Catalysts for exhaust gas purification

Abstract

According to the technology disclosed in the present application, a wall-flow type exhaust gas purification catalyst that takes into account both harmful gas purification performance and pressure drop suppression performance at a high level can be provided. The exhaust gas purification catalyst disclosed in the present application includes a substrate 11 and a catalyst layer 20. In addition, a first catalyst region 22 having a catalyst layer 20 is provided on the inlet side surface 16a of the partition wall 16 of the substrate 11, and a second catalyst region 24 having a catalyst layer 20 is provided on the wall surface 18a of the pore 18 in a specified area from the outlet side surface 16b of the partition wall to the inlet side chamber 12. In addition, a catalyst non-formed region 30 in which a catalyst layer is substantially not formed is provided between the first catalyst region 22 and the second catalyst region 24 in the thickness direction Y of the partition wall 16. Thus, PM can be prevented from being accumulated in the second catalyst region 24 formed in the pore 18 by the catalyst layer 20, and harmful gas purification performance and pressure drop suppression performance can be taken into account at a high level.

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification catalyst configured in an exhaust system of an internal combustion engine. In detail, it relates to an exhaust gas purification catalyst having a wall flow type substrate and a catalyst layer formed on the substrate. It should be noted that this international application claims priority based on Japanese Patent Application No. 2019-239344 filed on December 27, 2019, and the entire contents of the application are introduced as a reference. Background Art

[0002] The exhaust gas emitted from internal combustion engines such as automobile engines contains hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO x ) and other harmful gas components, particulate matter (PM), etc. Therefore, in the exhaust system of the internal combustion engine, an exhaust purification catalyst is arranged to purify the above-mentioned harmful gas components and capture PM.

[0003] For example, an exhaust gas purification catalyst includes a wall-flow type substrate and a catalyst layer formed on the substrate. The wall-flow type substrate includes an inlet chamber with only an end opening on the exhaust gas inlet side, an outlet chamber with only an end opening on the exhaust gas outlet side, and a porous partition wall separating the two chambers. In addition, a catalyst layer is formed on the partition wall of the substrate. The exhaust gas supplied to the exhaust gas purification catalyst of this structure flows into the inlet chamber and is discharged from the outlet chamber after passing through the partition wall. At this time, PM is captured by the porous partition wall, and the harmful gas components are purified by the catalyst layer formed on the partition wall.

[0004] As prior art documents regarding the above-mentioned wall-flow type exhaust purification catalyst, Patent Documents 1 to 3 can be cited. For example, Patent Document 1 discloses an exhaust purification catalyst having two catalyst layers arranged inside the partition wall (i.e., the wall surface of the pores of the partition wall). The exhaust purification catalyst disclosed in the document includes a first catalyst layer arranged in an area inside the partition wall and connected to the inlet chamber and a second catalyst layer arranged in an area inside the partition wall and connected to the outlet chamber. In addition, in the patent document, the ratio (D2 / D1) of the coating density D2 of the second catalyst layer to the coating density D1 of the first catalyst layer is set to be greater than 1.01 and less than 1.4.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Patent Publication No. 2016 / 133087

[0008] Patent Document 2: Japanese Patent Application Publication No. 2013-184075

[0009] Patent Document 3: Japanese Patent Application Publication No. 2018-187595 Summary of the invention

[0010] Problems to be solved by the invention

[0011] In order to improve the purification performance of harmful gas components in such exhaust gas purification catalysts, it is possible to consider increasing the amount of catalyst layer formed in the pores of the partition wall and increasing the contact frequency between the catalyst layer and the harmful gas components. On the other hand, when the catalyst layer is formed on the wall surface of the pores, since the pores become narrower, there is a concern that the pores will be clogged when PM is captured, causing a sharp increase in pressure drop (hereinafter also referred to as "pressure loss"). That is, in the wall flow type exhaust gas purification catalyst, the harmful gas purification performance and the pressure drop suppression performance are considered to be in a trade-off relationship.

[0012] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a wall-flow exhaust gas purification catalyst capable of achieving both harmful gas purification performance and pressure drop suppression performance at a high level.

[0013] Methods for solving problems

[0014] In order to achieve the above object, the present invention provides an exhaust gas purification catalyst according to the following aspects.

[0015] The exhaust gas purification catalyst disclosed in the present application includes a wall flow type substrate and a catalyst layer formed on the substrate. The substrate of the exhaust gas purification catalyst includes an inlet chamber with only an end opening on the exhaust gas inlet side, an outlet chamber with only an end opening on the exhaust gas outlet side, and a partition wall that separates the inlet chamber and the outlet chamber and forms a plurality of pores connecting the inlet chamber and the outlet chamber. In addition, a first catalyst region with a catalyst layer formed is provided on the surface (inlet side) connected to the inlet chamber of the partition wall, and a second catalyst region with a catalyst layer formed on the wall surface of the pores is provided in a specified area from the surface (outlet side) of the partition wall connected to the outlet chamber to the inlet chamber of the partition wall. In addition, between the first catalyst region and the second catalyst region in the thickness direction of the partition wall, a catalyst non-formed region is provided in which substantially no catalyst layer is formed.

[0016] The exhaust gas purification catalyst disclosed in the present application can fully remove PM in the exhaust gas in the first catalyst region and the region where the catalyst is not formed. Therefore, the catalyst layer can prevent PM from reaching the second catalyst region where the pores are narrowed, and the rapid increase in pressure drop caused by the pore blockage can be suppressed. In addition, in the exhaust gas purification catalyst disclosed in the present application, CO, HC, NO xThe purification of harmful gas components such as PM is mainly carried out in the second catalyst area. At this time, since the catalyst layer in the second catalyst area is prevented from being covered by PM, even if the amount of catalyst layer formed is not increased, the contact frequency between the catalyst layer and the harmful gas components can be fully ensured, and high harmful gas purification performance can be exerted. Therefore, by adopting this embodiment, it is possible to achieve both harmful gas purification performance and pressure drop suppression performance at a high level.

[0017] In a preferred embodiment of the exhaust gas purification catalyst disclosed in the present application, the first catalyst region, the second catalyst region and the catalyst non-formed region are respectively arranged in a region that is greater than 50% of the total length of the substrate from the end of the substrate on the exhaust gas inlet side to the end of the substrate on the exhaust gas outlet side.

[0018] Generally speaking, exhaust gas containing a large amount of PM is easily supplied to the partition wall near the end portion on the exhaust gas inflow side. Therefore, by providing a stacked structure having a first catalyst region, a second catalyst region, and a catalyst-free region in an area of ​​more than 50% from the exhaust gas inflow side, it is possible to achieve both harmful gas purification performance and pressure drop suppression performance at a sufficiently high level.

[0019] In a preferred embodiment of the exhaust gas purification catalyst disclosed in the present application, the size of the first catalyst region in the thickness direction of the partition wall is 3 μm or more and 50 μm or less.

[0020] The size of the first catalyst region in the thickness direction varies depending on various conditions such as the substrate size, cross-sectional area, chamber thickness, and pore diameter. For example, by ensuring that the size of the first catalyst region in the thickness direction is 3 μm or more, PM can be appropriately prevented from invading the pores of the partition wall. On the other hand, by making the size of the first catalyst region 50 μm or less, the initial pressure drop before exhaust gas supply can be reduced.

