JP2001190960A - Catalyst for exhaust gas cleaning - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the amount of HC discharged in a un cleaned state, in a region at from a low temperature to a high temperature. SOLUTION: The catalyst for exhaust gas cleaning comprises as oxidation catalyst or three-way catalyst and an HC absorbent. The HC adsorbent has a concentration distribution where the concentration is high on the upstream side in the flow direction of the exhaust gas and it is low on the downstream side. In the low temperature region, HC in the exhaust gas in adsorbed by the HC adsorbent of high concentration on the upstream side. The heat of the exhaust gas is quickly transferred to the oxidation catalyst or the three-way catalyst disposed on the upstream side, thereby quickly raising the temperature of the oxidation catalyst or the three-way catalyst to an activation temperature or higher. The ignition on the upstream side is transferred to the downstream side, so that the temperature rising is accelerated.

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 using a hydrocarbon adsorbent and an oxidation catalyst or a three-way catalyst, and more particularly to an exhaust gas purifying catalyst capable of purifying hydrocarbons (HC) in exhaust gas more efficiently. .

[0002]

2. Description of the Related Art Heretofore, as an exhaust gas purifying catalyst for automobiles, an oxidation catalyst having a noble metal such as platinum supported on a porous carrier such as alumina has been used. In this oxidation catalyst,
HC and CO in the exhaust gas are oxidized and purified.

[0003] By controlling the air-fuel ratio to the stoichiometric air-fuel ratio, the porous carrier catalyst carrying a noble metal such as platinum, such as alumina for performing the reduction of the oxidized and NO _x CO and HC in the exhaust gas simultaneously , Is called a three-way catalyst. As such a three-way catalyst, for example, a porous carrier layer composed of γ-alumina is formed on a heat-resistant honeycomb substrate composed of cordierite or the like, and platinum (Pt), rhodium (Rh ) Are widely used.

[0004] However, in the oxidation catalyst and the three-way catalyst,
There is a problem that a catalytic reaction does not occur until the supported noble metal has a temperature equal to or higher than its activation temperature. In order to do such as during-start or during a cold, a noble metal for the temperature of the exhaust gas is low does not reach the activation temperature, the purification of HC and NO _x is difficult.

Therefore, as disclosed in, for example, JP-A-5-057148 or JP-A-6-154538,
Exhaust gas purifying devices have been developed in which an HC adsorbent such as zeolite is disposed upstream of an oxidation catalyst or a three-way catalyst in the exhaust gas flow direction. In this exhaust gas purifying device, HC in exhaust gas is first adsorbed by an HC adsorbent at a low temperature, and the adsorbed HC is desorbed at the time of temperature rise and is disposed downstream to be an oxidation catalyst or a three-way catalyst having an activation temperature or higher. The catalyst is oxidized and purified. Therefore, according to such an exhaust gas purifying apparatus,
HC contained in the exhaust gas during cold or start-up is adsorbed by the HC adsorbent, which suppresses the emission. HC released from the HC adsorbent at high temperatures and HC in the exhaust gas are oxidized catalysts or three-way catalysts Therefore, HC emission can be suppressed from a low temperature to a high temperature, and the amount of HC discharged in an unpurified state can be reduced.

[0006] Further, in the monolithic catalyst having an integral honeycomb shape, a coat layer made of HC adsorbent powder is formed as a lower layer, and a coat layer made of an oxidation catalyst or a three-way catalyst powder is formed as an upper layer. Catalysts have also been proposed. In this exhaust gas purifying catalyst, at low temperatures, HC in exhaust gas passes through the upper layer, which is not at the activation temperature, and is adsorbed by the lower HC adsorbent, and the adsorbed HC is released as the temperature rises and becomes active. It is oxidized and purified by the upper oxidation catalyst or the three-way catalyst which is at or above the formation temperature. Therefore, the HC contained in the exhaust gas is adsorbed by the HC adsorbent at the time of cold or start-up, so the emission is suppressed, and the HC released from the lower HC adsorbent at high temperature and the HC in the exhaust gas are oxidation catalysts. Alternatively, since the catalyst is oxidized and purified by the three-way catalyst, the emission of HC can be suppressed from a low temperature to a high temperature.

[0007]

However, in an exhaust gas purifying apparatus in which an HC adsorbent such as zeolite is disposed on the upstream side of an oxidation catalyst or a three-way catalyst, the heat of exhaust gas is reduced by the HC on the upstream side.
Due to the deprivation of the adsorbent, the temperature rise of the downstream oxidation catalyst or the three-way catalyst is hindered, and the time required to raise the activation temperature of the supported noble metal becomes longer, during which the HC purification rate is low. was there.

In an exhaust gas purifying catalyst in which an HC adsorbent layer is formed as a lower layer and an oxidation catalyst layer or a three-way catalyst layer is formed above the HC adsorbent layer, the HC adsorbent is discharged from the HC adsorbent positioned upstream in the exhaust gas flow direction. The HCs are efficiently oxidized because they have a high probability of contacting the oxidation catalyst or the three-way catalyst located on the downstream side. However, the HC released from the HC adsorbent located on the downstream side has an activation temperature because the amount of the oxidation catalyst or the three-way catalyst located on the downstream side is small and the probability of contact with the oxidation catalyst or the three-way catalyst is low. Even in the high temperature range described above, there is a case where it is released without being oxidized.

The present invention has been made in view of such circumstances, and has as its object to further reduce the amount of HC discharged without purification from a low-temperature region to a high-temperature region.

[0010]

The feature of the exhaust gas purifying catalyst of the present invention which solves the above-mentioned problems is that the exhaust gas purifying catalyst comprises an oxidation catalyst or a three-way catalyst and an HC adsorbent. That is, it is contained with a high concentration on the upstream side in the exhaust gas flow direction and a small concentration distribution on the downstream side.

It is desirable that the concentration ratio of the HC adsorbent between the upstream side and the downstream side in the exhaust gas flow direction is upstream: downstream = 9〜7: 1７3. Further, it is desirable that the oxidation catalyst or the three-way catalyst has a concentration distribution that is small on the upstream side in the exhaust gas flow direction and large on the downstream side.

The concentration ratio between the HC adsorbent and the oxidation catalyst or the three-way catalyst at the upstream side and the downstream side in the exhaust gas flow direction is as follows: upstream (HC adsorbent: oxidation catalyst or three-way catalyst): downstream (HC
Adsorbent: oxidation catalyst or three-way catalyst) = (9: 1 to 7:
3): (1: 9 to 3: 7) is particularly desirable.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst of the present invention,
The HC adsorbent is contained with a high concentration on the upstream side in the exhaust gas flow direction and a small concentration distribution on the downstream side. Therefore, in the low temperature range, HC in the exhaust gas contains much HC in the upstream side.
Since it is mainly adsorbed by the adsorbent, the emission of unpurified HC is suppressed. And by adopting a configuration in which the oxidation catalyst or the three-way catalyst is also present on the upstream side in the exhaust gas flow direction,
The heat of the exhaust gas is quickly transmitted to the oxidation catalyst or the three-way catalyst present on the upstream side, and the oxidation catalyst or the three-way catalyst located on the upstream side is quickly heated to the activation temperature or more, so that the HC
HC released from the adsorbent and HC in exhaust gas are oxidized and purified. Further, since the ignition on the upstream side is promptly propagated to the downstream side, the temperature rise is promoted, and the oxidation catalyst or the three-way catalyst on the downstream side quickly becomes higher than the activation temperature. Thereby, the purification rate in the low temperature range is improved.

On the downstream side, the amount of HC adsorbed is small because the amount of HC adsorbent is small. Therefore, the amount of HC released from the HC adsorbent on the downstream side as the temperature rises and discharged in an unpurified state without contacting the oxidation catalyst or the three-way catalyst is relatively small. In addition, if the downstream side is configured to contain a large amount of the oxidation catalyst or the three-way catalyst, there is a high probability that HC released from the HC adsorbent and HC in the exhaust gas come into contact with the oxidation catalyst or the three-way catalyst. Therefore, the amount of HC discharged without purification is reduced, and HC discharged without purification even in a high temperature range.
The amount can be reduced.

As the HC adsorbent, ferrierite, ZSM-
5, zeolites such as mordenite and Y-type zeolite can be used. It is also preferable to use a zeolite carrying a noble metal such as Pd or Ag as the HC adsorbent.
By supporting the noble metal in this way, the adsorptivity of low molecular weight HC is further improved.

As the oxidation catalyst or the three-way catalyst, a conventional catalyst comprising a porous carrier and a noble metal supported on the porous carrier can be used. As the porous carrier, alumina, silica, silica-alumina, zirconia, titania, or the like can be used. Among them, γ-alumina having excellent adsorption characteristics and heat resistance is particularly preferable.

It is preferable that an oxygen storage / release material such as ceria or ceria-zirconia is carried or mixed on the porous carrier. The oxygen storage / release material can stabilize the oxygen concentration in the exhaust gas and further stabilize the exhaust gas into a stoichiometric atmosphere, so that the purification activity of the three-way catalyst is further improved.

The noble metals supported on the porous carrier include platinum (Pt), rhodium (Rh), palladium (Pd),
One or a plurality of iridium (Ir) or the like can be selected and used. The amount of the noble metal carried is preferably 0.1 to 10 g per liter of the porous carrier. If the amount is less than this, the purification activity is insufficient, and if the amount is more than this, the effect is saturated and the cost increases.

Both the HC adsorbent and the oxidation catalyst or the three-way catalyst can be used in the form of pellets or a honeycomb by mixing both powders in a powder state. In the case of a honeycomb shape, it can be manufactured by forming a coat layer from the mixed powder on a honeycomb carrier base material formed of cordierite or metal foil. Alternatively, a coat layer may be formed from a mixed powder of the HC adsorbent powder and the porous carrier powder, and the noble metal may be supported on the coat layer.

A coat layer made of an HC adsorbent powder;
A honeycomb-shaped exhaust gas purifying catalyst in which a coating layer made of an oxidation catalyst or a three-way catalyst powder is laminated can also be used. In this case, it is desirable to form a coat layer made of the powder of the HC adsorbent in the lower layer and to form a coat layer made of the powder of the oxidation catalyst or the three-way catalyst on the upper layer.

In the case of a catalyst for purifying exhaust gas in the form of pellets, in order to obtain a structure in which the HC adsorbent is contained with a high concentration on the upstream side in the exhaust gas flow direction and a small concentration distribution on the downstream side, it is necessary to use HC
A plurality of types of pellets having different mixing ratios of the adsorbent powder and the oxidation catalyst or the three-way catalyst powder are prepared, and the pellet having a high HC adsorbent powder concentration is arranged on the upstream side in the exhaust gas flow direction, and the HC adsorption is performed. Pellets having a low material powder concentration may be arranged on the downstream side in the exhaust gas flow direction.

Further, in an exhaust gas purifying catalyst having a coat layer made of a mixed powder, a structure in which the HC adsorbent is contained with a high concentration on the upstream side in the flow direction of the exhaust gas and a small concentration distribution on the downstream side is required. The HC adsorbent concentration may be increased on the upstream side in the exhaust gas flow direction and decreased on the downstream side. In order to form such a coat layer, a plurality of types of slurries having different mixing ratios of the HC adsorbent powder and the oxidation catalyst or the three-way catalyst powder are prepared in advance, and a slurry having a high HC adsorbent powder concentration is used for upstream. This can be performed by forming a coating layer on the downstream side and forming a coating layer on the downstream side with a slurry having a low concentration of the HC adsorbent powder.

Further, in an exhaust gas purifying catalyst having a configuration in which a coat layer of an HC adsorbent and a coat layer of an oxidation catalyst or a three-way catalyst are laminated, the concentration distribution of the HC adsorbent is high on the upstream side in the exhaust gas flow direction and low on the downstream side. In order to make the structure contained with, the thickness of the coat layer of the HC adsorbent is increased toward the upstream side,
This can be achieved by reducing the thickness toward the downstream side. In order to adjust the thickness of the coat layer in this way, for example, after adhering a slurry of the HC adsorbent powder to the honeycomb substrate, the honeycomb substrate is inclined so that the upstream side is downward, and the slurry is caused to flow. It can be carried out. Further, the number of steps of forming the coat layer on the upstream side may be larger than that on the downstream side. Alternatively, the slurry concentration may be different between the upstream side and the downstream side, or the method of sucking or blowing off the slurry may be adjusted.

The concentration distribution of the HC adsorbent may be changed in two steps or a plurality of steps which are high on the upstream side and low on the downstream side, or may gradually decrease from the upstream side to the downstream side. It is good also as a structure which changes continuously so that it may become.

