JPH0957066A - Exhaust gas purification catalyst - Google Patents

Abstract

(57) [PROBLEMS] To provide a practical catalyst for purifying exhaust gas, which is excellent in low-temperature activity, is less deteriorated even when used at high temperature for a long time, and is excellent in heat resistance and durability. SOLUTION: Platinum (P
t), palladium (Pd), rhodium (Rh), a first catalyst layer made of a refractory inorganic material carrying one or more precious metals selected from the group consisting of rhodium (Rh), and copper ( A catalyst body formed by providing a second catalyst layer made of an inorganic material mainly composed of a porous crystalline aluminosilicate carrying a Cu) component, wherein the first catalyst layer contains a barium (Ba) component. Let

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 efficiently purifying exhaust gas from an internal combustion engine such as an automobile engine and various combustors, and at the same time, has low temperature activity, heat resistance and durability. The present invention relates to an excellent exhaust gas purifying catalyst.

[0002]

2. Description of the Related Art Metal-supported zeolite catalysts obtained by supporting various metals on a crystalline aluminosilicate (hereinafter referred to as "zeolite") have been widely used in various fields. In particular, in recent years, such a catalyst system has been attracting attention because it has a remarkable ability to purify NO _x in the presence of hydrocarbons even in exhaust gas having a high oxygen content.

In particular, C carrying copper (Cu) as a metal
The u-zeolite catalyst has high NO _x activity and has NO _x purification performance over a relatively wide temperature range under high flow rate exhaust gas conditions. For this reason, purification of exhaust gas from a mobile source such as an automobile or a stationary engine for private power generation is expected.

However, the Cu-zeolite catalyst is
It is considered that the operating temperature range is relatively wide, but
It is necessary to significantly improve the NO _x purification performance in the low temperature range of 0 ° C. or lower. Further, it is necessary to have a purification performance that does not deteriorate for a long time even when exposed to a high temperature of 600 ° C. or higher. Therefore, in order to put the Cu-zeolite catalyst into practical use, it is necessary to improve low-temperature activity, heat resistance, and durability, and therefore many proposals have been made.

For example, in order to improve low-temperature activity, a method of co-supporting Cu and a noble metal component on zeolite, or a method of separately coating a catalyst layer supporting a noble metal and a Cu-zeolite catalyst layer on a monolith carrier. Is proposed.

In Japanese Patent Laid-Open No. 1-127044 and Japanese Patent Laid-Open No. 5-68888, a first catalyst layer in which a noble metal, which is a catalyst component effective for an oxidation reaction, is supported on alumina is provided on a carrier. A two-layer structure catalyst in which a second layer of Cu-zeolite catalyst is provided on one catalyst layer is disclosed.

In the catalyst disclosed in the above publication, the temperature of the upper Cu-zeolite catalyst is increased by the heat of oxidation reaction of coexisting reducing gas components (carbon monoxide, hydrocarbons) in the exhaust gas by the lower precious metal catalyst layer. The NO _x purification reaction smoothly proceeds from the state where the exhaust gas temperature is low.

Further, JP-A-1-310742 discloses a method in which Cu and a noble metal coexist using zeolite as a carrier, and JP-A-5-168939 discloses a zeolite catalyst layer in which Cu and a noble metal component coexist. As the first layer,
A catalyst having a two-layer structure in which a zeolite catalyst layer in which zirconia (Zr) and Cu coexist as the second layer is provided thereon is disclosed.

[0009]

However, the catalysts described in JP-A-1-127044 and JP-A-5-68888 are not sufficiently durable in practical use, and the oxidation reaction of the reducing gas component in the lower layer. The heat raises the bed temperature of the upper Cu-zeolite catalyst, thereby promoting catalyst degradation.