[0021] In a preferred embodiment of the exhaust gas purification catalyst disclosed in the present application, the size of the catalyst non-formed region in the thickness direction of the partition wall is 10 μm or more and 100 μm or less.

[0022] By ensuring that the size of the catalyst-free region in the thickness direction is 10 μm or more, PM can be properly prevented from reaching the second catalyst region. On the other hand, by making the size of the catalyst-free region 100 μm or less, the size of the second catalyst region can be ensured and the harmful gas purification performance can be fully exerted.

[0023] In a preferred embodiment of the exhaust gas purification catalyst disclosed in the present application, the catalyst layer comprises a three-way catalyst and a support for supporting the three-way catalyst. The three-way catalyst can oxidize CO and HC and convert NO x reduction.

[0024] By forming a catalyst layer containing a three-way catalyst, CO, HC and NO, which are harmful gas components, can be purified efficiently separately. x .

[0025] In the embodiment containing the three-way catalyst, the three-way catalyst preferably contains at least one of Pt, Pd, and Rh.

[0026] By using them as a three-way catalyst, the harmful gas purification performance can be improved more appropriately.

[0027] In the above embodiment containing a three-way catalyst, the content of the three-way catalyst per 1 L of the volume of the substrate is preferably 0.1 g / L or more and 7 g / L or less.

[0028] It should be noted that the above-mentioned "content of the three-way catalyst per 1L of the substrate" is the value obtained by dividing the total amount (g) of the three-way catalyst present in the first catalyst region and the second catalyst region by the capacity (L) of the substrate.

[0029] In the above embodiment containing a support, the support preferably contains at least one of alumina, ceria, zirconia, silica, and titania.

[0030] These metal oxides have a large specific surface area and high durability (especially heat resistance). Therefore, according to this embodiment, the harmful gas purification performance of the three-way catalyst can be efficiently exerted.

[0031] In the above-mentioned embodiment including a three-way catalyst and a carrier, the catalyst layer preferably contains an OSC material having an oxygen storage capacity.

[0032] As a result, the exhaust gas atmosphere inside the catalyst layer can be stably maintained near the theoretical air-fuel ratio (stoichiometric ratio), so the harmful gas purification performance of the three-way catalyst can be stably exerted. In addition, as a preferred example of the OSC material, a ceria-zirconia composite oxide can be cited.

[0033] In the above embodiment containing a three-way catalyst and a carrier, the catalyst layer contains any one or more of oxides or sulfates, carbonates, nitrates and chlorides of alkaline earth metals, rare earth metals, alkali metals and transition metals.

[0034] The catalyst layer in the exhaust gas purification catalyst disclosed in the present application is not limited to the embodiment consisting of only the three-way catalyst and the carrier. For example, the catalyst layer may contain the above-mentioned components.

[0035] In a preferred embodiment of the exhaust gas purification catalyst disclosed in the present application, the amount of the catalyst layer formed per 1L of the volume of the substrate is 20 g / L or more and 180 g / L or less.

[0036] As a result, it is possible to achieve both harmful gas purification performance and pressure drop suppression performance at a higher level. It should be noted that the above-mentioned "amount of catalyst layer formed per 1L capacity of the substrate" is the value obtained by dividing the total amount (g) of the catalyst layer present in the first catalyst region and the second catalyst region respectively by the capacity (L) of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a diagram schematically showing an exhaust system of an internal combustion engine provided with an exhaust gas purification device.

[0038] Figure 2 It is a perspective view schematically showing an exhaust gas purification catalyst according to an embodiment of the present invention.

[0039] Figure 3 It is a diagram schematically showing a cross section along the cylinder axis direction of an exhaust gas purification catalyst according to an embodiment of the present invention.

[0040] Figure 4 It is an enlarged cross-sectional view schematically showing a cross section of a partition wall of a substrate of an exhaust gas purifying catalyst according to an embodiment of the present invention.

[0041] Figure 5 This is a cross-sectional SEM photograph of a partition wall of a substrate of the exhaust gas purifying catalyst of the example, taken at a magnification of 200 times.

[0042] Figure 6 This is a cross-sectional SEM photograph of a partition wall of a substrate of the exhaust gas purification catalyst of the comparative example, taken at a magnification of 200 times.

[0043] Figure 7 It is a graph showing the measurement results of the initial pressure drop (kPa) in the test example.

[0044] Figure 8 It is a graph showing the measurement results of PM accumulation pressure drop (kPa) in the test example.

[0045] Fig. 9 It is a graph showing the measurement results of the PN capture rate (%) in the test example.

[0046] Fig.10 It is a graph showing the measurement results of T50 catalyst activity (° C.) in the test examples.

[0047] Fig.11It is an enlarged cross-sectional view schematically showing a cross section of a partition wall of a substrate of a conventional exhaust gas purifying catalyst. DETAILED DESCRIPTION

[0048] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following drawings, the same symbols are sometimes used for components and parts having the same function, and repeated descriptions are omitted or simplified. The dimensional relationships (length, width, thickness, etc.) in the figures do not necessarily reflect the actual dimensional relationships. It should be noted that matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention (for example, general matters regarding the installation of exhaust purification catalysts in exhaust systems, etc.) can be considered as design matters that can be mastered by those skilled in the art in this field based on the prior art. The present invention can be implemented based on the disclosure of this specification and the technical knowledge in this field.

[0049] <Exhaust gas purification device>

[0050] First, an exhaust gas purification device including an exhaust gas purification catalyst according to an embodiment of the present invention will be described. Figure 1 Schematically shows an exhaust system of an internal combustion engine equipped with an exhaust gas purification device. Figure 1 The arrow A in shows the flow of the exhaust gas. For the convenience of explanation, in this specification, the direction in which the exhaust gas is supplied is referred to as "upstream", and the direction in which the exhaust gas is discharged is referred to as "downstream".

[0051] The exhaust gas purification device 1 is provided in the exhaust system of an internal combustion engine (engine) 2. A mixed gas containing oxygen and fuel gas is supplied to the internal combustion engine 2. In the internal combustion engine 2, the mixed gas is burned to convert the combustion energy into mechanical energy. As an example, the internal combustion engine 2 is mainly composed of a gasoline engine. It should be noted that the internal combustion engine 2 may also be an engine other than a gasoline engine (for example, a diesel engine, etc.).

[0052] The mixed gas burned in the internal combustion engine 2 becomes exhaust gas and is discharged from the exhaust system. In the exhaust system of the internal combustion engine 2, an exhaust manifold 3, an exhaust pipe 4 and an exhaust purification device 1 are provided in order from the upstream side. The exhaust purification device 1 removes harmful gas components (CO, HC, NO) contained in the exhaust gas discharged from the internal combustion engine 2. x ) to purify and remove PM.

[0053] Specifically, the exhaust gas purification device 1 is connected to an exhaust port (not shown) of the internal combustion engine 2 via an exhaust manifold 3 and an exhaust pipe 4. Figure 1The exhaust gas purification device 1 shown includes a temperature increase catalyst 9. The temperature increase catalyst 9 has the function of increasing the temperature of the exhaust gas. The specific structure of the temperature increase catalyst 9 is not a part that gives characteristics to the technology of the present invention, so a detailed description is omitted. In addition, the temperature increase catalyst 9 is not a necessary structure of the exhaust gas purification device 1 and can also be omitted.

