Patent ID: 12251691

DESCRIPTION OF THE EMBODIMENTS

For example, Japanese Patent Publication No. 4473693 discloses a filter that has a porosity of 45 to 70%, a predetermined average pore diameter difference rate of 35% or less, an average pore diameter of 15 to 30 μm, and a maximum pore diameter of 150 μm or less, measured by a bubble point method. Based on Japanese Patent Publication No. 4473693, pressure loss during PM accumulation can be reduced through use of the above-described configuration.

In recent years, there has been demand for the exhaust gas purification filter to be provided with purification performance regarding toxic substances such as NOX. For example, the exhaust gas purification filter may support a NOXpurification catalyst. NOXhas a slow diffusion rate in a catalyst layer. Therefore, rather than a catalyst layer being thickly formed, the amount of NOXis more effectively reduced by the same amount of the catalyst layer being thinly and widely formed.

However, in a conventional exhaust gas purification filter such as that described in Japanese Patent Publication No. 4473693, a narrow portion is formed in a pore in which the catalyst is supported. Flow path resistance of a catalyst slurry increases, and the catalyst layer tends to be formed so as to be partially thick as a result of the catalyst being supported. Therefore, there is room for further improvement in purification performance regarding NOXin the catalyst layer of the conventional exhaust gas purification filter.

It is thus desired to provide an exhaust gas purification filter that is capable of exhibiting excellent NOXpurification performance by supporting a catalyst.

A first exemplary embodiment of the present disclosure provides an exhaust gas purification filter that is used so as to support a NOXpurification catalyst. The exhaust gas purification filter includes: a honeycomb structure portion that includes a partition wall in which numerous pores are formed, and a plurality of cells that are partitioned by the partition walls and form a flow path for an exhaust gas; and a plug portion that alternately seals an inflow end surface or an outflow end surface for the exhaust gas in the cells. The partition wall has a gas permeability coefficient that is equal to or greater than 0.35×10−12m2, a pore volume ratio of pore diameters of 9 μm or less that is equal to or less than 25%, and an average pore diameter that is equal to or greater than 12 μm.

A second exemplary embodiment of the present disclosure provides an exhaust gas purification filter that includes a substrate and a catalyst layer including a nitrogen oxide purification catalyst supported by the substrate. The substrate includes: a honeycomb structure portion that includes a partition wall in which numerous pores are formed, and a plurality of cells that are partitioned by the partition walls and form a flow path for an exhaust gas; and a plug portion that alternately seals an inflow end surface or an outflow end surface for the exhaust gas in the cells. The partition wall has a gas permeability coefficient that is equal to or greater than 0.35×10−12m2, a pore volume ratio of pore diameters of 9 μm or less that is equal to or less than 25%, and an average pore diameter that is equal to or greater than 12 μm. The catalyst layer is supported on the partition wall of the substrate. A supported amount of the catalyst layer is 30 to 150 g/L. An average thickness of the catalyst layer is equal to or less than 6 μm.

In the exhaust gas purification filter according to the above-described exemplary embodiments, the gas permeability coefficient of the partition wall, the pore volume ratio of pore diameters of 9 μm or less of the partition wall, and the average pore diameter of the partition wall are adjusted as described above. In such a partition wall, because flow path resistance of the pores is small, a catalyst layer is thinly and widely formed by the NOXpurification catalyst being supported. As a result, NOXthat has a slow diffusion rate is efficiently reduced. Consequently, high NOXreduction efficiency is exhibited by the NOXpurification catalyst being supported.

As described above, according to the above-described exemplary embodiments, the exhaust gas purification filter that is capable of exhibiting excellent NOXpurification performance by supporting a catalyst can be provided.

Reference numbers indicate corresponding relationships with specific means according to embodiments described hereafter, and do not limit the technical scope of the present disclosure.

First Embodiment

An embodiment of an exhaust gas purification filter1will be described with reference toFIGS.1to6. As shown inFIG.1, the exhaust gas purification filter1includes a honeycomb structure portion10and a plug portion16. For example, the honeycomb structure portion10may be made of by a ceramic, such as cordierite, and includes an outer shell11, a partition wall12, and a cell13.

As shown inFIGS.1and2, for example, the outer shell11may be a cylindrical body. For example, a specific shape of the outer shell11may be a circular cylinder of which a cross-sectional shape in a direction orthogonal to an axial direction Y of the outer shell11is a circle. However, the shape of the outer shell11may be a polygonal cylinder of which the cross-sectional shape is a polygon, such as a square. According to the present embodiment, the axial direction Y of this cylindrical outer shell11is described as the axial direction Y of the exhaust gas purification filter1. The axial direction Y of the exhaust gas purification filter is referred to, as appropriate, as a filter axial direction Y. In addition, arrows inFIG.2indicate a flow of exhaust gas G when the exhaust gas purification filter1is arranged on a path of the exhaust gas G, such as in an exhaust pipe.

The partition walls12partition an interior of the outer shell11into numerous cells13. The partition wall12is also commonly referred to as a cell wall. For example, the partition walls12may be provided in a lattice shape. The exhaust gas purification filter1is a porous body. As shown inFIG.3, numerous pores121are formed in the partition wall12. Therefore, the exhaust gas purification filter1is capable of accumulating and collecting PM that is contained in the exhaust gas G on a surface of the partition wall12and inside the pore121. The pore121is also commonly referred to as a pore. The PM is fine particles that are referred to as particulate substance, particulate matter, particulates, and the like. The outer shell11and the partition wall12are integrally formed.

As shown inFIGS.1and2, the exhaust gas purification filter1includes numerous cells13. The cell13is surrounded by the partition walls12and forms a flow path for the exhaust gas G. An extending direction of the cell12ordinarily coincides with the filter axial direction Y.

For example, a cell shape on a filter cross-section in a direction orthogonal to the filter axial direction Y may be a square. However, this is not limited thereto. The cell shape may be a polygon such as a triangle, a square, or a hexagon, a circle, or the like. In addition, the cell shape may be a combination of two or more differing types of shapes.

The exhaust gas purification filter1is used so as to support (carry) a NOXpurification catalyst. That is, the exhaust gas purification filter1before a catalyst is supported may be a substrate for supporting the NOXpurification catalyst. The NOXpurification catalyst is supported on at least the partition wall12. The exhaust gas purification filter1may have a support surface for supporting the NOXpurification catalyst on the partition wall12. For example, the support surface may be a flow path surface125and a pore wall surface124ashown inFIGS.2to5B. The flow path surface125is a portion in which the partition wall12faces the cell13. The pore wall surface124ais a portion in which a pore wall124faces the pore121. The NOXpurification catalyst is supported on the partition wall12as a catalyst layer17.

For example, the exhaust gas purification filter1may be a columnar body that has a circular columnar shape or the like, and dimensions thereof can be changed as appropriate. The exhaust gas purification filter1has an inflow end surface14and an outflow end surface15on both ends in the filter axial direction Y. The inflow end surface14is an end surface on a side on which the exhaust gas G flows in a state in which the exhaust gas purification filter1is arranged in the flow of the exhaust gas G, and the outflow end surface15is an end surface on a side on which the exhaust gas G flows out.

In a state in which the exhaust gas purification filter1is not arranged in the flow of the exhaust gas G, the inflow end surface14and the outflow end surface15refer to relative surfaces in the filter axial direction Y. That is, when either of the end surface is the inflow end surface14, the other is the outflow end surface14. For example, the inflow end surface14can also be referred to as a first end surface and the outflow end surface15may be referred to as a second end surface.

The exhaust gas purification filter1includes a plug portion16. For example, the plug portions16may seal the inflow end surface14or the outflow end surface15of the cells13in an alternating manner. For example, the plug portion16may be made of a ceramic, such as cordierite. However, other materials are also possible.

InFIG.2, a plug-shaped plug portion16is formed. However, the shape of the plug portion16is not particularly limited as long as the inflow end surface14or the outflow end surface15can be sealed. Here, although an illustration of a configuration is omitted, for example, the plug portion16can also be formed by a portion of the partition wall12being deformed on the inflow end surface14or the outflow end surface15. In this case, because the plug portion16is formed by a portion of the partition wall12, the partition wall12and the plug portion16are integrally and continuously formed.

For example, as the cells13, a first cell131and a second cell132may be provided. As shown inFIG.2, for example, in the first cell131, the inflow end surface14that serves as an inflow side for the exhaust gas G may be open and the outflow end surface15may be sealed by the plug portion16. For example, in the second cell132, the outflow end surface15that serves as an outflow side for the exhaust gas G may be open and the inflow end surface14may be sealed by the plug portion16.

For example, the first cells131and the second cells132may be formed in an alternately arrayed manner, so as to be adjacent to each other in a lateral direction X that is orthogonal to the filter axial direction Y and a vertical direction Z that is orthogonal to both the filter axial direction Y and the lateral direction X. That is, when the inflow end surface14or the outflow end surface15of the exhaust gas purification filter1is viewed from the filter axial direction Y, for example, the first cells131and the second cells132may be arranged in a checkered pattern.

As shown inFIG.2, the partition walls12separate the first cell131and the second cell132that are adjacent to each other. As shown inFIG.3, inside the partition wall12, numerous pores121are formed by the pore walls124. The pores121include a communicating pore121cthat communicates between the first cell131and the second cell132, and a non-communicating pore (not shown) that does not communicate therebetween. For example, the communicating pore121cmay be confirmed through electron microscope observation of a partition wall cross-section by a scanning electron microscope or the like.

InFIG.3, the pores121are shown so as to be simplified into a two-dimensional form. However, it is though that most of the pores121intersect in a three-dimensional manner. The pores121serve as paths for the exhaust gas G inside the partition wall12. As a result of the exhaust gas G passing through the pores121, the PM in the exhaust gas G is collected on the pore wall surfaces124a. In addition, as a result of the pore walls124supporting the NOXpurification catalyst, toxic gas components such as NOXthat are contained in the exhaust gas G that passes through the pores121are reduced by the NOXpurification catalyst. The cells13also serve as paths for the exhaust gas G in a manner similar to the pores121. The PM is also collected on the flow path surfaces125of the partition walls12. As a result of the flow path surfaces125supporting the NOXpurification catalyst, the NOXis also reduced on the flow path surfaces125.

As shown inFIG.4, for example, the catalyst layer17may be formed on the pore wall surface124aof the partition wall12. The catalyst layer17may be formed in a continuous manner or a non-continuous manner. For example, the catalyst layer17may be also formed on the flow path surface125of the partition wall12.

As a result of the communicating pores being increased as appropriate, reduction of pressure loss and improvement in PM collection efficiency can both be achieved. Pressure loss is referred to, hereafter, as “pressure loss”, as appropriate. A quantity, shape, and the like of the communicating pores can be adjusted with porosity, average pore diameter, and the like as indicators. From a perspective of appropriately increasing the communicating pores and from a perspective of maintaining strength of the exhaust gas purification filter1, the porosity is preferably 50 to 70%, more preferably 55 to 65%, and even more preferably 60 to 65%. The porosity is measured based on principles of a mercury injection method, as described in an experiment example.

The catalyst layer17contains the NOXpurification catalyst. As the NOXpurification catalyst, a three-way catalyst that is composed of precious metals, such as Pt, Rh, and Pd may be used. In this case, the NOXpurification catalyst can further purify toxic gas components such as CO and HC, in addition to NOX. The catalyst layer17may also further contain alumina, an auxiliary catalyst, and the like. As the auxiliary catalyst, ceria, zirconia, a ceria-zirconia solid solution, and the like may be used as examples.

A formation method for the catalyst layer17is not particularly limited. However, for example, a method in which the partition wall12is impregnated with a fluid that contains a catalyst such as a noble metal and baked may be common. For example, the fluid may be a liquid such as a catalyst slurry.

Because the diffusion rate of NOXin the catalyst layer is slow, when the catalyst layer is thick, diffusion of NOXin the catalyst layer is insufficient. NOXreduction efficiency increases by the catalyst layer17being thinly and widely formed on the pore wall surfaces124aand the like. A reason for this is as follows.

For example, when a predetermined amount of the catalyst layer17is formed in the exhaust gas purification filter1, as a result of the catalyst layer17being thinly formed, the catalyst layer17is formed in a wide area of the pore walls124. Therefore, in the exhaust gas purification filter1, contact frequency between the catalyst layer17and the NOXincreases, and the NOXis more easily reduced.

In addition, because the diffusion rate of NOXin the catalyst layer17is slow, purification may be sufficiently performed even when thickness of the catalyst layer17is small. During catalyst layer formation, the pore121forms flow paths for a fluid such as the catalyst slurry. As a result of the flow path resistance thereof being reduced, the fluid flows more easily, and the catalyst layer17is thinly and widely formed.

For example, to reduce the flow path resistance, increasing the pore diameter in the narrow portion127of the pore121, increasing an average pore diameter, or increasing pores121that have a large pore diameter is effective. The narrow portion127is a portion in which the pore diameter is smaller than that in the periphery. For example, the narrow portion127may be a narrowed portion of the pore121on a partition wall cross-section in a wall thickness direction. As a result of the narrow portion127being increased, a gas permeability coefficient of the partition wall12can be increased. In addition, as a result of the pores121that have a small pore diameter being reduced, the pores121that have a large pore diameter can be increased.

