JP4316586B2 - Exhaust gas purification catalyst - Google Patents

Description

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

  The exhaust gas purification catalyst for an internal combustion engine is increasingly required to have an improved purification performance as the exhaust gas regulations are tightened. For this reason, the 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, since the use temperature becomes high, further improvement in heat resistance is required.

  Conventionally, for example, in Patent Document 1, a slurry containing activated alumina, a cerium compound, a zirconium compound and a nickel compound is coated on a carrier, dried and fired, and then a noble metal component is supported on a washcoat carrier, It has been reported that a catalyst carrying a metal group component is excellent in CO and HC performance near the theoretical mixing ratio. Patent Document 2 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 insufficient for more severe demands for improving high temperature durability.

JP-A-5-277375 JP-A-6-279027

  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 purification catalyst for an internal combustion engine, a method for producing the same, and an exhaust gas purification catalyst having excellent catalytic performance after high temperature durability. It is to provide.

  As a result of diligent research, the present inventors have found that a composite oxide in which the weight ratio of alumina, ceria, and zirconia is in a specific range, a method for producing the composite oxide using a specific method, and the composite oxide It has been found that the exhaust gas purifying catalyst prepared by using the above can achieve the above-mentioned purpose.

The present invention has been made based on the above knowledge, and in an exhaust gas purifying catalyst comprising a carrier having a washcoat layer and a noble metal component supported on the carrier, the washcoat layer is made of alumina, ceria and zirconia. weight ratio of 4: 1: 1 to 0.5: 1: 10 to 60 1 containing der Ru double coupling oxide, and alumina, ceria, zirconia and nickel oxide, alumina weight as 100, ceria The present invention provides an exhaust gas purifying catalyst characterized by containing 10 to 60 zirconia and 2 to 8 nickel oxide .

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

Hereinafter, the composite oxide of the present invention will be described in detail.
In the composite oxide of the present invention, the weight ratio of alumina, ceria and zirconia is 4: 1: 1 to 0.5: 1: 1. That is, the weight ratio of ceria to 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 each for ceria and zirconia. However, the weight ratio of ceria and zirconia is not strictly required to be 1: 1, and those having a weight ratio of 40:60 to 60:40 can also be used.
If the weight ratio of alumina exceeds 4 for each of ceria and zirconia, the amount of ceria and zirconia when catalyzed will decrease, so the catalyst performance will be reduced, whereas if it is less than 0.5, The decrease in surface area due to the heat history becomes large, causing a decrease in catalyst performance.

  Since the composite oxide of the present invention is configured as described above, it is effective for improving the heat resistance (high temperature durability) of the exhaust gas purifying catalyst of the internal combustion engine. The reason why the exhaust gas purification catalyst is excellent in high-temperature durability performance by using the composite oxide of the present invention is not clear, but the composite of ceria and zirconia has improved oxygen storage capacity, As a result, alumina, ceria and zirconia interact with each other, that is, each component acts as a component for improving heat resistance, and the high specific surface area of alumina increases the specific surface area of the composite oxide. It is conceivable that

Here, an example of the composite oxide of the present invention will be given and the structure thereof will be described.
Separately, a composite oxide (A) in which the weight ratio of each oxide of alumina, ceria and zirconia is 1: 1: 1 (the composite oxide of the present invention) and the composite oxide (A) were prepared. Γ-alumina, cerium acetate and zirconium acetate were mixed in a ball mill and pulverized into a slurry at the same blending ratio as above, mixed oxide (B) prepared by a method of drying and firing this slurry [comparative product] FIG. 1 and FIG. 2 show charts of diffraction patterns by X-ray diffraction for “mixed oxide”. As is clear from these charts, Ce _0.5 Zr _0.5 O ₂ composite oxide was detected in the composite oxide (A), but CeO ₂ , ZrO ₂ and Al were detected in the mixed oxide (B). Only a single component oxide of ₂ O ₃ was detected.

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

  Further, the composite oxide composed only of ceria and zirconia produced by the same production method as the composite oxide (A) except that the composite oxide (A) and the mixed oxide (B) and alumina are not blended. The BET specific surface area of each product (C) [composite oxide as a comparative product] after each new product (before thermal aging) and after thermal aging (900 ° C., 1 hour) was measured, and the reduction rate thereof was also determined. The results are shown in [Table 1] below.

As shown in [Table 1] above, the mixed oxide (B) is mainly composed of a single component oxide, and has a large reduction rate of the specific surface area due to thermal aging. Moreover, since the said complex oxide (C) does not have an alumina, a specific surface area is small and the fall rate of a specific surface area is also large.
On the other hand, it is considered that the composite oxide (A) prevents a decrease in specific surface area due to the interaction of three components of alumina, ceria and zirconia.

