JP4696767B2 - Method for producing composite metal oxide porous body - Google Patents

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. The object is to provide a method capable of producing a composite metal oxide porous body 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:
The first metal oxide powder, which is an aggregate of primary particles of ceria-zirconia composite oxide having a diameter of 50 nm or less (more preferably 20 nm or less), is used with microbeads having a diameter of 150 μm or less (more preferably 10 to 100 μm). Dispersing in a dispersion medium to obtain first metal oxide fine particles having an average particle diameter of 1 to 50 nm and 80% by mass or more of particles having a diameter of 75 nm or less;
A dispersion medium comprising the first metal oxide fine particles and a second metal oxide powder that is an aggregate of primary particles made of alumina and having a diameter of 50 nm or less (more preferably 20 nm or less) and an average particle diameter of 200 nm or less. A dispersion and mixing step of obtaining a uniform dispersion of the first metal oxide fine particles and the second metal oxide fine particles by dispersing and mixing them in the medium;
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 dispersing medium prior Symbol dispersion mixing step, the code of the code and the zeta potential of the second metal oxide of the zeta potential of the first metal oxide It is preferable to set the pH in the opposite region.

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

  Further, in the dispersion mixing step, the first metal oxide fine particles and the second metal oxide powder are dispersed and mixed in a dispersion medium using microbeads having a diameter of 150 μm or less (more preferably 10 to 100 μm). Preferably.

  Furthermore, the method for producing a composite metal oxide porous body of the present invention further includes a supporting step of supporting a noble metal on the surface of the first metal oxide fine particles and / or the second metal oxide fine particles. Is preferred.

  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, the first metal oxide fine particles dispersed using fine micro beads having a diameter of 150 μm or less are dispersed and mixed with the second metal oxide fine particles having an average particle size of 200 nm or less, whereby both fine particles are nano-sized. Are mixed uniformly at the same level, and other types of metal oxide fine particles exist as barriers between the same type of metal oxide fine particles. The present inventors infer that the growth is sufficiently suppressed, and as a result, the specific surface area and the purification performance are maintained at a high level even at high temperatures.

  According to the present invention, the composite metal oxide porous body that is extremely excellent in high-temperature durability, maintains a high specific surface area and purification performance even at high temperatures, and is useful as an exhaust gas purification catalyst, etc. It becomes possible to do.

  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) The first metal oxide powder, which is an aggregate of primary particles having a diameter of 50 nm or less, is dispersed in a dispersion medium using microbeads having a diameter of 150 μm or less, and has an average particle diameter of 1 to 50 nm and 80 masses. % Of the first metal oxide fine particles having a diameter of 75 nm or less (dispersion step),
(ii) Dispersing and mixing the first metal oxide fine particles and the second metal oxide powder, which is an aggregate of primary particles having a diameter of 50 nm or less and an average particle size of 200 nm or less, in a dispersion medium; A uniform dispersion of the first metal oxide fine particles and the second metal oxide fine particles (dispersion mixing step);
(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 an exhaust gas purification catalyst, an oxygen storage material comprising ceria having an 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. Further, the average particle size of the first metal oxide powder used in the present invention is not particularly limited, but it is preferable that the average particle size is 200 nm or less from the viewpoint that nano-sized fine particles can be efficiently obtained. More preferably, it is 100 nm or less.

  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 step in the present invention must 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 step is preferably 250 to 1000 times the average particle diameter of the first 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.

  Also in the dispersion mixing step of the present invention, the first metal oxide fine particles and the second metal oxide powder are dispersed and mixed in a dispersion medium using microbeads similar to the microbeads used in the dispersion step. It is preferable.

  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 step and 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. Are preferably used. In addition, it is not particularly necessary to add other components to the dispersion medium, but when adjusting the pH of the dispersion medium as 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 step and a dispersion mixing step can mix the first metal oxide powder together with the microbeads in the dispersion medium to obtain first metal oxide fine particles to be described later. Further, the first metal oxide fine particles and the second metal oxide powder can be mixed in the same dispersion medium to obtain a uniform dispersion of the first metal oxide fine particles and the second metal oxide fine particles described later. Any material can be used as long as it is not particularly limited. For example, if “Ultra Apex Mill” manufactured by Kotobuki Industries Co., Ltd. is used, fine particles and microbeads can be efficiently separated by centrifugal force.

