JP2003265964A - Catalyst-supporting filter useful for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter for supporting a catalyst for cleaning an exhaust gas with which the lowering in the amount of the supported catalyst is prevented and thereby it becomes possible to realize high efficiency catalytic reaction for a long period of time. <P>SOLUTION: The filter for supporting the catalyst for cleaning the exhaust gas has a carrier 21 composed of a ceramic porous sintered compact as a constitution element. Ceramic particles 22 constituting the carrier 21 are each covered with a support material layer 23. A catalyst 25 is supported on each ceramic particle 22 through the support material layer 23. In the support material layer 23, ceramic fibers 27 having a fiber diameter of ≤1 μm and a fiber length of ≤20 μm are contained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a catalyst-carrying filter for purifying exhaust gas. More specifically, the present invention relates to a catalyst-carrying filter capable of removing carbon monoxide (CO), hydrocarbons (HC) and the like contained in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art The number of automobiles has increased dramatically,
In proportion to this, the amount of exhaust gas emitted from the internal combustion engine of automobiles is also rapidly increasing. In particular, various substances (C
O, HC, and NOx) cause pollution, and are now seriously affecting the world environment. Further, recently, research results have also been reported that particulates (PM: suspended particulate matter) contained in exhaust gas sometimes cause allergic disorders and decrease in sperm count. In other words, taking measures to remove harmful substances in the exhaust gas is considered to be an urgent task for humankind.

Under these circumstances, a catalyst-carrying filter provided with a carrier made of a porous ceramic sintered body has been conventionally proposed. This type of filter has a structure in which a catalyst made of a noble metal or an alkali metal is carried on a carrier made of a porous body of a sintered body represented by silicon carbide or cordierite. According to such a filter,
When the exhaust gas passes through the filter, CO and HC can be efficiently removed by oxidation, NOx by reduction and removal, and PM by removal.

By the way, it has been found that more catalyst can be supported on the carrier to improve the purifying ability of the filter, and more specifically, the specific surface area of the carrier can be increased. Therefore, in recent years, a technique has been proposed in which the catalyst is not directly supported on the surface of the ceramic particles constituting the carrier, but a support material layer for securing a specific surface area is formed on the surface of the particle, and the catalyst is supported therethrough. Has been done. In this case, as the support material layer, a ceramic oxide represented by γ-alumina or the like is suitable.

[0005]

However, since the ceramic material suitable for the carrier and the ceramic material suitable for the support material layer are usually different types, when the filter encounters a heat cycle, the difference in the coefficient of thermal expansion between the two causes a difference. The support material layer is easily cracked or peeled off. In such a case, there is a problem in that the amount of catalyst supported on the filter is substantially reduced and the efficiency of the catalytic reaction is reduced, so that the purifying ability of the filter is gradually deteriorated.

Further, if the carrier is made of a ceramic material having a coefficient of thermal expansion close to that of the support material layer, it is expected that the choice of the material will be narrowed and the manufacture of the carrier will be difficult.

The present invention has been made in view of the above problems, and an object thereof is to purify an exhaust gas capable of realizing an efficient catalytic reaction for a long period of time because a reduction of a catalyst carrying amount is prevented. Another object of the present invention is to provide a catalyst carrying filter.

[0008]

In order to solve the above-mentioned problems, in the invention described in claim 1, a support material layer for coating ceramic particles constituting a carrier made of a ceramic porous sintered body is formed. In the catalyst-carrying filter for purifying exhaust gas, wherein the catalyst is supported on the ceramic particles through the support material layer, the support material layer contains at least one of a ceramic fiber and a ceramic whisker. The subject matter is a catalyst-carrying filter for purifying exhaust gas.

According to the second aspect of the present invention, a support material layer covering the ceramic particles constituting the carrier made of the ceramic porous sintered body is formed, and the catalyst is supported on the ceramic particles via the support material layer. In the catalyst-carrying filter for purifying exhaust gas, the support material layer contains ceramic fibers and ceramic whiskers having a fiber diameter of 1 μm or less and a fiber length of 20 μm or less. The carrying filter is the gist.

According to a third aspect of the present invention, in the first or second aspect, the support material layer is made of a ceramic oxide. The invention according to claim 4 relates to claims 1 to 3.
In any one of the above items, the ceramic fiber,
The ceramic whiskers are made of a ceramic material having a catalytic function.

According to a fifth aspect of the present invention, in the second aspect, the support material layer is made of alumina, and the ceramic fiber is a ceramic fiber containing titanium oxide as a component.

According to a sixth aspect of the present invention, in the second aspect, the support material layer is made of alumina having a thickness of 1 μm or less, and the ceramic fiber has a fiber diameter of 0.05 μm.
It was assumed to be a potassium titanate fiber having a fiber length of m to 0.6 μm and a fiber length of 1 to 20 μm.

