JPH11130436A - Multiple oxide, its production and catalyst for purification of exhaust gas using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a multiple oxide effective in improving the heat resistance of a catalyst for purification of exhaust gas from an internal combustion engine and to obtain a catalyst for purification of exhaust gas excellent in catalytic performance after use at a high temp. over a long period of time. SOLUTION: The multiple oxide consists of alumina, ceria and zirconia in a weight ratio of 4:1:1 to 0.5:1:1. An aluminum compd., cerium nitrate and zirconium nitrate are stirred and dissolved in pure water to prepare a mixed soln. and this mixed soln. is dropped into an aq. ammonia soln. under stirring. After adjustment to pH 9-9.5, a formed precipitate is aged to produce the multiple oxide. The catalyst for purification of exhaust gas is produced using the multiple oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a composite oxide which can be used as a catalyst for purifying exhaust gas of an internal combustion engine and a method for producing the same.
Also, the present invention relates to an exhaust gas purifying catalyst having improved purification performance by using the composite oxide.

[0002]

2. Description of the Related Art Improvements in purification performance of exhaust gas purifying catalysts for internal combustion engines are increasingly demanded as exhaust gas regulations are tightened. Therefore, a catalyst is directly connected to a manifold close to the engine and used at a high exhaust gas temperature to improve the purification performance. However, in that case, the use temperature is increased, so that the improvement of heat resistance is further required.

[0003] Conventionally, for example, in Japanese Unexamined Patent Publication No. Hei 5-277375, a washcoat carrier obtained by coating a carrier with a slurry containing activated alumina, a cerium compound, a zirconium compound and a nickel compound, drying and calcining the carrier is used as a precious metal component. It has been reported that a catalyst carrying an alkaline earth metal component after carrying the compound has excellent CO and HC performance in the vicinity of the theoretical mixing ratio. Also, JP-A-6-2
Japanese Patent Application Laid-Open No. 79027 discloses a composite oxide containing ceria and zirconia as main components. However,
Even if these catalysts and composite oxides are used as exhaust gas purifying catalysts, they are not sufficient for more stringent demands for high-temperature durability.

Accordingly, an object of the present invention is to provide a composite oxide effective for improving the heat resistance (high temperature durability) of an exhaust gas purifying catalyst for an internal combustion engine, a method for producing the same, and an exhaust gas purifying catalyst having excellent catalytic performance after high temperature durability. To provide a catalyst for use.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a composite oxide in which the weight ratio of alumina, ceria, and zirconia is within a specific range, and a composite oxide obtained by using a specific method. It has been found that the production method and an exhaust gas purifying catalyst prepared using the composite oxide can achieve the above object.

[0006] The present invention has been made based on the above findings, and the weight ratio of alumina, ceria and zirconia is 4:
The present invention provides a composite oxide characterized by a ratio of 1: 1 to 0.5: 1: 1.

In the present invention, an alumina compound, cerium nitrate and zirconium nitrate are stirred and dissolved in pure water to obtain a mixed solution. The present invention provides a method for producing a composite oxide, which is characterized in that the produced precipitate is aged after adjusting to 9.5.

[0008] The present invention also provides an exhaust gas purifying catalyst produced by using the above composite oxide.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the composite oxide of the present invention will be described in detail. The composite oxide of the present invention is alumina,
The weight ratio of ceria and zirconia is from 4: 1: 1 to 0.
5: 1: 1. That is, the weight ratio of ceria and zirconia is constant at 1: 1 and the weight ratio of alumina is in the range of 4 to 0.5 with respect to 1 for each of ceria and zirconia. However, the weight ratio between ceria and zirconia does not need to be strictly 1: 1. A weight ratio of 40:60 to 60:40 can also be used. When the weight ratio of alumina exceeds 4 with respect to 1 each of ceria and zirconia, the amount of ceria and zirconia when catalyzed is reduced, so that the catalytic performance is reduced. The decrease in the surface area due to the heat history becomes large, which causes the catalyst performance to decrease.

Since the composite oxide of the present invention is constituted as described above, it is effective for improving the heat resistance (high-temperature durability) of an exhaust gas purifying catalyst for an internal combustion engine. By using the composite oxide of the present invention, the reason why the exhaust gas purifying catalyst is excellent in high-temperature durability performance is not clear, but the fact that ceria and zirconia are compounded to have excellent oxygen storage ability, Alumina, ceria, and zirconia interact with each other due to the chemical conversion, that is, each component acts as a heat resistance improving component, and the high specific surface area of alumina increases the specific surface area of the composite oxide to achieve heat resistance. Is considered to have been improved.

Here, the structure of the composite oxide of the present invention will be described by way of an example. The composite oxide (A) (the composite oxide of the present invention) in which the weight ratio of each oxide of alumina, ceria, and zirconia was 1: 1: 1, and the composite oxide (A) were separately prepared. Mixed oxide (B) [comparative product] prepared by mixing and pulverizing γ-alumina, cerium acetate and zirconium acetate with a ball mill to form a slurry at the same compounding ratio as above, and drying and firing this slurry. 1 and 2 are charts of the diffraction patterns obtained by X-ray diffraction. As apparent from these charts, in the composite oxide (A), but a composite oxide of Ce _0.5 Zr _{0. 5} O ₂ was detected, in the mixed oxide (B), CeO _2,
Only single component oxides of ZrO ₂ and Al ₂ O ₃ were detected.

The composite oxide of the present invention is not composed of a single component oxide, but is formed by the presence of a composite oxide such as Ce _0.5 Zr _0.5 O ₂ present in the composite oxide (A). It is considered that heat resistance is improved and oxygen storage capacity characteristics are improved.

The composite oxide (A) and the mixed oxide (B), and only ceria and zirconia produced by the same method as the composite oxide (A) except that alumina is not blended. Composite oxide (C)
[Composite oxide as a comparative product] B after each new product (before heat aging) and after heat aging (900 ° C., 1 hour)
The ET specific surface areas were measured, and their reduction rates were also determined. The results are shown in Table 1 below.

[0014]

[Table 1]

[0015] As shown in Table 1 above, the mixed oxide (B) is mainly composed of a single-component oxide, and the specific surface area is largely reduced by thermal aging. Further, since the composite oxide (C) does not have alumina, the specific oxide has a small specific surface area and a large reduction rate of the specific surface area. In contrast,
It is considered that the composite oxide (A) prevents the specific surface area from decreasing due to the interaction of the three components of alumina, ceria, and zirconia.

Next, the method for producing a composite oxide of the present invention will be described in detail. The method for producing a composite oxide of the present invention is a preferred method for producing the above-described composite oxide of the present invention, in which an alumina compound, cerium nitrate and zirconium nitrate are stirred and dissolved in pure water to obtain a mixed solution. The mixed solution is added dropwise to an aqueous ammonia solution while stirring,
After the pH is adjusted to 9 to 9.5, the formed precipitate is aged.

In the production method of the present invention, an alumina compound, cerium nitrate and zirconium nitrate are stirred and dissolved in pure water to obtain a mixed solution. It is particularly important to produce a precipitate after the pH of 9 to 9.5. That is,
Precipitate (co-precipitate) by co-precipitation of the three components of alumina compound, cerium nitrate and zirconium nitrate
It is particularly important to generate

Here, as a method of obtaining the above mixed solution from the alumina compound, cerium nitrate and zirconium nitrate, for example, a method of adding an alumina compound to an aqueous solution of cerium nitrate and zirconium nitrate, stirring and mixing, etc. Can be At this time, the amount of each component used is preferably such that it falls within the range of the weight ratio of alumina, ceria, and zirconia in the composite oxide of the present invention described above.

The concentration of the mixed solution as an oxide is preferably from 10 to 100 g / l,
More preferably, it is 〜80 g / l.

When the mixed solution is dropped into the aqueous ammonia solution while being mixed, the amount of the aqueous ammonia solution added is preferably 0.2 to 0.7 times the volume of the mixed solution. More preferably, the capacity is 0.3 to 0.6 times.

Then, as described above, the mixed solution is dropped into the aqueous ammonia solution to adjust the pH to 9 to 9.5. Here, if the pH is less than 9, precipitation is insufficient, while if it exceeds 9.5, complex salts are formed and redissolved, resulting in insufficient precipitation.

The time for aging the formed precipitate is preferably 10 to 20 hours, and 14 to 1 hour.
More preferably, it is 6 hours.

As the alumina compound used in the production method of the present invention, aluminum nitrate, boehmite alumina, activated alumina powder and the like are preferably used. Also,
The aqueous ammonia used in the production method of the present invention includes (1 + 9) aqueous ammonia, aqueous sodium hydroxide,
An aqueous solution of potassium hydroxide is mentioned, and an aqueous solution of (1 + 9) ammonia is particularly preferable.

In the production method of the present invention, after the precipitate is aged, the precipitate is washed with water by decantation, filtered, washed again with water, dried and pulverized by a generally known method. Bake. For example, the temperature at which the aged precipitate is washed with water, filtered and then dried is 10
0 to 200 ° C., preferably 140 to 160 ° C.
Is more preferable. The time for this drying is preferably 25 to 35 hours, and 28 to 35 hours.
More preferably, it is 33 hours. After the dried precipitate is pulverized and then fired, the temperature is set at 50.
0 to 700 ° C, preferably 550 to 650 ° C
Is more preferable. In addition, the time for this firing is preferably 2 to 7 hours, and more preferably 3 to 5 hours.

Next, the exhaust gas purifying catalyst of the present invention will be described in detail. The exhaust gas purifying catalyst of the present invention is produced using the above-described composite oxide of the present invention.

Here, an example of a method for preparing the exhaust gas purifying catalyst of the present invention will be described below. However, this does not limit the exhaust gas purifying catalyst of the present invention at all. The composite oxide (A), γ-alumina (activated alumina),
A nickel compound, alumina sol and pure water are charged into a ball mill at a predetermined ratio, mixed for about 20 hours, pulverized into a slurry to form a wash coat liquid, and then carried on an integral structure carrier, dried and fired, A washcoat carrier having a washcoat layer is prepared. Thereafter, a predetermined amount of a noble metal component of platinum, palladium and rhodium is impregnated, dried and fired. Thereafter, a predetermined amount of an aqueous solution of a barium compound is impregnated, dried and calcined to obtain a completed catalyst.

Here, in addition to the composite oxide (A), activated alumina, nickel compound, and alumina sol, cerium acetate and zirconium acetate can be added as a raw material of the washcoat liquid. The amount of each component carried in the wash coat layer was 100 parts by weight of alumina.
As ceria 10-60, zirconia 10-6
0, nickel oxide is preferably 2 to 8, and alkaline earth metal oxide is preferably 1.5 to 10. The ratio of the composite oxide in the washcoat layer is preferably 20 to 80% by weight.

Since the exhaust gas purifying catalyst of the present invention is produced using the above-described composite oxide of the present invention, it has excellent performance. In particular, the weight ratio of alumina, ceria, and zirconia in the composite oxide of the present invention is 1:
When the ratio is 1: 1, it has more excellent performance. This means that the value Y of the geometric mean √ (CO × NO _x ) of the conversion rates of CO and NO _x of the exhaust gas purifying catalyst of the present invention,
It is clear from the graph (see FIG. 3) showing the relationship between the weight ratio of alumina (X when the weight ratio of alumina, ceria, and zirconia is X: 1: 1) in the composite oxide of the present invention. That is, when the weight ratio of alumina, ceria, and zirconia is 1: 1: 1, the best performance is exhibited by the interaction of these three components, and the weight ratio of alumina becomes larger or smaller than this. Indicates that performance tends to decrease.

As described above, the composite oxide of the present invention comprises:
A complex oxide such as Ce _0.5 Zr _0.5 O ₂ is formed, and the oxygen storage ability is excellent, and alumina, ceria, and zirconia work together to improve the heat resistance of the three components. In addition, the rate of decrease in specific surface area due to thermal aging is small. The exhaust gas purifying catalyst of the present invention using the composite oxide has improved heat resistance and improved catalytic performance after high-temperature durability by improving the above-mentioned properties of the composite oxide.

[0030]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited in any way by these examples.

Example 1 a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) was added to a cerium nitrate solution (100 g as cerium oxide).
g) is added and a mixed solution is prepared. After adding boehmite alumina (100 g as alumina) to this mixed solution, the mixture is sufficiently stirred to prepare a 6 liter homogeneous solution. The concentration as oxide in this solution is 50 g / l. This solution was slowly added dropwise and neutralized to 2.1 liters of a (1 + 9) ammonia solution with stirring to adjust the pH to 9.3. The precipitate formed here is aged for 15 hours. Then, it is washed twice with decantation, filtered, and then cooled to 150 ° C.
For 28 hours. Thereafter, the mixture was pulverized and calcined at 620 ° C. for 4 hours to prepare a composite oxide (1). The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide (1) was 1: 1: 1.

