JP2001070792A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain high catalytic activity even after enduring exposure to high temperatures by forming a composite layer having Rh and Pt carried in coexistence by each of compound oxides A, B represented by a specific formula, on a heat-resistant support carrier and setting the weight of Rh carried by the compound oxide A not less than the weight of Rh carried by the compound oxide B. SOLUTION: A composite layer having Rh and Pt carried in coexistence by each of a compound oxide a represented by formula I (wherein, N is an alkaline earth metallic element and an alkaline rare earth element (excluding Ce and Zr), 0.65<1-(a+b)<=0.90, 0.10<=a<0.35, 0<=b<=0.20 and; C is an oxygen loss to be determined by N) and a compound oxide B represented by formula II (wherein, M is an alkaline earth metal element and an alkaline rare earth element (excepting Ce and Zr), 0.35<=1-(x+y)<=0.80, 0.20<=x<=0.65, 0<=y<=0.20 and: Z is an oxygen loss to be determined by M), is formed on a heat-resistant support carrier. In addition, the weight of Rh carried by the compound oxide A is set not less than the weight of Rh carried by the compound oxide B.

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]

2. Description of the Related Art NO _x , CO 2,
Alternatively, a so-called three-way catalyst using a noble metal such as platinum, palladium, or rhodium as an active material is one of the catalysts most widely used to purify harmful substances such as HC. These three-way catalyst, the reduction reaction from NO _X to N _2, or CO 2 from CO ₂ and HC
It acts as a catalyst for the oxidation reaction of CO 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] Therefore, various studies have been made to improve the activity of the three-way catalyst. For example, oxygen in the gas phase of cerium oxide (CeO ₂ ) is stored or released in the gas phase. Capacity (Oxygen storage capacity (OS
C)). That is, to jointly cerium oxide in a three-way catalyst and the gas phase atmosphere, the oxygen concentration in the gas phase atmosphere is adjusted by the cerium oxide, the reduction reaction of the NO _X by the three-way catalyst, as well as CO and H
The efficiency of the oxidation reaction of C is improved.

[0004]

By the way, catalysts for automobiles tend to be mounted below the floor at maniverters closer to the internal combustion engine in order to cope with increasingly severe cold emissions. Therefore, the exhaust gas purifying catalyst including the three-way catalyst may be practically exposed to a high temperature of, for example, 900 ° C. or more (in some cases, 1000 ° C. or more). Requires high catalytic activity at such high temperatures. On the other hand, high catalyst activity is required even at a relatively low temperature where the internal combustion engine is not sufficiently warmed, such as immediately after the internal combustion engine is started.

The present invention has been conceived under the circumstances described above, and can maintain a high catalytic activity even after being exposed to a high temperature condition, and can maintain a high catalytic activity even at a relatively low temperature. An object of the present invention is to provide an exhaust gas purifying catalyst that can function effectively.

[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 represented by the following general formula (3):
A zirconium-based composite oxide in which rhodium and platinum are co-supported,

Embedded image (In the formula (3), N is at least one element selected from the group consisting of an alkaline earth metal element and a rare earth element (excluding cerium and zirconium), and 0.65 <1- (a + b) ≦ 0 .90, 0.10 ≦
a <0.35, 0 ≦ b ≦ 0.20, and c represent the oxygen deficiency determined by the oxidation number and atomic ratio of N. )
A cerium-based composite oxide represented by the following general formula (4) and further supporting rhodium and platinum together;

Embedded image (In the formula (4), M is at least one element selected from the group consisting of an alkaline earth metal element and a rare earth element (excluding cerium and zirconium), and 0.35 ≦ 1- (x + y) ≦ 0 .80, 0.20 ≦
x ≦ 0.65, 0 ≦ y ≦ 0.20, and z represent the oxygen deficiency determined by the oxidation number and atomic ratio of M. )
Is formed on the heat-resistant support carrier, and the weight of rhodium supported on the zirconium-based composite oxide is equal to or greater than the weight of rhodium supported on the cerium-based composite oxide. And

The zirconium-based composite oxide has the general formula
As is clear from (3), this is a composite of zirconium oxide and cerium oxide, and contains an alkaline earth metal element and a rare earth element (excluding cerium and zirconium) as necessary. Such a zirconium-based composite oxide suppresses deterioration of catalyst performance due to solid solution of Rh into a carrier and grain growth, and improves heat resistance and durability in a coating layer mainly for long-term use of the catalyst. Used to make

In order to obtain such advantages, in the present invention, the ratio of zirconium atoms in the zirconium-based composite oxide is set to 0.65 <1- (a + b) ≦ as described above.
0.90, and the atomic ratio of cerium is 0.10 ≦ a ≦
It is set to 0.35.

The zirconium-based composite oxide may contain an alkaline earth metal element or a rare earth element (excluding cerium and zirconium) as necessary to improve the heat resistance of the zirconium-based composite oxide as a whole. It is.

In addition to the above advantages, taking into account the proportions of zirconium and cerium, the atomic proportions of the alkaline earth metal elements and rare earth elements (excluding cerium and zirconium) in the zirconium-based composite oxide are as follows:
As described above, 0 ≦ b ≦ 0.20.

The cerium-based composite oxide has the general formula
As is clear from (4), this is a composite of cerium oxide and zirconium oxide, and contains an alkaline earth metal element and a rare earth element (excluding cerium and zirconium) as necessary. Such a cerium-based composite oxide is added in the coating layer mainly to utilize the oxygen storage capacity (OSC) of cerium oxide. That is, by adjusting the oxygen concentration in the atmosphere by cerium oxide of cerium complex oxide, of the NO _X by the platinum and rhodium reduction reaction, as well as C
The efficiency of the oxidation reaction of O and HC is improved.

