JP2022111085A - Exhaust gas purification filter - Google Patents

Abstract

To provide an exhaust gas purification filter which can reduce pressure loss, and has high exhaust gas purification performance and particulate substance capturing performance.SOLUTION: An exhaust gas purification filter includes a filter base material 320 having a wall flow structure and an exhaust gas purification catalyst 33 carried on a diaphragm 323 of the filter base material, wherein a median pore diameter (D50) of the filter base material 320 after carry of the exhaust gas purification catalyst is 17 μm or more, a half-value width of pore distribution of the filter base material 320 is 7-15 μm, the exhaust gas purification catalyst 33 is unevenly carried on a high-density layer 331 having relatively high density of the exhaust gas purification catalyst, and a low-density layer 332 having relatively low density of the exhaust gas purification catalyst, and a maximum pore diameter of the high-density layer 331 is 11.7 μm or less.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to an exhaust purification filter provided with an exhaust purification catalyst.

2. Description of the Related Art Conventionally, direct-injection gasoline engines have been adopted in gasoline engines mounted on automobiles and the like from the viewpoint of improving combustion efficiency. However, direct injection gasoline engines emit more particulate matter such as PM than port injection (PI) engines. Along with this enhancement, studies are underway on a technique for providing an exhaust purification filter (Gasoline Particulate Filter, hereinafter referred to as "GPF") for trapping particulate matter in the exhaust passage of a gasoline engine.

In addition, a three-way catalyst (hereinafter referred to as "TWC") for purifying CO, HC and NOx contained in exhaust gas is provided in an exhaust passage of a gasoline engine while being supported on a honeycomb support. Especially in recent years, a plurality of TWCs are arranged in series in the exhaust passage in order to meet the required catalytic purification performance. Therefore, it is not preferable to newly provide a GPF in the exhaust passage in addition to these TWCs from the viewpoint of pressure loss and cost.

Therefore, a technique has been proposed in which a TWC is supported on a GPF to provide the GPF with a three-dimensional purification function in addition to the particulate matter trapping performance (see, for example, Patent Document 1).

JP 2017-082745 A

However, in order to obtain the desired particulate matter trapping performance, it is necessary to use a filter base material having a small pore size as the filter base material that constitutes the GPF. was there. Furthermore, as the travel distance increases, more particulate matter such as oil-derived ash (ash) is captured by the exhaust purification filter, and this problem becomes more pronounced.

In addition, there is a method of improving the particulate matter trapping performance by coating a catalyst, but in the case of catalyst loading on a filter base material with a pore size that is conventionally common, the amount of catalyst loaded on the GPF from the viewpoint of the above-mentioned pressure loss is large. It was limited, and the exhaust purification performance could not be expected as much as the conventional TWC. That is, the pressure loss, the exhaust purification performance, and the particulate matter trapping performance are in a trade-off relationship with each other.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object thereof is to provide an exhaust purification filter that can reduce pressure loss and has high exhaust purification performance and particulate matter trapping performance.

(1) In order to achieve the above objects, the present invention is provided in an exhaust passage (for example, an exhaust pipe 3, which will be described later) of an internal combustion engine (for example, an engine 1, which will be described later) to remove particulate matter in the exhaust of the internal combustion engine. An exhaust purification filter that captures and purifies exhaust gas, wherein a plurality of cells extending from an exhaust inflow side end face to an exhaust outflow side end face are partitioned by a porous partition wall (for example, a partition wall 323 to be described later), and the outflow side end face A filter base material (for example, a filter base material 320 to be described later) in which inflow-side cells with sealed openings in the inflow-side end face and outflow-side cells with sealed openings in the inflow-side end face are alternately arranged; an exhaust purification catalyst (for example, TWC33 to be described later) supported on a partition wall, and the median pore diameter (D50) of the filter base material after supporting the exhaust purification catalyst is 17 μm or more, and the filter base material The half-value width of the pore distribution is 7 μm to 15 μm, and the exhaust purification catalyst is composed of a high-density layer (for example, a high-density layer 331 described later) having a relatively high density of the exhaust purification catalyst, and a high-density layer 331 having a relatively high density of the exhaust purification catalyst. An exhaust purification filter (for example, , GPF 32 described below.

