JPH10272357A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for purifying exhaust gas having excellent low temp. activity in all of exhaust compsn. atmospheres of car, and a method for producing the same. SOLUTION: The catalyst component layer of the catalyst for purifying exhaust gas has a multilayered structure wherein a first catalyst component layer composed of inorg. matter based on activated alumina is arranged and a second catalyst component layer containing palladium as a catalyst component is arranged on the first catalyst component layer and a third catalyst component layer containing rhodium as a catalyst component is arranged on the second catalyst component layer.

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 a method for producing the same, and more particularly, to hydrocarbons (hereinafter referred to as "HC") and monoxide in exhaust gas discharged from an internal combustion engine of an automobile. The present invention relates to an exhaust gas purifying catalyst excellent in low-temperature activity, capable of effectively purifying carbon (hereinafter, referred to as “CO”) and nitrogen oxides (hereinafter, referred to as “NOx”) even at low temperatures, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, during a low temperature period from the start of an internal combustion engine until the catalyst temperature reaches a reaction temperature for exhaust gas purification, the exhaust gas purification performance is not sufficient. The development of gas purification catalysts is expected.

As such an exhaust gas purifying catalyst, for example, Japanese Patent Publication No. 58-20307 and Japanese Patent Laid-Open No. 4-274 are disclosed.
And Japanese Patent Application Laid-Open No. 6-378.

[0004] The catalyst for purifying exhaust gas described in Japanese Patent Publication No. 58-20307 has a composition comprising platinum, rhodium and cerium supported on a refractory carrier.
Specifically, it has a structure in which a platinum group element such as platinum, palladium, and rhodium is supported on alumina, cerium oxide, or the like, and this is coated on a monolithic carrier.

[0005] Also, Japanese Patent Application Laid-Open No. 4-27430 discloses that
There has been proposed an exhaust gas purifying catalyst in which an intermediate layer of a cerium oxide layer is provided on the surface of a catalyst carrier, and different noble metal components are respectively supported on a lower layer and an upper layer of the intermediate layer. Specifically, the lower layer has palladium as a catalyst component, the middle layer has cerium oxide, and the upper layer has rhodium.

[0006] JP-A-6-378 discloses that activated alumina and cerium oxide are mixed with at least one of platinum and palladium as catalyst components and potassium as a basic element.
An exhaust gas purifying catalyst supporting an oxide of at least one metal selected from the group consisting of cesium, strontium and barium has been proposed. In other words, the catalyst is a platinum group element, activated alumina, cerium oxide, etc.
In addition to those conventionally used as catalyst components, at least one of potassium compounds, cesium compounds, strontium compounds and barium compounds, which are basic elements, is combined.

[0007]

However, the conventional catalyst described in the above publication uses a large amount of precious metal which is not abundant in resources and expensive in order to obtain sufficient catalytic activity from a low temperature. doing. Therefore, it is expected to develop a catalyst that has a sufficient purification ability even with a small amount of precious metal based on palladium, which is relatively inexpensive among precious metals, or a catalyst that uses as little as possible even when rhodium is used. I have. However, when palladium is used alone, there is a problem that the low-temperature activity deteriorates when the amount of palladium is reduced.

Accordingly, an object of the present invention is to provide an exhaust gas purifying catalyst having excellent low-temperature activity in all exhaust composition atmospheres of automobiles and a production thereof, even if the amount of noble metal used is significantly reduced as compared with conventional catalysts. It is to provide a method.

[0009]

The present inventors have conducted research to solve the above-mentioned problems. As a result, the present inventors have found that the upper layer contains a rhodium-containing catalyst component-supporting layer and the middle layer contains palladium and nickel at a fixed composition ratio. By using a catalyst component layer containing an alumina-based composite oxide as a multilayered catalyst in which a catalyst component layer composed of an inorganic substance containing activated alumina as a main component is arranged as a lower layer, the catalytic performance of palladium can be improved, and in a low temperature region It has been found that the catalytic activity of the compound of the present invention is significantly improved, and the present invention has been achieved.

The exhaust gas purifying catalyst according to claim 1 is
In a monolithic catalyst having a catalyst component supporting layer, the structure of the catalyst component layer of the exhaust gas purifying catalyst is such that a first catalyst component layer made of an inorganic material containing activated alumina as a main component is arranged,
A multilayer structure in which a second catalyst component layer containing palladium as a catalyst component is disposed above the first catalyst component layer, and a third catalyst component layer containing rhodium as a catalyst component is disposed above the second catalyst component layer. It is a catalyst.

[0011] In the exhaust gas purifying catalyst according to claim 1, the first catalyst component layer is 20 to 1 in 1 liter volume of the catalyst.
100 g. If the amount is less than 20 g / l, a sufficient effect of improving the catalyst performance cannot be obtained.
Even when the value exceeds, the effect of improving the catalyst performance is saturated, or conversely, the catalyst performance is reduced.

In the exhaust gas purifying catalyst according to the second aspect, nickel aluminate is contained in order to improve the catalytic performance of palladium in an oxygen-deficient atmosphere and near a stoichiometric air-fuel ratio.

Further, the exhaust gas purifying catalyst according to claim 2 is selected from the group consisting of lanthanum, neodymium and zirconium in order to suppress sintering (particle growth) of palladium carried on the alumina-based composite oxide. A cerium oxide containing 1 to 40 mol% of at least one of the above compounds in terms of metal and 60 to 98 mol% of cerium is contained.

The exhaust gas purifying catalyst according to claim 3 is
To further increase the low-temperature activity of rhodium, lanthanum,
Zirconium oxide containing 1 to 40 mol% of at least one metal selected from the group consisting of neodymium and cerium in terms of metal and 60 to 98 mol% of zirconium is contained.

Furthermore, in order to further enhance the low-temperature activity of the exhaust gas purifying catalyst according to the first aspect and the catalytic activity in an oxygen-deficient (reducing) atmosphere, the second aspect of the exhaust gas purifying catalyst according to the first aspect. The catalyst component layer further contains at least one selected from the group consisting of an alkali metal and an alkaline earth metal.

The noble metals contained in the catalyst component-supporting layer of the exhaust gas purifying catalyst of the present invention include palladium and rhodium. The content of the palladium is 0.1 to 20 g per liter of the catalyst. If the amount is less than 0.1 g / l, the low-temperature activity and purification performance are not sufficiently exhibited.
If the amount exceeds g / l, the dispersibility of palladium becomes poor, the catalyst performance is not significantly improved, and it is not economically effective.

As the substrate on which the palladium is supported, an alumina-based composite oxide is suitable in order to improve the catalytic performance of palladium. In particular, nickel aluminate is contained in order to enhance the low-temperature activity and purification performance of palladium (particularly, NOx steady-state conversion performance in an oxygen-deficient atmosphere and near the stoichiometric air-fuel ratio). The amount of the alumina-based composite oxide used is 10 to 200 g per liter of the catalyst. If it is less than 10 g / l, a sufficient effect of improving the catalytic performance cannot be obtained, and if it exceeds 200 g / l, the effect of improving the catalytic performance is saturated or, conversely, the catalytic performance decreases.

Further, the exhaust gas purifying catalyst according to claim 2 further contains cerium oxide. The cerium oxide contains at least one element selected from the group consisting of lanthanum, neodymium and zirconium in an amount of 1 to 40 mol% in terms of metal and 60 to 98 mol% of cerium. The reason for setting the content to 1 to 40 mol% is that at least one element selected from the group consisting of lanthanum, neodymium and zirconium is added to cerium oxide (CeO ₂ ) and the oxygen storage capacity of cerium oxide and BET
It significantly improves specific surface area and thermal stability. If it is less than 1 mol%, it is not different from the case of only cerium oxide,
The effect of adding the above-mentioned elements does not appear, and if it exceeds 40 mol%, this effect is saturated or conversely decreases.

