JPH11138001A - Catalyst for exhaust gas purification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for exhaust gas purification comprising a noble metal catalyst whose catalytic activity does not deteriorate improperly even under severe conditions of 900 deg.C or higher. SOLUTION: This catalyst for exhaust gas purification is produced by depositing Pt and Rh together on a granular zirconium-containing compound oxide having the formula; Zr1-(x+y) Cex Ry O2-z (wherein R is one or more elements selected from rare earth elements and Al except cerium; z is the oxygen deficiency amount determined based on the oxidation number and the contents of rare earth elements and Al; 0.1<=x+y<=0.5; 0.1<=x<=0.5; and 0<=y<=0.2) and coating a heat resistant supporting carrier with the resultant zirconium- containing compound oxide together with oxygen-storage rare earth oxides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

The exhaust gas discharged from an internal combustion engine such as an automobile, NO _X, CO, and contains harmful substances such as HC, in view of global environmental protection, for the purification of these harmful substances Regulations are becoming increasingly strict. On the other hand, from the viewpoint of fuel saving, the internal combustion engine is in a leaner state (lean state) than a stoichiometric air-fuel mixture state (stoichiometric state) during normal driving except when the vehicle is idling or accelerating. Has been widely performed. Therefore, there is a strong demand for the development of a catalyst that can effectively purify the above harmful substances not only in the stoichiometric state but also in such a lean state.

The most widely used catalyst for purifying the above-mentioned harmful substances from exhaust gas is a so-called three-way catalyst using a noble metal such as platinum, palladium or rhodium as an active substance. This three-way catalyst has NO
_It functions as a catalyst for the reduction reaction from _X to N 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, acts as a catalyst for the reduction reaction under NO _X rich atmosphere, CO, the oxidation reaction under HC-rich atmosphere to act as a catalyst, NO _X contained in exhaust gas,
It can purify harmful substances such as CO and HC.

Therefore, various studies have been made to improve the activity of the three-way catalyst. For example, a function of occluding or releasing oxygen in the gas phase of cerium oxide (CeO ₂ ), that is, a so-called oxygen storage capacity ( OSC). That is, while adjusting the oxygen concentration in the gas phase atmosphere by adding the cerium oxide into the three-way catalyst, of the NO _X by the three-way catalyst in the adjusted gas phase atmosphere reduction reaction, as well as CO and HC
It is intended to improve the efficiency of the oxidation reaction.

Further, Japanese Patent Publication No. 5-47263 discloses that
Noble metals such as Pt and Rh are dispersed and supported on zirconia (ZrO ₂ ) in the form of fine particles, and a honeycomb-shaped heat-resistant support carrier is formed together with a heat-resistant inorganic oxide such as alumina and an oxygen-storing rare earth oxide such as cerium oxide. There is disclosed an exhaust gas purifying catalyst obtained by coating (wash coat) on an exhaust gas.
The catalyst of this configuration has a heat-resistant inorganic oxide or a rare earth oxide interposed between zirconia aggregated particles carrying a noble metal,
The purpose of the present invention is to prevent sintering between zirconia aggregated particles in a high-temperature oxidizing atmosphere, thereby suppressing a decrease in specific surface area and avoiding a decrease in catalytic activity.

[0006]

Although the exhaust gas purifying catalyst described in the above-mentioned publication suppresses sintering between zirconia aggregated particles, it does not prevent zirconia particles from growing. However, it did not achieve sufficient high-temperature durability. Further, depending on the mounting position of the exhaust gas purifying catalyst, the catalyst may be exposed to an extremely high temperature, thereby promoting the grain growth of zirconia. In particular, considering the future tightening of exhaust gas regulations, there is a growing demand to change the mounting position of the catalyst from under the vehicle floor to a manifold position closer to the engine so that the catalyst can warm up quickly and function immediately after the engine is started. In this case, the catalyst may be exposed to a high temperature of 900 ° C. or more, and sometimes 1000 ° C. or more. At such a high temperature, the grain growth of the zirconia particles themselves is promoted, and the specific surface area decreases. As a result, the catalytic activity of the noble metal supported on the zirconia particles is greatly reduced.

