JPH04267950A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To provide a catalyst for purifying exhaust gas to reduce NOx in the atmosphere of excessive oxygen at a high elimination ratio. CONSTITUTION:An H-type zeolite catalyst is positioned at the inflow side of exhaust gas, while another type of zeolite catalyst comprising at least one sort of catalyst component selected from a group consisting of copper, cobalt, platinum, palladium, rhodium, iridium, and ruthenium is placed at the outflow side of the exhaust gas.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a catalyst for purifying harmful components emitted from internal combustion engines, etc., and more specifically to a catalyst for purifying exhaust gas for purifying NOx in an oxygen-rich atmosphere at a high rate. be.

0002

2. Description of the Related Art Catalysts that simultaneously oxidize carbon monoxide (CO) and hydrocarbons (HC) and reduce nitrogen oxides (NOX) are used as exhaust gas purifying catalysts for automobiles. Such catalysts are basically made by coating a γ-alumina slurry on a refractory support such as cordierite, drying it, and then supporting metals such as platinum (Pt), palladium (Pd), and rhodium (Rh). This is what I did.

[0003] The purification performance of the catalysts that have been used or proposed so far is greatly affected by the set air-fuel ratio of the engine, and in lean mixtures, that is, on the lean side where the air-fuel ratio is high, the amount of oxygen (O2) is large even after combustion. The oxidizing action becomes active and the reducing action becomes inactive. On the contrary, on the rich side where the air-fuel ratio is small, the oxidizing action becomes inactive and the reducing action becomes active. The stoichiometric air-fuel ratio that balances this oxidation and reduction (
The catalyst works most effectively near A/F=14.6).

[0004] Therefore, when using a catalyst, in an automobile equipped with an exhaust gas purification device, the oxygen concentration in the exhaust system is detected and feedback control is performed to maintain the air-fuel mixture near the stoichiometric air-fuel ratio.

[0005] In addition, in recent years, catalysts in which copper is ion-exchanged supported on zeolite, platinum (Pt), and palladium (Pt) have been used as catalysts in lean atmospheres with excess oxygen.
d) A catalyst in which a noble metal selected from rhodium (Rh), iridium (Ir), and ruthenium (Ru) is ion-exchange supported is disclosed in JP-A-60-97047 and JP-A-1-135.
No. 541, etc.

[0006]

[Problem to be solved by the invention] In automobiles, in a lean atmosphere with excess oxygen, among the harmful components in exhaust gas, hydrocarbons (HC) and (CO) can be removed by oxidation, but NOX is removed by reduction. The problem was that I couldn't do it.

[0007] As mentioned above, as a catalyst used in a lean atmosphere with excess oxygen, there are catalysts in which copper is ion-exchanged supported on zeolite, platinum (Pt), palladium (Pd), rhodium (Rh), etc. Iridium (Ir)
A catalyst in which a noble metal selected from the group consisting of
OX purification performance is not sufficient, and further improvements are required for practical use.

[0008]

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems. , platinum (Pt), palladium (Pd),
Rhodium (Rh), Iridium (Ir), Ruthenium (
This exhaust gas purifying catalyst is characterized in that it is a zeolite catalyst containing at least one catalyst component from the group consisting of (Ru). Only one catalyst or a plurality of catalysts may be used.

[0009]

[Effect] The factors that purify NOX are not clear, but since H-type zeolite has a high HC adsorption capacity, it mainly adsorbs HC at low temperatures, and NOX At high temperatures, when purification begins with a zeolite catalyst containing at least one catalyst component from the group consisting of platinum, rhodium, iridium, and ruthenium, HC adsorbed at low temperatures is desorbed and NOx is released on the catalyst on the exhaust gas outlet side. It is thought that this reduces NOx and promotes the purification rate of NOx.

0010

[Examples] Examples of the present invention will be described below. Example 1 Zeolite slurry was prepared by mixing 100 parts of H-type zeolite, 50 parts of commercially available silica sol, and pure water.
A 1/4 length portion of a cordierite honeycomb carrier having a length of 100 mm and 300 cells was coated with 120 g of H-type zeolite per liter of the honeycomb carrier. The remaining 3/4 portion was coated with 120 g of zeolite per liter of the honeycomb carrier using a zeolite slurry prepared by mixing 100 parts of zeolite, 50 parts of commercially available silica sol, and pure water.

Next, 3/4 of the length of the honeycomb carrier coated with the zeolite was immersed in a copper acetate solution with ammonia water added to adjust the pH to 11, and 1 liter of copper was added to the honeycomb carrier. Catalyst A was obtained by ion-exchange loading so that the weight was 4 g.

Example 2 Catalyst B was obtained by carrying cobalt in an amount of 4 g per liter on a honeycomb carrier in the same manner as in Example 1 except that the copper acetate solution in Example 1 was replaced with a cobalt acetate solution.

Example 3 In the same manner as in Example 1, 3/4 of the length of the zeolite-coated honeycomb carrier was immersed in a copper acetate solution with aqueous ammonia added to adjust the pH to 11. Ion exchange loading was carried out so that the amount was 4 g per liter of carrier. Further, the part on which copper was supported by ion exchange was immersed in a tetravalent platinum ammine solution to support platinum in an amount of 1 g per liter of the honeycomb carrier, thereby obtaining catalyst C.

Example 4 4 g of copper per liter of honeycomb carrier was prepared in the same manner as in Example 1 except that the tetravalent platinum ammine solution in Example 3 was changed to a mixture of a tetravalent platinum ammine solution and a divalent palladium ammine solution. , 1 g of platinum and 1 g of palladium were supported to obtain catalyst D.

Example 5 Catalyst E was obtained by carrying 2 g of platinum per liter of honeycomb carrier in the same manner as in Example 1 except that the copper acetate solution in Example 1 was replaced with a tetravalent platinum ammine solution. .

Example 6 H-type zeolite was placed on a cordierite honeycomb carrier having a diameter of 93 mm, a length of 25 mm, and a number of cells of 300.
A catalyst was prepared by coating a cordierite honeycomb carrier with a length of 75 mm and a number of cells of 300 with copper ion-exchanged zeolite.

Next, a catalyst F was obtained in which a catalyst coated with H-type zeolite was disposed upstream and a catalyst coated with copper ion exchange zeolite was disposed downstream.

Comparative Example 1 A zeolite slurry was prepared by mixing 100 parts of zeolite, 50 parts of commercially available silica sol, and pure water. Next, a cordierite honeycomb carrier with a diameter of 93 mm, a length of 100 mm, and 300 cells was immersed in the slurry, the excess slurry was blown off, and after drying, the honeycomb carrier was coated with a weight of 120 g per liter. , catalyst G was obtained.

Comparative Example 2 The entire honeycomb carrier obtained in Comparative Example 1 was immersed in a solution in which ammonia water was added to a copper acetate solution and the pH was adjusted to 11, so that the amount of copper was 4 g per liter of the honeycomb carrier. Catalyst H was obtained by supporting the catalyst in this manner.

Comparative Example 3 Catalyst I was obtained by carrying 4 g of cobalt per liter of honeycomb carrier in the same manner as in Comparative Example 2, except that the copper acetate solution of Comparative Example 2 was immersed in a cobalt acetate solution.

Comparative Example 4 Catalyst G obtained in Comparative Example 2 was further immersed in a tetravalent platinum ammine solution to give 4 g of copper per liter of honeycomb carrier.
Catalyst J was obtained by supporting 1 g of platinum.

Comparative Example 5 Catalyst G obtained in Comparative Example 2 was further immersed in a mixed solution of a tetravalent platinum ammine solution and a divalent palladium ammine solution.
4g of copper, 1g of platinum per liter of honeycomb carrier,
Catalyst K was obtained by supporting 1 g of palladium.

Comparative Example 6 The entire honeycomb carrier obtained in Comparative Example 1 was immersed in a tetravalent platinum ammine solution to support 2 g of platinum per liter of the honeycomb carrier to obtain catalyst L. The NOX purification rate of catalysts A to K obtained in Examples and Comparative Examples was measured under the following conditions.
The results are shown in Table 1.

<NOX purification performance evaluation conditions> NOX:
500-1,000ppm Air-fuel ratio (A/F): 17-20 Space velocity (SV): 40,000/Hr Inlet gas temperature: 2
00℃, 300℃, 400℃

[0025]

[Table 1] Table 1 shows NOx under lean conditions where oxidation is active.
shows the purification rate. Catalysts A to E formed in Examples 1 to 5 of the present invention are catalysts H to L of Comparative Examples 2 to 6, respectively.
In contrast, an H-type zeolite catalyst is provided on the exhaust gas inflow side. each supported catalyst (e.g. copper,
Comparing the two for each (cobalt, etc.), the example shows a higher NOX purification rate.

It can be seen that especially when the inlet gas temperature is 300.degree. C. and 400.degree. C., the NOX purification rate is considerably higher in the example. At 200°C, the NOx purification rate may be slightly higher in the comparative example, but this is probably due to less desorption of HC adsorbed at low temperatures.

[0027] Also, Example 6 using a plurality of catalysts also had a high N.
It shows the purification rate of OX.

[0028]

[Effects of the Invention] As is clear from the results in Table 1, when the catalyst of the present invention is used in an oxygen-rich atmosphere, the NOx purification rate is higher than that of the conventional catalyst.

Furthermore, according to the present invention, it is possible to remove NOX in an oxygen-rich atmosphere, and
This makes it possible to remove NOX from a wide range of fields, including combustion exhaust gas from boilers, household kerosene stoves, and cooking appliances.

Claims (1)

[Claims] [Claim 1] H-type zeolite catalyst on the exhaust gas inflow side, copper, cobalt, platinum, palladium,
An exhaust gas purifying catalyst characterized in that it is a zeolite catalyst containing at least one catalyst component from the group consisting of rhodium, iridium, and ruthenium.