JPH11226425A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for purification of exhaust gas containing HC adsorbents which have excellent adsorption efficiency of cold HC of various kinds of molecular diameters and hardly desorb the adsorbed HC. SOLUTION: This catalyst for purification of exhaust gas contains two or more kinds of hydrocarbon adsorbents having different medians in the pore diameter distributions in the catalyst component layers, and the hydrocarbon adsorbents have 4 to 9 Å distribution of the pore diameters. The catalyst has a multilayered structure comprising each layer of two or more kinds of hydrocarbon adsorbents having different medians in the pore diameter distributions. The uppermost layer consists of a hydrocarbon adsorbent having a larger median in the pore diameter distribution, and from the uppermost layer, layers of adsorbents with smaller medians in the pore diameter distributions are successively formed. The hydrocarbon adsorbents are preferably arranged in such a manner that an exhaust gas is successively brought into contact with the hydrocarbon adsorbent having a larger median in the pore diameter distribution and then successively into contact with hydrocarbon adsorbents having smaller medians in the pore diameter distributions. Two or more catalysts for purification of exhaust gas are disposed in series along the exhaust gas stream.

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 catalyst and, more particularly, to a hydrocarbon (hereinafter, referred to as an exhaust gas) discharged from an internal combustion engine of an automobile or the like at a low temperature immediately after starting the engine.
Among HC, carbon monoxide (hereinafter, referred to as “CO”), and nitrogen oxides (hereinafter, referred to as “NO _x ”), particularly, exhaust gas purification capable of efficiently adsorbing HC For catalysts.

[0002]

2. Description of the Related Art Conventionally, exhaust gas purifying catalysts have not been sufficiently durable at high temperatures, and the catalyst has deteriorated and purification performance has been significantly reduced. HC (hereinafter referred to as "cold HC")
For the purpose of reducing CO, a method in which HC is temporarily stored by an adsorbent mainly composed of zeolite, and after the three-way catalyst is activated, the HC is desorbed from the adsorbent and purified by the three-way catalyst is used. Are being considered.

[0003] Examples of such an exhaust gas purifying catalyst using an HC adsorbent containing zeolite as a main component include, for example, JP-A-7-144119, JP-A-7-96179, and JP-A-7-88364. Some have been disclosed. Further, as an exhaust gas purifying catalyst using zirconium phosphate as a carrier of a catalyst component, for example, Japanese Unexamined Patent Publication No.
There is one disclosed in, for example, Japanese Patent No. 281116.

JP-A-8-24655 discloses a three-way catalyst upstream of an exhaust system of an automobile internal combustion engine, an HC adsorbent mainly composed of zeolite downstream thereof, and a three-way catalyst downstream thereof. There has been proposed a system for disposing a composite catalyst on which a catalyst is disposed to remove cold HC adsorption. JP-A-7-88364 proposes, as an HC adsorbent, an HC adsorption catalyst in which Ag or Cd is added to ZSM5 having improved heat resistance. Japanese Patent Application Laid-Open No. 8-281116 discloses an exhaust gas purification catalyst for purifying nitrogen oxides in an oxygen-excess atmosphere in which an alkali metal, an alkaline earth metal, a rare earth element, and a noble metal are supported on a zirconium phosphate carrier. Has been proposed.

[0005]

However, in such conventional HC adsorbents mainly composed of zeolite, the HC species that can be trapped are determined based on the pore diameter caused by various zeolite structures. Sufficient adsorption performance cannot be obtained for a wide range of HC species from HC species having a small diameter to HC species having a large molecular diameter, and the HC adsorbent has insufficient durability. Desorption is accelerated. Therefore, two or more types of zeolites having different pore diameters are mixed and used to improve the adsorption performance to various HCs, and a hot gas bypass method is used to delay the HC desorption. However, there has been a problem that the materials and the system configuration are complicated and the cost is increased.