In the invention of (1), in an exhaust purification filter in which an exhaust purification catalyst is supported on a so-called wall-flow filter substrate, the median pore diameter (D50) of the filter substrate after supporting the exhaust purification catalyst is 17 μm or more, which is relatively large. In addition, the exhaust purification catalyst carried on the filter base material is unevenly distributed in the relatively high-density layer and the low-density layer.
According to the invention of (1), a high-density layer in which the exhaust purification catalyst is arranged in a layered manner at a high density is provided in a part of the partition wall in the thickness direction in which a relatively large pore diameter is ensured after supporting the exhaust purification catalyst. Therefore, a sufficient flow path for the exhaust gas is ensured, and the uniformity of the flow of the exhaust gas is ensured. As a result, an increase in pressure loss can be suppressed within an allowable range.
Here, the applicant has found that there is a correlation between the initial increase in pressure loss due to particulate matter and the increase in pressure loss after accumulation of particulate matter. That is, if the initial increase in pressure loss due to particulate matter can be suppressed, the increase in pressure loss after accumulation of particulate matter can be reduced. In this respect, the pressure drop increase suppressing effect of the invention (1) described above is exerted from the initial stage, so according to the invention (1), it is possible to reduce the pressure drop increase after particulate matter deposition.

Further, according to the invention of (1), the exhaust purification catalyst has a high-density layer arranged in a layered and dense manner in a part of the partition wall in the thickness direction, and the maximum pore diameter of the high-density layer is relatively small. Since the diameter is 0.7 μm or less, the exhaust gas reliably passes through the flow path narrowed by the exhaust gas purification catalyst arranged at a high density, and high particulate matter trapping performance and high exhaust gas purification performance can be obtained.
Therefore, according to the invention of (1), it is possible to suppress an initial increase in pressure loss due to particulate matter, and reduce pressure loss after accumulation of particulate matter. As a result, the pressure loss can be reduced without limiting the supported amount of the exhaust purification catalyst, so that the pressure loss can be reduced, and an exhaust purification filter having high exhaust purification performance and particulate matter trapping performance can be provided.

Furthermore, in the invention (1), the half width of the peak in the pore distribution of the filter base material is 7 μm to 15 μm. That is, the exhaust purification filter according to the invention of (1) has a large pore diameter and a narrow half width of the pore distribution. As a result, when the exhaust purification catalyst is supported on the filter base material, the slurry containing the exhaust purification catalyst preferentially flows into the pores having a small pore diameter due to capillary action, thereby suppressing the clogging of the pores. . Therefore, it is possible to provide an exhaust purification filter capable of suppressing a decrease in the flow path of the exhaust gas in the partition wall even after supporting the exhaust purification catalyst, and further suppressing an increase in pressure loss after supporting the exhaust purification catalyst. In addition, the increased number of flow paths increases the probability of contact between exhaust gas containing particulate matter and the exhaust purification catalyst, so that an exhaust purification filter having higher exhaust purification performance and particulate matter trapping performance can be provided.

(2) In the exhaust purification filter of (1), the median pore diameter (D50) of the filter substrate after supporting the exhaust purification catalyst may be 20 μm or more.

In the invention of (2), the median pore diameter (D50) of the filter substrate after supporting the exhaust purification catalyst is 20 μm or more. As a result, an increase in pressure loss can be further suppressed, and the effect of the invention (1) is further enhanced.

(3) In the exhaust purification filter of (1) or (2), the maximum pore diameter of the high-density layer may be 7.7 μm or less.

In the invention of (3), the maximum pore diameter of the high-density layer is 7.7 μm or less. As a result, higher particulate matter trapping performance and higher exhaust purification performance are obtained, and the effect of the invention (1) is further enhanced.

(4) In the exhaust purification filter according to any one of (1) to (3), the filter base material may have a pore distribution half width of 7 μm to 9 μm.

In the invention of (4), the half value width of the peak in the pore distribution of the filter substrate before supporting the exhaust purification catalyst is 7 μm to 9 μm. As a result, even after the exhaust purification catalyst is carried, the reduction in the flow path of the exhaust gas in the partition wall can be suppressed, so that the effect of the invention (1) is further enhanced.

(5) In the exhaust purification filter according to any one of (1) to (4), the filter base material may have a porosity of 55% to 70%.

In the invention of (5), the porosity of the filter base material before supporting the exhaust purification catalyst is 55% to 70%. As a result, the exhaust flow path is more sufficiently secured, and the effect of the invention (1) is further enhanced.

Advantageous Effects of Invention According to the present invention, it is possible to provide an exhaust purification filter that can reduce pressure loss and has high exhaust purification performance and particulate matter trapping performance.

