JP2003314268A - Exhaust gas purifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem where HC which is easily exhausted after starting because HC starts to be detached from a HC trap before a three way catalyst reaches an active temperature after cold starting of an engine in an engine exhaust gas purifying system using a HC trap catalyst. <P>SOLUTION: One or more slit is formed at the downstream of a carrier traversing a cell of the honeycomb carrier, and an HC trap agent is carried so as to increase a carrying amount at the upstream of the carrier. The carrying amount is increased at the upstream of the carrier which easily increases in temperature so that the heat capacity is increased, and the HC trap agent is restrained in temperature increase. The slit restrains the heat transmission into the carrier downwards, also delaying increase in temperature at the downstream of the carrier to make increase the captured amount of the HC as a whole. The treating efficiency on HC detaching is also increased by the delay of increase in temperature. Exhaust gas introduced into the cell generates disturbance in a slit part, and increases the chance of contacting with the HC trap agent by the exhaust gas to increase HC trap efficiency. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalytic converter mainly applied to engine exhaust purification, and more particularly to a HC converter.
The present invention relates to an improvement of an exhaust emission control device having a trap function.

[0002]

2. Description of the Related Art In an exhaust gas purification system equipped with a three-way catalyst, treatment of HC during cold engine operation has become a problem. This is because HC that is easily discharged during combustion under low temperature conditions cannot be sufficiently purified until the catalyst reaches the activation temperature. As a solution to this problem, JP-A-9-85049 proposes a purification system to which an HC trapping agent is applied. The HC trapping agent has a function of temporarily trapping HC in the exhaust gas, and the trapped HC is desorbed from the trapping agent as the temperature rises. Therefore, in the above system, an HC trapping agent is provided on the upstream side of the three-way catalyst, and H
The emission of C is controlled. However, even if the trapped HC reaches the temperature at which desorption from the trapping agent starts, the three-way catalyst on the downstream side is not yet sufficiently activated at this point, so the effect of suppressing HC emission is not sufficient. Absent.

It is an object of the present invention to provide an exhaust emission control device which can more surely suppress the emission of HC even during cold engine operation.

[0004]

SUMMARY OF THE INVENTION The basic structure of the present invention is that one or more slits are formed so as to traverse cells of a honeycomb-shaped carrier and be unevenly distributed in a downstream portion of the carrier.

Since the slit formed in the carrier has a function of blocking the heat transfer in the carrier to the downstream side, the temperature rise is delayed by that much to increase the amount of trapped HC and the time until HC is desorbed. Can be long. Further, this allows time for the temperature of the catalytic metal to rise, so that the treatment efficiency at the time of HC desorption is also improved.

On the other hand, in the conventional exhaust emission control device, since a large number of cells formed in a honeycomb shape are continuous from the inlet to the outlet of the carrier, the gas flow in the cells is relatively regular and no turbulence occurs. Few. On the other hand, if a slit is formed in the carrier so as to cross the cell, the gas that has entered the cell divided in the flow direction by the slit causes turbulence at the slit portion. This turbulence increases the chances of the exhaust gas coming into contact with the HC trapping agent, and accordingly improves the HC trapping performance.

Further, in the exhaust gas purifying device having a continuous cell structure having no slit, the flow rate distribution and the temperature rising property of the gas passage are uneven on the cross section of the carrier. In other words, the HC trap performance and the conversion rate are cell by cell. It is difficult to use up the original performance of the exhaust gas purification device because of the unevenness in the exhaust gas. On the other hand, in the case of a carrier provided with slits, the turbulent flow action makes it possible to make the gas flow rate distribution in the cross-sectional direction of the carrier uniform, so that the controllability is improved and the original performance of the exhaust gas purification device can be fully exhibited. Become.

As a first aspect of the present invention, the carrier is further loaded with an HC trapping agent such as zeolite so that the loading amount becomes large in the upstream portion. With such a configuration, the heat capacity in the upstream portion increases and the temperature rise can be suppressed. Therefore, an increase in the amount of captured HC and a delay in the HC desorption timing in the upstream portion of the carrier, where the temperature easily rises, can be reduced. Can be planned. The amount of the HC trapping agent carried becomes relatively small in the downstream portion of the carrier, but the HC trapping efficiency can be secured by increasing the HC trapping efficiency by the action of the turbulence and heat transfer suppression by the slits described above. it can.

In the above structure, a carrier may be made to carry a catalytic metal such as Pt, Rh, or Pd so that the carried amount becomes large at the upstream portion. In the upstream part of the carrier, the catalyst is activated early by contact with high-temperature exhaust gas, so that a large amount of HC can be efficiently treated by increasing the amount of catalyst supported.

As a second aspect of the invention, in the basic structure in which slits are unevenly distributed in the downstream portion of the carrier, HC is added to the carrier.
The trapping agent is uniformly carried, and the catalytic metal is carried so that the carried amount becomes large in the downstream portion. In this case, the chance of contact between the exhaust gas and the catalytic metal increases due to the effect of turbulence due to the slit formed in the downstream portion of the carrier, so that the conversion efficiency of the catalyst in the downstream portion of the carrier can be improved.

Also in the second aspect of the present invention, by applying the structure in which the HC trapping agent is carried in the carrier upstream portion so that the carried amount becomes large, the HC trapping agent in the carrier upstream portion is applied.
It is possible to improve the trapping performance and further improve the purification performance as a whole.

Incidentally, as will be described in detail below as an embodiment, it is possible to set a unique characteristic for each according to the shape and size of the slit. The same applies to the catalyst metal and the HC trapping agent coated on the carrier, and various preferable characteristics can be given depending on the distribution and the setting of the layer structure.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an engine system to which an exhaust emission control device according to the present invention is applied. In the figure, 1 is an engine, 2 is its intake passage, and 3 is an exhaust passage. Reference numeral 4 is an EGR passage for returning a part of the exhaust gas from the exhaust passage 3 to the intake passage 2, and 5 is an EGR control valve for controlling the exhaust gas recirculation amount. Reference numeral 7 is a fuel injection valve, and 8 is a spark plug.

Reference numerals 9 to 11 denote exhaust purification devices provided in the exhaust passage 3. These three exhaust emission control devices 9-11 are
Basically, it is a three-way catalyst that has both the oxidation function of CO and HC and the reduction function of NOx, and any or all of them have the function of temporarily capturing HC by an HC trapping agent such as zeolite. It is configured as a provided HC trap catalyst. The upstream side 9 or 10 may be composed of an HC trap device having only an HC trap function.

Reference numerals 12 and 13 are exhaust gas sensors for detecting the air-fuel ratio or oxygen concentration of the exhaust gas upstream and downstream of the upstreammost exhaust purification apparatus 9, respectively, and 14 is a temperature for detecting the catalyst temperature of the exhaust purification apparatus 10 in the middle stage. It is a sensor.

Reference numeral 15 is a controller for controlling the air-fuel ratio and ignition timing on the basis of operating state signals such as engine speed and intake air amount, and is composed of a microcomputer including a CPU and its peripheral devices.

An embodiment of the honeycomb carrier 21 housed in the exhaust gas purification devices 9 to 11 is shown in FIG. In the present invention, basically, as shown in FIG. 2, one or more slits 2 are formed so as to cross the gas flow (direction of the arrow) of the carrier 21.
2 is formed so as to be unevenly distributed in the downstream portion of the carrier. in this case,
The slits 22 are arranged in the carrier 21 so that the distribution of the plurality of slits 22 in the gas flow direction becomes dense on the downstream side. When the carrier 21 is made of ceramics, the slits 22 are processed by grinding after firing. In the illustrated example, the slit 22 is formed so as to be orthogonal to the gas flow from one side surface side of the catalyst, and the non-slit portion 23 is left on the other side surface side. Further, the adjacent slits 22 are formed at different angles by 180 degrees around the carrier 21 and at equal intervals in the gas flow direction so that slits and non-slit portions are arranged alternately. On the cell surface of the carrier 21, an HC trap layer containing an HC trapping agent such as zeolite or a catalyst metal layer containing a catalyst metal such as Pt, Rh and Pd is formed by coating.

3 (a) to 3 (c) show an example of the distribution of the carried amount of the HC trap layer or the catalytic metal layer, and the hatched portion in the figure is designated by the symbol T is the HC trap. The portion where the amount of the supported agent is large, M indicates the portion where the supported amount of the catalytic metal is large. In the figure, the carrying amount is shown to change stepwise in the upstream and downstream directions, but the present invention is not limited to this, and the carrying amount may be changed continuously.

FIG. 3 (a) shows an example in which the respective loading amounts are set so that the thickness of the HC trap layer or the catalytic metal layer is large in the upstream portion of the carrier 21 (left in the figure; the same applies hereinafter). Is. FIG. 3B is an example in which the amount of the HC trap layer carried is set uniformly in the upstream and downstream directions of the carrier, and the thickness of the catalytic metal layer is increased in the downstream portion. FIG. 3 (c)
Is an example in which the thickness of the HC trap layer is set to be large in the upstream portion of the carrier and the thickness of the catalyst metal layer is set to be large in the downstream portion. The effect of setting the distribution of the carried amount of the HC trapping agent or the catalyst metal is as described above, and it is possible to increase the amount of HC trapped by the HC trapping agent and improve the conversion efficiency by the catalyst metal.

Further, the structure in which the plurality of slits 22 are vertically formed on the carrier 21 is advantageous in that the strength of the carrier is secured in addition to being relatively easy to manufacture. It is effective to increase the number of the slits 22 provided from the viewpoint of making the gas flow turbulent and suppressing heat transfer, but from the viewpoint of ensuring the required cell surface area and HC trap performance within a limited carrier volume. From the above, the configuration of the present invention in which the slits 22 are unevenly distributed in the downstream portion of the carrier is advantageous.

The effect of suppressing the heat transfer inside the carrier 21 by the slits 22 can be expected to some extent even if it is a metal carrier, but it becomes more remarkable when a ceramic material having a relatively small thermal conductivity is applied as the carrier. . The ceramic material has a good compatibility with the HC trapping agent such as zeolite and has an advantage that the strength of the coating is high.

If the amount of the HC trapping agent carried is increased to increase the amount of trapped HC, the passage area of the cell becomes smaller and the exhaust resistance increases accordingly. In this respect, in the present invention, since the HC trap performance is improved by the effects of the turbulent flow and the suppression of heat conduction described above, it is possible to reduce the cell density and reduce the exhaust resistance. Specifically, the cell density of a general three-way catalyst is 900 or more, whereas in the present invention, it can be 300 or less, or at least 600 or less. The unit of the cell density is the number of cells per square inch of the cross section of the carrier, and is a unit commonly used for transactions by those skilled in the art. The amount of the HC trapping agent loaded is, for example, about 350 when the cell density is 300, and 600 when the cell density is 600.
At that time, it is set to about 250. The unit of the supported amount is grams per cubic foot of the apparent volume of the carrier [g / c
f], which is a commercial unit used by those skilled in the art.

A plurality of exhaust gas purification devices 9 as shown in FIG.
In the exhaust gas purification system including Nos. 11 to 11, it is possible to reduce the exhaust resistance by making the cell density of the exhaust gas purification device 10 or 11 located on the downstream side smaller than that on the upstream side. Although the catalyst on the downstream side has a low temperature rising property and takes time to reach the activation temperature, the configuration of the exhaust gas purification device of the present invention can sufficiently enhance the HC trap performance.
The exhaust resistance can be reduced by making the cell density rough while ensuring the exhaust purification performance.

