JPH04122447A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

PURPOSE:To prepare a ternary catalyst for cleaning exhaust gas in low cost by providing the second catalyst layer consisting of a rare earth element mixture, manganese, copper and palladium on the first catalyst layer composed of a catalytic component effective for oxidation reaction provided on a carrier. CONSTITUTION:A catalyst has the first catalyst layer consisting of catalyst components effective for oxidation reaction and the second catalyst layer consisting of a rare earth element mixture, magnanese, copper and palladium. Both catalyst layers are provided on the carrier in the order of the first catalyst layer and the second catalyst layer. The catalyst components used in the first catalyst layer consist of ceria, a rare earth element mixture and cobalt, and the rare earth element mixture and cobalt have a perovskite structure. The second catalyst layer is constituted of perovskite type composite oxide (RMn1- yCuyO3-delta) constituted of a rare earth element mixture, manganese and copper or composite oxide such as CuMn2O4 or CuMnO2 and palladium. As the carrier, there is a porous sintered body such as cordierite, alumina or silica.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an exhaust gas purification catalyst for removing harmful components from the exhaust gas of an internal combustion engine.

BACKGROUND OF THE INVENTION In recent years, exhaust gas purifying catalysts for internal combustion engines, particularly automobile internal combustion engines, are required to have high performance in terms of durability, purification performance, and the like. This exhaust purification catalyst uses platinum (Pt), rhodium (Rh), and palladium (#
) and other precious metals are used. By sending exhaust gas to a catalytic converter filled with these catalysts, harmful substances in the exhaust gas, such as hydrocarbons (HC), -carbon oxides (CO), and nitrogen oxides (
NOx) is purified by oxidation or reduction. A catalyst that can purify these three components in exhaust gas at once is called a three-way catalyst. Conventionally, in order to improve the catalytic properties of a three-way catalyst, cerium oxide, nickel oxide, and zirconium oxide have been used alone or in combination.

In particular, a system containing a mixture of cerium oxide and zirconium oxide is said to have improved heat resistance as a catalyst.

Problems to be Solved by the Invention However, in the conventional three-way catalyst, Pt, Pd
, Rh, and other precious metals are used, so there is a problem that the cost is extremely high. Furthermore, there are also challenges in terms of stable supply.

For this reason, efforts are being made to construct catalysts using so-called heath metals other than noble metals. It has been reported that a composite oxide with a cobalt-based perovskite I structure exhibits Co, I(C) oxidation activity comparable to that of a platinum-based catalyst. However, cobalt-based perovskites are Compared to conventional precious metals, Rh has a drawback of low activity in purification performance.Rh is said to be essential for purifying NOx, but among precious metals, Rh is particularly effective in purifying carbon dioxide and nitrogen oxides. A first catalyst layer comprising a catalyst component effective for oxidation reaction is provided on a carrier, and a second catalyst comprising mixed rare earth, manganese, copper and palladium is further provided on the first catalyst layer. The present invention provides a catalyst for exhaust purification characterized by having layers.The catalyst according to the present invention has a first catalyst layer made of a catalyst component effective for oxidation reaction, and a second catalyst layer made of a mixed rare earth manganese, copper and palladium. It has a catalyst layer. Both catalyst layers are provided with a first catalyst layer on a carrier and a second catalyst layer thereon.The catalyst components used in the first catalyst layer are as follows: It consists of ceria, mixed rare earth, and cobalt, and the mixed rare earth and cobalt have a perovskite structure.

The second catalyst layer is made of a perovskite-type composite oxide (RMn, -ycuy) composed of mixed rare earth, manganese, and copper.
o, −-δ), or CuMn20a, CuMn0z
It is composed of complex oxides such as and palladium. Palladium uses various salts such as palladium nitrate as a starting material, and 0.0
It is supported in a range of 1 to 0.1 weight percent.

Next, examples of the carrier supporting the first catalyst layer include porous sintered bodies such as cordierite, alumina, and silica. As for the shape of the carrier, it is preferable to use an integral carrier such as a honeycomb-shaped carrier in order to improve contact with the exhaust gas, lower pressure loss, and improve the purification rate.

Further, the amount of the first catalyst layer supported on the carrier is preferably 10 g to 100 g per 1 of the carrier.

If it is less than 10 g, it is difficult to obtain the effect of the present invention, and even if it exceeds 100 g, it is difficult to obtain an effect commensurate with the supported amount.

Next, as a method of providing a second catalyst layer on the "-" of the first catalyst layer, for example, RMn, -yCuyO+-δ, CuMnz o4. C
This is carried out by making a slurry of a mixture of complex oxides such as uMnOz and the like on which palladium is supported, and coating the slurry. Therefore, it is preferable that the amount of the second catalyst layer supported on the carrier 11 is 1 g to 50 g. If the amount is less than 1 g, it is difficult to obtain the effect of the present invention, and if it exceeds 50 g, the effect corresponding to that amount is not obtained. difficult to obtain.

Note that the exhaust purification catalyst according to the present invention has a molecular weight of 200 to 800
Preferably, it is used at °C. In addition, the space velocity of the exhaust gas introduced into the catalyst layer is GHS V10,000 to 12
It is preferable to set it as 10,000/hour.

Function In the present invention, since the catalyst is configured by providing the first catalyst layer on the carrier and further providing the second catalyst layer thereon, it is possible to efficiently purify NOx, which has been difficult in the past. . Therefore, an excellent three-way catalyst can be provided. The reason why the catalyst of the present invention exhibits such excellent effects is not clear, but it is thought to be as follows. That is, when exhaust gas comes into contact with the catalyst, NOx in the gas
When it comes into contact with a mixture of perovskite-type complex oxides made of CU and Mn, it also selectively reacts with HC in the gas, and NOx is reduced. This purifies NOx into harmless substances.

Also, the remaining HC that did not react with the NOx.

and CO react with oxygen in the exhaust gas by the first catalyst layer to become R20 and Co2.

Examples Examples of the exhaust gas purification catalyst of the present invention will be described below. 400 cells/in 2 cordierite one-piece carrier with Ro, 9 CEO, cQo31oo parts and Ce0
It was immersed in a slurry prepared by ball milling 2100 parts of alumina sol and 50 parts of alumina sol together with water. Subsequently, the excess liquid was blown away with compressed air, the combined product was dried to remove free water, and then heated at 700'C.
After firing for 1 hour, a coating layer of 20 g was supported on each carrier 142. Next, according to X-ray diffraction, RMnab, Cuo, a
Ball milling 100 parts of a mixture of composite oxides in which individual oxides such as O3, CuMn2O3, and some MnO□ have been confirmed, and 50 parts of alumina sol together with water. , 20 g per 1 fV of carrier was coated in the same manner as in the first layer described in Section 2 above.

Subsequently, the support was immersed in an acidic aqueous solution of dinitrodiammine palladium in nitric acid, dried, and then calcined at 400'C for 1 hour to support Pd of 3g/ff at 1°C on the support.

As a comparison catalyst, 400 cells/in was prepared in the same manner as the above catalyst.
R8, qCea on z cordierite carrier.

C, O, carrier] was coated at 40 g per liter.

Subsequently, the carrier was coated on the carrier using an acidic aqueous solution of dinitrodiammine palladium in nitric acid in the same manner as the catalyst described above. 0.3 g/ρ of Pd was supported.

The above two types of catalysts were installed in the exhaust system of an engine, and the catalytic activity was examined. The catalyst according to the present invention is designated as No. 1, and the comparative catalyst is designated as No. 2. The results are shown in the table below.

As is clear from the table, the exhaust purification catalyst according to the present invention has R
It has a high NOx purification rate even without using h.

As described in 2. Effects of the Invention, the exhaust purification catalyst of the present invention is an excellent three-way catalyst. Furthermore, since expensive Rh was not used, the cost could be significantly reduced.

Furthermore, there are no fluctuations in supply, making stable supply possible.

Claims (6)

[Claims] (1) A first layer comprising a catalyst component effective for oxidation reaction on a carrier.
A catalyst for exhaust purification, which includes a catalyst layer and a second catalyst layer made of mixed rare earth, manganese, copper, and palladium on the first catalyst layer. (2) The exhaust purification catalyst according to claim 1, wherein the first catalyst layer is a catalyst made of ceria, mixed rare earth, and cobalt. (3) The exhaust purification catalyst according to claim 1, wherein the first catalyst layer is a catalyst supporting a perovskite type composite oxide. (4) The exhaust purification catalyst according to claim 1, wherein the second catalyst layer is a solid solution or composite oxide composed of mixed rare earth, manganese, and copper. (5) The exhaust purification catalyst according to claim 1, wherein the mixed rare earth is cerium oxide, lanthanum oxide, or neodymium oxide. (6) The exhaust purification catalyst according to claim 1, wherein the carrier is an integral carrier.