JP2000279814A - Exhaust gas purification catalyst and method of using the same - Google Patents

Abstract

(57) Abstract: Exhaust gas capable of improving NOx purification performance in a lean atmosphere, which did not show sufficient activity with a conventional catalyst, and sufficiently exhibiting a function as a three-way catalyst. Provided is a gas purifying catalyst and a method of using the same in which a NOx purifying action can be particularly effectively exerted. SOLUTION: An exhaust gas purifying catalyst comprises at least one noble metal selected from the group consisting of platinum, palladium and rhodium, and the following general formula: And a composite oxide represented by the formula:

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hydrocarbons (H
C), carbon monoxide (CO) and nitrogen oxides (NOx)
The present invention relates to an exhaust gas purifying catalyst for purifying NOx and a method of using the same, and more particularly to an exhaust gas purifying catalyst excellent in NOx purifying performance in an oxygen-excess atmosphere and a method of using the same.

[0002]

2. Description of the Related Art Conventionally, a three-way catalyst for purifying exhaust gas by simultaneously oxidizing CO and HC and reducing NOx has been used as an exhaust gas purifying catalyst for automobiles. As a three-way catalyst, for example, a catalyst in which a supporting layer is formed from γ-alumina on a refractory carrier such as cordierite and a noble metal catalyst such as Pt, Pd, and Rh is supported on the supporting layer is widely known. .

[0003] The purifying performance of such an exhaust gas purifying catalyst greatly varies depending on the air-fuel ratio (A / F) of the engine. That is, on the lean side where the air-fuel ratio is large, that is, the fuel concentration is lean, the amount of oxygen in the exhaust gas increases,
While the oxidation reaction for purifying NOx and HC is active, the reduction reaction for purifying NOx becomes inactive. Conversely, on the rich side where the air-fuel ratio is small, that is, on the rich side where the fuel concentration is high, the amount of oxygen in the exhaust gas decreases, and the oxidation reaction becomes inactive but the reduction reaction becomes active.

On the other hand, in the case of driving in an urban area, the vehicle frequently starts and stops, and the air-fuel ratio frequently changes within a range from near the theoretical value to an over-lean state. In order to meet the demand for fuel economy in such traveling, it is necessary to operate on the lean side, which supplies an air-fuel mixture as much as possible. Therefore, even on the lean side,
There is a demand for the development of a catalyst that can sufficiently purify Ox.

Conventionally, NOx in a lean atmosphere
Various catalysts for improving the purification performance have been proposed. For example, JP-A-5-168860 discloses a catalyst in which lanthanum or the like is supported on platinum (Pt) and lanthanum is used as a NOx absorbent. This is to absorb NOx in a lean atmosphere and to release and purify NOx in a stoichiometric or fuel-rich (rich) atmosphere.

However, the conventional NOx absorption catalyst (for example, a Pt-lanthanum catalyst) has a problem in that, when the vehicle is steadily driven in a lean atmosphere, the amount of absorbed NOx reaches saturation and the absorption action eventually disappears. , NOx purification performance is insufficient, the performance after durability is not sufficient, and NOx cannot be purified under a wide range of operating conditions.

[0007]

SUMMARY OF THE INVENTION Accordingly, claims 1 to 5 are provided.
The object of the invention described is to improve the NOx purification performance in a lean atmosphere, which has not exhibited sufficient activity with a conventional catalyst, and to achieve exhaust gas purification capable of fully exhibiting a function as a three-way catalyst. To provide a catalyst for use.

It is another object of the present invention to provide a method of using an exhaust gas purifying catalyst according to the present invention, in which the NOx purifying action of the exhaust gas purifying catalyst can be exhibited particularly effectively.

[0009]

According to a first aspect of the present invention, there is provided an exhaust gas purifying catalyst comprising at least one noble metal selected from the group consisting of platinum, palladium and rhodium;

(Equation 2) And a composite oxide represented by the formula:

According to a second aspect of the present invention, there is provided the exhaust gas purifying catalyst according to the first aspect, wherein the complex oxide is contained in an amount of 30 to 100 g per liter of the exhaust gas purifying catalyst. .

