JP2001162166A - Catalyst for purification of discharged gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for purification of exhaust gas having excellent light-off performance. SOLUTION: This catalyst for purification of exhaust gas consists of a catalyst carrier body having a tubular passage where the exhaust gas passes in the axial direction, a front part and a rear part. The front part consists of a front carrier layer formed by applying a wash coating slurry consisting of Al2O3 by 10 to 150 g/L on the surface of the catalyst carrier body in the upstream side of the exhaust gas, and of Pd deposited on the front carrier layer. The rear part consists of a rear carrier layer formed by applying a wash coating slurry containing Al2O3 and Ce oxide by 150 to 250 g/L on the surface of the catalyst carrier body in the downstream side of the exhaust gas, and of a noble metal catalyst deposited on the rear carrier layer. The catalyst for purification of exhaust gas has excellent light-off performance by decreasing the coating amount in the front part having Pd excellent in the activity at low temperature, and therefore by decreasing the heat capacity of the catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying catalyst for purifying exhaust gas.

[0002]

2. Description of the Related Art Exhaust gas emitted from an internal combustion engine such as an automobile engine includes hydrocarbons (HC) and carbon monoxide (C).
O) and harmful components such as nitrogen oxides (NOx). Exhausting the exhaust gas as it is causes pollution and environmental degradation. For this reason, exhaust gas containing these components is exhausted to the atmosphere after being purified using an exhaust gas purifying catalyst or the like.

[0003] The exhaust gas purifying catalyst has a structure in which a support layer made of alumina or the like is provided on the surface of a catalyst carrier base material, and a catalyst noble metal is supported on the support layer. Further, the exhaust gas purifying catalyst is classified into a monolithic shape, a granular shape, a pipe shape, and the like, depending on the shape of the catalyst carrier substrate. Further, as the material of the catalyst carrier substrate, a heat-resistant material is used because it is exposed to high-temperature exhaust gas. Examples of such a material include ceramics such as cordierite and heat-resistant metals such as stainless steel. Etc. can be given.

[0004] The exhaust gas purifying catalyst purifies the exhaust gas by converting NOx, HC and CO contained in the exhaust gas into harmless nitrogen, carbon dioxide and water by a catalytic noble metal carried on a carrier layer. . Here, in the purification of exhaust gas by the exhaust gas purifying catalyst, the purification of HC is strongly affected by the exhaust gas temperature, and is generally performed at a temperature of 300 ° C. or higher. For this reason, when the exhaust gas temperature is low, such as immediately after the start of the engine, HC in the exhaust gas has a low catalytic activity of the noble metal catalyst and is difficult to purify.

In addition, immediately after the engine is started, a large amount of H
C has been emitted. Furthermore, the proportion of HC in the emission is also increasing, and suppressing the emission of HC at low temperatures has become an important problem in exhaust gas purification.

[0006] As an exhaust gas purifying catalyst in which the emission of HC is suppressed, a support layer made of alumina or the like is formed on the surface of a catalyst carrier base material, and on this support layer, a catalytic noble metal and an NOx catalyst for HC purification are formed. For purifying exhaust gas in which a catalytic noble metal for purifying CO and CO is supported in the axial direction of the catalyst carrier, and a catalytic noble metal for purifying HC and NOx and C
There has been an exhaust gas purifying catalyst formed in a structure in which a catalytic noble metal that purifies O is laminated with a noble metal.

Further, a catalyst for purifying HC, NOx
There has been an exhaust gas purifying catalyst in which a catalyst for purification is formed as a separate catalyst and arranged along the direction in which exhaust gas flows. Such an exhaust gas purifying catalyst has a problem that if it is intended to improve exhaust gas purifying performance at a low temperature such as at the time of engine start, catalysts having different functions are required, and the cost as a catalyst system is increased. I was In addition, the increase in the number of catalysts increases the pressure loss of the exhaust system, increases the load on the engine, and increases the cost due to the increase in the amount of supported catalyst precious metal.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and exhibits an effective purification characteristic even in a low temperature range immediately after the start of an engine, that is, an exhaust gas purification with excellent light-off performance. It is an object to provide a catalyst for use.

[0009]

Means for Solving the Problems To solve the above-mentioned problems, the inventors of the present invention have conducted various studies, and as a result, have found that P
In a catalyst for purifying exhaust gas in which a front portion carrying d and a rear portion carrying a catalyst noble metal on the exhaust gas outlet side are integrally formed, a wash coat slurry for forming a catalyst carrying layer on the front portion is coated. It has been found that the above problem can be solved by reducing the amount. In the present invention, the coating amount of the washcoat slurry indicates an amount when the washcoat slurry is dried on the surface of the catalyst carrier substrate.

That is, the exhaust gas purifying catalyst of the present invention comprises:
A catalyst carrier substrate having a tubular passage through which the exhaust gas passes in the axial direction; and Al ₂ O _{3 on} the surface of the catalyst carrier substrate on the upstream side of the exhaust gas.
10 to 150 g / wash coat slurry
L on the front side supporting layer formed by coating with L, Pd supported on the front side supporting layer at 1 to 20 g / L, and the surface of the catalyst carrier base material on the downstream side of the exhaust gas. al ₂ O ₃ and Ce oxide in a weight ratio of 1: 1 to 2
Washcoat slurry having a 0: 1 ratio
It is characterized by comprising a rear support layer formed by coating at 0 to 250 g / L, and a rear portion composed of a catalytic noble metal supported on the rear support layer.

In the exhaust gas purifying catalyst of the present invention, since the coating amount of the wash coat slurry on the front side support layer is smaller than the coat amount of the wash coat slurry on the rear side support layer, the catalyst heat capacity at the front portion is smaller than that at the rear portion. Has become. For this reason, the front portion is heated by the exhaust gas to quickly reach the temperature at which Pd exerts catalytic activity, thereby purifying the exhaust gas. Further, Pd itself is also excellent in catalytic activity at low temperatures, and thus is an exhaust gas purifying catalyst having excellent light-off performance.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas purifying catalyst of the present invention comprises a catalyst carrier base, a front part, and a rear part.

The catalyst carrier substrate is a member having a tubular passage through which exhaust gas passes in the axial direction. That is, by having a structure having a tubular passage through which exhaust gas passes,
The exhaust gas purifying catalyst can increase the contact area with the exhaust gas and improve the exhaust gas purifying ability. As such an exhaust gas purifying catalyst, for example, a catalyst carrier substrate such as a monolith honeycomb carrier can be mentioned. The catalyst carrier substrate can be made of a material used for a conventional catalyst for purifying exhaust gas, and for example, a material such as a heat-resistant ceramic such as cordierite, a heat-resistant metal, or the like can be used.

The front portion includes a front-side support layer formed by coating a wash coat slurry made of Al ₂ O ₃ at a rate of 10 to 150 g / L on the surface of the catalyst carrier base material on the upstream side of the exhaust gas. Pd supported on the layer at 1-20 g / L. Here, the upstream side of the exhaust gas in the front portion specifically refers to a side where the exhaust gas is supplied to the tubular passage when the exhaust gas passes through the tubular passage when used as an exhaust gas purifying catalyst.

[0015] The front-side support layer is provided with a catalyst on the upstream side of the exhaust gas.
Al formed on the surface of the medium carrier substrate _TwoO_ThreeWatt consisting of
Coat the schkot slurry with 10-150g / L
It is formed. In other words, wash the front carrier layer
The coating amount of the coating slurry is 10 to 150 g / L.
This reduces the heat capacity in the front part.
Wash coat slurry coating on front side carrier layer
When the amount is less than 10 g / L, the catalyst noble metal (Pd) is
It is no longer possible to support and the exhaust gas contact surface
As a result, sufficient catalyst purification ability cannot be obtained,
If the coating exceeds 0 g / L, the heat capacity of the front part will be large.
And the catalyst bed temperature rises to a temperature that indicates catalytic activity.
It takes a long time, and the light-off performance is not improved.

The washcoat slurry for the front-side support layer preferably contains BaO. Since the washcoat slurry of the front-side supporting layer contains BaO, HC poisoning of the Pd supported on the front portion can be suppressed, so that a decrease in HC resolution can be suppressed.

BaO is preferably contained in the washcoat slurry at a weight ratio of BaO to Al ₂ O ₃ of 1:20 to 2: 3. If the weight ratio of BaO to Al ₂ O _{3 in the} washcoat slurry is less than 1:20, the effect of adding BaO is not seen, and if it is greater than 2: 3, the effect of the addition does not increase.

Pd is 1 to 20 g on the front support layer.
/ L. Pd decomposes HC and has excellent catalytic activity at low temperatures.
HC in exhaust gas can be sufficiently decomposed.

The rear portion has a weight ratio of Al ₂ O ₃ and Ce oxide of 1: 1 to _{2 on} the surface of the catalyst carrier substrate on the downstream side of the exhaust gas.
Washcoat slurry having a 0: 1 ratio
It comprises a rear support layer formed by coating at 0 to 250 g / L, and a catalytic noble metal supported on the rear support layer. Here, the downstream side of the exhaust gas in the rear section
FIG. 2 shows an end portion where exhaust gas is discharged from the tubular passage when the exhaust gas passes through the tubular passage when used as an exhaust gas purifying catalyst.

[0020] The rear-side support layer is composed of Al ₂ O ₃ and Ce oxide in a weight ratio of 1: _{2 on} the surface of the catalyst support substrate on the downstream side of the exhaust gas.
It is formed by coating a washcoat slurry having a ratio of 1 to 20: 1 at 150 to 250 g / L. That is, a sufficient amount of the catalytic noble metal can be supported by setting the coating amount of the wash coat slurry on the rear supporting layer to be larger than the coating amount of the front supporting layer.

The washcoat slurry for forming the rear support layer has a weight ratio of Al ₂ O ₃ and Ce oxide of 1: 1 to 20: 1. Since the wash coat slurry has Ce oxide, C
An e-oxide can be contained to improve the purification performance of the exhaust gas purifying catalyst. That is, by containing the Ce oxide in the carrier layer, the thermal stability of the carrier layer is improved, and oxygen in the three-way catalyst is stored and released, and the purification performance when the stoichiometric air-fuel ratio deviates is reduced. I do.

Here, Ce of the wash coat slurry is used.
If the weight ratio of the oxide to Al ₂ O ₃ is less than 1/20, the effect of the addition of Ce oxide will not be seen, and if it exceeds 1, the contact area will be small, and the catalyst performance will be reduced.

Here, the Ce oxide includes not only a Ce oxide but also a complex oxide with another element. Examples of such Ce oxide include Ce-Zr composite oxide and Al-
Oxides such as Ce-Zr composite oxide and Y-Ce-Zr composite oxide can be given.

