JP4265561B2 - Automobile exhaust gas purification catalyst body - Google Patents

Description

The present invention relates to an automobile exhaust gas purification catalyst body in which oxide particles such as alumina carrying a catalyst component are supported on a porous substrate such as cordierite.

  Conventionally, noble metals such as Pt, Pd, and Rh are generally used as catalyst components for purifying harmful components such as HC, CO, and NOx contained in automobile exhaust gas and the like.

  In addition, as such a catalyst component, one having a primary particle size on the order of nanometers or two or more kinds having higher activity and capable of exhibiting activity against a plurality of types of substances. Catalyst particles comprising a base particle which is a solid solution fine particle and a surface coating layer made of one or more kinds of noble metals or noble metal oxides covering at least a part of the surface of the base particles have been proposed (for example, Patent Documents). 1).

  Conventionally, in such a catalyst component, by using a porous base material made of cordierite, the catalyst component is supported on the surface of the porous base material in a highly dispersed manner.

  However, the surface area of cordierite is not sufficient to support the catalyst component in a highly dispersed manner, and the bonding force between cordierite and the catalyst component is weak, so that a sufficient loading amount cannot be ensured.

Therefore, conventionally, before carrying the catalyst component on the basis of particulate oxide particles having a high specific surface area represented by γ-alumina (Al ₂ O ₃ ), the oxide particles are corded. It was coated on the surface of the light to a thickness of about several tens of μm, and then the catalyst component was further supported on the coated oxide particles.
Japanese Patent Laid-Open No. 2003-80077

  However, in the conventional configuration in which the oxide particles made of γ-alumina are supported on the porous base material made of cordierite and the catalyst component is supported on the oxide particles, the γ-alumina that is the oxide particles Since the thickness is several tens of μm on cordierite, there are some problems as described below.

  First, in the conventional catalyst body, the catalyst component is present on the surface and inside of the γ-alumina, but the catalyst component existing inside the thick γ-alumina does not function sufficiently due to the diffusibility of the reaction gas. There's a problem.

  However, reducing the thickness of the γ-alumina coated on the cordierite monolith substrate means that when the catalyst component is supported on the γ-alumina, the catalyst component passes through the gaps of the γ-alumina particles, This was not possible because the cordierite monolith substrate reached the inside of the pores from the lower cordierite surface.

  In addition, γ-alumina has a high specific surface area, but itself has low heat resistance, so that the shape of γ-alumina changes due to long-term use, so that the catalyst component is buried inside γ-alumina. The catalyst function was to be deactivated.

  For this reason, in order to achieve the necessary exhaust gas purification performance, that is, sufficient catalyst function, it is necessary to carry an excess catalyst component from the initial stage, and the amount of catalyst component used is large and the utilization efficiency is low. There was a problem that.

  Furthermore, the γ-alumina layer coated on the cordierite monolith substrate is conventionally about several tens of μm thick as described above, and the area through which the reaction gas passes is small. It became a big ventilation resistance.

  Therefore, when a conventional catalyst body is used as a catalyst body for exhaust gas purification of an automobile, the engine output is reduced or the temperature rise is slowed by increasing the heat capacity. From the start of the engine to the activation of the catalyst body There was a problem that it took a long time.

  Furthermore, since the exhaust gas purifying catalyst body is used at a high temperature of about 1000 ° C. for a long time, the problem that the catalyst component described above is buried inside the γ-alumina with the use at this high temperature. In addition, there is a problem that sintering due to heat occurs.

  Then, due to this sintering, the catalyst components move or the catalyst components are combined with each other, the reaction-active specific surface area is reduced, and the purification performance is deteriorated. For this reason as well, it is necessary to carry, for example, about 70% more catalyst components than the amount of catalyst required in the initial stage, and there are problems of environmental burden and high cost.

The present invention has been made in view of the above problems, and in a catalyst body for exhaust gas purification of an automobile in which oxide particles carrying a catalyst are carried on a porous substrate, the reaction utilization efficiency of the catalyst component is improved. The purpose is to increase and reduce the amount of catalyst components used.

In order to achieve the above object, according to the first aspect of the present invention, a porous substrate (10) and a first coat layer comprising oxide particles sequentially laminated on the surface of the porous substrate (10). (21), the second coat layer (22), and a catalyst component (30) provided on the second coat layer (22), and the oxidation constituting the first coat layer (21) The particle size of the product particles is ½ to ¼ times the average pore size of the porous substrate (10), and the particle size of the oxide particles constituting the second coat layer (22) is There is provided an automobile exhaust gas purification catalyst body characterized in that the average pore diameter of the porous substrate (10) is 1/25 to 1/65 times .

  Here, in the catalyst body of the present invention, the particle diameter of the oxide particles is a commonly used average particle diameter, and even the primary particle diameter is the diameter of the secondary particles in which the primary particles are aggregated. Or either.

  According to this, the second coat layer (22) is made of oxide particles having a smaller particle diameter than the first coat layer (21). Therefore, the second coat layer (22) is a dense layer that does not allow the catalyst component (30) to pass therethrough and has a large surface area for supporting the catalyst component (30) because the particle size is small. Can do.

  Further, the first coat layer (21) having a large particle size is interposed between the second coat layer (22) having a small particle size and the porous substrate (10), whereby the first coat layer (21) is interposed. Since the layer (21) serves as a base and covers the pores of the porous base material (10), the second coat layer (22) thereon is used as the pores of the porous base material (10). You can keep out.

  Therefore, the second coat layer (22) supported on the porous base material (10) hardly penetrates into the pores of the porous base material (10), and the first coat It arrange | positions in the oxide particle of a layer (21), and its clearance gap. As a result, the second coat layer (22) is disposed on the surface of the porous substrate (10), and the thickness of the second coat layer (22) is made as thin as possible within the necessary range. be able to.

  In addition, since the first coat layer (21) can also have a large particle size of the oxide particles constituting the first coat layer (21), the pores of the porous base material (10) can be used as a base for the second coat layer (22). In order to occlude the film, it is not necessary to be so thick.

  Further, the oxide particles of the first coat layer (21) almost enter the pores only by covering the pores of the porous substrate (10) on the surface of the porous substrate (10). Therefore, voids due to the pores remain in the porous base material (10), and the function of relaxing expansion / contraction due to heat of the porous base material (10), that is, thermal shock resistance, is ensured.

  Thus, in the present invention, the catalyst component (30) is supported on the first and second coat layers (21, 22) formed thin on the surface of the porous substrate (10). Therefore, as a result, a configuration in which the catalyst component (30) is thinly arranged on the surface of the porous substrate (10) can be realized.

  Thus, according to the catalyst body of the present invention, the thickness of the oxide particle layer on the porous substrate (10) can be made as thin as possible compared to the conventional one, so that the above-mentioned ventilation resistance can be reduced, The catalyst component (30) hardly enters the pores of the porous substrate (10) under the oxide particles and is efficiently disposed on the surface of the porous substrate (10).

  Therefore, according to the present invention, in the catalyst body formed by supporting the oxide particles supporting the catalyst component (30) on the porous substrate (10), the reaction utilization efficiency of the catalyst component (30) is increased, The usage-amount of a catalyst component (30) can be reduced.

Further, in the invention according to claim 2, in the catalyst body according to claim 1, porous substrate (10) is cordierite, the grains of the oxide particles constituting the first coating layer (21) The diameter is 600 nm to 1000 nm, and the particle diameter of the oxide particles constituting the second coat layer (22) is 30 nm to 80 nm.

