Particulate filter, method for removing particulate matter from the exhaust gas of an internal combustion engine, and method for manufacturing a particulate filter

Abstract

This fine particle filter for removing a particulate material from the exhaust gas of an internal combustion engine comprises a wall flow filter that has a porous wall, and a ceramic layer that is composed of ceramic particles which are loaded within a flow channel of the wall flow filter; and the void fraction of the ceramic layer is from 20% to 41%. The ceramic particles may be formed of one substance that is selected from the group consisting of alumina, silica, zirconia, ceria, titania and zeolite.

Description

[Technical Field]

[0001] The present disclosure relates to a particulate filter for removing particulate matter from the exhaust gas of an internal combustion engine, a method for removing particulate matter from the exhaust gas of an internal combustion engine, and a method for manufacturing a particulate filter. [Background technology]

[0002] Exhaust gas emitted from internal combustion engines such as diesel and gasoline engines contains large amounts of particulate matter such as soot. This particulate matter is also known as Particulate Matter (PM). To prevent environmental pollution caused by PM, there is a need to efficiently remove PM from exhaust gas.

[0003] It is known that a wall-flow filter (hereinafter sometimes abbreviated as WF) is used as a main element for removing PM from exhaust gas. A WF has multiple gas flow paths separated by porous walls. The WF is configured so that exhaust gas flowing into a gas path of the WF passes through the porous wall and is discharged from another gas path. As the exhaust gas passes through the porous wall, PM contained in the exhaust gas is captured within the filter. As a result, PM is removed from the exhaust gas, and the exhaust gas is purified.

[0004] However, when purifying exhaust gases using a WF, PM can penetrate into the porous walls and clog the pores. When the pores become clogged, the pressure loss (pressure loss) of the filter increases. To solve this problem, it is known that ceramic particles are deposited on the surface of the porous walls of the WF to prevent PM from penetrating into the pores (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-224514 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional WFs having a layer of ceramic particles on the surface of porous walls have insufficient PM capture efficiency. Therefore, an object of the present disclosure is to provide a WF with improved capture efficiency. Another object of the present disclosure is to provide a method for removing PM from exhaust gas of an internal combustion engine using the WF. Yet another object of the present disclosure is to provide a method for producing the WF. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research. As a result, they have found that filter performance can be improved by adjusting the porosity of the layer made of ceramic particles to fall within a predetermined range. In light of this finding, the present application employs the following aspects to solve the above problems.

[0008] (1) A particulate filter for removing PM from exhaust gas of an internal combustion engine according to a first aspect includes a WF having porous walls and a ceramic layer made of ceramic particles supported in a flow path of the WF, and the porosity of the ceramic layer is 20% or more and 41% or less.

[0009] (2) In the particulate filter according to the above aspect, the ceramic particles may be one selected from the group consisting of alumina, silica, zirconia, ceria, titania, and zeolite.

[0010] (3) In the particulate filter according to the above aspect, the ceramic particles may have an average particle size (d50) of 1.5 μm or more and less than 5 μm.

[0011] (4) In the particulate filter according to the above aspect, the ceramic layer may be supported in an amount of 10 g / L or more and 50 g / L or less relative to the volume of the WF.

[0012] (5) The particulate filter according to the above aspect may have an exhaust gas purification catalyst between the WF and the ceramic layer.

[0013] (6) A method for removing PM from exhaust gas of an internal combustion engine according to a second aspect includes a step of passing exhaust gas of the internal combustion engine through the particulate filter according to the above aspect.

[0014] (7) A method for manufacturing a particulate filter according to a third aspect includes the steps of: mixing ceramic particles with air to prepare an aerosol; passing the aerosol through a flow path of a workpiece filter having a porous wall; adding water to the ceramic particles and the workpiece filter in an amount of 30 g / L or more and 300 g / L or less relative to the volume of the workpiece filter; and drying the workpiece filter.

[0015] (8) In the method for producing a particulate filter according to the above aspect, the density of the aerosol is 0.001 g / m 3 More than 1g / m 3 The following is fine.

[0016] (9) In the method for manufacturing a particulate filter according to the above aspect, the step of applying water may include a step of passing a gas containing moisture through the WF.

