JP2006035043A - Catalyst for purifying exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for purifying exhaust gas, the performance of which as a ternary catalyst can be kept excellent by a small amount of Ph over a long period of time. <P>SOLUTION: The activity of Ph is kept by combining a Ce-based compound oxide, in the crystal lattice or among atoms of which Rh is arranged and exposed on the surface of the crystal with activated alumina on which at least one of Pt and Pd is carried. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to an exhaust gas purification catalyst.

    Catalyst precious metals such as Pt, Pd, and Rh are used as a three-way catalyst for purifying HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) in engine exhaust gas. Pt and Pd It is generally known that acts on the oxidation of HC and CO, and Rh acts on the reduction of NOx. In addition, it is generally known that a three-way catalyst works effectively near the theoretical air-fuel ratio, and in order to expand the effective air-fuel ratio width (window), an oxygen storage material such as Ce oxide is included in the catalyst. Yes.

With regard to such an exhaust gas purifying catalyst, Patent Document 1 discloses that a honeycomb base material has an undercoat layer having a catalyst in which Pt is supported on a mixture of γ-Al ₂ O ₃ , CeO _2, and ZrO ₂ ; And forming an upper coat layer having a catalyst obtained by impregnating and supporting Rh on a hollow composite oxide made of Al ₂ O ₃ containing.

Further, the present applicant has previously developed a composite oxide containing Ce, Zr, Rh, and a composite oxide containing Ce, Zr, Nd, and Rh, which are useful as catalyst materials (see Patent Document 2). ). This document 2 discloses that a Ce-based double oxide containing this type of Rh is obtained by a coprecipitation method, a double oxide containing Ce, Zr, Nd, and Rh, and a composite oxide containing Ce, Zr, and Nd. When comparing the oxide with Rh supported later, the former has higher oxygen storage performance (oxygen storage amount and oxygen storage rate), and thus higher heat resistance and three-way catalyst performance. Is described as high.
JP 2002-1120 A JP 2004-174490 A

    As described above, the inventor of the present invention uses the Ce-based double oxide containing Rh as a three-way catalyst material. Therefore, the present inventor further improved the desired three-way catalyst performance while reducing the amount of Rh of the double oxide. In order to obtain this, research and experiments on the complex oxide were advanced.

    As a result, the double oxide is advantageous in terms of oxygen storage performance and suppression of Rh sintering because Rh is arranged between the crystal lattices or atoms of the Ce-based double oxide, but the Rh amount is low. It has been found that when the amount decreases, the catalyst deactivates relatively quickly, and one of the causes is a change in the air-fuel ratio of the engine. That is, the air-fuel ratio fluctuates between lean and rich depending on the operating state of the engine. In association with this, the three-way catalyst is repeatedly exposed to high-temperature, highly oxidizing exhaust gas. Therefore, as the use of the catalyst becomes longer, Rh exposed on the surface of the crystallite of the Ce double oxide is gradually oxidized, whereby the function of the Rh as a reduction catalyst decreases. In that case, if the amount of Rh is small, the deactivation of the catalyst is accelerated.

    Accordingly, an object of the present invention is to achieve the desired exhaust gas purification performance over a long period of time even if the Rh amount of the Ce-based double oxide containing Rh is reduced, and in particular, the Rh is oxidized. The object is to prevent the exhaust gas purification performance from deteriorating.

    In order to solve such problems, the present invention combines the Rh-containing Ce-based double oxide with Pt or Pd that effectively suppresses the oxidation of the Rh and further reduces the oxidized Rh. .

That is, the invention according to claim 1 is directed to a honeycomb-shaped carrier, at least two kinds of catalytic noble metals selected from Rh, Pt, and Pd, an oxygen storage material composed of a Ce-based double oxide, and a heat-resistant inorganic oxide. In an exhaust gas purification catalyst in which a catalyst layer containing is formed,
One kind of the catalyst noble metal is Rh, and at least a part of the Rh is arranged between the crystal lattices or atoms of the Ce-based double oxide, and the Ce-based double oxide crystal is in contact with the exhaust gas. Exposed on the child surface,
At least one of the Pt and Pd, which is another kind of the catalyst noble metal, is supported on the heat-resistant inorganic oxide.