The "action" of the present invention will be described below. According to the invention of claim 1, since the support material layer is reinforced by the fibrous substance made of ceramic, even if there is a difference in thermal expansion coefficient between the carrier and the support material layer, the support material layer is Be able to withstand thermal stress. Therefore, the support material layer is less likely to be cracked or peeled off, and the reduction in the amount of catalyst supported is prevented, so that an efficient catalytic reaction can be realized for a long period of time.

In particular, according to the invention as defined in claim 2, even when the density of the support material layer is made low or the thickness thereof is made thin for the purpose of increasing the specific surface area, if the ceramic fibers are finer than usual, the support material layer is contained in the support material layer. It can be reliably captured. Further, as a result of the ceramic fibers being less likely to project from the surface of the support material layer, the occurrence of cracking or peeling starting from the fiber projecting portion is avoided. That is, when the fiber diameter is more than 1 μm or the fiber length is more than 20 μm, there is a possibility that a fiber protruding portion that causes cracking or peeling is formed.

According to the third aspect of the present invention, when the ceramic particles are coated with the support material layer made of ceramic oxide, the specific surface area of the carrier is substantially increased, so that more catalyst can be supported. .

According to the invention described in claim 4, the catalytic reaction also occurs on the surface of the ceramic fiber or the ceramic whisker, so that the efficiency of the catalytic reaction is improved. According to the invention described in claim 5, when the ceramic particles are coated with the support material layer made of alumina, the specific surface area of the carrier is substantially increased, so that more catalyst can be supported. In addition, the ceramic fiber containing titanium oxide as a component has a NOx reducing action, which leads to higher functionality and higher added value of the filter.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which a catalyst-carrying filter for purifying exhaust gas according to the present invention is embodied in an exhaust gas purifying apparatus 1 for a diesel engine will be described in detail below with reference to FIGS.

As shown in FIG. 1, the exhaust gas purification device 1 is a device for purifying exhaust gas emitted from a diesel engine 2 as an internal combustion engine. The diesel engine 2 includes a plurality of cylinders (not shown). Each cylinder has an exhaust manifold 3 made of a metal material.
The branching parts 4 are connected to each other. Each branch 4 is 1
Each of them is connected to the main body 5 of the book. Therefore, the exhaust gas discharged from each cylinder is concentrated in one place.

On the downstream side of the exhaust manifold 3, a first exhaust pipe 6 and a second exhaust pipe 7 made of a metal material are arranged. The upstream end of the first exhaust pipe 6 is connected to the manifold body 5
Are linked to. Between the first exhaust pipe 6 and the second exhaust pipe 7, a tubular casing 8 also made of a metal material is arranged. The upstream end of the casing 8 is the first exhaust pipe 6
Is connected to the downstream side end of the casing 8 and the downstream side end of the casing 8 is the second
It is connected to the upstream end of the exhaust pipe 7. It can also be understood that the casing 8 is arranged along the exhaust pipes 6 and 7. As a result, the internal regions of the first exhaust pipe 6, the casing 8 and the second exhaust pipe 7 communicate with each other, and the exhaust gas flows therein.

As shown in FIG. 1, the casing 8 is formed so that its central portion has a larger diameter than the exhaust pipes 6, 7. Therefore, the inner region of the casing 8 is wider than the inner regions of the exhaust pipes 6 and 7. A DPF (diesel particulate filter) 9 is housed in the casing 8 as a catalyst-carrying filter.

A heat insulating material 10 is disposed between the outer peripheral surface of the DPF 9 and the inner peripheral surface of the casing 8. Insulation 10
Is a mat-like material formed containing ceramic fibers, and has a thickness of several mm to several tens of mm. Insulation 1
It is preferable that 0 has thermal expansion property. The term “thermally expandable” as used herein means that it has a function of releasing thermal stress because it has an elastic structure. The reason for this is to prevent heat from escaping from the outermost peripheral portion of the DPF 9 to minimize energy loss during regeneration. Further, since it has an elastic structure, it is possible to prevent the displacement of the DPF 9 caused by the pressure of the exhaust gas, the vibration due to traveling, and the like.

As shown in FIGS. 2 and 3, the DPF 9 of this embodiment is formed by bundling and integrating a plurality of honeycomb filters F1. The honeycomb filter F1 located in the central portion of the DPF 9 has a quadrangular prism shape, and a plurality of atypical honeycomb filters F1 that are not quadrangular prism shapes are arranged around the honeycomb filter F1. As a result, a cylindrical DPF 9 (diameter of about 135 mm) is formed as a whole. The outer peripheral surfaces of the honeycomb filter F1 forming the DPF 9 are adhered to each other via the ceramic sealing material layer 15.

