JP4083463B2 - Method for crystallizing pore walls of non-silica mesoporous oxides using a pore-filled template - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a mesoporous material having an improved pore wall while maintaining the pore shape and structure of the mesoporous material.
In this specification, the precursor of a mesoporous material means a mesoporous material composed of pore walls that are not amorphous or have no crystallinity.
[0002]
[Prior art]
Until now, various mesoporous materials having a crystal structure having nanoscale pores of 2 to 50 nm, including silica, have been synthesized. One of the techniques used for the synthesis of inorganic materials having the pore structure is a sol-gel method. The method synthesizes a porous material of an inorganic material using a sol-gel method for synthesizing an inorganic material and a pore structure template formed by a micelle aggregate formed by a surfactant added to the synthesis system. To do. The porous material synthesized in this way is expected as a material having various functions including a catalyst.
However, most of the non-silica mesoporous materials synthesized so far are amorphous or low in crystallinity, so that the field of use is limited from the viewpoint of poor structural stability. There was a problem. Under such circumstances, the present inventors have been working on the development of a technique that eliminates this problem, that is, the development of a technique that makes the material constituting the pore wall forming the mesoporous a crystal structure. Among them, synthesis of mesoporous transition metal oxides having mesopores having pore walls in which single crystals have developed, in particular, crystalline structures maintained throughout the primary particles, especially crystalline mesoporous NbTa oxides, etc. (Japanese Patent Application No. 2000-175306: June 12, 2000, Ceramics, 36 (2001) No. 12, p913-916). However, there are problems that the crystallinity of the pore walls is not sufficient, and that when the crystallization treatment is performed at a high temperature so that the degree of crystallinity is sufficiently high, the pores are collapsed or the periodic structure of the pores is destroyed. That is, when the pore wall of the mesoporous material is modified by heat treatment to have sufficient crystallinity, for example, atomic scale crystallinity, the pores before crystallization and the periodicity of the pores are maintained. It was difficult.
[0003]
Since the pore structure of the mesoporous material is greatly affected by the environment at the time of synthesis, the present inventors have proposed a transition metal oxide having a uniform pore diameter and a periodic pore structure, for example, NbTa oxide. We have also worked on the development of technology to synthesize, and succeeded in establishing a method for synthesizing mesoporous materials that simultaneously satisfy the pore structure and its uniformity and the uniformity of the period of the pore structure (Japanese Patent Application 2002- 61591, filed March 7, 2002).
However, when heat treatment is attempted to improve the crystallinity of the pore walls of the mesoporous material obtained by the improved method, the pores are maintained and the pore structure and uniformity thereof are maintained. There was a problem that it was difficult.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for improving the crystallinity of the pore wall that can maintain the pore structure and the uniformity thereof as much as possible after the crystallization heat treatment, and maintaining the pores before the heat treatment. . In order to solve the above-mentioned problems, the means for maintaining the pores of the precursor of the mesoporous material before the crystallization heat treatment, the pore structure and the uniformity thereof as much as possible were examined. In the examination, the pores can be filled, have heat resistance capable of maintaining the shape during the crystallization heat treatment, and can be removed from the pores after the completion of the crystallization heat treatment or afterwards. Based on the idea of using a pore-filling material (hereinafter sometimes referred to as a filling mold), various trials and errors were made in finding one useful as the filling mold. Among them, the pores are filled with an organic substance that undergoes partial carbonization or complete carbonization by carbonization, and the organic substance is carbonized or partially carbonized or completely carbonized by carbonization. It is possible to form a heat-resistant partially carbonized or completely carbide filled template in the pores by filling the inside, and the precursor of the mesoporous material is tetraethylorthosilicate (TEOS) or sodium silicate solution. And filling the solution into the pores and then gelling at 80 to 100 ° C. to form a filling template in the pores, the precursor of the mesoporous material and BaCl ₂ or NaCl A saturated casting solution of BaCl ₂ or NaCl is formed in the pores when the saturated aqueous solution of is mixed at room temperature and the solution is filled in the pores and then evaporated to dryness at 80 to 100 ° C. The means for forming the filled mold is found to be capable of forming the filled mold in the pores of the precursor of the mesoporous material, crystallization heat treatment, and then transforming the filled mold into the partially carbonized or fully carbonized. In this case, it was found that a mesoporous material with improved crystallinity of the pore wall was obtained by calcination, and in other cases by washing and removing with an acid or alkali solution or water.
