JPH11319563A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently purify NO in exhaust gas contg. HC. SOLUTION: The first catalyst 2 for oxidize NO to NO2 is arranged on the upstream side in the flow direction of exhaust gas and the second catalyst 3 for reducing the oxidized NO2 is arranged on the downstream side. The first catalyst 2 comprises a catalyst wherein Ag is carried on γ-alumina and the second catalyst 3 comprises a catalyst wherein Ag or Co is carried on a zeolite matrix and Pt is carried by ion exchange.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, exhaust gas of a diesel engine (oxygen concentration of 10% or more) and exhaust gas of a lean burn engine (oxygen concentration of 4% or more, A / F>
The present invention relates to an exhaust gas purifying catalyst suitable for purifying NOx in exhaust gas having a high oxygen concentration as in 22).

[0002]

2. Description of the Related Art JP-A-63-49255 discloses that
A first catalyst for oxidizing O (nitrogen monoxide) to NO ₂ (nitrogen dioxide) is provided upstream in the exhaust gas flow direction and N
An exhaust gas purifying catalyst including a second catalyst for reducing and decomposing O ₂ into N ₂ (nitrogen) is disclosed. Metals such as Ag and Mn, oxides or halides of Cu are used as the first catalyst, and zeolite is used as the second catalyst.

[0003] JP-A-8-192050 discloses that A
An exhaust gas purifying catalyst comprising a first catalyst comprising g, Co or Ni supported on alumina on the upstream side in the exhaust gas flow direction and a second catalyst comprising Ag on mordenite being disposed on the downstream side. Has been disclosed. In this catalyst, the first catalyst contributes to oxidize NO to NO ₂ and the second catalyst
It is thought to contribute to reducing O ₂ .

Japanese Patent Application Laid-Open No. 8-276131 discloses that Ag
Is supported on alumina or titania on the upstream side in the exhaust gas flow direction, and a second catalyst on Ag, Cu or Ni is supported on alumina, titania, zeolite, silica or zirconia, and a metal such as Pt. Discloses a catalyst for purifying exhaust gas, in which a mixture with a third catalyst, which is supported on alumina, titania, zeolite, silica or zirconia, is disposed on the downstream side. This is because NO is reduced to N ₂ by bringing exhaust gas containing NO and ethanol into contact with the first catalyst, and a nitrogen-containing compound such as nitrite ester and ammonia generated at that time is mixed with the second catalyst and the third catalyst.
The nitrogen compound is removed by contact with a mixture with a catalyst.

[0005]

The former two of the above-mentioned prior arts oxidize NO in exhaust gas to NO ₂ and then reduce and decompose this NO. It is a catalyst that reduces NO in exhaust gas containing methanol to N ₂ and removes nitrogen compounds, which are by-products at that time, more efficiently, and has a different concept from the former two.

[0006] Now, as in the catalyst structure of the former two, if you are from the oxidation of NO to NO ₂ and try to reduce it to N _2, when its reduction, efficiently NO ₂ in the reduction catalyst It is important to attract. Also, NO
It is important to efficiently oxidize to O ₂ .

Therefore, the present invention provides an exhaust gas purifying catalyst capable of efficiently purifying NO in exhaust gas having a high oxygen concentration from such a viewpoint.

[0008]

One of the inventions of this application is an exhaust gas purifying catalyst for purifying exhaust gas containing NO, which is a first catalyst for oxidizing NO in exhaust gas to NO ₂ . A catalyst, and a second catalyst for reducing oxidized NO ₂ , wherein the second catalyst includes a catalyst metal for reducing NO ₂ , a group 1B element such as Ag, Cu, and Au and Co. And at least one promoter metal selected from the group consisting of:

In such an exhaust gas purifying catalyst, high NOx purifying performance can be obtained. Although the reason is not clear, at least one selected from the group 1B element and Co contained in the second catalyst as the promoter metal is:
It is considered that the function of attracting NO ₂ generated by the first catalyst is excellent, and therefore, the reduction reaction of NO ₂ using HC as a reducing agent proceeds efficiently on the catalyst metal of the second catalyst. Such a promoter function of attracting NO ₂ is particularly excellent when the promoter metal is an oxide.

The cocatalyst metal of the second catalyst is Ag.
And Co are preferable. When the second catalyst is used by being supported on a carrier, the amount of Ag per 1 L of the carrier is set to 0.1.
The amount is preferably from 8 to 6.4 g, and in the case of Co, the amount supported per 1 L of the carrier is preferably from 0.9 to 2.7 g. This is because when the amount of Ag carried or the amount of Co carried is within this range, the NOx purification rate increases.

As the first catalyst, A is used as a catalyst metal.
Those containing g are preferred. When the first catalyst is provided supported on a carrier, the amount of Ag carried per liter of the carrier is preferably 15 to 150 g. This is because if the amount of Ag carried is in this range, the conversion rate of NO to NO ₂ increases.

The catalyst metal of the second catalyst is preferably a noble metal. Above all, those in which this noble metal, for example, Pt is supported on zeolite by ion exchange are preferable. Not only has high ability to reduce NO ₂ to N ₂ but also NO
This is because the ability to reduce N to N ₂ is also high.

It is preferable that the first catalyst and the second catalyst are arranged so that the former is on the upstream side in the exhaust gas flow direction and the latter is on the downstream side. This is because NO ₂ oxidized and generated by the first catalyst can be supplied to the second catalyst together with HC.

As is clear from the above, an exhaust gas purifying catalyst for purifying exhaust gas containing NO, a first catalyst containing Ag as a catalyst metal, a catalyst metal for reducing NOx, Ag and The one provided with the second catalyst in which at least one of Co is supported on zeolite has high NOx purification performance.

In particular, it is preferable that the first catalyst contains Ag present in a simple substance (metal) state, and the second catalyst contains Ag or Co supported on the zeolite in an oxide state. . This is because Ag in a single state adsorbs a large amount of oxygen in the exhaust gas, and is advantageous in oxidizing NO in the exhaust gas using the adsorbed oxygen. On the other hand, Ag or Co in the oxide state is more likely to adsorb NO ₂ than oxygen in the exhaust gas, which is advantageous for reducing NO ₂ using a reducing agent (HC) on the catalyst metal. is there.

In general, when alumina is used as a supporting base material, the ratio of Ag present in a simple substance (metal) state becomes higher than that in an oxide state, and when zeolite is used as a base material, Ag is in a simple state. The ratio present in the oxide state is higher than that in the oxide state. This is presumably because zeolite has a much higher specific surface area than alumina, so that Ag is supported in a highly dispersed state and easily oxidized. Therefore, it is preferable that alumina is used as the base material of the first catalyst and zeolite is used as the base material of the second catalyst. However, it is to make the relationship between the degree of dispersion and the oxidization easy and the same, but Ag is likely to be present in a single state when the carried amount is large, and easily oxidized when the carried amount is small. Therefore, it is preferable that the amount of Ag is larger in the first catalyst and smaller in the second catalyst.

The exhaust gas purifying catalyst containing the catalytic metal for reducing NO ₂ and at least one of Ag and Co is effective for purifying the exhaust gas containing NO ₂ .

[0018]

Therefore, according to the invention of this application, NO
A first catalyst for oxidizing NO to NO ₂ and oxidized NO
_{And a second} catalyst for reducing N2.
Containing a catalytic metal and a co-catalyst metal to reduce O ₂ ,
Since the co-catalyst metal is at least one selected from the group 1B elements and Co, NO ₂ oxidized by the first catalyst is efficiently reduced on the catalyst metal of the second catalyst using HC as a reducing agent. High NOx that can be decomposed
Purification performance is obtained.

In particular, when the promoter metal of the second catalyst is an oxide, or when Ag or Co is employed as the promoter metal and supported on zeolite, When Ag is used as the catalyst metal of the catalyst, it is advantageous for improving the NOx purification rate. Alternatively, a noble metal is used as the catalyst metal of the second catalyst, and the noble metal is supported on zeolite by ion exchange. This will be more advantageous for improving NOx purification performance.

Further, if the first catalyst and the second catalyst are arranged such that the former is on the upstream side in the exhaust gas flow direction and the latter is on the downstream side, NO generated by oxidation by the first catalyst is obtained.
₂ can be supplied to the second catalyst together with HC, and NOx
Purification performance is improved.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

<Structure of Exhaust Gas Purifying Catalyst> FIG. 1 shows an exhaust gas of an automobile diesel engine (NO concentration is, for example, 50 to 600 ppm and HC concentration is, for example, 10 to 100 ppm).
1 shows a structural example of an exhaust gas purifying catalyst 1 for purifying an exhaust gas of 0 ppmC. In the figure, 2 is NO for N
The first catalyst for oxidizing to O ₂ , 3 is the oxidized NO ₂
These two catalysts 2 and 3 are arranged in series such that the former is on the upstream side in the exhaust gas flow direction and the latter is on the downstream side. in this case,
The first catalyst 2 and the second catalyst 3 may be separately supported on the same carrier, or may be supported on different carriers and connected back and forth.

Although not shown, the first catalyst 3 and the third catalyst 3 may be supported on the same carrier in a layered manner. When the two catalysts 2 and 3 easily interfere with each other in catalytic function, a buffer layer may be provided between the two catalyst layers to prevent the interference therebetween. Of course, if both catalysts 2 and 3 do not interfere with each other, both can be mixed and supported on a carrier.

<Specific Example of Exhaust Gas Purification Catalyst> Example 1 The first catalyst on the upstream side is composed of an Ag / Al ₂ O ₃ catalyst in which Ag is supported on an alumina base material as a catalyst metal. For the downstream second catalyst, the synthetic zeolite ZSM5 (MF
I) Ag is solidly supported on the base material and Pt is used as a catalyst metal.
Was composed of a Pt ⁺ / ZSM5 (Ag supported) catalyst supported by ion exchange. The preparation method is as follows.

Preparation of First Catalyst Ag / Al ₂ O ₃ A high specific surface area γ-alumina powder was used as an alumina base material, and a 5: 1 hydrated alumina powder (binder) was used.
, And ion-exchanged water was added thereto and stirred to obtain a slurry. A monolith honeycomb carrier (having a capacity of 12.5 mL, 400 cells / square inch, and a wall thickness of 6 milliinch) made of cordierite is immersed in the slurry, and the slurry is pulled up and dried. The loading amount of the alumina base material is 13
0 g / L (the amount per 1 L of the honeycomb carrier; hereinafter the same). The drying temperature is 150 ° C. Then, the support was fired at 500 ° C. for 2 hours in an air atmosphere.

On the other hand, silver nitrate is dissolved in pure water (dissolution amount that does not saturate), a predetermined amount of this aqueous solution is impregnated into a carrier supporting the alumina base material, dried at 150 ° C., and further dried at 500 ° C. in an air atmosphere. Time calcination was performed. The amount of Ag carried on the first catalyst was 30 g / L. This first
In the catalyst Ag / Al ₂ O ₃ , the ratio of Ag present as a simple substance is higher than the ratio present as an oxide.

Note that silver acetate may be used instead of silver nitrate. The amount of impurities in the catalyst is 1% or less. This is the same for the other catalysts described below.

Preparation of Second Catalyst Pt ⁺ / ZSM5 (Ag supported) Silver nitrate (which may be silver acetate) is dissolved in pure water (dissolved amount that does not saturate).
The SM5 powder was charged, and Ag was supported on the ZSM5 by an evaporation to dryness method. Then, this was fired at 500 ° C. for 2 hours in an air atmosphere.

The ZSM5 powder carrying the above-mentioned Ag in a dry state is poured into water, heated with stirring, and when the liquid temperature reaches 80 ° C., hexaammineplatinum tetrachloride Pt (NH ₄ ) ₆
A predetermined amount of an aqueous solution of Cl ₄ was added, and stirring and heating were continued for 3 hours. This was allowed to cool and filtered, and the obtained solid was washed with pure water and further dried to obtain a powder. This is 3
By calcining at 50 ° C. for 2 hours, a Pt ⁺ / ZSM5 (Ag supported) catalyst powder was obtained. In this catalyst powder, most of Ag is Ag ₂ O.

The Pt ⁺ / ZSM5 (supporting Ag) catalyst powder and the hydrated alumina powder (binder) were weighed at a weight ratio of 5: 1, and ion-exchanged water was added thereto and stirred to obtain a slurry. A carrier similar to the carrier of the first catalyst (with a capacity of 2
5 mL), and then withdrawn and dried, ZSM in this carrier is repeated.
5 The supporting amount of the base material is 130 g / L, and the supporting amount of Pt is 0.3 g.
/ L (exactly 0.0015 mol / L, the same applies hereinafter),
Ag carrying amount was 1.6 g / L (more precisely, 0.015 mol / L
L). The drying temperature is 150 ° C. Then, this was fired at 500 ° C. for 2 hours in an air atmosphere.