[0017] (10) The method for manufacturing a particulate filter according to the above aspect may include a step of wash-coating an exhaust gas purification catalyst inside the flow path of the WF before the step of passing the aerosol through the flow path of the WF. [Effects of the Invention]

[0018] The particulate filter according to the present disclosure has an improved PM capture efficiency. Furthermore, the method for manufacturing a particulate filter according to the present disclosure can remove PM from exhaust gas with high efficiency. Furthermore, the method for manufacturing a particulate filter according to the present disclosure can provide a particulate filter with an improved PM collection efficiency. [Brief explanation of the drawings]

[0019] [Figure 1]1 is a schematic perspective view of a particulate filter according to an embodiment of the present invention; [Figure 2A] 1 is a schematic cross-sectional view of a particulate filter according to an embodiment of the present invention; [Figure 2B] 1 is a schematic cross-sectional view of a particulate filter with a low porosity ceramic layer. [Figure 2C] 1 is a schematic cross-sectional view of a particulate filter with a high porosity ceramic layer. [Figure 2D] 1 is a schematic cross-sectional view of a particulate filter having an in-wall coating. [Figure 2E] 1 is a schematic cross-sectional view of a particulate filter having an on-wall coating. [Figure 3] 1 is a scanning electron microscope (SEM) image of a cross section of a particulate filter. [Figure 4] 1 is an SEM image of a cross section of a particulate filter. [Figure 5] FIG. 1 is a plot of collection efficiency against porosity. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present application will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate changes can be made within the scope of the present invention.

[0021] [Particulate filter] FIG. 1 shows a schematic perspective view of a particulate filter 10 for removing PM from exhaust gas of an internal combustion engine according to this embodiment. in The exhaust gas is introduced into the particulate filter 10 according to the dashed arrows in F outThe dashed arrows in the figure indicate that exhaust gas is discharged. The particulate filter 10 includes a wall-flow filter (WF) having porous walls. The WF has a plurality of flow passages extending adjacent to each other. The plurality of flow passages may be parallel to each other. The plurality of flow passages are arranged such that flow passages having openings 12 on the exhaust gas inlet side and flow passages having sealing portions 14 on the exhaust gas inlet side are alternately arranged.

[0022] The flow path of the WF is sealed on the exhaust gas discharge side when it has an opening 12 on the exhaust gas inlet side, and is open on the exhaust gas discharge side when it has a sealing part 14 on the exhaust gas inlet side. Therefore, the exhaust gas introduced into the particulate filter 10 from the opening 12 passes through the porous wall of the WF and is discharged from the adjacent flow path.

[0023] 2A is a schematic cross-sectional view of a particulate filter 10 according to this embodiment. The particulate filter 10 according to this embodiment includes a ceramic layer 16 made of ceramic particles supported in the flow passages of a WF. That is, the WF also functions as a carrier for the ceramic layer 16. FIG. 2A illustrates PM originating from exhaust gases trapped in the particulate filter 10.

[0024] "Wall flow filter (WF)" The WF may be the same as that used in general exhaust gas purification filters. The total length of the WF 10 is not particularly limited, and is preferably 10 mm or more and 1000 mm or less, more preferably 50 mm or more and 300 mm or less, and even more preferably 80 mm or more and 150 mm or less. Here, the total length of the WF 10 refers to the length from the exhaust gas inlet side to the exhaust gas outlet side of the WF 10. The WF may have a honeycomb structure. Preferably, the WF is a gasoline particulate filter (GPF).

[0025] The number of openings 12 and sealing portions 14 of the WF can be set within an appropriate range, taking into consideration the type of exhaust gas to be treated, gas flow rate, pressure loss, removal efficiency, etc. For example, a cell density (number of cells / unit cross-sectional area) of 100 to 1200 cells / square inch is sufficient for use, preferably 150 to 900 cells / square inch, and more preferably 200 to 700 cells / square inch. There are no limitations on the shape of the gas passage openings (cell shape) of the WF, and it can be, for example, hexagonal, rectangular, triangular, or corrugated.

[0026] The WF allows gas to flow to other flow paths through minute pores present in the wall surface of the flow path, and exhaust gas introduced through the openings 12 passes through the other flow paths and exits the WF. The WF can filter out PM contained in the exhaust gas.

[0027] The WF flow channels are separated from adjacent flow channels by porous walls, the thickness of which can be from 1 mil (0.0254 mm) to 100 mils (2.54 mm), preferably from 5 mils (0.127 mm) to 30 mils (0.762 mm).

[0028] The pore size of the porous wall of the WF can be set within an appropriate range, taking into consideration the type of exhaust gas to be treated, gas flow rate, pressure loss, removal efficiency, etc. For example, the porous wall of the WF has a pore size (d50) of 0.1 μm to 30 μm. below Any diameter can be used, preferably 10 μm or more and 25 μm or less, and particularly preferably 15 μm or more and 20 μm or less. Herein, the pore diameter (d50) of the porous wall means the pore diameter that accounts for 50% of the total pore volume, as determined by mercury intrusion porosimetry.

