JPH082408B2 - Diesel particulate collection filter - Google Patents

Description

The present invention relates to a diesel particulate filter of a diesel particulate trapping device used for trapping particulate matter contained in exhaust gas of a diesel engine and burning the particulate particulate matter. The present invention relates to a filter for collecting curate.

[Prior Art and Problems Thereof] Particulates discharged from a diesel engine are known to be harmful to the human body and the environment, and efforts have been made to reduce the amount thereof. As one of them, many devices for collecting and burning particulates in a filter have been studied. This particulate collection device consists of a diesel particulate collection filter such as a ceramic filter or a honeycomb filter, and an ignition device such as a heater and a burner that is mounted in close proximity to the upstream end surface of the diesel particulate collection filter. Used by mounting. Exhaust gas from a diesel engine is relatively low temperature, while 600 to burn particulates.
Since a high temperature of ℃ or more is required, it is necessary to burn the particulates on the filter using an external ignition device such as a heater or a burner.

During this combustion, a catalyst is temporarily used in order to improve the ignitability and the combustion propagating property. As a component of the catalyst, Cu,
A material having a high thermal conductivity such as Ag is used.
However, when the catalyst is used at high temperature, the catalytic ability is lowered and the reproducibility is deteriorated. In order to prevent this, measures such as coating the filter material with a catalyst carrier having a high heat resistance and a high specific surface area such as alumina, and coating a metal catalyst coating on the filter material have not been obtained sufficiently. For example Cu
Shows good reproducibility when it is new, but when exposed to a high temperature atmosphere, it has a problem that it diffuses into the alumina layer and forms a solid solution to form copper aluminate, which lowers reproducibility. Further, without the carrier coating layer, Cu, which must be retained on the surface of the filter, easily diffuses into the filter material at high temperature, which causes a significant decrease in performance.

As a catalyst component for improving the reproducibility of the diesel particulate filter, JP-A-55-24597 discloses a platinum group metal catalyst and JP-A-58-109139 discloses a C component.
Metal catalyst components such as u, Mn and V are disclosed, and
Japanese Unexamined Patent Publication (Kokai) No. 61-252821 discloses that there is an effect of improving the reproducibility by plating Cu and Ag, but no satisfactory result has been obtained.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a filter for collecting diesel particulates having high reproducibility by preventing solid solution of a carrier coating layer and a metal catalyst coating.

[Means for Solving the Problems] The present invention is to form a coating layer of a metal oxide having a spinel structure represented by the general formula AB ₂ O _{4 on the} surface of the filter material in the particulate collection filter, and the upper layer thereof. Is characterized in that a layer (catalyst layer) made of copper or a copper compound is formed.

In the metal oxide (AB ₂ O ₄ ) having the spinel structure, B is Al or Cr, and Al is particularly preferable. A is a divalent metal, Sr, Cu, Mo, Mn, Fe, Co, N
It is preferable to use at least one of the group consisting of i and Zn.

The coating layer of the metal oxide having the spinel structure may be formed by pulverizing the metal oxide having the spinel structure, preparing a slurry containing the metal oxide as a main component, coating the slurry on the filter, and then firing the slurry. Good or
A slurry mainly composed of a mixture of a compound of metal A (for example, an oxide) and a compound of metal B (for example, an oxide) which forms a metal oxide having a spinel structure by firing is coated on the filter. You may form after baking.

The copper compound is preferably CuO or CuCr ₂ O ₄ .

Further, aluminum nitrate, alumina sol or the like may be added to the slurry as a binder and a pH adjuster.

[Examples] The present invention will be specifically described below by showing Examples of the present invention.

Example 1 On a filter collecting surface of a cylindrical honeycomb filter (made of cordierite) having a diameter of 30 mm and a length of 50 mm, a slurry containing magnesia powder and alumina powder as main components, aluminum nitrate, alumina sol and distilled water was prepared. Then, the slurry was uniformly coated by the dipping method. In the slurry, the mixing molar ratio of magnesia powder and alumina powder was 1: 2, and the average particle size was 5 μm. The solid content ratio was 30% by weight. Next, the honeycomb filter coated with the slurry was fired at 1000 ° C. to form a MgAl ₂ O ₄ spinel layer. The amount of the coating layer formed was 50 g per honeycomb filter capacity. About 80% or more of the magnesia and alumina react with each other in the calcined filter, and Mg
It was confirmed by X-ray diffraction that a spinel structure of Al ₂ O ₄ was formed. Then, the filter having the spinel layer formed thereon was dipped in a commercially available electroless copper plating solution to perform copper plating. At this time, the amount of copper plating is 20 for 1 filter capacity.
It became g.

Example 2 A slurry consisting mainly of ZnAl ₂ O ₄ powder, alumina sol, aluminum nitrate, zinc nitrate and distilled water was sufficiently crushed using a ball mill, and then a honeycomb filter (made of cordierite) was processed in the same manner as in Example 1. ) Was coated on the filter collection surface. Next, it was baked at 700 ° C. to form a ZnAl ₂ O ₄ spinel layer, and electroless copper plating was performed in the same manner as in Example 1. The ZnAl ₂ O ₄ powder was prepared by mixing zinc oxide powder with alumina powder in a molar ratio of 1: 2, molding it into pellets having a diameter of 3 mm with a Marumerizer (tablet molding machine), and baking it at 1000 ° C or higher. It was pulverized and used after being bonded to form a ZnAl ₂ O ₄ spinel structure.

Example 3 An iron oxide sol and an alumina sol were mixed, and a honeycomb filter was coated in the same manner as in Example 1. Next, the filter was fired at 1100 ° C. to form a coating layer of FeAl ₂ O ₄ having a spinel structure, and then electroless copper plating was performed in the same manner as in Example 1. The iron oxide sol and the alumina sol had a molar ratio of Fe and Al contained of 1: 1.

Example 4 A solution of copper nitrate and aluminum nitrate was adjusted to pH 5.5 with aqueous ammonia, the resulting gel was allowed to stand, aged, and diluted with distilled water to coat the filter in the same manner as in Example. Next, the filter was fired at 930 ° C. to form a CuAl ₂ O ₄ layer having a spinel structure, and then electroless copper plating was performed in the same manner as in Example 1. The copper nitrate and aluminum nitrate solutions were adjusted so that the molar ratio Cu: Al after firing was 1: 2.

Examples 5 to 7 In the same manner as in Example 1, strontium, cobalt,
The main component was a mixture of γ-alumina powder with a molar ratio of 1: 2 to nickel oxide powder, and a slurry was prepared by mixing alumina sol, aluminum nitrate and distilled water, and the slurry was coated on the filter. Then filter 900
SrAl ₂ O ₄ , C with spinel structure after firing at ~ 1200 ℃
After forming a coating layer containing 80% or more of oAl ₂ O ₄ and NiAl ₂ O ₄ , electroless copper plating was performed in the same manner as in Example 1 to obtain Examples 5, 6, and 7, respectively.

Comparative Example 1 A filter was coated with a slurry composed of γ-alumina powder, alumina sol, aluminum nitrate, and distilled water in the same manner as in Example 1 using the dip method. The filter was fired at 700 ° C. for about 3 hours to form a γ-alumina layer on the filter. Next, electroless copper plating was performed in the same manner as in Example 1.

The qualitativeness of the spinel structure of the alumina layers of Examples 2 to 7 and Comparative Example 1 was confirmed by X-ray diffraction similar to that of Examples.

Comparative Example 2 The same honeycomb filter as in Example 1 was subjected to electroless copper plating in the same manner as in Example 1.

The filters of Examples 1 to 7 and Comparative Examples 1 and 2 shown above were attached to the exhaust system of a turbulent chamber type diesel engine with a displacement of 2400cc (12 can be attached at the same time).
It was operated for 2 hours and 15 minutes under the conditions of 2000 revolutions / minute and a torque of 1 kg · m, and 0.6 to 0.65 g of particulates was attached to each filter.

Next, the filter was incorporated into an experimental device for collecting particulates, which had a feed gas preheating section and a heater for igniting particulates on the upstream end surface of the filter position, and the filter was incorporated into the device, and N ₂ 4.5 / min, O ₂ The heater was energized at a gas flow rate of 0.5 / min to measure the burning rate of particulates. The burning rate was measured by changing the temperature of the filter-side end portion close to the heater in three stages depending on the heater energization amount. For the measurement, first measure the burning rate of particulates when the filter is new, and then in the electric furnace.
The heat treatment was carried out at 1000 ° C. for 3 hours, and the burning rate was measured by the same method as described above. The results are shown in Table 1.

Each filter exhibited almost the same particulate burning rate when new, but after heat treatment at 1000 ° C for 3 hours,
It was confirmed that Examples 1 to 7 were extremely superior to Comparative Examples 1 and 2.

From the X-ray diffraction diagram of each filter after the heat treatment, Comparative Example 1
It was confirmed that Cu as a catalyst component formed a solid solution with alumina to form CuAl ₂ O ₄ , while in Examples 1 to 7, copper on the filter was retained as CuO on the upper part of the coating layer having a spinel structure. It became clear that it is being done. Further, in Comparative Example 2, Cu was diffused into the cordierite filter material by heating and was hardly confirmed on the filter collection surface.

[Advantages of the Invention] In the filter for collecting diesel particulates of the present invention, the catalyst carrier coating layer is formed by forming a catalyst carrier coating layer having a spinel structure on the filter collection surface, and then coating the catalyst metal coating layer. And prevent solid solution of catalytic metal coating,
Prevents catalyst deterioration due to heating. Therefore, the filter for collecting diesel particulate according to the present invention,
The reproducibility is higher than that of the conventional filter.

Claims (1)

[Claims] 1. An AB on the collecting surface of the particulate filter.
A coating layer of a metal oxide having a spinel structure represented by ₂ O ₄ (A is a divalent metal, B is Al or Cr), and a copper or copper compound layer is further formed thereon A filter for collecting diesel particulates, which is characterized in that