KR20080094752A - Mixed particles and honeycomb structure - Google Patents

Abstract

A particulate mixture composed of noble metal particles, the first particles made of at least one metal oxide selected from the group consisting of Al2O3, SiO2, ZrO2 and TiO2, and the second particles made of a metal oxide having higher adsorptivity for the noble metal of the noble metal particles metal than that of the metal oxide of the first particles, wherein the majority of the noble metal particles are supported on the second particles with the minority thereof on the first particles.

Description

MIXED PARTICLES AND HONEYCOMB STRUCTURE}

The present invention relates to mixed particles and honeycomb structures.

As a catalyst carrier for purifying exhaust gas emitted from an internal combustion engine such as a bus or a truck or a construction machine, various exhaust gas purifiers using a honeycomb structure made of porous ceramics have been proposed. In such a catalyst carrier, noble metal catalysts such as platinum (Pt), rhodium (Rh) and palladium (Pd) are supported via a catalyst support layer made of an oxide such as γ-Al ₂ O ₃ (alumina). As a catalyst carrying layer, it was common to use γ-alumina to increase the specific surface area, but recently, in order to promote the purification of exhaust gas using the chemical properties of the carrier, ceria (CeO ₂ ) and zirconia (ZrO) are used. ₂ ) and using materials such as titania (TiO ₂ ) and γ-Al ₂ O ₃ (alumina) in combination are also proposed.

In particular, it is known that ceria can suppress sintering (particle growth) of platinum because of its large adsorptive interaction with platinum supported thereon. Here, if platinum is sintered while the catalyst carrier is used as the exhaust gas purification apparatus, the specific surface area of platinum, that is, the active point is reduced, and the exhaust gas purification capability of the catalyst is lowered. On the other hand, since ceria is relatively easy to sinter, the platinum carried in ceria may be sintered as ceria is sintered.

Patent Document 1 discloses a catalyst carrier in which ceria primary particles and alumina primary particles are mixed with each other, and an exhaust gas purification catalyst in which platinum is supported on the catalyst carrier. This catalyst carrier can be obtained by forming a mixed sol of ceria sol and alumina sol, agglomerating ceria sol and alumina sol from the mixed sol to form an aggregate, and drying and firing the obtained aggregate.

Patent Document 1: Japanese Unexamined Patent Publication No. 2006-43683

Problems to be Solved by the Invention

However, since the exhaust gas purification catalyst of Patent Document 1 mixes primary particles of ceria and primary particles of alumina and supports platinum in the obtained mixture, most of platinum is supported on alumina. For this reason, there exists a problem that the platinum supported by the primary particle of alumina is easy to sinter.

In view of the problems of the prior art, an object of the present invention is to provide a mixed particle and honeycomb structure which can suppress sintering of platinum.

Means to solve the problem

The invention according to claim 1 is characterized in that the noble metal particles made of a noble metal, the first particles made of one or more metal oxides selected from the group consisting of Al ₂ O ₃ , SiO ₂ , ZrO ₂ and TiO ₂ , and the first particles It is a mixed particle which consists of 2nd particle | grains which consist of metal oxides with the adsorptive interaction with the said noble metal larger than a metal oxide, It is characterized by that the said noble metal particle is carried by the said 2nd particle more than the said 1st particle.

Invention of Claim 2 is the mixed particle of Claim 1 WHEREIN: The said 1st particle | grains and the said 2nd particle | grains are each characterized by the secondary particle.

In the invention according to claim 3, in the mixed particles according to claim 2, the average particle diameter of the first particles is larger than the average particle diameter of the second particles, and the average particle diameter of the first particles is 0.5 to 2 µm, The average particle diameter of 2 particle | grains is characterized by being 0.1-1 micrometer.

In the invention according to claim 4, in the mixed particles according to claim 1, the first particles are primary particles, and the second particles are secondary particles.

Invention of Claim 5 is the mixed particle of Claim 4 WHEREIN: The average particle diameter of a said 2nd particle is 5-50 nm, It is characterized by the above-mentioned.