The alkali metals and / or alkaline earth metals used include lithium, potassium, cesium, magnesium, calcium, strontium and barium. Its content is 1 to 1 liter of catalyst.
40 g. If it is less than 1 g / l, adsorption poisoning of hydrocarbon species and sintering of palladium cannot be suppressed, and if it exceeds 40 g / l, a significant effect of increasing the amount cannot be obtained, and consequently the performance is deteriorated.

Further, in the catalyst for purifying exhaust gas according to the third aspect, the catalyst component-supporting layer contains rhodium and alumina powder. The content of rhodium is 0.1% in 1 liter volume of the catalyst.
When the amount is less than 0.001 g / l, the effect of rhodium on improving the low-temperature activity is not sufficiently exhibited.
If the amount exceeds g / l, the dispersibility of rhodium becomes poor, and the low-temperature activity performance of rhodium is not significantly improved and is not effective.

As the substrate on which the rhodium is supported,
In order to increase the dispersibility of rhodium and improve catalyst performance,
Alumina containing zirconium is suitable. Especially,
The alumina powder contains 0.1 to 10 mol% of zirconium in terms of metal in order to suppress rhodium from dissolving in alumina at high temperature and increase durability. If zirconium is less than 0.1 mol%, the effect of improving zirconium added to alumina cannot be obtained, and alumina (Al
₂ O ₃₎ and unchanged, also to lower the physical properties of the specific surface area of the alumina exceeds 10 mol%, the dispersibility of the noble metal is deteriorated, not sufficient performance can be obtained. The amount of the alumina powder used is 1 to 10 per liter of the catalyst.
0 g. If it is less than 1 g / l, no sufficient dispersibility of the noble metal can be obtained, and if it is more than 100 g / l, no remarkable improvement in performance is observed.

Further, the exhaust gas purifying catalyst according to claim 3 contains zirconium oxide. The zirconium oxide contains at least one element selected from the group consisting of lanthanum, neodymium and cerium in an amount of 1 to 40 mol% in terms of metal, and zirconium in an amount of 60 to 98%.
Mol%. The content of 1 to 40 mol% is determined by adding at least one element selected from the group consisting of lanthanum, neodymium, and cerium to zirconium oxide (ZrO ₂ ), and adding oxygen storage capacity and BET specific surface area of the zirconium oxide. , To significantly improve the thermal stability. If it is less than 1 mol%, the effect of adding the above-mentioned elements does not appear as in the case of zirconium oxide alone,
If it exceeds mol%, this effect is saturated or conversely decreases.

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

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

The amount of the catalyst component coat layer adhered to the honeycomb material is preferably 50 to 400 g per liter of the catalyst in total of the entire catalyst components. The more catalyst components, the more
Although preferable in terms of catalyst activity and catalyst life, if the coating layer is too thick, reactive gases such as HC, CO, and NOx will be poorly diffused. The effect is saturated, and the gas passage resistance is increased. Therefore, the amount of the coating layer is 50 to 400 g per liter of the catalyst.
Is preferred.

More preferably, the obtained exhaust gas purifying catalyst can be impregnated and supported with an alkali metal and an alkaline earth metal. Alkali metals and alkaline earth metals that can be used include lithium, sodium,
It is one or more elements selected from the group consisting of potassium, cesium, magnesium, calcium, strontium, and barium.

The alkali metal and alkaline earth metal compounds which can be used include oxides, acetates, hydroxides, nitrates,
It is water-soluble such as carbonate. This makes it possible to carry the alkali metal and / or alkaline earth metal as a basic element in the vicinity of palladium with good dispersibility.
At this time, the starting compounds of the alkali metal and the alkaline earth metal may be contained simultaneously or separately.