[0029] The material of the WF may be the same as that used in general exhaust gas purification filters. For example, the WF may be made of metal or ceramic, and is preferably made of cordierite, stainless steel, silicon carbide (SiC), mullite, alumina (α-alumina), or silica, and more preferably made of cordierite, stainless steel, or SiC. When the WF is made of cordierite, stainless steel, or SiC, the durability of the particulate filter 10 is particularly improved.

[0030] "Ceramic layer" The ceramic layer 16 is composed of ceramic particles, and the porosity of the ceramic layer 16 is 20% or more and 41% or less. The porosity of the ceramic layer 16 is preferably 25% or more and 40% or less, more preferably 30% or more and 39% or less, and even more preferably 32% or more and 39% or less. A porosity of the ceramic layer 16 less than 20% is undesirable because, while PM can be effectively captured by the ceramic layer as shown in FIG. 2B, exhaust gas does not easily flow through the ceramic layer 16. Furthermore, a porosity of the ceramic layer 16 greater than 41% is undesirable because, as shown in FIG. 2C, a large amount of PM passes through the ceramic layer 16, resulting in a reduced capture efficiency. That is, when the porosity of the ceramic layer 16 is within the range of the present invention, PM is effectively captured by the ceramic layer 16, and exhaust gas effectively flows through the ceramic layer 16. As a result, the PM capture efficiency and exhaust gas purification performance are high. The ceramic layer 16 only needs to be able to capture PM, and the ceramic layer 16 does not need to include an exhaust gas purification catalyst that decomposes exhaust gas.

[0031] The porosity of the ceramic layer 16 can be determined by image processing. Specifically, a cross section of the ceramic layer 16 is first photographed using a scanning electron microscope (SEM). Next, for example, the photographed SEM image is subjected to binarization processing to separate the ceramic particle regions and void regions from the photographed ceramic layer 16. The area of ​​the ceramic particle regions and the area of ​​the void regions are then calculated by image processing. The porosity of the ceramic layer 16 within the area photographed in the SEM image can be determined by dividing the area of ​​the void regions by the total area of ​​the ceramic particle regions and the void regions. The porosity of the ceramic layer 16 can be calculated for any five points, and the average of these values ​​can be used as the porosity of the ceramic layer 16.

[0032] Conventional manufacturing methods have not been able to inexpensively achieve a porosity of the ceramic layer 16 within the above range. That is, applying a slurry and drying it results in a small porosity, while simply spraying an aerosol results in a large porosity. In contrast, by manufacturing the ceramic layer 16 using the method of the present disclosure, it is possible to achieve a ceramic layer 16 with a desirable porosity.

[0033] The material of the ceramic particles is not particularly limited. For example, the ceramic particles may be made of a material that is stable even at high temperatures of about 500°C, and are preferably made of one selected from the group consisting of alumina, silica, zirconia, ceria, titania, and zeolite. Alumina has high heat resistance, stability, and low reactivity, so it is particularly preferable that the ceramic particles be made of alumina.

[0034] The average particle size (d50) of the ceramic particles is preferably 1.5 μm or more and less than 5 μm, more preferably 2 μm or more and 4.5 μm or less, and even more preferably 2.4 μm or more and 4 μm or less. When the average particle size (d50) of the ceramic particles is 1.5 μm or more, the ceramic particles are less likely to enter the pores of the porous wall, preventing the pores of the WF from becoming smaller. Furthermore, when the average particle size (d50) of the ceramic particles is less than 5 μm, the ceramic particles and the ceramic layer 16 are firmly attached to the WF, preventing peeling. Here, in this specification, the average particle size (d50) of the ceramic particles means the 50% particle size (median size) on a volume basis measured using a laser diffraction method.

[0035] The ceramic layer 16 is preferably supported in an amount of 10 g / L or more and 50 g / L or less relative to the volume of the WF. By supporting the ceramic layer 16 in the above range, it is possible to achieve both a high PM capture rate and high exhaust gas purification performance due to high gas flowability. The ceramic layer 16 is more preferably supported in an amount of 15 g / L or more and 40 g / L or less relative to the volume of the WF, and even more preferably supported in an amount of 20 g / L or more and 30 g / L or less.

[0036] "Exhaust gas purification catalyst" 2D and 2E are schematic cross-sectional views of a particulate filter according to another embodiment. The particulate filter 10 according to FIGS. 2D and 2E has an exhaust gas purification catalyst 20 between the WF and the ceramic layer 16. By having the exhaust gas purification catalyst 20 in the particulate filter 10, the particulate filter 10 can not only capture PM but also decompose exhaust gas. Therefore, it is preferable that the particulate filter 10 has the exhaust gas purification catalyst 20.

