JP3406001B2 - Exhaust gas purification catalyst - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention is carbon monoxide BACKGROUND OF THE (CO), which hydrocarbons (THC) and nitrogen oxide (NOx) purifying ability excellent exhaust gas purifying three way catalyst was supported on a refractory support it relates to.

[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 alumina alone 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, T
Practical application is expected as an inexpensive three-way catalyst for purifying HC and NOx for exhaust gas purification (JP-A-59-870).
46, JP-A-60-82138). This perovskite-type composite oxide has an excellent purification ability for CO and HC, but has a slightly inferior purification ability for NOx.
It is not sufficient for practical use as a three-way catalyst for automobile exhaust gas. Therefore, a noble metal is made to coexist in order to enhance the NOx purification ability of the perovskite type complex oxide catalyst (Japanese Patent Laid-Open Nos. 1-168343 and 2-9094).
(See Japanese Patent No. 7). In order to further enhance the catalytic activity and heat resistance, Ce is used together with the perovskite type complex oxide catalyst.
Heat resistant oxides such as O ₂ , (CeZrY) O ₂ and SrZrO ₃ are also made to coexist as a co-catalyst.

These catalysts are used by being supported on a heat resistant carrier such as a cordierite honeycomb carrier. The supporting method is to add water to a powder containing a perovskite-type composite oxide powder or a cocatalyst such as a heat-resistant oxide powder added thereto, and grind or stir with a ball mill or the like to form a slurry. This is a method in which the slurry is applied to a carrier, baked, and then an aqueous solution of a noble metal is impregnated or adsorbed on the coated carrier and then baked.

[0004]

The exhaust gas purifying catalyst for automobiles is exposed to high-velocity gas, is exposed to high temperatures, is repeatedly heated and cooled, and is subjected to mechanical stress such as vibration and shock. Used over a period of time. As a result, there arises a problem that the active ingredient of the catalyst peels off from the carrier and falls off. In the conventional noble metal catalyst (Pt-Pd-Rh), alumina sol is used as a binder between the alumina particles supporting the catalyst and the honeycomb carrier. However, when an alumina sol is used as a perovskite oxide catalyst containing a rare earth metal, the alumina sol easily reacts with the rare earth metal at the A site in the perovskite (ABO ₃ ), and the LnAlO ₃ compound (Ln is a rare earth metal other than Ce) is used during use. Is generated to lower the catalytic activity. An object of the present invention is to provide an exhaust gas purifying catalyst in a supported state in which the activity of a catalytically active component is prevented from decreasing due to reaction, peeling and the like.

[0005]

In the present invention, a perovskite-type composite oxide, a noble metal , and a general formula of a cocatalyst are used.
(CeZrLn) O ₂ (Ln is a rare earth metal except Ce)
In refractory oxide represented is, zirconia sol, ceria sol, yttria sol or mixtures thereof sols, or Zr, Ce, solid solution oxide sol containing 2 or more of Y
Which is a catalyst for exhaust gas purification carried on a heat-resistant carrier by using a metal oxide sol as a binder ,
Perovskite complex oxides, precious metals, heat-resistant oxides and
And metal oxide sols are perovskite type compounds other than precious metals.
Mixed oxide powder, heat resistant oxide powder and metal oxide sol
Add water to the containing mixture and stir mix to form a slurry
Then, the slurry is coated on a heat resistant carrier and baked.
After that, the salt of the noble metal in the coated carrier is dissolved in water.
Heat-resistant by impregnating and / or adsorbing liquid and baking
It is carried on a sexual carrier . An example of the binder sol is as follows. Examples of zirconia sol include products "NZS-20A" and "NZS" manufactured by Nissan Chemical Industries, Ltd.
S-30A "," NZS-30B ", zirconia-yttriasol as product" NZS-20A3Y "manufactured by Nissan Chemical Industries, Ltd., and ceriasol as product" Needral W-15-01 "manufactured by Taki Chemical Co., Ltd. ",
As an example of yttria sol, a product “Yttrium oxide sol” manufactured by Taki Chemical Co., Ltd. can be used. 0.5 to 50 parts by weight per 100 parts by weight of the total amount of these metal oxides perovskite composite oxide solid content of the sol or further refractory oxide, more preferably 1 to 10
Parts by weight. This is because when the content of the metal oxide sol is less than 0.5 part by weight, the effect as a binder is not observed, and when it is more than 50 parts by weight, the catalytic activity decreases due to masking.

The perovskite complex oxide has the general formula Ln
_1- xAxMO ₃ (Ln is a rare earth metal except Ce, A is C
e or alkaline earth metal, M is Mn, Fe, Co, N
It is a transition metal composed of i, Cu, Pd and Ru, and each is an oxide represented by 0 <x <1), which is one kind or two or more kinds. The noble metal is one or more metals selected from the group consisting of Pd, Pt, Ru, Rh and Ir, and particularly P
d is preferable because it improves the low humidity purification activity and the NOx purification activity.

[0007] cocatalyst is intended to improve the purification activity at high temperature, Ce and Zr, further refractory oxide at least partially comprises a rare earth metal other than Ce is a composite oxide and / or solid solution Yes , (CeZr
Y) O ₂ , (CeZrLa) O ₂ , (CeZrNd) O ₂
Etc. are complex oxides represented by the general formula (CeZrLn) O ₂ (Ln is a rare earth metal except Ce) . CeO ₂
Than is excellent in effect of increasing (CeZr) excellent effects towards O ₂ increases the purification activity at high temperature, further (CeZrLn) purification activity towards O ₂ is at high temperature.

In the exhaust gas purifying catalyst of the present invention, when impregnating and / or adsorbing the noble metal aqueous solution on the coated carrier, 100 parts by weight of the mixture of the perovskite type complex oxide and the metal oxide sol, or the perovskite type complex is used. Mixtures of oxides, refractory oxides and metal oxide sols 1
00 a total noble metal in terms of the weight part is impregnated and / or adsorbing a noble metal with a noble metal salt aqueous solution containing 0.2 to 5.0 parts by weight, it is fired at a temperature of drying after 250 to 800 ° C. Preferred . The pH of the precious metal aqueous solution at this time is 1
It has been found by the inventor of the present invention that a catalyst having a high catalytic activity can be obtained even at a low temperature by setting the alkalinity to be greater than 0 or the acidity to be less than 4, and a patent is pending separately.

When the aqueous noble metal solution is made alkaline, tetraamine palladium dichloride Pd (NH ₃ ) ₄ Cl _{2 is used.}
And tetraamine palladium hydroxide Pd (NH ₃ ) ₄ (OH) ₂
PH by adding aqueous ammonia or acid to a basic aqueous solution such as
Prepared so as to be> 10, or used PdCl ₂ , P
Chlorides such as tCl ₂ and RuCl ₃ 3H ₂ O, Pd (N
_{O 3) 2, Ru (NO} 3) 3, Rh (NO 3) nitrates such as _3, or _{Pd (NO 2) 2 (NH} 3) 2, Pt (NO 2) 2 ( dinitrodiamine such NH _{3) 2} Ammonia water is added to an acidic aqueous solution such as salt to prepare a pH of> 10.

When the precious metal aqueous solution is made acidic, when the perovskite type complex oxide is immersed in the precious metal salt aqueous solution adjusted to pH 4 or less, some elements in the crystal are eluted, and the perovskite type complex oxide powder which remains without elution is obtained. A plurality of salts containing a noble metal are attached around the core of the or heat-resistant oxide powder as a core. By drying and calcining it in the air, perovskite type complex oxide crystals in which a noble metal is solid-dissolved are formed around the nuclei to form an oxide double structure. Excess noble metal that cannot be completely dissolved in the recrystallized perovskite type complex oxide crystal is dispersed in a metallic state or as a noble metal oxide. Examples of water-soluble noble metal salts for acidifying the noble metal aqueous solution include PdCl ₂ and PtC.
l ₂ , chlorides such as RuCl ₃ .3H ₂ O, Pd (NO ₃ ) ₂ ,
Ru (NO ₃ ) ₃ , nitrates such as Rh (NO ₃ ) ₃ , Pd (N
A dinitrodiamine salt such as O ₂ ) ₂ (NH ₃ ) ₂ or Pt (NO ₂ ) ₂ (NH ₃ ) ₂ is preferably one whose aqueous solution exhibits strong acidity.

