JPH05220395A - Production of ternary catalyst excellent in low-temperature activity - Google Patents

Abstract

PURPOSE:To obtain the ternary catalyst capable of sufficiently purifying even a low-temp, exhaust gas by impregnating a perovskite-structure multiple oxide carrier or further a carrier contg. a heat-resistant oxide with an aq. soln. of noble metal salts with the pH specified, drying and then calcining the impregnated carrier. CONSTITUTION:A carrier is impregnated with an aq. soln. of noble metal salts adjusted to >=pH10, and the impregnated carrier is dried and then calcined. One or >=2 kinds of metals are selected from the group consisting of Pd, Pt, Ru, Rh and Ir and used as the noble metals, and Pd is especially preferable. The carrier is the perovskite-structure multiple oxide expressed by the formula Ln1-xAxMo3 (Ln is the rare-earth metals except Cl, A is Cl or alkaline-earth metals, M is one or >=2 kinds among the transition metals consisting of Mn, iron, Co, Ni, Cu, Pd and Ru and 0<x<1). Meanwhile, a heat-resistant oxide contg. Cl, Zn and rare-earth metals other than Ce and at least a part of which forms a multiple oxide is further incorporated as a promoter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an exhaust gas purifying three-way catalyst excellent in carbon monoxide (CO), hydrocarbon (HC) and nitric oxide (NOx) purifying ability, particularly in a gasoline engine for automobiles. The present invention relates to a three-way catalyst that exhibits purifying activity even under conditions of low exhaust gas temperature such as during idling, and a method for producing the same.

[0002]

2. Description of the Related Art As an exhaust gas purifying three-way catalyst, a noble metal catalyst in which a noble metal such as Pt, Rh, or Pd is supported on a simple substance of alumina has been put into practical use and widely used. Further, a complex oxide having a perovskite structure composed of a rare earth metal, an alkaline earth metal and a transition metal is CO, H
Practical use is expected as an inexpensive three-way catalyst for purifying C and NOx for exhaust gas (Japanese Patent Laid-Open No. 59-8704).
No. 6, JP-A-60-82138). Although this perovskite type composite oxide has excellent CO and HC purification ability, it is slightly inferior in NOx purification ability and is not sufficient for practical use as a three-way catalyst for automobile exhaust gas. Therefore, NO of the perovskite type complex oxide catalyst
It has also been proposed to coexist with a noble metal in order to enhance the x-purifying ability (see JP-A-1-168343 and JP-A-2-90947). In particular, JP-A-2-909
Japanese Patent Publication No. 47 discloses a method of impregnating a perovskite type complex oxide carrier with an aqueous solution of a noble metal salt having a pH adjusted to 7 to 10, drying and firing.

[0003]

These catalysts show excellent purifying activity in a gasoline engine of an automobile when the exhaust gas temperature is high, such as when the vehicle is running, but they are sufficient in the exhaust gas temperature that is low, such as when idling. It does not show effective purifying activity. With the tightening of exhaust gas regulations, there is a demand for a catalyst that exhibits sufficient purifying activity even under such a low exhaust gas temperature condition. It is an object of the present invention to provide a method for producing a three-way catalyst that exhibits sufficient purification activity even under conditions where the exhaust gas temperature is low.

[0004]

In the present invention, the pH is adjusted to 10
Impregnate the carrier with a larger adjusted precious metal salt aqueous solution,
After drying, it is baked. The noble metal is one or more metals selected from the group consisting of Pd, Pt, Ru, Rh and Ir, and Pd is particularly preferable. The carrier is Al ₂ O ₃ or a general formula Ln ₁ -xAxMO ₃ (Ln is a rare earth metal except Ce, A is Ce or an alkaline earth metal, M is Mn, Fe,
A transition metal composed of Co, Ni, Cu, Pd and Ru,
All of them are one kind or two or more kinds, and are complex oxides having a perovskite structure represented by 0 <x <1).

In order to maintain the purifying activity even at high temperatures with this catalyst, Ce and Zr, or even C
A heat resistant oxide containing a rare earth metal other than e and at least a part of which is a composite oxide or a solid solution is further included as a cocatalyst. The carrier is impregnated with a noble metal salt aqueous solution containing 0.2 to 5.0 parts by weight in terms of noble metal and having a pH adjusted to be higher than 10 and dried to 250 to 80 parts by weight.
Bake at a temperature of 0 ° C.