[0037] More specifically, Fig. 2D is a schematic cross-sectional view of a particulate filter having an in-wall coating of an exhaust gas purification catalyst 20, and Fig. 2E is a schematic cross-sectional view of a particulate filter having an on-wall coating of an exhaust gas purification catalyst 20. In the in-wall coating, the WF is coated with the exhaust gas purification catalyst 20 up to the inside of the WF. On the other hand, in the on-wall coating, the exhaust gas flow path side of the WF is selectively coated with the exhaust gas purification catalyst 20. The exhaust gas purification catalyst 20 may be in-wall coated as shown in Fig. 2D or on-wall coated as shown in Fig. 2E.

[0038] The exhaust gas purification catalyst 20 according to the present disclosure may be any catalyst capable of purifying hydrocarbons (HC), carbon monoxide (CO), or nitrogen oxides (NOx) contained in exhaust gas. The exhaust gas purification catalyst 20 preferably contains a precious metal and a porous inorganic oxide or an oxygen storage material, more preferably contains a precious metal, a porous inorganic oxide, and an oxygen storage material, and even more preferably contains at least one selected from the group consisting of magnesium and alkaline earth metals, a precious metal, a porous inorganic oxide, and an oxygen storage material. Hereinafter, the mass of the exhaust gas purification catalyst 20 may be expressed based on the volume of the WF. That is, the mass of each component per liter of WF may be expressed as "g / L."

[0039] (precious metals) The noble metal may be any noble metal commonly used for purifying exhaust gases, and is preferably platinum (Pt), palladium (Pd), or rhodium (Rh). The noble metals may be used alone or in combination. The noble metals can be appropriately changed depending on the target to be purified. For example, when treating HC, CO, and NOx, platinum or palladium and rhodium can be used, with palladium and rhodium being particularly effective. Furthermore, platinum and / or palladium can be used for treating HC or CO.

[0040] The amount of precious metal supported is determined by the exhaust gas flow rate (SV(h -1 )) can be changed appropriately depending on the concentration of HC, etc. in the exhaust gas.

[0041] The amount of precious metals carried is calculated as metal equivalent per liter of WF. 0.05 The amount of the noble metal to be supported varies depending on the noble metal used. For example, when platinum, palladium, or rhodium is used, the amount is as follows:

[0042] When palladium is used, the amount of palladium supported per liter of WF may be 0.1 g to 10 g, preferably 0.2 g to 5 g. A palladium supported amount of 0.1 g / L to 10 g / L is suitable because it can satisfactorily oxidize hydrocarbons (HC).

[0043] When rhodium is used, the amount of rhodium supported per liter of WF may be 0.05 g or more and 3 g or less, and preferably 0.2 g or more and 1 g or less. 0.05 It is preferable that the concentration is 3 g / L or more and 3 g / L or less, since NOx can be efficiently reduced.

[0044] When platinum is used, the amount of platinum supported per liter of WF may be 0.1 g to 3 g, and preferably 0.2 g to 1 g. A platinum support amount of 0.1 g / L to 3 g / L is preferable because it allows efficient oxidation of hydrocarbons and the like.

[0045] (Porous inorganic oxide) The porous inorganic oxide may be any porous inorganic oxide typically used in exhaust gas purification, preferably alumina (Al2O3) such as α, γ, δ, or θ, zirconia (ZrO2), titania (TiO2), a mixture thereof, or a composite oxide thereof. Considering the effective utilization and durability of the exhaust gas purification catalyst, the porous inorganic material is preferably an oxide that remains porous not only at low exhaust gas temperatures but also at high exhaust gas temperatures and has a large specific surface area. The preferred average particle size (d50) of the porous inorganic oxide varies depending on the application method to the WF. When the exhaust gas purification catalyst 20 is formed by an in-wall coating method, a particle size greater than 0 μm and less than 1.5 μm is preferred. Having an average particle size within this range enables a catalyst slurry containing the porous inorganic oxide to be applied to the inside of the partition walls of the WF. When the exhaust gas purification catalyst 20 is formed by an on-wall coating method, the average particle size (d50) of the porous inorganic oxide may be 5 μm or more and less than 15 μm, and preferably 8 μm or more and 12 μm or less. The average particle size within this range is preferable because it makes it difficult for the catalyst slurry containing the porous inorganic oxide to penetrate into the partition walls of the WF. In other words, by controlling the average particle size of the porous inorganic oxide, it becomes possible to support the catalyst component containing the porous inorganic oxide at the intended support location by each method. Here, the average particle size (d50) of the porous inorganic oxide means the 50% particle size (median size) on a volume basis measured using a laser diffraction method.