To sufficiently improve the NOXreduction efficiency by thinly and widely forming the catalyst layer17, it is effective to increase the gas permeability coefficient of the partition wall12to be equal to or greater than a predetermined value, increase the average pore diameter to be equal to or greater than a predetermined value, and reduce the pores121that have a small pore diameter to be equal to or less than a predetermined value. Specifically, as a result of the gas permeability coefficient being equal to or greater than 0.35×10−12m2, the average pore diameter being equal to or greater than 12 μm, and a pore volume ratio of pore diameters of 9 μm or less than being equal to or less than 25%, the NOXreduction efficiency can be sufficiently increased.

In addition, as a result of the flow path resistance being reduced, the catalyst layer17can be thinly formed in a wider area even with the same coating amount. Therefore, because the NOXreduction efficiency can be improved without the coating amount of the catalyst layer17being increased, the NOXreduction efficiency can be improved while increase in pressure loss is suppressed. In addition, the NOXpurification performance after a catalyst is supported can be improved by pore control of the exhaust gas purification filter1that serves as a carrier for the NOXpurification catalyst.

For example, the catalyst layer17may be thinly and widely formed on the pore wall surfaces124aand the like by the above-described common formation method using a catalyst slurry, and the exhaust gas purification filter1after a catalyst is supported exhibits excellent NOXpurification performance. Measurement and calculation methods for the gas permeability coefficient, the average pore diameter, and the pore volume ratio are described in the experiment example. The pore volume ratio refers to a proportion of a volume of the pores121that have a predetermined pore diameter in relation to an overall pore volume, and is calculated from a pore diameter distribution that is measured based on the principles of the mercury injection method as described in the experiment example.

From a perspective of suppressing worsening of the PM collection efficiency, the gas permeability coefficient is preferably equal to or less than 3.0×10−12m2, more preferably equal to or less than 2.5×10−12m2, and even more preferably equal to or less than 2.0×10−12m2, When the gas permeability coefficient is too high, the exhaust gas easily slips through inside the partition wall12, and the collection efficiency is thought to become worse because more PM contained in the exhaust gas also slips through. From a similar perspective, the average pore diameter is preferably equal to or less than 25 μm, more preferably equal to or less than 23 μm, and even more preferably equal to or less than 20 μm. Because the PM more easily slips through when the average pore diameter is too large as well, the collection efficiency is thought to worsen.

A pore wall area per unit volume of the partition wall12is preferably equal to or greater than 70000 μm2/μm3. In this case, an area of the pore wall surface124athat serves as the support surface on which the catalyst layer is formed is sufficiently large. Therefore, for example, when the same amount of catalyst is supported, the catalyst layer may be more thinly and widely formed. Consequently, the NOXthat has a slow diffusion rate is efficiently reduced in the catalyst layer and the reduction efficiency is improved.

From a perspective of improving the NOXreduction efficiency, the pore wall area per unit volume of the partition wall12is more preferably equal to or greater than 85000 μm2/μm3, and even more preferably equal to or greater than 90000 μm2/μm3. Meanwhile, from a perspective of further improving the NOXreduction efficiency, the pore wall area per unit volume of the partition wall12is preferably equal to or less than 200000 μm2/μm3, more preferably equal to or less than 190000 μm2/μm3, and even more preferably equal to or less than 180000 μm2/μm3.

A reason for this is that, although the catalyst layer being thinly and widely formed as described above is advantageous in improving the NOXreduction efficiency, from a perspective of sufficiently maintaining a diffusion distance (specifically, a reaction time) of the NOX, having a certain degree of thickness is thought to be advantageous. The pore wall area is an area of the pore wall surface124aand is an area of a portion in which the pore wall124that forms the pore121faces the pore121. For example, the pore wall area may also be referred to as a geometric surface area inside the partition wall12. The pore wall area is referred to, hereafter, as “GSA”, as appropriate. A measurement method for the GSA is described in the experiment example.

For example, the catalyst layer17may be formed in the exhaust gas purification filter1. A supported amount of the catalyst layer17is preferably 30 to 150 g/L. In this case, sealing of the pores121by the catalyst layer17is suppressed while required purification performance is ensured.

An average thickness of the catalyst layer17is preferably equal to or less than 6 μm. In this case, NOXpurification is more efficiently performed in the catalyst layer17. A reason for this is that, for example, when a predetermined amount of the catalyst layer17is formed, the catalyst layer17may be formed in a wider area of the pore wall surface124awhen the catalyst layer17is formed with a small thickness, such as 6 μm, than when the catalyst layer17is formed with a large thickness. In the purification of NOXof which the diffusion speed is slow, the catalyst layer17being thinly and widely formed, rather than thickly and narrowly formed, is more advantageous.

As described above, NOXpurification can be sufficiently efficiently performed as a result of the average thickness of the catalyst layer17being equal to or less than 6 μm. Therefore, the NOXpurification performance further improves. From a perspective of further improving the NOXpurification performance, the average thickness of the catalyst layer17is more preferably equal to or less than 5 μm. In addition, when the thickness of the catalyst layer17is too thin, from a perspective of risk of decrease in the NOXpurification performance, the average thickness of the catalyst layer17is preferably equal to or greater than 2 μm. For example, the average thickness of the catalyst layer17can be adjusted by an amount of the catalyst slurry that is used during formation of the catalyst layer17.

For example, the exhaust gas purification filter1according to the present embodiment may be manufactured in the following manner. First, a green body that contains cordierite formation raw materials is fabricated. The green body is fabricated by silica, talc, aluminum hydroxide, and the like being adjusted to form a cordierite composition, a binder such as methyl cellulose, a pore-forming material such as graphite, a lubricating oil, water, and the like being added as appropriate and mixed. Alumina and kaolin may be added to form the cordierite composition. As the silica, porous silica may be used.

In the cordierite formation raw materials, silica and talc may be pore formation raw materials101. The pore formation raw material101is a material that forms the pores121. The pore formation raw materials101produce a liquid phase component during firing, and the pores121are formed as a result. Meanwhile, in the cordierite formation raw materials, aluminum hydroxide, alumina, and kaolin may be aggregate raw materials102. The aggregate raw material102is a material that forms a ceramic portion other than the pores121.

Next, the green body is molded, dried, and fired. As a result, the honeycomb structure portion10is formed. The honeycomb structure portion10is a portion that is configured by the outer shell11, the partition walls12, and the cells13. The plug portions16are formed after firing of the honeycomb structure portion10or before firing. Specifically, for example, the plug portions16may be formed by the end surfaces of the cells13in the honeycomb structure portion10after firing or a honeycomb-structured molded body before firing being alternately sealed using a slurry for formation of the plug portion and fired.

The catalyst layer17is formed in the honeycomb structure portion10before the formation of the plug portions16or the honeycomb structure portion10after the formation of the plug portions16. The catalyst layer17is formed by the partition walls12being impregnated with the catalyst slurry that contains a noble metal, alumina, an auxiliary catalyst, and the like, and a solid component of the slurry being burned into the partition walls12. During impregnation, for example, suction may be applied.

According to the present embodiment, because the gas permeability coefficient, the average pore diameter, and the pore volume ratio of pore diameters of 9 μm or less are adjusted to predetermined ranges, the flow path resistance of the catalyst slurry decreases. Therefore, the catalyst layer17is thinly and widely formed without the amount of catalyst being changed. As a result, the NOXthat has a slow diffusion rate is efficiently reduced. To reduce the flow path resistance, for example, the narrow portion127may be made larger in the following manner.

In the molded body during firing, for example, it may be thought that there are portions in which the pore formation raw materials101and the aggregate raw materials102are arranged in patterns shown inFIGS.6A to6E.

Pattern inFIG.6Aand pattern inFIG.6Care cases in which a plurality of pore formation raw materials101athat have a large grain size are close to each other. Pattern inFIG.6Bis a case in which the pore formation raw materials101athat have a large grain size and pore formation raw materials101bthat gave a small grain size are in contact. Pattern inFIG.6Dand pattern inFIG.6Eare cases in which the pore formation raw materials101are not in contact with each other, and the aggregate raw materials102are arranged between the pore formation raw materials101. In pattern inFIG.6D, aggregate raw materials102athat have a large grain size are arranged between the pore formation raw materials101. In pattern inFIG.6E, aggregate raw materials102bthat have a small grain size are arranged between the pore formation raw materials101.

When cases in which the narrow portion127is formed by the patterns of raw material arrangement shown as examples inFIGS.6A to6Eare assumed, a size of the narrow portion127is as follows. As a result of the pore formation raw materials101being placed in contact with each other as shown in patterns inFIGS.6A to6C, the narrow portion127is enlarged and the large narrow portion127can be formed. Meanwhile, when the pore formation raw materials101and the aggregate raw materials102are placed in contact as shown in patterns inFIGS.6D and6E, the narrow portion127becomes small. For example, a medium-sized narrow portion127may be formed in pattern inFIG.6Dand a small-sized narrow portion127is formed in pattern inFIG.6E.

Therefore, as a result of a contact pattern between the pore formation raw materials101and the aggregate raw materials102being controlled, the size of the narrow portion127can be adjusted. Specifically, through use of at least two types of pore formation raw materials101that have opposite positive and negative electric charges from each other, the pore formation materials101are more easily placed in contact with each other as in patterns inFIGS.6A to6C.

Therefore, the narrow portion127can be made larger. More specifically, for example, the pore formation raw materials101may be silica and talc. Silica can be imparted a positive (+) charge and talc can be imparted a negative (−) charge. The positive and negative may be interchanged therebetween. In addition, a portion of a mixture of silica and talc may be imparted a positive (+) charge and a portion or an entirety of the remaining mixture may be imparted a negative (−) charge. Electric charge may be imparted to all pore formation raw materials101used in the manufacture of the exhaust gas purification filter1. Alternatively, a portion of the pore formation raw materials101may be imparted electric charge.

For example, to impart electric charge, an anionic dispersant or a cationic dispersant may be used. Specifically, the pore formation raw material101and the dispersant are mixed in advance. Mixing of the pore formation raw material101and the dispersant is referred to as pre-kneading. As a result of pre-kneading, the dispersant is attached to the pore formation raw material101and the pore formation raw material101is charged. A positively charged pore formation raw material101and a negatively charged pore formation raw material101are obtained. After pre-kneading, the pore formation raw material101to which the dispersant is attached, the aggregate raw material102, and other raw materials are further mixed.

When a pre-kneading time is too long, connectivity between the pores121may be lost. Therefore, the pre-kneading time is preferably appropriately adjusted. In addition, when the grain size of the aggregate raw materials102surrounding the pore formation raw materials101increases, connectivity between the pores121may be lost. Therefore, a grain size ratio between the pore formation raw materials101and the aggregate raw materials102is also preferably appropriately adjusted.

The gas permeability coefficient, the average pore diameter, and the pore volume ratio of pore diameters of 9 μm or less can be controlled to the above-described desired ranges by the grain size ratio of the pore formation raw materials101and the aggregate raw materials102, a type of the dispersant, an added amount of the dispersant, the pre-kneading time, rotation speed during extrusion, a drying time of clay, and the like being adjusted.

Comparative Example 1

Next, an exhaust gas purification filter that has a narrow portion that has a small pore diameter will be described with reference toFIGS.7A to7C.FIGS.7A to7Cshow a partition wall92of the exhaust gas filter of the present example.FIGS.7A to7Cschematically shows communicating pores (that is, pores911,912, and913) of the partition wall92with simplified shapes.

As shown inFIG.7A, in the partition wall92of the exhaust gas purification filter, various pores911,912, and913that have differing pore diameters are formed. In the present example, for convenience of description, the pores are described so as to be classified into three types: an hourglass-type pore911that has a large pore diameter and a narrow portion917that has a small pore diameter; a pore912that has a medium-sized pore diameter, and a pore913that has a small-sized pore diameter.

For example, when a predetermined amount of a catalyst layer97is formed on the partition wall92using a catalyst slurry, as shown inFIG.7B, in the narrow portion917that has a high flow path resistance, the catalyst layer97that is partially thicker than that in the periphery may be formed. Meanwhile, in the pore913that has a small pore diameter, because the flow path resistance is high, the catalyst slurry does not easily enter the pore913, and the catalyst layer97is difficult to form. Because the pore913that has a small pore diameter is advantageous for collection of PM, the PM collection efficiency increases by the small-sized pores being increased. However, the NOXpurification performance after the catalyst layer97is supported decreases.

In addition, as shown inFIG.7C, as a result of the supported amount of the catalyst being increased, the catalyst layer97can be formed in the pore913that has a small pore diameter. However, in this case, manufacturing cost increases by an amount of increase in the catalyst. Furthermore, in this case, because the narrow portions917and the medium-sized pores912are at least partially sealed by the catalyst layer97, pressure loss increases.

Experiment Example 1

In a present example, as shown in Table 1, a plurality of exhaust gas purification filters1that have differing average pore diameters, gas permeability coefficients, and pore volume ratios of pore diameters of 9 μm or less are manufactured. In addition, the catalyst layer17that contains the NOXpurification catalyst is formed on the partition walls12of the exhaust gas purification filters1, and the NOXreduction efficiency, the PM collection efficiency, and the like are compared and evaluated.