[0054] In addition, Figure 1 In the exhaust system of the internal combustion engine 2 shown, a pressure sensor 8 is arranged downstream of the exhaust purification device 1. The pressure sensor 8 is connected to the ECU (Engine Control Unit) 5. The ECU 5 is a control device that controls the operation of the internal combustion engine 2. The ECU 5 may include a storage device (storage medium) such as a central processing unit (CPU) that executes commands of a control program, a ROM (read only memory) that stores the control program executed by the CPU, a RAM (random access memory) used as a work area for developing the control program, and a memory that stores various information. For example, as one of the information when controlling the operation of the internal combustion engine 2, the ECU 5 can use the pressure drop value detected by the pressure sensor 8.

[0055] Furthermore, the exhaust gas purification catalyst 10 involved in the present embodiment is arranged inside the exhaust gas purification device 1 (typically on the downstream side of the temperature rise catalyst 9). In the exhaust gas purification catalyst 10, the purification of harmful gas components and the removal of PM are performed. The specific structure of the exhaust gas purification catalyst 10 involved in the present embodiment is described below.

[0056] <Catalysts for exhaust gas purification>

[0057] Figure 2 It is a perspective view schematically showing the exhaust gas purification catalyst according to the present embodiment. Figure 3 It is a diagram schematically showing a cross section along the cylinder axis direction of the exhaust gas purification catalyst according to the present embodiment. Figure 4 FIG. 2 is an enlarged cross-sectional view schematically showing a cross-section of a partition wall of a substrate of an exhaust gas purification catalyst according to the present embodiment. Figure 1 same, Figure 2 to Figure 4 Arrow A in FIG. 1 represents the flow of exhaust gas. Figure 2 to Figure 4 The symbol X in denoted by 'extending direction of the partition wall', and the symbol Y denoted by 'thickness direction of the partition wall of the substrate'.

[0058] like Figure 2 to Figure 4As shown, the exhaust gas purifying catalyst 10 according to the present embodiment includes a wall flow type substrate 11 and a catalyst layer 20 formed on the substrate 11 .

[0059] 1. Substrate

[0060] The substrate 11 constitutes the skeleton of the exhaust gas purifying catalyst 10. Figure 2 As shown in FIG. 1 , in this embodiment, a cylindrical substrate 11 is used. It should be noted that the outer shape of the substrate is not particularly limited, and it may be an elliptical cylindrical shape, a polygonal cylindrical shape, etc. In addition, the total length and capacity of the substrate 11 are not particularly limited, and can be adjusted according to the internal combustion engine 2 (see FIG. 1 ). Figure 1 ) can be appropriately changed according to the performance of the substrate 11. In addition, various materials that have been used in this application can be appropriately used as the substrate 11. As an example, a high heat-resistant material represented by ceramics such as cordierite, aluminum titanate, silicon carbide (SiC), and alloys such as stainless steel can be used as the material of the substrate 11.

[0061] The substrate 11 in this embodiment is a wall flow type substrate. Specifically, Figure 2 and Figure 3 As shown, the substrate 11 includes an inlet chamber 12 having an opening only at the end on the exhaust gas inlet side, an outlet chamber 14 having an opening only at the end on the exhaust gas outlet side, and a porous partition wall 16 separating the inlet chamber 12 from the outlet chamber 14. Specifically, the inlet chamber 12 is a gas flow path having an opening at the end on the exhaust gas inlet side and an end on the exhaust gas outlet side blocked by a sealing portion 12a. On the other hand, the outlet chamber 14 is a gas flow path having an end on the exhaust gas inlet side blocked by a sealing portion 14a and an opening at the end on the exhaust gas outlet side. In addition, the partition wall 16 is a partition material having a plurality of pores through which exhaust gas can pass. The partition wall 16 has a plurality of pores 18 (see Figure 4 It should be noted that in the exhaust gas purification catalyst 10 according to the present embodiment, the shape of the inlet chamber 12 (outlet chamber 14) of the cross section of the partition wall 16 perpendicular to the extension direction X is a square (see Figure 1 ). However, the shape of the inlet chamber (outlet chamber) in a cross section perpendicular to the extension direction is not limited to a square, and various shapes can be used. For example, a rectangular shape such as a parallelogram, a rectangle, a trapezoid, a triangle, other polygonal shapes (for example, a hexagon, an octagon), a circle, and other geometric shapes.

[0062] In addition, the partition wall 16 of the substrate 11 is preferably formed in consideration of PM collection performance and pressure drop suppression performance. For example, the thickness of the partition wall 16 is preferably about 25μm to 100μm. Moreover, the porosity of the partition wall 16 is preferably about 20% by volume to 70% by volume. In addition, from the perspective of fully ensuring the ventilation of the partition wall 16 and suppressing the increase in pressure drop, the average pore diameter of the pores 18 is preferably 8μm or more, more preferably 12μm or more, and more preferably 15μm or more. On the other hand, from the perspective of ensuring appropriate PM collection performance, the upper limit value of the average pore diameter of the pores 18 is preferably 30μm or less, more preferably 25μm or less, and more preferably 20μm or less. It should be noted that the porosity and average pore diameter of the partition wall 16 are values ​​measured by mercury intrusion.

[0063] 2. Catalyst layer

[0064] like Figure 4 As shown, the catalyst layer 20 is formed on the partition wall 16 of the substrate 11 (specifically, formed on the inlet side surface 16a of the partition wall 16 and the wall surface 18a of the pore 18). In the exhaust gas purification catalyst 10 involved in this embodiment, the formation amount of the catalyst layer 20 per 1L capacity of the substrate 11 is preferably 20g / L or more, more preferably 40g / L or more, more preferably 60g / L or more, and particularly preferably 80g / L or more from the viewpoint of improving the harmful gas purification performance. On the other hand, the upper limit of the formation amount of the above-mentioned catalyst layer 20 is preferably 180g / L or less, more preferably 160g / L or less, more preferably 140g / L or less, and particularly preferably 120g / L or less from the viewpoint of improving the pressure drop suppression performance. It should be noted that the "formation amount of the catalyst layer 20" here refers to the total formation amount of the catalyst layer 20 formed in the first catalyst region 22 and the second catalyst region 24 described later.

[0065] The catalyst layer 20 is a porous layer containing a catalyst metal. Typically, the catalyst layer 20 is formed by aggregating composite particles carrying a catalyst metal on a carrier. For example, the catalyst layer 20 contains a three-way catalyst and a carrier carrying the three-way catalyst. The three-way catalyst is a catalyst that oxidizes CO and HC in the exhaust gas and converts NO xReduced catalyst metal. By forming a catalyst layer 20 containing such a three-way catalyst, harmful gas components in the exhaust gas can be efficiently purified. As an example of the three-way catalyst, particles containing platinum group elements such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), and iridium (Ir) as the main body can be listed. In addition, among these platinum group elements, due to the high oxidation activity of Pt, Pd, and Rh, particularly suitable harmful gas purification performance can be exerted. In addition, from the viewpoint of improving the harmful gas purification performance, the content of the three-way catalyst in each 1L capacity of the substrate 11 is preferably 0.1g / L or more, more preferably 0.5g / L or more, and particularly preferably 1g / L or more. On the other hand, from the viewpoint of reducing material costs, the upper limit of the content of the above-mentioned three-way catalyst is preferably 10g / L or less, more preferably 8g / L or less, and particularly preferably 7g / L or less. It should be noted that, similar to the above-mentioned “formation amount of catalyst layer”, the “content of the three-way catalyst” here refers to the total content of the catalyst layer 20 formed in the first catalyst region 22 and the second catalyst region 24 described later.