As the water-soluble noble metal salt, aqueous ammonia or acid is added to a basic aqueous solution such as tetraamine palladium dichloride Pd (NH ₃ ) ₄ Cl ₂ or tetraamine palladium hydrochloride Pd (NH ₃ ) ₄ (OH) _2. It is prepared by adding it to pH> 10 or used, or PdCl ₂ , PtCl ₂ , Ru
Chlorides such as Cl ₃ .3H ₂ O, Pd (NO ₃ ) ₂ and Ru (NO
₃ ) ₃ , nitrates such as Rh (NO ₃ ) ₃ or Pd (NO ₂ ) ₂ (N
Ammonia water is added to an acidic aqueous solution of a dinitrodiamine salt such as H ₃ ) ₂ or Pt (NO ₂ ) ₂ (NH ₃ ) ₂ to obtain a pH> 1.
It is prepared so that it becomes 0 before use.

[0007]

The catalyst produced by the method of the present invention can exhibit purifying activity even when the exhaust gas temperature is as low as one hundred and tens to two hundred and several tens degrees Celsius during idling. Moreover, when a heat-resistant oxide is further included, the catalyst becomes durable even at a high temperature of 900 ° C. or higher.

[0008]

【Example】

(Example 1) 25 parts by weight of a palladium nitrate solution (Pd content: 4.4% by weight) was diluted with 1700 parts by weight of pure water. Pd
It was 1.1 parts by weight in terms of conversion. Since the pH of this solution was 1.7, aqueous ammonia was added to prepare a solution having a pH of 11.0. The perovskite type complex oxide and the heat resistant oxide used as the carrier were prepared as follows.
To prepare the perovskite type complex oxide by the coprecipitation method, 103.9 g of lanthanum nitrate and 26.1 of cerium nitrate were used.
g, cobalt nitrate 34.9 g, iron nitrate 72.7 g in an aqueous solution of 0.3 liter, and sodium carbonate 50 g as a neutralizing coprecipitant in an aqueous solution of 0.5 liter were prepared. The co-precipitating agent was added dropwise to the above aqueous solution to obtain a co-precipitate. The coprecipitate was thoroughly washed with water, filtered, and dried under vacuum. This is baked at 600 ° C. for 3 hours in the air, crushed, and then baked at 800 ° C. for 3 hours in the air,
Perovskite-type composite oxide was further pulverized (La _{0. 8} C
_{e 0. 2) (Co 0} . 4 Fe 0. 6) to create a powder of O _3. In order to prepare a heat resistant oxide, a commercially available cerium oxide powder having a high specific surface area (CeO ₂ specific surface area 170 m ² / g, purity 99.
91.9 / TREO (total rare earth oxide) 111.9 g was prepared, and zirconium oxynitrate (ZrO (NO ₃ ) ₂ ) was added to this.
Aqueous solution (liquid density 1.51, 25.0 in terms of ZrO ₂ in the liquid
% By weight) 147.9 g, and yttrium nitrate
26.0 g of (Y (NO ₃ ) ₃ ) aqueous solution (liquid specific gravity: 1.62, containing 21.7% by weight in terms of Y ₂ O _{3 in} the liquid) was added, and the mixture was stirred well at 10 ° C. at 110 ° C. Dried in air for hours. Thereafter, conducted for 3 hours at 600 ° C. in _{air, (Ce 0. 65 Zr 0} . 30 Y 0. 05) the O ₂ composite oxide of about 15
0 g was obtained.

[0009] In order to obtain a slurry coating carrier, previous perovskite-type composite oxide _{(La 0. 8 Ce 0.} 2) (Co 0. 4 F
e _{0. 6)} 50 parts by weight of O ₃ and, heat-resistant oxide (Ce _{0. 65} Zr
_{0. 30} Y _{0. 05)} and 50 parts by weight of O ₂ was added to 100 parts by weight of pure water, a slurry obtained by grinding for 12 hours in a ball mill for pouring a refractory honeycomb carrier cordierite, a slurry of Amarube After being blown off with an air stream and dried (for example, at 130 ° C. for 24 hours), it was baked at 600 ° C. in the atmosphere for 3 hours to obtain a carrier on which the perovskite type complex oxide and the heat-resistant oxide were uniformly coated. The above palladium salt aqueous solution (pH = 11.0) was kept at 40 ° C., impregnated with the above coating carrier, and kept for 2 hours to adsorb palladium. It was dried at 130 ° C. for 24 hours and calcined in air at 600 ° C. for 3 hours to obtain a sample of Example 1.

(Example 2) 40 parts by weight of a palladium nitrate solution (4.4% by weight of Pd) was diluted with 1700 parts by weight of pure water to obtain a solution having a Pd conversion of 1.76 parts by weight and a pH of 1.4. Ammonia water was added to this to prepare a solution having a pH of 10.7. Carrier, perovskite-type composite oxide was prepared by the neutralization coprecipitation _{(La 0. 8 Sr 0.} 2)
_{(Co 0. 4 Fe 0.} 6) 50 parts by weight of O ₃ and, refractory oxide which was a solid solution of zirconia to ceria _{(Ce 0. 8 Zr 0.} 2)
Using 20 parts by weight of O ₂ , a cordierite heat-resistant honeycomb carrier was uniformly coated with the perovskite-type composite oxide and the heat-resistant oxide in the same manner as in Example 1 to obtain a carrier. This carrier was impregnated with the above-mentioned aqueous solution of palladium salt (pH = 10.7) to adsorb palladium in the same manner as in Example 1, dried, and then dried in air at 250 ° C. for 3 days.
The sample of Example 2 was obtained by firing for a time.

Example 3 Tetraamine palladium nitrate aqueous solution (Pd content 4.6% by weight solution, pH = 8.5) 2
To 3.9 parts by weight (0.5 parts by weight in terms of Pd), 100 parts by weight of pure water was added, and aqueous ammonia was added to prepare a solution having a pH of 11.2. Carrier, perovskite-type complex oxide _{(La 0. 8 Sr 0.} 2) (Co 0. 4 Fe 0. 6) 5 of the O ₃
The cordierite-type heat-resistant honeycomb carrier was uniformly coated with the perovskite-type composite oxide and the heat-resistant oxide in the same manner as in Example 1 by using 0 part by weight and 50 parts by weight of commercially available SrZrO ₃ . A carrier was obtained. The carrier was impregnated with the whole amount of the above-mentioned palladium salt aqueous solution (pH = 11.2), dried, and then calcined in the air at 600 ° C. for 3 hours to obtain a sample of Example 3.

Example 4 Tetraamine palladium dichloride aqueous solution (Pd content: 8.4% by weight, pH = 8.7)
Aqueous ammonia was added to 13 parts by weight and ion exchange was performed to remove chlorine ions, and 127 parts by weight of an aqueous solution having a pH of 12.0 was obtained. The same coated carrier as used in Example 1 was prepared, and the above-mentioned palladium salt aqueous solution (pH
= 12.0), and after drying, 25 in the air
The sample of Example 4 was obtained by baking at 0 ° C. for 3 hours.

Example 5 100 parts by weight of pure water was added to 23.9 parts by weight of tetraamine palladium nitrate aqueous solution (4.6% by weight of Pd) (0.5 parts by weight in terms of Pd), and aqueous ammonia was added. A solution was prepared so that the pH was 12.0. Carrier perovskite-type composite oxide was prepared by neutralization coprecipitation _{(La 0. 9 Ce 0.} 1) (Co 0. 38 Fe 0. 56 R
u _{0. 06)} 50 parts by weight of O ₃ and was prepared in Example 1 (Ce _0.
A carrier obtained by uniformly coating a cordierite-type heat-resistant honeycomb carrier with a perovskite-type composite oxide and a heat-resistant oxide in the same manner as in Example 1 using ₆₅ Zr _{0. 30} Y _{0 .05} ) O ₂ . Got The carrier was impregnated with the whole amount of the above-mentioned aqueous solution of palladium salt (pH = 12.0), dried and then calcined in the air at 250 ° C. for 3 hours to obtain a sample of Example 5.

(Example 6) 100 parts by weight of pure water was added to 34.5 parts by weight of hexaammine tetrachloride platinum aqueous solution (Pt content 1.45% by weight) (0.5 parts by weight in terms of Pt), and ammonia water was added. A solution was prepared by adding and adjusting the pH to 11.3. Carrier is perovskite type complex oxide
_{(La 0. 8 Sr 0.} 2) (Co 0. 4 Fe 0. 6) O 3 80 parts by weight by using a commercially available SrZrO ₃ 20 parts by weight, heat resistance of cordierite in the same manner as in Example 1 A uniform honeycomb carrier was obtained by uniformly coating the perovskite type complex oxide and the heat-resistant oxide. This carrier was impregnated with the entire amount of the above platinum salt aqueous solution (pH = 11.3), dried, and then calcined at 600 ° C. for 3 hours in the air to obtain a sample of Example 6.

(Comparative Example a) A sample of Comparative Example a was obtained in the same manner as in Example 1 except that aqueous ammonia was added to the aqueous palladium nitrate solution to adjust the pH to 6.9. (Comparative Example b) A sample of Comparative Example b was obtained in the same manner as in Example 1 except that aqueous ammonia was added to the aqueous palladium nitrate solution to adjust the pH to 8.5. (Comparative Example c) A sample of Comparative Example c was obtained in the same manner as in Example 1 except that aqueous ammonia was added to the aqueous palladium nitrate solution to adjust the pH to 9.7.

Comparative Example d 25 parts by weight of a palladium nitrate solution was diluted with 100 parts by weight of pure water to obtain an aqueous solution having a pH of 1.7. Carrier perovskite complex oxide (La _{0. 8} S
_{r 0. 2) (Co 0} . 4 Fe 0. 6) 50 parts by weight of O ₃ and commercial Sr
The same coated carrier as in Example 3 made with 50 parts by weight of ZrO ₃ was used. Other conditions were the same as in Example 1 to obtain a sample of Comparative Example d. (Comparative Example e) A Pt-Rh / γ-Al ₂ O ₃ catalyst, which is a widely used three-way catalyst for automobiles, was used as Comparative Example e.
The content of Pt-Rh was 0.43 part by weight. These results are summarized in Table 1.

[0017]

[Table 1]

Using the samples of these Examples and the samples of Comparative Examples, the catalytic activity was measured and the durability test was conducted under the following conditions. Measurement of catalytic activity Each sample (diameter 30 mm, length 5) supported on a honeycomb-shaped (cell number 300 / inch ² ) cordierite carrier
0 mm) was measured for activity with the following model gas. The gas temperature is indicated by the gas temperature at the entrance to the catalyst, and the temperature is raised from room temperature,
The temperature at which each of NO, CO, and HC (C ₃ H ₆ + C ₃ H ₈ ) has dropped to 50% of the initial concentration is defined as the 50% purification temperature.
Further, the rich gas and the lean gas were switched every one second. The space velocity (SV) of the gas flow through the catalyst is 30,
000 / hour.

Rich gas Lean gas CO 2.6% 0.7% HC (concentration of C ₁ ) 0.19% 0.19% H ₂ 0.87% 0.23% CO ₂ 8% 8% NO 0.17% 0.17% O ₂ 0.65% 1.8% H ₂ O 10% 10% N ₂ balance balance

Durability test 9 times by switching the rich gas and the lean gas every 5 seconds.
A durability test was conducted by repeating a cycle of 30 minutes at 00 ° C. and 30 minutes at 750 ° C. 15 times 15 times. After the durability test, the catalyst activity was measured by the above method. Table 2 shows the measurement results of the catalyst activity before the durability test and the test results of the catalyst activity after the durability test.

[0021]

[Table 2]

As is clear from the results shown in Table 1, the 50% purification temperature is low in each example and high in each comparative example.

Claims (5)

[Claims] 1. A method for producing a catalyst, which comprises impregnating a carrier with an aqueous solution of a noble metal salt having a pH adjusted to be higher than 10, drying and then calcining. 2. The noble metal is Pd, Pt, Ru, Rh and I.
The method for producing a catalyst according to claim 1, 2 or 3, wherein the metal is one or more metals selected from the group consisting of r. 3. The method for producing a catalyst according to claim 4, wherein the noble metal is Pd. 4. The carrier has the general formula Ln ₁ -xAxMO ₃ (Ln
Is a rare earth metal except Ce, A is Ce or an alkaline earth metal, M is Mn, Fe, Co, Ni, Cu, Pd and Ru.
A transition metal consisting of 1 or 2 or more, 0 <
The method for producing a catalyst according to claim 1, which is a complex oxide having a perovskite structure represented by x <1). 5. The production of the catalyst according to claim 4, further comprising a co-catalyst containing Ce and Zr, or a refractory oxide containing a rare earth metal other than Ce and at least a part of which is a solid solution. Method.