JPH06269672A - Exhaust gas purification catalyst - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a catalyst with improved heat resistance using zeolite that can efficiently purify nitrogen oxides in exhaust gas discharged from an internal combustion engine of an automobile or the like in a lean atmosphere of the exhaust gas. An exhaust gas purifying catalyst comprising a monolithic honeycomb carrier and a zeolite ion-exchanged with at least one metal selected from the group consisting of copper and cobalt, and a coat layer made of an inorganic substance containing gallium oxide. .

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 of an internal combustion engine such as an automobile.

[0002]

2. Description of the Related Art Conventionally, zeolite has been used to purify exhaust gas emitted from internal combustion engines of automobiles,
Nitrogen oxide (NOx) in the exhaust gas when the oxygen concentration in the exhaust gas exceeds the stoichiometric air-fuel ratio (lean atmosphere)
As a catalyst for purifying the air, there is a catalyst disclosed in JP-A-1-127044. Further, as a catalyst for removing NOx in the exhaust gas by using a crystalline gallosilicate containing gallium in the zeolite skeleton, there is disclosed in
There is one disclosed in Japanese Patent Publication No. 171048. Further, as a catalyst for removing NOx in the exhaust gas by using gallium as an ion-exchange metal for zeolite and a method for producing the same, there is one disclosed in JP-A-4-222632.

However, the NOx purification performance of these zeolites, gallosilicates, and gallium ion-exchanged zeolites is due to the effects of their crystallinity and ion-exchange metals. It is easily damaged by. In addition, in catalysts that use gallium in the skeleton of zeolite or as an ion-exchange metal, gallium is used for the purpose of improving the NOx purification performance of zeolite or substances having a zeolite structure. It does not improve heat resistance, which is important as a catalyst for automobiles.

Therefore, an object of the present invention is to efficiently purify nitrogen oxides in exhaust gas discharged from an internal combustion engine of an automobile or the like even in a lean atmosphere of the exhaust gas and to improve heat resistance of the exhaust gas using zeolite. It is to provide a purification catalyst.

[0005]

Means for Solving the Problems First, the present inventor newly found that gallium oxide is excellent as a NOx purification catalyst for hydrocarbons (HC) in an oxygen excess atmosphere. However, when this gallium oxide is used as a catalyst for purifying automobile exhaust gas, the physical properties of the catalyst gradually change, and there is a problem that the initial NOx purification performance cannot be maintained. Therefore, in the present invention, NOx of gallium oxide
As a result of earnest research to maintain the purification performance and to make the zeolite usable under low temperature exhaust gas conditions, gallium nitrate was directly impregnated and supported on the zeolite, and gallium oxide was mixed into the catalyst coating layer as needed. As a result, they have found that the object is satisfied, and have accomplished the present invention.

Therefore, the present invention provides a monolithic honeycomb carrier with a zeolite ion-exchanged with at least one metal selected from the group consisting of copper and cobalt, and a coat layer made of an inorganic substance containing gallium oxide. The present invention relates to an exhaust gas purifying catalyst characterized by the above.

[0007]

[Operation] Next, the operation will be described. The catalyst of the present invention is derived from the fact that gallium oxide itself has NOx purification performance in a lean atmosphere. Rather than existing in the framework of zeolite or as an ion exchange metal, gallium exists as gallium oxide in the vicinity of zeolite, which has the effect of improving NOx purification performance in a wide temperature range from low temperatures, and this low temperature activity improvement As a result, the present catalyst containing zeolite having poor heat resistance can be arranged at a position on the exhaust gas system passage where the influence of heat is small. Further, by allowing gallium to exist in the catalyst coating layer like the catalyst of the present invention, the specific surface area of gallium oxide can be secured and maintained. In addition, in the catalyst of the present invention, more gallium oxide can be added to the catalyst coating layer than the conventional catalyst using gallosilicate. At this time, the content of gallium oxide in the catalyst coating layer is preferably 1 to 60% by weight. When the content of gallium oxide exceeds 60% by weight, the interaction with other substances is reduced and the activity and durability cannot be maintained. When the gallium oxide content is less than 1% by weight, the catalytic activity of the substance is not reflected in the actual NOx removal due to the lack of gallium oxide.

[0008]

EXAMPLES The present invention will be described below with reference to Examples, Comparative Examples and Test Examples. Example 1 To 1820 g of a zeolite powder in which copper was ion-exchanged with 0.2 mol / L of copper nitrate or copper acetate, an aqueous gallium nitrate solution was added so as to be 3.0% by weight of gallium,
It was dried in an oven at 150 ° C for 3 hours and calcined in an air stream at 400 ° C for 2 hours. At this time, the supported gallium nitrate became gallium oxide on the surface of the zeolite, and copper ion-exchanged zeolite powder supporting gallium oxide was obtained. This powder, gallium oxide 488g, silica sol (solid content 2
0%) 1150 g and water 1100 g are put into a magnetic ball mill,
Coating amount after firing the slurry obtained by crushing to honeycomb carrier
Apply 250 g / piece and dry, then at 400 ℃ 2
Catalyst No. 1 was prepared by firing in air for a period of time. On this occasion,
Gallium oxide is 25% by weight in the honeycomb coat layer. Alumina sol can be used instead of the silica sol.

Example 2 Catalyst No. 2 was prepared in the same manner as Catalyst No. 1 of Example 1 except that cobalt was used as the ion exchange metal species.
The aqueous solution for ion exchange of cobalt is not particularly limited, but nitric acid or cobalt acetate solution is preferably used.

Example 3 Catalyst No. 3 was prepared in the same manner as Catalyst No. 1 of Example 1 except that the content of gallium oxide in the coating layer was 4.0% by weight. 1.0% by weight of gallium impregnated into copper ion-exchanged zeolite and 35% of gallium oxide mixed into the slurry
Catalyst No. 3 was prepared in the same manner as Catalyst No. 1 of Example 1 except that g was changed to g.

Example 4 Catalyst No. 4 was prepared in the same manner as Catalyst No. 1 of Example 1 except that the content of gallium oxide in the coating layer was changed to 50.0% by weight.
Was prepared. 10.0% by weight of gallium impregnated into copper ion-exchanged zeolite, gallium oxide mixed into the slurry
Catalyst No. 4 was prepared in the same manner as Catalyst No. 1 of Example 1 except that the amount was 1072 g.

Comparative Examples 1 and 2 As Comparative Examples, Catalyst A of Comparative Example 1 and Catalyst B of Comparative Example 2 were prepared in the same manner except that the coating layers of Catalyst Nos. 1 and 2 did not contain gallium oxide. Obtained.

Comparative Example 3 1820 g of zeolite powder in which gallium was on-exchanged with 0.2 mol / L of gallium nitrate, 1150 g of silica sol, and water
1100 g was put into a magnetic ball mill, and the slurry obtained by pulverizing was applied to a honeycomb carrier to give a coating amount of 250 g / piece, dried, and then baked in air at 400 ° C. for 2 hours.
Catalyst C was prepared. Gallium is 3 in the honeycomb coating layer
Became weight percent.

Comparative Example 4 Using gallium nitrate and sodium silicate, "catalyst" vo.
A crystalline gallosilicate powder was prepared in the same manner as described in 1, 28, No. 2, 1986. 0.2 mol of this powder
The copper was ion exchanged with L copper nitrate or copper acetate.
1820 g of this copper ion exchange gallosilicate powder, 1150 g of silica sol, and 1100 g of water were charged into a magnetic ball mill,
Coating amount after firing the slurry obtained by crushing to honeycomb carrier
After coating and drying to 250 g / piece, 2 at 400 ℃
Catalyst D was prepared by firing in air for a period of time. Gallium was 4% by weight in the honeycomb coat layer.

Comparative Example 5 A catalyst E was prepared in the same manner as the catalyst No. 1 of Example 1 except that the content of gallium oxide in the coating layer was 0.5% by weight. Gallium impregnated into copper ion-exchanged zeolite
0.1% by weight, 5.5 g of gallium oxide mixed in the slurry
Catalyst E was prepared in the same manner as catalyst No. 1 of Example 1 except that
Was prepared.

Comparative Example 6 Catalyst E was prepared in the same manner as Catalyst No. 1 of Example 1 except that the content of gallium oxide in the coating layer was 80% by weight. 3 gallium impregnated in copper ion exchanged zeolite
Catalyst F was prepared in the same manner as Catalyst No. 1 of Example 1 except that 065% by weight of gallium oxide mixed in the slurry was 865 g.

Test Example Each of the catalysts of Examples and Comparative Examples was filled in an experimental converter, and after being subjected to durability under the conditions shown in Table 1 below with engine exhaust gas, the results are shown in Table 2 below using an exhaust model gas. A performance evaluation test was performed under the conditions. The results are shown in Table 3.

[Table 1] Endurance conditions Engine displacement 2000 cc Endurance temperature: 550 ° C Endurance time: 100 hours Endurance medium inlet emission CO 0.4 to 0.6% O ₂ 0.5 ± 0.1% NO 1500 ppm HC 1000 ppm CO ₂ 14.9% ± 0.1%

[0018]

[Table 2] Performance evaluation conditions Catalyst capacity: 0.12L Evaluation device: Exhaust model gas evaluation device (gas used is cylinder gas) Catalyst inlet temperature 400 ℃ Space velocity approx. 20,000 h ^-1 A / F = 18.0 model gas HC equivalent = 2500 ppm (Cl terms) NO = 500 ppm CO = 1200 ppm CO 2 = 14.0% O 2 = 4.5% H 2 O = 10% N 2 = remainder

[0019]

[Table 3]

[0020]

As described above, according to the present invention, a honeycomb carrier is coated with an inorganic material containing a mixture of zeolite and gallium oxide whose composition is copper and / or cobalt ion exchange. As a result, the effect of having NOx removal activity in the lean region can be obtained.

Claims (2)

[Claims] 1. A monolithic honeycomb carrier comprising a zeolite ion-exchanged with at least one metal selected from the group consisting of copper and cobalt, and a coat layer made of an inorganic material containing gallium oxide. Exhaust gas purification catalyst to be. 2. The exhaust gas-purifying catalyst according to claim 1, wherein gallium oxide is contained in the coating layer provided on the carrier in an amount of 1 to 60% by weight.