The present invention has been conceived in view of the above circumstances, and has been developed for exhaust gas purification in which the catalytic activity of a noble metal is not unduly reduced even under severe conditions of 900 ° C. or more. It is an object to provide a catalyst.

[0008]

DISCLOSURE OF THE INVENTION In order to solve the above-mentioned problems, the present invention has a general formula

Embedded image Wherein R represents a rare earth element other than cerium or at least one element of Al, z represents an oxygen deficiency determined by the oxidation number and the content of the rare earth element or Al, and 0.1 ≦ x + y ≦ 0.5, 0.1 ≦ x ≦ 0.5, 0
Pt and Rh are co-supported and supported on a particulate zirconium-based composite oxide in which ≦ y ≦ 0.2, and the heat-resistant support is coated with the zirconium-based composite oxide at least together with an oxygen-storing rare-earth oxide. Provided is a gas purification catalyst.

That is, the feature of the present invention resides in that a part of zirconium in zirconia (ZrO ₂ ) is replaced by cerium (Ce) and, if necessary, a rare earth element other than cerium or Al. As a result, the mass transfer of zirconium at a high temperature is suppressed, so that the zirconia particles do not grow unduly. As a result, the catalytic activity of Pt and Rh co-supported on the zirconia particles can be maintained at a certain level or more even at high temperatures.

The zirconium-based composite oxide is
It is preferable that at least a part thereof is a solid solution. Thereby, the mass transfer of zirconium is further suppressed, and the durability at high temperatures is further improved.

In addition, Pt and Rh as noble metals are co-supported on the particulate zirconium-based composite oxide.
For the following reasons. That is, when Pt alone is supported on the zirconium-based composite oxide, Pt particles tend to grow due to Pt mass transfer in a high-temperature atmosphere. On the other hand, when Rh coexists, the mass transfer of Pt can be suppressed and the grain growth can be prevented. (Possibly, a layer of rhodium oxide is formed on the surface of the Pt particles to make the mass transfer of Pt.) Is estimated to suppress).

In the above general formula, 0.1 ≦ x + y ≦
The reason for setting the value to 0.5 is that the effect of suppressing the mass transfer of zirconium decreases even if the substitution ratio with cerium or the like is larger or smaller than this range. In the above general formula, 0.1 ≦ x ≦ 0.5 is set for the same reason.
On the other hand, if the substitution ratio is larger than the above range, the catalytic activity may be lowered due to the interaction between Pt and Rh supported on the zirconium-based composite oxide. In the above general formula, the value of x + y is 0.2 to 0.3.
And the value of x is preferably in the range of 0.1 to 0.28.

The rare earth elements other than cerium to be replaced include yttrium (Y) and scandium (S
c), lanthanum (La), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (S
m), eurobium (Eu), gadolinium (Gd),
Terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (T
m), ytterbium (Yb), and lutetium (L
u), of which lanthanum and neodymium are preferred. These rare earth elements stabilize the fluorite-type cubic crystal lattice structure in the zirconium-based composite oxide, and also suppress the mass transfer of zirconium at high temperatures together with the cerium.

Further, aluminum (Al) may be substituted for the rare earth element or in addition to the rare earth element. In this case, it is preferable to replace with aluminum alone or to combine aluminum and yttrium.

In the above general formula, the value of y is from 0 to 0.
2, preferably in the range of 0.02 to 0.2. As described above, the value of y may be 0, and it is not always necessary to include a rare earth element other than cerium (therefore, in the above general formula, the ranges of x + y and x match). This is because the grain growth of the zirconium-based composite oxide can be suppressed to some extent only by replacing zirconium with only cerium. However, when a rare earth element other than cerium and / or aluminum is contained, the effect of suppressing grain growth is further enhanced, so that the value of y is preferably in the range of 0.02 to 0.2. When the value of y exceeds 0.2, compounds other than the desired composite oxide are undesirably produced as by-products.

In the present invention, commercially available cerium oxide or a cerium-based composite oxide can be used as the oxygen-storing rare-earth oxide coated on the support together with the zirconium-based composite oxide. In addition to supporting Pt and Rh coexisting on the zirconium-based composite oxide, a noble metal such as palladium (Pd) may be supported on the oxygen-storing rare earth oxide.

