JPH04293546A - Exhaust gas purifying catalyst - Google Patents

Abstract

PURPOSE:To obtain a catalyst composition generating no catalytic activity even in a reducing atmosphere at high temp. 200 deg.C or higher and excellent in durability. CONSTITUTION:Cerium oxide is preliminarily supported on a honeycomb carrier and a composition based on a fine powder of a perovskite multicomponent oxide, a fine powder of zirconia, iron oxide and at least one or more kinds of a noble metal element is applied to the cerium oxide layer to obtain a catalyst composition excellent in durability shown by Fig. 1.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an exhaust gas purification catalyst.
In particular, the present invention relates to an exhaust gas purification catalyst that cleanly purifies exhaust gas from various household and industrial combustors and automobiles using oil or gas as fuel.

0002

[Prior Art] Conventionally, the catalyst composition for this type of exhaust gas purification catalyst is one in which cerium oxide is supported on a ceramic carrier, fine perovskite composite oxide powder is supported on the ceramic carrier, and a noble metal is further supported on the ceramic carrier. Kaisho 01-3
04046), and one in which the supporting order of cerium oxide and perovskite composite oxide powder is reversed (Japanese Unexamined Patent Publication No. 1987-30
4048).

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 the perovskite type composite oxide may There was a problem that the durability was poor, such as the catalytic activity gradually decreasing due to diffusion.

[0004] The present invention solves the above problems, and aims to provide an exhaust gas purification catalyst mainly composed of a catalyst composition having excellent durability.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the exhaust gas purification catalyst of the present invention is provided by applying cerium oxide to a honeycomb carrier of heat-resistant ceramics mainly composed of cordierite, and further applying ABO3 basic fine powder of perovskite composite oxide having a structure, fine zirconia powder, iron oxide, and one or more elements among noble metal elements such as platinum, palladium, and rhodium, and alumina sol,
Al2O3 is added to the honeycomb carrier on which the cerium oxide is supported by firing with aluminum nitrate.
It is attached together with a supporting agent that forms a film.

[0006]

[Operation] With the above configuration, the exhaust gas purification catalyst of the present invention has
By completely covering the exposed surface of the honeycomb carrier with cerium oxide, aluminum and perovskite composite oxide (A
It is possible to suppress the formation of a spinel compound with the transition metal element which is the B site component of BO3), and the composition mainly contains perovskite composite oxide, zirconium oxide and one or more noble metal elements in addition to cerium oxide. By making it a perovskite composite oxide, grain growth of the noble metal and diffusion of the noble metal into the perovskite composite oxide can be suppressed even in a reducing atmosphere at a high temperature of 200° C. or higher.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An exhaust gas purification catalyst according to an embodiment of the present invention will be described below with reference to the drawings.

[0008] Commercially available cordierite (2MgO・5S
A catalyst was prepared using an iO2 .2Al2 O3) honeycomb carrier (manufactured by NGK Insulators). The honeycomb carrier used had a cylindrical cross section with an outer diameter of 76 mm and a length of 75 mm, having a cross section of about 400 gas flow cells per square inch, and had a volume of about 340 ml.

Cerium nitrate [Ce(NO3)3 .6H
2 O] in pure water to make an aqueous solution with a specific gravity of 1.33, the honeycomb carrier was immersed in this aqueous cerium nitrate solution and then taken out, and the excess cerium nitrate aqueous solution in the honeycomb carrier was removed by blowing with compressed air. do. Then 100℃
After drying in dry air for 30 minutes, it was calcined in air at 800°C for 1 hour to obtain a product on which cerium oxide (CoO2) was supported. Next, ABO3 (A is at least one element among rare earth elements such as La, Ce, and Sr or alkaline earth elements,
B is at least one element among transition metal elements such as Co and Ni) Among perovskite composite oxides having a basic structure of La0.9 Ce0.1 CoO3, fine particles of perovskite composite oxide with a structure of La0.9 Ce0.1 CoO3 (surface area 19.
8m2/g, primary particle size 1μ or less) 100g, 20g of zirconium oxide (ZrO2) powder, 50g of alumina sol (acidic acid, solid content 1/10), palladium nitrate [Pd
(NO3)2] 0.9g, ferric nitrate [Fe(NO3)
)3 ・9H2 O] 4.3 g and 150 g of water were mixed and stirred to prepare a slurry, the cordierite honeycomb carrier was immersed in the slurry, and after being pulled up, the excess slurry in the cells was blown with compressed air. to remove all clogging. Next, dry at 200℃ for 1 hour with dry air and then 650℃
It was fired in

[0010] The composition of the catalyst body after firing is about 24% by weight of the catalyst composition including the cerium oxide of the pre-coat, about 76% by weight of the carrier, and 48.5% by weight of the perovskite type composite oxide in the catalyst composition. , cerium oxide 38.8% by weight, zirconium oxide 9.7% by weight, aluminum oxide 2.
4% by weight, palladium 0.27% by weight, iron oxide 0.
It was 28% by weight.

(Comparative Example 1) As a comparative example, commercially available cordierite (same as the example) was used, and cerium oxide (Ce
O2) was supported. (The supporting method is the same as in the example.) Next, La0 was prepared by the alkaline precipitation method (details of the preparation method are omitted).
．． 9 100 g of perovskite composite oxide fine particles having a structure of Ce0.1 CoO3 (surface area 19.8 m2/g, primary particles 1 μ or less) and 50 g of acetic acid acidic alumina sol
g (manufactured by Nissan Chemical) and water at a weight ratio of 1:1:1.
The mixture was thoroughly kneaded using a ball mill kneader, water was added, and the specific gravity was adjusted to 121 to prepare a perovskite oxide slurry. In this slurry, the Ce
After the carrier loaded with O2 was immersed and pulled up, the excess slurry in the cell was blown out with compressed air to remove any clogging. Next, after drying with dry air at 200℃ for 1 hour,
It was fired at 00°C. Next, 400 mg of palladium (Pd) per liter of the above carrier.
to carry. 400 per liter of carrier by impregnating
palladium nitrate [Pd(NO3)2
] An aqueous solution was prepared, the carrier was immersed therein, and the excess aqueous solution in the carrier was blown out with compressed air to remove clogging from all cells. Next, after drying for 1 hour in dry air at 100℃,
It was fired in air at 00°C for 30 minutes to support a predetermined amount of palladium.

(Comparative Example 2) As another comparative example, commercially available cordierite (same as in Example) was used, and cerium oxide (
CeO2) was supported. (The loading method is the same as in the example),
Next, perovskite composite oxide fine particles with a structure of La0.9 Ce0.1 CoO3 (surface area 19.8 m2/
g, primary particles 1μ or less), 50 g of acetic acid acidic alumina sol, palladium nitrate [Pd(NO3)2] 1
．． A slurry was prepared by mixing and stirring 0 g and 140 g of water, into which the cordierite honeycomb carrier was immersed, and after being pulled up, the excess slurry in the cells was blown with compressed air to remove all clogging. . Next, it was dried at 200°C for 1 hour with dry air and then fired at 650°C.

[0013] The three types of catalyst bodies produced above were compared in terms of initial characteristics of catalyst performance and durability.

[0014] The test conditions were as follows, and the test results were expressed as (
Table 1) shows the results.

[0015]

[Table 1]

As the catalyst performance test conditions, a reaction gas consisting of 1% NO, 1% CO, and 98% helium was used as the gas composition (based on volume). Also, the space velocity is 1250
It was set as 0/Hr. Furthermore, as a measurement method, the reaction was carried out using a fixed bed flow system, and the conversion rate of NO to N2 was determined using gas chromatography. Reaction temperature is 300℃
It is.

From Table 1, it is clear that the coexistence of zirconia and iron oxide is essential for the durability of catalyst performance.

Next, changes in catalyst performance over time were measured for the three types of catalyst bodies mentioned above. In FIG. 1, the catalyst body of this example showed excellent durability.

The test conditions at this time were as follows. The catalyst was treated in air at 900°C in an electric furnace and changes in activity were examined.

[0020] Gas composition (volume basis): NO1%,
A reaction gas consisting of 1% CO and 98% helium was used. Moreover, the space velocity was set to 12500/Hr. Furthermore, as a 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 clostography. The reaction temperature is 300°C.

[0021] In the examples, the case where palladium was used as an example of the noble metal was explained, but similar effects could be obtained by using platinum or rhodium in part or in whole in addition to palladium.

[0022]

Effects of the Invention As is clear from the above description of the embodiments, according to the exhaust gas purification catalyst of the present invention, by completely covering the exposed surface of the carrier containing alumina with cerium oxide, aluminum and perovskite Complex oxide (ABO3
) can suppress the formation of a spinel compound with the transition metal that is the B site component, and is a composition mainly containing perovskite composite oxide, zirconium oxide in addition to cerium oxide, and one or more noble metal elements. By doing so, it has excellent durability that suppresses the grain growth of the noble metal and the diffusion of the noble metal into the perovskite composite oxide even in a reducing atmosphere at a high temperature of 200° C. or higher.

[Brief explanation of drawings]

[Figure 1] Graph showing durability of catalyst performance of an example of the present invention and a comparative example

Claims (1)

[Claims] [Claim 1] Cerium oxide is supported on the honeycomb carrier by impregnating a cerium nitrate solution into a large number of pores inside a honeycomb carrier made of heat-resistant ceramics mainly composed of cordierite, and firing the honeycomb carrier. , and then ABO3 (A is at least one element among rare earth or alkaline earth elements such as La, Ce, and Sr,
B is fine powder of perovskite composite oxide having a basic structure of at least one element among transition metal elements such as Co and Ni, fine zirconia powder, iron oxide, and noble metal elements such as platinum, palladium, and rhodium. An exhaust gas purification catalyst in which the honeycomb carrier supporting the cerium oxide is energized together with a supporting agent that forms an Al2 O3 film by firing one or more types of elements, alumina sol, and aluminum nitrate.