JPH11207190A - Catalyst for purification of exhaust gas and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow oxide of a metal such as Mn or Co to effectively exhibit catalytic action by adding a liq. mixture of a soln. of an NOx occluding material and a noble metal soln. to the oxide to support the noble metal and the NOx occluding material. SOLUTION: The catalyst has a honeycomb carrier 1 comprising cordierite excellent in heat resistance and two catalyst layers on the carrier 1. One of the catalyst layers is an inside catalyst layer 2 (lower catalyst layer) closer to the surface of the carrier 1 and the other is an outside catalyst layer 3 (upper catalyst layer) on the inside catalyst layer 2. In the inside catalyst layer 2, a noble metal as a catalyst metal and an NOx occluding material are supported on oxide of a metal selected from Mn, Co, Ti and Fe, alumina and CeO2 . In the outside catalyst layer 3, the noble metal and the NOx occluding material are supported on a zeolite layer. Platinum is particularly used as the noble metal. Barium is particularly used as the NOx occluding material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying catalyst and a method for producing the same.

[0002]

2. Description of the Related Art When an engine is operated at a lean air-fuel ratio with a low fuel concentration, the exhaust gas has a high oxygen concentration,
In a conventional three-way catalyst, NOx (nitrogen oxide) in exhaust gas
Is difficult to decompose and purify.

[0003] As an exhaust gas purifying catalyst effective for purifying NOx in such a case, Japanese Patent Laid-Open Publication No. Hei 7-155601 discloses that a NOx occluding material (alkaline earth metal such as Ba) and Pt are deposited on a carrier. An inner supporting layer containing alumina and
Patent Document 1 discloses an outer support layer containing an oxide of at least one metal selected from the group consisting of Fe, Co, Ni, Cu, and Mn. This is because the SOx in the exhaust gas is oxidized by the outer metal oxide to produce SO ₃
To produce a SOx salt,
The purpose is to prevent the inner supporting layer from being poisoned by SOx. In the method for producing this catalyst, an alumina layer is formed on a carrier, and Pt is impregnated into the alumina layer, followed by drying and firing.
Ba impregnation, drying and firing are performed in this order (formation of an inner support layer), and then a mixture layer of alumina powder and iron oxide powder (outer support layer) is formed thereon.

[0004] Japanese Patent Application Laid-Open No. 9-38493 discloses that
An exhaust gas purifying catalyst is described in which a catalyst precious metal and a NOx storage material are sequentially supported on a support made of a composite oxide of at least one of Co and La and alumina.
This is because at high temperatures, the alumina reacts with the NOx storage material to cause a decrease in the specific surface area of alumina and blockage of pores.
Sintering of precious metal occurs, but alumina or Co or L
In the case of a composite oxide with a, the thermal degradation could be suppressed. In the method for producing this catalyst, an alumina layer is formed on a carrier and impregnated with Co →
A Co-alumina composite oxide layer is formed by performing drying → firing, and firing is performed by sequentially performing Pt impregnation → drying and Rh impregnation → drying, followed by Ba impregnation → drying → firing. That is.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide Mn and C which have conventionally been used from the viewpoint of catalyst stability such as measures against SOx poisoning and improvement of thermal stability of alumina as described above.
Oxides of metals such as o are actively utilized for the catalytic action, which aims to improve not only the heat resistance of the exhaust gas purifying catalyst but also its activity. is there. In particular, even when the engine is operated at an air-fuel ratio A / F = 18 or more and the oxygen concentration in the exhaust gas becomes 4-5% or more, for example, more than 20%, the NOx in the exhaust gas is efficiently decomposed and purified. Is what you can do.

[0006]

According to the study of the present inventor, a NOx storage material such as Ba stores NOx in exhaust gas in the form of nitrate. However, oxides of certain metals such as Mn and Co are used. Has the effect of oxidizing NO in exhaust gas to NO ₂ , which is considered to work effectively for the occlusion.
Therefore, in the present invention, such an oxide is used as a catalyst, and the noble metal particles and the NOx occluding material particles are brought close to each other and are highly dispersed and supported.