FIG. 4 shows an example of the support structure of the carrier 21, in which 34 is a catalyst container and 35 is a heat-resistant mat made of ceramic fiber or alumina fiber. The carrier 21 is fixed in the catalyst container 34 via a heat-resistant mat 35 wound around the outer periphery thereof. In this embodiment, the outer periphery of the open portion of the slit 22 is the carrier 2
It is filled with a filler 36 having the same coefficient of linear expansion as 1. By providing the filling material 36 in this way, it is possible to prevent the problem that the mat 35 is wind-eroded and worn by the exhaust gas passing through the slit 22. Also, the carrier 2
By using the filler 36 having the same linear expansion coefficient as that of No. 1, the strength of the carrier 21 can be improved.

FIG. 5 shows another embodiment of the carrier structure. As shown in the figure, the width d of the slits 22 located on the downstream side is increased.

According to this embodiment, it is possible to further promote the turbulent flow of exhaust gas in the downstream portion where the slit width d is increased, and it is also possible to increase the heat transfer suppressing effect. Slit 22 with a large width d
Since the gas turbulence is so large in the portion (2), the gas flow rate distribution in the cross-sectional direction of the carrier on the downstream side becomes uniform, so that both the HC trap performance and the desorbed HC purification performance are improved. This embodiment is suitable when the temperature of the downstream portion of the carrier tends to rise.

6 to 10 are embodiments relating to the layer structure of the HC trapping agent and the catalytic metal. The HC trapping agent and the catalyst metal may be mixed in the same layer, but since layering each of them inside and outside causes a time difference in temperature rise, purification treatment is performed at the same timing as HC desorption and catalyst activation. It is possible to improve the efficiency of.

In particular, as shown in FIG. 6, in the structure in which the lower layer side of the cell 24 is coated with the HC trap layer 25 containing the HC trapping agent and the upper layer side is coated with the catalytic metal layer 26 containing the catalytic metal, respectively, Since the catalyst metal of the layer 26 is activated early by contact with the exhaust gas, the HC trap layer 25 in contact with the carrier 21 can be kept at a relatively low temperature.
It is possible to satisfy the contradictory requirements of securing the amount of C trap and improving the conversion efficiency by the catalyst.

FIG. 7 shows an embodiment in which a heat insulating layer 29 made of alumina or the like is formed adjacent to the HC trap layer 25 to have a uniform thickness. Since the heat insulating layer 29 can reduce the amount of heat transfer from the catalyst metal layer 26 to the HC trap layer 25, it is possible to increase the amount of HC trap while increasing the temperature of the catalyst metal layer 26 earlier, and to improve the purification performance.

As shown in FIG. 8, the heat insulating layer 29 is formed so that its thickness becomes larger toward the upstream side of the carrier, so that the upstream side HC trap layer is likely to be heated by exhaust heat and catalytic reaction. It is possible to suppress the temperature rise of the above and further improve the HC trapping performance.

FIG. 9 shows an embodiment in which the heat insulating layer 29 is formed close to the surface of the catalytic metal layer 26 on the upstream side of the carrier. According to this embodiment, it is possible to increase the heat capacity of the HC trap layer 25 in the upstream portion where the temperature rise is relatively fast, delay the temperature rise, and improve the HC trap performance.

FIG. 10 shows an embodiment in which the heat insulating layer 29 is formed on the downstream side so as to be close to the surface of the carrier. According to this embodiment, the catalytic metal layer 2 in the downstream portion where the temperature rise is relatively slow
It is possible to accelerate the activity of No. 6 and further improve the contradictory performances of the HC trapping performance and the purification performance after desorption of HC.

