JPH04367731A - Catalyst composition - Google Patents

Abstract

PURPOSE:To obtain a catalyst composition generating no lowering of catalytic activity even in a high temp. reductive atmosphere of 500 deg.C or higher and having excellent durability. CONSTITUTION:A catalyst composition excellent in durability is obtained by preparing a composition consisting of perovskite composite oxide containing a rare-earth element and one or more kind of a component among aluminum oxide, cobalt oxide, oxide of one or more kinds of barium and calcium and a noble metal.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention deals with hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (HC) contained in exhaust gas.
The present invention relates to a catalyst composition used in an exhaust gas purification catalyst body, etc., which converts NOx) into water, carbon dioxide, and nitrogen through an oxidation or reduction reaction.

0002

[Prior Art] A conventional catalyst composition of this type is one consisting of a rare earth element oxide, a perovskite type composite oxide, and palladium (Japanese Patent Laid-Open No. 156349/1983).
Palladium or palladium and other noble metals are supported as catalyst components on a catalyst carrier having a layer containing a perovskite-type composite oxide and an O2 storage rare earth oxide on the surface (Japanese Patent Laid-Open No. 162948/1982). was there.

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, cobalt oxide, and aluminum oxide, and comprises one of calcium or barium. It consists of one or more oxides and one or more 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, 100g of cerium oxide (CeO2) powder, 50g of alumina sol (acidic acid, solid content 1/10), 0.9g of palladium nitrate [Pd(NO3)2] and 4.5g of cobalt nitrate [Co(NO3)2]. A slurry was prepared by mixing and stirring 4.2 g of barium nitrate [Ba(NO3)2] and 150 g of water. In the above slurry, 400 cells/(inch)2 of cordierite (2MgO・5SiO2・2Al2O3
) was immersed in the honeycomb carrier, and after being pulled up, excess slurry was blown off with an air stream. Then the carrier was heated to 200°C.
The mixture was dried for 1 hour at 650° C. and calcined for 1 hour to obtain a catalyst body containing about 24% by weight of the catalyst composition and about 76% by weight of the carrier. The catalyst composition contains 47.8% by weight of perovskite composite oxide, 2.40% by weight of aluminum oxide, 0.27% by weight of palladium, 0.28% by weight of cobalt oxide, and 0.5% by weight of barium oxide. Met.

As comparative examples, a catalyst supporting a catalyst composition consisting of perovskite type composite oxide, cerium oxide, aluminum oxide and palladium (Comparative Example 1) and a catalyst composition comprising perovskite type composite oxide and palladium were supported. A catalyst body (Comparative Example 2) 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).

[0011]

[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.

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℃.

[0015] Although the case where palladium was used as the noble metal was explained, similar effects could be obtained by using platinum or rhodium in part or in whole in addition to palladium.

[0016]

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, aluminum oxide, cobalt oxide, barium, or calcium oxide. thing,
Furthermore, it is a highly durable catalyst that is made of one or more noble metals and suppresses grain growth and diffusion of noble metals into the perovskite composite oxide even in high-temperature atmospheres of 500° C. or higher.

[Brief explanation of drawings]

[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 catalyst composition comprising a perovskite-type composite oxide containing a rare earth element, a rare earth oxide, aluminum oxide, cobalt oxide, one or more oxides of calcium or barium, and one or more noble metals. thing.