The invention according to claim 6 is the mixed particles according to any one of claims 1 to 5, wherein the first particles are made of Al ₂ O ₃ , and the second particles are made of CeO ₂ .

Invention of Claim 7 is the mixed particle in any one of Claims 1-6, The said noble metal particle consists of Pt, It is characterized by the above-mentioned.

In the invention according to claim 8, in the mixed particles according to any one of claims 1 to 7, the weight ratio of the second particles to the first particles is 0.05 to 3.0.

Invention of Claim 9 is an average particle diameter of 1-5 micrometers in the mixed particle in any one of Claims 1-8, It is characterized by the above-mentioned.

Invention of Claim 10 is a honeycomb structure in which the cell which has a hole is provided in multiple numbers by the longitudinal direction, and contains the mixed particle in any one of Claims 1-9, It is characterized by the above-mentioned.

In the invention according to claim 11, in the honeycomb structure according to claim 10, the mixed particles are supported on the partition wall with the holes of the adjacent cells interposed therebetween.

Effects of the Invention

According to this invention, the mixed particle and honeycomb structure which can suppress sintering of platinum can be provided.

It is a cross-sectional schematic diagram which shows an example of the mixed particle of this invention.

1B is an SEM photograph showing an example of the mixed particles of the present invention.

It is a cross-sectional schematic diagram which shows another example of the mixed particle of this invention.

2B is an SEM photograph showing another example of the mixed particles of the present invention.

3 is a perspective view showing an example of the honeycomb structured body of the present invention.

4A is a perspective view illustrating the honeycomb unit of FIG. 3.

4B is a cross-sectional view illustrating the honeycomb unit of FIG. 3.

Explanation of the sign

10, 20: mixed particles

11, 21: secondary particles of CeO ₂

12: secondary particles of Al ₂ O ₃

13, 23: Pt

22: primary particles composed of Al ₂ O ₃

30: honeycomb structure

31: honeycomb block

31a: Honeycomb Unit

31b: adhesive layer

32: coating layer

41: cell

41a: hole

42: outer wall

43: bulkhead

Implement the invention  Best form for

Next, the best mode for implementing this invention is demonstrated with drawing.

The mixed particles of the present invention are precious metal particles composed of precious metals, first particles composed of at least one metal oxide selected from the group consisting of Al ₂ O ₃ , SiO ₂ , ZrO _2, and Ti0 ₂ , and metal oxides of the first particles. It consists of the 2nd particle | grains which consist of a metal oxide with the interaction of the noble metal particle with a noble metal with larger adsorption | suction. At this time, more precious metal particles are supported on the second particles than the first particles. Moreover, as a noble metal of a noble metal particle | grain, platinum, palladium, rhodium, etc. are mentioned, for example, You may use together 2 or more types. Thereby, sintering of platinum can be suppressed.

In this invention, the adsorption interaction with a noble metal means the adsorption energy with a noble metal. In Table 1, adsorption energy of Pt and a metal oxide is shown as an example of simulation by a computer.

Further, the smaller the adsorption energy, that is, the larger the negative value of the adsorption energy, the larger the adsorption interaction.

An example of the mixed particle of this invention is shown to FIG. 1A and 1B. The mixed particles 10 have secondary particles 11 of CeO ₂ and secondary particles 12 of Al ₂ O ₃ , and Pt 13 is supported on the secondary particles 11 of CeO ₂ , Since the secondary particles 12 of Al ₂ O ₃ and the secondary particles 11 of CeO ₂ are dispersed and mixed, sintering of the secondary particles 11 of CeO ₂ can be suppressed. Also can be due to the interaction of the adsorption property of the secondary particles (11) and Pt (13) of the CeO ₂ size, it suppressed the sintering of Pt (13), which is supported on the secondary particle 11 in the CeO ₂ . At this time, the average particle diameter of the secondary particles 12 of Al ₂ O ₃ is larger than the average particle diameter of the secondary particles 11 of CeO ₂ . This makes it possible to effectively suppress the sintering of the secondary particles 11 of CeO _2. At this time, the secondary particles 11 of CeO ₂ preferably have an average particle diameter of 0.1 to 1 μm, and the secondary particles 12 of Al ₂ O ₃ preferably have an average particle diameter of 0.5 to 2 μm. .

