JPH06154614A - Diesel engine exhaust gas purifying catalyst - Google Patents

Abstract

PURPOSE:To maintain a high SOF adsorptivity level over a long time even at the time of continuously driving a diesel engine car at a low speed by adding magnesium oxysulfate to a catalyst supporting layer of a diesel engine exhaust gas purifying catalyst comprising a carrier base material, the catalyst supporting layer and the catalyst metal. CONSTITUTION:The diesel engine exhaust gas purifying catalyst comprises the carrier base material, the catalyst supporting layer formed on the surface of the carrier base material and the catalyst metal supported on the catalyst supporting layer. The catalyst supporting layer contains magnesium oxysulfate. Although the catalyst supporting layer may consist of magnesium oxysulfate only, it desirably consists of both active alumina and magnesium oxysulfate. At this time the adhesion of the coating layer is improved. This catalyst shows high SOF adsorption performance even at the time of continuously driving a diesel engine car over a long time at a low speed. When the exhaust gas temperature is raised to the active temperature region of the catalyst metal, the adsorbed SOF is burned and removed by the catalytic action.

Description

Detailed Description of the Invention

[0001]

The present invention relates to H contained in exhaust gas from a diesel engine (hereinafter referred to as DE).
The present invention relates to an exhaust gas purification catalyst that purifies C, CO and SOF (Soluble Organic Fraction).

[0002]

2. Description of the Related Art With respect to gasoline engines, toxic substances in exhaust gas have been steadily reduced due to strict regulations on exhaust gas and advances in technology capable of coping with the regulations. But DE
With regard to the above, due to the peculiar circumstances in which harmful components are mainly discharged as particulates, the regulations and the development of technology are behind that of the gasoline engine, and the development of an exhaust gas purification device that can surely purify is desired.

As a DE exhaust gas purifying apparatus which has been developed up to now, a method using a trap (without a catalyst and with a catalyst) and an open type SOF decomposition catalyst are known. Of these, the method that uses a trap is
It traps diesel particulates to control emissions, and is particularly effective for exhaust gas with a high proportion of dry suits. However, a regeneration treatment device is required, and many problems remain for practical use, such as cracking of the catalyst carrier during regeneration, blockage due to ash, or complicated system.

On the other hand, the open type SOF decomposition catalyst is, for example, as disclosed in Japanese Patent Application Laid-Open No. 3-38255, a catalyst in which an oxidation catalyst such as a platinum group metal is supported on a catalyst supporting layer such as activated alumina as in a gasoline engine. Used, C
SO in diesel particulate along with O and HC
F is oxidatively decomposed and purified. This open type SOF decomposition catalyst has the drawback that the removal rate of dry suit is low, but the amount of dry suit can be reduced by improving DE and fuel itself, and a great advantage that a regeneration treatment device is unnecessary. Therefore, further improvement of technology is expected in the future.

By the way, the above-mentioned open type SOF decomposition catalyst decomposes and purifies SOF by the oxidizing action of the catalyst metal. However, the catalytic metal does not exert a catalytic action below the activation temperature range, and SOF is discharged as it is when the exhaust gas temperature is low at the time of starting or running at low speed. Therefore, conventionally, activated alumina having excellent adsorption performance is used for the catalyst supporting layer, SOF is adsorbed on the catalyst supporting layer at a low temperature to prevent emission, and when the exhaust gas temperature rises, it is adsorbed by an oxidation catalyst metal such as Pd. The SOF is burned and removed for purification.

[0006]

Activated alumina has a higher SOF adsorption performance than other coating materials such as silica, titania and zirconia. However, DE
Exhaust gas temperature is considerably lower than that of a gasoline engine. For example, when traveling at a vehicle speed of 80 km / h or less,
The reality is that the exhaust gas temperature does not rise to the active temperature range of the catalytic metal.

Therefore, when the vehicle continuously travels at a low speed of 80 km / h or less for a long time, the SOF is adsorbed without being removed by combustion, and the adsorption is finally saturated, so that the SOF is discharged. there were. The present invention has been made in view of such circumstances, and even if the vehicle continuously travels at a low speed, the SOF is continued for a longer time.
The purpose is to maintain a high adsorption rate of.

[0008]

The exhaust gas purification catalyst of DE of the present invention for solving the above problems is a carrier substrate, a catalyst carrier layer formed on the surface of the carrier substrate, and a catalyst carrier layer supported on the catalyst carrier layer. In a catalyst for purifying exhaust gas of a diesel engine, which comprises the catalyst metal, the catalyst supporting layer is characterized by containing magnesium oxysulfate [MgSO ₄ · nMg (OH) ₂ ].

The catalyst-supporting layer may be composed of magnesium oxysulfate alone, but is preferably composed of both magnesium oxysulfate and activated alumina. This improves the adhesion of the coat layer. In this case, the optimum mixing ratio of magnesium oxysulfate and activated alumina is about 4: 1 to 1: 2. By setting it in this range, the highest SOF adsorption capacity can be obtained.

[0010]

In the exhaust gas purifying catalyst of the present invention, the catalyst supporting layer contains magnesium oxysulfate [MgSO ₄ .nMg (OH) ₂ ]. Due to the presence of this magnesium oxysulfate, although the reason is unknown, it exhibits a high SOF adsorption performance even when continuously running at a low speed for a long time, and the adsorption capacity is remarkably increased.

When the exhaust gas temperature rises to the active temperature range of the catalytic metal, the adsorbed SOF is burned and removed by the catalytic action of the catalytic metal.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 An autoclave treatment was performed using an aqueous magnesium sulfate solution as a raw material to obtain a whisker of magnesium oxysulfate [MgSO ₄ .3Mg (OH) ₂ ]. 50 parts by weight of the whiskers were put into a mixed solution of 100 parts by weight of distilled water and 100 parts by weight of alumina sol (alumina content 10% by weight), and dispersed in a ball mill for 24 hours to prepare a slurry.

Next, a commercially available cordierite honeycomb carrier (diameter 103 mm, length 100 mm, 400 cells / i)
n ² ) after absorbing water, immersed in the above slurry for 1 minute,
After pulling up and blowing off the excess slurry, it was dried and calcined to form a catalyst supporting layer containing magnesium oxysulfate as a main component and alumina as a secondary component. This catalyst carrying layer was formed in an amount of 75 g per liter of the honeycomb carrier.

Then, the honeycomb carrier on which the catalyst supporting layer is formed is dipped in an aqueous solution of palladium chloride for 1 minute, pulled up to blow off an excess solution, dried and calcined to obtain 1.5 g of palladium per liter of carrier volume. The catalyst was supported to obtain an exhaust gas purification catalyst of this example. The displacement of this catalyst is 2.4
Installed in the exhaust system of a liter swirl chamber type DE, vehicle speed 60k
Continuous operation was performed under conditions equivalent to m / h (inlet gas temperature 235 ° C.), and the SOF reduction rate was measured every predetermined time. The results are shown in Fig. 1. Note that the SOF reduction rate is obtained by sampling the particulates on the upstream side and the downstream side of the catalyst by the direct sampling method and determining the SOF contained in each particulate.
Was calculated by chemical analysis.

Although a cordierite honeycomb carrier is used in this embodiment, the carrier substrate is not limited to this, and a known carrier substrate such as a metal honeycomb carrier substrate or a pellet carrier substrate can be used. it can. The catalyst supporting layer may contain magnesium oxysulfate, and silica, titania, zirconia or the like can be used in addition to alumina. In addition to palladium, known catalyst metals such as platinum and rhodium can be used as the catalyst metal.

In this embodiment, [MgSO ₄ .3Mg (OH) ₂ ] with n = 3 was used as the magnesium oxysulfate, but n = 1, 2, 5, etc. can be used in addition to this. . Example 2 25 parts by weight of the same magnesium oxysulfate [MgSO ₄ .3Mg (OH) ₂ ] whiskers used in Example 1 and 25 parts by weight of activated alumina powder were added to 100 parts by weight.
A slurry was prepared in the same manner as in Example 1 by introducing into a mixed solution of 100 parts by weight of distilled water and 100 parts by weight of alumina sol.

Using this slurry, a catalyst supporting layer was formed in the same manner on a honeycomb body as in Example 1. The catalyst-supporting layer contains magnesium oxysulfate [MgSO ₄ / 3M
g (OH) ₂ ] and activated alumina are contained in a weight ratio of 1: 1. The catalyst supporting layer was formed in an amount of about 75 g per liter of the honeycomb carrier. Then, in the same manner as in Example 1, the same amount of palladium was carried to obtain the catalyst of Example 2. The SOF reduction rate was measured in the same manner, and the results are shown in FIG. (Comparative Example 1) The structure is the same as that of Example 1 except that the catalyst supporting layer is made of alumina. The slurry used for forming the catalyst supporting layer had a composition of 100 parts by weight of activated alumina powder, 50 parts by weight of alumina sol, and 100 parts by weight of distilled water.

The SOF reduction rate of this catalyst was similarly measured, and the results are shown in FIG. (Comparative Example 2) The structure is the same as that of Example 1 except that the catalyst supporting layer is composed of magnesia (MgO) and alumina. The slurry used to form the catalyst-supporting layer was 25 parts by weight of commercially available magnesia powder, 25 parts by weight of activated alumina powder, and 100 parts by weight of alumina sol.
The composition is 100 parts by weight of distilled water.

The SOF reduction rate of this catalyst was also measured, and the results are shown in FIG. (Comparative Example 3) Using the same slurry as in Comparative Example 1, a catalyst supporting layer made of activated alumina was similarly formed. Next, this honeycomb carrier was immersed in an aqueous solution of magnesium sulfate (MgSO ₄ ), absorbed by the amount of water absorption and pulled up to blow off excess droplets, and then dried and fired to carry about 38 g of magnesium sulfate. Further, palladium was loaded in the same manner as in Example 1 to obtain a catalyst of Comparative Example 3.

The SOF reduction rate of this catalyst was similarly measured, and the results are shown in FIG. (Evaluation) From FIG. 1, the SOF adsorption capacity of the catalyst of Comparative Example 1 having a conventional structure disappeared in about 30 hours, whereas the catalysts of Examples 1 and 2 of the present invention gradually Although decreasing, SOF of 30% or more after 70 hours
The adsorption rate is shown.

That is, the catalyst of this example has a high SOF adsorption capacity even when it is run at a low speed for a long time, which is apparently due to the fact that the catalyst supporting layer contains magnesium oxysulfate. is there. From the results of Comparative Example 2 and Comparative Example 3, even if the catalyst-supporting layer contains magnesia (MgO) or magnesium sulfate (MgSO ₄ ), no effect can be obtained. Therefore, it is unique only in the form of magnesium oxysulfate. It is considered that the adsorption action is exhibited.

[0022]

EFFECTS OF THE INVENTION According to the DE exhaust purification catalyst of the present invention, since the SOF adsorption characteristic is extremely excellent and the adsorption capacity is remarkably increased, the SOF emission can be achieved even when traveling at a low speed for a long time. Can be prevented.

[Brief description of drawings]

FIG. 1 S when DE is driven for a long time under low-speed running conditions
It is a graph which shows change of OF adsorption rate.

Claims (1)

[Claims] 1. A catalyst for exhaust emission purification of a diesel engine, which comprises a carrier substrate, a catalyst carrier layer formed on the surface of the carrier substrate, and a catalyst metal supported on the catalyst carrier layer, wherein the catalyst carrier is Layer is magnesium oxysulfate [Mg
SO ₄ · nMg (OH) ₂ ], which is a catalyst for exhaust gas purification of a diesel engine.