JPH0249913A - Particulate collecting filter - Google Patents

Abstract

PURPOSE:To enhance the reproducibility of a filter by forming potassium titanate fiber, SiO2, a Cu-plated layer, and an Ag-plated layer one after another on the collecting surfaces of particulates in a honeycomb filter of ceramic type, and thereby enlarging surface area. CONSTITUTION:A filter is made in honeycomb form, a bulkhead 1 constituting a number of cells oriented in the exhaust gas flowing direction is formed from porous ceramic. On the surface of this bulkhead 1 a layer is formed composite with potassium titanate fiber 2. A SiO2 particle layer 4 is formed on the surface of potassium titanate fiber 2. A Cu-plated layer 5 and an Ag-plated layer 6 are formed on the surface of a SiO2 particle layer 4. Thereby the area of a catalyzer surface is enlarged to increase the contact of catalyzer with particulates, which should enhance the reproducibility of the filter.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a filter for purifying exhaust gas emitted from an internal combustion engine, and particularly to a filter for collecting particulates emitted from a diesel engine. .

(Prior Art) Conventionally, a honeycomb-shaped or foam-shaped ceramic structure has been used as a filter for collecting particulates discharged from a diesel engine. Among these, the honeycomb-shaped ceramic structure has, for example, as shown in FIG. It has a structure in which openings are alternately closed with plugs 18.

The filter made of the above honeycomb-shaped ceramic structure is
The cell 17 is attached to the exhaust system of the engine with its opening facing upstream and downstream of the exhaust gas, and the exhaust gas 16 passes through the 1° pore of the partition wall to the adjacent cell, as shown by the arrow in FIG. Particulates in the exhaust gas flow into the cell 17, and at that time, particulates in the exhaust gas are captured by the partition wall 1°.

By the way, as the filter is used repeatedly, particulates accumulate on the partition walls and the exhaust efficiency decreases, so it is necessary to periodically incinerate the captured particulates and regenerate the filter. As an ignition means for incineration, an external ignition method using a heating means such as a heater or a burner is used for boat fishing. In the external ignition method, particulates are ignited on the upstream side of the filter, and combustion is propagated to the downstream side of the filter to perform regeneration. However, if the combustion efficiency of particulates is poor at this time, especially the particulates on the downstream side will remain. If particulates remain, not only does regeneration cause a problem in that the exhaust efficiency of the filter is not fully recovered, but the remaining particulates are also combusted during the next regeneration, resulting in a significantly higher combustion temperature. , the problem arises that the filter becomes overheated. This can cause the filter to crank or melt.
If the temperature of the filter increases significantly, the catalyst supported on the filter may deteriorate.

Therefore, in the particulate collection filter,
Improving the reproducibility of filters is a critical issue;
Various methods have been proposed.

For example, JP-A-55-2497 discloses a filter that supports platinum group elements such as platinum and palladium as a catalyst, and JP-A-58-109136 discloses a filter that supports copper, manganese, etc. as a catalyst. A filter carrying a base metal element such as vanadium has been disclosed.

Furthermore, JP-A-61-252821 proposes forming a metal coating on the particulate collection surface to improve combustion propagation.

Furthermore, Japanese Patent Application No. 62-76996 discloses a method in which a γ-alumina coating layer containing potassium titanate fibers is formed on the particulate collection surface, and a copper and silver plating layer as a catalyst is formed on the surface. Proposed. here,
Potassium titanate fiber means needle-like crystals of potassium titanate. In this method, since the T-alumina coat layer containing potassium titanate fibers has a rough surface due to the needle-like crystals of the potassium titanate fibers, the surface area of the copper and silver plating layer formed on the surface is expanded. , the opportunity for contact between the particulates and the catalyst (contact area) increases, and as a result, the regeneration performance of the filter improves.

(Problems to be Solved by the Invention) Among the above, in the production of a filter carrying a catalyst, the catalyst is carried by impregnating the filter with a catalyst solution, and the catalyst is applied to a ceramic honeycomb filter. However, in order to burn the particulates, direct contact between the particulates and the catalyst is required, and the particulates hardly enter the inside of the pores, so it is sufficient to burn the particulates. No effect can be obtained.

