JP2005015323A - Porous alumina crystalline particle, and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide high heat resistant porous alumina crystalline particles having a high specific surface area, also stably holding a meso-structure even at a higher temperature, low in the reduction ratio of the specific surface area and excellent in heat resistance, and in which the size and shape of primary crystalline particles can strictly be controlled by an efficient synthesis method in a short time, and to provide the efficient production method. <P>SOLUTION: In the porous alumina crystalline particles, an X-ray diffraction peak lies in the diffraction angle of 0.5 to 3°(CuKα), also, a diffraction pattern assigned to crystalline alumina is shown in the diffraction angle of ≥10°(CuKα), the specific surface area by heating treatment at 700°C is 300 to 500 m<SP>2</SP>/g, also, the specific surface area by heating treatment at 900°C is 180 to 300 m<SP>2</SP>/g, and the peak of a pore diameter distribution curve lies in the range of 2 to 20 nm. Alternatively, the porous alumina crystalline particles comprise silica. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a high specific surface area suitable for materials useful for industrial and environmental conservation as toxic gases, ion separation / adsorbents, and catalysts for decomposition, as well as raw materials for the production of various ceramic products. The present invention relates to porous alumina crystalline particles having excellent heat resistance and a method for producing the same.

  Alumina is currently used as a catalyst, catalyst carrier, adsorbent, separating agent, raw material powder for functional ceramics synthesis, etc., and is used in various industrial and environmental purification processes. It is a serious substance.

Prior to the discovery of mesoporous materials, this alumina mostly uses pores due to the interstices of primary or secondary particles regardless of whether they are amorphous or crystalline, and the constituent particles are not uniform. In addition, both the specific surface area and the pore volume were 250 m ² / g or less and 0.5 cc / g or less.

  In addition, porous alumina particles synthesized by applying a method for synthesizing mesoporous materials, such as alumina particles synthesized using a cationic surfactant or a nonionic surfactant, Although having porosity due to the pores, all of them are amorphous and have low thermal stability, which has been a major obstacle for application as a catalyst or the like.

That is, when a block copolymer such as a nonionic amphiphilic polyalkylene oxide is used as the surfactant, the silica mesoporous material and the silica-based mesoporous material in which a part of silicon is substituted with other metal atoms are thick. A meso metal oxide porous body in which fine crystal phases are uniformly dispersed in the pores of the amorphous oxide is obtained. Specifically, the raw material contains aluminum chloride (AlCl ₃ ) and PEO (polyethylene oxide). By using a nonionic surfactant such as a triblock copolymer (trade name Pluronic P123), an amorphous material having a specific surface area of 300 m ² / g, a pore volume of 0.61 cc / g, and a pore diameter of 14 nm Alumina is said to be obtained (Non-Patent Document 1).

On the other hand, two kinds of nonionic surfactants containing PEO (polyethylene oxide) are used, each dissolved in sec-butanol together with Al (s-OC ₄ H ₈ ), water, dipropylamine (DAP) and sec -Slowly drop the mixed solution with butanol, stir and let stand at room temperature for 24 hours, filter and wash the resulting gel-like substance, dry at 40 ° C for 2 days, and heat at 95 ° C for 6 hours, soxhlet extraction After that, a method for obtaining porous alumina crystalline particles by drying and heat treatment has been reported (Non-patent Document 2).

In this document, the porous alumina crystalline particles are subjected to heat treatment at 700 ° C., and one peak derived from the mesostructure is present in the low angle, and the peak of γ-alumina is present in the high angle. It has been confirmed that the specific surface area is 230 to 270 m ² / g, the pore volume is 0.53 to 0.81 cc / g, and the pore diameter is 5 to 10 nm. Also, it is inferred from the TG-DTA analysis that boehmite is formed as an intermediate product in the heating process, and that the porous alumina crystalline particles are arranged in a lamellar shape, forming irregular pore arrays. ing.

  However, the porous alumina crystalline particles described in this document are not so large in specific surface area and have a texture extending in one direction, so that the thermal stability is low. Then, destruction and fusion of constituent particles occur, the pore arrangement structure collapses, and there is a problem that the specific surface area is remarkably reduced. In addition, since water is actively used in the synthesis process, the reaction mechanism is Not only does this cause problems such as rapid hydrolysis of the raw material alkoxide, and the regularity of the mesostructure formed by the nanocrystal particles cannot be maintained, but also the reaction process and its management become complicated. Included many problems such as long reaction time. Furthermore, there has been no research example in which a silica component is compounded at a nano level in a crystalline alumina porous body having a meso structure.

Yang, P .; Zhao, D .; Margolese, D. I .; Chmelka, B. F .; Stucky, G. D., Nature 1998, 396, 152. and the author Chem. Mater. 1999, 11, 2813. Gonzalez-Pena, V., Diaz, I., Marquez-Alvarez, C., Sastre, E., Perez-Pariente, J., Micropor. Mesopor. Mater. 2001, 44, 203.

  The present invention has been made in view of the above-described prior art, has a high specific surface area, stably maintains a mesostructure even at higher temperatures, has a small reduction rate of the specific surface area, and has excellent heat resistance. In addition, a highly heat-resistant porous alumina crystalline particle capable of strictly controlling the size and shape of a crystallite that is a basic constituent unit of a mesostructure by an efficient synthesis method in a shorter time, and its An object is to provide an efficient manufacturing method.

  The present inventors have found that non-ionic surfactants that are non-toxic, biodegradable and have different hydrophilic / hydrophobic balance form various nano-interface structures with dissolved alumina species or dissolved alumina-silica composite species in the solution phase. In particular, in order to control the shape and size of the primary particles during gelation, aluminum alkoxide is used as the alumina source, and it is nonionic in a hydrophilic solvent such as ethanol in the substantial absence of water. High heat-resistant porous alumina with high specific surface area when organic component is removed from gel substance (organic inorganic mesostructure) obtained in the process of making sol solution with surfactant and then evaporating solvent The inventors have found that crystalline particles can be obtained and have completed the present invention. Furthermore, by adding silicon alkoxide, it is combined with alumina-dissolved species at the nano level and gelled, so that an alumina crystallite in which Si is nano-composited uniformly at the atomic level is generated. Since the grain growth due to the diffusion of Al atoms is suppressed, the heat resistance is further improved, and at the same time, the solid acid amount that causes the catalytic ability to be increased and the acid amount can be adjusted.

That is, according to the present invention, the following inventions are provided: (1) An X-ray diffraction peak is present at a diffraction angle of 0.5 to 3 degrees (CuKα), and crystallinity is greater than a diffraction angle of 10 degrees (CuKα). has a diffraction pattern attributed to the alumina, the specific surface area by the heat treatment of 700 ° C. was 300~500m ² / g, and specific surface area by heat treatment of 900 ℃ 180~300m ² / g, pore diameter distribution curve Porous alumina crystalline particles having a peak of 2 to 20 nm.
(2) The porous alumina crystalline particles according to (1) above, wherein the alumina crystalline particles are γ, δ, θ, α-type alone or two or more mixed phases.
(3) A mesostructure based on a texture composed of square microcrystalline particles having a major axis of 20 nm or less is formed by transmission microscope observation, and has a pore structure resulting from the mesostructure. The porous alumina crystalline particle according to the above (1) or (2).
(4) The porous alumina crystalline particle according to any one of the above (1) to (3), wherein the alumina crystalline particle contains a silica component.
(5) A solution containing a nonionic surfactant dissolved in a water-miscible organic solvent and an aluminum alkoxide alone or a suspension solution prepared by mixing aluminum alkoxide and silicon alkoxide is allowed to stand at a constant temperature. The method for producing porous alumina crystalline particles according to any one of the above (1) to (4), wherein an organic component is removed from the gel-like substance produced by the step.
(6) The production method as described in (5) above, wherein the nonionic surfactant is used in an amount of 0.01 to 0.10 per mole of Al ₂ O ₃ .
(7) The production method as described in (5) or (6) above, wherein the silicon alkoxide is used in an amount of 0.02 to 0.09 per mole of Al ₂ O ₃ .
(8) The production method according to any one of (5) to (7) above, wherein the water-miscible organic solvent is used in an amount of 5 to 8 moles per mole of Al ₂ O ₃ .
(9) The production method according to any one of (5) to (8) above, wherein the nonionic surfactant is a nonionic surfactant containing polyethylene oxide (PEO).
(10) The production method according to any one of (5) to (9) above, wherein the weight ratio of polyethylene oxide (PEO) is 60% or less.
(11) The production method according to any one of (5) to (10) above, wherein the water-miscible organic solvent is a monohydric or polyhydric alcohol.
(12) The production method according to any one of (5) to (11) above, wherein the aluminum alkoxide and / or silicon alkoxide is an alcohol chain having 1 to 4 carbon atoms.
(13) An aluminum alkoxide alone or a mixed solution obtained by adding aluminum alkoxide and silicon alkoxide to a homogeneous solution in which a nonionic surfactant is dissolved in a water-miscible organic solvent, at a reaction temperature of 30 ° C. to 50 ° C. The mixture according to any one of (5) to (12) above, wherein the mixture is stirred and mixed for 15 to 60 minutes, and the suspension is allowed to stand for 12 hours or more under standing at 40 ° C or higher and 70 ° C or lower. Manufacturing method.
(14) A catalyst or catalyst carrier comprising the porous alumina crystalline particles according to any one of (1) to (4).
(15) A raw material powder for functional ceramics synthesis comprising the porous alumina crystalline particles according to any one of (1) to (4) above.

