JPH09225265A - Exhaust gas purification device - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide an exhaust gas purifying device capable of sufficiently purifying exhaust gas when an engine is started. SOLUTION: In an exhaust gas purifying apparatus at the time of starting an internal combustion engine, the concentration of palladium in an inorganic substance containing activated alumina as a main component at the exhaust gas inflow side is 4 wt% / g or more.
Use powder supported so as to be less than wt% / g, and carry a palladium amount of 100 g / cf or more, 500 g / c
The catalyst A, which is a three-way catalyst for purifying hydrocarbons, carbon monoxide, and nitrogen oxides near the stoichiometric air-fuel ratio by coating the honeycomb carrier so as to be f or less, is arranged. The adsorption catalyst B coated with zeolite effective for adsorbing the above was placed. Further, a catalyst layer selected from the group consisting of a combination of platinum, rhodium and palladium as a noble metal component was provided on these zeolite layers.

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 apparatus that purifies exhaust gas of an internal combustion engine when the engine is started.

[0002]

As an exhaust gas purifying apparatus using a conventional hydrocarbon adsorption catalyst, a catalyst coated with a three-way catalyst is arranged on the exhaust inflow side as shown in the specification of Japanese Patent Application No. 5-319931. At least one selected from the group consisting of mordenite, USY, β-zeolite, and ZSM5 is used as a zeolite on the exhaust gas outflow side, and platinum is used as a catalyst component in a powder containing activated ceria / or alumina as a main component on these zeolite layers. An exhaust gas purifying apparatus has been proposed in which an adsorption catalyst having a catalyst layer containing one or more noble metals selected from the group consisting of palladium, rhodium and the like is arranged.

[0003]

However, in such an exhaust gas purification apparatus, (1) the purification performance of the three-way catalyst used on the exhaust inflow side reaches the activation temperature because the exhaust gas is not sufficient in a low temperature range. Before, hydrocarbons are desorbed from the hydrocarbon adsorption catalyst on the exhaust gas outflow side. (2) Hydrocarbons are desorbed from the zeolite layer before the activation temperature is reached because the purification performance of the catalyst layer coated on the zeolite waste is insufficient. There are problems such as
Exhaust gas at engine start cannot be purified sufficiently.

[0004]

In order to solve such a conventional problem, an exhaust gas purifying apparatus of the present invention has a hydrocarbon adsorbent in an exhaust system of an internal combustion engine and at least one or more hydrocarbon adsorbents upstream thereof. In an exhaust gas purifying apparatus at the time of starting an internal combustion engine equipped with a three-way catalyst, the concentration of palladium in the inorganic material containing activated alumina as a main component on the exhaust gas inflow side is 4 wt%
/ G or more and 15 wt% / g or less of the supported powder, and a palladium carrier amount of 100 g / cf or more and 500 g / cf or less applied to the honeycomb carrier to give a hydrocarbon near the theoretical air-fuel ratio. The catalyst A, which is a three-way catalyst for purifying carbon monoxide and nitrogen oxides, is arranged, and the adsorption catalyst B, which is a honeycomb carrier coated with zeolite effective for adsorbing hydrocarbons, is arranged on the exhaust gas outflow side. As described in claim 2, at least one selected from the group consisting of mordenite, Y, USY, β-zeolite and ZSM-5 with the adsorption catalyst B as zeolite.
A catalyst layer selected from the group consisting of platinum and rhodium, palladium, palladium and rhodium, platinum and a combination of palladium and rhodium may be provided as a noble metal component on these zeolite layers by using one or more species.

[0005]

Embodiments of the present invention will be described below. P
1410 g of activated alumina powder carrying 4 wt% of d, 590 g of activated alumina, and 2000 g of 2% nitric acid solution were charged in a magnetic pot and mixed and pulverized by a vibration mill device to produce a washcoat slurry. This slurry was applied to a cordierite monolith carrier (1.3 L 400 cells), dried, and then calcined at 400 ° C. for 1 hour in an air atmosphere. The coating amount is about 2 after firing.
Repeated until it became 00g / L, and the amount of Pd supported was 160g.
(Catalyst A1) on the exhaust gas inflow side was obtained such that the ratio became / cf. Next, H-type USY zeolite (SiO ₂ / Al ₂
O ₃ = 50) 1000 g, silica sol (solid content 20%)
1000 g of water and 1000 g of water were put into a ball mill pot and pulverized to obtain a slurry, which was coated on a cordierite monolith carrier (1.3 L 400 cells) and dried.
It was calcined at 0 ° C. for 1 hour in an air atmosphere. This coating operation is repeated until the applied amount becomes about 150 g / L after firing. Further, in the same manner as above, a Pd-alumina catalyst layer was applied onto the USY layer so as to have a concentration of 100 g / L, dried and then calcined at 400 ° C. for 1 hour to remove (adsorption catalyst B1) on the exhaust gas outflow side. Obtained. Catalyst A on the exhaust inflow side
1. The adsorption catalyst B1 was combined with the exhaust gas outflow side to obtain a tandem type adsorption catalyst-1.

Next, the operation will be described. In the exhaust gas purifying apparatus of the present invention, a powder in which an inorganic material mainly composed of activated alumina is supported on the exhaust gas inflow side so that the concentration of palladium is 4 wt% / g or more and 15 wt% / g or less, and palladium is used. Carrying capacity 80g / cf or more, 500
A catalyst A, which is a three-way catalyst that is applied to the honeycomb carrier so as to be less than or equal to g / cf and purifies hydrocarbons, carbon monoxide, and nitrogen oxides near the stoichiometric air-fuel ratio, is arranged. An adsorption catalyst B coated with zeolite effective for adsorbing hydrocarbons is arranged, and the adsorption catalyst B is at least one selected from the group consisting of mordenite, Y, USY, β-zeolite and ZSM-5 as the zeolite.
Exhaust gas characterized by comprising a catalyst layer selected from the group consisting of platinum and rhodium, palladium, palladium and rhodium, a combination of platinum and palladium and rhodium as precious metal components on these zeolite layers using at least one species It is used as a purification device.

Palladium as a noble metal component is excellent in oxidation performance in a low temperature range, but it is not always possible to obtain sufficient oxidation activity in a low temperature range only by using palladium. Therefore, by setting the supported concentration of palladium to 4 wt% or more, the particle size of the supported palladium is set in advance to a particle size suitable for the catalytic reaction to improve the oxidation performance in the low temperature range. On the contrary, when the loading concentration is 15 wt% or more, the particle size of the loaded Pd becomes too large, the active sites of the catalytic reaction decrease, and the sufficient activity improving effect in the low temperature range cannot be obtained.

Zeolite used for the adsorption catalyst is Y, US, which corresponds to the diameter of hydrocarbon contained in the exhaust gas.
Y, mordenite, β-zeolite, ZSM5 can be used. Further, in order to efficiently adsorb many kinds of hydrocarbons, it is possible to mix two or more kinds of zeolites having different pore sizes.

Although various zeolites have sufficient adsorption ability even in the H type, they carry metal components such as Pd, Pt, Cu, Co and Ag by a usual method such as ion exchange, impregnation method and immersion method. As a result, the hydrocarbon adsorption and desorption characteristics can be further improved. Although each supported amount may be arbitrary, for example, about 0.1 to 15 wt% is preferable. If it is less than 0.1 wt%, the adsorption property of hydrocarbons and the desorption suppressing effect are small, and conversely, if it exceeds 15 wt%, the effect does not change.

Further, by coating the zeolite layer with a three-way catalyst layer of platinum and rhodium catalyst, palladium catalyst, palladium and rhodium catalyst, platinum and palladium and rhodium catalyst, etc. Hydrogen can be purified when it is desorbed when the exhaust temperature rises, and under the condition that the exhaust temperature rises sufficiently, the unpurified hydrogen that could not be sufficiently purified by the upstream three-way catalyst The exhaust gas component can be purified, and the exhaust gas component can be sufficiently purified from the condition that the exhaust temperature is low when the engine is started.

Another embodiment will be described below. (Example 2) An exhaust gas purifying apparatus similar to that of Example 1 was adopted except that the concentration of Pd carried in Example 1 was changed to 8 wt% instead of 4 wt% and the coating amount was changed to 150 g / L. Pd 8w
A magnetic pot was charged with 940 g of activated alumina powder supporting t%, 1060 g of activated alumina and 2000 g of a 2% nitric acid solution, and the mixture was ground by a vibration mill device to produce a washcoat slurry. It is applied to a cordierite monolith carrier (1.3 L 400 cells), dried, and then 400 ° C.
Calcination for 1 hour in an air atmosphere. This coating operation was repeated until the applied amount became about 150 g / L after firing so that the Pd carrying amount became 160 g / cf to obtain (catalyst A2) on the exhaust gas inflow side. A catalyst A2 was combined with the exhaust inflow side and an adsorption catalyst B1 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-2.

(Embodiment 3) The concentration of Pd supported in Embodiment 1 is set to 4
12 wt% instead of wt% and the coating amount is 150 g / L
Except for the above, the same exhaust gas purification device as in Example 1 was used. Activated alumina powder 630 carrying 12% by weight of Pd
g, activated alumina 1370 g, 2% nitric acid solution 2000 g
Was charged into a magnetic pot and mixed and pulverized with a vibration mill device to produce a wash coat slurry. It was applied to a cordierite monolith carrier (1.3 L 400 cells), dried, and then calcined at 400 ° C. for 1 special period in an air atmosphere.
The coating amount is about 150g after firing.
The amount of Pd carried was repeatedly set to 160 g / cf until it became / L to obtain (catalyst A3) on the exhaust gas inflow side. A catalyst A3 was combined with the exhaust inflow side and an adsorption catalyst B1 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-3.

(Embodiment 4) The concentration of Pd supported in Embodiment 1 is set to 4
8 wt% instead of wt%, coating amount 150 g / L
The exhaust gas purifying apparatus was the same as in Example 1 except that the amount of Pd carried was 240 g / L. 1410 g of activated alumina powder carrying 8 wt% of Pd, activated alumina 590
g, a 2% nitric acid solution (2000 g) was charged into a magnetic pot and mixed and pulverized with a vibration mill device to produce a washcoat slurry. Cordierite monolith carrier (1.3L
400 cells) and dried, then at 400 ℃ for 1 hour,
It was calcined in an air atmosphere. This coating operation is repeated until the coating amount becomes about 150 g / L after firing.
The amount of ad supported was set to 240 g / cf to obtain (catalyst A4) on the exhaust gas inflow side. The catalyst A4 was combined with the exhaust inflow side and the adsorption catalyst B1 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-4.

(Embodiment 5) The concentration of Pd supported in Embodiment 1 is set to 4
The exhaust gas purifying apparatus was the same as that of Example 1 except that the coating amount was 220 g / L and the Pd carrying amount was 480 g / L instead of 8 wt%. 1920g of activated alumina powder carrying 8wt% of Pd, 80g of activated alumina, 2
% Nitric acid solution (2000 g) was charged in a magnetic pot and mixed and pulverized by a vibration mill device to produce a washcoat slurry. Cordierite monolith carrier (1.3L 40
(0 cell), dried, and then calcined at 400 ° C. for 1 hour in an air atmosphere. This coating operation was repeated until the applied amount became about 220 g / L after firing, and the Pd loading amount was set to 480 g / cf, to obtain the catalyst A5 on the exhaust gas inflow side. The catalyst A5 is combined with the exhaust inflow side and the adsorption catalyst B1 is combined with the exhaust outflow side to form a tandem type adsorption catalyst-5).
I got

Example 6 An exhaust gas purifying apparatus similar to that of Example 1 was used except that a mixture of USY zeolite and β zeolite was used instead of the USY zeolite of Example 1. H-type USY zeolite (SiO ₂ / Al ₂ O ₃ = 5
0) 500 g, H-type β zeolite (SiO ₂ / Al ₂ O
₃ = 100) 500 g, silica sol (solid content 20%)
1000 g of water and 1000 g of water were put into a ball mill pot and pulverized to obtain a slurry, which was coated on a cordierite monolith carrier (1.3 L 400 cells) and dried.
Calcination was performed at 0 ° C. for 1 hour in an air atmosphere. This coating operation is repeated until the applied amount becomes about 150 g / L after firing. Further, USY and β were obtained by the same method as in Example 1.
A Pd-alumina catalyst layer was formed on the zeolite warming layer 10 times.
It was coated so as to be 0 g / L, dried and calcined at 400 ° C. for 1 hour to obtain (adsorption catalyst B2) on the exhaust gas outflow side. The catalyst A1 is on the exhaust inflow side, and the adsorption catalyst B2 is on the exhaust outflow side.
Were combined to obtain a tandem type adsorption catalyst-6.

(Example 7) Instead of the USY zeolite of Example 1, USY zeolite, β zeolite and ZSM5
An exhaust gas purifying apparatus similar to that in Example 1 was used except that the mixture of No. 1 was used. H-type USY zeolite (SiO ₂ / Al ₂
O ₃ = 50) 200 g, H type β zeolite (SiO ₂ /
Al ₂ O ₃ = 100) 400 g, H-type ZSM5 zeolite (SiO ₂ / Al ₂ O ₃ = 700) 400 g, silica sol (solid content 20%) 1000 g, and water 1000 g were put into a ball mill pot and pulverized to obtain a slurry. Cordierite monolith carrier (1.3L 400 cells)
After being applied and dried, it was calcined at 400 ° C. for 1 hour in an air atmosphere. This coating operation is repeated until the applied amount becomes about 150 g / L after firing. Furthermore, Example 1
In the same manner as above, a Pd-alumina catalyst layer was coated on the mixed layer of USY, β-zeolite and ZSM5 so as to be 100 g / L, dried and calcined at 400 ° C. for 1 hour. Obtained. Catalyst A1 on the exhaust inflow side,
An adsorption catalyst B3 was combined with the exhaust gas outflow side to obtain a tandem type adsorption catalyst-7.

(Example 8) An exhaust gas purifying apparatus similar to that of Example 1 was used except that a combination of β zeolite and ZSM5 was used instead of the USY zeolite of Example 1. H type β
Zeolite (SiO ₂ / Al ₂ O ₃ = 100) 500
g, H type ZSM5 zeolite (SiO ₂ / Al ₂ O ₃ =
700) 500 g, silica sol (solid content 20%) 100
0 g and 1000 g of water were placed in a ball mill pot and pulverized to obtain a slurry, which was applied to a cordierite monolith carrier (1.3 L 400 cells), dried, and then calcined at 400 ° C. for 1 hour in an air atmosphere. . This coating operation is repeated until the applied amount becomes about 150 g / L after firing. Further, β zeolite and Z were prepared in the same manner as in Example 1.
100g of Pd-alumina catalyst layer on the mixed layer of SM5
/ L, and dried and baked at 400 ° C. for 1 hour to obtain an adsorption catalyst B4 on the exhaust gas outflow side. A catalyst A1 was combined with the exhaust inflow side and an adsorption catalyst B4 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-8.

Example 9 An exhaust gas purifying apparatus similar to that of Example 1 was used except that a mixture of β zeolite and mordenite was used instead of the USY zeolite of Example 1. H
Type β zeolite (SiO ₂ / Al203 = 100) 50
0 g, H-type mordenite (SiO ₂ / Al203 = 20
0) 500 g, silica sol (solid content 20%) 1000
g, 1000 g of water was thrown into a ball mill pot and pulverized, and the resulting slurry was applied to a cordierite monolith carrier (1.3 L 400 cells), dried, and then calcined at 400 ° C. for 1 hour in an air atmosphere. did. This coating operation is repeated until the applied amount becomes about 150 g / L after firing. Further, in the same manner as in Example 1, 10 Pd-alumina catalyst layers were formed on the mixed layer of β zeolite and mordenite.
It was coated so as to be 0 g / L, dried and calcined at 400 ° C. for 1 hour to obtain an adsorption catalyst B5 on the exhaust gas outflow side. The catalyst A1 was combined with the exhaust inflow side and the adsorption catalyst B5 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-9.

