JP2010099632A - Apparatus for purifying exhaust gas - Google Patents

Abstract

[PROBLEMS] To improve warm-up characteristics in a tandem type exhaust gas purification apparatus in which a carrier base material in a pre-stage catalyst is a metal base material.
A tandem type exhaust gas purification apparatus includes a front catalyst 2 and a rear catalyst 3 disposed on the downstream side of the exhaust gas at a distance from the front catalyst 2. The carrier base material in the pre-stage catalyst 2 is a metal base material. The front catalyst 2 has a low radiation part having a surface radiation rate of 0.3 or lower, which is lower than the surface radiation rate of the catalyst coat layer in the rear catalyst 3, in at least a part of the catalyst coat layer.
[Selection] Figure 1

Description

  The present invention relates to an exhaust gas purifying device for purifying exhaust gas discharged from an internal combustion engine, and more specifically, a tandem type exhaust gas comprising a front-stage catalyst and a rear-stage catalyst disposed at a downstream side of the exhaust gas at a distance from the front-stage catalyst. The present invention relates to a purification device.

  As exhaust gas purification catalysts for purifying exhaust gas from automobile engines, oxidation catalysts, three-way catalysts, NOx selective reduction catalysts, NOx storage reduction catalysts, and the like are widely used. These exhaust gas-purifying catalysts are generally composed of a carrier substrate having a honeycomb structure having a large number of cells and a catalyst coat layer formed on the cell wall surface of the carrier substrate. The catalyst coat layer is composed of a carrier powder made of a porous oxide such as alumina or ceria, and a catalyst metal made of a noble metal such as Pt, Rh, or Pd or a transition metal such as Fe or Co and supported on the carrier powder. There are many things to become.

  By the way, the exhaust gas purifying catalyst is generally used in a state of being housed in a catalytic converter. The catalytic converter has a shape having cone portions on both sides of the cylindrical portion, and the diameter of the exhaust pipe connected to the cone portion is smaller than the diameter of the cylindrical portion. For this reason, the exhaust gas flowing into the exhaust gas purifying catalyst has a larger flow velocity toward the center, and a flow velocity distribution is generated in which the flow velocity decreases from the central portion of the exhaust gas purifying catalyst toward the outer peripheral portion. As a result, a temperature distribution is generated in which the temperature is higher at the center of the exhaust gas purification catalyst and lower at the outer periphery. Catalyst metals such as precious metals do not function very well at low temperatures. For this reason, there has been a problem that the catalytic metal does not function effectively at the outer periphery of the exhaust gas purifying catalyst having a low temperature.

  Therefore, a so-called tandem type exhaust gas purification device in which a plurality of catalysts are arranged in series in a catalytic converter is known (see, for example, Patent Documents 1 and 2). In the tandem type exhaust gas purifying apparatus, the temperature distribution of the rear catalyst can be made uniform in the radial direction by making the exhaust gas flow turbulent between the front and rear catalysts arranged in series. For this reason, the catalyst metal can be made to function effectively even in the outer peripheral portion of the rear catalyst, and the purification rate of the catalyst as a whole can be improved.

  However, in such a tandem type exhaust gas purification device, when a metal base material is adopted as the carrier base material in the upstream catalyst, there is a problem that the effect of improving the purification rate at the start of the engine is reduced as described below. There is.

That is, as described above, most of the exhaust gas flowing into the catalytic converter from the exhaust pipe mainly passes through the central portion of the preceding catalyst. If the carrier substrate in the former catalyst is a metal substrate, the heat of the exhaust gas that mainly passes through the center of the former catalyst tends to be transferred to the outer periphery through the metal substrate due to the high thermal conductivity of the metal. The temperature distribution in the radial direction tends to be uniform. As a result, the exhaust gas passing through the pre-stage catalyst loses much heat to the pre-stage catalyst. For this reason, the temperature increase of the latter catalyst is delayed, and the activation of the catalyst metal in the latter catalyst is also delayed. Therefore, the effect of improving the purification rate when starting the engine is reduced.
Japanese Patent Laid-Open No. 11-218019 JP 09-155203 A

  This invention is made | formed in view of the said situation, and makes it the subject which should be solved to improve a warm-up characteristic in the exhaust gas purification apparatus of the tandem type | mold whose support base material in a pre-stage catalyst consists of a metal base material.

