JPH09215922A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the NOX purification capacity and heat resistance of an exhaust gas purification catalyst in which palladium, rhodium, and barium are supported on a porous carrier by a method in which rhodium and barium are supported with at least parts of them separated from each other. SOLUTION: In a ternary catalyst for purifying automobile exhaust gas, a coat layer 2 is formed on the base material 1 of a heat resistant carrier, catalyst metal selected from platinum group elements including platinum, rhodium, and palladium is supported. In consideration of the hindrance of the catalytic effect of rhodium by the contact with barium, they are supported on a porous carrier so that parts of them are separated from each other. In this way, the acceleration of oxygen poisoning of rhodium by barium is hindered, improving the NOX purification capacity and heat resistance of the catalyst. Besides, barium keeps the oxidization condition of palladium to prevent the sintering of palladium.

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 for purifying exhaust gas, and more particularly to a Pd-based catalyst carrying palladium as a catalytic metal.

[0002]

2. Description of the Related Art Conventionally, a three-way catalyst for purifying exhaust gas by oxidizing CO and HC and reducing NO _x has been used as an exhaust gas purifying catalyst for automobiles. As such a three-way catalyst, for example, a coat layer made of γ-alumina is formed on a heat-resistant carrier base made of cordierite or the like, and platinum (Pt), rhodium (R)
h) and those carrying a catalytic metal selected from platinum group elements such as palladium (Pd) are widely known.

Of these, Pt and Pd mainly contribute to the oxidative purification of CO and HC, and Rh mainly contributes to the reduction purification of NO _x , and also has the function of preventing sintering of Pt or Pd, and the heat resistance is improved. I know that. Therefore, it is known that it is desirable to use Pt or Pd and Rh together in a three-way catalyst. Among the platinum group elements, Pd is cheaper than Pt and Rh, and the cost of the exhaust gas purifying catalyst can be reduced by using Pd. However, even if Rh coexists, Pd is greatly deteriorated due to sintering at high temperature.
The d-Rh-based catalyst has a problem that it is inferior in durability.

Therefore, for example, Japanese Patent Application Laid-Open No. 3-106446 discloses an exhaust gas purifying catalyst in which barium (Ba) and cerium (Ce) are further allowed to coexist in a Pd-Rh type catalyst. In this exhaust gas-purifying catalyst, since Pd is always in an oxidized state due to the action of Ba, it is possible to prevent sintering that occurs in the metallic Pd state. Therefore, by using Pd, it is possible to secure a catalytic performance that is almost equal to that of the Pt-Rh-based catalyst, and it is possible to provide an inexpensive exhaust gas purifying catalyst.

On the other hand, in recent years, carbon dioxide (CO ₂ ) in exhaust gas emitted from internal combustion engines such as automobiles has become a problem from the viewpoint of protecting the global environment, and as a solution to this problem, so-called lean combustion in which oxygen is excessively burned is used. Burn is promising. In this lean burn, the amount of fuel used is reduced in order to improve fuel efficiency, and as a result, the generation of CO ₂ as combustion exhaust gas can be suppressed.

On the other hand, in the conventional three-way catalyst, when the air-fuel ratio is the stoichiometric air-fuel ratio (stoichiometric), CO, H in the exhaust gas
It purifies by oxidizing and reducing C and NO _x at the same time, and does not show sufficient purification performance for reducing and removing NO _x in an oxygen excess atmosphere of exhaust gas during lean burn. Therefore, even in an oxygen-excess atmosphere, N
There is a demand for the development of a catalyst and a purification system capable of purifying O _x .

Therefore, the applicant of the present application has previously proposed an exhaust gas purifying catalyst in which an alkaline earth metal and Pt are supported on a porous carrier such as alumina (Japanese Patent Laid-Open No. 5-317652), or lanthanum and Pt on a porous carrier. An exhaust gas purifying catalyst that is carried (JP-A-5-168860) or an exhaust gas-purifying catalyst that carries an alkali metal and Pt on an alumina carrier (JP-A-6-31139) is proposed. According to these exhaust gas purifying catalysts, NO _x
Are alkaline earth metal oxides or lanthanum oxides (NO
_x storage element), which reacts with reducing components such as HC and CO on the stoichiometric or rich side, so that the lean side also has excellent NO _x purification performance.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the exhaust gas purifying catalyst described in JP-A-06446, Pd
And Rh and Ba coexist. Therefore, it is expected that sintering of Pd is prevented and that the NO _x storage rate of Ba improves the NO _x purification rate. However, in this exhaust gas-purifying catalyst, P containing no Ba
The performance is not so much improved as compared with the d-Rh catalyst,
There is a problem that the effect of further adding Ba cannot be fully brought out.

The present invention has been made in view of such circumstances, and an object thereof is to provide an exhaust gas purifying catalyst capable of sufficiently exhibiting the performance of each element when Rh and Ba coexist in Pd. And

[0010]

The characteristics of the exhaust gas-purifying catalyst of the present invention for solving the above-mentioned problems are that Pd and R are added to the porous carrier.
In the exhaust gas purifying catalyst supporting h and Ba,
At least a part of Rh and Ba is carried on the porous carrier in a state of being separated from each other.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that Pd contains Rh and Ba.
As a result of earnest research on the catalytic behavior of the catalyst which was supported by contacting with, it was discovered that the catalytic action of Rh was hindered by the contact of Ba, and the present invention was completed. That is, Pd and Ba
In the case of carrying NO in contact, the NO50% reduction temperature after endurance greatly decreases as the addition amount of Ba increases, as shown in FIG. 3, and the NO _x purification performance improves. However, R
When h and Ba were carried in contact with each other, as shown in FIG. 4, it was revealed that the NO 50% reduction temperature after endurance increased as the addition amount of Ba increased and the NO _x purification performance decreased. .

Ba for such Pd catalyst or Rh catalyst
The change in activity due to addition may be due to adsorption poisoning of the exhaust gas component on Pd or Rh. Therefore, the present inventors
With respect to the Pd catalyst, the Rh catalyst, and the catalyst to which Ba was added to them, the change in the reaction order of the HC-O ₂ reaction represented by the following formula (1) was measured. Table 1 shows the results. C ₃ H ₆ was used as HC. In the equation (1), V is the reaction rate, k is a constant, p is the concentration of HC, and P is O.
₂ concentrations are shown respectively.

V = k [p (HC)] ^m × [P (O ₂ )] ⁿ (1)

[0014] Since the reaction order (m, n) becomes negative and the larger the value, the larger the adsorption poisoning, it can be seen from Table 1 that the addition of Ba in the Pd catalyst reduces the adsorption poisoning by HC. . However, it is considered that the addition of Ba increases the adsorption poisoning by O _{2 in the} Rh catalyst, and thus the activity is lowered. Therefore, when Ba is further added to the Pd-Rh-based catalyst, oxygen poisoning of Rh is promoted and the action of Rh is not sufficiently extracted.
In the exhaust gas purifying catalyst described in JP-A-106446, B
It was speculated that the effect of further adding a could not be brought out sufficiently.

Therefore, in the present invention, Rh and Ba are loaded on the porous carrier in a state of being separated from each other. This prevents Ba from promoting oxygen poisoning of Rh,
Since the inhibition of the function of is prevented, the NO _x purification performance is improved and the heat resistance is also improved. On the other hand, Ba further improves the NO _x purification performance by its NO _x storage and release action, and
The Pd oxidation state (PdO) is maintained as follows.
Prevent sintering. That is, Ba easily forms a peroxide (BaO ₂ ), which is easily decomposed by heat or a gas atmosphere into barium oxide (BaO).
Oxygen released at this time combines with Pd to form palladium oxide (PdO). Since the sintering of Pd occurs in the state of metallic palladium, it becomes palladium oxide to prevent sintering.

In order to support Rh and Ba in a state where Rh and Ba are separated as described above, Rh-supporting powder in which Rh is supported in the porous carrier and Ba-supporting powder in which Ba is supported on the porous carrier are prepared respectively. However, it can be performed by mixing these. At this time, Pd may be co-loaded on at least one of the powders. Further, Pd can be supported after mixing the above two kinds of powders.