[0066] On the other hand, the carrier for supporting the catalyst metal preferably uses a metal oxide. As an example of the metal oxide, aluminum oxide (Al2O3), cerium oxide (CeO2), zirconium oxide (ZrO2), silicon dioxide (SiO2), titanium oxide (TiO2) and the like can be cited. These metal oxides have a large specific surface area and high durability (especially heat resistance), so the harmful gas purification performance of the catalyst metal (typically, a three-way catalyst) can be efficiently exerted.

[0067] In addition, the catalyst layer 20 may also contain other additives. As an example of such other additives, OSC material can be cited. OSC material refers to a material that has oxygen storage capacity (OSC: Oxygen Storage capacity) and can absorb and release oxygen. By adding the OSC material, the exhaust atmosphere in contact with the catalyst layer 20 can be stably maintained near the theoretical air-fuel ratio (stoichiometric ratio), so the catalytic action of the three-way catalyst can be stabilized. As an example of the OSC material, cerium oxide-zirconium oxide composite oxides and the like can be cited. In addition, as additives other than OSC materials, NOx adsorbents and stabilizers having NOx absorption capacity can be cited. Moreover, the catalyst layer 20 may also contain trace components derived from raw materials or manufacturing processes. For example, the catalyst layer 20 may contain any one or more of oxides or sulfates, carbonates, nitrates, and chlorides of alkaline earth metals (Be, Mg, Ca, Ba, etc.), rare earth metals (Y, La, Ce, etc.), alkali metals (Li, Na, K, etc.), and transition metals (Mn, Fe, Co, Ni, etc.).

[0068] In addition, in the exhaust gas purification catalyst 10 according to the present embodiment, the region (catalyst region) where the catalyst layer 20 is formed is determined from the viewpoint of achieving both high levels of harmful gas purification performance and pressure drop suppression performance. Figure 3 and Figure 4 As shown, the partition wall 16 of the substrate 11 in this embodiment is provided with a first catalyst region 22 and a second catalyst region 24. In addition, in this embodiment, a catalyst non-formed region 30 is also provided where the catalyst layer 20 is substantially not formed. Hereinafter, each region will be described in detail.

[0069] (1) First catalyst region

[0070] like Figure 3 and Figure 4 As shown, the first catalyst region 22 is provided on the surface (entry side surface 16a) that is in contact with the inlet chamber 12 of the partition wall 16. By providing the first catalyst region 22, the opening of the pore 18 on the inlet chamber 12 side is covered by the catalyst layer 20. Therefore, most of the PM in the exhaust gas is captured by the upstream side (inside the inlet chamber 12) of the first catalyst region 22 before entering the pore 18. Thus, it is possible to prevent a large amount of PM from accumulating inside the pore 18 and clogging the pore 18.

[0071] In addition, the catalyst layer 20 in the first catalyst region 22 is preferably formed in a manner that can appropriately capture PM and ensure sufficient air permeability. From the viewpoint of being able to form a catalyst layer having such an appropriate density, the catalyst layer 20 of the first catalyst region 22 is preferably composed of composite particles having a particle size smaller than that of the pores 18 of the partition wall 16. Specifically, the average particle size of the composite particles contained in the catalyst layer 20 of the first catalyst region 22 is preferably 5 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less, for example, about 1 μm. By using such fine particles, PM can be reliably prevented from invading the interior of the pores 18. In addition, the lower limit of the average particle size of the above-mentioned composite particles is not particularly limited, and can be 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, or 0.5 μm or more. It should be noted that in this specification, "average particle size" refers to the cumulative 50% particle size (D 50). Specifically, the average particle size can be measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd., LA-920) with the refractive index set to 1.20+0.01i (i is an imaginary term). It should be noted that the "primary particles" here refer to tiny particles that are aggregated into secondary particles by agglomeration, sintering, etc.

[0072] In addition, the size t1 of the first catalyst region 22 in the thickness direction Y is preferably 3 μm or more, more preferably 5 μm or more, and particularly preferably 10 μm or more. Thus, the PM collection performance in the first catalyst region 22 can be fully ensured, and PM can be appropriately prevented from invading the pores 18 of the partition wall 16. On the other hand, there is a tendency that the air permeability decreases and the initial pressure drop increases as the size t1 of the first catalyst region 22 in the thickness direction Y becomes longer. From this point of view, the size t1 of the first catalyst region 22 in the thickness direction Y is preferably 50 μm or less, more preferably 40 μm or less, and particularly preferably 30 μm.

[0073] (2) Catalyst-free area

[0074] As described above, the catalyst non-formed region 30 is a region where substantially no catalyst layer is formed. The catalyst non-formed region 30 is provided between the first catalyst region 22 and the second catalyst region 24 in the thickness direction Y of the partition wall 16. In other words, the catalyst non-formed region 30 is a region provided from the inlet side surface 16a of the partition wall 16 toward the outlet side chamber 14, and is a region where most of the wall surface 18a of the pore 18 is exposed. Figure 4 As shown, in the exhaust gas purification catalyst 10 involved in the present embodiment, most of the PM in the exhaust gas is captured by the first catalyst region 22. However, when a catalyst layer is formed on the wall surface of the pore, the pore becomes very narrow, so even if a small amount of PM passes through the first catalyst region 22 and accumulates, there is a possibility that the pore is blocked. In response to this, in the present embodiment, a catalyst non-formed region 30 where a catalyst layer is not formed is provided on the downstream side of the first catalyst region 22. Thus, it is possible to reliably prevent PM from reaching the region (second catalyst region 24) where the pore 18 is narrowed by the catalyst layer 20.

[0075] In this specification, "substantially no catalyst layer is formed" means that the catalyst layer is intentionally not formed on the wall surface of the pore. Therefore, the situation where a trace amount of catalyst layer exists in the area between the first catalyst area 22 and the second catalyst area 24 due to errors during manufacturing is also included in the concept of "substantially no catalyst layer is formed" in this specification. In addition, whether a catalyst-unformed area is provided in the specified exhaust gas purification catalyst (that is, whether a catalyst layer is actively formed in the area between the first catalyst area and the second catalyst area) can be determined by the operation described in "4. Determination of each area" described later.

[0076] In addition, the size t2 of the catalyst-free region 30 in the thickness direction Y of the partition wall 16 is preferably 10 μm or more, more preferably 15 μm or more, and particularly preferably 20 μm or more. Thus, it is possible to suppress the PM passing through the first catalyst region 22 from reaching the second catalyst region 24 and increasing the pressure drop. On the other hand, the size of the catalyst-free region 30 in the thickness direction Y is preferably 100 μm or less, more preferably 90 μm, and particularly preferably 80 μm. Thus, it is possible to ensure that the region where the second catalyst region 24 is formed can fully exert the harmful gas purification performance.