Example 2 For the first catalyst on the upstream side, Ag / Al ₂
Composed of O ₃ catalyst, for the second catalyst downstream, ZSM
Pt ⁺ / ZSM5 (Co supported) in which Co is solid-supported on a base material and Pt is supported as a catalytic metal by ion exchange
It consisted of a catalyst. The preparation method is the same as that of Example 1 except that cobalt nitrate or cobalt acetate is used as the Co source of the second catalyst and silver nitrate is not used. The amount of supported Co is 0.9 g / L (accurately 0.015 mol
l / L).

Comparative Example 1 For the first catalyst on the upstream side, Ag / Al ₂
A Pt ⁺ / ZSM5 catalyst in which Pt is supported on a ZSM5 base material as a catalytic metal by ion exchange (Ag and Co are not supported on ZSM5), and the downstream second catalyst is constituted by an O ₃ catalyst. Configured. The preparation method is the same as that of Example 1 except that there is no Ag loading step in the preparation of the second catalyst.

Comparative Example 2 For the first catalyst on the upstream side, Ag / Al ₂
Composed of O ₃ catalyst, for the second catalyst downstream, ZSM
Pt ⁺ / ZSM5 (Ba supported) in which Ba is supported on dry basis and Pt is supported as a catalyst metal by ion exchange
It consisted of a catalyst. The preparation method is the same as that of Example 1 except that barium nitrate or barium acetate is used as the Ba source of the second catalyst and silver nitrate is not used. The amount of Ba supported is 2.1 g / L (accurately 0.015 mol
l / L).

Comparative Example 3 For the first catalyst on the upstream side, Ag / Al ₂ was used as in Example 1.
Composed of O ₃ catalyst, for the second catalyst downstream, ZSM
Pt ⁺ / ZSM5 (Mn supported) in which Mn is supported on a solid basis by drying and Pt is supported as a catalytic metal by ion exchange
It consisted of a catalyst. The preparation method is the same as that of Example 1 except that manganese nitrate or manganese acetate is used as the Mn source of the second catalyst and silver nitrate is not used. The amount of supported Mn is 0.8 g / L (more precisely, 0.015 mol
l / L).

Comparative Example 4 Both the first catalyst on the upstream side and the second catalyst on the downstream side were made of Ag / Al ₂ O ₃
It consisted of a catalyst. However, the capacity of the carrier of the second catalyst is 25 mL as in the other examples.

Comparative Example 5 Both the first catalyst on the upstream side and the second catalyst on the downstream side were Pt ⁺ / ZSM5
The catalyst (ZSM5 does not carry Ag or the like). However, the capacity of the carrier of the second catalyst is 25 mL as in the other examples.

<Measurement of NOx Purification Rate> In each of the above Examples and Comparative Examples, the first catalyst and the second catalyst were simulated such that the former was on the upstream side in the gas flow direction and the latter was on the downstream side. The maximum NOx purification rate was measured by incorporating a simulated exhaust gas having the following composition into an exhaust gas distribution device. In this measurement, the gas temperature at the first catalyst inlet was 150 ° C.
To 400 ° C. at a rate of 25 ° C./min. The space velocity is 56000 / h.

HC (C ₃ H ₆ ): 170 ppm C, NO: 17
0 ppm, CO: 200 ppm, CO ₂ : 2%, H ₂ O:
5%, O ₂ : 10%

The results are shown in FIG. According to the figure, Comparative Example 1 has a higher NOx purification rate than Comparative Examples 4 and 5, and therefore uses an Ag / Al ₂ O ₃ catalyst as the first catalyst and Pt ⁺ / ZSM5 as the second catalyst. The use of a catalyst is
It turns out that it is advantageous for improvement of the Ox purification rate. Therefore,
The NOx purification rates of Examples 1 and 2 and Ag and Comparative Examples 2 and 3 in which ZSM5 in Pt ⁺ / ZSM5 of this second catalyst was loaded were highest in Example 1 in which Ag was loaded, and Co
Example 2 in which Ba was supported was followed by this, and Comparative Example 2 in which Ba was supported and Comparative Example 3 in which Mn was supported had lower NOx purification rates than Comparative Example 1 in which no such metal was supported. ing.