It is also possible to stack a layer supporting Rh and a layer supporting Ba. In this case, either of the upper and lower layers may be arranged, but in order to prevent sulfur poisoning of Ba, the layer supporting Rh is preferably the upper layer. Further, Pd can be supported on at least one layer, but it is desirable to support Pd on a layer containing at least Ba in order to prevent loss of Rh characteristics due to solid solution of Pd and Rh. Since the lower layer cannot be effectively used if the upper layer is too thick, it is desirable that the thickness of the upper layer is 70 μm or less, and the ratio of the thickness of the lower layer to that of the upper layer is 2: 1 to 4: 1. Is desirable.

As the porous carrier, alumina, silica,
Conventional materials such as zirconia, titania, silica-alumina, and zeolite can be used. Of these, alumina, which has a high specific surface area even after durability, is particularly desirable. This porous carrier may be coated on a heat-resistant inorganic carrier substrate such as cordierite or a metal carrier substrate as a coat layer, or the carrier substrate may be formed from the porous carrier itself.

In the exhaust gas-purifying catalyst of the present invention, the loading amount of each catalyst component is as follows. Pd is preferably loaded in the range of 1 to 20 g with respect to the volume of the exhaust gas purifying catalyst of 1 liter. If the amount is less than 1 g, the effect cannot be obtained, and if the amount exceeds 20 g, the effect is saturated and the cost is increased. Particularly desirable range is 5 to 1
0 g. Rh is preferably loaded in the range of 0.01 to 1 g with respect to the volume of the exhaust gas purifying catalyst of 1 liter. If the amount is less than 0.01 g, the effect of the addition is not obtained, and even if the amount exceeds 1 g, the effect is saturated and the cost is increased. A particularly desirable range is 0.1-0.
It is 5 g. Further, Ba is preferably in the range of 0.05 to 0.4 mol with respect to the volume of the exhaust gas purifying catalyst of 1 liter. If the amount is less than 0.05 mol, the effect of addition cannot be obtained, and if the amount is more than 0.4 mol, the effect is saturated and the cost is increased. A particularly desirable range is 0.1
０．２0.2 mol.

The exhaust gas-purifying catalyst of the present invention may carry a known catalyst metal or co-catalyst component in addition to the above catalyst components. For example, when cerium (Ce) is supported, the reaction between Ba and oxygen is likely to occur even in exhaust gas in a rich atmosphere due to the oxygen storage / release capacity of Ce.
It is possible to prevent further sintering. The optimal amount of Ce carried is in the range of 0.1 to 0.5 mol per 1 liter of the exhaust gas purifying catalyst. It is also preferable to support Ce as a complex oxide with zirconium. Further, it is also preferable to support lanthanum (La). Since lanthanum oxide is particularly excellent in NO _x storage capacity,
The NO _x purification performance is further improved. The amount of La carried is
0.05 to 1 liter of exhaust gas purifying catalyst volume
The optimum range is 0.4 mol.

[0021]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. In addition, all "parts" mentioned below mean parts by weight. 60 parts of alumina powder <Preparation of _{Pd-Ba / Al 2 O 3} > ( Example 1), and a predetermined amount of an aqueous palladium nitrate solution having a predetermined concentration, and barium acetate 40 parts of pure water 120 parts were mixed and stirred, 100
After drying at 50 ° C. for 10 hours, it was calcined at 500 ° C. for 1 hour to prepare a Pd-Ba supported alumina powder.