Further, for example, in an oxidizing atmosphere, oxygen in the atmosphere is occluded by cerium oxide, so that the amount of oxygen in the oxidizing atmosphere is reduced. This properly prevents platinum from growing in an oxidizing atmosphere,
The decrease in the activity of the exhaust gas purifying catalyst is suppressed.

In order to obtain such advantages, in the present invention, the ratio of cerium atoms in the cerium-based composite oxide is determined as follows:
As described above, 0.40 ≦ 1− (x + y) ≦ 0.80.

The reason that zirconium oxide is contained in the cerium-based composite oxide is mainly to suppress the grain growth of cerium oxide and to improve the heat resistance of the cerium-based composite oxide as a whole.

In order to obtain such advantages, in the present invention, the ratio of zirconium atoms in the cerium-based composite oxide is set to 0.20 ≦ x ≦ 0.65 as described above.

If necessary, the cerium-based composite oxide contains an alkaline earth metal element or a rare earth element (excluding cerium and zirconium) in the same manner as the zirconium-based composite acid contains these elements. For the reason, alkaline earth metal elements and rare earth elements (excluding cerium and zirconium) in cerium-based composite oxides
Is set to 0 ≦ y ≦ 0.20 as described above.

The alkaline earth metal elements contained in the cerium-based composite oxide and the zirconium-based composite oxide include:
Beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (B
a), and radium (Ra). Of these alkaline earth metal elements, Mg and Ca are preferably used.

The rare earth elements (excluding cerium and zirconium) contained in the cerium-based composite oxide and the zirconium-based composite oxide include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), Neodymium (Nd), Promethium (Pm),
Samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er),
Thulium (Tm), ytterbium (Yb), and lutetium (Lu). Among these rare earth elements, Y, La, Pr, Nd, Gd, and Tb are preferably used.

Platinum has a high catalytic activity for the oxidation reaction of CO and HC, while rhodium has a high catalytic activity for CO and HC.
It has a high catalytic ability for both the oxidation reaction of C and the reduction reaction of NO _x , and is particularly superior in catalytic ability to NO _x reduction to platinum. Therefore, as the exhaust gas purifying catalyst of the present invention, rhodium and platinum, to jointly supported on the same carrier, both the reduction reaction of the oxidation reaction and NO _x in the CO and HC to allow good balance Become. Accordingly, the zirconium complex oxide and the exhaust gas purifying catalyst of the present invention which rhodium and platinum both cerium complex oxide is co-supported, can effectively purify CO, HC, and NO _x. Even when rhodium and platinum are co-supported on the same carrier, these noble metals do not form an alloy that impairs their properties at high temperatures.

As mentioned above, the zirconium-based composite oxide has higher heat resistance than the cerium-based composite oxide,
Moreover, rhodium has a higher catalytic activity than NO for reducing NO _x . Therefore, in order for the exhaust gas purifying catalyst to function effectively for a long period of time, N
It is preferred that a large amount of rhodium having a higher O _x reducing ability be supported on the zirconium-based composite oxide, which hardly causes performance deterioration due to grain growth or the like. Therefore, in the present invention, the supported amount of rhodium of the zirconium-based composite oxide is set to be equal to or larger than the supported amount of rhodium of the cerium-based composite oxide. Preferably, the weight ratio of the supported amount of rhodium of the zirconium-based composite oxide to the supported amount of rhodium of the cerium-based composite oxide is 1
/ 1 to 19/1, more preferably 1/1 to 19/1.
The range is 5/1, more preferably about 3/1.

On the other hand, it is preferable that at least half of the total amount of platinum supported on the cerium-based composite oxide and the zirconium-based composite oxide be supported on the cerium-based composite oxide.

As described above, in the exhaust gas purifying catalyst of the present invention, two types of carriers (zirconium-based composite oxide and cerium-based composite oxide) having different main purposes or functions are used, and the function of each carrier is determined. The loading ratio of each noble metal on each support is adjusted according to the catalytic performance of the noble metal. Therefore, the exhaust gas purifying catalyst of the present invention has C
O, can effectively purify three components of HC and NO _x, yet can effectively maintain the catalyst performance after the repeated exposure to adverse conditions (e.g., high temperature).

Here, examples of the heat-resistant support carrier include a honeycomb carrier composed of cordierite, mullite, α-alumina, metal (for example, stainless steel), etc. and having a large number of cells formed thereon. When this honeycomb carrier is used, the inner surface of each cell is coated with a cerium-based composite oxide or a zirconium-based composite oxide supporting a predetermined noble metal (known washcoat).
This is used as an exhaust gas purifying catalyst.

The coating layer may be constituted as a single layer,
Moreover, you may comprise as multiple layers. For example, the coating layer includes a first coating layer formed on the surface of the heat-resistant support carrier and a second coating layer formed on the surface of the first coating layer.
In the case of a layered structure, at least one of the coating layers contains both a zirconium-based composite oxide and a cerium-based composite oxide in which rhodium and platinum are co-supported.

Also, the first coating layer contains palladium,
A configuration in which the second coating layer contains both a zirconium-based composite oxide and a cerium-based composite oxide in which rhodium and platinum are co-supported may be employed. vice versa,
A configuration in which both the zirconium-based composite oxide and the cerium-based composite oxide in which rhodium and platinum are co-supported in the first coating layer and palladium is included in the second coating layer may be adopted. Palladium is a catalyst having excellent low-temperature activity, and a catalyst for purifying exhaust gas containing the same can satisfactorily purify low-temperature exhaust gas, particularly HC. Thus, even when the internal combustion engine is not sufficiently warmed up, exhaust gas such as HC can be sufficiently purified.

The cerium-based composite oxide and zirconium-based composite oxide can be adjusted to a desired composition by a known method (a coprecipitation method or an alkoxide method).