Next, the method for producing the 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, and an alumina compound, cerium nitrate and zirconium nitrate are stirred and dissolved in pure water to obtain a mixed solution. The mixed solution is dropped into an aqueous ammonia solution while stirring to adjust the pH to 9 to 9.5, and then 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. The mixed solution is dropped into an aqueous ammonia solution while stirring, and the pH is adjusted to 9 to 9. It is particularly important to produce a precipitate after 9.5. That is, it is particularly important to generate a precipitate (coprecipitate) by a method in which the three components of alumina compound, cerium nitrate, and zirconium nitrate are simultaneously coprecipitated.

  Here, as a method of obtaining the above mixed solution from an 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, and the like can be mentioned. At this time, the amount of each component used is preferably an amount that is 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 oxide in the mixed solution is preferably 10 to 100 g / l, and more preferably 30 to 80 g / l.

  In addition, when the above mixed solution is added dropwise to the aqueous ammonia solution while mixing, the amount of the aqueous ammonia solution is preferably 0.2 to 0.7 times the volume of the mixed solution, 0.3 to More preferably, the capacity is 0.6 times.

  And as above-mentioned, the said mixed solution is dripped in the said ammonia aqueous solution, and pH is set to 9-9.5. Here, when the pH is less than 9, precipitation becomes insufficient, while when it exceeds 9.5, a complex salt is generated and redissolved, resulting in insufficient precipitation.

  In addition, the time for aging the generated precipitate is preferably 10 to 20 hours, and more preferably 14 to 16 hours.

As the alumina compound used in the production method of the present invention, aluminum nitrate, boehmite alumina, activated alumina powder or the like is preferably used.
Examples of the aqueous ammonia solution used in the production method of the present invention include (1 + 9) aqueous ammonia solution, caustic soda aqueous solution, caustic potash aqueous solution and the like, and (1 + 9) aqueous ammonia solution is particularly preferable.

In the production method of the present invention, after aging the precipitate, the precipitate is washed with water by decantation by a generally known method, filtered, washed again with water, dried, pulverized, and fired.
For example, the temperature at which the aged precipitate is washed with water and filtered and then dried is preferably 100 to 200 ° C, and more preferably 140 to 160 ° C. The time for drying is preferably 25 to 35 hours, and more preferably 28 to 33 hours.
Moreover, it is preferable that it is 500-700 degreeC, and, as for the temperature at the time of baking after pulverizing the dried said deposit, it is still more preferable that it is 550-650 degreeC. Moreover, it is preferable that the time at the time of baking is 2 to 7 hours, and it is still more preferable that it is 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 is shown below. However, this does not limit the exhaust gas purifying catalyst of the present invention.
After the composite oxide (A), γ-alumina (active alumina), nickel compound, alumina sol and pure water are put into a ball mill at a predetermined ratio, mixed and pulverized for about 20 hours to form a washcoat solution. This is supported on an integral structure carrier, dried and fired to prepare a washcoat carrier having a washcoat layer. Thereafter, a predetermined amount of noble metal components of platinum, palladium and rhodium are impregnated, dried and fired. Thereafter, a predetermined amount of an aqueous solution of a barium compound is impregnated, dried and fired to obtain a finished 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 for the washcoat solution.
The amount of each component in the washcoat layer is as follows: the weight of alumina is 100, ceria is 10 to 60, zirconia is 10 to 60, nickel oxide is 2 to 8, and alkaline earth metal oxide is 1. It is preferable that it is 5-10.
Moreover, it is preferable that the ratio of the complex oxide in the said washcoat layer is 20 to 80 weight%.

  Since the exhaust gas purifying catalyst of the present invention is manufactured using the above-described composite oxide of the present invention, it has excellent performance. In particular, when the weight ratio of alumina, ceria, and zirconia in the composite oxide of the present invention is 1: 1: 1, further excellent performance is obtained. This is because the value Y of the geometric mean √ (CO × NOx) of CO and NOx conversion rate of the exhaust gas purifying catalyst of the present invention and the weight ratio of alumina in the composite oxide of the present invention (weight of alumina, ceria, zirconia). It is also clear from the graph (see FIG. 3) showing the relationship with X) when the ratio is X: 1: 1. That is, when the weight ratio of alumina, ceria, and zirconia is 1: 1: 1, the best performance is achieved by the interaction of these three components, and the weight ratio of alumina increases or decreases. Indicates that the performance tends to decrease.

