JPH0451864Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Industrial Application Field) This invention is designed to reduce nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO) in exhaust gas emitted from internal combustion engines of vehicles, etc. This invention relates to an exhaust gas purifying catalyst that simultaneously efficiently purifies and reduces. (Prior Art) As a conventional catalyst for purifying automobile exhaust gas, there is a catalyst in which a single coating layer is attached to a honeycomb substrate and noble metals such as platinum and rhodium are uniformly supported. (Problem that the invention aims to solve) However, although such conventional exhaust gas purification catalysts support large amounts of expensive precious metals such as platinum and rhodium, which are catalyst components, precious metals is not effectively used in the reaction and does not contribute to the reaction, so Pt's HC and CO purification rate effect, Rh's
There was a problem that the NOx purification rate effect was not fully demonstrated. (Means for solving the problem) The present invention was developed by focusing on such conventional problems, and has two or more coat layers attached to the honeycomb substrate, one coat layer containing Ce and Ce. Pt
The present invention attempts to solve the above problems by creating an exhaust gas purifying catalyst in which Rh is supported on the other coat layer and Rh and Zr are supported on the other coat layer. (Function) In order to enhance the purification effect of each component (HC, CO, NOx), this idea uses two or more coating layers to be attached to the honeycomb base material, and the surface layer is coated with precious metals that meet needs in a stable form. It was carried by For example, in order to enhance the purification effect of HC and CO, Pt is made to be localized in the surface layer as shown in Fig. 3. That is, a catalyst layer 5 consisting of a lower coat layer 3 containing Rh and Zr and an upper coat layer 4 containing Pt and Ce is adhered to the surface of the substrate 2 to form the catalyst 1. In addition, in order to enhance the NOx purification effect,
Rh is localized on the surface as shown in the figure. That is,
Contrary to FIG. 3, the lower coat layer 3 contains Pt and Ce, and the upper coat layer 4 contains Rh and Zr. As a result, the reaction HC+O ₂ →H ₂ O+CO ₂ CO+O ₂ →CO ₂ in FIG. 3 is promoted, and the reaction NOx+H ₂ →1/2N ₂ +H ₂ O in FIG. 4 is promoted. In addition, by having Pt and Ce in the same layer,
Ce releases O ₂ in a reducing atmosphere and has the effect of assisting the reaction of CO + O ₂ → CO ₂ in which the active ingredient Pt acts. On the other hand, providing Rh and Zr in the same layer has the effect of preventing the formation of inert rhodium aluminate. (Example) The present invention will be described below based on Examples, Comparative Examples, and Test Examples. Example 1 Particulate carrier mainly composed of γ-Al ₂ O ₃ (particle size 2~
4mm) in a cerium nitrate aqueous solution, dried,
It was fired in air at 600° C. for 1 hour to obtain a carrier containing 1% by weight of cerium oxide based on alumina in terms of metal. Next, alumina sol (boehmite alumina
Sol obtained by adding 10% by weight _HNO3 to a 10% by weight suspension) 1419g activated alumina granular support containing 2478.0g cerium, commercially available ceria powder
After mixing 103.2g in a ball mill and pulverizing for 6 hours, this alumina-containing liquid (hereinafter referred to as coating liquid) was applied to a monolithic carrier base material (1.7,400 cells).
and baked at 650°C for 2 hours. After supporting this coat layer with platinum of 0.77 g,
An alumina coating solution was applied as a second coating layer and fired at 650°C for 2 hours. Catalyst 1 was obtained by supporting 0.13 g of rhodium and 0.12 g of zirconium on this coat layer using a mixed solution of zirconyl nitrate and rhodium nitrate. Example 2 Rhodium was added to the first layer by the same method as Example 1.
0.13g, zirconium 0.12g, platinum 0.77g in the second layer,
A catalyst 2 containing 0.55 g of cerium was obtained. Example 3 By the same method as in Example 1, only alumina was added to the first layer, and 0.13 g of rhodium and zirconium were added to the second layer.
A catalyst 3 was obtained in which the third layer contained 0.77 g of platinum and 0.55 g of cerium. Comparative Example 1 In Example 1, the coating liquid was applied to a monolith carrier base material (1.7L, 400 cells), and after baking at 650°C for 2 hours, catalyst A was obtained by supporting 0.77 g of platinum and 0.13 g of rhodium. Ta. (zirconium
Comparative Example 2 Catalyst B was obtained in the same manner as in Comparative Example 1 except that Ce and Zr were removed. Comparative Example 3 Catalyst C was obtained in the same manner as in Comparative Example 1, except that Zr was removed. Comparative Example 4 Catalyst D was obtained in the same manner as in Comparative Example 1, except that Ce was removed. Example 4 Using a method similar to Example 1, the first layer contained only alumina, the second layer contained 0.77 g of platinum, 0.55 g of cerium, and 3
The layers contained 0.13 g of rhodium and 0.12 g of zirconium to obtain catalyst 4. Test Examples Catalysts 1 to 4 obtained from Examples 1 to 4, Comparative Examples 1 to 4
A durability test was conducted on the catalysts A to D obtained in 4 under the following conditions, and the purification rate of 10 mode emission [in gas] was determined using Nissan Motor Co., Ltd.'s Sedlik (trade name) displacement 2000cc engine. The results are shown in Table 1. Durability test conditions Catalyst Monolithic precious metal catalyst Catalyst outlet temperature 750℃ Space velocity Approximately 70,000H ^-1 Durability time 100H Engine Displacement 2000c.c. Gas composition CO 0.4-0.6%, O ₂ 0.4-0.6%, NO
2500ppm HC 1000ppm, _CO2 14.9±0.1%, _N2
remainder

[Table] (Effects of the invention) As explained above, according to this invention,
The structure consisted of two or more coat layers attached to the honeycomb substrate, one coat layer supported Ce and Pt, and the other coat layer supported Rh and Zr, so the resulting catalyst was the test example. As is clear from the results, compared to the catalyst of the comparative example, even with the same amount of noble metal, a remarkable effect of high exhaust gas purification performance can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the catalyst of the present invention, Fig. 2 is a sectional view of its main parts, Figs. 3 and 4 are enlarged views of the main parts, and Fig. 3 shows Rh and Ce in the lower layer, and Rh and Ce in the upper layer. Pr and Ce
Figure 4 shows Pt and Ce in the lower layer, and Pt and Ce in the upper layer.
It is a diagram showing Rh and Zr supported. 1...Catalyst, 2...Carrier, 3...Lower coat layer, 4...Upper coat layer, 5...Catalyst layer.

Claims (1)

[Scope of utility model registration request] A catalyst consisting of an integrally molded substrate and at least two coating layers deposited on the surface of the substrate, one coating layer supporting platinum and cerium, and the other coating layer supporting rhodium and zirconium. A catalyst for automobile exhaust gas treatment characterized by having a layer.