[0005]
[Means for Solving the Problems]
In the present invention, at least the pores of the precursor of the mesoporous material maintain the shape during the crystallization heat treatment of the pore walls, and can be removed by firing, water, or water added with an acid or alkali after the heat treatment. Forming a mold, and performing the crystallization heat treatment in the presence of the filling mold, and then firing the filling mold and removing the filling mold with water to which water, an acid or an alkali is added to improve the crystallinity. It is a method of forming. Preferably, the means for forming a filling template in at least the pores of the precursor of the mesoporous material forms an organic substance in the pores that is partially or completely carbonized by carbonization, and the organic substance is carbonized to form the pores. The method includes a step of forming a filling mold made of partially carbonized or completely carbonized therein, or a step of filling the pores with partially carbonized or completely carbonized by carbonization to form a filled mold. More preferably, the organic material partially carbonized or completely carbonized by carbonization treatment is a polymer of furfuryl alcohol, -glucose, fructose, or a derivative thereof. Carbonization treatment used in the step of filling the pores with partially or completely carbonized carbonization treatment to form a filling mold. The method for forming a mesoporous material with improved crystallinity is characterized in that the compound to be produced is a hydrocarbon, and the carbonization treatment is thermal decomposition treatment or / and dehydration decomposition treatment of concentrated sulfuric acid. Is obtained by adding a transition metal salt or / and metal alkoxide, which is a precursor of a transition metal oxide, to a solution in which a precursor of a mesoporous material is dissolved in a polymer surfactant in an organic solvent, and dissolving the transition metal. A salt or / and metal alkoxide is hydrolyzed, polymerized and self-assembled into a sol solution, a gel having a stabilized tissue is obtained from the sol solution, and the gel is baked at 350 ° C. to 550 ° C. in an atmosphere containing oxygen. The crystallization heat treatment is performed at a temperature higher than the firing temperature in the absence of oxygen. That said is a method of forming a mesoporous having improved the crystallinity.
[0006]
Further, the means for forming a filling template in at least the pores of the precursor of the mesoporous material comprises mixing the precursor with tetraethylorthosilicate (TEOS) or sodium silicate solution at room temperature, and tetraethylorthosilicate. -A step of gelling at 80 to 100 ° C after filling the pores with TEOS or sodium silicate solution, or mixing the precursor with a saturated aqueous solution of BaCl ₂ or NaCl at room temperature and, after filling a saturated aqueous solution of BaCl ₂ or NaCl in the pores, it is intended to include the step of forming the pores filling mold BaCl ₂ or NaCl in and evaporated to dryness at 80 to 100 ° C. pore A method for forming a mesoporous film with improved crystallinity.
More preferably, the transition metal salt or / and metal alkoxide, which is the precursor of the transition metal oxide, is added to the solution in which the precursor of the mesoporous material is dissolved in the polymer surfactant in the organic solvent, and the transition is performed. A metal salt or / and metal alkoxide is hydrolyzed, polymerized and self-assembled into a sol solution, and a tissue-stabilized gel is obtained from the sol solution, and the gel is 350 ° C. to 550 ° C. in an atmosphere in which oxygen exists. The mesoporous material with improved crystallinity is obtained by firing at a temperature higher than the firing temperature in the presence of oxygen. It is a method of forming.
[0007]
[Embodiments of the present invention]
The present invention will be described in more detail.
A. The features of the present invention will be described with reference to FIG. 1 in the case of improving the crystallinity of the amorphous pore walls using the mold made of the carbon material.
In FIG. 1, (A) shows an amorphous amorphous pore wall. The state of carbonization treatment after introducing the carbon source into the pore is shown in (B). A state in which the amorphous pore wall filled with carbon is crystallized by heat treatment is shown in FIG. A state in which the carbon source is oxidized and removed after the crystallization is completed is shown in (D). As understood from this, carbon exhibits the function of maintaining the shape of the pores when crystallized by heat treatment.
The process consisting of (A) and (B) has the following aspects 1 to 3.