  First, in the present invention, the first metal oxide powder is dispersed in a dispersion medium using the microbeads, and the average particle size is 1 to 50 nm (more preferably 1 to 30 nm) and 80% by mass. A sufficiently small nano-sized first metal oxide fine particle in which the above particles have a diameter of 75 nm or less (more preferably, 80% by mass or more of the particles have a diameter of 50 nm or less) is obtained (dispersing step). In the case where the average particle diameter of the obtained first metal oxide fine particles exceeds 50 nm, and the proportion of fine particles having a diameter of 75 nm or less is less than 80% by mass, it is nano-level in the dispersion mixing step described later. A uniform mixed state is not achieved, and as a result, a composite metal oxide porous body sufficiently excellent in high temperature durability cannot be obtained.

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

  In such a dispersion step, it is preferable that the pH of the dispersion medium is a pH in a region where the absolute value of the zeta potential of the first metal oxide is 20 mV or more. When the absolute value of the zeta potential of the first metal oxide is less than 20 mV, the fine particles of the obtained first metal oxide are easily re-aggregated and segregation is likely to occur, and it is difficult to obtain sufficiently small nano-sized fine particles. There is a tendency. For example, the zeta potential of the ceria-zirconia composite oxide (CZ) and alumina is as shown in FIG. 1, and when the ceria-zirconia composite oxide is used as the first metal oxide, the pH of the dispersion medium in the dispersion step is It is preferably 3.5 or less or 7 or more.

  Following the dispersion step, in the present invention, the first metal oxide fine particles obtained in the step and the second metal oxide powder are dispersed and mixed in a dispersion medium, and the first metal oxide is obtained. A uniform dispersion in which the fine particles and the second metal oxide fine particles are in a nano-level uniform mixed state is obtained (dispersion mixing step). At this time, the average particle diameter of the obtained second metal oxide fine particles is preferably 1 to 130 nm, and 80% by mass or more of the particles are preferably 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 sufficient nano-level uniform mixing state is obtained. It is difficult and the high temperature durability of the resulting composite metal oxide porous body tends to decrease.

  The specific conditions for the dispersion and mixing treatment in such a dispersion and mixing step are not particularly limited, and a treatment time of about 10 to 100 minutes is usually employed at a temperature of about room temperature to 80 ° C.

  Further, in such a dispersion mixing step, it is preferable that the pH of the dispersion medium is a pH in a region where the sign of the zeta potential of the first metal oxide and the sign of the zeta potential of the second metal oxide are opposite. More preferably, the pH of the region where the difference is 10 mV or more. When the sign of the zeta potential of the first metal oxide and the sign of the zeta potential of the second metal oxide are the same sign, the resulting fine particles of the first metal oxide and the fine particles of the second metal oxide are aggregated. Segregation is likely to occur, and the high temperature durability of the resulting composite metal oxide porous body tends to decrease. 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 5 to 9 (range indicated by A in FIG. 1).

  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, it is preferable that the present invention further includes a supporting step of supporting a noble metal (noble metal fine particles) on the surface of the first metal oxide fine particles and / or the second metal oxide fine particles. In such a supporting step, the noble metal supported on the metal oxide fine particles is not particularly limited, and examples thereof include at least one kind of 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 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 metal oxide fine particles supported. 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 fine particles is not particularly limited. For example, the metal oxide fine particles are brought into contact with a solution of a noble metal salt, and further, reduction treatment and / or firing treatment is performed as necessary. Such a method is appropriately adopted. 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 way, the supported metal oxide fine particles may be either the first metal oxide fine particles or the second metal oxide fine particles, and the finally obtained composite metal oxide porous body A metal may be supported. However, when the first metal oxide fine particles are used as the optimum carrier for supporting the noble metal, that is, when it is preferable to support the noble metal on the first metal oxide fine particles, such a supporting step is a dispersion step and a dispersion step. It is preferably present during the mixing step. By doing so, it becomes possible to support the noble metal only on the first metal oxide fine particles, 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. On the other hand, if it is possible to support the noble metal in a highly dispersed state, the noble metal may be supported before the dispersing step.

In the composite metal oxide porous body obtained by the method of the present invention described above, the first metal oxide fine particles and the second metal oxide fine particles (in the case where noble metal is supported, further noble metal fine particles) are nano-level uniform. It is agglomerated in a mixed state, and its 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 the adsorption isotherm using the 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 location and method of use, 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
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, is dispersed in an aqueous solution of pH 3 for 90 minutes using zirconia microbeads having a diameter of 50 μm. CZ fine particles having an average particle diameter of 22 nm and particles having a diameter of 80% by mass or more having a diameter of 43 nm or less (D80 = 43 nm) were obtained (dispersing step).

  Subsequently, the obtained CZ fine particles were loaded with Pt as follows using a nitric acid solution of Pt nitrate (Pt concentration: 4.5 wt%), and Ct fine particles carrying Pt (Pt / CZ fine particles). Was obtained (supporting step). That is, a Pt nitric acid solution was impregnated and supported on CZ fine particles, 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 fine particles.

Next, the obtained Pt / CZ fine particles and an aggregate of primary particles having a diameter of about 10 nm and an alumina powder having an average particle size of 162 nm are mixed in a pH 7 aqueous solution using zirconia microbeads having a diameter of 50 μm. After dispersing and mixing for 30 minutes (dispersing and mixing step), the obtained uniform dispersion is frozen with liquid nitrogen and left in a vacuum vessel at room temperature (drying step) to form a catalyst comprising Pt / CZ fine particles and alumina fine particles. A powder (average particle size: 120 nm) was obtained. At that time, it was visually confirmed that there was no melting in the drying step. 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 fine particles and alumina fine particles in the dispersion mixing step is 1: 1, and the average particle size of the alumina fine particles obtained in the dispersion mixing step is 110 nm and 80% by mass or more. The particles had a diameter of 150 nm or less (D80 = 150 nm). Further, the specific surface area of the obtained catalyst was as shown in Table 3.

(Example 2)
In the dispersion step, CZ fine particles shown in Table 1 obtained with a dispersion treatment time of 120 minutes are used, and in the dispersion and mixing step, an aggregate of primary particles having a diameter of about 10 nm and an alumina powder having an average particle size of 110 nm are used. A catalyst was obtained in the same manner as in Example 1 except that. The specific surface area of the obtained catalyst was as shown in Table 3.

(Example 3)
A catalyst was obtained in the same manner as in Example 1 except that the CZ fine particles shown in Table 1 obtained by setting the pH of the aqueous solution in the dispersing step to 5 were used. The specific surface area of the obtained catalyst was as shown in Table 3.

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 4. The specific surface area of the obtained catalyst was as shown in Table 3.

(Example 5)
A catalyst was obtained in the same manner as in Example 1 except that the drying step was changed to the heat drying treatment using the following surfactant. That is, while stirring the uniform dispersion obtained in the dispersion mixing step using a propeller stirrer, a nonionic surfactant (manufactured by Lion Corporation, trade name: Leocon, substance name: polyoxyethylene polyoxypropylene mono- 2-ethylhexyl ether) was added so as to have the same mass as the CZ fine particles. 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. The specific surface area of the obtained catalyst was as shown in Table 3.

(Example 6)
Pt was not supported on CZ fine particles, 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. 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 3.

(Comparative Example 1)
A catalyst was obtained in the same manner as in Example 1 except that alumina powder having a primary particle aggregate of about 10 nm in diameter and an average particle diameter of 259 nm was used in the dispersion mixing step. The specific surface area of the obtained catalyst was as shown in Table 3.

(Comparative Example 2)
The same procedure as in Example 1 was conducted except that the CZ microparticles shown in Table 1 obtained using zirconia microbeads having a diameter of 200 μm were used in the dispersion step, and zirconia microbeads having a diameter of 200 μm were further used in the dispersion mixing step. A catalyst was obtained. The specific surface area of the obtained catalyst was as shown in Table 3.

(Comparative Example 3)
First, a nitric acid solution of Pt nitrate (Pt concentration: 4.5 wt%) is used as a cerium-zirconium composite oxide (CZ) powder that 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 (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 aggregate of primary particles having a diameter of about 10 nm and an alumina powder having an average particle size of 110 nm are prepared by using a zirconia pot having a volume of 1 liter and a zirconia ball having a diameter of 5 mm. The mixture was dispersed and mixed in an aqueous solution of pH 7 for 120 minutes using a ball mill using a single dispersion step (single dispersion step), and the resulting uniform dispersion was stirred using a propeller stirrer, and a nonionic surfactant ( Lion Co., Ltd. (trade name: Leocon) 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 single dispersion step is 1: 1, and the average particle size of the Pt / CZ fine particles obtained in the single dispersion step is 86 nm. 80% by mass or more of the particles have a diameter of 97 nm or less (D80 = 97 nm), the average particle size of the alumina fine particles obtained in the single dispersion step is 92 nm, and 80% by mass or more of the particles has a diameter of 113 nm or less (D80 = 113 nm). )Met. Further, the specific surface area of the obtained catalyst was as shown in Table 3.

<High temperature durability test 1>
Each pellet-like catalyst obtained in the Examples and Comparative Examples 1 and 2 in an atmosphere in which rich gas and lean gas having the composition shown in Table 4 are alternately flowed at intervals of 5 minutes so that the total flow rate is 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 3.

<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 with an inlet gas temperature of 100 to 500 ° C., with a rich gas and a lean gas having the composition shown in Table 5 being circulated at intervals of 1 second so that the total flow rate is 7 L / min. Was measured, and the HC50 purification temperature of each was determined. The obtained results are shown in Table 3.

  As is apparent from the results shown in Table 3, the catalysts (Examples 1 to 6) composed of the composite metal oxide porous body obtained by the method of the present invention have high specific surface area and purification performance even at high temperatures. It was maintained at a standard and was very excellent in high temperature durability. Among them, the catalysts (Examples 1 to 2 and 5) made of the composite metal oxide porous body obtained by adjusting the pH of the dispersion medium in the dispersion step and the dispersion mixing step in a suitable range in the method of the present invention are particularly resistant to high temperatures. The catalyst (Example 5) comprising a porous composite metal oxide obtained by heating and drying using a surfactant was further excellent in high temperature durability.

  As described above, according to the present invention, it is possible to produce a composite metal oxide porous body that is very excellent in high-temperature durability and maintains a high specific surface area and purification performance even at high temperatures. Is possible. 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 (7)

The first metal oxide powder, which is an aggregate of primary particles having a diameter of 50 nm or less composed of ceria-zirconia composite oxide , is dispersed in a dispersion medium using microbeads having a diameter of 150 μm or less, and the average particle diameter is 1 to 50 nm. And a dispersion step of obtaining first metal oxide fine particles in which 80% by mass or more of the particles have a diameter of 75 nm or less;
The first metal oxide fine particles and the second metal oxide powder, which is an aggregate of primary particles made of alumina and having a diameter of 50 nm or less and having an average particle diameter of 200 nm or less, are dispersed and mixed in a dispersion medium, A dispersion mixing step of obtaining 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.   The pH of the dispersion medium in the dispersion and mixing step is a pH in a region where the sign of the zeta potential of the first metal oxide is opposite to the sign of the zeta potential of the second metal oxide. The manufacturing method of the composite metal oxide porous body of description.   3. The composite metal oxide according to claim 1, wherein the second metal oxide fine particles have an average particle diameter of 1 to 130 nm and 80% by mass or more of particles have a diameter of 160 nm or less. A method for producing a porous body.   In the dispersion mixing step, the first metal oxide fine particles and the second metal oxide powder are dispersed and mixed in a dispersion medium using microbeads having a diameter of 150 μm or less. 4. The method for producing a composite metal oxide porous body according to any one of 3 above.   The composite according to any one of claims 1 to 4, further comprising a supporting step of supporting a noble metal on the surface of the first metal oxide fine particles and / or the second metal oxide fine particles. A method for producing a metal oxide porous body.   In the said drying process, after adding and mixing surfactant in the said uniform dispersion liquid, it heat-drys, The composite metal oxide porous body as described in any one of Claims 1-5 characterized by the above-mentioned. Production method. 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 1-6 characterized by the above-mentioned.

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