Exhaust gas purification catalyst

Abstract

DEPCT6922 / 09 / 2568 This invention provides a catalytic converter for exhaust gas purification which both suppresses It is toxic due to phosphorus and its potential for improved exhaust gas purification has been compromised. The effect was achieved. The catalytic converter for exhaust gas purification, which is revealed here, is a catalyst for... A flue gas purification system designed to purify flue gases emitted from... Internal combustion engine. Catalytic converter for exhaust gas purification, including base material 11, layer. The catalyst 20, which is arranged on a base material 11 and consists of a catalyst metal and OSC material, and a phosphorus-trapping layer 30, which is arranged on a catalyst layer 20, consists of... Calcium sulfate and / or calcium carbonate as phosphorus-trapping components; And, containing almost no metal catalyst, the phosphorus-binding layer 30 is arranged from the section. The ends of the base material 11 from the upstream to the downstream side in the direction of exhaust gas flow;

Description

Exhaust gas purification catalyst

[0001] The present invention relates to an exhaust gas purification catalyst. More specifically, the present invention relates to an exhaust gas purification catalyst that is disposed in the exhaust path of an internal combustion engine and purifies exhaust gas emitted from the internal combustion engine. This application claims priority based on Japanese Patent Application No. 2022-210636 filed on December 27, 2022, the entire contents of which are incorporated herein by reference.

[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 and the like. This phenomenon is generally called "phosphorus poisoning." Such phosphorus poisoning can reduce the catalytic activity of the catalytic metal, for example, 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.

[0005] Japanese Patent Publication No. 2897367 International Publication No. 2021 / 261363 Japanese Patent Application Publication No. 2013-6179

[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 the catalytic metal but also to an OSC (oxygen storage capacity) material having oxygen storage and release capacity, reducing the oxygen storage and release capacity of the OSC material. However, Patent Document 1 does not consider phosphorus poisoning of the OSC material.

[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 when a large amount of phosphorus compounds flows in, the purification performance of the exhaust gas purification catalyst decreases. 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, and therefore the purification performance of the exhaust gas purification catalyst decreases.

[0008] Furthermore, it was found that when a poison capture region not containing 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 absence of catalytic metal upstream of the exhaust gas purification catalyst can significantly reduce warm-up performance.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide an exhaust gas purification catalyst which is capable of suppressing poisoning by phosphorus and exhibiting excellent exhaust gas purification performance.

[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 purification catalyst (1) disclosed herein is an exhaust gas purification catalyst for purifying exhaust gas emitted from an internal combustion engine. The exhaust gas purification 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 and 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 an upstream end of the substrate toward a downstream end in the exhaust gas flow direction.

[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 a sufficient content of catalytic metal and OSC material to exhibit purification performance. Furthermore, by disposing the phosphorus-trapping layer on the catalyst layer at a position including the upstream end, it is possible to effectively capture phosphorus compounds contained in exhaust gas. 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] In the exhaust gas purifying catalyst (2) disclosed herein, the catalyst layer of the exhaust gas purifying catalyst (1) is arranged on the substrate, and the catalyst layer includes a first catalyst layer containing at least Pd as the catalytic metal, and a second catalyst layer arranged on the first catalyst layer and containing at least Rh as the catalytic metal, thereby enabling efficient purification of HC, CO, and NOx.

[0014] In the exhaust gas purifying catalyst (3) disclosed herein, in the exhaust gas purifying catalyst (1) or (2), the phosphorus-trapping layer contains an Al-containing oxide in addition to the phosphorus-trapping component, thereby further improving the phosphorus trapping performance of the phosphorus-trapping layer.

[0015] In the exhaust gas purifying catalyst (4) disclosed herein, the specific surface area of ​​the Al-containing oxide in the exhaust gas purifying catalyst (3) is 50 m ２ / g or more, the phosphorus trapping performance of the phosphorus trapping layer is more suitably improved.

[0016] In the exhaust gas purification catalyst (5) disclosed herein, in any of the exhaust gas purification catalysts (1) to (4), the length of the phosphorus-trapping layer in the extension direction is 30% to 80% of the total length from the upstream end to the downstream end of the substrate, which is taken as 100%. This allows the phosphorus-trapping layer to suppress phosphorus poisoning on the upstream side of the catalyst layer, and the downstream side of the catalyst layer is more likely to come into contact with exhaust gas, thereby more suitably exhibiting purification performance.

[0017] In the exhaust gas purifying catalyst (6) disclosed herein, in any of the exhaust gas purifying catalysts (1) to (5), the catalyst layer is not disposed downstream of the phosphorus trapping layer in the exhaust gas flow direction, thereby achieving favorable purification performance even immediately after engine start.

[0018] FIG. 1 is a schematic diagram of an exhaust gas purification system according to one embodiment. FIG. 2 is a perspective view schematically illustrating an exhaust gas purification catalyst according to one embodiment. FIG. 3 is a diagram schematically illustrating the configuration of a catalyst layer in an exhaust gas purification catalyst according to one embodiment. FIG. 4 is a graph comparing the OSC maintenance rates of Examples 1 and 2 with those of Comparative Examples 1 to 4. FIG. 5 is a graph comparing the 50% purification achievement temperatures of Examples 1 and 2 with those of Comparative Examples 1 to 4. FIG. 6 is a graph comparing the OSC maintenance rates of Examples 2 and 11 with those of Comparative Examples 12 to 14. FIG. 7 is a graph comparing the 50% purification achievement temperatures of Examples 2 and 11 with those of Comparative Examples 12 to 14. FIG. 8 is a graph comparing the OSC maintenance rates of Examples 1, 2, 21, and 22, Comparative Example 1, and Reference Example 23. FIG. 9 is a graph comparing the 50% purification achievement temperatures of Examples 1, 2, 21, and 22, Comparative Example 1, and Reference Example 23. Fig. 10 is a graph comparing the OSC maintenance rates of Examples 2 and 31 to 34 with those of Comparative Example 12. Fig. 11 is a graph comparing the 50% purification achievement temperature of Examples 2 and 31 to 34 with those of Comparative Example 12. Fig. 12 is a graph comparing the OSC maintenance rates of Examples 2 and 41 to 44 with those of Comparative Example 12. Fig. 13 is a graph comparing the 50% purification achievement temperature of Examples 2 and 41 to 44 with those of Comparative Example 12.