  (1) An exhaust gas purification apparatus of the present invention that solves the above problems is a tandem type exhaust gas purification apparatus that includes a front-stage catalyst and a rear-stage catalyst that is disposed on the downstream side of the exhaust gas with a space from the front-stage catalyst. Each of the front catalyst and the rear catalyst includes a support base material and a catalyst coat layer formed on the surface of the support base material, and the support base material in the front catalyst is a metal base material. Thus, the pre-stage catalyst has a low radiation part having a surface radiation rate of 0.3 or less in at least a part of the catalyst coat layer.

  In the exhaust gas purification apparatus of the present invention, the carrier base material in the pre-stage catalyst is a metal base material. Since the metal substrate has a high thermal conductivity, the exhaust gas that passes through the front catalyst during use tends to lose heat to the front catalyst.

  In this regard, in the exhaust gas purifying catalyst of the present invention, at least a part of the catalyst coat layer in the preceding catalyst is a low radiation portion. The surface radiation rate of this low radiation part is as low as 0.3 or less. When the surface emissivity of the catalyst coat layer is low, heat reflection is likely to occur on the surface of the catalyst coat layer. If the amount of heat reflection on the surface of the catalyst coat layer in the pre-stage catalyst increases, the amount of heat absorbed by the pre-stage catalyst decreases. For this reason, the exhaust gas that passes through the front catalyst during use does not absorb much heat in the front catalyst. Accordingly, the temperature of the rear catalyst can be quickly raised by the heat of the exhaust gas when the engine is started, and the rear catalyst can be activated quickly. Therefore, the warm-up characteristic can be improved by the rapid activation of the latter stage catalyst.

  The exhaust gas purifying apparatus of the present invention preferably has at least one of the configurations shown in the following items (2) to (4). The exhaust gas purifying apparatus of the present invention may have the configuration shown in each item of the following items (2) to (4) alone, or shown in each item of the following items (2) to (4). Two or more configurations may be combined.

  (2) In the exhaust gas purifying apparatus of the present invention, preferably, the surface radiation rate of the low radiation part is 0.1 to 0.2.

  (3) In the exhaust gas purifying apparatus of the present invention, preferably, the entire catalyst coat layer in the preceding catalyst is the low radiation portion.

  (4) In the exhaust gas purification apparatus of the present invention, preferably, the value of La / Lb is 0.1 to 0.4, where La is the volume of the front catalyst and Lb is the volume of the rear catalyst.

  Therefore, according to the present invention, it is possible to improve warm-up characteristics in a tandem type exhaust gas purification apparatus in which the carrier base material in the pre-stage catalyst is a metal base material.

  In addition, since the exhaust gas purification apparatus of the present invention is a tandem type, turbulence is generated in the exhaust gas between the front catalyst and the rear catalyst arranged in series, and the temperature distribution of the rear catalyst is uniform in the radial direction. Can be. For this reason, the catalyst metal can be made to function effectively even in the outer peripheral portion of the rear catalyst, and the purification rate of the catalyst as a whole can be improved.

  Hereinafter, embodiments of the exhaust gas purifying apparatus of the present invention will be described in detail. In addition, embodiment described is only an example and the exhaust gas purification apparatus of this invention is not limited to the following embodiment. The exhaust gas purifying apparatus of the present invention can be implemented in various forms that have been modified or improved by those skilled in the art without departing from the scope of the present invention.

  The exhaust gas purifying apparatus of the present embodiment is a tandem type exhaust gas purifying apparatus. As schematically shown in FIG. 1, the catalytic converter 1 and a pre-stage catalyst 2 disposed in the catalytic converter 1 The rear stage catalyst 3 is disposed in the catalytic converter 1 and is disposed downstream of the exhaust gas at a predetermined distance d from the front stage catalyst 2.

  The catalytic converter 1 is made of metal and includes an upstream cone portion 11, an intermediate cylindrical portion 12, and a downstream cone portion 13.

  Each of the pre-stage catalyst 2 and the post-stage catalyst 3 includes a support base material, a catalyst coat layer formed on the surface of the support base material, and a catalyst metal contained in the catalyst coat layer.

  The shape of the carrier substrate in the front catalyst 2 and the rear catalyst 3 is not particularly limited, and a honeycomb shape or a foam shape can be used. A honeycomb-shaped honeycomb substrate has a large number of cell passages, and a catalyst coat layer is formed on the surface of the cell wall that defines the cell passages.

  In the exhaust gas purification apparatus of the present embodiment, the material of the carrier base material in the pre-stage catalyst 2 is a metal such as a heat-resistant alloy. That is, the carrier substrate in the pre-stage catalyst 2 is made of a metal substrate. On the other hand, the material of the carrier base material in the post-catalyst 3 is not particularly limited as long as it has predetermined heat resistance, and may be a metal such as a heat resistant alloy or a ceramic such as cordierite.

  The catalyst coat layer in the front catalyst 2 and the rear catalyst 3 is composed of a porous oxide and a catalyst metal supported on the porous oxide. Examples of the porous oxide include single items such as alumina, ceria, zirconia, titania, and silica, a mixture of a plurality of types selected from these, and a plurality of types of composite oxides selected from these.

  Examples of the catalyst metal include noble metals selected from Pt, Rh, Pd, Ir, Ag, Ru, and the like, and base metals selected from Fe, Cu, Co, W, Ni, V, and the like. These single items may be used, or a plurality of types may be supported in combination. The carrying amount can be set according to the purpose. In addition, an alkali metal such as K and Cs, and a promoter metal such as an alkaline earth metal such as Ba and Mg (NOx occlusion material, etc.) can also be supported.

  In the exhaust gas purification apparatus of the present embodiment, the pre-stage catalyst 2 has a low radiation part in at least a part of the catalyst coat layer.

  The low radiation part of the front catalyst 2 has a surface radiation rate of 0.3 or less, which is lower than the surface radiation rate of the catalyst coat layer in the rear catalyst 3. When the surface radiation rate of the low radiation part is larger than 0.3, the amount of heat reflection on the surface of the low radiation part is reduced, and the effect of the present invention becomes insufficient. From the viewpoint of increasing the amount of heat reflection on the surface of the low radiation part, the surface radiation rate of the low radiation part is preferably 0.2 or less. The lower the surface emissivity of the low-radiation part, the better because the amount of heat reflection on the surface of the low-radiation part increases, but in relation to the emissivity of the components constituting the catalyst coat layer, The lower limit of the surface emissivity is about 0.1.

  From the viewpoint of increasing the amount of heat reflection on the surface of the catalyst coat layer in the pre-stage catalyst 2, the entire catalyst coat layer in the pre-stage catalyst 2 is preferably a low radiation part. Note that only a part of the catalyst coat layer in the pre-stage catalyst 2 may be the low radiation part, but in this case, it is preferable that the catalyst coat layer in at least the inner periphery of the pre-stage catalyst 2 is the low radiation part. The flow velocity distribution of the exhaust gas flowing through the pre-stage catalyst 2 is higher in the inner peripheral portion than in the outer peripheral portion. Compared with the case where it does, the effect of this invention can be exhibited more effectively.

  The surface emissivity of the catalyst coat layer in the rear catalyst 3 is higher than 0.3 and can be about 0.4 to 0.5.

  The surface emissivity of the catalyst coat layer is determined depending on the type of constituents constituting the catalyst coat layer (such as porous oxide, catalyst metal and promoter metal, which are essential constituents for performing the original function of the catalyst coat layer) It may be adjusted by the amount, or may be adjusted by mixing a specific substance for adjusting the surface emissivity in the catalyst coat layer or coating the surface of the catalyst coat layer.

