JP3144880B2 - Method for producing three-way catalyst with excellent low-temperature activity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-way catalyst for purifying exhaust gas which is excellent in purifying carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx), and particularly to a gasoline engine for automobiles. The present invention relates to a three-way catalyst that exhibits purification 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 a three-way catalyst for purifying exhaust gas, a noble metal catalyst in which a noble metal such as Pt, Rh, or Pd is supported on alumina alone has been put to practical use and widely used. A composite oxide having a perovskite structure composed of a rare earth metal, an alkaline earth metal, and a transition metal includes CO, H
It is expected to be put to practical use as an inexpensive three-way exhaust gas purifying catalyst for purifying C and NOx (Japanese Patent Laid-Open No. 59-8704).
No. 6, JP-A-60-82138). This perovskite-type composite oxide has excellent purification ability of CO and HC, but slightly inferior purification ability of NOx, and is not sufficient for practical use as a three-way catalyst for automobile exhaust gas. Therefore, the NO of the perovskite-type composite oxide catalyst
It has also been proposed to coexist a noble metal in order to enhance the x purification ability (see JP-A-1-168343 and JP-A-2-90947). In particular, JP-A-2-909
No. 47 describes a method of impregnating a perovskite-type composite oxide carrier with an aqueous solution of a noble metal salt adjusted to a pH of 7 to 10, drying and firing.

[0003]

These catalysts exhibit excellent purification activity in a gasoline engine of an automobile under high exhaust gas temperature conditions such as during running, but they do not sufficiently exhibit low exhaust gas temperature conditions such as during idling. It does not show any purification activity. With the tightening of exhaust gas regulations, catalysts that exhibit sufficient purification activity even under such low exhaust gas temperature conditions are desired. An object of the present invention is to provide a method for producing a three-way catalyst exhibiting sufficient purification activity even under conditions of low exhaust gas temperature.

[0004]

According to the present invention, a pH of 10
Impregnate the carrier with a precious metal salt aqueous solution that has been adjusted to a greater extent,
After drying, bake. The noble metal is one or more metals selected from the group consisting of Pd, Pt, Ru, Rh and Ir, and Pd is particularly preferred. Carrier, one general formula Ln _1-x
AxMO ₃ (Ln is a rare earth metal other than Ce, A is Ce or an alkaline earth metal, M is Mn, Fe, Co, Ni, C
A transition metal composed of u, Pd, and Ru, each of which is a composite oxide having a perovskite structure represented by 0 <x <1), one or two or more of them.

[0005] In order that this catalyst can maintain the purifying activity even at a high temperature, Ce and Zr, or even C
As a co-catalyst, a heat-resistant oxide containing a rare earth metal other than e and at least a part of which is a complex oxide or a solid solution is further included. Impregnated with a noble metal salt aqueous solution containing 0.2 to 5.0 parts by weight of noble metal and having a pH adjusted to be greater than 10 with respect to 100 parts by weight of the carrier, and dried, and then 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 hydroxide Pd (NH ₃ ) ₄ (OH) _2. It is used by adjusting to pH> 10 or by adding PdCl ₂ , PtCl ₂ , Ru
Chlorides such as Cl ₃ .3H ₂ O, Pd (NO ₃ ) ₂ , Ru (NO
₃ ) ₃ , nitrate such as Rh (NO ₃ ) ₃ or Pd (NO ₂ ) ₂ (N
Ammonia water is added to an acidic aqueous solution such as a dinitrodiamine salt such as H ₃ ) ₂ or Pt (NO ₂ ) ₂ (NH ₃ ) ₂ to adjust pH> 1.
Prepare and use to be 0.

[0007]

The catalyst produced by the method of the present invention can exhibit purification activity even when the exhaust gas temperature is as low as one hundred and several hundred to several hundred and several degrees Celsius during idling. 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 conversion. Since this solution had a pH of 1.7, aqueous ammonia was added to prepare a solution so that the pH became 11.0. The perovskite-type composite oxide and the heat-resistant oxide used for the carrier were prepared as follows.
In order to produce a perovskite-type composite oxide by a coprecipitation method, 103.9 g of lanthanum nitrate and 26.1 g of cerium nitrate were used.
g, 34.9 g of cobalt nitrate and 72.7 g of iron nitrate in pure water, 0.3 liter, and 0.5 liter of an aqueous solution of 50 g of sodium carbonate as a neutralizing coprecipitant were prepared. The coprecipitant was dropped into the above aqueous solution to obtain a coprecipitate. The coprecipitate was sufficiently washed with water, filtered, and dried under vacuum. This is fired at 600 ° C. for 3 hours in the air, and then pulverized, and then fired 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 refractory oxide, a commercially available high specific surface area cerium oxide powder (CeO ₂ specific surface area 170 m ² / g, purity 99.
111.9 g of 9% / TREO (total rare earth oxide) was prepared, and zirconium oxynitrate (ZrO (NO ₃ ) ₂ ) was added thereto.
Aqueous solution (liquid specific gravity: 1.51, ZrO ₂ conversion in liquid: 25.0)
147.9 g) and yttrium nitrate
26.0 g of (Y (NO ₃ ) ₃ ) aqueous solution (liquid specific gravity 1.62, contained in liquid 21.7% by weight in terms of Y ₂ O ₃ ) was added, and the mixture was stirred at 110 ° C. with good stirring. 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 blown off with an air stream and dried (for example, at 130 ° C. for 24 hours), it was calcined at 600 ° C. for 3 hours in the air to obtain a carrier uniformly coated with a perovskite-type composite oxide and a heat-resistant oxide. The palladium salt aqueous solution (pH = 11.0) was kept warm at 40 ° C., impregnated with the above-mentioned coating carrier, and kept for 2 hours to adsorb palladium. It was dried at 130 ° C. for 24 hours and fired 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) were diluted with 1700 parts by weight of pure water to obtain a solution having a Pd equivalent of 1.76 parts by weight and a pH of 1.4. Was added thereto, and aqueous ammonia was added thereto to prepare a solution so that the pH became 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 carrier in which a perovskite-type composite oxide and a heat-resistant oxide were uniformly coated on a cordierite-based heat-resistant honeycomb carrier was obtained in the same manner as in Example 1. This carrier was impregnated with the above aqueous solution of palladium salt (pH = 10.7), palladium was adsorbed in the same manner as in Example 1, dried, and dried at 250 ° C.
After firing for a time, a sample of Example 2 was obtained.

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

Example 4 Aqueous solution of tetraamine palladium dichloride (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, thereby obtaining 127 parts by weight of an aqueous solution having a pH of 12.0. The same coating carrier as that used in Example 1 was prepared, and the above-mentioned aqueous solution of palladium salt (pH
= 12.0), dried and dried in air at 25
The sample of Example 4 was obtained by firing at 0 ° C. for 3 hours.

Example 5 100 parts by weight of pure water were added to 23.9 parts by weight (0.5 parts by weight in terms of Pd) of an aqueous solution of tetraamine palladium nitrate (Pd content: 4.6% by weight), and ammonia water was added. Then, a solution was prepared so that the pH became 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.
65 Zr 0. 30 Y 0.} 05) by using the O _2, perovskite-type composite oxide and refractory oxide in refractory honeycomb carrier cordierite in the same manner as in Example 1 was uniformly coated carrier I got The carrier was impregnated with the entire amount of the above-mentioned aqueous solution of palladium salt (pH = 12.0), dried, and calcined at 250 ° C. for 3 hours in the atmosphere to obtain a sample of Example 5.

(Example 6) 100 parts by weight of pure water was added to 34.5 parts by weight (0.5 parts by weight in terms of Pt) of an aqueous solution of platinum platinum hexaammine (1.45% by weight of Pt), and ammonia water was added. A solution was prepared so that the pH was adjusted to 11.3 by addition. The carrier is a perovskite-type composite 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 carrier in which a perovskite-type composite oxide and a heat-resistant oxide were uniformly coated on a porous honeycomb carrier was obtained. The carrier was impregnated with the entire amount of the above-mentioned aqueous solution of platinum salt (pH = 11.3), dried, and calcined at 600 ° C. for 3 hours in the atmosphere 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 the pH was adjusted to 6.9 by adding aqueous ammonia to an aqueous solution of palladium nitrate. (Comparative Example b) A sample of Comparative Example b was obtained in the same manner as in Example 1 except that the pH was adjusted to 8.5 by adding aqueous ammonia to an aqueous solution of palladium nitrate. (Comparative Example c) A sample of Comparative Example c was obtained in the same manner as in Example 1 except that the pH was adjusted to 9.7 by adding aqueous ammonia to an aqueous solution of palladium nitrate.

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 prepared using 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 comparative example e is a Pt-Rh / γ-Al ₂ O ₃ catalyst which is a widely used three-way catalyst for automobiles.
The Pt-Rh content was 0.43 parts by weight. These results are summarized in Table 1.

[0017]

[Table 1]

Using the samples of these examples and the samples of the comparative examples, the catalytic activity was measured and the durability test was performed under the following conditions. Measurement of catalytic activity Each sample (diameter 30 mm, length 5 mm) 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 temperature of the gas at the inlet to the catalyst.
The temperature at which each of NO, CO, and HC (C ₃ H ₆ + C ₃ H ₈ ) has decreased to 50% of the initial concentration is defined as a 50% purification temperature.
The rich gas and the lean gas were switched every one second. The space velocity (SV) of the gas stream through the catalyst is 30,
000 / hour.

The rich lean CO 2.6% 0.7% HC (C 1 concentration in terms _{of) 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

Endurance test The above rich gas and lean gas were switched every 5 seconds to 9
A durability test was performed by repeating a cycle of 00 ° C. for 30 minutes and 750 ° C. for 30 minutes 15 times. After the durability test, the catalytic 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 in Table 1, the 50% purification temperature is low in each example, and high in each comparative example.

────────────────────────────────────────────────── (5) References JP-A-56-144746 (JP, A) JP-A-62-269747 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53/94

Claims (4)

(57) [Claims] 1. An aqueous solution of a noble metal salt whose pH has been adjusted to be greater than 10 is prepared using a general formula Ln _1-x AxMO ₃ (Ln is a diluent excluding Ce).
Earth metal, A is Ce or alkaline earth metal, M is Mn,
Transition gold composed of Fe, Co, Ni, Cu, Pd and Ru
Genus, one or more of which are represented by 0 <x <1)
A method for producing a catalyst, comprising impregnating a composite oxide carrier having a perovskite structure , drying and calcining. 2. The noble metal is composed of Pd, Pt, Ru, Rh and I.
The method for producing a catalyst according to claim 1 , wherein the catalyst is one or more metals selected from the group consisting of r. 3. The method according to claim 2 , wherein the noble metal is Pd. 4. The catalyst according to claim 1 , further comprising, as a co-catalyst , a heat-resistant oxide containing Ce and Zr or a rare earth metal other than Ce and at least a part of which is a complex oxide or a solid solution. Production method.