Accordingly, it is an object of the present invention to provide an excellent adsorption efficiency for cold HC of various molecular diameters,
It is an object of the present invention to provide an exhaust gas purifying catalyst containing an HC adsorbent that is difficult to desorb.

[0007]

Means for Solving the Problems As a result of research conducted to solve the above problems, the present inventors have combined hydrocarbon adsorbents having different crystal structures and pore sizes, controlled such pore size distribution, The present inventors have found that the formation efficiency of cold HC can be improved by forming the hydrogen adsorbent into a multilayer structure, and that the desorption of the adsorbed HC can be delayed, thereby achieving the present invention.

[0008] The exhaust gas purifying catalyst according to the first aspect of the present invention contains two or more hydrocarbon adsorbents having different median pore diameter distributions in the catalyst component layer, and the hydrocarbon adsorbent has a pore diameter distribution. 4 to 9 °, two or more hydrocarbon adsorbents having different median pore diameter distributions are used as a multilayer structure for each of the adsorbents, and a hydrocarbon adsorbent having a large median pore diameter distribution is formed in the upper layer. A hydrocarbon adsorbent having a small median pore size distribution is sequentially disposed in the lower layer.

According to a second aspect of the present invention, there is provided the exhaust gas purifying catalyst according to the first aspect, wherein the hydrocarbon adsorbing material is ZSM12, ZSM22, ZSM34, MF.
It is characterized by combining at least two or more kinds of hydrocarbon adsorbents selected from the group consisting of I, β-zeolite and USY zeolite.

According to a third aspect of the present invention, there is provided the exhaust gas purifying catalyst according to the first or second aspect, wherein the exhaust gas has a pore size distribution starting from a hydrocarbon adsorbent having a large median pore size distribution. Wherein the hydrocarbon adsorbent is arranged so as to come into contact with the hydrocarbon adsorbent having a small median value.

According to a fourth aspect of the present invention, there is provided the exhaust gas purifying catalyst according to any one of the first to third aspects.
It is characterized in that two or more are arranged in series with respect to the exhaust gas flow.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The exhaust gas purifying catalyst of the present invention is
In purifying exhaust gas, particularly low-temperature exhaust gas discharged from an internal combustion engine immediately after engine startup, in order to improve the adsorption efficiency of HC and suppress desorption, the catalyst component layer has different median pore diameter distributions. At least two kinds of hydrocarbon adsorbents having a pore diameter distribution of 4 to 9 mm, and different medians of the pore diameter distribution. , A hydrocarbon adsorbent having a large median pore size distribution is disposed in the upper layer, and a hydrocarbon adsorbent having a small median pore size distribution is sequentially disposed in the lower layer.

The hydrocarbon adsorbent contained in the catalyst component layer forms a pore size distribution suitable for the molecular size distribution of the HC species in the low-temperature exhaust gas immediately after the start of the engine, thereby improving the adsorbability. Two or more hydrocarbon adsorbents having different median pore size distributions are used. Such hydrocarbon adsorbents having different pore diameters include ZSM12, ZSM22, ZS3
4. At least two or more hydrocarbon adsorbents selected from the group consisting of MFI, β-zeolite and USY zeolite are used in combination.

The two or more hydrocarbon adsorbents preferably have different pore structures and median pore diameter distributions, and the pore diameter distribution is preferably in the range of 4 ° to 9 °. When the pore size distribution is within the above range, various cold HC species can be widely and efficiently adsorbed, and the desorption of the adsorbed HC can be delayed.

The amount of the hydrocarbon adsorbent used is the catalyst 1
5 to 400 g per L. If it is less than 5g, sufficient HC
The adsorption ability is not obtained, and even if it is used more than 400 g, the HC adsorption ability is saturated and is not effective.

Further, in order to improve the adsorbing ability of the hydrocarbon adsorbent having a small median pore diameter distribution, when the low-temperature exhaust gas immediately after the start of the engine passes through the catalyst component layer, the center of the pore diameter distribution is first determined. After the exhaust gas is brought into contact with the hydrocarbon adsorbent having a large value to adsorb HC having a large molecular diameter, the hydrocarbon is adsorbed so that the hydrocarbon adsorbent having a small median pore size distribution and the exhaust gas are sequentially contacted. The materials are arranged in a multilayer structure.

As described above, by forming two or more kinds of hydrocarbon adsorbents having different median values of the pore diameter distribution into a multilayer structure for each hydrocarbon adsorbent, the adsorption of cold HC components in the exhaust gas can be prevented. Since a suitable complicated pore structure network can be formed, the HC adsorption ability is further improved, and the adsorbed HC is hardly released, so that the desorption can be further delayed.

[0018] The layer structure formed of such a hydrocarbon adsorbent is not particularly limited.
Layers are preferred. If the number of layers is less than two, a multilayer structure having a sufficient HC adsorption ability cannot be obtained, and even if more than five layers are used, the HC adsorption ability by the multilayer structure is not so much improved.

Further, in order to improve the ability to adsorb HC species in the low-temperature exhaust gas immediately after starting the engine, the catalyst component layer contains two or more hydrocarbon adsorbents having different median pore diameter distributions. A plurality of the above-described catalysts in which two or more kinds of hydrocarbon adsorbents having different median pore diameter distributions in the catalyst component layer are arranged in a multilayer structure of two or more layers, and are arranged in series with respect to the exhaust gas flow. Preferably, the catalysts arranged in series may be the same or different.

The number of such catalysts having a multilayer structure of the hydrocarbon adsorbent is not particularly limited.
A catalyst volume of 0.3 L to 2.6 L per piece, in particular
It is preferable to arrange two to five in series. If the catalyst capacity is less than 0.3 L layer, sufficient HC adsorption capacity cannot be obtained, and
Even if it is larger than 6 L, the HC adsorption capacity by a single volume is saturated and is not more effective. If the number is less than 2, sufficient HC adsorption capacity cannot be obtained.
This is because the C adsorption capacity does not further improve.

[0021]

The present invention will be described with reference to the following examples and comparative examples. Example 1 500 g of MFI (pore diameter 5.5 to 6.5 °: median of pore diameter distribution 5.8 °), 100 g of silica sol, and 10 pure water
00g was charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was attached to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried, and baked at 400 ° C. for 1 hour, and the coat weight was 60 g. / L-support catalyst was obtained (catalyst A).

Β-zeolite (pore diameter 5.5 to 7.5)
Å: 500 g of median pore size distribution), 100 g of silica sol and 1000 g of pure water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid is adhered to the above-mentioned catalyst A, the excess slurry in the cell is removed by an air stream, dried, baked at 400 ° C. for 1 hour, and the coating weight 60 g / L (total coating weight 120 g / L) -A catalyst for purifying the exhaust gas of the carrier was obtained (catalyst B).

Example 2 500 g of ZSM22 (pore size: 4.5 to 5.0 mm: median of pore size distribution: 4.7 mm), 100 g of silica sol and 1000 g of pure water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. Obtained. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air flow, and dried,
Calcination was carried out at 1 ° C. for 1 hour to obtain a catalyst having a coating weight of 60 g / L-support (catalyst C).

500 g of MFI (pore diameter 5.5-6.5 °: median of pore diameter distribution 5.8 °), 100 g of silica sol
And 1000 g of pure water into a magnetic ball mill.
The slurry was obtained by crushing. This slurry liquid is mixed with the above catalyst C
The excess slurry in the cell is removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a coating weight of 6
A catalyst of 0 g / L (total coating amount: 120 g / L) -carrier was obtained (catalyst D).

Β-zeolite (pore diameter 5.5 to 7.5)
Å: 500 g of median pore size distribution), 100 g of silica sol and 1000 g of pure water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid is adhered to the above catalyst D, the excess slurry in the cell is removed by an air stream, dried, and baked at 400 ° C. for 1 hour, so that the coat weight is 60 g / L (total coat amount 180 g / L). A catalyst on the carrier was obtained (catalyst E).

500 g of USY (pore size: 7.0-8.0 °: median of pore size distribution: 7.6 °), 100 g of silica sol
And 1000 g of pure water into a magnetic ball mill.
The slurry was obtained by crushing. This slurry liquid is mixed with the above catalyst E
The excess slurry in the cell is removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a coating weight of 6
0 g / L (total coating amount 240 g / L) -a catalyst for purifying exhaust gas of a carrier was obtained (catalyst F).

Example 3 500 g of ZSM34 (pore size distribution 4.2 to 4.8%: median of pore size distribution 4.6), 100 g of silica sol and 1000 g of pure water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. I got This slurry liquid was adhered to a cordierite-based monolith carrier (1.3 L, 400 cells),
The excess slurry in the cell is removed by air flow and dried,
By calcining at 00 ° C. for 1 hour, a catalyst having a coat weight of 60 g / L-carrier was obtained (catalyst G).

500 g of MFI (pore diameter 5.5 to 6.5 °: median of pore diameter distribution 5.8 °), 100 g of silica sol
And 1000 g of pure water into a magnetic ball mill.
The slurry was obtained by crushing. This slurry liquid was used as the catalyst G
The excess slurry in the cell is removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a coating weight of 6
0 g / L (total coating amount 120 g / L) -a catalyst for purifying exhaust gas of a carrier was obtained (catalyst H).

500 g of ZSM12 (pore size: 5.8 to 6.5 °: median of pore size distribution: 6.2 °), silica sol 10
0 g and 1000 g of pure water were put into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid is adhered to the above catalyst H, excess slurry in the cell is removed by an air stream, dried, baked at 400 ° C. for 1 hour, and coat weight 60 g / L (total coat amount 180 g / L). -A catalyst for purifying the exhaust gas of the carrier was obtained (catalyst I).

Β-zeolite (pore diameter 5.5 to 7.5)
Å: 500 g of median pore size distribution), 100 g of silica sol and 1000 g of pure water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid is adhered to the above-mentioned catalyst I, the excess slurry in the cell is removed by an air stream, dried, and baked at 400 ° C. for 1 hour, and the coat weight is 60 g / L (total coat weight 240 g / L). -The catalyst on the carrier was obtained (Catalyst J).

500 g of USY (pore size: 7.0 to 8.0 °: median of pore size distribution: 7.6 °), 100 g of silica sol
And 1000 g of pure water into a magnetic ball mill.
The slurry was obtained by crushing. This slurry liquid is mixed with the above catalyst J
The excess slurry in the cell is removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a coating weight of 6
0 g / L (total coating amount: 300 g / L) -a catalyst for purifying exhaust gas of a carrier was obtained (catalyst K).

Example 4 A catalyst for exhaust gas purification was obtained by disposing a catalyst F upstream of the exhaust flow and a catalyst K downstream thereof.

Example 5 A catalyst for purifying exhaust gas was obtained by arranging the catalyst B on the upstream side and the catalyst K on the downstream side with respect to the exhaust gas flow.

Example 6 An exhaust gas purifying catalyst was obtained by disposing the catalyst K on the upstream side and the catalyst K on the downstream side with respect to the exhaust gas flow.

Comparative Example 1 1500 g of ZSM34 (pore size 4.2-4.8 mm: median pore size distribution 4.6), 100 g of silica sol and 1000 g of pure water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. Obtained. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), and excess slurry in the cells was removed by an air stream and dried to obtain a slurry.
By calcining at 0 ° C. for 1 hour, an exhaust gas purifying catalyst having a coat weight of 300 g / L-carrier was obtained (catalyst M).

Comparative Example 2 1500 g of USY (pore diameter 7.0-4.8 °: median of pore diameter distribution 7.6 °), silica sol 100 g and pure water 1
000 g was put into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), and excess slurry in the cells was removed by an air stream and dried, and then dried at 400 ° C.
For 1 hour to obtain an exhaust gas purifying catalyst having a coat weight of 300 g / L-carrier (catalyst N).

Comparative Example 3 500 g of USY (pore size: 7.0-8.0 °: median of pore size distribution: 7.6 °), 100 g of silica sol, and 10 g of pure water
00g was charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was attached to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried, and baked at 400 ° C. for 1 hour, and the coat weight was 60 g. / L-carrier exhaust gas purifying catalyst was obtained (catalyst O).

Β-zeolite (pore diameter 5.5 to 7.5)
Å: 500 g of median pore size distribution), 100 g of silica sol and 1000 g of pure water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid is adhered to the catalyst O, the excess slurry in the cell is removed by an air stream, dried, and baked at 400 ° C. for 1 hour, so that the coat weight is 60 g / L (total coat amount 120 g / L). A catalyst on the carrier was obtained (catalyst P).

500 g of ZSM12 (pore size: 5.8 to 6.5 °: median of pore size distribution: 6.2 °), silica sol 10
0 g and 1000 g of pure water were put into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid is attached to the catalyst P, the excess slurry in the cell is removed by an air stream, dried, baked at 400 ° C. for 1 hour, and the coating weight 60 g / L (total coating 180 g / L) -A catalyst for purifying the exhaust gas of the carrier was obtained (catalyst Q).

500 g of MFI (pore diameter 5.5 to 6.5 °: median of pore diameter distribution 5.8 °), 100 g of silica sol
And 1000 g of pure water into a magnetic ball mill.
The slurry was obtained by crushing. This slurry liquid is mixed with the above catalyst Q
The excess slurry in the cell was removed by an air stream, dried, and fired at 400 ° C. for 1 hour. Coat weight 6
0 g / L (total coating amount 240 g / L) -a catalyst for purifying exhaust gas of a carrier was obtained (catalyst R).

500 g of ZSM22 (pore size 4.5-5.5 °: median of pore size distribution 4.7 °), silica sol 10
0 g and 1000 g of pure water were put into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was attached to the catalyst R, excess slurry in the cell was removed with an air stream, dried, and calcined at 400 ° C. for 1 hour. A coat weight 60 g / L (total coat amount 300 g / L) -a catalyst for purifying exhaust gas of a carrier was obtained (catalyst S).

Comparative Example 4 500 g of ZSM22 (pore size: 4.5-5.5 °: median of pore size distribution: 4.7 °), MFI (pore size: 5.5-6.
5 °: median pore size distribution 5.8 °) 500 g, ZSM
34 (pore size 4.2 to 4.8Å: median pore size distribution 4.6Å) 500 g, β-zeolite (pore size 5.5 to 5.5)
7.5%: median pore size distribution 6.3%) 500 g, U
500 g of SY (pore diameter 7.0 to 8.0 °: median of pore diameter distribution 7.6 °), 500 g of silica sol and 30 parts of pure water
00g was charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a coating weight of 300 g. A catalyst for purifying exhaust gas of / L-carrier was obtained (catalyst T).

Comparative Example 5 A catalyst for purifying exhaust gas was obtained by disposing a catalyst N on the upstream side and a catalyst M on the downstream side with respect to the exhaust gas flow.

The specifications of the exhaust gas purifying catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 5 are shown in FIGS.

Test Examples The exhaust gas purifying catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 5 were subjected to durability under the following durability conditions.
The catalytic activity was evaluated under the following evaluation conditions using the system of FIG. The system shown in FIG.
1.0L upstream of the exhaust gas purifying catalyst obtained in
Of the three-way catalyst Pd / Rh = 240 g / cf-11 / 1
The exhaust gas purifying catalysts are arranged in a row in a row and an exhaust gas purifying catalyst is arranged downstream of the individual rows.

Endurance conditions Engine displacement 3000cc Fuel unleaded gasoline Catalyst inlet gas temperature 650 ° C Endurance time 100 hours Inlet gas composition CO 0.5 ± 0.1% O ₂ 0.5 ± 0.1% HC About 1100ppm NO 1300ppm CO ₂ 15% A / F fluctuation 5500 times (65 seconds / cycle) Cycle: A / F = 14.655 seconds Fuel cut 5 seconds Rich spike 5 seconds

Evaluation conditions Engine displacement Nissan Motor Co., Ltd. V-6 3.3 L fuel Unleaded gasoline Evaluation mode ECE The above exhaust gas purifying catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 5 were evaluated as described above. Under the conditions, the amount of cold HC adsorbed was measured by the following method.

Measurement of Cold HC Adsorption In the vehicle system shown in FIG. 2, a catalyst in which only activated alumina (300 g / L) is supported on cordierite (1: 1.
3L + 2: 1.3L) based on the discharged HC amount (0.65 g / test) when placed under the floor, and from 0 seconds of ECE to about 60 seconds (the section where the discharged HC amount falls below the base) as the adsorption section. The amount reduced from the base was defined as the amount of adsorbed HC. Table 1 shows the obtained results.

[0049]

[Table 1]

[0050]

The exhaust gas purifying catalyst according to claim 1 is
It is excellent in the ability to adsorb HC in low-temperature exhaust gas immediately after the start of the engine discharged from the internal combustion engine, and can delay the desorption of the adsorbed HC.

The exhaust gas purifying catalyst according to the second aspect has, in addition to the above effects, further excellent HC adsorbing ability and can adsorb HC in the exhaust gas efficiently.

The exhaust gas purifying catalyst according to the third aspect can improve the adsorption capacity for various HC species from HC species having a small molecular diameter to HC species having a large molecular diameter, in addition to the above effects.

The exhaust gas purifying catalyst according to the fourth aspect can further improve the adsorbing ability and reduce the uncollected HC content among the HC species contained in the low-temperature exhaust gas.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a structural specification of an exhaust gas purifying catalyst of the present invention.

FIG. 2 is a schematic diagram showing an example of an evaluation system for evaluating the amount of cold HC adsorbed by the exhaust gas purifying catalyst of the present invention.

FIG. 3 is a diagram showing an example of a relationship between a vehicle evaluation elapsed time (SEC) and an HC emission amount of the exhaust gas purifying catalyst of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 29/70 B01D 53/36 C 35/02 104Z

Claims (4)

[Claims] 1. A catalyst component layer comprising two or more hydrocarbon adsorbents having different median pore diameter distributions, wherein the hydrocarbon adsorbent has a pore diameter distribution of 4 to 9 °, and the pore diameter distribution is At least two types of hydrocarbon adsorbents having different median distributions are used as a multilayer structure for each adsorbent, and a hydrocarbon adsorbent having a large median pore size distribution is provided in an upper layer, and a median pore size distribution is provided in a lower layer sequentially. An exhaust gas purifying catalyst comprising a hydrocarbon adsorbent having a small particle size. 2. The exhaust gas purifying catalyst according to claim 1, wherein the hydrocarbon adsorbent is ZSM12, ZSM22, ZSM22.
An exhaust gas purification catalyst comprising a combination of at least two or more hydrocarbon adsorbents selected from the group consisting of SM34, MFI, β-zeolite and USY zeolite. 3. The exhaust gas purifying catalyst according to claim 1, wherein the hydrocarbon adsorbent is such that the exhaust gas has a median pore diameter distribution in order from a hydrocarbon adsorbent having a large median pore diameter distribution. An exhaust gas purifying catalyst, which is arranged to be in contact with a small hydrocarbon adsorbent. 4. An exhaust gas purifying catalyst, wherein two or more exhaust gas purifying catalysts according to claim 1 are arranged in series with respect to an exhaust gas flow.