WO2006028322A1

WO2006028322A1 - Apparatus for purifying diesel exhaust gas with coated photocatalyst layer and electrode, and manufacturing method thereof

Info

Publication number: WO2006028322A1
Application number: PCT/KR2005/000296
Authority: WO
Inventors: Geon Seog Son
Original assignee: Neophotech, Inc.
Priority date: 2004-09-07
Filing date: 2005-02-01
Publication date: 2006-03-16
Also published as: JP4225428B2; US20060051264A1; US20060051273A1; KR100603008B1; US7596943B2; US7607294B2; KR20060022453A; EP1786542A1; EP1786542A4; JP2006528063A

Abstract

The present invention relates to an apparatus for purifying diesel exhaust gas with a coated inner photocatalyst layer and integral electrodes, and a manufacturing method thereof. The present invention provides an apparatus for purifying diesel exhaust gas with a coated inner photocatalyst layer and integral electrodes, and a manufacturing method thereof, wherein in an apparatus for purifying diesel exhaust gas, including a filter for filtering the diesel exhaust gas and an electrode device for regenerating captured particulate matters and a manufacturing method thereof, an inner surface of a porous ceramic honeycomb monolith carrier is coated with a photocatalyst, opposite ends of respective unit cells of the porous ceramic honeycomb monolith carrier with the inner surface coated with the photocatalyst are alternately blocked by means of plugging conductive metal, both end surfaces of the porous ceramic honeycomb monolith carrier plugged by the conductive metal are coated with conductive metal, the porous ceramic honeycomb monolith carrier is subjected to heat-treatment, and the heat-treated porous ceramic honeycomb monolith carrier is contained in a case formed with a power supply terminal.

Description

APPARATUS FOR PURIFYING DIESEL EXHAUST GAS WITH COATED PHOTOCATALYST LAYER AND ELECTRODE, AND MANUFACTURING

METHOD THEREOF

Technical field

The present invention relates to an apparatus for purifying diesel exhaust gas with a coated inner photocatalyst layer and integral electrodes, and a manufacturing method thereof. More particularly, the present invention relates to an apparatus for purifying diesel exhaust gas with a coated photocatalyst layer and integral electrodes, and a manufacturing method thereof, wherein openings of unit cells at both end surfaces of a honeycomb monolith carrier coated with a photocatalyst, are plugged by conductive metal and then coated further with the conductive metal so that the carrier can be used as a filter of a converter to capture particulate matters existing in exhaust gas flowing along porous walls. The captured particulate matters is removed through oxidation by applying a high voltage to the both end surfaces and the conductive metal plugged at one ends of the unit cells to generate cold plasma and thereby exciting the photocatalyst coated on wall surfaces of the unit cells using ultraviolet rays present in the generated cold plasma.

Background Art

Generally, conventional exhaust gas post-processing systems for diesel engines are roughly comprised of a diesel oxidation catalyst (DOC), a diesel particulate matter filter (DPF), and a NOx converter. As for DOC described above, only an oxidation function of existing three-way catalysts is enhanced and poison resistance is increased. Since the DOC is technically reasonable, it has been mounted on diesel vehicles. However, the DOC has disadvantages in that in case of fuel with a great deal of sulfur as a component thereof, a large amount of particulate matters with sizes of 100 nm or less, which are harmful to human respiratory organs, are discharged at a rear end of the DOC, and the catalyst is poisoned by the sulfur component, resulting in degraded durability.

Table 1 below shows techniques studied currently in foreign countries as those for processing particulate matters that are the subject to be solved by the present invention and one of critical problems with exhaust gas of a diesel vehicle.

Table 1

Techniques for processing particulate matters contained in exhaust gas of diesel engine

As shown in Table 1 , CRT (Continuously Regenerating Trap or Technologies) developed by Johnson-Matthey PIc. and DPX (Diesel Particulate Filter) developed by

Engelhard Corporation comprise a suction part, a catalyst part, a filtering part and an exhaust part. In theses apparatuses, the filtering unit is DPF 101 employing a ceramic honeycomb monolith filter, and a diesel oxidation catalyst (DOC) 102 that is the catalyst part using noble metal is placed in front of the DPF 101 for capturing particulate matters contained in diesel exhaust gas flowing thereinto so as to react abundant oxygen and nitrogen oxides existing in the exhaust gas with each other, thereby producing nitrogen dioxide with superior oxidizing power, and oxidizing and removing the particulate matters captured by the DPF 101.

As for the principle that such type of DPF 101 captures the particulate matters, as shown in Fig. 2, exhaust gas flows into the DPF 101 through unit cells 103 with open upstream ends at an inlet of the filter, and downstream ends of the unit cells 103 with the open upstream ends are blocked by plugging 104 made of the same material as the filter, so that gaseous components of the exhaust gas pass through porous walls 105 into adjacent unit cells 106 with closed upstream ends and particulate matters which are solid components cannot pass through pores in the walls and thus are captured. Meanwhile, if nitrogen dioxide (NO₂) is sufficiently generated in the exhaust gas,

CRT would have superior removal performance for the particulate matters 107. However, the generation of nitrogen dioxide is very sensitive to the temperature of the exhaust gas. That is, if the temperature of the exhaust gas is low, a noble metal catalyst cannot be activated and thus nitric monoxide(NO) is not caused to react with oxygen, resulting in rapid reduction in a generation rate of nitrogen dioxide. Further, there is a disadvantage in that the noble metal catalyst is poisoned by sulfur component existing in diesel exhaust gas, resulting rapid degradation in its performance.

Moreover, as shown in Fig. 3, there has been developed a method of regenerating the DPF 101 through oxidation of nitric monoxide into nitrogen dioxide regardless of the temperature of exhaust gas and sulfur component by installing a plasma generator 1 11 in front of the DPF 101 to use strong oxidizing power of plasma, based on the same regeneration concept as described above. However, there are disadvantages as follows. Since such a method employing only plasma as a regeneration means requires a large amount of electric power to generate plasma, the method cannot be used in view of the capacity of a current battery 112. An inverter 113 for generation of plasma is expensive and has a large size.

In addition, as shown in Fig. 4, SiC-DPF developed by Ibiden Co., Ltd. is manufactured by changing cordierite ceramic used as the material of a conventional DPF into silicone carbide with superior mechanical strength, and is improved in that intermediate layers can be coated through increase in the porosity of walls of unit cells of the filter.

Therefore, there is a method of forcibly burning captured particulate matters using a heating means 121 such as a hot wire positioned in front of the DPF 101. However, this method has a problem in that since electric power consumption is very high in raising the temperature of exhaust gas containing a large amount of moisture up to 35O⁰C or higher that is a forcible combustion temperature for particulate matters, it is difficult to commercially implement the method using current batteries for diesel vehicles.

In addition to the aforementioned techniques for purifying diesel exhaust gas, ^■ there has been developed a method of adding an additive to fuel, wherein Ce or Fe is added as a catalyst to the fuel on the order of ppm. This method has advantages in that the metal catalyst contained in the fuel lowers the regeneration temperature of the DPF upon regeneration of the DPF and shortens a regeneration period of time. However, this method has disadvantages in that since the catalyst is metal, it increases back pressure of the DPF in cooperation with ash of engine oil and shortens the period of exchange of the DPF.

Meanwhile, as shown in Fig. 5, there is a system for purifying exhaust gas using a photoreaction, which has been developed as an apparatus for removing harmful substances contained in exhaust gas of an internal combustion engine but does not reside in techniques for removing particulate matters contained in diesel exhaust gas as described above. This system has an advantage in that it can be operated with low electric power regardless of the temperature, air-fuel ratio and sulfur component of exhaust gas.

That is, in the aforementioned system contrary to the DPF for removing particulate matters contained in exhaust gas, a honeycomb monolith carrier 30 including unit cells 34 each of which is open at both ends thereof is coated with a photocatalyst and high voltage is applied to the both ends using electrodes 40 formed of metal nets or plates so that plasma can be generated within the unit cells 34 of the honeycomb monolith carrier 30, thereby exciting the photocatalyst and effectively reducing gas- phase harmful components existing in exhaust gas.

Although the conventional exhaust gas purifying system using the photoreaction described above is effective for removal of gas-phase harmful components on the basis of strong oxidizing power and reducing power, the system has a problem in that since it takes more time for solid-phase components such as particulate matters contained in diesel exhaust gas to be oxidized as compared with gas-phase components, the solid- phase particulate matters cannot be sufficiently oxidized while passing though the unit cells with the open ends, and thus, it is impossible to remove the particulate matters.

Therefore, it is possible to simply conceive a method of combining the photoreaction system with the existing DPF that is a method of capturing particulate matters and oxidizing them for a sufficient period of time to remove the particulate matters. However, such a combination, i.e., a method of substituting the existing ceramic honeycomb monolith carrier with a DPF coated with a photocatalyst and applying high voltage to both ends of the DPF to generate plasma, has the following problems. First, since either one of the both ends of the honeycomb monolith carrier of the

DPF is blocked by ceramic plugging, an insulator(that is, ceramic plugging) is disposed between the electrodes 40 positioned at the both ends of the monolith carrier 30, so that plasma cannot be generated.

Second, since photocatalyst coating is made at atmospheric pressure in a state where either one of the both ends of the honeycomb monolith carrier is blocked by the plugging, space through which air escapes lacks. This results in an increase of coating time and an uneven coating layer. Consequently, mass productivity is deteriorated and the generation of plasma may not be made or may not be uniform, so that the overall purification performance may be deteriorated and there may be a high possibility that an electric current will be concentrated on a single position, resulting in reduction of system stability and durability.

As similar prior arts, Japanese Patent Laid-Open Publication Nos. (Sho)61 - 164014, (Hei)5-272326 etc. disclose apparatuses for purifying diesel exhaust gas, wherein both ends of cells of a honeycomb monolith carrier are alternately plugged, the disclosures of which are considered to be a part herein.

Disclosure of Invention

Technical Problem

The present invention is conceived to solve the problems in the prior arts or in simple combinations of the prior arts. An object of the invention is to provide an apparatus for purifying diesel exhaust gas with a coated inner photocatalyst layer and integral electrodes, and a manufacturing method thereof, wherein a photocatalyst honeycomb monolith carrier with integral electrodes is first manufactured by coating an inner surface of a honeycomb monolith carrier made of ceramic with a photocatalyst material, by alternately blocking inlets and outlets of adjacent unit cells of the carrier at both ends thereof by means of plugging conductive metal, and by coating the surfaces of the plugged inlets and outlets with the conductive metal, and is then employed in an exhaust gas purifying system, so that plasma is generated on the photocatalyst with low power to activate the photocatalyst and continuously and efficiently remove particulate matters captured in the photocatalyst filter using oxidizing power of the activated photocatalyst.

Technical Solution

To achieve the object, the present invention provides an apparatus for purifying diesel exhaust gas, including a filter for filtering the diesel exhaust gas and an electrode device for regenerating the filter by removing captured particulate matters. The apparatus comprises a porous ceramic honeycomb monolith carrier with an inner surface coated with a photocatalyst, for capturing the particulate matters by filtering the diesel exhaust gas; conductive metal for alternately plugging inlets and outlets of respective unit cells of the porous ceramic honeycomb monolith carrier; and metal layers coated on both end surfaces of the porous ceramic honeycomb monolith carrier plugged by the conductive metal. The carrier is contained within a case formed with a power supply terminal. Accordingly, the apparatus has the coated inner photocatalyst layer and the integral electrodes. Further, in the apparatus of the present invention, thermal expansion properties of the conductive metal for plugging the porous ceramic honeycomb monolith carrier and the metal layers coated on the both end surfaces of the porous ceramic honeycomb monolith carrier may be similar to those of the porous ceramic honeycomb monolith carrier. Moreover, when the porous ceramic honeycomb monolith carrier is contained within the case, both ends of the carrier may be fixed by insulators and side portions thereof may be supported by shock-absorbing mats for performing a shock-absorbing function with respect to the case.

Meanwhile, the present invention provides a method of manufacturing an apparatus for purifying diesel exhaust gas, including a filter for filtering the diesel exhaust gas and an electrode device for regenerating the filter by removing captured particulate matters. The method comprises the steps of coating an inner surface of a porous ceramic honeycomb monolith carrier with a photocatalyst; alternately blocking inlets and outlets of respective unit cells of the porous ceramic honeycomb monolith carrier with the inner surface coated with the photocatalyst by means of plugging conductive metal; coating both end surfaces of the porous ceramic honeycomb monolith carrier plugged by the conductive metal with conductive metal; heat-treating the porous ceramic honeycomb monolith carrier; and causing the heat-treated porous ceramic honeycomb monolith carrier to be contained in a case formed with a power supply terminal, whereby the apparatus has the coated inner photocatalyst layer and the integral electrodes.

Further, in the steps of plugging the porous ceramic honeycomb monolith carrier by the conductive metal and coating the both end surfaces of the porous ceramic honeycomb monolith carrier plugged by the conductive metal with the conductive metal, the plugging and coating may be performed by selecting a metal with a thermal expansion property similar to that of the porous ceramic honeycomb monolith carrier.

Moreover, in the step of causing the porous ceramic honeycomb monolith carrier to be contained in the case, both ends of the porous ceramic honeycomb monolith carrier may be fixed within an inner space of the case by means of insulators, and side portions of the porous ceramic honeycomb monolith carrier may be supported by means of shock-absorbing mats to absorb impact with respect to an inner wall of the case.

Brief Description of the Drawings

Fig. 1 is a schematic view showing a conventional CRT reactor available from Johnson-Matthey PIc.

Fig. 2 is a view illustrating gas streams in a DPF system of the conventional CRT reactor available from Johnson-Matthey PIc.

Fig. 3 is a schematic view showing a conventional DPF system employing a plasma generator. Fig. 4 is a schematic view showing a conventional DPF system employing a heating means.

Fig. 5 is a schematic view showing a conventional photocatalyst reaction system. Fig. 6 is a sectional view showing the entire configuration of an apparatus for purifying diesel exhaust gas with a coated inner photocatalyst layer and integral electrodes according to the present invention.

Fig. 7 shows a sectional view and an enlarged view of a porous honeycomb monolith carrier of the apparatus for purifying diesel exhaust gas with the coated inner photocatalyst layer and the integral electrodes according to the present invention.

Fig. 8 shows an operation state of the porous honeycomb monolith carrier of the apparatus for purifying diesel exhaust gas with the coated inner photocatalyst layer and the integral electrodes according to the present invention.

Explanation of reference numerals for designating main components in the drawings> 101 : DPF 102: Diesel oxidation catalyst (DOC) 1 1 1 : Plasma generator 112: Battery

1 13: Inverter for plasma generation 121 : Heating means

203: Photocatalyst material 204: Plugging conductive metal

205: Coated metal layer 207a, 207b: Unit cell 208: Porous ceramic honeycomb monolith carrier

209: Shock-absorbing mat 210: Case

21 1 : Exhaust portion 212: Inflow portion 214: Power supplying terminal

Best Mode for Carrying out the Invention

Fig. 6 is a sectional view showing the entire configuration of an apparatus for purifying diesel exhaust gas with a coated inner photocatalyst layer and integral electrodes according to the present invention, and Fig. 7 shows a sectional view and an enlarged view of a porous honeycomb monolith carrier of the apparatus for purifying diesel exhaust gas with the coated inner photocatalyst layer and the integral electrodes according to the present invention.

The specific configuration and operation of the present invention will be described in connection with a preferred embodiment with reference to the accompanying drawings. However, the embodiment of the present invention is only for illustrative purposes and does not limit the scope of the invention.

As shown in Fig. 6, the apparatus for purifying diesel exhaust gas according to the present invention is constructed in such a manner that a porous ceramic honeycomb monolith carrier 208 is contained within a hollow case 210 made of a metal material.

The porous ceramic honeycomb monolith carrier 208 takes the shape of a cylinder comprised of a plurality of unit cells 207a and 207b that are formed through extrusion of general ceramic. Although the unit cells 207a and 207b may have a variety of sectional shapes such as a triangle, a rectangle, a pentagon, a hexagon and a circle, the present invention will be described herein in connection with an embodiment in which the sectional shapes of the unit cells 207a and 207b are a rectangle. As described above, the porous ceramic honeycomb monolith carrier 208 of the present invention is an integral assembly of the unit cells 207a and 207b each of which has a rectangular sectional shape and is open at both ends thereof.

An inner surface of the porous ceramic honeycomb monolith carrier 208 is coated with a photocatalyst material 203 activated by a light source. The coating process employs a typical process of dipping the porous ceramic honeycomb monolith carrier 208 into a solution with the photocatalyst material 203 dissolved therein.

