JP2000237589A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase hydrocarbon-purifying performance, particularly the high purifying performance to an unpurified hydrocarbon component under the wide atmosphere condition from the rich to the lean around a stoichiometric point. SOLUTION: In an integrated structure type catalyst having a catalyst component carrying layer, two kinds of a Zr multiple oxide (A) containing as catalyst components at least one kind selected from among Pt, Pd and Rh, and moreover containing at least one kind selected from group 2A elements and group 3B elements (Ce is excluded) and a Zr multiple oxide (B) containing at least one kind selected from among Ce, group 3A elements and group 6B elements are used as a Pt carrying base material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst, and more particularly to hydrocarbons (hereinafter referred to as "HC"), which are harmful components in exhaust gas discharged from an internal combustion engine of an automobile or the like, and monoxide. Among the three-way catalysts for simultaneously removing carbon (hereinafter, referred to as “CO”) and nitrogen oxides (hereinafter, referred to as “NO _x ”), exhaust gas purification that purifies highly flame-retardant HC with high efficiency. For catalysts.

[0002]

2. Description of the Related Art Conventionally, when exhaust gas purifying catalysts are arranged in multiple stages to purify HC with high efficiency, unburned exhaust gas contains flame-retardant HC (mainly saturated hydrocarbon: paraffin).
Therefore, the efficiency of the catalyst downstream of the exhaust gas is lower than that of the upstream catalyst. Therefore, development of an exhaust gas purifying catalyst having excellent flame retardant HC purifying ability is expected.

As such an exhaust gas purifying catalyst, for example, Japanese Patent Application Laid-Open No. 62-282641, Japanese Patent Application Laid-Open No. 5-49
929 and JP-A-8-24644. Japanese Unexamined Patent Publication (Kokai) No. 62-282641 discloses an exhaust gas purification catalyst in which rhodium is supported on zirconium oxide. Specifically, zirconium oxide containing rhodium, activated alumina, cerium oxide and alumina sol are disclosed. Is applied to a carrier, dried and calcined, and then loaded with platinum.

JP-A-5-49929 discloses that an integrated structure having a catalyst supporting layer made of activated alumina has palladium and rhodium supported on an inlet side where exhaust gas flows in and an outlet side on which exhaust gas flows out. There is disclosed an exhaust gas purifying catalyst in which platinum and rhodium are supported, wherein the amount of rhodium supported is larger on the outlet side than on the inlet side.

[0005] Japanese Patent Application Laid-Open No. Hei 8-24644 discloses that an exhaust gas flows into a catalyst supporting layer coated on the surface of a carrier base material in the case of a catalyst comprising an active component comprising palladium, platinum and an alkaline earth metal. There is disclosed an exhaust gas purifying catalyst characterized in that platinum is carried on the inlet side.

[0006]

However, in the conventional catalyst described in the above-mentioned publication, when it is attempted to increase the catalyst capacity and further reduce the residual ratio of harmful components in the exhaust gas, it is difficult to reduce the harmful components remaining in the exhaust gas downstream. Since the purification by the catalyst proceeds, the HC component ratio that is difficult to convert increases.
As a result, even when the exhaust gas atmosphere is an oxidizing atmosphere suitable for HC combustion, there is a problem that the purification performance is deteriorated.

Accordingly, an object of the present invention is to improve the HC purification performance as compared with the conventional exhaust gas purifying catalyst and catalyst system, and particularly to improve the HC component, which has not been purified, up to the stoichiometric center. Another object of the present invention is to provide an exhaust gas purifying catalyst having high purifying performance under a wider range of atmosphere conditions.

[0008]

Means for Solving the Problems As a result of research conducted to solve the above problems, the present inventors have found that a catalyst component for improving the catalytic activity on paraffinic hydrocarbons, which is a main component of unpurified HC, is used. By including Pt and two types of Zr-based composite oxides in the support layer and carrying a predetermined amount of Pt on the Zr composite oxide, the purification performance of the HC component which has not been purified conventionally is remarkably improved and wide. Pt that is maintained under an atmosphere and has a slightly leaner NO _x purification performance than stoichiometric
Characteristics effectively to express the, slight lean of the NO _x performance it found that improved, thereby achieving the present invention.

