Exhaust gas purification catalytic converter filter for gasoline engines

Abstract

The purpose of the present invention is to provide an exhaust gas purification catalyst filter which has enhanced soot collecting performance without increasing pressure loss caused by the formation of a catalyst layer in a partition wall of a wall flow-type substrate. This exhaust gas purification catalyst filter for a gasoline engine purifies exhaust gas from a gasoline engine and comprises: a wall flow-type substrate in which an introduction-side cell having an opened end part on an exhaust gas introduction side, and a discharge-side cell adjacent to the introduction-side cell and having an opened end part on an exhaust gas discharge side are defined by a porous partition wall; and a catalyst layer formed in a pore of the partition wall, wherein the absolute value of the uneven distribution degree of the catalyst layer formed in the pore of the partition wall is at most 4.50, the wash coat amount, excluding the mass of a platinum group, in the catalyst layer formed in the pore of the partition wall is 40-50 g / L, the catalyst layer formed in the pore of the partition wall is a single layer, and the catalyst layer does not contain Ba.

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification catalyst filter for a gasoline engine.

Background Art

[0002] Exhaust gas discharged from an internal combustion engine contains particulate matter (PM) mainly composed of carbon, ash composed of non-combustible components, etc., and is known to cause air pollution. Conventionally, in a diesel engine that is relatively more likely to discharge particulate matter than a gasoline engine, the discharge amount of particulate matter has been strictly regulated. In recent years, however, the regulation of the discharge amount of particulate matter in gasoline engines has also been strengthened.

[0003] As a means for reducing the discharge amount of particulate matter, a method of providing a particulate filter for the purpose of depositing and collecting particulate matter in the exhaust gas passage of an internal combustion engine is known. In particular, in recent years, from the viewpoint of space saving of the mounting space, etc., in order to simultaneously suppress the discharge of particulate matter and remove harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), it has been studied to provide a catalyst layer by applying a catalyst slurry to a particulate filter and firing it.

[0004] For a particulate filter provided with a wall-flow type substrate in which an introduction-side cell having an open end on the exhaust gas introduction side and a discharge-side cell adjacent to the introduction-side cell and having an open end on the exhaust gas discharge side are defined by a porous partition wall, as such a method for forming a catalyst layer, a method of adjusting properties such as the viscosity and solid content ratio of the slurry, pressurizing one of the introduction-side cell or the discharge-side cell, and causing a pressure difference between the introduction-side cell and the discharge-side cell to adjust the penetration of the catalyst slurry into the partition wall is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] A particulate filter, such as the one described in Patent Document 1, has a wall-flow structure from the viewpoint of removing particulate matter, and is configured so that exhaust gas passes through the pores of the partition wall. However, there is still room for improvement in terms of soot collection performance.

[0007] The present invention has been made in view of the above problems, and its purpose is to provide an exhaust gas purification catalyst filter with improved soot collection performance without increasing pressure loss associated with the formation of a catalyst layer within the partition wall of a wall-flow type substrate. However, the present invention may also be considered to have other objectives, such as achieving effects that cannot be obtained by conventional techniques, as derived from the various configurations shown in the embodiments for carrying out the invention described later. [Means for solving the problem]

[0008] The inventors of the present invention have diligently studied methods to improve soot collection performance without increasing pressure loss associated with the formation of a catalyst layer within the partition walls of a wall-flow type substrate. As a result, they have found that by adjusting the degree of uneven distribution of the catalyst layer formed within the partition walls of the wall-flow type substrate and the amount of wash coat applied to the catalyst layer, soot collection performance can be improved while suppressing the increase in pressure loss, thus completing the present invention. That is, the present invention provides various specific embodiments as shown below.

[0009] [1] This is an exhaust gas purification catalytic filter for purifying exhaust gases from a gasoline engine, A wall-flow type substrate is defined by a porous partition wall, comprising an inlet cell with an open end on the exhaust gas inlet side and an outlet cell adjacent to the inlet cell with an open end on the exhaust gas discharge side, It consists of a catalyst layer formed within the pores of the aforementioned partition wall, The absolute value of the degree of segregation of the catalyst layer formed within the pores of the partition wall is 4.50 or less. The amount of wash coat in the catalyst layer formed within the pores of the partition wall, excluding the platinum group metal mass, is 40 g / L or more and 50 g / L or less. The catalyst layer formed within the pores of the partition wall is a single layer. The catalyst layer does not contain Ba. Exhaust gas purification catalytic converter filter for gasoline engines. [2] The catalyst layer formed within the pores of the partition wall consists of a catalyst metal and a support component, wherein the catalyst metal is Pd and / or Rh, and the support component is an oxide of Al, Zr and / or Ce. [1] Exhaust gas purification catalytic filter for gasoline engines. [3] A method for manufacturing an exhaust gas purification catalytic filter for purifying exhaust gas from a gasoline engine, A step of preparing a wall-flow type substrate in which an inlet cell with an open end on the exhaust gas inlet side and an outlet cell adjacent to the inlet cell with an open end on the exhaust gas discharge side are defined by a porous partition wall, An impregnation step is performed in which a catalyst slurry containing ammonium carbonate is impregnated into the end of the wall-flow type substrate on the exhaust gas introduction side or the exhaust gas discharge side, A coating step in which gas is introduced into the wall-flow type substrate from the end side impregnated with the catalyst slurry, thereby coating the catalyst slurry impregnated in the wall-flow type substrate onto the pore surface of the partition wall, The invention comprises a firing step of firing the coated catalyst slurry to obtain an exhaust gas purification catalyst filter in which the absolute value of the degree of uneven distribution of the catalyst layer formed in the pores of the partition wall is 4.50 or less, and the amount of wash coat of the catalyst layer, excluding the platinum group metal mass per liter of the wall-flow type substrate, is 40 g / L or more and 50 g / L or less. The catalyst layer formed within the pores of the partition wall is a single layer. The catalyst layer does not contain Ba. A method for manufacturing an exhaust gas purification catalytic filter for gasoline engines. [4] After the firing step of obtaining the exhaust gas purification catalyst filter, the catalyst layer in the pores of the partition walls of the exhaust gas purification catalyst filter is measured with an electron beam microanalyzer, and the absolute value of the degree of non-uniform distribution of the catalyst layer is inspected. The method for manufacturing an exhaust gas purification catalyst filter for a gasoline engine according to [3]. [Advantages of the Invention]

[0010] According to the present invention, it is possible to provide an exhaust gas purification catalyst filter for a gasoline engine with high soot collection performance without increasing the pressure loss. By mounting such a catalyst filter, further high performance of the exhaust gas treatment system can be achieved. [Brief Description of the Drawings]

[0011] [Figure 1] It is a cross-sectional view schematically showing one aspect of the exhaust gas purification catalyst of the present embodiment. [Figure 2] It is a diagram showing the degree of non-uniform distribution of the catalyst layers of Examples 1 to 3 and Comparative Examples 1 to 3. [Figure 3] It is a diagram showing the relationship between the soot collection rate and the pressure loss of Examples 1 to 3 and Comparative Examples 1 to 3. [Modes for Carrying Out the Invention]

[0012] Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples (representative examples) of embodiments of the present invention, and the present invention is not limited thereto. Further, the present invention can be arbitrarily modified and implemented within the scope not departing from the gist thereof. In this specification, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Also, the dimensional ratios in the drawings are not limited to the ratios shown.

[0013] Furthermore, in this specification, when a number or physical property value is enclosed before or after the "~" symbol, it is used to mean that the values ​​before and after the symbol are included. For example, the notation "1~100" for a numerical range includes both the lower limit "1" and the upper limit "100". The same applies to other numerical range notations.

[0014] [Exhaust gas purification catalyst] The exhaust gas purification catalyst filter of this embodiment is an exhaust gas purification catalyst filter 100 for purifying exhaust gas discharged from a gasoline engine, and comprises a wall-flow type substrate 10 defined by a porous partition wall 13, comprising an introduction-side cell 11 with an open end 11a on the exhaust gas introduction side and an exhaust-side cell 12 adjacent to the introduction-side cell 11 with an open end 12a on the exhaust gas discharge side, and a catalyst layer 21 formed in the pores of the partition wall 13, wherein the degree of non-uniformity of the catalyst layer 21 when it is formed is 4.50 or less, the wash coat amount (hereinafter also referred to as "WC amount") of the catalyst layer 21 excluding the platinum group mass is 40 g / L or more and 50 g / L or less, the catalyst layer 21 formed in the pores of the partition wall 13 is a single layer, and the catalyst layer 21 does not contain Ba.

[0015] The following describes each component with reference to the schematic cross-sectional view of the exhaust gas purification catalyst filter of this embodiment shown in Figure 1. The exhaust gas purification catalyst filter of this embodiment has a wall-flow type structure. In an exhaust gas purification catalyst filter 100 having such a structure, exhaust gas discharged from a gasoline engine flows into the introduction-side cell 11 from the exhaust gas introduction-side end 11a (opening), passes through the pores of the partition wall 13 and flows into the adjacent discharge-side cell 12, and flows out from the exhaust gas discharge-side end 12a (opening). In this process, particulate matter (PM) that has difficulty passing through the pores of the partition wall 13 generally accumulates on the partition wall 13 and / or inside the pores of the partition wall 13 in the introduction-side cell 11, and the accumulated particulate matter is removed by the catalytic function of the catalyst layer 21 or by combustion at a predetermined temperature (for example, about 500 to 700°C). Furthermore, the exhaust gas comes into contact with the catalyst layer 21 formed in the pores of the partition wall 13. This oxidizes carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas to water (H2O) and carbon dioxide (CO2), and reduces nitrogen oxides (NOx) to nitrogen (N2), thereby purifying (detoxifying) harmful components. In this specification, the removal of particulate matter and the purification of harmful components such as carbon monoxide (CO) are collectively referred to as "exhaust gas purification performance." Each component will be described in more detail below.

[0016] (Degree of uneven distribution of the catalyst layer) In this embodiment, the degree of catalyst layer segregation is an indicator of the dispersion of the catalyst layer within the partition wall 13. In this embodiment, the degree of segregation can be calculated using the following formula based on the catalyst layer within each wall measured by an electron beam microanalyzer (hereinafter also referred to as "EPMA"). Degree of distribution = |(Degree of distribution of catalyst layer within the wall in portion 13a on the exhaust gas introduction side of partition wall 13 D1) - (Degree of distribution of catalyst layer within the wall in portion 13b on the exhaust gas discharge side of partition wall 13 D2)| Intrawall distribution degree D1 = (Partial distribution degree of catalyst in region 13at on the introduction side cell 11 in part 13a D11) - (Partial distribution degree of catalyst in region 13ab on the discharge side cell 12 in part 13a D12) The local distribution degree D11 is the sum of the local distribution degrees of the catalyst in regions 1 to 5, which are derived by dividing part 13a into 10 equal parts and considering each region 1 to 10. The local distribution degree D12 = the sum of the local distribution degrees of the catalyst in regions 6 to 10, which are derived by dividing part 13a into 10 equal parts. Intrawall distribution degree D2 = (Partial distribution degree of catalyst in region 13bt on the introduction side cell 11 in section 13b D21) - (Partial distribution degree of catalyst in region 13bb on the discharge side cell 12 in section 13b D22) The local distribution degree D21 is the sum of the local distribution degrees of the catalyst in regions 1 to 5, which are derived by dividing part 13b into 10 equal parts and considering each region 1 to 10. The local distribution degree D22 = the sum of the local distribution degrees of the catalyst in regions 6 to 10, which are derived by dividing region 13b into 10 equal parts.

[0017] As described above, the degree of non-uniformity in this embodiment can be expressed as the difference between the degree of non-uniformity of the catalyst in the thickness direction of the partition wall 13 (internal non-uniformity D1 and D2) determined for the exhaust gas introduction side portion 13a and the exhaust gas discharge side portion 13b, respectively.

[0018] Here, the exhaust gas inlet portion 13a is the portion located 0.15T from the exhaust gas inlet end 11a (opening) to the inside of the exhaust gas purification catalytic filter 100, and the exhaust gas outlet portion 13b is the portion located 0.15T from the exhaust gas outlet end 12a (opening) to the inside of the exhaust gas purification catalytic filter 100. Here, T represents the total length of the exhaust gas purification catalytic filter 100 in the extension direction. The width W of portions 13a and 13b is not particularly limited as long as it is a sample width that can be measured by EPMA, but can be, for example, 200 to 1000 μm.

[0019] Regions 13at and 13ab of section 13a, and regions 13bt and 13bb of section 13b, are regions obtained by dividing section 13a and section 13b in half in the thickness direction, respectively. Within section 13a, region 13at is located on the inlet side cell 11, and region 13ab is located on the outlet side cell 12. Similarly, within section 13b, region 13bt is located on the inlet side cell 11, and region 13bb is located on the outlet side cell 12. From the perspective of exhaust gas flow, the exhaust gas passes through region 13at or region 13bt before passing through region 13ab or region 13bb.

[0020] The intrawall segregation degree D1, expressed as the difference in catalyst abundance between regions 13at and 13ab obtained as described above, represents the bias in catalyst abundance in the thickness direction within portion 13a. The intrawall segregation degree D1 will be explained in detail. Portion 13a is divided into 10 equal parts in the thickness direction to obtain the catalyst abundance in regions 1 to 10. From this, the average value Ave of catalyst abundance in regions 1 to 10 is calculated, and the local segregation degree for each region 1 to 10 is calculated. (Example) Local distribution degree of region 1 = ((Amount of catalyst in region 1) - (Average value Ave)) / (Average value Ave) The partial distribution degree D11 of the catalyst in region 13at (regions 1-5) can be calculated from the local distribution degrees in regions 1-5, as follows. Similarly, the partial distribution degree D12 of the catalyst in region 13ab (regions 6-10) can be calculated from the local distribution degrees in regions 6-10, as follows. Note that unless the partial distribution degrees D11 and D12 are equal, one of them will be a positive value and the other a negative value. Partial distribution degree D11 = Σ (local distribution degree of catalyst in regions 1 to 5) Partial distribution degree D12 = Σ (local distribution degree of catalyst in regions 6 to 10)

[0021] Here, the difference between partial segregation degree D11 and partial segregation degree D12 corresponds to the intrawall segregation degree D1, so the intrawall segregation degree D1 can be expressed by the following formula. Therefore, the intrawall segregation degree D1 expressed by the above formula is a value that indicates the bias in the amount of catalyst present in the thickness direction in part 13a. The same applies to the intrawall segregation degree D2. Intra-wall eccentricity D1 = Local eccentricity D11 - Local eccentricity D12 =Σ(Local distribution of catalysts in regions 1-5)-Σ(Abundance of catalysts in regions 6-10) =Σ((Amount of catalyst in regions 1-5)-(Average Ave) / (Average Ave))- Σ((Amount of catalyst in region 6-10)-(Average value Ave) / (Average value Ave)) ) =(Σ(Amount of catalyst in regions 1-5)-Σ(Amount of catalyst in regions 6-10)) / Average value Ave

[0022] The amount of catalyst present in regions 13at and 13ab can be determined by measuring the corresponding region of part 13a using EPMA, binarizing the EPMA measurement data which is a two-dimensional map of the catalyst's locations, and calculating the integrated amount of catalyst in each region from the area ratio of the binarized measurement data. Similarly, the amount of catalyst present in regions 13bt and 13bb can also be determined by measuring the corresponding region of part 13b using EPMA and calculating the integrated amount of catalyst in each region. The two-dimensional mapped EPMA measurement data includes information on the amount of catalyst present in the depth direction. Therefore, in order to appropriately evaluate the amount of catalyst present in the two-dimensional cross-section being measured, it is preferable to binarize the data as described above and calculate the integrated amount of catalyst in each region from the area ratio of the binarized measurement data.

[0023] In this embodiment, the degree of non-uniformity of the catalyst layer formed within each wall is specified as 4.50 or less. The degree of non-uniformity of the catalyst layer formed within each wall is 4.50 or less, preferably 3.50 or less, more preferably 2.50 or less, even more preferably 1.50 or less, and even more preferably 1.00 or less. By having a degree of non-uniformity of the catalyst layer of 4.50 or less, the soot collection performance tends to be further improved while suppressing an increase in pressure loss of the exhaust gas purification catalytic filter for gasoline engines.

[0024] Furthermore, the amount of WC in the catalyst layer within each wall is preferably 40 g / L to 50 g / L, more preferably 40 g / L to 49 g / L, and even more preferably 42 g / L to 46 g / L. When the amount of WC in the catalyst layer is within the above range, the balance between pressure loss and soot collection performance of the exhaust gas purification catalytic filter for gasoline engines tends to be better.

[0025] (base material) The wall-flow type substrate 10 has a wall-flow type structure in which an introduction-side cell 11 with an open end 11a on the exhaust gas introduction side and an exhaust-side cell 12 adjacent to the introduction-side cell 11 with an open end 12a on the exhaust gas discharge side are separated by a porous partition wall 13.

[0026] As the base material 10, various materials and shapes conventionally used for this type of application can be used. For example, the base material is preferably made of a heat-resistant material so that it can withstand exposure to high-temperature exhaust gas (e.g., 400°C or higher) generated when a gasoline engine is operated under high-load conditions, or when particulate matter is burned and removed at high temperatures. Examples of heat-resistant materials include ceramics such as cordierite, mullite, aluminum titanate, and silicon carbide (SiC), and alloys such as stainless steel. The shape of the base material can be adjusted as appropriate from the viewpoint of exhaust gas purification performance and suppression of increased pressure loss. For example, the outer shape of the base material can be cylindrical, elliptical, or polygonal. Depending on the space in which it will be incorporated, the capacity of the base material (total volume of the cell) is preferably 0.1 to 5 L, more preferably 0.5 to 3 L. The total length of the base material in the stretching direction (total length of the partition wall 13 in the stretching direction) is preferably 10 to 500 mm, more preferably 50 to 300 mm.

[0027] The inlet cell 11 and the outlet cell 12 are arranged regularly along the axial direction of the cylindrical shape, and adjacent cells are alternately sealed at one open end and the other open end in the extension direction. The inlet cell 11 and the outlet cell 12 can be set to an appropriate shape and size considering the flow rate and composition of the supplied exhaust gas. For example, the opening shapes of the inlet cell 11 and the outlet cell 12 can be triangles; rectangles such as squares, parallelograms, rectangles, and trapezoids; other polygons such as hexagons and octagons; and circles. Furthermore, the inlet cell 11 may have a High Ash Capacity (HAC) structure in which the cross-sectional area of ​​the inlet cell 11 and the cross-sectional area of ​​the outlet cell 12 are different.

[0028] The number of inlet-side cells 11 and outlet-side cells 12 can be appropriately set to promote the generation of turbulence in the exhaust gas and suppress clogging by particulate matter contained in the exhaust gas, and is not particularly limited, but is preferably 200 cpsi to 400 cpsi. The thickness of the partition wall 13 (length in the thickness direction perpendicular to the stretching direction) is preferably 6 to 12 mil, and more preferably 6 to 10 mil.

[0029] The partition walls 13 separating adjacent cells are not particularly limited as long as they have a porous structure through which exhaust gas can pass, and their configuration can be appropriately adjusted from the viewpoint of exhaust gas purification performance, suppression of increased pressure loss, and improvement of the mechanical strength of the substrate. For example, when a catalyst layer 21 is formed on the surface of the pores in the partition walls 13 using a catalyst slurry described later, if the pore diameter (for example, the mode diameter (the pore diameter with the largest proportion of appearance in the frequency distribution of pore diameters (maximum value of the distribution))) and pore volume are large, blockage of the pores by the catalyst layer 21 is less likely to occur, and the resulting exhaust gas purification catalyst filter tends to have less increased pressure loss, but the ability to collect particulate matter decreases, and the mechanical strength of the substrate also tends to decrease. On the other hand, if the pore diameter and pore volume are small, the pressure loss tends to increase, but the ability to collect particulate matter improves, and the mechanical strength of the substrate also tends to improve.

[0030] (catalyst layer) Next, the catalyst layer 21 formed within the pores of the partition wall 13 will be described. In this embodiment, the catalyst layer 21 is a single layer consisting of a catalyst metal and a support component, and does not contain Ba. Furthermore, in the catalyst layer 21, it is preferable that the catalyst metal is Pd and / or Rh, and the support component is an oxide of Al, Zr and / or Ce.

[0031] Examples of such catalyst layers 21 include those formed by calcining a catalyst slurry containing predetermined catalyst metal particles and predetermined support particles. The catalyst layer 21 formed by calcining a catalyst slurry containing various particles in this way has a microporous structure in which the particles are bound together by the calcination process.

[0032] The catalytic metal contained in the catalyst layer 21 is preferably palladium (Pd) and / or rhodium (Rh). Of these, palladium (Pd) is preferred from the viewpoint of oxidation activity, and rhodium (Rh) is preferred from the viewpoint of reduction activity. Furthermore, a synergistic effect can be expected from using these two types of catalytic metals in combination, as they have different catalytic activities.

[0033] Furthermore, the presence of a catalytic metal in the catalyst layer 21 can be confirmed by scanning electron microscopy of the cross-section of the partition wall 13 of the exhaust gas purification catalytic filter 100. Specifically, this can be confirmed by performing energy-dispersive X-ray analysis in the field of view of the scanning electron microscope. In addition, the support component is preferably an oxide of Al, Zr, and / or Ce, and the catalyst layer does not contain Ba.

[0034] The carrier particles supporting the catalyst metal in the catalyst layer 21 are oxides of Al, Zr, and / or Ce. Such oxides are not particularly limited, but examples include oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO2) and ceria-zirconia composite oxide (CZ composite oxide), oxides such as aluminum oxide (alumina: Al2O3) and zirconium oxide (zirconia: ZrO2), and composite oxides mainly composed of these oxides. These may also be composite oxides or solid solutions to which rare earth elements such as lanthanum and yttrium, or transition metal elements, are added. These carrier particles may be used individually or in combination of two or more. Here, an oxygen storage material (OSC material) refers to a material that absorbs oxygen from the exhaust gas when the air-fuel ratio of the exhaust gas is lean (i.e., an oxygen-rich atmosphere) and releases the absorbed oxygen when the air-fuel ratio of the exhaust gas is rich (i.e., a fuel-rich atmosphere).

[0035] [Manufacturing method for exhaust gas purification catalytic filters] The manufacturing method of this embodiment is a method for manufacturing an exhaust gas purification catalyst filter 100 that purifies exhaust gas discharged from a gasoline engine, and comprises a step S0 of preparing a wall-flow type substrate 10 in which an introduction-side cell 11 with an open end 11a on the exhaust gas introduction side and an exhaust-side cell 12 adjacent to the introduction-side cell 11 and with an open end 12a on the exhaust gas discharge side are defined by a porous partition wall 13, and a catalyst layer forming step S1 of coating a catalyst slurry onto at least a part of the pore surface within the partition wall 13 of the wall-flow type substrate 10 to form a catalyst layer 21, and the catalyst layer forming step In S1, the absolute value of the degree of segregation of the catalyst layer formed in the pores of the partition wall of the wall-flow type substrate is 4.50 or less, the amount of wash coat of the catalyst layer excluding the platinum group metal mass per 1 L of wall-flow type substrate is 40 g / L or more and 50 g / L or less, the catalyst layer 21 formed in the pores of the partition wall 13 is a single layer and consists of a catalyst metal and a support component, the catalyst metal is Pd and / or Rh, the support component is an oxide of Al, Zr and / or Ce, and the catalyst layer 21 does not contain Ba, thereby manufacturing an exhaust gas purification catalyst filter 100.

[0036] The following describes each step. In this specification, the wall-flow type substrate before the formation of the catalyst layer 21 is referred to as "substrate 10," and the wall-flow type substrate after the formation of the catalyst layer 21 is referred to as "exhaust gas purification catalyst filter 100."

[0037] <Preparation process> In this preparation step S0, the wall-flow type substrate 10 described above in relation to the exhaust gas purification catalyst filter 100 is prepared as the substrate.

[0038] <Catalyst layer formation process> In this catalyst layer formation step S1, a catalyst slurry is applied to the pore surface of the partition wall 13, dried, and then fired to form a catalyst layer 21. The method of applying the catalyst slurry is not particularly limited, but for example, one method is to impregnate a part of the substrate 10 with the catalyst slurry and spread it over the entire partition wall 13 of the substrate 10. More specifically, one method is to impregnate the exhaust gas inlet end 11a or the exhaust gas outlet end 12a with a catalyst slurry containing ammonium carbonate; to apply the catalyst slurry impregnated in the substrate 10 to the partition wall 13 by introducing gas into the substrate 10 from the end side impregnated with the catalyst slurry; to dry the applied catalyst slurry in a drying step S1c; and to fire the applied catalyst slurry in a firing step S1d.

[0039] The method of impregnating the catalyst slurry in the impregnation step S1a is not particularly limited, but one example is to immerse one end of the substrate 10 in the catalyst slurry. In this method, if necessary, the catalyst slurry may be pulled up by discharging (suctioning) gas from the opposite end. The end to be impregnated with the catalyst slurry may be either the exhaust gas inlet end 11a or the exhaust gas outlet end 12a.

[0040] Furthermore, in the coating process S1b, the catalyst slurry moves from the introduction side of the substrate 10 towards the back along the flow of gas F, reaching the end on the gas F discharge side. During this process, the catalyst slurry passes through the pores of the partition wall 13, allowing the catalyst slurry to be coated into the pores, and the entire partition wall is coated with catalyst slurry.

[0041] In drying step S1c, the coated catalyst slurry is dried. The drying conditions in drying step S1c are not particularly limited as long as the conditions cause the solvent to evaporate from the catalyst slurry. For example, the drying temperature is preferably 100 to 225°C, more preferably 100 to 200°C, and even more preferably 125 to 175°C. The drying time is preferably 0.5 to 2 hours, and more preferably 0.5 to 1.5 hours.

[0042] In the firing process S1d, the catalyst slurry is fired to form the catalyst layer 21. The firing conditions in the firing process S1d are not particularly limited as long as they allow the catalyst layer 21 to be formed from the catalyst slurry. For example, the firing temperature is not particularly limited, but is preferably 400 to 650°C, more preferably 450 to 600°C, and even more preferably 500 to 600°C. The firing time is preferably 0.5 to 2 hours, and more preferably 0.5 to 1.5 hours.

[0043] (Catalyst slurry) The catalyst slurry for forming the catalyst layer 21 will now be described. The catalyst slurry contains ammonium carbonate, catalyst powder, and a solvent such as water. The catalyst powder is a collection of multiple catalyst particles, each containing catalyst metal particles and carrier particles that support the catalyst metal particles, and forms the catalyst layer 21 through a calcination process described later. The catalyst particles are not particularly limited and can be appropriately selected from known catalyst particles. From the viewpoint of coating into the pores of the partition wall 13, the solid content of the catalyst slurry is preferably 1 to 50% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 35% by mass. By having such a solid content, the catalyst slurry tends to be easier to coat into the introduction-side cell 11 within the partition wall 13.

[0044] The D90 particle size of the catalyst powder contained in the catalyst slurry is preferably 1 to 8 μm, more preferably 1 to 6 μm, and even more preferably 1 to 4 μm. A D90 particle size of 1 μm or more tends to shorten the grinding time when crushing the catalyst powder with a milling device, thereby improving work efficiency. Furthermore, a D90 particle size of 8 μm or less tends to suppress the blockage of pores within the partition wall 13 by coarse particles, thereby suppressing an increase in pressure loss. In this specification, the D90 particle size can be measured using a laser diffraction particle size distribution analyzer (for example, the SALD-3100 laser diffraction particle size distribution analyzer manufactured by Shimadzu Corporation).

[0045] The catalyst metal included in the catalyst slurry is not particularly limited, and various metal species capable of functioning as oxidation or reduction catalysts can be used. Examples include palladium (Pd) and rhodium (Rh). Among these, palladium (Pd) is preferred from the viewpoint of oxidation activity, and rhodium (Rh) is preferred from the viewpoint of reduction activity.

[0046] As carrier particles supporting the catalytic metal particles, inorganic compounds conventionally used in this type of exhaust gas purification catalytic filters can be considered. For example, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO2) and ceria-zirconia composite oxide (CZ composite oxide), oxides such as aluminum oxide (alumina: Al2O3) and zirconium oxide (zirconia: ZrO2), and composite oxides mainly composed of these oxides can be cited. These may also be composite oxides or solid solutions to which rare earth elements such as lanthanum and yttrium, or transition metal elements have been added. These carrier particles may be used individually or in combination of two or more types. Here, an oxygen storage material (OSC material) is one that absorbs oxygen from the exhaust gas when the air-fuel ratio of the exhaust gas is lean (i.e., an atmosphere with excess oxygen) and releases the absorbed oxygen when the air-fuel ratio of the exhaust gas is rich (i.e., an atmosphere with excess fuel). Furthermore, from the viewpoint of exhaust gas purification performance, the specific surface area of ​​the carrier particles contained in the catalyst slurry is preferably 10 to 500 m². 2 / g, more comfortably 30-200m 2 It is / g.

[0047] [Application] A gasoline engine is supplied with a mixture of oxygen and fuel gas, which is burned, and the combustion energy is converted into mechanical energy. The burned mixture is then discharged into the exhaust system as exhaust gas. The exhaust system is equipped with an exhaust gas purification device that includes an exhaust gas purification catalytic filter. The exhaust gas purification catalytic filter purifies harmful components contained in the exhaust gas (e.g., carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx)) and also captures and removes particulate matter (PM) contained in the exhaust gas. In particular, the exhaust gas purification catalytic filter 100 of this embodiment is preferably used in a gasoline particulate filter (GPF) that can capture and remove particulate matter contained in the exhaust gas of a gasoline engine. [Examples]

[0048] The features of the present invention will be further described below with reference to test examples, examples, and comparative examples, but the present invention is not limited in any way by these. That is, the materials, amounts used, proportions, processing content, processing procedures, etc., shown in the following examples can be changed as appropriate, as long as they do not depart from the spirit of the present invention. Furthermore, the various manufacturing conditions and evaluation result values ​​in the following examples have meaning as preferred upper or lower limits in embodiments of the present invention, and the preferred range may be defined by a combination of the aforementioned upper or lower limits and the values ​​of the following examples or the values ​​of the examples themselves.

[0049] (Example 1) Alumina powder was impregnated with an aqueous solution of palladium nitrate, and then calcined at 500°C for 1 hour to obtain Pd-supported powder. Similarly, alumina-zirconia composite oxide powder was impregnated with an aqueous solution of rhodium nitrate, and then calcined at 500°C for 1 hour to obtain Rh-supported powder.

[0050] 1.0 kg of the obtained Pd-supported powder and 1.0 kg of Rh-supported powder were mixed with 1.0 kg of ceria-zirconia composite oxide powder, 190 g of 23% lanthanum nitrate aqueous solution, 60% nitric acid, and deionized water. The resulting mixture was placed in a ball mill, and after the catalyst powder had reached a predetermined particle size distribution (D90 particle size of 3.0 μm), 44 g of ammonium carbonate was added to obtain a catalyst slurry.

[0051] Next, a cordierite wall-flow type honeycomb substrate (cell count / mil thickness: 300 cpsi / 8.5 mil, diameter: 118.4 mm, total length: 127 mm, pore size (median diameter): 20 μm, porosity: 63%) was prepared. The exhaust gas inlet end of this substrate was immersed in catalyst slurry, and reduced pressure suction was applied from the opposite end to impregnate and retain the catalyst slurry at the substrate end. Gas was introduced into the substrate from the exhaust gas inlet end to coat the pore surface within the partition wall with catalyst slurry, and excess catalyst slurry was blown away from the exhaust gas discharge end of the substrate to stop the gas inflow. After that, the substrate coated with catalyst slurry was dried at 150°C, and then fired at 550°C in an atmospheric environment to produce an exhaust gas purification catalyst filter. The amount of WC in the catalyst layer after firing was 44 g per liter of substrate (excluding the mass of platinum group metals).

[0052] (Example 2) Except for changing the amount of WC in the catalyst layer on the partition wall of the wall-flow type honeycomb substrate, an exhaust gas purification catalytic filter was fabricated in the same manner as in Example 1. The amount of WC in the catalyst layer after firing was 49 g per liter of substrate (excluding the mass of platinum group metals).

[0053] (Example 3) Except for changing the amount of WC in the catalyst layer on the partition wall of the wall-flow type honeycomb substrate, an exhaust gas purification catalyst filter was fabricated in the same manner as in Example 1. The amount of WC in the catalyst layer after firing was 40 g per liter of substrate (excluding the mass of platinum group metals).

[0054] (Comparative Example 1) Exhaust gas purification catalyst filters were manufactured in the same manner as in Example 1, except that ammonium carbonate was not added during the catalyst slurry manufacturing process. The amount of WC in the catalyst layer after calcination was 44 g per liter of substrate (excluding the mass of platinum group metals).

[0055] (Comparative Example 2) Except for changing the amount of WC in the catalyst layer on the partition wall of the wall-flow type honeycomb substrate, an exhaust gas purification catalyst filter was fabricated in the same manner as in Comparative Example 1. The amount of WC in the catalyst layer after firing was 61 g per liter of substrate (excluding the mass of platinum group metals).

[0056] (Comparative Example 3) Except for changing the amount of WC in the catalyst layer on the partition wall of the wall-flow type honeycomb substrate, an exhaust gas purification catalyst filter was fabricated in the same manner as in Example 1. The amount of WC in the catalyst layer after firing was 61 g per liter of substrate (excluding the mass of platinum group metals).

[0057] [Measurement of particle size distribution] The D90 particle size of the catalyst slurry was measured using the laser scattering method with a Shimadzu Corporation SALD-3100 laser diffraction particle size distribution analyzer.

[0058] [Measurement of the degree of uneven distribution of the catalyst layer within the partition wall] The presence or absence of the catalyst layer within the partition wall of the exhaust gas purification catalyst filters for gasoline engines fabricated in the examples and comparative examples was measured using a JEOL Electron Probe Micro Analyzer (EPMA) JXA-8100, and the degree of uneven distribution was calculated from the obtained two-dimensional data.

[0059] [Measurement of pressure loss] The exhaust gas purification catalyst filters prepared in the examples and comparative examples, as well as the substrates before the catalyst slurry was applied, were placed in a pressure loss measuring device (manufactured by Tsukuba Rika Seiki Co., Ltd.), and room temperature air was introduced into the installed exhaust gas purification catalyst filters. When the amount of air discharged from the exhaust gas purification catalyst filter was 4 m³ 3The pressure difference between the air intake and exhaust sides when the pressure was at / min was measured and the resulting value was defined as the pressure loss of the exhaust gas purification catalytic filter.

[0060] [Measurement of soot collection performance] The exhaust gas purification catalysts prepared in the examples and comparative examples were installed in a vehicle equipped with a 1.5L direct injection turbo engine, and the amount of soot emitted during WLTC mode driving (PN) was measured using a solid particle count analyzer (Horiba, Ltd., product name: MEXA-2100 SPCS). test The amount of soot (PN) measured was used when the above test was performed without an exhaust gas purification catalytic filter installed. blank The rate of decrease from ) was calculated using the following formula. Soot collection rate (%) = (PN blank -PN test ) / PN blank × 100(%)

[0061] The results are shown below.

[0062] [Table 1]

[0063] Based on the above, in the example, the degree of uneven distribution of the catalyst layer is below a predetermined value, and the amount of WC in the catalyst layer is within a predetermined value, thereby suppressing an increase in pressure loss while improving the soot collection efficiency. In the comparative example, the pressure loss increases or the soot collection efficiency decreases. [Industrial applicability]

[0064] The exhaust gas purification catalytic filter of the present invention can be widely and effectively used as an exhaust gas purification catalytic filter to remove particulate matter contained in the exhaust gas of a gasoline engine. [Explanation of symbols]

[0065] 10 ···Wall-flow type substrate 11 ···Introduction-side cell 11a... End on the exhaust gas inlet side 12 ···Discharge side cell 12a... End on the exhaust gas discharge side 13...bulkhead 21 ···Catalyst layer 100 ·· Exhaust gas purification catalytic converter filter

Claims

1. This is an exhaust gas purification catalytic filter for purifying exhaust gases from a gasoline engine, A wall-flow type substrate is defined by a porous partition wall, comprising an inlet cell with an open end on the exhaust gas inlet side and an outlet cell adjacent to the inlet cell with an open end on the exhaust gas discharge side, It consists of a catalyst layer formed within the pores of the aforementioned partition wall, The absolute value of the degree of uneven distribution of the catalyst layer formed within the pores of the partition wall is 0.10 or more and 1.00 or less. The amount of wash coat excluding the platinum group metal mass of the catalyst layer formed in the pores of the partition wall is 40 g / L or more and 50 g / L or less. The catalyst layer formed within the pores of the partition wall is a single layer. The catalyst layer does not contain Ba. Exhaust gas purification catalytic converter filter for gasoline engines.

2. The catalyst layer formed within the pores of the partition wall consists of a catalyst metal and a support component, wherein the catalyst metal is Pd and / or Rh, and the support component is an oxide of Al, Zr and / or Ce. The exhaust gas purification catalyst filter for a gasoline engine according to claim 1.

3. A method for manufacturing an exhaust gas purification catalytic filter for purifying exhaust gas from a gasoline engine, A step of preparing a wall-flow type substrate in which an inlet cell with an open end on the exhaust gas inlet side and an outlet cell adjacent to the inlet cell with an open end on the exhaust gas discharge side are defined by a porous partition wall, An impregnation step is performed in which a catalyst slurry containing ammonium carbonate is impregnated into the end of the wall-flow type substrate on the exhaust gas introduction side or the exhaust gas discharge side, A coating step in which gas is introduced into the wall-flow type substrate from the end side impregnated with the catalyst slurry, thereby coating the catalyst slurry impregnated in the wall-flow type substrate onto the pore surface of the partition wall, A firing step to obtain an exhaust gas purification catalyst filter in which the coated catalyst slurry is fired so that the absolute value of the degree of uneven distribution of the catalyst layer formed in the pores of the partition wall is 4.50 or less, and the amount of wash coat of the catalyst layer excluding the platinum group metal mass per liter of the wall-flow type substrate is 40 g / L or more and 50 g / L or less, The process includes, after the firing step to obtain the exhaust gas purification catalyst filter, measuring the catalyst layer within the pores of the partition wall of the exhaust gas purification catalyst filter using an electron beam microanalyzer, and inspecting the absolute value of the degree of uneven distribution of the catalyst layer. The catalyst layer formed within the pores of the partition wall is a single layer. The catalyst layer does not contain Ba. A method for manufacturing an exhaust gas purification catalytic filter for gasoline engines.

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