B) Preparation of catalyst: 180 g of composite oxide (1), BET specific surface area: 150 m
213 g of activated alumina having an average particle size of 30 μm ² / g, nickel nitrate equivalent to 12 g of nickel oxide, and 15 g of alumina
The contained alumina sol and 550 g of distilled water are put into a ball mill and pulverized and mixed for 20 hours to obtain a wash coat liquid. After a cordierite honeycomb carrier (400 cells, capacity 0.34 liter) is immersed in the washcoat solution, excess washcoat solution in the cells is removed by air blow and dried. After immersion and drying in the washcoat solution twice, baking is performed at 500 ° C. for 2 hours. The wash coat amount of this wash coat carrier is 140
g / l, 96 g / l alumina, 20 g / ceria
1, 20 g / l of zirconia and 4 of nickel oxide
g / l. Next, palladium nitrate and rhodium chloride were dissolved in distilled water, and the palladium concentration was 1.67 g /
1 to prepare an impregnation solution having a rhodium concentration of 0.167 g / l. After immersing the washcoat carrier in 300 ml of the impregnating solution, the excess impregnating solution in the cell is removed by air blow, and then the cell is dried. Then, it was calcined at 500 ° C. for 2 hours to obtain a catalyst (No. 1). The resulting catalyst is Pd
1.47 g / l and 0.147 g / l of Rh were carried.

Example 2 a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) was added to a cerium nitrate solution (100 g as cerium oxide).
g) is added and a mixed solution is prepared. After aluminum nitrate (100 g as alumina) is added to this mixed solution, it is sufficiently stirred to make a homogeneous solution. The concentration as oxide in this solution is 50 g / l. Six liters of this solution was slowly added dropwise and neutralized to 3 liters of (1 + 9) ammonia solution with stirring to adjust the pH to 9.0. The precipitate formed here is aged for 15 hours. Then, it is washed twice by decantation, filtered, and dried at 150 ° C. for 28 hours. Thereafter, the mixture was pulverized and calcined at 620 ° C. for 4 hours to prepare a composite oxide (2). The resulting composite oxide (2)
The weight ratio of alumina, ceria, and zirconia is 1:
1: 1. b) Preparation of catalyst Example 1 except that 180 g of the composite oxide (2) was used.
And a catalyst (No. 2) was obtained. The supported amount of each component (Pd, Rh, hereinafter the same) in the obtained catalyst is the same as in the example of Example 1.

Example 3 a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) was added to a cerium nitrate solution (100 g as cerium oxide).
g) is added and a mixed solution is prepared. After adding boehmite alumina (200 g as alumina) to this mixed solution, it is sufficiently stirred to obtain a homogeneous solution. The concentration as oxide in this solution is 50 g / l. 8 liters of this solution was slowly added dropwise and neutralized to 2.8 liters of (1 + 9) ammonia solution with stirring to adjust the pH to 9.5. The precipitate formed here is aged for 15 hours. Then, it is washed twice with decantation, filtered and then filtered at 150 ° C. for 28 hours.
Let dry for hours. Thereafter, the mixture was pulverized and calcined at 620 ° C. for 4 hours to prepare a composite oxide (3). The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide (3) was 2: 1: 1. b) Preparation of catalyst 240 g of composite oxide (3) and BET specific surface area of 15
153 g of activated alumina having an average particle size of 30 μm at 0 m ² / g
The catalyst (N) was prepared in the same manner as in Example 1 except that
o. 3) was obtained. The amount of each component carried in the obtained catalyst is the same as in the example of Example 1.

Example 4 a) Preparation of Composite Oxide A zirconium nitrate solution (100 g as zirconium oxide) was added to a cerium nitrate solution (100 g as cerium oxide).
g) is added and a mixed solution is prepared. After aluminum nitrate (400 g as alumina) is added to this mixed solution, it is sufficiently stirred to make a uniform solution. The concentration as oxide in this solution is 50 g / l. Twelve liters of this solution was slowly dropped into 6 liters of (1 + 9) ammonia solution with stirring to neutralize the solution, and the pH was adjusted to 9.1. The precipitate formed here is aged for 15 hours. Then, it is washed twice by decantation, filtered, and dried at 150 ° C. for 28 hours. Thereafter, the mixture was pulverized and calcined at 620 ° C. for 4 hours to prepare a composite oxide (4). The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide (4) was 4: 1: 1. b) Preparation of catalyst 360 g of composite oxide (4) and a BET specific surface area of 15
The catalyst was prepared in the same manner as in Example 1 except that 33 g of activated alumina having a mean particle size of 30 μm and 0 m ² / g was used.
4) was obtained. The amount of each component carried in the obtained catalyst is the same as in the example of Example 1.