1, furfuryl alcohol vapor is passed through the crystallization precursor, and at least the furfuryl alcohol in the pores is deposited, and the deposited furfuryl alcohol is heated or solid acid, p-toluenesulfonic acid, etc. The polymer is polymerized with an acid catalyst, and the polymerized product is carbonized (dry distillation) to form a filled mold made of carbon.
The organic matter that is decomposed to carbon by dehydration of concentrated sulfuric acid such as 2, sucrose and D (+)-glucose is made into a dilute sulfuric acid solution, and this solution is mixed with the precursor of the mesoporous material at room temperature. The solution is filled in the pores, and then dilute sulfuric acid is concentrated in an oven heated to 100 ° C. to form concentrated sulfuric acid, and the organic matter is partially carbonized by dehydration. Increase the temperature to dry. By repeating this operation, a filled mold made of carbon (quality) is formed at least in the pores. If necessary, it is fully decomposed into carbon by dry distillation.
3. The hydrocarbon vapor is passed through the precursor of the mesoporous material while thermally decomposing, and carbon (quality) is deposited at least in the pores.
In any case, after the crystallization of the pore walls, the carbon present in the pores is removed as CO ₂ by heating in a heating means such as an electric furnace in an air atmosphere [FIG. C), (D)].
[0008]
B. When silica is used as the filling mold.
A precursor of a mesoporous material and a tetraethylorthosilicate (TEOS) or sodium silicate solution are mixed at room temperature, at least the pores are filled with the solution, and then gelled at 80 to 100 ° C. Next, it is crystallized by firing in an electric furnace in an air atmosphere. Then, mesoporous material with improved crystallinity can be formed by removing silica by washing with alkali.
C. When using BaCl ₂ or NaCl as a filling mold.
A precursor of a mesoporous material and a saturated aqueous solution of BaCl ₂ or NaCl are mixed at room temperature, and at least the pores are filled with the solution, then evaporated to dryness at 80 to 100 ° C., and filled with BaCl ₂ or NaCl. To form. Next, crystallization is performed by firing in an electric furnace in an atmosphere in which oxygen is present, for example, in an air atmosphere. Thereafter, the BaCl ₂ or NaCl filling mold is removed by washing with water.
[0009]
D. As the precursor of the mesoporous material, those formed by a conventionally known method can be used, but those obtained by the method for producing a mesoporous material composed of a transition metal oxide developed by the present inventors are preferable. Can be cited as a thing.
As a method for producing the precursor of the mesoporous material, a transition metal salt or / and a metal alkoxide that is a precursor of a transition metal oxide is added to and dissolved in a solution in which a polymer surfactant is dissolved in an organic solvent. A transition metal salt or / and metal alkoxide is hydrolyzed, polymerized and self-assembled into a sol solution, and a stabilized tissue gel is obtained from the sol solution, and the gel is heated at 350 ° C. to 550 in an atmosphere containing oxygen. In particular, a sol containing 0.003 to 0.01 mol of TaCl ₅ , NbCl ₅ or a mixture thereof and Al isopropoxide mixed with 10 g of an aliphatic linear alcohol and 1 g of a template compound. A solution-forming mixture is prepared, and water or an inorganic acid aqueous solution is added to the mixture in an amount of 5 to 3 with respect to the metal compound. Mole-fold addition is carried out to form a sol solution by hydrolysis and polycondensation, and the sol is transferred to an atmosphere in which oxygen exists and aged at a temperature of 40 ° C. to 100 ° C. to form a gel. And a method for producing a mesoporous oxide comprising firing at 350 ° C to 550 ° C.
The transition metal oxide mesoporous material is produced using at least one selected from the group consisting of chlorides such as La, Ta, Nb, Ti, Zr, Mg, Al, and alkoxides as precursor compounds. .