[0046] The specific surface area of ​​porous inorganic oxides is measured using nitrogen gas in a BET specific surface area measurement. 2 / g or more, 500m 2 / g or less, preferably 70m 2 / g or more, 400m 2 / g or less. 50m 2 / g or more is preferable because the noble metal or oxygen storage material can be efficiently dispersed. 2 / g or less is preferable because the porous inorganic oxide has high heat resistance.

[0047] The amount of porous inorganic oxide supported may be the amount typically used in exhaust gas purification catalysts, for example, 1 g / L or more and 100 g / L or less, preferably 5 g / L or more and 50 g / L or less, and more preferably 10 g / L or more and 30 g / L or less. A content of 1 g / L or more is preferable because the precious metal or oxygen storage material can be sufficiently dispersed, thereby enabling efficient purification of exhaust gas. A content of 100 g / L or less is preferable because back pressure does not increase and the load on the engine is small.

[0048] (oxygen storage material) The oxygen storage material has the function of absorbing and adsorbing oxygen in exhaust gas and releasing it. Any oxygen storage material that is normally used for exhaust gas purification may be used. Specifically, rare earth oxides are preferred, and cerium oxide (CeO2) is more preferred. For the purpose of improving heat resistance and specific surface area, zirconium oxide (ZrO2), lanthanum oxide (La2O3), yttrium oxide (Y2O3), neodymium oxide (Nd2O3), praseodymium oxide (Pr6O 11 ) and an oxygen storage material to form a composite oxide, which may be used as the oxygen storage material.

[0049] The amount of oxygen storage material carried may be the amount normally used in an exhaust gas purification catalyst, for example, 1 g / L or more and 50 g / L or less, preferably 5 g / L or more and 50 g / L or less, and more preferably 10 g / L or more and 40 g / L or less. If it is 1 g / L or more, oxygen in the exhaust gas can be sufficiently absorbed and discharged, and catalytic performance can be improved, which is preferable. If it is 50 g / L or less, back pressure does not increase and the load on the engine is small, which is preferable.

[0050] (Other ingredients) The exhaust gas purification catalyst may contain other components depending on the target to be purified.

[0051] [Method for removing PM from exhaust gas of internal combustion engines] A method for removing PM from exhaust gas of an internal combustion engine according to the present disclosure includes passing the exhaust gas of the internal combustion engine through a particulate filter according to the present disclosure.

[0052] The space velocity of the exhaust gas is 50,000 h -1 Over 250,000h -1 Preferably less than 100,000h, more preferably -1 Over 200,000h -1 By adopting such a space velocity, PM in the exhaust gas can be sufficiently captured.

[0053] The exhaust gas temperature is not particularly limited, but is preferably 200° C. or higher. The exhaust gas temperature is preferably 600° C. or lower, and more preferably 400° C. or lower. By adopting such an exhaust gas temperature, if the particulate filter has an exhaust gas purification catalyst, the catalytic reaction can be sufficiently induced and deterioration of the catalyst can be suppressed.

[0054] In the method for removing PM from exhaust gas of an internal combustion engine, the particulate filter according to the present disclosure may be used alone, or an additional filter including an exhaust gas purification catalyst may be used. The additional filter including an exhaust gas purification catalyst may be disposed between the internal combustion engine and the particulate filter according to the present disclosure, or may be disposed after the particulate filter according to the present disclosure. The additional filter including an exhaust gas purification catalyst may be, for example, a filter carrying a known three-way catalyst. By using an additional filter including an exhaust gas purification catalyst in addition to the particulate filter according to the present disclosure, the exhaust gas can be more appropriately purified.

[0055] [Method of manufacturing particulate filters] The method for manufacturing a particulate filter according to the present disclosure includes (1) an aerosol production step, (2) a ceramic particle introduction step, (3) a humidification step, and (4) a drying step. By manufacturing a particulate filter using this method, it is possible to manufacture a particulate filter in which the ceramic layer has a desired porosity.

[0056] (Aerosol production process) In the step of producing an aerosol, the density of the aerosol is 0.001 g / m 3 More than 1g / m 3 Preferably, it is 0.01 g / m or less. 3 More than 0.1g / m 3 It is more preferable that the aerosol density is equal to or less than 1000 kJ / cm. By using such an aerosol density, it is easy to adjust the porosity of the ceramic layer to a desired range. Furthermore, by using such an aerosol density, it is possible to uniformly deposit a ceramic layer made of ceramic particles.