Further, the washcoat slurry may contain an additive contained in a general support layer of an exhaust gas purifying catalyst. Examples of such additives include additives such as La salts.

The coating amount of the rear supporting layer in the rear portion is preferably 1.3 to 25 times the coating amount of the front portion.

The rear part has a volume ratio of 1 to 15 with the front part.
Preferably it is twice. The rear portion is a portion that imparts ternary purification performance to the exhaust gas purification catalyst, and a sufficient purification performance can be exhibited by setting the volume of the rear portion to 1 to 15 times the volume of the front portion. . Here, the volume ratio between the rear part and the front part can be determined by taking the ratio of the axial length of the rear part and the front part when the shape of the catalyst carrier is a rod having the same diameter.

The catalytic noble metal is preferably at least one of Pt, Pd and Rh. That is, ternary catalytic performance can be imparted to the rear portion by using at least one of Pt, Pd, and Rh as the catalytic noble metal for imparting catalytic activity to the rear portion.

(Catalyst temperature rise) The decrease in the heat capacity of the catalyst by reducing the coating amount of the front-side washcoat slurry in the front portion, and the fact that the catalyst activation temperature can be quickly reached is explained by the washcoat in the front portion. Using the exhaust gas purifying catalyst in which the slurry coating amount was changed, the ease with which the catalyst bed temperature rose was measured, and the measurement results are shown in FIG.

The catalyst bed temperature was measured by preparing exhaust gas purifying catalysts having different washcoat slurry coating amounts on the front part, and measuring the relationship between the gas input temperature and the catalyst bed temperature using each catalyst.

That is, three types of exhaust gas purifying catalysts formed by coating the wash coat slurry at 50 g / L, 150 g / L and 250 g / L on the front-side supporting layer of the front portion were prepared, and these exhaust gas purifying catalysts were produced. The catalyst bed temperature when exhaust gas from the engine was introduced into the catalyst for use was measured.

Here, the exhaust gas purifying catalyst used for the measurement was a monolith type catalyst having an axial length of 100 mm, and the front part and the rear part were formed at a volume ratio of 1: 4. . That is, 20 upstream of the exhaust gas purifying catalyst.
The front part was formed at 80 mm, and the rear part was formed at 80 mm on the downstream side. In addition, the front portion was coated with 50 g / L, 150 g / L and 250 g / L of the slurry composed of Al ₂ O _3.
And a Pd supported on the front-side supporting layer at 10 g / L, and the rear portion is composed of Al ₂ O ₃ and Ce oxide in a weight ratio of 8: 5. The rear supporting layer coated with the slurry having a ratio of 195 g / L and the rear supporting layer had 1.5 g / L and 0.1 g / L, respectively.
It was formed from Pt and Rh supported at 3 g / L.

(Evaluation Test) Exhaust gas purifying catalysts having different coating amounts of the washcoat slurry on the front-side support layer were mounted on an actual vehicle testing machine (displacement: 2.2 l), and the testing machine was operated. And the catalyst bed temperature were measured. The measurement results are shown in FIG. Here, the measurement site of the catalyst bed temperature was the temperature at the axial center of the exhaust gas purifying catalyst.

The running condition of the actual vehicle running test machine was an idling state for 22 to 23 seconds from the start, and the running state indicated by the vehicle speed thereafter was the running state specified in the LA # 4 mode. .

FIG. 1 shows that the smaller the amount of the washcoat slurry in the front portion, the higher the catalyst bed temperature. In other words, the smaller the coating amount of the washcoat slurry, the lower the heat capacity of the catalyst, indicating that the temperature can quickly reach the catalyst activation temperature.

For this reason, the exhaust gas purifying catalyst of the present invention comprises:
Even when the exhaust gas temperature is low, such as when the engine is started, the components such as HC can be purified by quickly reaching the catalyst activation temperature.

(Production of Exhaust Gas Purifying Catalyst) The exhaust gas purifying catalyst of the present invention can be produced, for example, by the following production method. At this time, the method for producing the exhaust gas purifying catalyst of the present invention is not limited to the following method.

The exhaust gas purifying catalyst of the present invention can be manufactured by forming a front portion from one end face side and a rear portion from the other end face side on the surface of the catalyst carrier base material.

More specifically, a wash coat slurry containing Al ₂ O ₃ for forming a front-side support layer is coated at a predetermined coating amount from one end face side of the catalyst carrier substrate, and then dried, fired, and dried. P on the rear support layer
The front portion is formed by arranging Pd on the front-side support layer by using a method such as impregnation with d solution, drying and firing.

Subsequently, a wash coat slurry containing Al ₂ O ₃ and Ce oxide is coated on the monolith honeycomb carrier from the end side where the front side support layer is not formed, and dried and fired to form a rear support. After forming the layer,
The rear noble metal solution is contacted with the catalyst noble metal solution, the catalytic noble metal is disposed on the rear noble metal layer using a method such as impregnation, and the rear portion is formed by drying and calcining. The catalyst can be manufactured.

The supporting of the catalyst noble metal may be carried out by a method of impregnating the rear supporting layer with a mixed solution of a plurality of kinds of catalyst noble metals, or by a method of separately supporting each catalyst noble metal.

In the exhaust gas purifying catalyst of the present invention, since the heat capacity of the front portion is formed smaller than the heat capacity of the rear portion, the temperature of the front portion can be quickly raised to a temperature at which catalytic activity is exhibited. Further, since Pd, which exhibits catalytic activity even at a relatively low temperature, is used for the front portion, exhaust gas can be sufficiently purified even when the temperature of the catalyst is low, such as when starting the engine.

