JP2024093964A - Exhaust gas purification catalyst - Google Patents

Abstract

To provide an exhaust gas purifying catalyst which achieves both suppression of poisoning by phosphorus and excellent exhaust gas purification performance.SOLUTION: There is provided an exhaust gas purifying catalyst for purifying exhaust gas emitted from an internal combustion engine. The exhaust gas purifying catalyst comprises a base material 11, a catalyst layer 20, which is disposed on the base material 11 and contains a catalyst metal and an OSC material and a phosphorus trapping layer 30 which is disposed on the catalyst layer 20 and contains calcium sulfate and/or calcium carbonate as phosphorus trapping components and substantially contains no catalyst metal. The phosphorus trapping layer 30 is disposed from the end on the upstream side of the base material 11 in the exhaust gas flow direction to the downstream side.SELECTED DRAWING: Figure 3

Description

The present invention relates to a catalyst for purifying exhaust gas. More specifically, the present invention relates to a catalyst for purifying exhaust gas that is disposed in the exhaust path of an internal combustion engine and purifies the exhaust gas discharged from the internal combustion engine.

Exhaust gas emitted from internal combustion engines of vehicles and other vehicles contains 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 gas.

Exhaust gas contains phosphorus compounds derived from lubricating oil additives, etc. When these phosphorus compounds flow into an exhaust gas purification catalyst together with the exhaust gas, they may adhere to the catalytic metal and other surfaces. 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. Examples of prior art documents related to the suppression of such phosphorus poisoning include Patent Documents 1 to 3.

Patent Document 1 describes the provision of a poisoning prevention layer containing a non-oxide containing at least one of the metal elements calcium and magnesium 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 on the upstream side of the catalyst 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.

Patent Publication No. 2897367 International Publication No. 2021/261363 JP 2013-6179 A

As a result of the inventors' investigations, they found that exhaust gas purification catalysts are susceptible to phosphorus poisoning, particularly in the surface layer on the upstream side. In addition, phosphorus poisoning can adhere not only to the catalyst metal but also to OSC (oxygen storage capacity) materials that have the ability to store and release oxygen, reducing the oxygen storage and release capacity of the OSC material. However, Patent Document 1 does not consider phosphorus poisoning of OSC materials.

In recent years, the number of years that exhaust gas purification systems are in use has been increasing, and the amount of phosphorus compounds that accumulate on exhaust gas purification catalysts has also been on the rise. For this reason, technology is needed to 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. In addition, when the content of the phosphorus trapping agent is increased to improve the phosphorus capture performance, the content of the catalytic metal and OSC material decreases relatively, and the purification performance of the exhaust gas purification catalyst decreases.

In addition, it was found that when a poison capture region that does not contain catalytic metal is arranged upstream of the catalyst layer, as in the configuration described in Patent Document 3, purification performance is not favorable when the exhaust gas purification catalyst is not sufficiently warmed up, for example, immediately after the engine is started. According to the inventors' investigations, if the amount of catalytic metal is the same, favorable purification performance is exhibited even immediately after the engine is started by arranging the catalytic metal upstream in the exhaust gas purification catalyst. Therefore, in the configuration described in Patent Document 3, the warm-up performance may be significantly reduced because the catalytic metal is not arranged upstream of the exhaust gas purification catalyst.

The present invention was made in consideration of the above circumstances, and aims to provide an exhaust gas purification catalyst that suppresses phosphorus poisoning and has excellent exhaust gas purification performance.

To achieve the above objective, the technology disclosed herein provides an exhaust gas purification catalyst having the following configuration.

The exhaust gas purification catalyst (1) disclosed herein is an exhaust gas purification catalyst that purifies exhaust gas discharged from an internal combustion engine. The exhaust gas purification catalyst comprises 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.

Calcium sulfate and/or calcium carbonate capture more phosphorus per gram than conventional phosphorus-capturing components such as barium sulfate. This allows the amount of phosphorus captured to be increased while ensuring sufficient catalytic metal and OSC material content to achieve purification performance. In addition, by arranging the phosphorus-capturing layer on the catalyst layer and at a position including the upstream end, phosphorus compounds contained in exhaust gas can be effectively captured. With this configuration, it is possible to realize an exhaust gas purification catalyst that suppresses poisoning by phosphorus and has excellent exhaust gas purification performance.

In the exhaust gas purifying catalyst (2) disclosed herein, in the exhaust gas purifying catalyst (1), the catalyst layer is disposed on the substrate, and includes a first catalyst layer containing at least Pd as the catalytic metal, and a second catalyst layer is disposed on the first catalyst layer and contains at least Rh as the catalytic metal.
This allows HC, CO, and NOx to be purified efficiently.

In the exhaust gas purifying catalyst (3) disclosed herein, in the exhaust gas purifying catalyst (1) or (2) described above, 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.

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

In the exhaust gas purifying catalyst (5) disclosed herein, in any of the exhaust gas purifying catalysts (1) to (4), the length in the extension direction of the phosphorus trapping layer 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 contacted with exhaust gas, thereby more suitably exhibiting the purification performance.

In the exhaust gas purifying catalyst (6) disclosed herein, in any one 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.
This allows for optimal purification performance even immediately after the engine is started.

FIG. 1 is a schematic diagram of an exhaust gas purification system according to one embodiment. FIG. 2 is a perspective view that illustrates an exhaust gas purifying catalyst according to one embodiment. FIG. 3 is a diagram showing a schematic configuration of a catalyst layer in an exhaust gas purifying catalyst according to one embodiment. FIG. 4 is a graph comparing the OSC retention 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 and Comparative Examples 1 to 4. FIG. 6 is a graph comparing the OSC retention 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 and 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 retention 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 Comparative Example 12. FIG. 12 is a graph comparing the OSC retention 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 Comparative Example 12.