1 is a diagram showing the configuration of an exhaust purification system for an internal combustion engine according to one embodiment of the present invention; FIG. It is a sectional view of GPF concerning the above-mentioned embodiment. FIG. 4 is a cross-sectional view of a partition wall of the GPF according to the embodiment; FIG. 4 is a schematic cross-sectional view showing an example of the structure of the partition walls of the GPF according to the embodiment; FIG. 4 is a schematic cross-sectional view showing another example of the structure of the partition walls of the GPF according to the embodiment; FIG. 4 is a schematic cross-sectional view showing another example of the structure of the partition walls of the GPF according to the embodiment; It is a figure which shows the measurement point of a perm porometer and a mercury porosimeter. FIG. 4 is a diagram showing the relationship between median pore diameter and initial pressure loss. FIG. 4 is a diagram showing the relationship between the maximum pore diameter of a high-density layer and the PN reduction rate; It is a figure which shows the relationship between the maximum pore diameter of a high-density layer, and CPI. FIG. 5 is a diagram showing the relationship between the PN collection rate and the pressure loss after Ash deposition in each example and comparative example. It is a figure which shows the relationship between CPI and the pressure loss after Ash deposition in each Example and a comparative example.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an exhaust purification system 2 of an internal combustion engine (hereinafter referred to as "engine") 1 according to this embodiment.
The engine 1 is a direct injection gasoline engine. As shown in FIG. 1, the exhaust purification device 2 includes a TWC 31 and a GPF 32 as an exhaust purification filter, which are provided in order from the upstream side of an exhaust pipe 3 through which exhaust flows.

The TWC 31 purifies the exhaust gas by oxidizing or reducing HC to H ₂ O and CO ₂ , CO to CO ₂ , and NOx to N ₂ , respectively. For the TWC 31, for example, a carrier made of an oxide such as alumina, silica, zirconia, titania, ceria, or zeolite, carrying a noble metal such as Pd or Rh as a catalytic metal, is used. This TWC 31 is usually carried on a honeycomb support.

TWC 31 also includes an OSC material having OSC capabilities. As an OSC material, in addition to CeO ₂ , a composite oxide of CeO ₂ and ZrO ₂ (hereinafter referred to as “CeZr composite oxide”) or the like is used. Among them, the CeZr composite oxide is preferably used because of its high durability. The catalyst metal may be supported on these OSC materials.

The method for preparing TWC31 is not particularly limited, and it is prepared by a conventionally known slurry method or the like. For example, after preparing a slurry containing the above oxides, noble metals, OSC materials, etc., the prepared slurry is coated on a cordierite honeycomb support and fired.

GPF 32 traps and cleans particulate matter in the exhaust. Specifically, when the exhaust gas passes through fine pores in the partition wall, which will be described later, the particulate matter accumulates on the surface of the partition wall, thereby trapping the particulate matter.

Here, particulate matter in the present specification includes particulate matter such as soot (carbon soot), oil residue (SOF), ash that is oil ash, and PM. In recent years, emission regulations for these particulate matter have been tightened. The number of discharged small particulate matter with a particle diameter of 2.5 μm or less is being regulated (PN regulation). On the other hand, the GPF 32 according to this embodiment can comply with these PM regulations and PN regulations.

FIG. 2 is a cross-sectional view of the GPF 32 according to this embodiment.
As shown in FIG. 2 , the GPF 32 includes a filter base material 320 and an exhaust purification catalyst (TWC 33 in this embodiment) supported on partition walls 323 of the filter base material 320 .
The filter base material 320 has, for example, a cylindrical shape elongated in the axial direction, and is made of a porous material such as cordierite, mullite, or silicon carbide (SiC). The filter base material 320 is provided with a plurality of cells extending from the inflow side end face 32 a to the outflow side end face 32 b , and these cells are partitioned by partition walls 323 .

The filter base material 320 includes an inflow-side plugging portion 324 that seals the opening in the inflow-side end surface 32a. The cell whose opening on the inflow side end surface 32a is sealed by the inflow side plugging portion 324 is closed at the inflow side end and is open at the outflow side end, allowing the exhaust gas passing through the partition wall 323 to flow downstream. An outflow-side cell 322 for outflow is configured.
The inflow-side plugging portion 324 is formed by filling the inflow-side end surface 32 a of the filter base material 320 with a plugging cement.

The filter base material 320 includes an outflow-side plugging portion 325 that seals the opening in the outflow-side end face 32b. The cell whose opening on the outflow side end face 32b is sealed with the outflow side plugging portion 325 has an inflow side end that is open and an outflow side end that is closed. A cell 321 is constructed.
The outflow-side plugging portion 325 is formed by enclosing a plugging cement from the outflow-side end surface 32b of the filter base material 320 .

By alternately sealing the openings on the inflow-side end surface 32a and the openings in the outflow-side end surface 32b, the inflow-side cells 321 whose openings in the outflow-side end surface 32b are plugged and the inflow-side end surface 32a are sealed. are alternately arranged with outlet-side cells 322 in which the openings in are sealed. More specifically, the inflow-side cells 321 and the outflow-side cells 322 are arranged adjacent to each other in a grid pattern (checkered pattern).

As indicated by arrows in FIG. 2 , the exhaust gas that has flowed into the inflow-side cell 321 flows into the partition wall 323 from the airflow layer, passes through the partition wall 323 , and flows out to the outflow-side cell 322 . The side where the exhaust gas flows into the partition wall 323 is the inlet side (Inlet), and the side where the exhaust gas flows out of the partition wall 323 is the outlet side (Outlet).

The pore distribution of the filter substrate 320 according to this embodiment is measured by a mercury porosimeter. This pore distribution is represented by the pore diameter (μm) on the horizontal axis and the Log differential pore volume distribution dV/d (log D) (ml/g) on the vertical axis. In the present embodiment, the volume-based median pore diameter (D50) of the filter base material 320 after supporting the exhaust purification catalyst is 17 μm or more. More preferably, the volume-based median pore diameter (D50) of the filter base material 320 after supporting the exhaust purification catalyst is 20 μm or more.

That is, the filter base material 320 of the present embodiment has relatively large pores with a median pore diameter of 17 μm or more even after supporting the exhaust purification catalyst. This ensures a sufficient flow path for the exhaust gas flowing into the partition wall 323 . In particular, as will be described later, in this embodiment, by devising the supporting position of the TWC 33 as an exhaust purification catalyst, the pore diameter of the pores in the filter base material 320 is suppressed from being narrowed (closed) by the TWC 33. As a result, the pressure loss can be reduced as a result of ensuring a sufficient flow path for the exhaust gas.

Here, the half width in the pore distribution is an index representing the degree of sharpness of the peak of the pore distribution. In this embodiment, the half-value width of the pore distribution of the filter base material 320 before supporting the exhaust purification catalyst is 7 to 15 μm, which is narrow. A more preferable half width is 7 to 9 μm.

That is, the filter base material 320 of the present embodiment has a large pore diameter and a narrow half width of the pore distribution before supporting the exhaust purification catalyst. Since the half width is 7 to 15 μm, when the TWC 33 is supported on the filter base material 320, the slurry containing the TWC 33 preferentially flows into pores with small pore diameters due to capillary action, thereby clogging the pores. can be suppressed. Therefore, even after supporting the exhaust purification catalyst, it is possible to suppress the reduction of the flow path of the exhaust gas in the partition wall 323, and it is possible to provide the GPF 32 that can further suppress the increase in pressure loss after supporting the exhaust purification catalyst. In addition, the increased number of flow paths increases the probability of contact between the exhaust gas containing particulate matter and the TWC 33, so that higher exhaust purification performance and particulate matter trapping performance can be obtained.

The porosity of the filter base material 320 before supporting the exhaust purification catalyst is preferably 55% to 70%. If the porosity of the filter base material 320 before supporting the exhaust purification catalyst is 55% to 70%, it is possible to suppress the rapid increase in pressure loss when the TWC 33 is supported.

Moreover, the average pore diameter of the filter substrate before supporting the exhaust purification catalyst is preferably 20 μm to 30 μm. If the filter base material has an average pore diameter of 20 μm to 30 μm before supporting the exhaust purification catalyst, the median pore diameter of the filter base material 320 can be 17 μm or more even after supporting the exhaust purification catalyst.

The thickness of the partition 323 is preferably between 5 and 15 mils. If the thickness of the partition wall 323 is 5 to 15 mil, the pressure loss can be reduced, and high exhaust purification performance and particulate matter trapping performance can be obtained.

FIG. 3 is a cross-sectional view of the partition wall 323 of the GPF 32 according to this embodiment. In FIG. 3, the shaded area represents the filter base material 320, the white area represents the pores, and the black area represents the TWC (three-way catalyst) 33 as an exhaust purification catalyst. In addition, the upper side of FIG. 3 is the inlet side (Inlet) of the partition wall 323 and the lower side is the outlet side (Outlet) of the partition wall 323 . That is, the inlet side (Inlet) of the partition wall 323 constitutes the inner wall surface of the inflow-side cell 321 , and the outlet side (Outlet) of the partition wall 323 constitutes the inner wall surface of the outflow-side cell 322 .

A high-density layer 331 in which the TWC 33 is carried at high density is arranged on a part of the partition wall 323 in the thickness direction, ie, on the inlet side of the partition wall 323 in the example shown in FIG. As described above, in the GPF 32 of the present embodiment, the TWC 33 is unevenly distributed in the high-density layer 331 having a relatively high density and the low-density layer 332 having a relatively low density.