Here, reference numbers used in the experiment example 1 and subsequent thereto that are the same as those used in earlier embodiments indicate constituent elements and the like that are similar to those according to the earlier embodiments unless otherwise stated.

The exhaust gas purification filter1has a circular columnar shape with a diameter of 118 mm and a length in the filter axial direction Y of 120 mm. A main ingredient of the exhaust gas purification filter1is cordierite. The exhaust gas purification filter1of the present example has 300 cpsi. A thickness of the partition wall12is 0.216 mm. The supported amount of the catalyst layer17is 65 g/L.

First, as the cordierite formation raw materials, silica, talc, and aluminum hydroxide were prepared. The silica and the talc are the pore formation raw material101, and the aluminum hydroxide is the aggregate raw material102.

A mixed powder of silica and talc was divided into two parts. An anionic dispersant and water were added to one part and mixed, and a cationic dispersant and water were added to the other part and mixed. In this manner, a slurry-like first mixture that contains the pore formation raw material101to which a negative (−) charge is imparted and a slurry-like second mixture that contains the pore formation raw material101to which a positive (+) charge is imparted were obtained.

An added amount of the anionic dispersant in the first mixture is 2 to 15 wt % in relation to a total amount of 100 wt % of silica and talc. An added amount of water is half an amount required to fabricate the green body. As the anionic dispersant, “NOPCOSPERSE 44-C” manufactured by Sanyo Chemical, Ltd. was used. In addition, an added amount of the cationic dispersant in the second mixture is 2 to 15 wt % in relation to a total amount of 100 wt % of silica and talc. The added amount of water is half the amount required to fabricate the green body. As the cationic dispersant, “NOPCOSPERSE 092” manufactured by Sanyo Chemical, Ltd. was used.

Next, the first mixture, the second mixture, aluminum hydroxide, a dispersant, and a lubricating oil were mixed and kneaded. In this manner, the green body was fabricated. As the dispersant, polyoxyethylene polyoxypropylene glyceryl ether that has an average molecular weight of 4550 was used. In the present example, porous silica was used as the silica in the cordierite formation raw material. The porous silica functions as a pore forming material. During fabrication of the green body, for example, graphite may be added as the pore forming material. The pore forming material provides a function for improving the porosity of the exhaust gas purification filter1.

After the green body was extrusion-molded and fired at 1410° C., the plug portions16were formed, and the exhaust gas purification filter1was thereby obtained. In addition, the catalyst layer17was formed in the exhaust gas purification filter1in a manner similar to that according to the first embodiment. As a result of a D50grain size of the mixture of silica and talc (that is, the pore formation raw material) being changed within a range of 5 μm to 35 μm, for example, the average pore diameter of the exhaust gas purification filter1can be adjusted to a desired range that is equal to or greater than 12 μm.

In addition, as a result of the added amounts of the cationic and anionic dispersants being changed within a range of 1 to 15 wt %, for example, the gas permeability coefficient of the exhaust gas purification filter1can be adjusted to a desired range that is equal to or greater than 0.35×10−12m2.

As a result of a stirring time of the first mixture and the second mixture, and the kneading time of the green body being respectively adjusted within a range of 5 minutes to 150 minutes, for example, the pore volume ratio of pore diameters of 9 μm or less can be adjusted to a desired range that is equal to or less than 25%. In the present example, ten types of exhaust gas purification filters1were obtained as shown in Table 1 through combinations of these adjustments.

Next, measurement values shown in Table 1 were examined by methods described hereafter for each exhaust gas purification filter1. The measurement value is a value of a measurement sample that is taken from the exhaust gas purification filter1. The measurement sample is taken from a sampling position in the exhaust gas purification filter1described below.

(Sampling Position of the Measurement Sample)

The sampling positions are shown inFIGS.8A to8C. As shown inFIGS.8A to8C, the sampling positions are three sites: a center portion1ain the filter axial direction Y that passes through a center portion of a diameter of the exhaust gas purification filter1; a portion1bjust on an inner side of the plug portion16on the inflow end surface14side; and a portion1cjust on an inner side of the plug portion16on the outflow end surface15side. As shown inFIGS.8A to8C, the measurement samples are taken from the center of the exhaust gas purification filter1in a direction (specifically, the radial direction) orthogonal to the filter axial direction. A reason for this is that, because a gas flow rate is fast and the NOXeasily blows through at the center, as a result of the gas permeability coefficient, the average pore diameter, the pore volume ratio of pore diameters of 9 μm or less, and the like being adjusted to the above-described predetermined ranges at at least the center, an improvement effect on the NOXreduction efficiency can be sufficiently exhibited. The measurement value shown in Table 1 is an arithmetic mean of the measurements at the three sites described above.

(Porosity and Average Pore Diameter)

Measurement was performed in a state in which the catalyst layer17is not formed, or specifically, on the exhaust gas purification filter1before catalyst layer formation. The measurement sample was taken from the partition wall12of the exhaust gas purification filter1, and the porosity and the average pore diameter of the measurement sample were measured by a mercury porosimeter using the principles of the mercury injection method. The measurement sample is substantially a cube that has a length of 1 cm in the filter axial direction Y, a length of 1 cm in the wall thickness direction, and a length of 1 cm orthogonal to the filter axial direction and the wall thickness direction. The average pore diameter is also referred to as an average pore diameter. AutoPore IV9500 manufactured by Shimadzu Corporation was used as the mercury porosimeter.

Specifically, first, the measurement sample was housed inside a measurement cell of the mercury porosimeter, and an interior of the measurement cell was depressurized. Then, mercury was introduced into the measurement cell, and the measurement cell was pressurized. The pore diameter and the pore volume was measured based on pressure during pressurization and a volume of mercury that is introduced into the pores in the measurement sample.

The measurement was performed within a pressure range of 0.5 to 20000 psia. Here, 0.5 psia corresponds to 0.35×10−3kg/mm2. 20000 psia corresponds to 14 kg/mm2. A range of pore diameters that corresponds to this pressure range is 0.01 to 420 μm. As normal numbers for calculating the pore diameter from pressure, a contact angle of 140° and a surface tension of 480 dyn/cm were used. The average pore diameter is the pore diameter at 50% of an integrated pore volume. The porosity was calculated by the following relational expression.
porosity (%)=total pore volume/(total pore volume+1/true specific gravity of cordierite)×100.

Here, a true specific gravity of cordierite is 2.52.

(Pore Volume Ratio of Pore Diameters of 9 μm or Less)

Measurement was performed in a state in which the catalyst layer17is not formed, or specifically, on the exhaust gas purification filter1before catalyst layer formation. The pore diameter distribution of each measurement sample was examined by a mercury porosimeter using the principles of the mercury injection method. The measurement was performed based on methods and conditions similar to those for the above-described porosity and average pore diameter. The volume ratio of the pores121that have pore diameters of 9 μm or less was determined from the pore diameter distribution.

