JP2011089503A - Exhaust gas purification structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purification structure which can burn and remove a sedimentary PM by a low amount of electric power which does not heat the whole structure without being influenced by an exhaust condition (gas temperature etc.) of exhaust gas. <P>SOLUTION: Silver electrodes 5 are provided at an upstream side and a downstream side of the gas fluid communication direction of a side surface of a segment structure 10 formed in a cylindrical shape containing four SiC segments 4 with cross-sectional quadrangles having silver coatings on side surfaces, respectively, and the silver coating and the silver electrodes 5 of the SiC segments are connected by a conductive element 7. PM ignition combustion by a low amount of electric power and oxidation removal of HC, CO and the like are performed by heating a part of the SiC segments 4 of the segment structure 10 by the application of a voltage from the outside. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gas purification structure suitable for purifying particulate matter, such as soot, soluble organic components, and so on contained in exhaust gas from a heat engine such as an engine. .

In addition to various combustion / incineration facilities, for example, exhaust gas (hereinafter also referred to as exhaust gas) emitted from an internal combustion engine such as a diesel engine is generally nitrogen oxide (NO _x ) or carbon monoxide (CO). In addition to hydrocarbons (HC), soot, particulate matter with carbon as the main component (SOF: Soluble Organic Fraction) such as fuel and engine oil, (PM) May be abbreviated as ")".

  Therefore, in the development and use of an internal combustion engine, a method for purifying exhaust gas discharged from the internal combustion engine has been studied from the viewpoint of preventing pollution of the atmosphere, soil, and the like. In recent years, especially in diesel engines, PM purification and oxidation removal of gas components such as HC and CO have attracted attention.

  Regarding the technology for purifying PM, for example, a filter that reduces particulate matter in exhaust gas discharged from a heat engine such as an internal combustion engine (eg, diesel engine) [DPF (= Diesel particulate filter); To do. ] Is known. This DPF includes a DPF catalyst in which a noble metal is supported inside a DPF base material and a noble metal is supported on the surface thereof.

  However, in a diesel hybrid vehicle, for example, even if the motor drive is switched to the engine drive, the exhaust gas temperature may be maintained at a low temperature of, for example, 150 ° C. or less after switching. In such a case, even if it is going to perform the combustion process of PM deposited on DPF, it becomes difficult to raise the temperature by catalytic combustion of a reducing agent (eg, fuel). In addition, immediately after switching to engine driving, the catalyst is in a cold state, so it becomes difficult to purify the exhaust gas.

  As measures against such a situation, conventionally, for example, an exhaust gas purification catalyst metal carrier for automobiles with an electric heating device in which a honeycomb structure laminated with flat stainless steel foils is loaded in a cylinder having positive and negative electrodes, Like a catalytic converter having a monolith catalyst and a heater having a heating means for heating a metal sintered body, an electrically heated catalyst device provided with a local heat generating part connected to a catalyst carrier in a locally energizable manner, etc. A technique for arranging an electric heater catalyst (EHC) on the upstream side in the exhaust gas flow direction has been proposed.

In vehicles equipped with diesel engines equipped with oxidation catalysts, DPFs, NO _x reduction catalysts, etc., further mounting of EHC is likely to be restricted in terms of mounting space and cost, and other catalysts are installed in the direction of exhaust gas flow with low temperature. It will also shift to the downstream side, which is disadvantageous in the system configuration.

  On the other hand, a diesel engine-equipped vehicle is equipped with DPF for PM purification, but when one of the main materials of this DPF is conductive silicon carbide (SiC), it can be used as a heater, There is a possibility that the EHC function can be efficiently functioned.

  In this connection, in order to increase the thermal conductivity of the DPF, techniques such as a particulate collection filter in which a silver film and a copper film are formed on the particulate collection surface of the collection filter are known. However, there is no function as a heater.

  Further, a silicon carbide honeycomb structure that can incinerate and regenerate combustible fine particles collected by a porous wall by electric heating is disclosed (for example, see Patent Document 2), and clogging of the porous film is disclosed. It is said that a large amount of flammable fine particles can be collected by suppressing it.

Japanese Utility Model Publication 4-22013 JP-A-9-71466

  However, in the above conventional silicon carbide honeycomb structure, since the entire honeycomb structure is heated, the EHC generally used for a DPF having a capacity of several liters more than the displacement of the engine becomes large, and a large amount Electric power is required and is not practical.

  The present invention has been made in view of the above, and is capable of burning and removing deposited PM with a low power amount that does not heat the entire structure regardless of the influence of exhaust gas discharge conditions (gas temperature, etc.). The object is to provide a gas purification structure and to achieve the object.