In the exhaust gas purifying catalyst according to the first aspect,
The monolithic catalyst having a catalyst component-supporting layer contains at least one selected from the group consisting of Pt, Pd, and Rh as a catalyst component, and further includes a group 2A element and a group 3B (excluding Ce) element. Two kinds of Zr composite oxides (A) containing at least one selected from the group consisting of Pt and Zr composite oxides (B) containing at least one selected from the group consisting of Ce and Group 3A and Group 6B elements It is characterized in that it is used as a supporting substrate.

In the exhaust gas purifying catalyst according to the second aspect,
The amount of Pt contained in the exhaust gas purifying catalyst according to claim 1 is 1 g / L to 15 g / L in order to more effectively exhibit the catalytic activity for paraffin components in a rich to lean atmosphere near the stoichiometric atmosphere. , The ratio of the amount of Pt carried to the Zr composite oxide is at least 10 wt% or more of the total Pt amount in the catalyst.

Further, in order to maintain high catalytic activity on paraffin components of the exhaust gas purifying catalyst according to the first or second aspect and to stably develop the paraffin component, the exhaust gas purifying catalyst according to the third aspect has the following features. 3. The element ratio of the Zr composite oxide according to 1 or 2 is 1 to 40% in terms of atomic ratio with respect to Zr.

The exhaust gas purifying catalyst according to claim 4, wherein the catalyst for purifying exhaust gas according to claim 1 to 3 exhibits high catalytic activity on paraffin components in a wide air-fuel ratio (hereinafter referred to as A / F) atmosphere. In the exhaust gas purifying catalyst according to any one of claims 1 to 3, the content ratio (A / (A + B)) of the two kinds of Zr composite oxides used in the Pt-supporting base material is 10 to 90 wt%. %.

Further, in the exhaust gas purifying catalyst according to any one of claims 1 to 4, the catalyst for purifying exhaust gas according to claim 5 has two kinds of Zr composite oxides so as to exhibit high purification performance even after durability. The crystal structure measured by X-ray diffraction of
It is characterized in that the ratio of the tetragonal system is at least 10% or more in terms of integrated intensity.

Further, in the exhaust gas purifying catalyst according to any one of the first to fifth aspects, the exhaust gas purifying catalyst according to the sixth aspect is capable of maintaining a high catalytic activity by mitigating a change in the catalyst state due to a rich / lean atmosphere change. The catalyst for use is further characterized by containing a cerium oxide containing at least one selected from the group consisting of lanthanum, neodymium and zirconium in an atomic ratio of 1 to 40%.

Furthermore, in order to stably express the claims 1 to an exhaust purifying catalyst 6 according paraffin purification activity and scan write lean NO _x activity, the exhaust gas purifying catalyst according to claim 7, wherein the catalytically active component Is characterized in that Pd does not coexist with Pt in the same catalyst layer.

The noble metal contained in the catalyst component supporting layer of the main exhaust gas purifying catalyst of the present invention contains at least platinum. The content of Pt is 1 to 15 g in 1 L of the catalyst. If the amount is less than 1 g, the low-temperature activity and purification performance are not sufficiently exhibited. Conversely, if the amount exceeds 15 g, the catalytic activity of Pt is saturated, and the performance improvement corresponding to the added amount cannot be obtained, resulting in poor economy.

The substrate on which the Pt is supported is Pt
In order to improve the paraffin conversion performance in a rich atmosphere, a Zr composite oxide containing at least one element selected from a group 2A element and a group 3B (rare earth: excluding Ce) element is used. Of the above elements, more preferably,
Mg, Ca, Y, La, Pr, Nd, and Gd.

In order to improve the paraffin conversion performance in a lean atmosphere, a Zr composite oxide containing Ce and at least one element selected from Group 3A and Group 6B elements is used. Of the above elements, more preferably, Ce, W,
Al and In.

Further, the concentration of Pt supported on the Zr composite oxide is not particularly limited, but is set to 1.
The range of 0 to 10 wt% is preferable. If the content is less than 1.0 wt%, the thermal durability of Pt decreases, and if it is 10 wt% or more, the Pt particles are too high and the Pt particles are too coarse, which is not effective.

The amount of the Zr composite oxide used is as follows:
It is 10 to 200 g per liter of the catalyst. If the amount is less than 10 g, sufficient durability of the noble metal cannot be obtained, and even if the amount is more than 200 g, the improvement effect is saturated and is not effective. More preferably, the initial surface area of the Zr oxide is more than 30 m ² per gram. This is to secure a particle size appropriate for the carried Pt to exhibit an activity, and is 30 m / g.
^A ratio of ² or less is not preferable because the initial activity decreases and its effectiveness is lost.