[0042]

The present invention will be described below with reference to examples.

As an example of the present invention, an exhaust gas purifying catalyst was manufactured.

Example 1 An exhaust gas purifying catalyst of Example 1 is a catalyst having a monolith honeycomb carrier, a front portion formed at one end of the monolith honeycomb carrier, and a rear portion formed at the other end. is there. The front and rear portions inside the monolith honeycomb carrier are formed such that their ends are in contact with each other. This exhaust gas purifying catalyst is shown in FIG.

More specifically, the monolith honeycomb carrier has a front part formed with a width of 20 mm from one end face and a rear part formed with a width of 80 mm from the other end face. At this time, the volume of the rear part is
It was four times the volume of the front part.

The monolith honeycomb support is a columnar catalyst support substrate formed of cordierite and having a diameter of 93 mm, a length of 100 mm, and a capacity of 0.679 L.

The front portion has a front support layer formed with a width of 20 mm from one end face of the monolith honeycomb carrier, and a Pg supported on the front support layer at 10 g / L.
d.

The front support layer was formed by coating a wash coat slurry of Al ₂ O ₃ at 50 g / L.

The rear portion is composed of a rear support layer formed with a width of 80 mm from the other end face of the monolith honeycomb carrier, and a catalytic noble metal supported on the rear support layer.

The rear support layer was formed by coating a rear washcoat slurry obtained by mixing Al ₂ O ₃ and Ce oxide at a weight ratio of 8: 5 at 195 g / L.

The exhaust gas purifying catalyst of Example 1 was produced by the following procedure.

First, after a front side supporting layer was formed on the surface of the monolith honeycomb carrier, a front portion was formed by supporting Pd.

More specifically, 100 g of γ-alumina powder, 3 g of boehmite powder, and 40%
A front-side washcoat slurry mixed at a ratio of 5 g and pure water 110 g was prepared, and this slurry was placed 20 m from the end face on one end side of the surface of the monolith honeycomb carrier.
After coating with alumina at 50 m / L in a width of m, drying and firing were performed to form a front-side support layer.

Subsequently, Pd was carried on the front carrier layer. Pd was loaded by contacting and impregnating the front loading layer with a Pd solution. Specifically, 85g /
After the front-side supporting layer was contact-impregnated with an aqueous Ld Pd solution, it was dried and fired, whereby Pd was supported on the front portion at a rate of 10 g / L.

Subsequently, a rear portion was formed at the other end where the front portion was not formed. The rear portion is formed by forming Pt and R on the rear support layer after forming the rear support layer.
h.

Specifically, 100 g of γ-alumina powder, 3 g of boehmite powder, aluminum nitrate nonahydrate 40% 65
g, Ce-Zr composite oxide 65 g, La carbonate carbonate crystal 30 g
Then, a rear washcoat slurry mixed at a ratio of 110 g of pure water was prepared, and this slurry was coated at 195 g / L from the other end face of the monolith honeycomb carrier having the front portion so as not to overlap the front portion. After drying and firing, a rear-side support layer was formed.

Subsequently, Pt and Rh are added to the rear support layer.
Was carried. Pt and Rh were loaded by loading Rh on the rear support layer and then loading Rh. Specifically, after the rear support layer is brought into contact with and impregnated with a 0.76 g / L Pt solution, drying and firing are performed. Subsequently, after contacting and impregnating the rear-side support layer with a 0.15 g / L Rh solution, the rear part was dried and calcined, whereby Pt was added to the rear part at a ratio of 1.5 g / L, and 0.4 g / L of 0.4 g / L. R in percentage
h was carried.

Comparative Example 1 Comparative Example 1 was performed except that the coating amount of the front washcoat slurry of the front support layer was the same as that of the rear washcoat slurry of the rear support layer. This is the same exhaust gas purifying catalyst as in Example 1. At this time, the coating amount of the rear-side wash coat slurry on the rear-side supporting layer, the Pd supported on the front-side supporting layer, and the supported amounts of Pt and Rh supported on the rear-side supporting layer were determined according to Example 1. It was the same amount as the catalyst.

More specifically, Comparative Example 1 includes a front-side supporting layer formed by coating the surface of a monolith honeycomb carrier with a front-side washcoat slurry at 195 g / L;
Pd supported at 10 g / L on the front support layer, and 1
A rear-side support layer formed by coating the rear-side wash coat slurry at 95 g / L,
An exhaust gas purifying catalyst comprising Pt supported at a supported amount of g / L and Rh supported at a supported amount of 0.3 g / L.

The exhaust gas purifying catalyst of Comparative Example 1 is the same as that of Example 1.
The catalyst was manufactured using the same material as that used in the manufacture of the exhaust gas purifying catalyst.

In the preparation of Comparative Example 1, the front side support layer was formed by coating the front side wash coat slurry at 195 g / L on the surface of the monolith honeycomb carrier, and then Pd was supported at a support amount of 10 g / L. It was done by. The coating of the front-side washcoat slurry and the loading of Pd were performed in the same manner as in the method for manufacturing the exhaust gas purifying catalyst of Example 1.

Thereafter, a rear portion was formed in the same manner as in Example 1. That is, the coat amount of the rear-side wash coat slurry and the carried amounts of Pt and Rh were formed to have the same values as those of the exhaust gas purifying catalyst of Example 1.

By the above procedure, the exhaust gas purifying catalyst of Comparative Example 1 was produced.

(Comparative Example 2) Comparative Example 2 was the same as Example 1, except that the coating amount of the wash coat slurry of the rear support layer was the same as that of the front support layer. It is a catalyst. At this time, the coating amount of the washcoat slurry on the front-side supporting layer, the Pd supported on the front-side supporting layer and the supported amounts of Pt and Rh supported on the rear-side supporting layer are the same as those of the exhaust gas purifying catalyst of Example 1. The same amount.

More specifically, Comparative Example 2 includes a front support layer in which a monolith honeycomb carrier surface is coated with a front washcoat slurry at 50 g / L, a Pd supported on the front support layer at 10 g / L, The rear-side support layer coated with 50 g / L of the rear-side washcoat slurry, Pt supported on the rear-side support layer at a load of 1.5 g / L, and Pt supported on the rear-side support layer at a load of 0.3 g / L R
h.

The exhaust gas purifying catalyst of Comparative Example 2 is the same as that of Example 1.
The catalyst was manufactured using the same material as that used in the manufacture of the exhaust gas purifying catalyst.

The exhaust gas purifying catalyst of Comparative Example 2 was manufactured by forming a front portion by the same means as in Example 1 and then forming a rear portion in which the amount of the wash coat slurry on the rear side was reduced. Was.

The front part was formed by using the method of forming the front part in the first embodiment. That is, the coating amount of the front-side washcoat slurry is 50 g / L, P
The formed amount of d was 10 g / L.

The rear portion was formed by coating a rear washcoat slurry at 50 g / L on the end of the monolith honeycomb carrier where the front portion was not formed to form a rear support layer. 1.5 g / L,
The loading was performed at a loading of 0.3 g / L.

By the above procedure, the exhaust gas purifying catalyst of Comparative Example 2 was produced.

(Example 2) In Example 2, the amount of Pt carried on the rear portion was 1.5 g / L,
Is an exhaust gas purifying catalyst similar to that of Example 1 except that 0.5 g / L was supported.

Specifically, in Example 2, a monolith honeycomb carrier surface was coated with a front washcoat slurry at 50 g / L and a front support layer was coated with Pd supported at 10 g / L on the front support layer. 195g / L
, A Pt supported on the rear support layer at a load of 1.0 g / L, and a Rh supported at a load of 0.3 g / L on the rear support layer.
And Pd supported at a supported amount of 0.5 g / L.

The exhaust gas purifying catalyst of the second embodiment is the same as that of the first embodiment.
The catalyst was manufactured using the same material as that used in the manufacture of the exhaust gas purifying catalyst.

In the preparation of the exhaust gas purifying catalyst of the second embodiment, a front portion is formed by the same means as in the first embodiment, and then a rear portion supporting Pt, Rh and Pd is formed on the rear supporting layer. It was done by.

The front portion was formed by using the method of forming the front portion in the first embodiment. That is, the coating amount of the front-side washcoat slurry is 50 g / L, P
The formed amount of d was 10 g / L.

The rear portion was formed by coating a rear washcoat slurry at 195 g / L on the end of the monolith honeycomb carrier where the front portion was not formed to form a rear support layer. 1.0 g of Pd
/ L, 0.3 g / L, and 0.5 g / L. The loading of Pt, Rh and Pd was carried out by separately loading Pt, Rh and Pd on the rear support layer in the order of Pt, Rh and Pd. Specifically, Pt
After contacting and impregnating the rear support layer with the solution, drying and firing are performed. Subsequently, the rear support layer is brought into contact with the Rh solution,
After impregnation, drying and firing were performed, and then the rear side support layer was brought into contact with and impregnated with a Pd solution, followed by drying and firing, whereby Pt, Rh and Pd were supported on the rear portion.

By the above procedure, the exhaust gas purifying catalyst of Comparative Example 2 was produced.

(Comparative Example 3) Comparative Example 3 was the same as Example 2 except that the washcoat slurry of the front support layer was coated in the same amount as the rear support layer. It is a catalyst.

More specifically, in Comparative Example 3, a monolith honeycomb carrier surface was coated with a front-side washcoat slurry at 195 g / L with a front-side washcoat slurry, Pd supported at 10 g / L on the front-side support layer, and 195g /
L, a rear support layer coated with the rear wash coat slurry, Pt supported on the rear support layer at a load of 1.0 g / L, and R supported at a load of 0.3 g / L on the rear support layer.
h and Pd supported at a loading of 0.5 g / L.

The preparation of the exhaust gas purifying catalyst of Comparative Example 3 was carried out by setting the coating amount of the front-side washcoat slurry to 195.
It was produced in the same manner as in Example 2 except that g / L was used. At this time, the exhaust gas purifying catalyst of Comparative Example 3 was produced using the same material as that used for producing the exhaust gas purifying catalyst of Example 2.

Example 3 In Example 3, the washcoat slurry amount of the front support layer was 20 g / g.
L, an exhaust gas purifying catalyst similar to that of Example 1, except that the coating amount of the washcoat slurry of the rear-side support layer was 215 g / L.

More specifically, in Example 3, the monolith honeycomb carrier was coated with a front-side washcoat slurry at 50 g / L at a front-side washcoat slurry, and was supported at 10 g / L on the front-side support layer. Pd and 21
A rear-side support layer formed by coating the rear-side washcoat slurry at 5 g / L;
/ Pt supported at a supported amount of / L and Rh supported at a supported amount of 0.3 g / L.

In the preparation of the exhaust gas purifying catalyst of Example 3, the coating amount of the front-side washcoat slurry of the front-side support layer was set to 20 g / L, and the coating amount of the rear-side washcoat slurry of the rear-side support layer was set to 215 g / L. Except for changing to L, it was produced in the same manner as in Example 1. At this time,
The exhaust gas purifying catalyst of Example 3 was manufactured using the same materials as those used for manufacturing the exhaust gas purifying catalyst of Example 1.

Comparative Example 4 Comparative Example 4 was performed except that the coating amount of the front washcoat slurry of the front support layer was the same as that of the rear washcoat slurry of the rear support layer. This is the same exhaust gas purifying catalyst as in Example 3.

More specifically, Comparative Example 4 includes a front-side supporting layer formed by coating the surface of a monolith honeycomb carrier with a front-side washcoat slurry at 215 g / L;
Pd supported at 10 g / L on the front support layer;
The rear-side support layer formed by coating the rear-side wash coat slurry at 15 g / L, and the rear-side support layer
An exhaust gas purifying catalyst comprising Pt supported at a supported amount of g / L and Rh supported at a supported amount of 0.3 g / L.

The exhaust gas purifying catalyst of Comparative Example 4 was produced in the same manner as in Example 3 except that the coating amount of the front washcoat slurry of the front support layer was 215 g / L. At this time, the exhaust gas purifying catalyst of Comparative Example 4 was manufactured using the same material as that used for manufacturing the exhaust gas purifying catalyst of Example 3.

(Comparative Example 5) Comparative Example 5 was the same as Example 3 except that the coat amount of the wash coat slurry of the rear support layer was the same as the coat amount of the front support layer. It is a catalyst.

More specifically, in Comparative Example 5, the front side support layer in which the surface of the monolith honeycomb carrier was coated with the front side wash coat slurry at 20 g / L, Pd supported on the front side support layer at 10 g / L, The rear-side support layer coated with the rear-side washcoat slurry at 20 g / L, the Pt supported on the rear-side support layer at a support amount of 1.5 g / L, and the Pt supported at a support amount of 0.3 g / L. R
h.

The catalyst for purifying exhaust gas of Comparative Example 5 was produced in the same manner as in Example 3 except that the coating amount of the rear washcoat slurry of the rear support layer was changed to 20 g / L. At this time, the exhaust gas purifying catalyst of Comparative Example 5 was:
The catalyst was manufactured using the same material as that used for manufacturing the exhaust gas purifying catalyst of Example 3.

Example 4 In Example 4, the coating amount of the washcoat slurry of the front support layer was 150 g /
Except for L, the exhaust gas purifying catalyst was the same as in Example 1.

More specifically, Example 4 shows that a monolith honeycomb carrier surface was coated with a front washcoat slurry at 150 g / L and a front support layer was coated with Pd supported at 10 g / L on the front support layer. 195g /
A rear support layer coated with the rear washcoat slurry with L, Pt supported on the rear support layer at a load of 1.5 g / L, and Rh supported at a load of 0.3 g / L. And an exhaust gas purifying catalyst comprising:

The exhaust gas purifying catalyst of Example 4 was prepared in the same manner as in Example 1 except that the coating amount of the rear washcoat slurry of the rear support layer was 195 g / L. At this time, the exhaust gas purifying catalyst of Example 4 was manufactured using the same material as that used for manufacturing the exhaust gas purifying catalyst of Example 1.

Comparative Example 6 Comparative Example 6 was performed except that the coating amount of the front washcoat slurry of the front support layer was the same as that of the rear washcoat slurry of the rear support layer. This is the same exhaust gas purifying catalyst as in Example 4.

More specifically, Comparative Example 6 includes a front-side support layer formed by coating the surface of a monolith honeycomb carrier with a front-side washcoat slurry at 195 g / L;
Pd supported at 10 g / L on the front support layer, and 1
A rear-side support layer formed by coating the rear-side wash coat slurry at 95 g / L,
An exhaust gas purifying catalyst comprising Pt supported at a supported amount of g / L and Rh supported at a supported amount of 0.3 g / L.

The catalyst for purifying exhaust gas of Comparative Example 6 was produced in the same manner as in Example 4, except that the coating amount of the front washcoat slurry of the front support layer was 195 g / L. At this time, the exhaust gas purifying catalyst of Comparative Example 6 was produced using the same material as that used for producing the exhaust gas purifying catalyst of Example 4.

Example 5 Example 5 is an exhaust gas purifying catalyst in which both the coating amount of the wash coat slurry of the rear supporting layer and the coating amount of the front supporting layer are coated at 150 g / L.

More specifically, Comparative Example 7 includes a front-side support layer in which the surface of a monolith honeycomb carrier is coated with a front-side washcoat slurry at 150 g / L, a Pd supported on the front-side support layer at 10 g / L, 150g /
A rear support layer coated with the rear washcoat slurry with L, Pt supported on the rear support layer at a load of 1.5 g / L, and Rh supported at a load of 0.3 g / L. And an exhaust gas purifying catalyst comprising:

The exhaust gas purifying catalyst of Example 5 was produced in the same manner as in Example 4 except that the coating amount of the rear washcoat slurry of the rear support layer was 150 g / L. At this time, the exhaust gas purifying catalyst of Example 5 was manufactured using the same material as that used for manufacturing the exhaust gas purifying catalyst of Example 4.