In a preferred embodiment of the present invention, the zirconium-based composite oxide is not only coated on the heat-resistant support carrier together with the oxygen-storing rare earth oxide,
In addition, the heat-resistant support is coated with the heat-resistant inorganic oxide, and the Pt and Rh are selectively carried only on the particles of the zirconium-based composite oxide.
As the heat-resistant inorganic oxide, commercially available alumina, silica, titania, magnesia and the like can be used, and activated alumina is particularly advantageous.

In order to use the present invention as a catalyst,
The catalyst component is used after being coated on a heat-resistant support. As the heat-resistant support, cordierite, mullite, α
-A honeycomb carrier made of alumina, metal (for example, stainless steel) or the like can be used, and the apparent volume of the honeycomb carrier (heat-resistant support carrier) per liter is
For example, 10 to ²⁰⁰ g of the zirconium-based composite oxide having a specific surface area of 50 to 160 m ² / g, for example, 30 to 150 g of the oxygen-absorbing rare earth oxide having a specific surface area of 100 to 200 m ² / g, for example, 150 to 150 g 2
00 m ² / g of the above heat-resistant inorganic oxide, for example, from 0 to 20
Coat at a rate of 0 g (known wash coat). The zirconium-based composite oxide preferably has an average particle size of, for example, 0.1 to 2 μm, and the zirconium-based composite oxide has a Pt of 0 per liter of an apparent volume of the heat-resistant support. 0.2 to 2 g, with Rh of 0.
It is carried so as to be 04 to 1 g.

In the present invention, the zirconium-based composite oxide can be prepared to a desired composition by a known method (a coprecipitation method or an alkoxide method). For example, a salt solution containing zirconium, cerium, and a rare earth element other than cerium (and / or aluminum) is prepared so as to have a predetermined stoichiometric ratio, and this solution is added to an alkaline aqueous solution or an organic solution. An acid is added to coprecipitate a salt containing zirconium, cerium, and a rare earth element (and / or aluminum), and then the coprecipitate is oxidized, or zirconium, cerium, and a rare earth element (and / or aluminum) are co-precipitated. ) Is prepared, deionized water is added to the mixed alkoxide solution, coprecipitation or hydrolysis is performed, and the coprecipitate or hydrolysis product is heat-treated.
The zirconium source used here may contain 1 to 3% of hafnium used for general industrial use. In the present invention, the hafnium content is also calculated as zirconium.

In this case, as the salt to be used, inorganic salts such as zirconium oxychloride, oxynitrate and oxysulfate, and organic salts such as oxyacetate can be used. As the salts of cerium and rare earth elements other than cerium (and / or aluminum), inorganic salts such as sulfates, nitrates, hydrochlorides, and phosphates, and organic salts such as acetates and oxalates may be used. Can be. Further, as the alkaline aqueous solution, an aqueous sodium carbonate solution, an aqueous ammonia solution, an aqueous ammonium carbonate solution, or the like is used, and as the organic acid, oxalic acid, citric acid, or the like is used.

As the alkoxide of the mixed alkoxide solution, methoxide, ethoxide, propoxide, butoxide of zirconium, cerium, and rare earth elements, and ethylene oxide adducts thereof are used.

Further, when the obtained coprecipitate or hydrolysis product is subjected to a heat treatment, the coprecipitate or hydrolysis product is filtered and washed, preferably about 50 to 20.
After drying at 0 ° C. for about 1 to 48 hours,
0-1000 ° C, preferably about 400-700 ° C for about 1
This is performed by firing for 12 hours.

Next, in order to support Pt and Rh on the zirconium-based composite oxide obtained after the calcination, a salt solution containing these platinum group metals is prepared and impregnated into the zirconium-based composite oxide. After that, heat treatment may be performed. As the solution of the platinum group metal salt, a nitrate aqueous solution, a dinitrodiamine nitrate solution, a chloride aqueous solution, or the like is used. Further, the platinum group metal salt solution contains about 1 to 20% by weight of the platinum group metal salt, and the heat treatment after the impregnation is preferably about 50 to 2%.
Dried at 00 ° C. for about 1 to 48 hours,
It is performed by baking at 00 ° C., preferably 400 to 700 ° C. for about 1 to 12 hours.