Further, in the exhaust gas purifying catalyst according to the third aspect, in order that the Pt-supported Zr composite oxide is stable even at a high temperature and has excellent post-durability performance, the content ratio of the element contained with respect to Zr is reduced. The atomic ratio is 1 to 40%. If it is less than 1%, the effect of the added element is not sufficiently exhibited, and if it exceeds 40%, the stability of the Zr oxide itself is impaired, so that it is not effective.

Further, in order to exhibit a high catalytic activity for paraffin components in a wide A / F atmosphere, the exhaust gas purifying catalyst according to claim 4 contains two kinds of Zr composite oxides used for a Pt-supporting substrate. Rate {A / (A + B)}
Is 10 to 90 wt%. Outside the above range, the highly active A / F range is not effective because it is narrowed.

The two kinds of Zr composite oxides are represented by X
As a crystal structure measured by line diffraction, a ratio of a tetragonal crystal measured from an integrated intensity ratio is at least 10% or more. Although ZrO ₂ is originally monoclinic, it is stabilized to a tetragonal system by solid solution of the added element, and the phase change is suppressed, so that the supported Pt is less likely to sinter, and even after durability, the Pt is supported on the paraffin component. High catalytic activity can be maintained. If it is less than 10%, the above effect is not sufficient and is not effective.

In order to maintain the catalytic activity of the exhaust gas purifying catalyst according to any one of claims 1 to 5 with respect to atmospheric fluctuations, the exhaust gas purifying catalyst according to claim 6 further comprises lanthanum,
Cerium oxide containing at least one element selected from the group consisting of neodymium and zirconium in an atomic ratio of 1 to 40% is contained. The reason for setting the content to 1 to 40% is to remarkably improve the original oxygen absorption / release capacity and the BET specific surface area (thermal stability) of CeO ₂ by adding the above additive to cerium oxide (CeO ₂ ). If less than 1%, CeO
The effect of the additional element does not appear because it is not different from the case of only ₂ and the effect is saturated or reduced at 40% or more.

Further, the exhaust gas purifying catalyst according to claim 7 has a structure in which Pd which is a catalytically active component in the exhaust gas purifying catalyst according to claim 1 does not coexist with Pt in the same catalyst layer. . Pd and Pt are be lost by Pd that when coexisting in the same catalyst layer Pt surface condition particularly excellent in paraffin purification · NO _x purification characteristic of the lean zone in intimate contact, impaired substrate effect of precious This is because

In producing the exhaust gas purifying catalyst of the present invention, Zr having an initial surface area of 30 m ² / g or more is used.
The exhaust gas purifying catalyst according to claim 1 is obtained by impregnating and supporting Pt on the composite oxide and further performing a heat treatment.

The method of supporting Pt on the Zr composite oxide can be appropriately selected from known methods such as an impregnation method and a kneading method, but it is particularly preferable to use the impregnation method.

As the raw material compound of Pt, any compound can be used as long as it is water-soluble such as nitrate.

[0029] In the exhaust gas purifying catalyst according to the first aspect, the substrate supporting at least one selected from Pd and Rh may include a refractory inorganic material such as activated alumina, Ce oxide and Zr oxide. An oxide can be used. Especially P
It is preferable that d is distributed and supported on activated alumina and Ce oxide, and Rh is inactivated on activated alumina, so that it is supported on Zr-stabilized alumina or Zr oxide. Is preferred.

Further, in addition to the catalyst components in the exhaust gas purifying catalyst according to any one of claims 1 to 6, in order to enhance the adhesion to the carrier, one selected from the group consisting of activated alumina, boehmite alumina and alumina sol. Preferably, a seed is added.

As the raw material compounds of Pd and Rh, any compounds can be used as long as they are water-soluble, such as dinitrodiamminate, chloride and nitrate.

The exhaust gas purifying catalyst according to the present invention thus obtained can be used effectively without a carrier. However, the catalyst is pulverized and slurry, coated on the catalyst carrier and calcined at 400 to 900 ° C. It is preferable to use them. The catalyst carrier can be appropriately selected from known catalyst carriers and used, and examples thereof include a monolith carrier made of a refractory material and a metal carrier.

One kind selected from the group consisting of the obtained Pt-supported Zr composite oxide powder, activated alumina, boehmite alumina, and alumina sol is added and wet-milled to form a slurry, which is then attached to a catalyst carrier. ~ 650 ° C
The catalyst for purifying exhaust gas according to claim 1 is obtained by performing calcination in air and / or under a flow of air at a temperature in the range described above.

Further, one selected from the group consisting of Pd-supported alumina powder, Pd-supported cerium oxide powder, Rh-supported powder, activated alumina, boehmite alumina, and alumina sol is added, and the mixture is pulverized by a wet method to form a slurry to form Pt. The PtPd, PtRh, or PtPd according to claim 1, which is disposed on the inner layer or the surface layer of the Pt catalyst layer in the same procedure as the layer.
A PtPdRh-based exhaust gas purifying catalyst is obtained.

Although the shape of the catalyst carrier is not particularly limited, it is usually preferable to use the catalyst carrier in the form of a honeycomb, and the catalyst powder is applied to various honeycomb substrates to be used.
As the honeycomb material, cordierite-based materials such as ceramics are generally used in general, but it is also possible to use a honeycomb material made of a metal material such as ferrite stainless steel, and further, the catalyst component powder itself is formed into a honeycomb shape. It may be molded. By making the shape of the catalyst into a honeycomb shape, the contact area between the catalyst and the exhaust gas is increased and the pressure loss can be suppressed, so that it is extremely effective when used as an exhaust gas purifying catalyst for automobiles.

The amount of the catalyst component coat layer adhered to the honeycomb material is preferably 50 g to 400 g per liter of the catalyst in total of the entire catalyst components. The larger the number of catalyst component supporting layers, the more preferable in terms of catalyst activity and catalyst life.However, if the coating layer is too thick, the reaction gas will be insufficiently diffused inside the catalyst component supporting layer and will not be able to contact the catalyst sufficiently. The effect of increasing the amount of gas is saturated, and the gas passage resistance is increased. For this reason, the coat layer amount is
The amount is preferably 50 g to 400 g per liter of the catalyst.

[0037]

The exhaust gas purifying catalyst according to claim 1 is a Pt catalyst.
And at least one of Pd and Rh, wherein Pt is 2
When used in a state of being supported on a kind of Zr composite oxide, the A / F range capable of selectively purifying stable and hardly combustible paraffin in the unpurified HC component is widened, and more stable activity can be exhibited. . Further, as a synergistic effect, NO _x purification in a slightly lean atmosphere from stoichiometric conditions is improved. This is because the Pt surface state on the two kinds of Zr composite oxides can be controlled to a surface (oxidized) state suitable for paraffin adsorption in rich and lean atmospheres.

Furthermore, in the exhaust gas purifying catalyst according to the second aspect, the amount of Pt is set to 1 g / L to 15 g / L, and the amount of Pt carried on the Zr composite oxide is limited to 10 wt% or more of the total Pt amount. Thereby, the above-mentioned combination effect can be more effectively exhibited.

The exhaust gas purifying catalyst according to the third aspect uses the Zr composite oxide catalyst used for supporting Pt in an amount of 1 to 40 mol%. This is because the Zr oxide is stabilized by the added element,
This is because it is suitable for maintaining the t state.

The exhaust gas purifying catalyst according to the fourth aspect is the exhaust gas purifying catalyst according to the first to third aspects.
The paraffin activity near stoichiometry and NO _x
The activity can be expressed in a well-balanced manner.

The exhaust gas purifying catalyst according to the fifth aspect is the exhaust gas purifying catalyst according to the first to fourth aspects,
Further, it limits the crystal structure of the Zr composite oxide. It is known that the stabilized Zr oxide in which the additive element is dissolved forms a tetragonal system and suppresses a phase change to a monoclinic system, and the high-temperature durability is further improved.

The exhaust gas purifying catalyst according to a sixth aspect of the present invention is the exhaust gas purifying catalyst according to the first to fifth aspects, further comprising a Ce composite oxide having an oxygen absorbing / releasing ability. This is to provide the function of bringing the surface of the noble metal, which is the active main component, into an optimum state for purification against a sudden A / F fluctuation.

The exhaust gas purifying catalyst according to claim 7 has a structure in which Pd and Pt in the catalytically active components do not coexist in the same catalyst layer. This is due to the aforementioned Pt-supported Zr
This is because the effect of the composite oxide prevents the active surface state from changing due to the close contact with Pt due to the coexistence of Pd.

[0044]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, which are not intended to limit the scope of the present invention.

<Example 1> Nd-Zr composite oxide ｛Nd
= 0.2% (atomic ratio)｝ The powder was impregnated with an aqueous solution of dinitrodiammine platinum, dried at 150 ° C. for 12 hours,
By baking at 0 ° C. for 1 hour, a Pt-supported Nd—ZrO ₂ powder (powder A) was obtained. The Pt concentration of this powder is 2.0 wt%
Met. A Ce-Zr composite oxide {Ce = 0.2% (atomic ratio)) powder is impregnated with an aqueous solution of dinitrodiammine platinum, dried at 150 ° C for 12 hours, and calcined at 400 ° C for 1 hour to obtain Pt-supported Ce— A ZrO ₂ powder (powder B) was obtained. The Pt concentration of this powder was 2.0% by weight. 100 g of powder A and 100 g of powder B, 1% (atomic ratio) of lanthanum ( ₂ wt% in terms of La ₂ O ₃ ) and 32% (atomic ratio) of zirconium (25 wt% in terms of ZrO ₂ )
Oxide containing cerium (La _0.01 Zr _0.32 Ce _0.67 O
_x ) 50 g of powder and 250 g of nitric acid aqueous solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was applied to a cordierite monolithic carrier (1.7 L, 40 L).
(0 cells / square inch), excess slurry in the cells was removed by air flow, dried, and fired at 500 ° C. for 1 hour. A catalyst A having a coating weight of 50 g / L-carrier was obtained.
The platinum carrying amount was 2.37 g / L (67 g / cf).

Ce—Zr composite oxide ｛Ce = 0.2%
(Atomic ratio)｝ Impregnate the powder with rhodium nitrate aqueous solution
After drying at 0 ° C. for 12 hours, baking was performed at 400 ° C. for 1 hour to obtain a Rh-supporting Ce—ZrO ₂ powder (powder C). The Rh concentration of this powder C was 1.0 wt%. 195 g of the above powder C, 5 g of boehmite alumina, and 30 of nitric acid aqueous solution
0 g was charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was further adhered to the catalyst A, and the excess slurry in the cell was removed by an air flow, dried, and calcined at 400 ° C. for 1 hour. Rh slurry 50g /
L, a catalyst B having a total weight of the coat layer of 200 g / L-carrier was obtained. Rh carrying amount is 0.47 g / L (13 g / cf),
The Pt / Rh ratio was 5/1.

<Example 2> In the catalyst B of Example 1,
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that Y-ZrO ₂ (Y = 0.2 mol%) was used instead of Nd-ZrO ₂ .

<Example 3> In the catalyst B of Example 1,
Ca-ZrO ₂ (Ca = 0 instead of Nd-ZrO _2.
Except for using 2 mol%), an exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

Example 4 In the catalyst B of Example 1,
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that W-ZrO ₂ (W = 0.2 mol%) was used instead of Ce-ZrO ₂ .

<Example 5> In the catalyst B of Example 1,
Al-ZrO ₂ (Al = 0 instead of Ce-ZrO _2.
Except for using 2 mol%), an exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

<Example 6> In the catalyst B of Example 1,
Pt supported substrate Nd-ZrO ₂ and the weight ratio of Ce-ZrO ₂ is a Nd-ZrO ₂ is 30%, Ce-ZrO ₂ is 7
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that the catalyst was changed to 0%.

<Example 7> In the catalyst B of Example 1,
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that 50 wt% of the total Pt amount was replaced with activated alumina from Nd-ZrO ₂ and Ce-ZrO ₂ which are Pt-supported substrates.

<Example 8> In the catalyst B of Example 1,
Under the Pt and Rh supporting layers, a Pd supporting layer (Pd supporting base material is activated alumina, Pd 2.83 g / L, coating amount 50)
g / L) was obtained in the same manner as in Example 1 except that g / L) was added.

<Comparative Example 1> In the catalyst B of Example 1,
But replacing _{Nd-ZrO 2, Ce-ZrO} 2 is Pt carrier substrates all activated alumina to obtain an exhaust gas purifying catalyst in the same manner as in Example 1.

<Comparative Example 2> In the catalyst B of Example 1,
Of _{Nd-ZrO 2, Ce-ZrO} 2 is supported Pt substrate, except that the 95 wt% of the total amount of Pt was replaced with activated alumina to obtain an exhaust gas purifying catalyst in the same manner as in Example 1.

<Comparative Example 3> In the catalyst B of Example 1,
The weight ratio of the Nd-ZrO ₂ and Ce-ZrO ₂ is supported Pt substrate Nd-ZrO _2, except for changing to be 5%, was obtained exhaust gas purifying catalyst in the same manner as in Example 1 .

<Comparative Example 4> In the catalyst B of Example 1,
The weight ratio of the Nd-ZrO ₂ and Ce-ZrO ₂ is supported Pt substrate Ce-ZrO _2, except for changing to be 5%, was obtained exhaust gas purifying catalyst in the same manner as in Example 1 .

<Comparative Example 5> In the catalyst B of Example 1,
Additional element of Nd-ZrO ₂ and Ce-ZrO ₂ is a Pt carrying substrate (Nd, Ce) except for changing the content ratio of 50 mol%, to give the exhaust gas purifying catalyst in the same manner as in Example 1 Was.

<Comparative Example 6> In the catalyst of Example 7, P
A Pd-supporting layer (Pd-supporting substrate is activated alumina, Pd
(2.83 g / L, coating amount: 50 g / L) was obtained.

<Test Example> Examples 1 to 8 and Comparative Example 1
With respect to the exhaust gas purifying catalysts Nos. 1 to 6, the catalytic activity was evaluated using a model gas. The evaluation temperature was 350 ° C. and the gas flow rate was 40 L / min. (SV = 80,000h ^-1 ). The gas composition is shown in Table 1.

[0061]

[Table 1]

The noble metal loading (content of platinum, palladium and rhodium in 1 liter of catalyst) of the exhaust gas purifying catalysts studied in the above Examples 1 to 8 and Comparative Examples 1 to 6 and the type and characteristics of the loading substrate in addition, the evaluation condition that conversion catalytic activity evaluation results of (oxygen excess) as HC and NO _x purification performance of the exhaust gas purifying catalyst (%), respectively Table 2, are summarized in Table 3.

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

As described above, in the exhaust gas purifying catalyst according to the present invention, the HC component which has not been purified so far can be subjected to a wider range of atmosphere conditions from rich to lean, mainly stoichiometric. And high purification performance can be achieved.

Continued on the front page F term (reference) 4G069 AA03 AA08 BA01B BA13B BB06A BB12B BC08A BC15A BC24A BC38A BC42A BC42B BC43A BC43B BC44A BC44B BC51A BC51B BC71A BC71B BC72A BC72B BC75A BC75B CA03 CA09 CA13 CA19 EC13 CA19

Claims (7)

[Claims] 1. A monolithic catalyst having a catalyst component-supporting layer, wherein the catalyst component contains at least one selected from the group consisting of Pt, Pd, and Rh, and further comprises a Group 2A element and a Group 3B element (except for Ce). A) a Zr composite oxide (A) containing at least one element selected from the elements, and a Zr composite oxide (B) containing at least one element selected from the group consisting of Ce, group 3A and group 6B. A catalyst for purifying exhaust gas, wherein two types of the above are used as a Pt-supporting substrate. 2. The exhaust gas purifying catalyst according to claim 1, wherein the amount of Pt contained is 1 g / L to 15 g / L.
An exhaust gas purifying catalyst, wherein the ratio of the amount of Pt carried to the r composite oxide is at least 10 wt% or more of the total amount of Pt in the catalyst. 3. The exhaust gas purifying catalyst according to claim 1, wherein the element ratio of the Zr composite oxide used for the Pt-supporting substrate is 1 to 40% in atomic ratio with respect to Zr. A catalyst for purifying exhaust gas. 4. The exhaust gas purifying catalyst according to claim 1, wherein the content ratio (A / (A + B)) of the two kinds of Zr composite oxides used for the Pt-supporting substrate is 10 to 90 wt%. An exhaust gas purifying catalyst characterized by the following. 5. The exhaust gas purifying catalyst according to claim 1, wherein the crystal structure of the two Zr composite oxides measured by X-ray diffraction has an integral intensity of at least 10% tetragonal. %
An exhaust gas purifying catalyst characterized by the above. 6. The exhaust gas purifying catalyst according to claim 1, wherein at least one selected from the group consisting of lanthanum, neodymium, and zirconium has an atomic ratio of 1 to 40.
% Of cerium oxide. 7. The exhaust gas purifying catalyst according to claim 1, wherein Pd, which is a catalytically active component, does not coexist with Pt in the same catalyst layer.