[0011]

INDUSTRIAL APPLICABILITY In the present invention, when a powder containing a perovskite-type composite oxide powder and a heat-resistant oxide that is a cocatalyst is supported on a heat-resistant carrier, zirconia sol, ceria sol, yttria sol or a combination thereof is used as a binder. Mixed sol,
Alternatively, by using a solid solution oxide sol containing two or more kinds of Zr, Ce, and Y and firing it, volatile components contained in the sol are scattered to form a fine oxide having a large specific surface area and further to form a catalyst system. The mechanical bond strength with the carrier is increased, the deterioration of the catalyst due to thermal and mechanical stress in the environment where the catalyst is used is mitigated, and the catalyst can withstand long-term use. Further, these metal oxide sols do not mask the catalyst or react with the catalyst during use to reduce the catalytic activity.

[0012]

【Example】

(Example 1) 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, 0.3 liter of an aqueous solution prepared by dissolving 103.9 g of lanthanum nitrate, 26.1 g of cerium nitrate, 34.9 g of cobalt nitrate and 72.7 g of iron nitrate in pure water. Then, 0.5 liter of an aqueous solution in which 50 g of sodium carbonate as a neutralizing coprecipitating agent was dissolved was prepared, and the neutralizing coprecipitating agent was added dropwise to the above aqueous solution to obtain a coprecipitate. The coprecipitate was thoroughly washed with water, filtered, and dried under vacuum. This is baked at 600 ° C. for 3 hours in the air, pulverized, and then 8
00 performs calcined for 3 hours in air at ° C., the perovskite-type composite oxide was further pulverized _{(La 0. 8 Ce 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 high specific surface area cerium oxide powder (CeO ₂ specific surface area 170
m ² / g, purity 99.9% / TREO (total rare earth oxide) 111.9 g were prepared, and zirconium oxynitrate (ZrO (NO ₃ ) ₂ ) aqueous solution (liquid specific gravity 1.51, in the liquid) was prepared. (25.0% by weight in terms of ZrO ₂ is included) 147.9
g, and 26.0 g of an yttrium nitrate (Y (NO ₃ ) ₃ ) aqueous solution (liquid specific gravity: 1.62, the liquid contains 21.7% by weight in terms of Y ₂ O ₃ ) and well mixed with stirring. While 11
It was dried in the air at 0 ° C. for 10 hours. Then 6 in the atmosphere
00 ° C. conducted for 3 hours _{at, (Ce 0. 65 Zr 0} . 30 Y 0.
₀₅ ) About 150 g of O ₂ composite oxide was obtained.

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, a zirconia sol manufactured by Nissan Chemical Industries, Ltd. NZS-30B (solid content 30.
44 wt%, pH = 10.62) was added to 100 parts by weight of pure water so as to be 5 parts by weight in terms of solid content, and the resulting slurry was mixed by a ball mill for 12 hours to obtain a cordierite-like heat-resistant honeycomb carrier. After pouring, the remaining slurry is blown off with an air stream, dried (for example, at 130 ° C. for 24 hours), and then baked at 600 ° C. in the air for 3 hours to uniformly coat the perovskite-type composite oxide and the heat-resistant oxide. A carrier was obtained.

In order to support Pd as a noble metal, a total of 10 perovskite type complex oxides and heat-resistant oxides are used.
56.8 parts by weight of an aqueous solution of palladium nitrate (a product of Tanaka Kikinzoku Kogyo Co., Ltd., 4.4% by weight of Pd) was weighed so as to be 2.5 parts by weight in terms of Pd with respect to 0 parts by weight of diluted nitric acid. It was dissolved in 100 parts by weight. The pH of this solution is 0.
It was 2. After impregnating the coating honeycomb carrier with the whole amount of this solution, it was dried at 130 ° C. for 24 hours,
It was fired in the air at 600 ° C. for 3 hours.

(Example 2) As in Example 1, except that the metal oxide sol of the binder was ceria sol instead of zirconia sol, Nedral W manufactured by Taki Chemical Co., Ltd.
-10-01 (solid content 10.1% by weight, pH = 5.0) was used, and the content was 2 parts by weight in terms of solid content.