As described above, the GPF 32 of the present embodiment has a high-density layer 331 in which the TWC 33 is arranged in a layered and dense manner in a part of the partition wall 323 having the relatively large pores 34 with a median pore diameter of 20 μm or more in the thickness direction. As a result, it is possible to suppress an increase in pressure loss within a permissible range as a result of securing a sufficient flow path for the exhaust gas and securing the uniformity of the flow of the exhaust gas.
Here, the applicant has found that there is a correlation between the initial increase in pressure loss due to particulate matter and the increase in pressure loss after accumulation of particulate matter. That is, if the initial increase in pressure loss due to particulate matter can be suppressed, the increase in pressure loss after accumulation of particulate matter can be reduced. In this regard, since the effect of suppressing the increase in pressure loss described above is exerted from the initial stage, according to the present embodiment, it is possible to reduce the increase in pressure loss after particulate matter deposition.

In addition, in the GPF 32 of the present embodiment, as shown in FIG. 3 , the pores 34 in the high-density layer 331 have narrower pore diameters due to the TWC 33 supported on the inner wall surfaces of the pores 34 compared to the low-density layer 332 . Specifically, the maximum pore diameter of the high-density layer 331 of this embodiment is 11.7 μm or less. A more preferable maximum pore diameter of the high-density layer 331 is 7.7 μm or less.

The TWC 33 has a high-density layer 331 that is layered and densely arranged in a part of the partition wall 323 in the thickness direction, and the maximum pore diameter of the high-density layer 331 is relatively small, 11.7 μm or less. ensures a relatively large median pore diameter of 20 μm or more, and partly in the high-density layer 331, the exhaust gas reliably passes through the flow path narrowed by the TWCs 33 arranged at high density. High particulate matter trapping performance and high exhaust purification performance are obtained.

Therefore, according to the present embodiment, it is possible to suppress the initial increase in pressure loss due to particulate matter, and reduce the pressure loss after particulate matter deposition. As a result, the pressure loss can be reduced without limiting the amount of TWC 33 carried, so that the pressure loss can be reduced and high exhaust purification performance and particulate matter trapping performance can be obtained.

FIG. 4 is a schematic cross-sectional view showing an example of the structure of the partition wall 323 of the GPF 32 according to this embodiment. More specifically, it is a diagram schematically showing the structure of the partition wall 323 of the GPF 32 shown in FIG. As shown in FIGS. 3 and 4, the TWCs 33 are supported on the inner wall surfaces of the pores 34 over the entire partition walls 323, and in particular, the TWCs 33 are supported at high density on the inlet side (high-density layer 331) of the partition walls 323. be done. However, the arrangement of the high-density layer 331 is not limited to this, and may be arranged at any part in the thickness direction of the partition wall 323 .

FIG. 5 is a schematic cross-sectional view showing another example of the structure of the partition wall 323 of the GPF 32 according to this embodiment. In the example shown in FIG. 5, a high-density layer 331 in which the TWCs 33 are layered and densely arranged is arranged on and near the outer surface of the partition wall 323 . More specifically, the high-density layer 331 is arranged on the inlet-side outer surface of the partition wall 323 and in the vicinity thereof.

FIG. 6 is a schematic cross-sectional view showing another example of the structure of the partition wall 323 of the GPF 32 according to this embodiment. In the example shown in FIG. 6, a high-density layer 331 in which the TWCs 33 are layered and arranged at high density is arranged substantially in the center of the partition wall 323 in the thickness direction.

In each high-density layer 331 in each of the above examples, it is preferable that 50% by mass or more of the total amount of TWC 33 carried in one partition 323 be TWC 33 . As a result, the above-described effects of the present embodiment can be exhibited more reliably, pressure loss can be further reduced, and higher exhaust purification performance and particulate matter trapping performance can be obtained.

The TWC 33 purifies the exhaust gas by oxidizing or reducing HC to H ₂ O and CO ₂ , CO to CO ₂ , and NOx to N ₂ in the same manner as the TWC 31 described above. For the TWC 33, for example, a carrier made of an oxide such as alumina, silica, zirconia, titania, ceria, or zeolite, carrying a noble metal such as Pd or Rh as a catalyst metal, is used.

In addition, the TWC 33 contains an OSC material (oxygen-absorbing material). As the OSC material, in addition to CeO ₂ , a composite oxide of CeO ₂ and ZrO ₂ (hereinafter referred to as “CeZr composite oxide”) or the like is used. Among them, the CeZr composite oxide is preferably used because of its high durability. The catalyst metal may be supported on these OSC materials. In order to effectively generate the catalytic action of the above TWC at the same time, the ratio of fuel and air (hereinafter referred to as "air-fuel ratio") is kept close to the stoichiometric ratio in complete combustion reaction (hereinafter referred to as "stoichiometric"). Preferably, by using an OSC material having an oxygen storage/release capacity of absorbing oxygen under an oxidizing atmosphere and releasing oxygen under a reducing atmosphere together with the catalyst metal as a co-catalyst, higher catalytic purification performance can be obtained.