  In the present invention, a DPF made of silicon carbide generally has a structure in which a plurality of segments are joined to alleviate thermal expansion to form a joined body. By making it a structure with a metal member on its side surface and functioning as a heater, it is possible to efficiently remove PM combustion and oxidize HC, CO gas, etc. due to the high thermal conductivity of SiC while having low power. It was achieved based on such knowledge.

  In order to achieve the above object, an exhaust gas purifying structure of the present invention includes a gas flow hole through which a gas flows, and silicon carbide having metal members on a part of the side in the gas flow direction on the upstream side and the downstream side, respectively. A segment structure in which a plurality of segments are joined; an electrode member provided on at least a part of each of the upstream side and the downstream side in the gas flow direction of the side surface of the segment structure; Provided on each of the upstream side and the downstream side in the gas flow direction, a conductive member that conducts the metal member and the electrode member is provided.

  In the exhaust gas purification structure of the present invention, among the segment structures formed by joining a plurality of silicon carbide (SiC) segments, the upstream side and the downstream side in the gas flow direction on the side of some of the SiC segments Each side is provided with a metal member that is electrically connected to the electrode portion on the side surface of the segment structure, so that a part of the SiC segment can be heated to function as a heater, and the interior of the segment structure is partially It can be configured to be heated. Thereby, the segment structure formed by joining the segments made of SiC having relatively high thermal conductivity, for example, when the engine is cold started when the catalyst temperature is low, or when the gas temperature is stopped and the catalyst temperature is Even when the engine is stopped intermittently in a descending hybrid vehicle, or during low-speed operation where the catalyst temperature decreases as the exhaust gas temperature decreases, the entire structure is heated by heat generated in a part of the SiC segments joined together. Is held, and the deposited PM can be ignited and burned with a low power amount that does not heat the entire structure, and further, gas components such as HC and CO can be oxidized and removed.

  In the present invention, the metal member electrically connected to the metal member on the side surface of the SiC segment is further connected to the metal member on the side surface of the SiC segment in order to facilitate connection with the conductive member that forms the conduction with the electrode member on the side surface of the segment structure. It can arrange | position in a part of each end surface of the gas distribution direction upstream and downstream.

  Moreover, the metal member which has in the side surface of a SiC segment can be provided so that the peripheral direction of the side surface of a SiC segment may be covered entirely in the upstream and downstream of the gas distribution direction of a segment. In this way, by providing the metal members in regions of a predetermined width along the side surfaces from the upstream and downstream end surfaces in the gas flow direction of the SiC segment, the SiC segment functions as a heater that can efficiently generate heat.

The plurality of silicon carbide segments constituting the segment structure in the present invention include a porous wall through which a gas can pass, a gas inflow side cell that is partitioned by the porous wall and closed on the downstream side in the gas flow direction, and the porous A gas outflow side cell that is partitioned by a porous wall and is adjacent to the gas inflow side cell through the porous wall and is closed on the upstream side in the gas flow direction, and the gas that has flowed into the gas inflow side cell passes through the porous wall. It can be configured to pass through and flow out to the gas outflow side cell. At this time, the exhaust gas flowing into the gas inflow side cell passes through the porous wall of the gas inflow side cell and enters the gas outflow side cell adjacent to the gas inflow side cell, and when the gas passes through the porous wall. While collecting PM, the collected PM is ignited and burned. Furthermore, gas components such as HC and CO in the exhaust gas are oxidized and removed.
In this case, a noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh) is supported on the wall of the porous wall or in the wall (preferably the wall of the porous wall constituting the gas inflow side cell). It is preferable.

  The metal member on the side surface of the SiC segment has, on its side surface, an entire region having a predetermined width from one end on the upstream side in the gas flow direction and an entire region from the center position of the SiC segment to the other end on the downstream side in the gas flow direction. Can be provided. That is, it is preferable that a region where no metal member is provided, that is, a heat generation region serving as a heater, is provided on the side surface of the SiC segment upstream from the center position of the SiC segment in the gas flow direction.

  Heat in the SiC segment is transmitted along the flow direction from one end on the upstream side to the other end on the downstream side when the exhaust gas flows through the SiC segment, and the upstream side is easily heated by the heat of the exhaust gas. The amount of electric power is further reduced by providing the exothermic region to be upstream from the center position of the SiC segment.

  In the segment structure in the present invention, a form in which the SiC segment having the metal member is disposed in the innermost part of the plurality of SiC segments joined to each other (for example, the position closest to the axis of the segment structure) is preferable. Since the SiC segment having a metal member is surrounded by another SiC segment, heat easily propagates to the segment that does not generate heat, and the entire SiC segment constituting the segment structure is efficiently and quickly heated. It is possible.