In the coprecipitation method, a solution of cerium, zirconium, and, if necessary, a salt solution containing an alkaline earth metal element and a rare earth element (excluding cerium and zirconium) is adjusted to have a predetermined stoichiometric ratio. An alkaline aqueous solution is added to this solution to coprecipitate a salt containing cerium, zirconium, and, if necessary, an alkaline earth metal element and a rare earth element (excluding cerium and zirconium), and then heat-treating the coprecipitate. Thus, the composite oxide is adjusted.

The salts of alkaline earth metal elements and salts of rare earth elements (including cerium and zirconium) 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.

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

In the alkoxide method, a mixed alkoxide solution containing cerium, zirconium and, if necessary, an alkaline earth metal element or a rare earth element (excluding cerium and zirconium) is prepared, and deionized water is added to the mixed alkoxide solution. The composite oxide is prepared by hydrolysis and heat treatment of the hydrolysis product.

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

The zirconium source used in these methods may contain about 1 to 3% of hafnium used in general industrial applications. In such a case, the present invention uses the zirconium content in the present invention. And the composition is calculated.

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.

The supporting of rhodium and platinum on the composite oxide obtained after the calcination is carried out by preparing a solution of a salt containing rhodium and platinum, impregnating the solution with the composite oxide, and then performing a heat treatment.

As the rhodium or platinum salt solution, a nitrate aqueous solution, a chloride aqueous solution or the like is used.
The rhodium or platinum salt solution contains about 1 to 20% by weight of rhodium or platinum salt.

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 composite oxide carrying rhodium or platinum is coated on a heat-resistant support. When a honeycomb carrier is used as the heat-resistant support carrier, as described above, a coating layer is formed on the inner surface of each cell. This coating layer is formed by the same method as a known wash coat layer. For example, a cerium-based composite oxide powder carrying rhodium and platinum is pulverized and mixed to form a slurry, and this slurry is adhered to a honeycomb carrier and fired in an electric furnace or the like at, for example, 600 ° C. for 3 hours. It is performed by

[0039]

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 Zr _0.80 Ce _0.16 La _0.04
Zirconium-based composite oxide (ZCL) of O _1.98 and C
After preparing a cerium-based composite oxide (CZY) of e _0.55 Zr _0.38 Y _0.07 O _1.97 , platinum and rhodium were co-supported on each of the composite oxides.

A coating layer was formed on the inner surface of each cell of the monolithic carrier with each of the composite oxides supporting noble metal, CZY not supporting noble metal, and alumina (Al ₂ O ₃ ). An exhaust gas purification catalyst was used.

After the exhaust gas purifying catalyst was endured at 1100 ° C., 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 1 shows the results.

(Monolith Carrier) Monolith carriers include:
A column made of cordierite having a diameter of 105 mm, a length of 171 mm, a capacity of 1.5 liter, a wall thickness of 0.1 mm, and a density of 600 cells / inch ² was used.

(Preparation of Composite Oxide) Zirconium-based composite oxide (ZCL) and cerium-based composite oxide (CZY)
) Was adjusted by the so-called alkoxide method. ZC
L is firstly zirconium methoxypropylate 0.1
6 mol, cerium methoxypropylate 0.032
mol, lanthanum methoxy propylate 0.08 mol
Was 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 was distilled off and evaporated to dryness to prepare a precursor. The precursor was air-dried at 60 ° C. for 24 hours, and then dried in an electric furnace.
Heat-treated at 0 ° C for 3 hours, Zr _0.80 Ce _0.16 La _0.04 O
A ZCL powder having a composition of _1.98 was obtained. About CZY, cerium methoxypropylate 0.11mo
1, zirconium methoxypropylate 0.076mo
l, and yttrium methoxypropylate 0.01
Adjustment was carried out through the same operation as for ZCL, except that a mixed alkoxide solution was prepared as 4 mol.

(Supporting of Catalyst on Composite Oxide) ZCL is impregnated with an aqueous solution of rhodium nitrate adjusted to be 0.6% by weight in terms of rhodium element, and dried, and then dried. The rhodium-supported zirconium-based composite oxide (Rh / Z
CL) was obtained. Further, it is impregnated with a dinitrodiammine platinum nitrate solution adjusted to be 0.8% by weight in terms of platinum element, and dried and dried.
By firing at 3 ° C. for 3 hours, a platinum-supported zirconium-based composite oxide (Pt-Rh / ZC
L) was obtained. By a similar operation, a cerium-based composite oxide supporting rhodium and platinum (Pt-R
h / CZY).

(Formation of Coating Layer) Powder Pt-Rh / ZCL, Pt-Rh / C of the composite oxide thus obtained
A slurry is prepared from a mixture of ZY, CZY in which noble metal is not supported, and alumina (Al ₂ O ₃ ) mixed and pulverized by a ball mill, and the slurry is attached to the inner surface of the cell of the monolith carrier and dried. By firing at 600 ° C. for 3 hours, an exhaust gas purifying catalyst of this example was obtained. In this embodiment, the weight of each component in the coating layer of the exhaust gas purifying catalyst is
Per dm ³ , 50 g of ZCL, 0.3 g and 0.4 g of the supported amount of rhodium and platinum, 50 g of CZY as a carrier of the noble metal, 0.3 g and 0.4 g of the supported amount of rhodium and platinum, 30 g of CZY and 55 g of alumina were used. That is, the weight ratio of the supported amount of rhodium and the supported amount of platinum between ZCL and CZY was 1/1.

(1100 ° C. Endurance Test) In this endurance test, a 4-liter V-type 8-cylinder engine was mounted on a real vehicle,
This was carried out by mounting the exhaust gas purifying catalyst of this embodiment on one bank (four cylinders) of this engine. Specifically, the cycle described below was one cycle (60 seconds), and this cycle was repeated 3,000 times for a total of 50 hours. As shown in FIG. 1, the stoichiometric air-fuel ratio (A / F = 14.
6) The mixture maintained in the 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. 40 ~
During 44 seconds, while the feedback is open, the fuel is excessively injected and the fuel is rich (A / F =
The mixture of 11.2) was supplied to the engine. 44-56
During the second, while the feedback is open and the fuel is excessively supplied, the 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 exhaust gas purification is performed. Excess fuel and secondary air were reacted inside the catalyst 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. Last 56-60
During this period, the secondary air was supplied while the feedback was kept open without supplying excess fuel, and the fuel cell was in a lean state. The temperature of the catalyst bed was measured by a thermocouple inserted at the center of the honeycomb carrier.

[0048] For (CO-NO _X crosspoint purification ratio and HC measurements purification rate) exhaust gas purifying catalyst of the present embodiment was subjected to durability test as described above, the lean air-fuel mixture from the fuel-rich supplies while changing the engine, which were measured the rate at which CO and NO _X contained in exhaust gas discharged when burned in the engine is purified by a catalyst for purifying exhaust gases of this embodiment, the purification rate when the purification rate of these components match was CO-NO _X crosspoint purification rate. At this time, the HC purification rate was measured simultaneously. 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 its space velocity SV is 90000 / h.
And

(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 was performed at a space velocity (SV) of the exhaust gas of 90000 / 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, the composition of the zirconium-based composite oxide was changed to Zr _0.78 Ce _0.16 La _0.02 N in the same manner as in Example 1.
After adjusting the composition of d _0.04 O _1.97 (ZCLN) and the cerium-based composite oxide to Ce _0.50 Zr _0.45 Y _0.05 O _1.98 (CZY), platinum and rhodium were co-supported on each composite oxide.

A coating layer was formed on the inner surface of each cell of the monolithic carrier using the same method as in Example 1 by using each of the composite oxides and platinum, on which platinum and rhodium were co-supported, and alumina. An exhaust gas purification catalyst was used.
The weight of each component of the coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of ZCLN, the loading amounts of rhodium and platinum were 0.45 g and 0.4 g, and CZY
75 g, with a loading of rhodium and platinum of 0.1 g.
15 g and 0.4 g, and 55 g of alumina were used. That is, the weight ratio of the supported amount of rhodium and the supported amount of platinum between ZCLN and CZY was 3/1 and 1/1.

The exhaust gas purifying catalyst was subjected to an endurance test at 1100 ° C. in the same manner as in Example 1;
NO _x cross point purification rate, HC purification rate, and HC
The catalyst performance was evaluated by measuring the 50% purification temperature. Table 1 shows the results.

Example 3 In this example, the composition of the zirconium-based composite oxide was changed to Zr _0.80 Ce _0.16 La _0.04 O in the same manner as in Example 1.
_1.98 (ZCL), the composition of cerium-based composite oxide
After adjusting to _0.60 Zr _0.32 Y _0.08 O _1.96 (CZY), rhodium and platinum were co-supported on each composite oxide.

These composite oxides and alumina (Al
₂ O ₃ ), a coating layer was formed on the inner surface of each cell of the monolithic carrier in the same manner as in Example 1 to obtain an exhaust gas purifying catalyst of this example. In addition, monolith carrier 1dm
^The weight of each of the components of the coating layer relative to ³ is ZCL50
g, carrying 0.5 g of rhodium and platinum.
And 0.4 g, CZY 90 g, the supported amounts of rhodium and platinum were 0.1 g and 0.4 g, and alumina 80 g. That is, the weight ratio of the supported amount of rhodium and the supported amount of platinum between ZCL and CZY was 5/1 and 1/1.

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

Example 4 In this example, the composition of the zirconium-based composite oxide was changed to Zr _0.78 Ce _0.16 La _0.02 N in the same manner as in Example 1.
After adjusting the composition of d _0.04 O _1.97 (ZCLN) and the cerium-based composite oxide to Ce _0.50 Zr _0.45 Y _0.05 O _1.98 (CZY), platinum and rhodium were co-supported on each composite oxide.

A coating layer was formed on the inner surface of each cell of the monolithic carrier using the same method as in Example 1 by using each of the composite oxide and platinum supported on platinum and rhodium together, and alumina. An exhaust gas purification catalyst was used.
The weight of each component of the coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of ZCLN, the supported amounts of rhodium and platinum were 0.34 g and 0.4 g, and CZY
75 g of which the supported amount of rhodium and platinum is 0.
11 g and 0.4 g, and 55 g of alumina were used. That is, the weight ratio of the supported amount of rhodium and the supported amount of platinum between ZCLN and CZY was 33/11 and 1/1.

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

Comparative Example 1 In this example, the composition of the zirconium-based composite oxide was changed to ZrO _2.00 (Z) and the composition of the cerium-based composite oxide was changed to Ce _0.80 Zr _0.20 O _2.00 (CZ) in the same manner as in Example 1. )
After the adjustment, rhodium and platinum were supported on these composite oxides.

Using a composite oxide carrying a noble metal and alumina (Al ₂ O ₃ ), a coating layer was formed on the inner surface of each cell of the monolithic carrier in the same manner as in Example 1 to obtain a comparative example. Exhaust gas purification catalyst. The weight of each component of the coating layer with respect to 1 dm ³ of the monolithic carrier was 0.5 g and 0.4 g of Z50 g, the supported amount of rhodium and platinum, 75 g of CZ, and 0.7 g of the supported amount of rhodium and platinum. And 0.4 g,
Alumina g55 was used. That is, the weight ratio of the supported amount of rhodium and the supported amount of platinum between Z and CZ was 5/7 and 1/1.