[0077] (3) Second catalyst region

[0078] like Figure 4 As shown, the second catalyst region 24 is a region where the catalyst layer 20 is formed on the wall surface 18a of the pore 18 of the partition wall 16. The second catalyst region 24 is provided in a predetermined region from the surface (the outlet side surface 16b) of the partition wall 16 that is in contact with the outlet chamber 14 to the inlet chamber 12. As described above, in the exhaust gas purification catalyst 10 involved in the present embodiment, since PM is sufficiently captured in the first catalyst region 22 and the catalyst non-formed region 30, PM can be prevented from reaching the second catalyst region 24 where the pore 18 is narrowed by the catalyst layer 20. Therefore, it is possible to prevent the pore 18 from being clogged in the second catalyst region 24 and causing a sharp increase in pressure drop. Moreover, in the present embodiment, the catalyst layer 20 of the second catalyst region 24 is not easily covered by PM. Therefore, the contact frequency between the catalyst layer 20 and the exhaust gas can be sufficiently ensured in the second catalyst region 24, and a high harmful gas purification performance can be exerted.

[0079] The catalyst layer 20 in the second catalyst region 24 may have the same composition as the catalyst layer 20 in the first catalyst region 22, or may have a different composition. Among them, the catalyst layer 20 in the second catalyst region 24 is preferably configured so that the pores 18 are not blocked and the frequency of contact with the exhaust gas can be ensured. From this point of view, the catalyst layer 20 in the second catalyst region 24 is preferably composed of composite particles having a particle size smaller than the pores 18 of the partition wall 16, as in the first catalyst region 22. That is, the average particle size of the composite particles contained in the catalyst layer 20 in the second catalyst region 24 varies depending on the pore size of the partition wall 16 of the substrate 10, preferably less than 5 μm, more preferably 2.5 μm, and even more preferably less than 2 μm, for example, about 1 μm. By using such fine particles, the clogging of the pores 18 can be prevented, and the frequency of contact with the exhaust gas can be fully ensured. The lower limit of the average particle size of the composite particles is not particularly limited, and may be 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, or 0.5 μm or more.

[0080] In addition, the size t3 of the second catalyst region 24 in the thickness direction Y of the partition wall 16 can be obtained based on the size t2 of the catalyst non-formed region 30. As described above, when the size t2 of the catalyst non-formed region 30 is increased and the size t3 of the second catalyst region 24 is reduced, there is a tendency that the pressure drop suppression performance can be improved. On the other hand, when the size t2 of the catalyst non-formed region 30 is reduced and the size t3 of the second catalyst region 24 is increased, there is a tendency that the harmful gas purification performance can be improved.

[0081] 3. Purification of Exhaust Gas in the Present Embodiment

[0082] Hereinafter, exhaust gas purification using the exhaust gas purification catalyst of the present embodiment will be described in comparison with a conventional exhaust gas purification catalyst. Fig.11 It is an enlarged cross-sectional view schematically showing a partition wall of a substrate of a conventional exhaust gas purifying catalyst.

[0083] like Fig.11As shown, in the conventional general exhaust gas purification catalyst, the catalyst layer 120 is formed only on the wall surface 118a of the pore 118 of the partition wall 116. Therefore, there is no division into an area for PM capture and an area for purifying harmful gas components, and PM is captured inside the pore 118 narrowed by the catalyst layer 120. Therefore, when a certain amount of exhaust gas is supplied and PM is accumulated in the pore 118, there is a concern that the pore 118 is clogged and the pressure drop increases sharply. Moreover, since the accumulated PM covers the catalyst layer 120, the frequency of contact between the catalyst layer 120 and the exhaust gas decreases, and there is also a concern that the harmful gas purification performance is reduced. In addition, the exhaust gas purification catalyst cannot capture PM that exceeds the volume of the pore 118, so there is a tendency for the PM capture performance to decrease over time.

[0084] In contrast, Figure 4 As shown, in the exhaust gas purification catalyst 10 involved in the present embodiment, after PM in the exhaust gas is fully captured in the first catalyst region 22 and the catalyst non-formed region 30, the harmful gas components are purified in the second catalyst region 24. That is, it is divided into a region for capturing PM and a region for purifying harmful gas components. As a result, PM can be prevented from reaching the region (second catalyst region 24) where the pores 18 are narrowed due to the catalyst layer 20, and a sharp increase in pressure drop caused by clogging of the pores 18 can be prevented. In addition, the catalyst layer 20 of the second catalyst region 24 can be prevented from being covered by PM, and the harmful gas purification performance of the second catalyst region 24 can be maintained at a high state. In this way, the exhaust gas purification catalyst 10 involved in the present embodiment can achieve both harmful gas purification performance and pressure drop suppression performance at a high level. In addition, in the present embodiment, most of the PM in the exhaust gas is captured by the first catalyst region 22 and remains in the inlet side chamber 12. Since the inlet side chamber 12 has a volume much larger than the pores 18, it is possible to suppress the PM capture performance from decreasing over time.

[0085] 4. Judgment operation of each area

[0086] The first catalyst region 22, the second catalyst region 24 and the catalyst non-formed region 30 in the above-mentioned embodiment are determined based on the following determination operations (a) to (k). That is, whether the three regions of the first catalyst region, the second catalyst region and the catalyst non-formed region are provided in the predetermined exhaust gas purification catalyst can be determined based on the following determination operation.

[0087] (a) An exhaust gas purification catalyst to be inspected was decomposed, and 10 test pieces were prepared in which the partition walls of the substrate were embedded with a resin.

[0088] (b) The sample piece was cut to expose the cross section of the partition wall. The exposed cross section of the partition wall was then observed using a scanning electron microscope (SEM) to obtain a cross-sectional SEM observation image (reflected electron image, observation magnification 200 times).

[0089] (c) The cross-sectional SEM observation image is automatically binarized using two-dimensional image analysis software (product name: ImageJ (registered trademark)) to obtain a binary image showing only the catalyst layer.

[0090] (d) The images before and after the automatic binarization process are compared, and the catalyst layer confirmed on the entrance side surface of the partition wall is regarded as the "first catalyst region".

[0091] (e) Count the "total number of pixels of the catalyst layer" and the "number of pixels of the entire binary image" confirmed in the above binary image. Then, calculate the value obtained by dividing the "total number of pixels of the catalyst layer" by the "number of pixels of the entire binary image" and use it as the "catalyst layer presence rate of the entire partition wall".

[0092] (f) Compare the images before and after automatic binarization processing, set an arbitrary area from the exit side of the partition wall to the entry side chamber, calculate the value of "the number of pixels of the catalyst layer in the set area" divided by the "total number of pixels in the set area", and use it as the "existence rate of the catalyst layer in the set area".

[0093] (g) Calculate the value obtained by dividing the "catalyst layer presence rate in the set area" by the "catalyst layer presence rate of the entire partition wall", and determine whether the value is greater than the first threshold value. In addition, the first threshold value in this process is set to 1.05 (preferably 1.1, more preferably 1.15, more preferably 1.2, and particularly preferably 1.25), for example.

[0094] (h) The "arbitrary area from the exit side of the partition wall to the entrance side chamber" described in (f) above is gradually expanded toward the entrance side chamber, and the "catalyst layer presence rate in the set area" is calculated each time, and the value obtained by dividing the "catalyst layer presence rate in the set area" by the "catalyst layer presence rate of the entire partition wall" is calculated. Thereafter, the set area is expanded until the value is lower than the first threshold value.

[0095] (i) When the result of the process in (h) above is confirmed to be a region below the first threshold, the region where the previous determination was made is regarded as the "second catalyst region". Thereafter, the region between the "first catalyst region" and the "second catalyst region" is regarded as the "third region".