(Gas Permeability Coefficient)

The gas permeability coefficient is determined from a relationship between gas flow rate and pressure loss. For example, the relationship between the gas flow rate and pressure loss may be measured by a measurement sample being fabricated from the exhaust gas purification filter1and measurement being performed based on the measurement sample. For measurement of the gas permeability coefficient, a measurement sample that has a circular columnar shape that has a diameter of 30 mm and a length in the filter axial direction Y of 25 mm, and a thickness of the partition wall12of 200 μm was used.

For example, the measurement sample may be the exhaust gas purification filter1that has a smaller outer dimension than an actual product for in-vehicle use and may be obtained by a filter of a desired dimension being cut out from an actual product. The sampling positions of the measurement samples are the three sites described above. For example, an outer shell of the filter that is cut out may be formed by cementing.

Next, polyester tape is attached to both end surfaces in the filter axial direction Y of the measurement sample. For example, the polyester tape may be partially removed by a soldering iron or the like such that the plug portions16that alternately seal the end surfaces as described above are formed by the polyester tape. That is, here, the plug portion16that is simulated by the polyester tape is formed.

Next, a gas is sent from the inflow end surface14to the outflow end surface15of the measurement sample, and the relationship between the gas flow rate and pressure loss is measured by a perm porometer. As the perm porometer, for example, a CEP-1100AXSHJ manufactured by Porous Materials, Inc. may be used. Specifically, the pressure loss when the gas flow rate is changed is measured by the perm porometer. Then, a relationship diagram of the gas flow rate (X-axis) and the pressure loss (Y-axis) is determined.

FIG.9shows an example of the relationship diagram of the gas flow rate (X-axis) and a pressure loss ΔP (Y-axis) within the cell13. The relationship diagram indicates an actual measurement value (plot point) of the perm porometer and a calculation value (such as a broken line) determined by the following expressions (i) to (viii). Expressions (i) to (viii) will be described below.

The pressure loss ΔP (unit: Pa) in the exhaust gas purification filter1, a sum ΔPinlet/exit(unit: Pa) of condensed pressure loss ΔPinletwhen the gas flows into the cell13and expanded pressure loss ΔPexitwhen the gas flows out of the cell13, pressure loss ΔPchannel(unit: Pa) during passage of gas inside the cell13, and pressure loss ΔPwall(unit: Pa) during passage of gas in the partition wall13satisfy a relationship in the following expression (i).
ΔP=ΔPinlet/exit+ΔPchannel+ΔPwall(i)

In addition, ΔPinlet/exit, an opening area Aopen(unit: m2) of the cell13, an opening area Ain(unit: m2) of the cell13on the inflow end surface14of the exhaust gas, a gas flow rate Vchannel(unit: m/s) inside the cell13, and air density ρ (unit: kg/m3) satisfy a relationship in the following expression (ii).

Δ⁢Pi⁢nlet/exit=(1-Ao⁢ρ⁢e⁢nAi⁢n)2·12⁢ρ⁢Vchannel2+(0.04-(10.582+0.04181.1-(AopenAi⁢n)-0.5))2·12⁢ρ⁢Vc⁢h⁢a⁢nnel2(ii)

Furthermore, ΔPchannel+ΔPwall, a gas permeability coefficient k (unit: m2), a length L (unit: m) in the filter axial direction Y of the exhaust gas purification filter1, a hydraulic diameter a1(unit: m) of the cell13, a thickness w (unit: m) of the partition wall12, a coefficient of friction F (unit: dimensionless) inside the cell13, Reynold's number (unit: dimensionless), gas viscosity μ (unit: Pa·s), and the gas flow rate Vchannel(unit: m/s) inside the cell13satisfy relationships expressed by the following expressions (iii) to (viii). Here, in expression (iii), e is an exponential function exp.

Δ⁢Pchannel+Δ⁢Pwall={(eg⁢1+1)⁢(eg⁢2+1)⁢(g2-g1)4⁢(eg⁢2-eg⁢1)+A22}·μ⁢Vchannel⁢a1⁢w4⁢L⁢k(iii)g1=A1-A12+2⁢A2(iv)g2=A1+A12+2⁢A2(v)A1=ka1⁢w⁢4⁢La1⁢Re(vi)A2=4⁢F⁢ka1⁢w⁢(La1)2(vii)Re=ρ⁢Vc⁢h⁢a⁢nnel⁢a1μ(viii)

A pressure loss value is calculated based on expressions (i) to (viii) above. The broken line formed by the calculation values shown in the relationship diagram of the gas flow rate (X-axis) and pressure loss (Y-axis) shown as an example inFIG.9is the pressure loss value determined by calculation. As is understood from expressions (i) to (viii), the pressure loss value is calculated by measuring the filter length L, the opening area Aopenof the cell13, the hydraulic diameter a1, and the thickness w of the partition wall12, excluding the gas permeability coefficient k. These values do not change even when the gas flow rate is changed. Therefore, as a result of an arbitrary value being inputted to the gas permeability coefficient, the calculation values in the relationship drawing of the gas flow rate (X-axis) and pressure loss (Y-axis) can be derived.

For example, when a value that has a large gas permeability coefficient is inputted, the pressure loss value becomes lower than an actual measurement value. The calculation value falls below the actual measurement value. Meanwhile, when a value that has a small gas permeability coefficient is inputted, the calculation value exceeds the actual measurement value. Here, the gas permeability coefficient k at which the difference between the calculation value and the actual measurement value is minimum is calculated by a least-squares method such that the calculation value is approximated to be closest to the actual measurement value. The calculation value is the gas permeability coefficient k. That is, the gas permeability coefficient k is a value that is the gas permeability coefficient calculated back by expressions (i) to (viii) from the actual measurement value of the pressure loss measured by the perm porometer.

(GSA)

Measurement was performed in a state in which the catalyst layer17is not formed, or specifically, on the exhaust gas purification filter1before catalyst layer formation. Continuous tomographic images of the partition wall12of the measurement sample taken from the exhaust gas purification filter1were acquired. The samplings positions are the three sites described above.

An X-ray computed tomography (CT) apparatus “Versa XRM-500” manufactured by Xradia, Inc. was used to capture the continuous tomographic images. Imaging conditions are voltage: 80 kV, step: 0.1°, and resolution: 0.684787 μm/pixel. For example, the continuous tomographic image may be in Tag Image File (TIF) format. The continuous tomographic images were loaded under a condition of 0.687478 μm/voxel using an importGeo-Vol function that is an interface of a micro-structure simulation software “GeoDict” manufactured by Math2Market GmbH.