The carrier 21 constituting these honeycomb filters F1 is made of a ceramic porous sintered body, and specific examples thereof include porous sintering of silicon carbide, silicon nitride, sialon, alumina, zirconia, cordierite, mullite and the like. It consists of the body etc. In this case, as the ceramic porous sintered body, a non-oxide type ceramic porous sintered body containing silicon carbide as a main component is preferably selected. The reason is that such a ceramic porous sintered body is superior in heat resistance and thermal conductivity as compared with other ceramic porous sintered bodies. The phrase “mainly containing silicon carbide” means that the composition contains 50% or more by weight of silicon carbide.

As shown in FIG. 3 etc., these filters F1 are so-called honeycomb structures. The reason why the honeycomb structure is adopted is that there is an advantage that the pressure loss is maintained at a small value even when the amount of trapped PM is increased. In each filter F1, a plurality of through holes 12 each having a substantially square cross section are regularly formed along the axial direction. Each through hole 12 is separated from each other by a thin cell wall 13.

The opening of each through hole 12 is sealed by a sealing body 14 (here, a porous silicon carbide sintered body) on the side of either one of the end faces 9a, 9b. Therefore, the end faces 9a and 9b as a whole have a checkered pattern. As a result, the filter F1 is formed with a large number of cells having a rectangular cross section. Cell density is 200 cells /
The thickness of the cell wall 13 is set to about 0.3 square inch and is 0.3.
The cell pitch is set to about 1.8 mm and the cell pitch is set to about 1.8 mm. Of the many cells, about half are open on the upstream end surface 9a, and the remaining cells are open on the downstream end surface 9b.

As shown in FIG. 4, the surface of the ceramic particles 22 constituting the carrier 21 is covered with a support material layer 23 made of a ceramic oxide. By covering the ceramic particles 22 with the support material layer 23 made of a ceramic oxide, the specific surface area of the carrier 21 is substantially increased, so that more catalyst can be supported. The ceramic oxide suitable for the support material layer 23 supporting the catalyst 25 includes at least one selected from alumina, zirconia, titania and silica. Of these, alumina is particularly preferable. The reason is that, in general, alumina has a high specific surface area and is suitable as a thin film for supporting the catalyst 25. Moreover, since alumina has excellent heat resistance, it is suitable for the DPF 9 for the exhaust gas purifying apparatus.

The support material layer 23 in this embodiment is
The surface of the carrier 21 itself is not uniformly coated, but the surface of the individual ceramic particles 22 that substantially constitute the carrier 21 is coated. Therefore, the voids (that is, pores) between the ceramic particles 22 are not plugged, and suitable air permeability of the DPF 9 is ensured. That is, the DPF 9 is unlikely to have a large pressure loss.

The alumina needle crystals forming the support material layer 23 are made of at least one of γ-Al ₂ O ₃ , δ-Al ₂ O ₃ and θ-Al ₂ O ₃ . The diameter of the acicular alumina crystal is about 2 nm to 50 nm, and the total length is 20 nm.
˜300 nm, and the ratio of total length / diameter is preferably 5 to 50.

If the diameter of the crystal is less than 2 nm, it is preferable from the viewpoint of increasing the specific surface area, but on the other hand, the crystal becomes brittle and easily broken, and the catalyst 25 and the like cannot be physically supported. On the contrary, when the diameter of the crystal is larger than 50 nm, it becomes difficult to secure a specific surface area having a preferable size. Further, if the total length of the crystals is less than 20 nm, it becomes difficult to secure a specific surface area having a preferable size, and it becomes difficult to support the catalyst 25 and the like. Conversely, if the total length of the crystal exceeds 300 nm, it is preferable from the viewpoint of increasing the specific surface area, but on the other hand, the crystal becomes brittle and easily broken,
The catalyst 25 and the like cannot be physically supported.

The thickness of the support material layer 23 is 1 μm or less, preferably 0.1 μm to 0.5 μm. The reason is that when the support material layer 23 is thicker than 1 μm, fine pores are easily filled, and the specific surface area cannot be sufficiently increased. Here, the “thickness of the support material layer 23” refers to the average value of the distance from the surface of the carrier 21 to the farthest part of the acicular alumina crystals.

A catalyst 25 is held in the support material layer 23 as conceptually shown by a black circle in FIG. That is, the catalyst 25 is supported on the ceramic particles 22 through the support material layer 23. In addition,
The catalyst 25 is preferably dispersed uniformly in the support material layer 23.