The method for preparing TWC33 is not particularly limited, and it is prepared by a conventionally known slurry method or the like. For example, it is prepared by milling a slurry containing the above oxides, noble metals, OSC materials, etc., and then coating the filter substrate 320 with the prepared slurry and baking it.

The washcoat amount of TWC33 having the above structure is preferably 30 to 150 g/L. If the washcoat amount of the TWC 33 is within this range, high catalytic purification performance and particulate matter trapping performance can be obtained while reducing pressure loss increase.
In this embodiment, the TWC 33 may contain other noble metals such as Pt as catalyst metals.

GPF32 which concerns on this embodiment provided with the above structure is manufactured, for example by a piston push-up method. In the piston push-up method, a slurry containing a predetermined amount of the constituent material of the TWC 33 is produced by milling, and the inflow side end face of the filter base material 320 is used as the slurry inflow inlet by the piston push-up method, and the filter base material is obtained with a WC amount of 60 g / L. 320 is loaded with TWC 33 . Then, GPF32 is obtained by making it dry and baking.

An example of a method for forming (arranging) the high-density layer 331 on and near the outer surface of the filter substrate 320 is a method in which the filter substrate 320 is impregnated with high-viscosity slurry and the suction pressure is set low. be done. Another method is to use a slurry in which relatively large particles remain by shortening the milling time during preparation of the slurry.
As an example of a method of forming (arranging) the high-density layer 331 on the inlet side/outlet side of the partition wall 323 of the filter base material 320, the filter base material 320 is impregnated with high-viscosity slurry and the suction pressure is set high. is mentioned.
An example of a method for forming (arranging) the high-density layer 331 in the center of the thickness direction of the filter base material 320 is to impregnate the filter base material 320 with low-viscosity slurry and set a short suction time.

In the GPF 32 of the present embodiment manufactured as described above, the median pore diameter of the filter substrate 320 after carrying the TWC 33 described above is measured by a mercury porosimeter. More specifically, the median pore diameter of the filter substrate 320 after supporting the TWC 33 is the median pore diameter of the entire portion P1 indicated by the dashed line in FIGS.

Also, in this embodiment, the maximum pore diameter in the high-density layer 331 is measured by a perm porometer. More specifically, the maximum pore diameter in the high density layer 331 is the maximum pore diameter at the portion P2 indicated by the dashed line in FIGS.

Here, FIG. 7 is a diagram showing measurement points of a perm porometer and a mercury porosimeter. In FIG. 7, the inflow side of the GPF 32 described above is TOP, the distance from the inflow side is T and the distance from the outflow side is T in the flow direction of the inflowing gas, and the central portion is MID, and the outflow side is BTM. is displayed as

The maximum pore diameter in the high-density layer 331 is measured using a perm porometer at three locations, TOP, MID and BTM, shown in FIG. 7, and their average value is adopted. However, if the cell length is determined to be uniform by EPMA or the like, the BTM measurement value may be used as the representative value. This perm porometer measures the through hole distribution of the partition wall 323 by the bubble point method. More specifically, the GPF 32 is immersed in alcohol, and the through hole distribution is measured from the pressure released when the gas pressure is increased. It is a pore size distribution when observing the partition wall surface of the side cell 322 .

In addition, the median pore diameter of the filter substrate 320 after supporting TWC 33 is measured using a mercury porosimeter by measuring three locations, TOP, MID and BTM, shown in FIG. 7, and adopting the average value thereof. This mercury porosimeter immerses the GPF 32 in mercury, changes the pressure, and measures the pore diameter from the pressure when the mercury permeates. More specifically, for all pores (including non-penetrating pores) other than obturator pores, the pore distribution reflects the pore diameter of the entire area from the partition wall surface of the inflow-side cell 321 to the partition wall surface of the outflow-side cell 322. be.

Next, the results of simulating the initial pressure loss, the PN reduction rate, and the honeycomb resistance of the GPF 32 according to the present embodiment having the above configuration will be described. The simulation was carried out in a model adapted to the real thing by allowing the exhaust to flow in the same way as the real thing.

FIG. 8 is a diagram showing the relationship between median pore diameter and initial pressure drop. As shown in FIG. 8, it can be seen that the initial pressure loss can be sufficiently reduced when the median pore diameter of the filter substrate 320 after supporting the TWC 33 is 17 μm or more. As described above, there is a correlation between the initial increase in pressure loss due to particulate matter and the increase in pressure loss after accumulation of particulate matter. Therefore, it can be said that an increase in pressure loss after deposition of particulate matter can be reduced.