Example 5 a) Preparation of Composite Oxide In a cerium nitrate solution (100 g as cerium oxide),
Zirconium nitrate solution (100 as zirconium oxide)
g) and γ-alumina powder (400 g) are added, pulverized and mixed in a ball mill for 16 hours to prepare a slurry.
The concentration as oxide in this slurry is 75 g / l. Eight liters of this slurry was slowly added dropwise and neutralized to 2.4 liters of (1 + 9) ammonia solution with stirring to adjust the pH to 9.4. The precipitate formed here is washed with water, filtered, and dried at 150 ° C. for 28 hours. Thereafter, the mixture was pulverized and calcined at 620 ° C. for 4 hours to prepare a composite oxide (5). The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide (5) was 4: 1: 1. b) Preparation of catalyst 360 g of composite oxide (5) and BET specific surface area of 15
The catalyst was prepared in the same manner as in Example 1 except that 33 g of activated alumina having a mean particle size of 30 μm and 0 m ² / g was used.
5) was obtained. The amount of each component carried in the obtained catalyst is the same as in the example of Example 1.

Example 6 a) Preparation of Composite Oxide A zirconium nitrate solution (100 g as zirconium oxide) was added to a cerium nitrate solution (100 g as cerium oxide).
g) is added and a mixed solution is prepared. After adding boehmite alumina (50 g as alumina) to this mixed solution, it is sufficiently stirred to obtain a homogeneous solution. The concentration as oxide in this solution is 50 g / l. 5 liters of this solution was slowly added dropwise and neutralized to 1.8 liters of (1 + 9) ammonia solution with stirring to adjust the pH to 9.0. The precipitate formed here is aged for 15 hours. Then, it is washed twice by decantation, filtered, and dried at 150 ° C. for 28 hours. Then, it was pulverized and calcined at 620 ° C. for 4 hours to prepare a composite oxide (6). The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide (6) was 0.5: 1: 1. b) Preparation of catalyst 150 g of composite oxide (6) and BET specific surface area of 15
243 g of activated alumina having an average particle size of 30 μm at 0 m ² / g
The catalyst (N) was prepared in the same manner as in Example 1 except that
o. 6) was obtained. The amount of each component carried in the obtained catalyst is the same as in the example of Example 1.

Comparative Example 1 a) Preparation of Composite Oxide A zirconium nitrate solution (100 g as zirconium oxide) was added to a cerium nitrate solution (100 g as cerium oxide).
g) is added and a mixed solution is prepared. The concentration as an oxide in this mixed solution is 50 g / l. 4 liters of this mixed solution was gradually added dropwise to 2 liters of (1 + 9) ammonia solution with stirring to neutralize the solution, and the pH was adjusted to 9.3. The precipitate formed here is aged for 15 hours. Then, it is washed twice with decantation, filtered, and then cooled to 150 ° C.
For 28 hours. Thereafter, the mixture was pulverized and calcined at 620 ° C. for 4 hours to prepare a composite oxide (a). The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide (a) was 0: 1: 1. b) Preparation of catalyst 120 g of composite oxide (a) and BET specific surface area of 15
273 g of activated alumina having an average particle size of 30 μm at 0 m ² / g
The catalyst (N) was prepared in the same manner as in Example 1 except that
o. a) was obtained. The amount of each component carried in the obtained catalyst is the same as in the example of Example 1.

Comparative Example 2 a) Preparation of Mixed Oxide A cerium nitrate solution (100 g as cerium oxide) and a zirconium nitrate solution (100 g as zirconium oxide)
g), γ-alumina (100 g) and pure water were pulverized and mixed by a ball mill for 16 hours, dried at 150 ° C. for 28 hours, pulverized and calcined at 620 ° C. for 4 hours to prepare a mixed oxide (b). did. The weight ratio of alumina, ceria, and zirconia in the obtained mixed oxide (b) was 1: 1: 1. b) Preparation of catalyst 180 g of mixed oxide (b) and BET specific surface area of 15
213 g of activated alumina having an average particle size of 30 μm at 0 m ² / g
The catalyst (N) was prepared in the same manner as in Example 1 except that
o. b) was obtained. The amount of each component carried in the obtained catalyst is the same as in the example of Example 1.

Example 7 New products of the composite oxides (1) to (6) prepared in Examples 1 to 6 and the composite oxide (a) and the mixed oxide (b) prepared in Comparative Examples 1 and 2 The BET specific surface area of the (sample before heat endurance) and the sample after heat endurance in an electric furnace at 900 ° C. for 1 hour were measured. The results are shown in Table 2 below. A in the composite oxide or mixed oxide
The following Table 2 also shows the l ₂ O ₃ / CeO ₂ / ZrO ₂ ratio (weight ratio) and the type of alumina used.

[0041]

[Table 2]

As is clear from the results of the above [Table 2],
The decrease rate of the specific surface area due to the heat endurance of the composite oxides (1) to (6) [product of the present invention] is the specific surface area due to the heat endurance of the composite oxide (a) and the mixed oxide (b) [comparative product] It can be seen that the composite oxide of the present invention has excellent heat resistance, which is smaller than the decrease rate.

Example 8 X of the composite oxides (1) to (6) prepared in Examples 1 to 6 and the composite oxide (a) and mixed oxide (b) prepared in Comparative Examples 1 and 2 The compounds detected as a result of analysis by line diffraction are shown in [Table 3] below.

[0044]

[Table 3]

As is clear from the results of Table 3 above,
From the composite oxides (1) to (6) and (a), Ce, Z
A composite oxide of r and O (Ce _0.5 Zr _0.5 O ₂ ) was detected. From the mixed oxide (b), single component oxides of ceria and zirconia were detected, but no composite oxide was detected. Was.

Example 9 The catalysts prepared in Examples 1 to 6 (No. 1 to No. 6) and the catalysts prepared in Comparative Examples 1 and 2 (No. a and No. b) were prepared under the following conditions. After the durability test, performance evaluation was performed. Evaluation is CO, HC,
It was expressed as the conversion of each of the square roots of NO _x and CO × NO _x . The results are shown in Table 4 below.・ Durability test conditions Engine: Displacement 2000cc Catalyst temperature: 980 ° C × 20 hours + 600 ° C × 5 hours A / F: 14.6 ± 0.5, 1Hz ・ Performance evaluation conditions Vehicle: 660cc, EFI vehicle Evaluation mode: 10- 15 modes

[0047]

[Table 4]

As is clear from the results of the above [Table 4],
Catalyst using the composite oxide of the present invention (No. 1 to No. 6)
It can be seen that has excellent performance after the high temperature durability test.

[0049]

The composite oxide of the present invention is effective for improving the heat resistance (high temperature durability) of an exhaust gas purifying catalyst for an internal combustion engine. Further, according to the production method of the present invention, a composite oxide effective for improving the heat resistance (high-temperature durability) of an exhaust gas purifying catalyst for an internal combustion engine can be obtained. Further, the exhaust gas purifying catalyst of the present invention has excellent performance after a high-temperature durability test.

[Brief description of the drawings]

FIG. 1 is a chart of a diffraction pattern of the composite oxide of the present invention by X-ray diffraction.
The diffraction peak of _0.5 Zr _0.5 O ₂ and the X mark indicate the diffraction peak of alumina, respectively.

FIG. 2 is a chart of a diffraction pattern of a comparative mixed oxide by X-ray diffraction, in which □ indicates a ceria diffraction peak, Δ indicates a zirconia diffraction peak, and x indicates a diffraction of alumina. Each peak is shown.

FIG. 3 is a diagram showing a value Y of a geometric mean √ (CO × NO _x ) of CO and NO _x conversion rates of an exhaust gas purifying catalyst of the present invention;
4 is a graph showing the relationship between the weight ratio of alumina (X when the weight ratio of alumina, ceria, and zirconia is X: 1: 1) in the composite oxide of the present invention.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 18, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

[0041]

[Table 2]
────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 28, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

When the mixed solution is dropped into the aqueous ammonia solution while being mixed, the amount of the aqueous ammonia solution is preferably 0.2 to 0.7 times the volume of the mixed solution. The capacity is more preferably 0.3 to 0.6 times.

Claims (4)

[Claims] 1. A composite oxide, wherein the weight ratio of alumina, ceria and zirconia is from 4: 1: 1 to 0.5: 1: 1. 2. A mixed solution is obtained by stirring and dissolving an alumina compound, cerium nitrate and zirconium nitrate in pure water, and the mixed solution is dropped into an aqueous ammonia solution with stirring to adjust the pH to 9 to 9.5. And then aging the produced precipitate. 3. The method according to claim 1, wherein the alumina compound is aluminum nitrate, boehmite alumina or activated alumina powder.
A method for producing a composite oxide according to claim 2. 4. An exhaust gas purifying catalyst produced using the composite oxide according to claim 1.