[0024]

Next, examples of the present invention will be described in detail together with comparative examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, Oxide in the chemical formula representing the zirconium-based composite oxide indicates that the oxide is an oxide, and the subscript indicating the ratio of oxygen is the ratio of other components. The display is omitted because it is uniquely determined by the setting.

[0025]

Example 1 In this example, the composition was Zr _0.80 Ce _0.16
A catalyst was prepared using a zirconium-based composite oxide of La _0.02 Nd _0.02 Oxide.

[0026] 0.080 mol of (zirconium-base compound oxide of Preparation) zirconium oxychloride _{(ZrOCl 2 · 8H 2 O)} , 0.016 mol of cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O), nitric acid 0.002 lanthanum _{(La (NO 3) 3 ·} 6H 2 O) of 0.002 molar and neodymium nitrate _{(Nd (NO 3) 3 ·} 5H 2 O)
The moles were dissolved in 100 ml of deionized water to prepare a mixed aqueous solution.

Next, 25. sodium carbonate (Na ₂ CO ₃ ).
0 g was dissolved in 200 ml of deionized water to prepare a neutralizing coprecipitant solution, and the mixed aqueous solution was gradually dropped into the neutralizing coprecipitant solution to obtain a coprecipitate. This coprecipitate was sufficiently washed with water and filtered, and then 100 ml of isopropyl alcohol was added.
And a commercially available zirconia (3 mol Y ₂ O ₃ stabilized Zr
O ₂ ) Pulverized in a ball mill for 24 hours.

Then, after filtering the ground slurry,
Vacuum dried at 80 ° C. After sufficient drying, 650
C. for 3 hours to obtain a zirconium-based composite oxide powder in which cerium, lanthanum, and neodymium were dissolved.

Further, 2 liters of isopropyl alcohol was added to 2 kg of the zirconium composite oxide powder obtained by repeating the above steps, and isopropyl alcohol was added as needed in an attrition mill using a commercially available zirconia ball having a diameter of 3 mm. Crushed for hours and after filtration 80
Vacuum dried at ℃. After the obtained ground powder is loosened in a mortar, it is passed through a 325 mesh sieve to give an average particle size of 1.
A zirconium-based composite oxide powder of 4 μm (measured by a laser diffraction scattering method) in which cerium, lanthanum, and neodymium were dissolved was used.

(Preparation of catalyst) Platinum 1.5 was added to 50 g of the zirconium-based composite oxide powder obtained as described above.
g of dinitroammineplatinum aqueous solution containing 0.3 g of rhodium, and then impregnated with an aqueous solution of rhodium nitrate containing 0.3 g of rhodium, dried at 110.degree. C. for 12 hours, and further calcined at 500.degree. A zirconium-based composite oxide powder supporting 3 g was obtained.

Next, 130 g of a commercially available stabilized alumina powder obtained by partially dissolving La in the metal-supported zirconium-based composite oxide powder and a cerium-based composite oxide having a composition of Ce _0.6 Zr _0.3 Y _0.1 Oxide An aqueous slurry was prepared by adding 75 g of powder and wet-milling for 12 hours in a ball mill. Then, this aqueous slurry was subjected to 400 cells /
It was coated on a cordierite monolith honeycomb carrier of in ² (62 cells / cm ² ), diameter of 105.7 mm and length of 100 mm, dried at 110 ° C. for 12 hours, and calcined at 500 ° C. for 3 hours to obtain a catalyst.

[0032]

Embodiment 2 In this embodiment, as in Embodiment 1,
A catalyst was prepared using a zirconium-based composite oxide having a composition of Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 Oxide. However, when producing the zirconium-based composite oxide, the process up to the preparation of the coprecipitate is the same as in Example 1, but the subsequent pulverization and screening by a sieve are omitted. As a result, the average particle size of the zirconium-based composite oxide powder used for preparing the catalyst was 5.2.
μm (measured by laser diffraction scattering method). All other points are the same as in the first embodiment.

[0033]

Embodiment 3 In this embodiment, the composition is Zr _0.80 Ce _0.16
A catalyst was prepared using a zirconium-based composite oxide of La _0.04 Oxide.

[0034] (Preparation of zirconium complex oxide) oxy 0.080 mol of zirconium chloride _{(ZrOCl 2 · 8H 2 O)} , 0.016 mol and nitrate of cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) A mixed aqueous solution was prepared by dissolving 0.004 mol of lanthanum (La (NO ₃ ) ₃ .6H ₂ O) in 100 ml of deionized water.

Next, sodium carbonate (Na ₂ CO ₃ ) 25.
0 g was dissolved in 200 ml of deionized water to prepare a neutralizing coprecipitant solution, and the mixed aqueous solution was gradually dropped into the neutralizing coprecipitant solution to obtain a coprecipitate. The coprecipitate was sufficiently washed with water, filtered, and dried at 80 ° C. under vacuum. After sufficient drying, the powder was calcined at 650 ° C. for 3 hours in the atmosphere to obtain a zirconium-based composite oxide powder in which cerium and lanthanum were dissolved. The average particle size of this powder was 6.1 μm (measured by a laser diffraction scattering method).

(Preparation of Catalyst) Zirconium-based composite oxide powder 5 having an average particle size of 6.1 μm obtained as described above
Using 0 g, a catalyst was produced in exactly the same manner as in Example 1.

[0037]

Embodiment 4 In this embodiment, the composition is Zr _0.70 Ce _0.16
A catalyst was prepared using a zirconium-based composite oxide of Al _0.06 Y _0.08 Oxide.

[0038] 0.070 mol of (zirconium-base compound oxide of Preparation) zirconium oxychloride _{(ZrOCl 2 · 8H 2 O)} , 0.016 mol of cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O), nitric acid 0.006 aluminum _{(Al (NO 3) 3 ·} 9H 2 O)
0 molar and yttrium nitrate _{(Y (NO 3) 3 ·} 6H 2 O).
Example 3 except that 008 mol was used as the starting material.
A zirconium-based composite oxide powder having an average particle size of 7.0 μm (measured by a laser diffraction scattering method) was prepared in the same manner as described above.

(Preparation of Catalyst) Zirconium-based composite oxide powder 5 having an average particle size of 7.0 μm obtained as described above
Using 0 g, a catalyst was produced in exactly the same manner as in Example 1.

[0040]

Embodiment 5 In this embodiment, the composition is Zr _0.70 Ce _0.10
A catalyst was prepared using a zirconium-based composite oxide of Al _0.20 Oxide.

[0041] (Preparation of zirconium complex oxide) oxy 0.070 mol of zirconium chloride _{(ZrOCl 2 · 8H 2 O)} , 0.010 mol and nitrate of cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 0.02 aluminum _{(Al (NO 3) 3 ·} 9H 2 O)
A zirconium-based composite oxide powder having an average particle size of 7.3 μm (measured by a laser diffraction scattering method) was prepared in the same manner as in Example 3, except that 0 mol was used as a starting material.

(Preparation of Catalyst) Zirconium-based composite oxide powder 5 having an average particle size of 7.3 μm obtained as described above
Using 0 g, a catalyst was produced in exactly the same manner as in Example 1.

[0043]

Embodiment 6 In this embodiment, the composition is Zr _0.80 Ce _0.20
A catalyst was prepared using zirconium-based composite oxide of Oxide.

[0044] (Preparation of zirconium complex oxide) starting 0.020 mol 0.080 mol and cerium nitrate zirconium oxychloride _{(ZrOCl 2 · 8H 2 O)} (Ce (NO 3) 3 · 6H 2 O) A zirconium-based composite oxide powder having an average particle size of 6.3 μm (measured by a laser diffraction scattering method) was prepared in the same manner as in Example 3, except that the powder was used as a raw material.

(Preparation of catalyst) Zirconium-based composite oxide powder 5 having an average particle size of 6.3 μm obtained as described above
Using 0 g, a catalyst was produced in exactly the same manner as in Example 1.

[0046]

Embodiment 7 In this embodiment, the composition is Zr _0.90 Ce _0.10
A catalyst was prepared using zirconium-based composite oxide of Oxide.

