Exhaust gas purifying catalyst

Abstract

To achieve excellent exhaust gas purification performance by achieving both a phosphorus poisoning suppression effect and a warm-up performance improvement effect at a high level.SOLUTION: The exhaust gas purification catalyst disclosed herein is an exhaust gas purification catalyst that purifies exhaust gas discharged from an internal combustion engine. The exhaust gas purification catalyst includes a substrate 11, a catalyst layer 20 disposed on the substrate 11 and containing a catalytic metal and an OSC material, and a phosphorus trapping layer 30 disposed on the catalyst layer 20 and containing calcium sulfate and / or calcium carbonate as a phosphorus trapping component and containing substantially no catalytic metal. The phosphorus capture layer 30 is disposed from the upstream end of the substrate 11 toward the downstream side in the exhaust gas flow direction. The phosphorus capture layer 30 includes an inlet region 32 occupying the upstream side of the phosphorus capture layer 30 and an outlet region 34 occupying the downstream side of the phosphorus capture layer 30. The phosphorus trapping component is present in a larger amount in the inlet region 32 than in the outlet region 34.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas purifying catalyst, and more particularly to an exhaust gas purifying catalyst that is disposed in an exhaust passage of an internal combustion engine and purifies exhaust gas emitted from the internal combustion engine. [Background technology]

[0002] Exhaust gases emitted from internal combustion engines of vehicles contain harmful components such as nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO). Exhaust gas purification catalysts have traditionally been used to efficiently react and remove these harmful components from exhaust gases.

[0003] Exhaust gas contains phosphorus compounds derived from lubricating oil additives and the like. When these phosphorus compounds flow into an exhaust gas purification catalyst together with the exhaust gas, they may adhere to the periphery of the catalytic metal, etc. This phenomenon is generally called "phosphorus poisoning." Such phosphorus poisoning can reduce the catalytic activity of, for example, the catalytic metal, and can reduce the purification performance of the exhaust gas purification catalyst. Patent Documents 1 to 3, for example, are prior art documents related to the suppression of such phosphorus poisoning.

[0004] Patent Document 1 describes the provision of a poisoning prevention layer containing a non-oxide containing at least one of calcium and magnesium metal elements to prevent poisoning of exhaust gas purification catalyst components by silicon compounds and phosphorus compounds. Patent Document 2 describes the provision of a phosphorus collection layer containing a complex oxide having a specific structure to suppress poisoning by phosphorus. Patent Document 3 describes the provision of a poison capture region that does not contain catalytic metal upstream of the catalytic layer in an exhaust gas purification catalyst. It also describes the provision of a region with a high concentration of catalytic metal downstream of the poison capture region. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2897367 [Patent Document 2] International Publication No. 2021 / 261363 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-6179 Summary of the Invention [Problem to be solved by the invention]

[0006] As a result of studies by the present inventors, it was found that exhaust gas purification catalysts are susceptible to phosphorus poisoning, particularly in the surface layer portion on the upstream side. Furthermore, phosphorus poisoning can adhere not only to catalytic metals but also to OSC (oxygen storage capacity) materials, which have oxygen storage and release capacity, and can reduce the oxygen storage and release capacity of the OSC material. However, Patent Document 1 does not consider phosphorus poisoning of OSC materials.

[0007] In recent years, the number of years that exhaust gas purification systems have been in use has been increasing, and the amount of phosphorus compounds that accumulate on exhaust gas purification catalysts has also been increasing. For this reason, there is a demand for technology that can capture large amounts of phosphorus. However, the configurations described in Patent Documents 1 and 2 do not have sufficient phosphorus capture performance, and the purification performance of the exhaust gas purification catalyst decreases when a large amount of phosphorus compounds flows in. Furthermore, when the content of the phosphorus scavenger is increased to improve the phosphorus capture performance, the content of the catalytic metal and OSC material decreases relatively, resulting in a decrease in the purification performance of the exhaust gas purification catalyst.

[0008] Furthermore, it has been found that when a poison capture region that does not contain catalytic metal is disposed upstream of the catalyst layer, as in the configuration described in Patent Document 3, the purification performance is unfavorable when the exhaust gas purification catalyst is not sufficiently warmed up, for example, immediately after starting the engine. According to the inventors' investigations, if the amount of catalytic metal is the same, arranging the catalytic metal upstream in the exhaust gas purification catalyst will provide favorable purification performance even immediately after starting the engine. Therefore, in the configuration described in Patent Document 3, the warm-up performance may be significantly reduced because the catalytic metal is not disposed upstream of the exhaust gas purification catalyst.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas purification catalyst which achieves both a high level of phosphorus poisoning suppression effect and a high level of warm-up performance improvement effect, and realizes excellent exhaust gas purification performance. [Means for solving the problem]

[0010] In order to achieve the above object, the technology disclosed herein provides an exhaust gas purification catalyst having the following configuration.

[0011] The exhaust gas purifying catalyst (1) disclosed herein is an exhaust gas purifying catalyst for purifying exhaust gas emitted from an internal combustion engine. The exhaust gas purifying catalyst includes a substrate, a catalyst layer disposed on the substrate and containing a catalytic metal and an OSC material, and a phosphorus-trapping layer disposed on the catalyst layer, containing calcium sulfate and / or calcium carbonate as a phosphorus-trapping component and substantially free of the catalytic metal. The phosphorus-trapping layer is disposed from the upstream end of the substrate toward the downstream side in the exhaust gas flow direction. Furthermore, the phosphorus-trapping layer of the exhaust gas purifying catalyst disclosed herein includes an inlet region that occupies half of the entire length of the phosphorus-trapping layer from the upstream end toward the downstream side, and an outlet region that occupies half of the entire length of the phosphorus-trapping layer from the downstream end toward the upstream side. The inlet region of the phosphorus-trapping layer has a higher amount of the phosphorus-trapping component than the outlet region.

[0012] Calcium sulfate and / or calcium carbonate capture a larger amount of phosphorus per gram than conventional phosphorus-trapping components such as barium sulfate. Therefore, it is possible to increase the amount of phosphorus captured while ensuring sufficient catalytic metal and OSC material content to achieve purification performance. Furthermore, by disposing the phosphorus-trapping layer on the catalyst layer at a position including the upstream end, phosphorus compounds contained in exhaust gas can be effectively captured. This configuration makes it possible to realize an exhaust gas purification catalyst that simultaneously suppresses phosphorus poisoning and achieves excellent exhaust gas purification performance.

[0013] Furthermore, the inventors' investigations revealed that because exhaust gas containing a large amount of phosphorus is supplied upstream of the exhaust gas purification catalyst, some of the phosphorus may pass through the phosphorus-trapping layer and reach the catalyst layer. On the other hand, because exhaust gas from which phosphorus has been sufficiently removed is supplied downstream of the exhaust gas purification catalyst, unreacted phosphorus-trapping layer may be observed. Based on these findings, the phosphorus-trapping layer of the exhaust gas purification catalyst disclosed herein is configured so that the amount of phosphorus-trapping component is greater in the inlet region than in the outlet region. This prevents phosphorus from reaching the catalyst layer upstream of the exhaust gas purification catalyst, thereby improving exhaust gas purification performance over long-term use. Furthermore, because the amount of phosphorus-trapping component in the outlet region is relatively reduced, the heat capacity downstream of the exhaust gas purification catalyst is reduced. As a result, the warm-up performance of the exhaust gas purification catalyst is improved, thereby improving exhaust gas purification performance during warm-up operation.

[0014] In the exhaust gas purifying catalyst (2) disclosed herein, the inlet region of the exhaust gas purifying catalyst (1) has a larger average thickness than the outlet region. According to this configuration, it is possible to easily construct a phosphorus-trapping layer in which the amount of phosphorus-trapping components present is greater in the inlet region than in the outlet region.

[0015] In the exhaust gas purifying catalyst (3) disclosed herein, the phosphorus trapping layer in the exhaust gas purifying catalyst (2) has a thickness that continuously decreases from the upstream end toward the downstream end. This makes it easy to build a phosphorus-trapping layer that is thicker in the inlet region than in the outlet region.

[0016] In the exhaust gas purifying catalyst (4) disclosed herein, the phosphorus trapping layer in the exhaust gas purifying catalyst (2) is disposed on the catalyst layer and includes a lower layer extending from the upstream end of the substrate toward the downstream side, and an upper layer disposed on the lower layer and extending from the upstream end of the substrate toward the downstream side, and the downstream end of the upper layer is disposed upstream of the downstream end of the lower layer. This makes it easy to build a phosphorus-trapping layer that is thicker in the inlet region than in the outlet region.

[0017] In the exhaust gas purifying catalyst (5) disclosed herein, the concentration of the phosphorus trapping component in the upper layer of the exhaust gas purifying catalyst (4) is higher than the concentration of the phosphorus trapping component in the lower layer. This can further improve the phosphorus poisoning suppression performance.

[0018] In the exhaust gas purifying catalyst (6) disclosed herein, in any of the exhaust gas purifying catalysts (1) to (5), the ratio (A / B) of the amount A of the phosphorus trapping component present in the inlet region to the amount B of the phosphorus trapping component present in the outlet region is 1 or more and 5 or less. This allows both phosphorus poisoning suppression performance and warm-up performance to be achieved at a higher level.

[0019] The exhaust gas purifying catalyst (7) disclosed herein is any one of the exhaust gas purifying catalysts (1) to (6), wherein the catalyst layer is disposed on the substrate and includes a first catalyst layer containing at least Rh as the catalytic metal, and a second catalyst layer disposed on the first catalyst layer and containing at least Pd as the catalytic metal. This makes it possible to more effectively prevent the catalyst layer from being poisoned by phosphorus.

[0020] In the exhaust gas purifying catalyst (8) disclosed herein, in any one of the exhaust gas purifying catalysts (1) to (7), the phosphorus trapping layer contains an Al-containing oxide in addition to the phosphorus trapping component. This can further improve the phosphorus trapping performance of the phosphorus trapping layer.

[0021] In the exhaust gas purifying catalyst (9) disclosed herein, the specific surface area of ​​the Al-containing oxide in the exhaust gas purifying catalyst (8) is 50 m 2 / g or more. This more suitably improves the phosphorus trapping performance of the phosphorus trapping layer.

[0022] In the exhaust gas purifying catalyst (10) disclosed herein, in any of the exhaust gas purifying catalysts (1) to (9), the length of the phosphorus trapping layer in the extension direction is 30% or more and 80% or less of the total length from the upstream end to the downstream end of the substrate, which is taken as 100%. As a result, the upstream side of the catalyst layer can be prevented from being poisoned by phosphorus due to the phosphorus-trapping layer, and the downstream side of the catalyst layer can be more easily brought into contact with exhaust gas, thereby more effectively demonstrating purification performance.

[0023] In the exhaust gas purifying catalyst (11) disclosed herein, in any one of the exhaust gas purifying catalysts (1) to (10), the catalyst layer is not disposed downstream of the phosphorus trapping layer in the exhaust gas flow direction. This allows for better purification performance even immediately after the engine is started. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram of an exhaust gas purification system according to the first embodiment. [Figure 2] FIG. 2 is a perspective view that schematically shows the exhaust gas purifying catalyst according to the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view that schematically shows a cross section of the exhaust gas purifying catalyst according to the first embodiment, taken along the cylinder axis direction. [Figure 4] FIG. 4 is a cross-sectional view that schematically shows a cross section of the exhaust gas purifying catalyst according to the second embodiment, taken along the cylinder axis direction. [Figure 5]FIG. 5 is a graph showing the measurement results of the amount of non-methane organic gas emissions in Example 1 and Comparative Example 1. [Figure 6] FIG. 6 is a graph showing the measurement results of the total emissions of non-methane organic gases and NOX in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0025] Preferred embodiments of the present invention will be described below with reference to the drawings. Matters necessary for implementing the present invention other than those specifically mentioned in this specification can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function are designated by the same reference numerals, and redundant explanations may be omitted or simplified. Dimensional relationships (length, width, thickness, etc.) in each drawing do not necessarily reflect actual dimensional relationships. Furthermore, in this specification, the notation "A to B" (A and B are arbitrary numbers) indicating a range means A or more and B or less.

[0026] [First embodiment] <Exhaust gas purification system> FIG. 1 is a schematic diagram of an exhaust gas purification system 1 according to a first embodiment. The exhaust gas purification system 1 includes an internal combustion engine (engine) 2 and an exhaust gas purification device 3. The exhaust gas purification system 1 purifies harmful components contained in exhaust gas emitted from the internal combustion engine 2, such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), and also captures particulate matter (PM) contained in the exhaust gas. The arrows in FIG. 1 indicate the flow direction of the exhaust gas. In the following description, the side closer to the internal combustion engine 2 along the flow of the exhaust gas is referred to as the upstream side (also referred to as the "exhaust gas inflow side" or "front side"), and the side away from the internal combustion engine 2 is referred to as the downstream side (also referred to as the "exhaust gas outflow side" or "rear side").

[0027] Here, the internal combustion engine 2 is primarily configured as a gasoline engine for a gasoline vehicle. However, the internal combustion engine 2 may also be an engine other than a gasoline engine, such as a diesel engine or an engine installed in a hybrid vehicle. The internal combustion engine 2 has a combustion chamber (not shown). The combustion chamber is connected to a fuel tank (not shown). In this example, gasoline is stored in the fuel tank. However, the fuel stored in the fuel tank may be diesel fuel (light oil) or the like. In the combustion chamber, fuel supplied from the fuel tank is mixed with oxygen and burned. This converts combustion energy into mechanical energy. The combustion chamber is connected to an exhaust port. The exhaust port is connected to an exhaust gas purification device 3. The burned fuel gas becomes exhaust gas and is discharged to the exhaust gas purification device 3. The exhaust gas contains unburned components (harmful components).

[0028] The exhaust gas purification device 3 includes an exhaust path 4, an engine control unit (ECU) 7, a sensor 8, a first catalyst 10, and a second catalyst 9. The exhaust path 4 is an exhaust gas flow path through which exhaust gas flows. In this embodiment, the exhaust path 4 includes an exhaust manifold 5 and an exhaust pipe 6. One end (upstream end) of the exhaust manifold 5 is connected to an exhaust port (not shown) of the internal combustion engine 2. The other end (downstream end) of the exhaust manifold 5 is connected to the exhaust pipe 6. In the middle of the exhaust pipe 6, the first catalyst 10 and the second catalyst 9 are arranged in this order from the upstream side.

[0029] The second catalyst 9 may be the same as a conventional catalyst and is not particularly limited. The second catalyst 9 may be, for example, a conventionally known oxidation catalyst (DOC), a three-way catalyst, or a NOx adsorber-reduction catalyst (LNT). The second catalyst 9 may include, for example, a carrier and a precious metal, such as rhodium (Rh), palladium (Pd), or platinum (Pt), supported on the carrier. The second catalyst 9 is not an essential component and may be omitted.

[0030] Here, the first catalyst 10 is the catalyst that first comes into contact with exhaust gas. The first catalyst 10 is an example of a catalyst for purifying exhaust gas disclosed herein. Hereinafter, the first catalyst 10 may be referred to as the "catalyst for purifying exhaust gas 10." As will be described in detail later, the first catalyst 10 has the function of purifying HC, CO, and NOx, which are harmful components of exhaust gas. The arrangement of the first catalyst 10 and the second catalyst 9 may be arbitrarily changed. Furthermore, the number of first catalysts 10 and second catalysts 9 is not particularly limited, and multiple first catalysts 10 and multiple second catalysts 9 may be provided. Furthermore, upstream of the first catalyst 10, a catalyst having a different configuration from the first catalyst 10 and the second catalyst may be further arranged, such as a NOx storage-reduction (NSR) catalyst that stores NOx during normal operation (lean conditions) and purifies NOx using HC and CO as reducing agents when a large amount of fuel is injected (rich atmosphere).

[0031] The ECU 7 controls the internal combustion engine 2 and the exhaust gas purification device 3. The configuration of the ECU 7 may be the same as that of a conventional device and is not particularly limited. The ECU 7 is, for example, a processor or an integrated circuit. The ECU 7 is electrically connected to sensors 8 (e.g., pressure sensors, oxygen sensors, temperature sensors, etc.) installed at various locations in the internal combustion engine 2 and the exhaust gas purification device 3. Information detected by the sensors 8 is received by the ECU 7 as an electric signal via an input port (not shown). The ECU 7 receives information such as the operating state of the vehicle and the amount, temperature, and pressure of exhaust gas emitted from the internal combustion engine 2. The ECU 7 transmits a control signal via an output port (not shown), for example, in accordance with the received information. The ECU 7 controls the start and stop of the exhaust gas purification device 3 in accordance with, for example, the amount of exhaust gas emitted from the internal combustion engine 2, etc.