FIG. 9 is a diagram showing the relationship between the maximum pore diameter of the high-density layer 331 and the PN reduction rate. As shown in FIG. 9, when the maximum pore diameter of the high-density layer 331 is 11.7 μm or less, a sufficient PN reduction rate exceeding 80% can be obtained.

FIG. 10 is a diagram showing the relationship between the maximum pore diameter of the high-density layer 331 and CPI. Here, CPI (Coat Performance Index) is obtained by dividing the NOx purification rate of GPF by the NOx purification rate of TWC supported on a normal honeycomb carrier (without plugging), and is the NOx purification index of GPF with respect to TWC. is. As shown in FIG. 10, it can be seen that even when the maximum pore diameter of the high-density layer 331 is 11.7 μm or less, sufficient purification performance can be obtained.

The present invention is not limited to the above-described embodiments, and includes modifications and improvements within the scope of achieving the object of the present invention.
Although the exhaust purification filter according to the present invention is applied to the GPF in the above embodiment, it is not limited to this. The exhaust purification filter according to the present invention may be applied to DPF. In this case, the exhaust purification catalyst is not limited to the TWC, and other exhaust purification catalysts may be used, such as an oxidation catalyst such as a PM combustion catalyst.

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[Examples 1 to 4, Comparative Examples 1 to 7]
First, an aqueous solution of Pd nitrate and Rh nitrate and an Al ₂ O ₃ carrier (commercially available γ-alumina) are put into an evaporator, and the Al ₂ O ₃ carrier is impregnated with Pd and Rh at a mass ratio of 6/1. let me After drying, calcination was performed at 600° C. to obtain a Pd—Rh/Al ₂ O ₃ catalyst. Similarly, Pd nitrate, Rh nitrate and CeO ₂ were prepared to obtain a Pd--Rh/CeO ₂ catalyst. In both cases, the supported amount of noble metals was 1.51% by mass for Pd and 0.25% by mass for Rh. The size of the filter base material (carrier) used was φ118.4×91 mm and 1 L size. The average pore diameter of the filter base material used was 20 to 30 μm, the half width of pore distribution was 7 to 15 μm, the porosity was 55 to 70%, the wall thickness was 5 to 15 mil, and the amount of catalyst supported was 30 to 150 g/L. Met.

Next, equal amounts of the Pd--Rh/Al ₂ O ₃ catalyst and the Pd--Rh/CeO ₂ catalyst were mixed, water and a binder were mixed, and the mixture was milled with a ball mill to prepare a slurry. In each example and comparative example, by adjusting the slurry viscosity and adjusting the slurry suction pressure in the catalyst loading step, a high-density layer of the exhaust purification catalyst is arranged on the inflow side as shown in FIGS. did. Finally, each GPF was obtained by drying at 150° C. and firing at 600° C. while flowing air. Table 1 shows the median pore diameter (μm) of the filter substrate after supporting the exhaust purification catalyst and the maximum pore diameter (μm) of the high-density layer.

[Actual vehicle particulate matter collection test]
For the GPF according to each example and comparative example, the GPF to be tested was mounted in the rear stage of a 1L three-way catalyst directly under a gasoline direct injection engine vehicle with a displacement of 1.5L, and the room temperature was 25°C and the humidity was 50%. , the number of PM (PN) before and after the GPF at that time was measured, and the PM number (PN) collection rate was calculated. In the measurement, as a pretreatment, WLTP was run for one cycle to remove particulate matter on which GPF remained, followed by soaking at room temperature of 25° C. for 24 hours, and measurement was performed from the cold state to obtain data.

[Pressure loss test after Ash endurance]
A durability test was conducted using gypsum as simulated ash for the GPFs according to the respective examples and comparative examples. Specifically, after calcining the gypsum, the gypsum was milled until it had a particle size close to that of the actual ash. Next, using a self-made suction device (a large dry pump (design displacement 1850L/min) is connected to the tank for vacuuming), a predetermined amount of simulated ash is sucked into the filter base material to simulate the durability of actual driving. did. The amount of deposited ash was set to 150 g.

[Pressure loss]
The pressure drop of the GPF according to each example and comparative example was measured using a catalyst carrier pressure drop tester manufactured by Tsukubarika Seiki. Specifically, a full-size GPF (φ118.4×91 mm) was set, air was flowed at a flow rate of 2.17 m ³ /min (COLD FLOW), and the pressure loss was measured.