[0096] (j) Calculate the value obtained by dividing the "number of pixels of the catalyst layer in the third region" by the "total number of pixels in the third region", and use it as the "existence rate of the catalyst layer in the third region". Next, calculate the value obtained by dividing the "existence rate of the catalyst layer in the third region" by the "existence rate of the catalyst layer in the entire image". Thereafter, when this value is below the second threshold value, the "third region" is determined to be a "catalyst non-formed region" (i.e., a catalyst non-formed region between the first catalyst region and the second catalyst region). In addition, the second threshold value in the present processing is set to, for example, 0.65 (preferably 0.5, more preferably 0.4, more preferably 0.3, and particularly preferably 0.25).

[0097] (k) When the treatments (b) to (j) are performed on all 10 sample pieces and regions without catalyst formation are confirmed between the first catalyst region and the second catalyst region in more than 50% of the sample pieces, it is determined that the exhaust gas purification catalyst under inspection has "a region without catalyst formation provided between the first catalyst region and the second catalyst region."

[0098] It should be noted that the above-mentioned "dimensions t1 to t3 of each region in the thickness direction Y (see Figure 4 )" can be measured based on the boundaries of each area identified in the above-mentioned judgment operation. Specifically, the "sizes t1 to t3 of each area in the thickness direction Y" in this specification are the average values ​​of the sizes of each area confirmed in each of the 10 sample pieces.

[0099] <Method for producing exhaust gas purification catalyst>

[0100] The exhaust gas purifying catalyst 10 according to the present embodiment can be produced, for example, by the following operation.

[0101] 1. Filling with organic solid ingredients

[0102] In this manufacturing method, the organic solid component is initially filled into the pores 18 of the partition wall 16 from the inlet chamber 12. Specifically, a pore filling slurry is prepared to disperse the organic solid component in a specified dispersion medium, and the pore filling slurry is introduced into the interior of the substrate 11 from the inlet chamber 12. Then, the pore filling slurry is infiltrated into the pores 18 by suction from the outlet chamber 14 of the substrate 11. Then, by implementing a drying process, the dispersion medium is removed to obtain a substrate 11 filled with organic solid components in the pores 18. It should be noted that the organic solid component can be any existing known material as long as it is a component that is burned out in the firing process described later. As an example of an organic solid component, resin beads composed of polyethylene, polypropylene, melamine resin, polymethyl methacrylate (PMMA) resin, etc. can be cited. In addition, as another example, resin fibers such as cellulose microfibers can also be used. In addition, the organic solid component is preferably adjusted to a size that can be appropriately filled into the pores 18 of the partition wall 16. For example, when resin beads are used as organic solid components, it is preferred that the average particle size be less than 100 μm (more preferably less than 50 μm, more preferably less than 30 μm). In addition, the dispersion medium can be used without particular restrictions as long as it is a liquid material that does not dissolve the organic solid component. As an example of the dispersion medium, water, alcohol, etc. can be cited. In addition, the concentration of the organic solid component in the pore filling slurry is preferably appropriately adjusted in consideration of the porosity of the partition wall 16 of the substrate 11.

[0103] 2. Preparation of Catalyst Layer Forming Slurry

[0104] Then, a catalyst layer forming slurry of the precursor material of the noon catalyst layer 20 is prepared. Specifically, the metal oxide that will become the carrier and the compound that will become the supply source of the catalyst metal are mixed in a specified ratio to prepare a mixed solution. Then, after the prepared mixed solution is dried, it is fired at a specified temperature and time to produce composite particles with the catalyst metal carried on the carrier. Then, the composite particles are mixed with a desired additive (such as an OSC material) together with an appropriate solvent (such as ion exchange water). Thus, a catalyst layer forming slurry is obtained. It should be noted that the specific contents of the catalyst metal, the carrier, and other additives have been described, so repeated descriptions are omitted.

[0105] 3. Formation of the first catalyst region

[0106] In this process, after the catalyst layer forming slurry is applied to the inlet side surface 16a of the partition wall 16, the catalyst layer 20 is formed on the inlet side surface 16a of the partition wall 16 by drying and firing, and the first catalyst region 22 is formed. Specifically, after the catalyst layer forming slurry is supplied to the inlet side chamber 12 of the substrate 11, it is sucked from the outlet side chamber 14. At this time, since the pores 18 of the partition wall 16 are filled with organic solid components, the slurry does not penetrate the inside of the partition wall 16 and adhere to the inlet side surface 16a. By performing drying and firing in this state, the first catalyst region 22 in which the catalyst layer 20 is formed on the inlet side surface 16a of the partition wall 16 is formed. In addition, in this firing treatment, the organic solid components are burned off, and the clogging of the pores 18 is eliminated. In addition, from the viewpoint of reliably burning off the organic solid components, the temperature of the firing treatment is preferably 400°C or more, more preferably 500°C or more, and more preferably 600°C or more. Similarly, in order to reliably burn off the organic solid components, the firing time is preferably about 2 to 4 hours. The conditions for the drying treatment are not particularly limited, and can be appropriately adjusted to conditions under which the catalyst layer forming slurry is appropriately dried.

[0107] 4. Formation of the Second Catalyst Region

[0108] In this process, first, the catalyst layer forming slurry is infiltrated from the outlet side 16b of the partition wall 16 to the inside of the partition wall 16, so that the catalyst layer forming slurry is attached to the wall 18a of the pore 18. Specifically, the catalyst layer forming slurry is supplied in the outlet chamber 14 of the substrate 11, and suction is performed from the inlet chamber 12. In this process, the area where the slurry penetrates is controlled in a manner that does not allow the slurry to penetrate into the inlet side 16a of the partition wall 16. In addition, the penetration of the slurry in this process is affected by many conditions such as the supply amount of the slurry, the viscosity of the slurry, the particle size of the components of the slurry (composite particles, additives, etc.), the porosity of the partition wall of the substrate, the pressure during suction, and the suction time. Therefore, it is preferred to conduct preliminary tests that appropriately change these conditions, and control the area where the slurry penetrates based on the knowledge obtained from the test. It should be noted that the slurry used in this process can be the same as the slurry used to form the first catalyst region 22, or a different slurry can be used.

[0109] Then, in this process, a drying process and a firing process are performed. Thus, a second catalyst region 24 is formed in the region infiltrated with the catalyst layer forming slurry. Next, the region in which the catalyst layer forming slurry is not infiltrated becomes a catalyst non-forming region 30 in which substantially no catalyst layer 20 is formed (the partition wall 18a of the pore 18 is exposed). It should be noted that the firing temperature in this process is the same as when the above-mentioned first catalyst region 22 is formed, preferably above 400°C, more preferably above 500°C, and more preferably above 600°C. In addition, the firing time is also preferably about 2 to 4 hours. Thus, the organic solid components remaining in the pores 18 can be reliably removed.

[0110] As described above, through the above-mentioned manufacturing method, a catalyst 10 for exhaust purification can be manufactured, which has a first catalyst region 22 on the inlet side surface 16a of the partition wall 16, a second catalyst region 24 in a specified area from the outlet side surface 16b of the partition wall 16 to the inlet side chamber 12, and a catalyst unformed region 30 between the first catalyst region 22 and the second catalyst region 24.

[0111] It should be noted that the above-mentioned manufacturing method is an example of a method for manufacturing the exhaust gas purification catalyst 10 involved in the present embodiment, and is not intended to limit the exhaust gas purification catalyst disclosed in the present application. That is, the manufacturing method of the exhaust gas purification catalyst 10 having the first catalyst region 22, the second catalyst region 24 and the catalyst non-formed region 30 is not limited to the above-mentioned method. For example, in the above-mentioned method, after the first catalyst region 22 is formed and the organic solid component is removed by firing treatment, the slurry for forming the second catalyst region 24 is given. However, the slurry for forming the second catalyst region 24 can also be given before the organic solid component is removed by firing treatment. In this case, by performing the subsequent firing treatment, "forming the first catalyst region 22", "removing the organic solid component" and "forming the second catalyst region 24" can be performed simultaneously, so that the manufacturing efficiency can be improved. In addition, if the first catalyst region 22 can be formed without the slurry penetrating into the partition wall, the exhaust gas purification catalyst disclosed in the present application can also be manufactured without filling the pores 18 with resin solid components. As an example, by adjusting the viscosity of the slurry, the particle size of the composite particles, the porosity of the partition wall, the pressure during suction, the suction time and other conditions, and filling and pre-filling of the specified components to replace the organic solid components, the first catalyst region 22 is formed without allowing the slurry to penetrate into the partition wall.

[0112] <Other methods of exhaust gas purification catalyst>

[0113] It should be noted that the exhaust gas purification catalyst disclosed herein is not limited to the above-mentioned embodiment. For example, in the above-mentioned embodiment, a stacked structure in which the first catalyst region 22, the catalyst layer unformed region 30 and the second catalyst region 24 are stacked in sequence is set in the entire region of the partition wall 16 in the extension direction X. However, the stacked structure having the characteristics of the technology disclosed in the present application can be set in a specified region on the upstream side of the extension direction of the partition wall, and is not limited to the above-mentioned embodiment. Specifically, in a conventional exhaust gas purification catalyst, exhaust gas with a high PM content is supplied on the upstream side of the extension direction, and there is a tendency for the PM content in the exhaust gas to decrease as it goes downstream. Therefore, as long as the above-mentioned stacked structure is set in the region on the upstream side of the extension direction of the partition wall, it is possible to fully take into account both the harmful gas purification performance and the pressure drop suppression performance at a high level. At this time, the region where the above-mentioned stacked structure is set is preferably a region of more than 40% of the total length of the substrate from the end of the exhaust gas inflow side of the substrate, more preferably a region of more than 50%, more preferably a region of more than 60%, and particularly preferably a region of more than 70%. It should be noted that the remaining portion may be provided with a catalyst region where the catalyst layer is formed over the entire region in the thickness direction, or may be provided with a region where the catalyst layer is not formed.

[0114] [Test example]

[0115] Hereinafter, test examples according to the present invention will be described, but the present invention is not intended to be limited to the test examples.

[0116] 1. Preparation of test specimens

[0117] (Example)

[0118] First, as a substrate, a cylindrical honeycomb substrate (made of cordierite, pixel 300 cpsi, partition wall thickness 8 mm, average pore diameter 20 μm, porosity 60%) having a substrate volume of 1.7 L and a length of 152.4 mm was prepared.

[0119] Then, resin beads (polyethylene) with an average particle size of 1 μm were dispersed in ion exchange water to prepare a slurry for filling fine pores. Next, the slurry for filling fine pores was supplied to the inlet chamber of the honeycomb substrate, and then the outlet chamber was sucked to make it penetrate into the fine pores of the partition walls. Next, a drying treatment (100° C., 30 minutes) was performed to obtain a honeycomb substrate in which the fine pores of the partition walls were filled with resin beads.

[0120] Then, a rhodium nitrate solution (Rh content: 0.2g), a powder (40g) of needle-shaped Al2O3 (γ-Al2O3) as a carrier, and an appropriate amount of ion exchange water were mixed, and the mixture was dried and then fired (500°C, 1 hour) to obtain composite particles (Rh-loaded-Al2O3 powder) carrying a catalyst. Next, the Rh-loaded-Al2O3 powder was mixed with an OSC material (cerium oxide-zirconia composite oxide) in a ratio of 1:1 to prepare a catalyst layer forming slurry. Next, after supplying 200ml of the catalyst layer forming slurry to the inlet chamber of the honeycomb substrate, the outlet chamber was sucked, thereby applying the catalyst layer forming slurry to the inlet side of the partition wall. Next, a drying treatment (100°C, 30 minutes) and a firing treatment (600°C, 120 minutes) were performed to burn out the resin beads and form a catalyst layer.

[0121] Then, after supplying 200 ml of the catalyst layer forming slurry into the outlet chamber of the honeycomb substrate, suction was applied to the inlet chamber, thereby allowing the slurry to penetrate from the outlet side of the partition wall into the inlet chamber. Next, a drying treatment (100° C., 30 minutes) and a firing treatment (500° C., 60 minutes) were performed to form a catalyst layer on the wall surface of the pores inside the partition wall.

[0122] (Comparative Example)

[0123] In the comparative example, after the catalyst layer forming slurry is supplied into the inlet chamber, the outlet chamber is sucked so that the slurry penetrates from the inlet side of the partition wall to the outlet chamber. Next, a drying treatment (100°C, 30 minutes) and a firing treatment (500°C, 60 minutes) are performed to form a catalyst layer on the wall surface of the pores inside the partition wall. It should be noted that in the comparative example, the same substrate and catalyst layer forming slurry as in the embodiment are used. In addition, the total amount of the catalyst layer forming slurry supplied from the inlet chamber in the comparative example is the same as that used in the embodiment (400 ml).

[0124] 2. Evaluation test

[0125] (1) Observation of the catalyst area

[0126] The partition wall of the substrate is cut out from each of the above-mentioned exhaust purification catalysts, and 10 sample pieces in which the partition wall is embedded in a resin are prepared. Then, a cross section of the partition wall is cut out from each sample piece, and a SEM observation image of the cross section is obtained (reflected electron image, observation magnification: 200 times). Then, the cross-sectional SEM observation image is automatically binarized (discriminant analysis method) to obtain a binary image in which the skeleton of the partition wall and the catalyst layer are extracted. An example of a cross-sectional SEM observation image taken in the embodiment is shown in Figure 5 An example of a cross-sectional SEM observation image taken in the comparative example is shown in Figure 6 .

[0127] Then, for each example, a determination was made according to "4. Determination operation of each region" to determine whether the first catalyst region, the second catalyst region, and the catalyst-free region were formed in the partition wall of the exhaust gas purification catalyst of the test object. As a result, in the example, the first catalyst region 22, the second catalyst region 24, and the catalyst layer-free region 30 were confirmed in the sample (refer to Figure 5 ) is 70% of the whole sample piece. Therefore, in the embodiment, it is judged that the first catalyst region 22, the second catalyst region 24 and the catalyst layer non-formed region 30 are provided on the partition wall 16 of the substrate. On the other hand, in the comparative example, only the sample piece (refer to Figure 6 ).

[0128] (2) Determination of pressure drop

[0129] The exhaust gas purification catalyst of each example is set in a soot generating device (DPG, manufactured by Cambustion), and the gas containing soot is supplied to the exhaust gas purification catalyst by burning light oil. Next, the pressure in the upstream piping and the pressure in the downstream piping of the exhaust gas purification catalyst are measured, and the pressure drop (kPa) is calculated based on these. It should be noted that in this test, the pressure drop immediately after the start of the test is taken as the "initial pressure drop", and the pressure drop when the PM accumulation amount in the catalyst reaches 1g / L is taken as the "PM accumulation pressure drop". The measurement results of the initial pressure drop are shown in Figure 7 The PM accumulation pressure drop measurement results are shown in Figure 8 .

