JP2001070791A - Exhaust gas cleaning catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst, which keeps high catalytic activity even after being subjected to a high temperature condition and can effectively react even at a relatively low temperature, for example, immediately after the start of actuation of an internal combustion engine. SOLUTION: In an exhaust gas cleaning catalyst where a coating layer containing a noble metal catalyst is formed on the surface of a heat resistant support carrier, the coating layer is made to have a two-layer structure consisting of a first coating layer directly supported and formed on the surface of the heat resistant support carrier and a second coating layer formed on the surface of the first coating layer, and the first coating layer is made to contain at least one of Pt and Rh as a noble metal catalyst and the second coating layer is made to contain Pd as a noble metal catalyst in a state that the heat resistant inorganic oxide is carried. The heat resistant inorganic oxide preferably consists of an oxide containing at least one of CeO2 and ZrO2, or of Al2 O3, and the second coating layer preferably contains at least one element selected from a group consisting of Ba, Ca, Cs, K, Mg, and La.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to nitrogen oxides (NO _x ), carbon monoxide (CO), and hydrocarbons (H) contained in exhaust gas discharged from an internal combustion engine such as an automobile.
The present invention relates to an exhaust gas purifying catalyst for efficiently purifying C) and the like.

[0002]

BACKGROUND OF THE INVENTION NO _X from the exhaust gases of automobiles, as a catalyst most widely used conventionally to purify harmful substances such as CO or HC was platinum, palladium, noble metals such as rhodium and active substance There is a so-called three-way catalyst. These three-way catalyst, N from NO _X
It acts as a catalyst for the reduction reaction to ₂ , or the oxidation reaction from CO to CO ₂ and HC to CO ₂ and H ₂ O. That is, the three-way catalyst may act as both a catalyst for the reaction of oxidation and reduction reactions, NO _X contained in the exhaust gas, CO, harmful substances such as HC can be purified.

[0003] By the way, the exhaust gas purifying catalyst for automobiles and the like is discharged at a relatively low temperature where the internal combustion engine and the exhaust gas purifying catalyst are not sufficiently warmed in order to cope with the increasingly severe cold emission. High catalytic activity is also required for exhaust gas. In order to improve the low-temperature activity of the exhaust gas purifying catalyst, various proposals have been made to utilize the high-temperature purifying ability of palladium at low temperatures. As one of them, there is an exhaust gas purifying catalyst in which a coating layer is formed on a honeycomb carrier and palladium (impregnated) is supported on the surface of the coating layer. However, in response to the above-mentioned cold emission, there is a tendency that the exhaust gas purifying catalyst is mounted below the floor at a maniverter position closer to the internal combustion engine so as to exhibit high purification performance early after the internal combustion engine starts. . For this reason, the exhaust gas purifying catalyst may be practically exposed to a high temperature of, for example, 900 ° C. or more (in some cases, 1000 ° C. or more). Therefore, in a configuration in which palladium is supported on the surface of the coating layer, the palladium deteriorates due to grain growth and the like when exposed to a high temperature, and cannot maintain a high low-temperature activity for a long period of time.

In order to solve such a problem,
For example, there is an exhaust gas purifying catalyst in which a coating layer having a two-layer structure is formed on a honeycomb carrier and palladium is present on the inner layer side (Japanese Patent Application Laid-Open No. 11-151439). In this configuration, palladium is certainly not exposed on the surface of the coating layer, so that the growth of palladium grains at high temperatures can be suppressed. However, since palladium is present in the inner layer, the high catalytic activity of palladium at low temperatures cannot be fully utilized, and exhaust gas cannot be purified with good responsiveness immediately after the start of the internal combustion engine.

The present invention has been conceived in view of the above circumstances, and can maintain a high catalytic activity even after being exposed to a high temperature condition, and immediately after starting the internal combustion engine. It is an object of the present invention to provide an exhaust gas purifying catalyst which can function effectively even at a relatively low temperature.

[0006]

DISCLOSURE OF THE INVENTION In order to solve the above-mentioned problems, the present invention takes the following technical means.

That is, the exhaust gas purifying catalyst provided by the present invention is an exhaust gas purifying catalyst in which a coating layer containing a noble metal catalyst is formed on the surface of a heat-resistant support.
The coating layer is composed of a first coating layer formed directly on the surface of the heat-resistant support carrier and a second coating layer formed on the surface of the first coating layer. Is
Platinum (Pt) and rhodium (R
h) is included, and the second
For the coating layer, palladium (Pd) as a noble metal catalyst
Is contained in a state supported by the heat-resistant inorganic oxide.

In this configuration, in the coating layer having a two-layer structure composed of the first coating layer and the second coating layer, Pd is contained in the second coating layer, which is the outer layer, while being supported by the heat-resistant inorganic oxide. Therefore, the following advantages can be obtained.

First, as compared with the case where Pd is carried on the surface of the coating layer, Pd is less likely to grow and deteriorate even at high temperatures because Pd is incorporated in the second coating layer. . In addition, since Pd is supported on the heat-resistant inorganic oxide, the inorganic oxide which is a carrier grows at high temperatures, and Pd is buried in the carrier. It is unlikely to occur. Therefore,
Advantageous Effects of Invention The exhaust gas purifying catalyst of the present invention has an advantage that the catalytic performance of Pd is hardly deteriorated even in an environment where the catalyst is repeatedly exposed to a high-temperature atmosphere.

Second, in the two-layered coating layer, if palladium is contained in the second outer coating layer, the palladium is contained in the first inner coating layer as in the conventional case. The exhaust gas can be purified with good responsiveness immediately after the start of the internal combustion engine, and the high catalytic activity at a low temperature of Pd can be effectively used.

Further, in the exhaust gas purifying catalyst of the present invention, since the first coating layer, which is the inner layer, contains at least one of Pt and Rh, if the temperature of the exhaust gas purifying catalyst reaches a certain temperature or higher. The exhaust gas can be efficiently purified by effectively utilizing the catalytic activities of Pt and Rh.

As described above, the catalyst for purifying exhaust gas of the present invention has a high catalytic activity in a wide temperature range from a relatively low temperature range to a high temperature range even in an environment where it is repeatedly exposed to a high temperature atmosphere. And exhaust gas can be efficiently purified.

Here, examples of the heat-resistant support carrier include a honeycomb carrier made of cordierite, mullite, alumina, metal (for example, stainless steel), etc. and having a large number of cells formed thereon. When a honeycomb carrier is used, a coating layer composed of a first coating layer and a second coating layer is formed on the inner surface of each cell by a known wash coat, and used as an exhaust gas purifying catalyst.