The concentration ratio of the HC adsorbent between the upstream side and the downstream side in the exhaust gas flow direction may be, for example, 9: 7: 1 to 3 at the upstream end and the downstream end. desirable. If the concentration of the HC adsorbent on the upstream side is lower than this range, the amount of adsorbed HC in the low temperature range is reduced, and the HC purification rate in the low temperature range is lowered. If the concentration of the HC adsorbent on the upstream side is higher than this range, the heat of the exhaust gas is taken away by the HC adsorbent, so that the time required for the oxidation catalyst or the three-way catalyst on the downstream side to reach the activation temperature is prolonged, resulting in purification. The rate may be lower. Upstream: Downstream = 9 to 8: 1 to 2 is preferable, and Upstream: Downstream = 8: 2 is particularly desirable.

It is desirable that the oxidation catalyst or the three-way catalyst has a concentration distribution that is small on the upstream side in the exhaust gas flow direction and large on the downstream side. With such a configuration, the above-described action of the exhaust gas purifying catalyst of the present invention in which the concentration distribution is formed in the HC adsorbent is maximized. In order to form such a concentration distribution in the oxidation catalyst or the three-way catalyst, the same method as in the case of the HC adsorbent described above can be used.

The concentration ratio between the HC adsorbent and the oxidation catalyst or the three-way catalyst at the upstream side and the downstream side in the exhaust gas flow direction is, for example, at the upstream end and the downstream end, the upstream (HC adsorbent:
Oxidation catalyst or three-way catalyst): Downstream side (HC adsorbent: oxidation catalyst or three-way catalyst) = (9: 1 to 7: 3): (1: 9 to 3:
7) is desirable. If the concentration of the HC adsorbent on the upstream side is lower than this range, the amount of adsorbed HC in the low temperature range is reduced, and the HC purification rate in the low temperature range is lowered. Also, if the concentration of the upstream oxidation catalyst or the three-way catalyst is lower than this range, the time until the upstream oxidation catalyst or the three-way catalyst becomes the activation temperature becomes longer and the propagation of ignition becomes less likely to occur, The purification rate will be low.

[0028]

The present invention will be specifically described below with reference to examples and comparative examples.

(Example 1) When the molar ratio of SiO ₂ / Al ₂ O ₃ is 2000
100 parts by weight of zeolite powder obtained by mixing ZSM-5 powder, Y type zeolite powder having a molar ratio of SiO ₂ / Al ₂ O ₃ of 400 at a ratio of ZSM-5: Y type zeolite = 7: 3 by weight, and a binder Was mixed with 75 parts by weight of silica sol having a solid content of 40% and 25 parts by weight of water to prepare a slurry.

A cordierite honeycomb substrate having a capacity of 1300 cc was prepared, immersed in the above slurry, lifted up, and air was drawn out from the end face, which is the upstream end face, to remove excess slurry. At this time, the amount of slurry attached was increased from the downstream end face toward the upstream end face by adjusting the air extraction speed. And 12
After drying at 0 ° C. for 120 minutes, it was baked at 500 ° C. for 120 minutes to form a zeolite coat layer. The zeolite coat layer is
180 g was formed per liter of the honeycomb substrate.

Next, a mixed powder obtained by mixing the γ-Al ₂ O ₃ powder and the CeO ₂ —ZrO ₂ composite oxide powder (atomic ratio Ce: Zr = 1: 1) in a weight ratio of 3: 2 is used. It was prepared, impregnated with a predetermined amount of a dinitrodiammineplatinum nitric acid aqueous solution having a predetermined concentration, and evaporated to dryness to carry Pt. Further, a predetermined amount of an aqueous solution of rhodium nitrate having a predetermined concentration was impregnated and evaporated to dryness to carry Rh. The loading amounts of Pt and Rh are 1.54% by weight of Pt and 0.31% by weight of Rh.

160 parts by weight of the three-way catalyst powder obtained above and alumina sol having a solid content of 40% as a binder were mixed with 50 parts by weight.
Parts by weight and 130 parts by weight of water were mixed to prepare a slurry. Then, the honeycomb substrate on which the zeolite coat layer was formed was immersed in the slurry and then pulled up, and air was extracted from the end face side which was the downstream end face to remove excess slurry. At this time, the amount of slurry attached was increased from the upstream end face to the downstream end face by adjusting the air extraction speed. And at 120 ° C
After drying for 120 minutes, it was baked at 500 ° C. for 120 minutes to form a three-way catalyst coat layer. The three-way catalyst coat layer is formed in an amount of 130 g per liter of the honeycomb substrate, Pt is 2 g, Rh is 0.4 g
g is carried.

