JPH02261511A - Catalyst for removing fine grain in diesel exhaust and its filter - Google Patents

Abstract

PURPOSE:To obtain the catalyst for removing fine grains excellent in heat resistance and durability by replacing a part of the Ba site of the BaAl12O19 compd. with K, etc., and a part of the Al site with Cr, etc. CONSTITUTION:The Ba site of the BaAl11O19 compd. is replaced partly or wholly with one among K, Ca, Sr, La and Ag, and a part of the Al sits is replaced with one among Cr, Mn, Fe, Co, Ni, Cu and Pd to obtain a catalyst consisting of a substituted layered aluminate for removing fine grains in the diesel exhaust. The catalyst is deposited on a ceramic filter to obtain the filter or directly formed into the filter. The catalyst is excellent in heat resistance and durability, and the highly durable filter for removing fine grains in the diesel exhaust is obtained from the catalyst. The fine grains depositing on the filter are automatically burned by this method without using a special combustion device.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a filter for removing particulates from diesel engine exhaust that automatically burns particulates attached to a filter for removing particulates without using a special combustion device. This invention relates to a catalyst and its filter.

(Prior Art) Exhaust from a diesel engine contains particulates, which are combustible and fine carbon compounds. These fine particles self-ignite and burn when the exhaust temperature is 500°C or higher. 800℃
In this case, the residence time is about 1 second and the burnout occurs, but if the exhaust temperature is 500
During steady driving or idling (accounting for more than 90% of vehicle operation) when the temperature is below °C, it is directly emitted into the atmosphere.

In order to prevent such discharge of particulates into the atmosphere, a filter for collecting particulates is provided in the exhaust passage.

If the exhaust temperature is lower than 500'C, the collected particulates will not burn and will continue to accumulate in the filter, eventually blocking the exhaust passage and making it impossible for the engine to operate normally, or causing the exhaust temperature to drop. When the temperature exceeds 500° C., the excessively accumulated particulates are combusted and the filter itself becomes abnormally high temperature and may be damaged. Therefore, it is necessary to remove particulates from the filter at an appropriate time by some method.

(1) Previously S A E Technical Pap
There is a method of burning and removing particulates on a filter by attaching a combustion device to the filter and operating the combustion device as necessary, as described in Japanese Patent Laid-Open No. 61-46413. Recently, a filter has been proposed in which an electric resistance heating element is provided inside the filter.

However, methods using combustion equipment require optimal control of numerous devices such as valves, pumps, compressors, and blowers, making the system complex and costly. There is a drawback. Furthermore, when using an electric resistance heating element, there are problems with the durability of the heating element and the operating cost.

(2) 5AEPap for these external heating methods
As described in er 860294, K, supporting an oxidation catalyst such as a noble metal on the filter, or 5AEPap
Particulates can be removed by various methods such as spraying a solution containing a catalyst component from the front of the filter as shown in ER 860290, or supplying a catalyst component to the fuel system as described in JP-A-62-38816. A method has been proposed to lower the self-ignition temperature of However, methods other than supporting the catalyst on the filter have the drawback that heavy metal compounds such as copper, which are catalyst components, are scattered into the atmosphere, causing secondary pollution. On the other hand, in the catalyst supported filter method,
No mechanical control is required, and there is little risk of secondary pollution (
It has advantages such as relatively low operating cost.

(Problems to be Solved by the Invention) However, catalyst-supported filters have not yet been put to practical use because low-temperature active gas is insufficient and durability is poor. Among these, the insufficiency of low-temperature activation can be addressed by restricting the intake air and raising the exhaust gas temperature, but the problem of poor durability remains unresolved. The cause of the deterioration of such particulate combustion catalysts is
It is thought that there is a problem with the heat resistance of the catalyst. Conventionally, it has been thought that the combustion of particulates on a catalyst filter is 500°C to 600°C, and in fact, as a heat resistance evaluation test for catalysts, K, catalyst The catalyst activity (fine particle ignition temperature) after being treated at 500°C to 600°C for a certain period of time is evaluated. However, the combustion of fine particles on the catalyst shifts to the catalytic combustion of the continuous components in the fine particles and the rapid combustion of the collective carbon components due to the accompanying increase in temperature, and the actual temperature of the catalyst surface is about 1000℃~ It is thought that the temperature has reached 1300°C. In such high-temperature conditions, catalyst components such as precious metals become oxides and are scattered into the atmosphere, leading to deterioration of catalyst activity.

The present invention aims to solve these problems by providing a catalyst with excellent high-temperature heat resistance (difficult sinterability).

(Means for solving problems) In order to achieve the above object, the present invention provides BaA 1□0. .

In the compound, part or all of the Ba site is replaced by Kr.
Replace with one of Ca, Sr, La + Ag, and replace a part of the Al site with Cr, Mn, Fe, Go
+ A catalyst made of a substituted layered aluminate substituted with any one of Ni, Cu, Pd, and Pt,
The filter is characterized by having the above catalyst supported on a ceramic filter, or by forming the above catalyst into a honeycomb shape.

(Function) With the above structure, the substituted layered aluminate compound has excellent high-temperature heat resistance (difficult to sinter), so it can suppress fine particles in diesel exhaust at a catalyst surface temperature of 1000°C to 300°C. It can be burned. Further, fine particles can be efficiently collected using a filter using the catalyst.

(Example) Hereinafter, the present invention will be explained in detail using Examples and Comparative Examples.

Example I Ba(OiPr)z 25g-^j2 in N2 stream
(OiPr) 521g isopropyl alcohol 5
00mj2, and 1001111 of MnCl□ aqueous solution having a concentration of IM was added thereto. This solution was gelatinized, dried and pulverized, and then calcined at 800"C for 1 hour. The resulting powder was analyzed by X-ray diffraction as BaMnA l
It was confirmed that 10 g of this catalyst was mixed with 1 g of fine particles collected from the exhaust of a diesel engine, and the sample was TC;-DTA (differential thermal and thermogravimetric analysis).
Catalytic activity was measured using As shown in Figure 1, the catalyst was evaluated using K, 1 cc of fine particles combusted by the action of the catalyst, and catalyst activation temperature Tc.
The K and catalytic activity of the samples kept at 0° C. for 3000 hours were similarly evaluated. These results are shown in Table 1, Example 1.

Note that no change was observed in the surface area and particle size of the catalyst measured by the BET method before and after the heat treatment.

Example 2 Ba (OiPr) z 25 g in N2 gas flow
3228 g of SA E (OiPr) was dissolved in 500 mf of isopropyl alcohol, and Pd at a concentration of IM was added to this.
50 ml of Cffi□ aqueous solution was added. The obtained powder was determined by X-ray diffraction as BaPdo, 5A l 11.50
+ 9- (It was confirmed that the composition was X. Catalytic activity evaluation was performed in the same manner as in Example 1.

These results are shown in Table 1 and Example 2.

Comparative Example 1 Alumina powder with a particle size of 5 μm was mixed with PdCf2 at a concentration of 0.5M.
It was immersed in an aqueous solution for 5 hours. After drying this, 600°
C for 1 hour to obtain an alumina-supported palladium catalyst. The obtained catalyst was heated at 1000°C in the same manner as in Example 1.
Catalytic activity was evaluated before and after heat treatment for 300 hours.

The particle size of the catalyst grows due to heat treatment, and the specific surface area becomes 1.
15, so for the measurement of catalyst generation after the heat treatment, a catalyst amount five times that used for the activity measurement before the heat treatment was used. These results are shown in Table 1, Comparative Example 1.

(Effects of the Invention) As explained above, the present invention uses a substituted K aluminate compound as a particulate combustion catalyst, and has superior heat resistance and durability compared to conventional products.

Therefore, by supporting this catalyst on a ceramic filter or forming it directly on the filter, it is possible to remove particulates from diesel exhaust with excellent durability. It is a chart showing DTA measurement results.

Claims (3)

[Claims] (1) In the BaAl_1_2O_1_9 compound, B
Part or all of the a site is K, Ca, Sr, La,
Substituting one of Ag and replacing a part of the Al site with Cr
A catalyst for removing particulates from diesel exhaust, characterized in that it is made of a substituted layered aluminate substituted with any one of , Mn, Fe, Co, Ni, Cu, and Pd. (2) A filter for removing particulates from diesel exhaust, characterized in that the catalyst described in item 1 is supported on a ceramic filter. (3) A filter for removing particulates from diesel exhaust, characterized in that the catalyst described in item 1 is formed in a honeycomb shape.