  Thus, when the porous substrate (10) is cordierite, the particle diameter of the oxide particles constituting the first coat layer (21) is 600 nm to 1000 nm, and the second coat layer. The particle size of the oxide particles constituting (22) is preferably 30 nm to 80 nm.

  In the case where the porous base material (10) is cordierite, the average pore diameter of the cordierite pore diameter is 1 μm to 2 μm according to the results of the investigation conducted by the present inventor. It was confirmed that it was preferable.

Further, in the invention according to claim 3, in the catalyst body according to claims 1 to 2, oxide particles constituting the first and second coating layer (21, 22) _is, CeO 2, ZrO ₂ , Al ₂ O ₃ , TiO ₂ , SiO ₂ , MgO, Y ₂ O ₃ , Ni ₂ O ₃ and any one or more compounds selected from these compositions .

According to this, it is possible to provide oxide particles that are carriers of the catalyst component that have better heat resistance than conventional γ-alumina. That is, among these, θ-alumina, titania (TiO ₂ ), zirconia (ZrO ₂ ), etc., which are more excellent in heat resistance, can be used as oxide particles, thereby reducing the shape change of the oxide particles themselves. It is possible to prevent the catalyst component from being buried.

More specifically, as in the invention described in claim 4 , in the catalyst body described in claim 3 , those made of θ-alumina or δ-alumina can be employed as the oxide particles.

  The inventor examined heat resistance of conventional γ-alumina. When the temperature of γ-alumina is raised from around 600 ° C., it changes to θ-alumina around 800 ° C., passes through δ-alumina, and changes to α-alumina around 1200 ° C.

Here, the specific surface area of γ-alumina is 150 to 300 m ² / g, the specific surface area of θ-alumina and δ-alumina is 30 to 100 m ² / g, and the specific surface area of α-alumina is 1 to ² m ^2. / G. The specific surface area of cordierite is approximately the same as that of α-alumina.

  In other words, if θ-alumina or δ-alumina is used as the oxide particles, the specific surface area is somewhat smaller than that of γ-alumina, but there is no practical problem and the oxide has excellent heat resistance. Particles can be provided.

It is preferable as defined in claim 5, in the catalyst body according to claim 3, oxide particles, SiO ₂ is also suitable.

According to the study of the present inventor, by using SiO ₂ as a raw material for the coating layers (21, 22), the adhesion with the catalyst component (30) is improved, and the catalyst is used for a long time use at a high temperature. Catalyst degradation due to aggregation of the component (30), that is, sintering, can be suppressed.

As a result, it is possible to maintain a highly active catalyst function, and it is possible to provide a catalyst body with improved durability at high temperatures. Incidentally, specific combinations of the coating layer (21, 22) -catalyst component (30) that can be expected to improve heat resistance include SiO ₂ coat-CeO ₂ fine particles, SiO ₂ coat-CeO ₂ .ZrO ₂ composite oxide fine particles. Etc.

Further, in the invention according to claim 6, wherein in the section 1 catalyst body according to claim 5, the catalyst component (30), a kind having a primary particle size of 1nm~100nm single particulates or of two or more The catalyst particles are characterized by comprising base particles (1) which are compound fine particles and one or more metals or compositions thereof covering at least a part of the surface of the base particles (1).

  Here, one kind of single particle is a fine particle made of one kind of element or compound, and two or more kinds of compound fine particles are fine particles in which two or more kinds of elements or compounds are dissolved. Further, the solid solution fine particles in the present invention include a state in which the substances A and B are mixed, and a state in which the substances A and B react to differ from the initial structure.

According to the present invention, the catalyst component (30) can be made to have a size of nanometer order (in the present specification, meaning a range of 1 nm to 100 nm) as a whole catalyst particle, The specific surface area is larger than that of precious metal catalyst particles of the metric order and can be made highly active.

  In the present invention, the base particles can also have catalytic activity so that the base particles and one or more metals or compositions thereof exhibit catalytic activity against different substances. Since it can be selected, the activity can be exhibited with respect to plural kinds of substances with one kind of catalyst particle.

  In the present invention, one of the base particles and one or more metals or their composition can be used as a catalyst, and the other as a promoter. That is, as the catalyst component (30), it is possible to provide catalyst particles that are more active and can exhibit activity against a plurality of types of substances.

Here, as in the invention according to claim 7, those in the catalyst body according to claim 6, the group particles (1), made of one selected metal oxide, a metal carbide and carbon material Can be.

Specifically, as in the invention according to claim 8 , in the catalyst body according to claim 7 , the metal oxide includes Ce, Zr, Al, Ti, Si, Mg, W, Sr, Ni. It is possible to employ one kind of simple substance selected from these oxides and their compositions, or one comprising two or more kinds of compounds.

As in the invention described in claim 9 , in the catalyst body described in claim 7 or claim 8 , the metal carbide may be composed of SiC or a compound thereof.

It is preferable as defined in claim 10, in the catalyst body according to claim 7 to claim 9, as the carbon material, can be employed graphite.

Further, in the invention according to claim 11, in the catalyst body according to claims 6 to claim 10, at least a portion of one or more metals or coating the compound of their surface groups particle (1) is, 50 nm It is characterized by ultrafine particles having a particle size of less than.

  One or more metals or compounds thereof covering at least a part of the base particle (1) can be coated in the form of particles or layers, but in the case of particles, the particle size is less than 50 nm. It is preferable to have ultrafine particles. When the particle diameter is 50 nm or more, it is difficult to coat the nanometer-sized base particle surface.

Further, in the invention according to claim 12, in the catalyst body according to claims 6 to claim 11, of metal or composition thereof one or more covering at least part of the surface of the base particles (1) It is a coating layer (2) consisting of 1 to 30 atomic layers.

  On the other hand, when the 1 or more types of metal which coats at least one part of base particle (1) or those compositions is a layer, it is preferable that it is a coating layer (2) which consists of 1-30 atomic layers. If the surface coating layer is thicker than 30 atomic layers, it is not preferable because it becomes difficult to ensure the size of the nanometer order as a whole catalyst particle, and the surface coating layer itself becomes particles to reduce the specific surface area.

Further, according to the invention described in claim 13, in the catalyst body according to claims 6 to claim 12, at least a portion of one or more metals or covering the composition of their surface groups particles (1) The product preferably has a purity of 99% or more.

Furthermore, as in the invention according to claim 14, in the catalyst body according to claims 6 to claim 13, some but not total surface of the base particles (1) comprises one or more metals or their It is preferable to coat with the composition.

  According to this, in the case where the base particles have catalytic activity, the characteristics of the base particles are effectively improved through the surface of the base particles exposed without being coated with one or more metals or their compositions. You can make use of it.

It is preferable as defined in claim 15, in the catalyst body according to claims 6 to claim 14, wherein the one or more metals or compositions thereof, Pt, Rh, Pd, Au, Ag , Ru, and oxides thereof, one or more simple substances or two or more compounds can be employed.

Furthermore, in the invention according to claim 16 , in the catalyst body according to claims 1 to 15 , the second coat layer (22) is further formed on the second coat layer (22). A third coat layer (23) made of oxide particles having a larger particle diameter than the oxide particles is provided, and a catalyst component (30) is provided on the third coat layer (23). It is characterized by that.

  As described above, since the oxide particles constituting the second coat layer (22) have a small particle size, the surface area can be secured, but the particle size is too small and the second coat layer (22) becomes dense. If too much, the surface area may be reduced.

  In such a case, a third coat layer (23) made of oxide particles having a particle size larger than that of the second coat layer (22) is provided on the second coat layer (22), and a catalyst component is provided on the third coat layer (22). If (30) is supported, the surface area for supporting the catalyst component (30) can be appropriately secured.