Example 6 Example 6 is an exhaust gas purifying catalyst similar to Example 1, except that the volume ratio between the front part and the rear part was 1: 9.

Specifically, in the sixth embodiment, the length in the axial direction is 1
An exhaust gas purifying catalyst comprising a front portion formed with a width of 10 mm from one end face of a cylindrical monolith honeycomb carrier of 00 mm, and a rear portion formed with a width of 90 mm from the other end face. At this time, the front portion is composed of a front supporting layer in which the surface of the monolith honeycomb carrier is coated with the front wash coat slurry at 50 g / L, and Pd supported on the front supporting layer at 10 g / L, The part is a rear support layer coated with 150 g / L of the rear washcoat slurry, a Pt supported on the rear support layer at a load of 1.5 g / L, and a load of 0.3 g / L. Supported Rh,
Consists of

The exhaust gas purifying catalyst of Example 6 was manufactured in the same manner as in Example 1 except that the front portion was formed to have a length of 10 mm from the end face and the rear portion was formed to be 90 mm from the end face. The same was done.

That is, the front side wash coat slurry is coated on one end side of the surface of the monolith honeycomb carrier with alumina so as to have a width of 10 mm from the end face so as to be 50 g / L with alumina, and then dried and calcined. A side support layer was formed.

Subsequently, Pd was supported on the front support layer. Pd was loaded by contacting and impregnating the front loading layer with a Pd solution.

Thereafter, a rear portion was formed at the other end where the front portion was not formed. The rear portion is formed by forming Pt and Rh on the rear support layer after forming the rear support layer.
Was carried out.

More specifically, 195 g of the wash wash slurry on the rear side is applied to the monolith honeycomb carrier having the front portion so as not to overlap the front portion from the other end face of the monolith honeycomb carrier.
After coating with L, drying and firing were performed to form a rear-side support layer.

Subsequently, Pt and Rh are added to the rear supporting layer.
Was carried. Pt and Rh were carried by the same means as in Example 1.

By the above procedure, the exhaust gas purifying catalyst of Example 6 was produced.

Comparative Example 7 Comparative Example 7 was carried out except that the coating amount of the front washcoat slurry of the front support layer was the same as that of the rear washcoat slurry of the rear support layer. This is the same exhaust gas purifying catalyst as in Example 6.

More specifically, Comparative Example 7 includes a front-side carrier layer formed by coating a monolith honeycomb carrier surface with an axial coat length of 10 mm and a front-side washcoat slurry at 195 g / L; Pd supported on the support layer at 10 g / L, a coat length of 90 mm in the axial direction, and 1
A rear support layer formed by coating at 95 g / L, Pt supported on the rear support layer at a support amount of 1.5 g / L, and Rh supported at a support amount of 0.3 g / L; An exhaust gas purifying catalyst comprising:

The catalyst for purifying exhaust gas of Comparative Example 7 was produced in the same manner as in Example 6, except that the coating amount of the front washcoat slurry of the front support layer was 195 g / L. At this time, the exhaust gas purifying catalyst of Comparative Example 6 was produced using the same material as that used for producing the exhaust gas purifying catalyst of Example 6.

Table 1 shows the types of the exhaust gas purifying catalysts of Examples 1 to 6 and Comparative Examples 1 to 7.

[0112]

[Table 1]

(Evaluation) The evaluation of the exhaust gas purifying catalyst was performed by operating the engine while actually mounted on the vehicle and purifying the exhaust gas discharged from the engine.

The test method was as follows: First, an endurance test was conducted by flowing a test gas at 900 ° C. for 50 hours to the exhaust gas purifying catalysts of Examples and Comparative Examples. This test gas was exhaust gas when an engine mounted on an actual vehicle was operated at 3000 rpm.

The exhaust gas purifying catalyst subjected to the durability test was mounted on an actual vehicle (displacement: 2.2 l) such that the front portion was on the upstream side of the exhaust gas, that is, on the engine side. Thereafter, the engine of the actual vehicle is operated to purify the exhaust gas discharged from the engine, and the amount of HC component and the amount of N contained in the exhaust gas discharged from the exhaust gas purifying catalyst are reduced.
Evaluation was performed by measuring the amount of the Ox component.

Amount of HC component contained in exhaust gas and NO
The measurement of the amount of the x component was performed by sampling from a tail pipe using a chassis dynamo and performing measurement by an analyzer for automobile exhaust gas. The test conditions of the actual vehicle were performed in the LA # 4 mode.

The test results are shown in FIGS. 3, 4 and Table 2. Here, FIG. 3 shows the measured amount of HC in the exhaust gas, and FIG.
Indicates the measured amount of NOx. Table 2 shows specific measured values. Table 2 shows the measured amounts of the HC component and the NOx component, but since the LA # 4 mode (authentication mode in the United States) was used, the value of g / mile is also shown as a reference value.

[0118]

[Table 2]

3 and 4 and Table 2 show that the measured values of HC and NOx of the exhaust gas purifying catalyst of Example 1 are both low and have excellent HC and NOx purifying ability.

The exhaust gas purifying catalyst of Comparative Example 1 in which the coating amount of the front and rear wash coat slurries is excessive is excellent in NOx purifying ability, but the measured value of HC is 0.027 g / km ( 0.043g / mile)
And is higher. Comparative Example 2 in which the coating amount of the washcoat slurry on the front side and the rear side was small.
The exhaust gas purifying catalyst of No. 1 has a high HC purifying ability, but has a low NOx purifying ability.