[0019] 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 figure 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.

[0020] <Exhaust Gas Purification System> FIG. 1 is a schematic diagram of an exhaust gas purification system 1. 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. Note that arrows in FIG. 1 indicate the flow direction of exhaust gas. In the following description, the side closer to the internal combustion engine 2 along the flow of exhaust gas is referred to as the upstream side (also referred to as the "exhaust gas inlet side" or "front side"), and the side away from the internal combustion engine 2 along the flow of exhaust gas is referred to as the downstream side (also referred to as the "exhaust gas outlet side" or "rear side").

[0021] Here, the internal combustion engine 2 is primarily configured as a gasoline engine for a gasoline vehicle. However, the internal combustion engine 2 may 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 includes 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).

[0022] 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. The first catalyst 10 and the second catalyst 9 are arranged in the exhaust pipe 6, in that order from the upstream side.

[0023] 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 supported on the carrier, such as rhodium (Rh), palladium (Pd), or platinum (Pt). Note that the second catalyst 9 is not an essential component and may be omitted.

[0024] Here, the first catalyst 10 is the catalyst that first comes into contact with exhaust gas. The first catalyst 10 is an example of an exhaust gas purification catalyst disclosed herein. Hereinafter, the first catalyst 10 may be referred to as the "exhaust gas purification catalyst 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 with 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 larger amount of fuel is injected (rich atmosphere).

[0025] 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 in various locations of 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 electrical 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 response to the received information. The ECU 7 controls the start and stop of the exhaust gas purification device 3 in response to, for example, the amount of exhaust gas emitted from the internal combustion engine 2.

[0026] <Exhaust Gas Purification Catalyst> FIG. 2 is a perspective view schematically illustrating the exhaust gas purification catalyst 10 disclosed herein. FIG. 3 is a cross-sectional view schematically illustrating a cross section of the exhaust gas purification catalyst 10 taken along the cylinder axis direction. Note that arrows in FIGS. 2 and 3 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 represents 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 aligned with 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).

[0027] The first 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 using XRF (X-ray fluorescence analysis) or the like. The end of the first catalyst 10 on the X1 side is an exhaust gas inlet 10a, and the end on the X2 side is an exhaust gas outlet 10b. The outer shape of the first catalyst 10 is cylindrical. However, the external shape of the first 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.

[0028] 3 , the first 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.

[0029] The substrate 11 forms the framework of the first 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) and the volume of the internal cells 12.

[0030] 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, for example, taking into consideration the flow rate and components of the exhaust gas supplied to the first 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.

[0031] 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 first catalyst 10 comes into contact with the catalyst layer 20 while flowing through the flow path (cell 12) of the first 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.

[0032] 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.

[0033] In the example shown in Fig. 3, the catalyst layer 20 has a layered structure in which two catalyst layers with different configurations are stacked 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 wall 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 further 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.

[0034] 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 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, with Pt, Rh, and Pd being more preferred. The catalytic metal content 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.

[0035] 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 Pd. The second catalytic layer 22 contains a reduction catalyst with high reduction activity. The second catalytic layer 22 preferably contains Rh 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 is suppressed, allowing the purification performance of each catalytic metal to be optimally exhibited.

[0036] In the exhaust gas purification catalyst 10 disclosed herein, it is preferable that the first catalytic layer 21 contains Pd as a catalytic metal and the second catalytic layer 22 contains Rh as a catalytic metal. Rh contributes greatly to the purification of both HC and CONOx, and particularly contributes greatly to the purification of NOx. Furthermore, disposing Rh on the surface layer side of the catalytic layer 20 (i.e., the second catalytic layer 22) is preferable because it enables efficient purification of HC, CO, and NOx. However, compared with Pd, Rh tends to be more susceptible to activity reduction due to phosphorus poisoning. Therefore, disposing Rh on the surface layer side in a phosphorus-poisoned environment is not preferable. Therefore, in the exhaust gas purification catalyst 10 disclosed herein, a phosphorus-trapping layer 30 (described later) is provided on the Rh-containing second catalytic layer 22, thereby suitably suppressing phosphorus poisoning of the second catalytic layer 22. According to this configuration, phosphorus poisoning of Rh can be suitably suppressed, and therefore Rh can be arranged on the surface layer side, thereby realizing an exhaust gas purification catalyst that can suitably purify all of HC, CO, and NOx.

[0037] The catalytic metal is preferably in the form of sufficiently small particles from the viewpoint of increasing 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).

[0038] 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. The carrier may be, for example, alumina (Al ２ O ３ ), zirconia (ZrO ２ ), silica (SiO ２ ), ceria (CeO ２ ), titania (TiO ２ Examples of suitable carrier particles include metal oxides such as zirconia and ceria, solid solutions thereof (e.g., ceria-zirconia composite oxide), and combinations thereof. The shape (external shape) of the carrier material is not particularly limited, but from the viewpoint of ensuring a larger specific surface area, powders (e.g., alumina powder) are preferably used. The carrier particles are preferably those having a specific surface area of ​​50 m ２ / g or more 500m ２ / g or less (for example, 200m ２ / g or more 400m ２ / g or less) is preferable 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).

[0039] 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-supported material that does not support a catalytic metal. Specific examples of OSC materials include metal oxides (Ce-containing oxides) containing ceria (CeO2) that have 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. The Ce-containing oxide may be an oxide containing Zr, such as CeO, from the viewpoint of improving heat resistance and durability. ２ -ZrO ２ The CZ composite oxide may be, for example, La ２ O ３ , Pr ６ O １０ , Nd ２ O ３ , Y ２ O ３ The oxide may further contain rare earth metal oxides such as:

[0040] 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. When the ceria content is within the above range, the effects of the technology disclosed herein and heat resistance can be achieved at a high level.

[0041] 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, alkaline earth metal elements in the form of oxides, hydroxides, carbonates, nitrates, sulfates, phosphates, acetates, formates, oxalates, halides, and the like. The content of such alkaline earth metal elements, such as Ba, in the catalyst layer 20 may be, for example, approximately 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 allowing Pd as the catalytic metal to 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 be allowed to coexist with Pd.

[0042] The catalyst layer 20 may be provided along the cylinder axis direction X from the exhaust gas inlet 10a toward the downstream side, or may be provided along the cylinder axis direction X from the exhaust gas outlet 10b toward the upstream side. Preferably, the catalyst layer 20 is provided along the cylinder axis direction X from the exhaust gas inlet 10a toward the downstream side. The catalyst layer 20 may be provided continuously or intermittently on the substrate 11. The entire coating width (average length) L1 of the catalyst layer 20 in the cylinder 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 purifying 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 entire length of the exhaust gas purifying catalyst 10 in the cylinder axis direction X.

[0043] 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 high levels of improvement in the purification performance of harmful components and low pressure loss. The thickness of the catalyst layer 20 is not particularly limited and may be appropriately designed taking into account 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.

[0044] 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 purification catalyst 10 on the exhaust gas inlet side (upstream side) 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 purification 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 inlet 10 a (i.e., the upstream end) toward the downstream side. This allows the phosphorus compounds contained in exhaust gas to be suitably trapped, 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 preferably, for example, 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.

[0045] 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 the like are known as phosphorus-trapping components, the inventors discovered that, among these, calcium 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 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 are 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 by, for example, 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).

[0046] 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 and 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, preventing the release of captured phosphorus. 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.

[0047] The phosphorus-trapping layer 30 preferably contains an Al-containing oxide in addition to the above phosphorus-trapping component. When the phosphorus-trapping layer 30 contains an Al-containing oxide, for example, the phosphorus trapping performance can be further improved. Furthermore, when the phosphorus-trapping layer 30 contains an Al-containing oxide, at least one of the functions of improving the heat resistance of the phosphorus-trapping layer 30, improving the durability of the phosphorus-trapping layer 30, and suppressing peeling of the phosphorus-trapping layer 30 from the catalyst layer 20 is improved. The Al-containing oxide is alumina (Al ２ O ３ ) or a composite oxide of alumina and a metal oxide other than alumina (for example, a rare earth metal oxide). From the viewpoint of improving heat resistance and durability, the Al-containing oxide may be, for example, La ２ O ３ -Al ２ O ３ It is preferable that the La be a composite oxide. ２ O ３ -Al ２ O ３ The composite oxide may be La-rich or Al-rich. ２ O ３ -Al ２ O ３The mixing ratio of the metal oxide other than alumina in the composite oxide is not particularly limited. ２ O ３ -Al ２ O ３ When the entire composite oxide is taken as 100 mass %, the metal oxide other than alumina is, for example, less than 50 mass %, and may be 0.1 mass % to 20 mass %.

[0048] 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 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 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.

[0049] As described above, the exhaust gas purification catalyst 10 can increase the amount of phosphorus trapped 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 cylinder 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 cylinder axis direction X.

[0050] 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.

[0051] As described above, the catalyst layer 20 contains a catalytic metal and an OSC material. When the catalytic metal is poisoned by phosphorus, its catalytic performance deteriorates. Furthermore, when the OSC material is poisoned by 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 have 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 perspective, 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 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, when forming another layer or when using the exhaust gas purification catalyst, it is acceptable for the above components to be unintentionally mixed in from another layer. It goes without saying that the unavoidable presence of trace components is also acceptable. While 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 mass% or less (preferably 0.5 mass% or less, more preferably 0.1 mass% or less, and even more preferably 0 mass%).

[0052] As described above, the phosphorus-trapping layer 30 is provided along the cylinder axis direction X from the exhaust gas inlet 10 a (i.e., the upstream end) toward the downstream side. The phosphorus-trapping layer 30 is preferably provided continuously on the catalyst layer 20. This makes it possible to suitably suppress phosphorus poisoning of the catalyst layer 20. Although not particularly limited, when the upstream end and the downstream end in the cylinder axis direction X of the exhaust gas purifying catalyst 10 are taken as 0% and 100%, respectively, 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, or may be provided with a coating width of, for example, 100% (i.e., the entire length in the cylinder axis direction X). This allows the inflowing exhaust gas to come into contact with the phosphorus-trapping layer 30 before coming into contact with the catalyst layer 20, thereby suitably capturing phosphorus compounds and suppressing phosphorus poisoning of the catalyst layer 20. On the other hand, from the viewpoint of the contactability between the exhaust gas and the catalyst layer 20, the phosphorus-trapping layer 30 may be disposed on the catalyst layer 20 on the upstream side of the exhaust gas purifying catalyst 10, but may not be disposed on the catalyst layer 20 on the downstream side. Specifically, when the upstream end of the exhaust gas purifying catalyst 10 in the cylinder axis direction X is taken as 0% and the downstream end is taken as 100%, the phosphorus-trapping layer 30 is preferably provided with a coating width of 90% or less, more preferably 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 is preferably provided from the upstream end toward the downstream side with a coating width of 30% to 90% (preferably 30% to 80%). This effectively suppresses phosphorus poisoning on the upstream side of the exhaust gas purification catalyst 10, and effectively brings the exhaust gas into contact with the catalyst layer 20 on the downstream side, thereby improving the overall purification performance of the exhaust gas purification catalyst 10.

[0053] In the exhaust gas purification catalyst 10 disclosed herein, it is preferable that a catalyst layer 20 containing a catalytic metal is not disposed downstream of the phosphorus-trapping layer 30. This is because, for exhaust gas purification catalysts 10 with the same catalytic metal content, arranging the catalytic metal downstream reduces purification performance when the exhaust gas purification catalyst 10 is not sufficiently warmed up. This is because, since the catalyst warms up sequentially from the upstream side during the warm-up process, arranging the catalytic metal upstream for the same amount of catalytic metal ensures purification performance even during warm-up. However, the downstream side warms up more slowly than the upstream side, and if the catalytic metal is disposed downstream, purification performance is not fully exhibited until the catalytic metal reaches its activation temperature. Therefore, from the above perspective, it is preferable that a catalyst layer 20 is not disposed downstream of the phosphorus-trapping layer 30.

[0054] 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 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 (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.

[0055] <Method for Manufacturing Exhaust Gas Purification Catalyst> The above-described exhaust gas purification catalyst 10 can be produced, 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.

[0056] Next, the first catalyst layer forming slurry, the second catalyst layer forming slurry, and the phosphorus trapping layer forming slurry are applied to the substrate 11. These slurries can be applied by conventional methods, such as impregnation or washcoating. In one example, the first catalyst layer forming slurry prepared above is first introduced into the cells 12 from the inlet 10a end of the substrate 11, supplied to a predetermined length along the cylindrical axis direction X, dried, and then fired. Next, the second catalyst layer forming slurry prepared above is introduced into the cells 12 from the inlet 10a end of the substrate 11, supplied to a predetermined length along the cylindrical axis direction X, dried, and then fired. Then, the phosphorus trapping layer forming slurry is introduced into the cells 12 from the outlet 10b end of the substrate 11, supplied to a predetermined length along the cylindrical axis direction X, dried, and then fired. The methods (time, temperature, etc.) for drying and firing the slurries may be the same as conventional methods. This allows the catalyst layer 20 and the phosphorus trapping layer 30 to be formed on the substrate 11. In this manner, the exhaust gas purifying catalyst 10 can be formed.

[0057] 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.

[0058] 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. In the following test examples, the unit "g / L" indicates the content per 1 L of volume of the portion of the substrate on which a predetermined layer is formed in the cylindrical axial direction.

[0059] <First Test> In this test, exhaust gas purifying catalysts with different configurations were produced using five types of slurries (A) to (E) with different compositions, and a study was conducted to determine a configuration that can suitably suppress phosphorus poisoning.

[0060] 1. Preparation of each example First, a cylindrical honeycomb substrate (made of cordierite, capacity: 1.2 L, substrate diameter: 118 mm, substrate total length: 112 mm) was prepared. Next, the following five types of slurries (slurry for forming the first catalyst layer, slurry for forming the second catalyst layer, slurry for forming the phosphorus trapping layer, slurry for forming the first mixed layer, and slurry for forming the second mixed layer) were prepared. Note that the alumina used was composite alumina containing La (Al ２ O ３ ) and the specific surface area is 100 m ２ The OSC material used was ceria-zirconia (CeO ２ -ZrO ２ (A) Slurry for forming the first catalyst layer: a mixture of an OSC material, alumina, an aqueous solution of Pd nitrate, and barium sulfate (BaSO ) as a promoter. ４) and an alumina-based binder were mixed in distilled water. Then, the mixture was milled to control the particle size, and a slurry for forming a first catalyst layer was prepared. (B) Slurry for forming a second catalyst layer: An OSC material, alumina, a Rh hydrochloride aqueous solution, and an alumina-based binder were mixed in distilled water. Then, the mixture was milled to control the particle size, and a slurry for forming a second catalyst layer was prepared. (C) Slurry for forming a phosphorus-trapping layer: Calcium sulfate (CaSO ) was used as a phosphorus-trapping component. ４ ), alumina, and an alumina-based binder were mixed in distilled water. Then, the mixture was milled to control the particle size, and a slurry for forming the phosphorus trapping layer was prepared. (D) Slurry for forming the first mixed layer: A slurry containing an OSC material, alumina, an aqueous solution of Pd nitrate, and calcium sulfate (CaSO ) as a phosphorus trapping component. ４ ) and an alumina-based binder were mixed in distilled water. Then, the mixed solution was milled to control the particle size, and a slurry for forming a first mixed layer containing Pd as a catalytic metal and calcium sulfate as a phosphorus-trapping component was prepared. (E) Slurry for forming a second mixed layer: A slurry containing an OSC material, alumina, a Rh hydrochloride aqueous solution, and calcium sulfate (CaSO ) as a phosphorus-trapping component. ４ ) and an alumina-based binder were mixed in distilled water, and the mixture was milled to control the particle size, thereby preparing a slurry for forming a second mixed layer containing Rh as a catalytic metal and calcium sulfate as a phosphorus-trapping component.

[0061] Comparative Example 1: A first catalyst layer-forming slurry was poured into the substrate from the upstream side (exhaust gas inlet side) and suctioned with a blower, thereby coating the substrate over a portion corresponding to 100% of the entire length in the axial direction. The coating amount of the first catalyst layer-forming slurry was adjusted so that the Pd content was 2.83 g / L. The slurry was then dried in a dryer at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. This formed a first catalyst layer on the surface of the partition walls of the substrate. Next, a second catalyst layer-forming slurry was poured into the substrate from the upstream side and suctioned with a blower, thereby coating the substrate over a portion corresponding to 100% of the entire length in the axial direction. The coating amount of the second catalyst layer-forming slurry was adjusted so that the Rh content was 0.12 g / L. The slurry was then dried in a dryer at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. In this way, a second catalyst layer was formed on the surface of the first catalyst layer formed as described above. In this way, an exhaust gas purifying catalyst of Comparative Example 1, which did not have a phosphorus trapping layer, was obtained.

[0062] Comparative Example 2 The slurry for forming the first catalyst layer was coated on a substrate in the same manner as in Comparative Example 1, followed by drying and firing. This formed a first catalyst layer on the surface of the partition walls of the substrate. Next, the slurry for forming the second mixed layer was poured into the substrate from the upstream side and sucked with a blower, thereby coating the substrate over a portion corresponding to 100% of the entire length in the cylindrical axis direction. The coating amount of the slurry for forming the second mixed layer was adjusted so that the Rh content was 0.12 g / L and the phosphorus-trapping component content was 30 g / L in terms of calcium sulfate. The mixture was then dried in a dryer at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. This resulted in a second mixed layer containing Rh as a catalytic metal and calcium sulfate as a phosphorus-trapping component being formed on the surface of the first catalyst layer formed above. In this manner, a catalyst for purifying exhaust gas of Comparative Example 2 having a second mixed layer on the surface of the first catalyst layer was obtained.

[0063] Comparative Example 3: The first mixed layer slurry was poured into the substrate from the upstream side and sucked with a blower to coat the substrate over a portion corresponding to 100% of the entire length in the cylindrical axis direction. The coating amount of the first mixed layer slurry was adjusted so that the Pd content was 2.83 g / L and the phosphorus trapping component content was 30 g / L in terms of calcium sulfate. The slurry was then dried in a dryer at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. This resulted in a first mixed layer containing Pd as a catalytic metal and calcium sulfate as a phosphorus trapping component on the surface of the partition wall of the substrate. Next, the second catalyst layer slurry was coated on the substrate in the same manner as in Comparative Example 1, followed by drying and firing. This resulted in a second catalyst layer being formed on the surface of the first mixed layer. In this manner, the exhaust gas purification catalyst of Comparative Example 3, which had a second catalyst layer on the surface of the first mixed layer, was obtained.

[0064] Comparative Example 4 The slurry for forming the first catalyst layer was coated on a substrate in the same manner as in Comparative Example 1, followed by drying and firing. This formed a first catalyst layer on the surface of the partition walls of the substrate. Next, the slurry for forming the second catalyst layer was coated on the substrate in the same manner as in Comparative Example 1, followed by drying and firing. This formed a second catalyst layer on the surface of the first catalyst layer. The slurry for forming the phosphorus-trapping layer was then poured into the substrate from the downstream side (exhaust gas outlet side) and sucked with a blower, thereby coating a portion of the substrate that corresponded to 40% of the downstream side in the cylindrical axis direction (i.e., a portion from 60% to 100%, where the upstream end of the substrate in the cylindrical axis direction is 0% and the downstream end is 100%). The amount of the slurry for forming the phosphorus-trapping layer was adjusted so that the content of the phosphorus-trapping component was 30 g / L in terms of calcium sulfate. This was dried in a dryer at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. As a result, a phosphorus-trapping layer containing calcium sulfate as a phosphorus-trapping component was formed on the surface of the second catalytic layer formed above, covering 40% of the surface from the downstream side in the axial direction of the substrate. In this way, a catalyst for purifying exhaust gases of Comparative Example 4 was obtained, which had the first catalytic layer and the second catalytic layer over the entire length of the substrate in the axial direction of the substrate, and the phosphorus-trapping layer covering 40% of the surface from the downstream side in the axial direction of the substrate.

[0065] Example 1: A first catalyst layer-forming slurry was poured into the substrate from the upstream side (exhaust gas inlet side) and sucked with a blower, thereby coating the substrate over a portion corresponding to 100% of the entire length in the axial direction. The coating amount of the first catalyst layer-forming slurry was adjusted so that the Pd content was 2.83 g / L. The slurry was then dried in a dryer at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. This resulted in a first catalyst layer containing Pd as a catalytic metal being formed on the surface of the partition walls of the substrate. Next, a second catalyst layer-forming slurry was poured into the substrate from the upstream side and sucked with a blower, thereby coating the substrate over a portion corresponding to 100% of the entire length in the axial direction. The coating amount of the second catalyst layer-forming slurry was adjusted so that the Rh content was 0.12 g / L. The slurry was then dried in a dryer at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. As a result, a second catalytic layer containing Rh as a catalytic metal was formed on the surface of the first catalytic layer formed above. The phosphorus-trapping layer-forming slurry was then poured into the substrate from the upstream side and sucked with a blower, thereby coating the substrate over a portion corresponding to 100% of the entire length in the axial direction of the tube. The amount of the phosphorus-trapping layer-forming slurry coated was such that the alumina content was 50 g / L and the phosphorus-trapping component content was 30 g / L in terms of calcium sulfate. This was dried in a dryer at 250°C for 1 hour and then fired in an electric furnace at 500°C for 1 hour. As a result, a phosphorus-trapping layer containing calcium sulfate as a phosphorus-trapping component was formed on the surface of the second catalytic layer formed above. In this way, the exhaust gas purifying catalyst of Example 1 was obtained, which had the first catalytic layer, the second catalytic layer, and the phosphorus-trapping layer along the entire length of the substrate in the axial direction of the tube.

[0066] Example 2 The phosphorus-trapping layer-forming slurry was poured into the substrate from the upstream side and sucked with a blower to coat a portion of the substrate that accounted for 40% from the upstream side in the cylindrical axis direction (i.e., a portion between 0% and 40%, where the upstream end of the substrate in the cylindrical axis direction is 0% and the downstream end is 100%). Other than this, the procedure was the same as in Example 1. In this way, an exhaust gas purifying catalyst of Example 2 was obtained, which had a first catalyst layer and a second catalyst layer over the entire length of the substrate in the cylindrical axis direction, and a phosphorus-trapping layer covering a portion of the substrate that accounted for 40% from the upstream side in the cylindrical axis direction.

[0067] [Phosphorus Poisoning Durability Test] For each example of the exhaust gas purification catalyst, a durability test with and without phosphorus poisoning was conducted. The durability test with phosphorus poisoning was conducted as follows. First, each example of the exhaust gas purification catalyst was installed in the exhaust system of a 5-liter V-type engine. Next, commercially available gasoline was mixed with engine oil containing a high concentration of phosphorus (P), and the gasoline was burned in the engine to generate exhaust gas containing phosphorus compounds. A durability test with phosphorus poisoning was conducted in which exhaust gas containing phosphorus compounds was passed through each example of the exhaust gas purification catalyst to cause phosphorus poisoning, while the catalyst temperature was maintained at 950°C for 150 hours. Note that the phosphorus poisoning of the exhaust gas purification catalyst at this time was controlled to be 13 g in terms of elemental phosphorus per catalyst.

[0068] The durability test without phosphorus poisoning was carried out as follows. Each example of the exhaust gas purification catalyst was installed in the exhaust system of a 5L V-type engine. Commercially available gasoline was then burned in the engine, and the catalyst temperature was maintained at 950°C for 150 hours to carry out the durability test without phosphorus poisoning.

[0069] [Evaluation of OSC Retention Rate] The OSC retention rate of each example of the exhaust gas purification catalyst was calculated by determining the OSC amount A of the exhaust gas purification catalyst subjected to a durability test with phosphorus poisoning and the OSC amount B of the exhaust gas purification catalyst subjected to a durability test without phosphorus poisoning, and then calculating the ratio of the OSC amount A to the OSC amount B. That is, the OSC retention rate of each example can be calculated from the formula: OSC retention rate of each example (%) = (OSC amount A of the exhaust gas purification catalyst of each example / OSC amount B of the exhaust gas purification catalyst of each example) × 100.

[0070] The OSC amount A of each example of the exhaust gas purifying catalyst was determined as follows. The exhaust gas purifying catalyst of each example after the durability test with phosphorus poisoning was installed in the exhaust system of a 2L L-type engine, and O ２ The air-fuel ratio (A / F) of the mixed gas supplied to the engine was periodically switched between rich and lean at predetermined intervals. ２The OSC amount A of the exhaust gas purifying catalyst of each example was calculated from the delay in the behavior of the sensor. The OSC amount B of the exhaust gas purifying catalyst of each example was calculated in the same manner as the OSC amount A, except that the exhaust gas purifying catalyst of each example after the durability test without phosphorus poisoning was installed in the exhaust system of a 2L L-type engine. Using the calculated OSC amount A and OSC amount B of each example, the OSC maintenance rate (%) of the exhaust gas purifying catalyst of each example was calculated according to the above formula. The results are shown in Figure 4.

[0071] [Evaluation of CO, HC, and NOx Purification Performance] Evaluation tests were conducted to evaluate the CO purification performance, HC purification performance, and NOx purification performance of each example of the exhaust gas purification catalyst that had undergone the durability test with phosphorus poisoning. First, the exhaust gas purification catalyst of each example that had undergone the durability test with phosphorus poisoning was installed in the exhaust system of a 2L L-type engine. Then, while supplying engine outlet gas with an A / F ratio of 14.6, the temperature was raised from 150°C to 500°C at a heating rate of 10°C / min. At this time, the CO purification rate, HC purification rate, and NOx purification rate were continuously measured from the ratio of the CO, HC, and NOx concentrations in the inflow gas to the inflow gas from the exhaust gas purification catalyst, and the temperature of the inflow gas when the purification rate of each component reached 50% (50% purification achievement temperature) was determined. The HC purification rate was calculated as the total hydrocarbon (THC) purification rate. The lower the temperature at which 50% purification is achieved, the better the purification performance. The results are shown in Figure 5.

[0072] As shown in Figure 4, the exhaust gas purification catalysts of Examples 1 and 2, which have a catalyst layer containing a catalyst metal and an OSC material and a phosphorus-trapping layer containing a phosphorus-trapping component in a region on the surface of the catalyst layer including the upstream end, have a high OSC maintenance rate even after phosphorus poisoning treatment and durability testing. Furthermore, as shown in Figure 5, the exhaust gas purification catalysts of Examples 1 and 2 have significantly high CO purification performance, HC purification performance, and NOx purification performance even after phosphorus poisoning treatment and durability testing. This is presumably because the provision of the phosphorus-trapping layer in a region including the upstream end can suppress poisoning of both the catalyst metal and the OSC material contained in the first catalyst layer and the second catalyst layer. This is presumably because sufficient oxygen is supplied to the catalyst metal, improving the purification performance of CO, HC, and NOx.

[0073] Furthermore, comparing Example 1 and Example 2, it is found that Example 2, which has a phosphorus-trapping layer covering 40% of the upstream end, has higher CO purification performance, HC purification performance, and NOx purification performance. This is presumably because the phosphorus-trapping layer is provided in a region including the upstream end which is susceptible to phosphorus poisoning, and the second catalyst layer is exposed on the downstream side which is less susceptible to phosphorus poisoning, which makes it easier for the second catalyst layer to come into contact with exhaust gas, thereby improving purification performance.

[0074] <Second Test> Here, the phosphorus trapping component contained in the slurry for forming the phosphorus trapping layer was changed to examine a component that can suitably suppress phosphorus poisoning.

[0075] Example 11 The phosphorus trapping component contained in the slurry for forming the phosphorus trapping layer was changed to calcium carbonate (CaCO ３ The coating amount of the slurry for forming the phosphorus trapping layer was changed so that the content of the phosphorus trapping component was 30 g / L in terms of calcium carbonate. Except for this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gases of Example 11.

[0076] [Comparative Example 12] Instead of the slurry for forming the phosphorus-trapping layer, a slurry containing no phosphorus-trapping component was prepared. The coating amount of this slurry was adjusted so that the alumina content was 50 g / L. Except for this, the same procedure as in Example 2 was repeated to obtain a catalyst for purifying exhaust gases of Comparative Example 12 containing no phosphorus-trapping component.

[0077] Comparative Example 13 The phosphorus trapping component contained in the slurry for forming the phosphorus trapping layer was replaced with barium sulfate (BaSO ４ The coating amount of the slurry for forming the phosphorus trapping layer was changed so that the content of the phosphorus trapping component was 30 g / L in terms of barium sulfate. Except for this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gases of Comparative Example 13.

[0078] Comparative Example 14 The phosphorus trapping component contained in the slurry for forming the phosphorus trapping layer was replaced with strontium sulfate (SrSO ４ The coating amount of this phosphorus-trapping layer-forming slurry was changed so that the content of the phosphorus-trapping component was 30 g / L in terms of strontium sulfate. Except for this, the same procedure as in Example 2 was repeated to obtain a catalyst for purifying exhaust gases of Comparative Example 14.

[0079] [Evaluation of OSC Retention Rate] The OSC retention rate was evaluated for the exhaust gas purification catalysts of Example 11 and Comparative Examples 12 to 14 prepared as described above. That is, for each example, a durability test was conducted with and without phosphorus poisoning. Then, the OSC amount A of the exhaust gas purification catalyst subjected to the durability test with phosphorus poisoning and the OSC amount B of the exhaust gas purification catalyst subjected to the durability test without phosphorus poisoning were determined, and the OSC retention rate of each example was calculated from the ratio of the OSC amount A to the OSC amount B. The results are shown in Figure 6. Note that Figure 6 also shows the results of Example 2.

[0080] [Evaluation of CO, HC, and NOx Purification Performance] The CO purification performance, HC purification performance, and NOx purification performance of the exhaust gas purification catalysts of Example 11 and Comparative Examples 12 to 14, which had been subjected to a durability test with phosphorus poisoning, were evaluated in the same manner as above. The lower the 50% purification achievement temperature, the better the purification performance. The results are shown in Figure 7. Note that Figure 7 also shows the results of Example 2.

[0081] As shown in Figure 6, it can be seen that in Examples 2 and 11, which contain calcium sulfate and calcium carbonate as phosphorus trapping components, the OSC maintenance rate is high even after the phosphorus poisoning treatment and durability test. Also, as shown in Figure 7, it can be seen that the exhaust gas purifying catalysts of Examples 2 and 11 have significantly high CO purification performance, HC purification performance, and NOx purification performance even after the phosphorus poisoning treatment and durability test. This is presumably because calcium traps a large amount of phosphorus per gram and is highly reactive with phosphorus, and therefore can suitably suppress poisoning of the catalytic metal and OSC material.

[0082] <Third Test> Here, the coating width of the phosphorus-trapping layer in the cylinder axis direction was changed to study a configuration that can suitably suppress phosphorus poisoning.

[0083] [Example 21] The slurry for forming the phosphorus trapping layer was poured into the substrate from the upstream side and sucked with a blower to coat a portion of the substrate corresponding to 30% from the upstream end in the cylindrical axis direction. An exhaust gas purifying catalyst of Example 21 was obtained in the same manner as in Example 1, except for this.

[0084] [Example 22] The slurry for forming the phosphorus trapping layer was poured into the substrate from the upstream side and sucked with a blower to coat 80% of the substrate from the upstream end in the cylindrical axis direction, but in the same manner as in Example 1, a catalyst for purifying exhaust gas of Example 22 was obtained.

[0085] The slurry for forming the phosphorus trapping layer was poured into the substrate from the upstream side and sucked with a blower to coat a portion of the substrate corresponding to 15% from the upstream end in the cylindrical axis direction. An exhaust gas purifying catalyst of Reference Example 23 was obtained in the same manner as in Example 1, except for this.

[0086] [Evaluation of OSC Retention Rate] The OSC retention rate of each of the exhaust gas purification catalysts of Examples 21 and 22 and Reference Example 23 prepared above was evaluated in the same manner as described above. That is, for each exhaust gas purification catalyst, one was subjected to a durability test with phosphorus poisoning and another was subjected to a durability test without phosphorus poisoning. Then, the OSC amount A of the exhaust gas purification catalyst subjected to the durability test with phosphorus poisoning and the OSC amount B of the exhaust gas purification catalyst subjected to the durability test without phosphorus poisoning were determined, and the OSC retention rate of each example was calculated from the ratio of the OSC amount A to the OSC amount B. The results are shown in Figure 8. Note that Figure 8 also shows the results of Examples 1 and 2 and Comparative Example 1.

[0087] [Evaluation of CO, HC, and NOx Purification Performance] The CO purification performance, HC purification performance, and NOx purification performance of the exhaust gas purification catalysts of Examples 21 and 22 and Reference Example 23, which had been subjected to durability tests with phosphorus poisoning, were evaluated in the same manner as above. The lower the 50% purification achievement temperature, the better the purification performance. The results are shown in Figure 9. Note that Figure 9 also shows the results of Examples 1 and 2 and Comparative Example 1.

[0088] As shown in Figure 8, the exhaust gas purification catalysts of Examples 1, 2, 21, and 22, in which the phosphorus-trapping layer is provided with a coating width of at least 30% from the upstream end toward the downstream side, exhibit significantly high OSC maintenance rates even after phosphorus poisoning treatment and durability testing. Furthermore, as shown in Figure 9, the exhaust gas purification catalysts of Examples 1, 2, 21, and 22 exhibit significantly high CO purification performance, HC purification performance, and NOx purification performance even after phosphorus poisoning treatment and durability testing. This is presumably because the region of the exhaust gas purification catalyst from the upstream end to approximately 30% is particularly susceptible to phosphorus poisoning. Therefore, by arranging the phosphorus-trapping layer with a coating width of at least 30% from the upstream end toward the downstream side, phosphorus poisoning can be suitably suppressed, allowing the exhaust gas purification catalyst to exhibit a high level of purification performance.

[0089] <Fourth Test> Here, the content of alumina contained in the slurry for forming the phosphorus trapping layer was changed to study a configuration that can suitably suppress phosphorus poisoning.

[0090] [Example 31] An exhaust gas purifying catalyst of Example 31 was obtained in the same manner as Example 2, except that the alumina content in the phosphorus trapping layer-forming slurry was changed and the coating amount of the phosphorus trapping layer-forming slurry was changed so that the alumina content was 10 g / L.

[0091] [Example 32] An exhaust gas purifying catalyst of Example 32 was obtained in the same manner as Example 2, except that the alumina content in the phosphorus trapping layer-forming slurry was changed and the coating amount of the phosphorus trapping layer-forming slurry was changed so that the alumina content was 30 g / L.

[0092] [Example 33] An exhaust gas purifying catalyst of Example 33 was obtained in the same manner as Example 2, except that the alumina content in the phosphorus trapping layer-forming slurry was changed and the coating amount of the phosphorus trapping layer-forming slurry was changed so that the alumina content was 80 g / L.

[0093] [Example 34] An exhaust gas purifying catalyst of Example 34 was obtained in the same manner as in Example 2, except that the alumina content in the phosphorus trapping layer-forming slurry was changed and the coating amount of the phosphorus trapping layer-forming slurry was changed so that the alumina content was 100 g / L.

[0094] [Evaluation of OSC Retention Rate] The OSC retention rate of each of the exhaust gas purification catalysts of Examples 31 to 34 prepared above was evaluated in the same manner as described above. That is, for each exhaust gas purification catalyst, one was subjected to a durability test with phosphorus poisoning and another was subjected to a durability test without phosphorus poisoning. Then, the OSC amount A of the exhaust gas purification catalyst subjected to the durability test with phosphorus poisoning and the OSC amount B of the exhaust gas purification catalyst subjected to the durability test without phosphorus poisoning were determined, and the OSC retention rate of each example was calculated from the ratio of the OSC amount A to the OSC amount B. The results are shown in Figure 10. Note that Figure 10 also shows the results of Example 2 and Comparative Example 12.

[0095] [Evaluation of CO, HC, and NOx Purification Performance] The CO purification performance, HC purification performance, and NOx purification performance of the exhaust gas purification catalysts of Examples 31 to 34, which had been subjected to durability tests with phosphorus poisoning, were evaluated in the same manner as above. The lower the 50% purification achievement temperature, the better the purification performance. The results are shown in Figure 11. Note that Figure 11 also shows the results of Example 2 and Comparative Example 12.

[0096] As shown in Figure 10, it can be seen that when the phosphorus-trapping layer contains alumina in addition to the phosphorus-trapping component, the OSC maintenance rate is high even after the phosphorus-poisoning treatment and the durability test. Also, as shown in Figure 11, it can be seen that when the phosphorus-trapping layer contains alumina in addition to the phosphorus-trapping component, the CO purification performance, HC purification performance, and NOx purification performance are high even after the phosphorus-poisoning treatment and the durability test. This is presumably because the phosphorus-trapping layer contains alumina together with the phosphorus-trapping component, and is therefore able to suitably trap phosphorus that has flowed into the exhaust gas purification catalyst. It is presumed that this makes it possible to suppress poisoning of the catalytic metal and the OSC material.

[0097] 10 and 11 , when Examples 2, 32, and 33, in which the alumina content in the phosphorus-trapping layer is 30 g / L or more and 80 g / L or less, are compared with Example 31, in which the alumina content in the phosphorus-trapping layer is 10 g / L, and Example 34, in which the alumina content in the phosphorus-trapping layer is 100 g / L, it is found that Examples 2, 32, and 33 have higher OSC retention rates and better purification performance. This is presumably because, when the phosphorus-trapping layer contains alumina in addition to the phosphorus-trapping component, and the alumina content in the phosphorus-trapping layer is 30 g / L or more, the amount of phosphorus trapped is particularly favorably increased. Furthermore, when the alumina content is about 100 g / L, the phosphorus-trapping layer tends to become thicker, making it more difficult for the inflowing exhaust gas to come into contact with the catalyst layer.

[0098] <Fifth Test> Here, the specific surface area of ​​alumina contained in the phosphorus trapping layer forming slurry was changed to study a configuration capable of suitably suppressing phosphorus poisoning. The specific surface area of ​​alumina was adjusted by heat treating the alumina.

[0099] [Example 41] The alumina contained in the slurry for forming the phosphorus trapping layer was ２ / g of alumina. Except for this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gases of Example 41.

[0100] [Example 42] The alumina contained in the slurry for forming the phosphorus trapping layer was ２ / g of alumina. Except for this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gases of Example 42.

[0101] [Example 43] The alumina contained in the slurry for forming the phosphorus trapping layer was ２ / g of alumina. Except for this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gases of Example 43.

[0102] [Example 44] The alumina contained in the slurry for forming the phosphorus trapping layer was ２ / g of alumina. Except for this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gases of Example 44.

[0103] [Evaluation of OSC Retention Rate] The OSC retention rate of each of the exhaust gas purification catalysts of Examples 41 to 44 prepared above was evaluated in the same manner as described above. That is, for each exhaust gas purification catalyst, one was subjected to a durability test with phosphorus poisoning and another was subjected to a durability test without phosphorus poisoning. Then, the OSC amount A of the exhaust gas purification catalyst subjected to the durability test with phosphorus poisoning and the OSC amount B of the exhaust gas purification catalyst subjected to the durability test without phosphorus poisoning were determined, and the OSC retention rate of each example was calculated from the ratio of the OSC amount A to the OSC amount B. The results are shown in Figure 12. Note that Figure 12 also shows the results of Example 2 and Comparative Example 12.

[0104] [Evaluation of CO, HC, and NOx Purification Performance] The CO purification performance, HC purification performance, and NOx purification performance of the exhaust gas purification catalysts of Examples 41 to 44, which had been subjected to durability tests with phosphorus poisoning, were evaluated in the same manner as above. The lower the 50% purification achievement temperature, the better the purification performance. The results are shown in Figure 13. Note that Figure 13 also shows the results of Example 2 and Comparative Example 12.

[0105] As shown in FIG. 12, when the phosphorus-trapping layer contains alumina in addition to the phosphorus-trapping component, and the specific surface area of ​​the alumina is 50 m ２ / g or more 200m ２ It can be seen that in Example 2 and Examples 42 to 44, where the OSC retention rate is 0.05 / g or less, the OSC retention rate is particularly high even after the phosphorus poisoning treatment and durability test. Furthermore, as shown in Figure 13, it can be seen that the exhaust gas purification catalysts of Example 2 and Examples 42 to 44 have particularly high CO purification performance, HC purification performance, and NOx purification performance even after the phosphorus poisoning treatment and durability test. This is presumably because the specific surface area of ​​alumina is equal to or greater than a certain level, which makes it possible to suitably capture phosphorus that has flowed into the exhaust gas purification catalyst. It is presumed that this makes it possible to more suitably suppress poisoning of the catalytic metal and OSC material.

[0106] 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.

Claims

DEPCT6922 / 09 / 25681. A catalytic converter designed to purify exhaust gases emitted from internal combustion engines, consisting of: a substrate; a catalytic layer arranged on the substrate and containing a catalyst metal and OSC material; and a phosphorus capture layer arranged on the catalytic layer, containing calcium sulfate and / or calcium carbonate as phosphorus capture components, and virtually no catalyst metal, where the phosphorus capture layer is arranged from the upstream end of the substrate to the downstream end in the direction of exhaust gas flow.

2. A catalytic converter according to claim 1, in which the catalytic layer consists of: a first catalytic layer arranged on the substrate and containing at least Pd as a catalyst metal; and a second catalytic layer arranged on the first catalytic layer and containing at least Rh as a catalyst metal.3.Catalyst for flue gas purification under claim 1, where the phosphorus capture layer consists of an Al-containing oxide in addition to the phosphorus-capturing component; 4. Catalyst for flue gas purification under claim 3, where the specific surface area of ​​the Al-containing oxide is equal to or greater than 50 m³ / g; 5. Catalyst for flue gas purification under claim 1 or 2, where the average length of the phosphorus capture layer in the flue gas flow direction is at least equal to or greater than 30% when the total length of the substrate material from the upstream end to the downstream end is treated as 100%; 6. Catalyst for flue gas purification under claim 1, where the catalytic layer is not arranged at the downstream end of the phosphorus capture layer in the flue gas flow direction.

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