Here, as in the invention described in claim 17 , the particle diameter of the oxide particles constituting the third coat layer (23) can be 100 nm to 1000 nm.

  In addition, the code | symbol in the bracket | parenthesis of each said means is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Configuration / Production method]
FIG. 1 is a cross-sectional view showing a schematic configuration of a catalyst body according to an embodiment of the present invention.

  As shown in FIG. 1, the catalyst body of the present embodiment is roughly composed of a porous substrate 10 and a first coat layer 21 composed of oxide particles sequentially laminated on the surface of the porous substrate 10. The second coating layer 22 and the catalyst component 30 provided on the second coating layer 22 are configured.

  Here, the porous substrate 10 is a structure having pores on the surface, such as cordierite. In this example, as the porous base material 10, according to an actual measurement result performed by the present inventor, an average pore diameter, that is, a cordierite having an average pore diameter of about 1 μm to 2 μm is adopted. .

  Further, as shown in FIG. 1, in the catalyst body of the present embodiment, the particle size of the oxide particles constituting the first coat layer 21 is the particle size of the oxide particles constituting the second coat layer 22. It is larger than the diameter. Here, the particle diameter of the oxide particles is a commonly used average particle diameter, and may be either the primary particle diameter or the secondary particle diameter in which the primary particles are aggregated.

  Specifically, the particle diameter of the oxide particles constituting the first coat layer 21 is ½ to ¼ times the average pore diameter of the porous substrate 10, and the second coat layer 22. The particle size of the oxide particles constituting the is 1/25 to 1/65 times the average pore size of the porous substrate 10.

  With such a particle size of the oxide particles, the oxide particles constituting the first coat layer 21 hardly enter the pores of the porous substrate 10 and are densely formed by the second coat layer 22. Thus, a layer of oxide particles having a large surface area can be appropriately realized.

  Since the oxide particles of the lower first coat layer 21 are applied to the surface of the porous substrate 10 in a slurry state, as will be described later, the particle size of the oxide particles is the porous substrate 10. Even if it is smaller than the average pore diameter, the oxide particles hardly penetrate into the pores of the porous substrate 10 due to the surface tension in the slurry state, etc., if it is 1/2 times to 1/4 times.

  The oxide particles of the upper second coat layer 22 are also applied on the porous substrate 10 on which the first coat layer 21 is formed, as will be described later. At this time, the pores of the porous substrate 10 are covered with the first coat layer 21 as a base of the second coat layer 22.

  Therefore, if the particle diameter of the oxide particles of the second coat layer 22 is 1/25 to 1/65 times the average pore diameter of the porous substrate 10, the oxide particles are The fine particles are arranged in the oxide particles of the first coat layer 21 and the gaps in a state of hardly entering the inside of the pores to form a dense layer.

  More specifically, as in this example, when the porous substrate 10 is cordierite, the particle size of the oxide particles constituting the first coat layer 21 is 600 nm to 1000 nm, and the second The particle diameter of the oxide particles constituting the coat layer 22 is preferably 30 nm to 80 nm.

  As described above, this is because, when the porous substrate 10 is cordierite, the average pore diameter of cordierite is 1 μm to 2 μm according to the measurement results of the present inventors. Based on the actually measured values of the pores of such a cordierite monolith substrate, the particle diameter of the oxide particles as described above is preferable.

  As shown in FIG. 1, the catalyst component 30 is supported and fixed on the upper second coat layer 22 in the catalyst body.

Here, the oxide particles constituting the first and second coat layers 21 and 22 include CeO ₂ , ZrO ₂ , Al ₂ O ₃ , TiO ₂ , SiO ₂ , MgO, Y ₂ O ₃ , and Ni ₂ O. ₃ or any one of two or more compounds selected from these compositions can be employed.

More specifically, such oxide particles can be made of θ-alumina, δ-alumina or SiO ₂ . In this example, SiO ₂ having a strong detergency with the catalyst component 30 is used as oxide particles.

In FIG. 1, each oxide particle is shown as an independent particle. However, when SiO ₂ (silica) is used as the oxide particle, in practice, each oxide particle is baked at a temperature equal to or higher than the glass transition temperature of silica. The oxide particles melt and become connected.

  Further, as the catalyst component 30, noble metal particles such as Pt, Pd, and Rh that are generally used in the past can be adopted, but any other one that has a catalytic function may be used.

  In this example, as shown in FIG. 2, as a catalyst component 30 that is more active and capable of exhibiting activity against a plurality of types of substances, a kind of simple particles having a primary particle size on the order of nanometers. Alternatively, catalyst particles comprising base particles 1 that are two or more kinds of compound fine particles and a surface coating layer 2 made of one or more kinds of noble metals or noble metal oxides covering at least a part of the surface of the base particles 1 are employed. ing.

  Here, the primary particle diameter of the base particle 1 is the diameter of the single base particle 1, and the primary particle diameter is usually 100 nm or less when the primary particle diameter is nano-order. In this example, the primary particle diameter of the base particle 1 is about 1 nm to 50 nm.

  In addition, as the base particle 1, a kind of single particle is a fine particle made of an element or a compound such as a kind of ceramic or metal, and two or more kinds of compound fine particles are two or more kinds of ceramic or metal. A fine particle in which an element or a compound is dissolved.

  Such base particles 1 can be made of a metal oxide, a metal carbide and a carbon material.

  Specifically, as the metal oxide, one kind of simple substance selected from Ce, Zr, Al, Ti, Si, Mg, W, Sr, Ni oxides and compositions thereof, or two or more kinds of compounds are employed. SiC or a compound thereof can be used as the metal carbide, and graphite can be used as the carbon material.

  The method for preparing the base particle 1 which is such a nano-order fine particle is not particularly limited, and examples thereof include a coprecipitation method, a sol-gel method, a plating method, and an ultrasonic assisted reduction method.

  In addition, the properties and composition ratios of the two or more compounds are not particularly limited, and the properties and composition ratios of these two or more compounds are set in order to improve purification performance such as temperature characteristics and durability characteristics. What is necessary is just to adjust suitably.

  And the catalyst component 30 shown by FIG. 2 shall cover at least one part of the surface of such a base particle 1 with a 1 or more types of metal or those compositions. Here, a noble metal or a noble metal oxide having a catalytic function can be used as the one or more metals or compositions thereof.

  Then, these one or more metals or their compositions are attached to the surface of the base particle 1 as ultrafine particles having a particle size of less than 50 nm, or the surface of the base particle 1 as a coating layer composed of one or a plurality of atomic layers. Adhere to.

  As described above, when ultrafine particles or a coating layer is formed on the nano-order base particles 1, highly active catalyst particles can be realized as the catalyst component 30. This is considered due to the following reasons.

  As the particle size decreases, the specific surface area increases and the number of sites having catalytic activity increases. Therefore, since the catalyst particles are highly active, even if the amount of the catalyst is reduced, the current level of performance can be satisfied.

  In addition, regarding the effectiveness of the catalyst component 30 as such catalyst particles, cerium oxide (ceria) is used as the base particles, and Pt is used as the ultrafine particles existing on the base particles, and this is applied to an exhaust gas purification catalyst for automobiles. An example will be described.

Ceria, the base particle, has the ability to absorb and release oxygen (oxygen storage and desorption function). When the oxygen concentration in the exhaust gas is high, Ce is oxidized to 4 ⁺ and oxygen is taken in. To become CeO ₂ . Further, when the oxygen concentration is low, Ce is reduced to 3 ⁺ and becomes CeO _3/2 .

In this case, it is considered that it is easier for the O ₂ molecule to enter and exit the atomic state O than to enter and exit the ceria directly. On the other hand, Pt as a catalyst is considered to play a role of assisting in dissociation of oxygen. Therefore, it can be said that the closer the cocatalyst and the catalyst are, the faster the oxygen can enter and exit, and the better the oxygen storage / desorption rate.

  From the above, when the catalyst particles are formed by forming the ultrafine particles or the surface coating layer 2 on the nano-order base particles 1, not only the specific surface area is high and the activity is high, but also the oxygen concentration in the exhaust gas changes rapidly. It can correspond to.

  Moreover, highly active catalyst particles can be obtained simply by allowing ultrafine particles having a particle size of less than 50 nm to be present on the surface of the base particles 1 such as ceria. In particular, crystalline base particles such as ceria can be obtained. By forming a surface coating layer of several atomic layers on the surface as a catalyst layer, more highly active catalyst particles can be obtained.

  This is because the catalyst layer of several atomic layers formed on the surface of the base particle 1 can take a lattice structure reflecting the crystal structure of the base particle. In other words, the method of attaching one or more metals or their composition as a coating layer to the surface of the base particle 1 adopts a structure different from the surface lattice structure in the case of existing as ultrafine particles, so that the electronic state changes. Therefore, the catalytic activity is considered to increase.

  Therefore, in the example of FIG. 2, the surface coating layer 2 is formed on at least a part of the surface of the base particle 1. Hereinafter, the feature points described below for the catalyst particles as the catalyst component 30 are applicable even when the surface coating layer 2 is replaced with ultrafine particles covering the surfaces of the base particles 1.

  The surface coating layer 2 is made of one or more kinds of noble metals or noble metal oxides that coat the surfaces of the base particles 1 with a thickness of 1 to 30 atomic layers. The surface coating layer 2 can be made of a noble metal such as Pt, Rh, Pd, Au, Ag, or Ru, and one or more simple substances selected from those noble metal oxides, or a combination of two or more kinds.

  The surface coating layer 2 at the level of 1 to 30 atomic layers is very dense and highly crystalline, has no lattice defects, and has few impurities, but one or more noble metals or noble metals constituting the surface coating layer. The oxide purity is preferably 99% or more. Such properties and purity of the surface coating layer 2 can be confirmed by a TEM image, an elemental analysis method or the like.

  Examples of the method for forming the surface coating layer 2 include a co-evaporation method, a coprecipitation method, a sol-gel method, a plating method, an ultrasonic assisted reduction method, and the like. It is excellent in that a complex composition can be obtained.

  As described above, the catalyst particles shown in FIG. 2 have nano-order base particles 1 as carriers, and at least a part of the surface of the base particles 1 is an atom of 1 to 30 atomic layers by the surface coating layer 2 having a catalytic function. It is coated to a layer level (about several nm) thickness.

  Therefore, the entire catalyst particle including the surface coating layer 2 can have a nano-order size (about 100 nm or less), and has a larger specific surface area and higher activity than conventional nano-order noble metal catalyst particles. can get.

  If the surface coating layer 2 is thicker than 30 atomic layers, it is difficult to ensure the nano-order size of one catalyst particle as a whole, and the surface coating layer 2 itself grows and the specific surface area decreases, which is not preferable. .

  The thickness in the case of this surface coating layer 2 is demonstrated to the case of Pt as an example.

  Although there are some differences depending on the plane orientation, the Pt layer spacing is about 0.2 nm. In the catalyst particles of this example, it is preferable to form the surface coating layer 2 by the co-evaporation method which is the gas phase method described above. However, the surface coating layer 2 is 30 atomic layers or more, and the thickness of the Pt layer is 6 nm or more. become.

  As a result of examination, it is difficult to stack 30 atomic layers or more by the co-evaporation method. Further, when the thickness of the laminated layer is increased, the reflection effect of the crystal structure of the base particles 1 expected for the surface coating layer 2 is reduced, the properties as the catalyst particles are enhanced, and the merit as the surface coating layer is reduced.

  From the above, the thickness of the surface coating layer 2 is suitably 1 to 30 atomic layers.

  Further, in the case of ultrafine particles, the particle size is not limited by the above-described atomic layer, and a particle size of less than 50 nm is preferable. With a particle size of 50 nm or more, it becomes difficult to coat the nanometer-sized base particle surface.

  In addition, the catalyst particles as the catalyst component 30 shown in FIG. 2 are selected so that the base particles 1 also have catalytic activity, and the base particles 1 and the surface coating layer 2 exhibit catalytic activity against different substances. Therefore, one kind of catalyst particle can exhibit activity against a plurality of kinds of substances.

  For the above reasons, the details of the mechanism are not well understood, but the catalytic function can be synergistically enhanced, and catalyst particles having high decomposition activity against a plurality of toxic substances can be realized.

Specifically, the combination of the base particles 1 coated with the surface coating layer 2 that can be expected to have a synergistic effect on the catalyst function includes CeO ₂ fine particles coated with Pt and CeO ₂ —ZrO ₂ coated with Pt. Examples thereof include solid solution fine particles, TiO ₂ fine particles coated with Au, and carbon particles coated with Pt.

  Thus, according to the catalyst particles shown in FIG. 2, it is possible to provide the catalyst component 30 that has higher activity and exhibits activity against a plurality of types of substances.

  In the catalyst particles, it is preferable that a part of the surface of the base particle 1 is coated with the surface coating layer 2 instead of the whole surface. By coating in this way, when the base particle 1 is not a simple carrier but has catalytic activity, the base particle is exposed through the surface of the base particle 1 exposed without being covered with the surface coating layer 2. The characteristic of 1 can be utilized effectively.

For example, as the catalyst particles, those obtained by coating CeO ₂ (base particles 1) with Pt (surface coating layer 2) are used as exhaust gas purification catalysts for automobiles as described above. At this time, Pt which is the surface coating layer 2 functions as a catalyst for performing oxidation of HC and reduction of NOx, but CeO ₂ which is the base particle 1 has a function of absorbing and releasing oxygen (oxygen absorption / release capability). It functions as a co-catalyst.

Therefore, depending on the oxygen deficiency in the catalyst the ambient atmosphere (exhaust gas), or oxygen from the CeO ₂ is released, by the CeO ₂ oxygen or is absorbed, in order to perform reduction of the oxidized and NOx of HC Therefore, the exhaust gas purification can be performed appropriately.

Such a function is considered to be effectively performed at the boundary portion where CeO ₂ and Pt are in contact with each other. As shown in FIG. 3, the surface of the CeO ₂ particle as the base particle 1 By covering a part, not the whole, with the Pt layer which is the surface coating layer 2, the boundary area can be increased, which is effective.

  The coverage ratio of the surface of the base particle 1 by the surface coating layer 2 can be confirmed by a TEM image or the like. According to the study of the present inventors, it is preferable to cover about 0.5 to 60% of the surface of the base particle 1.

  The catalyst body of this embodiment shown in FIG. 1 is prepared as follows.

  First, a slurry in which the oxide particles constituting the first coat layer 21 are dispersed is prepared, and the slurry is impregnated with the porous substrate 10, and then dried and baked to form the first coat layer 21. The formed porous substrate 10 is obtained.

  Subsequently, a slurry in which the oxide particles constituting the second coat layer 22 are dispersed is prepared, and this slurry is impregnated with the porous substrate 10 with the first coat layer 21, and then dried and fired. By doing so, the porous substrate 10 on which the second coat layer 22 is formed on the first coat layer 21 is obtained.