Examples of the heat-resistant inorganic oxide include an oxide containing at least one of cerium oxide and zirconium oxide, or alumina (Al ₂ O ₃ ).

Cerium oxide (CeO)_Two) And gall oxide
Conium (ZrO_TwoAn acid containing at least one of the following:
The compound is CeO_Two, ZrO_Two, CeO_TwoAnd ZrO
_TwoComposite oxide (Ce-Zr composite oxide),
Alkaline earth metal elements and rare earth elements in Zr composite oxide
Compounds of oxides (excluding Ce and Zr)
(Ce-Zr-based composite oxide), CeO_TwoAlkaline earth
Oxidation of metal elements and rare earth elements (except Ce and Zr)
Compound (Ce-based composite oxide), ZrO _TwoTo
Alkaline earth metal elements and rare earth elements (Ce and Zr
Excluding) (Zr-based composite oxide)
Is mentioned.

The Ce-Zr-based composite oxide, Ce-based composite oxide, or alkaline earth metal elements that can constitute the Zr-based composite oxide include beryllium (Be), magnesium (Mg), calcium (Ca), Strontium (S
r), barium (Ba), and radium (Ra). These alkaline earth elements may be used alone or in combination of two or more. Of the alkaline earth metal elements exemplified, Mg or Ca is preferably used.

As a rare earth element (excluding Ce and Zr) which can constitute the Ce-Zr-based composite oxide, Ce-based composite oxide, or Zr-based composite oxide, scandium (S
c), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), promethium (P
m), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (E)
r), thulium (Tm), ytterbium (Yb), and lutetium (Lu). These rare earth elements may be used alone or in combination of two or more.
Among the rare earth elements exemplified, Y, La, Pr, Nd, and G
d or Tb is preferably used.

In a preferred embodiment, barium (Ba), calcium (Ca), cesium (Cs), potassium (K), magnesium (M
g), and at least one element selected from the group consisting of lanthanum (La). Among these elements, Ba is preferably used.

Pd is easily poisoned and deteriorated by HC and phosphorus (P).
Poisoning of Pd from HC can be prevented. Such a measure can also prevent Pd from deteriorating.

Each of the exemplified elements is contained in the second coating layer as, for example, a sulfate, a nitrate, or an acetate, and a sulfate is particularly preferably used. Since these salts of the above-described elements are thermally stable, they can exhibit a function of preventing HC poisoning over a long period of time even in an environment where they are repeatedly exposed to a high-temperature atmosphere.

As the noble metal catalyst contained in the first coating layer, at least one of Pt and Rh may be used as described above. These noble metal catalysts include, for example, CeO ₂ and ZrO ₂ . It is preferable to include the oxide in the first coating layer in a state where the oxide is supported on at least one of the oxides. As mentioned earlier, CeO ₂ and Zr
Examples of the oxide containing at least one of O ₂ include C 2
eO ₂ , ZrO ₂ , Ce-Zr composite oxide, Ce-Zr
-Based composite oxides, Ce-based composite oxides, and Zr-based composite oxides. Since these oxides are excellent in heat resistance, even if Pt or Rh is supported using such an oxide as a carrier, a situation in which the carrier grows at high temperature hardly occurs. Therefore, P due to the grain growth of the carrier
A situation where the function of t or Rh is impaired is unlikely to occur.

Of course, Pt and Rh may be used in combination. In this case, these noble metals may be supported on the same carrier or may be supported on different carriers. Pt and R
when used in combination with h may utilize a high catalytic ability for oxidation of CO and HC that Pt has, both high catalytic activity for reduction of an higher NO _x which Rh has. In addition, if these noble metals are supported on the same carrier, both a catalyst having strong oxidizing ability and a catalyst having strong reducing ability coexist on one carrier, so that the oxidizing ability and the reducing ability are balanced as a whole. Become. Even if these noble metals are co-supported, their characteristics are not impaired at high temperatures. On the other hand, Rh and Pd may become alloys that impair each property. For this reason, as in the exhaust gas purifying catalyst of the present invention, if the coating layer has a two-layer structure, and the first coating layer contains Rh and the second coating layer contains Pd, the respective layers are alloyed. It does not impair the function of precious metals.

The first coating layer and the second coating layer include:
Alumina (Al ₂ O ₃ ) may be added to improve the heat resistance of these coating layers.

The Ce-Zr composite oxide, Ce-Zr-based composite oxide, Ce-based composite oxide, and Zr-based composite oxide are adjusted to a desired composition by a known method (a coprecipitation method or an alkoxide method). Can be.

In the coprecipitation method, cerium (Ce), zirconium (Zr), an alkaline earth metal element, and a rare earth element (excluding Ce and Zr) are selected so as to have a predetermined stoichiometric ratio. A solution of the salt containing the element thus obtained is prepared, an alkaline aqueous solution is added to the solution to coprecipitate the salt containing the desired element, and the coprecipitate is heat-treated to prepare the composite oxide.

Examples of the salts of alkaline earth metal elements and salts of rare earth elements (including Ce and Zr) include inorganic salts such as sulfates, oxysulfates, nitrates, oxynitrates, chlorides, oxychlorides and phosphates. Salts and organic salts such as acetate, oxyacetate and oxalate can be mentioned.

As an aqueous alkaline solution for producing a coprecipitate, an aqueous ammonia solution, an aqueous ammonia carbonate solution,
An aqueous sodium hydroxide solution or the like can be used.

On the other hand, in the alkoxide method, an element selected from the group consisting of Ce, Zr, an alkaline earth metal element, and a rare earth element (excluding Ce and Zr) is provided so as to have a predetermined stoichiometric ratio. The mixed alkoxide solution is prepared, deionized water is added to the mixed alkoxide solution, the mixture is hydrolyzed, and the hydrolysis product is heat-treated to prepare the composite oxide.

As the alkoxide of the mixed alkoxide solution, methoxide, ethoxide, propoxide, butoxide, etc., and ethylene oxide adducts thereof are employed.

The Zr source used in these methods may contain about 1 to 3% of hafnium (Hf) used in general industrial applications. The composition is calculated by regarding the minute as Zr.

In the heat treatment of the obtained coprecipitate or hydrolysis product, the coprecipitate or hydrolysis product is filtered and washed, and then dried at about 50 to 200 ° C. for about 1 to 48 hours. The obtained dried product is calcined at about 350 to 1000C, preferably 400 to 800C for about 1 to 12 hours.

