JPH09192486A - Exhaust gas purifying catalyst for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent deterioration in purifying rate of exhaust gas by suppressing the generation of HC poisoning due to the chemical adsorption of high b.p. HC components contained in the exhaust gas to cerium oxide. SOLUTION: This exhaust gas purifying catalyst is provided in the exhaust gas system of an engine and produced by providing a catalyst layer 4 containing a catalyst novel metal composed of palladium or the like, cerium oxide having occluding capacity, a zeolite having excellent adsorption of the high b.p. HC components, for example, FAU(faujasite) β type zeolite, MOR(mordenite), LTL(L type zeolite) or MF1(ZSM-5) on a catalyst carrier 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust gas purifying catalyst for purifying engine exhaust gas.

[0002]

2. Description of the Related Art Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 3-56139, a first coat layer made of an alumina layer containing rhodium is provided on a catalyst carrier,
An exhaust gas purifying catalyst has been proposed in which a second coat layer composed of palladium-fixed cerium oxide particles and activated alumina particles is provided on the first coat layer.

The above-mentioned exhaust gas purifying catalyst is a three-way catalyst in which palladium is used in place of platinum which is generally used as a catalytic noble metal constituting a three-way catalyst to improve the low temperature activity of the catalyst. , By suppressing the sintering (aggregation) by supporting the palladium above and below the catalyst carrier separately, and by effectively absorbing the exhaust gas by occluding oxygen in the cerium oxide. is there.

[0004]

An exhaust gas purifying catalyst (Pd-based catalyst) having the above catalytic noble metal made of palladium and cerium oxide and the like, and general exhaust gas using the catalytic noble metal made of platinum as described above. When the relationship between the traveling distance of the automobile and the emission amount of the HC (hydrocarbon) component of the purification catalyst (Pt-based catalyst) was compared, the data shown in FIG. 10 was obtained. The HC emission amount shown in FIG. 10 represents the total emission amount in the running test in the FTP mode which is the US standard test mode.

From the above data, since palladium is excellent in low-temperature activity in the Pd-based catalyst, the catalytic action of the palladium and the oxygen-releasing action of the cerium oxide cause the HC emission amount of the exhaust gas at the initial stage of traveling to be the Pt-based catalyst. Although it is smaller than that of the above, it can be seen that the HC emission amount of the exhaust gas increases remarkably as the traveling distance increases, and the purification rate of the exhaust gas tends to decrease early.

The early reduction of the purification rate of the Pd-based catalyst causes HC poisoning in which cerium oxide in the catalyst layer has a high-boiling HC component such as toluene chemisorbed, which causes oxygen in the cerium oxide particles. The storage capacity is reduced,
It is considered that this is because cerium oxide does not function as an oxygen supply source. That is, when the state of the Pd-based catalyst in which the purification rate of the exhaust gas is lowered is analyzed, the cerium oxide in the catalyst layer has a high boiling point HC such as toluene
It was confirmed that a large amount of components were adsorbed, and this HC
It was found that the poisoning causes a reduction in the exhaust gas purification rate.

The present invention has been made in order to solve the above problems, and has a high boiling point HC contained in exhaust gas.
(EN) An exhaust gas purifying catalyst for an engine capable of suppressing generation of HC poisoning due to chemical adsorption of components to cerium oxide and effectively preventing a reduction in exhaust gas purification rate.

[0008]

The invention according to claim 1 is
An exhaust gas purification catalyst installed in an exhaust system of an engine, the catalyst layer containing a catalytic noble metal, cerium oxide having an oxygen storage capacity, and zeolite having an excellent adsorbability for a high boiling HC component. Is provided.

According to this structure, since the high boiling point HC component contained in the exhaust gas is effectively adsorbed by the zeolite contained in the catalyst layer, the cerium oxide in the catalyst layer has a high boiling point. H due to chemisorption of the HC component of
The occurrence of C poisoning will be effectively suppressed.

According to a second aspect of the present invention, in the engine exhaust gas purifying catalyst according to the first aspect, the cerium oxide catalyst particles in which the catalyst noble metal made of palladium is carried on the particles formed of cerium oxide and the zeolite are used. A catalyst layer is formed by the formed particles and zeolite catalyst particles in which a catalytic noble metal made of palladium is carried.