The porous alumina crystalline particles of the present invention have an ordered structure in which primary particles of 20 nm or less are assembled, pores of 5 to 20 nm are arranged at the same time, and the primary particles are mainly high in catalytic activity. It consists of alumina.
Moreover, since the porous alumina crystalline particles of the present invention are a completely new mesostructured body having a high specific surface area, high heat resistance, uniformity of pore diameter, and γ-alumina particles as main components, Adsorption, separation, storage agent, deodorizing agent, humidity control agent, catalyst carrier, catalyst useful for both industrial and environmental conservation because it can effectively trap various useful or harmful molecules and ions by exerting selectivity Furthermore, application as a functional ceramic material is expected. In particular, because it has a new mesostructure different from conventional activated alumina, it can be used not only as a substitute for conventional products but also as a catalyst / catalyst support for new chemical processes and adsorption separation agents by utilizing a unique fine structure. There is a possibility. In particular, while maintaining the size and texture of the alumina crystallites that form the mesostructure, by combining with silica at the nano level, the heat resistance of the γ-alumina particles is improved and at the same time the solid acidity is increased. Therefore, it can be applied as a new silica / alumina catalyst.
Further, the production method of the present invention uses a nonionic surfactant containing polyethylene oxide (PEO) as a pore structure control agent, and simply evaporates the solvent from a mixed solution of aluminum alkoxide and alcohol. In a very simple reaction system, the organic / inorganic nanocomposite that becomes a precursor of porous alumina crystalline particles at a very low temperature under normal pressure can be obtained in a short time from a mixture ratio of reactants and surfactants containing various PEO. Since the desired porous alumina crystalline particles can be easily obtained simply by removing the solvent from this, it can be said to be an industrially extremely advantageous production method. In addition, research and development has been conducted on the premise that the mesopores of conventional oxide mesoporous materials are caused by a continuous wall structure having periodicity, but there are problems with heat resistance in many oxide mesostructures. It is left. The present porous alumina crystalline particles having pores based on the texture of nano-sized crystal pieces are considered to have value as a new model of future oxide mesostructures. That is, this synthesis method can be applied to other metal alkoxides, and porous metal oxides in which mesostructures are formed by various kinds of nano-sized crystalline metal oxide particles and two or more kinds of composite oxide nanoparticles. Production of physical crystalline particles can be expected.

The porous alumina crystalline particles of the present invention are 1. X-ray diffraction peak showing regularity of pores at low angle (diffraction angle 0.5 to 3 degrees (CuKα)) and X of crystalline alumina such as γ-alumina at high angle (diffraction angle 10 degrees (CuKα)) Shows the line diffraction pattern,
2. Also not be basic skeleton structure is destroyed, the specific surface area has a 700 ° C. But 300~500m ² / g, 900 ℃ even 180~300m ² / g at high temperature,
More preferably,
3. The crystalline alumina particles are γ, δ, θ, α type alone or a mixed phase of two or more types,
4). Forming a mesostructure based on a texture composed of square microcrystalline particles having a major axis of 20 nm or less in transmission microscope observation, and having a pore structure resulting from the mesostructure;
5. Further, preferably the alumina crystalline particles further contain a silica content,
It is characterized by.

  Due to the above characteristics, the porous alumina crystalline particles of the present invention have a high specific surface area porosity that retains a mesostructure up to a high temperature and is excellent in thermal stability. In addition to the use of alumina, it can be used as a raw material for various functional ceramic raw materials by mixing with other substances.

Among porous alumina crystalline particles, conventional γ-alumina is currently applied to various chemical processes as a catalyst, catalyst support, etc., but both the specific surface area and pore volume are about 250 m ² / g or less, 0 It is known that the porosity is caused by the particle gap. On the other hand, in the method of synthesizing a mesoporous material, a method using a molecular assembly as a template, in many cases, it is amorphous alumina, and even γ-alumina is porous due to the interstices of fibrous particles. Most of them show. Then, in either case, with the specific surface area due to heat treatment of 700 ℃ 300~500m ² / g, and specific surface area by heat treatment of 900 ° C. but of high specific surface area of 180~300m ² / g, Moreover, since it is a texture extending in one direction, the thermal stability is low, and the synthesis method is also complicated and requires a long time. Furthermore, no studies have been reported so far in which a silica component is compounded at a nano level in a crystalline alumina porous body having a meso structure.

  In contrast, the porous alumina crystalline particles of the present invention use aluminum alkoxide, alcohol, and a nonionic surfactant as raw materials, and do not actively add moisture during the synthesis reaction process. Unprecedented mesostructures as intermediates without inducing strong interactions between molecules that form mesostructures by the combination of the ability to form a coordinated order with nonionic surfactants and the solvent volatilization method By being routed, it can be easily synthesized, and has a high specific surface area porosity excellent in thermal stability that maintains a mesostructure up to a high temperature. Furthermore, the addition of silica increases the high-temperature stability, and it is possible to adjust the solid acidity that is a factor in the expression of catalytic ability.

  Such a porous crystalline alumina of the present invention is obtained by dissolving a nonionic surfactant in a water-miscible organic solvent and further adding aluminum alkoxide alone or aluminum alkoxide and silicon alkoxide under stirring. A turbid solution can be obtained by removing organic components and the like from a gel-like substance produced by standing at a constant temperature.

  Next, the alumina raw material, nonionic surfactant, and alcohol solvent used in the production method of the present invention will be described.

  As the alumina raw material used in the present invention, any aluminum alkoxide that dissolves in alcohol can be used, and aluminum tri-sec-butoxide that is in a solution state at room temperature is preferable.

As the nonionic surfactant, any polymer surfactant containing polyethylene oxide (PEO) can be used. Polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) or polypropylene oxide In addition to a triblock copolymer made of polyethylene oxide-polypropylene oxide (PPO-PEO-PPO), polyoxyethylene alkyl ether or the like can be used.
In the nonionic surfactant, there is no particular limitation on the polymerization ratio of the block copolymer and the average molecular weight of various polymers, but in the triblock copolymer (PEO-PPO-PEO), the weight average molecular weight is about 2000. The weight ratio of the hydrophilic block (PEO) is preferably 60% or less. If it exceeds 60%, the hydrophilicity of the nonionic surfactant increases and the size of the alumina crystallites becomes relatively large, which is not preferable because the specific surface area of the porous alumina particles decreases.
Nonionic surfactants having a hydrophilic block (PEO) weight ratio of 60% or less include, for example, trade names Pluronic P65 (PEO content (50) wt%), P85 (PEO content (50) wt%), P105 ( PEO content (50) wt%), L64 (PEO content (40) wt%), P104 (PEO content (40) wt%), P103 (PEO content (30) wt%), P123 (PEO content (30) wt %), L121 (PEO content (10)% by weight)), and polyoxyethylene alkyl ether, C _m H _{2m + 1} (PEO) _n (OH), where m is 12 to 18, n Is preferably 2 to 23, and preferably m is 18 and n is 2 to 23 in the formula of C _m H _2m-1 (PEO) _n (OH).

The nonionic surfactant used in the present invention is preferably used in a molar ratio of 0.002 to 0.25 with respect to Al ₂ O ₃ . However, it is difficult to produce porous alumina crystalline particles having a low and satisfactory specific surface area. If the amount is too large, the amount of alcohol required for dissolution increases, which hinders production efficiency and increases the gelation time. This is not preferable because the regularity of the mesostructure is lowered.

  As the alcohol, methanol, ethanol, propanol, butanol and the like can be used, and ethanol is preferably used.

  As the silicate ester as a silica raw material used in the present invention, Si-alkoxide, tetramethyl orthosilicate, tetraethyl orthosilicate, tetraisopropyl orthosilicate, tetra-n-butyl orthosilicate and the like can be preferably used. Tetraethylorthosilicate (hereinafter abbreviated as TEOS) is used.

In the synthesis of the porous alumina crystalline particles of the present invention, the mixing molar ratio of the starting materials is Al ₂ O ₃ : nonionic surfactant: alcohol = 1: 0.002-0.25: 0.25-1 Is preferred. Further, when Si is added, the mixing molar ratio of the starting materials is Al ₂ O ₃ : nonionic surfactant: alcohol: SiO ₂ = 1: 0.002 to 0.25: 0.25 to 1 : It is preferable that it is 0.02-0.09.

Furthermore, describing reaction conditions, the dissolution temperature of the nonionic surfactant with alcohol is preferably in the range of 30 to 50 ° C., and the reaction temperature for promoting gelation is preferably in the range of 40 to 80 ° C. The reaction temperature affects the gelation rate, but if the reaction is carried out at a temperature higher than the above temperature range, the regularity of the mesostructure tends to deteriorate. Since dehydration of the hydrophilic group portion in the agent is likely to occur, it is presumed that the regularity of the mesostructure is lost as a result. On the other hand, when the reaction temperature is lowered, the reaction time required for gelation is too long, and it becomes difficult to produce porous alumina crystalline particles having a satisfactory mesostructure.
Furthermore, even when the intermediate gel-like substance is heat-treated, the regularity of the mesostructure is lost, and therefore it is necessary to sufficiently perform the gelation until it becomes a solidified body. Excessive gelation time has a small effect on the product but is economically disadvantageous due to production efficiency issues.

  Finally, in order to remove the organic component from the gel substance as an intermediate to produce porous alumina crystalline particles, heat treatment is directly performed at 400 ° C. or higher for 2 hours or longer, preferably 600 ° C. or higher for 1 hour. Alternatively, after the organic component is extracted from the gel substance using a solvent such as ethanol, it may be heat-treated at 400 ° C. or higher for 1 hour or longer, preferably 500 ° C. or higher for 1 hour or longer.

Alumina porous body of the present invention, as described above, coordinated regular collection of the alcoholic solution, polyethylene oxide (PEO) non-ionic surfactants comprising a (S ^o) and the aluminum alkoxide (I ^o) The body (S ^o I ^o ) is formed by hydrogen bonding, and no other substances are added to the S ^o I ^o ordered assembly, and the nonionic surfactant is dissolved and mixed with the alkoxide. The synthesis is performed by evaporating and removing the alcohol solvent used for the purpose of promotion. This synthesis procedure will be described with reference to the drawings.

FIG. 1 shows a hydrophilic block surrounded by a triblock copolymer (PEO-PPO-PEO) that forms spherical micelles with a hydrophobic block (polypropylene oxide; PPO) as a core, utilizing the order-forming ability. It shows that the mesostructure can be induced by the interaction between (PEO) and aluminum dissolved species. This reaction is preferably carried out at 30 to 50 ° C., and water is not actively added, but hydrolysis of aluminum alkoxide proceeds by moisture in the atmosphere, and higher order assembly is caused by the association of S ^o I ^o micelles. A body (mesostructure) is formed. In FIG. 1, Si dissolved element can coexist with Al dissolved species, and nanocomposite can be achieved at the atomic level.

Next, as shown in FIG. 2, by evaporating alcohol as a solvent at a constant temperature, a gel-like organic-inorganic nanocomposite (meso-layer) retaining the structure of a higher-order ordered assembly (S ^o I ^o ) is obtained. Structure). Furthermore, porous alumina crystalline particles are synthesized as a mesostructure by removing the organic component. Since the porous alumina crystalline particle of the present invention has a mesostructure formed by a nanospace surrounded by an aggregate of nanosized crystallites of uniform size, even if it is an Al pure component, The γ-alumina porous body is superior in heat resistance. Furthermore, by combining Si with the Al dissolved species in FIG. 1, alumina crystallites in which Al and Si are nanocomposited at the atomic level are generated, and grain growth due to diffusion of Al atoms at high temperature is suppressed. As a result, the heat resistance can be further improved, and at the same time, the solid acid amount and the acid amount can be adjusted, which are the causes of the catalytic ability.

The porous alumina crystalline particles of the present invention are mainly γ-alumina, but may be γ, δ, θ, α type alone or in a mixed phase of two or more types. In general, it is known that γ-alumina is produced by heating boehmite (AlO (OH)). However, in this reaction system, water is not actively added, so that the gel form corresponding to FIG. There is a significant difference from the conventional synthesis method in that boehmite (AlO (OH)) cannot be confirmed as an intermediate even when the material is heat-treated at 200 to 400 ° C. (FIG. 3). Furthermore, since conventional porous alumina crystalline particles synthesized in the presence of a surfactant mainly exhibit a fibrous or unidirectionally elongated micro form, the temperature is higher than 700 ° C., and even higher. There is a problem with the heat resistance in and pore parameters such as specific surface area have not been reported. On the other hand, the porous alumina crystalline particles of the present invention are aggregates of nano-sized thin plate-like crystallites, and the pores have a texture of small particles having the same size as shown in FIG. that due to is the cause of excellent heat resistance, specific surface area by heat treatment of 700 ° C. was 300~500m ² / g, and even the specific surface area by the heat treatment of 900 ° C. at 180~300m ² / g In addition, since the specific surface area and the heat resistance are improved as compared with the conventional products, the application of new functions can be expected.

FIG. 4 is an X-ray diffraction pattern of an example of the mesostructure obtained by removing the organic component, that is, the porous alumina crystalline particle of the present invention. A diffraction peak is clearly observed at a low angle up to 900 ° C. (FIG. 4A) shows that the pores are regularly arranged. In addition, a diffraction pattern peculiar to γ-alumina is observed at a high angle (FIG. 4B). Even at 900 ° C., a sharp rise is observed at a low angle, and the regularity of the pores is not completely destroyed. Further, at 1000 ° C., the crystallization of α-alumina is slightly observed with an increase in the diffraction intensity of γ-alumina, but the specific surface area maintains a high value at 166 m ² / g (FIG. 4B; ○ mark). .

  FIG. 5 is a transmission electron micrograph of an example of the porous alumina crystalline particles of the present invention obtained by using a surfactant having a PEO weight ratio of less than 60%. It can be seen that a mesostructure is formed by a nanospace (FIG. 2) surrounded by an assembly of these fine crystalline particles. Moreover, three strong lines can be confirmed by the limited field diffraction image, and it is clear that the nano-sized primary particles are γ-alumina, confirming the result of the X-ray diffraction pattern.

  FIG. 6 is a transmission electron micrograph of an example of porous alumina crystalline particles obtained by using a surfactant having a PEO weight ratio of 70% or more, and an assembly of nano-sized crystalline particles as in FIG. Although the mesostructure is formed by the nano space surrounded by (FIG. 2), the size of the nanoparticles is larger than that of FIG. 5, which is considered to cause a decrease in the specific surface area.

  FIG. 7 is a nitrogen adsorption isotherm of an example of porous alumina crystalline particles of the present invention obtained using a surfactant having a PEO weight percentage of less than 60%.

  FIG. 8 is a BJH pore distribution curve corresponding to FIG. This porous alumina crystalline particle shows a mesopore-specific IV type isotherm, and the average pore diameter at 700 ° C. is about 6 nm. On the other hand, as the heating temperature rises, the adsorption amount decreases and the average pore diameter increases, but although a decrease in pore volume is observed even at 900 ° C., a clear peak can be recognized and the mesostructure is destroyed. It can be seen that it has high heat resistance.

FIG. 9 is an XRD diffraction pattern showing the effect of adding Si. A and B are heat-treated at 900 ° C., and C and D are heat-treated at 1000 ° C. The bottom diffraction pattern a is a pure γ-alumina porous body without addition of Si. This corresponds to Example 3-1) and 1000 ° C. b and c were added as 0.05 and 0.09 mol, respectively, with respect to Al ₂ O ₃ as SiO _2. FIG. 9A corresponds to the porous alumina bodies of Example 4-2 and Example 4-4, respectively. To do. As shown in FIG. 4, the γ-alumina porous body without Si added at 1000 ° C. is crystallized by α-alumina (marked with ○). As shown in FIG. Insufficient crystallization (Example 4-4), and at 1000 ° C., silica and alumina react and crystallization of mullite (□) is observed. Moreover, at 900 ° C., the low angle peak of 0.5 to 2 ° disappears with an increase in the amount of Si added (FIG. 9A-c; Example 4-4). It can be seen that the regularity of the mesostructure based on the texture of the alumina crystallites decreases and the effect of addition is not recognized. On the other hand, in FIG. 9C-b (Example 4-3), since a peak exists in the vicinity of 1 °, the mesostructure is not destroyed even at 1000 ° C., and the heat resistance is improved by the addition of Si.

FIG. 10 is a pore size distribution curve showing that the heat resistance of pure porous alumina crystalline particles is significantly improved by the addition of Si. As is clear from FIG. 8, when Si is not added (Example 3-1), a remarkable deterioration in heat resistance is observed at 900 ° C. However, when 0.05 mol of SiO ₂ is added to Al ₂ O ₃ , it has a pore characteristic value equivalent to that at 700 ° C. without addition at 900 ° C. (Example 4-2). It is clear that it has excellent heat resistance even at 1000 ° C. (Example 4-3). However, when the addition amount is too large, it can be seen that the addition effect is not recognized in terms of the pore structure as described in FIG. 9 (Example 4-4).

FIG. 11 is a transmission electron micrograph of porous alumina crystalline particles (Example 4-3) heat-treated at 1000 ° C. with 0.05 mol of Si added to Al ₂ O ₃ . The SiO ₂ 0.05 added to Al ₂ O _3, it is a transmission electron micrograph of heat-treated porous alumina crystal particles (Example 4-3) at 1000 ° C.. It is confirmed that nano-sized crystallites having relatively uniform sizes can be confirmed, and that the mesostructure is formed by the nanospace (FIG. 2) surrounded by an assembly of these fine crystalline particles. This is the same as the added porous alumina crystalline particles (Example 1-1; FIG. 5). This shows that nano-sized γ-alumina crystallites do not grow even when heat-treated at 1000 ° C. due to the slight addition of Si. The lack of sintering between microcrystallites is a factor that maintains high heat resistance.

  Furthermore, it is possible to control the solid acidity which influences a catalyst characteristic by addition of a silica. FIG. 12 shows an ammonia temperature-programmed desorption spectrum of the porous alumina crystalline particles of the present invention. Since there is no significant change in the peak position of the spectrum, there is no significant change in the solid acid strength depending on the amount of Si contained, but a significant difference is observed in the amount of solid acid. The fact that there is no significant difference in acid strength is thought to be due to the relatively small difference in silica-alumina ratio. Furthermore, as shown in Table 3, it can be seen that the amount of solid acid at a high temperature is remarkably increased by the addition of silica. On the other hand, the amount of solid acid does not simply increase with the amount of Si added, but it is necessary to add an appropriate amount of Si in order to provide stability of the pore structure and a high amount of solid acid. .