Further, the photocatalyst material coated on the inner surface of the porous ceramic honeycomb monolith carrier 208 can be selected from the group consisting of TiO₂, ZnO, CdS, ZrO₂, SnO₂, V₂O₂, WO₃, SrTiO₃, and a mixture thereof, which are known as having photocatalyst effects. The embodiment of the present invention is described with TiO₂. The photocatalyst effects are excited by light with a specific wavelength. In this process, when the light with the specific wavelength is irradiated onto the photocatalyst material, TiO₂, electrons e^" and holes h⁺ are generated and react with O₂ and H₂ of air to generate two kinds of reactive oxygen, i.e., superoxide anion O₂ ^" and hydroxyl radical *OH or OH^", on the surface of TiO₂, thereby causing reactions by which harmful substances are decomposed due to strong oxidation or reduction actions.

After the inner surface of the respective unit cells 207a and 207b of the porous ceramic honeycomb monolith carrier 208 is coated with the photocatalyst material 203 in accordance with the aforementioned principle, upstream and downstream portions of the unit cells 207a and 207b of the carrier 208 are alternately plugged using conductive metal (powder) 204 that has superior electrical conductivity and thermal stability.

That is, the alternate plugging of the upstream and downstream portions of the unit cells 207a and 207b means that if the upstream portion of one of the unit cells 207a or 207b is plugged by the conductive metal 204 to shut off the inflow gas, a portion of the unit cell opposite thereto is not plugged but open, and that if the upstream portion of one of the unit cells 207a or 207b is open to allow the introduction of the inflow gas, the portion of the unit cell opposite thereto is plugged by the conductive metal 204, as shown in Fig. 6 (b).

Further, as shown in Fig. 7, one of the unit cells 207a or 207b and adjacent unit cells 207b or 207a of the porous ceramic honeycomb monolith carrier 208 of the present invention are alternately plugged. That is, if any one of the unit cells 207a or 207b is plugged, four unit cells 207b or 207a adjacent to the plugged unit cell are not plugged.

Here, the present invention and the prior art are distinguished from each other in that a material for plugging cells of a DPF in the prior art is ceramic identical to that of the cells of the DPF, whereas the present invention employs metal (powder) 204 with superior electrical conductivity. Further, they are also distinguished from each other in that a catalytic intermediate layer is optionally coated after both ends of the DPF 101 (see Figs. 1 to 4) are blocked by the plugging 104 (see Fig. 2) in the prior art, whereas the photocatalyst is coated and plugging is then made by the conductive metal 204 with superior electrical conductivity and thermal properties similar to those of the ceramic monolith carrier 208 in the present invention.

As for the conductive metal 204 that is a plugging material, metal or alloy powder with thermal properties, such as a thermal expansion coefficient, similar to those of the ceramic honeycomb monolith carrier 208 is used, thereby preventing damage to the honeycomb monolith carrier 208 due to difference in thermal expansion resulting from enormous oxidation heat that is produced during a granular powder-regenerating process. Examples of the plugging material include a combination of stainless steel, aluminum (Al), titanium (Ti), molybdenum (Mo), Copper (Cu), iron oxide (FeO₂) and the like at a proper ratio. The combination and the ratio thereof may be changed to be suitable to thermal properties of the honeycomb monolith carrier 208 made of ceramic.

When the plugging process for the porous ceramic honeycomb monolith carrier 208 is completed in such a manner, both end surfaces of the ceramic honeycomb monolith carrier 208 are coated with the same metal (alloy) as the material of the plugging to form metal layers 205. It is preferred that such powder coating processing be performed using metal

(alloy) powder. In this case, a volatile solvent is added to and mixed with metal powder, and the mixture is then coated on the both end surfaces of the ceramic honeycomb monolith carrier 208 and subjected to heat treatment so that the conductive metal 204 for plugging the respective unit cells 207a and 207b and the metal layers 205 coated on the both end surfaces can be strongly bonded mutually to the honeycomb monolith carrier 208 and the metal (powder).

That is, the plugging metal 204 and the coated metal layer 205 are sintered through the heat treatment at high temperature and electrically connected to each other so that they have an identical phase. Thus, they become a united single electrode when a high voltage is applied thereto.

Accordingly, each of the unit cells 207a and 207b of the porous ceramic honeycomb monolith carrier 208, which was open at both ends thereof, has one end alternately blocked by the plugging metal 204, thereby capturing particulate matters contained in exhaust gas from a diesel engine. Further, since the metal layers 205 made of the same material as the plugging are coated and sintered on the both end surfaces of the honeycomb monolith carrier 208, it is considered that the electrodes 40 (see Fig. 5) installed in the conventional photoreaction system (see Fig. 5) have been replaced with structures having electrodes formed integrally with the carrier 208 in the present invention. Moreover, since the inner surfaces of the respective unit cells 207a and 207b of the ceramic honeycomb monolith carrier 208 with the integral electrodes according to the present invention are coated with the photocatalyst material 203, the same oxidation reaction as the conventional photoreaction system occurs within the ceramic honeycomb monolith carrier 208 of the present invention. The ceramic honeycomb monolith carrier 208 of the present invention constructed as above is contained within the hollow case 210 made of a metal material, as shown in Fig. 6. That is, the ceramic honeycomb monolith carrier 208 of the present invention is contained within the case in such a manner that the longitudinal direction of the unit cells 207a and 207b is coincident with a direction in which exhaust gas flows within the hollow case 210 formed with an inflow portion 212 and an exhaust portion 211 for the exhaust gas.

Carrier supports 215 are formed on an inner wall of the case 210 at an interval corresponding to the length of the ceramic honeycomb monolith carrier 208 of the present invention. The material of the carrier supports 215 comprises an insulation material that is electrically non-conductive, so that a current cannot flow toward the case 210 even when a current flows through the ceramic honeycomb monolith carrier 208.

Moreover, shock-absorbing mats 209 are interposed between an outer wall of the ceramic honeycomb monolith carrier 208 contained in the case 210 and the inner wall of the case 210 to perform a shock-absorbing function of protecting the ceramic honeycomb monolith carrier 208 from an external impact. The shock-absorbing mats 209 are made of an insulative fibrous material such as asbestos or mica that can withstand high temperature.

Meanwhile, a power supply terminal 214 capable of supplying electrical power is provided on an outer surface of the case 210. That is, the power supply terminal 214 installed to penetrate through the case 210 is arranged to be electrically insulated from the case 210 and to be in electrical contact with the outer wall of the ceramic honeycomb monolith carrier 208 contained in and fixed to the case 210.

The apparatus for purifying diesel exhaust gas according to the present invention constructed as above performs purification of the exhaust gas by substituting for the DPF 101, the plasma generator 111 and the heating means 121 of the purifying system shown in Figs. 3 and 4.

Now, the operation of the present invention will be described.

Fig. 8 is an enlarged partial view showing the operation of the porous honeycomb monolith carrier 208 of the apparatus for purifying diesel exhaust gas according to the present invention. The diesel exhaust gas introduced (as designated by solid arrows) through the unit cell 207a with the upstream portion (inlet portion) that is not plugged by the conductive metal 204 enters the adjacent unit cells 207b while being filtered by the porous wall of the unit cell 207a and is exhausted therethrough (as designated by dotted arrows) since the downstream portion (outlet portion) of the unit cell 207a is plugged by the metal.

At this time, the porous honeycomb monolith carrier 208 of the present invention receives a high voltage from the power supply terminal 214 installed at the case 210 and generates plasma for the photocatalyst with low electric power to activate the photocatalyst. The oxidizing power of the activated photocatalyst is used to efficiently and consecutively remove particulate matters that have been filtered out and captured by the porous wall of the unit cell 207a. Such a reaction for removing the particulate matters occurs all the unit cells

207a and 207b of the porous ceramic honeycomb monolith carrier 208, thereby effectively removing the captured particulate matters.

Industrial Applicability According to the present invention described above, a photocatalyst is coated on a conventional porous honeycomb monolith carrier and each of unit cells of the porous honeycomb monolith carrier is alternately plugged at one of both ends thereof by a metal material (powder) with superior electrical conductivity and thermal stability. Thus, it is possible to solve the problems of uneven coating and prolonged coating time that occur during the process of coating an intermediate layer bearing a catalyst on a conventional DPF. Accordingly, the photocatalyst is uniformly and rapidly coated, resulting in improved mass productivity. Particularly, since electrical properties are uniformly distributed during the process of generating cold plasma through application of a high voltage, there is an advantage in that the stable generation of the plasma can be secured. Further, according to the present invention, the photocatalyst is coated on the porous ceramic honeycomb monolith carrier, and each of some unit cells of the porous honeycomb monolith carrier are plugged at one of both ends thereof by conductive metal and each of unit cells adjacent thereto is plugged at an end of both ends thereof apposite to the plugged end of the above unit cell. Thereafter, both end surfaces of the carrier are coated further with a material identical to the plugging metal and subjected to heat treatment and sintering at high temperature. Thus, integral electrodes capable of exhibiting the same effects as electrodes employed in a conventional photoreaction system are formed. When a high voltage is applied to the carrier, plasma is generated to activate the photocatalyst coated on the unit cells, thereby inducing an oxidation reaction by which oxygen existing in exhaust gas and captured particulate matters are reacted with each other to continuously regenerate the filter. Further, since the filter for capturing the particulate matters and the electrodes for forcibly regenerating the captured particulate matters are integrally formed in the carrier, there is an advantage in that the assembly process is simplified and a purifying system also becomes simple. Furthermore, in a purifying system employing the purifying apparatus of the present invention, since the plasma is generated within the filter (carrier), there is an advantage in that oxidizing power and ultraviolet rays of the plasma can be directly used so that energy consumption is reduced and the configuration of the system is simplified.

Claims

1. An apparatus for purifying diesel exhaust gas, including a filter for filtering the diesel exhaust gas and an electrode device for regenerating the filter by removing captured particulate matters, the apparatus comprising: a porous ceramic honeycomb monolith carrier with an inner surface coated with a photocatalyst, for capturing the particulate matters by filtering the diesel exhaust gas; conductive metal for alternately plugging inlets and outlets of respective unit cells of the porous ceramic honeycomb monolith carrier; and metal layers coated on both end surfaces of the porous ceramic honeycomb monolith carrier plugged by the conductive metal, wherein the carrier is contained within a case formed with a power supply terminal, whereby the apparatus has the coated inner photocatalyst layer and the integral electrodes.

2. The apparatus as claimed in claim 1, wherein the conductive metal for plugging the porous ceramic honeycomb monolith carrier and the metal layers coated on the both end surfaces of the porous ceramic honeycomb monolith carrier comprise a metal with a thermal expansion property similar to that of the porous ceramic honeycomb monolith carrier.

3. The apparatus as claimed in claim 1 , wherein when the porous ceramic honeycomb monolith carrier is contained within the case, both ends of the carrier are fixed by insulators and side portions thereof are supported by shock-absorbing mats for performing a shock-absorbing function with respect to the case.

4. A method of manufacturing an apparatus for purifying diesel exhaust gas, including a filter for filtering the diesel exhaust gas and an electrode device for regenerating the filter by removing captured particulate matters, the method comprising the steps of: coating an inner surface of a porous ceramic honeycomb monolith carrier with a photocatalyst; alternately blocking inlets and outlets of respective unit cells of the porous ceramic honeycomb monolith carrier with the inner surface coated with the photocatalyst by means of plugging conductive metal; coating both end surfaces of the porous ceramic honeycomb monolith carrier plugged by the conductive metal with conductive metal; heat-treating the porous ceramic honeycomb monolith carrier; and causing the heat-treated porous ceramic honeycomb monolith carrier to be contained in a case formed with a power supply terminal, whereby the apparatus has the coated inner photocatalyst layer and the integral electrodes.

5. The method as claimed in claim 4, wherein in the steps of plugging the porous ceramic honeycomb monolith carrier by the conductive metal and coating the both end surfaces of the porous ceramic honeycomb monolith carrier plugged by the conductive metal with the conductive metal, the plugging and coating are performed using a metal with a thermal expansion property similar to that of the porous ceramic honeycomb monolith carrier.

6. The method as claimed in claim 4, wherein the step of causing the porous ceramic honeycomb monolith carrier to be contained in the case comprises fixing both ends of the porous ceramic honeycomb monolith carrier within an inner space of the case by means of insulators, and supporting side portions of the porous ceramic honeycomb monolith carrier by means of shock-absorbing mats to absorb impact with respect to an inner wall of the case.