As described above, in the composite oxide of the present invention, a composite oxide such as Ce _0.5 Zr _0.5 O ₂ is formed, and the oxygen storage ability is excellent. By the composite, alumina, ceria, and zirconia are mutually bonded. By acting together, the heat resistance of the three components is improved, and the reduction rate of the specific surface area due to thermal aging is reduced. And the exhaust gas-purifying catalyst of the present invention using the composite oxide has improved heat resistance and improved catalyst performance after high-temperature durability due to the improvement of the characteristics of the composite oxide.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples.

[Example 1]
a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) is added to a cerium nitrate solution (100 g as cerium oxide), and a mixed solution is prepared. Boehmite alumina (100 g as alumina) is added to this mixed solution, and then sufficiently stirred to prepare 6 liters of a uniform solution. The concentration as oxide in this solution is 50 g / l. This solution was gradually added dropwise to 2.1 liters of (1 + 9) ammonia solution while stirring to neutralize the solution to 9.3. The precipitate formed here is aged for 15 hours. Thereafter, it is washed twice with decantation, filtered, and dried at 150 ° C. for 28 hours. Then, it grind | pulverized and baked at 620 degreeC for 4 hours, and prepared complex 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), 213 g of activated alumina having a BET specific surface area of 150 m ² / g and an average particle size of 30 μ, nickel nitrate equivalent to 12 g of nickel oxide, alumina sol containing 15 g of alumina, and 550 g of distilled water Put into a ball mill and grind and mix for 20 hours to obtain a washcoat solution. After 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 blowing and dried. After dipping and drying twice in this washcoat solution, baking is performed at 500 ° C. for 2 hours. The washcoat amount of this washcoat carrier was 140 g / l, alumina was 96 g / l, ceria was 20 g / l, zirconia was 20 g / l, and nickel oxide was 4 g / l.
Next, palladium nitrate and rhodium chloride are dissolved in distilled water to prepare an impregnation solution having a palladium concentration of 1.67 g / l and a rhodium concentration of 0.167 g / l. The washcoat carrier is immersed in 300 ml of the impregnating solution, and then the excess impregnating solution in the cell is removed by air blowing, followed by drying. Then, it baked at 500 degreeC for 2 hours, and obtained the catalyst (No. 1). The obtained catalyst supported 1.47 g / l of Pd and 0.147 g / l of Rh.

[Example 2]
a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) is added to a cerium nitrate solution (100 g as cerium oxide), and a mixed solution is prepared. After adding aluminum nitrate (100 g as alumina) to this mixed solution, it is sufficiently stirred to make a uniform solution. The concentration as oxide in this solution is 50 g / l. 6 liters of this solution was gradually added dropwise to 3 liters of (1 + 9) ammonia solution while stirring to neutralize the solution to 9.0. The precipitate formed here is aged for 15 hours. Thereafter, it is washed twice with decantation, filtered, and dried at 150 ° C. for 28 hours. Then, it grind | pulverized and baked at 620 degreeC for 4 hours, and prepared complex oxide (2). The weight ratio of alumina, ceria and zirconia in the obtained composite oxide (2) was 1: 1: 1.
b) Preparation of catalyst A catalyst (No. 2) was prepared in the same manner as in Example 1 except that 180 g of the composite oxide (2) was used. The amount of each component (Pd, Rh, the same applies hereinafter) in the obtained catalyst is the same as in Example 1.

Example 3
a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) is added to a cerium nitrate solution (100 g as cerium oxide), and a mixed solution is prepared. After adding boehmite alumina (200 g as alumina) to this mixed solution, it is sufficiently stirred to make a uniform solution. The concentration as oxide in this solution is 50 g / l. 8 liters of this solution was gradually added dropwise to 2.8 liters of (1 + 9) ammonia solution while stirring to neutralize the solution to 9.5. The precipitate formed here is aged for 15 hours. Thereafter, it is washed twice with decantation, filtered, and dried at 150 ° C. for 28 hours. Then, it grind | pulverized and baked at 620 degreeC for 4 hours, and prepared complex oxide (3). The weight ratio of alumina, ceria and zirconia in the obtained composite oxide (3) was 2: 1: 1.
b) Preparation of catalyst The catalyst was prepared in the same manner as in Example 1 except that 240 g of the composite oxide (3) and 153 g of activated alumina having a BET specific surface area of 150 m ² / g and an average particle size of 30 μm were used. 3) was obtained. The amount of each component supported in the obtained catalyst is the same as in Example 1.