In addition, in this invention, an average particle diameter is measured by observing using microscopes, such as a scanning electron microscope (SEM) and a transmission electron microscope (TEM).

2A and 2B show another example of the catalyst of the present invention. The catalyst 20 has secondary particles 21 of CeO ₂ and primary particles 22 of Al ₂ O ₃ , and Pt 23 is supported on secondary particles 21 of CeO ₂ . _Since the adsorptive interaction of the secondary particles 21 of 2 and Pt 23 is large, the sintering of the Pt 23 supported on the secondary particles 21 of CeO ₂ can be suppressed. In addition, since the secondary particles 21 of CeO ₂ and the primary particles 22 of Al ₂ O ₃ are dispersed and mixed, sintering of the secondary particles 21 of CeO ₂ can be suppressed. Secondary particles 11 at this time, CeO ₂ is preferably, an average particle diameter of 5 ~ 50 ㎚.

1B and 2B are SEM photographs and TEM photographs, respectively, and can define particles similarly by elemental analysis.

It is preferable that the mixed particle of this invention is 0.05-3.0 with a weight ratio of the 2nd particle with respect to a 1st particle.

Moreover, when the mixed particle of this invention is added and used for the raw material face mentioned later, it is preferable that average particle diameter is 1-5 micrometers.

The production method of the mixed particle of the invention is, for example, CeO ₂ with the step of carrying the Pt particles, and the step of dispersing in a dispersion medium, the CeO ₂ particles of Pt-supported, Pt-supported CeO ₂ particles are dispersed and a step of further disperse the Al ₂ O ₃ particles in a dispersion medium, Al ₂ O ₃ particles is a step of assembling by using the more dispersed the dispersion medium. Specifically, first, Pt is supported on the secondary particles of CeO ₂ (average particle diameter of 5 mu m) using a platinum dinitroamine solution, and then fixed by heating at about 600 ° C. under a reducing atmosphere. Next, if necessary, secondary particles of CeO ₂ supported with Pt are dispersed in a dispersion medium such as water to which a dispersant such as a surfactant is added. Further, secondary particles of Al ₂ O ₃ (average particle size 2 μm) are dispersed in the dispersion medium and mixed. Next, the granulated particles of the present invention can be obtained by granulation using the obtained dispersion.

In the honeycomb structured body of the present invention, a plurality of cells having holes are formed in parallel in the longitudinal direction, and the mixed particles of the present invention are contained, but the mixed particles may be supported on the partition wall with the holes of adjacent cells interposed therebetween. . Thereby, sintering of platinum can be suppressed.

3, an example of the honeycomb structural body of this invention is shown typically. 4A, an example of the honeycomb unit which is a basic unit of the honeycomb structural body of FIG. 3 is shown typically. 4B, the cross section in the A-A 'line | wire shown in FIG. 4A is typically shown.

As shown in FIG. 3, the honeycomb structure 30 is a columnar shape in which a quadrilateral honeycomb unit 31a is joined via an adhesive layer 31b and a part of the outer peripheral portion is cut. The coating layer 32 is formed in the outer peripheral part of the honeycomb block 31. In addition, although the shape of the honeycomb structure 30 and the honeycomb block 31 is cylindrical, if it is columnar, it will not specifically limit, Elliptical columnar shape, a columnar shape, etc. may be sufficient. Similarly, the shape of the honeycomb unit 31a is not particularly limited.

In the honeycomb unit 31a, as shown in FIG. 4A and FIG. 4B, the cell 41 which has the through-hole 41a is formed in parallel in the longitudinal direction in multiple numbers. At this time, the honeycomb unit 31a has the outer edge wall 42 at the outer edge part, and the through-hole 41a which the adjacent cell 41 has is separated by the partition 43. As shown in FIG. That is, the exhaust gas which flowed in from the one opening part of the through-hole 41a of the honeycomb unit 31a comes into contact with mixed particle, when passing through the through-hole 41a, and is therefore harmful in the exhaust gas. The components (eg CO, HC, NO _x, etc.) are purified. Moreover, the purified exhaust gas is discharged | emitted from the other opening part of the through hole 41a.