  Here, as a preferable embodiment in the case of adjusting the surface emissivity of the catalyst coat layer in the pre-stage catalyst 2 depending on the type of constituents constituting the catalyst coat layer, alumina as the porous oxide, Rh as the catalyst metal, and Can be mentioned. If the catalyst coat layer is formed by supporting Rh on alumina, the surface emissivity can be adjusted to about 0.1 to 0.5 depending on the amount of Rh supported. Another example is a combination of silica as a porous oxide and Pt as a catalyst metal. In the case of a catalyst coating layer in which Pt is supported on silica, the surface emissivity can be adjusted to about 0.1 to 0.5 depending on the amount of Pt supported.

  As a preferred embodiment in the case of adjusting the surface radiation rate of the catalyst coating layer in the pre-stage catalyst 2 with a specific substance for adjusting the surface radiation rate, a catalyst coat in which Rh as a catalyst metal is supported on alumina as a porous oxide An example of mixing or coating SiC as a specific substance on the layer can be given. In this case, the surface emissivity can be adjusted to about 0.2 to 0.8, although it depends on the mixing amount or coating amount of the specific substance. As another example, an example in which SiC as a specific substance is mixed or coated on a catalyst coat layer in which Pd as a catalyst metal is supported on silica as a porous oxide. In this case, the surface emissivity can be adjusted to about 0.2 to 0.8, although it depends on the mixing amount or coating amount of the specific substance.

  Further, as a preferred embodiment example of the catalyst coat layer having a surface emissivity of about 0.4 to 0.5 in the rear catalyst 3, a catalyst metal is used for alumina and ceria-zirconia composite oxide as a porous oxide. And a catalyst coat on which Pt and Rh are supported. Another example is a catalyst coat in which Pd and Rh as catalyst metals and Ba as a promoter metal are supported on alumina and ceria-zirconia composite oxide as a porous oxide. be able to.

  In the exhaust gas purifying apparatus of the present embodiment, when the volume of the front catalyst 2 is La and the volume of the rear catalyst 3 is Lb, the value of La / Lb is preferably 0.1 to 0.4. More preferably, it is 2 to 0.3. If the value of La / Lb is too small, the resistance (back pressure) in the front catalyst 2 becomes small, and the rectifying effect on the gas entering the rear catalyst 3 becomes small. On the other hand, if the value of La / Lb is too large, the absolute amount of the heat of the exhaust gas that passes through the front catalyst 2 is absorbed by the front catalyst 2, so that the effect of the present invention becomes insufficient.

  In the exhaust gas purifying apparatus of the present embodiment, since the carrier base material in the pre-stage catalyst 2 is made of a metal base having high thermal conductivity, the exhaust gas that passes through the pre-stage catalyst 2 during use is easily deprived of heat by the pre-stage catalyst 2. However, since at least a part of the catalyst coat layer in the pre-stage catalyst 2 is a low radiation portion having a surface radiation rate as low as 0.3 or less, the amount of heat reflection on the surface of the catalyst coat layer is increased. The amount of heat absorbed by the pre-stage catalyst 2 is reduced. For this reason, the exhaust gas that passes through the front catalyst 2 during use does not absorb much heat in the front catalyst 2. Therefore, the temperature of the rear catalyst 3 can be quickly raised by the heat of the exhaust gas when the engine is started, and the rear catalyst 3 can be activated quickly. Therefore, the warm-up characteristic can be improved by the rapid activation of the rear catalyst 3.

  Hereinafter, the present invention will be specifically described with reference to test examples, examples and comparative examples.

Example 1
<Preparation of pre-stage catalyst>
As a metal base material for the pre-catalyst 2, a honeycomb base material (diameter: 80 mm, total length: 20 mm, volume) formed by winding and winding a ferrite stainless steel foil (foil thickness: 30 μm) flat plate and corrugated plate La: about 0.1 L, the number of cells: 600) was prepared.

  Moreover, as a slurry for the pre-stage catalyst 2, 200 parts by mass of activated alumina powder, 50 parts by mass of industrial pure water, and 15 parts by mass of a binder (alumina sol) were mixed to prepare slurry A.

  And the slurry A was apply | coated to the metal base material for the upstream catalyst 2, and it dried at 350 degreeC for 1 hour, Then, it baked at 600 degreeC for 1 hour, and formed the coating layer (coating amount: 80 g / L). Next, the metal substrate on which this coating layer was formed was immersed in a rhodium chloride solution having a predetermined concentration for 1 hour and then pulled up to blow off excess slurry and dried at 250 ° C. for 1 hour.

  Thus, the pre-stage catalyst 2 in which the catalyst coat layer formed by supporting Rh on alumina was formed on the entire surface of the metal substrate was completed.

  The surface emissivity of the catalyst coat layer of this pre-stage catalyst 2 was 0.1. That is, the entire catalyst coat layer in the pre-stage catalyst 2 was a low radiation portion having a surface radiation rate of 0.1. The surface emissivity ε was measured at 700 ° C. using a separation black body method.

  In addition, the amount of catalyst metal supported in the pre-stage catalyst 2 was Rh: 0.5 g / L.

<Preparation of latter stage catalyst>
As a metal substrate for the post-catalyst 3, a honeycomb substrate (diameter: 80 mm, total length: 80 mm, volume) formed by winding and winding a ferrite stainless steel foil (foil thickness: 30 μm) flat plate and corrugated plate Lb: about 0.4 L, number of cells: 600) was prepared. In addition, the value of La / Lb was 1/4.

Further, as a slurry for the post-catalyst 3, 70 parts by mass of activated alumina powder, 180 parts by mass of CeO ₂ —ZrO ₂ composite oxide powder, 50 parts by mass of industrial pure water, and 20 parts by mass of binder (alumina sol) The slurry B was prepared by mixing.

  And slurry B was apply | coated to the metal base material for back | latter stage catalysts 3, and it dried at 350 degreeC for 1 hour, and baked at 600 degreeC for 1 hour, and formed the coating layer (coat amount: 200 g / L). Next, the metal base material on which this coating layer was formed was immersed in a mixed solution of dinitrodiamine platinum and rhodium chloride having a predetermined concentration for 1 hour and then pulled up to blow off excess liquid and dried at 250 ° C. for 1 hour.

In this way, the post-catalyst 3 was completed in which a catalyst coat layer formed by supporting Pt and Rh on alumina and a CeO ₂ —ZrO ₂ composite oxide was formed on the entire surface of the metal substrate.

  The surface emissivity of the catalyst coat layer of the pre-stage catalyst 3 was 0.45. Moreover, the catalyst metal loadings in the rear catalyst 3 were Pt: 1.0 g / L and Rh: 0.2 g / L.

  Finally, the pre-stage catalyst 2 and the post-stage catalyst 3 are disposed in a predetermined catalytic converter 1 to complete the tandem type exhaust gas purification apparatus of Example 1.

  In this exhaust gas purification apparatus, the front catalyst 2 is disposed in the intermediate cylindrical portion 12 on the upstream cone portion 11 side, and the rear catalyst 3 is disposed in the intermediate cylindrical portion 12 on the downstream cone portion 13 side. A predetermined distance d (d: 5 mm) is formed between the second catalyst 2 and the rear catalyst 3.

(Example 2)
An exhaust gas purification apparatus of Example 2 was manufactured in the same manner as the exhaust gas purification apparatus of Example 1 except that the surface emissivity of the catalyst coat layer in the upstream catalyst 2 was changed to 0.2.

  As a slurry for adjusting the surface emissivity, 10 parts by mass of SiC powder having a secondary particle diameter of 10 to 20 μm, 100 parts by mass of industrial pure water, and 15 parts by mass of a binder (alumina sol) are mixed to obtain a slurry. C was prepared.

  Then, slurry C was applied to the pre-stage catalyst 2 obtained by the same method as in Example 1, dried at 250 ° C. for 1 hour, and then fired at 600 ° C. for 1 hour, and a SiC coating layer for adjusting the surface radiation rate (coated) Amount: 10 g / L) was formed on the outermost surface of the catalyst coating layer.

  The surface emissivity of the catalyst coat layer in the pre-stage catalyst 2 of Example 2 obtained in this way was 0.2. That is, the entire catalyst coat layer in the pre-stage catalyst 2 was a low radiation portion having a surface radiation rate of 0.2.

(Example 3)
An exhaust gas purification apparatus of Example 2 was manufactured in the same manner as the exhaust gas purification apparatus of Example 1 except that the surface emissivity of the catalyst coat layer in the pre-stage catalyst 2 was changed to 0.3.

  As slurry for adjusting the surface emissivity, 20 parts by mass of SiC powder having a distribution with a secondary particle diameter of 10 to 20 μm, 100 parts by mass of industrial pure water, and 15 parts by mass of binder (alumina sol) are mixed. C was prepared.

  Then, slurry C was applied to the pre-stage catalyst 2 obtained by the same method as in Example 1, dried at 250 ° C. for 1 hour, and then fired at 600 ° C. for 1 hour, and a SiC coating layer for adjusting the surface radiation rate (coated) Amount: 20 g / L) was formed on the outermost surface of the catalyst coating layer.

  The surface emissivity of the catalyst coat layer in the pre-stage catalyst 2 of Example 3 obtained in this way was 0.3. That is, the entire catalyst coat layer in the pre-stage catalyst 2 was a low radiation portion having a surface radiation rate of 0.3.

(Comparative Example 1)
An exhaust gas purification device of Comparative Example 1 was manufactured in the same manner as the exhaust gas purification device of Example 1 except that the surface emissivity of the catalyst coat layer in the upstream catalyst 2 was changed to 0.4.

  As a slurry for adjusting the surface emissivity, 30 parts by mass of SiC powder having a distribution with a secondary particle diameter of 10 to 20 μm, 100 parts by mass of industrial pure water, and 15 parts by mass of a binder (alumina sol) are mixed to obtain a slurry. C was prepared.

  Then, slurry C was applied to the pre-stage catalyst 2 obtained by the same method as in Example 1, dried at 250 ° C. for 1 hour, and then fired at 600 ° C. for 1 hour, and a SiC coating layer for adjusting the surface radiation rate (coated) Amount: 30 g / L) was formed on the outermost surface of the catalyst coat layer.

  The surface radiation rate of the catalyst coat layer in the pre-stage catalyst 2 of Comparative Example 1 thus obtained was 0.4.

(Comparative Example 2)
An exhaust gas purification device of Comparative Example 2 was manufactured in the same manner as the exhaust gas purification device of Example 1 except that the surface emissivity of the catalyst coat layer in the upstream catalyst 2 was changed to 0.6.

  As a slurry for adjusting the surface emissivity, 50 parts by mass of SiC powder having a distribution with a secondary particle size of 10 to 20 μm, 100 parts by mass of industrial pure water, and 15 parts by mass of a binder (alumina sol) are mixed. C was prepared.

  Then, slurry C was applied to the pre-stage catalyst 2 obtained by the same method as in Example 1, dried at 250 ° C. for 1 hour, and then fired at 600 ° C. for 1 hour, and a SiC coating layer for adjusting the surface radiation rate (coated) Amount: 50 g / L) was formed on the outermost surface of the catalyst coating layer.

  The surface emissivity of the catalyst coat layer in the pre-stage catalyst 2 of Comparative Example 2 obtained in this way was 0.6.

(Comparative Example 3)
An exhaust gas purification device of Comparative Example 3 was manufactured in the same manner as the exhaust gas purification device of Example 1 except that the surface emissivity of the catalyst coat layer in the pre-stage catalyst 2 was changed to 0.8.

  As a slurry for adjusting the surface emissivity, 70 parts by mass of SiC powder having a secondary particle size distribution of 10 to 20 μm, 100 parts by mass of industrial pure water, and 15 parts by mass of a binder (alumina sol) are mixed to obtain a slurry. C was prepared.

  Then, slurry C was applied to the pre-stage catalyst 2 obtained by the same method as in Example 1, dried at 250 ° C. for 1 hour, and then fired at 600 ° C. for 1 hour, and a SiC coating layer for adjusting the surface radiation rate (coated) Amount: 70 g / L) was formed on the outermost surface of the catalyst coating layer.

  The surface emissivity of the catalyst coat layer in the pre-stage catalyst 2 of Comparative Example 3 obtained in this way was 0.8.

(Examination / Evaluation)
The exhaust gas purifying apparatuses of Examples 1 to 3 and Comparative Examples 1 to 3 are arranged directly below the engine with a displacement of 2 L, respectively, and exhaust gas from the engine flows into the catalytic converter 1 from the upstream cone portion 11 side and the downstream cone It was made to flow out from the part 13 side. An endurance test was conducted in which the composition of the gas discharged from the engine was constant at A / F = 14.7, and the catalyst temperature was 950 ° C. and maintained for 50 hours.

  After the endurance test, the time until the HC purification rate reaches 80% is measured by measuring the HC purification rate after the exhaust gas of 500 ° C. exhausted from the engine with the displacement of 2 L starts to flow into the catalytic converter 1: T80 ( Second) and compared the warm-up performance of each exhaust gas purification device. These results are shown in Table 1 and FIGS.

  Table 1 summarizes the surface emissivity of the catalyst coat layer in the upstream catalyst 2 of the exhaust gas purifying apparatuses of Examples 1 to 3 and Comparative Examples 1 to 3.

  FIG. 2 shows the exhaust gas purifying apparatus of Example 3 in which the surface radiation rate of the catalyst coat layer in the front catalyst 2 is 0.3, and Comparative Example 2 in which the surface radiation rate of the catalyst coat layer in the front catalyst 2 is 0.6. 2 shows the relationship between the time (seconds) from when the exhaust gas starts to flow into the catalytic converter 1 and the HC purification rate (%). From FIG. 2, T80 in the exhaust gas purifying apparatus of Example 3 having a surface emissivity of 0.3 was shorter by about 5 seconds than the exhaust gas purifying apparatus of Comparative Example 2 having a surface emissivity of 0.6.

  FIG. 3 shows the relationship between the surface radiation rate of the catalyst coat layer in the pre-stage catalyst 2 and T80. From FIG. 3, T80 in the exhaust gas purification apparatuses of Examples 1 to 3 in which the surface emissivity of the catalyst coat layer in the upstream catalyst 2 is in the range of 0.1 to 0.3 is the surface of the catalyst coat layer in the upstream catalyst 2 The emissivity was about 5 seconds shorter than T80 in the exhaust gas purification apparatuses of Comparative Examples 1 to 3 in the range of 0.4 to 0.8.

  Therefore, it was found that when the surface emissivity of the catalyst coat layer in the pre-stage catalyst 2 is in the range of 0.1 to 0.3, the warm-up performance is remarkably improved.

It is explanatory drawing which shows typically the whole structure of the exhaust gas purification apparatus of embodiment of this invention. It is a graph which shows the relationship between the elapsed time after exhaust gas begins to flow in, and the HC purification rate about the exhaust gas purification device of Example 3 and the exhaust gas purification device of Comparative Example 2. About the exhaust gas purification apparatus of Examples 1-3 and Comparative Examples 1-3, it is a graph which shows the relationship between the surface radiation rate of the catalyst coat layer in a pre-stage catalyst, and time until HC purification rate reaches | attains 80%: T80. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Catalytic converter 2 ... Front stage catalyst 3 ... Rear stage catalyst

Claims (4)

A tandem type exhaust gas purification apparatus comprising a front stage catalyst and a rear stage catalyst disposed on the downstream side of the exhaust gas at a distance from the front stage catalyst,
Each of the pre-stage catalyst and the post-stage catalyst includes a support base material, and a catalyst coat layer formed on the surface of the support base material,
The carrier substrate in the pre-stage catalyst is a metal substrate;
The exhaust gas purifying apparatus, wherein the front catalyst has a low radiation portion having a surface radiation rate of 0.3 or less in at least a part of the catalyst coat layer.   The exhaust gas purification apparatus according to claim 1, wherein the surface radiation rate of the low radiation part is 0.1 to 0.2.   The exhaust gas purification apparatus according to claim 1 or 2, wherein the entire catalyst coat layer in the preceding catalyst is the low radiation portion.   The exhaust gas purification according to any one of claims 1 to 3, wherein a value of La / Lb is 0.1 to 0.4, where La is a volume of the upstream catalyst and Lb is a volume of the downstream catalyst. apparatus.

Images