(Example 3) In the same manner as in Example 1, except that NZS-30B manufactured by Nissan Chemical Industries, Ltd., which is a zirconia sol as the metal oxide sol of the binder (solid content 30.
44% by weight, pH = 10.62) and 1 part by weight in terms of solid content, and Ceria sol Nidral W10-01 manufactured by Taki Chemical Co., Ltd. (solid content 10.1% by weight, pH = 5.0).
Were used together so as to be 5 parts by weight in terms of solid content.

(Example 4) The same procedure as in Example 1 was repeated except that a high specific surface area cerium oxide (CeO ₂ , specific surface area 170 m ² / g, purity 99.9% /) was used as a heat-resistant oxide.
TRIS) to 50 parts by weight, and NZS-20 manufactured by Nissan Chemical Industries, Ltd. which is a zirconia-yttria sol instead of zirconia as the metal oxide sol of the binder.
A3Y (solid content 10.77% by weight, pH = 4.12) was used, and its content was set to 10 parts by weight in terms of solid content.

(Comparative Example a) The same procedure as in Example 1 was repeated except that the binder metal oxide sol was not used. (Comparative Example b) As in Example 4, except that the binder metal oxide sol was not used. (Comparative Example c) Same as in Example 1, but using AS-100 (solid content 10.23% by weight, pH, manufactured by Nissan Chemical Industries, Ltd.) which is an alumina sol as a metal oxide sol of a binder.
= 3.91) and its content was 10 parts by weight.

The catalysts of Examples and Comparative Examples were used in an atmosphere of 8
Put into an electric furnace maintained at 00 ° C and hold for 15 minutes,
After 500 cycles of a test in which the engine was taken out of the electric furnace and cooled with an air blow pressurized to 500,000 Pa for 20 minutes, heat exchange was performed using exhaust gas when the engine was operated at A / F = 14.6. The temperature of the exhaust gas is raised by the reactor, and NOx, CO, THC in the exhaust gas are increased.
Of 50% of the initial concentration (50% purification temperature)
Table 1 shows the test results obtained. At this time, the space velocity (SV) of the exhaust gas passing through the catalyst is about 100,000.
It was adjusted to be / hr.

[0021]

[Table 1]

In Table 1, the content of the sol represents parts by weight in terms of solid content when the total amount of the perovskite type complex oxide and the heat resistant oxide is 100 parts by weight. From this result, it can be seen that when the conventional alumina sol is used as the binder, the catalytic activity is lowered during use. When the sol is not used as the binder, the deterioration of the catalyst progresses.
% Purification temperature is getting higher. On the other hand, in the present invention, the effect of the selected sol alleviates the deterioration of the catalyst due to thermal and mechanical stress and makes it possible to withstand long-term use.

Continuation of front page (56) Reference JP-A-3-157140 (JP, A) JP-A-4-346837 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 21 / 00-38/74 B01D 53 / 86,53 / 94

Claims (2)

(57) [Claims] 1. A perovskite complex oxide and a noble metal ,
Furthermore, a general formula (CeZrLn) O ₂ (Ln
Is a heat-resistant oxide represented by rare earth metals (excluding Ce)
Is zirconia sol, ceria sol, yttria sol or mixed sol thereof, or 2 of Zr, Ce and Y
Metal oxidation which is any of the solid solution oxide sols containing
Things sol as a binder, a discharge that is supported on the refractory support
A catalyst for purifying air and gas, which comprises the above-mentioned perovskite-type composite oxide, noble metal, heat-resistant oxidation
And metal oxide sols are perovskates other than the above precious metals.
Ito-type complex oxide powder, heat-resistant oxide powder and metal oxide
Water is added to the mixture containing the product sol, and the mixture is stirred and mixed to form a slurry.
And the slurry is coated on the refractory carrier.
After firing and firing, the coated carrier is
Baking with an impregnated and / or adsorbed salt solution of a noble metal
Thus , the exhaust gas purifying catalyst is carried on the heat resistant carrier . 2. A according to claim 1 wherein the content of the metal oxide sol is 0.5 to 50 parts by weight relative to the total amount 100 parts by weight of the perovskite-type composite oxide and the heat-resistant oxide
Exhaust gas purification catalyst .