<Preparation of Rh / Al ₂ O ₃ > Alumina powder 100 parts was mixed with a predetermined amount of a rhodium nitrate aqueous solution having a predetermined concentration and pure water 120 parts, and the mixture was stirred and dried at 100 ° C. for 10 hours. A Rh-supported alumina powder was prepared by firing at 1 ° C. for 1 hour. <Preparation of catalyst> 50 parts of Pd-Ba supported alumina powder,
50 parts of Rh-supported alumina powder, 10 parts of alumina sol (10% by weight of alumina), and 120 parts of pure water were mixed and stirred to prepare a slurry. Then, the honeycomb carrier base material made of cordierite (volume: 1.7 liter) was immersed in water, and after blowing off excess water, it was immersed in this slurry. Take it out, blow off the excess slurry, dry at 80 ° C for 20 minutes,
The catalyst for exhaust gas purification of Example 1 was obtained by firing at 600 ° C. for 1 hour.

In this exhaust gas purifying catalyst, Pd was 10 g and Rh was 0.
4 g and 0.1 mol of Ba are carried. (Example 2) <Preparation of _{Pd-Rh / Al 2 O 3} > alumina powder 100
Parts, a predetermined amount of a palladium nitrate aqueous solution having a predetermined concentration, a predetermined amount of a rhodium nitrate aqueous solution having a predetermined concentration, and 120 parts of pure water were mixed and stirred, and after drying at 100 ° C. for 10 hours, 50
Firing was performed at 0 ° C. for 1 hour to prepare a Pd—Rh-supported alumina powder.

<Preparation of Catalyst> 50 parts of Pd-Ba-supporting alumina powder, 50 parts of Pd-Rh-supporting alumina powder, 10 parts of alumina sol, and 120 parts of pure water were mixed and stirred in the working examples. Example 2 as in Example 1
A catalyst for purification of exhaust gas was obtained. This exhaust gas-purifying catalyst contains 10 g of Pd per liter of the honeycomb carrier substrate,
0.4 g of Rh and 0.1 mol of Ba are supported.

(Example 3) <Preparation of Rh-Pt / Al ₂ O ₃ > Alumina powder 100
Part, a predetermined amount of a predetermined concentration of rhodium nitrate aqueous solution, a predetermined concentration of a predetermined concentration of dinitrodiammine platinum nitric acid aqueous solution,
120 parts of pure water was mixed and stirred, dried at 100 ° C. for 10 hours, and then calcined at 500 ° C. for 1 hour to prepare an Rh—Pt-supported alumina powder.

<Preparation of catalyst> Pd-Ba-supported alumina powder 50 parts, Rh-Pt-supported alumina powder 50 parts, alumina sol 10 parts, and pure water 120 parts were mixed and stirred in the working examples. Example 3 as in Example 1
A catalyst for purification of exhaust gas was obtained. This exhaust gas-purifying catalyst contains 10 g of Pd per liter of the honeycomb carrier substrate,
Rh is 0.4 g, Pt is 1 g, and Ba is 0.1 mol.

[0027] (Example 4) and Pd-Ba-carrying alumina powder 50 parts, and Rh supported alumina powder, 50 parts of CeO ₂ -
ZrO ₂ composite oxide powder (molar ratio Ce / Zr = 5:
1) An exhaust gas purifying catalyst of Example 4 was obtained in the same manner as in Example 1 except that a slurry obtained by mixing 50 parts, 10 parts of alumina sol, and 120 parts of pure water was stirred. This exhaust gas-purifying catalyst carries 10 g of Pd, 0.4 g of Rh, 0.3 mol of CeO ₂ —ZrO ₂ composite oxide, and 0.1 mol of Ba per liter of the honeycomb carrier substrate.

(Example 5) A slurry prepared by mixing 50 parts of Pd-Ba-supporting alumina powder, 50 parts of Rh-supporting alumina powder, 20 parts of lanthanum carbonate, 10 parts of alumina sol, and 120 parts of pure water was used. An exhaust gas purifying catalyst of Example 5 was obtained in the same manner as in Example 1 except for the above. This exhaust gas purifying catalyst contains P per liter of honeycomb carrier substrate.
d is 10 g, Rh is 0.4 g, La is 0.1 mol, Ba
Is supported by 0.1 mol.

(Embodiment 6) FIG. 1 shows the structure of an exhaust gas purifying catalyst of this embodiment. This exhaust gas-purifying catalyst comprises a honeycomb carrier base material 1 and a coat layer 2 formed on the surface of the carrier base material 1, and the coat layer 2 contains Pd-Ba-supported alumina powder 20 and Rh-supported alumina powder 21. , CeO ₂ −
ZrO ₂ composite oxide powder 22 and lanthanum oxide powder 23
And Rh and Ba are separately carried. This exhaust gas-purifying catalyst was prepared as follows.

50 parts of alumina powder supporting Pd-Ba and R
50 parts of h-supported alumina powder, 50 parts of CeO ₂ —ZrO ₂ composite oxide powder (in molar ratio Ce / Zr = 5: 1),
20 parts lanthanum carbonate, 10 parts alumina sol, 1 pure water
An exhaust gas purifying catalyst of Example 6 was obtained in the same manner as in Example 1 except that 20 parts of the slurry was mixed and stirred.
This exhaust gas-purifying catalyst contains 10 g of Pd, 0.4 g of Rh, and CeO ₂ -Z per liter of the honeycomb carrier substrate.
0.3 mol of rO ₂ composite oxide, 0.1 mol of La, B
a is supported by 0.1 mol.

(Example 7) <Preparation of Pd-Pt-Ba / Al ₂ O ₃ > A predetermined amount of an aqueous solution of palladium nitrate having a predetermined concentration and a predetermined amount of an aqueous solution of dinitrodiammine platinum nitric acid having a predetermined concentration were added to 60 parts of alumina powder. 40 parts of barium acetate and 120 parts of pure water were mixed and stirred, dried at 100 ° C. for 10 hours, and then dried at 500 ° C. for 1 hour.
Firing was carried out for a period of time to prepare a Pd-Pt-Ba supported alumina powder.

<Preparation of catalyst> Pd-Pt-Ba-supported alumina powder 50 parts, Rh-supported alumina powder 50 parts, alumina sol 10 parts, and pure water 120 parts were mixed and stirred in the working examples. Example 7 as in Example 1.
A catalyst for purification of exhaust gas was obtained. This exhaust gas-purifying catalyst contains 10 g of Pd per liter of the honeycomb carrier substrate,
Rh is 0.4 g, Pt is 1 g, and Ba is 0.1 mol.

Example 8 <Preparation of Rh / ZrO ₂ > To 100 parts of zirconia powder,
A predetermined amount of a rhodium nitrate aqueous solution having a predetermined concentration and pure water 120
Parts were mixed and stirred, dried at 100 ° C. for 10 hours, and then 5
A Rh-supported zirconia powder was prepared by firing at 00 ° C. for 1 hour.

<Preparation of catalyst> Example 1 except that 50 parts of Pd-Ba supported alumina powder, 50 parts of Rh supported zirconia powder, 10 parts of alumina sol and 120 parts of pure water were mixed and stirred. Similarly, an exhaust gas purifying catalyst of Example 8 was obtained. This exhaust gas purifying catalyst carries 10 g of Pd, 0.4 g of Rh, and 0.1 mol of Ba per liter of the honeycomb carrier substrate.

(Example 9) <Preparation of Rh / ZrO ₂ -Al ₂ O ₃ > Alumina powder 1
00 parts was immersed in an aqueous zirconium nitrate solution, ammonia water was added dropwise to coprecipitate zirconia on alumina. To 100 parts of this zirconia coprecipitated alumina powder, a predetermined amount of an aqueous rhodium nitrate solution having a predetermined concentration and 120 parts of pure water were mixed and stirred, dried at 100 ° C. for 10 hours, and then dried at 500 ° C.
It was calcined for an hour to prepare a Rh-supported zirconia coprecipitated alumina powder.

<Preparation of catalyst> 50 parts of Pd-Ba-supporting alumina powder and Rh-supporting zirconia coprecipitated alumina powder 50
Parts, 10 parts of alumina sol, and 120 parts of pure water were mixed and stirred in the same manner as in Example 1 except that a slurry was used.
An exhaust gas-purifying catalyst of Example 9 was obtained. In this exhaust gas purifying catalyst, Pd is 1 per liter of the honeycomb carrier substrate.
0 g, 0.4 g of Rh and 0.1 mol of Ba are supported.

