JPH06378A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst for purification of exhaust gas having such performance that exhaust gas which varies considerably in compsn. from the internal- combustion engine of an automobile, etc., can be purified at a high rate of purification. CONSTITUTION:This catalyst for purification of exhaust gas is a monolithic catalyst with a catalytic component supported layer formed by supporting at least one of Pt and Pd and the oxide of at least one kind of metal selected from among K, Cs, Sr and Ba as catalytic components on activated alumina and cerium oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention purifies exhaust gas, which purifies hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) in exhaust gas discharged from internal combustion engines such as automobiles. For catalysts.

[0002]

2. Description of the Related Art As a conventional exhaust gas purifying catalyst, for example, an exhaust gas purifying catalyst in which a composition consisting of platinum, rhodium and cerium disclosed in Japanese Patent Publication No. 58-20307 is supported on a refractory carrier is disclosed. As described above, a structure in which a platinum group element such as platinum, palladium and rhodium is supported on alumina, cerium oxide or the like and the monolith carrier is coated with the platinum group element is used.

[0003]

However, in an exhaust gas purifying catalyst for treating exhaust gas whose composition varies widely from reducing properties to oxidizing properties, strong adsorption of hydrocarbons is observed especially under conditions of high hydrocarbon concentration and insufficient oxygen concentration. When the catalytically active metal is poisoned, the purification reaction is hindered, and the purification rate of harmful components becomes low.

[0004]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to such conventional problems as described above.
Exhaust with high hydrocarbon concentration and low oxygen concentration by combining at least one of potassium compounds, cesium compounds, strontium compounds, and barium compounds in addition to those conventionally used as catalyst components such as activated alumina and cerium oxide. It has been found that a high purification rate can be achieved even for gas, and the present invention has been achieved.

Therefore, the exhaust gas purifying catalyst of the present invention is an integral structure type catalyst having a catalyst component supporting layer, wherein the catalyst component supporting layer comprises activated alumina and cerium oxide, and at least one of platinum and palladium as catalyst components and potassium. , Cesium, strontium, and barium, and at least one metal selected from the group consisting of oxides is carried.

In the catalyst of the present invention, the amounts of platinum (Pt) and palladium (Pd) supported are preferably 0.1 to 10 g per liter of the finished catalyst. In addition, the supported amounts of the potassium compound, the cerium compound, the strontium compound, and the barium compound are respectively those of the finished catalyst 1
It is preferably 1 to 30 g in terms of oxide per liter, and if it is less than 1 g / L, the desired effect is to achieve a high purification rate even for exhaust gas with high hydrocarbon concentration and low oxygen concentration. However, even if the amount is more than 30 g / L, the effect is not improved.

Next, a method for producing the catalyst of the present invention will be described. First, activated alumina and cerium oxide are impregnated with an aqueous solution containing at least one compound selected from the group consisting of potassium, cesium, strontium and barium. The compounds used are nitrates, chlorides, carbonates, acetates,
Any water-soluble substance such as hydroxide may be used. After this is dried, it is calcined in air at 500 ° C. for 1 hour, for example, and powder (a) containing 1 to 30% by weight of these elements relative to activated alumina
To get At the same time, at least one selected from the group consisting of zirconium, cerium, lanthanum and neodymium may be added to the activated alumina.

Next, this powder (a) is impregnated with an aqueous solution containing a salt of at least one platinum group element of platinum and palladium, dried and then calcined in the air at 400 ° C. for 1 hour, for example, to obtain a finished catalyst. On the other hand, powder (b) containing 0.1 to 10% by weight of platinum group element is obtained. The above powder (b) and alumina sol,
If necessary, cerium oxide or the like is mixed and pulverized to form a slurry, which is attached to a catalyst carrier, for example, a monolith carrier substrate, and calcined at a temperature of 400 to 650 ° C. to obtain an exhaust gas purifying catalyst. It is also possible to prepare several kinds of slurries having different components and attach them in layers to the carrier substrate. Further, in order to further improve the performance, a catalyst layer containing rhodium may be additionally provided.

[0009]

[Function] Exhaust gas purification catalysts must treat exhaust gas whose composition varies widely from oxidizing to reducing, but the purification rate for strongly reducing gases with high hydrocarbon concentration and low oxygen concentration Is easy to decrease. This is probably because strong adsorption of hydrocarbons occurs and the surface of the active metal is covered with hydrocarbon species, so that other gases such as oxygen cannot be adsorbed and the reaction does not proceed. As a result of intensive research, the present inventors have found that addition of a potassium compound, a cesium compound, a strontium compound, and a barium compound is effective for improving the purification rate in this reducing gas atmosphere, and completed the present invention. .

[0010]

The present invention will be described with reference to the following examples, comparative examples and test examples. Example 1 Activated alumina was impregnated with an aqueous cerium nitrate solution and an aqueous potassium nitrate solution, dried, and then calcined at 500 ° C. for 1 hour. At this time, the supported concentration of cerium was 7% by weight, and the supported concentration of potassium was 5% (8.4 g of potassium oxide per liter of complete catalyst).
The powder thus obtained was impregnated with an aqueous palladium nitrate solution, dried and then calcined at 400 ° C. for 1 hour to obtain a Pd-supported activated alumina powder. The supported concentration of Pd is 1.00% by weight. This powder 700g, cerium oxide powder 300g, alumina sol 1
A slurry obtained by mixing and crushing 000 g with a ball mill was attached to a monolith carrier substrate (1.3 L, 400 cells) and baked (400 ° C., 1 hour). The adhesion amount at this time is 200 g /
Set to L. Thus, the catalyst (A) was obtained. The amount of Pd in the catalyst (A) was 1.8 g / piece.

Example 2 A catalyst (B) was obtained in the same manner as in Example 1 except that potassium nitrate was changed to cesium nitrate and the supported concentration of cesium was changed to 5% (7.4 g of cesium oxide per 1 L of the complete catalyst).

Example 3 In Example 1, potassium nitrate was changed to strontium acetate, and the supported concentration of strontium was 5% (complete catalyst 1 L
A catalyst (C) was obtained in the same manner except that strontium oxide was 8.3 g per unit.

Example 4 In Example 1, potassium nitrate was changed to barium acetate,
A catalyst (D) was obtained in the same manner except that the supported concentration of barium was changed to 5% (barium oxide: 7.8 g per 1 L of the complete catalyst).

Example 5 A catalyst (E) was obtained in the same manner as in Example 1 except that a dinitrodiammine platinum solution was used in place of the palladium nitrate solution and the supported concentration of platinum was set to 1%. The amount of platinum in the catalyst (E) was 1.8 g / piece.

Example 6 A catalyst (F) was obtained in the same manner as in Example 5 except that potassium nitrate was changed to cesium nitrate and the supported concentration of cesium was changed to 5% (7.4 g of cesium oxide per 1 L of the complete catalyst).

Example 7 In Example 5, potassium nitrate was changed to strontium acetate, and the supported concentration of strontium was 5% (complete catalyst 1
A catalyst (G) was obtained in the same manner except that the amount of strontium oxide was 8.3 g per L.

Example 8 In Example 5, potassium nitrate was changed to barium acetate,
A catalyst (H) was obtained in the same manner except that the supported concentration of barium was 5% (barium oxide: 7.8 g per 1 L of the complete catalyst).

Comparative Example 1 A catalyst (I) was obtained in the same manner as in Example 1 except that potassium nitrate was not used.

Comparative Example 2 A catalyst (J) was obtained in the same manner as in Example 1 except that potassium nitrate was not used, the palladium nitrate solution was changed to a dinitrodiammine platinum solution, and the platinum supported concentration was set to 1%. The amount of platinum in the catalyst (J) was 1.8 g / piece.

Test Example Regarding the catalysts of Examples 1 to 8 and Comparative Examples 1 and 2,
Activity evaluation after endurance was performed under the following conditions.

[0021]

[Table 1]

The evaluation results are shown in Table 1. The catalytic activity of the example was higher than that of the comparative example, and the effect of the present invention was confirmed. Incidentally, Examples 1 to 4 and Comparative Example 1 show the results of the catalyst using palladium as the platinum group element, and Examples 5 to 8 and Comparative Example 2 show the results of the catalyst using platinum as the platinum group element.

[0023]

[Table 2]

[0024]

As described above, the catalyst of the present invention is selected from the group consisting of potassium, cesium, strontium and barium in the catalyst composition having the catalytically active component-supporting layer containing at least one of platinum and palladium. By including at least one kind of metal oxide, it is possible to alleviate the adsorption poisoning effect and maintain high performance even in a gas atmosphere in which the purification performance is deteriorated due to adsorption poisoning in the conventional catalyst. . Therefore, it exhibits higher activity than the conventional catalyst for purification of engine exhaust gas whose composition fluctuates greatly, so that it is possible to improve catalyst performance or reduce catalyst cost.

Claims (1)

[Claims] 1. An integrated structure type catalyst having a catalyst component supporting layer, wherein the catalyst component supporting layer comprises activated alumina and cerium oxide, and at least one of platinum and palladium as a catalyst component and potassium, cesium, strontium and barium. An exhaust gas-purifying catalyst, which comprises an oxide of at least one metal selected from the group.