The preferred embodiment of the present invention will be described below with reference to the drawings. Matters other than those specifically mentioned in this specification that are necessary for implementing the present invention 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. In the following drawings, the same reference numerals are used for components and parts that perform the same function, and duplicated explanations may be omitted or simplified. The dimensional relationships (length, width, thickness, etc.) in each figure do not necessarily reflect the actual dimensional relationships. 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.

<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 the exhaust gas discharged from the internal combustion engine 2, such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), and collects 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 close 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 inlet 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 outlet side" or "rear side").

Here, the internal combustion engine 2 is mainly configured as a gasoline engine of a gasoline vehicle. However, the internal combustion engine 2 may be an engine other than gasoline, such as a diesel engine or an engine mounted on 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). Here, 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, the fuel supplied from the fuel tank is mixed with oxygen and burned. This converts the 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).

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 that order from the upstream side.

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

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

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 the conventional one, 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 (e.g., pressure sensors, oxygen sensors, temperature sensors, etc.) 8 installed at 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 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 discharged from the internal combustion engine 2. The ECU 7 transmits a control signal via an output port (not shown) in response to, for example, 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 discharged from the internal combustion engine 2.

<Exhaust gas purification catalyst>
FIG. 2 is a perspective view showing the catalyst 10 for purifying exhaust gas disclosed herein. FIG. 3 is a cross-sectional view showing the catalyst 10 for purifying exhaust gas cut along the cylinder axis direction. The arrows in FIG. 2 and FIG. 3 indicate the flow of exhaust gas. That is, in FIG. 2 and FIG. 3, the left side is the upstream side (front side) of the exhaust path 4 relatively close to the internal combustion engine 2, and the right side is the downstream side (rear side) of the exhaust path 4 relatively far from the internal combustion engine 2. In addition, in FIG. 2 and FIG. 3, the symbol X represents the cylinder axis direction of the catalyst 10 for purifying exhaust gas (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. In the following, in the cylinder axis direction X, the X1 side is the upstream side (also referred to as the exhaust gas inflow side, the front side), and the X2 side is the downstream side (also referred to as the exhaust gas outflow side, the rear side).

The first catalyst 10 has the function of purifying HC, CO, and NOx, which are harmful components in exhaust gas. The exhaust gas purification catalyst 10 disclosed herein can preferably 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 is poisoned. Although not particularly limited, the exhaust gas purification catalyst 10 can preferably purify CO, HC, and NOx in the exhaust gas even if the content of phosphorus compounds per exhaust gas purification catalyst is about 8g to 13g in terms of phosphorus element. The content of phosphorus compounds per exhaust gas purification catalyst can be confirmed by XRF (X-ray fluorescence analysis) or the like. The end of the X1 side of the first catalyst 10 is the exhaust gas inlet 10a, and the end of the X2 side is the exhaust gas outlet 10b. The outer shape of the first catalyst 10 is cylindrical here. 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, etc.

As shown in FIG. 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, the 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 effectively 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, and therefore it is possible to exhibit favorable purification performance.

The substrate 11 constitutes 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, silicon carbide, etc., or may be a metal carrier made of stainless steel (SUS), Fe-Cr-Al alloy, Ni-Cr-Al alloy, etc. As shown in FIG. 2, the substrate 11 has a honeycomb structure here. The substrate 11 has a plurality of cells (cavities) 12 regularly arranged in the cylindrical axis direction X, and partition walls (ribs) 14 that separate 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 internal cells 12.

The cells 12 are exhaust gas flow paths. 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 the 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, for example, a square, parallelogram, rectangle, trapezoid, or other rectangular shape, or other geometric shapes such as other polygons (e.g., triangles, hexagons, octagons), circles, etc. The partition walls 14 face the cells 12 and separate the 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 below) 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.

The catalyst layer 20 is a place 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. Also, for example, NOx is reduced by the catalytic function of the catalyst layer 20 and converted (purified) into nitrogen.

As shown in FIG. 3, the catalyst layer 20 is provided closer to the surface of the substrate 11 than the phosphorus capture 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 wall 14. However, the catalyst layer 20 may be partially or entirely permeated into the interior of the catalyst layer 20. The catalyst layer 20 is typically a porous body having a large number of interconnected voids.

In the example shown in FIG. 3, the catalyst layer 20 has a laminated structure in which two catalyst layers with different configurations are laminated in the 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. In addition, a third layer (intermediate layer) with different composition and 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.

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 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), iridium (Ir); gold (Au); and silver (Ag). These may be used alone or in combination of two or more. Among them, 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, for example, 0.05 g/L to 10 g/L per 1 L of the volume of the portion of the base material on which the catalytic layer 20 is formed along the cylinder axis direction X, and may be 0.1 g/L to 5 g/L.

In the exhaust gas purification catalyst 10 disclosed herein, it is preferable that the first catalyst layer 21 and the second catalyst layer 22 contain different types of catalytic metals. For example, it is preferable that the first catalyst layer 21 contains an oxidation catalyst with high oxidation activity, and the second catalyst layer 22 contains a reduction catalyst with high reduction activity. Specifically, it is preferable that the first catalyst layer 21 contains at least one of Pd and Pt as a catalytic metal, and it is more preferable that it contains Pd. In addition, the second catalyst layer 22 contains a reduction catalyst with high reduction activity. It is preferable that the second catalyst layer 22 contains Rh as a catalytic metal. This makes it possible to suitably purify all of HC, CO, and NOx contained in the exhaust gas. In addition, by arranging the catalytic metals in different layers, sintering of the precious metals is suppressed, and the purification performance of each catalytic metal can be suitably exhibited.

