JPH0663404A - Catalyst for exhaust gas cleaning - Google Patents

Abstract

PURPOSE:To provide an exhaust gas cleaning catalyst having a high nitrogen oxide cleaning efficiency especially in lean burning atmosphere, wherein the catalyst is for cleaning an exhaust gas discharged out of an internal combustion engine of automobiles, etc. CONSTITUTION:A catalyst for cleaning an exhaust gas is a catalyst provided with a coating layer consisting of an inorganic material of mainly activated alumina which carries silicon and at least one kind of metal selected from the group consisting of active metals except silicon, preferably cobalt, copper, nickel, zinc, and iron.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for purifying exhaust gas discharged from an internal combustion engine such as an automobile. In particular, the present invention relates to an exhaust gas purification catalyst having an excellent purification rate of nitrogen oxides (NO _x ) in a lean burn atmosphere.

[0002]

2. Description of the Related Art Many catalysts for purifying exhaust gas emitted from internal combustion engines of automobiles have been proposed.
The purification rate of NO _x in a lean atmosphere of exhaust gas has attracted attention and attempts have been made to improve it. At academic societies, etc., an NO _x removal catalyst in a lean atmosphere carries an active metal selected from transition metals. It has been reported that the activated alumina prepared is effective (for example, Hamada et al., 68th Proceedings of Catalytic Discussion Meeting (A) Proceedings (1991) 18).

[0003]

The exhaust gas purification test in the above report is conducted under the condition that water does not enter the reaction system. When the supported activated alumina is used as an exhaust gas purifying catalyst, the NO _x conversion activity decreases due to the influence of water contained in the exhaust gas. Therefore, the present invention is to provide an exhaust gas purifying catalyst whose NO _x conversion activity does not decrease due to water contained in the exhaust gas.

[0004]

The exhaust gas purifying catalyst of the present invention, which has achieved the above object, is provided with a coating layer composed of silicon and an inorganic material whose main component is activated alumina carrying an active metal other than silicon. It is characterized by As the active metal, it is preferable to use at least one metal selected from the group consisting of cobalt (Co), copper (Cu), nickel (Ni), zinc (Zn) and iron (Fe). Further, the blending amount of silicon in the coat layer is 0.5 to 20% by weight, preferably 0.5 to 15% by weight. When the amount of silicon exceeds 20% by weight, SiO ₂ is deposited on the surface, which adversely affects the performance, while when it is less than 0.5% by weight, the effect is not recognized.

[0005]

[Operation] Next, the operation will be described. In the exhaust gas purifying catalyst of the present invention, silicon fixed in the powder stage is present on the activated alumina in addition to the above-mentioned metal which is the active component. A conventional catalyst in which silicon is not present on activated alumina has a characteristic that the NO _x selective reduction reaction does not proceed due to the influence of water. However, due to the presence of silicon, the coordination environment of the supported active metal is changed, and an active component effective for removing NO _x in lean exhaust gas containing water can be obtained.

[0006]

EXAMPLES The present invention will be described below with reference to Examples, Comparative Examples and Test Examples. Example 1 Activated alumina powder 1000 containing γ-alumina as a main component
Tetraethylammonium silicate aqueous solution was added to g so as to be 1% by weight of silicon and well stirred, and then placed in an oven
It was dried at 150 ° C. for 3 hours and calcined at 400 ° C. for 2 hours in an air stream to prepare a silicon-supported alumina powder. Next, a cobalt nitrate solution was added to 1000 g of alumina of the silicon-supported alumina powder so that the cobalt content was 3% by weight, and the mixture was similarly dried and calcined at 750 ° C. for 2 hours in an air stream. 900 g of this cobalt-silicon-supported alumina, 1170 g of silica sol (solid content 20%), and 1170 g of water were put into a ball mill pot and pulverized for 8 hours to obtain a slurry. The resulting slurry was applied to a monolith carrier base material (1.3 L, 400 cells) so that the applied amount was 340 g / piece, and dried.
Catalyst No. 1 was prepared by firing at 00 ° C. for 2 hours in an air atmosphere. Example 2 Catalyst No. 2 was prepared in the same manner as Catalyst No. 1 of Example 1 except that copper was used instead of cobalt as the supporting metal.
Activated alumina powder 1000 containing γ-alumina as the main component
Aqueous tetraethylammonium silicate solution was added to silicon so as to be 1% by weight of silicon, stirred well, dried in an oven at 150 ° C for 3 hours, and calcined at 400 ° C for 2 hours in an air stream. Silicon-supported alumina powder made. Then, a solution of copper nitrate was added to 1000 g of alumina of the silica-supported alumina powder so that the copper content was 3% by weight, and the mixture was similarly dried and calcined in an air stream at 750 ° C. for 2 hours.
900 g of this copper-silicon-supported alumina, 1170 g of silica sol (solid content 20%), and 1170 g of water were put into a ball mill pot and pulverized for 8 hours to obtain a slurry. Monolith carrier substrate (
1.3 L, 400 cells) and dried, and then calcined at 400 ° C. for 2 hours in an air atmosphere to prepare catalyst No. 2. Example 3 Catalyst No. 3 was prepared in the same manner as Catalyst No. 1 of Example 1 except that the metals supported on alumina were cobalt and nickel. To 1000 g of activated alumina powder containing γ-alumina as a main component, tetraethylammonium silicate aqueous solution was added so as to be 1% by weight of silicon and well stirred,
It was dried in an oven at 150 ° C. for 3 hours and calcined in an air stream at 400 ° C. for 2 hours to prepare a silicon-supported alumina powder. Then, this silicon-supported alumina powder, Alumina 1000
A cobalt nitrate solution and a nickel nitrate solution were simultaneously added to g so that each cobalt content was 3% by weight and nickel content was 3% by weight, and the mixture was similarly dried and calcined at 750 ° C. for 2 hours in an air stream. This cobalt-nickel-silicon supported alumina 900g, silica sol (solid content 20%) 1170g, water 11
70 g was put into a ball mill pot and pulverized for 8 hours to obtain a slurry. The resulting slurry was applied onto a monolith carrier substrate (1.3 L, 400 cells) so that the coating amount was 340 g / piece, dried, and then calcined at 400 ° C. for 2 hours in an air atmosphere to prepare catalyst No. 3. . Example 4 Catalyst No. 4 was prepared in the same manner as Catalyst No. 1 of Example 1 except that the metal supported on alumina was nickel. Example 5 Catalyst No. 5 was prepared in the same manner as Catalyst No. 1 of Example 1 except that zinc was used as the metal supported on alumina. Example 6 Catalyst No. 6 was prepared in the same manner as Catalyst No. 1 of Example 1 except that the amount of silicon supported on alumina was changed to 0.5% by weight. Example 7 Catalyst No. 7 was prepared in the same manner as Catalyst No. 1 of Example 1 except that the amount of silicon supported on alumina was changed to 5% by weight. Example 8 Catalyst No. 8 was prepared in the same manner as Catalyst No. 1 of Example 1 except that the amount of silicon supported on alumina was changed to 15% by weight. Example 9 A catalyst No. 9 was prepared in the same manner as in Example 1 except that colloidal silica was used instead of the tetraethylammonium silicate aqueous solution of the catalyst No. 1. To 1000 g of activated alumina powder containing γ-alumina as a main component, colloidal silica dispersed in distilled water was added so as to be 1% by weight of silicon, and the mixture was stirred well and dried in an oven at 150 ° C for 3 hours to 400 ° C. The powder was calcined in an air stream for 2 hours to prepare a silicon-supported alumina powder. Next, to 1000 g of alumina of this silicon-supported alumina powder, a cobalt nitrate solution was used to add 3% by weight of cobalt, and the mixture was dried in the same manner.
Firing was performed at 750 ° C. for 2 hours in an air stream. 900 g of this cobalt-silicon-supported alumina, silica sol (solid content 20
%) 1170 g and water 1170 g are put into a ball mill pot, and 8
The slurry was obtained by pulverizing for a time. The monolith carrier substrate (1.3 L,
(400 cells), dried, and calcined at 400 ° C. for 2 hours in an air atmosphere to prepare catalyst No. 9. Example 10 A catalyst No. 10 was prepared in the same manner as the catalyst No. 1 of Example 1 except that Fe was used as the metal supported on alumina. Example 11 A catalyst No. 11 was prepared in the same manner as the catalyst No. 1 of Example 1 except that the amount of silicon supported on alumina was set to 20% by weight. Thus, the starting material for silicic acid used in the present invention is
Any material can be used as long as it can be supported on alumina.

Comparative Examples 1 to 5 Catalyst No. Catalysts A, B, C, D and E were prepared in the same manner except that 1,2,3,4,5 was not loaded with silicon. Comparative Examples 6 and 7 As comparative examples, 0.3% by weight of catalyst No. 1 silicon,
Catalysts F and G were prepared in the same manner except that 23% by weight was loaded.

Test Example A performance evaluation test was conducted on the catalysts of Examples 1 to 11 and Comparative Examples 1 to 7 under the following conditions, and the results are shown in Table 1.

[0009]

[Table 1]

Performance Evaluation Vehicle Vehicle Sunny Displacement 1600cc (with SVC) HC: 3000ppm, NO: 500ppm, O ₂ :
_{6.0% H 2 O: 10%} , CO 2: 10%, CO: 2
000ppm

[0011]

As described above, according to the present invention, the structure is composed of silicon on the surface of the carrier and an active metal other than silicon, preferably Co, Cu, Ni, Zn and Fe. By providing the coating layer made of an inorganic material mainly composed of activated alumina carrying at least one selected metal, the catalytic activity for removing NO _x in the exhaust gas containing lean atmosphere is improved. Has the effect of

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Claims (3)

[Claims] 1. An exhaust gas purifying catalyst comprising a carrier and a coating layer formed on the surface of the carrier, the coating layer being composed of silicon and an inorganic substance containing active metal other than silicon and having activated alumina as a main component. 2. The active metal supported on the activated alumina in the inorganic material is one or more kinds of metals selected from the group consisting of cobalt, copper, nickel, zinc and iron. Exhaust gas purification catalyst. 3. The exhaust gas purifying catalyst according to claim 1, which contains 0.5 to 20% by weight of silicon.