That is, an aqueous solution of a powder comprising an alkali metal compound and / or an alkaline earth metal compound is impregnated into the above-mentioned carrier carrying a washcoat component, dried, and then dried under air and / or under a stream of air for 200 to 200 hours. It is baked at 600 ° C. This is because, once the alkali metal and alkaline earth metal raw material compounds are heat-treated at a low temperature and contained in the coat layer in the form of an oxide, it becomes difficult to form a composite oxide even when exposed to a high temperature later. If the calcination temperature is lower than 200 ° C., the alkali metal compound and the alkaline earth metal compound cannot be sufficiently converted into an oxide form. If the calcination temperature exceeds 600 ° C., the raw material salt is rapidly decomposed, and However, it is not preferable because it may crack.

[0029]

In an integrated structure type catalyst having a catalyst component supporting layer, the structure of the catalyst component layer of the exhaust gas purifying catalyst is such that a first catalyst component layer made of an inorganic material containing activated alumina as a main component is disposed. By forming a second catalyst component layer containing palladium as a catalyst component above the component layer and a third catalyst component layer containing rhodium as a catalyst component above the second catalyst component layer, to form a multilayer structure. In addition, the gas diffusion property to the catalyst component layer containing palladium and nickel aluminate powder, which is an exhaust gas purification catalyst, is maintained, and the amount of heat applied to the catalyst component layer containing palladium and nickel aluminate powder is reduced. Therefore, sintering of palladium is suppressed, and the durability of palladium is improved. In addition, since the first catalyst component layer contains activated alumina as a main component, the heat of reaction due to the oxidation reaction in the first catalyst component layer can be suppressed, so that the deterioration of the second catalyst component layer due to the heat of reaction proceeds. Can be suppressed. In addition, when the alumina layer is disposed between the rhodium layer and the palladium layer, the gas diffusion into the palladium layer is impaired, so that the catalytic performance is reduced.

Further, the catalyst for purifying exhaust gas according to claim 2 is characterized in that the catalyst component supporting layer further contains cerium oxide containing at least one selected from the group consisting of lanthanum, neodymium and zirconium. In order to make the oxidation state of palladium suitable for exhaust gas purification, cerium oxide with high oxygen storage capacity releases lattice oxygen and adsorbed oxygen in an oxygen-deficient (reducing) atmosphere and near the stoichiometric air-fuel ratio. It is possible to suppress a decrease in catalytic ability due to reduction. In addition, by contacting the nickel aluminate in the catalyst component-supporting layer, it is possible to suppress a decrease in catalytic ability due to reduction of the nickel aluminate.

Further, the exhaust gas purifying catalyst according to the second aspect of the present invention includes a powder in which rhodium is supported on zirconium-containing alumina powder, the palladium and nickel aluminate powders, and if necessary, cerium oxide. By containing the catalyst component in the catalyst component-supporting layer, the low-temperature activity and the purification performance in an oxygen-deficient atmosphere can be further improved.

Further, the exhaust gas purifying catalyst according to claim 3 is in close contact with an alkali metal and / or an alkaline earth metal together with the palladium, alumina-based composite oxide powder and, if necessary, cerium oxide. By doing so, an effect of improving the purification performance can be obtained. Alkali metals and alkaline earth metals have the ability to mitigate the poisoning of hydrocarbons,
When these are contained in the catalyst component supporting layer, sintering of palladium can be suppressed, and the activity in a low-temperature region and an oxygen-deficient atmosphere can be further improved.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of an exhaust gas purifying catalyst according to the present invention will be specifically described with reference to Examples, Comparative Examples and Test Examples.

Example 1 An aqueous solution obtained by dissolving 485 parts of nickel nitrate in 1000 parts of pure water was converted to alumina (Al).
After adding 1700 parts of alumina sol of 20% by weight in terms of ₂ O ₃ ) to a suspension in which 2500 parts of pure water was dispersed, 5% aqueous ammonia was added with stirring to adjust the pH to 8.0. After drying this solution at 150 ° C. for 24 hours, 400
The mixture was calcined at 2 ° C. for 2 hours, at 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours to obtain Ni _0.5 Al _2.0 O _x (powder A). This powder A was impregnated with an aqueous solution of palladium nitrate, dried, and calcined at 400 ° C. for 2 hours to obtain a Pd-supported nickel aluminate powder (powder C). The powder C had a Pd-supporting concentration of 2.0% by weight.

In 600 parts of activated alumina powder (powder C),
A nitric acid aqueous solution (600 parts) was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was attached to a cordierite-based monolithic carrier (1.3 liter, 400 cells), baked at 400 ° C. for 1 hour, and a coating layer weight of 80
g / l of catalyst (catalyst 1) were obtained.

350 parts of powder (powder D) supporting 2.0% by weight of palladium and 1 mol% of lanthanum (La ₂ O ₃
2% by weight) and 32 mol% of zirconium (Z
A nitric acid aqueous solution was added to 240 parts of powder (powder E) in which 0.75 parts by weight of palladium was supported on a cerium oxide powder containing 25% by weight in terms of rO ₂ and 10 parts of activated alumina.
0 parts were put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid is adhered to the catalyst 1 and 400
C. for 1 hour to obtain a catalyst (catalyst 2) having a total coat layer weight of 160 g / l and a palladium carrying amount of 40 g / cf (1.41 g / l).

Next, a barium acetate solution was adhered to the cordierite monolithic carrier (catalyst 2) supporting the catalyst component, and calcined at 400 ° C. for 1 hour to obtain BaO 15 g / l.
(Catalyst 3).

137 parts of zirconium oxyacetate was added to pure water 5
The resulting mixture was dissolved in 00 parts and impregnated into 1000 parts of activated alumina.
After drying this at 150 ° C. for 24 hours, it is baked at 400 ° C. for 2 hours, then at 1000 ° C. for 2 hours, and Zr 3 mol%
An added alumina powder (powder F) was obtained. A 3 mol% Zr-added alumina powder (powder F) is impregnated with an aqueous rhodium nitrate solution, dried and calcined at 400 ° C. for 2 hours to obtain a Rh-supported Z powder.
A 3 mol% added alumina powder (powder G) was obtained. The Rh-supporting concentration of the powder F was 1.40% by weight.

Zr carrying 1.40% by weight of rhodium
135 parts of 3 mol% added alumina powder (powder G) and Zr
Includes 450 parts of 3 mol% added alumina powder (powder F), 1 mol% of lanthanum (2 wt% in terms of La ₂ O ₃ ), and 20 mol% of cerium (13 wt% in terms of CeO ₂ ). To 400 parts of zirconium oxide powder (powder H) and 15 parts of activated alumina, 1000 parts of a nitric acid aqueous solution was charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This was coated with a coat layer having a weight of 175 g / l (80 g / l of a layer composed of an inorganic material containing activated alumina as a main component, 80 g / l of a palladium-containing coat layer, and 40 g / cf of palladium carrying amount).
(1.41 g / l) and the catalyst 1 (1.3 liter, 400 cells) carrying BaO 15 g / l), this slurry liquid was adhered, and calcined at 400 ° C. for 1 hour to obtain a total coat layer weight. 255 g / l (rhodium-containing catalyst component supporting layer 50 g / l), palladium carrying amount 40 g / cf (1.4
1 g / l), rhodium carrying amount 2 g / cf (0.071 g)
/ L) of a catalyst (catalyst 4).

Example 2 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the coating amount of the first catalyst component layer was changed to 20 g / l.

Example 3 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the coating amount of the first catalyst component layer was changed to 100 g / l.

Example 4 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the amount of barium acetate was changed and BaO was contained at 5 g / l.

Example 5 Example 1 was repeated except that the amount of barium acetate deposited was changed to contain 25 g / l of BaO.
An exhaust gas purifying catalyst was obtained in the same manner as described above.

Comparative Example 1 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that activated alumina (Al ₂ O ₃ ) was used instead of nickel aluminate in the second catalyst component layer. .

Comparative Example 2 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that the coating amount of the first catalyst component layer was changed to 10 g / l.

Comparative Example 3 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the amount of the first catalyst component layer was changed to 120 g / l.

