JPS63310615A - Particulate collecting filter - Google Patents

Abstract

PURPOSE:To obtain a filter for exhaust gas which exceeds in regeneration performance by catalystic function, by carrying noble metal along the collecting surface consisting of a porous ceramic structure and plating a copper film and a silver film on the noble metal layer. CONSTITUTION:Honeycomb type particulate collecting filter consists of the porous ceramic structure 11. On the particulate collecting surface of the porous ceramic structure 11, alumina film 12 is formed, and the noble metal supporting layer 13, the copper film 14 and the silver film 15 are formed on the alumina film 12. The noble metal carrying layer 13 is formed by soaking the filter coated with the alumina film 12 into palladium chloride solution. The copper and the silver films are respectively formed by soaking into electroless copper plating liquid and silver nitrate solution. Consequently, when this filter is used for a exhaust gas treatment, the noble metal prevents the copper and silver from being deteriorated by heat with the result that the life of the filter is elongated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a filter for purifying exhaust gas discharged from an internal combustion engine, and particularly to a filter for collecting particulates discharged from a diesel engine.

(Prior Art) Conventionally, ceramic structures have been generally used as filters for collecting particulate matter discharged from diesel engines due to their collection efficiency and heat resistance. This ceramic structure is formed into a honeycomb shape or a foam shape. For example, a honeycomb ceramic structure is made of porous ceramic (usually cordierite) as shown in FIGS. 3 and 4. It has a structure in which a large number of cells 2 are formed by partition walls 1, and openings at both ends of the cells 20 are alternately closed with plugs 3. Further, in order to increase the catalyst supporting ability, there is also one in which a γ-alumina film 4 is provided on the upper layer of the partition wall 1. Such a filter is used by being attached to the exhaust system of the engine so that the openings of the cells 2 are directed upward and downward fiK. When in use, the exhaust gas collects particulates from one engine while flowing through the partition wall 1 into the adjacent cell 2, as shown by the arrows in FIG.

However, as this filter continues to be used, the back pressure increases due to the accumulation of particulate matter and the exhaust efficiency decreases, so it is necessary to periodically incinerate the collected particulate matter and perform a regeneration process. This regeneration process is carried out by an external ignition method using heating means such as heaters and burners, but □ Since combustion of particulates requires a considerable high temperature, it is difficult to increase the combustion efficiency. There is also a problem in that it is not possible to increase regeneration as desired due to the generation of toxic gas due to incomplete combustion.

As an attempt to improve this regeneration property, Japanese Patent Laid-Open No. 55-24597 discloses that a platinum group element is supported on the partition wall 1 as a catalyst component, and base metals such as manganese, vanadium, etc. are supported on the partition wall 1. is published in Japanese Patent Publication No. 58-109
No. 156 and Japanese Unexamined Patent Publication No. 109159/1987, respectively, and it has been confirmed that these methods allow particulates to be combusted at a lower temperature.

The inventor of the present application has discovered that the regeneration performance of the filter is improved by forming a silver film with excellent catalytic performance and a silver film that protects the silver film on the particulate collection surface of the ceramic structure. It is disclosed in Japanese Patent Application No. 1988-192018.

(Problems to be Solved by the Invention) Formation of a metal film on the particulate collection surface of the ceramic structure as described above improves ignitability and combustion propagation to some extent in regeneration treatment using external ignition means. let However, when forming a film using platinum group elements or base metals, ignitability and durability are still insufficient, and satisfactory reproducibility cannot be obtained. In addition, although steel with high thermal conductivity and silver film formation exhibit better reproducibility, the film deteriorates due to oxidation or sulfidation at relatively low temperatures.
There was a problem that the reproducibility deteriorated quickly.

The present invention has been made to solve these problems, and an object of the present invention is to provide a particulate-collecting filter that suppresses deterioration due to heat and maintains excellent reproducibility.

(Means for Solving the Problems) In the particulate collecting filter of the present invention, a noble metal is supported on the particulate collecting surface of a porous ceramic structure, and a copper coating is formed on the upper layer of the noble metal, and a copper coating is formed on the upper layer of the silver coating. It is characterized by a silver film formed on the surface.

The particulate collection filter of the present invention is formed by laminating the porous ceramic structure K and each film as described above, and the porous shape is maintained even after the lamination.

The porous ceramic structure may have a honeycomb shape or a foam shape, and also includes one in which an r-alumina film is provided on the particulate collection surface in order to enhance the catalyst supporting ability.

The noble metal supported on the particulate collection surface is not particularly limited, but includes, for example, platinum group elements, particularly palladium, rhodium, platinum, and the like. In addition, if this supported amount is too small, the effect of suppressing the upper layer silver film and the deterioration caused by heat of the silver film will decrease, and conversely, even if it exceeds the appropriate amount, there will be no change in the effect, so α5t or more per filter volume 12 201 is preferred, to? to zOt are particularly preferred.

In addition, the thickness of the copper coating is preferably α3 to 10 μm because if it is too thin, the catalytic effect of the steel cannot be developed, and if it is too thick, the heat capacity increases and has a negative effect on combustion propagation. .

Furthermore, if the thickness of the silver film is too thin, it will not be effective as a protective film for the underlying copper, and if it is too thick, the catalytic effect of the copper will be reduced, so it is preferable that the thickness of the silver film is 5 μm in α05.

To support the noble metal, for example, the ceramic structure is immersed in a chloride solution of the noble metal, such as a palladium chloride solution.
- followed by reduction, drying, and calcination steps. Next, to form the copper film, for example, a method of immersion in an electroless steel plating solution can be adopted. Further, in order to form a silver film on the silver film, for example, a method can be adopted in which the ceramic structure after the copper polishing is immersed in a silver nitrate solution and silver displacement plating is performed.

(Function) As described above, the particulate collection filter of the present invention has excellent catalytic performance (oxidation performance) and the presence of a copper film with good thermal conductivity, which improves particulate ignition performance and the collection surface. The combustion propagation performance at the top of the filter is improved, and good filter regeneration performance can be ensured. In addition, the presence of the silver film formed on the copper film not only makes it possible to maintain stable regeneration properties over a long period of time by protecting the copper from oxidizing or sulfuric atmospheres, but also because of the excellent thermal conductivity of silver itself. , it becomes possible to achieve further improvement in combustion propagation performance. Furthermore, by supporting noble metals such as palladium in advance as a base for such copper coatings and silver coatings, deterioration of the upper layer steel and silver due to heat is suppressed, and the effects of the steel and silver coatings are maintained, It becomes possible to maintain reproducibility more stably.

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

FIG. 1 shows the main structure of the particulate collection filter of the present invention. It should be noted that this embodiment shows an example of application to a honeycomb filter, and its overall structure is the same as that shown in FIG. 3 above, so the explanation thereof will be omitted here.

The feature of this embodiment is that an alumina film 12 is formed on the particulate collection surface of the porous ceramic structure 11, and a noble metal support layer 16, a silver film 14, and a silver film 15 are formed thereon. It is in.

An example of the manufacturing process of the above-mentioned filter will be explained next.

First, a commercially available ceramic structure made of cordierite 1
1 was immersed in a slurry consisting of r-alumina powder, alumina sol, aluminum nitrate, and distilled water, and γ was applied to the collection surface.
- forming an alumina film 12 consisting of an alumina layer;

Next, this filter is immersed in a palladium chloride solution of α57/It for 30 minutes, and then undergoes reduction, drying, and firing steps to form a noble metal support layer 13 on which palladium is supported with a filter volume of 11L to [Lst. Example A
). At this time, by changing the concentration of palladium chloride and the immersion time, the amount of palladium supported per filter volume of 11 tot (Example B) and zap (Example C)
oh! and s, op (Example D) were also produced.

Next, each filter is immersed in a commercially available electroless steel plating solution for 30 minutes to perform steel plating to form a copper film 14.

The amount of plating at this time was about 209 per 12 filter volumes.

Next, it was immersed in a solution consisting of silver nitrate 7.5 t/It, NH, 0f ((2s weight qb>& wow odor, Na, 5t03 26 t/It, silver displacement plating was performed, and the silver film 1
form 5.

The filter thus obtained was subjected to a combustion test, which will be described later. The sample filters are Examples A to D included in the present invention.For comparison, the alumina film 12 was similarly formed on the same ceramic structure 11 L2,
Then, it was immersed in a palladium chloride solution of tat7i for 1 hour, and then washed with water, dried, and fired to form a filter carrying 1 t of palladium per 1 n of filter capacity (Comparative Example 1) and an alumina film 12. - After being immersed in a palladium chloride solution for 3 minutes, it is reduced with an aqueous sodium borohydride solution to form electroless plating nuclei on the collection surface of the filter (activation of the filter), and then the copper and silver A product with a film formed thereon (Comparative Example 2) was also manufactured, and a combustion test was similarly conducted on these products as well.

The combustion test was carried out using the above-mentioned Examples 1 to 2 and Comparative Examples 1 and 2.
Filters (all sizes are 30μ in diameter and 50μ in length) are installed in the exhaust system of a swirl chamber type diesel engine with a displacement of 2400cc (12 filters can be installed at the same time), and the conditions are: rotation speed 200 rpm, torque 5 ume・m 1160 to 1651 per filter after 25 hours of operation
particulates were attached. Next, this filter was assembled into the test equipment shown in Fig. 2, and nitrogen was heated at 4.5 A/min.
and the heater 20 under a gas flow rate of oxygen α5jl/min.
The particulates were energized to burn the particulates, and the combustion rate was measured.

In FIG. 2, reference numeral 16 indicates a reaction tube having a gas inlet 17 at one end and an exhaust port 18 at the other end. It is divided into an annular electric furnace 19, and a heater 20 is provided inside the furnace.

In the test, the sample filter 10 and the monolith carrier 21 for rectification are placed in the reaction tube 16 with the heater 20 sandwiched between them, and gas is introduced into the reaction tube 16 from the gas inlet 17 and then electrically charged. It is preheated by the heat of the furnace 19, and at the same time, the heater 20 is energized to heat the end face of the filter 10 and burn particulates.

The combustion rate was measured by changing the temperature of the end face of the filter 10 near the heater 20 to three levels depending on the amount of current applied to the heater. For each filter, after measuring the particulate combustion rate when new, heat treatment was performed at 800°C for 5 hours in the air in an electric furnace, and the combustion rate was measured in the same manner as described above. Thereafter, heat treatment was performed at 1000°C for 3 hours, and the combustion rate was further measured.

The test results are shown in the table below.

From this, Comparative Example 1 shows little deterioration due to heat, but even if it is new, a sufficient combustion rate cannot be obtained unless the temperature is extremely high, and the regeneration performance is poor. Furthermore, in Comparative Example 2, although the regeneration performance of the new product was good, the degree of deterioration due to heat was extremely large. On the other hand, when compared with Example Au according to the present invention and Comparative Example 2, the performance is the same when new and after heat treatment at 800°C for 3 hours, but the reproducibility is improved after heat treatment at 1000°C for 3 hours. There is. In addition, although the amount of palladium supported in Dld and Dld was gradually increased, deterioration due to heat treatment was suppressed in accordance with the amount of palladium up to Example C. However, the performance in Example 1 was comparable to that of Example C. From this, the palladium loading t
It can be said that [1L5t to 2t] per filter volume 11 is appropriate.

Similar tests were also conducted using platinum, rhodium, and the like as noble metals to be supported separately, and good results similar to those for palladium were obtained in both cases.

(Effects of the Invention) As explained in detail above, the present invention enables the particulate collection surface of a porous ceramic structure to support a noble metal such as palladium in advance, and then laminates a copper film and a silver film. Therefore, precious metals suppress the thermal deterioration of steel and silver, thereby increasing the excellent catalytic performance and thermal conductivity of steel.
Silver's protective effect on steel and excellent thermal conductivity last for a long time. From this, the particulate-collecting filter of the present invention has excellent reproducibility, and the reproducibility lasts for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the main part structure of the particulate collection filter of the present invention, FIG. 2 is a cross-sectional view showing the combustion device of the filter, and FIG. 3 is a cross-sectional view showing the structure of a conventional filter. FIG. 4 is a detailed view of section A of the filter shown in FIG. 5. 11... Ceramic structure 12... Alumina film 13... Noble metal support layer

Claims (1)

[Claims] On the particulate collection surface of the porous ceramic structure,
1. A filter for collecting particulates, characterized in that a noble metal is supported, a copper film is formed on the upper layer, and a silver film is formed on the copper film.