  The metal member on the side surface of the SiC segment and the electrode member on the side surface of the segment structure can be formed using silver and / or copper.

  The present invention maintains heat that is difficult to maintain stably due to the influence of operating conditions such as cold engine start, intermittent engine stop in a hybrid vehicle, and low speed operation, and stable and excellent exhaust gas purification performance. For example, an exhaust purification catalyst system such as a diesel hybrid vehicle can be constructed.

  According to the present invention, there is provided an exhaust gas purification structure capable of burning and removing deposited PM with a low power amount that does not heat the entire structure regardless of the influence of exhaust gas exhaust conditions (gas temperature, etc.). be able to.

It is a schematic sectional drawing which shows schematic structure of the exhaust system of the exhaust-gas purification catalyst system of the diesel engine vehicle of this embodiment. It is a perspective view which shows schematic structure of SiC DPF with a heater of this embodiment. It is a perspective view which shows schematic structure of the SiC segment of this embodiment. It is the schematic sectional drawing which looked at the internal structure of the SiC segment of Drawing 3 from the side. It is a schematic sectional drawing which expands and shows the part of A of FIG.

  Hereinafter, with reference to FIGS. 1-5, embodiment of the exhaust gas purification structure of this invention is described in detail. However, the present invention is not limited to the following embodiment.

  As shown in FIG. 1, in this embodiment, in an exhaust gas purification catalyst system for a diesel engine vehicle, platinum is sequentially formed in the exhaust gas distribution direction in an exhaust system for distributing and discharging the exhaust gas discharged from the diesel engine body 3. An oxidation catalyst 1 carrying (Pt) and an SiC DPF 2 with a heater as an exhaust gas purification structure are arranged.

  As shown in FIG. 2, the SiC DPF 2 with heater includes a segment structure 10 formed by joining a plurality of SiC segments, a silver film (silver electrode) 5 on the side of the segment structure, and a segment structure. A conductive body 7 for connecting a part of the SiC segment and the silver electrode 5 is provided.

  The segment structure 10 is formed by joining a plurality of SiC segments to each other and processing them into a cylindrical shape. In this embodiment, the cross-sectional shape (cross section orthogonal to the flow direction of the exhaust gas (gas)) is normal. It is formed by joining four rectangular SiC segments and twelve SiC segments arranged so as to surround these four.

  An adhesive layer (not shown) is provided between the adjacent SiC segments 4, and the adjacent SiC segments are fixed to each other. The adhesive layer is not particularly limited as long as the material can fix the segments, and for example, an inorganic adhesive such as alumina sol, silica sol, or cement, or an organic adhesive such as methyl cellulose or ethyl cellulose can be used.

  As shown in FIG. 3, the four SiC segments provided in the central part of the segment structure 10 have four side surfaces, which are the four sides forming the side surface on the upstream side in the gas flow direction of the exhaust gas (gas). Silver films (metal members) 21a and 21b are formed in a region having a width length c from one end and a region having a width length d from the center position P in the gas flow direction to the other end on the downstream side. Since the silver coating is partially formed on the upstream side and the downstream side in the gas flow direction, the SiC segment has a gas flow direction from the center position P that is equidistant from the inflow end surface and the outflow end surface of the exhaust gas. On the upstream side, there is a silver film non-formation region (region of width length e− (c + d)) 23, and this region generates heat and functions as a heater. In the present embodiment, the heat generation silver film non-formation region is provided on the upstream side in the gas flow direction from the central position P that is equidistant from the inflow side end surface and the outflow side end surface of the exhaust gas. Moreover, since the upstream side is easily heated by the heat of the exhaust gas, power consumption is reduced.

The silver films 21a and 21b (hereinafter also collectively referred to as “silver film 21”) are metal films having a thickness of 1 μm, and may be metal films having electrical conductivity. In addition to silver (Ag), copper ( It can be formed using a metal such as Cu), aluminum (Al), or magnesium (Mg).
The thickness of the silver film 21 is preferably formed in the range of 1 to 10 μm from the viewpoint of durability.

  In a preferred form of the SiC segment, the silver film 21 is formed on the side surface of the SiC segment from both ends in the gas flow direction, and is upstream from the center position P that is equidistant from the inflow side end surface and the outflow side end surface of the side surface of the SiC segment. This is a case where the width {e− (c + d)} of the non-formation region of the silver film provided on the side is in the range of 30 to 45% with respect to the segment total length e.