On the other hand, in the filter coated with the above catalyst metal,
Since the catalyst component can be attached only to the surface of the partition wall of the filter, the regeneration effect is greater in that a higher density catalyst component acts on the particulates than in the filter in which the catalyst component is dispersed. However, the surface of the partition wall is relatively smooth, and it cannot be said that there is a sufficient opportunity for contact between the catalyst and the particulates, so a filter with even better regenerating properties is desired.

The method using potassium titanate fibers is improved in terms of contact opportunities because the fibers overlap on the filter surface to form a three-dimensional surface. However, this filter has 1
When exposed to high temperatures of 000°C or higher for a certain period of time, the acicular crystals of the potassium titanate fibers collapse, the particulate collection surface becomes smooth and the surface area decreases, and copper and silver lose their catalytic function. There is a problem with doing so. especially,
Diesel carrot particulate collection filters are often exposed to high temperatures of 1000°C or higher during use, so even at high temperatures the needle-like crystals of the potassium titanate fibers may collapse or the catalyst may be deactivated. without doing,
A particulate collection filter with sufficient durability is required.

In the above method using potassium titanate fibers, we investigated the cause of fiber collapse and found that filters coated with potassium titanate fibers without copper plating or silver coating were heat treated at 1000°C for 3 hours. , potassium titanate fibers do not disintegrate and remain intact, and potassium titanate (K2
The melting point of 0.6 TiO It is presumed that this is because copper or copper reacts at high temperatures of 1000°C or higher.

Therefore, the present invention provides a filter for particulate collection in which the particulate collection surface is coated with potassium titanate fibers, and the fibers are plated with copper and silver as a catalyst. An object of the present invention is to provide a filter for collecting particulates in which needle-like crystals of potassium acid fibers do not collapse and can maintain good opportunities for contact between a catalyst and particulates.

(Means for Solving the Problems) In order to achieve the above object, the particulate-collecting filter of the present invention coats the particulate-collecting surface of a ceramic honeycomb filter with potassium titanate fibers. 5iO on the surface of potassium titanate fiber
A z layer is formed, and a copper coating layer and a silver plating layer are formed on the surface of the 5iOz layer.

The 5iOz layer is applied to a thickness that allows the unevenness caused by the potassium titanate fibers to be fully utilized and that the copper and roots formed on the StO□ layer do not react with the potassium titanate fibers. Specifically, it depends on the number of cells, but the filter volume is 1! If the amount is less than 5g, the effect of preventing the reaction between the potassium titanate fibers and copper or silver will not be obtained, and if it exceeds 50g, the gaps between the potassium titanate fibers will be filled and the plated surface formed on the surface will be The amount is preferably in the range of 5 g to 50 g because the surface becomes smooth and the effect of improving contact opportunities cannot be obtained.

In addition, if the particle size of the 5iOz particles is less than 10 nm, it will not be possible to form the desired unevenness on the potassium titanate fiber, and if it exceeds 50 nm, it will be difficult to coat the potassium titanate fiber. It is preferable to set it as the range of 10-50 nm.

(Function) In the particulate collection filter of the present invention, the particulate collection surface is coated with potassium titanate fibers, the surface of the potassium titanate fibers is coated with SiO□, and the surface of the Si is coated with copper. And grudges are given. The potassium titanate fibers overlap to form a three-dimensional structure, and the surface of the needle-like crystals is unevenly formed by SiO□ particles. In addition, since there is a heat-resistant StO□ coating layer between the potassium titanate fiber and the copper-silver plating,
Even at the above high temperatures, the potassium titanate fibers do not react with copper and silver, and therefore the potassium titanate fibers do not collapse and the copper and silver as catalysts do not become deactivated.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A commercially available cordierite honeycomb filter base material (30 mm in diameter, 50 mm in length) was immersed in a slurry consisting of 7 parts of potassium titanate fiber powder, 100 parts of distilled water, and 5 parts of polyvinyl alcohol, and then pulled up. After that, blow off the excess slurry with air, dry, and heat at 700°C
Fired for an hour. This resulted in the formation of a layer of needle-like crystals of potassium titanate fibers. The amount of potassium titanate fiber coated was 20 g per 11 filter volumes.

This filter was immersed in commercially available silica sol (10%), blown off with air in the same manner as above, dried and heated to 700°C.
Firing was performed for 2 hours. As a result, a 5 in 2 particle layer is formed on the surface of the potassium titanate fiber. 5iOz
The coating amount was 5 g per 1 ρ of filter volume.