According to a third aspect of the present invention, there is provided the exhaust gas purifying catalyst according to the first or second aspect, wherein alumina is further added to the exhaust gas purifying catalyst.
It is characterized by containing up to 300 g.

According to a fourth aspect of the present invention, there is provided an exhaust gas purifying catalyst according to any one of the first to third aspects, wherein the exhaust gas purifying catalyst has a structure in which at least two layers are provided on an inorganic carrier. A layer containing a substance is provided as a lower layer, and a layer containing no composite oxide is provided as an upper layer.

According to a fifth aspect of the present invention, there is provided the exhaust gas purifying catalyst according to any one of the first to fourth aspects, wherein an average particle diameter of a material constituting the catalyst layer is 4 μm or less. Features.

Further, in order to exhibit an effective NOx absorption / release cycle of the exhaust gas purifying catalyst of the present invention,
According to a sixth aspect of the present invention, there is provided a method of using the exhaust gas purifying catalyst according to the present invention, wherein the exhaust gas purifying catalyst is used in a lean burn engine vehicle in which the air-fuel efficiency repeatedly ranges from 10 to 50.

According to a seventh aspect of the present invention, there is provided the exhaust gas purifying catalyst according to any one of the first to fifth aspects.
It is characterized in that it is used for a lean burn engine vehicle in which the air-fuel ratio repeatedly ranges from 10 to 14.8 and from 15 to 50.

[0016]

DETAILED DESCRIPTION OF THE INVENTION As the noble metal in the exhaust gas purifying catalyst of the present invention, at least one selected from the group consisting of platinum, palladium and rhodium is used. For example, Pt
And Rh, and various combinations such as Pd and Rh and Pd alone are possible. The content of the noble metal is not particularly limited as long as the NOx absorption capacity and the three-way catalyst performance are sufficiently obtained.
If the amount is less than 0.1 g, sufficient ternary performance cannot be obtained, and
g of the exhaust gas purifying catalyst of the present invention.
0 g is preferred.

Since the catalyst of the present invention also needs to function as a three-way catalyst at the time of stoichiometry, it is preferable that at least a part of the noble metal is supported on a porous body of an inorganic carrier, particularly supported on alumina. Preferably. The alumina used here is preferably one having high heat resistance, and among them, activated alumina having a specific surface area of 50 to 300 m ² / g is preferred. In order to improve the heat resistance of alumina, a rare earth compound such as cerium or lanthanum or an additive such as zirconium may be further added as conventionally used in a three-way catalyst. Their content may be an exhaust gas purifying catalyst 1L per 100 to 300 g, precious metals, from the viewpoint of NO _X oxidative activity required in the NO _X absorption reaction is maximized also particularly Pd.

Further, since the catalyst used in the present invention also needs to function as a three-way catalyst during stoichiometry, additives conventionally used in three-way catalysts may be further added. H to ceria and precious metals
Barium, which alleviates C adsorption poisoning, and zirconia, which contributes to improving the heat resistance of Rh.

The composite oxide contained in the exhaust gas purifying catalyst of the present invention has the following general formula:

(Equation 3) It is represented by

The composite oxide used in the exhaust gas purifying catalyst of the present invention contains a rare earth metal and a transition metal. Lanthanum, praseodymium and neodymium can be suitably used as the rare earth metal, and zirconium can be suitably used as the transition metal.

Such a composite oxide comprises a rare earth metal and
By avoiding compounding with alumina, adsorption of NOx becomes easy even after durability, and N
By utilizing the property of absorbing Ox, NO
It is possible to improve the purification performance of x.

If the value of α is 0.9 or more, it is equivalent to a single oxide of a rare earth metal. If it less than 0.4, decreases the NO adsorption capacity possessed by the rare earth elements, sufficient, since NO _X purification performance can not be obtained, it is preferable that 0.4 <α <0.9. The value of x is the amount of oxygen that satisfies the valence of each atom,
Approximately 0 <δ <4.

At least one selected from the group consisting of lanthanum, praseodymium, and neodymium forms a perovskite-type composite oxide with Zr, so that the composite of these rare earth metals and alumina is avoided, and even after durability, NO _X adsorption becomes easy. In the case where the composite oxide is not formed, for example, when La ₂ O ₃ and ZrO ₂ are mixed, the NO _X adsorption performance is greatly reduced especially after durability.

The composite oxide used in the present invention exhibits the ability to absorb NOx in a lean atmosphere. The absorption mechanism is that NOx in the gas phase is oxidized to NO ₂ on a noble metal, and NO ₃ is further formed on the oxide and absorbed on the composite oxide. Therefore, NOx under lean atmosphere
The composition of the composite oxide for effectively absorbing NO contains at least one element selected from the group consisting of La, Pr, and Nd, which has an effect of easily forming a NO ₃ salt,
It is important that it is compounded with Zr.

Each of the constituent elements of the composite oxide exerts the above-mentioned effects to the maximum when all of these contained in the catalyst are complexed, but at least a part of the complex oxide forms a complex. Even if it is possible, the above effect can be sufficiently obtained.

Each constituent element of the composite oxide can exist as a composite oxide without being separated as a separate oxide even after heat endurance, and this can be confirmed by, for example, X-ray diffraction measurement.

Each of the constituent elements in the composite oxide may contain a trace amount of impurities as long as the above-mentioned action is not impaired. For example, strontium contained in barium,
Cerium, neodymium, samarium contained in lanthanum and hafnium and sulfur contained in zirconium.

The content of the composite oxide powder is not particularly limited as long as the effect is obtained in the catalyst, but is not limited to 30 to 10 per liter of the exhaust gas purifying catalyst of the present invention.
It is preferable to contain 0 g from the viewpoint of obtaining sufficient and significant NOx absorption.

In the exhaust gas purifying catalyst of the present invention, the coexistence of the noble metal and the composite oxide makes it possible to obtain a NOx purifying action which cannot be obtained by itself. That is, when the exhaust gas atmosphere becomes lean, high NOx purification performance can be obtained by the NOx absorbing action of the composite oxide in the exhaust gas purification catalyst of the present invention. When the composite oxide absorbs NOx and the exhaust gas atmosphere changes from lean to stoichiometric,
Ox is released, and high NOx purification performance is obtained. It is intended to obtain excellent NOx purification performance which cannot be obtained by simply mixing individual components of the composite oxide.

Another exhaust gas purifying catalyst of the present invention has a structure in which at least two layers are provided on a refractory inorganic carrier.
A layer containing the composite oxide is provided as a lower layer, and a layer not containing the composite oxide is provided as an upper layer.

As described above, by forming a multilayer structure and incorporating the composite oxide in the inner layer, it is possible to efficiently purify NOx released at the time of stoichiometric to rich conditions, and to reduce the HC purifying function of the three-way catalytic function. Can be suppressed. That is, in order to effectively purify the released NOx, it is preferable to dispose the NOx in the upper layer that does not contain the composite oxide.
And the released NOx is purified by the upper layer not containing the composite oxide, and a more sufficient three-way catalytic function can be obtained.

The material constituting the catalyst layer of the present invention preferably has an average particle diameter (median diameter) of 4 μm or less. By setting the particle size in such a range, the NOx absorbing ability at the time of lean can be improved.

That is, the exhaust gas purifying catalyst can exhibit an excellent NOx absorbing effect when the gas flow speed is reduced, and such an effect is achieved by setting the average particle diameter in the above range, and as a result, a high NOx The absorption activity can be obtained.

Further, by setting the average particle diameter as described above, preferably, the noble metal suitably supported in the exhaust gas catalyst of the present invention can be highly dispersed, and the NOx absorbing effect can be enhanced.

In particular, in order to further improve the above effects, it is preferable that the average particle size is 2 to 4 μm. The average particle size in the present specification is measured by a laser diffraction type particle size distribution meter.

