JP2007063057A - Compound metal oxide porous body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compound metal oxide porous body having extremely excellent high temperature durability, keeping the specific surface area and cleaning performance at a high level even after a high-temperature durability test, and useful as a catalyst for purifying exhaust gas or the like. <P>SOLUTION: The compound metal oxide porous body comprises metal oxide fine particles comprising primary particles having diameters of 50 nm or less and alumina fine particles comprising primary particles having diameters of 50 nm or less and at least one crystal phase selected from a group consisting of γ-phase, δ-phase, θ-phase and α-phase and is characterized in that the content of the metal oxide is 45 mass% or more and that the specific surface area after a durability test at 1,000°C for 5 hours is 40 m<SP>2</SP>/g or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

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 and the like is desired.

  Under such a background, various catalysts for purifying exhaust gas have been developed. For example, JP-A-10-182155 (Patent Document 1) discloses at least one kind of cerium or zirconium, and Manufactured by a precursor forming step of forming a multi-element oxide precursor from a multi-element salt solution of aluminum in a short time, and a firing step of heating the oxide precursor to form a composite oxide. A composite oxide support characterized by the above is disclosed.

However, in the conventional composite oxide support as described in JP-A-10-182155, although alumina as a diffusion barrier is introduced by a so-called coprecipitation method in the synthesis process, the heat resistance of the diffusion barrier is low. There is a demand for the development of an exhaust gas purifying catalyst that is not always perfect and has excellent high-temperature durability, that is, the specific surface area and purification performance are maintained at a higher level even after a high-temperature durability test.
Japanese Patent Laid-Open No. 10-182155

  The present invention has been made in view of the above-mentioned problems of the prior art, and is very excellent in high temperature durability. Even after the high temperature durability test, the specific surface area and purification performance are maintained at a high level, and the exhaust gas is exhausted. An object of the present invention is to provide a composite metal oxide porous body useful as a purification catalyst or the like.

  As a result of intensive studies to achieve the above object, the present inventors have made metal oxide fine particles composed of primary particles having a diameter of 50 nm or less, and primary particles having a diameter of 50 nm or less, and a γ phase, δ phase, and θ phase. In addition, the inventors have found that the above object can be achieved by dispersing and mixing alumina fine particles having at least one crystal phase selected from the group consisting of α and α phases, and have completed the present invention.

That is, the composite metal oxide porous body of the present invention is a group consisting of metal oxide fine particles composed of primary particles having a diameter of 50 nm or less, and primary particles composed of particles having a diameter of 50 nm or less and composed of a γ phase, a δ phase, a θ phase, and an α phase. Alumina fine particles having at least one crystal phase selected from the above, the metal oxide content is 45% by mass or more, and the specific surface area after an endurance test at 1000 ° C. for 5 hours is 40 m ² / It is characterized by being g or more.

  In the composite metal oxide porous body of the present invention, the metal oxide fine particles and the alumina fine particles are preferably uniformly mixed at a nano level, and the metal oxide has an oxygen storage ability. Is more preferable.

  Moreover, it is preferable that the composite metal oxide porous body of the present invention satisfies at least one of the following conditions (I) to (III).

  (I) The pore volume of pores having a pore diameter of 5 to 30 nm after a durability test at 1000 ° C. for 5 hours and a pore diameter of 0.1 μm or less after the durability test is 0.2 cc / g or more. There is.

(II) The oxygen release rate after a 5 hour endurance test at 1000 ° C. is 1.5 μmol-O ₂ / g · sec or more.

(III) The total oxygen storage capacity after an endurance test at 1000 ° C. for 5 hours is 200 μmol-O ₂ / g or more.

  Furthermore, the composite metal oxide porous body of the present invention preferably further comprises a noble metal supported on the metal oxide fine particles and / or the alumina fine particles, thereby being useful as an exhaust gas purifying catalyst. Become.

Such a composite metal oxide porous body of the present invention is:
A metal oxide powder comprising primary particles having a diameter of 50 nm or less, and an alumina comprising primary particles having a diameter of 50 nm or less and having at least one crystal phase selected from the group consisting of γ phase, δ phase, θ phase and α phase Dispersion and mixing in a dispersion medium using microbeads having a diameter of 150 μm or less to obtain a uniform dispersion of metal oxide fine particles and alumina fine particles,
A drying step of drying the uniform dispersion to obtain a composite metal oxide porous body;
It is suitably obtained by a method comprising

  In addition, although the reason for which the composite metal oxide porous body which was very excellent in high temperature durability by this invention comes to be obtained is not necessarily certain, the present inventors guess as follows. That is, alumina fine particles having at least one crystal phase selected from the group consisting of a γ phase, a δ phase, a θ phase, and an α phase, which are composed of primary particles having a diameter of 50 nm or less and have been stabilized by heat treatment in advance, are diffused. As a barrier exists between the metal oxide fine particles, the particle growth of the metal oxide fine particles during the drying process and high temperature treatment is sufficiently suppressed, and as a result, even after the high temperature durability test The inventors speculate that the surface area and purification performance will be maintained at high levels.

  According to the present invention, the composite metal oxide porous body is very excellent in high temperature durability, has a high specific surface area and purification performance even after a high temperature durability test, and is useful as an exhaust gas purification catalyst or the like. Can be provided.

  Hereinafter, the composite metal oxide porous body of the present invention will be described in detail according to the preferred embodiments.

  The composite metal oxide porous body of the present invention is selected from the group consisting of metal oxide fine particles comprising primary particles having a diameter of 50 nm or less and primary particles having a diameter of 50 nm or less and comprising a γ phase, a δ phase, a θ phase and an α phase. And alumina fine particles having at least one crystal phase.

  The type of 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) , K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Rb, Sr, Zr, Nb, Mo, In, Sn, Cs, Ba, Ta, W, etc.), noble metal elements (Pt, Pd, Rh, Ru, Au, Ag, Os, Ir) and an oxide of at least one metal selected from the group consisting of metalloid elements (Si, Ge, As, Sb, etc.), among others, Ce, Zr, A single oxide or composite oxide of at least one metal selected from the group consisting of Ti, Si, Mg, Fe, Mn, Ni, Zn and Cu is preferred, and ceria, zirconia, ceria-zirconia composite oxide (solid solution). More preferred is at least one selected from the group consisting of 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.

  The metal oxide used in the present invention 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, a metal oxide having an oxygen storage capacity (OSC) for storing and releasing oxygen is preferable, and ceria, ceria-zirconia. Particularly preferred is at least one selected from the group consisting of complex oxide, iron oxide, praseodymium oxide and the like.

  The alumina used in the present invention has at least one crystal phase selected from the group consisting of γ phase, δ phase, θ phase, and α phase, and makes contact between primary particles of the metal oxide. It becomes a diffusion barrier that inhibits and suppresses the growth of particles. It can be confirmed by XRD that the crystal phase of alumina satisfies the above conditions. The content of the crystal phase in the alumina used in the present invention is preferably 70% by mass or more, and particularly preferably 90% by mass or more.

  Such metal oxide fine particles used in the present invention must be composed 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 such primary particles exceeds 50 nm, it cannot be dispersed and mixed with alumina fine particles at the nano level, and as a result, a composite metal oxide porous body sufficiently excellent in high temperature durability cannot be obtained.

  The metal oxide fine particles have an average particle diameter of 1 to 50 nm (more preferably 1 to 30 nm) and 80% by mass or more of particles having a diameter of 75 nm or less (more preferably 80% by mass or more of particles having a diameter of 50 nm. Or less). When the metal oxide fine particles do not satisfy these conditions, the high temperature durability of the obtained composite metal oxide porous body tends to be lowered.

  The alumina fine particles used in the present invention are also required to be composed of primary particles (crystallites) having a diameter of 50 nm or less (more preferably 20 nm or less, particularly preferably 2 to 10 nm). When the diameter of such primary particles exceeds 50 nm, it cannot be dispersed and mixed with the metal oxide fine particles at the nano level, and as a result, a composite metal oxide porous body sufficiently excellent in high temperature durability cannot be obtained. .

  The alumina fine particles have an average particle diameter of 1 to 130 nm (more preferably 1 to 50 nm) and 80% by mass or more of particles having a diameter of 160 nm or less (more preferably 80% by mass or more of particles having a diameter of 75 nm or less). It is preferable that When the alumina fine particles do not satisfy these conditions, the high temperature durability of the obtained composite metal oxide porous body tends to be lowered.

