JPH04371229A - Catalyst composition - Google Patents

Abstract

PURPOSE:To obtain a catalyst compsn. maintaining its catalytic activity even in a reducing atmosphere at a high temp. of >=500 deg.C and having excellent durability. CONSTITUTION:A perovskite type multiple oxide contg. a rare earth element is blended with the oxide of a rare earth element, zirconium oxide, aluminum oxide, cobalt oxide, the oxide of calcium and/or barium and one or more kinds of noble metals to obtain a catalyst compsn. having excellent durability.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention converts hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOX) contained in exhaust gas into water, carbon dioxide gas, and nitrogen through oxidation or reduction reactions. The present invention relates to a catalyst composition for use in exhaust gas purification catalysts and the like.

0002

[Prior Art] Conventional catalyst compositions of this type include those consisting of rare earth element oxides, perovskite-type composite oxides, and palladium (Japanese Unexamined Patent Publication No. 156349/1983), and those containing perovskite-type composite oxides on the surface. There has been a catalyst carrier provided with a layer containing a rare earth oxide having storage properties and supporting palladium or palladium and other noble metals as a catalyst component (Japanese Patent Application Laid-Open No. 162948/1983).

0003

[Problems to be Solved by the Invention] However, when the above-mentioned conventional catalyst composition is used for a long time in a reducing atmosphere at a high temperature of 200°C or higher, noble metals such as palladium may cause grain growth and may cause grain growth in the perovskite-type composite oxide. There was a problem that the durability was poor, such as the catalytic activity gradually decreasing due to diffusion.

The present invention solves the above problems and aims to provide a catalyst composition with excellent durability.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the catalyst composition of the present invention comprises a perovskite-type composite oxide containing a rare earth element, a rare earth oxide, zirconium oxide, aluminum oxide, cobalt oxide, and calcium or barium oxide. It consists of one or more kinds of oxides and one or more kinds of noble metals.

[0006]

[Function] With the above structure, the present invention suppresses the grain growth of noble metals and the diffusion into the perovskite composite oxide even in a high temperature atmosphere of 500° C. or higher.

[0007]

[Examples] Examples of the present invention will be described below.

Powder 10 of perovskite type composite oxide containing rare earth element La0.9Ce0.1CoO3
0g, 80g of cerium oxide (CeO2) powder, 20g of zirconium oxide (ZrO2) powder, 50g of alumina sol (acidic acid, solid content 1/10), 0.9g of palladium nitrate [Pd(NO3)2] and cobalt nitrate [
Co(NO3)2] 4.5 g, and barium nitrate [
A slurry was prepared by mixing and stirring 4.2 g of Ba(NO3)2 and 150 g of water. A honeycomb carrier made of cordierite (2MgO.5SiO2.2Al2 O2) having a lattice-like cross section and having a cross section of 400 cells/(inch)2 was immersed in the slurry, pulled up, and then the excess slurry was blown off by an air stream. After that, the carrier was heated to 200℃ for 1
After drying for 1 hour and calcining at 650°C for 1 hour, the catalyst composition
An exhaust gas purifying catalyst body containing 4% by weight and about 76% by weight of the carrier was obtained. The perovskite type composite oxide in the catalyst composition is 4
7.8% by weight, aluminum oxide 2.40% by weight, palladium 0.27% by weight, cobalt oxide 0.28% by weight, and barium oxide 0.56% by weight.

As a comparative example, a catalyst supporting a catalyst composition consisting of a perovskite-type composite oxide, cerium oxide, zirconium oxide, aluminum oxide, and palladium (Comparative Example 1) and a catalyst composition consisting of a perovskite-type composite oxide and palladium were prepared. A catalyst body (Comparative Example 2) supporting the following was produced.

[0010] The three types of catalyst bodies produced above were compared in terms of initial characteristics and durability of catalyst performance.

The test conditions were as follows, and the test results are shown in Table 1.

0012

[Table 1]

Catalyst performance test conditions (1) Gas composition (volume basis) A reaction gas consisting of 1% NO, 1% CO, and 98% helium was used. ■Space velocity: 12,500/Hr ■Measurement method The reaction was carried out using a fixed bed flow system, and the conversion rate of NO to N2 was determined by gas chromatography. The reaction temperature is 300°C. From the same table, it is clear that the presence of cobalt oxide and barium oxide is essential for the durability of catalyst performance.

[0014] Next, the changes in catalytic performance over time of the three types of catalyst bodies mentioned above were measured, and 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 were as follows. The catalyst was treated in an electric furnace at 900°C under an air atmosphere, and changes in activity were examined. ■Gas composition (volume basis) NO1% CO1% Helium 98% ■Space velocity
12500/Hr (2) Measuring method The reaction was carried out using a fixed bed flow system, and the conversion rate of NO to N2 was determined by gas chromatography. The reaction temperature is 3
It is 00℃.

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

[0017]

As explained above, the catalyst composition of the present invention comprises a perovskite-type composite oxide containing a rare earth element, a rare earth oxide, zirconium oxide, aluminum oxide, cobalt oxide, and one or more of calcium or barium. It is a highly durable catalyst that suppresses grain growth and diffusion of noble metals into perovskite composite oxides even in high-temperature atmospheres of 500° C. or higher.

[Brief explanation of the drawing]

[Fig. 1] A diagram showing the durability of catalyst performance of an example of the present invention and a comparative example.

Claims (1)

[Claims] Claim 1: A perovskite-type composite oxide containing a rare earth element, a rare earth oxide, zirconium oxide, aluminum oxide, cobalt oxide, one or more oxides of calcium or barium, and one or more noble metals. A catalyst composition consisting of: