JP2002361089A - Catalyst for cleaning exhaust gas and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for cleaning an exhaust gas, in which sintering of a noble metal being an active species, lowering of the specific surface area of a material for supporting the noble metal, or the like can be suppressed even at a high temperature condition (e.g. a high temperature position at directly below an exhaust manifold) and which keeps a good level in the cleaning performance to NOx, HC and CO under such a condition that A/F fluctuates in the wide range at driving a vehicle, even in the case where the use amount of the noble metal is reduced in comparison with the conventional use amount. SOLUTION: The catalyst for cleaning the exhaust gas is obtained by applying a catalyst layer on an integrated structure-type carrier having a cell cross section of a polygon through an under coat layer comprising an inorganic oxide. The inorganic oxide is alumina, and catalytically active components in the catalyst layer are platinum and/or rhodium. The ratio (Lmax./Lmin.) of the maximum thickness (Lmax.) of the catalyst layer at the corner of a cell to the minimum thickness (Lmin.) of the catalyst layer at the flat part of the cell is adjusted to be in the range of 1 to 10, and the thickness of the catalyst layer is controlled to be in the range of 5 to 200 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst and a method for producing the same, and more particularly, to a hydrocarbon (hereinafter referred to as "harmful component") in exhaust gas discharged from an internal combustion engine of an automobile or the like. "HC"), carbon monoxide (hereinafter, referred to as "HC").
The present invention relates to an exhaust gas purifying catalyst capable of purifying CO and nitrogen oxides (hereinafter, referred to as “NOx”) almost simultaneously and with high efficiency, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, platinum (Pt) and rhodium (R
In the case where the three-way catalyst using h) is used at a high temperature immediately below the exhaust manifold, there is a problem that the performance is deteriorated due to sintering of the noble metal which is an active species and a decrease in the specific surface area of the material supporting the noble metal. Was.
In particular, when the amount of the noble metal carried is reduced, the tendency becomes remarkable, and the purification performance of NOx, HC and CO under a wide range of A / F fluctuations during running of the vehicle cannot be maintained at a satisfactory level. Therefore, development of an exhaust gas purifying catalyst having excellent durability and a method for producing the same are expected.

[0003] As such an exhaust gas purifying catalyst, for example, JP-A-5-200287 and JP-A-8-246 are known.
44 and Japanese Patent Application Laid-Open No. 9-10585. Japanese Patent Application Laid-Open No. 5-49929 discloses that an integrated structure having a catalyst support layer made of activated alumina supports palladium and rhodium on the inlet side where exhaust gas flows, and platinum on the outlet side where exhaust gas flows out. There has been proposed an exhaust gas purifying catalyst that carries rhodium and uses a larger amount of rhodium on the outlet side than on the inlet side.

Further, in Japanese Patent Application Laid-Open No. Hei 8-24644,
An exhaust gas purifying catalyst has been proposed in which a catalyst supporting layer formed on the surface of a carrier base material contains an active component composed of palladium, platinum and an alkaline earth metal, and carries platinum on the inlet side where exhaust gas flows. I have.

Further, Japanese Patent Application Laid-Open No. 9-10585 discloses that activated alumina supporting 1 to 5% of a platinum group element (platinum and rhodium, palladium and rhodium, platinum, palladium and rhodium) and zirconium or a rare earth element are used. There has been proposed an exhaust gas purifying catalyst in which a catalyst layer is formed of a mixture of a converted cerium oxide and a refractory inorganic oxide mainly composed of activated alumina.

[0006]

In the exhaust gas purifying catalyst as described above, if the amount of noble metal is reduced, the heat resistance of the noble metal, which is a catalytically active species, is impaired, so that sufficient purification performance is exhibited. However, since palladium is used to exhibit low-temperature activity, sufficient purification performance cannot be exhibited and maintained unless a certain amount of noble metal is used.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a method for producing active species even under high-temperature conditions (such as a high-temperature position immediately below an exhaust manifold). Sintering of the noble metal and a decrease in the specific surface area of the material carrying the noble metal can be suppressed, and even when the amount of the noble metal used is reduced compared to the conventional case, it is possible to prevent a wide range of A / F fluctuations during running the vehicle. An object of the present invention is to provide an exhaust gas purifying catalyst having a good level of NOx, HC and CO purifying performance and a method for producing the same.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, provided an inorganic oxide layer on a carrier supporting a catalyst component, and provided a catalytically active component thereon. By providing a catalyst layer to contain, by setting the coverage of each layer and the ratio of the layer thickness in a well-balanced manner, by improving the low-temperature activity of the catalyst at the time of cold start (light-off function) and the catalyst activity after thermal durability deterioration, The inventors have found that the above problems can be solved, and have completed the present invention.

That is, the exhaust gas purifying catalyst of the present invention is characterized in that a catalyst layer is coated on an integrally-structured carrier having a polygonal cell cross section via an undercoat layer made of an inorganic oxide. And

In a preferred embodiment of the exhaust gas purifying catalyst according to the present invention, the catalyst layer has a thickest portion (Lma) of a cell angle.
x. ) And the thinnest portion (Lmin.) Of the cell flat portion (Lmin.) (L
max. / Lmin. ) Is in the range of 1 to 10, and 5
It has a thickness of about 200 μm.

In another preferred embodiment of the exhaust gas purifying catalyst according to the present invention, the catalyst layer comprises a first catalyst layer containing only platinum as a catalytically active component and a second catalyst layer containing platinum and rhodium as a catalytically active component. It is characterized in that the catalyst layer is sequentially coated.

Still another preferred embodiment of the exhaust gas purifying catalyst according to the present invention is that the platinum of the first catalyst layer is a carrier mainly composed of alumina and a carrier mainly composed of cerium oxide. And the first catalyst layer has a total platinum amount of 30%.
It is characterized in that about 80% is supported on the above-mentioned support material containing alumina as a main component.

In another preferred embodiment of the exhaust gas purifying catalyst according to the present invention, the second catalyst layer includes a carrier mainly composed of alumina and a carrier mainly composed of zirconium oxide. The support material containing alumina as a main component contains 1 to 10 mol% of at least one metal selected from the group consisting of cerium, zirconium and lanthanum in terms of metal, and the support material containing zirconia as a main component is , At least one metal selected from the group consisting of neodymium, yttrium, cerium and lanthanum in the range of 1-30
It is characterized by containing mol%.

Still another preferred embodiment of the exhaust gas purifying catalyst of the present invention is characterized in that the cerium has a crystallite diameter of 100 ° or less.

[0015] Furthermore, another preferred embodiment of the exhaust gas purifying catalyst of the present invention, the cerium oxide is in the following composition formula _{Ce a Nd b [X] c} O d ( in the composition formula, d = 2.0, a = 0.5-
0.99, b = 0.005-0.5, c = 0.0-0.
3, a + b + c = 1, X represents zirconium or lanthanum. However, a, b and c vary so as to satisfy d = 2.0 according to the valence of X. ).

[0016] Still another preferred embodiment of the exhaust gas purifying catalyst of the present invention, the cerium oxide is in the following composition formula _{Ce a Pr f [X] g} O h ( in the composition formula, h = 2.0, a = 0.5-
0.99, f = 0.005-0.5, g = 0.0-0.
3, a + f + g = 1, and X represents zirconium or lanthanum. However, a, f, and g vary so as to satisfy h = 2.0 according to the valence of X. ).

Further, the method for producing an exhaust gas purifying catalyst according to the present invention is a method for producing the above exhaust gas purifying catalyst, wherein the noble metal as an active species is impregnated and supported on the supporting material by an aqueous solution thereof. An organic acid is added to the aqueous solution of the noble metal salt.

Further, a preferred embodiment of the method for producing an exhaust gas purifying catalyst according to the present invention is characterized in that the organic acid has a carboxyl group.

Another method for producing an exhaust gas purifying catalyst according to the present invention is a method for producing the above exhaust gas purifying catalyst, wherein a noble metal serving as an active species is impregnated and supported on the supporting material by an aqueous solution thereof. At this time, the loading concentration is 0.1 to 3.0.
%.

Further, a preferred embodiment of the method for producing an exhaust gas purifying catalyst according to the present invention is characterized in that the weight ratio of the noble metal impregnating solution to the supporting material is 1: 1 to 3: 1.

Still another preferred embodiment of the method for producing an exhaust gas purifying catalyst according to the present invention is characterized in that the noble metal impregnating solution is
It is characterized by containing a noble metal in a ratio of 0.03 to 3%.

In still another preferred embodiment of the method for producing an exhaust gas purifying catalyst of the present invention, the slurry of the noble metal-impregnated carrier material has a viscosity of 0.05 to 1 [Pa · s]. .

[0023]

In the present invention, the undercoat layer made of an inorganic oxide and the catalyst layer are adjacent to each other, and the thickness of the catalyst layer is appropriately adjusted. Therefore, the purification cycle of NOx, HC, and CO is effectively performed, and the purification is uniformly performed over the entire catalyst layer.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the exhaust gas purifying catalyst of the present invention will be described in detail. In this specification, “%” indicates mass percentage unless otherwise specified.

As described above, the exhaust gas purifying catalyst of the present invention has an undercoat layer made of an inorganic oxide and a catalyst layer containing a catalytically active component. Each layer is formed on a monolithic carrier such as a monolith carrier. It is formed by coating an undercoat layer made of alumina and a three-way catalyst component layer in this order.

Here, by providing an undercoat layer made of an inorganic oxide on the monolithic carrier, the inorganic oxide layer was arranged at the corner of the cell of the carrier as shown in FIG. The catalytically active component, which is the catalyst layer coated on the undercoat layer, is locally uneven to the cell angle, the amount of the catalytically active component to be coated on the cell flat portion (cell wall portion) is significantly reduced, Can be prevented from falling off on the carrier, and remarkable improvement in purification performance after durability can be realized.

Further, the catalyst layer has a thickest part (L
max. ) And the thinnest part (Lmin.) Of the cell flat part (Lmax./Lmin.) Is Lmax. / Lmin.
= 1 to 10 and a thickness of 5 to 200 µm supported on the monolithic carrier, which further improves the activity of the catalytically active component after deterioration in heat durability.
When the ratio (Lmax./Lmin.) Between the thickest part and the thinnest part is 1.0 or more, the effect of the undercoat layer is high, and
When it is 0 or less, the effect of the undercoat layer is sufficiently exhibited, and the balance between the heat capacity of the carrier and the catalytic activity is improved. When the thickness of the catalyst layer is 5 μm or more, the catalytically active component disposed on the flat portion of the cell exhibits sufficient activity,
If it is 0 μm or less, the increase or decrease of the purification activity due to the uneven distribution of the catalytically active component is reduced, and the effect of the undercoat layer is increased.

Next, the coating amount and components of each layer will be described. First, alumina is most effective as the inorganic oxide used for the undercoat layer, but zirconia, titania, silica, silica alumina, and the like are also used. In the case of using alumina, alumina having a large specific surface area and high bulk is preferable, and alumina such as γ-alumina is particularly desirable. Specifically, those having an initial surface area of 100 m ² or more per gram are suitable. Further, the coating amount of the undercoat layer is preferably 20 to 50% of the total coating amount including the undercoat layer and the catalyst layer. More preferably, the range is 30 to 40%. This is because the durability of the exhaust gas purifying catalyst is improved and the purifying performance and the light-off performance at the time of cold start are easily maximized. Typically, it is desirable that the coating amount of alumina is 30 to 120 g / L.

Further, in the exhaust gas purifying catalyst of the present invention,
The total coating amount of the catalyst layer is preferably from 100 to 350 g / L, and more preferably from 150 to 250 g / L. The larger the total coating amount, the better in terms of catalyst activity and catalyst life, but if the coating amount is too large, the reaction gas will be poorly diffused inside the catalyst layer and will not be able to sufficiently contact the catalytically active component. In addition, the effect of increasing the amount of activity may be saturated, and the resistance to passage of exhaust gas may be increased.

Furthermore, it is preferable to use platinum (Pt) and / or rhodium (Rh) as a catalyst active component in the catalyst layer which is a catalyst component supporting layer. At this time, the content of the noble metal as the active species, that is, the content of Pt and Rh is 0.1 to 2.5 g and Rh is 0.0 to 1 g per 1 L of the catalyst.
It is preferably in the range of 5 to 0.5 g. Outside this range, low-temperature activity and catalytic performance may not be sufficiently exhibited,
In some cases, the catalyst activity is saturated and the performance cannot be improved in proportion to the content, resulting in poor economy.

Further, the concentration of Pt and Rh carried on the carrier in the catalyst layer is preferably 0.1 to 0.1 from the viewpoint of improving purification performance.
It is desirable to be 3.0%. Pt below 0.1%
Has a reduced thermal durability, and if it exceeds 3.0%, the concentration is high due to the high concentration.
This is not effective because the t particles may be too coarse.

Here, the above-mentioned catalyst layer has a first catalyst layer containing only Pt as a catalytically active component, and a second catalyst layer containing Pt and Rh as a catalytically active component, as shown in FIG. The first catalyst layer and the second catalyst layer may be coated on the undercoat layer in this order. Thereby, the purification performance at the time of A / F fluctuation is easily exhibited.

The amount of the noble metal contained in the second catalyst layer is
It is preferable that the amount is larger than the amount of the noble metal contained in the first catalyst layer. At this time, heat is easily transmitted from the exhaust gas to the second catalyst layer, and the purification activity is easily exhibited at a lower temperature.

Further, Pt contained in the first catalyst layer is:
A support material containing alumina as a main component and a support material containing cerium oxide as a main component are supported, and 30 to 80% of the total Pt amount of the first catalyst layer is supported on the support material containing alumina as a main component. Is preferred. In this case, the oxidation activity and the lean lean NOx activity of Pt can be effectively functioned, which is effective. Further, the cerium oxide is in the following composition formula _{Ce a Nd b [X] c} O d ( in the composition formula, d = 2.0, a = 0.5~
0.99, b = 0.005-0.5, c = 0.0-0.
3, a + b + c = 1, X represents zirconium or lanthanum. However, a, b and c vary so as to satisfy d = 2.0 according to the valence of X. It is preferable that the relationship represented by the formula (1) is satisfied. That is, ceria-supported P is contained in the catalyst component layer.
By containing t, sintering of alumina-supported Pt can be further suppressed. At this time, by containing a component mainly composed of neodymium in ceria, the thermal stability is improved, and the sintering suppressing action can be further improved. If the above composition formula is not satisfied, sintering of Pt proceeds, and Pt sinters.
In some cases, the oxidizing activity and the lean lean NOx activity cannot be effectively expressed. Further, the cerium oxide is in the following composition formula _{Ce a Pr f [X] g} O h ( in the composition formula, d = 2.0, a = 0.5~
0.99, f = 0.005-0.5, g = 0.0-0.
3, a + f + g = 1, and X represents zirconium or lanthanum. However, a, f, and g vary so as to satisfy d = 2.0 according to the valence of X. It is preferable that the relationship represented by the formula (1) is satisfied. That is, ceria-supported P is contained in the catalyst component layer.
By containing t, sintering of alumina-supported Pt can be further suppressed. At this time, by containing a component mainly composed of praseodymium in ceria, the oxygen releasing ability in a low temperature range is improved, and a sintering suppressing effect can be obtained in a wide temperature range. When the above composition formula is not satisfied, sintering of Pt proceeds, and a state may occur in which the oxidation activity of Pt and the NOx activity of light lean cannot be effectively exhibited.

The support material containing alumina as a main component improves heat resistance, suppresses thermal degradation of Pt in the first catalyst layer,
Cerium (Ce), zirconium (Zr) or lanthanum (L)
It is preferable to contain 1 to 10 mol% of the metal according to a) and any combination thereof in terms of metal. When these metals are contained in an amount of 1 to 10 mol%, the BET specific surface area (thermal stability) can be significantly improved. If the amount is less than 1 mol%, the same effect as in the case of using only alumina is not obtained, and if the amount exceeds 10 mol%, the effect is saturated and the economy tends to be poor. Further, it is preferable that the crystallite diameter of the cerium is 100 ° or less from the viewpoint of sufficient O ₂ storage capability. That is, when ceria is highly dispersed on alumina, the contact area between ceria and Pt increases, and the change in the oxidation-reduction state of Pt due to the change in the exhaust gas atmosphere can be reduced, so that sintering of Pt is suppressed. Even after the deterioration, a sufficient purification performance can be obtained with a small amount of support. Further, the angle is more preferably 50 ° or less, and the above-mentioned effect can be further improved. In addition, 1
When the temperature is less than 00 °, the ceria's O ₂ releasing ability is further improved,
Further, the interaction between Pt and ceria is also improved, and the above-described effect is more easily exhibited. Here, “crystallite” refers to an aggregate in which a single crystal form has the same directionality, and the crystallite diameter is obtained by the following Scherrer's formula (1) using the half-width of the XRD peak and θ. It is something that can be done. (Crystallite diameter) = λ / ((half width × 3.14 / 180) × COSθ) (1) An example of an X-ray diffraction pattern of cerium-containing alumina having a crystallite diameter of 100 ° or less of CeO ₂ is shown in FIGS. 4 and Tables 1-3
Shown in If the crystallite diameter of CeO ₂ is 100 ° or less,
In particular, the present invention is not limited to this X-ray diffraction pattern.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

The support material containing ceria as a main component improves the heat resistance, suppresses the thermal degradation of Pt in the first catalyst layer, and maintains the catalytic activity with respect to the change in atmosphere. Therefore, zirconium (Zr), neodymium (Nd), Praseodymium (P
It is preferable to contain 1 to 40 mol% of two or more kinds of metals related to r) or lanthanum (La) and any combination thereof in terms of metal. By containing these metals in an amount of 1 to 40 mol%, it becomes easy to remarkably improve the original oxygen storage / release capacity and the BET specific surface area of CeO ₂ . If the content is less than 1 mol%, the same effect as in the case of using CeO ₂ alone is not obtained, and if the content is more than 40 mol%, the effect is easily saturated or reduced.

Further, it is preferable that the Pt of the second catalyst layer is contained at a ratio of 20 to 70% with respect to the Pt amount in all the catalyst layers. Thus, thermal degradation (sintering) of Pt can be suppressed, and the CO and HC oxidation activities of Pt can be effectively functioned in a well-balanced manner.

The element ratio of Pt and Rh contained in the second catalyst layer preferably satisfies the relationship represented by the following formula: Pt / Rh ≦ 1.0. In this case, the atmosphere becomes rich or lean. More effective against fluctuations
And Rh can act. In addition, Pt / Rh
Exceeds 1.0, it is difficult to obtain a sufficient Rh purification effect.

Further, the second catalyst layer contains a carrier mainly composed of alumina and a carrier mainly composed of zirconium oxide, and the carrier mainly composed of alumina is made of cerium (Ce). , Zirconium (Zr) or lanthanum (La), and a metal obtained by arbitrarily combining them in an amount of 1 to 10 mol% in terms of metal, and the support material containing zirconia as a main component is neodymium (Nd), yttrium (Y ), Cerium (Ce) or lanthanum (La), and a metal in which these are arbitrarily combined, preferably in an amount of 1 to 30 mol% in terms of metal. This improves the heat resistance of the catalyst,
The NOx reduction performance of Rh can be effectively functioned. Furthermore, it is preferable that Pt of the second catalyst layer is supported on the above-described support material containing alumina as a main component. Thereby, the thermal durability of Pt is improved, and it becomes easier to effectively contact the exhaust gas component to be purified.

The material constituting the monolithic carrier used in the exhaust gas purifying catalyst of the present invention can be appropriately selected from the materials constituting the known catalyst carrier. For example,
Examples include a honeycomb carrier using a cordierite-based material such as a typical ceramic and a honeycomb carrier using a metal material such as a ferritic stainless steel. When a cordierite carrier is used, it is desirable to use the carrier as a thin walled carrier having a low heat capacity of 100 μm or less in consideration of the expression of purification performance from a low temperature. In addition, the number of cells of the monolithic carrier is preferably 400 to 2,000 cells / square inch. In particular, in consideration of the frequency of contact with the exhaust gas component to be purified, it is more preferably at least 800 cells / square inch.

Next, the method for producing the exhaust gas purifying catalyst of the present invention will be described in detail. In such a production method, when the supporting material is impregnated and supported with a noble metal serving as an active species in an aqueous solution thereof, an organic acid is added to the noble metal salt aqueous solution to obtain the exhaust gas purifying catalyst described above. By employing such a manufacturing method, thermal sintering of the noble metal is suppressed. It is preferable that the organic acid is added in a molar ratio of 0.1 to 10 times the noble metal contained in the noble metal salt aqueous solution. More preferably, it is added in a range of 1 to 5 times. This makes it easier to set a predetermined carrying concentration. Further, as the organic acid, those having a carboxyl group (—COOH) are preferable, and representative examples thereof include acetic acid, oxalic acid, and citric acid. Thereby, it is possible to effectively act on the noble metal salt.

The adhesion to the carrier can be enhanced by appropriately adding activated alumina, boehmite alumina, alumina sol, or any combination thereof to the undercoat layer or the catalyst layer. Further, a water-soluble compound such as a dinitroaminate, chloride and nitrate (raw material noble metal compound) is optionally used to form P on the catalyst layer.
t and Rh are included. Furthermore, as a supporting method on the carrier, the material constituting each layer is pulverized into a slurry,
It is preferable to apply it to a catalyst carrier having a honeycomb shape or the like.

Next, another method for producing the exhaust gas purifying catalyst of the present invention will be described in detail. In such a production method, when the noble metal serving as an active species is impregnated and supported on the supporting material by an aqueous solution thereof, the supporting concentration is set to 0.1 to 3.0% to obtain the exhaust gas purifying catalyst. By adopting such a manufacturing method, the noble metal can be efficiently and highly dispersed by efficiently utilizing the adsorption characteristics of the surface of the supporting material, and an exhaust gas purifying catalyst having high purification performance can be obtained. That is, when the content is 0.1% or more, the thermal durability of Pt is particularly improved, and when the content is 3.0% or less, Pt particles are not coarsened and the dispersibility of the noble metal is effectively maintained. It is. Further, the content is preferably in the range of 0.1 to 2.0%, and when manufactured in this range, a noble metal-supporting powder with little variation can be produced. Here, the “supporting material” refers to an active powder such as alumina, cerium oxide, or zirconia oxide, or ceria (Ce), zirconium (Zr), or lanthanum (La) And the like containing a metal such as The “supporting concentration” refers to the ratio (%) of the noble metal in the noble metal-supported powder obtained by impregnating the noble metal into the supporting material.

In the above-mentioned method of supporting the noble metal (Pt or Rh) as the active species on the support material in the catalyst layer, the aqueous solution containing the noble metal as the active species is brought into contact with the support material to carry out impregnation. At this time, among such impregnation support methods,
In particular, it is desirable to employ an immersion impregnation method in which the support material is immersed and impregnated in a solution containing a noble metal. This is because when the support material is sprayed with the noble metal impregnating solution, the noble metal impregnating solution penetrates due to the water absorption of the support material, but the amount of solvent that does not exceed the range of the water absorption of the support material is sprayed on the support material. Therefore, drying on the particle surface is fast, and the pores are easily blocked. For this reason, it is difficult to uniformly impregnate the inside of the support material, and a difference in the noble metal concentration is likely to occur between the vicinity of the surface of the support material particles and the inside. On the other hand, in the case of the immersion impregnation method, the noble metal impregnating solution can easily penetrate into the inside of the carrier material particles, and the noble metal raw material that has penetrated into the carrier material can be uniformly impregnated near and inside the surface of the carrier material particles. It is. Typically, when a supporting material having a specific surface area of 50 m ² / g or more is used, if the supporting concentration is 3% or less, the amount of noble metal adsorbed on the supporting material does not reach a saturated state. It is possible to highly disperse the noble metal adsorbed near and inside the surface. That is, as the loading concentration decreases, it is possible to produce a noble metal-supported powder having more excellent dispersibility. However, if the loading concentration is less than 0.1%, the ratio of the noble metal left in the pores closed due to the durability increases with respect to the noble metal used, so that an effective effect may not be obtained. %, It is considered that the amount of the noble metal adsorbed on the supporting material reaches a saturated state. In this case, the excess noble metal component moves to the vicinity of the surface of the supporting material particles during drying, so that the amount of the noble metal becomes high near the particle surface. The concentration is carried. Therefore, there is a possibility that it is difficult to obtain a performance improvement corresponding to the impregnation amount. In particular, the difference in the dispersibility of the noble metal-supported powder caused by the difference in the impregnation method is as follows when the total coating amount of the catalyst layer of the exhaust gas purifying catalyst is 100 to 350 g / L, which is a preferable amount. When the noble metal content per liter of the catalyst is in the range of 0.15 to 3.0 g, it is easy to effectively develop. The noble metal content per liter of the catalyst was 0.15.
If the amount is less than g, the reaction gas cannot be brought into sufficient contact with the catalytically active component, and the amount of the noble metal is insufficient, so that the catalytic performance cannot be sufficiently exhibited and is not effective. 3.0 g
When the content of the noble metal exceeds 0.1, the effect of improving the performance with respect to the increased amount of the noble metal is large, and the effect of improving the dispersibility of the noble metal-supported powder by the impregnation method may not be sufficiently exhibited.

In the immersion impregnation loading method, it is preferable that the weight ratio of the noble metal impregnation solution to the loading material is 1: 1 to 3: 1. By setting the content in this range, impregnation of the support material from the noble metal impregnating solution is performed efficiently.
Therefore, the movement of the noble metal to the surface of the supporting material particles generated during drying, that is, the segregation of the noble metal near the surface of the supporting material particles can be reduced. In addition, the above-mentioned "noble metal impregnation solution"
A solution prepared by adding a solvent such as water to a noble metal impregnated solution in order to obtain a slurry that does not generate appropriate fluidity or separation when the supporting material is charged. Inorganic acid salts, carbonates,
An ammonium salt, a halogen salt, an oxide salt, a sodium salt, an ammine complex compound, or the like, or a dispersion of a compound according to any combination thereof can be used.
In particular, it is desirable to use a water-soluble salt from the viewpoint of improving the dispersibility of the noble metal, in other words, from the viewpoint of improving the catalyst performance.

The noble metal impregnating solution is 0.03-
It is preferable to include a noble metal in a ratio of 3%, and by impregnating with a noble metal-containing aqueous solution in this range, the noble metal precipitates near the surface of the noble metal particles when the noble metal is impregnated into the noble metal impregnating solution. It is possible to suppress the dispersion of the dispersibility due to pore closing (high concentration) and non-reach to the inside of the particles (low concentration). Further, by using a solution containing a noble metal raw material, the pH can be adjusted by adding an acid or a base to the solution. By adjusting the pH, higher dispersion loading may be achieved. In order to suppress thermal sintering of the noble metal, an organic acid can be added to the noble metal impregnating solution in advance in the step of impregnating and supporting each supporting material with a noble metal salt aqueous solution as an active species. The amount of the organic acid to be added is 0.1 to 10 in a molar ratio with respect to the noble metal contained in the noble metal salt aqueous solution in order to set a predetermined supported concentration.
It is desirable to make it within the range of twice, more preferably 1 to
The amount is preferably 5 times. Further, as the organic acid added to effectively act on the noble metal salt, one having a carboxyl group (—COOH) is desirable, and examples thereof include acetic acid, oxalic acid, and citric acid.

In the immersion step, the loading of the supporting material into the noble metal impregnation solution is preferably performed while stirring the noble metal impregnation solution with a stirring rotor at 10 rpm to 100 rpm, and more preferably 20 rpm to 40 rpm.
It is good to carry out while stirring at m. Further, it is desirable that stirring is continued for 1 minute to 60 minutes after the loading of the support material into the noble metal impregnation solution. If the time is less than 1 minute, the adsorption of the noble metal onto the support material cannot be completely saturated, and there is a possibility that the powder performance varies. In addition, for 60 minutes or more, BET 50 m ² / g
This is a time sufficient for adsorbing no more than 3% of the noble metal onto the above-mentioned supporting material, and it is difficult to obtain a performance improvement corresponding to the impregnation time, and the economy is likely to be poor. Further, the viscosity of the noble metal-impregnated support material slurry after immersion and impregnation is 0.05 to 1
[Pa · s] is preferable. Thereby, separation of the supporting substrate in the slurry and impregnation failure of the noble metal impregnating solution are less likely to occur, and the noble metal can be stably dispersed. The “noble metal-impregnated support material slurry” refers to a mixture in which a support material is charged into a noble metal-impregnated solution and mixed.

Further, after the immersion and impregnation, the drying step includes heat resistance,
Place the noble metal impregnated support material slurry on the corrosion-resistant tray at a depth of 1
It is desirable to adjust so as to be 0 mm to 100 mm. If the thickness is less than 10 mm, the amount of drying cannot be increased, and the economy tends to be poor. In addition, if it exceeds 100 mm, the components in the noble metal-impregnated support material slurry may be separated,
It is not desirable in terms of the stability of the powder performance, and the dry surface with respect to the dry amount is small, so that the drying time is prolonged and the economy is likely to be poor. The drying temperature of the noble metal-impregnated support material slurry is preferably from 150 ° C to 200 ° C. 150
If the temperature is lower than 0 ° C, the drying time is prolonged, resulting in poor economy. If the temperature is higher than 200 ° C, there is a possibility that the noble metal raw material compound impregnated during drying or the impregnated support material thereof may be decomposed or burned.