Next, this filter was immersed in a solution containing 5 g of stannous chloride/ffi and washed with water. After that, PdC1z 0.5g/
After being immersed in an activation solution consisting of 1 for 3 minutes, excess droplets were blown off, reduced in an aqueous sodium borohydride solution, and copper plating was performed by immersing in an electroless copper plating solution. This results in 5i on potassium titanate fibers.
A copper plating layer was formed on the surface of the Oz particles. The amount of copper plating was 20 g/l.

For this filling, 8gNo: + 7.5g/l 5N
H40H (28 wt% > 6.4 ml/l, Naz
Silver displacement plating was performed using a silver plating solution consisting of Sz0326g/I-.

The amount of silver plating on the filter thus obtained was about 2 g per 11 filter volumes.

As a result, the second figure, which is an enlarged view of FIG.
As shown in the figure, a layer made of overlapping potassium titanate fibers 2 is formed on the surface of the partition wall 1 of the honeycomb filter base material, and the surface of the potassium titanate fibers 2 is coated with SiO□ particles 4. A particulate collection filter 3 having a copper plating layer 5 and a silver plating layer 6 formed on its surface was obtained.

Example 2 A layer of potassium titanate fibers was formed by the same coating method as in Example 1, except that the coating amount of SiO□ was 50 g per filter volume IP, and a layer of SjO□ was coated on the surface of the needle-like crystals. A particulate collection filter in which a particle layer, a copper plating layer, and a silver plating layer were formed was manufactured.

Comparative Example 1: A layer of potassium titanate fibers was formed by the same coating method as in Example 1, except that the coat i of SiO□ was 2 g per filter volume 11, and a layer of potassium titanate fibers was formed on the surface of the potassium titanate fibers. A particulate collection filter was manufactured in which a particle layer, a copper plating layer, and a silver plating layer were formed.

Comparative Example 2: Potassium titanate fibers were coated with a coating amount of 20 g per filter volume IP using the same coating method as in Example 1, and then copper coating and silver plating were performed using the same method as in Example 1. Thus, a particulate collection filter was manufactured in which a layer of potassium titanate fibers was formed, and a copper plating layer and a silver plating layer were formed on the surface of the potassium titanate fibers.

Comparative Example 3: A γ-alumina coat layer was formed on the same honeycomb filter base material as used in Example 1 using a slurry consisting of activated alumina powder, alumina sol, aluminum nitrate, and distilled water.

At this time, the coating amount was 75 g per 12 filter volumes.

Next, copper plating was performed using the same method as in Example 1.

Test example=.

The particulate collection filters manufactured in Examples 1 to 2 and Comparative Examples 1 to 3 were attached to the exhaust system of a vortex-type diesel engine with a displacement of 2400 cc, and the number of revolutions was 20.
0Orpm Torque 3kg - Under conditions of trust, 2.5
0.60-0.65g per filter after hourly operation
This particulate collection filter 3' was assembled into a test device 15 shown in FIG. 8, and the particulate combustion rate was measured.

In FIG. 8, reference numeral 9 denotes a reaction tube provided with a gas inlet 10 at one end and an exhaust port 11 at the other end, and inside the reaction tube 9 is a filter 3 for collecting particulates formed as described above. and a monolith carrier 12 for rectification.The reaction tube 9 is covered with a tubular electric furnace 13 on the side of the gas inlet 10, and the gas introduced into the reaction tube 9 from the gas inlet 1O is connected to the electric furnace. 13 and reaches the particulate collection filter 3°, where the trapped particulates are burned.The combustion rate was measured using nitrogen gas 4.5
Heater 1 at a gas flow rate of 1/min and oxygen gas 0.517 min.
The temperature of the end face of the filter near No. 4 was varied in three stages: 325°C, 1350°C, and 375°C depending on the amount of heater current. The results are shown in Table 1.

In addition, the particulate collection filters of the above-mentioned Examples and Comparative Examples were heated at 1000°C
After applying heat treatment for several hours, the temperature of the end face of the filter was adjusted to 525°C, 1550°C and 575°C using the test equipment shown in Figure 8.
By the same operation as above except for step C,
Particulate combustion rate was measured. The results are shown in Table 1.

In addition, the particulate collection surface of the filter that had been heat-treated for 1000×3 hours was observed using a SEM (scanning electron microscope). The results are shown in Table 2.

Table 1: Combustion rate (%) of each filter Table 2: SEM observation results From Table 1, regarding the regeneration properties of filters that are not heat treated at 1000°C for 3 hours, Example 1, Example 2,
Comparative Example 1 and Comparative Example 2 are equivalent and significantly superior to Comparative Example 3. This is because the particulate collection surface of the filter of Comparative Example 3 is smooth, whereas the filter of Example 1
On the particulate-1 collecting surface of the filters of Example 2, Comparative Example 1, and Comparative Example 2, a layer of overlapping needle-like crystals of potassium titanate fibers was formed, and the surface of the cough needle-like crystals Because it is plated with copper and silver as a catalyst,
This is because the surface area of the catalyst layer is large, and there are many opportunities for contact between particulates and the catalyst.

]000'CX Regarding the regeneration properties of filters that were heat-treated for 3 hours, Examples 1 and 2 were compared with Comparative Examples 1.2 and 3.
is better than. As can be seen from the observation results in Table 2, Comparative Examples 1, 2 and 3 have smooth collection surfaces (see Figures 5, 6 and 7), whereas Example In Examples 1 and 2, the potassium titanate fibers 2 are covered with 5i02 particles 4 that have good heat resistance and do not easily react with copper and silver (see Figures 3 and 4), and as in Comparative Example 2. Potassium titanate and copper or silver do not react to form a solid solution 7, and the catalytic action of potassium titanate, copper, and silver is not lost, and a three-dimensional collection surface similar to that before heat treatment is created. This is thought to be because it is possible to maintain This ensures good regeneration performance even after durability. On the other hand, in Comparative Example 1, SiOz
Coat -ffi is small, SiO□ particles cannot cover the entire potassium titanate fiber, the catalyst copper or roots reacts with potassium titanate to form a solid solution 7, and the catalyst is deactivated. Put it away. Furthermore, the collection surface of the filter is almost smooth, and the effect of coating with 5in2 is not apparent. Furthermore, in Comparative Example 3, the alumina coat 8 was smooth even after the heat treatment, and there were few chances of contact.

Furthermore, the coating amount of 5iOz is filter II! .

A particulate-collecting filter was manufactured in the same manner as in Example 1 except that the weight was 55 g per portion, and the above test was conducted, and the partition wall surface was observed by SEM. According to this, since the coated amount of SiOz particles was too large in this filter, the 5i02 particles entered the gaps between the potassium titanate fibers on the surface of the partition wall, and the collection surface became smooth. Therefore, it is thought that the opportunity for contact between the particulates and the catalyst decreases, leading to a decrease in regeneration performance.

(Effects of the Invention) The particulate collection filter of the present invention has a layer of overlapping potassium titanate fibers formed on the surface of the partition wall,
Since a 5iOz particle layer is formed on the surface of the potassium titanate fiber, and a copper plating layer and a silver plating layer are formed on the surface thereof, the surface area of the catalyst surface is increased, and there are many opportunities for contact between particulates and the catalyst. Improves reproducibility. Moreover, even when exposed to high temperatures of 1000'C or higher, as in diesel engine particulate collection filters, the potassium titanate fibers will not lose their shape or the catalyst will be deactivated. Excellent reproducibility can be maintained even during long-term use, and durability is improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the partition wall surface of a filter for particulate collection according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of section A in FIG. 1, and FIGS. FIG. 8 is an enlarged cross section showing a part of the partition wall surface of filters for particulate collection according to other examples and comparative examples. FIG. 9 is a sectional view showing a conventional particulate collection filter. 1.1'...Partition wall 2...Potassium titanate fiber 4...SiO2 particles 5...Copper plating layer 6...
Silver plating layer patent applicant: Toyota Motor Corporation, Toyota Central Research Institute, Ltd. Figure 1, Figure 8/15 Produced by Shun! O diagram

Claims (1)

[Claims] The particulate collection surface of the ceramic honeycomb filter was coated with potassium titanate fibers, a SiO_2 layer was formed on the surface of the potassium titanate fibers, and a copper plating layer and a silver plating layer were formed on the surface of the SiO_2 layer. A particulate collection filter characterized by: