JP2012236180A - Filter for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter for cleaning exhaust gas, the pressure loss of which can be reduced while ensuring thermal durability of a catalyst and in which the particulate captured on a partition wall can be burned efficiently.SOLUTION: The filter 1 for cleaning exhaust gas has: porous partition walls 2 arranged in a grid pattern; and a plurality of cells 3 each of which is surrounded by the partition walls 2 and formed in the axial direction thereof. In the cells 3, each of the downstream-side X2 end of an introduction cell 31 for introducing exhaust gas G and the upstream-side X1 end of a discharge cell 32 for discharging the exhaust gas G is plugged with a plug part. Both of a PM combustion catalyst 5 containing an alkali metal and a reaction suppressing layer 6, which is formed between the partition wall 2 and the PM combustion catalyst 5 and used for suppressing a reaction of the partition wall with the PM combustion catalyst, are deposited on the partition wall 2. The PM combustion catalyst 5 and the reaction suppressing layer 6 are deposited selectively on the introduction cell-side surface 201 of the partition wall 2 and on the inside of the partition wall 2 within a ≤D/2 distance (D is the thickness of the partition wall 2) from the surface 201 in the thickness direction thereof.

Description

  The present invention relates to an exhaust gas purifying filter for purifying exhaust gas discharged from an internal combustion engine such as a diesel engine.

  Conventionally, there has been known an exhaust gas purification filter that collects particulates (hereinafter, appropriately referred to as PM) in exhaust gas discharged from an internal combustion engine such as a diesel engine and purifies the exhaust gas. The exhaust gas purification filter has, for example, porous partition walls arranged in a lattice shape and a plurality of cells formed in the axial direction surrounded by the partition walls, and exhaust gas flows in the cells. There is one in which the end on the downstream side of the inflow cell and the end on the upstream side of the exhaust cell for discharging the exhaust gas are blocked by a plug portion.

  When exhaust gas is purified using the exhaust gas purification filter having the above configuration, exhaust gas flows into the inflow cell, passes through the porous partition wall, and is then discharged from the exhaust cell. At this time, PM in the exhaust gas is collected in the partition wall having a large number of pores, and the exhaust gas is purified. In addition, by loading a catalyst containing, for example, an alkali metal or the like on the partition wall, the PM collected on the partition wall can be efficiently burned and removed by a catalytic reaction.

By the way, the exhaust gas purification filter has a problem in that the partition and the catalyst containing alkali metal or the like supported on the partition react at a high temperature and the catalytic activity decreases.
Therefore, Patent Document 1 proposes an exhaust gas purification filter in which a reaction suppression layer (inorganic oxide, metal oxide) that suppresses the reaction between the partition wall and the catalyst (alkali metal sulfate or the like) is provided. ing. According to this, the reaction between the partition walls and the catalyst at a high temperature and the accompanying decrease in the catalyst activity can be suppressed, and the thermal durability of the catalyst can be improved.

JP 2010-51867 A

In the exhaust gas purification filter of Patent Document 1, a catalyst and a reaction suppression layer are supported on the entire partition including the surface and the inside of the partition. However, most of the PM in the exhaust gas penetrates and is trapped inside the partition wall in the inflow cell side region (region from the surface on the inflow cell side to half the thickness) of the partition wall. For this reason, the catalyst supported in the region on the discharge cell side of the partition wall did not act effectively in burning PM.
In addition, since the catalyst and the reaction suppression layer are supported on the entire partition wall, the three-dimensional structure of the exhaust gas purification filter as a whole changes, and there is a problem that the pressure difference (pressure loss) before and after passage of the exhaust gas increases. It was.

  The present invention has been made in view of such conventional problems, and can reduce the pressure loss while ensuring the thermal durability of the catalyst, and efficiently burn the particulates collected in the partition walls. It is an object to provide an exhaust gas purification filter that can perform the above-mentioned.

The present invention has a porous partition wall arranged in a lattice shape and a plurality of cells formed in the axial direction surrounded by the partition wall, and among the cells, downstream of an inflow cell into which exhaust gas flows. In the exhaust gas purification filter in which the end portion on the side and the end portion on the upstream side of the exhaust cell that exhausts exhaust gas are closed by the plug portion,
The partition wall is loaded with a PM combustion catalyst containing an alkali metal, and a reaction suppression layer that is formed between the partition wall and the PM combustion catalyst and suppresses the reaction between the two.
In the PM combustion catalyst and the reaction suppression layer, when the thickness of the partition wall is D, the surface of the partition wall on the inflow cell side and the inside of the partition wall in the range from the surface to a distance of D / 2 or less in the thickness direction. The exhaust gas purifying filter is selectively supported. (Claim 1)

  In the exhaust gas purification filter, the partition wall carries a PM combustion catalyst containing an alkali metal and a reaction suppression layer that suppresses a reaction between the partition wall and the PM combustion catalyst. The PM combustion catalyst and the reaction suppressing layer are selected on the surface of the partition wall on the inflow cell side and the interior of the partition wall in a range of D / 2 or less in the thickness direction from the surface when the partition wall thickness is D. Is supported.

  That is, the PM combustion catalyst is not supported on the entire partition wall, but the surface on the inflow cell side of the partition wall where the PM in the exhaust gas is likely to be collected on the surface and inside the partition wall, and the inside of the partition wall. A specific range is selectively supported. Therefore, the PM collected by the partition walls can be efficiently burned by the PM combustion catalyst that is intensively supported in a region where the PM is easily collected.

  The reaction suppression layer is supported in a region where it is necessary to suppress the reaction between the partition walls and the PM combustion catalyst, that is, a region where the PM combustion catalyst is supported. And it forms so that it may interpose between a partition and a PM combustion catalyst. Therefore, the reaction between the partition walls and the PM combustion catalyst at a high temperature can be sufficiently suppressed by the reaction suppression layer. Thereby, the thermal durability of the PM combustion catalyst can be sufficiently ensured.

  Further, as described above, the PM combustion catalyst and the reaction suppression layer are selectively supported on the surface on the inflow cell side of the partition wall and the specific range in the partition wall. Therefore, compared to the conventional case where the PM combustion catalyst and the reaction suppression layer are supported on the entire partition wall, the supported amount can be significantly reduced. Thereby, the increase in the pressure loss by carrying | supporting PM combustion catalyst and the reaction suppression layer can be suppressed. That is, pressure loss can be reduced as compared with the prior art.

  Thus, according to the present invention, there is provided an exhaust gas purification filter capable of reducing pressure loss and efficiently burning particulates collected in the partition wall while ensuring the thermal durability of the catalyst. can do.

1 is a perspective view showing an exhaust gas purification filter in Embodiment 1. FIG. FIG. 3 is an explanatory cross-sectional view showing an exhaust gas purification filter disposed in an exhaust gas passage in the first embodiment. Sectional explanatory drawing which expands and shows the partition in Example 1. FIG. Explanatory drawing which shows the result of PM combustion speed and differential pressure | voltage in Example 2. FIG.

  The exhaust gas purification filter is disposed in an exhaust gas passage of an internal combustion engine such as a diesel engine, and is used for collecting PM in exhaust gas discharged from the internal combustion engine and purifying the exhaust gas.

In addition, the PM combustion catalyst and the reaction suppression layer may have the partition wall in a range from the surface on the inflow cell side of the partition wall to a distance of D / 2 or less from the surface in the thickness direction, where D is the thickness of the partition wall. Is selectively carried in the inside.
Here, being carried inside the partition means that it is carried in the pores formed inside the porous partition.

The PM combustion catalyst and the reaction suppression layer are selectively supported in the specific region (the surface on the inflow cell side of the partition wall and the specific range in the partition wall). However, strictly speaking, it is not easy to carry only in the specific area and not to be carried in any other area.
Therefore, for example, when the entire PM combustion catalyst supported on the partition wall is 100% by mass, and 80% by mass or more of the PM combustion catalyst is supported in the specific region, the PM combustion catalyst is selectively selected in the specific region. What is necessary is just to carry | support to. The same applies to the reaction suppression layer.

Further, the PM combustion catalyst and the reaction suppression layer are selectively supported on the surface of the partition wall on the inflow cell side and in the partition wall in a range from the surface to a distance of D / 3 or less in the thickness direction. (Claim 2).
That is, most of the PM that has entered and collected inside the partition walls tends to be concentrated in a range from the surface on the inflow cell side of the partition walls to a distance of D / 3 or less in the thickness direction. Therefore, by narrowing the range in which the PM combustion catalyst and the reaction suppression layer are supported inside the partition wall to the specific range, it is possible to reduce the supported amount and further reduce the pressure loss.

Further, the PM combustion catalyst and the reaction suppression layer are supported at least on the surface of the partition wall on the inflow cell side and in the partition wall in a range from the surface to a distance of D / 5 in the thickness direction. Is preferred.
For example, when the region supporting the PM combustion catalyst and the reaction suppression layer is inside the partition wall in the range from the surface on the inflow cell side of the partition wall to a distance shorter than D / 5 in the thickness direction from the surface, There is a possibility that the PM collected in the catalyst cannot be sufficiently burned by the PM combustion catalyst.

The PM combustion catalyst preferably contains one or more selected from Na, K, Cs, and Rb.
In this case, the PM collected in the partition wall can be sufficiently burned by the PM combustion catalyst.

Moreover, it is preferable that the said reaction suppression layer contains 1 or more types chosen from Al, Zr, and La. (Claim 4).
In this case, the reaction suppression layer can sufficiently suppress the reaction between the partition walls and the PM combustion catalyst at a high temperature.

  Further, as a material constituting the exhaust gas purification filter, for example, cordierite, silicon carbide, silicon nitride, mullite, aluminum titanate, or the like can be used. In particular, cordierite has a low thermal expansion coefficient and excellent thermal shock resistance. Therefore, it is preferable as a material constituting an exhaust gas purification filter that is used at high temperatures and requires heat resistance and durability.

  Moreover, the exhaust gas purification filter needs to sufficiently secure PM collection performance, pressure loss, strength, and the like. Therefore, the thickness of the said partition can be 300-500 micrometers, for example. Moreover, the porosity of the said partition can be 35-70%, for example. Moreover, the average pore diameter of the said partition can be 10-30 micrometers, for example.

Example 1
An exhaust gas purification filter according to an embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the exhaust gas purification filter 1 of the present example includes porous partition walls 2 arranged in a lattice shape, and a plurality of cells 3 surrounded by the partition walls 2 and formed in the axial direction. In the cell 3, the end portion 312 on the downstream side X2 of the inflow cell 31 into which the exhaust gas G flows and the end portion 321 on the upstream side X1 of the exhaust cell 32 from which the exhaust gas G is discharged are blocked by the plug portion 4. ing.

As shown in FIG. 3, the partition wall 2 carries a PM combustion catalyst 5 containing an alkali metal, and a reaction suppression layer 6 formed between the partition wall 2 and the PM combustion catalyst 5 to suppress the reaction therebetween. ing. The PM combustion catalyst 5 and the reaction suppression layer 6 have the partition wall 2 having a surface 201 on the inflow cell side of the partition wall 2 and a partition wall 2 in a range from the surface 201 to a distance of D / 2 or less in the thickness direction, where D is the thickness of the partition wall 2. Is selectively carried in the inside.
This will be described in detail below.

As shown in FIGS. 1 and 2, the exhaust gas purification filter 1 is disposed in an exhaust gas passage 81 formed in an exhaust pipe 8 of a diesel engine, and removes PM (FIG. 3) in the exhaust gas G discharged from the diesel engine. It is used to collect and purify the exhaust gas G.
The exhaust gas purification filter 1 is composed of a honeycomb structure having porous partition walls 2 arranged in a quadrangular lattice shape and a plurality of cells 3 having a quadrangular cross section surrounded by the partition walls 2 and formed in the axial direction. The exhaust gas purification filter 1 is made of cordierite, and has an overall shape of a column having a diameter of 160 mm and a length of 100 mm.

As shown in the figure, the cell 3 includes an inflow cell 31 into which the exhaust gas G flows and an exhaust cell 32 from which the exhaust gas G is discharged. The end portion 312 on the downstream side X2 of the inflow cell 31 and the end portion 321 on the upstream side X1 of the discharge cell 32 are respectively closed by the plug portion 4. In addition, the end 311 on the upstream side X1 of the inflow cell 31 and the end 322 on the downstream side X2 of the discharge cell 32 open to the upstream side X1 and the downstream side X2, respectively.
In this example, the plug portions 4 are arranged in a so-called checkered pattern on the end surface 101 on the upstream side X1 and the end surface 102 on the downstream side X2 of the exhaust gas purification filter 1 so that the inflow cells 31 and the outflow cells 32 are alternately disposed. Has been.

As shown in FIG. 3, the partition wall 2 is porous and has a large number of pores 21 formed therein. The porosity of the partition walls 2 is 50%, and the average pore diameter is 12 μm.
The partition wall 2 carries a PM combustion catalyst 5 and a reaction suppression layer 6 that is formed between the partition wall 2 and the PM combustion catalyst 5 and suppresses the reaction therebetween. The PM combustion catalyst 5 and the reaction suppression layer 6 have a surface 201 on the inflow cell side of the partition wall 2 and a range from the surface 201 to a distance D / 2 in the thickness direction when the thickness of the partition wall 2 is D (in the figure). It is carried inside the partition 2 in range A). The partition wall 2 has a thickness D of 300 μm.

Specifically, as shown in the figure, the reaction suppression layer 6 is formed on the surface 201 of the partition wall 2 on the inflow cell side, and further formed on the inner surface 211 of the pore 21 in the range A of the partition wall 2. . Further, the PM combustion catalyst 5 is supported on the formed reaction suppression layer 6.
In addition, when the entire PM combustion catalyst 5 supported on the partition wall 2 is 100% by mass, 80% by mass or more of the PM combustion catalyst 5 is in the surface 201 on the inflow cell side of the partition wall 2 and inside the partition wall 2. Supported in range A. The reaction suppression layer 6 is the same.
The PM combustion catalyst 5 is made of a catalyst material in which potassium carbonate is supported on sodalite. The reaction suppression layer 6 is made of aluminum oxide.

Next, a method for manufacturing the exhaust gas purification filter 1 of this example will be briefly described.
First, it has a porous partition wall 2 arranged in a quadrangular lattice shape, and a plurality of cells 3 having a quadrangular cross section formed in the axial direction surrounded by the partition wall 2, and a plug portion 4 at a predetermined position. The provided cordierite honeycomb structure (see FIG. 1) was prepared.
Next, the honeycomb structure was dipped in a 0.5 mol / L aluminum nitrate aqueous solution (hereinafter referred to as an aqueous solution as appropriate) for a predetermined time, pulled up, and then excess water was blown off by air blowing.

Next, hot air at about 300 ° C. was supplied from the upstream side X1 of the honeycomb structure for 5 minutes, and the aqueous solution in the partition walls 2 was dried in order from the surface 201 of the partition walls 2 on the inflow cell side. At this time, the metal concentration in the aqueous solution increases in the portion where drying has started, and therefore moisture is drawn from the portion where moisture remains in order to make the concentration uniform. By this phenomenon, the aqueous solution is moved from the discharge cell side of the partition wall 2 to the inflow cell side, and inside the partition wall 2 in the range from the surface 201 on the inflow cell side of the partition wall 2 to a distance of 150 μm from the surface 201 in the thickness direction, Selectively deposited aluminum nitrate.
Next, the honeycomb structure was fired at 700 ° C. for 5 hours. As a result, the reaction suppression layer 6 made of aluminum oxide was carried on a predetermined region of the partition wall 2.

Next, a catalyst slurry in which an alkali metal catalyst was dispersed in alumina sol was prepared, the honeycomb structure was impregnated with distilled water, and the partition walls 2 were allowed to contain moisture. Then, after the honeycomb structure was immersed in the catalyst slurry and pulled up, excess water was blown off by air blowing from the upstream side of the honeycomb structure at a flow rate of about 10 L / min.
Next, the honeycomb structure was fired at 600 ° C. for 3 hours and subjected to a baking treatment. Thereby, the PM combustion catalyst 5 containing an alkali metal was carried in a predetermined region of the partition wall 2.
Thus, the exhaust gas purification filter 1 (FIGS. 1 to 3) was obtained.

Next, the effect of the exhaust gas purification filter 1 of this example will be described.
In the exhaust gas purification filter 1 of this example, the partition wall 2 carries a PM combustion catalyst 5 containing an alkali metal, and a reaction suppression layer 6 that suppresses the reaction between the partition wall 2 and the PM combustion catalyst 5. The PM combustion catalyst 5 and the reaction suppression layer 6 have a partition wall 2 with a thickness D of D / 2 or less in the thickness direction from the surface 201 of the partition wall 2 on the inflow cell side and the surface 201 (D / in this example). It is selectively carried inside the partition wall 2 in the range A (FIG. 3) up to the distance of 2).

  That is, the PM combustion catalyst 5 is not carried on the entire partition wall 2 but the surface 201 on the inflow cell side of the partition wall 2, which is an area where PM in the exhaust gas G is easily collected on the surface and inside the partition wall 2. The specific range A inside the partition 2 is selectively supported. Therefore, the PM collected by the partition walls 2 can be efficiently burned by the PM combustion catalyst 5 that is intensively supported in a region where the PM is easily collected.

  The reaction suppression layer 6 is supported in a region where it is necessary to suppress the reaction between the partition walls 2 and the PM combustion catalyst 5, that is, a region where the PM combustion catalyst 5 is supported. And it is formed so as to be interposed between the partition wall 2 and the PM combustion catalyst 5. Therefore, the reaction between the partition wall 2 and the PM combustion catalyst 5 at a high temperature can be sufficiently suppressed by the reaction suppression layer 6. Thereby, sufficient thermal durability of the PM combustion catalyst 5 can be ensured.

  Further, as described above, the PM combustion catalyst 5 and the reaction suppression layer 6 are selectively supported on the surface 201 on the inflow cell side of the partition wall 2 and the specific range A inside the partition wall 2. Therefore, compared to the conventional case in which the PM combustion catalyst 5 and the reaction suppression layer 6 are supported on the entire partition wall 2, the supported amounts can be significantly reduced. Thereby, the increase in the pressure loss by having carry | supported PM combustion catalyst 5 and the reaction suppression layer 6 can be suppressed. That is, pressure loss can be reduced as compared with the prior art.

  Thus, according to this example, the pressure loss can be reduced while ensuring the thermal durability of the catalyst (PM combustion catalyst 5), and the particulates (PM) collected in the partition walls 2 can be efficiently collected. The exhaust gas purification filter 1 that can be burned can be provided.

(Example 2)
In this example, the thermal durability and pressure loss of the catalyst of the exhaust gas purification filter are evaluated.
In this example, exhaust gas purification filters (test bodies E1 to E3) according to examples of the present invention in which the areas supporting the PM combustion catalyst and the reaction suppression layer are prepared are prepared, and further, an exhaust gas purification filter (test body C1) as a comparative example is prepared. To C3). Then, the thermal durability and pressure loss of the catalyst were evaluated for each specimen.

The test bodies E1 to E3 and C1 to C3 prepared in this example will be described.
For each of the test bodies E1 to E3 and C1 to C3, an exhaust gas purification filter (12 mil, 300 cpsi) made of cordierite having a diameter of 30 mm and a length of 50 mm was used. The partition wall thickness D was about 305 μm. The basic structures of the test bodies E1 to E3 and C1 to C3 are the same as those of the exhaust gas purification filter of Example 1 (see FIG. 1).

Next, the test bodies E1-E3 concerning the Example of this invention are demonstrated.
The test body E1 carries the PM combustion catalyst and the reaction suppression layer on the surface of the partition wall on the inflow cell side and in the partition wall in the range from the surface to a distance of D / 5 (about 60 μm) in the thickness direction.
In the test body E2, the PM combustion catalyst and the reaction suppression layer are carried on the surface of the partition wall on the inflow cell side and in the partition wall in the range from the surface to a distance of D / 3 (about 100 μm) in the thickness direction.
The test body E3 carries the PM combustion catalyst and the reaction suppression layer on the surface of the inflow cell side of the partition wall and the inside of the partition wall in the range from the surface to a distance of D / 2 (about 150 μm) in the thickness direction.

Next, the manufacturing method of the test bodies E1-E3 is demonstrated.
Test bodies E1 to E3 were manufactured by the same manufacturing method as the exhaust gas purification filter of Example 1.
First, a honeycomb structure (see FIG. 1) having partition walls and a plurality of cells and provided with plug portions at predetermined positions is prepared, and the honeycomb structure is placed in a 0.5 mol / L aluminum nitrate aqueous solution for a predetermined time. After dipping and pulling up, excess water was blown off by air blow.

Next, hot air of about 300 ° C. is supplied from the upstream side of the honeycomb structure for a predetermined time (test body E1: 5 minutes, test body E2: 3 minutes, test body E3: 1 minute), and the surface of the partition wall on the inflow cell side The aqueous solution in the partition was dried in order. Then, aluminum nitrate is selectively applied to the surface of the partition wall on the inflow cell side and a predetermined distance in the thickness direction from the surface (test body E1: about 60 μm, test body E2: about 100 μm, test body E3: about 150 μm). Was precipitated.
Next, the honeycomb structure was fired at 700 ° C. for 5 hours. Thereby, the reaction suppression layer which consists of aluminum oxide was carry | supported to the predetermined area | region of the partition.

Next, a catalyst slurry in which an alkali metal catalyst was dispersed in alumina sol was prepared, and the honeycomb structure was impregnated with distilled water so that the partition walls contained moisture. Then, after the honeycomb structure is immersed in the catalyst slurry and pulled up, a predetermined flow rate (test body E1: approximately 10 L / min, test body E2: approximately 15 L / min, test body E3: approximately from the upstream side of the honeycomb structure. 25 L / min), excess water was blown off by air blow.
Next, the honeycomb structure was fired at 600 ° C. for 3 hours and subjected to a baking treatment. Thereby, the PM combustion catalyst containing an alkali metal was carried in a predetermined region of the partition wall.
The test bodies E1-E3 were obtained by the above.

Next, test bodies C1 to C3 as comparative examples will be described.
The test body C1 carries only the PM combustion catalyst on the entire partition wall.
The test body C2 selectively carries only the PM combustion catalyst on the surface of the partition wall on the inflow cell side and in the range from the surface to the distance of D / 3 (about 100 μm) in the thickness direction.
The test body C3 carries the PM combustion catalyst and the reaction suppression layer on the entire partition wall.

Next, the manufacturing method of the test body C1 is demonstrated.
First, a catalyst slurry in which an alkali metal catalyst was dispersed in alumina sol was prepared. Then, after the honeycomb structure was immersed in the catalyst slurry and pulled up, excess water was blown off by air blow from the upstream side of the honeycomb structure.
Next, the honeycomb structure was fired at 600 ° C. for 3 hours and subjected to a baking treatment. Thereby, the PM combustion catalyst was supported on the entire partition wall.
The test body C1 was obtained by the above.

Next, the manufacturing method of the test body C2 is demonstrated.
First, a catalyst slurry in which an alkali metal catalyst was dispersed in alumina sol was prepared, and the honeycomb structure was impregnated with distilled water so that the partition walls contained moisture. Then, after the honeycomb structure was immersed in the catalyst slurry and pulled up, excess water was blown off by air blow from the upstream side of the honeycomb structure.
Next, the honeycomb structure was fired at 600 ° C. for 3 hours and subjected to a baking treatment. As a result, the PM combustion catalyst was supported in a predetermined region of the partition wall.
The test body C2 was obtained by the above.

Next, the manufacturing method of the test body C3 is demonstrated.
First, the honeycomb structure was dipped in a 0.5 mol / L aluminum nitrate aqueous solution for a predetermined time, pulled up, and then excess water was blown off by air blow.
Next, the honeycomb structure was dried at 150 ° C. for 60 minutes and further fired at 700 ° C. for 5 hours. Thereby, the reaction suppression layer which consists of aluminum oxide was carry | supported to the whole partition.

Next, a catalyst slurry in which an alkali metal catalyst was dispersed in alumina sol was prepared. Then, after the honeycomb structure was immersed in the catalyst slurry and pulled up, excess water was blown off by air blow from the upstream side of the honeycomb structure.
Next, the honeycomb structure was fired under a condition of 600 ° C. for 3 hours to be baked. As a result, the PM combustion catalyst was supported on the entire partition walls of the honeycomb structure.
The test body C3 was obtained by the above.

Next, a method for evaluating the thermal durability and pressure loss of the catalyst will be described.
For the evaluation of “thermal durability of the catalyst”, first, an initial (before durability) test specimen and a test specimen after durability at 750 ° C. for 20 hours were prepared. Next, each specimen was exposed to the exhaust gas of a diesel engine for a predetermined time, and about 7.0 g of PM was deposited per liter of the specimen. And the test body was heated in inert atmosphere, air was supplied in the stage which reached 500 degrees, and deposited PM was burned by hold | maintaining for a predetermined time. Thereafter, the mass of PM burned was calculated from the mass of the test body before and after PM combustion, and the PM burning rate per unit time was obtained by dividing this by the time of burning.

  For the evaluation of “pressure loss”, air is passed through the test specimen at a flow rate of 40 L / min, and the pressure difference (pressure) between the inlet and outlet of the specimen (between the upstream side and the downstream side of the exhaust gas purification filter) is measured. Loss) was measured with a differential pressure gauge.

Next, the evaluation results of the thermal durability and pressure loss of the catalyst are shown in FIG. In the figure, the PM burning rate of each test specimen is shown by a bar graph, and the differential pressure is shown by ●.
As can be seen from the figure, the specimens C1 and C2 carry only the PM combustion catalyst, so the differential pressure is small, but because the reaction suppression layer is not carried, the PM combustion rate after durability is very high. slow. That is, although the pressure loss is small, the thermal durability of the catalyst is very low.
Moreover, since the test body C3 carries the PM combustion catalyst and the reaction suppression layer on the entire partition wall, the PM combustion speed after durability is fast, but the differential pressure is very large. That is, the thermal durability of the catalyst is sufficiently ensured, but the pressure loss is large.

On the other hand, the specimens E1 to E3 have a PM burning rate after durability equal to or higher than that of the specimen C3, and the differential pressure is smaller than that of the specimen C3. Thereby, it turns out that the test bodies E1-E3 can reduce a pressure loss, ensuring sufficient thermal durability of a catalyst.
In particular, the specimen E2 has a PM burning speed after endurance higher than that of the specimen C3, and the differential pressure is much smaller than that of the specimen C3, which is equivalent to the specimen C1.
Further, the test body E1 has a very small differential pressure compared to the test body C3 and is equivalent to the test body C2, but the PM burning rate after durability is equivalent to that of the test body C3.

From the above results, the exhaust gas purification filter according to the example of the present invention can reduce the pressure loss while ensuring the thermal durability of the catalyst (PM combustion catalyst), and the particulates collected in the partition walls ( It was found that PM) can be burned efficiently.
Further, considering the balance between ensuring the thermal durability of the catalyst and reducing the pressure loss, the PM combustion catalyst and the reaction suppression layer are D / 3 (D: It has been found that it is preferable that the particles are selectively supported in a range up to a distance of (thickness of partition wall).
Also, considering that the PM trapped in the partition walls is sufficiently combusted, the PM combustion catalyst and the reaction suppression layer are at least the surface on the inflow cell side of the partition walls and a distance of D / 5 from the surface in the thickness direction. It was found that it was necessary to be supported in the range of.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification filter 2 Bulkhead 201 Surface (surface on the inflow cell side)
3 cell 31 inflow cell 312 end (downstream end)
32 discharge cell 321 end (upstream end)
4 Plug part 5 PM combustion catalyst 6 Reaction suppression layer G Exhaust gas X1 Upstream side X2 Downstream side

Claims (4)

A porous partition wall arranged in a lattice pattern, and a plurality of cells formed in the axial direction surrounded by the partition wall, of which the downstream end of the inflow cell into which exhaust gas flows In the exhaust gas purification filter in which the upstream end of the exhaust cell that exhausts exhaust gas is closed by a plug portion,
The partition wall is loaded with a PM combustion catalyst containing an alkali metal, and a reaction suppression layer that is formed between the partition wall and the PM combustion catalyst and suppresses the reaction between the two.
In the PM combustion catalyst and the reaction suppression layer, when the thickness of the partition wall is D, the surface of the partition wall on the inflow cell side and the inside of the partition wall in the range from the surface to a distance of D / 2 or less in the thickness direction. And an exhaust gas purification filter which is selectively supported.   2. The exhaust gas purification filter according to claim 1, wherein the PM combustion catalyst and the reaction suppression layer are formed on the inflow cell side surface of the partition wall and the partition wall in a range from the surface to a distance of D / 3 or less in the thickness direction. An exhaust gas purification filter that is selectively carried inside.   3. The exhaust gas purification filter according to claim 1, wherein the PM combustion catalyst contains at least one selected from Na, K, Cs, and Rb.   The exhaust gas purification filter according to any one of claims 1 to 3, wherein the reaction suppression layer contains at least one selected from Al, Zr, and La.

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