[0052]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 An activated alumina powder (BET specific surface area: 200 m ² / g, average particle size: 6 μm) and an aqueous nitric acid solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. Attached to cordierite monolithic carrier (1.0 L, 900 cells / square inch)
The excess slurry in the cell is removed by air flow and dried,
It was baked at 00 ° C. for 1 hour. Weight 75 as the first coat amount
The carrier A coated with the g / L-carrier was obtained.

To a dinitrodiammine platinum aqueous solution, citric acid was added in an amount twice as much as platinum atom ratio, and the mixture was stirred for 1 hour. The platinum aqueous solution containing citric acid was impregnated with activated alumina powder to which 2 mol% of Ce was added. After drying for an hour,
By baking at 400 ° C. for 1 hour, a Pt-supported Ce-alumina powder (powder A) was obtained. The Pt concentration of this powder is 0.55%
Met.

A solution similar to the citric acid-added platinum aqueous solution was mixed with 1 mol% of lanthanum (2% in terms of La ₂ O ₃ ), 10 mol% of praseodymium, and 22 mol% of zirconium.
(17% in terms of ZrO ₂ ), dried at 150 ° C. for 12 hours, and then dried at 400 ° C. for 1 hour.
After firing for a time, a Pt-supported LaZrPr-cerium oxide powder (powder B) was obtained. The Pt concentration of this powder was 0.37
%Met.

Powder A, powder B, boehmite alumina, and an aqueous nitric acid solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was further attached to the carrier A, and the excess slurry in the cell was removed by an air stream, dried, and fired at 400 ° C. for 1 hour. Catalyst A having a coat weight of 85 g / L-carrier was obtained as a second coat layer. Second
The platinum carrying amount of the coat layer was 0.38 g / L. At this time, the Pt distribution ratio to alumina / ceria was 62/38.
Met.

An activated rhodium nitrate aqueous solution containing 2 mol% of Zr was impregnated with activated alumina, dried at 150 ° C. for 12 hours, and calcined at 400 ° C. for 1 hour to obtain Rh-supported Zr-alumina powder (powder C). Was. The Rh concentration of this powder is 0.1.
5%. In addition, Pt-supported C
e-alumina powder (powder A2) was obtained. Pt of this powder
The concentration was 1.7%. This powder C, powder A2, and C
e, a zirconium oxide powder containing 20 mol% (24% in terms of CeO ₂ ), boehmite alumina and an aqueous nitric acid solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was further adhered to the catalyst A, excess slurry in the cell was removed by an air stream, dried, and calcined at 400 ° C. for 1 hour. Catalyst B having a coat weight of 60 g / L-carrier was obtained as a third coat layer. At this time,
The Rh support amount of the third coat was 0.18 g / L, and the Pt support amount was 0.15 g / L. Further, the total coating amount of the catalyst B was 220 g / L, and the total noble metal carried amount was 0.71 g / L.

Example 2 Example 1 was repeated except that the coating amount of the first coat layer was changed to 45 g / L in Catalyst B.
The same operation as described above was repeated to obtain an exhaust gas purifying catalyst of this example.

Example 3 The same operation as in Example 1 was repeated, except that the coating amount of the first coat layer was changed to 110 g / L in Catalyst B, to obtain an exhaust gas purifying catalyst of this example. Was.

Example 4 In the catalyst B, the Pt amount of the second coat layer was set to 0.43 g / L, and the Pt amount of the third coat layer
The same operation as in Example 1 was repeated, except that the amount was changed to 0.11 g / L, to obtain an exhaust gas purifying catalyst of this example.

Example 5 In the catalyst B, the Pt amount of the second coat layer was 0.17 g / L, and the Pt amount of the third coat layer was 0.17 g / L.
The same operation as in Example 1 was repeated, except that the amount was changed to 0.38 g / L, to obtain an exhaust gas purifying catalyst of this example.

(Example 6) In Catalyst B, the same operation as in Example 1 was repeated, except that the Pt powder composition of the second coat layer was changed and the Pt distribution (alumina / ceria) was changed to 80/20. Thus, an exhaust gas purifying catalyst of this example was obtained.

(Example 7) In Catalyst B, the same operation as in Example 1 was repeated except that the blending of Pt powder in the second coat layer was changed and the Pt distribution (alumina / ceria) was changed to 50/50. Thus, an exhaust gas purifying catalyst of this example was obtained.

(Example 8) In Catalyst B, the same operation as in Example 1 was repeated, except that the amount of citric acid added at the time of preparing the Pt powder was changed to 0.5 times the molar number of Pt. Thus, an exhaust gas purifying catalyst of this example was obtained.

Example 9 The same operation as in Example 1 was repeated, except that the citrate added in the preparation of the Pt powder in the catalyst B was changed to oxalic acid. Obtained.

Example 10 In the catalyst B, except that the citric acid added at the time of preparing the Pt powder was changed to acetic acid,
The same operation as in Example 1 was repeated to obtain an exhaust gas purifying catalyst of this example.

(Example 11) In the catalyst B, the Pt amount of the second coat layer was set to 0.24 g / L, and the Pt amount of the third coat layer was changed to 0.24 g / L.
The same operation as in Example 1 was repeated, except that the t amount was changed to 0.24 g / L and the Rh amount was changed to 0.24 g / L, to obtain an exhaust gas purifying catalyst of this example.

(Example 12) The Pt amount of the second coat layer was 0.1 g / L, and the Pt amount of the third coat layer was 0.25 g.
The same operation as in Example 1 was repeated, except that the / L and Rh amounts were changed to 0.35 g / L, to obtain an exhaust gas purifying catalyst of this example.

(Comparative Example 1) In Catalyst B, the same procedure as in Example 1 was carried out except that the first coat layer was not provided, alumina was added to the second coat layer, and the amount of the second coat layer was changed to 155 g / L.
The same operation as described above was repeated to obtain an exhaust gas purifying catalyst of this example.

Comparative Example 2 Example 1 was repeated except that the coating amount of the first coat layer was changed to 25 g / L in Catalyst B.
The same operation as described above was repeated to obtain an exhaust gas purifying catalyst of this example.

Comparative Example 3 The same operation as in Example 1 was repeated, except that the coating amount of the first coat layer was changed to 150 g / L in Catalyst B, to obtain an exhaust gas purifying catalyst of this example. Was.

(Comparative Example 4) In the catalyst B, the same operation as in Example 1 was repeated, except that the γ-alumina of the first coat layer was changed to silica (SiO ₂ ). A catalyst was obtained.

(Comparative Example 5) In the catalyst B, the Pt amount of the second coat layer was set to 0.53 g / L, and the Pt amount was added to the third coat layer.
The same operation as in Example 1 was repeated, except that the structure was changed to a structure containing no t, to obtain an exhaust gas purifying catalyst of this example.

(Comparative Example 6) In the catalyst B, the Pt amount of the second coat layer was set to 0.05 g / L, and the Pt amount of the third coat layer was set to 0.05 g / L.
The same operation as in Example 1 was repeated, except that the amount was changed to 0.48 g / L, to obtain an exhaust gas purifying catalyst of this example.

Comparative Example 7 The same operation as in Example 1 was repeated, except that the Rh amount of the third coat layer in Catalyst B was changed to 0.02 g / L, and the catalyst for purifying exhaust gas of this example was repeated. I got

(Comparative Example 8) In Catalyst B, the same operation as in Example 1 was repeated, except that the blending of Pt powder in the second coat layer was changed and the Pt distribution (alumina / ceria) was changed to 100/0. Thus, an exhaust gas purifying catalyst of this example was obtained.

(Comparative Example 9) In Catalyst B, the same operation as in Example 1 was repeated, except that the blending of Pt powder in the second coat layer was changed and the Pt distribution (alumina / ceria) was changed to 10/90. Thus, an exhaust gas purifying catalyst of this example was obtained.

(Comparative Example 10) Catalyst P was prepared in the same manner as in Example 1 except that the powder was prepared without adding citric acid when preparing Pt powder. Obtained.

(Comparative Example 11) The same procedure as in Example 1 was carried out except that in the catalyst B, a CeO ₂ powder was used instead of the Pt-supported Ce-cerium oxide powder (powder B) used in the second coat layer. The operation was repeated to obtain an exhaust gas purifying catalyst of this example.

<Activity Test> The exhaust gas purifying catalysts obtained in the above Examples 1 to 12 and Comparative Examples 1 to 11
Attached to a 2,000 cc engine and aged at 800 ° C. at the catalyst inlet temperature of the exhaust gas, the displacement was 1800 cc.
Drive in 10.15 mode on a vehicle with an engine and
The emissions of C, CO and NOx were measured, and an engine stand temperature rise test (temperature rise rate = 10 ° C./min) was also conducted.

Tables 4 and 5 show the types and characteristics of the coat layers of the exhaust gas purifying catalysts studied in the above Examples 1 to 12 and Comparative Examples 1 to 11. Table 6 summarizes the conversion rate (%) as the HC, CO, and NOx purification performance of the exhaust gas purification catalyst for the 15-mode running test, and the conversion temperature 50% attainment temperature (T50) for the engine platform rising temperature test. Shown.

[0082]

[Table 4]

[0083]

[Table 5]

[0084]

[Table 6]

The average platinum particle diameter after aging of the exhaust gas purifying catalysts studied in Examples 1, 9 and 10, and Comparative Example 9 was measured by TEM observation, and the results are shown in Table 7. Was.

[0086]

[Table 7]

From Table 6, it can be seen that the catalyst of the example has a higher catalytic activity and a lower temperature at which the conversion reaches 50% than the catalyst of the comparative example. Also, from Table 7, it can be seen that the Pt particle diameter of the catalyst of the example was smaller than that of the comparative example, and the catalyst was highly dispersed.

Example 13 Activated alumina powder (BET)
A specific surface area of 200 m ² / g, an average particle size of 6 μm) and an aqueous solution of nitric acid were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. Square inch), the excess slurry in the cell was removed with an air stream, dried, and fired at 400 ° C. for 1 hour. Carrier-1 coated with a weight of 70 g / L as the first coat amount was obtained. FIG.
Alumina powder containing 3 mol% of Ce (alumina 1) (Al 97 mol%, CeO ₂ crystallite diameter 80 °, B
ET specific surface area of 180 m ² / g) was impregnated with an aqueous solution of dinitrodiammine platinum or sprayed with high-speed stirring.
After drying at 50 ° C. for 12 hours, it was baked at 400 ° C. for 1 hour to obtain Pt-supported Ce-alumina powder (powder 1). The Pt concentration of this powder was 0.75%. Similarly,
Dinitrodiammine platinum aqueous solution is lanthanum 1 mol% (L
a ₂ O ₃ , 2%) and zirconium 32 mol%
(25% in terms of ZrO ₂ ) is impregnated or sprayed with high-speed stirring at 150 ° C.
After drying for an hour, it was baked at 400 ° C. for 1 hour to obtain Pt-supported LaZr-cerium oxide powder (powder 2). The Pt concentration of this powder was 0.5%. The powder 1, the powder 2, the boehmite alumina, and the nitric acid aqueous solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was further adhered to the carrier-1, and the excess slurry in the cell was removed by an air flow, dried, and fired at 400 ° C. for 1 hour. 80g coat weight as second coat layer
/ L-catalyst-1 was obtained. The platinum carrying amount of the second coat layer was 0.35 g / L. At this time, the distribution ratio of Pt to alumina / ceria was 70/30.

An activated rhodium nitrate aqueous solution was impregnated into activated alumina to which 2 mol% of Zr was added, dried at 150 ° C. for 12 hours, and calcined at 400 ° C. for 1 hour to obtain Rh-supported Zr-alumina powder (powder 3). Was. The Rh concentration of this powder is 0.1.
5%. The powder 3, powder 1, zirconium oxide powder containing 20 mol% of Ce (24% in terms of CeO ₂ ), boehmite alumina, and an aqueous solution of nitric acid are charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. Was. This slurry liquid was further attached to the catalyst-1 obtained above, excess slurry in the cell was removed with an air stream, dried, and calcined at 400 ° C. for 1 hour. As a third coat layer, catalyst-2 having a coat weight of 60 g / L-carrier was obtained. The amount of Rh supported on the third coat was 0.2 g / L, and the amount of Pt supported was 0.05.
g / L. The total coating amount of catalyst-2 was 210 g /
L, the total amount of the noble metal carried was 0.6 g / L.

(Examples 14 to 22 and Comparative Examples 12 to 1)
6) The same operation as in Example 13 was repeated except that alumina powder containing 3 mol% of Ce shown in FIGS. 2 to 4 was used and the first to third coat layer compositions shown in Table 8 were repeated. A catalyst was obtained. In Examples 13 to 22 and Comparative Examples 12 to 16, the L of the alumina undercoat layer
max. / Lmin. = 3/1 to 6/1, thickness is 10
The distribution ratio of Pt of the second coat layer to alumina / ceria was set to 62/32.

<Method for Preparing Sample for XRD Measurement> A powder sample was prepared by using an agate mortar and having a particle size of several hundred μm.
Crushed to the following. The pulverized sample was packed in a glass plate sample plate (0.5 mm deep) for XRD measurement, and the measurement surface was made flat.

<X-ray Diffraction Measurement Method> Apparatus: MACScience's wide-angle X-ray diffractometer (M
XPVAHF) X-ray source: CuKα, wavelength: 1.54056 °, tube current:
300 mA, tube voltage: 40 kV, data measurement range: 2θ
= 5-90 deg. , Scan width: 2θ / θ, scan speed: 4 deg. / Min. , Sampling interval: 0.
02 deg. Divergence slit: 1.0 deg. , Scattering slit: 1.0 deg. , Emission slit: 0.3mm

<Activity test> The exhaust gas purifying catalysts obtained in Examples 13 to 22 and Comparative Examples 12 to 16
Installed on a 000cc engine, catalyst inlet temperature of exhaust gas 8
After aging at 00 ° C, the vehicle with a displacement of 1800 cc engine was driven in 10.15 mode, and HC,
CO and NOx emissions were measured. FIG. 5 shows a schematic diagram of the test apparatus.

Table 8 shows the types and characteristics of the coat layers of the exhaust gas purifying catalysts studied in the above Examples and Comparative Examples. The results of the catalyst activity evaluation are shown in Table 10. The conversion rates (%) of the catalysts as HC, CO and NOx purification performance are summarized in Table 9 respectively.

[0095]

[Table 8]

[0096]

[Table 9]

From Table 9, it can be seen that, compared to the catalyst of the comparative example, the catalyst of the example exhibited a sufficient effect of suppressing Pt sintering by cerium oxide, so that the catalyst activity was high and 10.1
It can be seen that the five-mode conversion is high.

Example 23 Activated alumina powder (BET)
A specific surface area of 200 m ² / g, an average particle size of 6 μm) and an aqueous nitric acid solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry, and this slurry liquid was applied to a cordierite-based monolithic carrier (1.0 L, 900 cells). / Square inch), the excess slurry in the cell was removed by air flow, dried, and fired at 400 ° C. for 1 hour. As the first coat amount,
Carrier A coated with a weight of 70 g / L carrier was obtained. The aqueous solution of dinitrodiamine platinum was stirred with a stirring rotor at a speed of 30 rpm, and activated alumina powder to which 2 mol% of Ce was added was added thereto, followed by continuous stirring with a stirring rotor for 60 minutes, and immersion impregnation. After the impregnation, the activated alumina impregnated with the aqueous solution of dinitrodiamine platinum was put into the tray so as to have a depth of 30 mm, and dried at 150 ° C. for 12 hours.
C. for 1 hour to obtain Pt-supported Ce-alumina powder (powder A). The Pt concentration of this powder was 0.55%. The same solution as the above-mentioned platinum aqueous solution was stirred for 30
The mixture was stirred at a speed of 1 rpm, and 1 mol% of lanthanum (La ₂ O ₃
Cerium oxide powder containing 10% by mole of praseodymium and 22% by mole of zirconium (17% in terms of ZrO ₂ ), continuously stirred for 60 minutes with a stirring rotor, and immersed and impregnated. . After drying at 150 ° C. for 12 hours, it is baked at 400 ° C. for 1 hour to obtain Pt-supported LaZrP.
An r-cerium oxide powder (powder B) was obtained. The Pt concentration of this powder was 0.37%. Powder A, powder B, boehmite alumina and an aqueous solution of nitric acid were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was further adhered to the carrier A, and the excess slurry in the cell was removed by an air stream, and the slurry was fired at 400 ° C. for 1 hour. Second
Catalyst A having a coat weight of 85 g / L-carrier was obtained as a coat layer. The platinum carrying amount of the second coat layer was 0.38 g / L. An aqueous solution of rhodium nitrate is stirred at 30 rpm with a rotor.
Activated alumina to which Zr was added at 2 mol% was added, and the mixture was continuously stirred with a stirring rotor for 60 minutes.
Immersion impregnation. After the impregnation, activated alumina impregnated with a rhodium nitrate aqueous solution was poured into a SUS tray to a depth of 30 mm, dried at 150 ° C. for 12 hours, and then dried at 400 ° C. for 1 hour.
After firing for a time, Rh-supported Zr-alumina powder (powder C)
I got The Rh concentration of this powder was 0.5%. Further, Pt-supported Ce-alumina powder (powder A2) was obtained according to the method for producing powder A. The Pt concentration of this powder was 1.7%. The powder C and the powder A2 were mixed with Ce 20 mol% (C
A zirconium oxide powder containing 24% in terms of eO ₂ ), boehmite alumina and an aqueous nitric acid solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was further adhered to the above-mentioned catalyst A, excess slurry in the cell was removed by an air stream, dried, and calcined at 400 ° C. for 1 hour. 60 g / L coat weight as third coat layer
-The catalyst B of the support was obtained. At this time, the Rh amount of the third coat was 0.18 g / L, and the Pt amount was 0.15 g / L.
Met. The total coating amount of the catalyst B was 220 g /
L, the total amount of the noble metal carried was 0.71 g / L.

Example 24 In Example 23, except that the Pt concentration of the powder A was changed to 0.2% in the catalyst A, and the Pt concentration of the powder A2 was changed to 2.5% in the catalyst B.
The same operation as described above was repeated to obtain an exhaust gas purifying catalyst of this example.

(Example 25) In the catalyst A, the Pt concentration of the powder A was 0.2%, and in the catalyst B, the Rh concentration of the powder C was 1.0%, and the Pt concentration of the powder A2 was 2.
The same operation as in Example 23 was repeated, except that the catalyst was changed to 0%, to obtain an exhaust gas purifying catalyst of this example.

(Example 26) In the catalyst A, the coating amount of the second coat layer was set to 120 g / L, and
The concentration was set to 0.85%. In the catalyst B, the coating amount of the third coating layer was set to 40 g / L.
The same operation as in Example 23 was repeated, except that the t concentration was changed to 1.0%, to obtain an exhaust gas purifying catalyst of this example.

(Comparative Example 17) Except that the method of impregnating each noble metal impregnating solution into a carrier material was changed to a spray impregnation method,
The same operation as in Example 23 was repeated to obtain an exhaust gas purifying catalyst of this example.

Comparative Example 18 The same operation as in Example 24 was repeated, except that the method of impregnating the support material with each noble metal impregnating solution was changed to the spray impregnation method, to obtain the exhaust gas purifying catalyst of this example. Was.

Comparative Example 19 The same operation as in Example 25 was repeated, except that the method of impregnating each noble metal impregnating solution into the carrier material was changed to the spray impregnation method, to obtain the exhaust gas purifying catalyst of this example. Was.

Comparative Example 20 Example 26 was repeated except that the Pt concentration of the powder A was changed to 0.05% in the catalyst A, and the Pt concentration of the powder A2 was changed to 4.0% in the catalyst B. The same operation as described above was repeated to obtain an exhaust gas purifying catalyst of this example.

<Activity Test> The exhaust gas purifying catalysts obtained in the above Examples 23 to 26 and Comparative Examples 17 to 20 were mounted on an engine having a displacement of 3000 CC, and aged at an exhaust gas catalyst inlet temperature of 800 ° C. Later, displacement 1800
Driving in 10.15 mode with cc engine mounted vehicle,
HC, CO, and NOx emissions were measured, and an engine stand temperature rise test (temperature rise rate = 10 ° C./min) was also conducted.

The above Examples 23 to 26 and Comparative Examples 17 to
Table 10 shows the types and characteristics of the coat layers of the exhaust gas purifying catalyst studied in Table 20.
H of exhaust gas purifying catalyst for 0.15 mode running test
Conversion rates (%) as C, CO and NOx purification performance,
Table 11 shows the temperatures at which the conversion reaches 50% (T50) for the engine stand temperature rise test.

[0108]

[Table 10]

[0109]

[Table 11]

From Table 11, it can be seen that, compared to the catalyst of the comparative example, the catalyst of the example has a more excellent dispersion state of the supported noble metal and is less susceptible to deterioration at high temperature durability.
It can be seen that the mode conversion is high and the temperature at which the conversion reaches 50% is low.

Although the present invention has been described in detail with reference to preferred embodiments, the present invention is not limited to these embodiments.
Various modifications are possible within the scope of the present invention.

[0112]

As described above, according to the present invention, an inorganic oxide layer is provided on a carrier supporting a catalyst component,
On top of this, a catalyst layer containing a catalytically active component is provided, and the coverage of each layer and the ratio of the layer thicknesses are set in a well-balanced manner. By improving the activity, since the above problem can be solved, even under high temperature conditions,
Sintering of the noble metal, which is an active species, reduction of the specific surface area of the material carrying the noble metal, etc. can be suppressed, and even when the amount of the noble metal used is reduced compared to the conventional case, a wide range of A / F fluctuations during running the vehicle NOx, HC and C below
An exhaust gas purifying catalyst having a satisfactory level of O purification performance and a method for producing the same can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a washcoat layer structure of an exhaust gas purifying catalyst of the present invention.

FIG. 2 is a graph showing an example of an X-ray diffraction pattern of cerium-containing alumina powder 1.

FIG. 3 is a graph showing another example of the X-ray diffraction pattern of the cerium-containing alumina powder 2.

