JPS60235641A - Monolithic catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To improve the purifying capacity and durability of a monolithic catalyst by allowing an alumina layer to carry the catalyst component wherein the depth of the catalyst carried by the alumina layer is made larger at the inlet side of the exhaust gas and smaller at the outlet side of the exhaust gas. CONSTITUTION:Many cells are formed in the axial direction from the inlet side 3 toward the outlet side 4 of the exhaust gas, and an alumina layer 2 is formed on the inside wall of the cells. A monolithic catalyst 1 is formed by allowing the alumina layer 2 to carry the catalyst component. In this case, the depth of the catalyst to be carried by the alumina layer may be made gradually or stagewise smaller from the inlet side 3 toward the outlet side 4 of the exhaust gas. If it is formed stagewise smaller, a range corresponding to 1/5-1/2 of the total length along the axial direction at the inlet side 3 of the monolithic catalyst 1 is pref. made to have larger depth with the rest shallower.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a monolith catalyst for purifying exhaust gas of an internal combustion engine.

[Prior art]

Catalysts for purifying exhaust gas from internal combustion engines, particularly automobiles, are required to have extremely high performance in terms of durability, purification performance, and the like. Traditionally, monolithic catalysts and granular catalysts have been used as exhaust gas purification catalysts, but recently, monolithic catalysts have the advantage of having a smaller heat capacity, better warm-up performance, and lower back pressure than granular catalysts. As a result, monolithic catalysts are becoming widely adopted. This monolithic catalyst has activated alumina supported on a cordierite monolithic support having an integrally molded structure, and then an active component having a catalytic effect (usually a noble metal) supported thereon.

The catalyst components include platinum (Pt), rhodium (Rh
), palladium (Pd), and other noble metals are used. When a monolithic catalyst supporting these catalyst components is attached to a catalytic converter and exhaust gas is passed through, the harmful substances contained in the exhaust gas, such as hydrocarbons (HC), -carbon oxides (CO), and nitrogen oxides, are removed. (NOx) is efficiently purified by oxidation or reduction reaction. Conventionally, these catalyst components are supported at a uniform depth throughout the alumina layer of a monolithic catalyst.

By the way, -carbon oxide has a strong adsorption power with noble metals, so
Generally, as the carbon monoxide concentration increases, the reaction rate decreases. On the other hand, in monolithic catalysts, reactions occur while the exhaust gas passes through the cell from the inlet side to the outlet side, so reactants such as carbon monoxide generally have a high concentration near the inlet side, and reactants near the outlet side The concentration will be low. Therefore, there was a problem that the reaction rate was low on the inlet side of the cell, and the purification performance of the monolith catalyst as a whole was not sufficient.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to change the supporting depth of the catalyst in accordance with the concentration distribution of harmful substances, especially carbon oxide, thereby improving the monolithic structure. The objective is to improve the purification performance and durability of the catalyst.

[Structure of the invention]

According to the present invention, this object is achieved by the following monolithic catalyst for purifying exhaust gas.

That is, the monolithic catalyst for exhaust gas purification of the present invention has a columnar shape, and a large number of cells are provided in the axial direction from the exhaust gas inlet side to the outlet side, and an alumina layer is formed on the inner wall surface of the cells. This monolithic catalyst for exhaust gas purification has a catalyst component supported on the alumina layer, and is characterized in that the catalyst component is supported deeply on the exhaust gas inlet side and shallowly on the exhaust gas outlet side.

In the present invention, the supporting depth of the catalyst component may be made gradually shallower from the exhaust gas inlet side to the exhaust gas outlet side of the monolithic catalyst, or may be made shallower in stages. If the depth is to be made shallow in stages, it is preferable to deepen the depth from 115 to 1/2 of the total axial length from the inlet side to the outlet side of the monolithic catalyst, and make the other portions shallower.

[Action of the invention]

According to the monolithic catalyst for exhaust gas purification of the present invention, - Since the catalyst component is supported deeply on the inlet side of the monolithic catalyst where the concentration of carbon oxide is high, the concentration of carbon monoxide reaching the catalyst due to diffusion resistance in this part decreases, and the decrease in reaction rate due to -carbon oxide is suppressed. In addition, since the carbon oxide concentration has decreased by the time the catalyst component is shallowly supported, the reaction rate of the catalyst component on the outlet side is not significantly reduced by carbon monoxide. Therefore, the overall reaction rate of the catalyst components increases, and purification performance can be improved.

〔Effect of the invention〕

As described above, the monolithic catalyst for exhaust gas purification of the present invention has the following effects.

(a) - Since the reduction in the reaction rate on the inlet side of the monolith catalyst due to carbon oxide is suppressed, the reaction rate increases and the purification performance of the monolith catalyst as a whole improves.

(b) Phosphorus (P), lead (Pb), etc., which are poisonous substances,
It is captured on the inlet side of the monolithic catalyst before reaching the catalyst components. Therefore, high purification performance can be maintained.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

γ-alumina powder 1000g, alumina silua 00g1
150 g of aluminum nitrate aqueous solution (23% by weight) and 300 g of water were mixed and stirred to form a slurry. In this,
Cordierite monolith carrier 1 as shown in FIG.
(volume 1.7β) was immersed and pulled up, the excess slurry was blown off with an air stream, and after drying at 200°C for 1 hour,
It was baked at 00°C for 2 hours. As a result, the first alumina layer 2 was formed as shown in FIG.

Next, put the monolithic carrier 1 that has absorbed water in advance into a container that has the same shape as this monolithic carrier 1, and submerge it up to 1/3 of the total length in the axial direction from the inlet side 3 to the outlet side 4. Dinitrodiammine platinum aqueous solution (1,83g/l
) 310 mJ was added and left to stand for 2 hours to support platinum. Thereafter, a rhodium chloride aqueous solution (0,18
3g/β) was added to support rhodium. As a result, platinum and rhodium were supported on a ⅓ portion of the first alumina layer 2 from the inlet side 3.

This monolithic carrier 1 was again immersed in alumina slurry, and a second alumina I'i5 was formed in the same manner as the first alumina layer 2 described above. Next, the monolithic carrier 1 is placed in the above-mentioned container, and a dinitrodiammine platinum aqueous solution (1.83 g/j 6
20mj! was added and allowed to stand for 2 hours to support platinum.
Rhodium chloride aqueous solution <0.183g/j 620mj!
was added and allowed to stand for 2 hours to support rhodium. As a result, platinum and rhodium were supported on the second alumina layer 3 in a range of 2/3 of the total length in the axial direction from the exhaust gas outlet side 4.

In addition, in FIG. 2, for convenience of explanation, the portions where platinum and rhodium are supported are shown by hunting.

The monolithic catalyst obtained as above is referred to as catalyst a.

(Comparative Example) Using substantially the same monolith carrier as in the example, an alumina layer was formed in the same manner as in the example. At this time, in order to make the thickness of the alumina layer the same as in the example, it was dipped into the slurry twice. Next, the whole was placed in the same container as in the example, and dinitrodiammine platinum aqueous solution (1,83 g/f) 930
m12, then rhodium chloride water fgil&(0,1
Platinum and rhodium were supported on the entire alumina layer by immersing it in 930 m2 of water (83 g/l') and allowing it to stand for 2 hours. The resulting monolithic catalyst is used as a catalyst.

Each of the above two types of catalysts a and b was 2.8I! It was installed in the exhaust system of an engine, and after conducting a 200-hour durability test at an exhaust gas introduction temperature of 700°C, the purification performance was evaluated.

This evaluation is based on the temperature at which exhaust gas is introduced into the monolithic catalyst.
The purification rate was measured at two different temperatures: 0°C and 350°C. The results are shown in Table 1.

Table 1 Measurement results of purification rate (%) As is clear from Table 1, the monolithic catalyst for exhaust gas purification according to this example has higher activity than the conventional monolithic catalyst.

Although specific embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and includes various embodiments within the scope of the claims. .

For example, in the example, the catalyst component was deeply supported in the range of 1/3 from the exhaust gas inlet side of the monolith catalyst, but this range may be 115 to 1/2.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a monolithic catalyst for exhaust gas purification according to an embodiment of the present invention, and FIG. 2 is an enlarged view of the main part of FIG. 1. ■ - Monolith carrier 2 - First alumina layer 3 - Single population side 4 - One - Outlet side 5 - Second alumina layer

Claims (1)

[Claims] (11 columns, from the exhaust gas inlet side to the outlet side (IIJ
A monolithic catalyst for exhaust gas purification, in which a large number of cells are provided in the axial direction, an alumina layer is formed on the inner wall surface of the cell, and a catalyst component is supported on the alumina layer, the catalyst component being is a monolithic catalyst for exhaust gas purification that is supported deeply on the exhaust gas inlet side and shallowly supported on the exhaust gas outlet side.