JPH0538438A - Catalyst composition - Google Patents

Abstract

PURPOSE:To obtain a catalyst composition not lowered in its catalytic activity even in a reductive atmosphere at high temp. of 500 deg.C or higher and excellent in durability. CONSTITUTION:A catalyst composition excellent in durability is obtained from a composition consisting of perovskite multicomponent oxide containing a rare- earth element, rare earth oxide, aluminum oxide, chromium oxide, iron oxide and one or more kind of noble metals.

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, etc., which converts Ox) into water, carbon dioxide 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, chromium oxide, aluminum oxide, iron oxide, and among noble metals. One or more of.

[0006]

With the above-mentioned structure, the present invention suppresses grain growth of noble metal and diffusion into the perovskite complex oxide even in a high temperature atmosphere of 500 ° C. or higher.

[0007]

EXAMPLES Examples of the present invention will be described below.

La0.9Ce0.1CoO₃Of rare earth elements
100 g of perovskite-type composite oxide powder contained
Cerium oxide (CeO₂) Powder 100 g, aluminazo
50g (acetic acid acidity, solid content 1/10), palladium nitrate
Mu [Pd (NO₃)₂] 0.9 g and iron nitrate [Fe (N
O₃)₂] 4.5 g, chromium nitrate [Cr (NO₃)₃]
Prepare a slurry by mixing 5.8g and 150g of water with stirring.
did. 400 cells with a grid-like cross section in the slurry
(inch)²Cordierite (2MgO / 5SiO)
₂・ 2Al₂O₃) Honeycomb carrier is dipped and pulled up
After that, the excess slurry was blown off by an air stream. That
The post carrier was dried at 200 ° C for 1 hour and baked at 650 ° C for 1 hour.
About 24% by weight of the catalyst composition and about 76% by weight of the carrier.
A catalyst body of was obtained. Where the perovskite in the catalyst composition
Type composite oxide is 47.8% by weight, aluminum oxide is 2.4
0 wt%, palladium 0.27 wt%, iron oxide 0.28
% By weight, and chromium oxide was 0.48%.

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 chromium 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) NO 1%, CO 1%, 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 at least one of a perovskite complex oxide containing a rare earth element, a rare earth oxide, aluminum oxide, chromium oxide, iron oxide and a noble metal. Becomes, 500 ℃
It is a catalyst with excellent durability that suppresses grain growth of noble metals and diffusion into the perovskite composite oxide even in the above high temperature atmosphere.

[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 Shunichi Hayashi 300, Takatsuka-cho, Hamamatsu City, Shizuoka Prefecture Suzuki Stock Company

Claims (1)

[Claims] 1. A catalyst composition comprising a perovskite type composite oxide containing a rare earth element, a rare earth oxide, aluminum oxide, chromium oxide and iron oxide, and one or more kinds of noble metals.