Suitable catalysts 25 include alkali metal type, alkaline earth metal type, catalyst and noble metal type catalysts. Specifically, as the alkali metal catalyst, it is preferable to use a simple substance or a compound (binary alloy or ternary alloy) such as lithium (Li), sodium (Na), and potassium (K). As the alkaline earth metal-based catalyst, it is preferable to use a simple substance or a compound (binary alloy or ternary alloy) such as barium (Ba), magnesium (Mg), or calcium (Ca). As the noble metal-based catalyst, a rhodium (Rh), platinum (Pt), palladium (Pd), gold (Au), silver (Ag), copper (Cu), or other simple substance or compound (binary alloy or ternary alloy) Alloy, etc.) is preferably used. In the present embodiment, two kinds of lithium, which belongs to the alkali metal catalyst and platinum which belongs to the noble metal catalyst, are used as the catalyst 25.

As conceptually shown by an open triangle in FIG. 5, the support material layer 23 preferably holds a co-catalyst 26 in addition to the catalyst 25. A rare earth metal-based cocatalyst is suitable as the cocatalyst 26. Specific examples thereof include rare earth metal simple substances such as cerium (Ce) and lanthanum (La), or ceria (CeO).
₂ ) and rare earth oxides such as lantana (La ₂ O ₃ ). In this embodiment, ceria is used as the co-catalyst 26.

The reason is that ceria has an oxygen concentration adjusting action, so that the supply of oxygen into the exhaust gas becomes active and the PM combustion removal efficiency is improved. Also,
This is because the presence of ceria improves the heat resistance of alumina and thus the durability of the support material layer 23.

As conceptually shown in FIG. 5, the support material layer 23 includes ceramic fibers 27. In this case, it is desirable that the ceramic fibers 27 that are considerably finer than the ceramic fibers that are usually used are included. The reason is that the support material layer 23
Even if it is a thin layer, such a fine ceramic fiber 27 can be surely taken into the support material layer 23. The ceramic fiber 27 used in this embodiment is preferably a ceramic fiber made of a single crystal. This is because the fiber of single crystal has a higher strength of the fiber itself than that of other fibers such as polycrystal, and therefore, the higher reinforcing effect can be obtained by using the fiber.

As an example of the ceramic fiber 27,
Examples include ceramic fibers containing a silicon compound (silica or the like) as a component, ceramic fibers containing an aluminum compound (alumina or the like) as a component, and the like.
In addition, examples of the ceramic fiber 27 include a ceramic fiber containing a titanium compound (titania or the like) as a component, a ceramic fiber containing a zirconium compound (zirconia or the like) as a component, or the like. Of course, these ceramic fibers may be used alone or in combination of two or more.

Here, the ceramic fiber 27 is preferably made of a ceramic material having a catalytic function,
Suitable examples thereof include ceramic fibers containing titanium oxide (such as titanate) as a component. This is because this type of ceramic fiber has a catalytic action of reducing NOx. In the present embodiment, specifically, potassium titanate (K ₂ O.nTiO ₂ , n =
6 or 8) Fiber is used.

Here, the "fine ceramic fibers 27" means that the fiber diameter is 1 μm or less and the fiber length is 20 μm.
Refers to the following: Fiber diameter is over 1 μm or fiber length is 2
This is because if the thickness is more than 0 μm and the support material layer 23 is a thin layer having a thickness of 1 μm or less, there is a possibility that a fiber protruding portion that causes cracking or peeling is formed. That is, it is desirable that the ceramic fibers 27 have a thickness similar to or smaller than that of the support material layer 23. In such a case, as a result of increasing the proportion of the portion that sunk into the inside of the support material layer 23, the proportion of the protruding portion decreases,
This is because the ceramic fiber 27 is reliably held. The "fiber diameter" refers to a value (average value) obtained by observing the fiber with a microscope and measuring its diameter.
The "fiber length" refers to a value (average value) when the fiber is observed by a microscope and its length is measured.

In particular, when potassium titanate fiber is selected as the ceramic fiber 27, the fiber diameter is 0.
05 μm to 0.6 μm, fiber length is 1 μm
It is preferably m to 20 μm. Within the above range,
This is because there are no particular problems such as a decrease in the strength of the fiber itself and a difficulty in manufacturing. In addition, such a very fine potassium titanate fiber also has a large specific surface area and can exhibit a suitable NOx reduction action.

When the fiber diameter is less than 0.05 μm, the strength of the fiber itself becomes low, so that the support material layer 23 cannot be sufficiently reinforced, and it becomes difficult to manufacture the fiber in the first place. If the fiber length is less than 1 μm, the support material layer 23 cannot be sufficiently reinforced, and it becomes difficult to manufacture the fiber in the first place. Fiber length is 20 μm
When it exceeds, if the support material layer 23 is a thin layer, a fiber protruding portion may occur.

The amount of the ceramic fibers 27 in the support material layer 23, particularly when potassium titanate fibers are selected, is preferably 3% by weight to 60% by weight. If the amount of fibers is too small, the support material layer 23 may not be sufficiently reinforced. On the contrary, when the amount of fibers is too large, the other constituent elements in the support material layer 23 are relatively small. Therefore, basic properties of the support material layer 23 such as adhesion to the ceramic particles 22 may be impaired.

It is desirable that the ceramic fibers 27 contained in the support material layer 23 have the characteristics of high rigidity, high strength and high aspect ratio. The reason is that the support material layer 23 can be reliably reinforced by using the ceramic fiber 27 having the above properties. In view of this point, in the present embodiment, the potassium titanate fiber having the properties of high rigidity, high strength, and high aspect ratio is used. Specifically, a potassium titanate fiber having a Mohs hardness of 3 or more, a melting point of 1000 ° C. or more, a tensile strength of 5 GPa or more and a tensile elastic modulus of 200 GPa or more is used.

The average pore diameter of the carrier 21 with the support material layer 23 formed thereon is preferably 10 μm to 60 μm. If the average pore diameter is less than 10 μm, P
The honeycomb filter F1 may be significantly clogged due to the accumulation of M, and the pressure loss may increase rapidly. On the other hand, if the average pore diameter exceeds 60 μm, fine PM cannot be collected, and the collection efficiency will decrease.

The porosity of the carrier 21 with the support material layer 23 formed thereon is preferably 40% to 80%. If the porosity is less than 40%, the honeycomb filter F1 may become too dense, and exhaust gas may not be able to flow inside. On the other hand, when the porosity exceeds 80%, the honeycomb filter F1 has too many voids, resulting in weak strength and PM.
There is a possibility that the collection efficiency of will decrease.

A procedure for manufacturing the above DPF 9 will be briefly described. First, a carrier 21 made of a ceramic porous sintered body is manufactured according to a conventionally known method. First, a honeycomb structure is extruded from a slurry containing a ceramic raw material such as silicon carbide, and then the end face of the honeycomb structure is sealed in a checkered pattern using a ceramic paste.
Next, degreasing, preliminary firing, and main firing are performed to completely sinter the honeycomb structure and the sealing body 14. Next, a ceramic sealing material is applied to the outer peripheral surface of the obtained honeycomb filter F1, and the honeycomb filters F1 are bonded to each other via the sealing material. After this, cut the outer shape if necessary,
The carrier 21 has a circular cross section or an elliptical cross section.

Subsequently, the following steps are carried out in order: a) pretreatment step, b) solution impregnation step, c) drying step, d) temporary calcination step, e) hot water treatment step, and f) main calcination step. ,
The support material layer 23 is formed on the carrier 21.

In the pretreatment process, 800 ° C to 1600 ° C
Is heated for 5 to 100 hours to oxidize the surface of the ceramic particles 22. This treatment is performed for the purpose of providing the surface of each ceramic particle 22 with an amount of Si necessary to promote chemical bonding with alumina. Of course, if there is a sufficient oxide film on the surface of the ceramic particles 22, this step may be omitted.

In the solution impregnation step, the support material layer 23 is formed on the surface of the carrier 21 by the sol-gel method. When forming the support material layer 23 made of alumina, specifically, the carrier 21 is impregnated with a mixed aqueous solution of aluminum nitrate and cerium nitrate. By this impregnation treatment, the surface of each ceramic particle 22 is covered with the alumina thin film. At this time, in the present embodiment, a predetermined amount of the ceramic fibers 27 is uniformly dispersed in the mixed aqueous solution.

In the drying step, the solution is gelled and fixed on the surface of each ceramic particle 22 by evaporating and removing volatile components such as NO ₂ . At the same time, excess solution is removed. Specifically, the carrier 21 is set to 120
The heating is performed at ℃ to 170 ℃ for about 2 hours.

In the pre-baking step, the residual components are removed to make the alumina thin film amorphous. Specifically, the carrier 21 is heated to a temperature of 300 ° C to 500 ° C. In the hot water treatment step, in order to roughen the alumina thin film in the amorphous state, the temporarily fired carrier 21 is immersed in hot water. Immediately after such hot water treatment, the particles on the surface of the amorphous alumina thin film are subjected to peptization and released into the solution in a sol state. In other words, this hot water treatment forms the support material layer 23 having a flocked structure in which small fiber crystals are forested, in other words, the support material layer 23 having a high specific surface area. The temperature of hot water treatment is 20 ℃
A temperature of ~ 50 ° C is desirable.

In the main calcination step, boehmite produced by hydration is subjected to a treatment for film crystallization and alumina crystallization. Specifically, the carrier 21 is heated to a temperature of 500 ° C to 1000 ° C.

Support material layer 2 thus formed
After forming 3, the catalyst 25 and the co-catalyst 2 are formed by the following method.
6 is carried. For example, when Pt is used as the catalyst 25, a dinitrodiammine platinum nitric acid solution is prepared as a starting material. Next, this catalyst-containing solution was dropped onto both end faces of the carrier 21 with a pipette, and the surface of the carrier 21 began to get even slightly wet (incipient: I).
The dripping is stopped at the time when it becomes ncipient). Next, the carrier 21 is dried under the condition of 110 ° C. for about 2 hours, then transferred into a desiccator and left to stand. Next, the Pt is metallized by firing in a nitrogen atmosphere under the condition of about 500 ° C. for about 1 hour. In addition, when the catalyst 25 other than Pt is desired to be supported or the co-catalyst 26 is desired to be supported, basically the same procedure as described above may be adopted. The method of fixing the catalyst 25 and the like to the support material layer 23 is not limited to the above-mentioned incipient wetness method, and an impregnation method, an evaporation-drying method, an equilibrium adsorption method, a spray method or the like can be adopted.

[0053]

Examples and Comparative Examples (Production of Examples) 51.5% by weight of α-type silicon carbide powder and 22% by weight of β-type silicon carbide powder were wet mixed, and the resulting mixture was mixed with an organic binder (methyl cellulose) and water. And 6.5 wt% and 20 wt% respectively were added and kneaded. Next, a small amount of a plasticizer and a lubricant was added to the kneaded product, and the kneaded product was further kneaded to obtain a honeycomb green molded body. After drying the green molded body, the through holes 12 of the molded body were sealed with a sealing paste made of a porous silicon carbide sintered body. Subsequently, after degreasing the dried molded body at 400 ° C., it is further calcined in an argon atmosphere at a normal pressure, and then at 3200 at about 2200 ° C.
It was fired for an hour. As a result, a rectangular columnar porous silicon carbide sintered body honeycomb filter F1 (33 mm × 33 mm ×
167 mm) was obtained. Then, the sealing material layer paste was uniformly applied to the outer peripheral surface of the honeycomb filter F1 to bring the outer peripheral surfaces into close contact with each other. In this state, the ceramic sealing material layer 15 was dried by drying at 100 ° C. for 1 hour to integrate the honeycomb filters F1. Next, an outer shape cutting step was performed to adjust the shape, and then the outer peripheral coat layer 16 was formed, if necessary, to obtain a carrier 21 having a circular cross-section including 16 honeycomb filters F1 in total.

Next, the support material layer 23 made of needle crystals of alumina having a thickness of 0.5 μm is formed on the carrier 2 by the method described above.
Formed to 1. After that, the catalyst 2 is applied to the carrier 21 through the support material layer 23 by the incipient wetness method.
5 and the co-catalyst 26 were carried, and finally DPF9 was completed. In this example, 10% by weight of single crystal potassium titanate (K ₂ O · 8TiO ₂ ) fibers were dispersed in the support material layer 23. The potassium titanate fiber used here has a Mohs hardness of 4 and a melting point of 1300 ° C. to 1
350 ° C, tensile strength 7GPa, tensile modulus 280G
It was Pa. Here, the fiber diameter of the potassium titanate fiber was set to about 0.05 μm to 0.2 μm, and the fiber length was set to about 1 μm to 5 μm. Further, Pt as the noble metal catalyst 25, lithium as the alkali metal catalyst, and ceria as the co-catalyst 26 were respectively supported. (Comparative Example) In a comparative example, a DPF 9 having the same overall shape was produced in the same manner as in the above-described example except that the ceramic fiber 27 was not added to the support material layer 23 at all. (Test Method) The exhaust gas purifying apparatus 1 was actually configured using the DPF 9 of the examples and comparative examples, and these were installed on the way of the exhaust pipes 6 and 7 of the diesel engine 2. Then, the diesel engine 2 was driven to pass exhaust gas through the DPF 9 for a certain period of time, and then the soot accumulated inside was burned and removed by heating with a heater to regenerate the DPF 9. Then, such a regeneration process was performed three times, and the regeneration rate was investigated every time the regeneration was completed. Here, the "regeneration rate" is defined as the amount of soot removed from the DPF 9 by regeneration (C amount) / the amount of soot accumulated on the DPF 9 before regeneration (C amount) x 100
(%), And is defined.

As a result, the reproduction rates of the first, second and third times were almost constant at 45%, 44% and 44% in the examples, whereas they were 45% in the comparative examples. 40%,
It dropped to 25%. That is, in the example, the preferable purifying ability was maintained, and in the comparative example, the initially preferable purifying ability was gradually deteriorated.

Further, when the time required to reach the maximum temperature at the time of regeneration was measured at the same time, it was found that the working example tended to be shorter than the comparative example. Furthermore, the amount of THC (total hydrocarbons) before and after the DPF 9 was measured by a conventionally known method using the DPF 9 that has been subjected to the regeneration treatment three times.
The amount of CO and the amount of NOx were measured by an exhaust gas analyzer, and the purification rate with respect to temperature was obtained. As a result, it was recognized that the purification temperature of the example was lower by several tens of degrees Celsius than that of the comparative example. That is, in the embodiment, CO, H in the exhaust gas
It was demonstrated that the purifying ability of C and NOx was maintained.

Further, each of the DPFs 9 was taken out from the exhaust gas purifying apparatus 1, and the state of occurrence of cracks or peeling in the support material layer 23 was examined by microscopic observation.
As a result, in the examples, almost no cracking or peeling occurred, whereas in the comparative example, some places where cracking or peeling occurred. In other words, in the comparative DPF 9, a substantial reduction in the amount of catalyst carried occurs, while in the D of the embodiment
It was confirmed that it hardly occurred in PF9.

Therefore, according to this embodiment, the following effects can be obtained. (1) In the case of this DPF 9, the support material layer 23 is reliably reinforced by the fine single crystal ceramic fibers 27 contained in the support material layer 23. Therefore, the carrier 2
Even if there is a difference in thermal expansion coefficient between 1 and the support material layer 23, the support material layer 23 can withstand the thermal stress. Therefore, the support material layer 23 is less likely to be cracked or peeled off, and a reduction in the amount of catalyst supported can be prevented. Therefore, it is possible to provide the DPF 9 that can realize an efficient catalytic reaction for a long period of time.

(2) In the case of this DPF 9, the support material layer 23 is made of alumina needle crystals having a thickness of 1 μm or less.
Then, by coating the ceramic particles 22 with such a support material layer 23, the specific surface area of the carrier 21 can be substantially increased. Therefore, a larger amount of the catalyst 25 and the co-catalyst 26 can be supported, and the DPF 9 having excellent purification performance can be realized.

Further, a support formed of an alumina needle crystal thin film is used.
In the case of the coating material layer 23, sulfur oxide contained in the exhaust gas
(SO₂) Is oxidized and it reacts with water vapor to form sulfuric acid
(H₂SO _Four), The sulfuric acid becomes the support material layer 23.
Easy to leave. This means that the durability of DPF9 is improved.
Contribute to.

(3) In this DPF 9, the support material layer 2
As the ceramic fiber 27 included in No. 3, the fiber diameter is 0.05 μm to 0.6 μm and the fiber length is 1 μm to 20.
μm potassium titanate fiber is used.
Since the potassium titanate fiber has a function as a catalyst for reducing NOx, by including this in the support material layer 23 made of alumina, it is possible to make the DPF 9 highly functional and add value.

(4) In the case of this DPF 9, the rare earth metal type co-catalyst 26 is carried on each ceramic particle 22 constituting the carrier 21 via the support material layer 23. This kind of co-catalyst 26 has a function of adjusting the oxygen concentration in the exhaust gas. Therefore, compared with the case where the catalyst 25 is used alone, the supply of oxygen into the exhaust gas becomes active. Therefore,
The PM trapped in the DPF 9 can be burned and removed with high efficiency.

The embodiment of the present invention may be modified as follows. -A ceramic whisker is used instead of the ceramic fiber 27 as in the embodiment, and this is used as the support material layer 23.
It may be included in. "Ceramic whisker" is a name given because it resembles a beard of a cat, and refers to a fibrous single crystal with a diameter of micron order. Ceramic whiskers include oxides, nitrides,
There are silicides, carbides, borides, etc. Note that both the ceramic whiskers and the ceramic fibers may be included in the support material layer 23.

The carrier 21 is not limited to one in which a plurality of honeycomb filters F1 are adhered and integrated. -When it is not necessary to remove PM, the through hole 1
It is also possible to omit the sealing body 14 that has sealed one end side of 2 and have a structure in which exhaust gas can freely flow from one side of the same through hole 12 to the other side.

Carrier 2 composed of a ceramic porous sintered body
1 is not necessarily a honeycomb structure, and may be, for example, a foam-like structure (for example, ceramic foam).

In the above embodiment, the catalyst-carrying filter of the present invention is embodied in the DPF 9 used for purifying the exhaust gas of the diesel engine 2. In addition to such applications, the catalyst-carrying filter of the present invention may be embodied as a filter used for purification of exhaust gas discharged from an engine driven by gasoline or alcohol fuel, for example.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiment will be listed below. (1) In any one of claims 1 to 6, a co-catalyst is supported on the ceramic particles through the support material layer. Therefore, according to the invention described in this technical idea 1, the PM can be improved as compared with the case where only the catalyst is used.
Can be removed by burning with high efficiency.

(2) In any one of claims 1 to 6, the carrier is a honeycomb structure having a plurality of through holes defined by cell walls. (3) In any one of claims 1 to 6, both ends of the carrier are alternately plugged in a checkered pattern by a sealing body.

(4) For purification of exhaust gas, in which a support material layer covering ceramic particles constituting a carrier made of a ceramic porous sintered body is formed, and a catalyst is supported on the ceramic particles through the support material layer 2. The catalyst-carrying filter for purifying exhaust gas, wherein the support material layer contains a single crystal fine fibrous substance made of ceramic.

[0070]

As described in detail above, according to the first aspect of the present invention, since the reduction of the amount of catalyst supported is prevented, the exhaust gas purification capable of realizing an efficient catalytic reaction for a long period of time is achieved. A catalyst-carrying filter can be provided.

According to the second aspect of the invention, since the strength of the support material layer is further enhanced, it is possible to reliably prevent a decrease in the amount of catalyst supported. Claims 3, 4,
According to the inventions described in 5 and 6, it is possible to provide a catalyst-carrying filter for purifying exhaust gas, which is excellent in the purifying ability of the filter.

According to the fifth and sixth aspects of the present invention, it is possible to enhance the function and the added value of the filter.

[Brief description of drawings]

FIG. 1 is an overall schematic view of an exhaust gas purifying apparatus according to an embodiment of the present invention.

FIG. 2 is a front view of the DPF according to the embodiment.

FIG. 3 is an enlarged cross-sectional view of a main part of the DPF.

FIG. 4 is a conceptual diagram showing an enlarged view of ceramic particles and a support material layer forming the same DPF.

FIG. 5 is a conceptual diagram showing the support material layer of FIG. 4 in a further enlarged manner.

[Explanation of symbols]

9 ... DP as catalyst-carrying filter for purifying exhaust gas
F, 21 ... Carrier, 22 ... Ceramic particles, 23 ... Support material layer, 25 ... Catalyst, 27 ... Ceramic fiber.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/02 B01D 53/36 104A 104B F term (reference) 3G090 AA03 4D019 AA01 BA05 BB06 BC07 CA01 DA01 DA03 4D048 AA06 AA13 AA14 AA18 AB01 AB05 BA03X BA06X BA07X BA10X BA14X BA18X BA19X BA30X BA31Y BA33Y BA34Y BA35Y BA41X BA42X BA45X BB02 BB14 CC38 4G069 AA03 AA08 BA01A BA01B BA02A BA04A BA05A BA13A BA13B BB02A BB02B BB06A BB06B BB11A BB15A BB15B BC01A BC02A BC03A BC03B BC04A BC08A BC09A BC10A BC13A BC31A BC33A BC38A BC38B BC42A BC43A BC50A BC50B BC69A BC71A BC72A BC75A BC75B BD05A BD05B CA02 CA03 CA07 CA09 CA18 EA19 EA27 EB14Y EB15X EB15Y ED06 EE01 FA03 FB15 FB23

Claims (6)

[Claims] 1. A support material layer for coating ceramic particles constituting a carrier made of a ceramic porous sintered body is formed, and a catalyst is supported on the ceramic particles through the support material layer for purification of exhaust gas. A catalyst-carrying filter for purifying exhaust gas, wherein the support material layer contains at least one of a ceramic fiber and a ceramic whisker. 2. An exhaust gas purifying system, wherein a support material layer covering ceramic particles constituting a carrier made of a ceramic porous sintered body is formed, and a catalyst is supported on the ceramic particles via the support material layer. In the catalyst-carrying filter, the support material layer contains a ceramic fiber and a ceramic whisker having a fiber diameter of 1 μm or less and a fiber length of 20 μm or less, and a catalyst-carrying filter for purifying exhaust gas. 3. The catalyst-carrying filter for purifying exhaust gas according to claim 1, wherein the support material layer is made of a ceramic oxide. 4. The catalyst-carrying filter for purifying exhaust gas according to claim 1, wherein the ceramic fibers and the ceramic whiskers are made of a ceramic material having a catalytic function. 5. The catalyst-carrying filter for purifying exhaust gas according to claim 2, wherein the support material layer is made of alumina, and the ceramic fiber is a ceramic fiber containing titanium oxide as a component. 6. The support material layer is made of alumina having a thickness of 1 μm or less, and the ceramic fiber has a fiber diameter of 0.05 μm to 0.6 μm and a fiber length of 1 μm to 20 μm.
The catalyst-carrying filter for purifying exhaust gas according to claim 2, wherein the filter is a potassium titanate fiber of m.