(Example 10) Pt / Pd was used instead of the Pd catalyst layer on the mixture layer of β zeolite and ZSM5 of Example 8.
An exhaust gas purification apparatus similar to that in Example 8 was used except that the Rh catalyst layer was used. In the same manner as in Example 8, β zeolite and ZS
The mixture of M5 is applied so that the applied amount will be about 150 g / L after firing. Next, 1130 g of activated alumina powder carrying 2 wt% of Pt, 80 g of activated alumina powder carrying 3 wt% of Rh, 550 g of cerium oxide, 240 g of activated alumina, 2000 g of 2% nitric acid solution were charged in a magnetic pot and mixed and ground with a vibration mill device. To produce a washcoat slurry, and using this slurry, the coating amount after drying on the mixed layer of β zeolite and ZSM5 is 100 g /
It was coated so as to be L, dried, and calcined at 400 ° C. for 1 hour to obtain an adsorption catalyst B6 on the exhaust gas outflow side. The catalyst A1 was combined with the exhaust inflow side and the adsorption catalyst B6 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-10.

Example 11 Pd / Pd was used instead of the Pd catalyst layer on the mixture layer of β zeolite and ZSM5 of Example 8.
An exhaust gas purification apparatus similar to that in Example 8 was used except that the Rh catalyst layer was used. In the same manner as in Example 8, β zeolite and ZS
The mixture of M5 is applied so that the applied amount will be about 150 g / L after firing. Next, 1300 g of activated alumina powder carrying 4 wt% of Pd, 160 g of activated alumina powder carrying 3 wt% of Rh, 270 g of cerium oxide, 270 g of activated alumina, 2000 g of 2% nitric acid solution were charged in a magnetic pot and mixed and pulverized with a vibration mill device. A washcoat slurry is produced, and the slurry is used to apply a coating amount of 100 g / L on a mixed layer of β zeolite and ZSM5 after drying.
To obtain an adsorption catalyst B7 on the exhaust gas outflow side. The catalyst A1 is installed on the exhaust inflow side, and the adsorption catalyst B7 is installed on the exhaust outflow side.
A tandem type adsorption catalyst-11 was obtained.

(Example 12) Instead of the Pd catalyst layer on the mixture layer of β zeolite and ZSM5 of Example 8, Pt /
The same exhaust gas purification apparatus as in Example 8 was used except that the Pd / Rh catalyst layer was used. In the same manner as in Example 8, the coating amount of the mixture of β zeolite and ZSM5 was applied or about 150 g after firing.
/ L to apply. Next, 1180 g of activated alumina powder carrying 4 wt% of Pd, 160 g of activated alumina powder carrying 3 wt% of Rh, 240 g of activated alumina powder carrying 2 wt% of Pt, 270 g of cerium oxide,
150 g of activated alumina and 2000 g of 2% nitric acid solution were charged into a magnetic pot, mixed and pulverized by a vibration mill device to produce a wash coat slurry, and the slurry was used to apply a coating amount after drying on a mixed layer of β zeolite and ZSM5. Or 1
Coat to 00g / L, dry, 1 at 400 ℃
Firing was performed for an hour to obtain an adsorption catalyst B8 on the exhaust gas outflow side.
The catalyst A1 was combined with the exhaust inflow side and the adsorption catalyst B8 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-12. As the zeolite used in each example, in addition to H-type zeolite, P
Zeolites supporting metals such as t, Pd, Ag, Cu and Co can be used.

Comparative Example 1 1410 g of activated alumina powder carrying 2 wt% of Pd, 590 g of activated alumina, 2%
A nitric acid solution (2000 g) was charged in a magnetic pot and mixed and pulverized by a vibration mill device to produce a washcoat slurry. Cordierite monolith carrier (1.3L 40
(0 cell), dried, and then calcined at 400 ° C. for 1 hour in an air atmosphere. This coating operation was repeated until the coating amount became about 200 g / L after firing, and the Pd loading amount was set to 80 g / cf to obtain the catalyst A6 on the exhaust gas inflow side. A catalyst A6 was combined with the exhaust inflow side and an adsorption catalyst B1 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-R1.

COMPARATIVE EXAMPLE 2 H-type USY (SiO ₂ / Al
₂ O ₃ = 7) 1000 g, silica sol (solid content 20%)
1000 g of water and 1000 g of water were put into a ball mill pot and pulverized to obtain a slurry, which was coated on a cordierite monolith carrier (1.3 L 400 cells) and dried, and then 4
It was calcined in an air atmosphere at 00 ° C. for 1 hour. This coating operation was repeated until the coating amount became about 150 g / L after firing, to obtain adsorption catalyst B9. The catalyst A1 was combined with the exhaust inflow side and the adsorption catalyst B9 was combined with the exhaust outflow side to obtain a tandem type adsorption catalyst-R2.