Example 4
a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) is added to a cerium nitrate solution (100 g as cerium oxide), and a mixed solution is prepared. After adding aluminum nitrate (400 g as alumina) to this mixed solution, it is sufficiently stirred to make a uniform solution. The concentration as oxide in this solution is 50 g / l. 12 liters of this solution was gradually added dropwise to 6 liters of (1 + 9) ammonia solution while stirring to neutralize the solution to 9.1. The precipitate formed here is aged for 15 hours. Thereafter, it is washed twice with decantation, filtered, and dried at 150 ° C. for 28 hours. Then, it grind | pulverized and baked at 620 degreeC for 4 hours, and prepared complex oxide (4). The weight ratio of alumina, ceria and zirconia in the obtained composite oxide (4) was 4: 1: 1.
b) Preparation of catalyst The catalyst was prepared in the same manner as in Example 1 except that 360 g of the composite oxide (4) and 33 g of activated alumina having a BET specific surface area of 150 m ² / g and an average particle size of 30 μm were used. 4) was obtained. The amount of each component supported in the obtained catalyst is the same as in Example 1.

Example 5
a) Preparation of Composite Oxide A cerium nitrate solution (100 g as cerium oxide) is charged with a zirconium nitrate solution (100 g as zirconium oxide) and γ-alumina powder (400 g), and pulverized and mixed in a ball mill for 16 hours. Prepare. The concentration as oxide in this slurry is 75 g / l. 8 liters of this slurry was gradually added dropwise to 2.4 liters of (1 + 9) ammonia solution while stirring to neutralize the pH to 9.4. The precipitate formed here is washed with water, filtered, and dried at 150 ° C. for 28 hours. Then, it grind | pulverized and baked at 620 degreeC for 4 hours, and prepared complex oxide (5). The weight ratio of alumina, ceria and zirconia in the obtained composite oxide (5) was 4: 1: 1.
b) Preparation of catalyst The catalyst was prepared in the same manner as in Example 1 except that 360 g of the composite oxide (5) and 33 g of activated alumina having a BET specific surface area of 150 m ² / g and an average particle size of 30 μ were used. 5) was obtained. The amount of each component supported in the obtained catalyst is the same as in Example 1.

Example 6
a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) is added to a cerium nitrate solution (100 g as cerium oxide), and a mixed solution is prepared. After adding boehmite alumina (50 g as alumina) to this mixed solution, it is sufficiently stirred to make a uniform solution. The concentration as oxide in this solution is 50 g / l. 5 liters of this solution was gradually added dropwise to 1.8 liters of (1 + 9) ammonia solution while stirring to neutralize the solution to 9.0. The precipitate formed here is aged for 15 hours. Thereafter, it is washed twice with decantation, filtered, and dried at 150 ° C. for 28 hours. Then, it grind | pulverized and baked at 620 degreeC for 4 hours, and prepared complex 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 The catalyst was prepared in the same manner as in Example 1 except that 150 g of the composite oxide (6) and 243 g of activated alumina having a BET specific surface area of 150 m ² / g and an average particle size of 30 μm were used. 6) was obtained. The amount of each component supported in the obtained catalyst is the same as in Example 1.

[Comparative Example 1]
a) Preparation of composite oxide A zirconium nitrate solution (100 g as zirconium oxide) is added to a cerium nitrate solution (100 g as cerium oxide), and a mixed solution is prepared. The concentration as an oxide in the mixed solution is 50 g / l. While stirring, 4 liters of this mixed solution was gradually dropped into 2 liters of (1 + 9) ammonia solution while stirring to neutralize the pH to 9.3. The precipitate formed here is aged for 15 hours. Thereafter, it is washed twice with decantation, filtered, and dried at 150 ° C. for 28 hours. Then, it grind | pulverized and baked at 620 degreeC for 4 hours, and prepared complex oxide (a). The weight ratio of alumina, ceria and zirconia in the obtained composite oxide (a) was 0: 1: 1.
b) Preparation of catalyst The catalyst was prepared in the same manner as in Example 1 except that 120 g of the composite oxide (a) and 273 g of activated alumina having a BET specific surface area of 150 m ² / g and an average particle size of 30 μm were used. a) was obtained. The amount of each component supported in the obtained catalyst is the same as in Example 1.

[Comparative Example 2]
a) Preparation of mixed oxide A cerium nitrate solution (100 g as cerium oxide), a zirconium nitrate solution (100 g as zirconium oxide), γ-alumina (100 g) and pure water were pulverized and mixed in a ball mill for 16 hours, and then 150 ° C. And dried for 28 hours, pulverized and fired at 620 ° C. for 4 hours to prepare a mixed oxide (b). The weight ratio of alumina, ceria and zirconia in the obtained mixed oxide (b) was 1: 1: 1.
b) Preparation of catalyst The catalyst (No) was prepared in the same manner as in Example 1 except that 180 g of the mixed oxide (b) and 213 g of activated alumina having a BET specific surface area of 150 m ² / g and an average particle size of 30 μm were used. b) was obtained. The amount of each component supported in the obtained catalyst is the same as in Example 1.