In the structures shown in FIGS. 6 to 10, the HC trap layer 25 or the catalyst metal layer 26 may be composed of a plurality of layers having different characteristics. For example, as for the catalytic metal layer 26, when Pd is applied on the surface side, Pd-Rh system or Pt-Rh system is formed on the deep side.
Alternatively, the Pd layer has a relatively low density. It is possible to more appropriately control the HC desorption timing or the catalyst metal activation timing according to the temperature rising property due to the characteristics of the carrier and the HC trapping agent.

FIG. 11 shows an embodiment in which a plurality of slits 22 are formed alternately from both side surfaces of the carrier 21 and inclined toward the upstream side of the gas flow with respect to the cells. When viewed from the gas flow direction, the adjacent slits 22 are alternately arranged so as to partially overlap each other.

According to this embodiment, the inclined slits 22 facilitate the diffusion of the gas from the inside of the carrier to the outside thereof, so that the dead volume portion, that is, the flow of gas, is small in the outside portion of the carrier, and the functions of the HC trapping agent and the catalytic metal function. The dead volume portion can be reduced by applying this configuration when there is a portion that cannot fully utilize.

FIG. 12 shows the carrier 21 facing each other from both sides.
Further, it is an embodiment in which a plurality of slits 22 are formed so as to be inclined toward the upstream side of the gas flow with respect to the cell. In this embodiment, the slits 2 adjacent to each other when viewed from the gas flow direction
There is no portion where the two overlap, and the non-slit portion 23 remains in the central portion.

According to this embodiment, the strength of the carrier 21 can be increased by the central non-slit portion 23 while reducing the dead volume part in the outer region of the carrier as in the case of FIG.

FIG. 13 shows an embodiment in which the slit 22 is formed so as to penetrate both side surfaces of the carrier 21.

According to this embodiment, since the non-slit portions 23 are provided on both sides of the slit 22, the strength of the carrier 21 can be increased. Further, in this embodiment, since the side surface shape of the slit 23 is a mountain shape with the top facing the upstream side, it is possible to reduce the dead volume part in the outer region of the carrier as in the case of FIG. 15 or 16.

FIG. 14 shows an embodiment in which the width d of the slits 22 formed alternately from both side surfaces of the carrier 21 is formed in a wedge shape so as to become narrower toward the inside of the carrier. The adjacent slits 22 partially overlap each other when viewed from the gas flow direction.

According to this embodiment, since the slit width is larger in the outer peripheral region of the carrier, the gas turbulence in the outer peripheral region of the carrier can be further promoted and the dead volume portion can be reduced.

FIG. 15 shows a wedge-shaped slit 2 similar to FIG.
2 is an embodiment in which adjacent slits 22 are formed so as not to overlap each other when viewed from the gas flow direction.

According to this embodiment, the strength of the carrier 21 can be increased by the central non-slit portion 23 while reducing the dead volume part in the outer region of the carrier as in the case of FIG.

FIG. 16 shows an embodiment in which a slit 22 is formed so as to penetrate both sides of the carrier 21. Non-slit portions 23 remain on both sides of each slit 22 in the cross section of the carrier. Further, each slit 22 is formed in a polygonal shape so that its width d becomes larger toward the central portion.

According to this embodiment, since the gas turbulence in the inner region of the carrier becomes large due to the wide portion in the center of the slit 22, the dead volume can be obtained by applying this configuration when the dead volume part is generated in the inner part of the carrier. The volume part can be reduced. Further, since the non-slit portions 23 are provided on both sides of the slit 22, the strength of the carrier 21 is also advantageous.

FIG. 17 shows an embodiment in which a slit 22 is formed in a bent shape so as to penetrate both sides of the carrier 21 and has a plurality of tops in the upstream and downstream directions of the gas flow.

According to this embodiment, the curved slit shape complicates the gas flow in the central part of the carrier and makes the turbulence larger, so that the dead volume part of the carrier can be effectively reduced. Further, the strength of the carrier can be secured by the non-slit portions 23 on both sides of the slit.

FIG. 18 shows an embodiment in which the slit 22 is formed so as to penetrate both sides of the carrier 21 and has a convex curved shape in the upstream direction of the gas flow.

According to this embodiment, in addition to the effect of reducing the dead volume portion of the carrier as in the case of FIG. 17, the slit 22 has a curved shape and has no acute-angled portion, so that the carrier 21 is Stress concentration is less likely to occur when subjected to vibration or impact force, which is advantageous in terms of strength.

Each of the above drawings is a drawing for explaining the formation mode of the slits and the structure of the catalyst carrier, and the width, pitch, etc. of the slits are drawn with dimensions or ratios different from the actual ones for convenience of description. There is.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an engine system to which an exhaust emission control device according to the present invention is applied.

FIG. 2 is an explanatory view of a side shape showing an embodiment of a carrier according to the present invention.

FIG. 3 is an explanatory diagram of an embodiment of an amount distribution of an HC trapping agent or the like on a carrier according to the present invention.

FIG. 4 is a vertical sectional view showing an example of a carrier support structure of an exhaust emission control device according to the present invention.

FIG. 5 is an explanatory view of a side shape showing another embodiment of the carrier according to the present invention.

FIG. 6 is a detailed cross-sectional view of a cell portion of an embodiment relating to a layered structure of an HC trapping agent or the like of a carrier according to the present invention.

FIG. 7 is a detailed cross-sectional view of a cell portion of another embodiment relating to the layered structure of the HC trapping agent or the like of the carrier according to the present invention.

FIG. 8 is a detailed cross-sectional view of a cell portion of another embodiment relating to the layer structure of the carrier such as the HC trapping agent according to the present invention.

FIG. 9 is a detailed cross-sectional view of a cell portion of another embodiment of the layer structure of the carrier such as an HC trapping agent according to the present invention.

FIG. 10 is a detailed cross-sectional view of a cell portion of another embodiment relating to the layered structure of the HC trapping agent or the like of the carrier according to the present invention.

FIG. 11 is a side view of another embodiment of a carrier according to the present invention.

FIG. 12 is a side view of another embodiment of a carrier according to the present invention.

FIG. 13 is a side view of another embodiment of the carrier according to the present invention.

FIG. 14 is a side view of another embodiment of a carrier according to the present invention.

FIG. 15 is a side view of another embodiment of a carrier according to the present invention.

FIG. 16 is a side view of another embodiment of a carrier according to the present invention.

FIG. 17 is a side view of another embodiment of a carrier according to the present invention.

FIG. 18 is a side view of another embodiment of a carrier according to the present invention.

[Explanation of symbols]

1 engine 2 Intake passage 3 exhaust passage 9-11 Exhaust gas purification device 21 carrier 22 slits 23 Non-slit part 24 cells 25 HC trap layer 26 catalytic metal layer 29 Thermal insulation layer 34 Catalyst container

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/08 F01N 3/24 B 3/24 E L B01D 53/36 103Z (72) Inventor Shunichi Mitsuishi Yokohama City, Kanagawa Prefecture 2 Takaramachi, Kanagawa-ku Nissan Motor Co., Ltd. (72) Inventor Yoshinao Ugo Yoshinao, Takara-cho, Kanagawa-ku, Yokohama, Kanagawa F-Term (Nissan Motor Co., Ltd.) GB05W GB09Y HA18 HA27 HB05 4D048 AA18 BA10Y BB02 BB13 BB15 BB16 CC41 EA04 4G069 AA03 AA08 CA03 CA15 DA06 EA19 EB04 EC28 EC29 FA03 FB23

Claims (27)