  Here, a case will be described in which catalyst particles are formed by coating the surface of the base particles 1 as shown in FIG.

  The ultrasonic assisted reduction method is a method in which a base particle and a metal precursor are mixed in a solvent, and this solvent is irradiated with ultrasonic waves to form a metal having a metal precursor reduced on the surface of the base particle. A coating layer composed of metric metal fine particles or several atomic layers is deposited.

  First, a slurry in which the catalyst component 30 is dispersed is prepared. Specifically, an organic solvent such as water or ethanol is placed in a container such as a beaker, and the base particles and the metal precursor are dispersed in the solvent. And this container is set to an ultrasonic generator (sono reactor), and an ultrasonic wave is irradiated.

The principle of the ultrasonic assisted reduction method will be described by taking an example using CeO ₂ as the base particle and PtCl ₂ as the metal precursor. When the base particles and the metal precursor are dispersed in the solvent, CeO ₂ , Pt ²⁺ ions, and Cl ⁻ ions are dispersed in the solvent.

Then, the reducing agent contained in the solvent, by Pt ²⁺ ions active sites of CeO ₂ surface as nuclei metallized by reduction, Pt metal is deposited as a surface coating layer on the CeO ₂ surface.

Then, precipitation of Pt metal proceeds. At this time, cavities (bubbles) are generated on the CeO ₂ surface by ultrasonic waves. Due to the presence of the cavity, Pt metal is dispersed and precipitated on the CeO ₂ surface, and the crystal growth of the Pt metal is suppressed by the impact of the disappearance of the cavity.

  In the ultrasonic assisted reduction method, a catalyst formed by depositing a surface coating layer composed of metal fine particles of a nanometer order or several atomic layers on the surface of the base particle by the mechanism as described above. Particles can be prepared.

  Moreover, you may add the above-mentioned reducing agent as a means to activate ultrasonic assisted reduction. Such a reducing agent is not particularly limited, and examples thereof include alcohols, amines, saccharides, and surfactants. Specifically, the alcohols include ethanol, propanol, the amines include diethanolamine, the saccharides include sucrose, and the surfactant includes an alkaline activator.

  The amount of the reducing agent added is not particularly limited, and may be 0.01 wt% (wt%) or more with respect to the solvent, that is, the reducing agent may be 0.01 wt% or more in the liquid phase. However, by controlling the ratio of the reducing agent, it is possible to control the metal particle size that is reduced and deposited, and it is desirable to select the ratio of the reducing agent to the desired metal particle size.

  When the ratio of the reducing agent is large, the reaction becomes faster, so that the growth of the metal particles is promoted and the metal particle size is increased. On the other hand, when the ratio of the reducing agent is small, the growth of the metal particles is slow and the precipitation to other active sites is promoted more than the growth, so that the metal particle size tends to be small.

  In the ultrasonic assisted reduction method, the frequency of irradiation ultrasonic waves is not particularly limited, but is preferably 20 to 300 kHz. The optimum frequency differs depending on the metal precursor. Generally, for metal precursors that dissolve in the liquid phase, a high frequency is used, and for metal precursors that are insoluble in the liquid phase, It is desirable to use a low frequency.

  As described above, the catalyst component 30 as the catalyst particles shown in FIG. 2 is obtained by the ultrasonic assisted reduction method. The catalyst component 30 is dispersed in a solvent such as water or an organic solvent to form a slurry.

  The slurry in which the catalyst component 30 is dispersed is impregnated with the porous substrate 10 with the first and second coat layers 21 and 22, and then dried and fired. Thereby, the catalyst body of this embodiment shown in FIG. 1 is obtained.

[Effects]
According to the present embodiment, the porous substrate 10, the first coat layer 21, the second coat layer 22 made of oxide particles sequentially laminated on the surface of the porous substrate 10, and the second A catalyst component 30 provided on the coat layer 22, and the particle size of the oxide particles constituting the first coat layer 21 is larger than the particle size of the oxide particles constituting the second coat layer 22. Can be provided.

  Accordingly, the second coat layer 22 is made of oxide particles having a smaller particle diameter than the first coat layer 21. Therefore, the second coat layer 22 is a dense layer that does not allow the catalyst component 30 to pass therethrough and can be a layer having a large surface area for supporting the catalyst component 30 because the particle size is small.

  Further, the first coat layer 21 having a large particle diameter is interposed between the second coat layer 22 having a small particle diameter and the porous base material 10, whereby the first coat layer 21 becomes a foundation. As a result, the pores of the porous substrate 10 are closed, so that the second coat layer 22 thereon can be prevented from entering the pores of the porous substrate 10.

  Therefore, the second coat layer 22 supported on the porous substrate 10 hardly enters the pores of the porous substrate 10 and the oxide particles of the first coat layer 21 And disposed in the gap. As a result, the second coat layer 22 is disposed on the surface of the porous substrate 10, and the thickness of the second coat layer 22 can be made as thin as possible within a necessary range.

  In addition, since the first coat layer 21 can also have a large particle size of the oxide particles constituting it, in order to close the pores of the porous substrate 10 as the base of the second coat layer 22 , It doesn't have to be very thick.

  Further, since the oxide particles of the first coat layer 21 only block the pores of the porous substrate 10 on the surface of the porous substrate 10 and hardly enter the pores, the porous substrate 10 In 10, voids due to the pores remain, and the thermal shock resistance is ensured because the porous substrate 10 has a function of relaxing expansion and contraction due to heat.

  In other words, in order to achieve intensive loading of the catalyst component on the surface layer of the porous substrate without introducing the catalyst component into the pores of the porous substrate such as cordierite, the surface layer of the porous substrate The pores may be filled with some member and sealed.

  However, if it does so, the thermal shock performance utilizing the pore voids in the porous substrate will not be exhibited, and the heat resistance of the porous substrate and thus the catalyst body will decrease.

  In that respect, the catalyst body of the present embodiment has such pores in the porous substrate 10, so that such a problem is avoided.

  Thus, in this embodiment, since the catalyst component 30 is supported on the first and second coat layers 21 and 22 formed thinly on the surface of the porous substrate 10, as a result, A configuration in which the catalyst component 30 is thinly arranged on the surface of the porous substrate 10 can be realized.

  Thus, according to the catalyst body of the present embodiment, the thickness of the oxide particle layer on the porous substrate 10 can be made as thin as possible as compared with the prior art, so that the above-described ventilation resistance can be reduced, and the catalyst The component 30 hardly enters the pores of the porous substrate 10 below the oxide particles, and is efficiently formed on the surface of the porous substrate 10.

  Therefore, according to the present embodiment, in the catalyst body formed by supporting the oxide particles on which the catalyst component 30 is supported on the porous substrate 10, the reaction utilization efficiency of the catalyst component 30 is increased, and the use of the catalyst component 30 is improved. The amount can be reduced. And according to this embodiment, an environmentally friendly and inexpensive catalyst body can be provided.

  Further, in the catalyst body of the present embodiment, the particle diameter of the oxide particles constituting the first coat layer 21 is ½ times to ¼ times the average pore diameter of the porous substrate 10, One of the characteristics is that the particle diameter of the oxide particles constituting the second coat layer 22 is 1/25 to 1/65 times the average pore diameter of the porous substrate 10.

  As described above, when the particle size of such oxide particles is used, the oxide particles constituting the first coat layer 21 hardly enter the pores of the porous substrate 10, and the second The coat layer 22 can appropriately realize a dense oxide particle layer having a large surface area.