In addition to the composite oxide thus obtained,
CeO_Two, ZrO_TwoOr Al _TwoO_ThreeHeat resistance
The loading of Pd on the conductive inorganic oxide involves the solution of a salt containing Pd.
Heat treatment after adjusting and impregnating it with the exemplified compounds
It is done by doing. Also, composite oxide, CeO
_Two, ZrO_TwoThe loading of Pt and Rh on Pt and Rh
After preparing a salt solution and impregnating it with the desired carrier
Is performed by heat treatment.

As the solution of the salt of Pd, Pt or Rh, an aqueous nitrate solution, an aqueous chloride solution or the like is used.

The heat treatment after the impregnation is preferably about 50-2.
After about 1-48 hours at 00 ° C., about 350-1
About 1 to 12 at 000 ° C (preferably 400 to 800 ° C)
It is performed by firing for a time (preferably about 2 to 4 hours).

The coating layer is made of a honeycomb as a heat-resistant support carrier.
When a carrier is used, a known washer is used as described above.
In the same way as the coat layer,
You. For example, the first coating layer has a low Pt and Rh content.
CeO carrying one of them _TwoAnd ZrO_TwoOxides containing
Powder, if necessary Al_TwoO_ThreeCrush and mix powder
The slurry is made into a slurry, and this slurry is
Attach it to the carrier and use an electric furnace or the like.
It is performed by firing for a time. The second coating layer is made of Pd
Of a predetermined oxide carrying BaSO, if necessary
_FourAnd Al_TwoO_ThreeCrushed and mixed powder such as
And make this slurry adhere to the honeycomb carrier.
Baking at 600 ° C for 3 hours in an electric furnace
It is performed by

[0036]

Next, examples of the present invention will be described together with comparative examples, but the present invention is not limited to these examples.

Example 1 In this example, first, the composition was Ce _0.50 Zr _0.45 Y _0.05 O
_1.98 Ce-Zr-based composite oxide (CZY) and Zr
A Ce-Zr-based composite oxide (ZCL) of _0.80 Ce _0.16 La _0.04 O _1.98 was prepared. Next, palladium (Pd) is independently supported on CZY (Pd / CZY), and platinum (Pt) and rhodium (Rh) are simultaneously supported on another CZY (Pt-Rh / CZY).
Pt was independently supported on ZCL (Pt / ZCL).

A first coating layer was formed on the inner surface of each cell of the monolithic carrier using Pt-Rh / CZY, Pt / ZCL, and alumina (Al ₂ O ₃ ). Then, Pd / C
ZY, Al ₂ O ₃ , and barium sulfate (BaS
O ₄ ) was used to form a second coating layer on the surface of the first coating layer to obtain an exhaust gas purifying catalyst of this example.

For this exhaust gas purifying catalyst, 110
The 0 ℃ durability test after performing 20 hours, CO-NO _x cross-point purifying rate, HC purification rate, and by measuring the HC50% purification temperature was evaluated for catalytic performance. Table 1 shows the results.

(Monolith carrier) As the monolith carrier,
105mm in diameter, 171mm in length, 1.5dm capacity
In ³ of the cylindrical wall thickness 0.1 mm, it was used those made of 400cell / inch ² density cells formed in the cordierite.

(Preparation of Ce-Zr-based composite oxide)
The Zr-based composite oxide was prepared by a so-called alkoxide method. For CZY, first, 0.1 mol of cerium methoxypropylate, 0.09 mol of zirconium methoxypropylate, and 0.01 mol of yttrium methoxypropylate were dissolved in 200 ml of toluene to prepare a mixed alkoxide solution. Then, 80 ml of deionized water was dropped into the mixed alkoxide to hydrolyze the alkoxide. Further, the solvent and H ₂ O were distilled off from the hydrolyzed solution and evaporated to dryness to prepare a precursor. The precursor was air-dried at 60 ° C. for 24 hours.
Heat treated at 450 ° C for 3 hours in an electric furnace and then Ce _0.50 Zr
CZY powder having a composition of _0.45 Y _0.05 O _1.98 was obtained. ZCL was adjusted through the same operation as CZY, except that a mixed alkoxide solution was prepared using 0.16 mol of zirconium methoxypropylate, 0.032 mol of cerium methoxypropylate, and 0.008 mol of lanthanum methoxypropylate.

(Loading of Noble Metal Catalyst on Ce-Zr-Based Composite Oxide) The loading of the noble metal catalyst on the Ce-Zr-based composite oxide is performed by using a solution of a salt containing a noble metal to be supported on the Ce-Zr-based composite oxide. After the impregnation, the heat treatment was performed.

Specifically, CZY is impregnated with an aqueous solution of palladium nitrate adjusted to be 3.0% by weight in terms of Pd element with respect to CZY, dried, and then dried at 600 ° C. for 3 hours. By calcining, a powder of a Ce-Zr-based composite oxide (Pd / CZY) on which Pd was solely supported was obtained.

The co-presence of Pt and Rh on CZY was carried out by first adding a dinitrodiammine platinum nitrate solution adjusted to 1.5% by weight in terms of Pt element in CZY.
Y was impregnated, dried, and calcined at 600 ° C. for 3 hours to obtain Pt-supported Ce—Zr-based composite oxide (Pt / CZY) powder. This powder was further impregnated with an aqueous rhodium nitrate solution adjusted to 1.0% by weight in terms of Rh element, dried, and calcined at 600 ° C. for 3 hours to obtain Rh. Was further coexisted and supported to obtain a powder of a Ce-Zr-based composite oxide (Pt-Rh / CZY).

Further, ZCL is impregnated with a dinitrodiammine platinum nitrate solution adjusted to be 1.5% by weight in terms of Pt element, dried, and then dried at 600 ° C. for 3 hours.
Pt-supported Ce-Z by firing for a time
An r-based composite oxide (Pt / ZCL) powder was obtained.

(Formation of Coating Layer) The coating layer is formed by preparing a slurry of a powder of a component constituting the first coating layer, applying the slurry to the inner surface of the cell of the monolithic carrier, heat treating the slurry, and further forming a second coating layer. It was formed by applying a slurry of powder of components to be formed into a layer to the surface of the first coating layer and then performing a heat treatment.

Specifically, the first coating layer is made of Pt-Rh /
CZY powder, Pt / ZCL powder, Al ₂ O ₃ powder and alumina sol were mixed and pulverized with a ball mill, distilled water was added to the slurry, and the slurry was adhered to the inner surface of each cell of the monolithic carrier. After drying by drying, it was formed by firing at 600 ° C. for 3 hours. In this example, the weight of each component in the first coating layer was CZY5 per 1 dm ³ of the monolithic carrier.
0 g, their Pt and Rh loadings are 0.75 g and 0.5 g, ZCL 50 g, their Pt loadings are 0.75 g
g and Al ₂ O ₃ 55 g.

The second coating layer is made of Pd / CZY powder, Al
₂ O ₃ powder, alumina sol, and BaSO ₄ powder
Distilled water was added to the mixture mixed and pulverized with a ball mill to form a slurry. The slurry was attached to the inner surface of each cell of the monolith carrier, dried, and then fired at 600 ° C. for 3 hours to form a slurry. In this embodiment,
The weight of each component in the second coating layer was 50 g of CZY, 1.5 g of Pd carried thereon, 45 g of Al ₂ O ₃ , and 40 g of BaSO ₄ per 1 dm ³ of the monolith carrier.

(1100 ° C. Endurance Test) In the 1100 ° C. endurance test, a 4-liter V-type 8-cylinder engine was mounted on an actual vehicle, and the exhaust gas purifying catalyst of this embodiment was installed in one bank (4 cylinders) of this engine. Was carried out. Specifically, one cycle (30
This cycle is repeated 2400 times for a total of 20 seconds.
Time went on. As shown in FIG. 1 (two cycles are shown in the figure), the stoichiometric state of the stoichiometric air-fuel ratio (A / F = 14.6) is maintained by feedback control from 0 to 5 seconds. The mixed gasoline / air mixture was supplied to the engine, and the internal temperature of the exhaust gas purifying catalyst (catalyst bed) was set to be around 850 ° C.
During 5 to 7 seconds, the feedback is opened and the fuel is excessively injected to make the fuel rich (A / F
= 12.5) was supplied to the engine. 7 to 28
During the second, while the feedback is open and the fuel is excessively supplied, secondary air is blown from the outside of the engine through the introduction pipe from the upstream side of the exhaust gas purification catalyst, and the inside of the catalyst bed is Excess fuel was reacted with secondary air to raise the catalyst bed temperature. At this time, the maximum temperature was 1100 ° C., and the A / F was maintained at about 14.8, which is approximately the stoichiometric air-fuel ratio. During the last 28 to 30, secondary air was supplied without supplying fuel, and the fuel cell was in a lean state. The fuel was engine oil (Cosmo 5W-30).
(SG class) and supplied in the form of gasoline containing phosphorus (P) to create an environment where Pd is easily poisoned. At this time, the addition amount of P is calculated by adding the total amount during the durability test to 0.27 in terms of element.
g. Further, the catalyst bed temperature was measured by a thermocouple inserted at the center of the honeycomb carrier.

[0050] For (CO-NO _X crosspoint purification ratio and the HC purification rate measurement) exhaust gas purifying catalyst of the present embodiment was subjected to durability test as described above, first, 900
Annealed at 2 ° C. for 2 hours. Next, the air-fuel mixture was supplied to the engine while changing from a fuel-rich state to a lean state, and when the mixture was burned by the engine, exhaust gas was purified by the exhaust gas purifying catalyst of the present embodiment. At this time, the rates of purification of CO and NO _X were measured, and the purification rate when the purification rates of these components were the same was defined as the CO-NO _X cross point purification rate. Further, A / F in the CO-NO _X crosspoint purification rate
The purification rate of HC in the gas discharged from the air-fuel mixture having the value was measured and defined as the HC purification rate in the present embodiment. The measurement of the purification rate was performed not in a state where the engine was actually mounted on an automobile, but in a state of only the engine. The temperature of the exhaust gas supplied to the exhaust gas purifying catalyst is 460.
° C and the space velocity SV was 90000 / h.

(Measurement of HC 50% Purification Temperature) A stoichiometric air-fuel mixture is supplied to an engine, and the temperature of exhaust gas discharged by combustion of the air-fuel mixture is increased at a rate of 30 ° C./min. The temperature at which the HC was supplied to the exhaust gas purifying catalyst and the HC in the exhaust gas was purified by 50% was measured. This measurement is performed when the space velocity SV of the exhaust gas is 90.
000 / h. The mixture supplied to the engine was maintained in a substantially stoichiometric state by feedback control, and the A / F value was 14.6 ± 0.2.

Example 2 In this example, first, the compositions were Ce _0.70 Zr _0.26 Y _0.04 O _1.98 (CZY) and Zr _0.70 Ce _0.22 La _0.02 Nd _0.04 O _1.97 (ZCLN) in the same manner as in Example 1.
) Was prepared. Next, Pd is individually supported on CZY (Pd / CZY
) To allow Pt and Rh to coexist on ZCLN (Pt-Rh / ZCLN).

Pt-Rh / ZCLN and Al ₂ O
_{According to 3} , a first coating layer was formed on the inner surface of each cell of the monolithic carrier using the same method as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolith carrier was 50 g of ZCLN, the loadings of Pt and Rh were 0.75 g and 0.75 g, and 50 g of Al ₂ O ₃ .

Pd / CZY, Al ₂ O ₃ , and Ba
A second coating layer was formed on the surface of the first coating layer using SO _{4 in the same} manner as in Example 1 to obtain an exhaust gas purifying catalyst of this example. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier was 70 g of CZY, the amount of Pd supported thereon was 1.5 g, Al ₂ O _{3 was} 20 g, and BaS was 20 g.
O _{4 was} 20 g.

The exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 1, and then annealed to measure the CO—NO _x cross-point purification rate, HC purification rate, and HC 50% purification temperature. By doing
The catalyst performance was evaluated. Table 1 shows the results.

Example 3 In this example, first, the same method as in Example 1 was used to first prepare a composition of Ce— with a composition of Ce _0.60 Zr _0.30 Y _0.10 O _1.95 (CZY) and Zr _0.80 Ce _0.16 La _0.04 O _1.98 (ZCL). Z
Each r-type composite oxide was adjusted. Then, CZY
Pt alone (Pd / CZY), and Pt alone (Pt / CZY) on another CZY.
Y). Further, Rh was independently carried on ZCL (Rh / ZCL).

Rh / ZCL, Pt / CZY, and A
Using 1 ₂ O ₃ , a first coating layer was formed on the inner surface of each cell of the monolithic carrier in the same manner as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolith carrier was 50 g of ZCL, 0.8 g of Rh supported thereon, 20 g of CZY, and 1.0 g of Pt supported thereon.
g and 80 g of Al ₂ O ₃ .

Pd / CZY, CZY, Al_TwoO_Three,
And BaSO_FourBy using the same method as in the first embodiment
To form a second coating layer on the surface of the first coating layer.
An exhaust gas purification catalyst was used. In addition, monolith carrier 1dm
^ThreeThe weight of each component of the second coating layer with respect to
40 g of CZY as a body, and the Pd carrying amount thereof is 2.0
g, CZY10g with no noble metal supported, Al_Two
O_Three10g, BaSO _Four20 g.

The exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 1, and then annealed to measure the CO—NO _x cross-point purification rate, HC purification rate, and HC 50% purification temperature. By doing
The catalyst performance was evaluated. Table 1 shows the results.

Comparative Example 1 In this comparative example, the composition was changed to C by the same method as in Example 1.
A Ce-Zr composite oxide of e _0.50 Zr _0.50 O _2.00 (CZ) was prepared. In addition, Pt and Rh with respect to Al ₂ O ₃
Was co-supported (Pt-Rh / Al ₂ O ₃ ).

A first coating layer was formed on the inner surface of each cell of the monolithic carrier using Pt-Rh / Al ₂ O ₃ and CZ in the same manner as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier is
50 g of Al ₂ O ₃ , the supported amounts of Pt and Rh were 1.5 g and 0.5 g, and CZ was 80 g.

Example 1 was prepared using Al ₂ O ₃ and CZ.
The second coating layer was formed on the surface of the first coating layer by using the same method as described above. Note that the second with respect to the monolith carrier 1 dm ³
The weight of each component of the coating layer was 50 g of Al ₂ O ₃ ,
45 g.

Further, palladium nitrate was applied to the second coating layer.
And then dried at 600 ° C.
By baking for 3 hours, Pd is applied to the surface of the second coating layer.
Is impregnated and supported to obtain an exhaust gas purifying catalyst of this comparative example.
Was. In addition, monolith carrier 1dm ^ThreeSupported amount of Pd
Was 1.5 g.

The exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 1, and then annealed to measure the CO—NO _x cross point purification rate, HC purification rate, and HC 50% purification temperature. By doing
The catalyst performance was evaluated. Table 1 shows the results.

[0065]

[Table 1]

The exhaust gas purifying catalysts of Examples 1 to 3 have a two-layer coating layer. The second coating layer, which is the outer layer, contains Pd in a state where the Pd is supported on a Ce—Zr-based composite oxide (a kind of heat-resistant inorganic oxide) in which the atomic ratio of Ce is higher than the atomic ratio of Zr, Further, BaSO ₄ is contained. In addition, the first coating layer, which is the inner layer, has Ce-
Pt and Rh are contained in a state of being supported on a Zr-based composite oxide (a kind of heat-resistant inorganic oxide), and Al ₂ O ₃ is further contained.

As can be seen from Table 1, the exhaust gas purifying catalyst of each embodiment having the above-mentioned structure has a coating layer of 2 μm.
Pd is impregnated and supported on the surface of the second coating layer, and Pt is supported on the first coating layer while being supported on Al ₂ O _3.
And Rh than coexistence supported exhaust gas purifying catalyst of Comparative Example 1, CO-NO _x cross-point purifying rate and the HC purification ratio after the high temperature durability is high, HC50% purification temperature is lower. That is, the exhaust gas purifying catalysts of the respective embodiments have excellent high-temperature durability and high exhaust gas purifying activity at low temperatures.

As described above, the catalyst performance of the exhaust gas purifying catalyst of each embodiment is improved as compared with the comparative example 1.
The following reasons are considered. First, in the exhaust gas purifying catalysts of the respective examples, Pd is supported on a Ce—Zr-based composite oxide that is a heat-resistant inorganic oxide, whereby Pd itself grows in grains, and Pd itself is supported. It is considered that this is because a situation in which Pd is buried in the carrier due to grain growth is appropriately avoided, and deterioration of Pd activity is suppressed. Second, it is considered that BaSO ₄ is contained in the second coating layer, thereby suppressing the poisoning of Pd by P and HC. Third, since Pd is contained in the second coating layer, which is the outer layer, Pd capable of exhibiting excellent catalytic activity in a low-temperature region can effectively purify exhaust gas (HC) early from the start of engine start. It is thought that it is. Fourth, in the exhaust gas purifying catalyst of each embodiment, the first coating layer contains Al ₂ O ₃ to improve the high-temperature durability of the first coating layer itself. And Rh are functioning effectively.

[0069] EXAMPLE 4 In this example, in the same manner as in Example 1, first, the composition is _{Ce 0.50 Zr 0.45 Y 0.05 O 1.98} (CZY) and Zr _0.80 Ce _0.16 La _0.04 O _1.98 in (ZCL) Ce- Z
Each r-type composite oxide was adjusted. Then, in the same manner as in Example, Pd was alone supported (Pd / Al ₂ O ₃₎ with respect to Al ₂ O _3, and the Pt and Rh coexist supported (Pt-Rh / ZCL) against ZCL .

Using Pt-Rh / ZCL and Al ₂ O ₃ , a first coating layer was formed on the inner surface of each cell of the monolithic carrier in the same manner as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of ZCL, and the amount of Pt and Rh supported on the ZCL was 0.1 g.
75 g and 0.5 g, and 55 g of Al ₂ O ₃ were used.

Pd / Al ₂ O ₃ , CZY, and Ba
A second coating layer was formed on the surface of the first coating layer using SO _{4 in the same} manner as in Example 1 to obtain an exhaust gas purifying catalyst of this example. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of Al ₂ O ₃ ,
The Pd carrying amount was 1.5 g, CZY 80 g, and BaS
O _{4 was} 40 g.

Example 1 for this exhaust gas purifying catalyst
After performing the same 1100 ° C. durability test for 30 hours, annealing was performed, and the CO-NO _x cross-point purification rate, HC
The catalytic performance was evaluated by measuring the purification rate and the HC 50% purification temperature. Table 2 shows the results.

Example 5 In this example, first, the compositions were Ce _0.55 Zr _0.38 Y _0.07 O _1.97 (CZY) and Zr _0.78 Ce _0.16 La _0.02 Nd _0.04 O _1.97 (ZCLN) in the same manner as in Example 1.
) Was prepared. Then, in the same manner as in Example, Al ₂ O ₃ Pd was alone supported (Pd / Al ₂ O ₃₎ with respect to, co Pt and Rh with respect CZY bearing (Pt-Rh / CZY
) To carry Rh alone on ZCLN (Rh /
ZCLN).

Pt-Rh / CZY, Rh / ZCLN
, And Al ₂ O ₃ , a first coating layer was formed on the inner surface of each cell of the monolithic carrier in the same manner as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier was 90 g of CZY,
And Rh loadings of 1.0 g and 0.4 g, ZCLN
40 g, the Rh carrying amount of which was 0.4 g, Al ₂ O ₃ 5
0 g.

Pd / Al_TwoO_Three, And BaSO_FourBy
Using the same method as in Example 1, the surface of the first coating layer
A second coating layer is formed, and the exhaust gas purifying catalyst of this embodiment is
did. In addition, monolith carrier 1dm^ThreeSecond coating layer for
Weight of each component of Al _TwoO_Three70g of this Pd
1.5 g of supported amount, BaSO_Four20 g.

The exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 1, and then annealed to measure the CO—NO _x cross-point purification rate, HC purification rate, and HC 50% purification temperature. By doing
The catalyst performance was evaluated. Table 2 shows the results.

Example 6 In this example, the composition was Ce _0.60 Zr _0.32 Y _0.08 O _1.96 (CZY) and Zr _0.75 Ce _0.19 La _0.02 Pr _0.04 O _1.97 (ZCLP) in the same manner as in Example 1.
Of Ce-Zr-based composite oxides were prepared. Next, Pd is independently supported on Al ₂ O ₃ (Pd / Al ₂ O ₃₎ .
O ₃ ) to carry Pt alone on CZY (Pt /
CZY), and Pt and Rh were co-supported on ZCLP (Pt-Rh / ZCLP).

Pt / CZY, Pt-Rh / ZCLP,
And the Al ₂ O _3, to form a first coating layer on the inner surfaces of cells of a monolithic carrier by using the same method as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier was 90 g of CZY, the amount of Pt carried thereon was 1.0 g, the amount of ZCLP was 50 g, and the amounts of Pt and Rh were
The loading amounts are 0.75 g and 1.0 g, respectively, and Al ₂ O
_The weight was 80 g.

Pd / Al ₂ O ₃ , CZY, and Ba
A second coating layer was formed on the surface of the first coating layer using SO _{4 in the same} manner as in Example 1 to obtain an exhaust gas purifying catalyst of this example. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of Al ₂ O ₃ ,
The Pd carrying amount was 1.5 g, CZY 20 g, and BaS
O _{4 was} 20 g.

The exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 1, and then annealed to measure the CO—NO _x cross point purification rate, HC purification rate, and HC 50% purification temperature. By doing
The catalyst performance was evaluated. Table 2 shows the results.

Example 7 In this example, the composition was changed to Zr _0.68 Ce _0.26 La _0.02 Nd _0.04 O _1.97 (ZCL
N) Ce-Zr-based composite oxide was prepared. Then
Pd supported alone on Al ₂ O ₃ (Pd / CZY)
Then, Pt and Rh were co-supported on ZCLN (Pt-Rh / ZCLN).

Pt-Rh / ZCLN and Al ₂ O
_{According to 3} , a first coating layer was formed on the inner surface of each cell of the monolithic carrier using the same method as in Example 1. The weight of each component of the first covering layer against the monolithic carrier 1 dm ³ is, ZCLN70g, which Pt and Rh support amount respectively 1.5g and 0.5g of, Al ₂ O ₃ 70
g.

Pd / Al ₂ O ₃ , Al ₂ O ₃ , and B
A second coating layer was formed on the surface of the first coating layer using aSO _{4 in the same} manner as in Example 1 to obtain an exhaust gas purifying catalyst of this example. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of Al ₂ O ₃ as a noble metal carrier, the amount of Pd supported was 2.0 g, and 20 g of Al ₂ O ₃ not supporting a noble metal. , BaSO ₄
20 g.

The exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 1, and then annealed to measure the CO—NO _x cross-point purification rate, HC purification rate, and HC 50% purification temperature. By doing
The catalyst performance was evaluated. Table 2 shows the results.

Comparative Example 2 In this comparative example, the composition was changed to C by the same method as in Example 1.
A Ce-Zr composite oxide of e _0.50 Zr _0.50 O _2.00 (CZ) was prepared. In addition, Pt and Rh with respect to Al ₂ O ₃
Was co-supported (Pt-Rh / Al ₂ O ₃ ).

A first coating layer was formed on the inner surface of each cell of the monolithic carrier using Pt-Rh / Al ₂ O ₃ and CZ in the same manner as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier is
50 g of Al ₂ O ₃ , the supported amounts of Pt and Rh were 0.75 g and 0.5 g, and CZ was 45 g.

Example 1 was prepared using Al ₂ O ₃ and CZ.
The second coating layer was formed on the surface of the first coating layer by using the same method as described above. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of Al ₂ O ₃ ,
5 g.

Further, palladium nitrate was applied to the second coating layer.
And then dried at 600 ° C.
By baking for 3 hours, Pd is applied to the surface of the second coating layer.
Is impregnated and supported to obtain an exhaust gas purifying catalyst of this comparative example.
Was. In addition, monolith carrier 1dm ^ThreeSupported amount of Pd
Was 1.5 g.

The exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 1, and then annealed to measure the CO—NO _x cross-point purification rate, HC purification rate, and HC 50% purification temperature. By doing
The catalyst performance was evaluated. Table 2 shows the results.

[0090]

[Table 2]

The exhaust gas purifying catalysts of Examples 4 to 7 have two coating layers. And the outer layer, the second
The coating layer contains Pd while being supported on Al ₂ O ₃ (a kind of heat-resistant inorganic oxide), and further contains BaSO ₄ . The first coating layer, which is the inner layer, has Ce
Pt and Rh are contained in a state of being supported on a -Zr-based composite oxide (a kind of heat-resistant inorganic oxide), and further, Al ₂ O ₃
Is included.

As is clear from Table 2, the exhaust gas purifying catalysts of the respective embodiments having the above-mentioned structures have the coating layer of 2 μm.
Pd is impregnated and supported on the surface of the second coating layer, and Pt is supported on the first coating layer while being supported on Al ₂ O _3.
And than the exhaust gas purifying catalyst of Comparative Example 2 Rh is included, CO-NO _x cross-point purifying rate and the HC purification ratio after the high temperature durability is high, HC50% purification temperature is lower. That is, the exhaust gas purifying catalysts of the respective embodiments have excellent high-temperature durability and high exhaust gas purifying activity at low temperatures.

As described above, the catalyst performance of the exhaust gas purifying catalyst of each embodiment is improved as compared with that of the comparative example 1.
The following reasons are considered. First, in the exhaust gas purifying catalysts of the respective embodiments, Pd is preliminarily supported and fixed on Al ₂ O ₃ , which is a heat-resistant inorganic oxide, so that Pd itself grows in a grain size, and It is considered that this is because a situation in which Pd is buried in the carrier due to grain growth is appropriately avoided, and deterioration of Pd activity is suppressed. In addition, similarly to the second to fourth reasons for the exhaust gas purifying catalysts of Examples 1 to 3 described above, the second coating layer contains BaSO ₄ and the first coating layer contains the heat-resistant inorganic oxide. This is considered to be because Pt and Rh are contained in a state of being supported on, and Al ₂ O ₃ is further contained.

Example 8 In this example, first, the composition was Ce _0.50 Zr _0.45 Y _0.05 O _1.98 (CZY), Zr
_0.80 Ce _0.16 La _0.04 O _1.98 (ZCL), and Zr
_0.80 Ce _0.15 Pr _0.05 O _1.98 (ZCP) Ce-Zr-based composite oxide was prepared. Next, Pd is independently supported on ZCP (Pd / ZCP), and Pt and Rh are co-supported on CZY (Pt-Rh / CZY).
) To carry only Pt on ZCL (Pt / ZC
L).

A first coating layer was formed on the inner surface of each cell of the monolithic carrier using Pt-Rh / CZY, Pt / ZCL, and Al ₂ O _{3 in the same} manner as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of CZY, the loading amounts of Pt and Rh were 0.5 g and 0.5 g, and ZCL50
g, the amount of supported Pt was 0.5 g, and Al ₂ O _{3 was} 55 g.

A second coating layer was formed on the surface of the first coating layer using Pd / ZCP, CZY, Al ₂ O ₃ , and BaSO _{4 in the same} manner as in Example 1, and the exhaust gas of this example was used. A catalyst for purification was used. In addition, monolith carrier 1dm ³
Weight of each component of the second coating layer with respect to
g, the amount of Pd carried thereon was 3.0 g, CZY 50 g, A
l ₂ O ₃ 45g, it was BaSO ₄ 40g.

The exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test described below for 20 hours, annealed for 2 hours in the same manner as in Example 1, and then subjected to CO-NO _x
Crosspoint purification rate, HC purification rate, and HC 50%
The catalytic performance was evaluated by measuring the purification temperature.
Table 3 shows the results.

(1100 ° C. Endurance Test) In the 1100 ° C. endurance test, a 4-liter V-type 8-cylinder engine was mounted on an actual vehicle, and the exhaust gas purifying catalyst of this embodiment was mounted on one bank (4 cylinders) of this engine. Was carried out. Specifically, one cycle (60
This cycle is repeated 1200 times for a total of 20 seconds.
Time went on. As shown in FIG. 2, during the period from 0 to 40 seconds, the stoichiometric air-fuel ratio (A / F =
14.6), which was maintained in a stoichiometric state, was supplied to the engine, and the internal temperature of the exhaust gas purifying catalyst (catalyst bed) was set to be around 850 ° C.
During the period of 40 to 44 seconds, the feedback is opened and the fuel is excessively injected to make the fuel rich state (A
/F=11.2) was supplied to the engine. 44
During a period of up to 56 seconds, while the feedback is open and the fuel is excessively supplied, secondary air is blown from the outside of the engine through the introduction pipe from the upstream side of the exhaust gas purifying catalyst, and the catalyst bed is discharged. Inside, excess fuel was reacted with secondary air to raise the catalyst bed temperature. At this time, the maximum temperature was 1100 ° C., and the A / F was maintained at about 14.8, which is approximately the stoichiometric air-fuel ratio. During the last 56 to 60, without supplying excess fuel, secondary air is supplied with the feedback open, and the lean state (A / F =
22.0). The fuel was supplied in the form of gasoline containing phosphorus (P) using engine oil (5W-30SG grade, manufactured by Cosmo) to provide an environment in which Pd was easily poisoned. At this time, the amount of P added is the total amount during the durability test,
It was 0.27 g in terms of element. The catalyst bed temperature was measured by a thermocouple inserted at the center of the honeycomb carrier.

Example 9 In this example, the composition was firstly changed to Zr _0.80 Ce _0.16 La _0.04 O _1.98 (ZCL) and Zr _0.70 Ce _0.22 La _0.02 Nd _0.04 O _1.97 (ZCLN) in the same manner as in Example 1.
) Was prepared. Next, Pd is independently supported on ZCL (Pd / ZCL)
Then, Pt and Rh were co-supported on ZCLN (Pt-Rh / ZCLN).

Pt-Rh / ZCLN and Al ₂ O
_{According to 3} , a first coating layer was formed on the inner surface of each cell of the monolithic carrier using the same method as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of ZCLN, the loadings of Pt and Rh were 0.75 g and 0.25 g, and 50 g of Al ₂ O ₃ .

Pd / ZCL, Al_TwoO_Three, And BaS
O_FourBy using the same method as in Example 1, the first coating layer
A second coating layer is formed on the surface of the exhaust gas to purify the exhaust gas of the present embodiment.
Catalyst. In addition, monolith carrier 1dm^ThreeThe first
2 The weight of each component of the coating layer is 70 g of ZCL,
5.0 g of Pd carrying amount, Al_TwoO_Three20g, BaSO _Four
20 g.

[0102] performed 1100 ° C. durability test in the same manner as in Example 8 to the exhaust gas purifying catalyst, after annealing in the same manner as in Example 1, CO-NO _x cross-point purifying rate, HC purification rate, and The catalyst performance was evaluated by measuring the HC 50% purification temperature. Table 3 shows the results.

Example 10 In this example, the composition was changed to Zr _0.70 Ce _0.22 La _0.02 Nd _0.04 O _1.97 (ZCL
N), Zr _0.80 Ce _0.16 La _0.04 O _1.98 (ZCL),
And Ce _0.60 Zr _0.30 Y _0.10 O _1.95 (CZY)
Each e-Zr-based composite oxide was prepared. Then, Z
Supports Pd alone on CLN (Pd / ZCLN)
And Rh alone on ZCL (Rh / ZCL)
To carry only Pt on CZY (Pt / CZ
Y).

Rh / ZCL, Pt / CZY, and A
Using 1 ₂ O ₃ , a first coating layer was formed on the inner surface of each cell of the monolithic carrier in the same manner as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolith carrier was 40 g of ZCL, and the Rh carrying amount of this was 0.1 g.
8 g, CZY 20 g, the Pt carrying amount of the same is 1.0 g,
Al ₂ O _{3 was} 80 g.

Pd / ZCLN, CZY, Al
_{A second} coating layer was formed on the surface of the first coating layer using ₂ O ₃ and BaSO _{4 in the same} manner as in Example 1 to obtain an exhaust gas purifying catalyst of this example. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier is:
ZCLN 60g, Pd carrying amount of this 4.0g, CZ
Y was 10 g, Al ₂ O _{3 was} 10 g, and BaSO _{4 was} 20 g.

This exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 8, and after annealing as in Example 1, the CO—NO _x cross point purification rate, HC purification rate, and The catalyst performance was evaluated by measuring the HC 50% purification temperature. Table 3 shows the results.

Comparative Example 3 In this comparative example, the composition was C
A Ce-Zr composite oxide of e _0.50 Zr _0.50 O _2.00 (CZ) was prepared. In addition, Pt and Rh with respect to Al ₂ O ₃
Was co-supported (Pt-Rh / Al ₂ O ₃ ).

The first coating layer was formed on the inner surface of each cell of the monolithic carrier using Pt-Rh / Al ₂ O ₃ and CZ in the same manner as in Example 1. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier is
50 g of Al ₂ O ₃ , and the amount of Pt and Rh supported thereon was 1.
0 g and 0.5 g, and CZ 70 g.

Example 1 was prepared using Al ₂ O ₃ and CZ.
The second coating layer was formed on the surface of the first coating layer by using the same method as described above. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of Al ₂ O ₃ ,
5 g.

Further, the second coating layer was impregnated with an aqueous solution of palladium nitrate, dried, and then dried.
By baking at 0 ° C. for 3 hours, Pd was impregnated and supported on the surface of the second coating layer to obtain an exhaust gas purifying catalyst of this comparative example. The amount of Pd carried was ³ g per 1 dm ³ of the monolithic carrier.

[0111] performed 1100 ° C. durability test in the same manner as in Example 8 to the exhaust gas purifying catalyst, after annealing in the same manner as in Example 1, CO-NO _x cross-point purifying rate, HC purification rate, and The catalyst performance was evaluated by measuring the HC 50% purification temperature. Table 3 shows the results.

[0112]

[Table 3]

The exhaust gas purifying catalysts of Examples 8 to 10 have a two-layer coating layer. And the outer layer, the second
Ce—Zr-based composite oxide (a kind of heat-resistant inorganic oxide) in which the atomic ratio of Zr is larger than the atomic ratio of Ce in the coating layer
Pd is contained in a state of being supported on BaSO ₄
Is included. In addition, the first coating layer, which is the inner layer,
Pt and Rh are contained in a state of being supported on a Ce-Zr-based composite oxide (a kind of heat-resistant inorganic oxide), and further, Al ₂
O ₃ is contained.

As is clear from Table 3, the exhaust gas purifying catalysts of the respective embodiments having the above-mentioned structures have a coating layer of 2 μm.
Pd is impregnated and supported on the surface of the second coating layer, and Pt is supported on the first coating layer while being supported on Al ₂ O _3.
Than the exhaust gas purifying catalyst and Rh comparison is included Example 3, CO-NO _x cross-point purifying rate and the HC purification ratio after the high temperature durability is high, HC50% purification temperature is lower. That is, the exhaust gas purifying catalysts of the respective embodiments have excellent high-temperature durability and high exhaust gas purifying activity at low temperatures.

As described above, the catalyst performance of the exhaust gas purifying catalyst of each embodiment is improved as compared with that of the comparative example 1.
The following reasons are considered. First, in the exhaust gas purifying catalysts of the respective examples, Pd is supported on a Ce—Zr-based composite oxide that is a heat-resistant inorganic oxide, whereby Pd itself grows in grains, and Pd itself is supported. It is considered that this is because a situation in which Pd is buried in the carrier due to grain growth is appropriately avoided, and deterioration of Pd activity is suppressed. In addition, similarly to the second to fourth reasons for the exhaust gas purifying catalysts of Examples 1 to 3 described above, the second coating layer contains BaSO ₄ and the first coating layer contains the heat-resistant inorganic oxide. It is considered that Pt and Rh are contained in a state of being supported on, and Al ₂ O ₃ is further contained.

[0116]

As described above, according to the present invention, it is possible to maintain a high catalytic activity even after endurance at a high temperature, and to effectively operate even at a relatively low temperature such as immediately after starting the internal combustion engine. An exhaust gas purifying catalyst is provided.

[Brief description of the drawings]

FIG. 1 is a cycle diagram for explaining a 1100 ° C. endurance test in Examples 1 to 3 (Examples 4 to 7) and Comparative Example 1 (Comparative Example 2).

FIG. 2 shows 1100 ° C. in Examples 8 to 10 and Comparative Example 3.
It is a cycle diagram for explaining a durability test.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hirohisa Tanaka 2-1-1 Taoyuan, Ikeda-shi, Osaka Daihatsu Kogyo Co., Ltd. F-term (reference) 4D048 AA06 AA13 AA18 AB05 AB07 AC06 BA01Y BA03X BA08X BA14Y BA15X BA18X BA19X BA30X BA31X BA33X BA39Y BA41X BA42X BA46X BB02 EA04 4G069 AA03 AA08 BA01A BA01B BA05A BA05B BB02A BB02B BB04A BB06A BB06B BB10A BB10B BC03A BC06A BC09A BC10A BC13A BC13B BC38A BC40A BC40B BC42A BC42B BC43A BC43B BC44A BC44B BC51A BC51B BC71A BC71B BC72A BC72B BC75A BC75B CA02 CA03 CA09 EA18 EA19 EB12Y EB14Y EB15Y EC28 ED06 FA03 FA06 FB15 FB23

Claims (5)

[Claims] 1. An exhaust gas purifying catalyst comprising a heat-resistant support carrier and a coating layer containing a noble metal catalyst formed on a surface thereof, wherein the coating layer is directly supported on the surface of the heat-resistant support carrier. 1 coating layer and a second coating layer formed on the surface of the first coating layer, and the first coating layer contains at least one of platinum and rhodium as a noble metal catalyst, An exhaust gas purifying catalyst, wherein the second coating layer contains palladium as a noble metal catalyst in a state of being supported on a heat-resistant inorganic oxide. 2. The exhaust gas purifying catalyst according to claim 1, wherein the heat-resistant inorganic oxide is an oxide containing at least one of cerium oxide and zirconium oxide, or alumina. 3. The exhaust gas according to claim 1, wherein the second coating layer contains at least one element selected from the group consisting of barium, calcium, cesium, potassium, magnesium, and lanthanum. Purification catalyst. 4. The exhaust gas according to claim 1, wherein platinum or rhodium in the first coating layer is supported on an oxide containing at least one of cerium oxide and zirconium oxide. Gas purification catalyst. 5. The exhaust gas purifying catalyst according to claim 1, wherein the first coating layer contains alumina.