  The composite metal oxide porous body of the present invention is a porous body composed of the aforementioned metal oxide fine particles and alumina fine particles, both of which are aggregated in a nano-level uniform mixed state, and the nanopores described later have Is formed. And in the composite metal oxide porous body of this invention, it is required that the content rate of the said metal oxide is 45 mass% or more, and it is more preferable that it is 50-80 mass%. When the content of the metal oxide is less than 45% by mass, sufficient purification activity is not achieved in the obtained composite metal oxide porous body. On the other hand, when the content of the metal oxide exceeds 80% by mass, the high temperature durability of the obtained composite metal oxide porous body tends to be lowered.

Composite metal oxide porous body of the present invention has a specific surface area after the durability test 5 hours ^{40 m} 2 / g or more at 1000 ° C. (more preferably, the specific surface area after the durability test of 5 hours at 1100 ° C. ^{40 m} 2 / g or more). If the specific surface area is less than 40 m ² / g, sufficient purification performance cannot be achieved.

Thus, although the composite metal oxide porous body of the present invention contains 45% by mass or more of the metal oxide, the specific surface area is maintained at a high level even after the high temperature durability test. Thus, it has been epoch-making that the composite metal oxide porous body excellent in high-temperature durability can be obtained, and was never achieved by the conventional composite metal oxide porous body. The composite metal oxide porous body of the present invention preferably has a specific surface area of 70 m ² / g or more immediately after production (fresh state).

Furthermore, the composite metal oxide porous body of the present invention preferably satisfies at least one of the following conditions (I) to (III).
(I) The pore volume of pores having a center pore diameter of 5 to 30 nm (more preferably 10 to 30 nm) after a durability test at 1000 ° C. for 5 hours and a pore diameter of 0.1 μm or less after the durability test. Is 0.2 cc / g or more (more preferably 0.3 cc / g or more).

(II) The oxygen release rate after a durability test at 1000 ° C. for 5 hours is 1.5 μmol-O ₂ / g · sec or more (more preferably 2.0 μmol-O ₂ / g · sec or more).

(III) The total oxygen storage capacity after an endurance test at 1000 ° C. for 5 hours is 200 μmol-O ₂ / g or more (more preferably 250 μmol-O ₂ / g or more).

Thus, the composite metal oxide porous body of the present invention further achieves at least one of the above conditions (I) to (III) despite containing 20 to 55 mass% of the alumina. can do. The fact that a composite metal oxide porous body excellent in high-temperature durability has been obtained from a multifaceted viewpoint is further epoch-making. Not achieved. In the composite metal oxide porous body of the present invention, immediately after production (fresh state), the pore volume of pores having a center pore diameter of 5 to 25 nm and a pore diameter of 0.1 μm or less is 0.00. It is preferably 3 cc / g or more, an oxygen release rate of 20 μmol-O ₂ / g · sec or more, and a total oxygen storage capacity of 250 μmol-O ₂ / g or more.

  In the present invention, (i) durability test at 1000 ° C. for 5 hours, (ii) center pore diameter, (iii) pore volume, (iv) oxygen release rate, (v) total oxygen storage capacity, (vi ) The specific surface area is measured by the following method.

(i) Endurance test for 5 hours at 1000 ° C. In an atmosphere in which rich gas and lean gas having the composition shown in Table 1 are alternately flowed at intervals of 5 minutes so that the total flow rate is 330 ml / min, the sample (diameter 0.5 (About 1 mm pellet catalyst) is held at 1000 ° C. for 5 hours (high temperature durability test).

(ii) Central pore diameter and (iii) Pore volume The central pore diameter is a value obtained by differentiating the pore volume (V) by the pore diameter (D) (dV / dD). It is a pore diameter in the maximum peak of the curve (pore diameter distribution curve) plotted against. The central pore diameter and pore volume can be determined by a mercury intrusion method using a mercury porosimeter.