  In the catalyst body of the present embodiment, when the porous substrate 10 is cordierite, the particle diameter of the oxide particles constituting the first coat layer 21 is 600 nm to 1000 nm, and the second One of the characteristics is that the particle diameter of the oxide particles constituting the coat layer 22 is 30 nm to 80 nm.

  As described above, according to the results of the investigation conducted by the present inventor, the average pore diameter of cordierite is 1 μm to 2 μm, and the particle diameter of the oxide particles described above is preferable based on this measured value.

In the catalyst body of this embodiment, the oxide particles constituting the first and second coat layers 21 and 22 are CeO ₂ , ZrO ₂ , Al ₂ O ₃ , TiO ₂ , SiO ₂ , MgO, Y ₂ O _3, Ni ₂ O _3, and it is intended to be constructed from any of these one selected from a composition or two or more compounds are also one of the features.

According to this, it is possible to provide oxide particles that are carriers of the catalyst component 30 that have better heat resistance than conventional γ-alumina. That is, among these, θ-alumina, titania (TiO ₂ ), zirconia (ZrO ₂ ), etc., which are more excellent in heat resistance, can be used as oxide particles, thereby reducing the shape change of the oxide particles themselves. It is possible to prevent the catalyst component from being buried.

  More specifically, as described above, in the catalyst body of the present embodiment, oxide particles made of θ-alumina or δ-alumina can be employed.

  The inventor examined heat resistance of conventional γ-alumina. When the temperature of γ-alumina is raised from around 600 ° C., it changes to θ-alumina around 800 ° C., passes through δ-alumina, and changes to α-alumina around 1200 ° C.

Here, the specific surface area of γ-alumina is 150 to 300 m ² / g, the specific surface area of θ-alumina and δ-alumina is 30 to 100 m ² / g, and the specific surface area of α-alumina is 1 to ² m ^2. / G. The specific surface area of the cordierite monolith substrate is approximately the same as the specific surface area of α-alumina.

  That is, if θ-alumina or δ-alumina is used as the oxide particles, the specific surface area is somewhat smaller than that of γ-alumina, but there is no practical problem and the oxide particles have excellent heat resistance. Can be provided.

As described above, in the present embodiment, the oxide particles may be made of SiO ₂ , and in this example, this is the case.

When SiO ₂ is used as a raw material for the coating layers 21 and 22, the detailed mechanism is unknown, but according to the study of the present inventors, by using SiO ₂ as a raw material for the coating layers 21 and 22, a catalyst component Thus, the deterioration of the catalyst, that is, the sintering due to the aggregation of the catalyst component 30 or the like can be suppressed for a long time use at a high temperature.

As a result, it is possible to maintain a highly active catalyst function, and it is possible to provide a catalyst body with improved durability at high temperatures. Specifically, examples of the combination of the coating layers 21, 22 and the catalyst component 30 that can be expected to improve heat resistance include SiO ₂ coat-CeO ₂ fine particles, SiO ₂ coat-CeO ₂ .ZrO ₂ composite oxide fine particles, and the like.

  Further, in the catalyst body of the present embodiment, the catalyst component 30 is a base particle 1 that is one kind of single particle or two or more kinds of compound fine particles having a primary particle size on the order of nanometers as shown in FIG. It is also one of the features to employ catalyst particles comprising one or more metals or compositions thereof covering at least a part of the surface of the base particle 1 and the composition thereof.

  According to this, the catalyst component 30 can be made to have a size of nanometer order (about 100 nm or less) as one whole catalyst particle, and the specific surface area is larger than the conventional noble metal catalyst particles of a simple nanometer order. Can be made highly active.

  In the present embodiment, the base particles 1 can also have catalytic activity, and the base particles 1 and one or more metals or compositions thereof exhibit catalytic activity against different substances. Therefore, the activity can be exhibited with respect to a plurality of kinds of substances with one kind of catalyst particle.

  In other words, according to the present embodiment, as the catalyst component 30, it is possible to provide catalyst particles that are more active and can exhibit activity against a plurality of types of substances. Further, as described above, the catalyst particles used as the catalyst component 30 shown in FIG. 2 have the above-described additional features and effects.

  Further, according to the present embodiment, the first coat layer 21 and the second coat layer 22 made of oxide particles are sequentially laminated on the surface of the porous substrate 10, and the second coat layer 22 is There is provided a method for producing a catalyst body comprising the catalyst component 30 supported thereon, wherein the following steps are carried out.

  (1) First, a slurry in which the oxide particles constituting the first coat layer 21 are dispersed is prepared, and after impregnating the porous substrate 10 in this slurry, the first coat layer 21 is formed by firing. The 1st process of creating the porous base material 10 made.

  (2) Following the first step, slurry in which particles larger than the particle size of the oxide particles constituting the second coat layer 22 are dispersed as oxide particles constituting the second coat layer 22 The porous base material 10 on which the first coat layer 21 is formed is impregnated in the slurry, and then the porous structure in which the second coat layer 22 is formed on the first coat layer 21 by firing. A second step of creating the base material 10.

  (3) A third step in which the slurry in which the catalyst component 30 is dispersed is impregnated with the porous substrate 10 on which the first and second coat layers 21 and 22 are formed, and then fired.

  As described above, the catalyst body of the present embodiment shown in FIG. 1 is completed by the first to third steps. Also in this manufacturing method, the same effect as described for the catalyst body of the present embodiment is exhibited.

  That is, according to the present manufacturing method, the catalyst body of the present embodiment can be appropriately manufactured, and in the catalyst body formed by supporting the oxide particles supporting the catalyst component 30 on the porous substrate 10. The reaction utilization efficiency of the catalyst component 30 can be increased, and the amount of the catalyst component 30 used can be reduced. In addition, an environmentally friendly and inexpensive catalyst body can be provided. .

  Further, in the manufacturing method of the present embodiment having such feature points, a manufacturing method having the following feature points can be obtained. In addition, the effect which concerns on each feature point in the following manufacturing methods is as having mentioned above.

  (4) The particle diameter of the oxide particles constituting the first coat layer 21 is ½ to ¼ times the average pore diameter of the porous substrate 10, and the second coat layer 22 is used. As the particle diameter of the oxide particles that constitute the material, one having an average pore diameter of 1/25 to 1/65 times the average pore diameter of the porous substrate 10 is used.

  (5) Cordierite is used as the porous substrate 10, and oxide particles constituting the second coat layer 22 are used as oxide particles constituting the first coat layer 21 having a particle diameter of 600 nm to 1000 nm. Use a particle size of 30 nm to 80 nm.

(6) as the oxide particles constituting the first and second coating layers _{21,22, CeO 2, ZrO 2,} Al 2 O 3, TiO 2, SiO 2, MgO, Y 2 O 3, Ni 2 O 3 And one composed of one or two or more compounds selected from these compositions.

(7) Use oxide particles made of θ-alumina, δ-alumina or SiO ₂ .

  (8) As the catalyst component 30, as shown in FIG. 2, a base particle 1 that is one kind of single particle or two or more kinds of compound fine particles having a primary particle size on the order of nanometers, and the surface of the base particle 1 A catalyst particle comprising at least one metal covering at least a part of the metal or a composition thereof, and the catalyst particles. As described above, the catalyst particles employed in the production method have the above-described additional features and effects.

[Modification]
Here, a modification of the present embodiment will be described. FIG. 3 is a cross-sectional view showing a schematic configuration of a catalyst body as a modification of the present embodiment.

  In the example shown in FIG. 3, a third coat layer 23 made of oxide particles having a larger particle diameter than the oxide particles constituting the second coat layer 22 is further formed on the second coat layer 22. The catalyst component 30 is provided on the third coat layer 23.

