JPH01274841A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To enhance the activity and refractoriness of the title catalyst by laminating a refractory coat layer contg. Nd2O3 carrying Pd and La2O3 carrying Rh on a refractory carrier to form the catalyst for purifying exhaust gas. CONSTITUTION:The powder of Nd2O3 is added to an aq. soln. of Pd salt, and the mixture is dried and then calcined to prepare the Nd2O3 carrying Pd. The La2O3 carrying Rh is prepared in the same way. The material for a refractory coat layer, the Nd2O3 carrying Pd, and the La2O3 carrying Rh are mixed in a specified ratio to prepare a slurry. A refractory carrier is dipped in the slurry, dried, and then calcined to form an exhaust gas purifying catalyst wherein the refractory coat layer 2 contg. Nd2O3-Pd and La2O3-Rh is laminated on the refractory carrier 1. Cordierite, etc., are used for the refractory carrier, and activated alumina, etc., are used for the refractory coat layer material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust gas purification catalyst, and more particularly to an exhaust gas purification catalyst containing palladium (Pd) and Rhodium A (Rh) as catalyst components. be.

[Conventional technology]

Among the harmful substances contained in the exhaust gas emitted from internal combustion engines such as automobiles, the main ones are hydrocarbons (HC), -
It consists of three components: carbon oxide (CO) and nitrogen compounds (NOx). A catalyst that can purify these three components at once is called a three-way catalyst. In three-way catalysts, a blue gold layer is used as a catalyst component; for example, platinum (Pt) or palladium is effective for oxidizing HC and CO, and Rh is effective for oxidizing HC and CO.
Effective in reducing Ox. Therefore, as a three-way catalyst (
Although PT or Pd)/Rh-based catalysts have been used, in recent years, attempts have been made to use Pd/Rh-based catalysts using Pd, which is more advantageous than PT in terms of resource amount and price.

In L-catalysts, Pd tends to grow grains in a reducing atmosphere, reducing its own surface area and reducing its activity. Furthermore, Pd tends to cover the surface of Rh or form an alloy with it, which poses problems in terms of catalytic activity and durability.

In order to solve the above-mentioned problems, the applicant has
In Publication No. 14341, alumina (AM2O3)
We have proposed an exhaust gas purifying catalyst in which Pd, Rh, and neodymium A (Nd) and/or samarium (Sm) are supported as catalyst components on a catalyst carrier made of the following materials.

In addition, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 82-571351 a monolith catalyst for exhaust gas purification in which an alumina coat layer is formed on a monolith carrier, and a catalyst component is supported on this alumina coat layer. Sm
an alumina coat layer supporting a catalyst component made of Pd doped with lanthanum (La) and yttrium (Y);
Or three layers consisting of an alumina coat layer supporting a catalyst component made of Rh to which scandium (Se) is added, and an alumino coat layer supporting a catalyst component made of Pt to which cerium (Ce) is added. We have proposed a monolithic catalyst for exhaust gas purification that has an alumina coat layer formed on it.

The above two proposals were made based on the knowledge that Nd and Sm form a composite oxide with Pd and thereby suppress the grain growth of Pd.

[Problem to be solved by the invention]

However, the exhaust gas purifying catalyst described in JP-A-60-114341 adds Nd and/or Sm to a catalyst carrier made of alumina or the like, and then supports Pd and Rh. All the Pd cannot be supported in some places, and the Pd supported in other parts tends to grow into grains.

Furthermore, La has a greater effect on Rh than Nd or Sm.

Furthermore, the monolithic catalyst for exhaust gas fraud described in JP-A No. 132-57851 requires the formation of three alumina coat layers, each carrying a different catalyst component, and the structure of the catalyst is complicated. Its preparation is not easy.

The present invention is intended to solve the above-mentioned problems in the prior art, and its purpose is to provide an exhaust gas that is easy to manufacture, has excellent activity and durability, and can effectively use expensive and precious precious metals. An object of the present invention is to provide a catalyst for gas purification.

[Means to solve the problem]

That is, the exhaust gas purifying catalyst of the present invention is formed of a refractory carrier and a refractory coat layer on the carrier, and the coat layer is coated with neodymium oxide (Nd2O3) on which palladium (Pd) has been previously supported. It is characterized by containing lanthanum oxide (La2O3) on which rhodium (Rh) is supported.

The material of the refractory press may be, for example, cordierite, mullite, alumina, heat-resistant metal, etc., and its size and shape are not particularly limited.

It is preferable to use a cordierite monolithic support, which may have a shape such as a pellet-like or honeycomb-like monolithic support.

Materials for the refractory coating layer include ceramics such as activated alumina.

To support Pd on Nd2O3, a conventional method such as a dipping method is used. That is, Nd2O3 is added to the Pd salt aqueous solution.
Powder is added, dried and fired. A similar method can be used to support Rh on La2O3.

Fire-resistant coating layer material and Pd-supported Nd, 03
The exhaust gas purifying catalyst of the present invention can be obtained by immersing a refractory carrier in a slurry prepared by mixing La2O3 and La2O3 with Rh in a desired ratio, drying the carrier, and then calcining it. Note that other components such as promoter components may be added to the slurry.

[For production]

Nd2O3 has the effect of suppressing grain growth of Pd. Further, Nd2O3 and Pd partially form a composite oxide, and this composite oxide also suppresses the grain growth of Pd. Similarly, La2O3 suppresses Rh(7) grain growth, and La2O3 also suppresses Rh(7) grain growth.
The composite oxide of 2O3 and Rh also suppresses Rh grain growth. Therefore, by supporting Pd on Nd2O3, La
By supporting Rh on 2O3, grain growth of both Pd and Rh can be effectively suppressed, thereby preventing a decrease in activity. Further, by using a porous fire-resistant coating layer, exhaust gas can be efficiently dispersed in the coating layer.

〔Example〕

The present invention will be explained in further detail in the following Examples and Comparative Examples. Note that the present invention is not limited to the following examples.

2O0 g of Nd2O3 powder was added to a palladium nitrate aqueous solution (1.2 wt%) and stirred, and after about 2 hours PiM was carried out.
The powder was dried at 100°C for 1 hour and then calcined at 600°C for 3 hours.
)make. Next, rhodium nitrate aqueous solution (0.15wt%)
180g of La2O3 powder was added to the container, stirred, and filtered for about 2 hours.The powder was dried at 100℃ for 1 hour and then heated to 600℃
La2O with 1.5g of Rh supported by firing at ℃ for 3 hours
3. Make powder (powder B). Next, activated alumina powder 10
00 g, the above powder A, powder B, aluminum nitrate aqueous solution (40 wt%) 300 g, and Kuroshio water 900 gtW
A slurry was prepared by mixing and stirring 2. A cordierite monolithic carrier (φ107X
78L) was immersed for 1 minute, then pulled out, excess moisture was blown off, dried at 100°C for 1 hour, and then baked at 700''C for 2 hours to coat 70g.

In this way, Nd203-Pd.

A catalyst structure supporting La2O3-Rh as a catalyst component was obtained. The figure is a schematic diagram of the exhaust gas purifying catalyst of the present invention.
In the figure, 1 represents the cordierite monolith carrier, and 2 represents the activated alumina coat layer.

Comparative Example 1 1000 g of activated alumina powder, 300 sr of aluminum nitrate aqueous solution (40 wt%), and 900 g of pure water were mixed and stirred to prepare slurry II. This slurry II
Cordierite monolith carrier (φ107 x 78
L) was immersed for 1 minute, then stretched to remove excess moisture, dried at 100°C for 1 hour, and then baked at 700°C for 2 hours to coat 70g. This carrier is lanthanum nitrate (2
After being immersed in a mixed aqueous solution of neodymium nitrate (28.9 wt%) and neodymium nitrate (28.9 wt%), it was pulled out, excess water was blown off, dried at 100°C for 1 hour, and then fired at 700°C for 2 hours. Next, this carrier was immersed in an aqueous palladium nitrate solution (0.44 wt%) for 2 hours while stirring, and then
Pulled up and dried. Further, this carrier was immersed in an aqueous rhodium nitrate solution (0,044 wt%) for 1 hour while stirring, and then pulled up and dried.

In this way, catalyst II supporting Nd, La, Pd, and Rh as catalyst components was obtained.

Comparative Example 2 Ndz03-Pd powder A is made as in Example. Next, 1000 g of activated alumina powder, powder A, 300 g of aluminum nitrate aqueous solution (40 wt%), and Kuroshio water 9
00 g was mixed and stirred to prepare slurry m.

A cordierite monolith carrier (
φ107 x 78L) was immersed for 1 minute, pulled out, blown off excess water, dried at 100°C for 1 hour, baked at 700″C for 2 hours, coated with 7°g, and then coated with rhodium nitrate. After being immersed in an aqueous solution (0,044 wt%) for 1 hour while stirring, it was pulled up and dried.

A catalyst (2) was obtained in which Nd2O3-Pd and Rh were supported as catalyst components.

Comparative Example 3 Powder B of La2O3-Rh is prepared as in Example. Next, 1000 g of activated alumina powder, Powder B, 300 g of aluminum nitrate aqueous solution (40 wt%), and Kuroshio water 7
00g were mixed and stirred to prepare slurry (■).

A cordierite monolithic carrier (
φ107 x 78L) was immersed for 1 minute, then pulled out and the excess water was blown off. After drying at 100℃ for 1 hour,
The carrier was calcined at 700°C for 2 hours, coated with 70g, and immersed in an aqueous palladium nitrate solution (0°44 wt%) for 2 hours with stirring, and then pulled up and dried.

In this way, a catalyst (2) supporting tPd and La2O3-Rh as catalyst components was obtained.

Table 1 shows the component content of each catalyst obtained in Examples and Comparative Examples 1, 2.3.

Durability test shown in Table 1> Durability tests were conducted on these four types of catalysts according to the following method12, and the purification performance was evaluated.

Durability test was conducted using a 6-cylinder 2800cc engine (5M-G)
A method of installing a catalyst in the exhaust system of the air-fuel ratio (A/F)
+4. +3, space velocity (SV) eooooH,
--i and catalyst bed temperature of 800°C for 200 hours.

Regarding the purification performance, a model exhaust gas imitating engine exhaust gas with an air-fuel ratio of 14.6 was used, and S = 85000.
Passed through the catalyst as Hr-1, CO2HC and NO
The purification rate of x was measured.

Table 2 shows the purification rates of CO, HC and NOx obtained as a result of the measurement.

Table 2 From Table 2, as shown in Table 11, the catalyst obtained in this example had even better activity after the durability test than the catalysts obtained in Comparative Examples 1, 2, and 3. This was recognized. This means that all Pd is Nd2O3, and all Te(7)Rh is La
This is thought to be because Pd is supported on 2O3 and grain growth is suppressed for all Pd and Rh.

〔Effect of the invention〕

As described above, the exhaust gas purifying catalyst of the present invention includes a catalyst component and Nd on which Pd is supported in advance in the fire-resistant coating layer.
Since it contains 2O3 and La2O3 on which Rh has been supported in advance, the grain I&length of all supported Pd and Rh is suppressed, allowing these precious metals to be used effectively without wasting them, and improving catalyst activity and durability. Direction 1-shi again. Also, P d
,! : Since R and h are separated, the bad interaction of Pd covering the surface of Rh and reducing its catalytic performance can be eliminated. Furthermore, by using porous activated alumina or the like for the fire-resistant coating layer, exhaust gas is efficiently dispersed in the coating layer, resulting in good purification efficiency.

[Brief explanation of the drawing]

The figure is a schematic configuration diagram of the exhaust gas purifying probe of the present invention. In the figure, l...Cordierite molybdenum/°lith carrier 2...Activated alumina coat layer Patent applicant Toyota Motor Corporation (and two others)

Claims (1)

[Claims] It is formed from a refractory carrier and a refractory coat layer on the carrier, and the coat layer includes neodymium oxide (Nd_2O_3) on which palladium (Pd) is supported in advance and rhodium (Rh).
) supported on lanthanum oxide (La_2O_3).