The exhaust gas purifying catalyst was subjected to an endurance test at 1100 ° C. in the same manner as in Example 1;
NO _x cross point purification rate, HC purification rate, and HC
The catalyst performance was evaluated by measuring the 50% purification temperature. Table 1 shows the results.

[0062]

[Table 1]

In Examples 1 to 4, rhodium and platinum were supported on the zirconium-based composite oxide and the cerium-based composite oxide, respectively, and the amount of rhodium supported on the zirconium-based composite oxide and the cerium-based composite oxide was determined. And the weight ratio of the amount of supported platinum is 1/1 to 1
Exhaust gas purification catalysts of 5/1 and 1/1 are designed. And as is clear from Table 1, Examples 1 to
4 of the exhaust gas purifying catalyst, as compared with the cerium complex oxide of rhodium supported large amount made exhaust gas purifying catalyst of Comparative Example 1, CO-NO _x cross-point purifying rate after the durability test, HC purification Each of the rate and the HC 50% purification temperature are improved. That is, the exhaust gas purifying catalysts of the respective embodiments maintain high catalytic performance even after high-temperature durability, and are excellent in HC purifying performance at low temperatures.

Example 5 In this example, the composition of the zirconium-based composite oxide was changed to Zr _0.80 Ce _0.16 La _0.04 O in the same manner as in Example 1.
_1.98 (ZCL), the composition of cerium-based composite oxide
After adjusting to _0.55 Zr _0.38 Y _0.07 O _1.97 (CZY), platinum and rhodium were co-supported on each composite oxide. In addition, alumina (Al ₂ O
_In contrast to ₃ ), palladium was supported by the same method as that of supporting rhodium and platinum on the composite oxide (impregnation with a palladium salt solution and heat treatment).

A first coating layer was formed on the inner surface of each cell of the monolithic carrier by the same method as in Example 1 using alumina carrying palladium and barium sulfate (BaSO ₄ ). The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier was 70 g of alumina, 1.5 g of palladium carried thereon, and 40 g of barium sulfate.

Then, on the surface of the first coating layer, the respective composite oxides Pt-Rh / ZCL, P with platinum and rhodium co-supported by the same method as the first coating layer.
t-Rh / CZY, CZY with no noble metal supported
, And alumina were used to form a second coating layer 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 Z
CL50g, rhodium and platinum loadings of 0.6g and 0.75g, CZ as a carrier of noble metal
Y was 50 g, the supported amounts of rhodium and platinum were 0.6 g and 0.75 g, CZY not supporting noble metal was 30 g, and alumina was 50 g. That is, in the second coating layer, the weight ratio of the supported amount of rhodium and the supported amount of platinum between ZCL and CZY were each set to 1/1.

After the exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test described below, the CO-NO _x cross-point purification rate, the HC purification rate, and the like were determined in the same manner as in Example 1.
And the catalyst performance was evaluated by measuring the HC 50% purification temperature. Table 2 shows the results.

(1100 ° C. Endurance Test) In this endurance test, a 4-liter V-8 engine was mounted on a real vehicle,
This was carried out by mounting the exhaust gas purifying catalyst of this embodiment on one bank (four cylinders) of this engine. Specifically, the cycle described below was one cycle (30 seconds), and this cycle was repeated 6000 times for a total of 50 hours. As shown in FIG. 2 (two cycles are shown in the figure), the stoichiometric state of the stoichiometric air-fuel ratio (A / F = 14.6) is maintained by the feedback control from 0 to 5 seconds. The supplied air-fuel mixture is supplied to the engine, and the internal temperature of the exhaust gas purifying catalyst (catalyst bed) becomes 850.
It was set to be around ℃. During the period of 5 to 7 seconds, the feedback was opened and the fuel was excessively injected to supply a fuel-rich mixture (A / F = 12.5) to the engine. During the period of 7 to 28 seconds, while the feedback is kept 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 exhaust gas is exhausted. Excess fuel and secondary air were reacted inside the gas purification catalyst to increase the catalyst bed temperature. The maximum temperature at this time is 1
100 ° C., and A / F is about 14.8, which is approximately the theoretical air-fuel ratio
Maintained. During the last 28-30, the secondary air was supplied while the feedback was kept open without supplying the excess fuel, and a lean state was established. The temperature of the catalyst bed was measured by a thermocouple inserted at the center of the honeycomb carrier.

Example 6 In this example, the composition of the zirconium-based composite oxide was changed to Zr _0.78 Ce _0.16 La _0.02 N in the same manner as in Example 1.
The compositions of d _0.04 O _1.97 (ZCLN) and the cerium-based composite oxide were adjusted to Ce _0.50 Zr _0.45 Y _0.05 O _1.98 (CZY), and CZY was adjusted. ZCLN and C
Rhodium and platinum were respectively co-supported on ZY. In addition, alumina (Al ₂ O ₃ ) is subjected to the same method (impregnation and heat treatment with a palladium salt solution) as in the case of supporting rhodium and platinum on a composite oxide.
Palladium was loaded.

Palladium-supported alumina, CZY
, And barium sulfate (BaSO _Four)
Inner surface of each cell of monolithic carrier using the same method as in 1.
Then, a first coating layer was formed. In addition, monolith carrier 1dm
^ThreeThe weight of each component of the first coating layer with respect to
50 g, a palladium carrying amount of 1.5 g, CZY4
5 g and barium sulfate 20 g.

Next, each composite oxide Pt-Rh / ZCLN, in which rhodium and platinum are coexistently supported on the surface of the first coating layer by the same method as the first coating layer,
A second coating layer was formed using Pt-Rh / CZY and alumina 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 ZCLN, and the supported amounts of rhodium and platinum were 0.9 g and 0.75 g.
Y 75 g, the supported amounts of rhodium and platinum were 0.3 g and 0.75 g, and alumina 55 g. That is, in the second coating layer, the weight ratio of the supported amount of rhodium and the supported amount of platinum between ZCLN and CZY is 3
/ 1 and 1/1.

After performing an endurance test on this exhaust gas purifying catalyst at 1100 ° C. in the same manner as in Example 5, the same procedure as in Example 1 was carried out, and the CO-NO _x cross-point purification rate, HC purification rate, The catalyst performance was evaluated by measuring the HC 50% purification temperature. Table 2 shows the results.

Example 7 In this example, the composition of the zirconium-based composite oxide was changed to Zr _0.80 Ce _0.16 La _0.04 O in the same manner as in Example 1.
_1.98 (ZCL), the composition of cerium-based composite oxide
After adjusting to _0.60 Zr _0.32 Y _0.08 O _1.96 (CZY), rhodium and platinum are co-supported on ZCL and CZY, respectively. Apart from CZY on which rhodium and platinum are supported, a composite oxide is formed on CZY. Palladium was independently supported by the same method as that for supporting platinum and rhodium (impregnation with a palladium salt solution and heat treatment).

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 using CZY, alumina, and barium sulfate on which palladium alone was supported. The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier was 20 g of CZY, 1.5 g of palladium carried thereon, 50 g of alumina, and 20 g of barium sulfate.

Next, on the surface of the first coating layer, the respective composite oxides Pt-Rh / ZCL, P, in which platinum and rhodium are co-supported by the same method as the first coating layer.
A second coating layer was formed using t-Rh / CZY and alumina 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 monolith carrier was 50 g of ZCL, the loading amounts of rhodium and platinum were 1.0 g and 0.75 g, and CZY
90 g, with a loading of rhodium and platinum of 0.1 g.
2 g and 0.75 g, and 80 g of alumina were used. That is, in the second coating layer, the weight ratio of the supported amount of rhodium and the supported amount of platinum between ZCL and CZY was 5/1 and 1/1.

After the exhaust gas purifying catalyst was subjected to a 1100 ° C. durability test in the same manner as in Example 5, the CO-NO _x cross-point purification rate was determined in the same manner as in Example 1.
The catalyst performance was evaluated by measuring the HC purification rate and the HC 50% purification temperature. Table 2 shows the results.

Example 8 In this example, the composition of the zirconium-based composite oxide was changed to Zr _0.78 Ce _0.16 La _0.02 N in the same manner as in Example 1.
After adjusting the composition of d _0.04 O _1.97 (ZCLN) and the cerium-based composite oxide to Ce _0.50 Zr _0.45 Y _0.05 O _1.98 (CZY), platinum and rhodium were co-supported on each composite oxide. In addition, alumina (A
l ₂ O ₃ ), the same procedure as for platinum or rhodium on composite oxides (impregnation with palladium salt solution)
Heat treatment) supported palladium.

Palladium-supported palladium-supported alumina, CZY, and barium sulfate (Ba)
Using SO ₄ ), 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 alumina, 1.5 g of palladium carried thereon, 20 g of CZY, and 20 g of barium sulfate.

Next, on the surface of the first coating layer, a composite oxide Pt-Rh / ZCLN, in which platinum and rhodium are coexistently supported by the same method as the first coating layer,
A second coating layer was formed using Pt-Rh / CZY and alumina 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 monolith carrier was 50 g of ZCLN, and the loading amounts of rhodium and platinum were 0.67 g and 0.75 g, respectively.
75 g of ZY, the supported amounts of rhodium and platinum were 0.23 g and 0.75 g, and 55 g of alumina. That is, in the second coating layer, ZCLN and CZ
The weight ratio of the supported amount of rhodium and platinum to Y was 67/23 and 1/1.

After the exhaust gas purifying catalyst was subjected to an endurance test at 1100 ° C. in the same manner as in Example 5, the same procedure as in Example 1 was carried out, and the CO—NO _x cross point purification rate,
The catalyst performance was evaluated by measuring the HC purification rate and the HC 50% purification temperature. Table 2 shows the results.

Comparative Example 2 In this comparative example, the composition of the zirconium-based composite oxide was changed to ZrO _2.00 (Z) and the composition of the cerium-based composite oxide was changed to Ce _0.80 Zr _0.20 O _2.00 (CZ) in the same manner as in Example 1. )
After the adjustment, rhodium and platinum were supported on these composite oxides. In addition, the same method (impregnation and heat treatment with palladium salt solution) as for supporting rhodium and platinum on the composite oxide was applied to alumina.
Palladium was loaded.

A first coating layer was formed on the inner surface of each cell of the monolithic carrier by the same method as in Example 1 using alumina carrying palladium and CZ. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier was 50 g of alumina, 1.5 g of palladium carried on the alumina, and 45 g of CZ.

Next, on the surface of the first coating layer, the same complex oxide Pt-Rh / Z, Pt-
A second coating layer was formed using Rh / CZ and alumina to obtain an exhaust gas purifying catalyst of this comparative example. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolith carrier was as follows: Z50 g, the amount of rhodium and platinum carried thereon was 0.5 g and 0.75 g, and the amount of CZ75 g, the amount of rhodium and platinum carried was 0.7 g. And 0.75
g and alumina g55. That is, the weight ratio of the supported amount of rhodium and the supported amount of platinum between Z and CZ is 5/7.
And 1/1.

After the exhaust gas purifying catalyst was subjected to an endurance test at 1100 ° C. in the same manner as in Example 5, the same procedure as in Example 1 was carried out, and the CO-NO _x cross-point purification rate,
The catalyst performance was evaluated by measuring the HC purification rate and the HC 50% purification temperature. Table 2 shows the results.

Comparative Example 3 In this comparative example, the composition of the zirconium-based composite oxide was ZrO _2.00 (Z) and the composition of the cerium-based composite oxide was Ce _0.80 Zr _0.20 O _2.00 (CZ), in the same manner as in Example 1. )
Then, rhodium and platinum are supported on these composite oxides, and separately from CZ on which rhodium and platinum are supported, a method similar to that of supporting platinum and rhodium on the composite oxide is applied to CZ. (Impregnation with a palladium salt solution and heat treatment) supported palladium alone.

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 using CZ carrying palladium and alumina (Al ₂ O ₃ ). The weight of each component of the first coating layer with respect to 1 dm ³ of the monolithic carrier was 45 g of CZ, 1.5 g of palladium carried thereon, and 60 g of alumina.

Next, the respective composite oxides Pt-Rh / Z, Pt- on which platinum and rhodium coexist and are supported on the surface of the first coating layer by the same method as the first coating layer.
A second coating layer was formed using Rh / CZ and alumina to obtain an exhaust gas purifying catalyst of this comparative example. The weight of each component of the second coating layer with respect to 1 dm ³ of the monolithic carrier is 0.5 g and 0.75 g of Z55 g, rhodium and platinum thereof, and 70 g of CZ, and 0 g of CZ 70 g of rhodium and platinum. 0.7 g and 0.7
5 g and 45 g of alumina were used. That is, in the second coating layer, the weight ratio of the supported amount of rhodium and the supported amount of platinum between Z and CZ was 5/7 and 1/1.

[0088] After the durability at 1100 ° C. in the same manner as in Example 5 to the exhaust gas purifying catalyst, in the same manner as in Example 1, CO-NO _x cross-point purifying rate, HC purifying ratio and HC50% purification The catalyst performance was evaluated by measuring the temperature. Table 2 shows the results.

[0089]

[Table 2]

In Examples 5 to 8, a first coating layer containing palladium was formed on the surface of each cell of the monolithic carrier, and rhodium and platinum were added to the zirconium-based composite oxide and the cerium-based composite oxide, respectively. Exhaust gas purification catalyst designed to be supported co-existing and the weight ratio of rhodium supported amount and platinum supported amount of zirconium-based composite oxide and cerium-based composite oxide to 1/1 to 5/1 and 1/1 are doing. And, as is clear from Table 2, the exhaust gas purifying catalysts of Examples 5 to 8 were compared with the exhaust gas of Comparative Examples 2 and 3 in which the rhodium carrying amount of the cerium-based composite oxide was larger than that of the zirconium-based composite oxide. compared to the catalyst for gas purification, CO-NO _x cross-point purifying rate after the durability test, HC purifying ratio, and each of the HC50% purification temperature are improved. That is, the exhaust gas purifying catalysts of the respective embodiments maintain high catalytic performance even after high-temperature durability, and are excellent in HC purifying ability at low temperatures.

Example 9 In this example, the second coating layer in Example 5 was used as the first coating layer, and the first coating layer was used as the second coating layer to form the exhaust gas purifying catalyst of this example.

After the exhaust gas purifying catalyst was subjected to a 1150 ° C. durability test described below, a CO—NO _x cross-point purifying rate, an HC purifying rate,
And the catalyst performance was evaluated by measuring the HC 50% purification temperature. Table 3 shows the results.

(1150 ° C. endurance test) This test was carried out by mounting a 4-liter V-type 8-cylinder engine on a real vehicle and mounting the exhaust gas purifying catalyst of this embodiment on one bank (four cylinders) of the engine. Was. Specifically, the cycle described below was one cycle (30 seconds), and this cycle was repeated 6000 times for a total of 50 hours. As shown in FIG. 3 (two cycles are shown in the figure), 0
During a period of up to 5 seconds, the air-fuel mixture maintained in a stoichiometric state having the stoichiometric air-fuel ratio (A / F = 14.6) by feedback control is supplied to the engine, and the inside of the exhaust gas purifying catalyst (catalyst bed) is supplied. The temperature was set to be around 850 ° C. During 5 to 7 seconds, the feedback was opened and the fuel was excessively injected to supply a fuel-rich mixture (A / F = 11.2) to the engine. During the period of 7 to 28 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 exhaust gas is exhausted. Excess fuel and secondary air were reacted inside the gas purification catalyst to increase the catalyst bed temperature. The maximum temperature at this time is 1150 ° C,
A / F was maintained at about 14.8, which is a stoichiometric air-fuel ratio. During the last 28-30, the secondary air was supplied while the feedback was kept open without supplying the excess fuel, and the fuel was in a lean state. The catalyst bed temperature was measured with a thermocouple inserted in the center of the honeycomb carrier.

Example 10 In this example, an exhaust gas purifying catalyst was formed using the second coating layer in Example 6 as the first coating layer and the first coating layer as the second coating layer.

[0095] After the durability at 1150 ° C. in the same manner as in Example 9 the exhaust gas purifying catalyst, in the same manner as in Example 1, CO-NO _x cross-point purifying rate, HC purifying ratio and HC50% purification The catalyst performance was evaluated by measuring the temperature. Table 3 shows the results.

Example 11 In this example, the second coating layer in Example 7 was used as the first coating layer, and the first coating layer was used as the second coating layer to form the exhaust gas purifying catalyst of this example.

After the exhaust gas purifying catalyst was subjected to a 1150 ° C. durability test in the same manner as in Example 9, the CO-NO _x cross-point purification rate and
The catalyst performance was evaluated by measuring the HC purification rate and the HC 50% purification temperature. Table 3 shows the results.

Example 12 In this example, the second coating layer in Example 8 was used as the first coating layer, and the first coating layer was used as the second coating layer to form the exhaust gas purifying catalyst of this example.

[0099] After performing the 1150 ° C. durability test in the same manner as in Example 9 the exhaust gas purifying catalyst, in the same manner as in Example 1, CO-NO _x cross-point purifying rate,
The catalyst performance was evaluated by measuring the HC purification rate and the HC 50% purification temperature. Table 3 shows the results.

Comparative Example 4 In this comparative example, an exhaust gas purifying catalyst was formed using the second coating layer in Comparative Example 3 as the first coating layer and the first coating layer as the second coating layer.

After the exhaust gas purifying catalyst was durable at 1150 ° C. in the same manner as in Example 9, the CO-NO _x cross-point purification rate, HC purification rate, and HC50 were measured in the same manner as in Example 1. The catalyst performance was evaluated by measuring the% purification temperature. Table 3 shows the results.

Comparative Example 5 In this comparative example, the second coating layer in Comparative Example 4 was used as the first coating layer, and the first coating layer was used as the second coating layer to form the exhaust gas purifying catalyst of this comparative example.

After the exhaust gas purifying catalyst was subjected to a 1150 ° C. endurance test in the same manner as in Example 9, the same procedure as in Example 1 was carried out, and the CO—NO _x cross point purification rate,
The catalyst performance was evaluated by measuring the HC purification rate and the HC 50% purification temperature. Table 3 shows the results.

[0104]

[Table 3]

Example 9 is Example 5, Example 10 is Example 6, Example 11 is Example 7, Example 12 is Example 8, Comparative Example 4 is Comparative Example 2, and Comparative Example 5 is Comparative Example 3. Each and the first
The exhaust gas purifying catalyst is designed by reversing the coating layer and the second coating layer. Also in this case, as is clear from Table 3, each of the exhaust gas purifying catalysts of Examples 9 to 12 has a higher cerium concentration than the zirconium-based composite oxide, similarly to the exhaust gas purifying catalysts of Examples 5 to 8. compared to Comparative examples 4 and 5 was made many loading amount of rhodium better system composite oxide, CO-NO _x cross-point purifying rate after the high-temperature durability test, HC purification rate, and each improvement of HC50% purification temperature Have been. That is, the exhaust gas purifying catalysts of the respective embodiments maintain high catalytic performance even after high-temperature durability, and are excellent in HC purifying ability at low temperatures.

[0106]

As described above, according to the present invention, there is provided an exhaust gas purifying catalyst which maintains a high catalytic activity even after endurance at a high temperature and can function effectively even at a relatively low temperature. .

[Brief description of the drawings]

FIG. 1 is a cycle diagram for explaining a 1100 ° C. durability test in Examples 1 to 4 and Comparative Example 1.

FIG. 2 shows 11 in Examples 5 to 8 and Comparative Examples 2 and 3.
FIG. 4 is a cycle diagram for explaining a 00 ° C. durability test.

FIG. 3 shows 11 in Examples 9 to 12 and Comparative Examples 4 and 5.
It is a cycle diagram for explaining a 50 degreeC 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 BA03X BA08X BA15X BA18X BA18Y BA19X BA30X BA33X BA42X BA46X BB02 CC38 CC46 EA04 4G069 AA03 AA08 BA01B BA05A BA05B BB06A BB06B BB10B BC08A BC08B BC13A BC13B BC38A BC38B BC40B BC42A BC42B BC43A BC43B BC44B BC51A BC51B BC71A BC71B BC75A BC75EB19 CA03B

Claims (6)

[Claims] Claims: 1. A method represented by the following general formula (1):
A zirconium-based composite oxide in which rhodium and platinum are co-supported; (In the formula (1), N is at least one element selected from the group consisting of an alkaline earth metal element and a rare earth element (excluding cerium and zirconium), and 0.65 <1- (a + b) ≦ 0 .90, 0.10 ≦
a <0.35, 0 ≦ b ≦ 0.20, and c represent the oxygen deficiency determined by the oxidation number and atomic ratio of N. A cerium-based composite oxide represented by the following general formula (2) and further supporting rhodium and platinum in coexistence: (In the formula (2), M is at least one element selected from the group consisting of an alkaline earth metal element and a rare earth element (excluding cerium and zirconium), and 0.35 ≦ 1- (x + y) ≦ 0 .80, 0.20 ≦
x ≦ 0.65, 0 ≦ y ≦ 0.20, and z represent the oxygen deficiency determined by the oxidation number and atomic ratio of M. And the weight of rhodium supported on the zirconium-based composite oxide is equal to or greater than the weight of rhodium supported on the cerium-based composite oxide. Characterized by being
Exhaust gas purification catalyst. 2. The method according to claim 1, wherein the ratio of the weight of rhodium supported on the zirconium-based composite oxide to the weight of rhodium supported on the cerium-based composite oxide is 1/1 to 19/1. Exhaust gas purification catalyst. 3. The exhaust purification catalyst according to claim 2, wherein the ratio is from 1/1 to 5/1. 4. The coating layer is formed as a two-layer structure comprising a first coating layer directly supported on the heat-resistant support and a second coating layer formed on the first coating layer. Yes,
At least one of the first coating layer and the second coating layer contains both a zirconium-based composite oxide in which rhodium and platinum are supported and a cerium-based composite oxide in which rhodium and platinum are supported. The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein 5. The first coating layer contains palladium, and the second coating layer has a zirconium-based composite oxide in which rhodium and platinum are co-supported and a rhodium and platinum co-supported. The exhaust gas purifying catalyst according to claim 4, wherein both of the cerium-based composite oxide are contained. 6. The first coating layer contains both a zirconium-based composite oxide in which rhodium and platinum are co-supported and a cerium-based composite oxide in which rhodium and platinum are co-supported. The exhaust gas purifying catalyst according to claim 4, wherein the two coating layers contain palladium.