FIG. 4 is a graph showing still another example of the X-ray diffraction pattern of the cerium-containing alumina powder 3;

FIG. 5 is a schematic diagram showing a test apparatus.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/10 B01D 53/36 104A 3/28 301 B01J 23/56 ZAB (72) Inventor Junji Ito Kanagawa Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama-shi (72) Inventor Mitsuhiro Onuma 2nd Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Nissan Motor Co., Ltd. 3G091 AB03 BA14 BA15 BA19 BA39 GA06 GB01X GB04X GB05W GB06W GB10X GB16X GB19X 4D048 AA06 AA13 AA18 AB05 BA03X BA10X BA18X BA19X BA30X BA33X BA41X BA42X BB02 BB16 DA02 DA08 4G069 AA02 AA08 BA01A BA01B BA05A BA05B BA13A BA13B BA21C BB02A BB02B BB06A BB06B BC40A BC42A BC42B BC43A BC43B BC44A BC44B BC71A BC71B BC75A BC75B BE08C CA02 CA03 CA09 EA19 EB12X EB12Y EC25 EC28 EE06 FA02 FA03 FB14 FB15 FB16 FC04 FC08

Claims (28)

[Claims] 1. An exhaust gas purifying catalyst comprising a carrier having an integral structure having a polygonal cell cross section and a catalyst layer coated thereon via an undercoat layer made of an inorganic oxide. 2. The exhaust gas purifying catalyst according to claim 1, wherein said inorganic oxide is alumina. 3. The catalyst layer of claim 1, wherein the catalytically active component of the catalyst layer is platinum and / or platinum.
3. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is rhodium. 4. In the catalyst layer, the ratio (Lmax./Lmin.) Between the thickest part (Lmax.) Of the cell angle and the thinnest part (Lmin.) Of the flat part of the cell is in the range of 1 to 10. The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the catalyst has a thickness of 5 to 200 µm. 5. The coating amount of the undercoat layer is 20 to 50% of the total coating amount including the undercoat layer and the catalyst layer.
4. The exhaust gas purifying catalyst according to any one of the items 4 to 5. 6. The catalyst layer has a total coating amount of 100 to 350.
The exhaust gas purifying catalyst according to any one of claims 1 to 5, wherein the catalyst is g / L. 7. The method according to claim 1, wherein the catalyst layer comprises:
0.1 to 2.5 g of platinum, 0.05 to 0.5 of rhodium
The exhaust gas purifying catalyst according to any one of claims 1 to 6, wherein g is contained. 8. The catalyst layer according to claim 1, wherein the first catalyst layer contains only platinum as a catalytically active component, and the second catalyst layer contains platinum and rhodium as catalytically active components. The exhaust gas purifying catalyst according to any one of Items 1 to 7. 9. The platinum of the first catalyst layer is supported on a carrier mainly composed of alumina and a carrier mainly composed of cerium oxide, and the total platinum amount of the first catalyst layer is 30 to 30%. 80
The exhaust gas purifying catalyst according to claim 8, wherein% of the catalyst is supported on the supporting material containing alumina as a main component. 10. The support material containing alumina as a main component is at least one metal selected from the group consisting of cerium, zirconium and lanthanum in a metal conversion of 1-10.
The carrier material containing ceria as a main component contains at least two metals selected from the group consisting of zirconium, neodymium, praseodymium and lanthanum in an amount of 1 to 40 mol% in terms of metal.
The exhaust gas purifying catalyst according to claim 9, wherein the catalyst is contained. 11. The method according to claim 8, wherein the platinum in the second catalyst layer is contained in a proportion of 20 to 70% with respect to the amount of platinum in all the catalyst layers. The exhaust gas purifying catalyst according to claim 1. 12. The element according to claim 8, wherein the content ratio of platinum and rhodium in the second catalyst layer satisfies a relationship represented by the following formula: Pt / Rh ≦ 1.0.
Item 2. The exhaust gas purifying catalyst according to any one of Items 1 to 4. 13. The second catalyst layer includes a carrier mainly composed of alumina and a carrier mainly composed of zirconium oxide, and the carrier mainly composed of alumina contains cerium, zirconium and The support material containing at least one metal selected from the group consisting of lanthanum in an amount of 1 to 10 mol% in terms of metal and containing zirconia as a main component is selected from the group consisting of neodymium, yttrium, cerium and lanthanum. 1 to 30 mol% of at least one metal in terms of metal
13. Any one of claims 8 to 12, characterized in that it contains
An exhaust gas purifying catalyst according to any one of the first to third aspects. 14. The exhaust gas purifying catalyst according to claim 13, wherein the platinum of the second catalyst layer is carried on the carrier containing alumina as a main component. 15. The exhaust gas according to claim 8, wherein the amount of the noble metal contained in the second catalyst layer is larger than the amount of the noble metal contained in the first catalyst layer. Purification catalyst. 16. The integrated structure type carrier has a cell number of 400.
The exhaust gas purifying catalyst according to any one of claims 1 to 15, wherein the catalyst has a capacity of 2000 cells / square inch. 17. The exhaust gas purifying catalyst according to claim 10, wherein a crystallite diameter of the cerium is 100 ° or less. 18. The method according to claim 10, wherein the cerium has a crystallite diameter of 50 ° or less.
An exhaust gas purifying catalyst according to any one of the first to third aspects. 19. The cerium oxide is in the following composition formula _{Ce a Nd b [X] c} O d ( in the composition formula, d = 2.0, a = 0.5~
0.99, b = 0.005-0.5, c = 0.0-0.
3, a + b + c = 1, X represents zirconium or lanthanum. However, a, b and c vary so as to satisfy d = 2.0 according to the valence of X. The exhaust gas purifying catalyst according to any one of claims 9 to 18, which satisfies a relationship represented by the following formula: 20. The cerium oxide is in the following composition formula _{Ce a Pr f [X] g} O h ( in the composition formula, h = 2.0, a = 0.5~
0.99, f = 0.005-0.5, g = 0.0-0.
3, a + f + g = 1, and X represents zirconium or lanthanum. However, a, f, and g vary so as to satisfy h = 2.0 according to the valence of X. The exhaust gas purifying catalyst according to any one of claims 9 to 18, which satisfies a relationship represented by the following formula: 21. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the supporting material is impregnated and supported with an aqueous solution of a noble metal serving as an active species. And a method for producing an exhaust gas purifying catalyst, comprising adding an organic acid to the aqueous solution of a noble metal salt. 22. The method for producing an exhaust gas purifying catalyst according to claim 21, wherein the organic acid is added in a molar ratio of 0.1 to 10 times the noble metal. 23. The method for producing a catalyst for purifying exhaust gas according to claim 21, wherein the organic acid has a carboxyl group. 24. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the noble metal as an active species is impregnated and supported on the supporting material by an aqueous solution thereof. And a carrier concentration of 0.1 to 3.0%. 25. The method for producing an exhaust gas purifying catalyst according to claim 24, wherein the carrier concentration is 0.1 to 2.0%. 26. The method for producing an exhaust gas purifying catalyst according to claim 24, wherein the weight ratio of the noble metal impregnating solution and the supporting material is 1: 1 to 3: 1. 27. The precious metal impregnating solution preferably contains 0.03 to 3
25. The composition according to claim 24, comprising a noble metal in a ratio of%.
29. The method for producing an exhaust gas purifying catalyst according to any one of items 26 to 26. 28. The exhaust gas purifying catalyst according to any one of claims 24 to 27, wherein the viscosity of the noble metal-impregnated support material slurry is 0.05 to 1 [Pa · s]. Manufacturing method.