[0057] (Ceramic particle introduction process) The step of passing the aerosol through the flow path of the WF can be performed by aspirating the aerosol from the side opposite to the aerosol introduction side of the WF. As the aerosol passes through the flow path of the WF, the ceramic particles contained in the aerosol are deposited on the porous walls of the WF. The flow velocity of the aerosol may be, for example, 1 m / s or more and 100 m / s or less, preferably 5 m / s or more and 30 m / s or less, and more preferably 10 m / s or more and 20 m / s or less. By adopting such a flow velocity, the ceramic particles can be appropriately deposited.

[0058] (humidification process) The amount of water added to the ceramic particles and WF is preferably 30 g / L or more and 300 g / L or less, more preferably 40 g / L or more and 200 g / L or less, and even more preferably 50 g / L or more and 100 g / L or less, relative to the volume of WF. By adding a predetermined amount of water to the ceramic particles and WF and drying, the porosity of the ceramic layer can be adjusted to a desired range. That is, by adding water in an amount of 30 g / L or more and drying, the porosity can be reduced compared to before adding water, and by adding water in an amount of 300 g / L or less, an excessively small porosity can be prevented.

[0059] The humidification step preferably includes passing a gas containing moisture through a WF. By humidifying the gas, the entire filter can be uniformly humidified, thereby uniformly adjusting the porosity of the ceramic layer. For example, water may be added by passing a gas containing moisture exceeding the saturated water vapor amount through a WF.

[0060] The temperature of the moisture-containing gas when introduced into the filter may be, for example, 0°C or higher and 100°C or lower, preferably 5°C or higher and 70°C or lower. below The temperature may be 10° C. or higher and more preferably 50° C. or lower. Gas at such a temperature can contain a large amount of moisture, so that water can be efficiently provided to the ceramic particles and WF.

[0061] The method for manufacturing a particulate filter according to the present disclosure preferably includes a step of wash-coating an exhaust gas purification catalyst inside the flow path of the WF before the step of passing an aerosol through the flow path of the WF. By including the step of wash-coating an exhaust gas purification catalyst, the manufactured particulate filter can also decompose exhaust gas. The step of wash-coating an exhaust gas purification catalyst can be performed by a known method. For example, the step of wash-coating an exhaust gas purification catalyst includes a step of wet-pulverizing the exhaust gas purification catalyst. For example, the wet-pulverization is performed using a ball mill. The solvent used for wash-coating is not particularly limited, and for example, water or any organic solvent can be used. It is preferable to use water as the solvent for wash-coating. [Example]

[0062] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples as long as they produce the effects of the present invention.

[0063] <Production of particulate filters> [Example 1] Alumina powder with an average particle size (D50) of 3 μm was mixed with air to obtain a powder of 0.020 g / m 3An aerosol having a density of 1000 MPa was produced. The aerosol was then passed through a cylindrical cordierite carrier, depositing a ceramic layer in an amount of 25.9 g / L relative to the volume of the cordierite carrier. The dimensions of the cylindrical cordierite carrier were 118.4 mm in diameter, 127 mm in length, 1.4 L in volume, 300 cells / in² in cell density, 10 mil wall thickness, and 15 μm pore size.

[0064] Next, air humidified using a commercially available humidifier was passed through the cordierite carrier. To control the air flow, air was sucked at a speed of 12.5 m / s from the side opposite the humidified air inlet side of the cordierite carrier at 25°C. The amount of moisture supplied by the humidifier was 280 mL / h.

[0065] While the humidified air was being passed through, the weight change of the cordierite carrier was measured, and when the amount of humidification reached 72.3 g / L relative to the volume of the cordierite carrier, the passage of the humidified air was stopped. Thereafter, the cordierite carrier was dried at 550°C in an air atmosphere to obtain a particulate filter A.

[0066] [Example 2] A particulate filter B was produced in the same manner as in Example 1, except that the loading amount of the ceramic layer was 26.0 g / L and the humidification amount was 185.3 g / L.

[0067] [Example 3] Particulate filter C was fabricated in the same manner as in Example 1, except that the ceramic layer loading was 25.5 g / L and the humidification rate was 213.4 g / L.

[0068] [Example 4] A particulate filter E was produced in the same manner as in Example 1, except that the ceramic layer loading was 25.7 g / L, the humidification rate was 168.6 g / L, and the humidified air intake speed was 5.0 m / s.

[0069] [Example 5] A particulate filter F was produced in the same manner as in Example 1, except that the ceramic layer loading was 26.4 g / L, the humidification rate was 173.4 g / L, and the drying temperature was 150°C.

[0070] [Example 6] A particulate filter G was produced in the same manner as in Example 1, except that the ceramic layer loading was 25.2 g / L, the humidification rate was 147.5 g / L, and the drying temperature was 350°C.