The composite oxide used in the present invention is prepared by mixing nitrate, acetate, carbonate, citric acid, hydrochloride and the like of each constituent element of the composite oxide in a desired composition ratio of the composite oxide, and calcining the mixture. And then pulverized and heat treated and calcined, and the nitrate, acetate, carbonate, hydrochloride,
Citrate and the like are mixed in a desired composite oxide composition ratio and dissolved in water, and then, if necessary, NH ₄ OH or NH ₃
A precipitate is formed by dropping an alkaline solution such as CO _{3 and the} like, and the precipitate can be prepared by a coprecipitation method in which the precipitate is dried, filtered, dried and calcined, but is not limited to these methods. Any other method may be used as long as the composite oxide is formed.

According to such a method, at least a part of each component constituting the composite oxide can be composited.

As described above, the raw material for preparing the catalyst of the composite oxide used in the present invention may contain a trace amount of impurities as long as the amount does not interfere with the above-mentioned effects. For example, cerium contained in rare earth metals, Neodymium, samarium, hafnium and sulfur contained in zirconium.

As the noble metal raw material compound of the noble metal used in the present invention, inorganic acid salts, carbonates, ammonium salts, organic acid salts, halides, oxides, sodium salts, ammine complex compounds and the like can be used in combination. However, it is particularly preferable to use a water-soluble salt from the viewpoint of improving the catalytic performance. The method of supporting the noble metal on the porous body is not limited to a special method, and various methods such as a known evaporating and drying method, a precipitation method, an impregnation method, and an ion exchange method can be used as long as there is no significant uneven distribution of components. Can be used. In particular, the impregnation method is preferable for supporting on alumina, from the viewpoint of increasing dispersibility.

In the case of the ion exchange method or the impregnation method, since the metal raw material is often used in a solution, the pH can be adjusted by adding an acid or a base to the solution. pH
By adjusting the value, it is possible that the particles can be further highly dispersed and supported.

The catalyst of the present invention is preferably used by being supported on a monolithic carrier. The composite oxide and the noble metal-supported inorganic carrier are pulverized into a slurry, and the slurry is coated on the catalyst carrier.
By firing at a temperature of 00 to 900 ° C., the exhaust gas purifying catalyst of the present invention can be obtained.

The pulverizing method for pulverizing the composite oxide and the noble metal-carrying inorganic carrier is not particularly limited. Preferably, an aqueous slurry containing these is wet-pulverized to adjust the average particle diameter to 4 μm or less. Can be used.

The apparatus that can be used for the pulverization is not particularly limited, and a commercially available ball-type vibrating mill can be used, and a desired particle size is obtained by adjusting the ball diameter, the pulverizing time, the amplitude, and the vibration frequency.

The catalyst carrier can be appropriately selected from known catalyst carriers, and includes, for example, a honeycomb carrier having a monolithic structure made of a refractory material, a metal carrier and the like.

Although the shape of the catalyst carrier is not particularly limited, it is generally preferable to use a honeycomb shape. As the honeycomb material, cordierite materials such as ceramics are generally used, but ferrite-based materials are generally used. It is also possible to use a honeycomb made of a metal material such as stainless steel, and further, the catalyst powder itself may be formed into a honeycomb shape. By making the shape of the catalyst into a honeycomb shape, the area of the catalyst and the exhaust gas becomes large, and the pressure loss is suppressed, which is extremely advantageous when the catalyst is used for an automobile or the like.

The use conditions of the exhaust gas purifying catalyst of the present invention are not particularly limited.
0 to 50, more preferably an air-fuel ratio of 10 to 14.8 and 1
It can be used for lean burn engine vehicles that repeat the range of 5 to 50. With such a method of use, the cycle of NOx absorption / release is extremely effectively established, and particularly efficient NOx purification becomes possible. That is,
High NOx purification performance is achieved by absorbing NOx in a large air-fuel ratio region (lean region) within an air-fuel ratio range of 10 to 50 and purifying NOx in a small air-fuel ratio region (rich and / or stoichiometric). More preferable ranges are 10 to 14.8 for a region having a small air-fuel ratio and 15 to 50 for a region having a large air-fuel ratio.

[0047]

The present invention will be described below with reference to the following examples and comparative examples. Example 1 Activated alumina powder was impregnated with an aqueous solution of Pd nitrate and dried,
It was calcined at 400 ° C. for 1 hour in the air to obtain Pd-supported alumina powder (powder 1). The Pd concentration of this powder 1 was 2.8% by weight. An activated alumina powder was impregnated with an aqueous solution of dinitrodiamine Pt, dried, and calcined in air at 400 ° C. for 1 hour to obtain a Pt-supported alumina powder (powder 2). The Pd concentration of this powder 2 was 2.8% by weight. Activated alumina powder is impregnated with an aqueous solution of Rh nitrate and dried.
It was calcined at 0 ° C. for 1 hour to obtain Rh-supported alumina powder (powder 3). The Rh concentration of this powder 3 was 0.7% by weight.

Citric acid was added to a mixture of lanthanum carbonate and zirconium nitrate, dried and calcined at 700 ° C.
Thus, a composite oxide powder (powder 4) was obtained. This powder 4 had a metal atom ratio of lanthanum / zirconium = 5/5.

180 g of powder 1 and 90 g of powder 2
g, 180 g of the powder 4 and 360 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. This slurry liquid was applied to a cordierite monolithic carrier (1.3 L, 400 L).
After drying at 130 ° C and baking at 400 ° C for 1 hour, coat layer weight 125g / L-catalyst of carrier (A)
I got

90 g of the powder 1 and 90 g of the powder 2
g, 180 g of powder 3 and 360 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. This slurry liquid is adhered to the catalyst (A), excess slurry in the cell is removed by an air stream, and the slurry is dried at 130 ° C.
It was calcined at 0 ° C. for 1 hour to obtain an exhaust gas purifying catalyst having a total coat layer weight of 250 g / L-carrier.

Example 2 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that La of powder 4 was changed to Nd.

Example 3 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that La in powder 4 was changed to Pr.

Example 4 180 g of the powder 1 obtained in Example 1 and 180 g of the powder 2 were obtained.
g, powder 3 180 g, powder 4 180 g, water 720 g
Was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. This slurry liquid was adhered to a cordierite type monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. Layer weight 250g /
An L-carrier exhaust gas purification catalyst was obtained.

Comparative Example 1 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that powder 4 was used and activated alumina powder containing 6 mol% of La was used instead.

Comparative Example 2 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that the average particle size of the slurry was adjusted to 8 μm.

Comparative Example 3 90 g of powder 1 and 90 g of powder 2 obtained in Example 1 were prepared.
180 g of powder 3 and 360 g of water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. This slurry liquid was adhered to a cordierite type monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed with an air stream, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. A catalyst (B) having a layer weight of 125 g / L-carrier was obtained.

90 g of Powder 1, 90 g of Powder 2, 180 g of Powder 4 and 360 g of water obtained in Example 1 were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. This slurry liquid is adhered to the catalyst (B), and the excess slurry in the cell is removed by an air stream and dried at 130 ° C.
Baking at 00 ° C for 1 hour, total coat layer weight 250g / L-
An exhaust gas purifying catalyst for the carrier was obtained.

Comparative Example 4 90 g of powder 1 and 90 g of powder 2 obtained in Example 1 were prepared.
60 g of powder 4, 120 g of activated alumina, 360 g of water
Was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. This slurry liquid was attached to a cordierite type monolithic carrier (1.3 L, 400 cells), and excess slurry in the cells was removed by an air stream and dried at 130 ° C.
Baking at 400 ° C for 1 hour, coat layer weight 125g / L-
A carrier catalyst (C) was obtained.

90 g of the powder 1 obtained in Example 1, 90 g of the powder 2, 180 g of the powder 3 and 360 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. This slurry liquid is adhered to the catalyst (C), excess slurry in the cell is removed by an air stream, and the slurry is dried at 130 ° C.
Baking at 00 ° C for 1 hour, total coat layer weight 250g / L-
An exhaust gas purifying catalyst for the carrier was obtained.