The silver film 21 can be formed by a method such as plating or vapor deposition of silver, or dipping or adhering to a solution containing silver. In this embodiment, the silver film 21a immerses a region (see FIG. 3) having a width c from one end of the SiC segment 4 in the gas flow direction in an activation solution composed of tin chloride (SnCl ₂ ) and hydrochloric acid (HCl). After being washed with water, it is formed by immersing in a silver solution consisting of silver nitrate (AgNO ₃ ), formaldehyde (HCHO), and distilled water for 10 minutes, pulling up, and washing with water. Further, the silver coating 21b is also formed by performing the same operation on a region having a width length d (see FIG. 3) from the other end of the SiC segment 4 in the gas flow direction.

  Each SiC segment constituting the segment structure 10 has a plurality of gas flow holes through which exhaust gas flows as shown in FIG. As shown in FIG. 4, each SiC segment has porous filter walls 11 configured to allow the exhaust gas flowing therethrough to pass therethrough as indicated by arrows, and are arranged substantially parallel to each other at a predetermined interval. The arranged filter walls 11 are closed by clogging every other filter wall with a packing material 12 at the downstream end of the gas flow direction (arrow direction in FIG. 3). At the end on the upstream side in the gas flow direction, every other filter wall that is not clogged on the downstream side of the filter wall is clogged with clogging material 12 and closed. Thereby, gas inflow side cells 18 are formed between the filter walls clogged downstream in the gas flow direction, and gas outflow side cells 19 are formed between the filter walls clogged upstream in the exhaust gas flow direction. Is formed.

  As described above, the gas inflow side cell 18 and the gas outflow side cell 19 are partitioned by the filter wall 11 and are adjacent to each other through the filter wall 11, and are circulated as shown in FIG. The exhaust gas that has entered the cell 18 is configured to be able to move from the gas inflow side cell 18 through the filter wall 11 to the gas outflow side cell 19.

As the filter wall, any filter wall can be used as long as it can circulate a gas having a large number of holes formed therein. Examples of the main component constituting the filter wall include silicon carbide. The “main component” means occupying 80% by mass or more of the components of the filter wall. Specific examples include SiC honeycomb substrates and metal honeycomb substrates.
The average pore diameter of the filter wall is preferably in the range of 5 to 30 μm.

  Inside the porous filter wall 11, catalyst particles in which Pt is supported on a carrier having an average particle diameter smaller than the average pore diameter of the filter wall may be supported. Examples of the noble metal of the catalyst particles include Pt, Pd, rhodium (Rh) and the like, and Pt and Pd are preferable from the viewpoint of PM combustion efficiency. The average particle diameter of the carrier is an average value of secondary particle diameters (average secondary particle diameter) measured by X-ray diffraction method and TEM observation, and is preferably 30 μm or less.

  A catalyst layer 15 in which Pt (platinum) is supported as a noble metal is formed on the filter wall 11 in the cell of the gas inflow side cell 18. The catalyst layer 15 carries Pt-supported catalyst particles having Pt supported on a carrier. Examples of the noble metal of the catalyst particles include Pt, Pd, rhodium (Rh) and the like, and Pt and Pd are preferable from the viewpoint of PM combustion efficiency. The average particle diameter of the carrier in the catalyst layer 15 is also an average secondary particle diameter measured by the same method as described above, and is preferably 20 μm or more.

As the carrier, zirconium dioxide (ZrO ₂ ), aluminum oxide (Al ₂ O ₃ ), silica, silica-alumina, ceria (CeO ₂ ), oxide particles such as zeolite, and mixed particles thereof may be used. it can.

  The catalyst layer 15 may have a structure in which a noble metal having catalytic ability is coated on a porous wall. By supporting the noble metal, combustion removal of PM (particulate matter) deposited on the wall surface of the porous wall is promoted, and PM combustibility can be further improved.

  The supported amount of the noble metal in the catalyst layer 15 is preferably 0.5 g / L or more and 3 g / L or less. When the amount of noble metal in the catalyst layer on the gas inflow side is 0.5 g / L or more, the PM combustion efficiency of the wall surface on which a relatively large amount of PM is deposited is improved, the thermal load received by the noble metal is suppressed, In the range of 3 g / L or less, it is advantageous in terms of cost. At this time, the amount of noble metal supported in the wall of the filter wall 11 is preferably 0.01 g / L or more and 0.5 g / L or less.

  Pt is excellent in PM combustion ability and oxidation activity of HC and CO in gas. Pd is also excellent in PM burning ability and HC and CO oxidation activity in gas. Further, when Pd is used, heat resistance is obtained, and it has an effect of suppressing Pt grain growth. For example, Pd can be present together with Pt to further increase the heat resistance. Thereby, the thermal deterioration of the noble metal (especially Pt) accompanying PM combustion can be suppressed effectively.

When Pt and Pd are contained in the layer, Pt-supported oxide particles supporting Pt and Pd-supported oxide particles supporting Pd may be mixed, or both Pt and Pd are supported. Oxide particles may be used. The Pt-supported oxide is, for example, a mixture of an oxide powder or granular material such as ZrO ₂ powder and a diammineplatinum platinum solution, a platinum chloride solution, an ammine platinum solution, etc. For example, about 800 ° C.). The oxide particles supporting both Pt and Pd are, for example, oxide powder such as ZrO ₂ powder and granular materials, diammine platinum nitrate solution, platinum chloride solution, ammine platinum solution, and palladium nitrate. It can be obtained by mixing a solution, a palladium chloride solution and the like, drying, firing (for example, about 400 to 800 ° C.), and the like.

  The silver coating 5 is a silver electrode having a thickness of 1 μm, and functions as an electrode for being electrically connected to the silver coatings 21 a and 21 b of the SiC segment 4 by the conductor 7 and energizing from the outside. As shown in FIG. 2, the silver coating 5 a is provided in a region having a width a from the one end on the upstream side in the gas flow direction on the side of the segment structure 10, and the silver coating 5 b is a side of the segment structure 10. Is provided in a region having a width b from the other end on the downstream side in the gas flow direction. The silver film 5a is electrically connected to the silver film 21a of the SiC segment 4 via the conductor 7, and the silver film 5b is electrically connected to the silver film 21b of the SiC segment 4 via the conductor 7. Yes.

When the silver coating 5 is energized from the outside, for example, immediately after switching to engine driving in a cold state, or when a low-temperature exhaust gas that does not reach the activation temperature range of the catalyst flows, The four SiC segments 4 at the center of the segment structure, on which the silver films 21a and 21b electrically connected through the conductor 7 are formed, are heated. The heated SiC segment serves as an ignition source, and heat is propagated to the other SiC segments surrounding the four SiC segments 4 through the SiC and silver film having relatively high thermal conductivity. As a result, heat is held in the entire structure by heat generated in a part of the SiC segments joined to each other at a low electric energy that does not heat the entire structure, and the deposited PM is ignited and burned, and HC and Oxidation removal of gas components such as CO can be performed.
During normal operation with an engine drive, PM functions as a DPF catalyst that collects and burns PM and oxidizes and removes gas components such as HC and CO.

  The silver film 5 may be a metal film having electrical conductivity, and can be formed using a metal such as Cu in addition to silver (Ag).

The silver film 5 can be formed by a method such as plating or vapor deposition of silver, or dipping or adhering to a solution containing silver. In the present embodiment, the silver film 5a forms an area having a width a (see FIG. 2) from one end in the gas flow direction of the segment structure 10 into an activation solution composed of tin chloride (SnCl ₂ ) and hydrochloric acid (HCl). After dipping and washing with water, it is formed by dipping for 10 minutes in a silver solution consisting of silver nitrate (AgNO ₃ ), formaldehyde (HCHO), and distilled water, pulling up, and washing with water. Further, the silver coating 5b is also formed by performing the same operation on a region having a width b (see FIG. 2) from the other end of the segment structure 10 in the gas flow direction.

  The film thickness in the silver films 5a and 5b is preferably in the range of 1 to 10 μm from the viewpoint of durability.

  The conductor 7 is formed on both end faces of the segment structure 10 along the adhesive layer between the SiC segments, and is formed on each film surface of the silver films 21a and 21b extending from each end face. The conductive body 7 is connected between the silver coating 5a and the silver coating 21a of the Si segment, and between the silver coating 5b and the silver coating 21b of the Si segment, and is in a conductive state. The conducting body 7 may be a metal film having electrical conductivity, and can be formed using a metal such as Ag or Cu. In this embodiment, Ag conducting wires are provided from both end faces of the segment structure 10 to the silver coating 5, and this is formed by applying and drying a silver paste containing Ag.

  The electrode rods 6 are directly joined to the film surfaces of the silver films 5a and 5b, respectively. The electrode rod 6 is made of copper and functions as an electrode terminal when energized from the outside. The electrode rod can be provided using a metal having electrical conductivity, and for example, copper, stainless alloy, chromium alloy, or the like can be used.

Between the side surface of the segment structure 10 and the silver coatings 5a and 5b, an alumina insulating film 8 having a thickness of 1 mm is provided so as to cover the entire outer peripheral surface (curved surface) that is the side surface of the segment structure 10. With the alumina insulating film 8, the segment structure is electrically insulated from the silver film 5 forming the electrode. The alumina insulating film is formed using, for example, a slurry containing aluminum oxide (Al ₂ O ₃ ). In this embodiment, it is formed by dipping in a slurry made of activated alumina powder, alumina sol, aluminum nitrate, and distilled water, and pulling up to blow off excess slurry, followed by drying and firing.

  The alumina insulating film 8 may be a film formed of an electrically insulating material, and can be formed using silica, zirconia, or the like in addition to alumina.

  The oxidation catalyst 1 arranged on the upstream side of the SiC DPF 2 with heater is a catalyst layer in which Pt and, if necessary, palladium (Pd) are supported on a cordierite honeycomb monolith support (support base material). Is provided.

The catalyst layer in the oxidation catalyst 1 is provided so as to contain at least Pt or Pd, or Pt and Pd (preferably supported on a carrier). In addition to Pt and Pd, the catalyst layer may further contain a NO _x storage material such as an alkali metal such as Li, K, Na, Mg, Ca, St, or Ba, or an alkaline earth metal.

Pt and Pd can be supported on a desired carrier and contained in the layer. As the carrier here, particles of oxide such as zirconium dioxide (ZrO ₂ ), aluminum oxide (Al ₂ O ₃ ), silica, silica-alumina, ceria (CeO ₂ ), zeolite, and mixed particles thereof are used. be able to.

When Pt and Pd are contained in the layer, Pt-supported oxide particles supporting Pt and Pd-supported oxide particles supporting Pd may be mixed, or both Pt and Pd are supported. Oxide particles may be used. The Pt-supported oxide is, for example, a mixture of an oxide powder or granular material such as ZrO ₂ powder and a diammineplatinum platinum solution, a platinum chloride solution, an ammine platinum solution, etc. For example, about 800 ° C.). The oxide particles supporting both Pt and Pd are, for example, oxide powder such as ZrO ₂ powder and granular materials, diammine platinum nitrate solution, platinum chloride solution, ammine platinum solution, and palladium nitrate. It can be obtained by mixing a solution, a palladium chloride solution and the like, drying, firing (for example, about 400 to 800 ° C.), and the like.

The catalyst layer is, for example, a powdery or granular material of Pt-supported oxide or Pd-supported oxide or oxide particles supporting Pt and Pd in a medium such as water (and necessary). Depending on the above, other components) may be added and stirred to form a slurry, and the resulting slurry may be coated on a desired support substrate and fired to form.
What is necessary is just to select suitably about a coating method, baking conditions, etc. by a composition, a scale, etc.

In the above embodiment, four pieces having a heater function with a silver film on the side surface at the center part (center part in a cross section orthogonal to the gas flow direction) of a segment structure formed of a plurality of SiC segments. However, the number of SiC segments having a heater function is not limited.
The number of SiC segments may be only one according to the purpose, the scale of the structure, the temperature of the inflowing gas, or the like, or may be only two that are located diagonally out of the four in the above embodiment. Or, as an arbitrary number of (n−2) ² (n ≧ 3) at the center of the segment structure in which n ² (n × n; n ≧ 3) SiC segments are joined. Also good. Specifically, for example, the total number of SiC segments is larger than that of the above-described embodiment (16), and for example, one of the centers of segment structures in which a total of 25 (5 × 5) are joined, or 9 central portions. Any 3 to 5 or all of them can be used.

  Moreover, in the said embodiment, although demonstrated centering on the case where a silver membrane | film | coat was formed in each side of a SiC segment and a segment structure, when not only silver but electrically conductive metal materials other than the said silver are used. The same effect can be obtained.

  Moreover, there is no restriction | limiting in the shape of the said embodiment about the shape and size of a SiC segment and a segment structure. The cross-sectional shape can be arbitrarily selected from shapes such as a circle, an ellipse, a rectangle, a triangle, and a hexagon, and the size such as the cross-sectional area and the length may be selected depending on the purpose and gas properties.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to a following example, unless the main point is exceeded.

Example 1
As a SiC segment having a porous wall, a DPF segment made of SiC (silicon carbide) having a square wall of 35 mm and a length of 118 mm and having a porous wall having a number of cells = 300 cells / square inch and a thickness = 0.25 mm (cross section) (Shape: regular square).

  This DPF segment has a porous wall, and as shown in FIG. 4, the inside of the porous walls of the plurality of porous walls 11 arranged in parallel is downstream of the exhaust gas flow direction (arrow direction). The gas inflow side cells 18 and the gas outflow side cells 19 are formed by alternately cuffing every other on the upstream side and the upstream side (average pore diameter: 11 μm, porosity: 42%). The gas inflow side cell and the gas outflow side cell have the same cell shape.

  The prepared DPF segment is first immersed in an activation solution composed of tin chloride and hydrochloric acid, and washed with water. Then, it is immersed for 10 minutes in the silver solution which mixed silver nitrate, formaldehyde, and distilled water. After being pulled up, it is washed with water and, as shown in FIG. 3, 10 mm (= width c) from one end of the DPF segment (end surface on the gas inflow side) and 60 mm from the other end (end surface on the gas outflow side) = Only the width d) forms a silver film having a thickness of about 1 μm on the side surface of the DPF segment and the inside of the gas inflow side cell.

Four DPF segments having a silver film formed thereon as described above were prepared, and twelve DPF segments having the same shape without the silver film were arranged so as to bundle and surround the four DPF segments, An adhesive layer is formed of silica sol (inorganic adhesive) containing SiO ₂ as a main component between the segments, combined, dried, and fired. Thereafter, the periphery is cut to produce a cylindrical DPF filter (segment structure) having a diameter of 143 mm and a diameter of 1.9 liters.

  Next, a slurry obtained by mixing activated alumina powder, alumina sol, aluminum nitrate, and distilled water is attached to the outer peripheral surface serving as the side surface of the produced DPF filter, and the excess slurry is blown off and dried and fired to obtain a thickness of about A 1 mm alumina layer (insulating layer) is formed.

  Next, in the same manner as described above, an activated solution composed of tin chloride and hydrochloric acid is first brought into contact with the alumina layer of the DPF filter on which the alumina layer is formed, and a water washing treatment is performed. Then, it is made to contact for 10 minutes to the silver solution which mixed silver nitrate, formaldehyde, and distilled water. Thereafter, a water washing treatment is performed, and as shown in FIG. 2, 30 mm (= width length a) from one end (end surface on the gas inflow side) of the DPF filter and 30 mm (= width) from the other end (end surface on the gas outflow side). Only for the length b), a silver film (electrode) having a thickness of about 1 μm is formed on the outer peripheral surface of the DPF filter.

  The silver film (electrode) formed on the outer peripheral surface of the DPF filter and the silver film of the four DPF segments on which the silver film is formed are electrically connected to both ends on the upstream side and the downstream side in the gas flow direction. As described above, the silver paste is applied to the both end faces of the DPF filter along the adhesive layer between the DPF segments, and the silver paste is applied from the end face to the silver film (electrode) on the side face and then baked.

Next, a catalyst layer is formed in the gas inflow side cell of the DPF filter as follows.
First, an acetic acid-based alumina sol in which aluminum oxide (Al ₂ O ₃ ) is dispersed is mixed with a dinitrodiammine platinum solution containing a predetermined amount of platinum (Pt), and the slurry is adjusted by adjusting the concentration with an appropriate amount of pure water. Prepare. The obtained slurry 20 g / liter is applied from one end (end surface on the gas inflow side) of the DPF filter, and coated in a region 60 mm from the end surface on the gas inflow side in the gas inflow side cell of the DPF filter. At this time, the amount of Pt supported is 0.5 g / liter. Thereafter, firing is performed at 500 ° C. for 1 hour, and a catalyst layer is formed on the porous wall in the gas inflow side cell as shown in FIG.

  A copper electrode rod is attached to the silver film formed on the outer peripheral surface of the DPF filter so that the electrode can be heated from the outside, and a SiC DPF filter with a heater having the structure shown in FIG. 2 is obtained.

The obtained SiC DPF filter with a heater is wrapped with an alumina mat and casing in a metal container. Thereafter, as shown in FIG. 1, the exhaust gas purification catalyst system of the diesel engine vehicle is mounted downstream of the oxidation catalyst in the exhaust pipe.
As the oxidation catalyst, cordierite honeycomb monolith having a cell number of 400 cells / in 2 and a thickness of 0.1 mm (diameter: 143 mm, length: 150 mm), β-zeolite 75 g / liter and γ-alumina A mixture of 75 g / liter is coated, and 2 g / liter of Pt is uniformly supported on the whole, and then baked at 500 ° C. for 1 hour.