[0071] [Example 7] A particulate filter I was produced in the same manner as in Example 1, except that an exhaust gas purification catalyst was supported, the ceramic layer loading was 24.8 g / L, the humidification amount was 190.2 g / L, and the drying temperature was 350°C.

[0072] The exhaust gas purification catalyst was supported as follows. First, palladium nitrate was used as a palladium raw material, lanthanum-containing alumina containing 4 mass% of lanthanum as La2O3, Ce-Zr-La-Y composite oxide (CeO2:ZrO2:La2O3:Y2O3 in a mass ratio of 24:60:3.5:12.5), Ce-Zr-La-Pr composite oxide (CeO2:ZrO2:La2O3:Pr6O 11 The raw materials were weighed out so that the mass ratio of Pd:lanthanum-containing alumina:Ce-Zr-La-Y composite oxide:Ce-Zr-La-Pr composite oxide:BaO:La2O3:BaSO4 was 0.52:16.32:19.08:19.08:0.24:0.48:4.44, with barium hydroxide octahydrate as the BaO raw material and lanthanum acetate and BaSO4 as the La2O3 raw materials.

[0073] Water was added to the mixture of each raw material so that the solid content was 38%, and the mixture was stirred for 1 hour. The resulting mixed solution was wet-pulverized using a ball mill to obtain a slurry. The median diameter of the slurry measured using a laser diffraction method was 1.45 μm. The slurry was used to wash-coat the cylindrical cordierite carrier from the exhaust gas inlet side. Next, the carrier was dried in air at 150°C for 15 minutes and calcined in air at 550°C for 30 minutes, thereby supporting the exhaust gas purification catalyst on the cordierite carrier. In this example, the exhaust gas purification catalyst was in-wall coated on the cordierite carrier. The weight of the cordierite carrier supporting the exhaust gas purification catalyst was measured, and it was confirmed that approximately 60 g of the exhaust gas purification catalyst was supported per liter of cordierite carrier.

[0074] After the exhaust gas purification catalyst was supported on the cordierite carrier, a ceramic layer was formed.

[0075] The exhaust gas purification catalyst was analyzed by inductively coupled plasma (ICP) emission spectrometry, and the composition of the exhaust gas purification catalyst after firing was found to be as shown in Table 1. Here, the composition is expressed as mass (g) relative to the volume (L) of the cordierite carrier.

[0076] [Table 1]

[0077] [Comparative Example 1] As Comparative Example 1, a single cordierite carrier containing neither a ceramic layer nor an exhaust gas purification catalyst was used as particulate filter D. In Comparative Example 1, the humidification step was not carried out.

[0078] Comparative Example 2 Particulate filter H was produced in the same manner as in Example 7, except that the loading amount of the ceramic layer was 25.0 g / L and the humidification step was not performed. Comparative Example 3 A particulate filter J was produced in the same manner as in Example 7, except that the ceramic layer was not produced after the exhaust gas purification catalyst was supported. In Comparative Example 3, the ceramic layer was not produced. In addition, the humidification step was not performed.

[0079] <Porosity analysis> The cross sections of the particulate filters obtained in the examples and comparative examples were observed with a scanning electron microscope (SEM) to measure the porosity. Fig. 3 is a cross-sectional SEM image of the particulate filter of Example 1. Fig. 3 is a cross-sectional SEM image of the interface between the ceramic layer and the cordierite carrier. Fig. 4 is a cross-sectional SEM image of the particulate filter of Example 3. Fig. 4 is a cross-sectional SEM image of the interface between the ceramic layer and the cordierite carrier. An enlarged view of the ceramic layer was subjected to binarization processing to calculate the porosity. The porosity was calculated in the same manner for any five points, and the average value was taken as the porosity of the ceramic layer in each example and comparative example.

[0080] The manufacturing conditions and porosities of the examples and comparative examples are summarized in Table 2 below.

[0081] [Table 2]

[0082] 3 and 4, it can be seen that the ceramic particles are deposited more densely in Fig. 4 than in Fig. 3. This corresponds to the fact that the porosity of Example 3 is smaller than the porosity of Example 1.

[0083] (Particulate filter evaluation) The capture efficiency of the fabricated particulate filter was measured in accordance with the Worldwide harmonized Light Vehicles Test Procedure (WLTP). The measurement results of the capture efficiency are shown in Table 3 below.

[0084] [Table 3]

[0085] Regarding the PM capture efficiency, the particulate filter of Comparative Example 1, which does not have a ceramic layer, had the smallest capture efficiency. When the capture efficiencies of the particulate filters of Examples 1 to 7 and Comparative Example 2, which have a ceramic layer, are plotted against the porosity, the result is as shown in Figure 5. The porosity of the ceramic layer of the Examples is smaller than that of Comparative Example 2, which does not undergo the step of adding water and drying. Furthermore, the particulate filter of the Examples, which has a smaller porosity of the ceramic layer, has a higher capture efficiency than the Comparative Example. In other words, it can be seen that the particulate filter according to the present disclosure, in which the ceramic layer has a predetermined porosity, has an improved PM capture efficiency.

[0086] <Exhaust gas purification performance> Durability tests were conducted on the particulate filters produced in Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3, and the performance of purifying a simulated exhaust gas was evaluated for the particulate filters after the durability tests. The durability tests were conducted by passing air containing 10% by volume of water at 700°C through the particulate filters for 40 hours. In the evaluation of the purification performance, a mixed gas containing 1200 ppm (methane equivalent) of C3H6, 500 ppm of NO, 0.17% of H2, 5% of CO, 0.5% of O2, 14% of CO2, 10% of H2O, and N2 as the balance gas was prepared as the simulated exhaust gas, and the gas was passed through the filter at a space velocity of 250,000 h -1 The conversion rates of HC, CO and NOx were measured at 400°C. The evaluation results are shown in Table 4 below.

[0087] [Table 4]

[0088] It can be seen from Table 4 that the particulate filter I according to Example 7, which had been subjected to the humidifying step and the drying step, exhibited excellent exhaust gas purification performance. [Industrial Applicability]

[0089] The particulate filter according to the present disclosure has an improved PM capture efficiency. The method for manufacturing a particulate filter according to the present disclosure can remove PM from exhaust gas with high efficiency. The method for manufacturing a particulate filter according to the present disclosure can provide a particulate filter with an improved PM collection efficiency. [Explanation of symbols]

[0090] 10 Particulate Filter 12 Opening 14 Sealing part 16 ceramic layers 20 Exhaust gas purification catalyst WF Wall flow filter PM particulate matter

Claims

1. A wall flow filter having porous walls and a ceramic layer made of ceramic particles, The wall-flow filter has a plurality of flow paths extending adjacent to each other, the flow paths being separated from adjacent flow paths by the porous wall; the plurality of flow paths are arranged alternately with first flow paths having openings on the side where exhaust gas is introduced into the wall-flow filter and second flow paths having sealing portions on the side where exhaust gas is introduced into the wall-flow filter, The wall surface of the first flow path or the wall surface of the second flow path is coated with an exhaust gas purification catalyst from the wall surface to the inside of the wall-flow filter, or the wall surface of the first flow path or the wall surface of the second flow path is selectively coated with an exhaust gas purification catalyst, A particulate filter for removing particulate matter from exhaust gases of an internal combustion engine, wherein the ceramic layer has a porosity of 20% or more and 41% or less.

2. 2. The particulate filter of claim 1, wherein the ceramic particles comprise one selected from the group consisting of alumina, silica, zirconia, ceria, titania, and zeolite.

3. 3. A particulate filter according to claim 1 or 2, wherein the ceramic particles have an average particle size (d50) of 1.5 μm or more and less than 5 μm.

4. 4. The particulate filter according to claim 1, wherein the ceramic layer is supported in an amount of 10 g / L or more and 50 g / L or less relative to the volume of the wall-flow filter.

5. 5. The particulate filter according to claim 1, further comprising an exhaust gas purification catalyst between said wall-flow filter and said ceramic layer.

6. A method for removing particulate matter from the exhaust gas of an internal combustion engine, comprising the step of passing the exhaust gas of the internal combustion engine through a particulate filter according to any one of claims 1 to 5.

7. A method for manufacturing a particulate filter according to any one of claims 1 to 5, comprising the steps of: mixing ceramic particles with air to form an aerosol; passing the aerosol through a flow channel of a wall-flow filter having porous walls; providing the ceramic particles and the wall-flow filter with water in an amount of 30 g / L or more and 300 g / L or less based on the volume of the wall-flow filter; and drying the wall-flow filter.

8. The density of the aerosol is 0.001 g / m ３ Above, 1g / m ３ 8. A method for manufacturing a particulate filter according to claim 7, wherein:

9. 9. A method for manufacturing a particulate filter according to claim 7 or 8, wherein the step of providing water comprises passing a gas containing moisture through the wall-flow filter.

10. The method for manufacturing a particulate filter according to any one of claims 7 to 9, further comprising a step of wash-coating an exhaust gas purification catalyst in the flow passages of the wall-flow filter before the step of passing the aerosol through the flow passages of the wall-flow filter.

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