In the exhaust gas purification catalyst 10 disclosed herein, it is preferable that the first catalyst layer 21 contains Pd as a catalytic metal, and the second catalyst layer 22 contains Rh as a catalytic metal. Rh contributes highly to the purification of both HC and CONOx, and particularly to the purification of NOx. In addition, it is preferable to place Rh on the surface side (i.e., the second catalyst layer 22) of the catalyst layer 20, since it is possible to efficiently purify HC, CO, and NOx. On the other hand, Rh tends to be more easily deactivated by phosphorus poisoning than Pd. For this reason, it is not preferable to place Rh on the surface side in a phosphorus poisoning environment. Therefore, in the exhaust gas purification catalyst 10 disclosed herein, the phosphorus poisoning of the second catalyst layer 22 is suitably suppressed by providing a phosphorus trapping layer 30 described later on the second catalyst layer 22 containing Rh. With this configuration, phosphorus poisoning of Rh can be effectively suppressed, so Rh can be placed on the surface side, resulting in an exhaust gas purification catalyst that can effectively purify HC, CO, and NOx.

The catalytic metal is preferably in the form of sufficiently small particles in order to increase the contact area with the exhaust gas. The average particle size 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 size" refers to the number-based average value of particle sizes of 20 or more particles determined by observation with a transmission electron microscope (TEM).

The first catalyst layer 21 and the second catalyst layer 22 each contain a carrier that supports a catalytic metal. The carrier is not particularly limited, and may be an inorganic compound that can be used in this type of catalyst. The carrier is preferably an inorganic porous body 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 (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), ceria (CeO ₂ ), titania (TiO ₂ ), and solid solutions thereof (e.g., ceria-zirconia composite oxide, etc.), and combinations thereof. The shape (outer shape) of the support material is not particularly limited, but a powder (e.g., alumina powder, etc.) can be preferably used from the viewpoint of ensuring a larger specific surface area. From the viewpoint of heat resistance and structural stability, the carrier particles preferably have a specific surface area of 50 m ² /g or more and 500 m ² /g or less (e.g., 200 m ² /g or more and 400 m ² /g or less), and the average particle diameter of the carrier particles is, for example, about 0.001 μm to 10 μm (preferably 0.01 μm to 5 μm).

The first catalyst layer 21 and the second catalyst layer 22 each contain an OSC material. The OSC material has a function (oxygen storage and release ability) 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, and is a component that has an effect of mitigating atmospheric fluctuations. The OSC material may function as a carrier for a catalytic metal, or may be a non-supporting body 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 viewpoint of improving heat resistance and durability, the Ce-containing oxide may be an oxide containing Zr, for example, a _CeO2 - _ZrO2 composite oxide (CZ composite oxide). The _CZ composite oxide may further contain rare earth metal oxides, such as _{La2O3 , Pr6O10} , _{Nd2O3 , and Y2O3} .

The CZ composite oxide may be Ce-rich or Zr-rich. In some embodiments, the mixing ratio of ceria 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 mixing ratio of ceria 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 mixing ratio of ceria is equal to or less than a predetermined value, the heat resistance can be improved. When the mixing ratio is within the above range, it is possible to achieve both the effect of the technology disclosed herein and heat resistance at a high level.

The catalyst layer 20 may contain other components in addition to the above-mentioned 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, etc. The content of such alkaline earth metal elements 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 the volume of the portion of the substrate on which the catalyst layer 20 is formed along the cylinder axis direction X. Although not particularly limited, by allowing Pd as a 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 first catalytic layer 21 contains the promoter component and allows it to coexist with Pd.

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, for example, taking into consideration 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, when the entire length of the exhaust gas purification catalyst 10 in the cylinder axis direction X is L.

The coating amount (molding 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, and 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 cylinder 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 (average length in the thickness direction perpendicular to the cylinder axis direction X) is, for example, 1 to 100 μm, and may be 5 to 100 μm.

The phosphorus trapping layer 30 has the function of trapping phosphorus compounds contained in exhaust gas. By trapping phosphorus compounds, the catalyst layer 20 can be prevented from being poisoned by phosphorus and the purification performance can be prevented from being deteriorated. According to the study by the inventors, it was found that the surface portion of the exhaust gas purification catalyst 10 on the inflow side (upstream side) of the exhaust gas is most susceptible to phosphorus poisoning. For this reason, as shown in FIG. 3, the phosphorus trapping layer 30 is disposed on the catalyst layer 20 (i.e., the side farther from the surface of the substrate 11 than the catalyst layer 20) in the thickness direction perpendicular to the cylinder axis direction X of the exhaust gas purification catalyst 10, and along the cylinder axis direction X from the inlet 10a (i.e., the end on the upstream side). This allows the phosphorus compounds contained in the exhaust gas to be suitably captured, the catalyst layer 20 is less likely to be poisoned by phosphorus, and sufficient purification performance is ensured. Although not particularly limited, the content of the phosphorus capture component in the phosphorus capture 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 capture 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.

The phosphorus trapping layer 30 contains calcium sulfate and/or calcium carbonate as a phosphorus trapping component. Calcium (Ca), barium (Ba), strontium (Sr), magnesium (Mg), etc. are known as phosphorus trapping components, but the inventors have found that calcium has a very large phosphorus trapping amount per gram and can trap a large amount of phosphorus with a small amount added. They also found that by including calcium as calcium sulfate and calcium carbonate in the phosphorus trapping layer 30, the reactivity with phosphorus is further improved. As a result, by including calcium sulfate and/or calcium carbonate as phosphorus trapping components, the amount of phosphorus trapping can be significantly increased even with the same content as that of conventional phosphorus trapping components. Therefore, the amount of catalytic metal, OSC material, etc. is sufficiently secured in the exhaust gas purification catalyst 10, so that phosphorus poisoning can be suppressed while fully demonstrating the 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).