[0010]
E. As the template material used for producing the mesoporous material, a conventionally used surfactant can be used, but a polyethylene oxide chain (CH ₂ CH ₂ O) _m and a polypropylene oxide chain [CH ₂ CH ( CH ₃ ) O] _n , a nonionic surfactant composed of a block copolymer (wherein m and n are 10 to 70, and the ends of the polymer are etherified with H, alcohol or phenol) For example, trade name: P123 and the like (manufactured by BASF) and trade name: P85, P103 [(HO (CH ₂ CH ₂ O) ₅₆ (CH ₂ CH (CH ₃ ) O) ₁₇ (CH ₂ CH ₂ O) ₅₆ H] and the like (manufactured by Asahi Denka Kogyo Co., Ltd.) are preferable from the viewpoint of forming a desired self-assembled sol and a stable gel from the sol. Examples of the organic solvent useful for forming the sol include aliphatic alcohols. Specifically, methanol, butanol, propanol, hexanol, or a mixture of two or more of these may be mentioned as preferable ones. it can.
[0011]
F. The characteristics of the obtained mesoporous oxide were measured by the following method.
1, XRD (Rigaku RINT 2100, CuKa line) method: X-ray diffraction method: A periodic structure of mesopores is observed by a low angle (1-6 °) peak pattern.
2, Nitrogen adsorption isotherm (Coulter SA3100): The relative pressure (P / P ₀ ) (X axis) region and the pore diameter of the nitrogen adsorption amount (Y axis / volume (mL / g)) increase rapidly Correspond. The degree of rise is related to the pore volume.
3, TEM: Transmission electron microscope (JEMOL JEM 2010F, acceleration voltage 200 kV): A TEM image of a hexagonal array structure of mesoporous NbTa oxide was observed.
4. Electron diffraction image (JEOL JEM 2010F, acceleration voltage 200 kV): An image of six pores regularly arranged at equal distances around one spot perpendicular to the pore. A hexagonal array structure was observed.
[0012]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not interpreted limitedly by this illustration.
Example 1,
Crystallization of mesoporous NbTa oxide, (NbTa) ₂ O ₅ .
As the surfactant, P123 [trade name, BASF _{Corp.: (HO (CH 2 CH 2} O) 20 (CH 2 CH (CH 3) O) 70 (CH 2 CH 2 O) 20) H ] 1g of the beaker Into this, 10 g of ethanol (manufactured by Kanto Chemical Co., Inc.) was added and stirred to dissolve the surfactant. A total of 0.003 to 0.01 mol of a mixture of niobium chloride (NbCl ₅ ) and tantalum chloride (TaCl ₅ ) was added thereto, and dissolved with stirring for 20 minutes. Next, 0.32 to 6.00 g (0.018 to 0.333 mol in terms of mole) of water was added for hydrolysis, and the mixture was further stirred for 10 minutes. The obtained transparent sol solution is transferred to a petri dish and aged for 3 to 7 days in an oven kept at a temperature of 40 ° C. to 80 ° C. in air to form a gel. Next, the obtained transparent gel was baked in an electric furnace in an air atmosphere at 400 to 550 ° C. for 5 hours to remove the surfactant (P123), which is a template component having a pore structure, and niobium chloride (NbCl ₅ ). A white NbTa oxide having a controlled pore structure according to the amount of the mixture of tantalum chloride and tantalum chloride (TaCl ₅ ) and the amount of added water was synthesized.
[0013]
Using the white NbTa oxide having the pore structure as the precursor of the mesoporous material, the following pore wall crystallization heat treatment was performed.
Crystallization heat treatment: Furfuryl alcohol vapor at 200 ° C. was supplied to the precursor of the mesoporous material for 3 hours using nitrogen gas as a carrier gas. As a result, the polymer was deposited and filled in the pores by the furfuryl alcohol polymerization reaction. Next, the polymer was thermally decomposed (dry distillation) by heat treatment at 400 ° C. to 600 ° C. in the absence of oxygen. At this time, crystallization of the pore walls did not proceed. Subsequently, crystallization of the amorphous pore walls proceeded by treatment at 650 ° C. for 1 to 10 hours in the absence of oxygen to prevent removal of carbon (quality) of the filling mold. Thereafter, the carbon (quality) was removed by firing in air, and a crystalline mesoporous NbTa oxide having a crystal structure at an atomic scale was obtained. Low angle X-ray diffraction (XRD) and high angle X-ray diffraction of the NbTa oxide are shown in FIGS. 2 and 3, respectively. From FIG. 2, it was possible to understand the characteristic of maintaining the periodicity of the pores, and from FIG.