When the obtained exhaust gas purifying catalyst of the present embodiment was cut and analyzed, the concentration ratio of zeolite to the three-way catalyst in the portion extending from the end face on the upstream side by １ ／ of the total length was as follows: The three-way catalyst was 93: 7. The concentration ratio of zeolite and three-way catalyst in a portion that was deeper by 1/4 of the entire length from the downstream end face was zeolite: three-way catalyst = 5: 95.

(Example 2) The removal rate of air during removal of excess slurry was adjusted, and the concentration ratio of zeolite to three-way catalyst at a portion that entered the back by 1/4 of the entire length from the upstream end face was determined. : Three-way catalyst = 87:13, and the concentration ratio of zeolite and three-way catalyst at a portion that is 1/4 of the entire length from the downstream end surface is zeolite: three-way catalyst =
An exhaust gas purifying catalyst of Example 2 was prepared in the same manner as in Example 1 except that the ratio was set to 11:89. The coating amount of each coating layer and the carrying amounts of Pt and Rh are the same as in Example 1.

(Example 3) The removal rate of air during removal of excess slurry was adjusted, and the concentration ratio of zeolite to three-way catalyst at a portion that was 奥 of the entire length from the upstream end face was determined. : Three-way catalyst = 82:18, and the concentration ratio of zeolite to three-way catalyst at a portion that is 1/4 of the entire length from the downstream end surface is zeolite: three-way catalyst =
An exhaust gas purifying catalyst of Example 3 was prepared in the same manner as in Example 1 except that the ratio was set to 19:81. The coating amount of each coating layer and the carrying amounts of Pt and Rh are the same as in Example 1.

(Example 4) The removal rate of air when removing excess slurry was adjusted, and the concentration ratio of zeolite to the three-way catalyst in the portion that entered the back by 1/4 of the entire length from the upstream end surface was determined. : Three-way catalyst = 79:21, and the concentration ratio between zeolite and three-way catalyst at a portion that is 1/4 of the entire length from the downstream end surface is zeolite: three-way catalyst =
An exhaust gas purifying catalyst of Example 4 was prepared in the same manner as in Example 1 except that the ratio was 20:80. The coating amount of each coating layer and the carrying amounts of Pt and Rh are the same as in Example 1.

(Example 5) The removal ratio of air when removing excess slurry was adjusted, and the concentration ratio of zeolite to three-way catalyst at a portion which was deeper by 1/4 of the entire length from the upstream end face was determined. : Three-way catalyst = 73:27, and the concentration ratio of zeolite and three-way catalyst at a portion that is 1/4 of the total length from the downstream end surface is zeolite: three-way catalyst =
An exhaust gas purifying catalyst of Example 5 was prepared in the same manner as in Example 1 except that the ratio was set to 24:76. The coating amount of each coating layer and the carrying amounts of Pt and Rh are the same as in Example 1.

(Example 6) The removal rate of air when removing excess slurry was adjusted, and the concentration ratio of zeolite and three-way catalyst at a portion that entered the back by 1/4 of the entire length from the upstream end face was determined. : Three-way catalyst = 67:33, and the concentration ratio of zeolite and three-way catalyst at a portion that is 1/4 of the total length from the downstream end surface is zeolite: three-way catalyst =
An exhaust gas purifying catalyst of Example 6 was prepared in the same manner as Example 1 except that the ratio was 31:69. The coating amount of each coating layer and the carrying amounts of Pt and Rh are the same as in Example 1.

(Comparative Example 1) Example 1 was the same as Example 1 except that the zeolite coat layer and the three-way catalyst coat layer were formed to be uniform over the entire length by adjusting the air extraction speed when removing excess slurry. Similarly, an exhaust gas purifying catalyst of Comparative Example 1 was prepared. The coating amount of each coating layer and the carrying amounts of Pt and Rh are the same as in Example 1. The concentration ratio between the zeolite and the three-way catalyst at the portion that is 1/4 of the total length from the upstream end surface is zeolite: three-way catalyst =
The ratio is 52:48, which is the composition over the entire length.

(Comparative Example 2) The same slurry as in Example 1 was used.
2 and then lifted, air was extracted from the upstream end face to remove excess slurry, dried and fired in the same manner as in Example 1, and a zeolite coat layer was applied to a half of the total length from the upstream end face. Formed.

Next, using the same slurry as in Example 1, １ ／ of the entire length was dipped from the downstream end face of the honeycomb base material having the zeolite coat layer on the half of the entire length from the upstream end face and then pulled up. Then, air was drawn from the downstream end face to remove excess slurry, and then dried and fired in the same manner as in Example 1 to form a three-way catalyst coat layer on a half of the entire length from the downstream end face. The zeolite coat layer and the three-way catalyst coat layer are each formed with a uniform thickness, and the coating amounts are the same as in Example 1. The amounts of Pt and Rh carried are the same as in Example 1.

<Test / Evaluation> Each of the exhaust gas purifying catalysts described above was attached to an evaluation device, and the room temperature (50 ° C.)
The actual engine exhaust gas of 300 ℃ from the state of the space velocity 2000h
^The amount of HC in the outgas when flowing at ^-1 for 2 minutes was measured. Each result is shown in FIG. 1 as a relative ratio when the HC amount of the exhaust gas purifying catalyst of Comparative Example 1 was 1.

As shown in FIG. 1, the exhaust gas purifying catalysts of the respective embodiments have a smaller amount of HC in the outgas compared with the comparative example.
It turns out that it is excellent in C purification performance. This is apparently the effect of forming the zeolite coat layer over the entire length and increasing the zeolite concentration on the upstream side and decreasing on the downstream side.

From the comparison between the examples, the exhaust gas purifying catalysts of Examples 2 to 5 emit less HC. Therefore, the concentration ratio between the zeolite and the three-way catalyst on the upstream side and the downstream side in the exhaust gas flow direction is the upstream side (zeolite:
Three-way catalyst): Downstream side (zeolite: Three-way catalyst) = (9:
It is clear that the range of 1-7: 3) :( 1: 9-3: 7) is particularly desirable.

[0045]

According to the exhaust gas purifying catalyst of the present invention, the excellent HC adsorption ability in the low temperature range and the rapid rise of the temperature to the activation temperature of the noble metal can be achieved. Can purify HC.

[Brief description of the drawings]

FIG. 1 is a graph showing the relative amounts of HC amounts in outgases in exhaust gas purifying catalysts of Examples and Comparative Examples of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/28 301 B01D 53/36 C F-term (Reference) 3G091 AA02 AA13 AB02 AB03 AB10 BA01 BA15 FB02 FB03 FC07 FC08 GA01 GA06 GA18 GB01Z GB05W GB06W GB07W GB09Y GB10Y GB17X GB17Z 4D048 AA13 AA18 AB01 BA03X BA08X BA10X BA11X BA19X BA30X BA33X BA41X BA42X BB02 BB16 4G066 AA22D AA61B BA05 BA07 BA01 BA01 A01 A02 A BB06B BB06C BC43B BC43C BC71A BC71B BC71C BC75A BC75B BC75C CA03 CA07 CA09 CA14 CA15 DA06 EA19 EE09 FA01 FB14 FB15 ZA04B ZA11B

Claims (4)

[Claims] 1. An exhaust gas purifying catalyst comprising an oxidation catalyst or a three-way catalyst and a hydrocarbon adsorbent, wherein the hydrocarbon adsorbent is contained in the exhaust gas with a high concentration on the upstream side and a small concentration distribution on the downstream side. An exhaust gas purifying catalyst, comprising: 2. The concentration ratio of the hydrocarbon adsorbent between the upstream side and the downstream side in the exhaust gas flow direction is: upstream side: downstream side = 9-7:
The exhaust gas purifying catalyst according to claim 1, wherein the number is 1 to 3. 3. The exhaust gas purifying catalyst according to claim 1, wherein the oxidation catalyst or the three-way catalyst has a concentration distribution that is small on the upstream side and high on the downstream side in the exhaust gas flow direction. 4. The concentration ratio between the hydrocarbon adsorbent and the oxidation catalyst or the three-way catalyst on the upstream side and the downstream side in the exhaust gas flow direction is determined on the upstream side (hydrocarbon adsorbent: oxidation catalyst or three-way catalyst): The exhaust gas purification according to claim 3, wherein the downstream side (hydrocarbon adsorbent: oxidation catalyst or three-way catalyst) = (9: 1 to 7: 3) :( 1: 9 to 3: 7). Catalyst.