    In the exhaust gas purifying catalyst, Pt or Pd works to oxidize HC and CO, and Rh works to reduce NOx. When Rh is exposed to an air-fuel ratio lean exhaust gas, it is oxidized and its catalytic function is lowered. To do. On the other hand, when the air-fuel ratio becomes rich, HC and CO that act as a reducing agent increase around Rh. However, when the ambient temperature of Rh is low, Rh cannot be reduced.

    On the other hand, Pt or Pd functions to oxidize and purify the HC and CO even when the air-fuel ratio is switched from lean to rich, and the catalytic reaction heat increases the atmospheric temperature of Rh and the catalytic reaction. As a result, high-activity HC partially oxidized is generated. For this reason, the oxidized Rh is easily reduced by HC and CO in the exhaust gas, and further partially oxidized HC, and its activity is maintained, which is advantageous for NOx reduction.

    Further, as described above, when the air-fuel ratio is switched from lean to rich, an atmosphere having a low oxygen concentration is formed around Rh due to the presence of Pt or Pd, so that the progress of oxidation of Rh is also suppressed. The

The invention according to claim 2 is the exhaust gas purifying catalyst according to claim 1,
As the catalyst layer, comprising two layers inside and outside laminated on the honeycomb-shaped carrier,
The inner catalyst layer includes a heat-resistant inorganic oxide supporting at least one of Pt and Pd,
The outer catalyst layer includes a Ce-based double oxide in which the Rh is arranged in a crystal lattice or between atoms.

    Therefore, HC and CO in the exhaust gas pass through the outer catalyst layer and reach the inner catalyst layer, where they are oxidized and burned by Pt or Pd. The heat of oxidation reaction of HC and CO is transmitted from the inner catalyst layer to the outer catalyst layer by heat conduction and by convection (movement of exhaust gas from the inner catalyst layer to the outer catalyst layer), and Rh of the outer catalyst layer. The ambient temperature of the Since this Rh is provided in the outer catalyst layer, it receives supply of HC partially oxidized by Pt or Pd from the inner catalyst layer, and also contacts HC and CO that act as a reducing agent in the exhaust gas. Easy to do. Therefore, when the air-fuel ratio is changed from lean to rich, the reduction of the Rh by the partial oxidation HC or HC or CO in the exhaust gas proceeds efficiently.

The invention according to claim 3 is the exhaust gas purifying catalyst according to claim 1,
As the catalyst layer, comprising two layers inside and outside laminated on the honeycomb-shaped carrier,
The inner catalyst layer includes a Ce-based double oxide in which the Rh is arranged between crystal lattices or atoms,
The outer catalyst layer includes a heat-resistant inorganic oxide supporting at least one of the Pt and Pd.

    In the case of this invention, since HC and CO in the exhaust gas are oxidized by Pt or Pd of the outer catalyst layer, the amount of reducing agent such as HC supplied to Rh provided in the inner catalyst layer is claimed in claim 2. The heat of oxidation of the reducing agent by Pt or Pd in the outer catalyst layer is caused by heat conduction or by convection (transfer of exhaust gas from the outer catalyst layer to the inner catalyst layer). Since it is transmitted to the catalyst layer, the ambient temperature of Rh becomes high. Therefore, when the air-fuel ratio is changed from lean to rich, the reduction of the Rh by the partial oxidation HC and HC in the exhaust gas proceeds efficiently.

The invention according to claim 4 is the exhaust gas purifying catalyst according to claim 1,
The Ce-based double oxide in which the Rh is arranged between crystal lattices or atoms and the heat-resistant inorganic oxide supporting at least one of Pt and Pd are mixed and included in one catalyst layer. It is characterized by.

    In the case of this invention as well, HC and the like in the exhaust gas are oxidized by Pt or Pd present around the Ce-based double oxide, so that the amount of reducing agent supplied to Rh of the Ce-based double oxide is considered to be small. However, since Rh and Pt or Pd are in close proximity, the temperature around Rh tends to be high due to oxidation reaction heat of HC or the like by Pt or Pd. Therefore, when the air-fuel ratio is changed from lean to rich, the reduction of the Rh by the partial oxidation HC and HC in the exhaust gas proceeds efficiently.

The invention according to claim 5 is the exhaust gas purifying catalyst according to any one of claims 1 to 4,
The Ce-based double oxide in which Rh is arranged between crystal lattices or atoms is a double oxide containing Ce, Zr, and Nd,
The heat-resistant inorganic oxide carrying at least one of Pt and Pd is activated alumina.

    Therefore, Ce-based double oxides have high heat resistance due to Zr, and Nd increases the catalytic activity of Rh at a low temperature, and active alumina enables high dispersion of Pt or Pd, which is advantageous for improving the catalyst performance. become.

    As described above, according to the first aspect of the present invention, Rh as the catalytic noble metal is disposed between the crystal lattices or atoms of the Ce-based double oxide and exposed to the crystallite surface of the Ce-based double oxide. Since at least one of Pt and Pd as a catalyst noble metal is supported on a heat-resistant inorganic oxide, the Ce-based double oxide containing Rh can improve oxygen storage characteristics, heat resistance, and three-way catalyst performance. Rt can be activated (inhibition of oxidation or reduction of oxidized Rh) using Pt or Pd, which is advantageous in maintaining excellent catalytic activity over a long period of time even with a small amount of Rh.

    According to the invention of claim 2, in claim 1, the heat-resistant inorganic oxidation comprising the inner and outer two catalyst layers laminated on the honeycomb-shaped carrier, and supporting at least one of the Pt and Pd on the inner catalyst layer. And the outer catalyst layer contains a Ce-based double oxide in which the Rh is arranged in the crystal lattice or between the atoms, so that the oxidation reaction heat of HC and CO by Pt or Pd in the inner catalyst layer Can be used to increase the ambient temperature of the Rh of the outer catalyst layer, and can sufficiently supply HC and CO in the exhaust gas to the Rh, which is advantageous in suppressing oxidation and reduction of the Rh. Become.

    According to the invention of claim 3, the Ce system according to claim 1, further comprising two catalyst layers laminated on the honeycomb-shaped carrier, wherein the Rh is disposed between the crystal lattice or the atoms in the inner catalyst layer. Since a double oxide is contained and the outer catalyst layer contains a heat-resistant inorganic oxide carrying at least one of Pt and Pd, heat of oxidation reaction of HC and CO by Pt or Pd in the outer catalyst layer As a result, the atmosphere temperature of Rh of the inner catalyst layer can be increased, and oxidation and reduction of the Rh can be achieved.

    According to the invention of claim 4, in claim 1, the Ce-based double oxide in which the Rh is disposed between crystal lattices or atoms, and the heat-resistant inorganic oxide carrying at least one of the Pt and Pd Are mixed and contained in one catalyst layer, which is advantageous in increasing the atmospheric temperature of Rh by the heat of oxidation reaction of HC and CO by Pt or Pd, and is intended to suppress and reduce the oxidation of Rh. Can do.

    According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the Ce-based double oxide in which the Rh is arranged between crystal lattices or atoms includes Ce, Zr, and Nd. Since the heat-resistant inorganic oxide that is a double oxide and supports at least one of Pt and Pd is activated alumina, it is advantageous for improving the heat resistance and low-temperature activity of the catalyst.

    Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

    FIG. 1 shows an exhaust gas purification catalyst 1 for an automobile engine according to the present invention. This catalyst 1 is formed by forming a catalyst layer containing a catalyst noble metal on each cell wall of a porous monolith support (honeycomb support) 2 having a large number of cells 3 penetrating in the exhaust gas flow direction. .

    As schematically shown in FIG. 2, the catalyst 1 includes an inner catalyst layer 6 formed on the cell wall 5 and an outer catalyst layer 7 stacked on the inner catalyst layer 6 as the catalyst layer. I have. In the present invention, as shown in FIG. 3, only one catalyst layer 8 may be formed, or three or more catalyst layers may be formed. Hereinafter, a specific configuration of the catalyst layer will be described with reference to examples.

<Examples 1-6 and Comparative Example Catalyst>
Example 1
This example is a case having a two-layer structure of an inner catalyst layer 6 and an outer catalyst layer 7 as shown in FIG. 2, and the inner catalyst layer 6 contains a heat-resistant inorganic oxide carrying at least one of Pt and Pd. The outer catalyst layer 7 contains a Ce-based double oxide in which Rh is arranged between crystal lattices or atoms. A part of Rh is disposed between the crystal lattices or atoms of the Ce-based double oxide and exposed on the crystallite surface of the double oxide (see FIG. 6 of Japanese Patent Application Laid-Open No. 2004-174490).