According to this structure, since the catalyst noble metal, which is excellent in low-temperature activity, is used, the exhaust gas is effectively purified at low temperature. Further, since the palladium is supported on the particles of cerium oxide and the particles of zeolite, respectively, it is effective that a sintering phenomenon occurs in the palladium due to the fact that palladium is supported at a high density in the particles of zeolite. Will be prevented.

The invention according to claim 3 is the exhaust gas purifying catalyst for an engine according to claim 1 or 2, wherein the catalyst layer contains zeolite having a pore size of 5 Å or more.

According to this structure, the zeolite constituting the catalyst layer has a pore size such as FAU (faujasite), β-type zeolite, MOR (mordenite), LTL (L-type zeolite) or MFI (ZSM-5). Since the high boiling point HC component contained in the exhaust gas is effectively adsorbed by the zeolite, an effect of effectively suppressing HC poisoning of cerium oxide can be obtained.

[0014] The invention according to claim 4 is the above-mentioned claims 1-3.
In the exhaust gas purifying catalyst for an engine according to any one of items 1 to 5, the ratio of zeolite to the total weight of cerium oxide constituting the catalyst layer and zeolite is 2.5 to 13 w.
It is set within the range of t%.

According to this structure, the zeolite can sufficiently exert the effect of suppressing the HC poisoning of cerium oxide, and the cerium oxide amount is sufficiently secured so that an appropriate amount of oxygen is stored in the cerium oxide. Will be.

The invention according to claim 5 is the above-mentioned claims 1 to 4.
In the exhaust gas purifying catalyst for an engine according to any one of the above, a second catalyst containing a catalytic noble metal, cerium oxide, and zeolite on a first catalytic layer containing aluminum oxide and a catalytic noble metal made of palladium. The layers are arranged.

According to this structure, the HC component in the exhaust gas is effectively purified by the aluminum oxide component and the palladium component of the first catalyst layer, and the HC component in the exhaust gas is distributed above it by the catalytic reaction heat of the first catalyst layer. By heating the provided second catalyst layer, HC poisoning of the cerium oxide contained in the second catalyst layer is effectively prevented.

[0018]

1 and 2 show an embodiment of an engine exhaust gas purifying catalyst according to the present invention.
This exhaust gas purifying catalyst has a honeycomb-shaped catalyst carrier 2 having a plurality of through holes 1 into which exhaust gas discharged from an engine is introduced, and a catalyst carrier 2 supported on the wall surface of the through holes 1 of the catalyst carrier 2. It has one catalyst layer 3 and a second catalyst layer 4 arranged above it.

The first catalyst layer 3 is composed of aluminum oxide catalyst particles 7 in which a catalytic noble metal made of palladium is supported on aluminum oxide (Al ₂ O ₃ ) particles. The second catalyst layer 4 includes cerium oxide catalyst particles 5 in which a noble metal catalyst made of palladium (Pd) is carried on particles made of cerium oxide (CeO ₂ ) having an oxygen storage capacity, and noble metal made of zeolite particles. It is formed of zeolite catalyst particles 6 carrying a catalyst.

Zeolite catalyst particles 5 of the second catalyst layer 4
The zeolite constituting the is a zeolite having an excellent adsorptivity for an HC component having a property of easily poisoning cerium oxide with HC, that is, a high-boiling HC component such as toluene, hexane, or benzene, such as FAU (forgery). Site) etc.

Further, the ratio of zeolite to the total weight of cerium oxide and zeolite constituting the second catalyst layer 4 is set within the range of 2.5 to 13 wt%. This is because when the proportion of zeolite is less than 2.5 wt%, the effect of suppressing HC poisoning of cerium oxide by the zeolite cannot be sufficiently obtained as described later, and when the proportion of zeolite is more than 13 wt%, This is because the amount of cerium oxide is relatively decreased and an appropriate amount of oxygen is not stored in this cerium oxide, and the function of purifying HC components in the exhaust gas by oxygen supplied from this cerium oxide decreases. is there.

The catalytic noble metal contained in the first and second catalyst layers 3 and 4 is not limited to the above palladium (Pd), but other noble metals such as platinum (Pt) or rhodium (Rh) can be used. However, when the above palladium is used, there is an advantage that it is excellent in low-temperature activity. The amount of the catalytic noble metal carried with respect to the volume of the catalyst carrier 2 is not particularly limited as long as it is 0.1 g / liter or more, but when palladium is used as the catalytic noble metal, its exhaust gas In order to prevent unnecessary catalyst noble metal from being supported while maintaining a sufficient purification function, it is desirable to set the amount supported on the catalyst carrier 2 within the range of 3 to 15 g / liter.

