JPH11217220A - Compound oxide, its production and exhaust gas-cleaning catalyst using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compound oxide having an improved catalyst performance after exposed to high temperature by using three components comprising alumina, ceria and zirconia and increasing the content of the zirconia on the basis of the ceria. SOLUTION: This compound oxide comprises the three components of alumina, ceria and zirconia. The ceria and the zirconia are contained in a weight ratio of 1/(>1 to 3). The weight ratio of the alumina to the total amount of the ceria and the zirconia is preferably 1/(1-4). The compound oxide is obtained by stirring and dissolving an alumina compound, cerium nitrate and zirconium nitrate in pure water, dropping the obtained mixture solution into an ammonia aqueous solution with agitation until to reach a pH of 9-9.5, and subsequently aging the produced precipitates. It is desirable that the mixture solution has an oxide concentration of 10-100 g/L.

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 supporting an alkaline earth metal component after carrying the compound has excellent CO and HC performance in the vicinity of the theoretical mixing ratio. In addition, Japanese Unexamined Patent Publication No.
Japanese Patent Publication No. 279027 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.

[0004] In order to solve the above-mentioned problems, the present inventors include three components of alumina, ceria and zirconia,
An exhaust gas purifying catalyst using a composite oxide in which the weight ratio of ceria to zirconia is 1 to 1 has been proposed (Japanese Patent Application No. 9-28).
9436). Although the high-temperature durability is improved by such an exhaust gas purifying catalyst, a further improvement in high-temperature durability has been demanded.

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 excellent in catalytic performance after high-temperature durability. An object of the present invention is to provide a purification catalyst.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies and as a result, have found that an exhaust gas purifying catalyst prepared by using a composite oxide containing a large amount of zirconia with respect to ceria can achieve the above object. I learned.

[0007] The present invention has been made based on the above findings, and comprises three components of alumina, ceria and zirconia,
An object of the present invention is to provide a composite oxide characterized in that the weight ratio of ceria to zirconia is more than 1 to 3 for ceria 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. It is another object of the present invention to provide a method for producing the above-mentioned composite oxide, wherein the produced precipitate is aged after adjusting to 9.5.

Further, the present invention provides an exhaust gas purifying catalyst produced by using the above composite oxide.

[0010]

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,
It is composed of three components, ceria and zirconia, and the weight ratio of the ceria and zirconia is more than 1 to 3 for 1 cerium. When the weight ratio of zirconia to ceria 1 is 1 or less, the rate of increase in the crystallite diameter of the composite oxide due to the thermal history increases, and the rate of decrease in the specific surface area also increases. Become. On the other hand, if it exceeds 3, the amount of ceria, which is an oxygen storage component, is reduced when the catalyst is formed, which causes a reduction in catalytic performance.

The weight ratio of the total amount of the ceria and zirconia to the alumina is preferably 1 to 4 in the total amount of the ceria and zirconia to the alumina. When the weight ratio of the total amount of the ceria and zirconia to the alumina is less than 1, the catalyst performance is deteriorated for unknown reasons, although the reason is not clear. On the other hand, if it exceeds 4, the rate of decrease in the specific surface area after 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.

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 If this dropping method is reversed, that is, if the aqueous ammonia solution is dropped into the mixed solution while stirring, each component starts to precipitate at a different pH, so that a coprecipitate is not obtained and an effective composite oxide is obtained. Absent.

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 oxide in the mixed solution is preferably 10 to 100 g / l, and more preferably 30 to 100 g / l.
More preferably, it is 〜80 g / l.

When the mixed solution is dropped into the aqueous ammonia solution with stirring, 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.

Then, as described above, the mixed solution is dropped into the ammonia aqueous solution to adjust the pH to 9 to 9.5. Here, when the pH is less than 9, precipitation is insufficient, and when the pH exceeds 9.5, the precipitation state does not change, and the aqueous ammonia solution to be used is wasted.

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.

The aqueous ammonia used in the production method of the present invention includes (1 + 9) aqueous ammonia,
An aqueous solution of caustic soda, an aqueous solution of potassium caustic, and the like are 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.

The temperature at which the dried precipitate is pulverized and then fired is preferably from 500 to 700 ° C, more preferably from 550 to 650 ° C. 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. The above-mentioned composite oxide, γ-alumina (activated alumina), nickel compound, alumina sol and pure water were charged into a ball mill at a predetermined ratio, mixed for about 20 hours, pulverized to form a slurry to obtain a washcoat liquid, and It is carried on an integral structure carrier, dried, fired,
A washcoat carrier having a washcoat layer is prepared. Thereafter, a predetermined amount of a noble metal component such as 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, cerium acetate or zirconium acetate can be added as a raw material of the washcoat liquid in addition to the composite oxide, activated alumina, nickel compound and alumina sol.

The amount of each component carried in the washcoat layer is 3% for ceria with respect to 100 weight of alumina.
~ 60, zirconia 5-60, nickel oxide 2 ~
It is preferable that 8 and the alkaline earth metal oxide be 1 to 10. The ratio of the composite oxide in the washcoat layer is preferably from 10 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, the catalyst has improved heat resistance and improved catalytic performance after high-temperature durability.

[0029]

The present invention will be described in more detail with reference to the following examples.

Example 1 a) Preparation of Composite Oxide A zirconium nitrate solution (150 g as zirconium oxide) in a cerium nitrate solution (50 g as cerium oxide)
Is added to prepare a mixed solution. 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 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 A. The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide A was 2: 1: 3.
Met.

B) Preparation of catalyst: 144 g of composite metal oxide A, having a BET specific surface area of 150 m
258 g of activated alumina having an average particle size of 30 μm ² / g, nickel nitrate equivalent to 12 g of nickel oxide, 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 143.
g / l, alumina 107 g / l, ceria 8 g / l
1, 24 g / l of zirconia and 4 of nickel oxide
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. 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 Rh of 0.147 g / l were carried.

Example 2 a) Preparation of Composite Oxide A cerium nitrate solution (100 g as cerium oxide) and a zirconium nitrate solution (100 g as zirconium oxide)
g) and boehmite alumina (100 as alumina)
Except for using g), the procedure of Example 1 was repeated to prepare a composite oxide B. The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide B was 2: 2: 2.

B) Preparation of catalyst Example 1 except that 144 g of the composite metal oxide B was used.
And a catalyst (No. 2) was obtained. The wash coat amount of the obtained catalyst was 143 g / l, alumina was 107 g / l, ceria was 16 g / l, and zirconia was 16 g / l.
g / l and nickel oxide was 4 g / l. The amount of the noble metal component (Pd, Rh) carried is the same as in Example 1.

Example 3 a) Preparation of Composite Oxide A cerium nitrate solution (100 g as cerium oxide), a zirconium nitrate solution (100 g as zirconium oxide)
g) and boehmite alumina (50 g as alumina)
Was prepared in the same manner as in Example 1 except that 6 liters of the homogeneous solution obtained by using the above was used to obtain a composite oxide C. The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide C was 1: 2: 2.

B) Preparation of catalyst A catalyst (N) was prepared in the same manner as in Example 1 except that 120 g of the composite metal oxide C and 282 g of activated alumina were used.
o. 3) was obtained. The wash coat amount of the obtained catalyst was 143 g / l, alumina was 107 g / l, and ceria was 1
6 g / l, zirconia 16 g / l and nickel oxide 4 g / l. In addition, noble metal components (Pd, R
The supported amount of h) is the same as in Example 1.

Example 4 a) Preparation of Composite Oxide Cerium nitrate solution (100 g as cerium oxide), zirconium nitrate solution (100 as zirconium oxide)
g) and boehmite alumina (200 as alumina)
A composite oxide D was prepared in the same manner as in Example 1 except that 6 liters of the homogeneous solution obtained using g) was used. The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide D was 4: 2: 2.

B) Preparation of catalyst A catalyst (N) was prepared in the same manner as in Example 1 except that 192 g of the composite metal oxide D and 210 g of activated alumina were used.
o. 4) was obtained. The wash coat amount of the obtained catalyst was 143 g / l, alumina was 107 g / l, and ceria was 1
6 g / l, zirconia 16 g / l and nickel oxide 4 g / l. In addition, noble metal components (Pd, R
The supported amount of h) is the same as in Example 1.

Comparative Example 1 a) Preparation of Composite Oxide Cerium nitrate solution (150 g as cerium oxide), zirconium nitrate solution (50 g as zirconium oxide)
A composite oxide E was prepared in the same manner as in Example 1, except that boehmite alumina (100 g as alumina) was used. Alumina, ceria, and the like of the obtained composite oxide E;
The weight ratio of zirconia was 2: 3: 1.

B) Preparation of the catalyst Example 1 except that 144 g of the composite metal oxide E was used.
And a catalyst (No. a) was obtained. The wash coat amount of the obtained catalyst was 143 g / l, alumina was 107 g / l, ceria was 24 g / l, and zirconia was 8 g.
/ L, and 4 g / l of nickel oxide. Also,
The amount of the noble metal component (Pd, Rh) carried was the same as in Example 1.

Comparative Example 2 a) Preparation of Composite Oxide A cerium nitrate solution (100 g as cerium oxide) and a zirconium nitrate solution (100 g as zirconium oxide)
A composite oxide F was prepared in the same manner as in Example 1, except that 6 liters of the homogeneous solution obtained using g) was used. The weight ratio of alumina, ceria, and zirconia in the obtained composite oxide F was 0: 2: 2.

B) Preparation of Catalyst A catalyst (No. 1) was prepared in the same manner as in Example 1 except that 96 g of the composite metal oxide F and 306 g of activated alumina were used.
b) was obtained. The obtained catalyst had a wash coat amount of 14
3g / l, alumina 107g / l, ceria 16g
/ L, zirconia was 16 g / l, and nickel oxide was 4 g / l. The amount of the noble metal component (Pd, Rh) carried is the same as in Example 1.

[Experimental Example 1] New composite oxides A to F (samples before heat endurance) prepared in Examples 1 to 4 and Comparative Examples 1 and 2 and 900 ° C. × 20 hours + 950 ° C. × in an electric furnace. 2
The BET specific surface area of the sample after heat endurance for 0 hour was measured. Table 1 shows the results. In addition, Al in the composite oxide
Table 1 also shows the ₂ O ₃ / CeO ₂ / ZrO ₂ ratio (weight ratio).

[0044]

[Table 1]

As is clear from the results in Table 1, Al ₂ O
₃ reduction rate of specific surface area by the thermal endurance of containing composite oxide A~E is smaller than the decreasing rate of the specific surface area due to the thermal durability of the composite oxide F containing no Al ₂ O _3, Al ₂ of the present invention
It can be seen that the O ₃ -containing composite oxide has excellent heat resistance.

[Experimental Example 2] New composite oxides A to F prepared in Examples 1 to 4 and Comparative Examples 1 and 2 (samples before heat endurance) and 900 ° C. × 20 hours + 950 ° C. × in an electric furnace. 2
Table 2 shows compounds detected by X-ray diffraction analysis of the sample after heat endurance for 0 hour.

[0047]

[Table 2]

As is clear from the results in Table 2, a composite oxide composed of Ce, Zr, and O corresponding to the compounding ratio was detected from the composite oxides BF. Composite oxide A was also detected ZrO ₂ because many ZrO ₂ ratio in addition to the composite oxide.

Table 3 shows the crystallite diameter calculated by the Scherrer equation from the same measurement by X-ray diffraction.

[0050]

[Table 3]

As is clear from the results in Table 3, the crystallite diameters of the composite oxides A to D after heat endurance are smaller than those of the composite oxides E to F. This indicates that the crystal growth is small and has heat resistance.

EXPERIMENTAL EXAMPLE 3 The catalysts prepared in Examples 1 to 4 (Nos. 1 to 4) and the catalysts prepared in Comparative Examples 1 and 2 (N
o. For a and b), after a durability test was performed under the following conditions, performance evaluation was performed. The evaluation was CO, HC, NO _x ,
The conversion was represented by the square root of CO × NO _x . The results are shown in Table 4 below.・ Durability test conditions Engine: Displacement 2000cc Catalyst temperature: 900 ° C × 20 hours + 950 ° C. × 20 hours A / F: 14.6 ± 0.5, 1Hz ・ Performance evaluation conditions Vehicle: 660cc, EFI vehicle Evaluation mode: 10- 15 modes

[0053]

[Table 4]

As is clear from the results in Table 4, Example 1
It can be seen that the catalysts of Nos. To 4 (Nos. 1 to 4) have excellent performance after the high-temperature durability test as compared with the catalysts of Nos. A to b of Comparative Examples 1 and 2.

[0055]

As described above, 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, it is possible to obtain the above-mentioned composite oxide which is effective for improving the heat resistance (high-temperature durability) of an exhaust gas purifying catalyst for an internal combustion engine. Further, the exhaust gas purifying catalyst of the present invention has excellent high-temperature durability.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 37/03 B01D 53/36 104A

Claims (5)

[Claims] 1. A composite oxide comprising three components of alumina, ceria and zirconia, wherein the weight ratio of said ceria and zirconia is more than 1 to 3 of zirconia to 1 of said ceria. 2. The composite oxide according to claim 1, wherein the weight ratio of the total amount of said ceria and zirconia to said alumina is 1 to 4 with respect to said alumina. 3. 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. 3. The method for producing a composite oxide according to claim 1, wherein the produced precipitate is aged after the formation. 4. The method according to claim 3, wherein the alumina compound is aluminum nitrate, boehmite alumina or activated alumina powder. 5. An exhaust gas purifying catalyst produced using the composite oxide according to claim 1 or 2.