In Example 2, the catalyst noble metal in the rear portion was Pt,
The exhaust gas purifying catalyst was Rh and Pd. Even when Pd was added, the measured values of HC and NOx were both low.
It turns out that it has excellent C and NOx purification ability.

Comparative Example 3 is excellent in NOx purifying ability but high in the measured value of HC because the coat amounts of the washcoat slurry on the front side and the rear side are excessive.

Example 3 is an exhaust gas purifying catalyst in which the coating amount in the front portion is reduced and the coating amount in the rear portion is increased. Even when the coating amount in the front portion is reduced, the measurement of HC and NOx is performed. The values are both low and H
It turns out that it has excellent C and NOx purification ability.

In Comparative Example 4, the amount of coating on the front portion was excessive, and the HC purification ability was reduced. In Comparative Example 5, since the amount of coating on the rear portion was small, the NOx purification ability was reduced.

Example 4 is an exhaust gas purifying catalyst in which the coating amount of the front portion is increased, and it can be seen that the catalyst has excellent HC and NOx purification performance even when the coating amount of the front portion increases.

In Comparative Example 6, since the coating amount at the front portion was excessive, the NOx purification ability was excellent but the HC purification ability was reduced.

Example 5 is an exhaust gas purifying catalyst in which the coating amounts of the front part and the rear part are both 150 g / L, and it can be seen that it is excellent in HC and NOx purifying ability.

The sixth embodiment is an exhaust gas purifying catalyst in which the volume ratio of the front portion and the rear portion is changed to reduce the volume ratio of the front portion. It turns out that it is excellent in NOx purification ability.

In Comparative Example 7, since the coating amount of the front part of the exhaust gas purifying catalyst of Example 6 was excessive, NOx
The purification ability is excellent, but the HC purification ability is reduced.

From this fact, if the amount of the supported catalyst is the same, the HC purifying ability is improved by reducing the coating amount of the front side wash coat slurry, and the coating amount of the rear side wash coat slurry is reduced. Is increased, the NOx purification ability becomes excellent.

In the exhaust gas purifying catalyst of the example, the coating amount of the front side wash coat slurry for forming the front side supporting layer of the front part is small, and the front part has excellent catalytic activity at low temperature. Since Pd is carried, the light-off performance is excellent.
In addition, since the rear-side support layer in the rear portion is formed of the rear-side wash coat slurry having a sufficient coating amount, the catalyst noble metal is sufficiently supported, and high NOx purification performance is maintained.

Since the exhaust gas purifying catalyst of the embodiment has a structure in which the front part and the rear part are integrally formed, even when actually mounted on a vehicle, the load of the engine is increased without increasing the load on the engine. It is an excellent exhaust gas purification catalyst.

[0133]

The exhaust gas purifying catalyst of the present invention has a low coating amount front portion having a small catalyst heat capacity. Therefore, even when the exhaust gas temperature is low, such as when the engine is started, the light-off performance is improved by easily raising the temperature of the front portion and quickly increasing to the catalyst activation temperature. Further, the P carried on the front part
The light-off performance is also improved because d has excellent catalytic activity at low temperatures. By improving the light-off performance, it is possible to sufficiently purify HC components generated in large amounts at low temperatures.

The exhaust gas purifying catalyst of the present invention has a structure in which the front part and the rear part are integrally formed.
There is no increase in the load on the engine when mounted on a vehicle. Further, since it is not necessary to increase the amount of expensive catalytic noble metal, an increase in cost of the exhaust gas purifying catalyst is suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of measuring the ease of raising the catalyst bed temperature depending on the coating amount of a front part.

FIG. 2 is a view showing an exhaust gas purifying catalyst of Example 1.

FIG. 3 is a diagram showing measured amounts of HC in exhaust gas.

FIG. 4 is a diagram showing measured amounts of NOx in exhaust gas.

Continued on front page F-term (reference) 4D048 AA06 AA13 AA18 AB01 AB02 AB05 BA03X BA08X BA18X BA19X BA30X BA31X BA33X BA41X BA42X BB02 BB16 CC46 4G069 AA08 BA01A BA01B BA05B BB02A BB02B BB04BBCBBC BCBC BCBC BCBC BC BC BC BC BC CA09 EA18 EA19 EA25 EB10 EB14Y EC28 EE09 FA06 FB15 FB23 FC08

Claims (3)

[Claims] 1. A catalyst carrier substrate having a tubular passage through which exhaust gas passes in the axial direction, and a wash coat slurry made of Al ₂ O _{3 on} the surface of the catalyst carrier substrate on the upstream side of the exhaust gas at 10 to 150 g / L
A front-side support layer formed by coating with the following, a Pd supported on the front-side support layer at 1 to 20 g / L, and a catalyst support base material downstream of the exhaust gas. a weight ratio Al ₂ O ₃ and Ce oxide on the surface 1: 1 to 20: the rear-side loading layer formed by coating a washcoat slurry 150 to 250 g / L with a ratio of 1, the rear A catalyst for purifying exhaust gas, comprising: a rear portion made of a catalyst noble metal supported on a side support layer. 2. The exhaust gas purifying catalyst according to claim 1, wherein the rear part has a volume ratio of 1 to 15 times the front part. 3. The catalyst noble metal comprises Pt, Pd and R
The exhaust gas purifying catalyst according to claim 1, which is at least one of h.