous solution, and while the pH is adjusted to 7 to 12, silica is gradually precipitated from the aqueous solution to prepare a slurry. The reason for adjusting to this pH range is that silica molecules precipitated in this pH range are smoothly cut and polymerized, and reconstructed into a homogeneous structure. However, if the pH is 12
Is exceeded, the solubility of silica increases, while pH
If it is less than 7, silica is rapidly precipitated, which is not preferable.

Then, the mixture is reacted and aged while being heated to form a complex of active silica and a surfactant. The reaction temperature of the silica and the cationic surfactant is usually 50 ° C. or higher, preferably 90 ° C. or higher. Even if the temperature is lower than 50 ° C., the reaction is carried out, but the reaction time is prolonged, which is not industrially advantageous, and is also not preferable because the physical properties tend to decrease. Although the reaction time differs depending on the temperature, it is usually 0.1 minutes, including the aging time.
5 to 20 hours. The aging reaction is preferably performed at 100 ° C. or lower.

In the first step, the silica is successively electrostatically bonded to the surfactant component, and a polymerization with silanol dehydration is caused between the silicas which have come close to each other to form a continuous precursor of the connected structure. . The reaction slurry thus obtained is filtered by a conventional method and recovered as a complex composed of silica and a cationic surfactant. In addition,
The formation of the complex of silica and activator formed in this step can be varied depending on the type of the cationic surfactant, particularly the length of the alkyl chain, and this is treated in the third step described below. When applied, it affects the physical properties of silica, especially the size of mesopores. Therefore, if the above-mentioned cationic surfactant is selected, one having a desired mesopore size can be prepared.

The second step is a step of removing excess Na ions from the complex comprising silica and the cationic surfactant obtained in the first step, so that the composite is substantially free of Na. . As such an operation method, washing treatment with water by means of repulping or the like may be performed until the Na content becomes 0.1% by weight or less. After washing, a complex consisting of silica in the form of solid powder substantially free of Na and a cationic surfactant can be recovered by drying at a temperature of 100 to 120 ° C.

The third step is a step of removing the surfactant by calcination from the composite subjected to the Na removal obtained in the second step. The firing temperature is not particularly limited and depends on the type of surfactant used, but is higher than the temperature at which the surfactant component disappears, usually 500 ° C. or higher. Firing at a higher temperature is advantageous for stabilizing the structure of silica and improving mechanical strength, but if it exceeds 1200 ° C., it tends not to contribute to stabilization of the structure. Also,
The firing time is appropriately set in relation to the processing temperature,
Usually 10 minutes to 3 hours.

The mesoporous silica obtained through the first to third steps is a mesoporous silica having the above-mentioned properties and having an average particle diameter of 30 to 90 μm. The particle size can be appropriately adjusted to a desired particle size according to the purpose of use.

The mesoporous silica of the present invention has a microporous composition having an average pore diameter of 20 to 100 angstroms and a pore diameter of mesopore size, and has a very large specific surface area of at least 1,000 m ² / g of nitrogen adsorption specific surface area. In particular, as compared with a conventional porous silica material, the content of Na is extremely small, and a uniform and sharp pore distribution is obtained. Mesoporous silica having such properties is Na
When used as a catalyst carrier because of its extremely low content, there is no change in the catalyst performance with time and the heat resistance is good. In addition, since it has a uniform and sharp pore distribution, organic substances can be selectively adsorbed more than conventional ones. Therefore, excellent performance is exhibited as a catalyst carrier and an adsorbent used under severe temperature and atmosphere conditions. Further, according to the production method of the present invention, the mesoporous silica can be industrially advantageously produced by sequentially performing the first to third steps.
In particular, a reaction between an aqueous solution of an alkali silicate and an acid is performed, and a reaction between the active silica continuously generated in the system and the surfactant is performed at a temperature of 95 ° C. or higher, whereby a more uniform micelle is formed. During ripening of the body, the silica structure is reconstructed on the micelle surface and smoothly becomes a precursor of mesoporous silica. Therefore, as described above, various precursors can be formed by changing the type of the surfactant and the reaction conditions, and a desired mesoporous silica can be efficiently produced by aging the precursor.

