JP2007044585A - Manufacturing method of porous composite metal oxide material - Google Patents

Manufacturing method of porous composite metal oxide material Download PDF

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JP2007044585A
JP2007044585A JP2005229319A JP2005229319A JP2007044585A JP 2007044585 A JP2007044585 A JP 2007044585A JP 2005229319 A JP2005229319 A JP 2005229319A JP 2005229319 A JP2005229319 A JP 2005229319A JP 2007044585 A JP2007044585 A JP 2007044585A
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metal oxide
nm
less
diameter
porous body
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Akihiko Suda
Toshio Yamamoto
敏生 山本
明彦 須田
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Toyota Central Res & Dev Lab Inc
株式会社豊田中央研究所
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of obtaining efficiently a porous composite metal oxide material useful as a catalyst for purifying exhaust gas, or the like, which is extremely excellent in durability for high temperature, and in which even under high temperatures a specific surface area and purification capability are maintained in a high level. <P>SOLUTION: The manufacturing method of the porous composite metal oxide material comprises a dispersion mixing process of dispersion-mixing a first metal oxide powder which is an agglomerate of primary particles having a diameter of 50 nm or less, and has an average particle diameter of 200 nm or less, and a second metal oxide powder which is an agglomerate of primary particles having a diameter of 50 nm or less, and has an average particle diameter of 200 nm or less, in a dispersion medium by using microbeads having a diameter of 150 μm or less, to obtain a uniform dispersion liquid of the first metal oxide powder with the second metal oxide powder, and a drying process of drying the uniform dispersion liquid to obtain the porous composite metal oxide material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for producing a composite metal oxide porous body, and more particularly, to produce a composite metal oxide porous body useful as an exhaust gas purification catalyst for purifying HC, NO x , CO x and the like in exhaust gas. Related to the method.

In recent years, the presence of harmful gases that can exist in the environment surrounding humans and can affect the human body has been regarded as a problem. For example, HC and NO that are harmful components in exhaust gas. Development of an exhaust gas purifying catalyst capable of more reliably purifying x , CO x and the like is desired.

  Under such a background, various catalysts for purifying exhaust gas have been developed. For example, JP-A-6-199582 (Patent Document 1) discloses 10 to 100 nm alumina particles and an average particle diameter of 50 nm. By mixing the following silica particles and the like, and JP-A-7-284672 (Patent Document 2), alumina particles having a particle size of 50% by mass or more and particles having a particle size of 100 nm or less and particles of 50% by mass or more are disclosed. Describes a method for producing a porous body having a large specific surface area even at a high temperature of 1200 ° C. or higher by mixing silica particles having a particle size of 100 nm or less. Furthermore, JP-A-10-249198 (Patent Document 3) is excellent in durability of purification activity by mixing ultrafine particles having an average particle diameter of 1 to 100 nm on which noble metals are supported and other particles. A method for producing an exhaust gas purifying catalyst is described.

However, under the recent situation where regulations on harmful components in exhaust gas are increasingly strengthened, the catalyst performance required for exhaust gas purification catalysts capable of more reliably purifying such harmful components becomes severe. On the other hand, it is desired to develop an exhaust gas purification catalyst that is more excellent in durability at high temperatures, that is, that maintains a specific surface area and purification performance at a higher level even under high temperatures.
JP-A-6-199582 JP-A-7-284672 JP-A-10-249198

  The present invention has been made in view of the above-described problems of the prior art, has excellent high-temperature durability, maintains a high specific surface area and purification performance even at high temperatures, and is used for exhaust gas purification. It is an object of the present invention to provide a method capable of efficiently producing a porous composite metal oxide useful as a catalyst or the like.

  As a result of intensive studies to achieve the above object, the present inventors have found that the first metal oxide fine particles dispersed using fine microbeads having a diameter of 150 μm or less have an average particle diameter of 200 nm or less. The inventors have found that the above object can be achieved by dispersing and mixing with the two metal oxide fine particles, and have completed the present invention.

That is, the method for producing a composite metal oxide porous body of the present invention includes:
A first metal oxide powder which is an aggregate of primary particles having a diameter of 50 nm or less (more preferably 20 nm or less) and an average particle size of 200 nm or less, and agglomeration of primary particles having a diameter of 50 nm or less (more preferably 20 nm or less). The second metal oxide powder, which is an aggregate and has an average particle size of 200 nm or less, is dispersed and mixed in a dispersion medium using microbeads having a diameter of 150 μm or less (more preferably 10 to 100 μm), and the first metal A dispersion mixing step of obtaining a uniform dispersion of oxide fine particles and second metal oxide fine particles;
A drying step of drying the uniform dispersion to obtain a composite metal oxide porous body;
It is the method characterized by including.

  In the method for producing a composite metal oxide porous body of the present invention, the pH of the dispersion medium in the dispersion mixing step is set so that the absolute values of the zeta potential of the first metal oxide and the zeta potential of the second metal oxide are both. It is preferable to set the pH in a region of 10 mV or more.

  Further, in the method for producing a composite metal oxide porous body of the present invention, the first metal oxide fine particles obtained in the dispersion mixing step have an average particle diameter of 1 to 50 nm and particles having a diameter of 80% by mass or more. Preferably, the second metal oxide fine particles obtained in the same step have an average particle diameter of 1 to 130 nm and 80% by mass or more of particles having a diameter of 160 nm or less. Preferably there is.

Furthermore, in the method for producing a composite metal oxide porous body of the present invention,
(i) a pre-supporting step of supporting a noble metal on the surface of the first metal oxide powder and / or the second metal oxide powder, or
(ii) a post-supporting step of supporting a noble metal on the surfaces of the first metal oxide fine particles and the second metal oxide fine particles;
Is preferably further included.

  Moreover, in the said drying process, it is preferable to heat-dry, after adding and mixing surfactant into the said uniform dispersion liquid.

  The reason why the composite metal oxide porous body having excellent high-temperature durability can be obtained by the production method of the present invention is not necessarily clear, but the present inventors speculate as follows. That is, by dispersing and mixing the first metal oxide powder and the second metal oxide powder satisfying a predetermined condition using fine micro beads having a diameter of 150 μm or less, the fine particles of both metal oxides can be obtained at the nano level. Since it is uniformly mixed and other types of metal oxide fine particles exist as barriers between the same type of metal oxide fine particles, the particle growth of each metal oxide fine particle during the drying process and high temperature treatment The present inventors presume that the specific surface area and the purification performance are maintained at a high level even when the temperature is sufficiently suppressed and the temperature is high.

  According to the present invention, the composite metal oxide porous body, which is very excellent in high temperature durability, maintains a high specific surface area and purification performance even at high temperatures, and is useful as a catalyst for exhaust gas purification, etc. It becomes possible to manufacture well.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

In the method for producing a composite metal oxide porous body of the present invention, first,
(i) an aggregate of primary particles having a diameter of 50 nm or less and an average particle diameter of 200 nm or less, and an aggregate of primary particles having a diameter of 50 nm or less and an average particle diameter of 200 nm or less. A second metal oxide powder is dispersed and mixed in a dispersion medium using microbeads having a diameter of 150 μm or less to form a uniform dispersion of the first metal oxide fine particles and the second metal oxide fine particles (dispersed and mixed) Process), and
(iii) The uniform dispersion is dried to obtain a composite metal oxide porous body (drying step).

  The type of the first metal oxide and the second metal oxide used in the present invention is not particularly limited, and base metal elements (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Rb, Sr, Zr, Nb, Mo, In, Sn, Cs, Ba, Ta, W, etc. ), An oxide of at least one metal selected from the group consisting of noble metal elements (Pt, Pd, Rh, Ru, Au, Ag, Os, Ir) and metalloid elements (Si, Ge, As, Sb, etc.) Among them, a single oxide or composite oxide of at least one metal selected from the group consisting of Ce, Zr, Al, Ti, Si, Mg, Fe, Mn, Ni, Zn and Cu is preferable, ceria, More preferably, it is at least one selected from the group consisting of zirconia, ceria-zirconia composite oxide (solid solution), alumina, titania, sepiolite, and zeolite. The metal according to the present invention includes metalloid (semimetal), and the metal oxide may contain a plurality of metal elements such as ceria-zirconia composite oxide, sepiolite, and zeolite.

  Further, the combination of the first metal oxide and the second metal oxide used in the present invention is not particularly limited, and is appropriately selected according to the intended use of the composite metal oxide porous body. For example, when obtaining a composite metal oxide porous body useful as a catalyst for exhaust gas purification, an oxygen storage material composed of ceria having oxygen storage capacity (OSC), ceria-zirconia composite oxide, iron oxide, praseodymium oxide, and the like; A combination with a diffusion barrier material made of alumina, zirconia, titania or the like that can serve as a diffusion barrier is preferable. Further, for example, from the viewpoint of a combination of oxides that can be diffusion barriers even after high temperature treatment, ceria-zirconia composite oxide and alumina, ceria and alumina, zirconia and alumina, ceria and titania, alumina and titania, alumina and silica, etc. The combination of is more preferable.

  The first metal oxide used in the present invention needs to be a powder made of an aggregate of primary particles (crystallites) having a diameter of 50 nm or less (more preferably 20 nm or less, particularly preferably 2 to 10 nm). is there. If the diameter of the primary particles exceeds 50 nm, sufficiently small nano-sized fine particles cannot be obtained even if dispersed using the microbeads described later, and as a result, the composite metal oxidation is sufficiently excellent in high-temperature durability. A porous material cannot be obtained. Moreover, the average particle diameter of the 1st metal oxide powder used by this invention needs to be 200 nm or less, and it is more preferable that it is 10-100 nm. When the average particle diameter of the first metal oxide powder exceeds 200 nm, a nano-level uniform mixed state is not achieved even when dispersed and mixed with the second metal oxide fine particles described later, resulting in high temperature durability. A sufficiently excellent composite metal oxide porous body cannot be obtained.

  Further, the second metal oxide used in the present invention is also required to be a powder composed of aggregates of primary particles (crystallites) having a diameter of 50 nm or less (more preferably 20 nm or less, particularly preferably 2 to 10 nm). . If the diameter of the primary particles exceeds 50 nm, sufficiently small nano-sized fine particles cannot be obtained even if dispersed using the microbeads described later, and as a result, the composite metal oxidation is sufficiently excellent in high-temperature durability. A porous material cannot be obtained. Moreover, the average particle diameter of the 2nd metal oxide powder used by this invention needs to be 200 nm or less, and it is more preferable that it is 10-100 nm. When the average particle diameter of the second metal oxide powder exceeds 200 nm, even if dispersed and mixed with the first metal oxide fine particles, a nano-level uniform mixed state is not achieved, resulting in high temperature durability. A sufficiently excellent composite metal oxide porous body cannot be obtained.

  In addition, the manufacturing method in particular of such 1st metal oxide powder and 2nd metal oxide powder is not restrict | limited, For example, what is called precipitation method using the solution of the metal salt used as a raw material, and precipitation obtained by it It can obtain suitably by the method of baking.

  The microbeads used in the dispersion mixing step in the present invention are required to have a diameter of 150 μm or less, more preferably 10 to 100 μm, and particularly preferably 15 to 50 μm. If the diameter of the microbeads exceeds 150 μm, sufficiently small nano-sized fine particles, and furthermore, a nano-level uniform mixed state cannot be achieved, and as a result, a composite metal oxide porous body sufficiently excellent in high-temperature durability is obtained. I can't get it. On the other hand, when the diameter of the microbead exceeds 150 μm, the composition of the particle itself is deformed and the crystal is broken, and sufficient heat resistance cannot be obtained from this viewpoint.

  The diameter of the microbeads used in the dispersion mixing step is preferably 250 to 1000 times the average particle diameter of the first metal oxide powder and the second metal oxide powder. If the diameter of the microbead is less than the lower limit, the dispersion efficiency tends to decrease. On the other hand, if the microbead exceeds the upper limit, sufficiently small nano-sized fine particles tend to be hardly obtained.

  Furthermore, the material of the microbead used in the present invention is not particularly limited, and examples thereof include zirconia and glass. The material of such microbeads is preferably selected as appropriate according to the first and / or second metal oxide used.

  The dispersion medium used in the dispersion mixing step in the present invention is not particularly limited as long as it is a liquid that can disperse the obtained first metal oxide fine particles and second metal oxide fine particles, but water or the like is preferably used. Used. In addition, it is not particularly necessary to add other components to such a dispersion medium, but when adjusting the pH of the dispersion medium as will be described later, an acid such as acetic acid, a base such as ammonia, a buffering agent, etc. are appropriately added. May be.

  A specific apparatus used in such a dispersion and mixing step is to mix the first metal oxide powder and the second metal oxide powder together with the microbeads in the above dispersion medium, and the first metal oxide fine particles and the first metal particles described later. There is no particular limitation as long as a uniform dispersion with two metal oxide fine particles can be obtained. For example, if “Ultra Apex Mill” manufactured by Kotobuki Industries Co., Ltd. is used, the efficiency of the fine particles and microbeads by centrifugal force Separation becomes possible.

  In the present invention, the first metal oxide powder and the second metal oxide powder are dispersed and mixed in a dispersion medium using the microbeads, and the first metal oxide fine particles and the second metal oxide fine particles are mixed. To obtain a uniform dispersion in a nano-level uniform mixing state (dispersing and mixing step). At this time, the average particle diameter of the obtained first metal oxide fine particles is preferably 1 to 50 nm (more preferably 1 to 30 nm), and 80% by mass or more of particles have a diameter of 75 nm or less (more preferably 80 nm). It is preferable that particles of mass% or more have a diameter of 50 nm or less. When the average particle diameter of the obtained first metal oxide fine particles exceeds 50 nm, and when the proportion of fine particles having a diameter of 75 nm or less is less than 80% by mass, a sufficiently nano-level uniform mixed state is obtained. It is difficult and the high temperature durability of the obtained composite metal oxide porous body tends to be lowered. Moreover, it is preferable that the average particle diameter of 2nd metal oxide fine particles is 1-130 nm, and it is preferable that 80 mass% or more of particles are 160 nm or less in diameter. When the average particle size of the obtained second metal oxide fine particles exceeds 130 nm, and when the proportion of fine particles having a diameter of 160 nm or less is less than 80% by mass, a sufficiently uniform nano-level mixed state is obtained. It is difficult and the high temperature durability of the resulting composite metal oxide porous body tends to decrease.

  Furthermore, it is preferable that there is no great difference in particle size between the first metal oxide powder and the second metal oxide powder before the treatment, and one average particle size is about 1 to 5 times the other average particle size. Is preferred.

  Specific conditions of the dispersion mixing process in such a dispersion mixing process are not particularly limited, and a treatment time of about 20 to 200 minutes is usually employed at a temperature of about room temperature to 80 ° C.

  Further, in the dispersion mixing step, it is preferable that the pH of the dispersion medium is a pH in a region where the absolute values of the zeta potential of the first metal oxide and the zeta potential of the second metal oxide are both 10 mV or more. . When the pH of the dispersion medium does not satisfy the above conditions, the dispersion efficiency tends to decrease depending on the pH. For example, as apparent from the zeta potential of the ceria-zirconia composite oxide (CZ) and alumina shown in FIG. 1, when using ceria-zirconia composite oxide as the first metal oxide and alumina as the second metal oxide, The pH of the dispersion medium in the dispersion mixing step is preferably 6-9.

  Further, the mixing ratio (mass ratio) of the first metal oxide and the second metal oxide mixed in the dispersion mixing step is not particularly limited, but (mass of the first metal oxide): (second metal oxide) The value of the mass of the product is preferably 1:10 to 5: 1. If the blending ratio of the first metal oxide is less than the lower limit, the effect of mixing with the fine particles tends to be small. On the other hand, if the blending ratio of the second metal oxide is less than the lower limit, the first metal oxide may be re-reacted depending on the pH. Aggregation tends to occur. Moreover, when using a 2nd metal oxide as a diffusion barrier, it exists in the tendency for the function as a diffusion barrier to fall.

  Following the above-described dispersion mixing step, in the present invention, a uniform dispersion of the first metal oxide fine particles and the second metal oxide fine particles obtained in the step is dried to obtain a composite metal oxide porous body. (Drying process). The specific conditions of the drying treatment for drying such a uniform dispersion are not particularly limited, and for example, normal temperature or heat drying that allows drying for about 1 to 24 hours at a temperature of about 80 to 400 ° C., liquid A technique such as freeze-drying in which nitrogen is used to freeze at a temperature of 0 ° C. or less and then dried under reduced pressure is appropriately employed.

  Moreover, in this invention, it is preferable to heat-dry, after adding and mixing surfactant in the said uniform dispersion liquid in a drying process so that it may explain in full detail below. By adopting such a drying method, a composite metal oxide porous body having a multilayer structure can be obtained, and the form of the layer can be controlled by the type of the surfactant. In addition, by adding a surfactant to the uniform dispersion, the secondary particles are coated with a surfactant to suppress the aggregation of secondary particles, and further the effect of dispersing the surfactant. Therefore, the dispersibility of secondary particles obtained by aggregation tends to be improved. By these actions, a composite metal oxide porous body having a desired central pore diameter (preferably 5 to 30 nm) and a desired pore volume (preferably 0.2 cc / g or more) can be obtained more efficiently. Further, the high temperature durability of the obtained composite metal oxide porous body tends to be further improved.

