JPH11123331A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for cleaning exhaust gas which can sufficiently function as a three way catalyst, and a using method therefor by which NOx cleaning action of the catalyst can be effectively carried out. SOLUTION: A catalyst for cleaning exhaust gas containing a metal oxide comprising tungsten and zirconium carrying at least one selected from the group consisting of platinum, palladium, rhodium, and iridium, or a metal oxide comprising tungsten, zirconium, and sulfur carrying at least one selected from the group consisting of palladium, rhodium, and the iridium, is arranged in the preceding stage with respect to the exhaust gas flow, and a catalyst containing at least one selected from the group consisting of platinum, palladium, rhodium, and iridium, is arranged in the subsequent stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an automobile (gasoline,
The present invention relates to an exhaust gas purifying catalyst for purifying hydrocarbons (HC), generalized carbon (CO) and nitrogen oxides (NOx) in exhaust gas discharged from internal combustion engines such as diesels and boilers, and a method for using the same. NOx in excess atmosphere
The present invention relates to an exhaust gas purifying catalyst having excellent purifying performance and a method of using the same.

[0002]

2. Description of the Related Art In recent years, fuel-efficient vehicles have been expected to be realized due to the depletion of petroleum resources and the problem of global warming. In particular, the development of lean-burn vehicles has been desired for gasoline vehicles. In a lean-burn vehicle, during lean-burn traveling, the exhaust gas atmosphere becomes an oxygen-excess atmosphere (hereinafter, referred to as a "lean atmosphere") as compared to the stoichiometric air-fuel ratio state. When a conventional three-way catalyst is used in this lean atmosphere, there has been a problem that the effect of excessive oxygen causes the NOx purification action to be insufficient. Therefore, development of a catalyst that can purify NOx even under a lean atmosphere has been expected.

Conventionally, NOx in a lean atmosphere has been
Various catalysts for improving purification performance have been proposed, and for example, many transition metals such as copper have been reported for zeolites (US Pat. No. 4,297,328).

However, such a conventional catalyst has a problem that moisture in the exhaust gas inhibits the NOx purification reaction or causes a structural change due to heat, and as a result, the purification performance of the exhaust gas is significantly deteriorated. I was

In view of such a problem, a catalyst containing a transition metal and a base metal in zeolite has been disclosed (JP-A-6-198188).

However, even with the above-mentioned conventional catalyst containing a transition metal and a base metal in zeolite, the NOx purification performance under a lean atmosphere, particularly the performance with respect to durability, is still insufficient, and a satisfactory one has been obtained. There was no current situation.

[0007]

SUMMARY OF THE INVENTION Accordingly, claims 1 to 5 are provided.
The purpose of the described invention, in conventional catalyst can improve _the NO _x purification performance in the lean atmosphere under which failed to show sufficient activity, and to express fully the function of the three-way catalyst An object of the present invention is to provide an exhaust gas purifying catalyst that can be used.

[0008] Another object of the invention of claim 6 and 7 wherein is to provide the use of an exhaust gas purifying catalyst that _the NO _x purification action of the exhaust gas purifying catalyst can be particularly effectively expression of the present invention .

[0009]

According to a first aspect of the present invention, there is provided a catalyst for purifying exhaust gas, wherein at least one selected from the group consisting of platinum, palladium, rhodium and iridium is supported, and the composite catalyst is composed of tungsten and zirconium. It is characterized by containing a metal oxide.

According to a second aspect of the present invention, there is provided an exhaust gas purifying catalyst comprising a composite metal oxide comprising tungsten, zirconium and sulfur, on which at least one selected from the group consisting of platinum, palladium, rhodium and iridium is supported. It is characterized by including.

An exhaust gas purifying catalyst according to a third aspect is characterized in that the exhaust gas purifying catalyst according to the first or second aspect further comprises a porous inorganic oxide.

According to a fourth aspect of the present invention, in the exhaust gas purifying catalyst of the third aspect, the porous inorganic oxide is selected from the group consisting of alumina, silica, ceria, zirconia, and zeolite. It is characterized by at least one kind.