From this, ZSM constituting the second catalyst
It can be seen that carrying Ag or Co on No. 5 is advantageous for improving the NOx purification rate. This is because Ag of the second catalyst
NO produced by oxidation of ₂ O or CoO by the first catalyst
Works effectively as a co-catalyst to attract ₂ and H on Pt
It is considered that the reduction reaction of NO ₂ using C proceeded efficiently.

<Regarding the First Catalyst> FIG. 3 shows the above Ag / Al ₂ O ₃
This is an evaluation of the suitability of the catalyst as a first catalyst. That is, the conversion rate from NO to NO ₂ was measured for each of the Ag / Al ₂ O ₃ catalyst, the Co / H-FAU catalyst, the Pt / Al ₂ O ₃ catalyst, and the Mn / Al ₂ O ₃ catalyst. The composition of the simulated exhaust gas used for this measurement and the contents of the Co / H-FAU catalyst, Pt / Al ₂ O ₃ catalyst and Mn / Al ₂ O ₃ catalyst are as follows, and the capacity of the honeycomb carrier was 25 mL.
It is. The temperature raising condition is the same as in the case of the measurement of the NOx purification rate.

HC (C ₃ H ₆ ): 170 ppm C, NO: 17
0 ppm, CO: 200 ppm, CO ₂ : 2.0%, H _{2
O: 5%, O 2:} 10%

Co / H-FAU This is a catalyst in which H-type FAU is used as a base material and Co is supported thereon as a catalytic metal.

Pt / Al ₂ O ₃ This is a catalyst in which γ-alumina is used as a base material and Pt is supported as a catalyst metal.

Mn / Al ₂ O ₃ This is a catalyst in which γ-alumina is used as a base material and Mn is supported thereon as a catalyst metal.

In each case, the same preparation method as that of the above-mentioned Ag / Al ₂ O ₃ catalyst was adopted for the preparation. The supported amount of the catalyst metal was 0.44 mol / L including the Ag / Al ₂ O ₃ catalyst.

According to FIG. 3, at a gas temperature of 250 ° C. or higher, the NO conversion rate of the Ag / Al ₂ O ₃ catalyst is the highest, and using this catalyst as the first catalyst is advantageous for NOx purification. Recognize.

<Ag carrying amount of Ag / Al ₂ O ₃ catalyst used for first catalyst> As described above, one of the reasons why the exhaust gas purifying catalyst according to the present invention is excellent is that the first catalyst is a catalyst for N
O is converted to NO ₂ . Therefore, the maximum NO conversion rate of the Ag / Al ₂ O ₃ catalyst was measured while varying the amount of Ag supported. The method for preparing the Ag / Al ₂ O ₃ catalyst was as described above, and the volume of the honeycomb support was 25 mL. The method for measuring the NO conversion is the same as that in FIG. The results are shown in FIG. The line L in FIG.
It is a maximum NO conversion line of a catalyst in which 2 g / L of Pt is supported on alumina.

According to the figure, the amount of Ag carried is 15-150.
g / L is preferable, and 20 to 120 g is more preferable.
/ L. Incidentally, the catalyst used for this measurement had a supported amount of alumina and binder together of 13
0 g / L, and the weight ratio of alumina to binder is 5: 1.

<Regarding the amount of Ag carried on the second catalyst> FIG. 5 shows the Ag / Al ₂ O ₃ used as the first catalyst and the Ag catalyst used as the second catalyst.
In Example 1 using Pt ⁺ / ZSM5 (supporting Ag), the effect of the amount of Ag supported on the NOx purification rate was examined. N
The measuring conditions and measuring method of the Ox purification rate are the same as those in FIG. In the same figure, Pt ⁺ / ZSM5 (supported after Ag) as the second catalyst
3 is also shown. Example 3
After preparing the above-mentioned Pt ⁺ / ZSM5 catalyst powder and supporting it on a carrier, the catalyst layer is impregnated with a silver nitrate solution, dried (150 ° C.) and calcined in air atmosphere (500 ° C.).
C. for 2 hours).