(iv) Oxygen release rate (OSC initial rate)
The oxygen release rate was measured under a transient atmosphere in which CO and O ₂ were alternately injected using a flow reactor described in T. Tanabe, et al., Stud. Sci. Catal., 138, 135 (2001). It is determined by measuring the amount of CO ₂ produced at. That is, for the measurement, a fixed bed flow type reaction apparatus usually used for catalytic reaction is used. This apparatus has an injector attached in the vicinity of the gas mixing portion, and has a structure capable of alternately supplying CO and O ₂ to the catalyst. By using this reaction apparatus and alternately supplying CO and O ₂ into the N ₂ carrier, a predetermined concentration of CO / N ₂ and O ₂ / N ₂ are alternately supplied to the sample. In this reaction, CO or O ₂ is not supplied to the sample at the same time, and CO is oxidized only by oxygen supplied from the sample. At this time, the amount of oxygen released from the sample is quantified by integrating the amount of CO ₂ produced by the reaction in the sample, and the saturated OSC of the sample can be calculated from the total integrated value at the measurement temperature. In addition, in order to obtain the OSC speed in the time domain of 1 Hz unit, the gas is switched from O ₂ to CO, and the slope of the time when CO ₂ starts to be generated (near 0 sec) is obtained. This inclination corresponds to the oxygen release amount per unit time immediately after the start of the reaction, that is, the oxygen release rate (OSC initial rate).

<Measurement conditions>
Injection gas: CO (100%), O ₂ (50%) / N2
Injection time: CO (180 sec), O ₂ (180 sec)
Carrier gas: N ₂
Gas concentration (when passing through the catalyst): CO (2%) / N ₂ , O ₂ (1%) / N ₂
Flow rate: 5L / min
Catalyst: 1g
Pretreatment conditions: 500 ° C., 18 min
Reaction temperature: 300 ° C
_{Analyzer: CO, CO 2 -NDIR, O} 2 - magnetic wind method.

(v) Total oxygen storage capacity (Total OSC)
Samples 15mg were weighed, and _{N 2} gas containing _{H 2} 20% while flowing _{O 2} alternating with _{N 2} gas containing 50%, repeated oxidation-reduction process of each sample at 500 ° C., a weight change caused The total oxygen storage capacity is determined by measurement using thermogravimetric analysis.

(vi) Specific surface area The specific surface area can be calculated as a BET specific surface area from the adsorption isotherm using the BET isotherm adsorption equation.

  Moreover, it is preferable that the composite metal oxide porous body of the present invention further includes a noble metal (noble metal fine particles).

  Such noble metal is not particularly limited, and includes at least one kind of noble metal selected from the group consisting of Pt, Pd, Rh, Ru, Au, Ag, Os, and Ir. Among them, Pt, Rh, Pd, Ir is preferable, and Pt is particularly preferable. The amount of the noble metal 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 composite metal oxide serving as a support. 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 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.

  In addition, in the conventional composite metal oxide porous body, noble metal had to be supported on the entire composite metal oxide constituting it, but in the present invention, either the metal oxide fine particles or the alumina fine particles are used. It becomes possible to carry a noble metal only on one side. Therefore, in the composite metal oxide porous body of the present invention, it is preferable that the noble metal is supported only on the most suitable carrier for supporting the noble metal, and the composite metal oxide porous body obtained by doing so is preferable. There is a tendency that the catalytic activity and the high-temperature durability of the catalyst are further improved. For example, when a ceria-zirconia composite oxide is used as the metal oxide, since the catalytic activity tends to be improved when the noble metal is on the surface of the ceria-zirconia composite oxide, 90% by mass of the noble metal The above is preferably supported on a ceria-zirconia composite oxide.

  The shape of the composite metal oxide porous body of the present invention described above 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 of 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 of 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 of 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-type or continuous. The harmful components can be purified by contact with each other. Examples of harmful components to be treated include NO _x , CO, HC, SO _x in exhaust gas.

  The method for obtaining the composite metal oxide porous body of the present invention is not particularly limited, but from the viewpoint that the metal oxide fine particles and the alumina fine particles can be more reliably dispersed and mixed at the nano level, the following. The method described in detail below is particularly preferred.

A method for producing a composite metal oxide porous body suitable for the present invention includes:
A metal oxide powder comprising primary particles having a diameter of 50 nm or less, and an alumina comprising primary particles having a diameter of 50 nm or less and having at least one crystal phase selected from the group consisting of γ phase, δ phase, θ phase and α phase Dispersion and mixing in a dispersion medium using microbeads having a diameter of 150 μm or less to obtain a uniform dispersion of metal oxide fine particles and alumina fine particles,
A drying step of drying the uniform dispersion to obtain a composite metal oxide porous body;
It is a method including.

  In addition, the manufacturing method of such a metal oxide powder and alumina powder is not particularly limited, for example, by a so-called precipitation method using a solution of a metal salt as a raw material, or a method of firing a precipitate obtained thereby, It can be obtained as appropriate. Further, the alumina powder having at least one crystal phase selected from the group consisting of γ phase, δ phase, θ phase, and α phase is, for example, 800 ° C. in the atmosphere with respect to amorphous alumina powder. It can obtain by performing the heat processing for 5 hours or more by the above.

  The average particle diameter of the metal oxide powder used in the present invention is not particularly limited, but is preferably 200 nm or less and more preferably 100 nm or less from the viewpoint that nano-sized fine particles can be efficiently obtained. preferable. The average particle size of the alumina powder used in the present invention is not particularly limited, but is preferably 200 nm or less, more preferably 100 nm or less from the viewpoint that nano-sized fine particles can be obtained efficiently. preferable. Furthermore, it is preferable that there is no great difference in the particle size between the metal oxide powder before the treatment and the alumina powder, and one average particle size is preferably about 1 to 5 times the other average particle size.

  The microbeads used in the dispersion and mixing step need 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 metal oxide powder and alumina 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 is not particularly limited, and examples thereof include zirconia and glass. The material of such microbeads is preferably selected as appropriate according to the metal oxide or alumina used.

  The dispersion medium used in the dispersion and mixing step is not particularly limited as long as it is a liquid that can disperse the obtained metal oxide fine particles and alumina fine particles, but water or the like is preferably 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 mixing step is to mix a metal oxide powder and an alumina powder together with microbeads in the above dispersion medium to obtain a uniform dispersion of metal oxide fine particles and alumina fine particles. Although it is not particularly limited as long as it can be used, for example, if “Ultra Apex Mill” manufactured by Kotobuki Industries Co., Ltd. is used, the fine particles and the microbeads can be efficiently separated by centrifugal force.

  In a method suitable for the present invention, the above-mentioned metal oxide powder and alumina powder are dispersed and mixed in a dispersion medium using the above microbeads, and the metal oxide fine particles and alumina fine particles are in a nano-level uniform mixed state. To obtain a uniform dispersion (dispersion mixing step). 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 such a 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 metal oxide to be used and the zeta potential of alumina 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 the ceria-zirconia composite oxide is used as the first metal oxide, the pH of the dispersion medium in the dispersion mixing step Is preferably 6-9.

  Furthermore, the mixing ratio (mass ratio) of the metal oxide and alumina mixed in the dispersion mixing step is such that the content of the metal oxide in the obtained composite metal oxide porous body is 45% by mass or more. It is necessary to mix metal oxide and alumina, and the value of (mass of metal oxide) :( mass of alumina) is preferably 45:55 to 80:20.

  In a method suitable for the present invention, following the above-described dispersion mixing step, a uniform dispersion of metal oxide fine particles and alumina fine particles obtained in the same 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 such a drying process, it is preferable to heat-dry after adding and mixing a surfactant to the uniform dispersion as described in 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 200 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 the method suitable for this invention, the baking process may be included after said drying process, In this baking process, the composite metal oxide porous body is 1-10 at the temperature of about 400-1000 degreeC. It is preferable to hold for about an hour. 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.

  Further, in a method suitable for the present invention, a pre-supporting step of supporting a noble metal (noble metal fine particles) on the surface of the metal oxide powder and / or the alumina powder, or surfaces of the metal oxide fine particles and the alumina fine particles. It is preferable that a post-supporting step for supporting a precious metal (noble metal fine particles) is further included in the base plate, and a pre-supporting step is more preferable. The specific method for supporting the noble metal in this way is not particularly limited. For example, a method in which powder or fine particles serving as a carrier is brought into contact with a solution of the noble metal salt, and further reduction treatment and / or firing treatment is performed as necessary. 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.

  In addition, when it is preferable to carry | support a noble metal on the said metal oxide, it is preferable that this carrying | support process exists before a dispersion | distribution mixing process (pre-carrying process). By doing so, it becomes possible to support the noble metal mainly on the 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. On the other hand, a post-supporting step may be used as long as the precious metal can be supported in a highly dispersed state.

  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, an amorphous alumina powder having an average particle diameter of 110 nm and an aggregate of primary particles having a diameter of about 10 nm was heat-treated at 1000 ° C. for 5 hours in the air. The specific surface area of the alumina powder after the heat treatment was 120 m ² / g, and when the crystal phase was confirmed by XRD, the crystal phases of γ phase, α phase and θ phase were mixed.

Next, this alumina powder and a cerium-zirconium composite oxide (CZ) powder (Ce: Zr = 1: 1 (molar ratio)) that is an aggregate of primary particles having a diameter of about 8 nm and an average particle diameter of 100 nm. Were dispersed and mixed for 120 minutes using a microbead made of zirconia having a diameter of 50 μm in an aqueous solution of pH 7 in which both were mixed at a mass ratio of 5: 5 (dispersion mixing step). Further, while stirring the obtained uniform dispersion 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 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 CZ fine particles and alumina fine particles. A composite oxide porous body (ACZ powder, average particle size: 120 nm) was obtained.

  Next, Pt is supported on the obtained ACZ powder using a nitric acid solution of Pt nitrate (Pt concentration: 4.5 wt%) as follows, and a composite oxide porous body (Pt / ACZ) supporting Pt is supported. Powder). That is, the Pt nitric acid solution was impregnated and supported on the ACZ powder and baked 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 ACZ powder.

Further, the obtained Pt / ACZ powder was compacted with 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 average particle size of the CZ fine particles obtained in the dispersion mixing step is 18 nm and 80% by mass or more of the particles have a diameter of 24 nm or less (D80 = 24 nm), and the average particle size of the alumina fine particles is 30 nm and 80 nm. More than mass% of particles had a diameter of 44 nm or less (D80 = 44 nm). The crystal phase of alumina contained in the obtained composite oxide porous body was a mixture of crystal phases of γ phase, α phase, and θ phase. Furthermore, the specific surface area, central pore diameter, and pore volume of the obtained composite oxide porous body were as shown in Table 3, respectively.

(Example 2)
A catalyst was obtained in the same manner as in Example 1 except that the mixing ratio of the alumina powder and the CZ powder was 4: 6 by mass ratio. The average particle diameters of CZ fine particles and alumina fine particles in the obtained catalyst are as shown in Table 2, and the specific surface area, central pore diameter, and pore volume of the obtained catalyst are as shown in Table 3, respectively. there were.

(Example 3)
The catalyst was obtained in the same manner as in Example 1 except that Pt was not supported on ACZ powder, and Pt was supported on CZ powder in advance as follows. That is, a Pt nitric acid solution (Pt concentration: 4.5 wt%) 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. The average particle diameters of CZ fine particles and alumina fine particles in the obtained catalyst are as shown in Table 2, and the specific surface area, central pore diameter, and pore volume of the obtained catalyst are as shown in Table 3, respectively. there were.

(Comparative Example 1)
A catalyst was obtained in the same manner as in Example 1 except that the amorphous alumina powder was used as it was without being subjected to a heat treatment. The average particle diameters of CZ fine particles and alumina fine particles in the obtained catalyst are as shown in Table 2, and the specific surface area, central pore diameter, and pore volume of the obtained catalyst are as shown in Table 3, respectively. there were.

(Comparative Example 2)
A catalyst was obtained in the same manner as in Example 1 except that the mixing ratio of the alumina powder and the CZ powder was 6: 4 by mass ratio. The average particle diameters of CZ fine particles and alumina fine particles in the obtained catalyst are as shown in Table 2, and the specific surface area, central pore diameter, and pore volume of the obtained catalyst are as shown in Table 3, respectively. there were.

(Comparative Example 3)
An aqueous solution in which 800 g of 25% aqueous ammonia solution was dissolved was stirred, and 2.8 mol of aluminum nitrate nonahydrate, 0.5 mol of cerium (III) nitrate, and 0.5 mol of zirconium nitrate dihydrate were mixed therein. The aqueous solution was quickly added and stirred for 10 minutes. The obtained precipitate was filtered, dried at 400 ° C. for 5 hours, and then fired at 700 ° C. for 5 hours to obtain a composite metal oxide porous body composed of CZ and alumina (ACZ powder, average CZ particle size: 9 nm). Obtained. And the catalyst was obtained like Example 1 except having used the ACZ powder obtained by doing in this way. The average particle diameters of CZ fine particles and alumina fine particles in the obtained catalyst are as shown in Table 2, and the specific surface area, central pore diameter, and pore volume of the obtained catalyst are as shown in Table 3, respectively. there were.

<High temperature durability test>
Each pellet-like catalyst obtained in the examples and the comparative examples in the atmosphere in which rich gas and lean gas having the composition shown in Table 1 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, central pore diameter, and pore volume after the durability test were measured. The obtained results are shown in Table 3.

<Catalyst performance evaluation test>
Using an atmospheric pressure fixed bed flow reactor, 1 g of each pellet-shaped catalyst (initial product) obtained in the examples and the comparative examples and 1 g of those subjected to a high temperature durability test (product after durability test) For each, 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 HC purification rate at each temperature was 100 to 500 ° C. Measurements were made to determine the respective 50% HC purification temperature. The obtained results are shown in Table 3.

<Oxygen release rate and oxygen storage capacity test>
For each of the pellet-like catalysts (initial products) obtained in the examples and comparative examples and those subjected to a high temperature durability test (products after the durability test), the oxygen release rate by the method described above. And the total oxygen storage capacity was measured. The obtained results are shown in Table 3.

  As is clear from the results shown in Table 3, the specific surface area and purification performance of the catalysts (Examples 1 to 3) composed of the composite metal oxide porous body of the present invention are maintained at a high level even after the high temperature durability test. It was excellent in high temperature durability. Especially, the catalyst (Example 3) which consists of a composite metal oxide porous body obtained by carrying | supporting a noble metal on the CZ powder in the pre-loading process was especially excellent in high temperature durability.

  As described above, according to the present invention, there is provided a composite metal oxide porous body that is very excellent in high-temperature durability and that maintains a high specific surface area and purification performance even after a high-temperature durability test. It becomes possible to do. Therefore, the present invention is very useful as a technique for providing an exhaust gas purifying catalyst and the like excellent in high temperature durability.

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

Claims (9)

Alumina fine particles comprising metal oxide fine particles composed of primary particles having a diameter of 50 nm or less, and primary particles composed of primary particles having a diameter of 50 nm or less and having at least one crystal phase selected from the group consisting of γ phase, δ phase, θ phase and α phase. And a metal oxide content of 45% by mass or more, and a specific surface area of 40 m ² / g or more after an endurance test at 1000 ° C. for 5 hours. Porous body.   2. The composite metal oxide porous body according to claim 1, wherein the metal oxide fine particles and the alumina fine particles are uniformly mixed at a nano level.   The composite metal oxide porous body according to claim 1 or 2, wherein the metal oxide has an oxygen storage capacity.   The pore volume of the pores having a center pore diameter of 5 to 30 nm after a durability test at 1000 ° C. for 5 hours and a pore diameter of 0.1 μm or less after the durability test is 0.2 cc / g or more. The composite metal oxide porous body according to any one of claims 1 to 3, wherein the porous body is a composite metal oxide. The mixed metal oxidation according to any one of claims 1 to 4, wherein an oxygen release rate after an endurance test at 1000 ° C for 5 hours is 1.5 µmol-O ₂ / g · sec or more. Porous material. The composite metal oxide porous body according to any one of claims 1 to 5, wherein a total oxygen storage capacity after an endurance test at 1000 ° C for 5 hours is 200 µmol-O ₂ / g or more. . A metal oxide powder comprising primary particles having a diameter of 50 nm or less, and an alumina comprising primary particles having a diameter of 50 nm or less and having at least one crystal phase selected from the group consisting of γ phase, δ phase, θ phase and α phase Dispersion and mixing in a dispersion medium using microbeads having a diameter of 150 μm or less to obtain a uniform dispersion of metal oxide fine particles and alumina fine particles,
A drying step of drying the uniform dispersion to obtain a composite metal oxide porous body;
The composite metal oxide porous body according to any one of claims 1 to 6, which is obtained by a method comprising:   The composite metal oxide porous body according to any one of claims 1 to 7, further comprising a noble metal supported on the metal oxide fine particles and / or the alumina fine particles.   The composite metal oxide porous body according to any one of claims 1 to 8, wherein the composite metal oxide porous body is an exhaust gas purifying catalyst.

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