JPH1179743A - Mesoporous body having hollandite type crystal structure and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mesoporous body of a hollandite type compd. having a large specific surface area and excellent in monodispersity of pore diameter distribution. SOLUTION: The mesoporous body has a chemical compsn. represented by the chemical formula Ax My N8 -y O16 (where A is an alkali metallic or alkaline earth metallic element, M is a di- or trivalent metallic element, N is a tetravalent metallic element, 0.8<x <=2 and 0.8<y <=2), a hollandite type crystal structure, >=10m<2> /g BET specific surface area calculated from the adsorption- desorption isotherm of nitrogen and a pore diameter distribution curve excellent in monodispersity and having about 2 nm half-width of a peak in the pore diameter range of 3-30 nm and about >=20 mm<3> .g peak height of pore area by the Dollimore-Heal method analysis method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention has the formula A _x M _y N
_8-y O ₁₆ (where A is an alkali or alkaline earth metal element, M is a divalent or trivalent metal element, N is a tetravalent metal element, 0.8 <x ≦ 2, 0.8 <y ≦ 2) The present invention relates to a porous compound having a hollandite-type crystal structure having a chemical composition represented by ≦ 2).

[0002]

2. Description of the Related Art There is a classification method for porous bodies according to the size of the pore diameter. That is, according to the IUPAC definition, the pore size is 2n.
Micropores of m or less are called micropores, pores in the range of 2 to 50 nm are called mesopores, and pores of 50 nm or more are called macropores. In a hollandite-type substance having a tunnel structure (pore diameter of about 0.35 nm or less), an example is known in which a crystal structure is micropore-pored by extracting an alkali metal ion or the like in the tunnel structure. No examples have been reported in which micropores, mesopores, or macropores were formed by controlling the size or shape. Conventional inorganic materials having pores in the mesopore region are silica gel, activated alumina, clay mesopore porous material, and porous glass. Since these materials exhibit the properties of a porous body,
Silica gel and porous glass are used as amorphous materials, and activated alumina and clay mesopore materials are used as amorphous or poorly crystalline.

[0003] That is, since the conventional mesopore porous body expresses porosity using an amorphous state or a poorly crystalline state, the structure in the pores and the chemical composition of the obtained porous body have a crystalline structure. It has the disadvantage that it does not have a defined homogeneity as defined and it varies between pores. For example, in a temperature range of about 500 ° C. where the mesopore porous body can be formed, alumina-based γ-alumina, which is a low-temperature phase, is formed, and thus has poor crystallinity.
In addition, since the clay mesopore porous body is formed by introducing fine particles of silica or the like as another component between the layers of the clay layer structure and crosslinking to form a porous body, the structure and chemical composition of the clay substance itself and the interlayer-introduced substance are not affected. Uniformity is also reflected in the pores. The mesopore porous body of silica gel or porous glass has an amorphous skeleton itself, and the surface structure and chemical composition in the pores lack homogeneity. As described above, in the conventional amorphous state of the mesopore porous body, the atomic arrangement does not have any periodicity, and the atomic planes forming the inner walls of the pores are different for each pore. For this reason, conventional mesoporous materials have selectivity based on the shape effect, but have a problem in the accuracy of reaction selectivity utilizing the chemical function of the pore surface. Properties derived from the functional function will have a distribution lacking homogeneity.

[0004] Further, conventionally, the formula _{A x M y N 8-y} O 16 ( where A is an alkali or alkaline earth metal element, M is 2
A trivalent or trivalent metal element, N is a tetravalent metal element, 0.8
The synthesis of the hollandite type compound represented by <x ≦ 2, 0.8 <y ≦ 2) is performed by using an oxide (eg, M ₂ O ₃ ) or a carbonate (A ₂ CO ₃ ) of the constituent metal element. In order to mix and react the above powdery raw materials, it is usually necessary to fire at a high temperature of 1200 ° C. or higher. However, this method remarkably promotes the growth of powder particles, the grain growth of the product reaches several μm or more, and the specific surface area is only about 1 m ² / g or less. For this reason, the porous material does not exhibit properties or exhibits a pore distribution having poor monodispersibility in the macropore region, and is not suitable for synthesizing a porous powder having a high specific surface area.

[0005] Some hollandite-type compounds, especially K _x Ga _x Sn _{8 -x} O ₁₆ , have been shown to have a large adsorption capacity for nitric oxide (hereinafter referred to as NO), and their characteristics have been demonstrated. Utilizing hydrocarbons as reducing agents
It is expected to be a catalyst material for selectively reducing O, and in order to further improve its catalytic function, it is desired to synthesize a porous powder having a high specific surface area. But,
Chemical composition formula _{A x M y N 8-y} O 16 ( where A is an alkali or alkaline earth metal element, M is a divalent or trivalent metal element, N is the tetravalent metal elements, 0.8 < x ≦ 2, 0.
8 <y ≦ 2), there is no report on a material having a hollandite-type structure, a material having a high specific surface area and a porous body having excellent pore size distribution and excellent monodispersity, and a method for producing the same.

[0006]

The present inventors have conducted various studies on the above-mentioned hollandite-type compound in order to realize a mesopore porous body having a high specific surface area and excellent monodispersion of pore diameter distribution. The hollandite-type compound, which has excellent crystallinity in the stable phase, has a crystallization temperature of 700 ° C or more lower than before, and precisely controls the crystallization process to take advantage of its characteristics to achieve high crystallinity. The present invention was completed by realizing a low temperature and making the grain shape and grain size uniform, and the present invention has a high specific surface area and pore distribution characteristics with excellent chemical and structural homogeneity. It is an object of the present invention to provide a hollandite-type compound mesoporous material having excellent monodispersibility and a method for producing the same.

[0007]

Means for Solving the Problems The gist of the present invention, the chemical composition formula _{A x M y N 8-y} O 16 ( where A is an alkali or alkaline earth metal element, M is a divalent or trivalent A metal element, N is a tetravalent metal element, 0.8 <x ≦ 2, 0.8 <y
≦ 2), having a hollandite-type crystal structure, and having a BET specific surface area of 10 calculated from a nitrogen adsorption / desorption isotherm.
m ² / g or more, and 3 to 3
The peak half-value width of about 2 nm and 2 in the pore diameter range of 30 nm
A mesopore porous body characterized in that it exhibits a pore area peak height value of about 0 mm ³ / nm · g or more and gives a pore size distribution curve excellent in monodispersity. The alkoxides of the metal elements A, M, and N are weighed so as to obtain the target values of x and y in the formula, and they are dissolved and mixed in an organic solvent such as 2-methoxyethanol to prepare a sol solution. To the sol solution, a solution obtained by diluting the amount of water required for hydrolysis of all the metal alkoxides contained therein or about twice the amount of water with alcohol is added dropwise with stirring to form a wet gel, and the wet gel is evacuated or heated to 100 ° C. To a temperature of about 350 ° C. to remove the organic solvent and residual moisture, etc., and to dry the obtained dry gel at a rate of about 650 to 800 ° C./hour in an atmosphere or an equivalent oxygen-containing atmosphere at an hourly rate of about 180 to 420 ° C. The temperature was raised, was maintained above about 30 minutes, to produce the mesoporous material according to the present invention by cooling to.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the production method of the present invention will be described. In the present invention, in order to achieve crystallization at a low temperature from the viewpoint of suppressing grain growth, a metal alkoxide is used as a raw material, and a sol-gel method is used. Based on this, a synthetic process was constructed. The raw material of the metal element does not necessarily need to be a metal alkoxide, and any other chemical form may be used as long as the required metal component can be uniformly mixed using water or an organic solvent. As the solvent for dissolving the metal alkoxide, it is preferable to select a solvent that is as inexpensive and has high health and safety as possible. However, since there are three or more main component metal elements, the process up to mixing the component metal sol solution is simplified. It is preferable to employ the same solvent or mutually soluble solvent species. In addition, since the main component contains an alkali metal, the alkali component is eluted in the hydrolysis step, and the amount of water added to the mixed sol solution in the step is reduced in order to avoid that the final product contains a phase other than the hollandite-type compound. The minimum amount required for decomposition needs to be reduced to twice. If more than the minimum amount of water is added, to prevent the alkaline components from eluting into the excess water and leaving the system, evaporate to dryness without filtering the alcohol and excess water from the hydrolysis product. It is then necessary to thoroughly mill and mix the dried gel.

Next, precise control of the firing process of the gel obtained from the mixed sol solution is indispensable, and the balance between the amount of the gel, the rate of temperature rise during the firing process, and the supply amount of oxygen is important.
For example, when firing the gel in the normal atmosphere, if the gel is sufficiently pulverized, about 5 g of the gel is placed in a crucible having a capacity of about 30 cc which does not chemically react with the gel, and 180 to 4 g.
By heating at a rate of 20 ° C. and maintaining at a temperature of 650-730 ° C. or more and 800 ° C. or less at which an exothermic peak (crystallization) was confirmed by thermogravimetry / differential thermal analysis for 30 minutes or more, excellent characteristics were obtained. A mesopore porous body can be obtained. The holding temperature is preferably in the range of about 680 to 750 ° C. If a slight decrease in the specific surface area and a decrease in the monodispersibility of the pore distribution are to be expected, heating to about 850 to 900 ° C. is also possible in order to increase the mechanical strength of the porous body.

At a heating rate of 180 to 420 ° C./hour, 650
Raise the temperature to ８００800 ° C. If the heating temperature is too high, the combustion of the organic matter occurs rapidly and the temperature becomes locally high, so that crystallization occurs even at a temperature lower than the above exothermic peak. Loses the monodispersity of the pore distribution and impairs its intended function. Further, even when the heating rate is kept within the above range, if the amount of gel to be treated is large, the supply amount of oxygen cannot keep up, which also leads to loss of monodispersibility of pore size distribution and coking, It is important to increase the supply amount of oxygen or to devise the way of filling the gel so that oxygen is uniformly and sufficiently supplied to each part of the filled gel. Even when the temperature rise is too slow, a mesopore porous body having excellent characteristics cannot be obtained. In this case, although coking does not occur, non-uniform growth of crystal grains occurs and monodispersity of pore distribution is impaired. As described above, an example of the mesopore porous body having a hollandite-type crystal structure according to the present invention has been described, but the method for producing the mesoporous body according to the present invention is not limited thereto.

Next, the mesopore porous body having a hollandite type crystal structure of the present invention will be described. The mesopore porous body having a hollandite-type crystal structure of the present invention has a BET specific surface area of 10 m ² / calculated from a nitrogen adsorption / desorption isotherm.
g or more and 3 to 30 by the Drillmore-Heel analysis method.
The peak half width of about 2 nm and 20 m
It exhibits a pore area peak height value of about m ³ / nm · g or more and gives a pore diameter distribution curve excellent in monodispersity. That is, since the material according to the present invention exhibits a pore size distribution curve excellent in monodispersity in the mesopore region, it can be expected to be used as an adsorbent, a molecular sieve, a separating material, a catalyst material or a catalyst carrier. In particular, the present material has remarkably excellent crystallinity as compared with the conventional material. FIG. 1 shows an X-ray powder diffraction diagram of the present invention in this regard. Since the material according to the present invention has excellent crystallinity, variation between pores in the chemical composition and local structure in the pores is small. For this reason, adsorption,
Excellent in homogeneity of various functions such as molecular sieve and separation, and high performance separation material for bioactive substances etc.
It can be expected to be used as a filler for high-speed chromatography and a highly selective adsorbent for polar molecules.

Furthermore, since the material according to the present invention has a distinctly different chemical composition and crystal structure from conventional porous materials, new chemical properties based on them are added. For example, some hollandite-type compounds have extremely excellent NO adsorption properties, and the use of the catalyst material for selective reduction of NOx has been clarified by utilizing the characteristics (Reference 1). (Reference 1: T. Mori, et al., Applied Catalysis A:
General, 129, L1-L7 (1995)) Accordingly, it is expected that the high specific surface area and the porous body based on the present invention will further improve the catalytic function for NOx selective reduction.

[0013]

Examples and Comparative Examples Next, examples and comparative examples of the present invention will be described. In the synthesis process according to the present invention, the selection of metal alkoxides and the solvent in which they are dissolved, especially the amount of water during hydrolysis, the rate of temperature rise during heat treatment of the dried gel, and the like are important factors, which are caused when they are inappropriate. The results obtained are shown using a comparative example. Example 1 1.754 g of K (n-OC ₃ H ₇ ) and 5.163 g of Ga (n-OC ₄ H ₉ ) ₃ so that x ≒ 2 in the chemical formula K _x Ga _x Sn _8-x O ₁₆ . And 22.03 g of Sn (t
-OC ₄ H ₉ ) ₄ was weighed in a glove box in an argon atmosphere, and dissolved in 20 ml of dehydrated 2-methoxyethanol (dehydrated with molecular sieve 3A).
They were mixed and stirred at room temperature for about 5 hours to prepare a mixed sol solution. To the mixed sol solution taken out of the glove box is added, with stirring, an ethanol diluted solution of water (H ₂ O / C ₂ H ₅₎ slightly more than the theoretical equivalent required for hydrolysis.
(OH = 5.2 ml / 120 ml) was added dropwise at a rate of about 15 ml / min to effect hydrolysis. After the entire amount was dropped, the solution containing the gel was left for 30 minutes while stirring. Then about 11
Heat to 0 ° C. and evaporate to dryness to obtain a dry gel. The dried gel was crushed in a mortar and heat treated again at 110 ° C. Using about 50 mg of this dried gel, thermogravimetric / differential thermal analysis is performed at a rate of 5 ° C./min in the range of room temperature to 1000 ° C., and crystallization occurs in conjunction with the exotherm occurring at about 650 to 730 ° C. It was confirmed. FIG. 3 shows the measurement results. Thus, the dried gel was heated to 700 ° C. at a rate of 300 ° C./hour, held for 3 hours, then turned off and allowed to cool to room temperature. An X-ray powder diffraction measurement was performed on a part of the sample that had been returned to room temperature, and it was confirmed that the sample had a hollandite-type crystal structure (FIG. 1). 150 under vacuum (10 ^-3 Torr)
Hollandite-type crystal structure powder held at 5 ° C. for 5 hours,
Using about 1 g, a nitrogen adsorption / desorption isotherm was measured by a fully automatic nitrogen adsorption measuring apparatus (BELSORP28-SA, manufactured by Bell Japan Co., Ltd.), and a specific surface area of 22 m ² / g was obtained by BET theory.
In addition, it was confirmed by a Drillmore-Heel analysis that a peak having a half-value width of about 2 nm was observed at 10.67 nm and an excellent monodisperse pore diameter distribution curve was obtained in a pore diameter range of 100 nm (FIG. 2). FIG. 4 shows a scanning electron micrograph of the obtained material powder.

Example 2 0.796 g of K (n-OC ₃ H ₇ ), 0.974 so that x ≒ 1.7 in the chemical formula K _x Al _x Ti _8-x O ₁₆
g of Al (OCH _{3) 3} and 9.151g of Ti (n-O
C ₄ H ₉ ) ₄ was weighed in a glove box under an argon atmosphere, the alkoxides of K and Ti were dissolved in 20 ml of dehydrated 2-methoxyethanol (dehydrated with molecular sieve 3A), and the alkoxide of Al was 60 ml with the same solvent. Then, they were mixed and stirred at room temperature for about 5 hours to prepare a mixed sol solution. To the mixed sol solution taken out of the glove box, while stirring, an ethanol diluted solution of water (H ₂ O / C ₂ H ₅ OH = 2.8 ml / 200 ml) slightly more than the theoretical equivalent required for hydrolysis was added per minute. It was added dropwise at a rate of about 15 ml. After the entire amount was dropped, the solution was heated with stirring. It becomes slightly cloudy at about 35 ° C.
After completely gelling at 60 ° C., it was left at 65 ° C. for 30 minutes. Thereafter, the mixture was heated at about 110 ° C. for 1 hour and evaporated to dryness to obtain a dried gel. The dried gel was crushed in a mortar and heat treated again at 110 ° C. for 1 hour. About 50mg of this dried gel
, A thermogravimetric / differential thermal analysis was performed at a temperature rising rate of 5 ° C./min.
It was confirmed that crystallization occurred in association with the heat generated at 0 ° C. Therefore, the dried gel is heated at a rate of 200 ° C./hour for 7 hours.
After heating to 00 ° C. and holding for 3 hours, the power was turned off and allowed to cool to room temperature. Using a part of the sample returned to room temperature, X
A line powder diffraction measurement was performed, and it was confirmed that the powder had a hollandite-type crystal structure. 15 under vacuum (10 ^-3 Torr)
Using about 1.5 g of a powder having a hollandite-type crystal structure held at 0 ° C. for 5 hours, a nitrogen adsorption / desorption isotherm was measured and analyzed in the same manner as in Example 1 to obtain a specific surface area of 18 m ² /
g, a half width of about 2 nm and a pore area of 2 at 13.4 nm.
It was confirmed to have a pore diameter distribution curve showing a peak of 4 mm ³ / nm · g in a monodisperse manner.

Comparative Example 1 Following Example 1, K (n-OC ₃ H ₇ ), Ga (n-OC
_{Using 4} H ₉ ) ₃ and Sn (t-OC ₄ H ₉ ) ₄ as raw materials, a mixed sol solution was prepared such that _{x in} the chemical formula K _x Ga _x Sn ₈ -xO ₁₆ was almost 2. Example 1 was added to the mixed sol solution.
Unlike this, a solution in which three times the theoretical equivalent amount of water necessary for hydrolysis is diluted with ethanol (H ₂ O / C ₂ H ₅ OH = 15.
6 ml / 120 ml) was added dropwise at a rate of about 15 ml per minute to effect hydrolysis. Thereafter, the procedure was returned to the same procedure as in Example 1 to obtain a dried gel. The dried gel was crushed in a mortar and heat treated again at 110 ° C. In the same manner as in Example 1, the dried gel was heated to 700 ° C. at a rate of 300 ° C./hour, held for 3 hours, then turned off and allowed to cool to room temperature. As a result of performing X-ray powder diffraction measurement using a part of the sample returned to room temperature, as shown in FIG. 5, a clear diffraction pattern of tin oxide having a rutile-type crystal structure other than powder having a hollandite-type crystal structure was obtained. Clarified to be included.
The reason is considered that when the amount of water at the time of hydrolysis is about twice or more, the distribution of the potassium component in the gel lacks uniformity, and tin oxide having high stability is crystallized where the amount of potassium is insufficient. Can be

Comparative Example 2 Following Example 1, K (n-OC ₃ H ₇ ) and Ga (n-OC
Using H ₉ ) ₃ and Sn (t-OC ₄ H ₉ ) ₄ as raw materials, a mixed sol solution was prepared such that _{x of} the chemical formula K _x Ga _x Sn ₈ -xO ₁₆ was almost 2, and A dried gel was obtained through hydrolysis. A part of the dried gel was taken and subjected to a heat treatment different from that in Example 1. One was to insert the sample directly into a furnace set at 700 ° C., hold it for 3 hours, then turn off the power and let it cool down to room temperature. Otherwise, the temperature was raised to 700 ° C. at 100 ° C./hour and maintained for 3 hours, then the power was turned off and the temperature was allowed to cool to room temperature. As a result, in the former, remarkable coking occurs, the specific surface area decreases to 10 m ² / g or less, and the pore distribution characteristics are remarkably deteriorated as shown in FIG. Lost the features. In the latter, caulking does not occur, but the pore distribution characteristics are remarkably deteriorated similarly to the former, and the characteristics as a porous material excellent in monodispersibility have been lost. This is considered to be due to the non-uniform grain size due to abnormal growth of some grains whose grain size exceeds the threshold.

[0017]

The mesopore porous body according to the present invention thus obtained has excellent monodispersion of the pore size distribution and is free from contamination due to caulking, etc., and has an adsorbent, a molecular sieve, a separating material, and a catalyst material. It can be expected to be used as such.

[Brief description of the drawings]

1 shows a X-ray powder diffraction diagram of the porous material _{K x Ga x Sn 8-x} O 1 6 (x ≒ 2) having a hollandite-type crystal structure.

Figure 2 shows the pore size distribution curve of the porous material _{K x Ga x Sn 8-x} O 1 6 having a hollandite-type crystal structure (x ≒ 2).

FIG. 3 shows a thermogravimetric / differential analysis curve of a dried gel having a chemical composition of K _x Ga _x Sn _8-x O ₁₆ (x ≒ 2).

Figure 4 shows a porous material _{K x Ga x Sn 8-x} O 1 6 (x ≒ 2) scanning electron microscope image of having a hollandite-type crystal structure.

FIG. 5: The amount of water added during hydrolysis is inappropriate.
FIG. 4 is an X-ray powder diffraction diagram showing that impurities were generated in a product.

FIG. 6 shows pores indicating that the monodispersibility of the pore distribution of the product was significantly deteriorated and the pore area was significantly reduced due to the inappropriate rate of temperature rise during the heat treatment of the dried gel. It is a distribution curve figure.

Claims (2)

[Claims] 1. A chemical composition formula _{A x M y N 8-y} O 16 ( where A is an alkali or alkaline earth metal element, M is 2
A trivalent or trivalent metal element, N is a tetravalent metal element, 0.8
<X ≦ 2, 0.8 <y ≦ 2), has a hollandite crystal structure, has a BET specific surface area of 10 m ² / g or more calculated from a nitrogen adsorption / desorption isotherm, A heel analysis method provides a peak half width of about 2 nm and a pore area peak height of about 20 mm ³ / nm · g or more in a pore diameter range of ^{3 to 30} nm to give a pore diameter distribution curve excellent in monodispersity. A porous mesopore body, characterized in that: 2. An alkoxide of each of the metal elements A, M, and N in the above chemical formula is weighed so as to obtain a target value of x and y in the formula, and they are dissolved in an organic solvent such as 2-methoxyethanol and mixed. Then, a sol solution is prepared, and a solution obtained by diluting water in a calculated amount necessary for hydrolysis of all contained metal alkoxides or about twice the amount thereof with alcohol to the sol solution is added dropwise with stirring to form a wet gel, The wet gel is evacuated or heated to a temperature of about 100 ° C. to remove the organic solvent, residual moisture and the like, and the obtained dry gel is dried at 180 to 420 hours / hour in the air or an oxygen-containing atmosphere equivalent thereto.
The method for producing a mesopore porous body according to claim 1, wherein the temperature is raised to 650 to 800 ° C at a rate of about ° C, held for about 30 minutes or more, and then cooled.