Further, even in the catalysts described in JP-A-1-310742 and JP-A-5-168939, the influence of the heat of oxidation reaction by the noble metal catalyst portion cannot be avoided. Further, Cu becomes a poison of the noble metal catalyst, and if it is used in a coexisting state at a high temperature for a long time, the deterioration will be remarkably advanced. Such a problem is difficult to avoid even if the Cu-zeolite catalyst and the noble metal catalyst are divided and applied as separate layers as described above.
Even in the case of the two-layer catalyst in which the Cu-zeolite catalyst layer is arranged in the upper layer and the noble metal catalyst layer is arranged in the lower layer as in the catalyst described in Japanese Patent No. 27044, Cu in the upper layer diffuses to the lower layer.

As described above, in order to improve the low temperature activity of the Cu-zeolite catalyst, combination with a noble metal catalyst is one of the effective means. However, in the conventional method, the reducing component in the exhaust gas is converted into the noble metal. The catalyst layer is oxidized and the heat of reaction is used to improve the low temperature activity of the Cu-zeolite catalyst. Therefore, when it is exposed to high temperature exhaust gas, the heat of reaction is further added and the temperature of the catalyst becomes higher. Have been exposed,
As a result, the deterioration of the Cu-zeolite catalyst is promoted. Therefore, it is difficult to combine low temperature activity and heat resistance with a conventional combination of a Cu-zeolite catalyst and a noble metal catalyst, and as a vehicle exhaust gas purification catalyst used under severe conditions, a Cu-zeolite catalyst is used. The reality is that has not yet been put to practical use.

Therefore, the object of the present invention is to solve the problems of the above-mentioned conventional catalysts and to be excellent in low-temperature activity and practically excellent in heat resistance and durability with little deterioration even when used at high temperature for a long time. It is to provide a catalyst for purifying exhaust gas.

[0013]

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention provides platinum (Pt) and palladium (P) on a honeycomb monolith carrier.
d), a first catalyst layer made of a refractory inorganic material carrying one or more precious metals selected from the group consisting of rhodium (Rh) is provided, and a copper (Cu) component is further carried on the first catalyst layer. In the catalyst body formed by providing the second catalyst layer made of an inorganic material having a porous crystalline aluminosilicate as a main component, the first catalyst layer contains a barium (Ba) component.

Further, the invention according to claim 2 is that, in the constitution of the invention according to claim 1, the content of the Ba component in the first catalyst layer is 5 to 30 g / L in terms of BaO conversion. Characterize.

The invention of claim 3 is characterized in that, in the constitution of the invention of claim 1, the refractory inorganic material of the first catalyst layer is a porous crystalline aluminosilicate.

The invention of claim 4 is characterized in that, in the constitution of the invention of claim 1, the refractory inorganic material of the first catalyst layer is alumina.

According to a fifth aspect of the present invention, in the constitution of the first aspect of the invention, the porous crystalline aluminosilicate of the second catalyst layer is a ZSM5 type zeolite, and SiO ₂ / Al of the zeolite is used. It is characterized in that the molar ratio of ₂ O ₃ is 20 to 60.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas purifying catalyst of the present invention comprises:
A first catalyst layer made of a refractory inorganic material carrying one or more precious metals selected from the group consisting of Pt, Pd, and Rh is provided on a honeycomb-shaped monolith support, and a Cu component is further provided on the first catalyst layer. In a catalyst body formed by providing a second catalyst layer made of an inorganic material containing, as a main component, a porous crystalline aluminosilicate (zeolite), the first catalyst layer contains a Ba component.

Here, as the refractory inorganic material of the first catalyst layer, a general catalyst carrier such as alumina, silica, silica-alumina, magnesia, zirconia, titania, etc. can be used, but is limited thereto. is not. Further, as the refractory inorganic material, porous crystalline aluminokete salt (zeolite), layered clay mineral or the like can be selected. In particular, since zeolite has a characteristic micropore structure with a diameter of 1 nm or less, it exerts a molecular sieving action, and its large specific surface area makes it an effective catalyst carrier for obtaining a catalyst with excellent selectivity and low-temperature activity. is there. Further, alumina as a refractory inorganic material has a large specific surface area and is excellent in heat resistance, so that it is possible to support a precious metal in a highly dispersed manner, and it is possible to effectively utilize a smaller amount of the precious metal, which is a preferable catalyst carrier.

The oxidizing performance of the first catalyst layer (noble metal catalyst layer) in the present invention is suppressed to a low level by containing the Ba component, and the above-mentioned deterioration promoting effect of the Cu-zeolite catalyst due to the heat of reaction is prevented. Therefore, the noble metal catalyst layer in the present invention has a C mechanism different from that of the conventional catalyst.
It enhances the NO _x purification performance of the u-zeolite catalyst.

That is, by adding the Ba component, electrons are donated from the Ba component to the noble metal component, the interaction force with the hydrocarbons is weakened, and the strong oxidizing ability of the noble metal component is reduced. Hydrogen is more efficient NO _x
It is considered to be used for purification reaction. Furthermore, the addition of the Ba component also has the effect of increasing the trapping power for NO _x . That is, NO _x trapped in the noble metal catalyst layer
Is released when the exhaust gas temperature rises, but Cu in the upper layer
-It is purified as it passes through the zeolite catalyst layer, and it is therefore believed that NO _x purification proceeds from lower temperatures. Further, when the catalyst is used for a long time under a high temperature condition, it is necessary to prevent the Cu component of the second layer from diffusing into the first layer and deactivating the noble metal, and the Ba component is contained in the second layer. It is considered that it also has a function of protecting the noble metal component from Cu that diffuses from Cu, and can maintain high catalytic performance even when used for a long time.

Particularly preferably, when zeolite is used as the refractory inorganic compound of the first catalyst layer and the noble metal component is supported in the micropores, the contact between Cu and the noble metal diffused and transferred from the second catalyst layer. Is more efficiently suppressed, so that the effect of preventing poisoning deterioration of the noble metal component is enhanced.

In the exhaust gas purifying catalyst of the present invention, the noble metal catalyst layer is the first layer, and the upper layer (second layer) is Cu-
The structure of arranging the zeolite catalyst is NO trapped in the first layer.
_This is the configuration required to effectively purify _x .

Here, the second layer zeolite SiO ₂ /
The range of 20 to 60 is effective as the molar ratio of Al ₂ O ₃ . If the molar ratio of SiO ₂ / Al ₂ O ₃ is less than 20, the thermal stability of the zeolite will be insufficient and the heat resistance and durability of the catalyst will decrease. On the other hand, when the molar ratio exceeds 60, the amount of Cu, which is an active component, carried becomes small and the catalytic activity becomes insufficient.

The zeolite used in the present invention can be appropriately selected and used from known zeolites, and the pentasil type is particularly effective. Examples of such zeolite include mordenite, ferrierite, ZSM5, ZSM11, and the like, and ZSM5 is particularly preferable from the viewpoint of heat resistance and durability.

If zeolite is made to have good crystallinity or is stabilized by hydrothermal treatment, resynthesis, etc., a catalyst having higher heat resistance and durability can be obtained, so that the above treatment is also effective.

As the raw material of the Cu component used to obtain the exhaust gas purifying catalyst of the present invention, inorganic acid salts, oxides, organic acid salts, chlorides, carbonates, sodium salts, ammonium salts, ammine-rich compounds, etc. The various compounds described above can be used, and commonly used supporting methods such as an ion exchange method and an impregnation method can be used. Furthermore, a method of evaporating a Cu raw material at a high temperature and supporting it in a gas phase is also effective.

In the case of the usual ion exchange method or impregnation method,
The Cu raw material is often used as an aqueous solution, and if an acid or a base is added to the aqueous solution to adjust the pH appropriately, more preferable results are obtained.

On the other hand, as the raw material of the noble metal component, various general raw materials such as nitrates, ammonium salts and chlorides can be used and can be supported by the same method as the Cu raw material. In addition, as for the raw material of Ba, nitrate,
Various general raw materials such as acetic acid salt, chloride, carbonate, etc. can be used, and the loading method on the first catalyst layer should be a normal method such as impregnation method, mixed method or physical mixing method. You can

With respect to the noble metal component of the first catalyst layer of the present invention, the expected effect is exhibited even if the supported amount is relatively small, but 0.04 to 3 g / L is preferable per 1 L of the catalyst capacity, If it is less than 0.04 g / L, the loading effect cannot be obtained, and conversely, if it exceeds 3 g / L, the oxidation activity becomes remarkable,
The catalyst activity and durability are significantly reduced, and rare and expensive precious metal components are wasted.

The content of Ba in the first catalyst layer is preferably changed according to the amount of the noble metal supported, but a range of 5 to 30 g / L in terms of BaO is effective per 1 L of the catalyst capacity. When the Ba content is less than 5 g / L, the above B
The effect of adding the component a cannot be obtained, and if it exceeds 30 g / L, the precious metal component is excessively coated, and the effect of the precious metal component is not exhibited.

The amount of Cu supported in the second catalyst layer is preferably in the range of 5 to 15 g / L in terms of Cu per 1 L of catalyst capacity. If the Cu content is less than 5 g / L, the amount of the active ingredient is not sufficient, and conversely, if it exceeds 15 g / L, the copper oxide (CuO) remaining on the surface of the catalyst particles becomes excessive and the pores of the zeolite are blocked. cause. Furthermore, Cu for the first layer
The diffusion and movement of the noble metal becomes remarkable, which causes adverse effects such as poisoning deterioration of the precious metal component.

The second layer Cu-zeolite catalyst contains Cu
It is also effective to make at least one component selected from the group consisting of alkalis, alkaline earths, rare earths, transition metals and the like coexist in order to improve the stability of zeolite and to make it a more durable catalyst.

Since the catalyst of the present invention is used in a honeycomb shape, it is usually used by coating the catalyst on various honeycomb-shaped carriers. As such a honeycomb material, a cordierite material is generally used in many cases, but it is not limited to this, and a honeycomb carrier made of a metal material can be used. Furthermore, the catalyst powder itself is formed into a honeycomb shape. You may shape. Alternatively, the catalyst of the present invention can be obtained by directly supporting a noble metal component on a refractory inorganic material such as alumina, silica, cordierite or the like formed in a honeycomb shape, and providing a Cu-zeolite catalyst thereon. The honeycomb shape of the catalyst increases the contact area between the catalyst and the exhaust gas, and also suppresses the pressure loss, so there is severe vibration and a large amount of exhaust gas is processed in a limited space. Is extremely effective when used as an automobile catalyst that requires

[0035]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto.

Example 1 (1) Preparation of first layer catalyst powder and catalyst slurry NH ₄ type ZSM having a SiO ₂ / Al ₂ O ₃ molar ratio of about 34.
After impregnating 5 powders with a dinitrodiamine platinum aqueous solution, it was dried in an oven at 70 ° C. for 8 hours and then at 120 ° C. for 24 hours or more. The dry powder thus obtained was calcinated in an electric furnace at 500 ° C. for 6 hours in the atmosphere to obtain Pt of 0.8.
Pt-ZSM5 catalyst powder supported by weight% was obtained. C above
As in the case of the u-ZSM5 catalyst powder, the Pt-ZSM5 catalyst powder, the binder (alumina sol) and water were mixed with each other at 8:
The mixture was placed in a ball mill pot at a weight ratio of 2:10 and pulverized and mixed for 1 hour to obtain a first layer catalyst slurry.

(2) Preparation of Second Layer Catalyst Powder and Catalyst Slurry SiO ₂ / Al ₂ O ₃ was added to a 0.1 mol copper nitrate aqueous solution.
A powder of Na-type ZSM5 having a molar ratio of about 36 was added, well stirred, and then filtered to separate a solid liquid. The above stirring and filtering operation was repeated four times in order to increase the ion exchange rate of Cu into the zeolite. The amount of Cu in the aqueous copper nitrate solution used was an amount corresponding to 200% in terms of the ion exchange capacity of zeolite. The zeolite cake obtained after the stirring / filtering operation was placed in an oven for 12 hours.
Dry at 0 ° C for 24 hours or more, then in air at 500
By calcining at 6 ° C. for 6 hours, Cu-ZSM5 catalyst powder carrying 3.6 wt% of Cu was obtained. The Cu-ZSM5 catalyst powder obtained as described above, the binder (alumina sol) and water were placed in a ball mill pot at a weight ratio of 8.5: 1.5: 10, and mixed and pulverized for 1 hour to form a second layer. A slurry of catalyst was obtained.

(3) Formation of First Catalyst Layer The slurry of the first layer catalyst obtained in the above (1) was applied to a cordierite honeycomb carrier having about 400 channels per square inch cross section, After drying with hot air at 150 ° C, firing was performed at 300 ° C for 1 hour. Pt on honeycomb carrier
The coating amount of the ZSM5 catalyst powder was 60 g / L. The Pt-ZSM5 honeycomb catalyst was impregnated with an aqueous barium acetate solution, and then dried in an oven at 100 ° C.
It was baked at 400 ° C. for 30 minutes in an electric furnace, and Ba was carried by the impregnation method. The amount of Ba carried on the honeycomb-shaped catalyst of Pt-ZSM5 was 18 g / L in terms of BaO.

(4) Formation of Second Catalyst Layer The Ba-Pt-ZSM5 honeycomb catalyst obtained in (3) above was coated with the slurry of the second layer catalyst obtained in (2) and 150 ° C. After hot-air drying at 400 ° C., it is baked at 400 ° C. for 1 hour, and a Ba-Pt-Z honeycomb carrier made of cordierite is formed.
A honeycomb catalyst having an amount of SM5 (first catalyst layer) and a Cu-ZSM5 catalyst layer (second catalyst layer) was obtained. The coating amount of Cu-ZSM5 catalyst on the honeycomb carrier is 180 g /
L.

Example 2 (1) Preparation of first layer catalyst powder and catalyst slurry In the same manner as in Example 1 except that the dinitrodiammineplatinum aqueous solution was changed to a dinitrodiamminepalladium aqueous solution, 1.2% by weight of Pd was loaded. The obtained Pd-ZSM5 catalyst powder was obtained. Thereafter, a slurry of the first layer catalyst was obtained in the same manner as in Example 1.

(2) Preparation of Second Layer Catalyst Powder and Catalyst Slurry Second layer catalyst powder and catalyst slurry were prepared in the same manner as in Example 1.

(3) Formation of First Catalyst Layer The slurry of the first layer catalyst obtained in (1) above was applied onto a cordierite honeycomb carrier in the same manner as in Example 1 to form a Pd-ZSM5 honeycomb. A solid catalyst was obtained. The coating amount of Pd-ZSM5 catalyst powder on the honeycomb carrier was 60 g /
L. Thereafter, Ba was impregnated and carried in the same manner as in Example 1. The loading amount of Ba on the honeycomb catalyst of Pd-ZSM5 was 17 g / L in terms of BaO.

(4) Formation of Second Catalyst Layer In the same manner as in Example 1, the Ba-Pd-ZSM5 layer (first
A honeycomb catalyst having a catalyst layer) and a Cu-ZSM5 catalyst layer (second catalyst layer) was obtained. Cu for honeycomb carrier
The coating amount of -ZSM5 catalyst was 180 g / L.

Example 3 A honeycomb catalyst was obtained in exactly the same manner as in Example 1 except that rhodium nitrate was further added to the dinitrodiammineplatinum aqueous solution when preparing the catalyst for the first catalyst layer. The first catalyst layer of the obtained catalyst (Ba-Pt-Rh-Z
The supported amount of Pt and Rh in SM5) is ZSM5 zeolite (based on the dry state after removal of adsorbed water).
Respectively 0.8% by weight and 0.1% by weight,
The amount of carried Ba was 19 g / L in terms of BaO.

Example 4 In the step (1) of Example 1, SiO _{2 of} the first catalyst layer was formed.
Except that nitric acid acidic boehmite was used in place of the alumina sol used as the binder instead of the NH ₄ type ZSM5 powder having a molar ratio of / Al ₂ O ₃ of about 34, in place of the activated alumina powder containing γ alumina as the main component. A honeycomb catalyst was obtained in the same manner as in Example 1. The loading amount of Pt in the first catalyst layer (Ba-Pt-alumina) of the obtained catalyst was 0.9% by weight with respect to alumina, and the loading amount of Ba was 21 g / L in terms of BaO. Met.

Example 5 In Example 1, a cordierite honeycomb carrier was impregnated with a dinitrodiammineplatinum aqueous solution, dried, and fired to directly support Pt on the honeycomb carrier. Then, the honeycomb carrier is impregnated with a barium acetate aqueous solution,
After supporting a, it was dried and baked. Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 1. The amount of Pt carried in the first catalyst layer (Ba-Pt-cordierite honeycomb) of the obtained catalyst was 1.1 g / L, and the amount of Ba carried was 22 g / L in terms of BaO. .

Example 6 Na-type ZSM used in the catalyst of the second layer in Example 1
5 is a Na-type ZSM having a SiO ₂ / Al ₂ O ₃ molar ratio of 21.
A honeycomb catalyst was obtained in the same manner as in Example 1 except that 5 was used. C in Cu-ZSM5 of the obtained second catalyst layer
The amount of u supported was 5.9% by weight, and the coating amount of the second catalyst layer was 190 g / L.

Example 7 Na-type ZSM used in the catalyst of the second layer in Example 1
5 is a Na-type ZSM having a SiO ₂ / Al ₂ O ₃ molar ratio of 59.
A honeycomb catalyst was obtained in the same manner as in Example 1 except that 5 was used. C in Cu-ZSM5 of the obtained second catalyst layer
The amount of u supported was 2.3% by weight, and the coating amount of the second catalyst layer was 220 g / L.

Example 8 In Example 2, the Pd supported amount was 0.33% by weight of Pd.
A honeycomb catalyst was obtained in the same manner as in Example 2 except that the first catalyst layer was formed using -ZSM5 catalyst powder and the amount of BaO supported on the first layer was changed to 5.2 g / L.

Example 9 In Example 2, Pd-supported amount of Pd was 1.5% by weight.
Forming a first catalyst layer using ZSM5 catalyst powder, and
Example 2 except that the amount of BaO supported on the layer was 29 g / L.
A honeycomb catalyst was obtained in the same manner as in.

Comparative Example 1 A honeycomb catalyst was obtained in the same manner as in Example 1 except that Ba was not impregnated and supported in the process of forming the first catalyst layer.

Comparative Example 2 In Example 1, a honeycomb catalyst was obtained by changing the coating order of the first catalyst layer and the second catalyst layer on the honeycomb carrier. That is, as the first catalyst layer, the honeycomb carrier was coated with Cu-zeolite, which was the second catalyst layer in Example 1. On the other hand, as the second catalyst layer, a catalyst powder of Pt-ZSM5 was impregnated in an aqueous barium acetate solution, dried, and calcined, and then Ba-Pt-Z, which was the first catalyst layer in Example 1, was used.
SM5 catalyst powder was obtained. The obtained Ba-Pt-ZSM5 catalyst powder was slurried in the same manner as in Example 1, and the above Cu-
Coated on a honeycomb carrier coated with zeolite, dried,
A honeycomb catalyst was obtained by firing.

Comparative Example 3 Na-type ZSM used for the second layer catalyst powder in Example 1.
5 is a Na-type ZSM having a SiO ₂ / Al ₂ O ₃ molar ratio of 18
A honeycomb catalyst was obtained in the same manner as in Example 1 except that 5 was used. C in Cu-ZSM5 of the obtained second catalyst layer
The amount of u supported was 7.9% by weight, and the coating amount of the second catalyst layer was 210 g / L.

[0054]Comparative Example 4 In Example 1, Na-type ZSM used for the second layer catalyst powder
5 for SiO₂/ Al ₂O_ThreeNa-type ZS with a molar ratio of 62
Honeycomb catalyst as in Example 1 except that M5 was used instead.
I got In the obtained second catalyst layer Cu-ZSM5
The amount of supported Cu was 1.9% by weight, and the second catalyst layer was coated.
The amount was 210 g / L.

Comparative Example 5 In Example 2, the amount of BaO supported on the first layer was 4.5 g.
A honeycomb catalyst was obtained in the same manner except that / L was used.

Comparative Example 6 In Example 2, the amount of BaO supported on the first layer was 32 g /
A honeycomb catalyst was obtained in the same manner except that L was used.

Test Example Catalyst Performance Test Example Rapid durability treatment of the exhaust gas purifying catalysts obtained in Examples 1 to 9 and Comparative Examples 1 to 6 by the rapid durability treatment and activity evaluation test using the actual exhaust gas of the engine. NO _x after treatment
The purification performance was examined. (1) Activity evaluation conditions Evaluation device; Fixed bed flow type device using actual exhaust gas from engine Catalyst capacity; Honeycomb 60 cc gas space velocity; Approx. 44000 h ^-1 engine; Nissan Motor Co., Ltd. inline 6 cylinder 2L Engine usage Average air-fuel ratio (A / F); Approx. 21 Fuel; Unleaded regular gasoline (2) Rapid durability processing conditions Exhaust gas temperature at catalyst inlet; 610 ° C engine; Nissan V. 6-cylinder 3L engine used Average air-fuel ratio (A / F); Approximately 14.7 Fuel; Unleaded regular gasoline Processing time: 30 hours

Table 1 shows the NO _x purification performances of the catalysts of Examples 1 to 9 and Comparative Examples 1 to 6 after the rapid durability treatment, determined by the following formula.

[Equation 1] The NO _x purification performance is NO at the catalyst inlet temperature of 385 ° C.
_{Expressed as x} purification rate.

[0059]

[Table 1]

The exhaust gas purifying catalyst of the present invention is 600 ° C.
High NO _x purification performance is maintained even after rapid durability treatment at temperatures above 100 ° C, and heat resistance and durability are excellent. On the other hand, the factor that adversely affects the purification performance of the exhaust gas purification catalyst is the amount of Ba added to the first catalyst layer, which has a catalyst capacity of 1 L.
It is found that 5 to 30 g / L in terms of BaO equivalent is effective.

[0061]

The exhaust gas purifying catalyst of the present invention can purify NO _{x in} exhaust gas containing a large amount of oxygen with high efficiency and is excellent in heat resistance and durability.
It can be used for a long time even under a temperature condition of 0 ° C. or higher.
Furthermore, according to the exhaust gas purifying catalyst of the present invention,
NO _x from exhaust gas from automobiles equipped with a burn engine
Since it is possible to purify fuel with high efficiency, it is possible to provide an automobile with less environmental pollution and excellent economy (fuel consumption).

Claims (5)

[Claims] 1. A platinum (P
t), palladium (Pd), rhodium (Rh), a first catalyst layer made of a refractory inorganic material carrying one or more precious metals selected from the group consisting of rhodium (Rh), and copper ( In a catalyst body formed by providing a second catalyst layer made of an inorganic material mainly composed of a porous crystalline aluminosilicate carrying a Cu) component, the first catalyst layer contains a barium (Ba) component. An exhaust gas purification catalyst characterized by: 2. The exhaust gas purifying catalyst according to claim 1, wherein the content of the Ba component in the first catalyst layer is 5 to 30 g / L in terms of BaO conversion. catalyst. 3. The exhaust gas purifying catalyst according to claim 1, wherein the refractory inorganic material of the first catalyst layer is a porous crystalline aluminosilicate. 4. The exhaust gas purifying catalyst according to claim 1, wherein the refractory inorganic material of the first catalyst layer is alumina. 5. The exhaust gas purifying catalyst according to claim 1, wherein the porous crystalline aluminosilicate of the second catalyst layer is Z.
SM5 type zeolite, SiO _{2 of the} zeolite
An exhaust gas purifying catalyst, wherein the molar ratio of / Al ₂ O ₃ is 20 to 60.