  As described above, since the oxide particles constituting the second coat layer 22 have a small particle size, the surface area can be secured, but when the particle size is too small and the second coat layer 22 becomes too dense, On the contrary, the surface area may be reduced.

  In such a case, if a third coat layer 23 made of oxide particles having a particle size larger than that of the second coat layer 22 is provided on the second coat layer 22 and the catalyst component 30 is supported thereon, The surface area for supporting the catalyst component 30 can be appropriately ensured.

  Here, the particle diameter of the oxide particles constituting the third coat layer 23 is larger than the particle diameter of the oxide particles constituting the first coat layer 21 when the porous substrate 10 is cordierite. As a thing small and larger than the particle size of the oxide particle which comprises the 2nd coating layer 22, it can be set as about 100 nm-1000 nm, for example.

Further, as the oxide particles constituting the third coat layer 23, for example, CeO ₂ , ZrO ₂ , Al ₂ O ₃ , and the like as in the oxide particles constituting the first and second coat layers 21 and 22, TiO ₂ , SiO ₂ , MgO, Y ₂ O ₃ , Ni ₂ O ₃ and compositions thereof can be used.

  And the catalyst body of this example which has this 3rd coating layer 23 performs the oxide particle which comprises the 3rd coating layer 23 after performing a 1st process and a 2nd process in the said manufacturing method. A dispersed slurry is prepared, and the slurry is impregnated with the porous substrate 10 on which the first coat layer 21 and the second coat layer 22 are formed, and then fired onto the second coat layer 22. It can be manufactured by performing the step of creating the porous substrate 10 on which the third coat layer 23 is formed, and then performing the third step.

  Next, the present embodiment will be described more specifically based on the following examples. The present invention is not limited to the following examples.

In the examples described below, a cordierite monolith substrate is mainly used as a porous substrate, silica (SiO ₂ ) particles are used as oxide particles constituting the first and second coat layers, and a catalyst component is used. Is obtained by coating the surface of CeO ₂ · ZrO ₂ composite oxide (hereinafter referred to as Ce-Zr composite oxide) as base particles with Pt and Rh, which are noble metals, in accordance with FIG. It is.

  The catalyst body of the present embodiment can be applied in a wide variety of fields such as exhaust gas purification, environmental purification, and fuel cell, but it goes without saying that the present invention is not limited to this embodiment.

[First example]
About 16.7 g of silica particle powder having a particle size of about 800 nm and about 10% were mixed with 150 ml of pure water. Acetic acid was added to this solution to adjust the solution pH to 3-4 to improve dispersibility. This solution was pulverized with a pulverizer such as a ball mill for 16 hours to obtain a slurry of silica particles having a uniform particle size as a raw material for the first coat layer.

  The resulting silica particle slurry for the first coat layer was applied to the surface of the cordierite monolith substrate by the following method.

  The silica particle slurry was impregnated with a cordierite monolith substrate, and this was subjected to a drying process using a hot air generator at 150 ° C., thereby supporting 1.8 g of silica particles on the cordierite monolith substrate. Then, the target object was obtained by using this for a baking process of 1050 degreeC and 1 hour.

  In this way, a layer made of silica as the first coat layer is formed on the surface of the cordierite monolith substrate. This state is referred to as a first cordierite monolith substrate with a silica coat layer.

  As a raw material preparation method for the second coat layer, it was prepared by diluting and mixing a slurry of silica particles having a particle diameter of about 50 nm with pure water at a ratio of 1: 1. The silica particle slurry for the second coat layer was applied to the surface of the cordierite monolith substrate with the first silica coat layer by the following method.

  The silica particle slurry for the second coat layer is impregnated with the cordierite monolith substrate with the first silica coat layer, and this is subjected to a drying step using a hot air generator at 150 ° C. 1.0 g was supported on the base material. Then, the target object was obtained by using this for a baking process of 1050 degreeC and 1 hour.

  Thus, the first coat layer and the second coat layer made of silica are formed on the surface of the cordierite monolith substrate. This state is referred to as a cordierite monolith substrate with first and second silica coat layers.

  The cordierite monolith substrate impregnated in the silica particle slurry for the first coat layer and the cordierite monolith substrate with the first silica coat layer in the silica particle slurry for the second coat layer At the time of impregnation, for example, ultrasonic irradiation of about 100 kHz may be performed for the purpose of obtaining a coat layer with few gaps between silica particles.

  This can be performed, for example, by setting a container such as a beaker containing a slurry solution of silica particles in an ultrasonic generator (sono reactor) and an ultrasonic cleaner.

  Here, as a method for preparing the catalyst component, the ultrasonic assisted reduction method was used. As the method, first, 25 g of Ce—Zr composite oxide serving as base particles was weighed and dissolved in 1000 ml of a solvent composed of water or an organic solvent such as ethanol.

  Then, the obtained Ce—Zr composite oxide slurry was irradiated with ultrasonic waves while being stirred at 25 kHz for 30 minutes, so that the Ce—Zr composite oxide was refined in nano order and dispersed.

Then, 0.1 g of PtCl ₂ and 0.157 ml of RhCl ₃ solution were weighed as noble metal raw materials for the surface coating layer, and irradiated with ultrasonic waves while stirring, and mixed with the refined Ce-Zr composite oxide slurry. did. Further, about 10 ml of alkanolamine was added as a reducing agent for PtCl ₂ to Pt.

  This ultrasonic irradiation reduces platinum chloride and rhodium chloride into Pt particles and Rh particles. In addition, each ultrasonic irradiation mentioned above can be performed by setting the container containing the solvent which mixed each raw material mentioned above to an ultrasonic generator (sono reactor), for example.

  The mixed liquid thus obtained is washed with a centrifuge to obtain a solid as a precursor of catalyst particles. The solid as the precursor is obtained by supporting the noble metals Pt and Rh on the surface of the Ce—Zr composite oxide as the base particle. After that, if it is desired to obtain the catalyst body as a powder, the solid matter remaining after centrifugation may be calcined at 400 ° C.

  A solid solution thus obtained is dispersed in a solvent such as water or an organic solvent to prepare a dispersion solution. Then, nitric acid is added to this dispersion solution, and the pH of the solution is adjusted to about 3 to obtain a slurry that is easily supported on the cordierite monolith substrate. In addition, it is possible to prepare a slurry that can be easily supported on a cordierite monolith substrate by using a homogenizer, a medium stirring mill, or the like.

  Next, the catalyst component is refined to nano-order by irradiating the slurry prepared from the dispersion solution with ultrasonic waves again at 25 kHz. Thereby, the catalyst component slurry solution in which the catalyst component in the present example is dispersed is obtained.

  The catalyst component was supported on the cordierite monolith substrate with the first and second silica coat layers by the following method.

  The catalyst component slurry solution is impregnated with a cordierite monolith substrate with first and second silica coat layers, and subjected to a drying step using a hot air generator at 150 ° C. .4 g was loaded. Then, the target object was obtained by using this for the baking process of 500 degreeC and 2 hours.

  Thus, the catalyst body in this example is obtained in a state where the catalyst components are concentratedly supported on the surfaces of the cordierite monolith substrate with the first and second silica coat layers.

[Second example]
In this example, the loading amount of the silica particles for the second coat layer in the first example on the cordierite monolith substrate with the first silica coat layer was changed to 1.0 g instead of 1.0 g. Thereby, the second coat layer was made thinner. Other than that, the catalyst body was prepared in the same manner as in the first example up to the loading of the catalyst component.