In addition, in order to separate an aggregate portion (specifically, the ceramic portion) and a space portion in the loaded image, three-dimensional (3D) modeling of the partition wall12was performed using, as a threshold, an intersecting portion between two separated peaks in a graph of gray values as illustrated inFIG.10. Subsequently, noise was removed, and unnecessary portions were removed to achieve a desired size (in actuality, 900 voxel×600 voxel×partition-wall thickness voxel).

For a geometric surface area of the partition wall12, Estimate Surface Area in a Porodict function that is a module of GeoDict was used, and analysis details were introduced from “Estimate of real surface area” in J. Ohser and F. Mücklich, Statistical Analysis Microstructures in Materials Science, Wiley and Sons, 2000, p. 115. Here, F. Mücklich above should correctly be written with an umlaut symbol above the “u”. However, in the present specification, the name is written without the umlaut symbol. An average value of the measurement values at the three sites described above is given in Table 1 as the GSA.

(Average Thickness of the Catalyst Layer)

The average thickness of the catalyst layer is calculated from the average pore diameters of the exhaust gas purification filter before and after the catalyst is supported. Specifically, the average thickness of the catalyst layer is calculated from the following expression:
average thickness of the catalyst layer=(average pore diameter of the exhaust gas purification filter before the catalyst is supported−average pore diameter of the exhaust gas purification filter after the catalyst is supported)÷2.

An average value of ten exhaust gas purification filters was used as the average pore diameter. The sampling positions of the measurement samples of each exhaust gas purification filter are the three sites as shown inFIGS.8A to8C. Results of the calculation are shown in Table 1.

(NOXReduction Efficiency)

Measurement was performed in a state in which the catalyst layer17is not formed, or specifically, on the exhaust gas purification filter1before catalyst layer formation. As shown inFIG.11, the exhaust gas purification filter1was attached inside an exhaust pipe P of a 2.0 L, naturally aspirated, four-cylinder, gasoline direct-injection engine E. Specifically, a ceramic mat (not shown) was wrapped around the exhaust gas purification filter1, and the exhaust gas purification filter1was inserted into a filter case C.

Next, the filter case C was connected to the exhaust pipe P of the engine E with a fitting cone F therebetween, and the exhaust gas G was sent to the exhaust gas purification filter1from the engine E. Next, a value of A/F (that is, an air-fuel ratio: air/fuel) was controlled to 14.4 while being monitored by an A/F sensor8, and a NOXconcentration in the exhaust gas G was measured by a gas concentration meter7under conditions that an intake air amount is 10 g/s and a rotation speed of the engine E is 1500 rpm.

As the gas concentration meter7, a first gas concentration meter71for measuring the NOXconcentration on an entrance side before the exhaust gas G flows into the exhaust gas purification filter1and a second gas concentration meter72for measuring the NOXconcentration on an exit side on which the exhaust gas G flows out from the exhaust gas purification filter1were used. The first gas concentration meter71and the second gas concentration meter72are both “MEXA-7500” manufactured by Horiba, Ltd.

In addition, as the A/F sensor8, a first A/F sensor81for measuring an A/F concentration on the entrance side before the exhaust gas G flows into the exhaust gas purification filter1and a second A/F sensor82for measuring the A/F concentration on the exit side on which the exhaust gas G flows out from the exhaust gas purification filter1were used. A/F: 14.4 is an A/F value that is most frequent in Worldwide-harmonized Light vehicles Test Cycle (WLTC) mode traveling. The condition that the intake air amount is 50 g/s and the rotation speed of the engine E is 3500 rpm simulates driving conditions during high-load traveling.

For example, an exhaust gas temperature may reach a high-temperature region of 750° C. or higher. The NOXreduction efficiency is calculated from the NOXconcentration on the entrance side measured by the first gas concentration meter71and the NOXconcentration on the exit side measured by the second gas concentration meter72, based on the following expression:
NOXreduction efficiency=100×(NOXconcentration on entrance side−NOXconcentration on exit side)/NOXconcentration on entrance side.
(PM Collection Efficiency)

Measurement was performed in a state in which the catalyst layer17is not formed, or specifically, on the exhaust gas purification filter1before catalyst layer formation. As shown inFIG.12, in a manner similar to that in the measurement of the NOXreduction efficiency, the exhaust gas purification filter1was attached inside the exhaust pipe P of the 2.0 L, naturally aspirated, four-cylinder, gasoline direct-injection engine E.

In addition, the exhaust G was sent to the exhaust gas purification filter1from the engine E. A PM concentration on the entrance side before the exhaust gas G flows into the exhaust gas purification filter1and a PM concentration on the exit side on which the exhaust gas G flows out from the exhaust gas purification filter1were measured by a PM sensor6. Measurement conditions were a temperature of 720° C. and an exhaust-gas flow amount of 11.0 m3/min.

Both measurements were performed in an initial state in which the PM is not accumulated in the exhaust gas purification filter1. The PM concentration on the entrance side was measured by a first PM sensor61. The PM concentration on the exit side was measured by a second PM sensor62. The PM collection efficiency is calculated from the PM concentration on the entrance side and the PM concentration on the exit side, based on the following expression:
PMcollection efficiency=100(PMconcentration on entrance side−PMconcentration on exit side)/PMconcentration on entrance side.

TABLE 1Example/AverageGasPore volumeAverageNOxcomparativeporepermeabilityratio of poreGSAthickness ofreductionCollectionexamplePorositydiametercoefficientdiameters of(μm2/catalyst layerefficiencyefficiencyNo.(%)(μm)(×1012m2)9 μm or less (%)μm3)(μm)(%)(%)Example 16421.41.73131080565.096.273.0Example 26427.03.5012959625.297.665.0Example 36418.43.20141309455.297.469.2Example 46426.02.0220930165.197.267.2Example 56418.01.204981325.486.073.0Example 66418.00.8012882455.095.675.2Example 76418.00.4116868493.990.881.6Example 86412.20.3517854375.881.276.8Example 96414.60.3719710044.485.377.4Example 106418.00.3517705635.781.474.5Example 116418.00.3724867845.482.478.9Example 126418.71.74131307852.286.873.4comparative6411.50.3227809458.250.376.5example 1comparative6411.00.2221778517.658.478.6example 2comparative6412.50.3126710047.263.277.4example 3comparative6411.60.3828687596.276.477.4example 4comparative6416.51.5627556476.574.177.4example 5comparative6411.20.4824945786.678.677.4example 6comparative6412.40.2421578436.373.377.4example 7

As is clear from Table 1 andFIGS.13and14, the exhaust gas purification filters1of the examples have a gas permeability coefficient that is equal to or greater than 0.35×10−12m2, a pore volume ratio of pore diameters of 9 μm or less that is equal to or less than 25%, and an average pore diameter that is equal to or greater than 12 μm. Therefore, the NOXreduction efficiency is high in the examples. From a perspective of satisfying a reduction efficiency required as a U/F catalytic converter in a typical direct-injection engine, the NOXreduction efficiency is preferably equal to or greater than 80%. The U/F catalytic converter is also referred to as an under-floor catalyst. The U/F catalytic converter will be described according to a second embodiment.

As is clear from Table 1 andFIG.13, from the perspective of improving the NOXreduction efficiency, the gas permeability coefficient is equal to or greater than 0.35×10−12m2. However, from the perspective of further improving the NOXreduction efficiency, the gas permeability coefficient is preferably equal to or greater than 0.40×10−12m2and more preferably equal to or greater than 0.80×10−12m2. In addition, as is clear from Table 1 andFIG.15, from the perspective of improving the NOXreduction efficiency, the average pore diameter is equal to or greater than 12 μm. However, from the perspective of further improving the NOXreduction efficiency, the average pore diameter is more preferably equal to or greater than 14 μm.

Furthermore, as is clear from Table 1 andFIG.14, from the perspective of improving the NOXreduction efficiency, the pore volume ratio of pore diameters of 9 μm or less is equal to or less than 25%. However, from the perspective of further improving the NOXreduction efficiency, the pore volume ratio of pore diameters of 9 μm or less is preferably equal to or less than 20% and more preferably equal to or less than 15%. A reason for this is thought to be that, when the pore volume ratio of pore diameters of 9 μm or less is reduced, the pores121that exceed the pore diameter of 9 μm increase, and the catalyst layer17is thinly and widely formed by the catalyst being supported.

Moreover, as is clear from Table 1, from the perspective of suppressing the worsening of PM collection efficiency, the pore volume ratio of pore diameters of 9 μm or less is preferably equal to or greater than 3%, more preferably equal to or greater than 10%, and even more preferably equal to or greater than 15%. The pores121that have a pore diameter of 9 μm or less contribute greatly to the improvement of PM collection efficiency. Therefore, when the pores121that have a pore diameter of 9 μm or less are too few, PM collection performance may decrease.

As is clear from Table 1, the NOXreduction efficiency further improves when the pore wall area per unit volume (that is, the GSA) of the partition wall12is equal to or greater than 70000 μm2/μm3. From the perspective of further improving the NOXreduction efficiency, the GSA is more preferably equal to or greater than 85000 μm2/μm3, and even more preferably equal to or greater than 90000 μm2/μm3.

In contrast, in the comparative examples, a condition among the conditions that the gas permeability coefficient is equal to or greater than 0.35×10−12m2, a pore volume ratio of pore diameters of 9 μm or less is equal to or less than 25%, and an average pore diameter is equal to or greater than 12 μm is not met. Therefore, the NOXreduction efficiency is low in the comparative examples.

Second Embodiment

Next, arrangement examples of the exhaust gas purification filter1will be described. According to a present embodiment, an arrangement example in a case in which the exhaust gas purification filter1is mounted in a vehicle is given. As shown inFIG.15A, an S/C catalyst1A (that is, a start catalyst) is arranged inside the exhaust pipe P, on an upstream side in a flow direction of the exhaust gas G that is discharged from the engine E.

For example, the S/C catalyst1A may be a honeycomb structure that is formed from cordierite. Although an illustration of the configuration of the S/C catalyst1A is omitted, the S/C catalyst1A has a shape that is similar to the honeycomb structure portion10according to the first embodiment. Specifically, the S/C catalyst1A includes the outer shell11, the partition walls12, and the cells13, but does not include the plug portions. The honeycomb structure used in the S/C catalyst1A is also referred to as a monolithic carrier. A three-way catalyst is supported in partition walls12. Here, as the S/C catalyst, the exhaust gas purification filter1that includes the honeycomb structure portion10and the plug portions16can also be used.

As shown inFIG.16A, a U/F catalytic converter1B (that is, an under-floor catalytic converter) is arranged in a U/F position (that is, an under-floor position) that is under a floor of the vehicle downstream of the S/C catalyst1A. For example, as the U/F catalytic converter1B, the exhaust gas purification filter1according to the first embodiment may be used. The U/F catalytic converter1B is also commonly referred to as a second converter.

The S/C catalyst1A and the U/F catalytic converter1B are respectively inserted into differing cases C1and C2, and the cases C1and C2are connected to the exhaust pipe P. On a path of the exhaust pipe P, the S/C catalyst1A and the U/F catalytic converter1B are arranged a predetermined distance apart.

In addition, a tandem-type catalytic unit may be configured using the exhaust gas purification filter1. Specifically, as shown inFIG.16B, the S/C catalyst1A and a rear catalyst1C are inserted into the same case C3, and the case C3is connected to the exhaust pipe P. For example, as the rear catalyst1C, the exhaust gas purification filter1according to the first embodiment may be used.

The exhaust gas purification filter1is used as the U/F catalytic converter1B, the rear catalyst1C of the tandem-type catalytic unit, and the like, and is used on the downstream side of the S/C catalyst1A that supports a three-way catalyst. In the S/C catalyst1A that is arranged on the upstream side, toxic gas components such as CO, HC, and NOXare reduced by the three-way catalyst. Because the exhaust gas temperature is high, CO and HC are sufficiently reduced in the S/C catalyst1A.

Meanwhile, in the U/F catalytic converter1B or the rear catalyst1C of the tandem-type catalytic unit that is arranged downstream of the S/C catalyst1A, the NOXthat had not been sufficiently reduced by the S/C catalyst1A is mainly reduced. Because the exhaust gas purification filter1according to the first embodiment has excellent NOXpurification performance, the exhaust gas purification filter1is suitable for the U/F catalytic converter1B and the rear catalyst1C of the tandem-type catalytic unit that are arranged on the downstream side of the S/C catalyst1A.

The present disclosure is not limited to the above-described embodiments. Various embodiments are applicable without departing from the spirit of the invention. For example, although the exhaust gas purification filter1is used to purify the exhaust gas G of an internal combustion engine such as a diesel engine or a gasoline engine, the exhaust gas purification filter1may be suitable for application regarding emissions from a gasoline engine. That is, the exhaust gas purification filter1is preferably a gasoline particulate filter. The gasoline particulate filter is referred to as a GPF. The GPF requires not only PM purification performance, but also purification of toxic gas substances by being coated with a purification catalyst for toxic gas components such as NOX.

While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification examples and modifications within the range of equivalency. In addition, various combinations and configurations, and further, other combinations and configurations including more, less, or only a single element thereof are also within the spirit and scope of the present disclosure.