  In the exhaust gas purification catalyst system produced as described above, when the gas temperature of the exhaust gas discharged from the engine is low (for example, the temperature of the inflow gas to the oxidation catalyst is 100 ° C. or lower), the electrode of the SiC DPF filter with heater 200 VAC is applied to the surface, and the temperature of the exposed portion of the DPF segment having no silver coating on the side of the silver coating is increased to 250 ° C. or more to oxidize and remove HC and CO in the exhaust gas passing through the oxidation catalyst. be able to. In this case, PM accumulated in the DPF filter can be ignited and burned by supplying the fuel from the engine by post-injecting fuel as a reducing agent. At this time, even if only the DPF segment having the silver film is heated at the beginning, the PM combustion heat rapidly propagates to the surroundings due to the thermal conductivity of SiC. PM can be ignited and burned in the entire filter.

(Example 2)
In Example 1, except that the cell shape of the DPF segment having the silver film on the side surface is changed so that the volume of the gas inflow side cell is 1.2 times the volume of the gas outflow side cell. Similarly, a SiC-made DPF filter with a heater is manufactured, and this is mounted on an exhaust gas purification catalyst system, and combustion or the like is performed in the same manner.

  As a result, in the four DPF segments in the center of the DPF filter, the inflow resistance of the exhaust gas is smaller than that of the surrounding DPF segment without the silver film, so that it is easy to ignite PM, and HC and The purification rate when CO or the like is removed by oxidation is improved as compared with the first embodiment. Further, by improving the PM ignitability, the PM combustion heat easily propagates to the surroundings more rapidly, and as a result, the PM ignition combustion efficiency of the entire DPF filter is also improved.

(Comparative Example 1)
In Example 2, a SiC DPF filter with a heater was prepared in the same manner as in Example 1 except that a DPF segment having a silver film formed thereon was used for all the DPF segments forming the DPF filter. It is mounted on an exhaust gas purification catalyst system and burns in the same manner.

  In this case, since an applied current flows through all the DPF segments, about twice the amount of power is required to raise the temperature of the central portion of the DPF filter to the same temperature as in the first embodiment.

2 ... SiC DPF filter with heater 4 ... SiC segments 5, 5a, 5b ... Silver coating (electrode member)
6 ... Electrode rod 10 ... Segment structure 11 ... Porous wall (filter wall)
DESCRIPTION OF SYMBOLS 15 ... Catalyst layer 18 ... Gas inflow side cell 19 ... Gas outflow side cell 21,21a, 21b ... Silver film (metal member)

Claims (8)

A segment structure in which a plurality of silicon carbide segments each having a metal member are joined to a part of each of the upstream side and the downstream side in the gas flow direction on the side surface, including gas flow holes through which gas flows;
An electrode member provided on at least a part of each of the gas flow direction upstream side and the downstream side of the side surface of the segment structure, and capable of applying a voltage from the outside;
A conduction member provided on each of the upstream and downstream sides of the gas flow direction, and conducting the metal member and the electrode member;
An exhaust gas purification structure comprising:   Furthermore, it has a metal member in a part of each end surface of the gas flow direction upstream and downstream sides of the silicon carbide segment, and the metal member on each end surface is electrically connected to the metal member on the side surface. The exhaust gas purification structure according to claim 1, wherein:   3. The exhaust gas purification structure according to claim 1, wherein the metal member provided on the side surface of the silicon carbide segment is provided in the entire peripheral direction of the side surface of the silicon carbide segment.   The plurality of silicon carbide segments are defined by the porous wall through which the gas can pass, the gas inflow side cell which is partitioned by the porous wall and closed at the downstream side in the gas flow direction, and is partitioned by the porous wall and porous. A gas outflow side cell that is adjacent to the gas inflow side cell through the porous wall and whose upstream side in the gas flow direction is blocked, and the gas that has flowed into the gas inflow side cell passes through the porous wall to the gas outflow side cell. The exhaust gas purification structure according to any one of claims 1 to 3, wherein the exhaust gas purification structure is discharged.   The metal member on the side surface of the silicon carbide segment is provided in the entire region having a predetermined width from one end on the upstream side in the gas flow direction and in the entire region from the center position of the silicon carbide segment to the other end on the downstream side in the gas flow direction. The exhaust gas purification structure according to any one of claims 1 to 4, wherein the exhaust gas purification structure is provided.   The exhaust gas purification structure according to any one of claims 1 to 5, wherein the silicon carbide segment having the metal member is disposed at an innermost position among the plurality of silicon carbide segments. .   The exhaust gas purification structure according to any one of claims 1 to 6, wherein the metal member and the electrode member contain at least one of silver and copper.   The exhaust gas purification structure according to any one of claims 4 to 7, wherein a noble metal is supported on a surface of a porous wall in the gas inflow side cell.

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