[Purification performance (CPI)]
A CPI (Coat Performance Index) was calculated for the exhaust purification performance of the GPF according to each example and comparative example. Here, CPI is obtained by dividing the NOx purification rate of GPF by the NOx purification rate of TWC carried on a normal honeycomb carrier (without plugging), and is an NOx purification index of GPF with respect to TWC. Specifically, after aging under the aging conditions shown below, the NOx conversion rate of GPF and the normal honeycomb carrier (without plugging) supported by simulation measurement under the 400 ° C steady SV performance measurement conditions shown below The NOx purification rate of the TWC (hereinafter referred to as the NOx purification rate of the TWC) was measured, and the CPI was calculated by the following formula (1).

(Aging condition)
Rich/Air Aging (Rich: 80 seconds/Air: 20 seconds)
H20 ₌ 10%
Rich: _C3H6 = ₁ %, _O2 = 2.5%, _N2 = balance gas Air: _O2 = 21%, _N2 = balance gas 980°C x 10 hours

(400°C steady SV performance measurement conditions)
T/P size: φ1 inch × 30 mm (BTM part on the outflow side when plugged)
Gas flow rate: 63 → 51 → 38 → 25 L / min (SV = 250,000 / h → 200,000 / h → 150,000 / h → 100,000 / hour)
Gas composition: _CO2 = 14%, _O2 = 0.48%, _C3H6 = 400 ppm, CO = 5000 ppm, H2 = 1700 ppm, NO = 500 ppm, _H2O = ₁₀ %, _{N2 =} balance gas

[Number 1]

CPI=NOx purification rate of GPF/NOx purification rate of TWC Formula (1)

Each numerical value in Table 1 is a value rounded off to the second decimal place.

[Discussion]
FIG. 11 is a diagram showing the relationship between the PN collection rate and the pressure loss after Ash deposition in each example and comparative example. In FIG. 11, when the PN collection rate and the pressure loss after 150 g of Ash deposition, which are the characteristics required for the GPF in the actual vehicle, are compatible, the PN collection rate is 90% or more and the pressure loss after 150 g of Ash is 2.0 kPa or less. , and only Examples 1-4 were confirmed to be compatible.

FIG. 12 is a diagram showing the relationship between the purified CPI and the pressure loss after ash deposition in each example and comparative example. In FIG. 12, it is confirmed that only Examples 1 to 4 are compatible when the CPI and the pressure loss after depositing Ash 150 g are compatible with each other when the CPI is 0.9 or more and the pressure loss after Ash is 150 g is 2.0 kPa or less. rice field.

From the above results, the median pore diameter (D50) of the filter substrate after supporting the exhaust purification catalyst is 17 μm or more, the half width of the pore distribution of the filter substrate is 7 μm to 15 μm, and the maximum pore diameter of the high-density layer. is 11.7 μm or less, it was confirmed that the pressure loss can be reduced and high exhaust purification performance and particulate matter trapping performance can be obtained. Therefore, the effects achieved by the present invention have been verified.

1... Engine (internal combustion engine)
2 Exhaust purification device 3 Exhaust pipe (exhaust passage)
32 GPF (exhaust purification filter)
32a... Inflow side end face 32b... Outflow side end face 33... TWC (exhaust purification catalyst)
DESCRIPTION OF SYMBOLS 34... Pore 320... Filter base material 323... Partition wall 321... Inflow-side cell 322... Outflow-side cell 324... Inflow-side plugging part 325... Outflow-side plugging part 331... High-density layer 332... Low-density layer

Claims (5)

An exhaust purification filter provided in an exhaust passage of an internal combustion engine for trapping and purifying particulate matter in the exhaust of the internal combustion engine,
A plurality of cells extending from an exhaust inflow side end face to an outflow side end face are partitioned and formed by porous partition walls, and the inflow side cells in which the openings in the outflow side end face are sealed and the openings in the inflow side end face are eyes. a filter substrate alternately arranged with sealed outflow cells;
and an exhaust purification catalyst carried on the partition wall,
The median pore diameter (D50) of the filter base material after supporting the exhaust purification catalyst is 17 μm or more,
The half width of the pore distribution of the filter base material is 7 μm to 15 μm,
The exhaust purification catalyst is unevenly distributed and carried in a high-density layer in which the density of the exhaust purification catalyst is relatively high and a low-density layer in which the density of the exhaust purification catalyst is relatively low,
The exhaust purification filter, wherein the maximum pore diameter of the high-density layer is 11.7 μm or less. 2. The exhaust purification filter according to claim 1, wherein the median pore diameter (D50) of said filter base material after carrying said exhaust purification catalyst is 20 μm or more. 3. The exhaust purification filter according to claim 1, wherein said high-density layer has a maximum pore diameter of 7.7 [mu]m or less. The exhaust purification filter according to any one of claims 1 to 3, wherein the filter base material has a pore distribution half width of 7 µm to 9 µm. The exhaust purification filter according to any one of claims 1 to 4, wherein the filter base material has a porosity of 55% to 70%.

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