[Usage]
The porous alumina crystalline particles of the present invention have a porosity resulting from a mesostructure in which primary particles, which are nanometer-sized alumina crystallites of uniform size, are gathered, and are particularly useful in various chemical processes. Compared with γ-alumina of the type, the specific surface area is large, the pore diameter is sharp, and the mesostructure is maintained up to relatively high temperatures. It is expected to be realized. In addition to existing applications, it can be made into nanocomposites with oxides containing various metal species, and can be used as various ceramic raw material powders by utilizing the functionality of novel catalysts or metal components. Furthermore, this synthesis method can be applied to other metal alkoxides, and porous metal oxides in which mesostructures are formed by various nano-sized crystalline metal oxide particles and two or more kinds of composite oxide particles. Crystalline particles can be produced. In particular, the nano-level compounding with silica improves the heat resistance of γ-alumina particles and increases the solid acid amount, so that it can be applied as a new silica-alumina catalyst.

EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited by this Example.
In addition, each test method performed in the Example was performed by the following method.

(Measurement method)
(1) X-ray diffraction: Rigaku Rotorflex RU-300 was used and measured with a CuKα radiation source, an acceleration voltage of 40 kV, and 80 mA.
(2) High-resolution electron microscope: HI-CHI HF-2000 was used and observed at an acceleration voltage of 200 kV.
(3) Specific surface area and pore size distribution: BELSORP28 manufactured by Nippon Bell was used to determine the BET specific surface area from the nitrogen adsorption isotherm measured at liquid nitrogen temperature, and the pore size distribution was analyzed by the BJH method.
(4) Ammonia temperature programmed desorption spectrum: Measured under the following conditions using a TPD apparatus manufactured by Nippon Bell.
Pretreatment 500 ° C., 1 hour degassing with He gas flow system Ammonia adsorption 100 ° C., 60 minutes Physical adsorption ammonia removal 180 ° C., 30 minutes TPD measurement 100-700 ° C., heating rate 10 ° C./min
The analysis of the solid acid amount was calculated by setting the desorption amount of the h-peak of the reference catalyst JRC-Z5-70H as a catalyst society to 0.45 mmol / g.

(Example 1)
Various triblock copolymers (trade name Pluronics) having a PEO weight ratio of less than 60% by weight are dissolved in ethanol at 35 to 40 ° C., and then aluminum tri-sec-butoxide is added. The molar ratio of the mixed solution is shown in Table 1. The above mixed solution is further stirred for 30 minutes, and the resulting milky white sol solution is allowed to stand for 4 days in a drier previously set at 50 ° C. to obtain a gel-like substance as an intermediate. The gel substance is baked in an electric furnace at 700 ° C. for 1 hour to remove organic components and obtain porous alumina crystalline particles. Table 1 shows the pore characteristics of the porous alumina crystalline particles obtained using the respective triblock copolymers.

(Example 2)
A triblock copolymer (Pluronic P104) is dissolved in ethanol at 35 to 40 ° C., and then aluminum tri-sec-butoxide is added. The molar ratio of the mixed solution is shown in Table 1. The mixed solution is further stirred for 30 minutes, and the resulting milky white sol solution is allowed to stand for about 4 days in a drier previously set at 70 ° C. to obtain an intermediate gel-like substance. The gel substance is baked in an electric furnace at 700 ° C. for 1 hour to remove organic components and obtain porous alumina crystalline particles. Table 1 shows the pore characteristics of the obtained porous alumina crystalline particles.

Example 3
Of Example 1, pore characteristic parameters of porous alumina crystalline particles obtained by heat-treating a gel-like material prepared with three types of triblock copolymers (Pluronic P104, P103, P105) at 900 ° C. Is shown in Table 2.

(Example 4)
Various triblock copolymers (trade name Pluronics) with a weight ratio of less than 60% by weight of PEO are dissolved in ethanol at 35 to 40 ° C., tetraethylorthosilicate (TEOS) is added, and aluminum tri-sec-butoxide is further added. To do. The molar ratio of the mixed solution is shown in Table 3. The above mixed solution is further stirred for 30 minutes, and the resulting milky white sol solution is allowed to stand for 4 days in a drier previously set at 50 ° C. to obtain a gel-like substance as an intermediate. The gel material is baked in an electric furnace for 1 hour to remove organic components and obtain porous alumina crystalline particles containing a silica component. Table 3 shows the pore characteristics and solid acidity of the porous alumina crystalline particles obtained using the respective triblock copolymers.

(Comparative Example 1)
Various triblock copolymers (trade names Pluronic F127, F68, F88, F108) having a weight ratio of PEO of 70 w% or more are dissolved in ethanol at 35 to 40 ° C., and then aluminum tri-sec-butoxide is added. The molar ratio of the mixed solution is shown in Table 1. The above mixed solution is further stirred for 30 minutes, and the resulting milky white sol solution is allowed to stand for about 4 days in a drier previously set at 50 ° C. to obtain a gel-like substance as an intermediate. The gel substance is baked in an electric furnace at 700 ° C. for 1 hour to remove organic components and obtain porous alumina crystalline particles. Table 1 shows the pore characteristics of the porous alumina crystalline particles obtained using the respective triblock copolymers.