Further, the relative pressure P / P ₀ (X axis) region in which the nitrogen adsorption amount (volume / g; mL / g) on the Y axis of the nitrogen adsorption isotherm in FIG. 4 increases corresponds to the pore diameter, Since the degree of the rise is related to the pore volume, it was confirmed that the opening of the pores and the pores of the pores were maintained without being collapsed even after the crystal heat treatment.
Incidentally, in the absence of a filling mold made of carbon, the characteristics of FIGS. 2 and 3 were not observed.
From TEM (transmission electron microscope image) observation, an electron diffraction pattern indicating that the particles are crystallized, a lattice pattern indicating crystallization of the pore wall, a hexagonal structure of the pore opening, and a fine structure are observed. It was confirmed that the periodicity of the holes was maintained.
[0014]
Example 2: Crystallization treatment of mesoporous MgTa oxide.
A precursor of mesoporous material was prepared in the same manner as in Example 1 using a mixture of magnesium chloride and tantalum chloride as the metal source. At this time, MgCl ₂ and TaCl ₅ used as a metal source were mixed so that Mg: Ta = 1: 2.
The crystallization method was performed in the same procedure as in Example 1. However, as a condition, a method of firing at 850 ° C. for 1 hour in the absence of oxygen was performed.
As in Example 1, the low-angle pattern, high-angle pattern, and nitrogen adsorption isotherm shown in FIGS. 5 to 7 are worse than those in Example 1, but the pores are maintained, the structure and the periodicity are maintained. Can be confirmed.
[0015]
Example 3 Crystallization of mesoporous anatase TiO ₂ oxide.
As a nonionic surfactant, P85 [trade name, manufactured by Asahi Denka Kogyo Co., Ltd .: (HO (CH ₂ CH ₂ O) ₃₉ (CH ₂ CH (CH ₃ ) O) ₂₆ (CH ₂ CH ₂ O) ₃₉ ) H ] Is stirred and dissolved in a normal alcohol, followed by introduction of titanium tetraisopropoxide as a metal source. Into this, 37% hydrochloric acid is added as a reaction catalyst to obtain a transparent sol solution. Thereafter, the template was removed by aging and baking to obtain a precursor of a mesoporous material.
The crystallization method was performed in the same procedure as in Example 1. As conditions, crystallization was advanced by heat treatment under relatively mild conditions of 400 ° C. for 10 hours in the absence of oxygen. Carbon (quality) removal was performed in air at 350 ° C. for 15 hours. 8 to 10 confirm the maintenance of the pores, the maintenance of the structure and the periodicity, although the characteristics are worse than in the case of Example 1 from the low angle pattern, the high angle pattern and the nitrogen adsorption isotherm as in Example 1. it can.
[0016]
【The invention's effect】
As described above, by utilizing the present invention, that is, by subjecting the pore wall to crystallization heat treatment in a state where the pore is filled with the filling template, pore opening, pore periodicity, and A mesoporous material having a highly crystalline pore wall, which has been difficult to obtain in the past, was obtained by maintaining the pore vacancies and improving the crystallinity of the pore wall. It is clear that it will contribute greatly to the development of mesoporous materials technology.
[Brief description of the drawings]
FIG. 1 shows a conceptual diagram in the case of improving the crystallinity of an amorphous pore wall using a template made of a carbon material of one embodiment of the present invention. FIG. 2 shows the crystalline mesoporous NbTa of Example 1. 3 shows a low angle X-ray diffraction pattern of the oxide. FIG. 3 shows a high angle X-ray diffraction pattern of the crystalline mesoporous NbTa oxide of Example 1. FIG. 4 shows the crystalline mesoporous NbTa of Example 1. FIG. 5 shows a low angle X-ray diffraction pattern of the crystalline mesoporous MgTa oxide of Example 2. FIG. 6 shows the crystalline mesoporous MgTa oxide of Example 2. FIG. 7 shows the nitrogen adsorption isotherm of the crystalline mesoporous MgTa oxide of Example 2. FIG. 8 shows the crystalline mesoporous anatase TiO ₂ oxidation of Example 3. Shows low-angle X-ray diffraction pattern of objects Crystalline Mesopo of Example 3 - Las anatase showing a high angle X-ray diffraction pattern of TiO ₂ oxides [10] crystalline Example 2 Mesopo - nitrogen adsorption isotherm Las anatase TiO ₂ oxide Show

Claims (8)

At least the pores of the precursor of the mesoporous material are maintained in shape during the crystallization heat treatment of the pore walls, and after the heat treatment, a filling mold that can be removed by baking, water, or water added with acid or alkali is formed. A method of forming a mesoporous material having improved crystallinity by performing the crystallization heat treatment in the presence of the filling mold and then removing the filling mold by baking, water, or water added with an acid or an alkali. . The means for forming a filling template in at least the pores of the precursor of the mesoporous material forms an organic substance that is partially or completely carbonized by carbonization treatment, and oxidatively decomposes the organic substance formed in the pores. And a step of forming a filling mold consisting of partial carbonization or complete carbonization in the pores, or a step of filling the pores with partial carbonization or complete carbonization by carbonization to form a filling template. The method for forming a mesoporous material with improved crystallinity according to claim 1. The organic substance partially carbonized or completely carbonized by the carbonization treatment is a polymer of furfuryl alcohol, -glucose, fructose, or a derivative thereof. The compound used in the step of forming a filling mold is a hydrocarbon, and the carbonization treatment is thermal decomposition treatment and / or dehydration decomposition treatment of concentrated sulfuric acid. Forming a mesoporous material. A transition metal salt or / and metal alkoxide, which is a precursor of a transition metal oxide, is added to and dissolved in a solution in which a precursor of a mesoporous material is dissolved in a polymer surfactant in an organic solvent, and the transition metal salt or / And forming a sol solution obtained by hydrolyzing, polymerizing and self-organizing metal alkoxide, obtaining a gel having a stabilized structure from the sol solution, and baking the gel at 350 ° C. to 550 ° C. in an atmosphere containing oxygen. The crystal according to claim 1, 2 or 3, wherein the crystallization heat treatment is performed at a temperature higher than the firing temperature in the absence of oxygen. Of forming mesoporous materials with improved properties. Means for forming a filling template in at least the pores of the precursor of the mesoporous material is obtained by mixing the precursor with tetraethylorthosilicate (TEOS) or sodium silicate solution at room temperature, and tetraethylorthosilicate ( 2. The method for forming a mesoporous material with improved crystallinity according to claim 1, comprising a step of gelling at 80 to 100 ° C. after filling TEOS) or a sodium silicate solution into pores. 3. A transition metal salt or / and metal alkoxide, which is a precursor of a transition metal oxide, is added to and dissolved in a solution in which a precursor of a mesoporous material is dissolved in a polymer surfactant in an organic solvent, and the transition metal salt or / And forming a sol solution obtained by hydrolyzing, polymerizing and self-organizing metal alkoxide, obtaining a gel having a stabilized structure from the sol solution, and baking the gel at 350 ° C. to 550 ° C. in an atmosphere containing oxygen. The mesoporous film with improved crystallinity according to claim 5, wherein the crystallization heat treatment is performed at a temperature higher than the firing temperature in the presence of oxygen. How to form. Means for forming a filled mold into at least the pores of the precursor of the mesoporous material is filled with the precursor BaCl ₂ or mixed with a saturated aqueous solution at room temperature of NaCl, BaCl ₂ or a saturated aqueous solution of NaCl in the pores _{2. The method according} to claim 1, further comprising a step of forming a BaCl ₂ or NaCl filling template in the pores when evaporated to dryness at 80 to 100 ° C. A method of forming a mesoporous material. A transition metal salt or / and metal alkoxide, which is a precursor of a transition metal oxide, is added to and dissolved in a solution in which a precursor of a mesoporous material is dissolved in a polymer surfactant in an organic solvent, and the transition metal salt or / And forming a sol solution obtained by hydrolyzing, polymerizing and self-organizing metal alkoxide, obtaining a gel having a stabilized structure from the sol solution, and baking the gel at 350 ° C. to 550 ° C. in an atmosphere containing oxygen. The mesoporous film with improved crystallinity according to claim 7, wherein the crystallization heat treatment is performed at a temperature higher than the firing temperature in the presence of oxygen. How to form.

Images