JPS59127649A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst for purifying exhaust gas good in purifying capacity and reduced in deterioration, by separately supporting a noble metal, a lanthanide metal and a base metal in laminar forms by a carrier. CONSTITUTION:An alumina layer 2 supporting a rare earth metal such as cerium or lanthanum and a noble metal such as platinum or palladium is provided to the surface of an inorg. carrier substrate 1 such as cordierite and an alumina layer 3 supporting a base metal such as iron or nickel, a rare earth metal such as lanthanum and rhodium is further provided on said layer 2. By this method, purifying capacity is enhanced and capacity deterioration due to positioning is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst for purifying exhaust gas of an internal combustion engine.

Carbon monoxide (CO), carbide urea (HC), and nitrogen oxides (NOx) contained in the exhaust gas of internal combustion engines, especially automobiles, etc.
Exhaust gas purifying catalysts that decompose and remove harmful components such as ) through oxidation or reduction reactions are required to have extremely high purification properties, that is, reaction activity, selectivity, durability, etc. ? For such applications, platinum (Pt), platinum (Pt), etc. are used as catalyst components on an inorganic carrier or a carrier with an activated alumina layer thereon.
Catalysts supported with noble metals such as palladium (Pd) and rhodium (Rh) singly or in combination are said to have relatively strong purification performance and are widely used. In many cases, rare earth metals such as cerium (Ce) and lanthanum (La), and base metals such as nickel (Ni) and iron (Fe) are added to further improve the performance of the catalyst as described above. is being carried out.

However, the effects of additives vary depending on their combination with noble metals, and it is necessary to select the optimal combination to maximize the additive effects. For example, the activity of platinum and palladium is greatly improved by the addition of cerium and lanthanum, and the activity of rhodium is greatly improved by the addition of iron, nickel, and lanthanum. However, in the past, for example, noble metals such as platinum, rhodium, palladium, and additives were uniformly supported in a single alumina layer, making it impossible to maximize the effects of the additives.

The present invention is intended to solve the drawbacks in the above-mentioned prior art.

The purpose is to provide an exhaust gas purifying catalyst that maximizes the effects of additives.

5-That is, the exhaust gas purifying catalyst of the present invention has at least one rare earth metal such as cerium and lanthanum, platinum,
An alumina layer supporting at least one of palladium is provided, and an alumina layer supporting at least one of base metals such as iron, nickel, rare earth metals such as lanthanum, and rhodium is provided on the surface of the alumina layer. Features.

Cordierite is usually used as the inorganic carrier base material for the catalyst of the present invention. The shape can be chosen arbitrarily, but
It is preferable to have a monolithic shape such as a honeycomb shape. Generally, two alumina layers are sufficient to be provided on the inorganic carrier base material, but a larger number of alumina layers may be provided if necessary. The order in which the alumina layers with different compositions are formed is such that if an alumina layer containing a catalyst component that is easily deteriorated due to poisoning is placed inside, the deterioration of the exhaust gas purification performance of the catalyst as a whole is small.

For this purpose, in the present invention, the supported amounts of catalyst components such as platinum, palladium, rhodium, etc. and additive components such as cerium, lanthanum, iron, etc. supported on each alumina layer and their mutual blending amounts are the same as in the case of conventional catalysts. It's good.

Hereinafter, an example and a comparative example of the f-solvent for exhaust gas purification of the present invention will be explained with reference to the drawings and with reference to Tables 1 and 2.

The figure is an enlarged cross-sectional view showing the structure of the catalyst according to the present invention. In the figure, 1 is a monolith carrier base material made of cordierite, etc., and 2 is an alumina supporting at least one of platinum or palladium, cerium, and lanthanum. layer, 3
indicates an alumina layer supporting rhodium, iron, and lanthanum.

Next, a method for preparing an exhaust gas purifying catalyst according to the present invention will be described. In the examples, unless otherwise specified, 9 indicates weight.

Example 1: 40% aluminum nitrate aqueous solution 751% and distilled water 100% in 350% commercially available alumina sol with alumina content of 10%
f = i was added with stirring to prepare alumina slurry Ai. This alumina slurry was impregnated with cerium nitrate and lanthanum nitrate and fired at 700°C to produce alumina powder (containing 11 parts of cerium and 11 parts of lanthanum).
Add 397-5t and stir to form alumina sol+)-B-q
Obtained. The cordierite monolith carrier base material was immersed in this alumina slurry B for 1 minute, then pulled out, and the slurry remaining in the carrier base material was blown off with an air stream.
Dry for 1 hour, then dry at 100°C for 1 hour, then dry at 700°C.
After cooling the fired product for 1 hour, it was immersed in a dinitrodiaminoplatinum aqueous solution for 1 hour, pulled up, and dried at 200°C for 3 hours to form an alumina layer supporting cerium, rankan, and platinum.
The lower layer) was formed. ``Next, apply Menalumina'' slurry A again to hair and heels, 2. S Alumina powder containing lanthanum nitrate and ferric nitrate in this alumina slurry and calcining at 7'OO℃ (contains 1191 + 1 iron and 11 chloride) 397.5F
was added and stirred to obtain alumina slurry 〇-q. The carrier on which the alumina layer was formed was similarly immersed in this alumina slurry C, then dried and fired. After cooling this fired product, it was immersed in a rhodium chloride aqueous solution for 1 hour, then pulled up, and dried at 200°C for 3 hours to form an alumina layer (upper layer) supporting iron, lanthanum, and rhodium. Catalyst a was obtained.

Example 2: Using a palladium chloride aqueous solution instead of the dinitrodiaminoplatinum aqueous solution of Example 1, an alumina layer supporting cerium, lanthanum, and palladium was formed as a lower layer by the same method as in Example 1, and an alumina layer supporting iron, iron, and A catalyst for exhaust gas purification of the present invention was obtained in which an alumina layer supporting lanthanum and rhodium was formed.

Next, the preparation and method of a comparative example of the exhaust gas purifying catalyst of the present invention will be described.

Comparative Example 1: An alumina layer supporting cerium and lanthanum was formed on a monolithic monolithic carrier base material using a similar method using a slurry having the same composition as the lower layer of Example 1. The same operation was performed again to make the coating amount the same as in the example. This was immersed in dinitrodiaminoplatinum aqueous solution and rhodium chloride aqueous solution for 1 hour each, and then pulled out and heated to 200°C for 3 hours.
cerium, lanthanum, platinum, and alumina layer after drying for a while
Catalyst C supporting rhodium was obtained.

Comparative Example 2: Slurry with the same composition as the upper layer of Example 1! J-(4-use,
Iron, lanthanum, platinum,
A catalyst d supporting rhodium was obtained.

Comparative Example 3: Using palladium chloride instead of the dinitrodiaminoplatinum aqueous solution of Comparative Example 2, a catalyst e was obtained in which iron, lanthanum, palladium, and rhodium were supported on an alumina layer formed on a cordierite monolithic carrier base material. .

Comparative Example 4: The same alumina slurry A1r as in Example 1 was prepared, and the slurry A was impregnated with cerium nitrate, lanthanum nitrate, and dilute ferric acid, and then fired at 700°C. Aluminum powder (cerium'ia 5%, lanthanum All 11 pieces contain 5.5% iron.

)397.55' and stir to make alumina slurry Bk.
'? ! *. Using this alumina slurry B, an alumina layer supporting cerium, lanthanum, and iron was formed on a cordierite monolith carrier base material by a method similar to Examples 1 and 16J. The same operation was performed again to make the coating amount the same as in Example 1. This is dinitrodiaminoplatinum aqueous solution,
After being immersed in rhodium chloride aqueous solutions for 1 hour each, it was pulled up and dried at 200'C for 3 hours to obtain a catalyst f in which cerium, lanthanum, iron, platinum, and rhodium were supported on the alumina layer.

Table 1 shows the amount of metal supported in the six types of catalysts f(a to f) prepared in the above Examples and Comparative Examples.

Table 1 Amount of metal supported per ton of catalyst (y7t) These six types of fiB media were loaded into a catalytic converter, and the fl was continuously applied to the engine exhaust system, and the amount of metal supported per ton of catalyst was 1 ton under the following conditions.
I did a long test.

Durability test conditions: Air-fuel ratio (air amount/fuel amount) 146 Exhaust gas temperature 350C, 400t:
:Space velocity 6000Qhr-”
bWE floor temperature 72
Table 2 shows the purification performance after the 300 hr durability test at 0°C.

Table 2 Purification performance (purification rate: Q) shows a significant improvement in performance compared to conventional catalysts C, d, and 10. In addition, the catalyst of the present invention, which uses palladium instead of platinum in catalyst a, has improved performance compared to the conventional catalyst e, and is further free from phosphorus, lead, etc. contained in exhaust gas. Since the palladium support layer, which is susceptible to poisoning, is used as the lower layer, performance deterioration due to poisoning can be greatly reduced compared to Catalyst e.

As mentioned above, the catalyst according to the present invention has conventionally had one layer of aluminum uniformly supported in the layer, but by layering the noble metal, its activator, the lanthanide metal, and the base metal, it is possible to create the optimal combination in each layer. In addition to improving purification performance, it has become possible to reduce performance deterioration due to poisoning by making the entire lower layer support a noble metal that is easily poisoned.

[Brief explanation of the drawing]

The figure is an enlarged sectional view showing the structure of the catalyst in the present invention. In the figure, 1... Monolith carrier base material patent applicant Toyota Motor Corporation

Claims (1)

[Claims] At least one of rare earth metals such as cerium and lanthanum on the surface of an inorganic carrier base material such as cordierite, and
An alumina layer supporting at least one of platinum and radium is provided, and the alumina layer supports at least one of base metals such as iron and nickel, rare earth metals such as lanthanum, and rhodium on the surface of the alumina layer. An exhaust gas purifying catalyst characterized by comprising: