JP2007069153A - Exhaust gas cleaning filter and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning filter in which PM (particulate matter) in low-temperature exhaust gas within a practical use region of a diesel car can be burned continuously and which can be regenerated forcibly at low temperature even when the PM is accumulated therein, and to provide a method for manufacturing the exhaust gas cleaning filter. <P>SOLUTION: The exhaust gas cleaning filter arranged in an exhaust gas passage of an internal-combustion engine for removing the PM in the exhaust gas to be discharged from the internal-combustion engine is provided with: an exhaust gas inflow passage through which exhaust gas flows in; a filter medium which is used for forming the partition wall of the exhaust gas inflow passage and has voids; and an exhaust gas outflow passage for discharging the exhaust gas made to flow in the exhaust gas inflow passage and pass through the filtering material. A low contact-active catalyst 10 exhibiting high activity regardless of the chance to be in contact with the PM is deposited on the inside surface of the partition wall and a high contact-active catalyst 12 exhibiting high activity when the chance to be in contact with the PM is large is deposited on the inside surface of the void 9 in the filter medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification filter for purifying particulate matter (PM) (hereinafter also referred to as PM) contained in exhaust gas discharged from an internal combustion engine, and a method for manufacturing the same. In particular, the present invention relates to an exhaust gas purification filter capable of burning particulate matter at a low temperature and a method for manufacturing the same regardless of the contact state between the particulate matter and a catalyst.

  As a purification device for particulate matter (PM) contained in diesel exhaust gas, a diesel particulate filter (DPF) and a catalyzed soot filter (CSF) are known. In such a purification device, exhaust gas is purified by collecting and burning PM by a filter.

  However, combustion of PM usually requires a high temperature of 550 ° C to 650 ° C. For this reason, continuous combustion of PM in a practical range of a diesel vehicle is difficult, and the collected PM is gradually deposited on the filter. Therefore, in the continuous regeneration type purification device, in order to avoid excessive accumulation of the collected PM, the accumulated PM is forcibly burned (forced regeneration) using some heating means to regenerate the filter. Is doing.

  Further, even in CSF that performs purification using a catalyst, the combustion temperature of PM cannot be lowered so much. This is because the PM-catalyst reaction is a solid-solid reaction, and thus PM in good contact with the catalyst burns, but PM in poor contact is difficult to burn.

  When a catalyst is supported on a PM collection carrier used for CSF, the catalyst is usually applied to the wall surface or pores of the PM collection carrier. For this reason, as the amount of collected PM increases, PM gradually accumulates on the catalyst applied to the wall surface or pores. At this time, PM present at the interface (contact surface) with the catalyst has good contact with the catalyst, but PM stacked other than the interface is less likely to contact the catalyst. As a result, even if a catalyst having high activity with respect to PM is used, the performance of the catalyst cannot be fully exhibited depending on the contact state.

  For example, Patent Document 1 proposes a technique for separating the functions of a catalyst by applying the catalyst to a layer structure on a three-dimensional structure. According to this technology, by providing a catalyst layer having different characteristics in each of the three-dimensional structures, the reaction between the three-dimensional structure and the catalyst component is suppressed, and the deterioration due to the reaction between the catalyst layers is suppressed. The deterioration of the activity of the catalyst can be prevented, and as a result, a highly active purification material can be obtained.

  Patent Document 2 proposes a carrier in which a porous ceramic filter material is used as a PM trapping carrier and a catalyst is applied to the inner surface of the pores of the porous ceramic. By supporting the catalyst on the inner surfaces of the pores of the porous ceramic, PM can be burned in the process of exhaust gas flowing through the filter medium, and burned and removed simultaneously with PM filtration.

Furthermore, Patent Document 3 proposes a technique in which a catalyst is biased and supported in the pores of the DPF. According to this technique, it is possible to increase the PM collection rate while suppressing an increase in exhaust pressure loss, and to sequentially burn the PM collected with high efficiency in the pores carrying the catalyst.
JP 2001-157845 A JP 2002-221022 A Japanese Patent Application Laid-Open No. 2004-077617

  However, according to the technique of Patent Document 1, although the reaction between PM and the catalyst is a solid-solid reaction, the upper layer catalyst and PM can contact each other, but the lower layer catalyst and PM contact each other. Therefore, it has been difficult to fully exhibit the performance of the lower layer catalyst. Further, even in the upper layer catalyst, the PM laminated other than the contact portion between the PM and the catalyst cannot be supported by the catalyst, and therefore cannot be burned at a low temperature.

  Moreover, according to the technique of patent document 2 and patent document 3, PM more than the pore diameter of PM collection support | carrier is gradually deposited on the surface of a filter medium as the amount of PM collection increases. PM deposited on the surface of the filter medium cannot come into contact with the catalyst. For this reason, even when a catalyst having high activity against PM is supported, the performance of the catalyst cannot be fully exhibited. There wasn't.

  The present invention has been made in view of the above problems, and is capable of continuous combustion of PM in low-temperature exhaust gas, which is a practical range of diesel vehicles, and even when PM is deposited. Even if it exists, it aims at providing the exhaust gas purification filter which can be forcedly regenerated at low temperature, and its manufacturing method.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies focusing on the contact property between the particulate matter and the catalyst. As a result, it has been found that by using a high contact active catalyst and a low contact active catalyst in combination, PM can be combusted at a low temperature regardless of the contact state or deposition state of PM, and the present invention has been completed. More specifically, the present invention provides the following.

  (1) An exhaust gas purification filter that is disposed in an exhaust passage of an internal combustion engine and purifies particulate matter in exhaust gas discharged from the internal combustion engine, the exhaust gas inflow passage through which the exhaust gas flows, and a partition wall of the exhaust gas inflow passage And a filter medium having voids, and an exhaust gas outflow path that flows into the exhaust gas inflow path and flows out of the exhaust gas that has passed through the filter medium, and the inner surface of the partition wall includes the particulate matter. A highly catalytically active catalyst exhibiting a high activity when a low catalytically active catalyst exhibiting a high activity regardless of the contact property is supported and the inner surface of the void in the filter medium has a high contact property with the particulate matter. Exhaust gas purification filter carrying

  The exhaust gas purification filter of (1) exhibits high activity when the contact property between the low contact active catalyst showing high activity regardless of the contact property with the particulate matter (PM) and the particulate matter (PM) is high. The high contact active catalyst is used separately at a site where the contact property with the particulate matter is high and a site where the contact property is low. Specifically, a high contact active catalyst is disposed in the gap of the filter medium, and a low contact active catalyst is disposed on the surface of the filter medium.

  Here, “contactability” in the present invention refers to the contact ratio of PM and catalyst to the amount of deposited PM. The case where the contact property is high is a case where most of the deposited PM has a contact point with the catalyst, and the case where the contact property is low is a case where most of the deposited PM does not have a contact point with the catalyst. That is, the smaller the PM amount, the higher the contact ratio and the higher the contactability.

  In general, when purifying exhaust gas using DPF, PM having a diameter smaller than the gap diameter enters and is collected in the gap of the filter medium, while PM having a diameter larger than the gap diameter is It is collected on the surface of the filter medium. Since the smaller the particle size, the smaller the amount of PM present, the smaller the amount of PM collected in the pores of the filter medium. Therefore, the contact between the catalyst in the gap of the filter medium and the PM is high. On the other hand, since PM collected on the surface of the filter medium has a large particle size, it is laminated as the collected amount increases, and the contact with the catalyst is lowered, and furthermore, PM does not contact the catalyst. .

  According to the exhaust gas purification filter of (1), since the performance of each catalyst is sufficiently exhibited, the particulate matter (PM) can be burned efficiently, thereby reducing the combustion temperature of PM. Can do. Therefore, PM in low-temperature exhaust gas within the practical range of diesel vehicles can be continuously burned, and forced regeneration can be performed at low temperatures even when PM is deposited. As a result, according to the exhaust gas purification filter of (1), the loss of fuel consumption and catalyst deterioration due to forced regeneration can be suppressed, and the burden on the automobile can be reduced.

  Moreover, the exhaust gas purification filter of (1) can sufficiently exhibit the performance of each catalyst, and the catalyst can be used effectively. Therefore, it is possible to contribute to a reduction in costs in creating the exhaust gas purification filter.

  (2) The exhaust gas inflow passage and the exhaust gas outflow passage are formed from a large number of cells alternately arranged adjacent to each other through the filter medium, and the upstream end of the cell forming the exhaust gas inflow passage is open. The downstream end is plugged, and the cells forming the exhaust gas outflow passage are plugged at the upstream end and open at the downstream end, as described in (1). Purification filter.

  The exhaust gas purification filter (2) is a so-called wall flow type exhaust gas purification filter composed of a large number of cells. Since the exhaust gas purification filter of (2) has a honeycomb structure, exhaust gas can be efficiently processed with small deposition.

  (3) The exhaust gas purification filter according to (1) or (2), wherein the filter medium is a porous ceramic.

  Since the exhaust gas purifying filter of (3) is made of porous ceramic, the exhaust gas purifying filter has sufficient voids for supporting the high contact active catalyst, and is sufficient even under high temperature conditions such as forced regeneration. Can withstand.

  (4) The exhaust gas purification filter according to any one of (1) to (3), wherein the low contact active catalyst includes at least one transition metal element and at least one alkali metal element.

  In the exhaust gas purification filter of (4), the activity of the catalyst can be made higher by using a catalyst containing at least one transition metal element and at least one alkali metal element as the low contact active catalyst. . Further, in the exhaust gas purification filter according to the present invention, since the low contact active catalyst is entirely supported on the surface of the filter medium, the exhaust gas purification filter is compared with the case where an expensive catalyst containing a noble metal or the like is used. This can contribute to cost reduction.

  (5) The exhaust gas purification filter according to any one of (1) to (4), wherein the high contact active catalyst includes at least one kind of noble metal element.

  The exhaust gas purification filter of (5) uses a catalyst containing at least one kind of noble metal element as a high contact active catalyst. A catalyst containing a noble metal element is generally expensive. In the present invention, since the high contact active catalyst is supported only in the void portion of the filter medium, the amount of use can be suppressed. Therefore, according to the exhaust gas purification filter of (5), the amount of the catalyst containing an expensive noble metal element can be reduced, and this can contribute to a reduction in costs in producing the exhaust gas purification filter.

  (6) A method of manufacturing an exhaust gas purification filter that is disposed in an exhaust passage of an internal combustion engine and purifies particulate matter in exhaust gas discharged from the internal combustion engine, wherein a filter medium having a void is bonded to the particulate matter. A high contact active catalyst supporting step of passing a high contact active catalyst exhibiting high activity when the contact property is high and supporting the high contact active catalyst on the inner surface of the void in the filter medium; and the high contact active catalyst A low contact active catalyst exhibiting high activity regardless of the contact property with the particulate matter on the surface of the filter medium in which the high contact active catalyst is supported on the inner surface of the void in the filter medium by a supporting step. A method for producing an exhaust gas purifying filter, comprising: a low contact active catalyst carrying step for coating and carrying.

  According to the method for producing an exhaust gas purification filter of (6), a high contact active catalyst is disposed at a site having high contact with the particulate matter, and a low contact active catalyst is disposed at a portion having low contact with the particulate matter. can do. For this reason, the filter obtained by the manufacturing method of the exhaust gas purification filter of (6) has the effect of (1).

  According to the present invention, it is possible to continuously burn PM in low-temperature exhaust gas within the practical range of a diesel vehicle, and to perform forced regeneration at a low temperature even when PM accumulates. Can do. For this reason, fuel consumption loss and catalyst deterioration due to forced regeneration can be suppressed, and the burden on the automobile can be reduced.

  In addition, it is possible to use different catalysts according to the PM deposition state, so it is possible to reduce the amount of catalysts containing expensive precious metals, and as a result, contribute to cost reduction in the creation of exhaust gas purification filters. can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Overall configuration of exhaust gas purification filter]
FIG. 1 is a schematic cross-sectional view of a wall flow type DPF 1 according to an embodiment of the present invention in a direction parallel to a cell. The wall flow type DPF 1 according to the present embodiment flows into the exhaust gas inflow path 3 into which the exhaust gas (before passing through the filter medium) 2 flows, the filter medium 4 that forms the partition wall of the exhaust gas inflow path 3, and the exhaust gas inflow path 3. Thereafter, an exhaust gas outflow passage 6 through which exhaust gas (after passing through the filter medium) 5 that has passed through the filter medium 4 flows out is provided. Further, the downstream end of the exhaust gas inflow passage 3 and the upstream end of the exhaust gas outflow passage 6 are plugged with a plugging material 7.

  In the present embodiment, the exhaust gas (before passing through the filter medium) 2 is purified by flowing into the exhaust gas inflow passage 3 of the exhaust gas purification filter and being filtered by the filter medium 4, and as exhaust gas (after passing through the filter medium) 5, It is discharged from the exhaust gas outflow passage 6.

  FIG. 2 is a partially enlarged view of a dotted line range P in FIG. As shown in FIG. 2, the filter medium 8 has a gap 9 connected to the exhaust gas inflow passage 3 and the exhaust gas outflow passage 6. A low contact active catalyst 10 is supported on the surface of the filter medium 8 on the exhaust gas inflow path 3 side. A high contact active catalyst 11 is supported on the inner surface of the gap 9 of the filter medium 8.

  In the present embodiment, the PM 12 having a diameter equal to or smaller than the diameter of the gap 9 of the filter medium 8 passes through the gap 9 and contacts the high contact active catalyst 11 supported on the inner surface of the gap 9. Further, the PM 13 having a diameter equal to or larger than the diameter of the gap 9 of the filter medium 8 contacts the low contact active catalyst 10 carried on the surface of the filter medium 8 on the exhaust gas inflow path 3 side without passing through the gap 9.

  FIG. 3 is a partially enlarged view of the dotted line range Q in FIG. As shown in FIG. 3, the PM 12 having a diameter equal to or smaller than the diameter of the gap 9 of the filter medium 8 can enter the gap between the catalyst particles of the high contact active catalyst 11 supported on the inner surface of the gap 9. For this reason, the active point of a catalyst and the contact point of PM increase.

[Filtering media]
The filter medium 8 used in the present embodiment is not particularly limited. A known filter medium can be used as long as it has a void capable of supporting the high contact active catalyst 11 and can withstand the combustion temperature of PM. Examples of the filtering material used in the present embodiment include porous ceramics, ceramic foams, metal foams, and metal meshes. Among these, it is preferable to use a porous ceramic.

[Thickness of filter medium]
The thickness of the filter medium used in the present invention is not particularly limited, and the required degree of purification, the performance of the catalyst used, the size of the voids in the filter medium, the porosity, and the exhaust gas purification filter It can select suitably according to the magnitude | size of the purification apparatus to be used. The thickness of the filter medium in the present invention is preferably from 254 μm to 380 μm, and more preferably from 254 μm to 310 μm. If the thickness of the filter medium is within this range, it is possible to apply an optimum catalyst amount with respect to the PM amount entering the gap, and the catalyst performance can be sufficiently exhibited.

[Void size / porosity]
The size of the voids and the porosity in the filter medium used in the present invention are not particularly limited. The degree of purification required, the performance of the catalyst used, the thickness of the filter medium, and the size of the purification device using the exhaust gas purification filter can be selected as appropriate. In the present invention, the size of the gap of the filter medium is preferably in the range of 1 μm to 40 μm, and more preferably 9 μm to 24 μm. If the size of the voids is within this range, PM particle size having high contactability in contact with the catalyst can enter the voids, and the catalyst performance can be sufficiently exhibited. Further, the porosity of the filter medium in the present invention is preferably 30% or more and 98% or less, and more preferably 40% or more and 70% or less. If the porosity is within this range, PM can be purified while maintaining a sufficient PM collection rate.

[Plugging material]
The plugging material 7 used in the present embodiment is not particularly limited. As long as the exhaust gas inflow passage 3 and the exhaust gas outflow passage 5 have a size that can be plugged and can withstand the use of the combustion temperature of PM, a plugging material formed of a known material is used. It is possible to use. Examples of the plugging material used in the present embodiment include ceramic materials such as SiC, cordierite, alumina, and silica, and metal materials, but it is desirable to use the same material as the filter material 8.

[High catalytic activity catalyst]
The high contact active catalyst 11 used in the present embodiment is a catalyst exhibiting high activity when the contact property with the particulate matter is high. Since the highly active catalyst can burn PM at a low temperature when the contact state with PM is high, PM can be burned continuously even if the exhaust gas to be treated is at a low temperature. For this reason, PM can be burned sufficiently continuously even in a practical range in a diesel vehicle.

  Although it does not specifically limit as a high contact active catalyst used for this invention, For example, the catalyst containing at least 1 sort (s) of elements chosen from inorganic elements, such as a noble metal element and a transition metal element, can be mentioned. In these, the catalyst containing noble metal elements, such as ruthenium and palladium, is preferable.

[Low catalytic activity catalyst]
The low contact active catalyst 10 used in the present embodiment is a catalyst that exhibits high activity regardless of the contact property with the particulate matter. The low contact active catalyst not only can burn PM at a low temperature in a state where the contact state with PM is high, but can burn PM at a low temperature even in a state where the contact state with PM is low. This is presumed that low temperature combustion of PM is possible even in a low contact state due to the melting effect of the components contained in the low contact active catalyst such as alkali metal.

  The low contact active catalyst can burn PM only on the high temperature side when the contact with the PM is low as compared with the state where the contact property of the high contact active catalyst is high. PM can be combusted at a lower temperature than in a state where the contact is low. For this reason, the contact property between the high contact active catalyst and PM is low, and PM (for example, stacked PM) that could not be continuously burned is lower at a lower temperature than burning using a high contact active catalyst. Can burn.

  The low contact active catalyst used in the present invention is not particularly limited. For example, at least one element selected from inorganic elements such as noble metal elements, transition metal elements, alkali metals, and alkaline earth metals is used. Mention may be made of the catalyst comprising. Among these, a catalyst containing at least one transition metal element and at least one alkali metal element is preferable. Examples of the transition metal element include lanthanum, cerium, praseodymium, neodymium, manganese, cobalt, copper, molybdenum, and vanadium. A combination of cesium having the lowest electronegativity is particularly preferable as the oxide and the element having low ionization energy and the alkali metal element.

[Manufacturing method of exhaust gas purification filter (catalyst loading method)]
The method for producing an exhaust gas purification filter of the present invention includes a high contact active catalyst supporting step and a low contact active catalyst supporting step.

[High contact active catalyst loading process]
The high-contact active catalyst supporting step in the method for producing an exhaust gas purification filter is a method in which a high-contact active catalyst exhibiting high activity is passed through a filter material when the contact property with particulate matter is high, In this step, a highly catalytically active catalyst is supported on the surface.

[Low contact active catalyst loading process]
The low contact active catalyst supporting step in the method for producing an exhaust gas purification filter is a particulate material on the surface of the filter medium in which the high contact active catalyst is supported on the inner surface of the void in the filter medium by the high contact active catalyst support step. This is a step of applying and supporting a low contact active catalyst exhibiting high activity regardless of the contact property of the catalyst.

[Closing process]
In the present invention, when producing a wall flow type exhaust gas purification filter, after the above-described high contact active catalyst supporting step, a plugging step with a plugging material is performed, and then the exhaust gas inflow passage is By applying the low contact active catalyst from the inlet side, the low contact active catalyst supporting step can be carried out.

[Exhaust gas purification equipment]
The apparatus in which the exhaust gas purification filter of the present invention is used is not particularly limited. Exhaust gas purification devices are roughly classified into trap type exhaust gas purification devices (wall flow type) and open type exhaust gas purification devices (straight flow type). The exhaust gas purifying filter of the present invention can be suitably used in any type of exhaust gas purifying device. However, since it makes use of the advantage that PM can be efficiently burned at a low temperature, it is particularly a wall flow type. It is preferable to use for this exhaust gas purification apparatus.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

<Evaluation of catalyst>
First, PM combustion temperature was measured for the catalysts used in Examples and Comparative Examples.

[Measurement of PM combustion temperature]
In the test examples, examples, and comparative examples of the present invention, the PM combustion temperature was measured based on the following conditions.
〔Test conditions〕
Measuring device: TG / DTA (manufactured by SII Nano Technology, trade name: EXSTAR6000TG / DTA)
Temperature rising condition: 20 ° C / min
Atmosphere: Dry Air
Sample amount: 10 mg (internal PM amount: 5% by mass)
Flow rate: SV = 60000h ⁻¹
[Sample preparation conditions]
High contact state (tight contact: TC): pulverized and mixed to 2 μm or less with a mortar pestle Low contact state (loose contact: LC): Sprinkle PM on the sample

[Test Example 1 (RuO ₂ + PM: TC)]
Ruthenium chloride (a commercially available special grade reagent) was calcined at 800 ° C., and subsequently sized so as to obtain a powder of 2 μm or less. PM was pulverized and mixed with the catalyst A so as to be 20: 1 (mass ratio) to obtain a sample having high contact between PM and the catalyst. The PM combustion temperature was measured for the obtained sample. The combustion peak temperature is shown in Table 1.

[Test Example 2 (1 mass% Pd / CeO ₂ + PM: TC)]
Cerium nitrate (commercial special grade reagent), palladium chloride, and H ₂ O were weighed and mixed so as to have a predetermined composition to obtain an aqueous solution containing cerium and palladium. In a separate container, sodium hydroxide and H ₂ O were weighed and mixed so as to have a predetermined composition to obtain an aqueous sodium hydroxide solution. The obtained cerium and palladium-containing aqueous solution was dropped into an aqueous sodium hydroxide solution to obtain a precipitate. The pH at this time was 10. After aging at 60 ° C. for 1 hour, filtration and washing were carried out, and after calcination at 350 ° C., the particles were sized to become a powder of 2 μm or less. The obtained powder was calcined at 500 ° C. for 5 hours to obtain catalyst B. PM was pulverized and mixed with the catalyst B at a ratio of 20: 1 (mass ratio) to obtain a sample having a high contact property between the PM and the catalyst. About the obtained sample, the PM combustion temperature was measured in the same manner as in Test Example 1. The combustion peak temperature is shown in Table 1.

[Test Example 3 (10 mass% Cs ₂ CO ₃ / LaMnO ₃ + PM: TC)]
Lanthanum nitrate (a commercially available special grade reagent), manganese nitrate, and H ₂ O were weighed and mixed so as to have a predetermined composition to obtain an aqueous solution containing lanthanum and manganese. In another container, sodium carbonate and H ₂ O were weighed and mixed so as to have a predetermined composition to obtain an aqueous sodium carbonate solution. A lanthanum and manganese-containing aqueous solution was dropped into a sodium carbonate aqueous solution to obtain a precipitate. Subsequently, aging was performed at 60 ° C. for 1 hour, followed by filtration and washing with water, followed by provisional firing at 350 ° C., followed by sizing so as to obtain a powder of 2 μm or less. The obtained powder was calcined at 800 ° C. for 10 hours to obtain catalyst C. The catalyst C was pulverized and mixed to 10% by mass of cesium carbonate, and calcined at 800 ° C. for 1 hour to cause a solid phase reaction, whereby a catalyst D was obtained. PM was pulverized and mixed with the catalyst D at a ratio of 20: 1 (mass ratio) to obtain a sample having a high contact property between the PM and the catalyst. About the obtained sample, the PM combustion temperature was measured in the same manner as in Test Example 1. The combustion peak temperature is shown in Table 1.

[Test Example 4 (10% by mass Cs ₂ CO ₃ / LaMnO ₃ + PM: LC)]
The catalyst D obtained in Test Example 3 was sprinkled with PM at a ratio of 20: 1 (mass ratio) to obtain a sample with a low contact property between PM and the catalyst. About the obtained sample, the PM combustion temperature was measured in the same manner as in Test Example 1. The combustion peak temperature is shown in Table 1.

[Comparative Test Example 1 (PM only)]
The PM combustion temperature was measured in the same manner as in Test Example 1 for the PM powder collected from the diesel generator. The results are shown in Table 1.

[Comparative Test Example 2 (RuO ₂ + PM: LC)]
The catalyst A obtained in Test Example 1 was sprinkled with PM at a ratio of 20: 1 (mass ratio) to obtain a sample having a low contact property between PM and the catalyst. About the obtained sample, the PM combustion temperature was measured in the same manner as in Test Example 1. The combustion peak temperature is shown in Table 1.

[Comparative Test Example 3 (1% by mass Pd / CeO ₂ + PM: LC)]
The catalyst B obtained in Test Example 2 was sprinkled with PM at a ratio of 20: 1 (mass ratio) to obtain a sample having a low contact property between PM and the catalyst. About the obtained sample, the PM combustion temperature was measured in the same manner as in Test Example 1. The combustion peak temperature is shown in Table 1.

[Consideration from test examples]
Comparative Example Test Example 1 is a PM combustion peak temperature when no catalyst is used. The combustion peak temperature in the case of PM as it was was 668 ° C.

  Test Examples 1 and 2 are examples in which a high contact active catalyst was used in a state where contactability was high. As shown in Test Examples 1 and 2, when using a highly catalytically active catalyst with high contactability, 1st Peak of 300 ° C. or less and 2nd Peak of 500 ° C. or less are provided, and PM is burned at a low temperature. It is possible to make it. Although the influence of HC components in PM is also considered, 1st Peak is a peak due to combustion at the interface (contact surface) between PM and catalyst, and 2nd Peak is presumed to be a peak due to combustion of PM with low contact properties it can.

  On the other hand, as shown in Comparative Test Examples 2 and 3, when the high contact active catalyst was used in a low contact state, the 2nd Peak was significantly increased to 585 ° C. and 654 ° C., respectively. . Thus, it can be seen that PM cannot be burned at a low temperature when the high contact active catalyst is used in a low contact state.

  Test Example 3 is an example in which a low contact active catalyst was used in a state where contactability was high. From Test Example 3, it can be seen that PM can be burned at 375 ° C. at a low temperature. Even when the low catalytic activity catalyst is used in a state where the contact property is high, the combustion peak temperature is not so high. The low catalytic activity catalyst has lower original activity than the high catalytic activity catalyst. This is probably because of this.

  Test Example 4 is an example in which a low contact active catalyst was used in a state where contactability was low. The 1st Peak of Test Example 4 is 522 ° C., which is lower than the combustion peak temperature of PM alone (no catalyst), as well as the case where a high contact active catalyst is used in a state where the contact property is low (Test Example 2). Also, it can be seen that PM can be combusted at a low temperature as compared with 3). The reason why the catalytic performance is high even when the low catalytic activity catalyst is low is presumed to be that the catalytic activity at the active site is improved by the movement and melting of the active species.

  As described above, the high contact active catalyst and the low contact active catalyst are separately applied to the high contact portion and the low contact portion with the PM, thereby sufficiently exhibiting the performance of the catalyst, and combustion of the PM at a low temperature. It turns out that it can carry out efficiently.

<Example 1>
[Void: RuO ₂ + PM, Surface: 10% by mass Cs ₂ CO ₃ / LaMnO ₃ + PM]
Catalyst A, silica sol (Nissan Chemical Industry) obtained in Test Example 1 and H ₂ O were weighed so as to have a predetermined composition, and pulverized and mixed in a ball mill for 24 hours to obtain catalyst slurry A. . Further, the catalyst D, silica sol (Nissan Chemical Industries) obtained in Test Example 3 and H ₂ O were weighed so as to have a predetermined composition, and pulverized and mixed in a ball mill for 24 hours to obtain catalyst slurry D. Obtained.

  The obtained catalyst slurry A was impregnated and supported on a commercially available DPF (manufactured by Ibiden), and excess slurry on the surface was sufficiently removed with an air gun. Thereafter, baking was performed at 600 ° C. for 2 hours to load 50 g / L of catalyst A inside the gaps of the DPF. Subsequently, DPF was alternately plugged, the catalyst slurry D was impregnated and supported, and excess slurry was removed with an air gun. Thereafter, the catalyst D was supported on the surface of the DPF by 50 g / L by firing at 600 ° C. for 2 hours. Using the DPF carrying the obtained catalyst A and catalyst D, PM was collected by a PM collection holder installed in an exhaust gas pipe of a diesel generator. The amount of PM collected at this time was 5 g / L. The PM combustion temperature was measured for the DPF after PM collection. The combustion peak temperature is shown in Table 2.

<Comparative Example 1>
[Voids and surface: RuO ₂ + PM]
Commercially available DPF (made by Ibiden) was alternately plugged, impregnated and supported with the catalyst slurry A described above, and excess slurry was sufficiently removed with an air gun, followed by firing at 600 ° C. for 2 hours. A total of 100 g / L of catalyst A was supported on the voids and the surface. Using the obtained DPF carrying the catalyst A, PM was collected in the same manner as in Example 1, and the PM combustion temperature was measured for the DPF after PM collection. The combustion peak temperature is shown in Table 2.

<Comparative example 2>
[Void and surface: 10% by mass Cs ₂ CO ₃ / LaMnO ₃ + PM]
Commercially available DPF (made by Ibiden) was alternately plugged, impregnated and supported with the catalyst slurry D described above, and the excess slurry was sufficiently removed with an air gun, followed by firing at 600 ° C. for 2 hours. A total of 100 g / L of Catalyst D was supported on the voids and the surface. Using the obtained DPF carrying the catalyst D, PM was collected in the same manner as in Example 1, and the PM combustion temperature was measured for the DPF after PM collection. The combustion peak temperature is shown in Table 2.

<Comparative Example 3>
[Void and surface: 1% by mass Pd / CeO ₂ + 10% by mass Cs ₂ CO ₃ / LaMnO ₃ + PM]
Catalyst A, Catalyst D, silica sol (Nissan Chemical Industries), and H ₂ O of the above test examples were weighed so as to have a predetermined composition, and pulverized and mixed in a ball mill for 24 hours to obtain catalyst slurry E. By plugging commercially available DPF (made by Ibiden) alternately, impregnating and supporting the obtained catalyst slurry E, and removing excess slurry sufficiently with an air gun, by carrying out firing at 600 ° C. for 2 hours, A total of 100 g / L of the mixture of catalyst A and catalyst D was supported in the voids and the surface of the DPF. Using the DPF carrying the obtained mixture of the catalyst A and the catalyst D, PM was collected in the same manner as in Example 1, and the PM combustion temperature was measured for the DPF after PM collection. The combustion peak temperature is shown in Table 2.

<Comparative example 4>
[Void: 10% by mass Cs ₂ CO ₃ / LaMnO ₃ , surface: 1% by mass Pd / CeO ₂ + PM]
The catalyst slurry D is impregnated and supported in a commercially available DPF (made by Ibiden), and the excess slurry on the surface is sufficiently removed with an air gun, followed by firing at 600 ° C. for 2 hours, so that the inside of the DPF voids. Catalyst D was supported at 50 g / L. Subsequently, DPF was alternately plugged, the catalyst slurry A was impregnated and supported, and excess slurry was removed with an air gun. Thereafter, the catalyst D was supported on the surface of the DPF by 50 g / L by firing at 600 ° C. for 2 hours. Using the obtained DPF carrying the catalyst A and catalyst D, PM was collected in the same manner as in Example 1, and the PM combustion temperature was measured for the DPF after PM collection. The combustion peak temperature is shown in Table 2.

[Consideration from Examples and Comparative Examples]
Example 1 is an example in which a high contact active catalyst was applied to the inner surface of the filter medium and a low contact active catalyst was applied to the surface of the filter medium, and the combustion peak temperatures were 262 ° C. and 522 ° C. 262 ° C of 1st Peak is the combustion temperature of PM that is highly contactable with the high contact active catalyst in the void, and 522 ° C of 2nd Peak is laminated only on the surface of the filtering agent with PM that is not so high in the void. Thus, it is presumed that the combustion temperature overlaps with PM having low contactability with the low contact active catalyst.

  As shown in Example 1, when a high contact active catalyst was applied to the inside surface of the filter medium and a low contact active catalyst was applied to the surface of the filter medium, the PM amount is high in the contactability in the pores. When it is so small that only PM is constituted, PM can be continuously burned under the most frequent operating conditions (practical range: exhaust temperature 200 ° C. to 300 ° C.) in a diesel vehicle. Further, even when the amount of PM increases or when the PM particle size is larger than the void diameter, forced regeneration can be performed at a temperature significantly lower than before.

  Comparative Example 1 is an example in which only the high contact active catalyst is supported in both the voids and the surface of the filter medium, and the combustion peak temperatures are divided into 247 ° C, 481 ° C, and 579 ° C. 1st Peak 247 ° C. is the combustion temperature of PM in the gap and has high contact with the catalyst, and 2nd Peak 481 ° C. is PM in the gap and the combustion temperature of the contact with the catalyst is not so high. 3rd Peak of 579 ° C. is presumed to be the combustion temperature of low-contact PM present on the filter medium surface.

  From Comparative Example 1, when the amount of PM is small enough to be composed of only PM with high contact in the gap of the filter medium, PM can be burned at a low temperature, but when the amount of PM further increases, When the particle diameter is larger than the void diameter, the contact with the catalyst becomes low, and it can be understood that combustion cannot be performed at a low temperature.

  Comparative Example 2 was an example in which only the low contact active catalyst was supported in both the voids and the surface of the filter medium, and the combustion peak temperatures were 369 ° C and 536 ° C. It is estimated that 369 ° C of 1st Peak is the combustion temperature of PM in the gap and has high contact property with the catalyst, and 536 ° C of 2nd Peak is the combustion temperature of low contact property PM present on the filter medium surface. The

  From Comparative Example 2, when the amount of PM is large or when the PM particle size is larger than the gap diameter, the performance is the same as that of Example 1, but only PM with high contact with the catalyst in the gap is obtained. It can be seen that the combustion temperature is higher than that in Example 1 when the amount of PM is small enough to be configured.

  Comparative Example 3 was an example in which a mixture of a high contact active catalyst and a low contact active catalyst was supported both in the voids and on the surface of the filter medium, and the combustion peak temperatures were two at 373 ° C and 524 ° C. The 1st Peak of 373 ° C. is considered to be because the effect of the high contact active catalyst was lost by mixing because it was close to the case where the low contact active catalyst was applied in the gap (Test Example 3). 2nd Peak of 524 ° C. is presumed to be the combustion temperature of PM having low contact property with the catalyst present on the surface of the filter medium, and is considered to be the influence of the low contact active catalyst.

  From Comparative Example 3, as in Comparative Example 2, when the amount of PM is large, or when the PM particle size is larger than the void diameter, the performance equivalent to that of Example 1 is shown. It can be seen that the combustion temperature is higher than that in Example 1 when the amount of PM is small enough to be composed of only PM with high contactability.

  Contrary to Example 1, Comparative Example 4 is an example in which a low contact active catalyst is supported in the gap of the filter medium, and a high contact active catalyst is supported on the surface of the filter medium, and the combustion peak temperatures are 277 ° C., 375 ° C., It is divided into 579 ° C and three. 1st Peak 277 ° C is the combustion temperature of highly contactable PM present at the interface between the high contact active catalyst on the surface of the filter medium and PM, and 2nd Peak 375 ° C is the combustion temperature of PM in the gap with high contactability. 3rd Peak is presumed to be the combustion temperature of PM on the surface of the filter medium with low contactability.

  From Comparative Example 4, when the amount of PM is small enough to contact the interface with the catalyst on the surface of the filter medium, PM can be combusted at a low temperature, but PM having a diameter equal to or smaller than the void diameter is deposited in the pores. In this case, continuous combustion under the most frequent operating conditions (practical range: exhaust temperature 200 ° C. to 300 ° C.) in a diesel vehicle is impossible, and when the amount of PM is large or the PM particle size is void When the diameter is larger than the diameter, the contact property is deteriorated, so that it is understood that the combustion temperature is higher than that of the first embodiment.

  Therefore, in the case of DPF as well, it can be seen that, as in Example 1, it is optimal to separately apply a high contact active catalyst on the inner surface of the filter medium and a low contact active catalyst on the surface of the filter medium.

  In Example 1, the reason why the contact property of the high contact active catalyst is high is that the activity of the high contact active catalyst is high, the amount of PM is small, and the particle size of the PM is small. As shown in FIG. 3, it is presumed that the contact point between the catalyst active point and the PM is increased by PM entering the gaps between the particles of the high contact active catalyst, and the contact property is further increased. For example, in the case of DPF, the PM particles are classified by the DPF pores into those having a diameter equal to or smaller than the DPF pore size, so it is estimated that PM easily enters the gaps between the catalysts constituted by the high contact active catalyst particles. The

It is a cross-sectional schematic diagram of a direction parallel to the cell of a wall flow type DPF. It is the elements on larger scale of the dotted line range P in FIG. FIG. 3 is a partially enlarged view of a dotted line range Q in FIG. 2.

Explanation of symbols

1 Wall flow type DPF
2 Exhaust gas (before passing through filter media)
3 Exhaust gas inflow path 4 Filter material 5 Exhaust gas (after passing through the filter material)
6 Exhaust gas outflow passage 7 Plugging material 8 Filter material 9 Void 10 Low contact active catalyst 11 High contact active catalyst 12 PM having a diameter equal to or smaller than the void diameter
13 PM with a diameter larger than the void diameter

Claims (6)

An exhaust gas purification filter that is disposed in an exhaust passage of an internal combustion engine and purifies particulate matter in exhaust gas discharged from the internal combustion engine,
An exhaust gas inflow passage through which the exhaust gas flows; and
A filter medium that forms a partition wall of the exhaust gas inflow passage and has a gap;
An exhaust gas outflow passage that flows into the exhaust gas inflow passage and outflows the exhaust gas that has passed through the filter medium, and
The inner surface of the partition wall is loaded with a low contact active catalyst that exhibits high activity regardless of contact with the particulate matter,
An exhaust gas purifying filter in which a high contact active catalyst exhibiting high activity is supported on the inner surface of the void in the filter medium when contactability with the particulate matter is high. The exhaust gas inflow passage and the exhaust gas outflow passage are formed from a large number of cells alternately arranged adjacent to each other through the filter medium,
The cell forming the exhaust gas inflow path has an upstream end opened and a downstream end plugged.
2. The exhaust gas purification filter according to claim 1, wherein the cells forming the exhaust gas outflow passage are plugged at an upstream end and open at a downstream end.   The exhaust gas purification filter according to claim 1 or 2, wherein the filter medium is a porous ceramic.   The exhaust gas purification filter according to any one of claims 1 to 3, wherein the low contact active catalyst contains at least one transition metal element and at least one alkali metal element.   The exhaust gas purification filter according to any one of claims 1 to 4, wherein the high contact active catalyst includes at least one kind of noble metal element. An exhaust gas purification filter manufacturing method for purifying particulate matter in exhaust gas disposed in an exhaust passage of an internal combustion engine and exhausted from the internal combustion engine,
When the contact property with the particulate matter is high, the high contact active catalyst that exhibits high activity is passed through the filter medium having voids, and the high contact active catalyst is supported on the inner surface of the voids in the filter medium. A high contact active catalyst loading process;
The surface of the filter medium in which the high contact active catalyst is supported on the inner surface of the void in the filter medium by the high contact active catalyst support process exhibits high activity regardless of the contact property with the particulate matter. And a low contact active catalyst supporting step of applying and supporting the low contact active catalyst.

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