Comparative Example 4 350 parts of powder (powder D) supporting 2.0% by weight of palladium and 1 mol% of lanthanum
( ₂ % by weight in terms of La ₂ O ₃ ) and zirconium
A cerium oxide powder containing 2 mol% (25 wt% in terms of ZrO ₂ ), 240 parts of powder (powder E) carrying 0.75 parts by weight of palladium, 10 parts of activated alumina, and 600 parts of nitric acid aqueous solution It was put into a ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to the catalyst 1 and baked at 400 ° C. for 1 hour to obtain a coat layer weight of 80 g /
1, palladium carrying amount 40 g / cf (1.41 g / l)
Was obtained.

In 600 parts of activated alumina powder (powder C),
A nitric acid aqueous solution (600 parts) was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to the above-mentioned catalyst component-carrying cordierite monolithic carrier (1.3 liter, 400 cells) and calcined at 400 ° C. for 1 hour to obtain a catalyst (total weight of coat layer: 160 g / l, palladium-carrying layer) 80 g / l).

Next, a barium acetate solution was adhered to the cordierite monolithic carrier carrying the catalyst component.
It was calcined at 00 ° C. for 1 hour and contained 15 g / l of BaO.

Next, 135 parts of Zr 3 mol% added alumina powder (powder G) carrying 1.40% by weight of rhodium, 450 parts of Zr 3 mol% added alumina powder (powder F) and 1 mol% of lanthanum (La ₂ 2% by weight in terms of O ₃ and 20 mol% of cerium (13% in terms of CeO ₂ )
Weight%) of zirconium oxide powder (powder H) 40
To 0 parts and 15 parts of activated alumina, 1000 parts of a nitric acid aqueous solution were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This was coated with a coat layer weight of 175 g / l (80 g / l of a layer composed of an inorganic material containing activated alumina as a main component, 80 g / l of a palladium-containing coat layer, and 40 g / palladium carrying amount).
The catalyst 1 (1.3 liter, 400 cells) supporting cf (1.41 g / l) and BaO 15 g / l)
This slurry liquid is adhered and fired at 400 ° C. for 1 hour,
Total coat layer weight 225 g / l (rhodium-containing catalyst component support layer 50 g / l), palladium load 40 g / cf
(1.41 g / l), rhodium carrying amount 2 g / cf (0.
071 g / l) of the catalyst were obtained.

Comparative Example 5 Activated Alumina Powder (Powder C)
To 600 parts, 600 parts of a nitric acid aqueous solution was charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to the above-mentioned cordierite monolithic carrier (1.3 liter, 400 cells) carrying the catalyst component,
For 1 hour to obtain a catalyst (coat layer weight 80 g /
l).

Next, 135 parts of Zr 3 mol% added alumina powder (powder G) carrying 1.40 wt% of rhodium, 450 parts of Zr 3 mol% added alumina powder (powder F) and 1 mol% of lanthanum (La ₂ 2% by weight in terms of O ₃ and 20 mol% of cerium (13% in terms of CeO ₂ )
Weight%) of zirconium oxide powder (powder H) 40
To 0 parts and 15 parts of activated alumina, 1000 parts of a nitric acid aqueous solution were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This was coated with a coat layer weight of 175 g / l (80 g / l of a layer composed of an inorganic material containing activated alumina as a main component, 80 g / l of a palladium-containing coat layer, and 40 g / palladium carrying amount).
The catalyst 1 (1.3 liter, 400 cells) supporting cf (1.41 g / l) and BaO 15 g / l)
This slurry liquid is adhered and fired at 400 ° C. for 1 hour,
Coating layer total weight 130 g / l (activated alumina layer 80 g /
1 and a rhodium-containing layer of 50 g / l) were obtained.

350 parts of powder (powder D) supporting 2.0% by weight of palladium and 1 mol% of lanthanum (La ₂ O ₃
2% by weight) and 32 mol% of zirconium (Z
A nitric acid aqueous solution was added to 240 parts of powder (powder E) in which 0.75 parts by weight of palladium was supported on a cerium oxide powder containing 25% by weight in terms of rO ₂ and 10 parts of activated alumina.
0 parts were put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid is adhered to the catalyst 1 and 400
C. for one hour to obtain a catalyst having a coat layer weight of 210 g / l (active alumina layer: 80 g / l, rhodium-containing layer: 50 g / l, palladium-containing layer: 80 g / l).

Next, a barium acetate solution was adhered to the cordierite monolithic carrier carrying the catalyst component,
Calcined at 00 ° C. for 1 hour, containing 15 g / l BaO,
Total coat layer weight 225 g / l (rhodium-containing catalyst component support layer 50 g / l), palladium load 40 g / cf
(1.41 g / l), rhodium carrying amount 2 g / cf (0.
071 g / l) of the catalyst were obtained.

Comparative Example 6 The procedure of Example 1 was repeated except that the catalyst component layer mainly composed of activated alumina was not provided, and the total coating amount of the catalyst layer was 145 g / l.

Comparative Example 7 BaO 30 g / l and K ₂ O
Except for containing 30 g / l, an exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

The structure of the coat layer of the catalyst prepared in each of the examples and comparative examples, and the supported amounts (g / l) of Pd, Rh, and BaO
Is shown in Table 1.

[0058]

[Table 1]

(Test Example) Examples 1 to 5 and Comparative Example 1
After endurance was performed on the exhaust gas purifying catalysts No. to No. 7 under the following durability conditions, the catalyst activity was evaluated under the following evaluation conditions.

[0060]

Evaluation conditions: low-temperature activity Engine displacement 2000 cc Fuel unleaded gasoline Heating rate 10 ° C./min Measurement temperature range 150-500 ° C.

The low-temperature activity of each exhaust gas purifying catalyst after endurance is represented by the temperature (T50 / ° C.) when the conversion of HC, CO and NOx reaches 50%, and the results are shown in Table 2. The method of calculating the conversion is as follows.

[0063]

(Equation 1)

[0064]

(Equation 2)

[0065]

(Equation 3)

[0066]

[Table 2]

[0067]

As described above in detail, in the catalyst according to the present invention, the structure of the catalyst component layer of the exhaust gas purifying catalyst is such that the first component is made of an inorganic material mainly composed of activated alumina.
Disposing a catalyst component layer, disposing a second catalyst component layer containing palladium as a catalyst component above the first catalyst component layer,
By forming a catalyst having a multilayer structure in which a third catalyst component layer containing rhodium as a catalyst component is disposed above the second catalyst component layer, low-temperature activity is improved as compared with conventional catalysts, and low-temperature activity is maintained even after durability. You can do it. For this reason, the purification reaction can be started sooner after the engine is started, and the effect of reducing the emission of harmful substances can be obtained.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 23/63 B01D 53/36 102B 23/89 104A B01J 23/56 301A

Claims (3)

[Claims] 1. An integrated catalyst having a catalyst component-supporting layer, wherein the structure of the catalyst component layer of the exhaust gas purifying catalyst is such that a first catalyst component layer made of an inorganic material containing activated alumina as a main component is disposed. Multilayer structure in which a second catalyst component layer containing palladium as a catalyst component is disposed above the first catalyst component layer, and a third catalyst component layer containing rhodium as a catalyst component is disposed above the second catalyst component layer An exhaust gas purifying catalyst characterized in that it is a catalyst of the type described above. 2. The exhaust gas purifying catalyst according to claim 1, wherein the second catalyst component layer is at least one metal selected from the group consisting of palladium, nickel aluminate, lanthanum, neodymium and zirconium in terms of metal. 1-4
0 mol%, and cerium oxide is 60 to 9 in terms of metal.
An exhaust gas purifying catalyst characterized by containing 8 mol%. 3. The exhaust gas purifying catalyst according to claim 1, wherein the third catalyst component layer contains at least one selected from the group consisting of lanthanum, neodymium and cerium in an amount of 1 to 40 mol% in terms of metal, An exhaust gas purifying catalyst comprising zirconium oxide containing 60 to 98 mol% of zirconium, rhodium and alumina.