Furthermore, according to the results of the study by the present inventors, it was found that calcium has a higher reactivity with phosphorus than other materials and that the stability of the compound with phosphorus is high. Specifically, even if other materials such as alumina once combine with phosphorus to capture phosphorus, they decompose in a high-temperature environment (e.g., an environment of 800°C or higher) or in a severe redox atmosphere, and release phosphorus. The released phosphorus eventually reaches the catalyst layer 20 and poisons the catalyst metal (e.g., Rh or Pd). On the other hand, according to the results of the study by the present inventors, calcium forms a very stable compound with phosphorus, and the chemical state does not change even in a high-temperature environment of, for example, 1000°C or higher or in a severe redox atmosphere, and the captured phosphorus is not released. In this way, in the exhaust gas purification catalyst 10 disclosed herein, by using calcium as a phosphorus capture component, it is possible to suppress the re-release of phosphorus and prevent phosphorus from moving to the catalyst layer 20. Therefore, it is possible to more suitably protect the catalyst layer 20 from phosphorus poisoning.

The phosphorus trapping layer 30 preferably contains an Al-containing oxide in addition to the 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 may be alumina (Al ₂ O ₃ ), or may be a composite oxide of alumina and a metal oxide other than alumina (for example, a rare earth metal oxide). From the viewpoint of improving the heat resistance and durability, the Al-containing oxide may be, for example, a La ₂ O ₃ -Al ₂ O ₃ composite oxide. The La ₂ O ₃ -Al ₂ O ₃ composite oxide may be La-rich or Al-rich. The mixing ratio of metal oxides other than alumina in _{the La2O3} - _{Al2O3 composite} oxide is _{not particularly limited. From the viewpoint of suppressing deterioration over time with 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%.

In the exhaust gas purification catalyst 10 disclosed herein, the phosphorus trapping layer 30 preferably contains an Al-containing oxide having a specific surface area of 20 m ² /g or more, and more preferably contains an Al-containing oxide having a specific surface area of 50 m ² /g or more. More preferably, the phosphorus trapping layer 30 contains alumina having a specific surface area of 50 m ² /g or more. The specific surface area of alumina is preferably 80 m ² /g or more, and more preferably 100 m ² /g or more. The upper limit of the specific surface area is not particularly limited, but may be, for example, 220 m ² /g or less, and is preferably 200 m ² /g or less. By using alumina having a specific surface area of 50 m ² /g or more, the number of contact points with phosphorus compounds contained in exhaust gas is increased, and phosphorus compounds can be more suitably trapped. This can further suppress phosphorus poisoning of the catalyst layer 20, thereby improving the purification performance of the exhaust gas purification catalyst 10.

In the exhaust gas purification catalyst 10, as described above, the amount of phosphorus captured can be increased by including an Al-containing oxide in addition to the phosphorus capture component. From this viewpoint, 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 capture layer 30 is formed along the cylinder axis direction X. On the other hand, if the phosphorus capture layer 30 contains too much alumina, the thickness of the phosphorus capture layer 30 may become too large, which is undesirable because it makes it difficult for the exhaust gas to come into contact with the catalyst layer 20. From this viewpoint, 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 capture layer 30 is formed along the cylinder axis direction X.

The catalyst layer 20 may contain other components in addition to the above-mentioned catalyst metal and Al-containing oxide. Examples of other components include binders such as silica sol, various additives, etc.

As described above, the catalyst layer 20 contains a catalyst metal and an OSC material. When the catalyst metal is poisoned with phosphorus, its catalytic performance is reduced. In addition, when the OSC material is poisoned with phosphorus, the oxygen storage and release ability is not properly exhibited, and the purification performance of the catalyst as a whole is reduced. According to the results of the studies by the present inventors, even when calcium sulfate or calcium carbonate, which has a high phosphorus trapping ability, is mixed into the catalyst layer 20 as described above, it is difficult to suppress the phosphorus poisoning of the catalyst 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. In addition, from the above viewpoint, it is preferable that the phosphorus trapping layer 30 does not substantially contain a catalyst metal, and it is more preferable that the phosphorus trapping layer 30 does not substantially contain a catalyst metal and an OSC material.
In this specification, the phosphorus trapping layer being 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 other layers or when using the exhaust gas purification catalyst, it is acceptable for the above-mentioned component to be unintentionally mixed in from other layers. It goes without saying that the inclusion of unavoidable trace components is also acceptable. Although not particularly limited, the phosphorus trapping layer being 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%).

As described above, the phosphorus trapping layer 30 is provided from the exhaust gas inlet 10a (i.e., the upstream end) to the downstream side along the cylinder axis direction X. The phosphorus trapping layer 30 is preferably provided continuously on the catalyst layer 20. This can suitably suppress phosphorus poisoning of the catalyst layer 20. Although not particularly limited, when the upstream end of the exhaust gas purifying catalyst 10 in the cylinder axis direction X is 0% and the downstream end is 100%, the phosphorus trapping layer 30 is preferably provided with a coat width (average length) of at least 30%, may be provided with a coat width of 40% or more, may be provided with a coat width of 50% or more, and may be provided with a coat width of 100% (i.e., the entire length of the cylinder axis direction X). As a result, the exhaust gas that has flowed in 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 is suppressed. On the other hand, from the viewpoint of the contact 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, and the phosphorus trapping layer 30 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 0% and the downstream end is 100%, the phosphorus trapping layer 30 is preferably provided with a coat width of 90% or less, more preferably with a coat width of 80% or less, and may be provided with a coat width of 70% or less, or may be provided with a coat width of 60% or less. For example, when the length in the cylinder axis direction X is 100%, the phosphorus trapping layer 30 may be provided from the upstream end toward the downstream side with a coat width of 30% or more and 90% or less (preferably 30% or more and 80% or less). 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, improving the overall purification performance of the exhaust gas purification catalyst 10.

In the exhaust gas purification catalyst 10 disclosed herein, it is preferable that the catalyst layer 20 containing the catalytic metal is not arranged downstream of the phosphorus trapping layer 30. This is because, when the catalytic metal content is the same in the exhaust gas purification catalyst 10, arranging the catalytic metal downstream reduces the purification performance when the exhaust gas purification catalyst 10 is not sufficiently warmed up. This is because the catalyst warms up from the upstream side in the warm-up process, so if the amount of catalytic metal is the same, by arranging the catalytic metal upstream, purification performance can be ensured even during warm-up. On the other hand, the downstream side warms up slower than the upstream side, and when the catalytic metal is arranged downstream, purification performance is not fully exhibited until the activation temperature of the catalytic metal is reached. Therefore, from the above viewpoint, it is preferable that the catalytic layer 20 is not arranged downstream of the phosphorus trapping layer 30.