[0027]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the present invention. Example 1 A 7% aqueous solution containing a molar ratio of octadecyltrimethylammonium chloride to hexadecyltrimethylammonium chloride of 3: 7 was prepared. Pre OH ^- type and the anion exchange resin (Amberlite IRA-410;
(Rohm & Haas Co., Ltd.) to give a 3.8% aqueous solution containing octadecyltrimethylammonium hydroxide and hexadecyltrimethylammonium hydroxide. Next, No. 3 sodium silicate (SiO ₂ : 29%, Na ₂ O: 9.5%) was added to 587 g of the aqueous solution prepared above so that the molar ratio of SiO ₂ / surfactant was 5.
69 g was added to obtain a slurry. After adding 200 g of a 1N NaOH aqueous solution so that the slurry became transparent, the temperature was raised to 65 ° C. to completely dissolve SiO ₂ (pH 12.5). Then, 1N HCl was added to this aqueous solution.
383 g of an aqueous solution was gradually added over 30 minutes,
₂ was gradually precipitated to obtain a mixed slurry (pH 9.6). The temperature of the mixed slurry was raised to 95 ° C. while stirring, and the mixture was allowed to react for 3 hours, and then allowed to cool for 14 hours. The slurry was filtered by a conventional method, and the obtained silica-surfactant complex was washed with 1 L of distilled water and then heated at 110 ° C.
And dried all night long. The complex is then heated at 650 ° C. for 30 minutes.
The organic component was removed by baking for minutes. As a result of X-ray diffraction of the obtained fired product, 2θ = 2.06 °, 3.6
Peaks were observed at 0 degrees, 4.16 degrees and 5.52 degrees, and it was recognized that a skeleton of a mesoporous composition having a uniform pore diameter with an average pore diameter of 42.9 angstroms remained.

Example 2 A 7% aqueous solution containing a molar ratio of octadecyltrimethylammonium chloride to hexadecyltrimethylammonium chloride of 3: 7 was prepared. Pre OH ^- type and the anion exchange resin (Amberlite IRA-410;
(Rohm & Haas Co., Ltd.) to give a 3.8% aqueous solution containing octadecyltrimethylammonium hydroxide and hexadecyltrimethylammonium hydroxide. 2N was added to 1832 g of the aqueous solution prepared above.
NaOH aqueous solution (250 g) was added and the temperature was raised to 65 ° C.
No. 3 sodium silicate (SiO ₂ : 29%, Na ₂ O: 9.5%) 1 so that the molar ratio of SiO ₂ / surfactant would be 4
73 g was added to prepare a clear and uniform mixed solution (p
H11.8). Then, 431 g of a 2N HCl aqueous solution was gradually added to this aqueous solution over 30 minutes to gradually precipitate SiO ₂ , thereby obtaining a mixed slurry (pH 9.6).
This mixed slurry was heated to 95 ° C. while stirring,
The reaction was allowed to proceed for 3 hours and then allowed to cool for 14 hours. This slurry was filtered by a conventional method, and the obtained silica-surfactant complex was washed with 1 L of distilled water and dried at 110 ° C. overnight. Next, the composite was calcined at 650 ° C. for 2 hours to remove and remove organic components. As a result of X-ray diffraction of the obtained fired product, 2θ = 2.09 °, 3.63 °,
Peaks were found at 4.19 ° and 5.56 °, and it was confirmed that a skeleton of a mesoporous composition having a uniform pore size with an average pore size of 42.2 Å remained.

Example 3 A 5% aqueous solution of cetyltrimethylammonium chloride and 50 g of a 4N aqueous NaOH solution were mixed, and the temperature was raised to 65.degree. Then, No. 3 sodium silicate (SiO ₂ : 29%, Na ₂ ) was added so that the molar ratio of SiO ₂ / surfactant would be 5.
(O: 9.5%) was added to obtain a transparent and homogeneous mixed solution (pH 11.7). Then, 2N H was added to this aqueous solution.
139 g of an aqueous Cl solution was gradually added over 30 minutes,
iO ₂ was gradually precipitated to obtain a mixed slurry (pH 10). The temperature of the mixed slurry was raised to 95 ° C. while stirring, and the mixture was reacted for 3 hours, and then allowed to cool for 17 hours. The slurry was filtered by a conventional method, and the obtained silica-surfactant complex was washed with 1 L of distilled water and then heated at 110 ° C.
And dried all night long. Next, the composite was calcined at 650 ° C. for 2 hours to remove and remove organic components. As a result of X-ray diffraction of the obtained fired product, 2θ = 2.32 °, 3.98
At 4.58 and 6.02 degrees, and it was recognized that a skeleton of a mesoporous composition having a uniform pore size with an average pore size of 38.0 angstroms remained.

With respect to the mesoporous silica obtained in Examples 1 to 3, the BET specific surface area, average pore diameter, pore volume,
Determine the Na content, benzene adsorption and water vapor adsorption,
This is shown in Table 1. In addition, SEM photographs, TEM photographs, and pore size distributions of the appearance of the mesoporous silica particles obtained in Example 2 are shown in FIGS. 1, 2, and 3, respectively. The benzene adsorption amount, water vapor adsorption amount and pore size distribution are as follows:
It was determined by the following method.

(Evaluation of benzene adsorption amount) CAHN-20
After a benzene adsorption isotherm at 25 ° C. was prepared using a 00 type balance, the benzene adsorption amounts at relative vapor pressures of 0.05 and 0.5 were determined. (Evaluation of Amount of Water Vapor Adsorption) Using a CAHN-2000 balance, a water vapor adsorption isotherm at 25 ° C. was prepared, and then the amount of water adsorption at a relative vapor pressure of 0.8 was determined. (Pore size distribution) Dollimore-Heal method (J. Appl. Chem., 14, 10
8 to (1964)).

[0032]

[Table 1]

[0033]

The mesoporous silica of the present invention has a uniform and sharp pore distribution, and particularly has a Na content of 0.1 to 0.1.
Since it has a characteristic of being as low as 1% by weight or less and having a benzene adsorption amount of 60 g / 100 g or more at a relative vapor pressure of 0.5, it is particularly useful as a catalyst carrier or adsorbent used under severe conditions, for example. . Further, according to the production method of the present invention, the mesoporous silica of the present invention can be produced efficiently and in a short time without going through a process such as high temperature and high pressure, and therefore, its industrial utility value is extremely large.

[Brief description of the drawings]

FIG. 1 is an SEM photograph (magnification: 3000 times) showing the appearance of mesoporous silica particles obtained in Example 2.

FIG. 2 is a TEM photograph (magnification: 500,000) showing the porous structure of the mesoporous silica obtained in Example 2.
Times).

FIG. 3 is a view showing a pore size distribution curve of mesoporous silica obtained in Example 2.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-152317 (JP, A) JP-A-9-40417 (JP, A) JP-A-10-36109 (JP, A) JP-A-10- 231115 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 33/12-33/193 WPI (DIALOG) JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A silica having a porous structure having an average pore diameter of 20 to 100 angstroms, a nitrogen adsorption specific surface area by a BET method of not less than 1000 m ² / g, and a Na content of 0.1.
A mesoporous silica characterized by having a benzene adsorption amount of 8 g / 100 g or less at a relative vapor pressure of 0.05 or less and a benzene adsorption amount of 60 g / 100 g or more at a relative vapor pressure of 0.5 or less. 2. After dissolving sodium silicate and a cationic surfactant in an alkaline region, the pH is adjusted to 7 to 12 with an acid to precipitate silica, and then reacted under heating at 90 ° C. or higher , A first step of forming a complex of the silica and the cationic surfactant, a second step of washing the complex and removing Na, and then a third step of calcining the complex subjected to the removal of Na. 2. The method according to claim 1, wherein the steps are sequentially performed.
A method for producing the mesoporous silica according to the above. 3. The cationic surfactant is represented by the following general formula (1): [R ¹ (CH ₃ ) ₃ N] ⁺ [X] ⁻ (1) (wherein R ¹ is a linear alkyl group) And X represents a halogen atom or a hydroxyl group). 4. The method for producing mesoporous silica according to claim 2, which is a quaternary alkyltrimethylammonium halide or hydroxide represented by the following formula: