Exhaust gas purification catalyst

Abstract

This exhaust gas purification catalyst is provided with: a substrate (10) having a plurality of chambers (12) and partition walls (14) that partition the plurality of chambers (12); and a catalyst layer (20) that is provided on the surface of the partition walls (14). The catalyst layer (20) has a lower catalyst layer (22) and an upper catalyst layer (24). A lower-layer front section (A) containing Pd is provided upstream of the lower-layer catalyst layer (22), and a lower-layer rear section (B) containing Pd and / or Pt is provided downstream of the lower-layer catalyst layer (22). In addition, an upper layer front portion (C) containing Rh is provided on the upstream side of the upper layer catalyst layer (24), and an upper layer rear portion (D) containing Rh is provided on the downstream side of the upper layer catalyst layer (24). The CeO2 content of each of the lower-layer front portion (A), the lower-layer rear portion (B), the upper-layer front portion (C), and the upper-layer rear portion (D) is individually set. The carrier material contained in the upper catalyst layer has a volume-based average particle diameter (D50CD) of from 2 [mu] m to 5 [mu] m (inclusive) as determined by electron microscope observation. As a result, provided is an exhaust gas purification catalyst capable of exhibiting appropriate purification performance in accordance with the operating conditions of an internal combustion engine.

Description

Technical Field

[0001] The technology disclosed in the present invention relates to a catalyst for purifying exhaust gas. This international application claims priority based on Japanese Patent Application No. 2023-31270, filed on March 1, 2023, the entire contents of which are incorporated herein by reference. Background Art

[0002] Exhaust gas emitted from internal combustion engines such as automobile engines contains hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO x ) and other harmful components. Therefore, the exhaust system of the internal combustion engine is equipped with an exhaust gas purification catalyst for purifying harmful components. This exhaust gas purification catalyst has a substrate and a catalyst layer formed on the surface of the substrate. The catalyst layer contains, for example, a catalytic metal and an OSC material. The catalytic metal is a precious metal material that promotes the oxidation (or reduction) of the above-mentioned harmful components. In addition, the OSC material uses, for example, CeO2. The CeO2 stores oxygen during the supply of exhaust gas in a lean state (excess oxygen), and releases oxygen during the supply of exhaust gas in a rich state (lack of oxygen). As a result, even if the air-fuel ratio of the exhaust gas fluctuates, the exhaust gas can be stably purified.

[0003] In recent years, in the field of exhaust gas purification catalysts, proposals have been made to form multiple catalyst layers with different compositions on the surface of a substrate. For example, the exhaust gas purification catalyst described in Patent Document 1 has four catalyst layers consisting of an upstream lower coating layer, an upstream upper coating layer, a downstream lower coating layer, and a downstream upper coating layer. Moreover, in the exhaust gas purification catalyst described in Patent Document 1, the concentration of the catalytic metal (Pt, Pd, Rh) in each layer is different. This makes it possible to achieve a high level of both HC purification performance in a high-temperature environment and NO reduction performance in a low-temperature environment. x Purification capability. In addition, another example of an exhaust gas purification catalyst is disclosed in Patent Document 2. In the exhaust gas purification catalyst described in Patent Document 2, an OSC material is added to each of a plurality of catalyst layers.

[0004] Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 7061655 Patent Document 2: U.S. Patent Application Publication No. 2010 / 0104491 Summary of the Invention

[0005] Problems to be solved by the invention However, various elements of exhaust gas emitted from an internal combustion engine (such as temperature, flow rate, and air-fuel ratio) vary depending on the engine's operating conditions. For example, during warm-up operation immediately after startup, low-temperature, low-velocity exhaust gas is emitted. During high-speed operation, high-temperature, high-velocity exhaust gas is emitted. Furthermore, during normal operation, the exhaust gas flow rate and air-fuel ratio fluctuate due to factors such as fuel cutoff (F / C). Therefore, if exhaust gas purification catalysts are designed solely with a focus on specific conditions (such as warm-up operation), there is a risk of increased emissions of harmful components as the engine's operating conditions change.

[0006] The technology of the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an exhaust gas purification catalyst that can exhibit appropriate purification performance under various operating conditions.

[0007] Technical solutions to problems In order to solve the above-mentioned problems, the technology of the present invention provides an exhaust gas purification catalyst having the following structure.

[0008] The exhaust gas purification catalyst (1) of the present invention is arranged in the exhaust passage of an internal combustion engine to purify the exhaust gas discharged from the internal combustion engine. The exhaust gas purification catalyst includes: a substrate having a plurality of chambers and a partition wall separating the plurality of chambers; and a catalyst layer, which is a porous layer provided on the surface of the partition wall, having a catalytic metal and a supporting material for supporting the catalytic material. In addition, the catalyst layer has a stacked structure of at least two layers, with the side of the surface close to the partition wall being the lower catalyst layer and the side of the surface relatively far from the partition wall being the upper catalyst layer, and as the supporting material, contains at least OSC material, and the OSC material contains CeO2. In addition, the lower catalyst layer has: a portion extending from the upstream end of the substrate to the downstream side in the exhaust gas flow direction, and a CeO2 content A CeO2 0g / L~15g / L, and containing Pd as a catalytic metal lower front part A; and in the exhaust gas flow direction from the downstream side of the substrate end to the upstream side, CeO2 content B CeO2 The lower rear portion B contains at least one of Pd and Pt as a catalytic metal and has a CeO2 content of 20 g / L to 63 g / L. The upper catalyst layer has a CeO2 content of C extending from the upstream end of the substrate to the downstream in the exhaust gas flow direction. CeO2 1g / L~7g / L, and containing Rh as the catalytic metal upper front portion C; and in the exhaust gas flow direction from the downstream side of the substrate end portion to the upstream side, CeO2 content D CeO2 The upper rear portion D contains Rh as a catalytic metal and has a volume-based average particle size D50 of the support material contained in the upper catalyst layer of the exhaust gas purifying catalyst of the present invention, as observed by an electron microscope. CDIt is not less than 2μm and not more than 5μm.

[0009] As described above, the exhaust gas purification catalyst of the present invention comprises four catalyst layers (lower front layer A, lower rear layer B, upper front layer C, and upper rear layer D) differing in catalytic metal type and CeO₂ content. This allows for optimal purification performance under various operating conditions. This is described in detail below.

[0010] First, the lower front part A is an area that properly purifies the exhaust gas during the preheating operation just after the operation starts. Specifically, at the start of operation, most of the catalytic metal is oxidized and the catalytic activity decreases. Moreover, at the start of preheating operation, as the exhaust gas temperature rises, oxygen gradually dissociates from the catalytic metal, and the purification performance improves (recovers). On the other hand, at the start of operation, the OSC material (CeO2) also absorbs a large amount of oxygen. Therefore, when there is a large amount of CeO2 near the catalytic metal, the recovery of the purification performance may be hindered due to the supply of oxygen from CeO2. Here, the flow rate of the exhaust gas during the preheating operation is very slow, so it is easy to penetrate into the upstream side of the lower catalyst layer (the lower front part A). Taking this into consideration, in the exhaust gas purification catalyst of the present invention, the CeO2 content A of the lower front part A is set to 0.1%. CeO2 The concentration is set to 15 g / L or less. This facilitates recovery of purification performance during warm-up operation. Furthermore, in the exhaust gas purification catalyst of the present invention, Pd is used as the catalytic metal in the lower front portion A. Pd exhibits superior catalytic activity in an oxidized state to that of other catalytic metals. With this configuration, the lower front portion A can reduce emissions of harmful components during warm-up operation.

[0011] Secondly, the lower rear portion B is an area that responds to long-term exhaust gas air-fuel ratio fluctuations through air-fuel ratio control. Specifically, the lower rear portion B is located on the downstream side of the lower catalyst layer, so it is supplied with exhaust gas of various conditions. Therefore, when there is a large amount of CeO2 in the lower rear portion B, it is easy to respond to fluctuations in the air-fuel ratio that may occur during the operation of the internal combustion engine. Based on this perspective, the CeO2 content B in the lower rear portion B is CeO2 Set to 20g / L or more. This can reduce the emission of harmful components caused by fluctuations in the air-fuel ratio. In addition, in order to ensure that the amount of other components added to form the catalyst layer is above a certain level, the CeO2 content B in the lower rear part B is CeO2 The upper limit is set to 63 g / L or less. Furthermore, the lower rear portion B contains at least one of Pd and Pt as a catalytic metal. As described above, Pd can demonstrate adequate purification performance even during warm-up operation. Furthermore, Pt effectively purifies components generated in other areas (catalyst endogenous substances). Because exhaust gas from various conditions may be supplied to the lower rear portion B, it is preferable to contain at least one of these catalytic metals.

[0012] Again, the upper front C is intended to promote NO x First, the water-gas shift reaction shown in formula (1) occurs inside the exhaust gas purification catalyst to generate hydrogen (H2). Then, this hydrogen is converted into NO (shown in formula (2)). x It is used as a reducing agent in the purification reaction. That is, in order to reduce NO x For purification, the reactions shown in the following formulas (1) and (2) must occur appropriately.

[0013] CO + H2O → CO2 + H2 (1) NO x +H2→N2+H2O(2) Among them, the upper front portion C located on the upstream side of the upper catalyst layer is the first area to come into contact with the exhaust gas. Therefore, if the water-gas shift reaction occurs properly in the upper front portion C, NOx is likely to occur in other areas. x Purification reaction. Based on this perspective, the upper front C contains Rh, which has excellent performance in promoting the water-gas shift reaction. However, the activity of Rh in an oxidized state is significantly reduced, so it may not be able to fully promote the water-gas shift reaction during the warm-up operation. Therefore, in the exhaust gas purification catalyst of the present invention, the CeO2 content C of the upper front C is CeO2 This is set to 7 g / L or less. This can promote the recovery of the catalytic activity of Rh during the warm-up operation, and thus can appropriately reduce NO x However, if the CeO2 content of the upper front C CeO2 If the catalytic activity is too low, it will not be able to respond to the fluctuation of the air-fuel ratio. Therefore, even if the catalytic activity is fully restored, it may not be able to reduce the NO during the warm-up operation. x Therefore, in the technology of the present invention, the CeO2 content C of the upper front C is CeO2 The lower limit of is set to 1 g / L or more.

[0014] Secondly, the upper rear portion D is an area for purifying exhaust gas emitted during high-speed operation. Specifically, the flow rate of exhaust gas during high-speed operation is very fast, so it hardly penetrates into the lower catalyst layer, but mainly penetrates into the upper catalyst layer (especially the upper rear portion D). In this case, the contact opportunity between the exhaust gas and the catalyst layer is reduced, so there is a risk that the harmful components cannot be fully purified. In this regard, the upper rear portion D contains Rh as a catalytic metal. Rh has excellent ternary performance, so it can well purify exhaust gas during high-speed operation with a fast flow rate. However, Rh may be dissolved in CeO2 and significantly reduce the catalytic performance. In particular, the exhaust gas temperature during high-speed operation is very high, which promotes the solid dissolution of Rh and CeO2. Therefore, in the exhaust gas purification catalyst of the present invention, the CeO2 content D of the upper rear portion D is increased.CeO2 Set to 8g / L or less. This can reduce the amount of CeO2 around Rh and inhibit the solid solution of Rh and CeO2. On the other hand, if the CeO2 content D in the upper rear part D is CeO2 If it is too low, it will not be able to cope with the rapid fluctuation of the exhaust gas air-fuel ratio in a short period, and the emission of harmful components during high-speed operation may increase. Therefore, in the technology of the present invention, the CeO2 content D of the upper rear part D is increased. CeO2 The lower limit of is set to 2 g / L or more.

[0015] Furthermore, in the exhaust gas purification catalyst of the present invention, the average particle size D50 of the supporting material of the upper catalyst layer is CD It has been confirmed through experiments that when the upper catalyst layer is formed using such a fine supporting material, NO from the exhaust gas purification catalyst can be reduced. x It can be inferred that the NO x The improvement in purification performance is achieved by the following factors, but this does not limit the technology of the present invention. First, when the supporting material of the upper catalyst layer is miniaturized, the upper catalyst layer becomes denser. This can inhibit the intrusion of moisture in the exhaust gas into the catalyst layer. As a result, it can be inferred that the internal temperature of the catalyst layer is likely to increase, thereby enabling the catalytic metal to effectively exert its NOx removal function. x On the other hand, if the average particle size D50 of the supporting material of the upper catalyst layer CD If the particle size is too small, the upper catalyst layer will become too dense, resulting in the exhaust gas being unable to be supplied to the lower catalyst layer, and the exhaust gas purification performance may be reduced. Based on this perspective, in the exhaust gas purification catalyst of the present invention, the average particle size D50 of the supporting material of the upper catalyst layer is CD Set to 2 μm or more.

[0016] In the exhaust gas purifying catalyst (2) of the present invention, the supporting material in the exhaust gas purifying catalyst (1) includes an OSC material and Al2O3. This can appropriately prevent sintering of the catalytic metal and form a catalyst layer having an appropriate pore structure.

[0017] In the exhaust gas purifying catalyst (3) of the present invention, in the exhaust gas purifying catalyst (1) or (2), the volume-based average particle size of the supporting material contained in the lower catalyst layer based on electron microscope observation is set to D50 AB When the average particle size D50 CD and average particle size D50 AB The ratio of (D50 CD / D50 AB ) is 0.4 or more and 0.9 or less. Thus, NO from the exhaust gas purification catalyst can be further reduced. xEmissions.

[0018] In the exhaust gas purification catalyst (4) of the present invention, the average particle size D50 of the supporting material contained in the lower catalyst layer in the exhaust gas purification catalyst (3) is AB The particle size is 2.5 μm or more and 12.5 μm or less. This improves the exhaust gas diffusibility in the lower catalyst layer, thereby achieving better exhaust gas purification performance.

[0019] In the exhaust gas purifying catalyst (5) of the present invention, the average particle size D50 of the supporting material contained in the upper front portion A of any one of the exhaust gas purifying catalysts (1) to (4) is as large as 0.05 mm / s and as large as 0.06 mm / s, respectively, based on electron microscope observation. A By densifying the lower front portion A in addition to the upper catalyst layer, it is possible to more reliably prevent moisture from entering the catalyst layer.

[0020] In the exhaust gas purifying catalyst (6) of the present invention, the volume-based average particle size of the supporting material contained in the lower front portion A in the exhaust gas purifying catalyst (5) is set to D50 based on electron microscope observation. A The average particle size of the supporting material contained in the lower rear portion B based on electron microscope observation is set as D50 B When the average particle size D50 A and average particle size D50 B The ratio of (D50 A / D50 B ) is 0.4 or more and 0.9 or less. Thus, NO from the exhaust gas purification catalyst can be further reduced. x Emissions.

[0021] In the exhaust gas purification catalyst (7) of the present invention, the OSC material in any of the exhaust gas purification catalysts (1) to (6) is a CeO2-ZrO2 composite oxide. This can suppress sintering of CeO2, thereby exhibiting a better oxygen storage capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a diagram schematically showing an exhaust system in which an exhaust gas purifying catalyst is arranged.

[0023] Figure 2 It is a perspective view schematically showing an exhaust gas-purifying catalyst according to one embodiment.

[0024] Figure 3 This is a diagram schematically showing a cross section of an exhaust gas-purifying catalyst according to an embodiment, taken along the cylinder axis.

[0025] Figure 4 It will Figure 3 A partially enlarged cross-sectional view of the partition wall surface of the exhaust gas purifying catalyst shown.

[0026] Figure 5 3 is a graph showing the measurement results of the 50% HC purification time in the first test.

[0027] Figure 6 Yes means NO in the second test x A graph showing the results of purification rate measurements.

[0028] Figure 7 3 is a graph showing the measurement results of the 50% HC purification temperature in the third test.

[0029] Figure 8 Yes means NO in the fourth test x Graph showing emission measurement results. DETAILED DESCRIPTION

[0030] The following describes the implementation of the technology of the present invention. Among them, matters required for the implementation of the present invention other than those specifically mentioned in this specification can be understood as design matters based on the existing technology in this field by those skilled in the art. That is, the technology of the present invention can be implemented according to the contents of this specification and the technical common sense in this field. In addition, in the following drawings, components and parts that play the same role are marked with the same symbols. The dimensional relationships (length, width, thickness, etc.) in each figure do not always reflect the actual dimensional relationships. In addition, the expression "A~B" (A and B are arbitrary numerical values) indicating the range in this specification includes not only the meaning of above A and below B, but also the meaning of "preferably greater than A" and "preferably less than B".

[0031] [Exhaust system of internal combustion engine] First, the use of the exhaust gas purification catalyst of the present invention will be described. Figure 1 It is a diagram schematically showing an exhaust system in which an exhaust gas purifying catalyst is arranged.

[0032] Figure 1 The internal combustion engine 2 is a mechanism that generates kinetic energy by burning a mixed gas containing oxygen and fuel gas. The exhaust gas discharged from the internal combustion engine 2 contains gaseous harmful components (NO x, CO, HC), and particulate matter (PM). Exhaust gas is then discharged into an exhaust system 5 consisting of an exhaust manifold 3 and an exhaust pipe 4. Exhaust pipe 4 is also equipped with a sensor 6. This sensor 6 detects information related to the composition and temperature of the exhaust gas. Sensor 6 is connected to an engine control unit (ECU) 7. The information detected by sensor 6 is transmitted to ECU 7. ECU 7 appropriately refers to the detection results of sensor 6 when controlling the operation of the internal combustion engine 2.

[0033] Furthermore, the exhaust gas purification catalyst of the present invention is arranged in the exhaust system 5 ( Figure 1 Specifically, Figure 1 The exhaust pipe 4 shown has a first purification member 8 and a second purification member 9. The exhaust gas purification catalyst of the present invention can be used in at least one of the first purification member 8 and the second purification member 9. The exhaust gas purification catalyst purifies harmful components in the exhaust gas flowing through the exhaust pipe 4.

[0034] [Exhaust gas purification catalyst] Next, one embodiment of the exhaust gas-purifying catalyst of the present invention will be described. Figure 2 It is a perspective view schematically showing the exhaust gas-purifying catalyst according to the present embodiment. Figure 3 It is a diagram schematically showing a cross section of the exhaust gas-purifying catalyst according to the present embodiment, taken along the cylinder axis direction. Figure 4 It will Figure 3 A partially enlarged cross-sectional view of the partition wall surface of the exhaust gas purifying catalyst shown.

[0035] In the figures, the symbol X indicates the "cylinder axis direction" and the symbol Y indicates the "thickness direction of the substrate partition walls." In this specification, the direction in which exhaust gas flows is referred to as the "exhaust gas flow direction F." Furthermore, the side relatively close to the internal combustion engine is referred to as the "upstream side (of the exhaust gas flow direction F)," and the side farther from the internal combustion engine is referred to as the "downstream side (of the exhaust gas flow direction F)." In this specification, the upstream region of the exhaust gas-purifying catalyst 1 is referred to as the "front portion," and the downstream region is referred to as the "rear portion."

[0036] like Figures 2 to 4 As shown, the exhaust gas purifying catalyst 1 of the present embodiment includes a substrate 10 and a catalyst layer 20. Each configuration will be described below.

[0037] 1. Substrate The substrate 10 is a member constituting the skeleton of the exhaust gas purifying catalyst 1. Figure 2 As shown, the substrate 10 of this embodiment has a cylindrical shape extending along the cylindrical axis direction X. However, the shape of the substrate is not limited to Figure 2The shape shown in FIG. 1 is not limited to the shape shown in FIG. For example, the outer shape of the substrate may be an elliptical cylinder, a prismatic cylinder, or the like. Furthermore, the substrate 10 may be made of any conventionally known material without particular limitation. For example, the substrate 10 may be made of a ceramic such as cordierite, aluminum titanate, or silicon carbide. Alternatively, the substrate 10 may be made of an alloy such as stainless steel (SUS), an Fe-Cr-Al alloy, or a Ni-Cr-Al alloy.

[0038] In addition, if Figure 3 As shown, the substrate 10 is a DC type substrate. That is, the substrate 10 has a plurality of chambers 12 and partition walls 14 that separate the plurality of chambers 12. The chamber 12 is a gas flow channel that passes through the substrate 10 in the cylindrical axial direction X. The exhaust gas supplied to the exhaust gas purification catalyst 1 is discharged to the outside through the chamber 12. The shape, size, and number of the chambers 12 are not particularly limited. The composition of these chambers 12 can be appropriately changed in consideration of the flow rate and composition of the exhaust gas. For example, Figure 2 As shown, the front shape of the chamber 12 in this embodiment (the shape viewed along the cylindrical axis direction X) is a square. However, the front shape of the chamber may be a quadrilateral such as a parallelogram, rectangle, trapezoid, other polygons (e.g., triangle, hexagon, octagon), or a circle, among other geometric shapes.

[0039] On the other hand, the partition wall 14 is a dense component that separates two adjacent chambers 12. The partition wall 14 extends along the cylindrical axis direction X from the end 10a on the upstream side of the substrate 10 to the end 10b on the downstream side. Therefore, the exhaust gas flowing into the chamber 12 flows in a straight line along the cylindrical axis direction X. That is, in the exhaust gas purification catalyst 1 of this embodiment, the cylindrical axis direction X of the substrate 10 and the exhaust gas flow direction F are basically the same direction. In addition, the thickness of the partition wall 14 is not particularly limited, and is preferably 10 μm or more, more preferably 20 μm or more. In this way, the mechanical strength of the substrate 10 can be fully ensured. On the other hand, the thickness of the partition wall 14 is preferably 500 μm or less, more preferably 100 μm or less. In this way, the pore size of the chamber 12 can be fully ensured, so the increase in pressure loss caused by clogging of the chamber 12 can be suppressed.

[0040] In addition, the total length and capacity of the substrate 10 are not particularly limited and are preferably changed appropriately according to the performance of the internal combustion engine 2 and the size of the exhaust pipe 6. For example, the total length L of the substrate 10 in the cylinder axis direction X (see Figure 4 ) can be set within a range of 10 mm to 500 mm (preferably 50 mm to 300 mm). Furthermore, the volume of substrate 10 can be set within a range of, for example, 0.1 L to 10 L (preferably 1 L to 5 L). The term "substrate volume" used herein refers to the total volume of the space within substrate 10 (typically, chamber 12).

[0041] 2. Catalyst layer (1) Composition of the catalyst layer The catalyst layer 20 is a porous layer provided on the surface of the partition wall 14 of the substrate 10. The catalyst layer 20 of the present embodiment includes a catalytic metal and a supporting material.

[0042] (1-1) Catalytic Metal Catalytic metals are used to promote the x ) oxidized (or reduced) metal materials. Specifically, hydrocarbons (HC) or carbon monoxide (CO) come into contact with the catalytic metal, which promotes the oxidation reaction. HC and CO are thus converted into water (H2O) and carbon dioxide (CO2). On the other hand, nitrogen oxides (NO x ) contacts with the catalytic metal and promotes the reduction reaction. x Converted into water (H2O) and nitrogen (N2). Specific examples of catalytic metals include precious metal catalysts such as gold (Au), silver (Ag), palladium (Pd), platinum (Pt), rhodium (Rh), and ruthenium (Ru). Furthermore, in the exhaust gas-purifying catalyst 1 of this embodiment, the four regions (lower layer front portion A, lower layer rear portion B, upper layer front portion C, and upper layer rear portion D) that constitute the catalyst layer 20 contain different types of catalytic metals. Details of the catalytic metals in each region are described later.

[0043] The amount of catalytic metal present in the exhaust gas-purifying catalyst 1 is preferably 1.0 g / L or greater, more preferably 1.5 g / L or greater, and particularly preferably 2.0 g / L or greater. This allows for enhanced exhaust gas purification performance. On the other hand, considering material costs, the total amount of catalytic metal is preferably 8 g / L or less, more preferably 7 g / L or less, and particularly preferably 6 g / L or less. The term "catalytic metal amount" herein refers to the total amount of catalytic metal when the volume of the substrate 10 is normalized to 1 L.

[0044] (1-2) Carrying materials The supporting material is a material that supports the catalytic material. By supporting the catalytic metal on the supporting material, sintering of the catalytic metal can be suppressed. The exhaust gas-purifying catalyst 1 of this embodiment includes at least an OSC material as the supporting material.

[0045] OSC materials are metal oxides containing ceria (CeO2). This carrier material containing the OSC material has oxygen storage properties, which not only inhibits the sintering of the catalytic metal but also helps stabilize exhaust gas purification performance. Specifically, CeO2 absorbs oxygen when supplied with exhaust gas in a lean state. On the other hand, CeO2 releases oxygen when supplied with exhaust gas in a rich state. This allows for stable exhaust gas purification performance even when the air-fuel ratio of the exhaust gas fluctuates. Furthermore, the OSC material can also contain components other than CeO2. For example, the OSC material can be a CeO2-ZrO2 composite oxide. CeO2-ZrO2 composite oxides can inhibit the sintering of CeO2 in high-temperature environments, thereby stably exhibiting a high oxygen storage capacity. When a CeO2-ZrO2 composite oxide is used as an OSC material, the CeO2 content relative to the total weight of the composite oxide (100 wt%) is preferably 10 wt% or greater, more preferably 15 wt% or greater, even more preferably 17 wt% or greater, and particularly preferably 20 wt% or greater. This ensures sufficient CeO2 to fully utilize its oxygen storage capacity. Meanwhile, the CeO2 content relative to the total weight of the CeO2-ZrO2 composite oxide is preferably 70 wt% or less, more preferably 60 wt% or less, even more preferably 50 wt% or less, and particularly preferably 40 wt% or less. This ensures sufficient ZrO2 to inhibit CeO2 sintering.

[0046] Furthermore, in the exhaust gas-purifying catalyst 1 of this embodiment, the CeO2 content varies in each of the four regions (lower layer front portion A, lower layer rear portion B, upper layer front portion C, and upper layer rear portion D) that comprise the catalyst layer 20. Details of the CeO2 content in each region will be described later.

[0047] In addition, the catalyst layer 20 may also contain a supporting material other than the OSC material. Preferred examples of such supporting materials include heat-resistant materials specified in JIS R2001 (alumina (Al2O3), zirconium oxide (ZrO2), silicon dioxide (SiO2), magnesium oxide (MgO), calcium oxide (CaO), etc.). By using a supporting material containing these heat-resistant materials, the sintering of the catalytic metal can be better suppressed. Among them, when the total weight of the catalyst layer 20 is set to 100wt%, the content of the supporting material other than the OSC material is preferably 10wt% or more (more preferably 15wt% or more, further preferably 20wt% or more, and particularly preferably 30wt% or more). As a result, the sintering of the catalytic metal can be better suppressed. On the other hand, from the perspective of ensuring the content of the catalytic metal and the OSC material, the content of the supporting material other than the OSC material is preferably 95wt% or less, more preferably 92.5wt% or less, and particularly preferably 90wt% or less.

[0048] Furthermore, in the exhaust gas-purifying catalyst 1 of this embodiment, the average particle size of the supporting material in each of the four regions (lower layer front portion A, lower layer rear portion B, upper layer front portion C, and upper layer rear portion D) constituting the catalyst layer 20 also differs. Details of the average particle size of the supporting material in each region will be described later.

[0049] (1-3) Other additives In addition, the catalyst layer 20 may also contain other additives as long as they do not significantly hinder the technical effects of the present invention. As an example of such additives, NO x Adsorbents, stabilizers, HC adsorbents, etc. Furthermore, the catalyst layer 20 may contain trace components derived from raw materials or manufacturing processes. For example, the catalyst layer 20 may contain one or more compounds (oxides, sulfates, carbonates, nitrates, chlorides) containing alkaline earth metals (Be, Mg, Ca, Ba, etc.), rare earth elements (Y, La, Ce, etc.), alkali metals (Li, Na, K, etc.), transition metals (Mn, Fe, Co, Ni, etc.), and the like.

[0050] (2) Structure of the catalyst layer The structure of the catalyst layer 20 is described below. Figure 4 As shown, the catalyst layer 20 of this embodiment includes a lower catalyst layer 22 and an upper catalyst layer 24 .

[0051] The lower catalyst layer 22 is a catalyst layer provided on a surface side relatively close to the partition wall 14 . Figure 4 The lower catalyst layer 22 shown is disposed on the surface of the partition wall 14. The phrase "disposed on the surface of the partition wall" in this specification means that the majority of the lower catalyst layer 22 is present on the surface of the partition wall 14, and does not exclude the possibility that a portion of the lower catalyst layer 22 may intrude into the interior of the partition wall 14. Typically, if analysis based on a cross-sectional SEM image shows that more than 80% (typically more than 90%, for example, more than 95%) of the catalyst layer 20 is attached to the surface of the partition wall 14, the lower catalyst layer 22 is considered to be "disposed on the surface of the partition wall 14."

[0052] On the other hand, the upper catalyst layer 24 is a catalyst layer provided on the surface side relatively far from the partition wall 14 . Figure 4The upper catalyst layer 24 shown is disposed on the surface of the lower catalyst layer 22. The phrase "disposed on the surface of the lower catalyst layer 22" in this specification means that the majority of the upper catalyst layer 24 is attached to the surface of the lower catalyst layer 22, and does not exclude the possibility that a portion of the upper catalyst layer 24 intrudes into the interior of the lower catalyst layer 22. Typically, if analysis based on a cross-sectional SEM image shows that more than 50% (typically more than 60%, for example, more than 70%) of the upper catalyst layer 24 is attached to the surface of the lower catalyst layer 22, then "the upper catalyst layer 24 is disposed on the surface of the lower catalyst layer 22."

[0053] Furthermore, the catalyst layer 20 of this embodiment has four regions, consisting of a lower front portion A, a lower rear portion B, an upper front portion C, and an upper rear portion D. Furthermore, in this embodiment, each region of the catalyst layer 20 differs in the type of catalytic metal, the CeO2 content, and the particle size of the supporting material. This is described in detail below.

[0054] (2-1) Structure and composition of each region First, the structure and composition (particularly the type of catalytic metal and CeO 2 content) of each region from the lower front portion A to the upper rear portion D will be described below.

[0055] (a) Lower front part A The lower catalyst layer 22 has a structure extending from the upstream end 10a of the substrate 10 to the downstream side ( Figure 4 The lower front portion A extends from the right side of the lower catalyst layer 22 (see Figure 1). In other words, the lower front portion A is the upstream region of the lower catalyst layer 22. This lower front portion A is suitable for purifying the low-velocity exhaust gas supplied during the warm-up operation. Specifically, the exhaust gas flow rate during the warm-up operation is very slow, so it penetrates from the upstream side of the exhaust gas-purifying catalyst 1 into the interior of the catalyst layer 20 and reaches the lower front portion A.

[0056] In the exhaust gas purifying catalyst 1 of the present embodiment, the CeO2 content A in the lower front portion A is CeO2 It is set to be less than 15g / L. As a result, the purification performance during the warm-up operation is easily restored. Specifically, at the start of operation, most of the catalytic metal is oxidized and the catalytic activity is reduced. Moreover, at the start of the warm-up operation, as the exhaust gas temperature rises, oxygen gradually dissociates from the catalytic metal and the purification performance improves (recovers). On the other hand, at the start of operation, the OSC material (CeO2) also absorbs a large amount of oxygen. Therefore, when there is a large amount of CeO2 near the catalytic metal, the oxygen supply from CeO2 may hinder the recovery of the purification performance. In this regard, in the lower front part A of the present embodiment, the CeO2 content A CeO2By limiting the content of CeO2 to a certain value or less, the oxygen supply from CeO2 during the preheating operation can be suppressed. This can promote the dissociation of oxygen from the catalytic metal and restore the purification performance as soon as possible. In addition, from the perspective of further improving the preheating performance, the CeO2 content A in the lower front part A is CeO2 It is preferably 14 g / L or less, more preferably 13 g / L or less, and particularly preferably 12 g / L or less.

[0057] In addition, from the perspective of promoting the recovery of purification performance during the warm-up operation, the lower front portion A may not contain CeO2 (A CeO2 =0 g / L). On the other hand, the CeO2 content A in the lower front portion A CeO2 The lower limit of is preferably 2 g / L or more, more preferably 4 g / L or more, and particularly preferably 6 g / L or more. By giving a certain oxygen storage capacity to the lower front portion A, it is possible to construct an exhaust gas purification catalyst that can easily cope with fluctuations in the air-fuel ratio of the exhaust gas. In addition, experiments have confirmed that the CeO2 content A in the lower front portion A is CeO2 When the amount of CeO2 is small, the recovery hindrance caused by CeO2 will hardly occur.

[0058] Here, the CeO2 content A of the lower front portion A in this specification is CeO2 " refers to the volume V of the substrate in the area where the lower front part A is located A Assuming 1 L of liquid, the weight of CeO2 contained in the lower front portion A (g / L). The CeO2 content (g / L) of each region of the catalyst layer 20 can be measured using inductively coupled plasma analysis (ICP) and electron probe microanalyzer (EPMA). The CeO2 content A of the lower front portion A is given below. CeO2 and CeO2 content C in the upper front part CeO2 Taking the measurement steps of as an example, the measurement steps of "CeO2 content (g / L) in each area" are explained.

[0059] In this measurement, the upstream region containing only the lower front portion A and the upper front portion C is first removed from the exhaust gas purification catalyst 1. Next, the powder after crushing the upstream region is subjected to ICP analysis, thereby measuring the presence ratio (%) of the Ce element and the reference element in the upstream region. The type of "reference element" here is not particularly limited, and any element other than the Ce element can be appropriately selected. For example, when using a CeO2-ZrO2 composite oxide as the OSC material, the Zr element can be selected. In addition, when using Al2O3 as the supporting material, the Al element can be selected. The following is an example of the case where the Al element is selected.

[0060] The Ce and Al abundance ratios measured using ICP are converted to oxides to calculate the CeO2 and Al2O3 ratios. Next, the substrate 10 without the catalyst layer 20 is subjected to the same treatment to analyze the major elements of the substrate 10. The components originating from the substrate 10 are then subtracted from the components in the upstream region. This yields the CeO2 and Al2O3 ratios of the upstream region of the catalyst layer 20 after removing the components from the substrate 10. The CeO2 weight M (g) of the lower front portion A and the upper front portion C is then multiplied by the CeO2 ratio of the catalyst layer 20. Furthermore, the total Al2O3 weight N (g) of the lower front portion A and the upper front portion C can be calculated using the same procedure.

[0061] Next, EPMA analysis is performed on the cross section of the upstream region along the cylinder axis to obtain an elemental distribution map of the upstream region. The lower front portion A on the elemental distribution map is then analyzed using a specified image analysis software (such as Image-J) to calculate the ratio of the Al content to the Ce content in the lower front portion A (Ce A / Al A Then the upper front C is analyzed and the ratio of Al to Ce in the upper front C is calculated (Ce C / Al C ). The following will calculate the result Ce A / Al A Denoted as "a", Ce C / Al C Denoted as "c".

[0062] Next, let the total amount of Al2O3 and CeO2 in the lower front portion A be "X," and let the total amount of Al2O3 and CeO2 in the upper front portion C be "Y." In this case, the "total CeO2 weight M of the lower front portion A and the upper front portion C" and the "total Al2O3 weight N of the lower front portion A and the upper front portion C" measured by ICP are expressed by the following equations (4) and (5).

[0063] X + Y = M + N (4) aX+cY=M(5) Furthermore, since M, N, a, and c in the above-mentioned formulas (4) and (5) have been measured, by solving the simultaneous equations, the total amount X of the amount of Al2O3 and the amount of CeO2 in the lower front portion A, and the total amount Y of the amount of Al2O3 and the amount of CeO2 in the upper front portion C can be calculated. Then, by multiplying X by a, the CeO2 weight (g) of the lower front portion A can be calculated. On the other hand, by multiplying Y by c, the CeO2 weight (g) of the upper front portion C can be calculated. Then, by dividing each calculation result by the volume (L) of the upstream measurement sample, the "CeO2 content A of the lower front portion A" can be calculated. CeO2 (g / L)" and "CeO2 content of the upper front C CeO2 (g / L)".

[0064] In addition, the lower front portion A contains palladium (Pd) as a catalytic metal. Pd has a superior catalytic activity in an oxidized state compared to other catalytic metals. Therefore, even before the recovery (oxygen dissociation) achieved by the warm-up operation is fully completed, the lower front portion A containing Pd can still exert a certain exhaust gas purification performance. As a result, the emission of harmful components during the warm-up operation can be further reduced. The Pd content of the lower front portion A is preferably 0.5 g / L or more, more preferably 1.0 g / L or more, further preferably 2 g / L or more, and particularly preferably 2.8 g / L or more. As a result, the emission of harmful components during the warm-up operation can be further reduced. On the other hand, considering the balance between purification performance and material cost, the Pd content of the lower front portion A is preferably 10 g / L or less, more preferably 8 g / L or less, further preferably 6 g / L or less, and particularly preferably 5.3 g / L or less.

[0065] Among them, the "content of catalytic metal in each region (g / L)" in this specification is also measured by ICP and EPMA in the same manner as the above-mentioned "content of CeO2 in each region (g)". The following takes the measurement procedure of the Pd content in the lower front part A as an example to illustrate the measurement procedure of the "content of catalytic metal in each region (g / L)". In this measurement, the upstream side region containing only the lower front part A and the upper front part C is first taken out from the exhaust gas purification catalyst 1 to prepare an upstream measurement sample. Then, ICP analysis is performed on the powder after crushing the upstream measurement sample to measure the total weight (g) of Pd in ​​the upstream side region. EPMA analysis is then performed on the cross section of the upstream side region along the cylinder axis direction to obtain an element distribution map of the upstream side region. Then, based on this element distribution map, the amount of Pd present in the lower front part A is calculated. A The amount of Pd in ​​the upstream area A＋C The ratio of Pd A / Pd A＋C). The element distribution map can be analyzed using conventional image analysis software (such as Image-J). Then, the "total weight (g) of Pd in ​​the upstream region obtained by ICP is multiplied by the "existence ratio (Pd) obtained from the element distribution map". A / Pd A＋C )”, thereby calculating the weight (g) of Pd in ​​the lower layer front portion A. Then, by dividing the calculated result by the capacity (L) of the substrate 10, the “Pd content (g / L) in the lower layer front portion A” can be calculated.

[0066] Furthermore, the lower front portion A may contain catalytic metals other than Pd. However, when the total amount of catalytic metal in the lower front portion A is set to 100 wt%, the Pd content in the lower front portion A is preferably 80 wt% or greater (preferably 85 wt% or greater, more preferably 90 wt% or greater, and particularly preferably 95 wt% or greater). This ensures adequate exhaust gas purification performance during warm-up operation.

[0067] Furthermore, the lower front portion A preferably contains the highest catalytic metal content relative to the overall catalyst layer 20. Specifically, the catalytic metal content of the lower front portion A relative to the overall catalytic metal content of the catalyst layer 20 (100 wt%) is preferably 30 wt% or greater, more preferably 35 wt% or greater, and particularly preferably 40 wt% or greater. This ensures sufficient purification performance during warm-up operation and after a fuel cut, even when the overall catalytic metal content of the catalyst layer 20 is reduced to account for material costs. On the other hand, if the catalytic metal content of the lower front portion A is too high, the catalytic metal content in other regions may decrease as the overall catalytic metal content of the catalyst layer 20 is reduced, making it difficult for each region to achieve its desired function. In light of this, the catalytic metal content of the lower front portion A is preferably 80 wt% or less, more preferably 75 wt% or less, and particularly preferably 70 wt% or less.

[0068] In addition, the length L of the lower front portion A in the exhaust gas flow direction F is A There is no particular limitation as long as it is shorter than the total length L of the substrate 10. However, from the perspective of properly exerting the function of the lower front portion A (exhaust gas purification during warm-up operation), the length L of the lower front portion A is preferably A It is preferably 15% or more of the total length L of the substrate 10, more preferably 20% or more, further preferably 25% or more, and particularly preferably 40% or more. A It is preferably 85% or less of the total length L of the partition wall 14, more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less. BIn addition, since the composition of the catalytic metal and CeO2 in the lower front portion A is different from that in other regions, it can be distinguished from other regions by visual color. Therefore, the length L of the lower front portion A is A The other regions (such as the upper catalyst layer 24 ) can be scraped off with a brush or the like and then visually measured.

[0069] In addition, the thickness T of the lower front portion A A However, from the perspective of properly exerting the function of the lower layer front part A, the thickness T of the lower layer front part A is preferably A The thickness T of the lower layer front portion A is preferably 25% or more, more preferably 30% or more, further preferably 35% or more, and particularly preferably 40% or more relative to the total thickness T (100%) of the catalyst layer 20. A It is preferably 75% or less, more preferably 70% or less, further preferably 65% ​​or less, and particularly preferably 60% or less. C .

[0070] (b) Lower rear part B The lower catalyst layer 22 has a portion extending from the downstream end 10b of the substrate 10 toward the upstream side ( Figure 4 The lower rear portion B extends to the left side of the lower catalyst layer 22. In other words, the lower rear portion B is the downstream region of the lower catalyst layer 22. This lower rear portion B has the function of responding to air-fuel ratio fluctuations caused by fuel cuts (F / C) and other events. Specifically, various exhaust gases are supplied to the lower rear portion B, including those during warm-up operation and normal operation. Therefore, by providing the lower rear portion B with a high oxygen storage capacity, it is possible to construct an exhaust gas purification catalyst 1 that can easily respond to fluctuations in the exhaust gas air-fuel ratio.

[0071] Specifically, in the exhaust gas purifying catalyst 1 of the present embodiment, the CeO2 content B in the lower rear portion B is CeO2 It is set to 20 g / L or more. As a result, the lower rear portion B can be given a high oxygen storage capacity, so even when the air-fuel ratio fluctuates, the exhaust gas purification performance can be properly exerted. CeO2 It is preferably 22 g / L or more, more preferably 23 g / L or more, and even more preferably 24 g / L or more. This can impart a better oxygen storage capacity to the lower rear portion B.

[0072] On the other hand, the CeO2 content B in the lower rear part B CeO2 Above a certain level, the oxygen storage capacity of the lower rear portion B is saturated. Based on this perspective, the CeO2 content B in the lower rear portion B is CeO2Set to 63g / L or less. Thus, the content of other components (catalytic metal, supporting material, etc.) in the lower rear part B can be fully ensured. In addition, the CeO2 content B in the lower rear part B CeO2 It is preferably 50 g / L or less, more preferably 40 g / L or less, further preferably 30 g / L or less, and particularly preferably 28 g / L or less.

[0073] In addition, the CeO2 content B in the lower rear portion B in this specification is CeO2 " refers to the volume V of the substrate in the area where the lower rear part B is located B Assuming that the weight of CeO2 contained in the lower rear part B is 1L. CeO2 " and the above "CeO2 content A in the front part of the lower layer CeO2 ”Similarly, it can be determined using ICP and EPMA.

[0074] In addition, the lower rear portion B contains at least one of Pd and Pt as a catalytic metal. For example, the lower rear portion B is also supplied with exhaust gas during the preheating operation. Therefore, by containing Pd, which has excellent catalytic activity in an oxidized state, the emission of harmful components during the preheating operation can be reduced. In addition, the lower rear portion B is also supplied with exhaust gas that has passed through other areas (lower front portion A or upper front portion C, etc.). These exhaust gases that have passed through other areas sometimes contain substances in which harmful components have changed (catalyst endogenous substances). For example, a long-chain hydrocarbon that is one of the hydrocarbons (HC) sometimes becomes a short-chain hydrocarbon (methane (CH3), etc.) before decomposing into water and carbon dioxide. In addition, if NO x Excessive reduction in other regions may also result in the formation of ammonia (NH3). Because Pt can appropriately promote the decomposition of short-chain hydrocarbons and the oxidation of ammonia, it is suitable as a catalytic metal in the lower rear portion B. The combined Pd and Pt content in the lower rear portion B is preferably 0.1 g / L or greater, more preferably 0.25 g / L or greater, even more preferably 0.5 g / L or greater, and particularly preferably 0.8 g / L or greater. This ensures sufficient purification performance in the lower rear portion B. On the other hand, considering the balance between purification performance and material cost, the combined Pd and Pt content in the lower rear portion B is preferably 10 g / L or less, more preferably 7.5 g / L or less, even more preferably 5 g / L or less, and particularly preferably 3.4 g / L or less. The "combined Pd and Pt content (g / L) in the lower rear portion B" can be measured using the same procedure as for the "Pd content (g / L) in the lower front portion A" described above, so repeated explanation is omitted.

[0075] The lower rear portion B may also contain catalytic metals other than Pd and Pt. However, when the total amount of catalytic metals in the lower rear portion B is set to 100 wt%, the combined content of Pd and Pt in the lower rear portion B is preferably 80 wt% or greater (preferably 85 wt% or greater, more preferably 90 wt% or greater, and particularly preferably 95 wt% or greater). This can further reduce emissions of harmful components.

[0076] In addition, it is preferred that the lower rear portion B is the region with the second highest content ratio of catalytic metal relative to the catalyst layer 20 as a whole. Specifically, the content ratio of catalytic metal in the lower rear portion B relative to the catalyst layer 20 as a whole is preferably 10 wt% or more, more preferably 15 wt% or more, and particularly preferably 20 wt% or more. Thus, even in the lower rear portion B having a very high oxygen storage capacity, it is possible to ensure a purification performance of the catalytic metal above a certain level. On the other hand, when the content ratio of catalytic metal in the lower rear portion B is too high, while reducing the amount of catalytic metal in the catalyst layer 20 as a whole, the content of catalytic metal in other regions may be reduced, making it difficult to exert the functions required by each region. In view of this, the content ratio of catalytic metal in the lower rear portion B is preferably 50 wt% or less, more preferably 47 wt% or less, and particularly preferably 45 wt% or less.

[0077] In addition, the length L of the lower rear portion B in the cylinder axis direction X is B There is no particular limitation as long as it is shorter than the total length L of the partition wall 14. However, from the perspective of being able to properly exert the function of the lower rear portion B (response to air-fuel ratio fluctuation), the length L of the lower rear portion B is preferably B It is preferably 15% or more of the total length L of the partition wall 14, more preferably 20% or more, further preferably 25% or more, and particularly preferably 30% or more. B It is preferably 85% or less of the total length L of the partition wall 14, more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less. A .

[0078] Furthermore, the length L of the lower front portion A is A Length L of the lower rear part B B Total length (L A +L B ) can be greater than the total length L of the partition wall 14. In this case, the downstream end of the lower front portion A and the upstream end of the lower rear portion B overlap in the thickness direction Y. This prevents a gap from forming between the lower front portion A and the lower rear portion B, thereby better demonstrating the effects of the present invention. Specifically, the total length L is A +L BIt is preferably 100% or more of the total length L of the partition wall 14, more preferably 105% or more, further preferably 110% or more, and particularly preferably 115% or more. A +L B The upper limit is preferably 160% or less, more preferably 150% or less, further preferably 145% or less, and particularly preferably 140% or less of the total length L of the partition wall 14. This prevents the formation of an excessive amount of catalyst layer 20 and prevents an increase in pressure loss due to clogging of the chamber 12.

[0079] In addition, the thickness T of the lower rear portion B B However, from the perspective of fully utilizing the function of the lower rear portion B, the thickness T of the lower rear portion B is preferably B It is preferably 25% or more of the total thickness T of the catalyst layer 20, more preferably 30% or more, further preferably 35% or more, and particularly preferably 40% or more. B The upper limit of the thickness T of the catalyst layer 20 is preferably 85% or less, more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less. D .

[0080] (c) Upper front C The upper catalyst layer 24 has a portion extending from the upstream end 10a of the substrate 10 toward the downstream side ( Figure 4 The upper front portion C extends to the right side of the upper catalyst layer 24. In other words, the upper front portion C is the upstream side region of the upper catalyst layer 24. The upper front portion C has the function of increasing the NO x Purification performance function. Specifically, when exhaust gas is supplied to the exhaust gas purification catalyst 1, the water-gas shift reaction shown in the following formula (1) occurs to generate hydrogen (H2). Then, this hydrogen becomes the purified NO as shown in the following formula (2). x The upstream region of the upper catalyst layer 24, namely the upper front portion C, is the region that first contacts the exhaust gas under various conditions. Therefore, if the water-gas shift reaction in the upper front portion C is promoted, the NO reduction of the entire exhaust gas purification catalyst 1 can be improved. x Purification performance.

[0081] CO + H2O → CO2 + H2 (1) NO x +H2→N2+H2O(2) In this regard, the upper front portion C contains rhodium (Rh) as a catalytic metal. Rh is very good at promoting the water-gas shift reaction, and thus can increase the amount of H2 generated in the upper front portion C. As a result, the NOx reduction of the entire exhaust gas purifying catalyst 1 can be greatly improved. x Purification performance. The Rh content of the upper front part C is preferably 0.01 g / L or more, more preferably 0.05 g / L or more, further preferably 0.1 g / L or more, and particularly preferably 0.2 g / L or more. As a result, the water-gas shift reaction of the upper front part C can be better promoted. On the other hand, considering the balance between purification performance and material cost, the Rh content of the upper front part C is preferably 1 g / L or less, more preferably 0.5 g / L or less, further preferably 0.4 g / L or less, and particularly preferably 0.3 g / L or less. Among them, the "Rh content (g / L) of the upper front part C" can be measured according to the same procedure as the above-mentioned "Pd content (g / L) of the lower front part A", so repeated description is omitted.

[0082] In addition, from the perspective of appropriately promoting the generation of H2 in the upper front part C, the Rh content in the upper front part C is preferably 50wt% or more (more preferably 60wt% or more, further preferably 70wt% or more, and particularly preferably 80wt% or more) relative to the content of the catalytic metal in the upper front part C (100wt%).

[0083] On the other hand, Rh has the problem of significantly reducing its catalytic activity after being oxidized. Therefore, if the recovery of catalytic activity achieved by warm-up operation slows down, the amount of H2 generated in the upper front C will be greatly reduced, which may lead to NO x Therefore, in this embodiment, the CeO2 content C of the upper front part C is increased. CeO2 As described above, by reducing the CeO2 content around the catalytic metal, the oxygen supply from CeO2 during the warm-up operation can be suppressed, thereby quickly recovering the catalytic activity of Rh. This ensures the amount of H2 generated in the upper front C during the warm-up operation and reduces NO x In addition, NO emissions during warm-up operation can be further suppressed. x Emission angle, CeO2 content C in the upper front C CeO2 It is more preferably 6.5 g / L or less, and particularly preferably 6 g / L or less.

[0084] On the other hand, the CeO2 content C in the upper front part CeO2 If it is too small, it cannot cope with the rapid fluctuation of exhaust gas air-fuel ratio in a short period. x Therefore, in the technology of the present invention, the CeO2 content C of the upper front C is increased. CeO2The lower limit of NO is set to 1 g / L or more. x Emission angle, CeO2 content C in the upper front C CeO2 It is preferably 2 g / L or more, more preferably 2.5 g / L or more, and particularly preferably 3 g / L or more.

[0085] Here, the CeO2 content C of the upper front portion C in this specification is CeO2 " refers to the volume V of the substrate in the area where the upper front part C is located C Assuming that the weight of CeO2 contained in the upper front part C is 1L. The CeO2 content C in the upper front part C is CeO2 "As mentioned above, it can be measured by ICP and EPMA.

[0086] In addition, the length L of the upper front portion C in the cylinder axis direction X (exhaust gas flow direction F) is C There is no particular limitation as long as it is shorter than the total length L of the partition wall 14. However, from the perspective of more appropriate occurrence of the water-gas shift reaction, the length L of the upper front portion C is preferably C It is preferably 15% or more of the total length L of the partition wall 14, more preferably 20% or more, further preferably 25% or more, and particularly preferably 30% or more. D Angle, length L of the upper front part C C It is preferably 85% or less of the total length L of the partition wall 14 , more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less.

[0087] Furthermore, the thickness T of the upper front portion C is C However, from the perspective of more appropriate occurrence of the water-gas shift reaction, the thickness T of the upper front portion C is preferably C It is preferably 25% or more of the total thickness T of the catalyst layer 20, more preferably 30% or more, further preferably 35% or more, and particularly preferably 40% or more. A Angle, thickness T of the upper front part C C It is preferably 75% or less of the total thickness T of the catalyst layer 20 , more preferably 70% or less, further preferably 65% ​​or less, and particularly preferably 60% or less.

[0088] (d) Upper rear D The upper catalyst layer 24 has a portion extending from the downstream end 10b of the substrate 10 toward the upstream side ( Figure 4The upper rear portion D extends from the upper catalyst layer 24 (left side in the figure). In other words, the upper rear portion D is the downstream area of ​​the upper catalyst layer 24. This upper rear portion D has the function of purifying exhaust gas emitted during high-speed operation. Specifically, the flow velocity of exhaust gas during high-speed operation is very high, so it hardly penetrates the upstream part of the catalyst layer 20, but instead penetrates the upper catalyst layer 24 in the downstream part where the flow velocity begins to decrease. In other words, the exhaust gas during high-speed operation mainly penetrates the upper rear portion D, and the chance of contact with the catalyst layer 20 is reduced. To address this issue, the exhaust gas purification catalyst of the present invention uses rhodium (Rh) as the catalytic metal of the upper rear portion D. Rh is a metal with extremely excellent ternary properties, so even if the chance of contact with the exhaust gas is small, it can effectively purify harmful components. Therefore, the upper rear portion D of this embodiment can appropriately purify exhaust gas during high-speed operation. The Rh content of the upper rear portion D is preferably 0.01 g / L or greater, more preferably 0.05 g / L or greater, even more preferably 0.1 g / L or greater, and particularly preferably 0.2 g / L or greater. This allows for better purification of exhaust gas during high-speed operation. On the other hand, considering the balance between purification performance and material costs, the Rh content of the upper rear portion D is preferably 1 g / L or less, more preferably 0.5 g / L or less, even more preferably 0.4 g / L or less, and particularly preferably 0.3 g / L or less. The "Rh content (g / L) of the upper rear portion D" can be measured using the same procedure as for the "Pd content (g / L) of the lower front portion A" described above, so repeated explanation is omitted.

[0089] In addition, from the perspective of appropriately purifying exhaust gas during high-speed operation, the Rh content in the upper rear portion D is preferably 30 wt% or more (more preferably 40 wt% or more, further preferably 45 wt% or more, and particularly preferably 50 wt% or more) relative to the catalytic metal content in the upper rear portion D (100 wt%).

[0090] On the other hand, rhodium oxide is highly reactive with ceria, so once exposed to high temperature, it may form a solid solution with ceria, resulting in a significant decrease in catalytic activity. In particular, the exhaust gas temperature during high-speed operation is very high, which promotes the solid solution of rhodium oxide and ceria. In this regard, in the exhaust gas purification catalyst 1 of this embodiment, the CeO2 content D in the upper rear portion D is increased. CeO2 It is set to 8g / L or less. This can reduce the amount of CeO2 around Rh and suppress the solid solution of rhodium oxide and ceria. As a result, the exhaust gas during high-speed operation can be properly purified. In addition, from the perspective of better purification of exhaust gas during high-speed operation, the CeO2 content D in the upper rear portion D is CeO2 It is more preferably 7.5 g / L or less, and particularly preferably 7 g / L or less.

[0091] On the other hand, the CeO2 content D in the upper rear part D CeO2 When it is too little, it cannot cope with the rapid fluctuation of exhaust gas air-fuel ratio in a short period, so during high-speed operation, NO x Therefore, in the present invention, the CeO2 content D of the upper rear portion D is CeO2 The lower limit of NO is set to 2 g / L or more. x Emission angle, CeO2 content D in the upper rear part CeO2 It is preferably 2.5 g / L or more, more preferably 3 g / L or more, and particularly preferably 3.5 g / L or more.

[0092] In addition, the CeO2 content D of the upper rear portion D in this specification is CeO2 " refers to the volume V of the substrate in the area where the upper rear portion D is located D Assuming that the weight of CeO2 contained in the upper rear portion D is 1L. CeO2 ” is also consistent with the above “CeO2 content A in the lower front part A CeO2 "Similarly, it can be determined by ICP and EPMA.

[0093] Furthermore, it is preferred that the CeO2 content D of the upper rear portion D CeO2 Greater than the CeO2 content C in the upper front part CeO2 More specifically, the CeO2 content C in the upper front C CeO2 CeO2 content D in the upper rear part CeO2 The ratio (C CeO2 / D CeO2 ) is preferably 1.0 or less, more preferably 0.75 or less, and even more preferably 0.7 or less. This makes it easier to cope with fluctuations in the air-fuel ratio during high-load operation when high-speed exhaust gas is supplied. As a result, the purification performance of harmful components that cannot be fully purified in the upper front portion C is improved, thereby appropriately reducing the emission of harmful components during high-load operation. On the other hand, the above-mentioned C CeO2 / D CeO2 The lower limit of is not particularly limited, and may be 0.1 or more, 0.2 or more, 0.4 or more, or 0.5 or more.

[0094] In addition, the length L of the upper rear portion D in the cylinder axis direction X is D There is no particular limitation as long as it is shorter than the total length L of the partition wall 14. However, from the perspective of properly purifying the exhaust gas during high-speed operation, the length L of the upper rear portion D is preferably DIt is preferably 15% or more of the total length L of the partition wall 14, more preferably 20% or more, further preferably 25% or more, and particularly preferably 30% or more. C Angle, length L of the upper rear part D D It is preferably 85% or less of the total length L of the partition wall 14 , more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less.

[0095] Furthermore, the length L of the upper front portion C is C Length L of the upper rear part D D Total length (L C +L D ) can be longer than the total length L of the partition wall 14. In this case, the downstream end of the upper front portion C and the upstream end of the upper rear portion D are overlapped in the thickness direction Y. This can prevent a gap from being formed between the upper front portion C and the upper rear portion D, thereby better exerting the effect of the technology of the present invention. Specifically, the total length L C +L D It is preferably 100% or more of the total length L of the partition wall 14, more preferably 105% or more, further preferably 110% or more, and particularly preferably 115% or more. C +L D The upper limit is preferably 160% or less, more preferably 150% or less, further preferably 145% or less, and particularly preferably 140% or less of the total length L of the partition wall 14. This prevents the formation of an excessive amount of catalyst layer 20 and prevents an increase in pressure loss due to clogging of the chamber 12.

[0096] In addition, the thickness T of the upper rear portion D D There is no particular limitation. For example, the thickness T of the upper rear portion D is D It can be 25% or more, 30% or more, 35% or more, or 40% or more of the total thickness T of the catalyst layer 20. On the other hand, the thickness T of the lower rear portion D can be sufficiently ensured. D Angle, thickness T of the upper rear part D D It is preferably 75% or less of the total thickness T of the catalyst layer 20 , more preferably 70% or less, further preferably 65% ​​or less, and particularly preferably 60% or less.

[0097] (2-2) Average particle size of the supporting material in each region Furthermore, in the exhaust gas-purifying catalyst 1 of this embodiment, the average particle size of the supporting material varies in each of the four regions constituting the catalyst layer 20. The "average particle size of the supporting material" herein refers to the average particle size of the supporting material as a whole, including the OSC material and other supporting materials (such as Al2O3 powder). Furthermore, the "average particle size D50 of the supporting material" is the particle size (D50) at which the smallest particle size is 50% of the total particle size, as measured by a number-based cumulative particle size distribution curve of a plurality (e.g., 400) of supported particles observed in a target region using a scanning electron microscope (SEM).

[0098] In the following description, the average particle size D50 of the supporting material contained in the lower front portion A is referred to as "the average particle size D50 in the lower front portion A". A The average particle size D50 of the supporting material contained in the lower rear portion B is referred to as the average particle size D50 in the lower rear portion B. B In addition, the average particle size D50 of the supporting material contained in the upper front portion C is referred to as the "average particle size D50 in the upper front portion C". C The average particle size D50 of the supporting material contained in the upper rear portion D is referred to as the "average particle size D50 in the upper rear portion D". D Furthermore, the average particle size D50 of the supporting material contained in the lower catalyst layer 22 (lower front portion A and lower rear portion B) is referred to as the "average particle size D50 in the lower catalyst layer 22". AB The average particle size D50 of the supporting material contained in the upper catalyst layer 24 (upper front portion C and upper rear portion D) is referred to as the “average particle size D50 in the upper catalyst layer 24”. CD ”.

[0099] (a) Average particle size D50 in the upper catalyst layer CD First, the average particle size D50 in the upper catalyst layer 24 (upper layer front portion C and upper layer rear portion D) of the exhaust gas purifying catalyst 1 of the present embodiment is CD When such a small supporting material is used to form the upper catalyst layer 24, the upper catalyst layer 24 becomes dense. This can inhibit the intrusion of moisture in the exhaust gas into the catalyst layer 20. As a result, it is easy to increase the temperature inside the catalyst layer 20 during the exhaust gas supply process, and thus it is easy to exert the exhaust gas purification performance of the catalytic metal (for example, NO x Purification performance). In addition, from the perspective of further improving the exhaust gas purification performance, the average particle size D50 in the upper catalyst layer 24 CDIt is preferably 4.7 μm or less, more preferably 4.5 μm or less, further preferably 4.2 μm or less, and particularly preferably 4 μm or less. On the other hand, if the upper catalyst layer 24 becomes too dense, it will be difficult for the exhaust gas to diffuse into the lower catalyst layer 22, so the exhaust gas purification performance may be reduced. In particular, when the gas diffusion to the lower catalyst layer 22 is reduced, the above-mentioned preheating performance improvement effect of the lower front part A and the oxygen storage effect of the lower rear part B may not be properly exerted. Based on this perspective, in the exhaust gas purification catalyst 1 of this embodiment, the average particle size D50 in the upper catalyst layer 24 is CD In order to better ensure the gas diffusion to the lower catalyst layer 22, the average particle size D50 in the upper catalyst layer 24 is set to be 2 μm or more. CD It is preferably 2.2 μm or more, more preferably 2.5 μm or more, further preferably 2.7 μm or more, and particularly preferably 3 μm or more.

[0100] The specific average porosity of the upper catalyst layer 24 is preferably 30% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. This effectively prevents moisture from entering the interior of the catalyst layer 20. Meanwhile, the lower limit of the average porosity of the upper catalyst layer 24 is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 5% or more. This ensures sufficient gas diffusion into the lower catalyst layer 22. The "average porosity" in this specification is obtained by performing image analysis on a cross-sectional SEM photograph of the measurement target area (such as the upper catalyst layer 24), selecting an arbitrary number (30) of measurement areas (50 μm × 50 μm), measuring the ratio (%) of the pore area to the measurement area area, and calculating the average of the measurement results for each measurement area. This image analysis is performed using conventional analysis software such as Image-J.

[0101] (b) Average particle size D50 in the lower catalyst layer AB As described above, in the exhaust gas purifying catalyst 1 of this embodiment, the upper catalyst layer 24 is densified to prevent moisture from entering the catalyst layer 20. That is, in the exhaust gas purifying catalyst 1 of this embodiment, since the possibility of moisture in the exhaust gas reaching the lower catalyst layer 22 is low, it is preferable to make the lower catalyst layer 22 porous to improve gas diffusivity. From this perspective, the average particle size D50 in the lower catalyst layer 22 (lower layer front portion A and lower layer rear portion B) is ABIt is preferably 2.5 μm or more, more preferably 3 μm or more, further preferably 4 μm or more, and particularly preferably 5 μm or more. When such a large supporting material is used to form the lower catalyst layer 22, the lower catalyst layer 22 becomes porous, thereby ensuring appropriate gas diffusion. As a result, various catalytic properties (such as the preheating performance improvement effect of the lower front part A, the oxygen absorption and storage effect of the lower rear part B, etc.) can be better exerted. On the other hand, if the lower catalyst layer 22 is excessively porous, the catalyst layer 20 may be peeled off due to reduced strength. From this perspective, the average particle size D50 in the lower catalyst layer 22 AB It is preferably 12.5 μm or less, more preferably 10 μm or less, further preferably 9 μm or less, and particularly preferably 8 μm or less.

[0102] In addition, the specific average porosity of the lower catalyst layer 22 is preferably 1% or more, more preferably 2% or more, further preferably 3% or more, and particularly preferably 5% or more. In this way, the gas diffusivity of the lower catalyst layer 22 can be fully ensured, and appropriate catalytic performance can be exerted. On the other hand, the upper limit of the average porosity of the lower catalyst layer 22 is preferably 40% or less, more preferably 30% or less, further preferably 20% or less, and particularly preferably 15% or less. In this way, the strength reduction of the catalyst layer 20 can be suppressed. In addition, the average porosity of the lower catalyst layer 22 is not particularly limited, as long as it is greater than the average porosity of the upper catalyst layer 24.

[0103] Furthermore, the exhaust gas purification catalyst 1 of this embodiment preferably has an average particle size D50 in the upper catalyst layer 24. CD The average particle size D50 in the lower catalyst layer 22 AB The ratio of (D50 CD / D50 AB ) is controlled within the specified range. Specifically, the particle size ratio (D50 CD / D50 AB The upper limit of the particle size ratio (D50) is preferably 0.9 or less, more preferably 0.8 or less, and particularly preferably 0.7 or less. CD / D50 AB ) decreases, the upper catalyst layer 24 becomes relatively dense, and the lower catalyst layer 22 tends to be porous. This not only ensures sufficient gas diffusion to the lower catalyst layer 22, but also prevents moisture from entering the interior of the catalyst layer 20. On the other hand, as the particle size ratio (D50 CD / D50 AB) approaches 1, and the density difference between the upper catalyst layer 24 and the lower catalyst layer 22 disappears. In this case, the diffusibility of the exhaust gas to the lower catalyst layer 22 is likely to decrease and water may intrude into the catalyst layer 20. From this perspective, the particle size ratio (D50 CD / D50 AB ) is preferably 0.4 or less, particularly preferably 0.5 or less.

[0104] (c) Average particle size D50 in the lower front part A A Next, we will describe the average particle size D50 of the supporting material in each region from the lower front portion A to the upper rear portion D. First, similar to the upper catalyst layer 24 (upper front portion C and upper rear portion D), the lower front portion A preferably has a smaller average particle size D50 of the supporting material to achieve a denser structure. This has been shown experimentally to significantly improve exhaust gas purification performance (NOx). x Purification performance, etc.). It is speculated that this is because it can prevent moisture from invading the lower catalyst layer 22 (lower front part A) from the end 10a on the upstream side of the exhaust gas flow direction F. From this perspective, the average particle size D50 in the lower front part A is A It is preferably 5 μm or less, more preferably 4.5 μm or less, and particularly preferably 4 μm or less. On the other hand, from the perspective of gas diffusibility, the average particle size D50 of the supporting material of the lower front portion A is A It is preferably 2 μm or more, more preferably 2.5 μm or more, and particularly preferably 3 μm or more.

[0105] The specific average porosity of the lower front portion A is preferably 1% or greater, more preferably 2% or greater, even more preferably 3% or greater, and particularly preferably 5% or greater. Meanwhile, the upper limit of the average porosity of the lower catalyst layer 22 is preferably 30% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. This ensures sufficient gas diffusivity within the lower catalyst layer 22 (e.g., gas diffusivity toward the lower rear portion B), enabling appropriate catalytic performance.

[0106] (d) Average particle size D50 in the lower rear part B B Next, the lower rear portion B is supplied with exhaust gas that has passed through the other catalyst layers (lower front portion A, upper front portion C, and upper rear portion D). Therefore, even if the lower rear portion B becomes dense, it will hardly have the effect of preventing moisture from entering and improving purification performance. Therefore, the lower rear portion B is preferably made of a material with a larger average particle size than other regions to improve gas diffusion. From this perspective, the average particle size D50 in the lower rear portion B is BIt is preferably 4 μm or more, more preferably 4.5 μm or more, and particularly preferably 5 μm or more. On the other hand, if the lower catalyst layer 22 is too porous, the catalyst layer 20 may be peeled off due to the decrease in strength of the lower catalyst layer 22. From this perspective, the average particle size D50 in the lower rear portion B is B It is preferably 10 μm or less, more preferably 9.5 μm or less, and particularly preferably 8 μm or less.

[0107] In addition, the exhaust gas purifying catalyst 1 of this embodiment preferably has an average particle size D50 in the lower front portion A. A The average particle size D50 in the lower rear part B B The ratio of (D50 A / D50 B ) is controlled within the specified range. Specifically, the particle size ratio (D50 A / D50 B The upper limit of the particle size ratio (D50) is preferably 0.9 or less, more preferably 0.8 or less, and particularly preferably 0.7 or less. A / D50 B ) is reduced, the lower front portion A becomes relatively dense, and the lower rear portion B becomes porous, thereby not only ensuring sufficient exhaust gas diffusivity but also preventing moisture from entering. On the other hand, as the particle size ratio (D50 A / D50 B ) approaches 1, the difference in density between the lower front part A and the lower rear part B disappears, so the exhaust gas diffusivity is weakened and the possibility of water intrusion increases. From this perspective, the above particle size ratio (D50 A / D50 B ) is preferably 0.4 or less, particularly preferably 0.5 or less.

[0108] In addition, the specific average porosity of the lower rear portion B is preferably 3% or more, more preferably 4% or more, further preferably 5% or more, and particularly preferably 7% or more. This can appropriately suppress delamination of the catalyst layer 20 due to a decrease in the strength of the lower catalyst layer 22. On the other hand, the upper limit of the average porosity of the lower rear portion B is preferably 40% or less, more preferably 30% or less, further preferably 20% or less, and particularly preferably 15% or less. This can fully ensure the gas diffusivity of the lower rear portion B and exert appropriate catalytic performance. Furthermore, as described above, the average porosity of the lower rear portion B is preferably greater than the average porosity of the other catalyst layers (lower front portion A, upper front portion C, and upper rear portion D).

[0109] (e) Average particle size D50 in the upper front part C C Average particle size D50 of the supporting material in the upper front portion C CThe upper front portion C is the area that the exhaust gas supplied to the chamber 12 first contacts. Therefore, by reducing the average particle size D50 in the upper front portion C, the average particle size D50 in the upper front portion C is preferably 5 μm or less, more preferably 4.5 μm or less, and particularly preferably 4 μm or less. C Densifying the upper front portion C can effectively prevent moisture from entering the catalyst layer 20. On the other hand, if the upper front portion C is too dense, exhaust gas will have difficulty diffusing to other areas, and the purification performance may be reduced. From this perspective, the average particle size D50 in the upper front portion C is C It is preferably 2 μm or more, more preferably 2.5 μm or more, and particularly preferably 3 μm or more.

[0110] The specific average porosity of the upper front portion C is preferably 1% or greater, more preferably 2% or greater, even more preferably 3% or greater, and particularly preferably 5% or greater. This ensures sufficient gas diffusion to other areas (particularly the lower catalyst layer 24). Meanwhile, the average porosity of the upper front portion C is preferably 30% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. This effectively prevents moisture from entering the catalyst layer 20.

[0111] (f) Average particle size D50 in the upper rear portion D D Average particle size D50 in the upper rear part D D It is preferably 5 μm or less, more preferably 4.5 μm or less, and particularly preferably 4 μm or less. The upper rear portion D is the area that is most easily contacted by exhaust gas after the upper front portion C. Therefore, by making the upper rear portion D dense, it is possible to better prevent moisture from invading the interior of the catalyst layer 20. On the other hand, if the upper rear portion D is too dense, there is also a risk of reduced purification performance due to reduced gas diffusivity. From this perspective, the average particle size D50 in the upper rear portion D is D It is preferably 2 μm or more, more preferably 2.5 μm or more, and particularly preferably 3 μm or more.

[0112] The specific average porosity of the upper rear portion D is preferably 1% or greater, more preferably 2% or greater, even more preferably 3% or greater, and particularly preferably 5% or greater. This ensures sufficient gas diffusion to other areas (particularly the lower catalyst layer 24). Meanwhile, the average porosity of the upper rear portion D is preferably 30% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. This effectively prevents moisture from entering the catalyst layer 20.

[0113] In addition, the technology of the present invention is to determine the average particle size (D50 C 、D50C ) is not particularly limited as long as the average particle size D50 in the upper catalyst layer 24 (upper front portion C and upper rear portion D) is CD The upper front portion C and the upper rear portion D may have different average particle sizes. For example, since the upper front portion C is located upstream of the exhaust gas flow direction F, it has more opportunities to come into contact with the exhaust gas than the upper rear portion D. Considering this, it is preferred that the average particle size D50 in the lower front portion C be greater than that in the upper rear portion D. C Smaller than the average particle size D50 in the upper rear portion D D This can better prevent moisture from intruding into the catalyst layer 20 .

[0114] 3. Summary As described above, the exhaust gas purification catalyst 1 of the present embodiment includes a catalyst layer 20 having a lower front portion A, a lower rear portion B, an upper front portion C, and an upper rear portion D. The lower front portion A contains Pd having excellent catalytic activity in an oxidized state, and CeO2 is reduced in order to facilitate recovery of purification performance from an oxidized state. Therefore, the lower front portion A contributes to improvement of exhaust gas purification performance during warm-up operation. Secondly, the lower rear portion B contains a large amount of CeO2 and therefore has a high oxygen storage capacity. Therefore, the lower rear portion B contributes to improvement of exhaust gas purification performance when the air-fuel ratio fluctuates. Moreover, the upper front portion C contains Rh having excellent performance in promoting the water-gas shift reaction, and CeO2 is further reduced in order to facilitate recovery of the purification performance of Rh. Therefore, the upper front portion C contributes to improvement of NO of the exhaust gas purification catalyst 1 as a whole. x Purification performance. Furthermore, the upper rear portion D contains Rh, which excels in ternary performance, and reduces CeO2 to suppress solid solution formation between Rh and CeO2 in high-temperature environments. Therefore, the upper rear portion D contributes to improved exhaust gas purification performance during high-speed operation, when high-speed, high-temperature exhaust gas is supplied. As described above, the exhaust gas-purifying catalyst 1 of this embodiment is configured to exhibit appropriate purification performance under various operating conditions.

[0115] Furthermore, in the exhaust gas purifying catalyst 1 of the present embodiment, the average particle size D50 of the supporting material of the upper catalyst layer 24 is CD The upper catalyst layer 24 is thus denser, thereby suppressing the degradation of the catalytic metal performance caused by the intrusion of water into the catalyst layer 20. Moreover, the average particle size D50 of the supporting material of the upper catalyst layer 24 is CD By setting the diameter to 2 μm or more, the gas diffusibility to the lower catalyst layer 22 can be sufficiently ensured, and thus the exhaust gas purification function of the lower catalyst layer 22 can be appropriately exhibited.

[0116] [Method for producing exhaust gas-purifying catalyst] Next, an example of a method for producing the exhaust gas-purifying catalyst 1 having the above-described structure will be described. This production method includes at least a lower layer forming step and an upper layer forming step. Each step will be described below.

[0117] 1. Lower layer formation process In this step, the lower catalyst layer 22 is formed. This lower layer forming step includes a lower layer front portion forming step for forming the lower layer front portion A and a lower layer rear portion forming step for forming the lower layer rear portion B. In the lower layer front portion forming step, first, a slurry for forming the lower layer front portion A is supplied from the upstream end 10a of the substrate 10 into the chamber 12. Then, suction is applied to the chamber 12 from the downstream end 10b of the substrate 10. In this way, the slurry can be supplied from the upstream end 10a of the substrate 10 to the downstream end 10b. Figure 4 The slurry is applied to the surface of the partition wall 14 in a manner extending from the right side of the substrate 10. Drying and firing are performed in this state, thereby forming the lower front portion A. On the other hand, in the lower rear portion forming step, the slurry for forming the lower rear portion B is supplied from the downstream end 10b of the substrate 10 into the chamber 12. Then, suction is performed into the chamber 12 from the upstream end 10a of the substrate 10. In this way, the slurry can be supplied from the downstream end 10b of the substrate 10 to the upstream side ( Figure 4 The coating is applied to the surface of the partition wall 14 in a manner extending to the left side (in the figure). Drying and firing are performed in this state to form the lower layer rear portion B. However, the order of performing the lower layer front portion forming step and the lower layer rear portion forming step is not particularly limited. For example, the lower layer front portion A may be formed after the lower layer rear portion B is formed.

[0118] 2. Upper layer formation process In this step, the upper catalyst layer 24 is formed. This upper layer forming step includes an upper layer front portion forming step for forming the upper layer front portion C and an upper layer rear portion forming step for forming the upper layer rear portion D. In the upper layer front portion forming step, first, a slurry for forming the upper layer front portion C is supplied from the upstream end 10a of the substrate 10 into the chamber 12. Then, suction is applied to the chamber 12 from the downstream end 10b of the substrate 10. In this way, the slurry can be supplied from the upstream end 10a of the substrate 10 to the downstream end ( Figure 4 The slurry is applied to the surface of the lower catalyst layer 22 in a manner extending from the right side of the substrate 10 (the right side of the substrate 10). In this state, drying and firing are performed to form the upper front portion C. On the other hand, in the upper rear portion forming step, the slurry for forming the upper rear portion D is supplied from the downstream end 10b of the substrate 10 into the chamber 12. Then, suction is performed into the chamber 12 from the upstream end 10a of the substrate 10. In this way, the slurry can be supplied from the downstream end 10b of the substrate 10 to the upstream side ( Figure 4The coating is applied to the surface of the lower catalyst layer 22 in a manner extending from the left side (in the figure). Drying and firing are performed in this state to form the upper rear portion D. However, the order of performing the upper front portion forming step and the upper rear portion forming step is not particularly limited. For example, the upper front portion C may be formed after the upper rear portion D is formed.

[0119] The slurry used in each step can be prepared by dispersing the catalyst layer components (catalytic metal, OSC material, etc.) in a dispersion medium. This dispersion medium can be an aqueous medium primarily composed of water or a non-aqueous medium primarily composed of an organic solvent (e.g., alcohol). The slurry may also contain a binder for viscosity adjustment. By adjusting the slurry's viscosity, the length of each region along the cylinder axis direction X can be adjusted. Furthermore, the slurry may also contain a pore-forming agent (e.g., resin beads). This facilitates adjustment of the porosity of the fired catalyst layer 20.

[0120] However, the exhaust gas purification catalyst of the present invention is not limited to the catalyst produced by the above-mentioned manufacturing method. For example, in the above-mentioned manufacturing method, the slurry is dried and fired after each application. This allows the regions constituting the catalyst layer 20 to be formed one by one. However, the steps for forming the catalyst layer 20 are not limited to this. For example, after applying and drying the slurries of the lower layer front portion A to the upper layer rear portion D in sequence, all the dried films may be co-fired. This allows the lower layer front portion A to the upper layer rear portion D to be formed simultaneously, thereby improving the manufacturing efficiency of the exhaust gas purification catalyst.

[0121] [Other embodiments] The above describes one embodiment of the exhaust gas purifying catalyst of the present invention, but the exhaust gas purifying catalyst of the present invention is not limited to the above embodiment. For example, the catalyst layer 20 of the exhaust gas purifying catalyst 1 of the above embodiment is composed of only the lower catalyst layer 22 and the upper catalyst layer 24. However, the catalyst layer of the exhaust gas purifying catalyst of the present invention only needs to have a stacked structure of at least two layers including the lower catalyst layer and the upper catalyst layer. In other words, the exhaust gas purifying catalyst of the present invention includes Figure 4 In the embodiment, other catalyst layers are provided between the partition wall 14 and the lower catalyst layer 22, between the lower catalyst layer 22 and the upper catalyst layer 24, and on the surface of the upper catalyst layer 24. In the case of three or more catalyst layers, the side closer to the partition wall surface is used as the lower catalyst layer, and the side relatively farther away is used as the upper catalyst layer.

[0122] [Test example] Hereinafter, a test example of the technology of the present invention will be described. However, the following test example is not intended to limit the technology of the present invention to the following contents.

[0123] <First Test> In this test, the CeO2 content A of the lower front part A was made CeO2 Six different exhaust gas purification catalysts (Examples 1 to 6) were prepared, and the warm-up performance of each example was evaluated.

[0124] 1. Preparation of each example (1) Example 1 In Example 1, four slurries were prepared (slurry for the lower layer front portion A, slurry for the lower layer rear portion B, slurry for the upper layer front portion C, and slurry for the upper layer rear portion D). The slurry for the lower layer front portion A was a mixture of Pd nitrate (Pd content: 5.3 g), Al2O3 powder (40 g), and an aqueous solvent. Furthermore, the slurry for the lower layer rear portion B was a mixture of Pd nitrate (Pd content: 2.6 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 22 g), Al2O3 powder (50 g), and an aqueous solvent. The slurry for the upper layer front portion C was a mixture of Rh nitrate (Rh content: 0.2 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 20% (CeO2 content: 2.1 g), Al2O3 powder (90 g), and an aqueous solvent. The slurry for the upper rear portion D is a slurry obtained by mixing Rh nitrate (Rh content: 0.2 g), CeO2-ZrO2 composite oxide having a CeO2 content of 20% (CeO2 content: 2.1 g), Al2O3 powder (90 g), and an aqueous solvent.

[0125] Next, a cylindrical, straight-flow honeycomb substrate (diameter: 118.4 mm, axial length L: 114.3 mm, volume: 1.26 L) was prepared as a substrate. A catalyst layer comprising a lower front portion A, a lower rear portion B, an upper front portion C, and an upper rear portion D was formed according to the procedures described in the "Method for Manufacturing Exhaust Gas Purifying Catalyst" above. In this test, this exhaust gas purifying catalyst was used as the sample of Example 1.

[0126] (2) Example 2 to Example 6 In Examples 2 to 6, in addition to changing the CeO2 content A of the lower front portion A as shown in Table 1, CeO2 The exhaust gas purification catalyst was prepared in the same manner as in Example 1. Specifically, in Examples 2 to 6, a CeO2-ZrO2 composite oxide having a CeO2 content of 40% was added to the slurry for the lower front portion A so that the CeO2 content was A. CeO2 The amounts are shown in Table 1. In the slurries for the lower layer front portion A of Examples 2 to 6, the amount of Al2O3 powder added was reduced by an amount corresponding to the amount of CeO2-ZrO2 composite oxide added.

[0127] 2. Evaluation Test (1) Durability test In this test, each exhaust gas purification catalyst was subjected to an accelerated durability test equivalent to 120,000 kilometers. Specifically, each exhaust gas purification catalyst was mounted on a 4.8L engine rig. The engine was then started and maintained at a catalyst bed temperature of 1000°C for 50 hours.

[0128] (2) Preheating performance evaluation Next, the warm-up performance of the exhaust gas purification catalyst after the durability test was evaluated. Specifically, air was supplied to the exhaust gas purification catalyst after the durability test and cooled to 50°C. Then, while measuring the HC concentration on the upstream and downstream sides of the exhaust gas purification catalyst, exhaust gas at 450°C was supplied, and the time it took for the downstream HC concentration to reach 50% or less of the upstream HC concentration (50% HC purification time (seconds)) was measured. The results are shown in Tables 1 and Figure 5 The exhaust gas air-fuel ratio (AFR) in this test was set to λ (the ratio of the oxidizing gas component to the reducing gas component) of 1 (the stoichiometric air-fuel ratio).

[0129] [Table 1] As shown in Table 1 and Figure 5 As shown, in this test, it was confirmed that the CeO2 content A in the lower front part A CeO2 The 50% HC purification time tends to be shorter as the oxygen supply from CeO2 is reduced during the warm-up operation, which can be assumed to be due to the fact that the oxygen supply from CeO2 is suppressed, which in turn promotes the recovery of the purification performance of the catalytic metal (Pd) in the lower front portion A.

[0130] <Second Test> In this test, the CeO2 content B of the lower rear layer is made CeO2 Four different exhaust gas purification catalysts (Examples 7 to 10) were prepared, and the oxygen storage capacity of each example was evaluated.

[0131] 1. Preparation of each example (1) Example 7 In Example 7 of the second test, an exhaust gas-purifying catalyst was prepared by the same procedure as in Example 1 of the first test except that the components of each slurry (lower layer front portion A to upper layer rear portion D) were changed.

[0132] Specifically, the slurry for the lower front portion A in Example 7 was a mixture of Pd nitrate (Pd content: 2.8 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 15 g), Al2O3 powder (70 g), and an aqueous solvent. The slurry for the lower rear portion B was a mixture of Pd nitrate (Pd content: 0.8 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 28 g), Al2O3 powder (40 g), and an aqueous solvent. The slurry for the upper front portion C was a mixture of Rh nitrate solution (Rh content: 0.2 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 20% (CeO2 content: 6 g), Al2O3 powder (80 g), and an aqueous solvent. The slurry for the upper rear portion D is a slurry obtained by mixing a nitric Rh solution (Rh content: 0.2 g), a CeO2-ZrO2 composite oxide having a CeO2 content of 20% (CeO2 content: 6 g), Al2O3 powder (80 g) and an aqueous solvent.

[0133] (2) Example 8~Example 10 In Examples 8 to 10, in addition to changing the CeO2 content B of the lower rear layer B as shown in Table 2, CeO2 Otherwise, the exhaust gas purification catalyst was prepared in the same manner as in Example 7. In addition, the CeO2 content B in Examples 8 to 10 was adjusted. CeO2 The steps of the first test are the same as those of the adjustment of CeO2 content A in Examples 2 to 6. CeO2 The steps are the same, so repeated description is omitted.

[0134] 2. Evaluation Test (1) Durability test Following the same procedure as in the first test, an accelerated durability test equivalent to 120,000 kilometers was conducted on the exhaust gas purifying catalyst of each example.

[0135] (2) Air-fuel ratio fluctuation test In this test, an O2 sensor is first installed on the downstream side of the exhaust gas purification catalyst after the durability test. Then, while the temperature of the exhaust gas purification catalyst is maintained at 500°C, exhaust gas is supplied from the engine stand. Then, when the output voltage of the O2 sensor is 0.5V or above, it is determined that the exhaust gas purification catalyst is full of rich-burning gas, and lean-burning gas with a lambda of 1.035 is supplied. On the other hand, when the output voltage of the O2 sensor is lower than 0.5V, it is determined that the exhaust gas purification catalyst is full of lean-burning gas, and rich-burning gas with a lambda of 0.965 is supplied. This air-fuel ratio fluctuation test measures the NO x concentration for 5 minutes. Then, based on NO xThe concentration of NO was calculated based on the results. x The results are shown in Table 2.

[0136] [Table 2] As shown in Table 2 and Figure 6 As shown, in this test, it was confirmed that the CeO2 content B in the lower rear part B CeO2 Increase, NO when air-fuel ratio fluctuates x The purification rate tends to increase. This is presumably because the lower rear portion B, to which exhaust gas under various operating conditions is easily supplied, is endowed with a high oxygen storage capacity.

[0137] <Third Test> In this test, the CeO2 content of the upper front C is C CeO2 Four different exhaust gas purification catalysts (Examples 11 to 14) and the NO x The purification performance was evaluated.

[0138] 1. Preparation of each example (1) Example 11 In Example 11 of the third test, an exhaust gas-purifying catalyst was prepared by the same procedure as in Example 1 of the first test except that the components of each slurry (lower layer front portion A to upper layer rear portion D) were changed.

[0139] Specifically, the slurry for the lower front portion A in Example 11 was a mixture of Pd nitrate (Pd content: 3.4 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 8 g), Al2O3 powder (40 g), and an aqueous solvent. The slurry for the lower rear portion B was a mixture of Pd nitrate (Pd content: 3.4 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 22 g), Al2O3 powder (55 g), and an aqueous solvent. The slurry for the upper front portion C was a mixture of Rh nitrate (Rh content: 0.3 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 20% (CeO2 content: 3 g), Al2O3 powder (75 g), and an aqueous solvent. The slurry for the upper rear portion D is a slurry obtained by mixing Rh nitrate (Rh content: 0.3 g), CeO2-ZrO2 composite oxide having a CeO2 content of 20% (CeO2 content: 3 g), Al2O3 powder (75 g) and an aqueous solvent.

[0140] (2) Example 12 to Example 14 In Examples 12 to 14, in addition to changing the CeO2 content C of the upper front portion C as shown in Table 3,CeO2 The exhaust gas purification catalyst was prepared by the same procedure as in Example 11. In addition, the CeO2 content C in Examples 12 to 14 was adjusted. CeO2 The steps of the first test are the same as those of the adjustment of CeO2 content A in Examples 2 to 6. CeO2 The steps are the same, so repeated description is omitted.

[0141] 2. Evaluation Test (1) Durability test Following the same procedure as in the first test, an accelerated durability test equivalent to 120,000 kilometers was conducted on the exhaust gas purifying catalyst of each example.

[0142] (2) Preheating performance evaluation In this test, the exhaust gas purification catalyst after the durability test was evaluated for NO x Purification performance. Specifically, air was supplied to the exhaust gas purifying catalyst after the durability test and cooled to 200°C. Then, the NO x The exhaust gas temperature was raised to 500°C at a heating rate of 10°C / min. x The temperature when the purification rate reaches 50% (50% NO x Purification temperature (°C). The results are shown in Table 3 and Figure 7 The exhaust gas air-fuel ratio in this test is set to the theoretical air-fuel ratio (λ=1).

[0143] [Table 3] As shown in Table 3 and Figure 7 As shown in the figure, compared with Example 14, the 50% HC purification temperature of Example 12 is significantly reduced. CeO2 Increase, NO during warm-up operation x The purification performance will be reduced. It can be speculated that this is because the oxygen supply from CeO2 hinders the recovery of Rh catalytic activity, resulting in the water-gas shift reaction being difficult to occur in the upper front C. On the other hand, compared with Example 13, the 50% HC purification temperature of Example 11 is significantly lower. From this, it can be seen that if a certain amount of CeO2 is present in the upper front C, the preheating performance will be greatly improved. It can be speculated that this is because even when the exhaust gas air-fuel ratio is controlled to the theoretical air-fuel ratio, the actual air-fuel ratio will oscillate slightly between the rich side and the lean side. The presence of a small amount of CeO2 in the upper front C can cope with such subtle air-fuel ratio fluctuations.

[0144] <Fourth Test> In this test, the CeO2 content D of the upper rear part D is madeCeO2 Four different exhaust gas purification catalysts (Examples 15 to 18) were evaluated for their exhaust gas purification performance during high-speed operation.

[0145] 1. Preparation of each example (1) Example 15 In Example 15 of the fourth test, an exhaust gas-purifying catalyst was prepared by the same procedure as in Example 1 of the first test except that the components of each slurry (lower layer front portion A to upper layer rear portion D) were changed.

[0146] Specifically, the slurry for the lower front portion A in Example 15 was a mixture of Pd nitrate (Pd content: 3.4 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 8 g), Al2O3 powder (40 g), and an aqueous solvent. The slurry for the lower rear portion B was a mixture of Pd nitrate (Pd content: 3.4 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 22 g), Al2O3 powder (55 g), and an aqueous solvent. The slurry for the upper front portion C was a mixture of Rh nitrate solution (Rh content: 0.3 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 20% (CeO2 content: 3 g), Al2O3 powder (75 g), and an aqueous solvent. The slurry for the upper rear portion D is a slurry obtained by mixing a nitric Rh solution (Rh content: 0.3 g), a CeO2-ZrO2 composite oxide having a CeO2 content of 20% (CeO2 content: 3 g), Al2O3 powder (75 g) and an aqueous solvent.

[0147] (2) Example 16~Example 18 In Examples 16 to 18, except for changing the CeO2 content D of the upper rear portion D as shown in Table 4, CeO2 Otherwise, the same procedure as in Example 15 was followed to produce an exhaust gas-purifying catalyst.

[0148] 2. Evaluation Test (1) Durability test Following the same procedure as in the first test, an accelerated durability test equivalent to 120,000 kilometers was conducted on the exhaust gas purifying catalyst of each example.

[0149] (2) High-speed operation evaluation In this test, the exhaust gas purification catalyst after the durability test was evaluated for NO xPurification performance. Specifically, each exhaust gas purification catalyst was installed on a 1.5L turbocharged vehicle and actually drove in WLTC mode. Then, the NO x Emissions (mg / km) are considered as NO during high-speed operation x The results are shown in Table 4 and Figure 8 .

[0150] [Table 4] As shown in Table 4 and Figure 8 As shown in the figure, compared with Example 18, the NO x The emission is significantly reduced. It can be seen that if the CeO2 content D in the upper rear part is reduced CeO2 , the exhaust gas purification performance during high-speed operation will be improved. It can be inferred that this is because the CeO2 around Rh is reduced, resulting in the suppression of the solid solution of Rh and CeO2 caused by high-temperature exhaust gas. On the other hand, compared with Example 17, the NO x Emissions are significantly reduced. This suggests that the presence of a certain amount of CeO2 in the upper rear portion D improves exhaust gas purification performance during high-speed operation. This is presumably due to the ability to cope with rapid fluctuations in the exhaust gas air-fuel ratio over short periods.

[0151] <Fifth Test> In this test, twelve types of exhaust gas purifying catalysts (Examples 19 to 30) were produced, each having a different average particle size of a supporting material in each region, and their exhaust gas purification performance was evaluated.

[0152] 1. Preparation of each example (1) Example 19 In Example 19 of the fifth test, an exhaust gas-purifying catalyst was prepared by the same procedure as in Example 1 of the first test, except that the components of each slurry (lower layer front portion A to upper layer rear portion D) were changed.

[0153] Specifically, the slurry for the lower front portion A in Example 19 was a mixture of Pd nitrate (Pd content: 2.5 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 8 g), Al2O3 powder (40 g), and an aqueous solvent. The slurry for the lower rear portion B was a mixture of Pd nitrate (Pd content: 1.7 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 40% (CeO2 content: 22 g), Al2O3 powder (55 g), and an aqueous solvent. The slurry for the upper front portion C was a mixture of Rh nitrate solution (Rh content: 0.2 g), a CeO2-ZrO2 composite oxide with a CeO2 content of 20% (CeO2 content: 2.9 g), Al2O3 powder (75 g), and an aqueous solvent. The slurry for the upper rear portion D is a slurry obtained by mixing a nitric Rh solution (Rh content: 0.2 g), a CeO2-ZrO2 composite oxide having a CeO2 content of 20% (CeO2 content: 5.9 g), Al2O3 powder (75 g), and an aqueous solvent.

[0154] Then, as shown in Table 5 below, in Example 19, the particle sizes of the CeO2-ZrO2 composite oxide and Al2O3 powder were adjusted so that the average particle size (D50 A ~D50 D ) is 5μm.

[0155] (2) Examples 20 to 30 In Examples 20 to 30, the exhaust gas purifying catalysts were prepared by the same procedure as in Example 19 except that the average particle size D50 of the supporting material in each of the lower front portion A to the upper rear portion D was changed. A ~D50 D ) are shown in Table 5.

[0156] 2. Evaluation Test (1) Durability test Following the same procedure as in the first test, an accelerated durability test equivalent to 120,000 kilometers was conducted on the exhaust gas purifying catalyst of each example.

[0157] (2) Evaluation of exhaust gas purification performance In this test, the exhaust gas purification catalyst after the durability test was tested for NO x Evaluation of purification performance. Specifically, each exhaust gas purification catalyst was installed on a vehicle and actually driven in the WLTC mode. Then, the NO x Emissions (mg / km). The results are shown in Table 5.

[0158] [Table 5] As shown in Table 5, it can be confirmed that when the average particle size D50 in the upper catalyst layer is CD When the NO x The emission is reduced. It can be inferred that this effect is due to the fact that the upper catalyst layer becomes dense, thereby inhibiting the intrusion of moisture into the catalyst layer. On the other hand, as shown in Examples 24 and 25, it can be confirmed that if the average particle size D50 in the upper catalyst layer CD Reduce excessively, NO x The emission will increase instead. It can be speculated that this is because the upper catalyst layer becomes too dense, which hinders the diffusion of exhaust gas to the lower catalyst layer. Based on the above results, it can be seen that when the average particle size D50 in the upper catalyst layer is CD When the particle size is set to 2 μm or more and 5 μm or less, NO can be appropriately reduced. x Emissions.

[0159] In addition, as shown in Examples 28 to 30, it was confirmed that when not only the average particle size D50 in the upper catalyst layer (upper front portion C and upper rear portion D) was reduced, CD , also reducing the average particle size D50 in the lower front part A A When, NO x The emission rate is significantly reduced. This is presumably because the dense lower layer front portion A can suppress the intrusion of water from the upstream end.

[0160] Several embodiments of the present invention have been described above, but the above embodiment is only an example. The present invention can also be implemented in various other ways. The present invention can be implemented based on the contents of this specification and the technical common sense in the field. The technology described in the scope of protection requested includes various modifications and changes to the above-mentioned embodiments. For example, part of the above embodiment can be replaced by other modifications, or other modifications can be added to the above embodiment. In addition, as long as a certain technical feature is not described as a necessary technical feature, it can also be appropriately deleted.

[0161] Industrial applicability According to the present invention, there is provided an exhaust gas purification catalyst capable of exhibiting appropriate purification performance according to the operating conditions of an internal combustion engine.

[0162] Description of Reference Numerals 1: Exhaust gas purification catalyst; 2: Internal combustion engine; 3: Exhaust manifold; 4: Exhaust pipe; 5: Exhaust system; 6: Sensor; 7: Engine control unit (ECU); 8: First purification component; 9: Second purification component; 10: Substrate; 12: Chamber; 20: Catalyst layer; 22: Lower catalyst layer; 24: Upper catalyst layer; A: Front of lower layer; B: Rear of lower layer; C: Front of upper layer; D: Rear of upper layer.

Claims

1. An exhaust gas purification catalyst disposed in an exhaust passage of an internal combustion engine to purify exhaust gas discharged from the internal combustion engine, the exhaust gas purification catalyst comprising: a substrate having a plurality of chambers and partition walls separating the plurality of chambers; and The catalyst layer is a porous layer provided on the surface of the partition wall and comprises a catalytic metal and a supporting material for supporting the catalytic material. The catalyst layer has a stacked structure of at least two layers, with the side close to the surface of the partition wall being a lower catalyst layer and the side relatively far from the surface of the partition wall being an upper catalyst layer. As the supporting material, at least an OSC material containing CeO2 is contained, The lower catalyst layer has: The CeO2 content A extends from the upstream end of the substrate to the downstream side in the exhaust gas flow direction. CeO2 A lower front portion A having a concentration of 0 g / L to 15 g / L and containing Pd as the catalytic metal; and The CeO2 content B extends from the downstream end of the substrate to the upstream side in the exhaust gas flow direction. CeO2 The lower rear layer B contains at least one of Pd and Pt as the catalytic metal, The upper catalyst layer has: The CeO2 content C extends from the upstream end of the substrate to the downstream side in the exhaust gas flow direction. CeO2 The upper front portion C contains 1 g / L to 7 g / L of Rh as the catalytic metal; and The CeO2 content D extends from the downstream end of the substrate to the upstream side in the exhaust gas flow direction. CeO2 The upper rear portion D contains 2 g / L to 8 g / L of Rh as the catalytic metal. The average particle size D50 of the supporting material contained in the upper catalyst layer based on electron microscope observation is CD It is not less than 2μm and not more than 5μm.

2. The exhaust gas purification catalyst according to claim 1, characterized in that The supporting material contains the OSC material and Al2O3.

3. The exhaust gas purification catalyst according to claim 1 or 2, characterized in that The volume-based average particle size of the supporting material contained in the lower catalyst layer, as determined by electron microscope observation, is defined as D50. AB When the average particle size D50 CD With the average particle size D50 AB Ratio D50 CD / D50 AB It is greater than 0.4 and less than 0.

9.

4. The exhaust gas purification catalyst according to claim 3, characterized in that The average particle size D50 of the supporting material contained in the lower catalyst layer AB It is not less than 2.5μm and not more than 12.5μm.

5. The exhaust gas purification catalyst according to claim 1 or 2, characterized in that The average particle size D50 of the supporting material contained in the upper front portion A based on electron microscope observation is A It is not less than 2μm and not more than 5μm.

6. The exhaust gas purification catalyst according to claim 5, characterized in that The volume-based average particle size of the supporting material contained in the lower rear portion B based on electron microscope observation is defined as D50. B When the average particle size D50 A With the average particle size D50 B Ratio D50 A / D50 B It is greater than 0.4 and less than 0.

9.

7. The exhaust gas purification catalyst according to claim 1 or 2, characterized in that: The OSC material is CeO2-ZrO2 composite oxide.

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