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 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, and may be 30 g/L to 100 g/L, or may be 50 g/L to 100 g/L. By satisfying the above range, the phosphorus trapping layer 30 can optimally exhibit its phosphorus trapping function. In addition, 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 cylinder axis direction X) is, for example, 1 to 100 μm, and may be 5 to 100 μm.

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

Next, the slurry for forming the first catalyst layer, the slurry for forming the second catalyst layer, and the slurry for forming the phosphorus capture layer are applied to the substrate 11. These slurries can be applied 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 cell 12 from the end of the substrate 11 on the inlet 10a side, 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 cell 12 from the end of the substrate 11 on the inlet 10a side, supplied to a predetermined length along the cylindrical axis direction X, dried, and then fired. Then, the slurry for forming the phosphorus capture layer is flowed into the cell 12 from the end of the substrate 11 on the outlet 10b side, supplied to a predetermined length along the cylindrical axis direction X, dried, and then fired. The method of drying and firing the slurry (time, temperature, etc.) may be the same as in the past. This allows the catalyst layer 20 and phosphorus capture layer 30 to be formed on the substrate 11. In this way, the exhaust gas purification catalyst 10 can be formed.

The above-mentioned exhaust gas purification catalysts can be suitably used to purify exhaust gases 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 lawnmowers, chainsaws and trimmers, leisure products such as golf carts and four-wheeled buggies, power generation equipment such as cogeneration systems, and internal combustion engines such as waste incinerators.

Test examples relating to the present invention are described below, but it is not intended that the present invention be limited to those shown in the following test examples. Note that 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 specified layer is formed in the cylindrical axial direction.

First Test
Here, five types of slurries (A) to (E) having different compositions were used to prepare exhaust gas purification catalysts having different configurations, and a study was conducted on a configuration that can suitably suppress phosphorus poisoning.

1. Preparation of each example First, a cylindrical honeycomb substrate (made of cordierite, volume: 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. The alumina used was a composite alumina (Al ₂ O ₃ ) containing La, with a specific surface area of 100 m ² /g. The OSC material used was a ceria-zirconia (CeO ₂ -ZrO ₂ ) composite oxide containing La, Pr, Nd, and Y as additive components.
(A) Slurry for forming the first catalyst layer: OSC material, alumina, Pd nitrate aqueous solution, barium sulfate (BaSO ₄ ) as a promoter, and an alumina-based binder were mixed in distilled water. The mixture was then milled to control the particle size, and the slurry for forming the first catalyst layer was prepared.
(B) Slurry for forming second catalyst layer: OSC material, alumina, Rh hydrochloride aqueous solution, and alumina-based binder were mixed in distilled water. Then, the mixture was milled to control the particle size, and the slurry for forming second catalyst layer was prepared.
(C) Slurry for forming phosphorus trapping layer: Calcium sulfate (CaSO ₄ ) as a phosphorus trapping component, alumina, and an alumina-based binder were mixed in distilled water. The mixture was then milled to control the particle size, thereby preparing a slurry for forming the phosphorus trapping layer.
(D) Slurry for forming first mixed layer: OSC material, alumina, Pd nitrate solution, calcium sulfate (CaSO ₄ ) as a phosphorus trapping component, and alumina-based binder were mixed in distilled water. Then, the mixture was milled to control the particle size, and a slurry for forming the first mixed layer containing Pd as a catalytic metal and calcium sulfate as a phosphorus trapping component was prepared.
(E) Slurry for forming second mixed layer: OSC material, alumina, Rh hydrochloride aqueous solution, calcium sulfate (CaSO ₄ ) as a phosphorus trapping component, and alumina-based binder were mixed in distilled water. Then, the mixture was milled to control the particle size, and a slurry for forming second mixed layer containing Rh as a catalytic metal and calcium sulfate as a phosphorus trapping component was prepared.

[Comparative Example 1]
The slurry for forming the first catalyst layer was poured into the substrate from the upstream side (exhaust gas inlet side) and sucked with a blower to coat the substrate on a portion corresponding to 100% of the entire length in the cylindrical axis direction. The amount of the slurry for forming the first catalyst layer was set 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 wall of the substrate.
Next, the slurry for forming the second catalyst layer was poured into the substrate from the upstream side and sucked with a blower to coat the substrate on a portion corresponding to 100% of the entire length in the axial direction of the substrate. The amount of the slurry for forming the second catalyst layer was adjusted so that the Rh content was 0.12 g/L. The substrate 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 the formation of a second catalyst layer on the surface of the first catalyst layer formed above. In this manner, a catalyst for purifying exhaust gas of Comparative Example 1, which does not have a phosphorus capture layer, was obtained.

[Comparative Example 2]
The slurry for forming the first catalyst layer was coated on the substrate in the same manner as in Comparative Example 1, and then dried and fired. As a result, the first catalyst layer was formed on the surface of the partition wall of the substrate. Next, the slurry for forming the second mixed layer was poured from the upstream side of the substrate and sucked with a blower, so that the slurry was coated on a portion corresponding to 100% of the total length of the substrate in the axial direction. The coating amount of the slurry for forming the second mixed layer was set 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. Then, 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 second mixed layer containing Rh as a catalytic metal and calcium sulfate as a phosphorus trapping component was 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.

[Comparative Example 3]
The slurry for forming the first mixed layer was poured from the upstream side of the substrate and sucked with a blower, so that the slurry was coated on a portion corresponding to 100% of the total length of the substrate in the axial direction. The amount of the slurry for forming the first mixed layer was set 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. Then, 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 first mixed layer containing Pd as a catalytic metal and calcium sulfate as a phosphorus trapping component was formed on the surface of the partition wall 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, and dried and fired. As a result, a second catalyst layer was formed on the surface of the first mixed layer formed above. In this way, a catalyst for purifying exhaust gas of Comparative Example 3 having a second catalyst layer on the surface of the first mixed layer was obtained.

[Comparative Example 4]
The slurry for forming the first catalyst layer was coated on the substrate in the same manner as in Comparative Example 1, and then dried and fired. As a result, the first catalyst layer was formed on the surface of the partition wall 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, and then dried and fired. As a result, the second catalyst layer was formed on the surface of the first catalyst layer. Then, the slurry for forming the phosphorus trapping layer was poured from the downstream side (exhaust gas outlet side) of the substrate and sucked with a blower, so that the slurry was coated on a portion of the substrate that corresponds to 40% from the downstream side in the cylindrical axis direction (i.e., a portion that corresponds to 60% to 100% when the upstream end of the substrate in the cylindrical axis direction is 0% and the downstream end is 100%). The coating amount of the slurry for forming the phosphorus trapping layer was set 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 catalyst layer formed above, covering 40% of the surface area from the downstream side in the axial direction of the substrate. In this manner, a catalyst for purifying exhaust gas of Comparative Example 4 was obtained, which had the first catalyst layer and the second catalyst layer over the entire length of the substrate in the axial direction, and had the phosphorus trapping layer covering 40% of the surface area from the downstream side in the axial direction of the substrate.

[Example 1]
The slurry for forming the first catalyst layer was poured into the substrate from the upstream side (exhaust gas inlet side) and sucked with a blower to coat the substrate on a portion corresponding to 100% of the entire length in the cylindrical axis direction. The amount of the slurry for forming the first catalyst layer was set 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. As a result, a first catalyst layer containing Pd as a catalytic metal was formed on the surface of the partition wall of the substrate.
Next, the slurry for forming the second catalyst layer was poured into the substrate from the upstream side and sucked with a blower to coat the substrate on a portion corresponding to 100% of the entire length in the axial direction of the substrate. The amount of the slurry for forming the second catalyst layer was adjusted so that the Rh content was 0.12 g/L. The substrate 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 catalyst layer containing Rh as a catalytic metal was formed on the surface of the first catalyst layer formed above.
The phosphorus trapping layer forming slurry was poured into the substrate from the upstream side and sucked with a blower to coat the substrate on a portion corresponding to 100% of the substrate's overall length in the axial direction. The coating amount of the phosphorus trapping layer forming slurry was set so 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 the phosphorus trapping component was formed on the surface of the second catalyst layer formed above. In this way, the exhaust gas purification catalyst of Example 1 was obtained, which has the first catalyst layer, the second catalyst layer, and the phosphorus trapping layer over the entire length of the substrate in the axial direction.

[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 corresponds to 40% from the upstream side in the axial direction of the cylinder (i.e., a portion that corresponds to 0% to 40% when the upstream end of the substrate in the axial direction of the cylinder is taken as 0% and the downstream end is taken as 100%). The rest of the procedure was the same as in Example 1. In this way, an exhaust gas purifying catalyst of Example 2 was obtained, which has a first catalyst layer and a second catalyst layer over the entire length of the substrate in the axial direction of the cylinder, and has a phosphorus trapping layer in a portion that corresponds to 40% from the upstream side in the axial direction of the cylinder.

[Phosphorus poisoning durability test]
For each example of the exhaust gas purification catalyst, a durability test with and without phosphorus poisoning was carried out. The durability test with phosphorus poisoning was carried out as follows. First, the exhaust gas purification catalyst of each example was installed in the exhaust system of a 5L V-type engine. Next, engine oil containing a high concentration of phosphorus (P) was mixed into commercially available gasoline, and the gasoline was burned in the engine to generate exhaust gas containing phosphorus compounds. A durability test with phosphorus poisoning was carried out by passing exhaust gas containing phosphorus compounds through each example of the exhaust gas purification catalyst to perform phosphorus poisoning, while maintaining the catalyst temperature at 950°C for 150 hours. The phosphorus poisoning of the exhaust gas purification catalyst at this time was controlled to be 13g in terms of phosphorus element per catalyst.

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

[Evaluation of OSC maintenance 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 calculating it from 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.

The OSC amount A of each example of the exhaust gas purification catalyst was calculated as follows. The exhaust gas purification catalyst of each example after the durability test with phosphorus poisoning was installed in the exhaust system of a 2L L-type engine, and an _O2 sensor was attached downstream of the catalyst. The air-fuel ratio (A/F) of the mixed gas supplied to the engine was periodically switched between rich and lean at predetermined time intervals, and the OSC amount A of each example of the exhaust gas purification catalyst was calculated from the delay in the behavior of the _O2 sensor.
The OSC amount B of each example of the exhaust gas purification catalyst was calculated in the same manner as the OSC amount A, except that the exhaust gas purification catalyst of each example after the durability test without phosphorus poisoning was installed in the exhaust system of a 2L L-type engine.
The OSC maintenance rate (%) of the exhaust gas purifying catalyst of each example was calculated from the above formula using the calculated OSC amount A and OSC amount B of each example. The results are shown in FIG.

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

As shown in FIG. 4, the catalysts for purifying exhaust gas 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 on the surface of the catalyst layer in a region including the upstream end, have a high OSC maintenance rate even after phosphorus poisoning treatment and durability test. Also, as shown in FIG. 5, the catalysts for purifying exhaust gas 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 test. This is presumably because the phosphorus trapping layer is provided in a region including the upstream end, which can suppress the poisoning of both the catalyst metal and the OSC material contained in the first catalyst layer and the second catalyst layer. As a result, it is presumed that sufficient oxygen is supplied to the catalyst metal, improving the purification performance of CO, HC, and NOx.

Furthermore, comparing Example 1 and Example 2, it can be seen that Example 2, which has a phosphorus trapping layer in 40% of the area from 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 an area including the upstream end that is susceptible to phosphorus poisoning, and the second catalyst layer is exposed on the downstream side that 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.

<Second test>
Here, the phosphorus trapping components contained in the phosphorus trapping layer forming slurry were changed to study components that can suitably suppress phosphorus poisoning.

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

[Comparative Example 12]
Instead of the phosphorus trapping layer forming slurry, a slurry not containing a phosphorus trapping component was prepared. The coating amount of this slurry was set 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 exhaust gas purification of Comparative Example 12 not containing a phosphorus trapping component.

[Comparative Example 13]
The phosphorus trapping component contained in the phosphorus trapping layer forming slurry was changed to barium sulfate (BaSO ₄ ). The coating amount of this phosphorus trapping layer forming slurry was changed so that the phosphorus trapping component content was 30 g/L in terms of barium sulfate. Except for this, the exhaust gas purification catalyst of Comparative Example 13 was obtained in the same manner as in Example 2.

[Comparative Example 14]
The phosphorus trapping component contained in the phosphorus trapping layer forming slurry was changed to strontium sulfate (SrSO ₄ ). The coating amount of this phosphorus trapping layer forming slurry was changed so that the phosphorus trapping component content was 30 g/L in terms of strontium sulfate. Except for this, the exhaust gas purification catalyst of Comparative Example 14 was obtained in the same manner as in Example 2.

[Evaluation of OSC maintenance rate]
The OSC maintenance 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 of the exhaust gas purification catalyst, one in which a durability test was performed with phosphorus poisoning and one in which a durability test was performed without phosphorus poisoning were prepared. 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 obtained, and the OSC maintenance rate of each example was calculated from the ratio of the OSC amount A to the OSC amount B. The results are shown in FIG. 6. The results of Example 2 are also shown in FIG. 6.

[Evaluation of CO, HC and NOx purification performance]
The exhaust gas purification catalysts of Example 11 and Comparative Examples 12 to 14, which were subjected to the durability test with phosphorus poisoning, were evaluated in the same manner as above for CO purification performance, HC purification performance, and NOx purification performance. 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.

As shown in Figure 6, in Examples 2 and 11, which contain calcium sulfate and calcium carbonate as phosphorus trapping components, the OSC maintenance rate is high even after phosphorus poisoning treatment and durability testing. Also, as shown in Figure 7, in the exhaust gas purification catalysts of Examples 2 and 11, the CO purification performance, HC purification performance, and NOx purification performance are remarkably high even after phosphorus poisoning treatment and durability testing. This is presumably because calcium traps a large amount of phosphorus per gram and is highly reactive with phosphorus, which effectively suppresses poisoning of the catalyst metal and OSC material.

<Third Test>
Here, a configuration capable of suitably suppressing phosphorus poisoning by changing the coating width in the cylinder axis direction of the phosphorus trapping layer was examined.

[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. Except for this, the exhaust gas purifying catalyst of Example 21 was obtained in the same manner as in Example 1.

[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. Except for this, the exhaust gas purifying catalyst of Example 22 was obtained in the same manner as in Example 1.

[Reference Example 23]
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. Except for this, the exhaust gas purifying catalyst of Reference Example 23 was obtained in the same manner as in Example 1.

[Evaluation of OSC maintenance rate]
The OSC maintenance rate of each of the exhaust gas purification catalysts of Examples 21, 22 and Reference Example 23 prepared above was evaluated in the same manner as above. That is, for each of the exhaust gas purification catalysts, one in which a durability test was performed with phosphorus poisoning and one in which a durability test was performed without phosphorus poisoning were prepared. 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 obtained, and the OSC maintenance rate of each example was calculated from the ratio of the OSC amount A to the OSC amount B. The results are shown in FIG. 8. The results of Examples 1 and 2 and Comparative Example 1 are also shown in FIG. 8.

[Evaluation of CO, HC and NOx purification performance]
The catalysts for purifying exhaust gas of Examples 21 and 22 and Reference Example 23, which were subjected to the durability test with phosphorus poisoning, were evaluated for CO purification performance, HC purification performance, and NOx purification performance in the same manner as described 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.

As shown in FIG. 8, the exhaust gas purification catalysts of Examples 1, 2, 21, and 22, in which the phosphorus trapping layer is provided with a coat width of at least 30% from the upstream end toward the downstream side, have a remarkably high OSC maintenance rate even after phosphorus poisoning treatment and durability test. Also, as shown in FIG. 9, the exhaust gas purification catalysts of Examples 1, 2, 21, and 22 have remarkably high CO purification performance, HC purification performance, and NOx purification performance even after phosphorus poisoning treatment and durability test. This is presumably because the region of the exhaust gas purification catalyst from the upstream end to about 30% is particularly susceptible to phosphorus poisoning. Therefore, by arranging the phosphorus trapping layer with a coat width of at least 30% from the upstream end toward the downstream side, phosphorus poisoning can be suitably suppressed and the purification performance of the exhaust gas purification catalyst can be exhibited at a high level.

<Fourth test>
Here, the content of alumina contained in the phosphorus trapping layer forming slurry was changed to study a configuration capable of suitably suppressing phosphorus poisoning.

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

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

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

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

[Evaluation of OSC maintenance rate]
The OSC maintenance rate of each of the exhaust gas purification catalysts of Examples 31 to 34 prepared above was evaluated in the same manner as above. That is, for each of the exhaust gas purification catalysts, one in which a durability test was performed with phosphorus poisoning and one in which a durability test was performed without phosphorus poisoning were prepared. 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 obtained, and the OSC maintenance rate of each example was calculated from the ratio of the OSC amount A to the OSC amount B. The results are shown in FIG. 10. The results of Example 2 and Comparative Example 12 are also shown in FIG. 10.

[Evaluation of CO, HC and NOx purification performance]
The exhaust gas purification catalysts of Examples 31 to 34, which had been subjected to a durability test with phosphorus poisoning, were evaluated in the same manner as above for CO purification performance, HC purification performance, and NOx purification performance. 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.

As shown in FIG. 10, it can be seen that the OSC maintenance rate is high even after phosphorus poisoning treatment and durability testing because the phosphorus trapping layer contains alumina in addition to the phosphorus trapping component. Also, as shown in FIG. 11, it can be seen that the CO purification performance, HC purification performance, and NOx purification performance are high even after phosphorus poisoning treatment and durability testing because the phosphorus trapping layer contains alumina in addition to the phosphorus trapping component. This is presumably because the phosphorus trapping layer contains alumina along with the phosphorus trapping component, which allows it to effectively capture phosphorus that has flowed into the exhaust gas purification catalyst. It is presumed that this makes it possible to suppress poisoning of the catalyst metal and OSC material.

Furthermore, as shown in Figures 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 can be seen that Examples 2, 32, and 33 have a higher OSC maintenance rate and better purification performance. This is presumably because the phosphorus trapping layer contains alumina in addition to the phosphorus trapping component, and the phosphorus trapping layer has an alumina content of 30 g/L or more, which is particularly suitable for increasing the amount of phosphorus trapped. In addition, when the alumina content is about 100 g/L, the phosphorus trapping layer tends to become thicker, which is presumably because it becomes difficult for the inflowing exhaust gas to come into contact with the catalyst layer.

<Fifth test>
Here, a configuration capable of suitably suppressing phosphorus poisoning was studied by changing the specific surface area of alumina contained in the phosphorus trapping layer forming slurry. The specific surface area of alumina was adjusted by subjecting the alumina to a heat treatment.

[Example 41]
The alumina contained in the slurry for forming the phosphorus trapping layer was changed to alumina having a specific surface area of 20 m ² /g. Other than this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gas of Example 41.

[Example 42]
The alumina contained in the slurry for forming the phosphorus trapping layer was changed to alumina having a specific surface area of 50 m ² /g. Other than this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gas of Example 42.

[Example 43]
The alumina contained in the slurry for forming the phosphorus trapping layer was changed to alumina having a specific surface area of 80 m ² /g. Other than this, the same procedure as in Example 2 was repeated to obtain a catalyst for purifying exhaust gas of Example 43.

[Example 44]
The alumina contained in the slurry for forming the phosphorus trapping layer was changed to alumina having a specific surface area of 200 m ² /g. Other than this, the same procedure as in Example 2 was carried out to obtain a catalyst for purifying exhaust gas of Example 44.

[Evaluation of OSC maintenance rate]
The OSC maintenance rate of each of the exhaust gas purification catalysts of Examples 41 to 44 prepared above was evaluated in the same manner as above. That is, for each of the exhaust gas purification catalysts, one in which a durability test was performed with phosphorus poisoning and one in which a durability test was performed without phosphorus poisoning were prepared. 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 obtained, and the OSC maintenance rate of each example was calculated from the ratio of the OSC amount A to the OSC amount B. The results are shown in FIG. 12. The results of Example 2 and Comparative Example 12 are also shown in FIG. 12.

[Evaluation of CO, HC and NOx purification performance]
The exhaust gas purification catalysts of Examples 41 to 44, which had been subjected to the durability test with phosphorus poisoning, were evaluated in the same manner as above for CO purification performance, HC purification performance, and NOx purification performance. 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.

As shown in Fig. 12, in the case where 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 and 200 m ² /g or less, it is found that the OSC maintenance rate is particularly high even after the phosphorus poisoning treatment and the durability test in Example 2 and Examples 42 to 44. Also, as shown in Fig. 13, it is found 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 the durability test. This is presumably because the specific surface area of alumina is a certain level or more, so that phosphorus that has flowed into the exhaust gas purification catalyst can be suitably captured. It is presumed that this makes it possible to more suitably suppress poisoning of the catalyst metal and the OSC material.

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 technical common sense in the relevant field. The technology described in the claims includes various modifications and changes to the above-exemplified embodiments. For example, it is possible to replace part of the above-mentioned embodiments with other modified forms, and it is also possible to add other modified forms to the above-mentioned embodiments. Furthermore, if a technical feature is not described as essential, it can also be deleted as appropriate.

1 Exhaust gas purification system 2 Internal combustion engine
Reference Signs List 3 exhaust gas purification device 4 exhaust path 5 exhaust manifold 6 exhaust pipe 7 engine control unit 8 sensor 9 second catalyst 10 first catalyst 10a inlet 10b outlet 11 substrate 12 cell (cavity)
14 Partition (rib)
20 Catalyst layer 21 First catalyst layer 22 Second catalyst layer 30 Phosphorus capture layer

Claims (6)

An exhaust gas purification catalyst for purifying 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;
The phosphorus-trapping layer is disposed from an upstream end of the substrate toward a downstream end in a direction of exhaust gas flow. The catalyst layer is
A first catalyst layer disposed on the substrate and containing at least Pd as the catalytic metal;
2. The exhaust gas purifying catalyst according to claim 1, further comprising: a second catalyst layer disposed on said first catalyst layer, said second catalyst layer containing at least Rh as said catalytic metal. The exhaust gas purification catalyst according to claim 1, wherein the phosphorus trapping layer contains an Al-containing oxide in addition to the phosphorus trapping component. 4. The exhaust gas purifying catalyst according to claim 3, wherein the Al-containing oxide has a specific surface area of 50 m ² /g or more. The exhaust gas purification catalyst according to claim 1 or 2, wherein the average length of the phosphorus capture layer in the exhaust gas flow direction is at least 30% or more when the total length of the substrate in the exhaust gas flow direction from the upstream end to the downstream end is 100%. 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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