Comparative Example 5 90 g of powder 1 and 90 g of powder 2 obtained in Example 1 were prepared.
360 g of powder 4 and 540 g of water were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. This slurry liquid was adhered to a cordierite type monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed with an air stream, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. Layer weight 187.5 g / L—support catalyst (D)
I got

90 g of Powder 1, 90 g of Powder 2, 180 g of Powder 3 and 360 g of water obtained in Example 1 were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry liquid. At this time, the average particle size of the slurry was 2.8 μm. After this slurry liquid was attached to the catalyst (D), excess slurry in the cell was removed by an air stream and dried at 130 ° C.
Baking at 00 ° C for 1 hour, total coat layer weight 312.5 g /
An L-carrier exhaust gas purification catalyst was obtained.

Comparative Example 6 In Example 1, 45 g of La ₂ O ₃ was used instead of powder 4
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that 135 g of ZrO ₂ was used.

Comparative Example 7 In Example 1, powder 4 was prepared by changing the ratio of La to Zr to La /
An exhaust gas purifying catalyst was obtained in the same manner except that Zr was set to 1/9.

Table 1 shows the catalyst compositions of the exhaust gas purifying catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 7.

[0065]

[Table 1]

Test Examples The exhaust gas purifying catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 7 were evaluated for the initial and endurance catalytic activities under the following conditions. For the activity evaluation, an automatic evaluation device using a model gas simulating the exhaust gas of an automobile was used.

Endurance conditions A catalyst was mounted in an exhaust system of 4400 cc engine, and operation was performed at a catalyst inlet temperature of 700 ° C. for 50 hours to endurance.

Evaluation Conditions The catalyst activity was evaluated by mounting each catalyst in an exhaust system of an engine with a displacement of 2,000 cc, A / F = 14.6 (stoichiometric state) for 60 seconds, and then A / F = 22 (lean atmosphere).
For 10 seconds, then 1 at A / F = 50 (lean atmosphere)
One cycle of operation for 0 seconds was performed, and the average conversion was measured. The average conversion when A / F = 14.6 (stoichiometric state) and the average conversion when A / F = 22 (lean atmosphere). And the average conversion in the case of A / F = 50 (lean atmosphere) was averaged to obtain the total conversion. This evaluation was performed at the initial stage and after the endurance test, and the catalytic activity evaluation value was determined by the following equation. However, the catalyst inlet temperature was 350 ° C.

[0069]

(Equation 4)

Table 2 shows the catalytic activity evaluation results obtained as the total conversion. The catalytic activity of the example was higher than that of the comparative example, and the effect of the present invention described later could be confirmed.

[0071]

[Table 2]

[0072]

The exhaust gas purifying catalyst according to any one of claims 1 to 5 improves NOx purifying performance in a lean atmosphere, which has not exhibited sufficient activity with a conventional catalyst, and has a sufficient function as a three-way catalyst. And can exhibit excellent NOx purification performance even after heat endurance.

According to the method of using the exhaust gas purifying catalyst according to the sixth and seventh aspects, the effective NOx absorption / release cycle of the exhaust gas purifying catalyst of the present invention can be exhibited particularly efficiently.

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Claims (7)

[Claims] 1. At least one noble metal selected from the group consisting of platinum, palladium and rhodium, and the following general formula: And a perovskite-type composite oxide represented by the formula: 2. The exhaust gas purifying catalyst 1 L is mixed oxide.
The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is contained in an amount of 30 to 100 g per unit. 3. The exhaust gas purifying catalyst according to claim 1, further comprising 100 to 300 g of alumina per 1 L of the exhaust gas catalyst. 4. A structure comprising at least two layers provided on an inorganic carrier, wherein the layer containing the composite oxide is provided as a lower layer, and the layer not containing the composite oxide is provided as an upper layer. The exhaust gas purifying catalyst according to claim 1. 5. The catalyst layer has an average particle size of 4 μm.
The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein m is equal to or less than m. 6. An exhaust gas purifying catalyst according to any one of claims 1 to 5, wherein the catalyst is used in a lean burn engine vehicle having an air-fuel ratio in a range of 10 to 50.
How to use exhaust gas purification catalyst. 7. The exhaust gas purifying catalyst according to claim 1, wherein the air-fuel ratio is 10-14.8, 15-15.
A method for using an exhaust gas purifying catalyst, which is used for a lean burn engine vehicle that repeats a range of 0.