[Claims] 1. A slit is formed so as to traverse cells of a honeycomb-shaped carrier and be unevenly distributed in a downstream portion of the carrier, and an HC trapping agent is added to the carrier so that the amount of the carrier carried becomes large in the upstream portion. An exhaust gas purification device characterized by being carried. 2. The exhaust gas purifying apparatus according to claim 1, wherein the catalyst metal is carried on the carrier so that the carried amount becomes large in the upstream portion. 3. A slit is formed so as to cross the cells of the honeycomb-shaped carrier and be unevenly distributed in the downstream portion of the carrier, and the carrier is loaded with an HC trapping agent, and a large amount is loaded in the downstream portion. An exhaust emission control device, which carries a catalytic metal so that 4. The exhaust gas purification device according to claim 3, wherein the HC trapping agent is carried in the upstream portion of the carrier so as to have a large carrying amount. 5. The exhaust emission control device according to claim 1, wherein a plurality of the slits are arranged in the gas flow direction of the carrier. 6. The exhaust emission control device according to claim 5, wherein the width of the downstream side of the plurality of slits is larger than that of the upstream side. 7. The exhaust emission control device according to claim 1 or 3, wherein the carrier is formed of ceramics. 8. The exhaust gas purification device according to claim 1, wherein the HC trapping agent is composed of a plurality of layers having different characteristics. 9. The exhaust emission control device according to claim 2, wherein the catalyst metal is composed of a plurality of layers having different characteristics. 10. The carrier contains H containing an HC trapping agent.
The exhaust emission control device according to claim 2 or 4, wherein the C trap layer and the catalyst metal layer containing a catalyst metal are formed by coating, respectively. 11. The exhaust emission control device according to claim 10, wherein the HC trap layer is formed on the lower layer side and the catalytic metal layer is formed on the upper layer side. 12. The exhaust emission control device according to claim 11, wherein a heat insulating layer is formed between the HC trap layer and the catalytic metal layer. 13. The exhaust emission control device according to claim 12, wherein the heat insulating layer is formed to have a uniform thickness. 14. The exhaust emission control device according to claim 12, wherein the heat insulating layer is formed so that the thickness thereof becomes larger toward the upstream side of the carrier. 15. The exhaust emission control device according to claim 12, wherein the heat insulating layer is formed so as to be close to the surface of the catalytic metal layer on the upstream side. 16. The exhaust emission control device according to claim 12, wherein the heat insulating layer is formed so as to be close to the surface of the carrier on the downstream side. 17. The exhaust emission control device according to claim 5, wherein the plurality of slits are formed so as to face each other from opposite positions on the outer periphery of the carrier and perpendicular to the gas flow in the cell. 18. The exhaust emission control device according to claim 5, wherein the plurality of slits are formed so as to face each other from opposite positions on the outer periphery of the carrier and be inclined with respect to the gas flow in the cell. 19. The exhaust emission control device according to claim 17, wherein the opposing slits are formed so as not to overlap each other when viewed in the gas flow direction. 20. The exhaust emission control device according to claim 1, wherein the slit is formed so as to penetrate both side surfaces of the carrier. 21. The exhaust emission control device according to claim 1 or 3, wherein the slit is formed in a shape in which the width gradually narrows from the outer periphery of the carrier toward the inner side. 22. The exhaust emission control device according to claim 21, wherein a plurality of the slits are formed so as to face each other from opposite positions of the carrier and do not overlap each other when viewed in the gas flow direction. 23. The exhaust emission control device according to claim 20, wherein the penetrating slit is formed in a shape in which the width gradually increases from the outer periphery of the carrier toward the inner side when viewed from the penetrating direction. 24. The exhaust emission control device according to claim 20, wherein the penetrating slit is formed in a bent shape having a plurality of tops in the upstream and downstream directions when viewed from the penetrating direction. 25. The exhaust emission control device according to claim 20, wherein the penetrating slit is formed in a curved shape convex toward the upstream side when viewed from the penetrating direction. 26. The exhaust emission control device according to claim 1 or 3, wherein the carrier has a cell density of 600 or less. 27. The exhaust emission control device according to claim 1 or 3, wherein the coating amount of the HC trapping agent is 250 [g / cf] or more.