The honeycomb unit 31a contains the mixed particles of the present invention, and preferably further contains inorganic fibers and / or whiskers. Thereby, the intensity | strength of the honeycomb unit 31a can be improved.

Examples of the material of the inorganic fiber and / or whisker include alumina, silica, silicon carbide, silica, alumina, glass, potassium titanate, aluminum borate, and the like. Especially, aluminum borate whisker is preferable. In addition, in this specification, although an inorganic fiber and / or a whisker mean that an average aspect ratio (length / diameter) exceeds 5, it is preferable that average aspect ratio is 10-1000.

Content of the mixed particle in the honeycomb unit 31a is 30 weight% or more normally, 40 weight% or more is preferable, and 50 weight% or more is more preferable. On the other hand, content of the mixed particle in the honeycomb unit 31a is 97 weight% or less normally, 90 weight% or less is preferable, 80 weight% or less is more preferable, 75 weight% or less is especially preferable.

Content of the inorganic fiber and / or whisker in the honeycomb unit 31a is 3 weight% or more normally, 5 weight% or more is preferable, and 8 weight% or more is more preferable. On the other hand, content of the inorganic fiber and / or whisker in the honeycomb unit 31a is 70 weight% or less normally, 50 weight% or less is preferable, 40 weight% or less is more preferable, 30 weight% or less is especially desirable.

Moreover, it is preferable that the honeycomb unit 31a is manufactured using the raw material paste containing mixed particle, an inorganic fiber, and / or a whisker, and an inorganic binder. Thus, by using the raw material paste containing an inorganic binder, the honeycomb unit 31a of preferable strength can be obtained even if baking temperature is low.

As the inorganic binder, an inorganic sol, a clay binder, or the like can be used. As an inorganic sol, an alumina sol, a silica sol, titania sol, water glass, etc. are mentioned, for example. Moreover, as a clay type | system | group binder, double-chain structured clays, such as clay, kaolin, montmorillonite, sepiolite, and attapulgite, etc. are mentioned, for example. Among them, alumina sol, silica sol, titania sol, water glass, sepiolite and attapulgite are preferable. In addition, you may use together 2 or more types of inorganic binders.

The content of the inorganic binder in the raw material paste is usually 5% by weight or more, preferably 10% by weight or more, more preferably 15% by weight or more, based on the total weight of the mixed particles, the inorganic fibers and / or whiskers, and the inorganic binder. desirable. On the other hand, content of the inorganic binder in a raw material composition is 50 weight% or less normally with respect to the total weight of a mixed particle, an inorganic fiber, and / or a whisker, and an inorganic binder, 40 weight% or less is preferable, and 35 weight% or less More preferred. When content of an inorganic binder is less than 5 weight%, the intensity | strength of a honeycomb structure may fall, and when it exceeds 50 weight%, moldability may fall.

Although the thickness of the partition 43 of the honeycomb unit 31a is not particularly limited, the thickness of the honeycomb unit 31a or the partition 43 is preferably 0.1 mm or more, and in terms of gas purification performance or characteristics, It is preferable that it is 0.4 mm or less.

In the honeycomb structure according to the present invention, the honeycomb block may be constituted by one honeycomb unit. Moreover, the outer peripheral part of a honeycomb block does not need to be cut. In addition, the coating layer may just be formed as needed, for example, in the case of the honeycomb block in which the outer peripheral part is not cut, the coating layer does not need to be formed.

Next, the manufacturing method of the honeycomb structural body of this invention is demonstrated.

First, the honeycomb unit molded body can be obtained by molding such as extrusion molding using the raw material paste containing the mixed particles of the present invention, inorganic fibers and / or whiskers, and an inorganic binder.

In addition to these, the raw material paste may contain an organic binder, a dispersion medium, a molding aid, and the like in accordance with moldability. Although it does not specifically limit as an organic binder, For example, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, etc. are mentioned, You may use together 2 or more types. It is preferable that content of the organic binder in a raw material paste is 1-10 weight% with respect to the total amount of a mixed particle, an inorganic fiber and / or whisker, and an inorganic binder. Although it does not specifically limit as a dispersion medium, For example, water, organic solvents, such as benzene, alcohol (methanol etc.) etc. are mentioned. Although it does not specifically limit as a shaping | molding adjuvant, For example, ethylene glycol, dextrin, fatty acid, fatty acid soap, polyalcohol, etc. are mentioned.

Although a raw material paste is not specifically limited, Mixing and kneading | mixing are preferable, For example, you may mix using a mixer, an attritor, etc., and you may fully knead with a kneader.

Next, it is preferable to dry the honeycomb unit molded body. Although the dryer used for drying is not specifically limited, A microwave dryer, a hot air dryer, an oilfield dryer, a vacuum dryer, a vacuum dryer, a freeze dryer, etc. are mentioned.

Moreover, it is preferable to degrease the dried honeycomb unit molded object. The degreasing conditions are not particularly limited and can be appropriately selected depending on the type and amount of the organic substance contained in the honeycomb unit molded body, but generally 2 hours is preferable at 400 ° C.

It is also preferable to fire the degreased honeycomb unit molded product. Although baking conditions are not specifically limited, 600-1200 degreeC is preferable and 600-1000 degreeC is more preferable.

As described above, the honeycomb unit 31a can be obtained.

Next, after apply | coating an adhesive layer paste to the outer peripheral part of the honeycomb unit 31a with uniform thickness, it arrange | positions with another honeycomb unit 31a via an adhesive layer paste. By repeating this process, a honeycomb unit assembly can be obtained. In addition, the number of the honeycomb units 31a to be used can be suitably selected according to the size of the honeycomb structure 30 to be manufactured.

Although it does not specifically limit as an adhesive layer paste, For example, the mixture of an inorganic binder and ceramic particle, the mixture of an inorganic binder and an inorganic fiber, the mixture of an inorganic binder and ceramic particle, an inorganic fiber, etc. can be used. In addition, the adhesive layer paste may contain an organic binder. Although it does not specifically limit as an organic binder, For example, polyvinyl alcohol, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, etc. are mentioned, You may use together 2 or more types.

Next, the honeycomb unit assembly is heated, the adhesive layer paste is dried and solidified to form an adhesive layer 31b, and the honeycomb units 31a are bonded to each other. It is preferable that the thickness of the contact bonding layer 31b is 0.3-2 mm. When the thickness of the adhesive layer 31b is less than 0.3 mm, sufficient bonding strength may not be obtained, and when it exceeds 2 mm, the function of purifying exhaust gas may fall. Moreover, when the thickness of the contact bonding layer 31b exceeds 2 mm, a pressure loss may become large.

Next, a circumferential honeycomb block 31 can be obtained by cutting the honeycomb unit assembly into a columnar shape, for example, using a diamond cutter or the like. In addition, you may manufacture the circumferential honeycomb block 31 by joining the honeycomb unit 31a shape | molded in the shape of a fan-shaped cross section, and the shape of a square in cross section. Thereby, the process of cutting can be skipped.

Next, the honeycomb structured body 30 can be obtained by apply | coating a coating layer paste to the outer peripheral part of the honeycomb block 31, drying and solidifying, and forming the coating layer 32. FIG. The material constituting the coating layer paste is not particularly limited, but may be the same as or different from the material constituting the adhesive layer paste. In addition, when a coating layer paste and an adhesive layer paste are comprised from the same material, the structural ratio of material may be the same and may differ. In addition, the thickness of the coating layer 32 is not specifically limited.

Moreover, it is preferable to pre-fire the honeycomb block 31 in which the honeycomb block 31 or the coating layer 32 was formed. Accordingly, it can be degreased when the adhesive layer paste or the coating layer paste contains an organic binder. Although preliminary baking conditions can be suitably selected according to the kind and content of an organic binder, 2 hours are preferable at 700 degreeC in general.

In addition, the honeycomb structure 30 may be supported with a catalyst. Although it does not specifically limit as a catalyst, Alkali metal, alkaline-earth metal, oxide, etc. can be used. The alkali metal is potassium and the like, there may be mentioned, such as sodium, the alkaline earth metal may include barium, oxides include (such as _{La 0 .75 K 0 .25 MnO 3} ) perovskite. In addition, you may use together 2 or more types of catalysts.

In the present invention, instead of adding the mixed particles to the raw material paste, the mixed particles may be supported on a partition wall having a hole between the honeycomb structures.

Although the use of the honeycomb structure 30 is not specifically limited, For example, it can be used as an exhaust gas processing apparatus of a vehicle. In the exhaust gas treating apparatus, the honeycomb structured body is housed in a metal container in a state in which a sealing material is disposed on the outer peripheral portion of the honeycomb structured body of the present invention.

EXAMPLES 1-4

After adding 500 parts by weight of water to 100 parts by weight of CeO ₂ particles (secondary particles; average particle diameter of 0.3 μm), a predetermined amount (see Table 2) of Pt was added to the CeO ₂ particles by using a platinum dinitrodiamine solution. It was supported. Next, it dried at 100 ℃, by fixing in a reducing atmosphere at 600 ℃, to obtain a Pt-CeO ₂ particles. Further, a predetermined amount (see Table 2) of Pt-CeO ₂ particles and a predetermined amount (see Table 2) of γ-Al ₂ O ₃ particles (secondary particles; average particle diameter of 0.7 µm) were sufficiently mixed to have an average particle diameter of 2 µm. Mixed particles were obtained. The specific surface area after carrying out the endurance test of the obtained mixed particle at 850 degreeC for 5 hours is shown in Table 2.

Comparative Example 1

78.64 parts by weight of CeO ₂ particles (secondary particles; average particle diameter: 0.3 µm) and γ-Al ₂ O ₃ particles (secondary particles: average particle diameter: 0.7 µm) corresponding to 81 parts by weight of the Pt-CeO ₂ particles added in Example 1 ) 216 parts by weight was mixed to obtain a mixed powder. Next, based on 100 parts by weight of the mixed powder, followed by the addition of water to 500 parts by weight, using a platinum dinitrodiammine solution and carrying a 3% by weight Pt on CeO ₂ particles in the mixed powder. Furthermore, it dried at 100 degreeC, and fixed in 600 degreeC reducing atmosphere, and obtained the mixed particle whose average particle diameter is 2 micrometers. The specific surface area after carrying out the endurance test of the obtained mixed particle at 850 degreeC for 5 hours is shown in Table 2.

In addition, the specific surface area of Pt is, taking into account the oxygen absorption-storage capability (OSC performance) of CeO _2, was measured by the BET-CO adsorption method. In Table 2, compared with the mixed particle of the comparative example 1, the mixed particle of Examples 1-4 has a large specific surface area of Pt after an endurance test, and it turns out that the sintering of Pt is suppressed.

[Examples 5 to 8]

After adding 500 parts by weight of water to 100 parts by weight of CeO ₂ particles (secondary particles; average particle diameter of 5 μm), a predetermined amount (see Table 3) of Pt was added to the CeO ₂ particles by using a platinum dinitrodiamine solution. It was supported. Next, it dried at 100 ℃, by fixing in a reducing atmosphere at 600 ℃, to obtain a Pt-CeO ₂ particles. In addition, a predetermined amount (see Table 3) of Pt-CeO ₂ particles was added to a sufficient amount of water with ammonium polycarboxylic acid (suitable amount) of the dispersant, adjusted to pH 9 with ammonia, and dispersed. Next, a predetermined amount (see Table 3) of γ-Al ₂ O ₃ particles (secondary particles; average particle diameter of 2 μm) was added to the dispersion of Pt-CeO ₂ particles to form primary particles of γ-Al ₂ O ₃ . Disperse until obtained. Moreover, the dispersion liquid obtained using the spray dryer was granulated and the mixed particle whose average particle diameter is 2 micrometers was obtained. Table 3 shows the specific surface areas after the obtained mixed particles were subjected to a durability test at 850 ° C. for 5 hours.

Comparative Example 2

78.64 parts by weight of CeO ₂ particles (secondary particles; average particle diameter: 5 μm) corresponding to 81 parts by weight of the Pt-CeO ₂ particles added in Example 5, in a sufficient amount of water together with ammonium polycarboxylic acid (the appropriate amount) of the dispersant Was added, and the mixture was adjusted to pH 9 with ammonia and dispersed. Next, 216 parts by weight of γ-Al ₂ O ₃ particles (secondary particles; average particle diameter of 2 μm) were added to the dispersion of CeO ₂ particles and dispersed until the primary particles of γ-Al ₂ O ₃ were obtained. Moreover, the dispersion liquid obtained using the spray dryer was granulated and the mixed powder was obtained. Next, based on 100 parts by weight of the mixed powder, followed by the addition of water to 500 parts by weight, using a platinum dinitrodiammine solution was supported with Pt of 3% by weight of the CeO ₂ particles in the mixed powder. Furthermore, it dried at 100 degreeC, and fixed in 600 degreeC reducing atmosphere, and obtained the mixed particle whose average particle diameter is 2 micrometers. Table 3 shows the specific surface areas after the obtained mixed particles were subjected to a durability test at 850 ° C. for 5 hours.

Comparative Example 3

To 100 parts by weight of γ-Al ₂ O ₃ particles (secondary particles; average particle diameter of 2 μm), 500 parts by weight of water was added, and then, 3 parts of γ-Al ₂ O ₃ particles using a platinum dinitrodiamine solution. % Pt by γ-Al ₂ O ₃ It was supported on the particles. Furthermore, it dried at 100 degreeC and fixed in 600 degreeC reducing atmosphere, and obtained the particle whose average particle diameter is 2 micrometers. Table 3 shows the specific surface areas after the obtained particles were subjected to a durability test at 850 ° C. for 5 hours.

In Table 3, compared with the mixed particle of the comparative example 2, and the particle | grain of the comparative example 3, the mixed particle of Examples 5-8 shows that the specific surface area of Pt after an endurance test is large, and that sintering of Pt is suppressed. have.

Claims (11)

Noble metal particles made of noble metals, first particles made of one or more metal oxides selected from the group consisting of Al ₂ O ₃ , SiO ₂ , ZrO _2, and TiO ₂ , and the metal oxides of the first particles A mixed particle comprising a second particle made of a metal oxide having a large adsorptive interaction, wherein the noble metal particle is supported on the second particle more than the first particle. The mixed particle according to claim 1, wherein the first particle and the second particle are each secondary particles. The method of claim 2, wherein the average particle diameter of the first particles is larger than the average particle diameter of the second particles, the average particle diameter of the first particles is 0.5 to 2 ㎛, the average particle diameter of the second particles is 0.1 to 1 ㎛ Mixed particles, characterized in that. The mixed particle according to claim 1, wherein the first particle is a primary particle, and the second particle is a secondary particle. The mixed particle according to claim 4, wherein the average particle diameter of the second particles is 5 to 50 nm. The mixed particle according to any one of claims 1 to 5, wherein the first particle is made of Al ₂ O ₃ , and the second particle is made of CeO ₂ . The mixed particle according to any one of claims 1 to 6, wherein the noble metal particle is made of Pt. The mixed particle according to any one of claims 1 to 7, wherein a weight ratio of the second particles to the first particles is 0.05 to 3.0. The mixed particle according to any one of claims 1 to 8, wherein the average particle diameter is 1 to 5 µm. A honeycomb structured body in which a plurality of cells having holes are provided in the longitudinal direction, wherein the honeycomb structured body contains the mixed particles according to any one of claims 1 to 9. The honeycomb structure according to claim 10, wherein the mixed particles are supported on the partition wall with the holes of the adjacent cells interposed therebetween.

Images