The catalyst specifications of Examples 1 to 12 and Comparative Examples 1 and 2 described above are summarized in FIG.

Further, for each of the examples and comparative examples, the HC purification characteristic evaluation (FTP75 A-ba) was carried out under the following evaluation conditions.
g) was performed using a vehicle manufactured by Nissan Motor Co., Ltd. (displacement: 3 L). The result is shown in FIG.

Performance Evaluation Conditions As the evaluation conditions, the emission reduction rate of A-bag for 0 to 125 seconds was measured in order to evaluate the HC purification ability discharged at engine start.

Gas composition At engine start (0 to 125 seconds) 44.4% aromatics 33.3% paraffins 22.3% olefins The embodiments of the present invention have been described in detail above. The present invention is not limited to the embodiments, and changes and the like within the scope of the present invention are included in the present invention.

[0028]

As described above, the exhaust gas purifying apparatus at the time of starting the internal combustion engine, which is provided with the hydrocarbon adsorbent in the exhaust system of the internal combustion engine of the present invention and at least one or more three-way catalyst upstream thereof. In the exhaust gas inflow side, the concentration of palladium in the inorganic material mainly composed of activated alumina was 4 wt% /
a powder supported so as to be not less than g and not more than 15 wt% / g, and the amount of palladium carried is not less than 100 g / cf,
A catalyst A, which is a three-way catalyst that is applied to a honeycomb carrier so as to be 500 g / cf or less and purifies hydrocarbons, carbon monoxide, and nitrogen oxides near the stoichiometric air-fuel ratio, is arranged. An adsorption catalyst B coated with zeolite effective for adsorption of hydrocarbons is arranged, and the adsorption catalyst B is used as zeolite for mordenite, Y, USY, β.
One zeolite, at least one selected from the group consisting of ZSM-5 is used, and platinum and rhodium as precious metal components on these zeolite layers are selected from the group consisting of platinum and a combination of palladium and rhodium. With the exhaust gas purifying device characterized by being provided on these zeolite layers provided with the above-mentioned catalyst layer, the emission amount of hydrocarbons immediately after the engine is started can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing catalyst specifications of Examples 1 to 12 and Comparative Examples 1 and 2.

FIG. 2 is a diagram showing conditions for evaluating HC purification characteristics.

[Explanation of symbols]

 None

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location B01J 29/44 F01N 3/20 H F01N 3/20 3/22 321A 3/22 321 3/24 ZABE 3/24 ZAB B01D 53/36 ZAB

Claims (2)

[Claims] 1. In an exhaust gas purifying apparatus for starting an internal combustion engine, which comprises a hydrocarbon adsorbent in an exhaust system of the internal combustion engine and at least one three-way catalyst upstream thereof, activated alumina is provided on an exhaust inflow side. An inorganic substance used as a main component is a powder that is loaded so that the concentration of palladium is 4 wt% / g or more and 15 wt% / g or less, and the amount of palladium loaded is 1
The catalyst A, which is a three-way catalyst that is applied to the honeycomb carrier to remove hydrocarbons, carbon monoxide, and nitrogen oxides near the stoichiometric air-fuel ratio so as to be not less than 00 g / cf and not more than 500 g / cf, is arranged, and exhaust gas outflow An exhaust gas purifying device capable of purifying exhaust gas discharged at a low exhaust gas temperature at engine start-up, in which an adsorption catalyst B coated with zeolite effective for adsorbing hydrocarbons is arranged on the side. 2. The adsorption catalyst B uses at least one selected from the group consisting of mordenite, Y, USY, β-zeolite and ZSM-5 as zeolite, and platinum and rhodium as precious metal components on these zeolite layers.
The exhaust gas purifying apparatus according to claim 1, comprising a catalyst layer selected from the group consisting of palladium, palladium and rhodium, platinum and a combination of palladium and rhodium.