[0032] <Exhaust gas purification catalyst> Fig. 2 is a perspective view schematically showing the exhaust gas purifying catalyst 10 according to the first embodiment. Fig. 3 is a cross-sectional view schematically showing the cross section of the exhaust gas purifying catalyst 10 according to the first embodiment cut along the cylinder axis direction.

[0033] 2 and 3, arrows indicate the flow of exhaust gas. That is, in FIGS. 2 and 3, the left side is the upstream side (front side) of the exhaust path 4 that is relatively close to the internal combustion engine 2, and the right side is the downstream side (rear side) of the exhaust path 4 that is relatively far from the internal combustion engine 2. Also, in FIGS. 2 and 3, the symbol X indicates the cylinder axis direction of the exhaust gas purification catalyst 10 (first catalyst 10). The first catalyst 10 is installed in the exhaust path 4 so that the cylinder axis direction X is along the flow direction of the exhaust gas. Hereinafter, in the cylinder axis direction X, the side indicated by X1 is the upstream side (also referred to as the exhaust gas inflow side or front side), and the side indicated by X2 is the downstream side (also referred to as the exhaust gas outflow side or rear side).

[0034] The exhaust gas purification catalyst 10 functions to purify HC, CO, and NOx, which are harmful components in exhaust gas. The exhaust gas purification catalyst 10 disclosed herein can effectively purify exhaust gas containing phosphorus compounds. For example, the exhaust gas purification catalyst 10 can maintain high purification performance even if a large amount of phosphorus derived from oil reaches the catalyst and poisons it. Although not particularly limited, the exhaust gas purification catalyst 10 can effectively purify CO, HC, and NOx in exhaust gas even if the content of phosphorus compounds per exhaust gas purification catalyst is approximately 8 g to 13 g in terms of elemental phosphorus. The content of phosphorus compounds per exhaust gas purification catalyst can be confirmed by XRF (X-ray fluorescence analysis) or the like. An exhaust gas inlet is provided at an end of the upstream side X1 of the exhaust gas purification catalyst 10. An exhaust gas outlet is provided at an end of the downstream side X2 of the exhaust gas purification catalyst 10. The outer shape of the exhaust gas purification catalyst 10 is cylindrical. However, the external shape of the exhaust gas purifying catalyst 10 is not particularly limited, and may be, for example, an elliptical cylindrical shape, a polygonal cylindrical shape, a pipe shape, a foam shape, a pellet shape, a fiber shape, or the like.

[0035] As shown in Fig. 3, for example, an exhaust gas purification catalyst 10 includes a substrate 11, a catalyst layer 20 formed on the substrate 11, and a phosphorus-trapping layer 30 formed on the catalyst layer 20. With this configuration, exhaust gas that flows into the exhaust gas purification catalyst 10 comes into contact with the phosphorus-trapping layer 30 before the catalyst layer 20. This makes it possible to suitably prevent phosphorus compounds contained in the exhaust gas from adhering to the catalyst layer 20. As a result, the catalytic function of the catalytic metal contained in the catalyst layer 20 and the oxygen storage and release capacity of the OSC (oxygen storage capacity) material are not inhibited by phosphorus, allowing the catalyst to exhibit suitable purification performance.

[0036] The substrate 11 constitutes the framework of the exhaust gas purification catalyst 10. The substrate 11 is not particularly limited, and various materials and shapes conventionally used for this type of application can be used. In the illustrated example, a substrate with a straight flow structure is used as the substrate 11. The substrate 11 may be made of ceramics such as cordierite, aluminum titanate, or silicon carbide, or may be a metal carrier made of stainless steel (SUS), an Fe-Cr-Al alloy, or an Ni-Cr-Al alloy. As shown in FIG. 2, the substrate 11 has a honeycomb structure. The substrate 11 includes a plurality of cells (cavities) 12 regularly arranged in the cylindrical axis direction X and partition walls (ribs) 14 separating the plurality of cells 12. Although not particularly limited, the length (total length) of the substrate 11 along the cylindrical axis direction X may be approximately 10 mm to 500 mm, for example, 50 mm to 300 mm. The volume of the substrate 11 may be approximately 0.1 L to 10 L, for example, 1 L to 5 L. In this specification, the "volume of the substrate" refers to the apparent volume (bulk volume) including the volume of the substrate 11 itself (net volume) as well as the volume of the cells 12 inside.

[0037] The cells 12 are flow paths for exhaust gas. The cells 12 extend in the cylinder axis direction X. The cells 12 are through-holes that penetrate the substrate 11 in the cylinder axis direction X. The shape, size, number, etc. of the cells 12 can be designed taking into consideration, for example, the flow rate and components of the exhaust gas supplied to the exhaust gas purification catalyst 10. The shape of a cross section of the cells 12 perpendicular to the cylinder axis direction X is not particularly limited. The cross section of the cells 12 may be various geometric shapes, such as a square, parallelogram, rectangle, trapezoid, or other rectangular shape, or other polygonal shape (e.g., a triangle, hexagon, octagon), or a circle. The partition walls 14 face the cells 12 and separate adjacent cells 12. Although not particularly limited, the thickness of the partition walls 14 (the dimension in the direction perpendicular to the surface; the same applies hereinafter) may be approximately 10 μm to 500 μm, for example, 20 μm to 100 μm, from the viewpoint of improving mechanical strength and reducing pressure loss.

[0038] The catalyst layer 20 is a site where exhaust gas is purified. The catalyst layer 20 disclosed herein contains a catalytic metal and an OSC material. The exhaust gas that flows into the exhaust gas purification catalyst 10 comes into contact with the catalyst layer 20 while flowing through the flow paths (cells 12) of the exhaust gas purification catalyst 10. This purifies harmful components in the exhaust gas. For example, HC and CO contained in the exhaust gas are oxidized by the catalytic function of the catalyst layer 20 and converted (purified) into water, carbon dioxide, etc. Furthermore, for example, NOx is reduced by the catalytic function of the catalyst layer 20 and converted (purified) into nitrogen.

[0039] As shown in Fig. 3 , the catalyst layer 20 is provided closer to the surface of the substrate 11 than a phosphorus-trapping layer 30, which will be described later, in the thickness direction perpendicular to the cylinder axis direction X. The catalyst layer 20 is provided on the surface of the substrate 11, specifically on the partition walls 14. However, the catalyst layer 20 may partially or entirely penetrate into the interior of the catalyst layer 20. The catalyst layer 20 is typically a porous body having a large number of interconnected pores.

[0040] 3, the catalyst layer 20 has a laminated structure in which two catalyst layers with different configurations are laminated in a thickness direction perpendicular to the cylinder axis direction X. That is, the catalyst layer 20 here includes a first catalyst layer 21 provided on the surface of the partition walls 14 of the substrate 11 and a second catalyst layer 22 provided on the first catalyst layer 21. The first catalyst layer 21 and the second catalyst layer 22 may have different lengths or thicknesses. Furthermore, a third layer (intermediate layer) with different composition or properties may be provided between the first catalyst layer 21 and the second catalyst layer 22. The catalyst layer 20 may include the first catalyst layer 21, one or more third layers, and the second catalyst layer 22.

[0041] The first catalytic layer 21 and the second catalytic layer 22 each contain a catalytic metal. The catalytic metal is a precious metal that purifies harmful components in exhaust gas. The catalytic metal is not particularly limited, and any precious metal that has been conventionally used in this type of catalyst may be used. Specific examples of such precious metals include platinum group elements such as rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), osmium (Os), and iridium (Ir); gold (Au); and silver (Ag). These may be used alone or in combination of two or more. Among these, from the viewpoint of catalytic performance, Pt, Rh, Pd, Ir, and Ru are preferred, and Pt, Rh, and Pd are more preferred. The content of the catalytic metal is not particularly limited, but is preferably 0.05 g / L to 10 g / L, and may be 0.1 g / L to 5 g / L, per 1 L of volume of the portion of the substrate on which the catalytic layer 20 is formed along the cylindrical axis direction X.

[0042] In the exhaust gas purification catalyst 10 disclosed herein, the first catalytic layer 21 and the second catalytic layer 22 preferably contain different types of catalytic metals. For example, the first catalytic layer 21 may contain an oxidation catalyst with high oxidation activity, and the second catalytic layer 22 may contain a reduction catalyst with high reduction activity. Specifically, the first catalytic layer 21 preferably contains at least one of Pd and Pt as the catalytic metal, and more preferably Rh. The second catalytic layer 22 contains a reduction catalyst with high reduction activity. The second catalytic layer 22 preferably contains Pd as the catalytic metal. This allows for optimal purification of HC, CO, and NOx contained in exhaust gas. Furthermore, by arranging the catalytic metals in different layers, sintering of the precious metals and the like is suppressed, allowing the purification performance of each catalytic metal to be optimally exhibited.

[0043] In the exhaust gas purification catalyst 10 disclosed herein, it is preferable that the first catalytic layer 21 contains Rh as a catalytic metal and the second catalytic layer 22 contains Pd as a catalytic metal. Rh contributes significantly to the purification of both HC and CONOx, and particularly contributes significantly to the purification of NOx. However, Rh tends to be more susceptible to phosphorus poisoning than Pd. For this reason, in this embodiment, the second catalytic layer 22 containing Pd is formed on the first catalytic layer 21 containing Rh. This configuration can more effectively suppress phosphorus poisoning of Rh in the first catalytic layer 21. However, this configuration does not limit the technology disclosed herein. For example, the first catalytic layer 21 may contain Pd, and the second catalytic layer 22 may contain Rh. According to the technology disclosed herein, phosphorus poisoning of the second catalytic layer 22 containing Rh can be effectively suppressed by the phosphorus trapping layer 30 described below.

[0044] The catalytic metal is preferably in the form of sufficiently small particles in order to increase the contact area with exhaust gas. The average particle diameter of the catalytic metal is generally 0.1 nm to 15 nm, for example, 10 nm or less, and preferably 5 nm or less. In this specification, the "average particle diameter" refers to the number-based average value of particle diameters of 20 or more particles determined by observation with a transmission electron microscope (TEM).

[0045] The first catalytic layer 21 and the second catalytic layer 22 each contain a carrier that supports a catalytic metal. The carrier is not particularly limited, and any inorganic compound that has been conventionally used in this type of catalyst may be used. The carrier is preferably an inorganic porous material with a large specific surface area. In this specification, the term "specific surface area" refers to the specific surface area measured by the BET method, unless otherwise specified. Examples of the carrier include metal oxides such as alumina (Al2O3), zirconia (ZrO2), silica (SiO2), ceria (CeO2), and titania (TiO2), as well as solid solutions thereof (e.g., ceria-zirconia composite oxides), and combinations thereof. The shape (external shape) of the carrier material is not particularly limited, but a powder (e.g., alumina powder) is preferably used to ensure a larger specific surface area. The carrier particles should preferably have a specific surface area of ​​50 m2 or more. 2 / g or more 500m 2 / g or less (e.g., 200m 2 / g or more 400m 2 / g or less) from the viewpoint of heat resistance and structural stability. The average particle size of the carrier particles is, for example, about 0.001 μm to 10 μm (preferably 0.01 μm to 5 μm).

[0046] The first catalytic layer 21 and the second catalytic layer 22 each contain an OSC material. The OSC material has the function of storing oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is lean and releasing the stored oxygen when the air-fuel ratio of the exhaust gas is rich (oxygen storage and release capacity), and is a component that has the effect of mitigating atmospheric fluctuations. The OSC material may function as a support for a catalytic metal, or may be a non-supporting material that does not support a catalytic metal. Specific examples of the OSC material include metal oxides (Ce-containing oxides) containing ceria (CeO2) with high oxygen storage capacity. The Ce-containing oxide may be ceria, or may be a composite oxide of ceria and a metal oxide other than ceria. From the perspective of improving heat resistance and durability, the Ce-containing oxide may be an oxide containing Zr, such as a CeO2-ZrO2 composite oxide (CZ composite oxide). The CZ composite oxide may be, for example, La2O3, Pr6O 10 , Nd2O3, Y2O3, or other rare earth metal oxides.

[0047] The CZ composite oxide may be Ce-rich or Zr-rich. In some embodiments, the ceria content may be approximately 10% by mass to 70% by mass, for example 20% by mass to 60% by mass, when the entire CZ composite oxide is taken as 100% by mass. When the ceria content is equal to or greater than a predetermined value, the oxygen storage and release capacity can be further improved. On the other hand, when the ceria content is equal to or less than a predetermined value, the heat resistance can be improved. Within the above range, the effects of the technology disclosed herein and heat resistance can be achieved at a high level.

[0048] The catalyst layer 20 may contain other components in addition to the above-described catalyst metal and OSC material. Specifically, for example, the catalyst layer 20 may contain a promoter component. Suitable examples of the promoter component include alkaline earth metal elements such as barium (Ba) and strontium (Sr). The catalyst layer 20 may contain, for example, an alkaline earth metal element in the form of an oxide, hydroxide, carbonate, nitrate, sulfate, phosphate, acetate, formate, oxalate, halide, or the like. The content of such alkaline earth metal element, such as Ba, in the catalyst layer 20 may be, for example, about 0.1 g / L to 10 g / L (preferably 1 g / L to 10 g / L) per 1 L of volume of the portion of the substrate on which the catalyst layer 20 is formed along the cylindrical axis direction X. Although not particularly limited, by having Pd as the catalytic metal coexist with a promoter component (especially Ba) in the first catalytic layer 21, sintering of Pd is suppressed by electron donation from Ba to Pd, and the catalytic activity of Pd can be improved. Therefore, when a promoter component is included, it is preferable that the promoter component be included in the first catalytic layer 21 and coexist with Pd.

[0049] The catalyst layer 20 may be provided along the cylindrical axis direction X from the end 11a on the upstream side X1 of the substrate 11 toward the downstream side X2. Alternatively, the catalyst layer 20 may be provided along the cylindrical axis direction X from the end 11b on the downstream side X2 of the substrate 11 toward the upstream side X1. Preferably, the catalyst layer 20 is provided along the cylindrical axis direction X from the end 11a on the upstream side X1 of the substrate 11 toward the downstream side X2. The catalyst layer 20 may be provided continuously or intermittently on the substrate 11. The overall coating width (average length) L1 of the catalyst layer 20 in the cylindrical axis direction X may be designed taking into consideration, for example, the size of the substrate 11 and the flow rate of exhaust gas flowing through the exhaust gas purification catalyst 10. In some embodiments, the coating width L1 of the catalyst layer 20 in the cylinder axis direction X satisfies 0.5L≦L1≦L, preferably 0.8L≦L1≦L, for example, 0.9L≦L1≦L, where L is the total length of the exhaust gas purifying catalyst 10 in the cylinder axis direction X.

[0050] The coating amount (formed amount) of the catalyst layer 20 is not particularly limited. The coating amount of the catalyst layer 20 is, for example, 10 g / L to 500 g / L, or may be 100 g / L to 300 g / L, per 1 L of the volume of the portion of the substrate on which the catalyst layer 20 is formed along the cylindrical axis direction X. By satisfying the above range, it is possible to achieve both an improvement in the purification performance of harmful components and a reduction in pressure loss at a high level. In addition, the thickness of the catalyst layer 20 is not particularly limited, and may be appropriately designed taking into consideration durability, peeling resistance, and the like. The thickness of the catalyst layer 20 (the average length in the thickness direction perpendicular to the cylindrical axis direction X) is, for example, 1 to 100 μm, or may be 5 to 100 μm.

[0051] The phosphorus-trapping layer 30 has the function of trapping phosphorus compounds contained in exhaust gas. By trapping phosphorus compounds, the phosphorus-trapping layer 30 can prevent the catalyst layer 20 from being poisoned by phosphorus and thereby reducing purification performance. The inventors have found that the surface layer portion of the exhaust gas purifying catalyst 10 on the exhaust gas inflow side (upstream side X1) is most susceptible to phosphorus poisoning. Therefore, as shown in FIG. 3 , the phosphorus-trapping layer 30 is disposed above the catalyst layer 20 in the thickness direction perpendicular to the cylindrical axis direction X of the exhaust gas purifying catalyst 10 (i.e., on the side farther from the surface of the substrate 11 than the catalyst layer 20), and along the cylindrical axis direction X from the end 11a of the upstream side X1 of the substrate 11 toward the downstream side X2. This allows the phosphorus-trapping layer 30 to suitably trap phosphorus compounds contained in exhaust gas, making the catalyst layer 20 less likely to be poisoned by phosphorus and ensuring sufficient purification performance. Although not particularly limited, the content of the phosphorus trapping component in the phosphorus trapping layer 30 is, for example, preferably 1 g / L to 100 g / L per 1 L of volume of the portion of the substrate on which the phosphorus trapping layer 30 is formed along the cylinder axis direction X, more preferably 20 g / L to 80 g / L, and even more preferably 30 g / L to 80 g / L.

[0052] The phosphorus-trapping layer 30 contains calcium sulfate and / or calcium carbonate as a phosphorus-trapping component. While calcium (Ca), barium (Ba), strontium (Sr), magnesium (Mg), and other elements are known to trap phosphorus, the inventors discovered that calcium, among these, has an extremely high phosphorus trapping capacity per gram and can trap a large amount of phosphorus with a small amount added. They also discovered that incorporating calcium as calcium sulfate and calcium carbonate into the phosphorus-trapping layer 30 further improves its reactivity with phosphorus. Thus, by including calcium sulfate and / or calcium carbonate as the phosphorus-trapping component, the phosphorus trapping capacity can be significantly increased even with a content similar to that of conventional phosphorus-trapping components. Therefore, sufficient amounts of catalytic metals, OSC materials, and the like can be ensured in the exhaust gas purification catalyst 10, thereby suppressing phosphorus poisoning while fully demonstrating purification performance. The presence of calcium sulfate and / or calcium carbonate in the phosphorus trapping layer can be confirmed, for example, by observing the coating layer (phosphorus trapping layer) using SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy) or EPMA (Electron Probe Micro Analyzer), or by XRD (X-ray Diffraction) analysis of a scraped-off coating layer (phosphorus trapping layer).

[0053] Furthermore, the inventors have found that calcium has a higher reactivity with phosphorus than other materials and that its compounds with phosphorus are highly stable. Specifically, even if other materials, such as alumina, combine with phosphorus to capture phosphorus, they decompose and release phosphorus in high-temperature environments (e.g., environments above 800°C) or in severe redox environments. The released phosphorus eventually reaches the catalyst layer 20 and poisons the catalytic metal (e.g., Rh or Pd). On the other hand, the inventors have found that calcium forms very stable compounds with phosphorus, and its chemical state remains unchanged even in high-temperature environments (e.g., above 1000°C) or in severe redox environments, and the captured phosphorus is not released. Thus, the exhaust gas purification catalyst 10 disclosed herein uses calcium as a phosphorus capture component, thereby suppressing the re-release of phosphorus and preventing phosphorus from migrating to the catalyst layer 20. This more effectively protects the catalyst layer 20 from phosphorus poisoning.

[0054] Furthermore, the phosphorus trapping layer 30 of the exhaust gas purifying catalyst 10 according to this embodiment includes an inlet region 32 and an outlet region 34. The inlet region 32 extends from an end 30a of the phosphorus trapping layer 30 on the upstream side X1 toward the downstream side X2. The inlet region 32 occupies half of the total length L1 of the phosphorus trapping layer 30. On the other hand, the outlet region 34 extends from an end 30b of the phosphorus trapping layer 30 on the downstream side X2 toward the upstream side X1. The outlet region 34 also occupies half of the total length of the phosphorus trapping layer 30. The inlet region 32 of the phosphorus trapping layer 30 contains a higher amount of phosphorus trapping components than the outlet region 34. This achieves both a high level of phosphorus poisoning suppression effect and a high level of warm-up performance improvement effect, thereby achieving excellent exhaust gas purification performance. Specifically, exhaust gas containing a high concentration of phosphorus is likely to be supplied to the upstream side X1 of the exhaust gas purifying catalyst 10. In contrast, in this embodiment, an inlet region 32 is formed in which a large amount of the phosphorus trapping component is present. This prevents phosphorus in the exhaust gas from passing through the phosphorus trapping layer 30 and reaching the catalyst layer 20. As a result, the exhaust gas purifying catalyst 10 according to this embodiment can suppress performance degradation of the catalyst layer 20 due to phosphorus poisoning. Meanwhile, as described above, the phosphorus trapping component is a ceramic such as calcium sulfate or calcium carbonate, and therefore has a large heat capacity. Therefore, the region in which the phosphorus trapping layer 30 is formed tends to be less susceptible to temperature rise during warm-up operation. In contrast, in this embodiment, the amount of the phosphorus trapping component present in the outlet region 34 is relatively small. As a result, the warm-up performance of the exhaust gas purifying catalyst 10 is improved, and therefore the exhaust gas purification performance during warm-up operation can be improved.

[0055] Although details will be described later, the means for increasing the amount of the phosphorus trapping component in the inlet region 32 compared to the outlet region 34 is not limited to a specific means, and various means can be adopted. For example, as shown in FIG. 3, the exhaust gas purifying catalyst 10 according to this embodiment has a phosphorus trapping layer 30 whose thickness continuously decreases from an end 30a on the upstream side X1 toward an end 30b on the downstream side X2. In other words, the upper surface of the phosphorus trapping layer 30 shown in FIG. 3 has a downward slope from the upstream side X1 toward the downstream side X2. This makes the average thickness of the inlet region 32 thicker than the average thickness of the outlet region 34, so that the amount of the phosphorus trapping component in the inlet region 32 can be relatively increased.

[0056] The phosphorus trapping layer 30 does not have to be formed over the entire length of the substrate 11. For example, the phosphorus trapping layer 30 shown in FIG. 3 extends from an end 11a on the upstream side X1 of the substrate 11 toward the downstream side X2. However, the end 30b on the downstream side X2 of the phosphorus trapping layer 30 does not reach the end 11b on the downstream side X2 of the substrate 11. In the exhaust gas purifying catalyst 10 according to this embodiment, phosphorus can be sufficiently trapped in the inlet region 32 of the phosphorus trapping layer 30, so that even if the catalyst layer 20 on the downstream side X2 is exposed, a decrease in exhaust gas purification performance due to phosphorus poisoning can be suitably prevented. Furthermore, by adopting this configuration, the heat capacity of the downstream side X2 of the exhaust gas purifying catalyst 10 can be further reduced, thereby achieving better warm-up performance. When the end 11a on the upstream side X1 of the substrate 11 is taken as 0% and the end 11b on the downstream side X2 is taken as 100%, the phosphorus-trapping layer 30 is preferably provided with a coating width (average length) of at least 30% or more, and may be provided with a coating width of 40% or more, or may be provided with a coating width of 50% or more, for example, 100% (i.e., the entire length in the cylinder axis direction X). As a result, the inflowing exhaust gas contacts the phosphorus-trapping layer 30 before contacting the catalyst layer 20, so that phosphorus compounds can be suitably captured and phosphorus poisoning of the catalyst layer 20 can be suppressed. On the other hand, from the viewpoint of improving warm-up performance, the phosphorus-trapping layer 30 is preferably provided with a coating width of 90% or less, more preferably a coating width of 80% or less, and may be provided with a coating width of 70% or less, or may be provided with a coating width of 60% or less. For example, when the length in the cylinder axis direction X is taken as 100%, the phosphorus trapping layer 30 may be provided with a coating width of 30% to 90% (preferably 30% to 80%) from the end of the upstream side X1 toward the downstream side X2. This allows both phosphorus poisoning prevention performance and warm-up performance to be achieved at a higher level.

[0057] The phosphorus trapping layer 30 preferably contains an Al-containing oxide in addition to the phosphorus trapping component. The phosphorus trapping layer 30 may further improve, for example, its phosphorus trapping performance. Furthermore, the phosphorus trapping layer 30 may contain an Al-containing oxide, which improves at least one of the following: the heat resistance of the phosphorus trapping layer 30; the durability of the phosphorus trapping layer 30; and the peeling of the phosphorus trapping layer 30 from the catalyst layer 20. The Al-containing oxide may be alumina (Al2O3) or a composite oxide of alumina and a metal oxide other than alumina (e.g., a rare earth metal oxide). From the viewpoint of improving the heat resistance and durability, the Al-containing oxide may be, for example, a La2O3-Al2O3 composite oxide. The La2O3-Al2O3 composite oxide may be La-rich or Al-rich. The mixing ratio of the metal oxide other than alumina in the La2O3-Al2O3 composite oxide is not particularly limited. From the viewpoint of suppressing deterioration over time during use, when the entire La2O3-Al2O3 composite oxide is taken as 100 mass%, the metal oxides other than alumina may be, for example, less than 50 mass%, and may be 0.1 mass% to 20 mass%.

[0058] In the exhaust gas purifying catalyst 10 disclosed herein, the phosphorus trapping layer 30 has a specific surface area of ​​20 m 2 / g or more, and the specific surface area is 50m 2 More preferably, the phosphorus trapping layer 30 contains an Al-containing oxide having a specific surface area of ​​50 m / g or more. 2 The specific surface area of ​​the alumina is preferably 80 m / g or more. 2 / g or more, and 100m 2 The upper limit of the specific surface area is not particularly limited, but is, for example, 220 m 2 / g or less, and 2 / g or less. 2 / g or more, the number of contact points with the phosphorus compounds contained in the exhaust gas increases, and the phosphorus compounds can be more suitably captured. This further suppresses phosphorus poisoning of the catalyst layer 20, thereby improving the purification performance of the exhaust gas purifying catalyst 10.

[0059] As described above, the exhaust gas purification catalyst 10 can increase the amount of trapped phosphorus by including an Al-containing oxide in addition to the phosphorus trapping component. From this perspective, the alumina content is preferably, for example, 20 g / L or more, more preferably 30 g / L or more, per 1 L of the volume of the portion of the substrate on which the phosphorus trapping layer 30 is formed along the cylindrical axis direction X. On the other hand, if the phosphorus trapping layer 30 contains too much alumina, the thickness of the phosphorus trapping layer 30 may increase, which is undesirable because it makes it difficult for exhaust gas to come into contact with the catalyst layer 20. From this perspective, the alumina content is preferably 90 g / L or less, more preferably 80 g / L or less, per 1 L of the volume of the portion of the substrate on which the phosphorus trapping layer 30 is formed along the cylindrical axis direction X.

[0060] The catalyst layer 20 may contain other components in addition to the above-mentioned catalyst metal and Al-containing oxide, such as a binder such as silica sol, various additives, and the like.

[0061] As described above, the catalyst layer 20 contains a catalytic metal and an OSC material. When the catalytic metal is poisoned with phosphorus, its catalytic performance deteriorates. Furthermore, when the OSC material is poisoned with phosphorus, its oxygen storage and release capacity is not properly exhibited, resulting in a deterioration in the purification performance of the catalyst as a whole. According to the results of studies by the present inventors, even when calcium sulfate or calcium carbonate, which has high phosphorus trapping capacity, is mixed into the catalyst layer 20 as described above, it is difficult to suppress phosphorus poisoning of the catalytic metal and the OSC material. For this reason, in the exhaust gas purification catalyst 10 disclosed herein, as shown in FIG. 3 , the phosphorus trapping layer 30 and the catalyst layer 20 are independent, and the phosphorus trapping layer 30 is disposed on the catalyst layer 20. From the above viewpoint, it is preferable that the phosphorus trapping layer 30 is substantially free of the catalytic metal, and it is more preferable that the phosphorus trapping layer 30 is substantially free of the catalytic metal and the OSC material. In this specification, the phrase "the phosphorus-trapping layer is substantially free of a certain component" means that the component is not intentionally mixed in at least when the phosphorus-trapping layer is formed. Therefore, for example, it is acceptable for the component to be unintentionally mixed in from another layer when forming another layer or when using the exhaust gas purification catalyst. It goes without saying that the unavoidable presence of trace components is also acceptable. Although not particularly limited, the phrase "the phosphorus-trapping layer is substantially free of a certain component" means, for example, that the content of the component relative to the total mass of the phosphorus-trapping layer is 1% by mass or less (preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0% by mass).

[0062] In the exhaust gas purifying catalyst 10 disclosed herein, it is preferable that the catalyst layer 20 containing catalytic metal is not disposed on the downstream side X2 of the phosphorus trapping layer 30. This is because, for exhaust gas purifying catalysts 10 with the same catalytic metal content, disposing the catalytic metal on the downstream side X2 reduces purification performance when the exhaust gas purifying catalyst 10 is not sufficiently warmed up. This is because, during the catalyst warm-up process, the catalyst warms up sequentially from the upstream side X1. Therefore, if the amount of catalytic metal is the same, disposing the catalytic metal on the upstream side X1 can ensure purification performance even during warm-up. On the other hand, the downstream side X2 warms up more slowly than the upstream side X1. Therefore, if a catalytic metal is disposed on the downstream side X2, sufficient purification performance will not be achieved until the catalytic metal reaches its activation temperature. Therefore, from the above perspective, it is preferable that the catalyst layer 20 is not disposed on the downstream side X2 of the phosphorus trapping layer 30.

[0063] The coating amount (molding amount) of the phosphorus trapping layer 30 is not particularly limited. The coating amount of the phosphorus trapping layer 30 is, for example, 10 g / L to 200 g / L, or may be 30 g / L to 100 g / L, or may be 50 g / L to 100 g / L per 1 L of the volume of the portion of the substrate on which the phosphorus trapping layer 30 is formed along the cylindrical axis direction X. By satisfying the above range, the phosphorus trapping layer 30 can optimally exhibit its phosphorus trapping function. The thickness of the phosphorus trapping layer 30 is not particularly limited and may be appropriately designed taking into consideration durability, peel resistance, and the like. The thickness of the phosphorus trapping layer 30 (average length in the thickness direction perpendicular to the cylindrical axis direction X) is, for example, 1 to 100 μm, or may be 5 to 100 μm.

[0064] <Method of manufacturing exhaust gas purification catalyst> The exhaust gas purification catalyst 10 described above can be prepared, for example, by the following procedure. First, a substrate 11, a first catalyst layer forming slurry for forming the first catalyst layer 21, a second catalyst layer forming slurry for forming the second catalyst layer 22, and a phosphorus trapping layer forming slurry for forming the phosphorus trapping layer 30 are prepared. The first catalyst layer forming slurry and the second catalyst layer forming slurry may be similar to known catalyst layer forming slurries for forming catalyst layers containing three-way catalysts. For example, the first catalyst layer forming slurry and the second catalyst layer forming slurry can be prepared by dispersing a precious metal source (e.g., a solution containing precious metal ions), a carrier, and optional components (binder, various additives, etc.) in a dispersion medium. The phosphorus trapping layer forming slurry can be prepared by dispersing calcium sulfate and / or calcium carbonate as phosphorus trapping components, an Al composite oxide, and optional components (binder, various additives, etc.) in a dispersion medium.

[0065] Next, the substrate 11 is coated with a slurry for forming the first catalyst layer, a slurry for forming the second catalyst layer, and a slurry for forming the phosphorus trapping layer. These slurries can be coated by a conventional method, such as an impregnation method or a washcoat method. In one example, the slurry for forming the first catalyst layer prepared above is first flowed into the cells 12 from the end 11a of the upstream side X1 of the substrate 11, supplied to a predetermined length along the cylindrical axis direction X, dried, and then fired. Next, the slurry for forming the second catalyst layer prepared above is flowed into the cells 12 from the end 11a of the upstream side X1 of the substrate 11, supplied to a predetermined length along the cylindrical axis direction X, dried, and then fired. This allows the catalyst layer 20, which includes the first catalyst layer 21 and the second catalyst layer 22, to be formed on the substrate 11.

[0066] In this embodiment, a phosphorus trapping layer 30 is formed whose thickness continuously decreases from the end 30a on the upstream side X1 toward the end 30b on the downstream side X2. Specifically, a phosphorus trapping layer-forming slurry is applied to the end 11a on the upstream side X1 of the substrate 11, and then the slurry is dried. As a result, the opening area of ​​the cells 12 at the end 11a on the upstream side X1 is narrowed by the dried slurry. In this state, the end 11a on the upstream side X1 of the substrate 11 is again coated with the phosphorus trapping layer-forming slurry. Then, the inside of the cells 12 is suctioned from the end 11b on the downstream side X2 of the substrate 11. As a result, as shown in FIG. 3, a phosphorus trapping layer 30 whose thickness continuously decreases from the end 30a on the upstream side X1 toward the end 30b on the downstream side X2 can be formed. The methods (time, temperature, etc.) for drying and firing the slurry may be the same as conventional methods.

[0067] In forming the phosphorus trapping layer 30, the viscosity of the phosphorus trapping layer-forming slurry is preferably set to 100 mPa·s or less (preferably 90 mPa·s or less, more preferably 85 mPa·s or less, even more preferably 80 mPa·s or less, and particularly preferably 75 mPa·s or less). By introducing a low-viscosity slurry into the cell 12 after blocking the inlet of the cell 12 as described above, it is possible to more easily form the phosphorus trapping layer 30 whose thickness continuously decreases from the upstream end 30a on the X1 side toward the downstream end 30b on the X2 side. The lower limit of the viscosity of the phosphorus trapping layer-forming slurry is not particularly limited and may be 35 mPa·s or more, 40 mPa·s or more, 45 mPa·s or more, or 50 mPa·s or more. The slurry viscosity in this specification is the viscosity measured at a shear rate of 400 (1 / s) at 25°C.

[0068] The above-mentioned exhaust gas purification catalyst can be suitably used for purifying exhaust gas emitted from vehicles such as automobiles and trucks, motorcycles and mopeds, marine products such as ships, tankers, jet skis, personal watercraft and outboard motors, gardening products such as lawn mowers, chainsaws and trimmers, leisure products such as golf carts and four-wheeled buggies, power generation facilities such as cogeneration systems, and internal combustion engines such as waste incinerators.

[0069] The first embodiment of the exhaust gas purifying catalyst disclosed herein has been described above. In the exhaust gas purifying catalyst 10 configured as described above, the inlet region 32 of the phosphorus trapping layer 30 has a higher amount of phosphorus trapping components than the outlet region 34. This makes it possible to realize an exhaust gas purifying catalyst 10 that achieves both high levels of phosphorus poisoning suppression performance and high levels of warm-up performance. The exhaust gas purifying catalyst disclosed herein is not limited to the above embodiment, and various configurations can be modified as appropriate. Other embodiments of the exhaust gas purifying catalyst disclosed herein will now be described.

[0070] [Second embodiment] As shown in FIG. 3 , the thickness of the phosphorus-trapping layer 30 in the first embodiment continuously decreases from the end 30a on the upstream side X1 to the end 30b on the downstream side X2. This allows the amount of phosphorus-trapping component in the inlet region 32 to be greater than that in the outlet region 34. However, in the exhaust gas purifying catalyst disclosed herein, the amount of phosphorus-trapping component in the inlet region can be made greater than that in the outlet region by using a configuration different from that shown in FIG. 3 . For example, as shown in FIG. 4 , an exhaust gas purifying catalyst 10A according to a second embodiment includes a phosphorus-trapping layer 30 having a two-layer structure including a lower layer 36 and an upper layer 38. The lower layer 36 of this phosphorus-trapping layer 30 is disposed on the catalyst layer 20 and extends from the end 11a on the upstream side X1 of the substrate 11 toward the downstream side X2. The upper layer 38 is disposed on the lower layer 36 and extends from the end 11a on the upstream side X1 of the substrate 11 toward the downstream side X2. An end 38b of the upper layer 38 on the downstream side X2 is located further upstream X1 than an end 36b of the lower layer 36 on the downstream side X2. In other words, the phosphorus-trapping layer 30 has a two-layer structure in which the upper layer 38 is shorter than the lower layer 36. Even when such a configuration is adopted, the average thickness of the inlet region 32 is greater than the average thickness of the outlet region 34, and the amount of phosphorus-trapping component present in the inlet region 32 is greater than that in the outlet region 34. Therefore, the exhaust gas purifying catalyst 10A according to the second embodiment can also realize an exhaust gas purifying catalyst 10 that achieves both high levels of phosphorus poisoning suppression performance and high levels of warm-up performance.

[0071] 4, the two-layer structure of the phosphorus trapping layer 30 can be formed by supplying the slurry for forming the lower layer 36 into the substrate 11, drying it, and then supplying the slurry for forming the upper layer 38 into the substrate 11. In this case, the upper layer 38 can be made shorter than the lower layer 36 by adjusting the supply amount and suction force of each slurry.

[0072] 4, it is preferable to make the concentration of the phosphorus trapping component in the upper layer 38 higher than the concentration of the phosphorus trapping component in the lower layer 36. This improves the contact efficiency between phosphorus in the exhaust gas and the phosphorus trapping component, thereby further improving the phosphorus poisoning suppression performance.

[0073] [Test example] Test examples relating to the present invention will be described below, but it is not intended that the present invention be limited to those shown in the following test examples.

[0074] 1. Preparation of each example (1) Example 1 First, a cylindrical honeycomb substrate (made of cordierite, capacity: 1.1 L, substrate diameter: 120 mm, substrate overall length: 100 mm) was prepared. Next, a first catalyst layer (Rh layer), a second catalyst layer (Pd layer), and a phosphorus capture layer were formed in this order on the surface of the partition walls of this substrate, thereby producing the exhaust gas purification catalyst of Example 1. Specific procedures for forming each layer are described below.

[0075] (A) Formation of the first catalyst layer First, the catalyst source, alumina, OSC material, binder, and co-catalyst were mixed in distilled water. The catalyst source was a rhodium hydrochloride aqueous solution. La-containing composite alumina (Al2O3) was used as the alumina. The OSC material was a ceria-zirconia (CeO2-ZrO2) composite oxide containing La, Pr, Nd, and Y as additives. Barium sulfate (BaSO4) was used as the co-catalyst. This mixture was then milled to control particle size. After adjusting the pH to 6.1 by adding acetic acid, a polycarboxylic acid thickener was added to adjust the slurry viscosity to 120 mPa·s. This resulted in the preparation of a slurry for forming the first catalyst layer. The slurry for forming the first catalyst layer was then poured into the upstream end of the substrate and then sucked in from the downstream end with a blower. This coated the slurry for forming the first catalyst layer over 100% of the substrate's total length in the axial direction. Then, after drying at 250° C. for 1 hour, it was fired in an electric furnace at 500° C. for 1 hour, thereby forming a first catalyst layer on the surface of the partition walls of the substrate.

[0076] (B) Formation of the second catalyst layer Here, the slurry for forming the second catalytic layer was prepared under the same conditions and procedures as the slurry for forming the first catalytic layer, except that an aqueous solution of Pd nitrate was used as the catalyst source. Furthermore, the slurry for forming the second catalytic layer was coated according to the same procedures as for forming the first catalytic layer. The second catalytic layer was then formed on the surface of the first catalytic layer by performing drying and calcination treatments under the same conditions as for forming the first catalytic layer.

[0077] (C) Formation of phosphorus capture layer First, a phosphorus trapping component, alumina, and distilled water were mixed in a ratio of 2:2:6. Calcium carbonate was used as the phosphorus trapping component. Next, this mixture was milled to control the particle size. Acetic acid was added to adjust the pH to 3.7, and a polycarboxylic acid thickener was added to adjust the slurry viscosity to 71.3 mPa·s. This prepared a slurry for forming a phosphorus trapping layer. Next, in Example 1, the upstream end of the substrate was immersed in the phosphorus trapping layer forming slurry and then dried. This narrowed the opening area of ​​the cells at the upstream end. Then, while the upstream end of the substrate was immersed in the phosphorus trapping layer forming slurry, suction was performed from the downstream end with a blower. The suction conditions were adjusted so that the phosphorus trapping layer forming slurry coated a portion of the substrate corresponding to 34% of the total length in the cylindrical axis direction. In this test, the amount of slurry supplied was set so that 45 g of the phosphorus trapping component (calcium carbonate) was present throughout the phosphorus trapping layer. The substrate was then dried at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour, forming a phosphorus-trapping layer whose thickness continuously decreased from the upstream end to the downstream end (see Figure 3).

[0078] (2) Comparative Example 1 In Comparative Example 1, an exhaust gas purification catalyst was produced under the same conditions as in Example 1, except for a change in the procedure of "(C) Formation of the phosphorus trapping layer." Specifically, in Comparative Example 1, the viscosity of the phosphorus trapping layer forming slurry was adjusted to 118.9 mPa·s. Then, similar to the first catalyst layer forming slurry and the second catalyst layer forming slurry, the phosphorus trapping layer forming slurry was poured into the upstream end of the substrate and then sucked from the downstream end with a blower. Note that in Comparative Example 1, as in Example 1, the suction conditions were adjusted so that the phosphorus trapping layer forming slurry was coated on an area corresponding to 34% of the total length of the substrate in the cylindrical axis direction.

[0079] (3) Example 2 In Example 2, an exhaust gas purification catalyst was prepared under the same conditions as in Example 1, except for a change in the procedure of "(C) Formation of the phosphorus trapping layer." Specifically, in Example 2, two types of slurries for forming the phosphorus trapping layer were prepared. The first phosphorus trapping layer-forming slurry was prepared by mixing a phosphorus trapping component, alumina, and distilled water in a ratio of 1:2:7, and the slurry viscosity was adjusted to 166 mPa·s. On the other hand, the second phosphorus trapping layer-forming slurry was prepared by mixing a phosphorus trapping component, alumina, and distilled water in a ratio of 2:1:7, and the slurry viscosity was adjusted to 151 mPa·s. In Example 2, the first phosphorus trapping layer-forming slurry was poured into the upstream end of the substrate, and then sucked with a blower so that the slurry coated a portion corresponding to 34% of the total length of the substrate. The slurry was then dried at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. As a result, a lower phosphorus trapping layer was formed on the surface of the second catalyst layer. Next, the slurry for forming the second phosphorus trapping layer was poured into the upstream end of the substrate, and then sucked with a blower so that the slurry coated a portion of the substrate corresponding to 22% of the total length. The substrate was then dried at 250°C for 1 hour, and then fired in an electric furnace at 500°C for 1 hour. This resulted in an upper phosphorus trapping layer being formed on the surface of the lower phosphorus trapping layer. As described above, in Example 2, a two-layer phosphorus trapping layer (see FIG. 4) was formed in which the upper layer was shorter than the lower layer.

[0080] 2.Evaluation Test (1) Evaluation of the distribution of phosphorus capture layers In this test, the regions where the phosphorus trapping layer was formed were examined for Examples 1 and 2 and Comparative Example 1. Specifically, a region where the phosphorus trapping layer was reliably formed was cut out from the prepared exhaust gas purification catalyst. Specifically, as described above, the blower conditions and the like were adjusted so that the phosphorus trapping layer was formed 34% (i.e., 34 mm) from the upstream end of the substrate with a total length of 100 mm. Therefore, the region where the phosphorus trapping layer was reliably formed could be cut out by cutting the exhaust gas purification catalyst perpendicularly to the cylindrical axis direction at the 29 mm portion (34 mm - 5 mm). The cut sample was then divided into two at a position halfway along the cylindrical axis direction (14.5 mm point). The Ca weight (g / L) of the upstream sample was measured using ICP atomic emission spectrometry, and this measurement result was defined as "the amount A of the phosphorus trapping component present in the inlet region." Similarly, the Ca weight (g / L) of the downstream sample was measured and defined as "the amount B of the phosphorus trapping component present in the outlet region." The abundance ratio (A / B) of the phosphorus trapping component in the inlet region to the outlet region was then calculated. The results are shown in Table 1.

[0081] [Table 1]

[0082] As shown in Table 1, in Example 1, the abundance ratio (A / B) of the phosphorus trapping component in the inlet region to the outlet region was 1.19. This indicates that by adjusting the slurry viscosity or performing a blocking treatment during slurry supply, a phosphorus trapping layer with a higher abundance of the phosphorus trapping component in the inlet region than in the outlet region can be achieved. Furthermore, in Example 2, the abundance ratio (A / B) of the phosphorus trapping component in the inlet region to the outlet region was 1.61. This indicates that even when a phosphorus trapping layer with a two-layer structure of different lengths is formed, the abundance of the phosphorus trapping component can be made higher in the inlet region than in the outlet region. On the other hand, in Comparative Example 1, in Example 1, the abundance ratio (A / B) of the phosphorus trapping component in the inlet region to the outlet region was 0.9, indicating that the phosphorus trapping component was more abundant in the outlet region. This is presumably due to a large amount of slurry flowing downstream during suction by the blower.

[0083] (2) Evaluation of exhaust gas purification performance In this test, the exhaust gas purification performance of Example 1 and Comparative Example 1 from the above-mentioned examples was evaluated. Specifically, the exhaust gas purification catalyst of each example was attached to an engine bench (2.3LT), and a phosphorus poisoning treatment was performed by attaching 8 g of phosphorus. Next, after the phosphorus poisoning treatment, the engine bench was operated in FTP-75 driving mode, and the amount of NMOG (non-methane organic gas) emissions in each phase of Bag 1 to Bag 3 was measured. The Bag 1 phase indicates the cold start phase, the Bag 2 phase indicates the transient phase, and the Bag 3 phase indicates the hot start phase. The measurement results are shown in Figure 5. In this test, the total amount of NMOG and NOx emissions during the test was also measured. The measurement results are shown in Figure 6.

[0084] First, as shown in FIG. 6, Example 1 exhibited reduced NMOG and NOx emissions compared to Comparative Example 1. This indicates that excellent phosphorus poisoning suppression performance can be achieved by forming a phosphorus-trapping layer in which the amount of phosphorus-trapping component is greater in the inlet region than in the outlet region. Furthermore, as shown in FIG. 5, Example 1 exhibited a more favorable reduction in NMOG emissions in Bag 1, which indicates the cold start phase (i.e., warm-up operation). This is presumably due to the fact that the amount of phosphorus-trapping component in the outlet region was relatively reduced, thereby reducing the heat capacity and improving the warm-up performance. Furthermore, it is presumed that the relatively increased amount of phosphorus-trapping component in the inlet region also contributed to the reduction in catalytic activity due to a decrease in specific surface area caused by phosphorus poisoning.

[0085] Although several embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiments. For example, it is possible to replace part of the above-described embodiments with other modified embodiments, and it is also possible to add other modified embodiments to the above-described embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate. [Explanation of symbols]

[0086] 1 Exhaust gas purification system 2. Internal combustion engine 3. Exhaust gas purification equipment 4 Exhaust route 5 exhaust manifold 6 exhaust pipe 7 Engine Control Unit 8 sensors 9 Second catalyst 10 First catalyst (exhaust gas purification catalyst) 11 Base material 12 cells (hollow) 14 Partition (rib) 20 Catalyst layer 21 1st catalyst layer 22 Second catalyst layer 30 Phosphorus Capture Layer 32 Entry area 34 Exit area 36 Lower layer 38 Upper layer

Claims

1. An exhaust gas purification catalyst that purifies exhaust gas emitted from an internal combustion engine, A substrate; a catalyst layer disposed on the substrate, the catalyst layer comprising a catalytic metal and an OSC material; a phosphorus trapping layer disposed on the catalyst layer, the phosphorus trapping layer containing calcium sulfate and / or calcium carbonate as a phosphorus trapping component and substantially free of the catalytic metal; It is equipped with the phosphorus-trapping layer is disposed from an upstream end of the substrate toward a downstream end in the exhaust gas flow direction, The phosphorus trapping layer is an inlet region occupying half of the entire length of the phosphorus trapping layer from the upstream end of the phosphorus trapping layer toward the downstream side; an outlet region occupying half of the entire length of the phosphorus trapping layer from the downstream end of the phosphorus trapping layer toward the upstream side; Equipped with An exhaust gas purifying catalyst, characterized in that the amount of the phosphorus trapping component present is greater in the inlet region than in the outlet region.

2. 2. The exhaust gas purifying catalyst according to claim 1, wherein the inlet region has an average thickness greater than that of the outlet region.

3. 3. The exhaust gas purifying catalyst according to claim 2, wherein the thickness of the phosphorus-trapping layer continuously decreases from the upstream end toward the downstream end.

4. The phosphorus trapping layer is a lower layer disposed on the catalyst layer and extending from the upstream end of the substrate toward the downstream side; an upper layer disposed on the lower layer and extending from the upstream end of the substrate toward the downstream side; It is equipped with 3. The exhaust gas purifying catalyst according to claim 2, wherein a downstream end of the upper layer is disposed upstream of a downstream end of the lower layer.

5. 5. The exhaust gas purifying catalyst according to claim 4, wherein the concentration of the phosphorus trapping component in the upper layer is higher than the concentration of the phosphorus trapping component in the lower layer.

6. 6. The exhaust gas purification catalyst according to claim 1, wherein a ratio (A / B) of an amount A of the phosphorus trapping component present in the inlet region to an amount B of the phosphorus trapping component present in the outlet region is 1 or more and 5 or less.

7. The catalyst layer is a first catalytic layer disposed on the substrate and containing at least Rh as the catalytic metal; a second catalyst layer disposed on the first catalyst layer and containing at least Pd as the catalytic metal; The exhaust gas purifying catalyst according to claim 1, comprising:

8. 2. The exhaust gas purifying catalyst according to claim 1, wherein the phosphorus-trapping layer contains an Al-containing oxide in addition to the phosphorus-trapping component.

9. The specific surface area of ​​the Al-containing oxide is 50 m ２ 9. The exhaust gas purifying catalyst according to claim 8, wherein the Mo content is 1 / g or more.

10. 2. The exhaust gas purification catalyst according to claim 1, wherein, when the total length of the substrate in the exhaust gas flow direction from the upstream end to the downstream end is taken as 100%, the average length of the phosphorus capture layer in the exhaust gas flow direction is at least 30%.

11. 2. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst layer is not disposed downstream of the phosphorus trapping layer in the exhaust gas flow direction.

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