[0130] In addition, in this test, the "PM capture rate" is also measured while measuring the above-mentioned pressure drop. Specifically, the number of PM particles discharged from the downstream side of the exhaust purification catalyst when the PM accumulation amount reaches 0.02g / L is measured, and the ratio to the number of PM particles discharged from the outlet of the soot generating device is calculated as the PM capture rate (%). The results are shown in Fig. 9 .

[0131] like Figure 7 As shown in the figure, by comparing the examples, it can be seen that the initial pressure drop of the example is higher than that of the comparative example. This is considered to be because the opening of the pores on the inlet side of the example is covered by the catalyst layer (first catalyst region). However, the PM accumulation pressure drop measured when the PM accumulation amount reaches 1g / L (refer to Figure 8), the pressure drop of the comparative example increased sharply, and the pressure drop values ​​between the embodiment and the comparative example were reversed. It is speculated that this result is caused by the PM accumulation inside the pores of the partition wall in the comparative example, which blocked the pores. On the other hand, it can be considered that in the embodiment, most of the PM is captured in the first catalyst area and the area where the catalyst layer is not formed, and there is almost no PM accumulation in the second catalyst area, so the increase in pressure drop due to the blockage of the pores does not occur.

[0132] In addition, if Fig. 9 As shown, the exhaust gas purifying catalyst of the embodiment shows a higher PM trapping rate than the comparative example. This result is presumably because in the exhaust gas purifying catalyst of the embodiment, the PM trapped in the first catalyst region remains in the inlet chamber, thereby ensuring a sufficient space for trapping PM.

[0133] (3) Determination of T50 catalyst activity

[0134] The exhaust gas purification catalyst of each example was installed in the exhaust system of the engine frame, and the exhaust gas was supplied while the temperature was raised from 50°C at a heating rate of 50°C / min. The concentration of harmful gases was measured in the piping on the upstream side and the piping on the downstream side of the exhaust gas purification catalyst. Then, the exhaust temperature when the concentration of harmful gases measured in the piping on the downstream side reached 50 mol% or less of the concentration of harmful gases measured in the piping on the upstream side was evaluated as the T50 catalyst activity (°C). The results are shown in Fig.10 The lower the temperature of the T50 catalyst activity, the lower the temperature at which the harmful gas components can be purified. Therefore, it can be said that the harmful gas purification performance is excellent. It should be noted that in this evaluation, CO, HC and NO were measured as the harmful gas concentrations. x The temperature at which the concentrations of these three harmful gases all reached 50 mol % or less was evaluated as T50 catalyst activity (° C.).

[0135] like Fig.10 As shown, it is confirmed that the catalyst T50 of the embodiment has a lower temperature activity and excellent harmful gas purification performance compared with the comparative example. This result is presumed to be because the catalyst for exhaust gas purification in the embodiment can prevent PM from accumulating in the second catalyst area, thus fully ensuring the contact frequency between the catalyst layer and the exhaust gas.

[0136] (4) Summary of evaluation test

[0137] Through the above evaluation tests, it was confirmed that the exhaust purification catalyst having a first catalyst region arranged on the inlet side of the partition wall, a second catalyst region arranged inside the partition wall from the outlet side of the partition wall to the inlet side chamber, and an area where the catalyst layer is not formed arranged between the first catalyst region and the second catalyst region can exert harmful gas purification performance, pressure drop suppression performance and PM capture performance at a high level.

[0138] The specific examples of the present invention have been described in detail above, but these are only examples and do not limit the scope of the claims. The technology described in the claims also includes various modifications and changes to the specific examples described above.

[0139] Industrial Applicability

[0140] According to the present invention, a wall-flow exhaust gas purification catalyst having both high-level harmful gas purification performance and pressure drop suppression performance can be provided. The exhaust gas purification catalyst can purify the exhaust gas discharged from the internal combustion engine, such as an automobile engine, without reducing the performance of the internal combustion engine.

Claims

1. A catalyst for exhaust gas purification, characterized in that: The exhaust gas purifying catalyst comprises a wall flow type substrate and a catalyst layer formed on the substrate. The substrate comprises: An inlet chamber having an opening only at the end on the exhaust gas inflow side; An outlet chamber having only an end opening on the exhaust gas outlet side; and a partition wall which separates the inlet chamber from the outlet chamber and is formed with a plurality of fine holes connecting the inlet chamber and the outlet chamber, A first catalyst region having the catalyst layer formed therein is provided on a surface of the partition wall in contact with the inlet chamber. A second catalyst region having the catalyst layer formed on the wall surface of the pore is provided in a predetermined region from the surface of the partition wall in contact with the outlet chamber toward the inlet chamber, A catalyst non-formed region in which the catalyst layer is substantially not formed is provided between the first catalyst region and the second catalyst region in the thickness direction of the partition wall. The catalyst non-formed region is a region provided from the inlet side of the partition wall toward the outlet side chamber.

2. The exhaust gas purification catalyst according to claim 1, characterized in that: The first catalyst region, the second catalyst region, and the catalyst-unformed region are respectively provided in regions that are 50% or more of the entire length of the substrate from the end of the substrate on the exhaust gas inlet side toward the end on the exhaust gas outlet side.

3. The exhaust gas purification catalyst according to claim 1 or 2, characterized in that: The size of the first catalyst region in the thickness direction of the partition wall is 3 μm or more and 50 μm or less.

4. The exhaust gas purification catalyst according to claim 1 or 2, characterized in that: The size of the catalyst non-formed region in the thickness direction of the partition wall is 10 μm or more and 100 μm or less.

5. The exhaust gas purification catalyst according to claim 1 or 2, characterized in that: The catalyst layer contains a three-way catalyst and a carrier for carrying the three-way catalyst. The three-way catalyst can oxidize CO and HC and convert NO x reduction.

6. The exhaust gas purification catalyst according to claim 5, characterized in that: The three-way catalyst contains at least one of Pt, Pd and Rh.

7. The exhaust gas purification catalyst according to claim 5, characterized in that: The content of the three-way catalyst per 1 L of the capacity of the substrate is 0.1 g / L or more and 7 g / L or less.

8. The exhaust gas purification catalyst according to claim 5, characterized in that: The carrier contains at least one of alumina, cerium oxide, zirconium oxide, silicon dioxide and titanium oxide.

9. The exhaust gas purification catalyst according to claim 5, characterized in that: The catalyst layer contains an OSC material having oxygen storage capacity.

10. The exhaust gas purification catalyst according to claim 9, characterized in that: The OSC material is a cerium oxide-zirconia composite oxide.

11. The exhaust gas purification catalyst according to claim 5, characterized in that: The catalyst layer contains any one or two or more of oxides, sulfates, carbonates, nitrates, and chlorides of alkaline earth metals, rare earth metals, alkali metals, and transition metals.

12. The exhaust gas purification catalyst according to claim 1 or 2, characterized in that: The amount of the catalyst layer formed per 1 L of the capacity of the substrate is 20 g / L or more and 180 g / L or less.

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