An embodiment of the method for producing the exhaust gas purifying catalyst will be described below. First, γ-alumina (γ-
480 g of Al ₂ O ₃ ) powder, 120 g of boehmite,
1 liter of water and 10 cc of nitric acid (HNO ₃ ) are mixed and stirred to prepare a slurry, and then a catalyst carrier 2 made of a heat-resistant metal material or a ceramic material is immersed in the slurry to form the catalyst carrier 2 The above slurry is attached to and pulled up.

Then, after excess slurry attached to the catalyst carrier 2 is blown off by air blow, it is heated to 250 ° C.
After drying at moderate temperature for about 2 hours, 600 ° C
By calcining at a temperature of about 2 hours for about 2 hours, a γ-alumina layer having a large number of pores is formed on the inner wall surface of each through hole 1 formed in the catalyst carrier 2.

Next, the catalyst carrier 2 is immersed in a dinitrosamine palladium solution prepared so as to form a first catalyst layer 3 by supporting a predetermined amount of palladium on the γ-alumina layer, and the dinitrosine is then added. After depositing the amine palladium solution on the γ-alumina layer, drying is performed at a temperature of about 250 ° C. for about 2 hours and baking is performed at a temperature of about 600 ° C. for about 2 hours.
The first catalyst layer 3 is formed.

Further, cerium oxide and zeolite were mixed and stirred so that the ratio of zeolite to the total weight of cerium oxide and zeolite was 2.5 to 13 wt%, and then a predetermined amount of dinitrosaminepalladium was added thereto. Add the solution, stir and dry. Then, after calcining at a temperature of about 700 ° C. for about 2 hours, the calcined product is crushed by a ball mill to obtain cerium oxide catalyst particles 5 in which palladium is supported on cerium oxide powder, and zeolite. A zeolite catalyst powder 6 having palladium supported on the powder is formed.

Then, 540 g of a mixture of the cerium oxide catalyst powder 5 and the zeolite catalyst powder 6 described above, 60 g of boehmite, 1 liter of water, and 10 c of nitric acid (HNO ₃ ).
After mixing with c and stirring to form a slurry, the catalyst carrier 2 is dipped in the slurry, the slurry is attached to the carrier 2, and the catalyst 2 is pulled up. Then, after the excess slurry attached to the catalyst carrier 2 is blown off by air blow, it is dried at a temperature of about 200 ° C for about 2 hours and then calcined at a temperature of about 600 ° C for about 2 hours. Thereby, the second catalyst layer 4 composed of the cerium oxide catalyst powder 5 and the zeolite catalyst powder 6 is formed on the first catalyst layer 3.

The exhaust gas purifying catalyst having the above-mentioned structure comprises cerium oxide catalyst particles 5 in which a catalytic noble metal such as palladium is supported on particles formed of cerium oxide, and H having a high boiling point.
Since it has a catalyst layer composed of zeolite catalyst particles 6 in which a catalytic noble metal such as palladium is supported on particles formed of zeolite having excellent adsorptivity for C component, it has a high boiling point such as toluene. It is possible to effectively prevent HC components from being chemically adsorbed to cerium oxide and poisoning the cerium oxide with HC. Therefore, the cerium oxide absorbs a sufficient amount of oxygen, and the oxygen released from the cerium oxide and the catalytic action of the catalytic noble metal effectively oxidize the HC component in the exhaust gas to produce the exhaust gas. Can be purified.

An experimental example conducted for confirming the performance of the gas purification catalyst having the above catalyst layer will be described below.
In this experiment, a catalyst noble metal made of palladium whose loading amount on the catalyst carrier 2 was set to 10 g / liter,
An exhaust gas purifying catalyst according to Example A of the present invention, which comprises a catalyst layer containing cerium oxide and a zeolite made of FAU and having a ratio of the zeolite to the total weight of the cerium oxide and the zeolite set to 10 wt%. The exhaust gas purifying catalyst according to Comparative Example B having a catalyst layer composed of cerium oxide and a noble metal catalyst made of palladium was used by omitting the zeolite.

Then, each of the above exhaust gas purifying catalysts has 30
Simulated with 1000 ppm toluene flowing at 20 ° C. for 20 minutes to adsorb, and at 200 ° C. the air-fuel ratio (A / F) was set to 14.7 ± 0.9. Exhaust gas space velocity (SV) of 60,000 h ^-1
The purification rate of the HC component in the exhaust gas was measured.

As a comparison of how the purification rate of the HC component changes before and after adsorbing toluene on the exhaust gas purifying catalyst, as shown in FIG. In the exhaust gas purifying catalyst according to Example A of the invention, the purification rate of HC components hardly changed before and after the adsorption of toluene, whereas in the exhaust gas purifying catalyst according to Comparative Example B, the HC purification rate after adsorption of toluene It was confirmed that the purification rate of the components was significantly reduced.

Further, in the above experimental example, IR spectrum (infrared absorption spectrum) analysis for confirming the adsorption state of toluene on cerium oxide was carried out.
Then, as shown in FIG. 4, the peak value of the chemisorbed HC species is high, whereas in Example A of the present invention, as shown in FIG. 5, the peak value of the chemisorbed HC species is relatively high. It was confirmed to be low. This is because, as shown in the above-mentioned Example A, when the catalyst layer contains zeolite made of FAU, toluene is effectively adsorbed by the zeolite, so that the toluene which is chemically adsorbed by cerium oxide is It shows that the amount is decreased and the generation of HC poisoning is effectively suppressed.

Then, the exhaust gas purifying catalyst according to Example A of the present invention, the exhaust gas purifying catalyst according to Comparative Example B, and the aluminum oxide (instead of the zeolite of the exhaust gas purifying catalyst according to Example A above) Al ₂ O ₃ ) was used in Comparative Example C in which the catalyst layer was contained, and the change state of the purification rate of the HC component was measured when the circulation time of toluene was variously changed, and as shown in FIG. Data was obtained.

From the above data, in Example A of the present invention, even when the circulation time of toluene was lengthened, H
While the purification rate of the C component was not significantly lowered, in Comparative Example B in which neither the zeolite nor the aluminum oxide was contained in the catalyst layer, the amount of HC component It was confirmed that the purification rate was significantly reduced.

Further, in Comparative Example C in which aluminum oxide is contained in the catalyst layer instead of the above zeolite, the purification rate of the HC component is good when the toluene circulation time is short, while the toluene circulation time is long. It was confirmed that the purification rate of the HC component drastically decreases in accordance with the above. This indicates that the aluminum oxide contained in the catalyst layer has a small toluene absorption capacity, and the toluene adsorption capacity is impaired at an early stage.

Further, in the exhaust gas purifying apparatus according to the present invention, an experiment was conducted to confirm the effect of the proportion of zeolite contained in the catalyst layer on the purification rate of HC components. Was obtained. That is, the cerium oxide constituting the catalyst layer and the ratio of the zeolite to the total weight of the zeolite (wt%) is set to various values, and the purification rate of the HC component after the adsorption of toluene was measured, respectively. It was confirmed that the HC component in the exhaust gas can be effectively purified when the ratio (wt%) is set within the range of 2.5 to 13 wt%.

This is because the proportion of zeolite is 2.5 wt%
When the amount is less than the above, since the amount of zeolite is small, the effect of suppressing the HC poisoning of the cerium oxide by the zeolite becomes insufficient, and the ratio of zeolite is 13 wt%.
When the amount is larger than this, the amount of cerium oxide is relatively decreased, so that an appropriate amount of oxygen cannot be stored in this cerium oxide, and oxygen necessary for purifying the HC component cannot be obtained.

If the zeolite having a function of suppressing HC poisoning of cerium oxide is a zeolite having excellent adsorbability for HC components having a high boiling point, such as toluene, the FAU (forgery) However, zeolite having a pore size of 5 Å or more, such as β-type zeolite, MOR (mordenite), LTL (L-type zeolite) or MFI (ZSM-5) is applicable.

That is, as shown in FIG. 8, CHA (chabazite), FER (ferrierite), MFI (Z
SM-5), β-type zeolite, MOR (mordenite)
The purification rate of HC components after adsorption of toluene was measured using exhaust gas purification catalysts containing zeolite having various pore sizes such as LTL and LTL (L-type zeolite) in the catalyst layer. It was confirmed that the HC component in the exhaust gas can be effectively purified when the above-mentioned zeolite having a pore size of 1 is contained in the catalyst layer. If the pore size of zeolite is 5Å or more,
It is considered that this is because the high boiling point HC component having a large molecular weight can be effectively adsorbed and the cerium oxide can be effectively prevented from being poisoned by HC.

Further, in the above embodiment, the cerium oxide catalyst particles 5 in which the catalyst noble metal made of palladium is carried on the particles made of cerium oxide, and the catalyst noble metal made of palladium are carried in the particles made of zeolite. Since the catalyst layer is composed of the zeolite catalyst particles 6, the palladium can be dispersed and supported on the cerium oxide particles and the zeolite particles. Therefore, it is possible to prevent the catalytic noble metal made of palladium from being loaded at a high density and prevent the sintering phenomenon from occurring in the palladium. Moreover, since palladium, which is excellent in low-temperature activity, is used as the catalyst noble metal, exhaust gas can be effectively purified in the low-temperature region.

Further, as shown in the above embodiment, the second catalyst containing the above-mentioned catalyst noble metal, cerium oxide and zeolite is formed on the first catalyst layer 3 containing aluminum oxide and the catalyst noble metal comprising palladium. When the catalyst layer 4 is disposed, the HC component in the exhaust gas can be effectively purified by the aluminum oxide and palladium of the first catalyst layer 3, and the heat of the catalytic reaction by the first catalyst layer 3 can be obtained. The second catalyst layer 4 arranged above it can be heated.

Therefore, by effectively releasing the HC component adsorbed to the cerium oxide contained in the second catalyst layer 4, the generation of HC poisoning can be suppressed more effectively. . Moreover, by dispersing and supporting the catalytic noble metal made of palladium in the first catalyst layer 3 and the second catalyst layer 4 as described above, it is possible to effectively suppress the sintering (aggregation) of the palladium. is there.

The first catalyst layer 3 formed by supporting palladium on particles made of aluminum oxide, the cerium oxide catalyst particles 5 in which palladium is supported on particles of cerium oxide, and the palladium on catalyst particles of zeolite. Second composed of agitated zeolite catalyst particles 6
A catalyst layer 4 and first and second catalyst carriers 2.
Aside from the first embodiment A1 of the present invention in which the amount of palladium supported on the catalyst layers 3 and 4 is set to 5 g / liter, and the amount of palladium supported on the first catalyst layer 3 is set to half. A second embodiment A2 having the same structure as the first embodiment A1 and the same structure as the first embodiment A1 except that platinum (Pt) is used as the catalytic noble metal of the first catalyst layer 3. The third embodiment A3 and the third embodiment A3 were each measured for the purification rate of the HC component after the adsorption of toluene, and the data shown in FIG. 9 were obtained.

From the data shown in FIG. 9 above, regardless of the kind of the catalytic noble metal forming the lower first catalyst layer 3 and the amount of the supported precious metal, palladium oxide having an oxygen storage capacity and HC component having a high boiling point were selected. On the other hand, when the second catalyst layer 4 containing a zeolite having excellent adsorptivity and a catalytic noble metal made of palladium is provided, the second catalyst layer 4 made of a component obtained by supporting palladium on particles made of aluminum oxide is used. Compared to the exhaust gas purifying catalyst according to Comparative Example B, which has one catalyst layer and a second catalyst layer that is formed by omitting the zeolite and supporting a noble metal catalyst made of palladium on particles of cerium oxide, It was confirmed that the purification rate of the HC component after toluene adsorption could be maintained at an appropriate value.

[0045]

As described above, the invention according to claim 1 is an exhaust gas purifying catalyst installed in an exhaust system of an engine, comprising a catalytic noble metal, cerium oxide having an oxygen storage capacity, and a high boiling point. Since a catalyst layer containing a zeolite having an excellent adsorbability for the HC component of the above is provided, the cerium oxide is effectively poisoned by HC due to the chemical adsorption of the high boiling point HC component such as toluene to the cerium oxide. Can be prevented. Therefore, due to the oxygen released from the cerium oxide by causing the cerium oxide to store a proper amount of oxygen, and the catalytic action of the catalytic noble metal, H 2
There is an advantage that the C component can be effectively oxidized to purify the exhaust gas.

Further, the invention according to claim 2 is such that cerium oxide catalyst particles in which particles of cerium oxide are loaded with a catalytic noble metal of palladium, and particles of zeolite are loaded with a catalytic noble metal of palladium. Since the catalyst layer is composed of the zeolite particles thus prepared, it is possible to effectively prevent the sintering phenomenon of palladium due to the fact that palladium is loaded on the zeolite particles at a high density. Further, since palladium, which is excellent in low-temperature activity, is used as the catalyst noble metal, there is an advantage that exhaust gas can be effectively purified at low temperature.