[0007] That is, one of the inventions of this application is a method for producing an exhaust gas purifying catalyst comprising a NOx storage material having an action of storing NOx in exhaust gas and a noble metal having a catalytic action of decomposition of the NOx. Mn,
At least one selected from Co, Ti and Fe
The precious metal and the NOx storage material are supported by adding a mixed solution of the NOx storage solution and the noble metal solution to the seed metal oxide.

That is, the NOx storage material solution and the noble metal solution are simultaneously impregnated and supported on an oxide such as Mn, whereby the noble metal particles and the NOx storage material particles are brought close to each other and are highly dispersed and supported.

Therefore, NO in the exhaust gas is converted into NO ₂ by oxides such as Mn, so that the NO is easily stored in the NOx storage material (for example, when Ba is used as the NOx storage material, NO reacts with NO ₂ to form nitric acid). Ba easily). Further, in such a catalyst, the noble metal particles not only decompose and decompose NOx in the exhaust gas, but also decompose NOx which is stored in the NOx storage material in an oxygen-excess atmosphere and released when the oxygen concentration becomes low. Therefore, the fact that the noble metal particles and the NOx storage particles are arranged close to each other and in a highly dispersed state is effective in decomposing and purifying NOx.

Here, it should be noted that simply combining an oxide such as Mn with a noble metal / NOx storage material, that is, the NOx storage material is supported after the noble metal is supported on the oxide such as Mn. Even if the catalyst is supported, the NOx purification rate after the catalyst is exposed to a high temperature is not so high, and an unexpectedly high NOx purification rate can be obtained only by the simultaneous impregnation.

The NOx storage material is preferably at least one metal selected from alkali metals such as Na, alkaline earth metals such as Ba and Sr, and rare earth metals such as La. In particular, Ba is excellent in NOx storage properties. Further, among the above-mentioned Mn, Co, Ti and Fe, Mn and Co are more effective for decomposing and purifying NOx. Pt is preferable as the noble metal, and Rh
And other noble metals such as Ir and Pd.

The oxide such as Mn is made of alumina or CeO ₂
It is preferable to use them together. In that case, the above NOx is used for the mixture of the oxide, alumina, and CeO _2.
What is necessary is just to add a mixed solution of the solution of the storage material and the solution of the noble metal. Alumina has a high specific surface area and is effective for highly-dispersed loading of noble metals and NOx storage materials. In that sense, γ-alumina is particularly good. Since CeO ₂ has an oxygen storage capacity (O ₂ storage effect), when the engine is operated near the stoichiometric air-fuel ratio (λ = 1), the catalyst functions as a three-way catalyst, and not only NOx but also HC (Hydrocarbon) and CO
(Carbon monoxide) is also effective in purifying efficiently at the same time.

A catalyst layer comprising a mixture of an oxide such as Mn, alumina, and CeO ₂ carrying a NOx storage material and a noble metal on a support, and a zeolite carrying a NOx storage material and a noble metal on a zeolite. When the catalyst layer is formed in layers with the former on the inside and the latter on the outside, high N
Ox purification performance is obtained. The following method may be used for producing such an exhaust gas purifying catalyst.

It consists of Mn, Co, Ti and F on the support.
e, forming an inner layer composed of a mixture of an oxide of at least one metal selected from e, alumina and CeO ₂ , forming an outer layer composed of zeolite on the inner layer, A solution of a NOx storage material made of at least one metal selected from an alkaline earth metal and a rare earth metal and having a function of storing NOx in exhaust gas, and a solution of a noble metal having a catalytic action of decomposing NOx; A method for producing an exhaust gas purifying catalyst, characterized in that a mixed solution is added to impregnate the inner layer and the outer layer so that the NOx storage material and the noble metal are supported on the inner and outer layers.

According to this method, the predetermined amount of the NOx storage material can be easily carried on the inner layer. In other words, if the NOx storage material and the noble metal are supported on the inner layer, and then immersed in a slurry of zeolite to form the outer layer, NOx such as Ba supported on the inner layer can be formed.
Part of the occlusion material elutes into the zeolite slurry, and the NOx
It is difficult to adjust the amount of the occlusion material carried, but this method can solve this problem.

In this catalyst, the noble metal supported on the zeolite in the outer layer contains NOx and HC in the exhaust gas.
And the NO purification performance is enhanced. That is, NO in the exhaust gas becomes NO ₂ and is easily stored in the NOx storage material, and HC is easily energetically reacted by partial oxidation and cracking, and the activated HC reduces and decomposes NOx by this activated HC. The reaction proceeds easily.