  As the surfactant used in the drying step, any of anionic, cationic, and nonionic surfactants can be used. Among them, a shape in which the micelle to be formed can form a narrow space inside, for example, A surfactant that easily forms spherical micelles is preferred. A surfactant having a critical micelle concentration (cmc) of 0.1 mol / liter or less is preferable, and a surfactant having a critical micelle concentration (cmc) of 0.01 mol / liter or less is more preferable. The critical micelle concentration (cmc) is the lowest concentration at which a surfactant forms micelles.

As such a surfactant, at least one selected from the following can be used.
(i) Anionic surfactant:
Alkyl benzene sulfonic acid and its salt, α-olefin sulfonic acid and its salt, alkyl sulfate ester salt, alkyl ether sulfate ester salt, phenyl ether sulfate ester salt, methyl taurate, sulfosuccinate, ether sulfate, alkyl sulfate, ether Sulfonates, saturated fatty acids and salts thereof, unsaturated fatty acids such as oleic acid and salts thereof, other carboxylic acids, sulfonic acids, sulfuric acids, phosphoric acids, phenol derivatives and the like.
(ii) Nonionic surfactant:
Polyoxyethylene polypropylene alkyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polystyryl phenyl ether, polyoxyethylene polyoxypolypropylene alkyl ether, polyoxyethylene polyoxypropylene glycol, polyhydric alcohol (glycol Glycerin, sorbitol, mannitol, pentaerythritol, sucrose, etc.), polyhydric alcohol fatty acid partial ester, polyhydric alcohol polyoxyethylene fatty acid partial ester, polyhydric alcohol polyoxyethylene fatty acid ester, polyoxyethylenated castor oil , Polyglycerol fatty acid ester, fatty acid diethanolamide, polyoxyethylene alkylamine, triethanolamine Fatty acid partial esters, trialkylamine oxide and the like.
(iii) Cationic surfactant:
Fatty acid primary amine salt, fatty acid secondary amine salt, fatty acid tertiary amine salt, tetraalkylammonium salt, trialkylbenzylammonium salt, alkylpyrodinium salt, 2-alkyl-1-alkyl-1-hydroxyethylimidazolinium Quaternary ammonium salts such as salts, N, N-dialkylmorpholinium salts, polyethylene polyamines and fatty acid amide salts.
(iv) Amphoteric surfactant:
Betaine compounds and the like.

  The addition amount of such a surfactant is not particularly limited, but is in the range of 2 to 40% by mass with respect to the obtained composite metal oxide porous body, that is, the composite metal oxide porous body: surfactant in a mass ratio. = The range of 98-60: 2-40 is preferable. When the addition amount of the surfactant is less than 2% by mass, the effect of the addition is small. On the other hand, when the addition amount exceeds 40% by mass, the dispersibility of the secondary particles obtained by the aggregation of the surfactants decreases, and heating is performed. Since the amount of heat generated by combustion of the surfactant increases during drying, the metal oxide tends to aggregate and the specific surface area tends to decrease.

The stirring speed in the drying step is preferably 1000 sec −1 or more, and is preferably stirred at a temperature of 10 to 30 ° C. for 5 minutes or more. If the shearing force due to agitation is too large, heat will be generated or the apparatus will be exhausted too much. On the other hand, if the shearing force is too small, the dispersed state of the surfactant will tend to be insufficient. Further, if the temperature during stirring is lower than this range, the stirring time becomes longer, and on the other hand, if the temperature is higher than this range, heat generation and apparatus wear tend to occur.

  Moreover, it is preferable that the heating temperature in the drying method using such a surfactant shall be 150-800 degreeC. When this temperature is lower than 150 ° C., heat drying is required for a long time. On the other hand, when the temperature is higher than 800 ° C., aggregation of metal oxide occurs and the specific surface area tends to decrease. The heating time is not particularly limited, but is preferably about 1 to 10 hours.

  Furthermore, when adopting such a drying method, a uniform dispersion mixed with a surfactant is applied to a sprayer to generate aerosol droplets of uniform size with a carrier gas such as nitrogen, and then the droplets are removed. It is preferable to collect by a collecting means such as a Teflon filter through a heater. By doing so, a composite metal oxide porous body with high dispersibility tends to be obtained more efficiently. In this case, the flow rate is not particularly limited.

  Moreover, in this invention, the baking process may be included after said drying process, In this baking process, the composite metal oxide porous body is hold | maintained for about 1 to 10 hours at the temperature of about 400-1000 degreeC. It is preferable to do. By employing such a firing step, noble metal aggregation tends to be suppressed due to a decrease in the specific surface area of the carrier after the durability test.

  Furthermore, in the present invention, a pre-supporting step of supporting a noble metal (noble metal fine particles) on the surface of the first metal oxide powder and / or the second metal oxide powder, or the first metal oxide fine particles and the above-mentioned It is preferable that a post-supporting step of supporting a noble metal (noble metal fine particles) on the surface of the second metal oxide fine particles is further included, and a pre-supporting step is more preferable. In such a supporting step, the noble metal supported on the metal oxide powder or the fine particles is not particularly limited, and includes at least one noble metal selected from the group consisting of Pt, Pd, Rh, Ru, Au, Ag, Os, and Ir. Among these, Pt, Rh, Pd, and Ir are preferable from the viewpoint of catalytic activity, and Pt is particularly preferable. The amount of the noble metal supported on the metal oxide powder or fine particles is not particularly limited, but the amount of the noble metal is preferably about 0.1 to 10 parts by mass with respect to 100 parts by mass of the supported metal oxide. . When the amount of the noble metal is less than the above lower limit, the catalytic activity obtained by the noble metal tends to be insufficient, while when the amount exceeds the upper limit, the catalytic activity due to the noble metal is saturated and the cost tends to increase. Further, the specific method for supporting the noble metal on the metal oxide powder or fine particles is not particularly limited. For example, the metal oxide powder or fine particles are brought into contact with a solution of a noble metal salt, and if necessary, reduction treatment and / or A method of performing a baking treatment is appropriately employed. Further, the particle size of the noble metal fine particles supported is not particularly limited, but the average particle size is generally about 0.1 to 10 nm.

  When the noble metal is supported in this manner, the supported metal oxide fine particles may be either the first metal oxide powder or the second metal oxide powder, and the finally obtained composite metal oxide porous body A metal may be supported. However, when the first metal oxide is used as an optimum carrier for supporting the noble metal, that is, when it is preferable to support the noble metal on the first metal oxide, the supporting step is performed before the dispersion mixing step. It is preferably present (pre-loading step). By doing so, it becomes possible to mainly support the noble metal on the first metal oxide, and the catalytic activity and high-temperature durability of the resulting composite metal oxide porous body tend to be further improved. For example, when ceria-zirconia composite oxide is used as the first metal oxide and alumina is used as the second metal oxide, the catalytic activity tends to be improved when the noble metal is on the surface of the ceria-zirconia composite oxide. Therefore, it is preferable to support the noble metal on the ceria-zirconia composite oxide.

In the composite metal oxide porous body obtained by the method of the present invention described above, the above-mentioned first metal oxide fine particles and second metal oxide fine particles (more precious metal fine particles when noble metal is supported) are uniform at the nano level. The specific surface area is not particularly limited, but is preferably about 1 to 1000 m 2 / g. The specific surface area can be calculated as a BET specific surface area from an adsorption isotherm using a BET isotherm adsorption formula.

  Moreover, the shape of the composite metal oxide porous body obtained by the present invention is not particularly limited, and may be a powder or a thin film. In the case of powder, the particle size is not particularly limited and is appropriately adjusted according to the use and the like, but generally about 50 to 200 μm is preferable. Moreover, you may shape | mold and use the composite metal oxide porous body obtained by this invention as needed. Any molding means may be used, but extrusion molding, tablet molding, rolling granulation, compression molding, CIP and the like are preferable. The shape can be determined according to the place of use and method, and examples thereof include a columnar shape, a crushed shape, a spherical shape, a honeycomb shape, an uneven shape, and a corrugated plate shape.

Furthermore, the use of the composite metal oxide porous body obtained by the present invention is not particularly limited, and is effectively used as, for example, an exhaust gas purification catalyst, a VOCs purification catalyst, a reforming catalyst, an air cleaner catalyst, and the like. Further, the specific method of using the composite metal oxide porous body obtained by the present invention is not particularly limited. For example, when used as an exhaust gas purification catalyst, a gas containing a harmful component to be treated and a catalyst are batch-typed. Alternatively, harmful components can be purified by continuous contact. Examples of harmful components to be treated include NO x , CO, HC, SO x in exhaust gas.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
First, a nitric acid solution of Pt nitrate (Pt concentration: 4.5 wt%) is used as a cerium-zirconium composite oxide (CZ) powder which is an aggregate of primary particles having a diameter of about 8 nm and an average particle diameter of 100 nm. Pt was supported as follows to obtain CZ powder (Pt / CZ powder) supporting Pt (pre-supporting step). That is, a Pt nitric acid solution was impregnated and supported on CZ powder, and calcined at 300 ° C. for 3 hours. The amount of supported Pt was 1 part by mass with respect to 100 parts by mass of the CZ powder.

Next, the obtained Pt / CZ powder and an alumina powder having an average particle diameter of 110 nm and an aggregate of primary particles having a diameter of about 10 nm are dissolved in an aqueous solution of pH 7 using zirconia microbeads having a diameter of 50 μm. After dispersing and mixing for 120 minutes (dispersing and mixing step), the resulting uniform dispersion was stirred using a propeller stirrer, and a nonionic surfactant (manufactured by Lion, trade name: Leocon, substance name: Poly) Oxyethylene polyoxypropylene mono-2-ethylhexyl ether) was added so as to have the same mass as the CZ powder. The obtained dispersion was stirred for 10 minutes at room temperature using a homogenizer stirring simultaneously with propeller stirring (stirring speed: 200 sec −1 ), and then heat-dried at 400 ° C. for 5 hours to obtain Pt / CZ fine particles and A catalyst powder (average particle size: 120 nm) comprising alumina fine particles was obtained. Further, the obtained catalyst powder was compacted by a mold press (1 t / cm 2 ) and pulverized to obtain a pellet-shaped catalyst having a diameter of 0.5 to 1 mm.

  The mixing ratio (mass ratio) of Pt / CZ powder and alumina powder in the dispersion mixing step is 1: 1, and the average particle size of the Pt / CZ fine particles obtained in the dispersion mixing step is 34 nm and 80 mass. % Of particles having a diameter of 41 nm or less (D80 = 41 nm), the average particle diameter of alumina fine particles obtained in the dispersion mixing step was 87 nm, and 80% by mass or more of particles had a diameter of 112 nm or less (D80 = 112 nm). It was. The specific surface area of the obtained catalyst was as shown in Table 2.

(Example 2)
A catalyst was obtained in the same manner as in Example 1 except that the dispersion treatment time was 180 minutes in the dispersion mixing step. The specific surface area of the obtained catalyst was as shown in Table 2.

(Example 3)
A catalyst was obtained in the same manner as in Example 1 except that an alumina powder having an average particle diameter of 162 nm and an aggregate of primary particles having a diameter of about 10 nm was used. The specific surface area of the obtained catalyst was as shown in Table 2.

Example 4
A catalyst was obtained in the same manner as in Example 1 except that the pH of the aqueous solution in the dispersion mixing step was changed to 5. The specific surface area of the obtained catalyst was as shown in Table 2.

(Example 5)
Pt was not supported on the CZ powder, and a catalyst was obtained in the same manner as in Example 1 except that Pt was supported on the catalyst powder composed of CZ fine particles and alumina fine particles obtained in the drying step as follows. . That is, a Pt nitric acid solution (Pt concentration: 4.5 wt%) was impregnated and supported on the catalyst powder, and calcined at 300 ° C. for 3 hours (post-supporting step). The amount of supported Pt was 0.5 parts by mass with respect to 100 parts by mass of the total amount of CZ fine particles and alumina fine particles. The specific surface area of the obtained catalyst was as shown in Table 2.

(Comparative Example 1)
A catalyst was obtained in the same manner as in Example 1 except that alumina powder having an average particle diameter of 259 nm and an aggregate of primary particles having a diameter of about 10 nm was used in the dispersion and mixing step. The specific surface area of the obtained catalyst was as shown in Table 2.

(Comparative Example 2)
A catalyst was obtained in the same manner as in Example 1 except that zirconia microbeads having a diameter of 200 μm were used in the dispersion mixing step. The specific surface area of the obtained catalyst was as shown in Table 2.

(Comparative Example 3)
A catalyst was obtained in the same manner as in Example 1 except that alumina powder was not mixed. The specific surface area of the obtained catalyst was as shown in Table 2.

(Comparative Example 4)
A catalyst was obtained in the same manner as in Example 1 except that a ball mill using a zirconia pot having a volume of 1 liter and a zirconia ball having a diameter of 5 mm was used in the dispersion mixing step. The specific surface area of the obtained catalyst was as shown in Table 2.

<High temperature durability test 1>
Each pellet-like catalyst obtained in the above-mentioned Examples and Comparative Examples 1 and 2 in an atmosphere in which rich gas and lean gas having the composition shown in Table 3 were alternately flowed at intervals of 5 minutes so that the total flow rate was 330 ml / min. 5 g was held at 1000 ° C. for 5 hours, and the specific surface area after the durability test was measured. The obtained results are shown in Table 2.

<High temperature durability test 2>
Using a normal pressure fixed bed flow reactor, 1 g of each pellet-shaped catalyst (initial product) obtained in the above Examples and Comparative Examples, and 1 g of those subjected to high temperature durability test 1 (product after durability test), HC purification rate at each temperature in which a rich gas and a lean gas having the composition shown in Table 4 were circulated at intervals of 1 second so that the total flow rate was 7 L / min, and the inlet gas temperature was 100 to 500 ° C. Was measured, and the HC50 purification temperature of each was determined. The obtained results are shown in Table 2.

  As is apparent from the results shown in Table 2, the catalyst (Examples 1 to 5) comprising the composite metal oxide porous material of the present invention obtained by the method of the present invention had a specific surface area and purification even at high temperatures. The performance was maintained at a high level, and the high temperature durability was very excellent. Among them, the catalysts (Examples 1 to 4) composed of the composite metal oxide porous body obtained by supporting the noble metal on the first metal oxide powder in the pre-supporting step in the method of the present invention are particularly excellent in high temperature durability. Met.

  As described above, according to the present invention, the composite metal oxide porous body that is very excellent in high temperature durability and that maintains the specific surface area and the purification performance at a high level even under high temperature can be efficiently produced. It becomes possible to do. Therefore, the method of the present invention is very useful as a method for producing an exhaust gas purifying catalyst having excellent high temperature durability.

It is a graph which shows the zeta potential of a ceria-zirconia composite oxide (CZ) and alumina.

Claims (8)

  1. A first metal oxide powder that is an aggregate of primary particles having a diameter of 50 nm or less and an average particle diameter of 200 nm or less, and a second metal oxide powder that is an aggregate of primary particles having a diameter of 50 nm or less and an average particle diameter of 200 nm or less. Dispersing and mixing the metal oxide powder in a dispersion medium using microbeads having a diameter of 150 μm or less to obtain a uniform dispersion of the first metal oxide fine particles and the second metal oxide fine particles,
    A drying step of drying the uniform dispersion to obtain a composite metal oxide porous body;
    The manufacturing method of the composite metal oxide porous body characterized by including.
  2.   The pH of the dispersion medium in the dispersion mixing step is a pH in a region where the absolute values of the zeta potential of the first metal oxide and the zeta potential of the second metal oxide are both 10 mV or more. 2. A method for producing a composite metal oxide porous body according to 1.
  3.   3. The composite metal oxide according to claim 1, wherein the first metal oxide fine particles have an average particle diameter of 1 to 50 nm and 80% by mass or more of particles have a diameter of 75 nm or less. A method for producing a porous body.
  4.   The second metal oxide fine particles have an average particle diameter of 1 to 130 nm and 80% by mass or more of particles having a diameter of 160 nm or less. The manufacturing method of the composite metal oxide porous body as described in 2.
  5.   5. The method according to claim 1, further comprising a pre-supporting step of supporting a noble metal on a surface of the first metal oxide powder and / or the second metal oxide powder. A method for producing a composite metal oxide porous body.
  6.   The composite metal according to any one of claims 1 to 5, further comprising a post-supporting step of supporting a noble metal on the surfaces of the first metal oxide fine particles and the second metal oxide fine particles. Manufacturing method of oxide porous body.
  7.   The composite metal oxide porous body according to any one of claims 1 to 6, wherein in the drying step, a surfactant is added to and mixed with the uniform dispersion, followed by drying by heating. Production method.
  8.   The said composite metal oxide porous body is a catalyst for exhaust gas purification, The manufacturing method of the composite metal oxide porous body as described in any one of Claims 1-7 characterized by the above-mentioned.
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