Example 7
Composite oxides (1) to (6) prepared in Examples 1 to 6 and new composite oxides (a) and mixed oxides (b) prepared in Comparative Examples 1 and 2 (samples before heat durability) and The BET specific surface area of the sample after heat durability at 900 ° C. for 1 hour in an electric furnace was measured. The results are shown in [Table 2] below. The Al ₂ O ₃ / CeO ₂ / ZrO ₂ ratio (weight ratio) in the composite oxide or mixed oxide and the alumina type used are also shown in the following [Table 2].

  As is apparent from the results of [Table 2] above, the reduction rate of the specific surface area due to thermal durability of the composite oxides (1) to (6) [the product of the present invention] is the composite oxide (a) and the mixed oxide ( b) It is small compared with the reduction rate of the specific surface area by the heat endurance of [comparative product], and it turns out that the heat resistance of the complex oxide of this invention is excellent.

Example 8
Analysis results by X-ray diffraction of the composite oxides (1) to (6) prepared in Examples 1 to 6 and the composite oxides (a) and mixed oxides (b) prepared in Comparative Examples 1 and 2 were detected. The compounds are shown in [Table 3] below.

As is clear from the results of [Table 3] above, Ce, Zr, and O complex oxides (Ce _0.5 Zr _0.5 O ₂ ) were detected from the complex oxides (1) to (6) and (a). However, from the mixed oxide (b), single component oxides of ceria and zirconia were detected, but composite oxides were not detected.

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 subjected to an endurance test under the following conditions. Evaluation was performed. The evaluation was expressed by the conversion rate of each of the square roots of CO, HC, NOx, and CO × NOx. The results are shown in [Table 4] below.
Endurance test conditions Engine: displacement 2000cc
Catalyst temperature: 980 ° C. × 20 hours + 600 ° C. × 5 hours A / F: 14.6 ± 0.5, 1 Hz
Performance evaluation conditions Vehicle: 660cc, EFI vehicle Evaluation mode: 10-15 mode

  As is clear from the results of [Table 4] above, the catalysts (No. 1 to No. 6) using the composite oxide of the present invention have excellent performance after the high temperature durability test. I understand.

FIG. 1 is a chart of a diffraction pattern by X-ray diffraction of the composite oxide of the present invention, where ◯ indicates the diffraction peak of the composite oxide Ce _0.5 Zr _0.5 O ₂ , and X indicates the diffraction peak of alumina. FIG. 2 is a chart of a diffraction pattern by X-ray diffraction of a mixed oxide as a comparative product, where □ indicates a ceria diffraction peak, Δ indicates a zirconia diffraction peak, and x indicates an alumina diffraction peak. . FIG. 3 shows the value Y of the geometric mean √ (CO × NOx) of the CO and NOx conversion rate of the exhaust gas purifying catalyst of the present invention and the weight ratio of alumina in the composite oxide of the present invention (weight of alumina, ceria, zirconia). It is a graph showing the relationship with X) when the ratio is X: 1: 1.

Claims (5)

In the exhaust gas purifying catalyst comprising a carrier having a washcoat layer and a noble metal component supported on the carrier, the washcoat layer has a weight ratio of alumina, ceria and zirconia of 4: 1: 1 to 0.5: 1: 1 containing der Ru double coupling oxide, and alumina, ceria, zirconia and nickel oxide, alumina weight as 100, 2 ceria 10-60, zirconia 10-60 and nickel oxide An exhaust gas purifying catalyst comprising a ratio of 8 . The exhaust gas-purifying catalyst according to claim 1, wherein the washcoat layer is formed by drying and firing a washcoat solution containing the composite oxide, activated alumina, nickel compound and alumina sol . The exhaust gas-purifying catalyst according to claim 2, wherein the washcoat solution further contains cerium acetate or zirconium acetate . The composite oxide stirs and dissolves the alumina compound, cerium nitrate and zirconium nitrate in pure water to obtain a mixed solution. The mixed solution is dropped into the aqueous ammonia solution while stirring, and the pH is adjusted to 9-9. The exhaust gas-purifying catalyst according to any one of claims 1 to 3, wherein the produced precipitate is aged and then baked after being aged . The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein a ratio of the composite oxide in the washcoat layer is 20 to 80% by weight .

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