[0047] (Preparation of zirconium complex oxide) starting 0.010 mol 0.090 mol and cerium nitrate zirconium oxychloride _{(ZrOCl 2 · 8H 2 O)} (Ce (NO 3) 3 · 6H 2 O) A zirconium-based composite oxide powder having an average particle size of 7.8 μm (measured by a laser diffraction scattering method) was prepared in the same manner as in Example 3, except that the zirconium-based composite oxide was used as a raw material.

(Preparation of Catalyst) Zirconium-based composite oxide powder 5 having an average particle size of 7.8 μm obtained as described above
Using 0 g, a catalyst was produced in exactly the same manner as in Example 1.

[0049]

Example 8 In this example, the composition used in Example 2 was Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 Oxide and the average particle size was 5.
A catalyst having a slightly different composition was prepared using a 2 μm zirconium-based composite oxide powder.

(Preparation of Catalyst) That is, 50 g of the zirconium-based composite oxide powder having an average particle size of 5.2 μm was impregnated with an aqueous solution of dinitroammineplatinum containing 0.8 g of platinum and an aqueous solution of rhodium nitrate containing 0.3 g of rhodium. After drying at 110 ° C. for 12 hours, it was further baked at 500 ° C. for 3 hours to obtain a zirconium-based composite oxide powder supporting 0.8 g of platinum and 0.3 g of rhodium.

Next, 75 g of a cerium-based composite oxide powder having a composition of Ce _0.6 Zr _0.3 Y _0.1 Oxide was added to 0.7 g of platinum.
After impregnating in an aqueous solution of dinitroammine platinum containing
The resultant was dried at 110 ° C. for 12 hours, and further calcined at 500 ° C. for 3 hours to obtain a cerium-based composite oxide powder supporting 0.7 g of platinum.

Further, the above two types of composite oxide powders
Commercially available stabilized alumina powder 13 obtained by partially dissolving La
An aqueous slurry was prepared by adding 0 g and wet grinding in a ball mill for 12 hours. Then, this aqueous slurry was coated on a cordierite monolith honeycomb carrier having a cell diameter of 400 cells / in ² (62 cells / cm ² ), a diameter of 105.7 mm and a length of 100 mm, dried at 110 ° C. for 12 hours, and dried at 500 ° C. for 3 hours. It was calcined for a time to obtain a catalyst.

[0053]

Embodiment 9 In this embodiment, the composition is Zr _0.90 Ce _0.10
Example 7 is the same as Example 7 in that the zirconium-based composite oxide of Oxide was used, but the amount of the zirconium-based composite oxide powder was increased to 180 g, and alumina was added to the coat layer on the cordierite monolith honeycomb support. Example 7 differs from Example 7 only in that no powder was included.

[0054]

COMPARATIVE EXAMPLE 1 For comparison, a catalyst was constituted by using a commercially available zirconia powder having an average particle size of 7.6 μm (measured by a laser diffraction scattering method) instead of the zirconium-based composite oxide powder according to the present invention. did.

(Preparation of Catalyst) 50 g of the above commercially available zirconia powder was impregnated with an aqueous solution of dinitroammineplatinum containing 1.5 g of platinum and an aqueous solution of rhodium nitrate containing 0.3 g of rhodium, and dried at 110 ° C. for 12 hours. And further calcined at 500 ° C. for 3 hours to obtain 1.5 g of platinum
Further, zirconia powder carrying 0.3 g of rhodium was obtained.

Next, La was added to the metal-supported zirconia powder.
Commercially available stabilized alumina powder 130 obtained by partially dissolving
g and 75 g of a cerium-based composite oxide powder having a composition of Ce _0.6 Zr _0.3 Y _0.1 Oxide were added, and wet-ground in a ball mill for 12 hours to prepare an aqueous slurry. Then, this aqueous slurry was coated on a cordierite monolith honeycomb carrier having a cell diameter of 400 cells / in ² (62 cells / cm ² ), a diameter of 105.7 mm and a length of 100 mm,
After drying at 110 ° C. for 12 hours, it was calcined at 500 ° C. for 3 hours to obtain a catalyst.

[0057]

Comparative Example 2 In this comparative example, the zirconium-based composite oxide powder having an average particle size of 5.2 μm (measured by a laser diffraction scattering method) used in Example 2 was used.
The material to be loaded with platinum and rhodium was replaced with alumina instead of zirconium-based composite oxide.

(Preparation of Catalyst) 130 g of a commercially available stabilized alumina powder obtained by partially dissolving the above La was mixed with platinum 1.5
g of dinitroammineplatinum solution containing 0.3 g of rhodium and 0.3 g of rhodium, then dried at 110 ° C. for 12 hours, and further calcined at 500 ° C. for 3 hours to obtain 1.5 g of platinum and 0.1 g of rhodium. An alumina powder supporting 3 g was obtained.

Next, the above metal-carrying alumina powder was
Zirconium-based composite oxide powder 5 having an average particle size of 5.2 μm
0g and Ce_0.6Zr_0.3Y_0.1Commercially available with the composition of Oxide
75 g of cerium-based composite oxide powder was added, and the mixture was placed in a ball mill.
Aqueous slurry is prepared by wet grinding for 12 hours
did. Then, this aqueous slurry was subjected to 400 cells / in. ^Two
(62 cells / cm^Two), Diameter 105.7 mm, length 10
0mm cordierite monolith honeycomb carrier
3 hours at 500 ° C after drying at 110 ° C for 12 hours
It was calcined to obtain a catalyst.

[0060]

Comparative Example 3 In this comparative example, the amount of zirconia powder was 8 g.
And the amount of alumina powder was changed to 77 g, and commercially available pure ceria (CeO
₂ ), the amount was changed to 40 g, the supported amount of rhodium was changed to 0.15 g, and the supported amount of platinum was changed to 0.75 g. .

[0061]

Comparative Example 4 This comparative example was the same as Comparative Example 3 in that a commercially available zirconia powder having an average particle size of 7.6 μm was used. However, as described below, the amount of the zirconia powder and the platinum This is different from Comparative Example 3 in the point of the supporting material.

(Preparation of Catalyst) 6 g of the above commercially available zirconia powder was impregnated with an aqueous rhodium nitrate solution containing 0.15 g of rhodium, dried at 110 ° C. for 12 hours, and further calcined at 500 ° C. for 3 hours. A zirconia powder carrying 0.15 g was obtained.

Next, 77 g of commercially available stabilized alumina powder was impregnated with an aqueous dinitroammineplatinum solution containing 0.75 g of platinum, dried at 110 ° C. for 12 hours, and further calcined at 500 ° C. for 3 hours to obtain platinum 0 An alumina powder carrying 0.75 g was obtained.

Further, commercially available pure ceria 4 was added to the rhodium-supported zirconia powder and the platinum-supported alumina powder.
An aqueous slurry was prepared by adding 0 g and wet grinding in a ball mill for 12 hours. Then, this aqueous slurry was coated on a cordierite monolith honeycomb carrier having a cell diameter of 400 cells / in ² (62 cells / cm ² ), a diameter of 105.7 mm and a length of 100 mm, dried at 110 ° C. for 12 hours, and dried at 500 ° C. for 3 hours. It was calcined for a time to obtain a catalyst.

[0065]

[Evaluation of Performance of Each Catalyst] The exhaust gas purification performance of the catalysts according to Examples 1 to 9 and the catalysts according to Comparative Examples 1 to 4 was examined after high-temperature durability.

(Durability conditions) A 4-liter V8 cylinder engine is mounted on an actual vehicle, and one bank (4
Each of the catalysts was mounted on a cylinder, and exhaust gas discharged from the engine was supplied to each catalyst. Specifically, the cycle described below was one cycle (60 seconds), and this cycle was repeated 3000 times, for a total of 50 hours. FIG.
As shown in FIG. 5, the stoichiometric air-fuel ratio (A / F = 14.6), that is, the mixture maintained in the stoichiometric state is supplied to the engine by feedback control for 0 to 40 seconds, and the internal temperature of each catalyst is 850 ° C. It is set so as to be in the vicinity, the feedback is open for 40 to 44 seconds, and the fuel is excessively injected to make the fuel rich state (A
/F=11.7) was supplied to the engine. For 44 to 56 seconds, the feedback is opened continuously, and secondary air is blown from the outside of the engine via the introduction pipe from the upstream side of each catalyst while the fuel is excessively supplied. The temperature was increased by reacting the excess fuel with the secondary air inside of ()). The maximum temperature at this time was 1050 ° C. The air-fuel ratio during the 44 to 56 seconds when the excess fuel and the secondary air are supplied is slightly leaner than the stoichiometric state (A / F = 1).
4.8). During the last 56 to 60 seconds, the control is returned to the feedback control, but the secondary air is continuously supplied, and the inside of the catalyst is in a lean state (A / F = 18.0). The temperature of each of the catalysts was measured by a thermocouple inserted at the center of the honeycomb carrier.

(Evaluation Method) On the other hand, the exhaust gas purification performance of each catalyst was evaluated as follows. That is, the air-fuel mixture is supplied to the engine while changing from a fuel-rich state to a lean state, and CO and NOx contained in exhaust gas discharged when the supplied air-fuel mixture is burned by the engine are converted into the catalysts described above. Are measured, and the purification rate when the purification rates of these components match is determined by CO-NO.
It was measured as x cross point purification rate. Note that this measurement
The test was performed with the engine only, not with the engine actually mounted on the car. The temperature of the exhaust gas supplied to each of the catalysts is 460 ° C. (A / F amplitude: ± 1.
0) and the space velocity was 90000 / h.

(Evaluation Results) Table 1 shows the CO-NOx cross-point purification rates for each catalyst performed as described above, together with the configuration for each catalyst.

[0069]

[Table 1]

[0070]

As is clear from Table 1, Examples 1 to 9
Because platinum and rhodium are co-supported on a zirconium-based composite oxide corresponding to the above definition, the particle growth of the zirconium-based composite oxide is suppressed even after high-temperature durability, and the platinum particles themselves Since the growth is also suppressed, CO- is higher than the catalysts of Comparative Examples 1 to 4.
It shows the NOx cross point purification rate.

Examples 1 (where the average particle size of the zirconium-based composite oxide powder is 2 μm or less) and Example 2
From the comparison (the average particle size is increased), it is understood that the smaller the average particle size of the zirconium-based composite oxide powder is, the more the exhaust gas purification performance can be improved. further,
It is also understood from Examples 2 to 6 that the substitution solid solution of a rare earth element such as lanthanum, yttrium, neodymium or aluminum as the zirconium-based composite oxide improves the exhaust gas purification performance.

As described above, by coexisting and supporting Pt and Rh on the zirconium-based composite oxide, excellent catalytic activity can be expected even in a severe high-temperature environment such as a maniverter.

[Brief description of the drawings]

FIG. 1 is a timing chart for explaining high-temperature endurance conditions of exhaust gas purifying catalysts according to various examples and comparative examples of the present invention.

Claims (5)

[Claims] 1. A compound of the general formula Wherein R represents a rare earth element other than cerium or at least one element of Al, z represents an oxygen deficiency determined by the oxidation number and the content of the rare earth element or Al, and 0.1 ≦ x + y ≦ 0.5, 0.1 ≦ x ≦ 0.5, 0
Pt and Rh are co-supported and supported on a particulate zirconium-based composite oxide in which ≦ y ≦ 0.2, and the heat-resistant support is coated with the zirconium-based composite oxide at least together with an oxygen-storing rare-earth oxide. Gas purification catalyst. 2. The exhaust gas purifying catalyst according to claim 1, wherein the zirconium-based composite oxide is coated on the heat-resistant support carrier together with the oxygen-storing rare-earth oxide and the heat-resistant inorganic oxide. 3. In the above general formula, 0.2 ≦ x + y ≦
0.3, 0.1 ≦ x ≦ 0.28, 0.02 ≦ y ≦ 0.2
The exhaust gas purifying catalyst according to claim 1, wherein: 4. In the above general formula, R is La alone,
The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the catalyst is any one of Al alone, a combination of La and Nd, or a combination of Al and Y. 5. The exhaust gas purifying catalyst according to claim 1, wherein the zirconium-based composite oxide has an average particle size of 0.1 to 2 μm.