According to a fifth aspect of the present invention, in the exhaust gas purifying catalyst according to the third or fourth aspect, at least one selected from the group consisting of platinum, palladium, rhodium and iridium is supported. A metal oxide composed of tungsten and zirconium, or a metal oxide composed of tungsten, zirconium and sulfur carrying at least one selected from the group consisting of palladium, rhodium and iridium, and a porous inorganic oxide The ratio of the amounts is from 1 / 0.2 to 50 by weight.

According to a sixth aspect of the present invention, there is provided a method of using the exhaust gas purifying catalyst, wherein the exhaust gas purifying catalyst according to any one of the first to fifth aspects is used for a diesel engine vehicle.

According to a seventh aspect of the present invention, there is provided a method of using the exhaust gas purifying catalyst according to any one of the first to fifth aspects, wherein the exhaust gas purifying catalyst has an air-fuel ratio of stoichiometry and 15 to 50.
It is characterized by being used for lean-burn engine vehicles that repeat the above range.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst of the present invention, at least one selected from the group consisting of platinum, palladium, rhodium and iridium is used as a composite oxide carrier comprising tungsten and zirconium, or tungsten, zirconium. And a composite oxide carrier comprising sulfur.

The content of the noble metal is not particularly limited as long as the NOx absorption capacity and the three-way catalyst performance are sufficiently obtained.
If the amount is less than 0.1 g, sufficient ternary performance cannot be obtained, and
g of the exhaust gas purifying catalyst of the present invention.
0 g is preferred.

As the substrate for supporting the noble metal, a composite oxide which is a metal oxide composed of tungsten and zirconium, or a composite oxide composed of tungsten, zirconium and sulfur is used.

The method for producing the composite oxide is not particularly limited as long as W and Zr, or W, Zr and S are composited. For example, W compound or W is added to amorphous ZrO _2.
Impregnated with a compound and an S compound, and
There is a method of firing at 0 ° C. The metal oxide prepared thereby shows strong solid acidity, and W or W and S are Zr
It is very well dispersed on the surface of O ₂ .

The W compound at this time is not particularly limited as long as it is a hydroxyl W compound. For example, there is ammonium metatungstate.

The S compound is not particularly limited as long as it is a water-soluble S compound. For example, there is ammonium sulfate.

XR of the compound comprising W and ZrO ₂
In the D spectrum, no WO ₃ peak was observed at 2θ = 22 to 24, indicating that W and ZrO ₂ exist as a composite oxide. In the XRD spectrum of the compound consisting of W, S and ZrO ₂ , WO ₃ was found at 2θ = 22 to 24 °.
No peak was observed, and no diffraction peak of ammonium sulfate was observed. Therefore, W and ZrO ₂ , S and ZrO ₂
Is present as a composite oxide.

Pt, Pd,
When a noble metal such as Rh or Ir is carried, the interaction between the noble metal and the metal oxide moderately moderates the oxidizing action of the hydrocarbon of the noble metal, and generates a partially oxidized hydrocarbon. By using the partially oxidized hydrocarbon as a reducing agent, the performance of reducing nitrogen oxides in an oxygen atmosphere is improved.

The amount of the composite oxide composed of W and Zr or the composite oxide composed of W, S and Zr contained in the exhaust gas purifying catalyst of the present invention depends on the sufficient NOx purification performance. There is no particular limitation as long as possible, but the amount is preferably 10 to 200 g per liter of catalyst from the viewpoint of sufficiently exerting the action of the composite oxide.

Further, the exhaust gas purifying catalyst of the present invention may be a metal oxide composed of tungsten and zirconium carrying at least one selected from the group consisting of platinum, palladium, rhodium and iridium, or palladium or rhodium. And at least one selected from the group consisting of iridium and a metal oxide composed of tungsten, zirconium, and sulfur, and a porous inorganic oxide.

The metal oxide composed of tungsten and zirconium carrying at least one selected from the group consisting of platinum, palladium, rhodium and iridium, or at least one selected from the group consisting of palladium, rhodium and iridium The metal oxide composed of tungsten, zirconium, and sulfur, on which is carried, agglomerates due to heat, and this causes the purification performance to deteriorate after heat endurance. The contact becomes rough, and at least one selected from the group consisting of the platinum, palladium, rhodium and iridium is obtained;
The grain growth of a metal oxide composed of tungsten and zirconium carrying seeds or a metal oxide composed of tungsten, zirconium and sulfur carrying at least one selected from the group consisting of palladium, rhodium and iridium is suppressed. is to improve the heat resistance of the catalyst, it is possible to suppress deterioration of the catalyst, under in a lean atmosphere after durability NO _x
The absorption and purification performance can be improved.

The porous inorganic oxide is preferably at least one selected from the group consisting of alumina, silica, zirconia and zeolite, and particularly preferably activated alumina. Such a material has a small geometrical change such as a specific surface area even after heat endurance, and has a low N atmosphere under a lean atmosphere.
It is suitable for exhibiting O _x absorption purification performance. The amount of the porous inorganic oxide used is 50 to 30 per liter of the catalyst.
It is preferable that the amount is 0 g from the viewpoint of sufficiently exerting the action of the composite oxide.

For the purpose of increasing the heat resistant specific surface area, a rare earth element, zirconium or the like may be added thereto.

Also, a metal oxide composed of tungsten and zirconium carrying at least one selected from the group consisting of platinum, palladium, rhodium and iridium, or at least one metal selected from the group consisting of palladium, rhodium and iridium. A metal oxide consisting of tungsten, zirconium and sulfur loaded with seeds;
The content ratio with the porous inorganic oxide was 1: 0.
It is preferably 2 to 50. The above numbers are 1
If the amount is less than 0.2, the heat resistance of the catalyst deteriorates, and the desired reduction performance cannot be obtained. Further, even if it exceeds 1:50, a significant effect of increasing the amount cannot be obtained.

Further, the exhaust gas purifying catalyst of the present invention is preferably a metal oxide comprising tungsten and zirconium carrying at least one selected from the group consisting of platinum, palladium, rhodium and iridium, or palladium, rhodium and A catalyst comprising a metal oxide comprising at least one selected from the group consisting of iridium and comprising tungsten, zirconium and sulfur is disposed upstream of the exhaust stream, and a catalyst comprising platinum, palladium, rhodium and iridium is disposed downstream. A catalyst containing at least one selected from the group can be arranged.

In the lean atmosphere, hydrocarbons completely oxidized by the first catalyst and those partially oxidized are mixed, and the partially oxidized hydrocarbons are completely oxidized by the second catalyst. , And excellent exhaust gas purification performance can be obtained.

The catalyst disposed in the subsequent stage may be a usual three-way catalyst, for example, a catalyst containing a noble metal is used.

As such noble metals, platinum, rhodium,
At least one selected from the group consisting of palladium and iridium is used. For example, Pt and Rh, Pd and I
Various combinations such as only r and Pd are possible. The content of the noble metal in the catalyst is not particularly limited as long as the NOx absorbing ability and the three-way catalytic ability performance at the time of stoichiometry are sufficiently obtained, but if less than 0.1 g, sufficient three-way performance cannot be obtained,
The amount is preferably 0.1 to 10 g per liter of the catalyst since no significant improvement in properties is observed even when the amount is more than 10 g.

In order to ensure the dispersibility of the noble metal, particularly the noble metal after durability,
A heat-resistant inorganic material having a large specific surface area is suitable, and activated alumina is particularly preferable. Activated alumina to which a rare earth element such as cerium or lanthanum, zirconia, an iron group transition metal, an alkaline earth metal, or the like is added may be used to increase the heat resistant specific surface area. The amount of activated alumina used per liter of catalyst was
If the amount is less than 50 g, sufficient noble metal dispersibility cannot be obtained,
When the amount is more than 300 g, it is preferable to be 50 to 300 g from the viewpoint that the performance is reduced.

As the noble metal raw material compound for preparing the catalyst, nitrates, carbonates, ammonium salts, acetates, halides, oxides and the like can be used in combination.
It is particularly preferable to use a water-soluble salt from the viewpoint of improving the catalyst performance. The preparation method is not limited to a special method, and various methods such as a known evaporative drying method, a precipitation method, and an impregnation method can be used as long as there is no significant uneven distribution of components.

For example, alumina is impregnated with a water-soluble or dispersion liquid of a catalyst raw material containing a noble metal component. Then, the water is removed and dried, and the residue is heat-treated at a temperature of 300 ° C to 600 ° C in the air and / or under the flow of air to obtain Alnami noble metal-supported.

At least one metal selected from the group consisting of tungsten and zirconium carrying at least one selected from the group consisting of platinum, palladium, rhodium and iridium, or at least one selected from the group consisting of palladium, rhodium and iridium A catalyst containing a metal oxide composed of tungsten, zirconium and sulfur supported on the exhaust gas flow, and a catalyst containing at least one selected from the group consisting of platinum, palladium and rhodium in the exhaust gas flow. It is important to arrange the latter in the latter stage. For example, such an arrangement method is a method in which two kinds of catalysts are mounted and arranged in one catalytic converter, or the two kinds of catalysts are arranged in separate converters. A known method such as a method of inserting and installing the device can be used. The installation position of the catalyst is not particularly limited, and examples thereof include a position immediately below the manifold and a position under the floor. If the purification performance is not sufficient with one catalyst in each of the first and second stages of the catalyst system, one or both of the first and second stages may be further provided, or multiple catalysts may be added.

The exhaust gas purifying catalyst of the present invention can be used particularly for purifying exhaust gas of a diesel engine vehicle. HC in diesel engine exhaust
Is present, the catalyst of the present invention capable of purifying NOx in the lean region in the presence of HC can exhibit its function sufficiently.

The exhaust gas purifying catalyst of the present invention has the following features:
In particular, it can be used to purify exhaust gas of lean burn engine vehicles whose air-fuel ratio repeatedly fluctuates between stoichiometry and a range of 15 to 50. When used in such a manner, NOx purification in the lean region can be performed more efficiently. This is the exhaust gas purifying catalyst of the present invention,
This is because once exposed to stoichiometric gas, the NOx purification performance under a lean atmosphere is further improved.

For use in the present invention thus obtained,
At least one selected from the group consisting of tungsten and zirconium, or at least one selected from the group consisting of palladium, rhodium and iridium, on which at least one selected from the group consisting of platinum, palladium, rhodium and iridium is supported A metal oxide composed of tungsten, zirconium and sulfur, and each of the noble metal-containing carriers are pulverized into a slurry, each of which is coated on a catalyst carrier,
By firing at a temperature of 400 to 900 ° C., the exhaust gas purifying catalyst of the present invention can be obtained.

The catalyst carrier can be appropriately selected from known catalyst carriers and used, for example, a honeycomb carrier or a metal carrier having a monolith structure made of a refractory material. Although the shape of the catalyst carrier is not particularly limited, it is usually preferable to use a honeycomb shape. As the honeycomb material, cordierite materials such as ceramics are generally used.
It is also possible to use a honeycomb made of a metal material such as a ferritic stainless steel, and further, the catalyst powder itself may be formed into a honeycomb shape. By making the shape of the catalyst into a honeycomb shape, the area of the catalyst and the exhaust gas becomes large, and the pressure loss can be suppressed.

[0042]

The present invention will be described below with reference to the following examples and comparative examples. Example 1 A ZrO ₂ gel obtained by hydrolyzing ZrOCl ₂ with aqueous NH ₃ was impregnated with ammonium metatungstate and fired at 800 ° C. in air to obtain a composite oxide composed of W and ZrO ₂ .

The W-ZrO ₄ powder was impregnated with an aqueous solution of Pd (NO ₃ ) ₂ , dried at 150 ° C., and calcined at 400 ° C. for 2 hours to obtain a Pd-supported W-ZrO ₂ powder. Pd in the obtained Pd-supported W-ZrO ₄ powder was 3.0% by weight.

The obtained Pd / W-ZrO ₂ catalyst and activated alumina were mixed in a ball mill pot together with 30 g of boehmite alumina and water in a weight ratio of 1: 1, followed by grinding for 8 hours. Thus, a slurry liquid was obtained.
This slurry liquid is applied to a cordierite monolithic carrier (0.
(1 L, 400 cells), dried by removing excess slurry in the cells by an air stream, and calcined at 400 ° C. for 2 hours to obtain a catalyst for purifying exhaust gas of the present invention having a coat layer weight of 150 g / L. I got

Example 2 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to the} aqueous solution of Rh (NO ₃ ) ₃ .

Example 3 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1, except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to an} aqueous solution of IrCl ₃ .

Example 4 The Pd / W-ZrO ₂ catalyst obtained in Example 1 and SiO ₂
Was added to a ball mill pot together with 30 g of boehmite alumina and water so that the weight ratio became 1: 1.
The slurry was mixed and crushed for an hour to obtain a slurry. This slurry liquid is applied to a cordierite monolithic carrier (1.0 L, 400 cells)
After drying by removing excess slurry in the cell with an air stream, the mixture was calcined at 400 ° C. for 2 hours to obtain a catalyst for purifying exhaust gas of the present invention having a coat weight of 150 g / L.

Example 5 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 4, except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to the} aqueous solution of Rh (NO ₃ ) ₃ .

Example 6 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 4, except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to an} aqueous solution of IrCl ₃ .

Example 7 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the weight ratio of the Pd / W-ZrO ₂ catalyst to activated alumina was 1:10.

Example 8 A ZrO ₂ gel obtained by hydrolyzing ZrOCl ₂ with aqueous NH ₃ was impregnated with an aqueous solution in which ammonium metatungstate and ammonium sulfate were dissolved, and calcined at 800 ° C. in air. Thus, a composite oxide comprising W and S and ZrO ₂ was obtained.

Pd (NO ₃ ) _{2 is} added to the WS—ZrO ₂ powder.
An aqueous solution was impregnated, dried at 150 ° C., and calcined at 400 ° C. for 2 hours to obtain Pd-supported WS—WrO ₂ powder. Pd in the obtained Pd-supported WS-ZrO ₂ powder was 3.0% by weight.

The obtained Pd / WS-ZrO ₂ catalyst and activated alumina were put into a ball mill pot together with 30 g of boehmite alumina and water in a weight ratio of 1: 1, and mixed for 8 hours. This was crushed to obtain a slurry liquid. This slurry liquid was applied to a cordierite monolithic carrier (0.1 L, 400 cells), and the excess slurry in the cells was removed by air flow, dried, and baked at 400 ° C. for 2 hours to obtain a coat layer weight. 150 g / L of the exhaust gas purifying catalyst of the present invention was obtained.

Example 9 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 8, except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to the} aqueous solution of Rh (NO ₃ ) ₃ .

Example 10 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 8, except that the Pd (NO ₃ ) ₂ aqueous solution was changed to an IrCl ₃ aqueous solution.

Example 11 The Pd / WS—ZrO ₂ catalyst obtained in Example 8 and Si
O ₂ was added to a ball mill pot together with 30 g of boehmite alumina and water at a weight ratio of 1: 1 and mixed and pulverized for 8 hours to obtain a fully. This slurry liquid is applied to a cordierite monolithic carrier (1.0 L, 400 L).
The resultant was applied to a cell, dried by removing excess slurry in the cell with an air stream, and calcined at 400 ° C. for 2 hours to obtain a catalyst for purifying exhaust gas of the present invention having a coat weight of 150 g / L. .

Example 12 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 11, except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to the} aqueous solution of Rh (NO ₃ ) ₃ .

Example 13 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 11 except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to an} aqueous solution of IrCl ₃ .

Example 14 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 8, except that the weight ratio between the Pd / WS-ZrO ₂ catalyst and the activated alumina was changed to 1:10.

Comparative Example 1 Except for using activated alumina instead of W-ZrO ₂ ,
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

Comparative Example 2 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to the} aqueous solution of Rh (NO ₃ ) ₃ .

Comparative Example 3 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to an} aqueous solution of IrCl ₃ .

Comparative Example 4 The Pd / W-ZrO ₂ catalyst obtained in Example 1 and SiO ₂
And a weight ratio of 1:60, and charged into a ball mill pot together with 30 g of boehmite alumina and water,
A slurry was obtained by mixing and grinding for 8 hours. This slurry liquid was applied to a cordierite-based monolithic carrier (1.0 L, 400 cells), dried by removing excess slurry in the cells with an air stream, and baked at 400 ° C. for 2 hours to obtain a coating weight. An exhaust gas purification catalyst of 150 g / L was obtained.

Comparative Example 5 An exhaust gas purifying catalyst was obtained in the same manner as in Example 8 except that activated alumina was used instead of WS-ZrO ₂ .

Comparative Example 6 An exhaust gas purifying catalyst was obtained in the same manner as in Example 11 except that the aqueous solution of Pd (NO ₃ ) _{2 was changed to the} aqueous solution of Rh (NO ₃ ) ₃ .

Comparative Example 7 An exhaust gas purifying catalyst was obtained in the same manner as in Example 11 except that the Pd (NO ₃ ) ₂ aqueous solution was changed to an IrCl ₃ aqueous solution.

Comparative Example 8 The Pd / WS—ZrO ₂ catalyst obtained in Example 8 and Si
The O ₂ as a one sixty by weight, were charged into a ball mill pot with boehmite alumina 30g and water to obtain a slurry mixture for 8 hr. This slurry liquid is applied to a cordierite monolithic carrier (1.0 L, 400 L).
The resultant was applied to a cell, dried by removing excess slurry in the cell with an air stream, and then dried at 400 ° C. for 2 hours to obtain an exhaust gas purifying catalyst having a coat weight of 150 g / L.

Table 1 shows Examples 1 to 14 and Comparative Examples 1 to
8 shows the composition of the exhaust gas purifying catalyst of No. 8.

[0069]

[Table 1]

Test Example The catalysts for purifying exhaust gas obtained in Examples 1 to 14 and Comparative Examples 1 to 8 were initially evaluated for catalytic activity under the following conditions. For activity evaluation, bench evaluation using an actual engine was performed.

(Table evaluation conditions) Lean burn engine using gasoline fuel 2.0 L A / F = 14.6 to 50 Engine speed 2400 rpm Exhaust gas flow rate 85 m ³ / hour

Evaluation method The catalyst activity was evaluated by mounting each catalyst on the exhaust system of a gasoline engine with a displacement of 2000 cc, A / F = 14.6 (stoichiometric state) for 60 seconds, and then A / F = 22 (lean atmosphere). ) For 60 seconds, followed by one cycle of A / F = 50 (lean atmosphere) for 60 seconds, the catalyst inlet temperature was set to 350 ° C., and the average conversion was measured. The conversion was determined by the following equation.

[0073]

(Equation 1)

Table 2 shows the results of the catalyst activity evaluation. The catalytic activity of the example was higher than that of the comparative example, and the effect of the present invention described later could be confirmed.

[0075]

[Table 2]

FIG. 1 shows the relationship between the catalyst inlet temperature and the NOx conversion rate for the exhaust gas purifying catalysts obtained in Example 2 and Comparative Example 2.

[0077]

The exhaust gas purifying apparatus according to any one of claims 1 to 5,
The catalyst is not suitable for conventional catalysts.
NO under an atmosphere_XImprove purification performance and
It can fully exhibit its function as a primary catalyst,
Excellent NO even after heat endurance _XCan show purification performance
it can.

[0078] Using the exhaust gas purifying catalyst according to claim 6-7, wherein the the NO _X purification action in lean atmosphere exhaust gas purifying catalyst of the present invention, it is possible to particularly effectively expressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a catalyst inlet temperature and a NOx conversion rate.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 53/36 104A

Claims (7)

[Claims] 1. An exhaust gas purifying catalyst comprising a composite metal oxide of tungsten and zirconium, on which at least one selected from the group consisting of platinum, palladium, rhodium and iridium is carried. 2. An exhaust gas purifying apparatus comprising a composite metal oxide comprising tungsten, zirconium and sulfur, carrying at least one selected from the group consisting of platinum, palladium, rhodium and iridium. catalyst. 3. The exhaust gas purifying catalyst according to claim 1, further comprising a porous inorganic oxide. 4. The exhaust gas purifying catalyst according to claim 3, wherein the porous inorganic oxide is at least one selected from the group consisting of alumina, silica, ceria, zirconia, and zeolite. 5. The exhaust gas according to claim 3, wherein the content ratio between the metal oxide and the porous inorganic oxide is from 1 / 0.2 to 50 by weight. Purification catalyst. 6. A method for using an exhaust gas purifying catalyst according to claim 1, wherein the exhaust gas purifying catalyst is used for a diesel engine vehicle. 7. The exhaust gas purifying catalyst according to any one of claims 1 to 5, wherein the air-fuel ratio is stoichiometric, and
A method for using an exhaust gas purifying catalyst, wherein the method is used for a lean burn engine vehicle that repeats a range from 50 to 50.