In the invention according to claim 3, the catalyst layer has FAU (faujasite), β-type zeolite, and MO.
Since R (mordenite), LTL (L-type zeolite), MFI (ZSM-5), or other zeolite having a pore size of 5Å or more is contained, it effectively adsorbs the high-boiling HC component having a large molecular weight, and Cerium oxide HC
Poisoning can be effectively prevented. Therefore, the cerium oxide can store an appropriate amount of oxygen, and the oxygen released from the cerium oxide and the catalytic action of the catalytic noble metal can effectively oxidize the HC component to purify the exhaust gas. .

Further, in the invention according to claim 4, since the ratio of zeolite with respect to the total weight of cerium oxide constituting the catalyst layer and the zeolite is set within the range of 2.5 to 13 wt%, the amount of the above zeolite supported is set. With this zeolite, HC poisoning of cerium oxide can be surely suppressed by this zeolite, and a decrease in oxygen storage capacity due to a decrease in the amount of cerium oxide is prevented, and oxygen supplied from this cerium oxide is prevented. Due to H in the exhaust gas
The C component can be effectively purified.

Further, in the invention according to claim 5, the second catalyst layer containing the catalytic noble metal, cerium oxide and zeolite is disposed on the first catalyst layer containing the aluminum oxide and the catalytic noble metal. Therefore, the HC component in the exhaust gas can be effectively purified by the aluminum oxide and palladium of the first catalyst layer, and the second catalyst layer disposed thereabove is heated by the heat of the catalytic reaction by the first catalyst layer. As a result, there is an advantage that HC poisoning of the cerium oxide contained in the second catalyst layer can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is an overall explanatory view showing an embodiment of an exhaust gas purifying catalyst according to the present invention.

FIG. 2 is a partially enlarged explanatory view showing a main part of an exhaust gas purifying catalyst.

FIG. 3 is a graph showing changes in the purification rate of HC components due to the adsorption of toluene.

FIG. 4 is an IR spectrum diagram when toluene is adsorbed on a catalyst layer according to a comparative example.

FIG. 5 is an IR spectrum diagram when toluene is adsorbed on the catalyst layer according to the example of the present invention.

FIG. 6 is a graph showing the relationship between the circulation time of toluene and the changing state of the purification rate of HC components.

FIG. 7 is a graph showing the relationship between the proportion of zeolite and the purification rate of HC components.

FIG. 8 is a graph showing the relationship between the pore size of zeolite and the purification rate of HC components.

FIG. 9 is a graph showing the relationship between the components of the first catalyst layer and the purification rates of HC components.

FIG. 10 is a graph showing the relationship between the distance traveled by an automobile and the amount of HC component emitted.

[Explanation of symbols]

 3 First catalyst layer 4 Second catalyst layer 5 Cerium oxide catalyst particles 6 Zeolite catalyst particles

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/63 B01D 53/36 ZAB 29/068 ZAB 104A 29/12 B01J 23/56 301A (72) Inventor Kenji Okamoto 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd.

Claims (5)

[Claims] 1. An exhaust gas purifying catalyst installed in an exhaust system of an engine, comprising a catalytic noble metal, cerium oxide having an oxygen storage capacity, and zeolite having an excellent adsorbing ability for a high boiling point HC component. An exhaust gas purifying catalyst for an engine, characterized in that a catalyst layer containing is provided. 2. A catalyst comprising cerium oxide catalyst particles in which a catalytic noble metal made of palladium is supported on particles formed of cerium oxide, and zeolite catalyst particles in which a catalytic noble metal made of palladium is supported on particles formed of zeolite. The exhaust gas purifying catalyst for an engine according to claim 1, wherein the catalyst comprises a layer. 3. The catalyst layer containing zeolite having a pore size of 5 Å or more, according to claim 1 or 2.
Exhaust gas purifying catalyst for the engine described. 4. The ratio of zeolite to the total weight of cerium oxide and the zeolite constituting the catalyst layer is 2.5.
The exhaust gas purifying catalyst for an engine according to any one of claims 1 to 3, wherein the catalyst is set in a range of -13 wt%. 5. A second catalyst layer containing a catalytic noble metal, cerium oxide and zeolite is disposed on a first catalyst layer containing aluminum oxide and a catalytic noble metal. The exhaust gas purifying catalyst for an engine according to any one of 1 to 4.