[Third example]
In this example, the loading amount of the silica particles for the second coat layer in the first example on the cordierite monolith substrate with the first silica coat layer was set to 0.2 g instead of 1.0 g. Thereby, the second coat layer was made thinner. Other than that, the catalyst body was prepared in the same manner as in the first example up to the loading of the catalyst component.

[Fourth example]
In this example, the loading amount of the silica particles for the first coat layer in the first example on the cordierite monolith substrate was changed to 1.8 g instead of 1.8 g. Thereby, the first coat layer was made thinner. Other than that, the catalyst body was prepared in the same manner as in the first example up to the loading of the catalyst component.

[Fifth Example]
In this example, the amount of the silica particles for the first coat layer in the first example supported on the cordierite monolith substrate was changed to 1.8 g instead of 1.8 g. Thereby, the first coat layer was made thinner. Other than that, the catalyst body was prepared in the same manner as in the first example up to the loading of the catalyst component.

  And about each catalyst body of the said 1st-5th example in the said Example, it was confirmed whether the catalyst component was concentrated and carry | supported on the surface of the cordierite monolith base material. As the method, a confirmation method by element mapping of the monolith cross section with an electron beam microanalyzer (EPMA) was adopted.

  As a result, in each of the catalyst bodies of the first to fifth examples, it was confirmed that the catalyst component was concentratedly supported on the surface coat layer of the cordierite monolith substrate.

  Next, when the catalyst bodies of the first to fifth examples were used as exhaust gas purifying catalysts, their heat resistance was confirmed.

  Each catalyst body of the first to fifth examples was installed in the center of the electric furnace, and was heated and aged at 800 ° C. for 5 hours in the atmosphere. This aging heating condition is a condition in which, with a conventional catalyst body, sintering due to heat of the catalyst component occurs and deteriorates.

  And in each catalyst body of the first to fifth examples, the heat resistance was evaluated by measuring the noble metal particle diameter with a CO adsorption amount measuring device for those that were subjected to the above aging and those that were not. .

  As a result, the noble metal particle diameter in each of the catalyst bodies of the first to fifth examples hardly changed after aging. From this, it was confirmed that sintering due to heat was suppressed in the noble metal particles in the exhaust gas purifying catalyst bodies produced in the first to fifth examples of the present example.

  In the above embodiment, as the catalyst component 30, mainly as shown in FIG. 2, a base particle 1 which is a kind of single particle having a primary particle size of nanometer order or two or more kinds of compound particles, The example in which the catalyst particles comprising the surface coating layer 2 made of one or more kinds of noble metals or noble metal oxides covering at least a part of the surface of the base particles has been described. Needless to say, precious metal particles such as Pt, Pd, and Rh that are used in general, and those having a catalytic function other than that can be adopted in each embodiment.

  As described above, the catalyst body of the present invention includes a porous substrate, and the first coat layer, the second coat layer, and the second coat made of oxide particles sequentially laminated on the surface of the porous substrate. A catalyst component provided on the layer, and the particle size of the oxide particles constituting the first coat layer must be larger than the particle size of the oxide particles constituting the second coat layer. The other parts can be appropriately changed in design.

It is sectional drawing which shows the typical structure of the catalyst body which concerns on embodiment of this invention. It is a figure which shows an example of the catalyst component used for the said embodiment. It is sectional drawing which shows the typical structure of the catalyst body as a modification of the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base particle, 2 ... Surface coating layer, 10 ... Porous base material,
21 ... 1st coat layer, 22 ... 2nd coat layer, 30 ... Catalyst component.

Claims (17)

A porous substrate (10);
A first coat layer (21) composed of oxide particles sequentially laminated on the surface of the porous substrate (10), a second coat layer (22);
A catalyst component (30) provided on the second coat layer (22),
The particle diameter of the oxide particles constituting the first coat layer (21) is 1/2 to 1/4 times the average pore diameter of the porous substrate (10),
The particle size of the oxide particles in which the second constituting coating layer (22) is an automobile, wherein the a 1/25 times to 1/65 times the average pore diameter of the porous substrate (10) Exhaust gas purification catalyst body. The porous substrate (10) is cordierite;
The particle diameter of the oxide particles constituting the first coat layer (21) is 600 nm to 1000 nm, and the particle diameter of the oxide particles constituting the second coat layer (22) is 30 nm to 80 nm. The automobile exhaust gas purification catalyst body according to claim 1 , wherein the catalyst body is an exhaust gas purification catalyst body. The oxide particles first and second coating layer (21, 22) constituting _{the, CeO 2, ZrO 2, Al} 2 O 3, TiO 2, SiO 2, MgO, Y 2 O 3, Ni 2 O 3 The catalyst body for exhaust gas purification of automobiles according to claim 1 or 2 , wherein the catalyst body is composed of one or two or more compounds selected from these compositions. 4. The automobile exhaust gas purification catalyst body according to claim 3 , wherein the oxide particles are made of [theta] -alumina or [delta] -alumina. The oxide particles, the exhaust gas purifying catalyst of an automobile according to claim 3, characterized in that made of SiO _2. The catalyst component (30), a kind of a single particle or two or more of the compound fine particles in a group particles (1) having a primary particle size of 1 nm~100 nm, at least a portion of the surface of the base particles (1) The catalyst body for exhaust gas purification of an automobile according to any one of claims 1 to 5 , wherein the catalyst body comprises catalyst particles comprising at least one metal to be coated or a composition thereof. The catalyst body for exhaust gas purification according to claim 6 , wherein the base particles (1) are made of a metal oxide, a metal carbide and a carbon material. The metal oxide is composed of one or more compounds selected from oxides of Ce, Zr, Al, Ti, Si, Mg, W, Sr, Ni and compositions thereof, or two or more compounds. The catalyst body for exhaust gas purification of a motor vehicle according to claim 7 . 9. The automobile exhaust gas purification catalyst body according to claim 7 or 8 , wherein the metal carbide is composed of SiC or a compound thereof. 10. The automobile exhaust gas purifying catalyst body according to any one of claims 7 to 9 , wherein the carbon material is graphite. At least a portion of one or more metals or covering the composition of their surface of the base particles (1) is any one of claims 6 to 10, characterized in that ultrafine particles having a particle size of less than 50nm A catalyst body for purifying automobile exhaust gas according to one. Wherein at least a portion of one or more metals or covering the composition of their surface groups particle (1) is 6 to claim, characterized in that a coating layer consisting of 1 to 30 atomic layers (2) 11 The catalyst body for exhaust-gas purification | cleaning of the motor vehicle as described in any one of these. At least a portion of one or more metals or covering the composition of their surface of the base particles (1) is any one of claims 6 to 12, characterized in that the purity is not less than 99% A catalyst body for exhaust gas purification of automobiles as described in 1. Some rather than the whole of the base surface of the particles (1), according to any one of claims 6 to 13, characterized in that is coated with the one or more metals or their composition A catalyst body for automobile exhaust gas purification . The one or more metals or compositions thereof in the catalyst component (30) are one or more simple substances or two or more compounds selected from Pt, Rh, Pd, Au, Ag, Ru and oxides thereof. The catalyst body for exhaust gas purification of an automobile according to any one of claims 6 to 14 , characterized in that: On the second coat layer (22), there is further provided a third coat layer (23) made of oxide particles having a particle size larger than that of the oxide particles constituting the second coat layer (22). The automobile exhaust gas purification device according to any one of claims 1 to 15 , wherein the catalyst component (30) is provided on the third coat layer (23) . Catalyst body. The catalyst body for exhaust gas purification of an automobile according to claim 16 , wherein the particle size of the oxide particles constituting the third coat layer (23) is 100 nm to 1000 nm.

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