(Embodiment 10) FIG. 2 shows the structure of the exhaust gas purifying catalyst of this embodiment. This exhaust gas-purifying catalyst comprises a honeycomb carrier base material 1 and a coat layer 3 formed on the surface of the carrier base material 1, and the coat layer 3 has a two-layer structure of a lower layer 30 and an upper layer 31. The lower layer 30 contains Pd-Ba-supporting alumina powder, and the upper layer 31 contains Rh-supporting alumina powder. Therefore, Rh and Ba are separately carried. This exhaust gas-purifying catalyst was prepared as follows.

50 parts of Pd-Ba-supported alumina powder, 5 parts of alumina sol, and 60 parts of pure water were mixed and stirred to prepare a slurry. And a cordierite honeycomb carrier 1
(Volume 1.7 liter) was immersed in water, and after blowing off excess water, it was immersed in this slurry. It was taken out, the excess slurry was blown off, dried at 80 ° C. for 20 minutes, and then baked at 600 ° C. for 1 hour to form the lower layer 30.

Next, 50 parts of Rh-supported alumina powder, 5 parts of alumina sol, and 60 parts of pure water were mixed and stirred to prepare a slurry. Then, the honeycomb carrier base material 1 having the lower layer 30 was immersed in water, and after blowing off excess water, it was immersed in this slurry. Remove and blow off excess slurry to 80 ℃
After drying for 20 minutes at 600 ° C. for 1 hour, an upper layer 31 was formed on the surface of the lower layer 30 to obtain an exhaust gas purifying catalyst of Example 10. The lower layer 30 has a thickness of 100 μm, the upper layer 31 has a thickness of 50 μm, and the thickness ratio is lower layer: upper layer = 2: 1. The exhaust gas-purifying catalyst includes a honeycomb carrier substrate 1
Pd is 10 g, Rh is 0.4 g, and Ba is 0.1 mol per liter.

(Example 11) 50 parts of Pd-Rh-supported alumina powder, 5 parts of alumina sol, and 60 parts of pure water were mixed and stirred to prepare a slurry. Then, the honeycomb carrier base material having the lower layer formed in Example 10 was immersed in water, and after blowing off excess water, it was immersed in this slurry. Remove and blow off excess slurry, dry at 80 ° C for 20 minutes 6
The catalyst for flue gas purification of Example 11 was obtained by firing at 00 ° C. for 1 hour to form an upper layer on the lower layer surface. The thickness of the upper layer is 50μ
m, and the thickness ratio is lower layer: upper layer = 2: 1. This exhaust gas purifying catalyst carries 10 g of Pd, 0.4 g of Rh, and 0.1 mol of Ba per liter of the honeycomb carrier substrate.

(Example 12) 50 parts of alumina powder supporting Pd-Ba, 5 parts of alumina sol, and 60 parts of pure water were mixed and stirred to prepare a slurry. Then, the honeycomb carrier base material made of cordierite (volume: 1.7 liter) is immersed in water,
It was immersed in this slurry after blowing off excess water. It was taken out, the excess slurry was blown off, dried at 80 ° C. for 20 minutes, and then baked at 600 ° C. for 1 hour to form a lower layer.

Next, 50 parts of Rh-Pt-supported alumina powder, 5 parts of alumina sol, and 60 parts of pure water were mixed and stirred to prepare a slurry. Then, the honeycomb carrier base material having the lower layer was immersed in water, and after blowing off excess water, it was immersed in this slurry. Remove and blow away excess slurry, 80
After drying at 20 ° C. for 20 minutes and baking at 600 ° C. for 1 hour, an upper layer was formed on the lower layer surface to obtain an exhaust gas purifying catalyst of Example 12. The lower layer has a thickness of 100 μm, the upper layer has a thickness of 50 μm, and the thickness ratio is lower layer: upper layer = 2: 1. This exhaust gas purifying catalyst carries 10 g of Pd, 0.4 g of Rh, 1 g of Pt, and 0.1 mol of Ba per liter of the honeycomb carrier substrate.

Example 13 The same procedure as in Example 10 was repeated except that the upper layer had a thickness of 75 μm, the lower layer had the same thickness of 75 μm, and the thickness ratio was lower layer: upper layer = 1: 1. The exhaust gas-purifying catalyst of Example 13 was prepared. Also in this exhaust gas-purifying catalyst, Pd is 10 g, Rh is 0.4 g, Pt is 1 g, and Ba per liter of the honeycomb carrier substrate.
Is supported by 0.1 mol.

Comparative Example 1 <Preparation of Pd / Al ₂ O ₃ > To 100 parts of alumina powder,
A predetermined amount of palladium nitrate aqueous solution with a predetermined concentration and pure water 12
After mixing and stirring 0 parts and drying at 100 ° C. for 10 hours,
Pd-supported alumina powder was prepared by firing at 500 ° C. for 1 hour.

<Preparation of catalyst> Pd-supported alumina powder 10
An exhaust gas purifying catalyst of Comparative Example 1 was obtained in the same manner as in Example 1, except that 0 parts, 10 parts of alumina sol, and 120 parts of pure water were mixed and stirred. This exhaust gas-purifying catalyst contains Pd per liter of the honeycomb carrier substrate.
Is carried by 10 g.

Comparative Example 2 <Preparation of Catalyst> The same procedure as in Example 1 was carried out except that a slurry prepared by mixing 100 parts of Pd-Ba-supported alumina powder, 10 parts of alumina sol and 120 parts of pure water was stirred. An exhaust gas purifying catalyst of Comparative Example 2 was obtained. In this exhaust gas-purifying catalyst, Pd was 10 per liter of the honeycomb carrier substrate.
0.1 mol of g and Ba are supported.

Comparative Example 3 <Preparation of Catalyst> The same procedure as in Example 1 was repeated except that 100 parts of Pd-Rh-supported alumina powder, 10 parts of alumina sol and 120 parts of pure water were mixed and stirred. An exhaust gas purifying catalyst of Comparative Example 3 was obtained. In this exhaust gas-purifying catalyst, Pd was 10 per liter of the honeycomb carrier substrate.
0.4 g of g and Rh are carried.

(Comparative Example 4) <Preparation of Pd-Rh-Ba / Al ₂ O ₃ > 100 parts of alumina powder were charged with a predetermined amount of a palladium nitrate aqueous solution having a predetermined concentration and a predetermined amount of a rhodium nitrate aqueous solution having a predetermined concentration. 20 parts of barium acetate and 120 parts of pure water are mixed and stirred at 100 ° C.
After drying at 10 ° C for 10 hours, baking at 500 ° C for 1 hour
A d-Rh-Ba-supported alumina powder was prepared.

<Preparation of catalyst> Pd-Rh-Ba-supported alumina powder 100 parts, alumina sol 10 parts, and pure water 12
Example 1 except that a slurry obtained by mixing and stirring 0 parts was used.
An exhaust gas purifying catalyst of Comparative Example 4 was obtained in the same manner as in. This exhaust gas purifying catalyst carries 10 g of Pd, 0.4 g of Rh, and 0.1 mol of Ba per liter of the honeycomb carrier substrate.

Comparative Example 5 <Preparation of Rh—Ba / Al ₂ O ₃ > Alumina powder 100
A predetermined amount of an aqueous solution of rhodium nitrate having a predetermined concentration, 20 parts of barium acetate, and 120 parts of pure water are mixed and stirred in 100 parts.
After drying at 0 ° C. for 10 hours, it was baked at 500 ° C. for 1 hour to prepare an Rh-Ba-supported alumina powder.

<Preparation of catalyst> Pd-supported alumina powder 50
Parts, 50 parts of Rh-Ba supported alumina powder, 10 parts of alumina sol, and 120 parts of pure water were mixed and stirred in the same manner as in Example 1 to prepare an exhaust gas purifying catalyst of Comparative Example 5. Obtained. This exhaust gas purifying catalyst carries 10 g of Pd, 0.4 g of Rh, and 0.1 mol of Ba per liter of the honeycomb carrier substrate.

(Evaluation) Each of the above exhaust gas-purifying catalysts was housed in a catalytic converter and mounted in the exhaust system of a 2-liter engine, and the air-fuel ratio (A / F) was set to 14.6 (Stoichi), Amplitude: about 1 A / F, cycle: about 0.5
At a catalyst bed temperature of 100 ° C. and 50
An actual exhaust gas endurance test of operating for hours was performed. Then A / F
Under stoichiometric conditions of = 14.6, the catalyst bed temperature is raised from 240 ° C to 440 ° C, and HC, CO and NO _x at that time are increased.
The 50% purification temperature was measured. Table 2 shows the results of the respective exhaust gas purifying catalysts.

[0053]

[Table 2]

From the comparison between Comparative Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that the coexistence of Pd and Ba or Rh improves the catalytic performance after endurance. However, as in Comparative Example 4, even when both Rh and Ba coexisted with Pd, the catalytic performance was almost the same as in Comparative Example 3, and it can be seen that the effect of adding Ba is not exhibited. In Comparative Example 5, Rh
The catalytic performance is lower than in Comparative Example 4 because the probability of contact between Ba and Ba is high.

However, Example 1 shows a markedly higher catalytic performance than the Comparative Example, and it is clear that this is the effect of separating and supporting Rh and Ba. Then, as in Examples 2 and 3, the coexistence of Pd or Pt in the Rh-supported alumina slightly improved the catalytic performance as compared with Example 1. Also, as in Examples 4 to 6, CeO ₂
It can also be seen that the catalytic performance is slightly improved by further coexisting the --ZrO ₂ composite oxide and lanthanum oxide.
Further, even if Pt is further coexisted on Pd-Ba-supported alumina as in Example 7, the catalytic performance is slightly improved, and even if Rh is supported on zirconia or zirconia co-precipitated alumina as in Examples 8 and 9. It can be seen that the catalyst performance is slightly improved.

Further, it is clear from the comparison between Comparative Example 4 and Example 10 that catalytic performance is remarkably improved by separately carrying Rh and Ba in the lower layer and the upper layer of the coating layer. Then, as in Examples 11 and 12, R
It can be seen that the coexistence of Pd or Pt in h slightly improves the catalyst performance. However, in Example 13, conversely, the catalytic performance is lowered. It is considered that this is because the thick upper layer made it difficult to effectively use the catalyst component of the lower layer.

[0057]

According to the catalyst for purifying exhaust gas of the present invention, the action of each catalyst component of Pd, Rh and Ba can be maximized, and high catalyst performance can be ensured even after durability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an exhaust gas purifying catalyst of Example 6 of the present invention.

FIG. 2 is a schematic cross-sectional view showing the structure of an exhaust gas purification catalyst of Example 10 of the present invention.

FIG. 3 is a graph showing the relationship between the amount of Ba added to the Pd catalyst and the NO50% purification temperature.

FIG. 4 is a graph showing the relationship between the amount of Ba added to the Rh catalyst and the NO50% purification temperature.

[Explanation of symbols]

1: support substrate 2: coating layer 20: Pd-Ba-carrying alumina powder 21: Rh-carried alumina powder 22: CeO ₂ -
ZrO ₂ composite oxide powder 23: lanthanum oxide powder 30: lower layer 3
1: Upper layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoto Miyoshi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Hirobumi Shinjo 1 of 41, Yokoshiro, Nagakute Town, Aichi District, Aichi Prefecture Toyota Central Research Institute Co., Ltd. (72) Inventor Hideo Sofagawa 1 41st Yokomichi, Nagakute-cho, Aichi-gun, Aichi-gun

Claims (1)

[Claims] 1. A catalyst for exhaust gas purification, comprising palladium, rhodium and barium supported on a porous carrier, wherein at least a part of rhodium and barium are supported on the porous carrier in a state of being separated from each other. Exhaust gas purification catalyst.