Another invention of this application relates to an exhaust gas purifying catalyst obtained by the above method, wherein a catalyst layer formed on a carrier is selected from Mn, Co, Ti and Fe. And at least one NOx storage material having an action of storing NOx in the exhaust gas and a noble metal particle having a catalytic action of decomposing NOx in the oxide. And is highly dispersed and supported.

As described above, such a catalyst efficiently decomposes NOx in exhaust gas having a high oxygen concentration even after being exposed to a high temperature.

The catalyst layer is composed of a mixture of an oxide of at least one metal selected from Mn, Co, Ti and Fe, alumina and CeO ₂ . With an exhaust gas purifying catalyst in which the NOx storage material particles and the noble metal particles are highly dispersed and supported in close proximity to each other, higher NOx purifying performance can be obtained.

[0020] As apparent from the above description, the presence of oxides of Mn or the like is effective in improving the NOx purification performance is believed that it is because the changing NO in the exhaust gas to NO ₂ Thus, the catalyst layer formed on the carrier contains an oxide having an action of oxidizing NO in the exhaust gas, and the oxide has a particle of a NOx storage material having an action of storing NOx in the exhaust gas. The exhaust gas purifying catalyst in which the noble metal particles having the catalytic action of NOx decomposition are highly dispersed and supported in close proximity to each other, even after being exposed to a high temperature, the exhaust gas purifying catalyst has a high oxygen concentration. It is effective to decompose NOx efficiently.

[0021]

As described above, according to the invention of the present application, an oxide such as Mn having an action of converting NO to NO ₂ or a base material composed of a mixture of this and alumina and CeO ₂ is obtained. On the other hand, since the NOx storage material and the noble metal are simultaneously impregnated and supported, even after the catalyst is exposed to a high temperature, the NO contained in the oxide such as Mn is converted to NO ₂ It is considered that the action of converting to NOx effectively works for NOx decomposition and purification, and NOx can be efficiently purified in an atmosphere having a high oxygen concentration.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Structure of Catalyst> FIG. 1 shows a structure of an exhaust gas purifying catalyst C according to the present invention.
The catalyst C is disposed in an exhaust passage (not shown) for discharging exhaust gas of a lean combustion engine for a vehicle, and HC, CO, NOx, etc. in the exhaust gas during a stoichiometric air-fuel ratio combustion operation. Of air pollutants, and also effectively purifies NOx during lean combustion operation. That is, the catalyst C has a lean NOx purifying action, the oxygen concentration in the lean atmosphere is, for example, 4 to 5% to 20%, and the air-fuel ratio is A / F = 18 or more.

The catalyst C is made of, for example, a honeycomb-shaped carrier 1 made of cordierite, which is a carrier material having excellent heat resistance.
On the support 1, an inner catalyst layer 2 (lower catalyst layer) on the side close to the surface of the support 1, and an outer catalyst layer 3 (upper catalyst layer) on the side further away from the surface of the support 1. ) Are formed.

In the inner catalyst layer 2, a noble metal serving as a catalyst metal and a NOx storage material are converted into an oxide of at least one metal selected from Mn, Co, Ti and Fe, alumina and CeO ₂ . It is carried and provided. The outer catalyst layer 3 is provided with a noble metal serving as a catalyst metal and a NOx storage material supported on zeolite.

Pt is mainly used as the noble metal, and Rh, Ir, and Pd can be used in combination. As the NOx storage material, Ba is mainly used, but another alkaline earth metal, or an alkali metal or a rare earth metal may be used, or two or more metals selected from them may be used in combination. Can be. Ceria can be used as the CeO ₂ component, but a composite oxide of cerium and zirconium can also be used from the viewpoint of improving heat resistance. The impurities in each of the catalyst layers 2 and 3 are set to 1% or less.

<Preparation of Catalyst> Mn, Co, Ti and Fe
By mixing an oxide of at least one metal selected from the group consisting of alumina, CeO ₂ , a binder and water to form a slurry, wash-coating the slurry on the carrier 1 and drying and calcining the slurry, An inner coat layer for forming the catalyst layer 2 is formed.

Next, a slurry is formed by mixing the noble metal-supported zeolite, a binder and water, and this slurry is wash-coated on the carrier 1 having the inner coat layer, and dried and fired to form a slurry. An outer coat layer for forming the outer catalyst layer 3 is formed thereon.

Both the inner and outer coat layers of the carrier 1 thus obtained are impregnated with a mixed solution of a solution of a NOx storage material and a solution of a noble metal, and dried and fired to obtain a catalyst C.

<Evaluation of Catalyst> Each catalyst of the following Examples and Comparative Examples was prepared, and the catalyst performance was comparatively evaluated.

Example 1 Formation of Inner Coat Layer Gamma-alumina, CeO ₂ —ZrO ₂ composite oxide, manganese oxide (MnO ₂ ) and alumina binder were 25: 2.
The mixture was mixed at a weight ratio of 5: 2: 5, and ion-exchanged water was added thereto to prepare a slurry. A carrier having a honeycomb structure (420 g / L; this g / L means the weight per 1 L of the carrier; the same applies hereinafter) is immersed in the slurry, pulled up, and the excess slurry is blown off. The slurry was wash-coated so that the coating amount was 342 g / L. Next, this was dried and fired to form an inner coat layer. Drying is performed at a temperature of 100 to 200 ° C. for 1 hour,
The firing was performed at a temperature of 500 to 600 ° C. for 2 hours. These drying conditions and firing conditions are the same for "drying" and "firing" in the following description.

Formation of Outer Coat Layer On the other hand, a dinitrodiamine platinum solution and a rhodium nitrate solution are mixed so that the Pt: Rh ratio becomes Pt: Rh = 75: 1, and this is mixed with an MFI-type zeolite (SiO ₂ / Al _2). O
₃ = 80) and spray-dried by a spray-drying method, whereby Pt and Rh were supported on the zeolite in a total amount of 2.3 wt%. Next, this was baked to obtain a powder for the outer coat layer. Combine this powder with alumina binder and 5:
The mixture was mixed at a weight ratio of 1 and ion-exchanged water was added thereto to prepare a slurry. The slurry was applied to the carrier on which the inner coating layer was formed so that the coating amount after drying was 24 g / L. Then, the outer coat layer was formed by subjecting to a wash coat, followed by drying and firing.

Simultaneous impregnation and loading of Pt, Rh and Ba Next, a dinitrodiamineplatinum solution, a rhodium nitrate solution and barium acetate were mixed at a weight ratio of Pt: Rh: Ba = 20: 1: 300, and this mixed solution was mixed with the above mixture. Both the inner and outer coat layers of the carrier were impregnated so as to have a total of 32.1 g / L, and this was dried and calcined to obtain the catalyst of Example 1.

Therefore, the inner catalyst layer of this catalyst has 150 g / L of γ-alumina, 150 g / L of CeO ₂ -ZrO ₂ composite oxide and 12 g / L of manganese oxide as a base material, and the binder is 30 g / L. Yes, noble metal Pt 2g
/ L and Rh are 0.1 g / L. The outer catalyst layer of this catalyst was composed of 20 g / L of MFI and 4 g of binder.
/ L, noble metal: Pt 0.5 g / L, Rh 0.006
g / L. Ba is contained as a NOx storage material in an amount of 30 g / L in accordance with the inner and outer catalyst layers.

As shown in Table 1, the catalyst has a Mn oxide in the inner catalyst layer and Ba has P in the inner and outer catalyst layers.
The point is that they are simultaneously impregnated and supported together with t and Rh.

[0035]

[Table 1]

Example 2 A catalyst of Example 2 was obtained in the same manner as in Example 1 except that cobalt oxide (Co ₂ O ₃ ) was used instead of manganese oxide (see Table 1).

Comparative Example 1 Formation of Inner Coat Layer Gamma-alumina, CeO ₂ —ZrO ₂ composite oxide, and alumina binder were mixed at a weight ratio of 5: 5: 1, and ion-exchanged water was added thereto. A slurry was prepared, and this was wash-coated on a carrier having a honeycomb structure (420 g / L) so that the coating amount after drying was 330 g / L, followed by drying and baking to form an inner coat layer.

Impregnation of inner coat layer of Pt and Rh with dinitrodiamineplatinum solution and rhodium nitrate solution
The mixture was mixed at a weight ratio of t: Rh = 20: 1, impregnated into the inner coat layer so as to be 2.1 g / L, and dried and fired.

Formation of Outer Coat Layer Next, using the same material and method as in the example, the coating amount after drying was 2
An outer coat layer of 4 g / L was formed.

Ba Impregnation Carrier Barium acetate was impregnated into the inner and outer coat layers so that the Ba content was 30 g / L, followed by drying and firing.

The main differences between the catalyst of Comparative Example 1 obtained above and the catalyst of the present invention are that it does not have manganese oxide or cobalt oxide, and that Ba is not impregnated with Pt and Rh but is post-impregnated. (See Table 1), and the rest is the same as the first embodiment.

Comparative Example 2 Formation of Inner Coat Layer An inner coat layer having a coating amount after drying of 330 g / L was formed using the same material and method as in Comparative Example 1.

Formation of Outer Coat Layer An outer coat layer having a coating amount after drying of 24 g / L was formed on the inner coat layer by the same material and method as in the example.

Simultaneous Impregnation and Support of Pt, Rh and Ba Pt, Rh and Ba were simultaneously impregnated and supported on both the inner and outer coat layers by the same material and method as in Example 1 so that the total was 32.1 g / L.

The main difference between the catalyst of Comparative Example 2 obtained as described above and the catalyst of Example 1 is that it does not have manganese oxide or cobalt oxide (see Table 1). It is.

Comparative Example 3 Formation of Inner Coat Layer An inner coat layer having a coating amount after drying of 342 g / L was formed by the same material and method as in the example.

Impregnation of Pt and Rh on Inner Coat Layer Using the same material and method as in Comparative Example 1, Pt and Rh were added to the inner coat layer at a weight ratio of Pt: Rh = 20: 1 to a total of 2.1 g / Rh. L was impregnated and carried.

Formation of Outer Coat Layer The same material and the same method as in the example were used, and the coated amount after drying was 24 g.
/ L of the outer coat layer.

Ba Impregnation Carrier Barium acetate was impregnated into the inner and outer coat layers so that the Ba content was 30 g / L, followed by drying and firing.

The major difference between the catalyst of Comparative Example 3 obtained as described above and the catalyst of the present invention is that Ba is not impregnated with Pt and Rh, but is post-impregnated (see Table 1). Is the same as in the first embodiment.

-Evaluation Method- After subjecting the test catalyst to a heat aging treatment at 900 ° C. for 24 hours in the air, the catalyst is attached to a fixed-bed flow reaction evaluation apparatus. At first, the simulated exhaust gas having the lean air-fuel ratio is supplied to the catalyst until the NOx purification rate is stabilized. Next, the gas composition is switched to flow the simulated exhaust gas rich in the air-fuel ratio, and thereafter the gas composition is switched again to the lean air-fuel ratio, and the NOx purification rate is measured for 130 seconds from the switching point to evaluate the lean NOx purification performance. . The catalyst temperature and the simulated exhaust gas temperature were 350 ° C., the gas composition was as shown in Table 2, and the space velocity SV was 25000 h ⁻¹ .

[0052]

[Table 2]

The results are shown in FIG. Comparative Example 1 and Comparative Example 2 differ depending on whether Ba was post-impregnated or co-impregnated with Pt or the like, and the difference in purification rate (15.5%) between the two catalysts was Ba.
Is recognized as an effect of simultaneous impregnation. Further, Comparative Example 1 and Comparative Example 3 differ in the presence or absence of Mn oxide, and the difference in purification rate (18.9%) between the two catalysts is recognized as the effect of the addition of Mn oxide. On the other hand, the purification rate of Example 1 having Mn oxide and simultaneously impregnating with Ba was the same as Comparative Example 2,
3 compared with Comparative Example 1, and the difference is 33.9.
There are also percentages.

Degree of increase in purification rate due to simultaneous impregnation with Ba and Mn
When combined with the degree of increase in the purification rate due to the addition of oxides, 34.
However, in Example 1, the combination of the simultaneous impregnation of Ba and the addition of Mn oxide increased the NOx purification rate to a level comparable to the combined degree of increase alone. Become.

In general, for example, when the amount of the supported catalyst metal increases, the increase in the purification rate saturates, and it is usually difficult to further increase the purification rate as the purification rate increases. Considering this point, as described above, Ba
The fact that a combination of the simultaneous impregnation and the addition of the Mn oxide provides a high purification rate as a combination of the two implies a synergistic effect.

In the catalyst of Example 2, a high NOx purification rate comparable to that of Example 1 was obtained, and the combination of the addition of Co oxide and the simultaneous impregnation of Ba had the same effect as the case of Mn oxide. I can say.

Table 3 compares the effect of the type of metal oxide added to the inner catalyst layer on the NOx purification rate of the catalyst. The structures of these catalysts differ only in the type of metal oxide, and all other structures are the same. According to the table, Ti
Even in the case of O _2, a relatively high NOx purification rate is obtained,
Also, Fe ₂ O ₃ has a higher NOx purification rate than Comparative Example 2.

[0058]

[Table 3]

As described above, when the NOx storage material such as Ba is supported on the base material by simultaneous impregnation with the catalyst noble metal,
When combined with the use of a specific metal oxide as the catalyst component, NOx after the catalyst is exposed to high temperatures
It can be said that it is advantageous for improving the purification rate, and this is not limited to the two-layer coated catalyst as in the above embodiment, but can be similarly applied to a single-layer coated catalyst and a pellet type catalyst.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a catalyst structure according to an embodiment of the present invention.

FIG. 2 is a graph showing the NOx purification rates of an example catalyst and a comparative example catalyst.

[Description of Signs] 1 support 2 inner catalyst layer 3 outer catalyst layer C exhaust gas purification catalyst

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 23/76 B01J 29/12 A 29/12 F01N 3/08 A F01N 3/08 3/28 301C 3/28 301 B01D 53 / 36 104A (72) Inventor Makoto Kyogoku 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Kenji 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd.

Claims (7)

[Claims] 1. A method for producing an exhaust gas purifying catalyst comprising: a NOx storage material having an action of storing NOx in exhaust gas; and a noble metal having a catalytic action of decomposing the NOx, the method comprising: Mn, Co, Ti And adding a mixed solution of the solution of the NOx storage material and the solution of the noble metal to the oxide of at least one metal selected from Fe and Fe to support the noble metal and the NOx storage material. A method for producing a catalyst for purifying exhaust gas. 2. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the NOx occluding material is at least one metal selected from an alkali metal, an alkaline earth metal and a rare earth metal. A method for producing an exhaust gas purifying catalyst, characterized in that: 3. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein said mixed solution is added to a mixture of said oxide, alumina and CeO _2. A method for producing a purification catalyst. 4. An inner layer comprising a mixture of an oxide of at least one metal selected from Mn, Co, Ti and Fe, alumina and CeO ₂ on a carrier, After forming an outer layer made of zeolite, a solution of a NOx occluding material made of at least one metal selected from an alkali metal, an alkaline earth metal and a rare earth metal and having a function of occluding NOx in exhaust gas. ,
By impregnating the inner layer and the outer layer with a mixed solution of a solution of a noble metal having a catalytic activity for decomposition of NOx,
A method for producing an exhaust gas purifying catalyst, wherein the NOx storage material and the noble metal are supported on both the inner and outer layers. 5. A catalyst layer formed on a support, wherein Mn, C
o, an oxide of at least one metal selected from Ti and Fe, a particle of a NOx occluding material having an action of occluding NOx in exhaust gas, and a catalyst for decomposing the NOx. An exhaust gas purifying catalyst characterized in that particles of a noble metal having an action are carried in close proximity to each other in a highly dispersed manner. 6. The exhaust gas purifying catalyst according to claim 5, wherein the catalyst layer comprises an oxide of at least one metal selected from Mn, Co, Ti and Fe, alumina and C
An exhaust gas purifying catalyst comprising a mixture with eO ₂ , wherein the NOx occluding material particles and the noble metal particles are highly dispersed and supported on the mixture in close proximity to each other. 7. A catalyst layer formed on a carrier contains an oxide having a function of oxidizing NO in exhaust gas, and the oxide has a function of storing NOx in exhaust gas. And a noble metal particle having a catalytic activity for decomposing NOx is carried in close proximity to each other in a highly dispersed manner.