JPH0538448A - Catalyst composition - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to obtain a catalyst composition having excellent durability, in which the catalytic activity does not decrease even in a reducing atmosphere at a high temperature of 500 ° C or higher. [Composition] A perovskite-type composite oxide containing a rare earth element, a rare earth oxide, aluminum oxide, iron oxide, and one or more oxides of calcium or barium,
Furthermore, a catalyst composition having excellent durability is obtained by using a composition comprising at least one kind of noble metal.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (N) contained in exhaust gas.
The present invention relates to a catalyst composition used for an exhaust gas purifying catalyst or the like that converts O _x ) into water, carbon dioxide gas and nitrogen by an oxidation or reduction reaction.

[0002]

2. Description of the Related Art A conventional catalyst composition of this type comprises an oxide of a rare earth element, a perovskite complex oxide and palladium (Japanese Patent Laid-Open No. 156349/1983).
And palladium or palladium and other noble metals supported as catalyst components on a catalyst carrier having a layer containing a perovskite type complex oxide and an O ₂ storage rare earth oxide on its surface or the surface (JP-A-59-162948). )was there.

[0003]

However, when the above conventional catalyst composition is used for a long time in a reducing atmosphere at a temperature of 200 ° C. or higher, noble metal such as palladium causes grain growth, and the perovskite type complex oxide is contained in the noble metal. However, there is a problem that durability deteriorates because the catalyst activity gradually decreases due to diffusion.

The present invention has been made to solve the above problems, and an object thereof is to provide a catalyst composition having excellent durability.

[0005]

To achieve the above object, the catalyst composition of the present invention comprises a perovskite complex oxide containing a rare earth element, a rare earth oxide, and aluminum oxide.
It comprises iron oxide and one or more oxides of calcium or barium and one or more of noble metals.

[0006]

According to the present invention, grain growth of noble metal and diffusion into the perovskite complex oxide are suppressed even in a high temperature atmosphere of 500 ° C. or higher.

[0007]

EXAMPLES Examples of the present invention will be described below.

Perovskite type complex oxide powder 100 containing a rare earth element of La0.9Ce0.1CoO ₃ 100
g, cerium oxide (CeO ₂ ) powder 100 g, alumina sol (acetic acid acidity, solid content 1/10) 50 g, palladium nitrate [Pd (NO ₃ ) ₂ ] 0.9 g and iron nitrate [Fe
(NO ₃ ) ₂ ] 4.5 g, barium nitrate [Ba (N
O ₃ ) ₂ ] 4.2 g and 150 g of water were mixed and stirred to prepare a slurry. Cross section of the slurry is 4
00 cells / (inch) ² cordierite (2MgO
A honeycomb carrier made of 5SiO ₂ · 2A1 ₂ O ₃ ) was dipped and pulled up, and then excess slurry was blown off by an air stream. The carrier is then dried at 200 ° C for 1 hour and 650 ° C.
After being calcined for 1 hour, a catalyst body having a catalyst composition of about 24 wt% and a carrier of about 76 wt% was obtained. Here, 47.8% by weight of the perovskite-type composite oxide, 2.40% by weight of aluminum oxide, 0.27% by weight of palladium, 0.28% by weight of iron oxide, and 0.20% by weight of barium oxide in the catalyst composition. 56
% By weight.

As a comparative example, a catalyst body carrying a catalyst composition comprising perovskite type composite oxide, cerium oxide, aluminum oxide and palladium (Comparative Example 1) and a catalyst composition comprising perovskite type complex oxide and palladium were carried. A catalyst body (Comparative Example 2) was produced.

The initial characteristics of catalyst performance and durability of the three types of catalyst bodies produced above were compared. The test conditions are as follows, and the test results are shown in Table 1.

[0011]

[Table 1]

Catalyst Performance Test Conditions Gas composition (volume basis) A reaction gas composed of 1% NO, 1% CO and 98% helium was used. Space velocity: 12500 / Hr Measuring method The reaction was carried out by a fixed bed flow system, and the conversion rate of NO to N ₂ was determined by gas chromatography. The reaction temperature is 300 ° C. From the table, it is clear that the presence of iron oxide and barium oxide is essential for the durability of the catalyst performance.

Next, when the time-dependent changes in the catalyst performance of the above three types of catalyst bodies were measured, the results shown in FIG. 1 were obtained. From the figure, the catalyst body of this example showed excellent durability.

The test conditions at this time are as follows. The catalyst was treated in an electric furnace at 900 ° C. under a nitrogen atmosphere to examine the change in activity. Gas composition (volume basis) NO1% CO1% Helium 98% Space velocity 12,500 / Hr Measuring method The reaction was carried out by a fixed bed flow system, and the conversion rate of NO to N ₂ was determined by gas chromatography. Reaction temperature is 30
It is 0 ° C.

Although the case where palladium is used as the noble metal has been described, the same effect can be obtained by using platinum or rhodium in part or in whole in addition to palladium.

[0016]

As described above, the catalyst composition of the present invention comprises a perovskite complex oxide containing a rare earth element, a rare earth oxide, aluminum oxide, iron oxide, and at least one oxide of calcium or barium. Furthermore, it is a catalyst which is made of one or more of the noble metals and has excellent durability that suppresses the grain growth of the noble metals and their diffusion into the perovskite complex oxide even in a high temperature atmosphere of 500 ° C. or more.

[Brief description of drawings]

FIG. 1 is a diagram showing durability of catalyst performance of an example of the present invention and a comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumiaki Hirashima 300, Takatsukacho, Hamamatsu City, Shizuoka Prefecture Suzuki Stock Company

Claims (1)

[Claims] 1. A perovskite complex oxide containing a rare earth element, a rare earth oxide, aluminum oxide and iron oxide,
And a catalyst composition comprising one or more oxides of calcium or barium, and one or more of noble metals.