Specifically, the heat-resistant inorganic oxide of the inner catalyst layer 6 is activated alumina, and Pt is supported on the activated alumina. The inner catalyst layer 6 is formed by supporting activated alumina (Pt / Al ₂ O ₃ ) supporting Pt on a carrier with a binder. The supported amount of Pt / Al ₂ O ₃ (the supported amount per 1 L of the carrier, hereinafter the same) is 50 g / L, and the mass ratio of the components is Pt: Al ₂ O ₃ = 0.065: 100. is there.

The Ce-based double oxide of the outer catalyst layer 7 is a double oxide containing Ce, Zr, Nd, and Rh. The outer catalyst layer 7 is obtained by supporting this Ce-based double oxide on the inner catalyst layer 6 with a binder. The supported amount of Ce-based double oxide is 112 g / L, and the mass ratio of the components is Rh: CeO ₂ : ZrO ₂ : Nd ₂ O ₃ = 0.087: 22: 68: 10.

    In this case, the mass ratio of the catalyst noble metal is Pt: Rh = 1: 3, and the combined loading amount is 0.13 g / L.

    A method for producing the Ce-based double oxide will be described. First, a predetermined amount of each of zirconium oxynitrate, cerium nitrate, water containing neodymium (III) nitrate, and rhodium nitrate was mixed with water to make a total of 300 mL, and this mixed solution was stirred at room temperature for about 1 hour. This mixed solution was heated to 80 ° C. and heated, and then vigorously stirred rapidly using a glass rod, and 50 mL of 28% ammonia water prepared in another beaker was added at once and mixed. The addition and mixing of the ammonia water was completed within 1 second. The solution clouded by mixing with aqueous ammonia was allowed to stand overnight, and the resulting cake was centrifuged and washed thoroughly with water. The cake washed with water was dried at a temperature of about 150 ° C. and then calcined under the condition that it was kept at a temperature of 400 ° C. for 5 hours and then kept at a temperature of 500 ° C. for 2 hours.

    Since the Ce-based complex oxide obtained as described above is formed by adding the Rh component, Rh is arranged in the crystal lattice of the complex oxide in the same manner as Ce, Zr, and Nd. It is in a state of being strongly bonded to the oxide. Or Rh will be in the state arrange | positioned between the atoms of the said double oxide. In any case, Rh becomes a double oxide uniformly dispersed on the surface and inside of the double oxide, and a part of Rh is exposed on the crystallite surface of the double oxide.

-Example 2-
This example is also a case where the inner catalyst layer 6 and the outer catalyst layer 7 have a two-layer structure as shown in FIG. 2, but unlike the first embodiment, the inner catalyst layer 6 has Rh of crystal lattice or interatomic. The outer catalyst layer 7 contains a heat-resistant inorganic oxide carrying at least one of Pt and Pd. The Ce-based double oxide is the same as in Example 1, and the supported amount is also 112 g / L. Further, the heat-resistant inorganic oxide carrying at least one of Pt and Pd is Pt / Al ₂ O ₃ as in Example 1, and the carrying amount is also 50 g / L.

Example 3
In this example, a Ce-based double oxide in which Rh is arranged in a crystal lattice or between atoms and a heat-resistant inorganic oxide supporting at least one of Pt and Pd are mixed to form one catalyst layer shown in FIG. This is the case. The Ce-based double oxide is the same as in Example 1, and the supported amount is also 112 g / L. Further, the heat-resistant inorganic oxide carrying at least one of Pt and Pd is Pt / Al ₂ O ₃ as in Example 1, and the carrying amount is also 50 g / L.

Example 4
This example is a case having a two-layer structure of the inner catalyst layer 6 and the outer catalyst layer 7 as in Example 1, but the composition of the Ce-based double oxide of the outer catalyst layer 7 and the heat-resistant inorganic oxidation of the inner catalyst layer 6 The catalyst noble metal supported on the object is different.

That is, the Ce-based double oxide was prepared by the same method as in Example 1, but the mass ratio of the components was Rh: CeO ₂ : ZrO ₂ : Nd ₂ O ₃ = 0.058: 22: 68: 10. . The carrying amount is 112 g / L as in Example 1. On the other hand, the inner catalyst layer 6 was made of Pd supported on activated alumina (Pd / Al ₂ O ₃ ). The mass ratio of the components is Pd: Al ₂ O ₃ = 0.13: 100. The supported amount is 50 g / L as in Example 1. The mass ratio of the catalyst noble metal is Pd: Rh = 1: 1, and the combined loading amount is 0.13 g / L.

-Example 5
This example is also a case where the inner catalyst layer 6 and the outer catalyst layer 7 have a two-layer structure, but the configuration of the inner and outer catalyst layers is reversed from that in Example 4. That is, the inner catalyst layer 6 contains 112 g / L of the same Ce-based double oxide as in Example 4, and the outer catalyst layer 7 contains 50 g / L of Pd / Al ₂ O ₃ as in Example 4. Therefore, the mass ratio of the catalyst noble metal is Pd: Rh = 1: 1, and the combined loading amount is 0.13 g / L.

-Example 6
This example is also the mixed type case shown in FIG. 3 as in Example 3, but the same Ce-based double oxide as in Example 4 and Pd / Al ₂ O ₃ as in Example 4 are used, and the former is 112 g / L. The latter was mixed so as to be 50 g / L. Therefore, the mass ratio of the catalyst noble metal is Pd: Rh = 1: 1, and the combined loading amount is 0.13 g / L.

-Comparative example-
In the comparative example, a Ce-based double oxide in which Rh is arranged in a crystal lattice or between atoms and activated alumina (no noble metal supported) are mixed and contained in one catalyst layer shown in FIG. . The Ce-based double oxide was prepared by the same method as in Example 1, but the mass ratio of the components was Rh: CeO ₂ : ZrO ₂ : Nd ₂ O ₃ = 0.116: 22: 68: 10. The supported amount of this Ce double oxide is 112 g / L as in Example 1. Therefore, the supported amount of Rh is 0.13 g / L. On the other hand, the loaded amount of activated alumina is 50 g / L as in Example 1.

<Evaluation of catalyst>
Each catalyst of the above Examples and Conventional Examples was aged by heating to 1000 ° C. for 24 hours in an air atmosphere. Then, after attaching these catalysts to the model gas flow reactor and flowing an air-fuel ratio rich model gas (temperature 600 ° C.) for 20 minutes, a light-off temperature T50 relating to purification of HC, CO and NOx by the evaluation model gas. And the high temperature purification rate C500 was measured.

T50 is the gas temperature at the catalyst inlet when the temperature of the model gas flowing into the catalyst is gradually increased from room temperature and the purification rate reaches 50%. C500 is the purification rate when the catalyst inlet gas temperature is 500 ° C. The model gas for evaluation was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. The space velocity SV is 60000 h ⁻¹ , and the heating rate is 30 ° C./min.

    The result of T50 is shown in FIG. 4, and the result of C500 is shown in FIG. Regarding purification of HC, CO, and NOx, each catalyst of Example 1-6 has a lower T50 and higher C500 than the comparative example catalyst. Therefore, it can be seen that a good three-way catalyst performance can be obtained by using a Ce-based double oxide in which Rh is arranged in the crystal lattice or between atoms and an activated alumina supporting Pt or Pd.

And when Example 1 and Example 2 are compared, the former which arrange | positioned Ce type | system | group double oxide containing Rh in the outer side catalyst layer has improved the purification | cleaning property of HC, CO, and NOx. . To examine this point, if Pt / Al ₂ O ₃ does not have any effect on the Rh of the Ce-based double oxide, Pt / Al ₂ O ₃ advantageous for decomposition of HC and CO is obtained. Although it is considered that the HC and CO purification performance is better in Example 2 than in Example 1 when arranged on the outer catalyst layer that easily contacts exhaust gas, the results of FIGS. 4 and 5 are reversed. It has become.

Therefore, Pt / Al ₂ O ₃ itself is not only responsible for purifying HC, CO and NOx, but also acts to activate Rh of Ce-based double oxide. As a result, in Example 1, NOx is efficiently purified by Rh of the Ce-based complex oxide, and at the same time, HC and CO as reducing agents necessary for the purification of NOx are also efficiently decomposed. It is thought.

In this case, Pt / Al ₂ O ₃ oxidizes and purifies HC and CO in the exhaust gas even after the air-fuel ratio is switched from lean to rich. In addition to increasing the ambient temperature, it is considered that the partially oxidized HC having high reducibility is supplied to the Rh to promote the reduction, thereby activating the Rh.

Thus, the purification performance of HC, CO and NOx in Example 1 is better than that in Example 2. In Example 2, HC and CO in exhaust gas useful for reducing Rh are used. Is consumed by Pt / Al ₂ O _{3 in the} outer catalyst layer, and accordingly, the amount of HC and CO supplied to Rh of the Ce-based double oxide in the inner catalyst layer is reduced. This is probably because a large amount of HC and CO in the exhaust gas is supplied to Rh because Rh is provided in the outer catalyst layer.

In the case of the mixed type of Example 3, as in Examples 1 and 2, although the atmospheric temperature of Rh is increased by the oxidation reaction heat of HC and CO by Pt / Al ₂ O ₃ , the reducing agent in the exhaust gas is Ce. Since it is oxidized by Pt / Al ₂ O ₃ existing around the system double oxide, the amount of reducing agent supplied to the Rh of the Ce system double oxide is reduced. Therefore, the activation of Rh compared to Example 1 is increased. It is considered that the purification performance of HC, CO and NOx is low.

Examples 4 to 6 are cases in which Pd / Al ₂ O ₃ was used instead of Pt / Al ₂ O ₃ in Examples 1 to 3, but showed the same tendency as Examples 1 to 3. It can be seen that good results can be obtained even when Pd / Al ₂ O ₃ is used instead of Pt / Al ₂ O ₃ .

1 is a perspective view of an exhaust gas purifying catalyst according to an embodiment of the present invention. It is sectional drawing which expands and shows a part of the catalyst. It is sectional drawing which expands and partially shows the other example of the same catalyst. It is a graph which shows light-off temperature T50 of the Example and comparative example of this invention. It is a graph which shows the high temperature purification rate C500 of the Example and comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification catalyst 2 Honeycomb carrier 3 Cell 5 Cell wall 6 Inner catalyst layer 7 Outer catalyst layer 8 Catalyst layer

Claims (5)

A catalyst layer containing at least two kinds of catalytic noble metals selected from Rh, Pt, and Pd, an oxygen storage material made of Ce-based double oxide, and a heat-resistant inorganic oxide is formed on the honeycomb-shaped carrier. In the exhaust gas purification catalyst,
One kind of the catalyst noble metal is Rh, and at least a part of the Rh is disposed between crystal lattices or atoms of the Ce-based double oxide and exposed to the crystallite surface of the Ce-based double oxide. ,
An exhaust gas purifying catalyst, wherein at least one of the Pt and Pd, which is another kind of the catalyst noble metal, is supported on the heat-resistant inorganic oxide. In claim 1,
As the catalyst layer, comprising two layers inside and outside laminated on the honeycomb-shaped carrier,
The inner catalyst layer includes a heat-resistant inorganic oxide supporting at least one of Pt and Pd,
An exhaust gas purifying catalyst characterized in that the outer catalyst layer contains a Ce-based double oxide in which the Rh is arranged in a crystal lattice or between atoms. In claim 1,
As the catalyst layer, comprising two layers inside and outside laminated on the honeycomb-shaped carrier,
The inner catalyst layer includes a Ce-based double oxide in which the Rh is arranged between crystal lattices or atoms,
An exhaust gas purifying catalyst, characterized in that an outer catalyst layer contains a heat-resistant inorganic oxide carrying at least one of Pt and Pd. In claim 1,
The Ce-based double oxide in which the Rh is arranged between crystal lattices or atoms and the heat-resistant inorganic oxide supporting at least one of Pt and Pd are mixed and included in one catalyst layer. An exhaust gas purifying catalyst characterized by. In any one of Claims 1 thru | or 4,
The Ce-based double oxide in which Rh is arranged between crystal lattices or atoms is a double oxide containing Ce, Zr, and Nd,
The exhaust gas purifying catalyst, wherein the heat-resistant inorganic oxide carrying at least one of Pt and Pd is activated alumina.

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