It is a schematic diagram which shows the production | generation process of the porous alumina crystalline particle of this invention. It is a schematic diagram which shows the pore structure of the porous alumina crystalline particle of this invention. It is a powder X-ray diffraction pattern of the porous alumina crystalline particle precursor (unheated product) of the present invention (Example 1-1) and the porous alumina crystalline particles heat-treated at 200 to 500 ° C. It is an X-ray diffraction pattern of the porous alumina crystalline particle obtained by processing the porous crystalline alumina of the present invention (Example 1-1) at various heating temperatures. It is a transmission electron micrograph of a porous alumina crystalline particle of the present invention (Example 1-1), and a limited field diffraction image. It is a transmission electron micrograph of a comparative example (comparative example 1-1) porous alumina crystalline particle. The nitrogen adsorption isotherm of the porous alumina crystalline particle obtained by processing the porous alumina crystalline particle of the present invention (Example 1-1) at various heating temperatures is shown. The pore diameter distribution curve of the porous alumina crystalline particle obtained by processing the porous alumina crystalline particle of the present invention (Example 1-1) at various heating temperatures is shown. It is an XRD diffraction pattern which shows the addition effect of Si. In the figure, ○ and □ are diffraction peaks of α-alumina and mullite, respectively. It is a pore diameter distribution curve which shows the addition effect of Si. It is a transmission electron micrograph and a limited field diffraction image of porous alumina crystalline particles of the present invention (Example 4-3). It is an ammonia thermal desorption spectrum which shows the solid acidity of the porous alumina crystalline particle of this invention.

Claims (15)

X-ray diffraction peak exists at a diffraction angle of 0.5 to 3 degrees (CuKα), has a diffraction pattern attributed to crystalline alumina at a diffraction angle of 10 degrees (CuKα) or more, and a specific surface area by heat treatment at 700 ° C. Is a porous alumina crystalline particle having a specific surface area of 180 to 300 m ² / g by heat treatment at 900 ° C. and a peak of a pore diameter distribution curve of ² to 20 nm. 2. The porous alumina crystalline particle according to claim 1, wherein the alumina crystalline particle is γ, δ, θ, α type alone or two or more mixed phases. 3. A mesostructure based on a texture composed of tetragonal crystallites having a major axis of 20 nm or less by transmission microscope observation is formed, and has a pore structure resulting from the mesostructure. Porous alumina crystalline particles as described in 1. The porous alumina crystalline particle according to any one of claims 1 to 3, wherein the alumina crystalline particle contains a silica component. A solution containing a nonionic surfactant dissolved in a water-miscible organic solvent and aluminum alkoxide alone or a suspension solution prepared by mixing aluminum alkoxide and silicon alkoxide is produced by standing at a constant temperature. The method for producing porous alumina crystalline particles according to any one of claims 1 to 4, wherein an organic component is removed from the gel substance. 6. The production method according to claim 5, wherein the nonionic surfactant is used in an amount of 0.01 to 0.10 per mole of Al ₂ O ₃ . 7. The method according to claim 5, wherein the silicon alkoxide is used in an amount of 0.02 to 0.09 per mole of Al ₂ O ₃ . The method according to any one of claims 5 to 7, wherein the water-miscible organic solvent is used in an amount of 5 to 8 moles per mole of Al ₂ O ₃ . 9. The production method according to claim 5, wherein the nonionic surfactant is a nonionic surfactant containing polyethylene oxide (PEO). The production method according to claim 5, wherein a weight ratio of polyethylene oxide (PEO) is 60% or less. The production method according to claim 5, wherein the water-miscible organic solvent is a monohydric or polyhydric alcohol. The method according to any one of claims 5 to 11, wherein the aluminum alkoxide and / or the silicon alkoxide is an alcohol chain having 1 to 4 carbon atoms. Aluminum alkoxide alone or a mixed solution obtained by adding aluminum alkoxide and silicon alkoxide to a homogeneous solution in which a nonionic surfactant is dissolved in a water-miscible organic solvent, is added at a reaction temperature of 30 ° C. to 50 ° C. for 15 to 60 ° C. The method according to any one of claims 5 to 12, wherein the mixture is stirred and mixed for a minute and the suspension is allowed to stand for 12 hours or longer under standing at 40 ° C or higher and 70 ° C or lower. A catalyst or catalyst carrier comprising the porous alumina crystalline particles according to any one of claims 1 to 4. A raw material powder for functional ceramics synthesis comprising the porous alumina crystalline particles according to any one of claims 1 to 4.

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