According to the figure, the amount of Ag carried is 0.8-6.
It can be seen that a high NOx purification rate can be obtained in the range of 4 g / L. In particular, the supported amount is 1.6 to 5.0 g / L.
It can be said that the degree is preferable. This point is the same in Example 1 in which Ag was loaded on ZSM5 of the second catalyst prior to Pt, and Example 2 in which Ag was loaded later. However, it can be said that it is more preferable to carry Ag first.

<Regarding the amount of Co supported on the second catalyst> FIG. 6 shows the case where the above Ag / Al ₂ O ₃ is used as the first catalyst and the above is used as the second catalyst.
In the case of Example 2 using Pt ⁺ / ZSM5 (supporting Co), the effect of the amount of supported Co on the NOx purification rate is shown. N
The measuring conditions and measuring method of the Ox purification rate are the same as those in FIG. According to the figure, the supported amount of Co is 0.9 to 2.7 g.
/ L, it can be seen that a high NOx purification rate can be obtained.

[Brief description of the drawings]

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

FIG. 2 shows the maximum NO of each catalyst of Examples and Comparative Examples of the present invention.
The graph which shows x purification rate.

FIG. 3 is a graph showing temperature characteristics of NO → NO ₂ conversion of a plurality of catalysts.

FIG. 4 is a graph showing the relationship between the amount of Ag carried on the first catalyst and the NO → NO ₂ conversion rate.

FIG. 5 is a graph showing the relationship between the amount of Ag carried on the second catalyst and the NOx purification rate.

FIG. 6 is a graph showing the relationship between the amount of Co carried on a second catalyst and the NOx purification rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust gas purification catalyst 2 First catalyst 3 Second catalyst

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 29/44 B01J 29/46 ZABA 29/46 ZAB F01N 3/10 A F01N 3/10 3/28 301E 3/28 301 301P B01D 53/36 102H 102G (72) Inventor Yasuhito Watanabe 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation

Claims (11)

[Claims] A first catalyst for oxidizing NO in exhaust gas to NO ₂ and a second catalyst for reducing oxidized NO ₂ , wherein the second catalyst reduces NO ₂ Catalyst metal and 1
An exhaust gas purifying catalyst comprising: at least one promoter metal selected from Group B elements and Co. 2. The exhaust gas purifying catalyst according to claim 1, wherein the promoter metal of the second catalyst is an oxide. 3. The exhaust gas purifying catalyst according to claim 1, wherein the second catalyst is provided on a carrier, and contains Ag as the promoter metal. A per liter of the carrier
An exhaust gas purifying catalyst, wherein the supported amount of g is 0.8 to 6.4 g. 4. The exhaust gas purifying catalyst according to claim 1, wherein the second catalyst is provided on a carrier, and contains Co as the promoter metal. C per liter of the carrier
An exhaust gas purifying catalyst, characterized in that the amount of o carried is 0.9 to 2.7 g. 5. The exhaust gas purifying catalyst according to claim 1, wherein the catalytic metal of the second catalyst is a noble metal. 6. The exhaust gas purifying catalyst according to claim 5, wherein the noble metal is supported on zeolite by ion exchange. 7. The exhaust gas purifying catalyst according to claim 1, wherein the first catalyst is provided to be supported on a carrier, and contains Ag as a catalyst metal. An exhaust gas purifying catalyst, wherein the amount of Ag carried per liter is 15 to 150 g. 8. The exhaust gas purifying catalyst according to claim 1, wherein the second catalyst is disposed downstream of the first catalyst in an exhaust gas flow direction. Exhaust gas purification catalyst. 9. A zeolite carrying a first catalyst containing Ag as a catalyst metal and a catalyst metal for reducing NOx in exhaust gas, wherein the zeolite contains at least one of Ag and Co. An exhaust gas purifying catalyst comprising: a supported second catalyst. 10. The exhaust gas purifying catalyst according to claim 9, wherein the first catalyst contains Ag present in a single state, and the second catalyst is supported on the zeolite in an oxide state. An exhaust gas purifying catalyst characterized by containing Ag or Co. 11. A exhaust gas purifying catalyst for purifying exhaust gas containing NO _2, and a noble metal catalyst for reducing NO _2, and at least one of Ag and Co is supported on zeolite An exhaust gas purifying catalyst, comprising: