JP2018171615A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for purifying exhaust gas at a low cost, capable of suitably suppressing phosphorus poisoning of a metal catalyst, and retaining sufficient exhaust gas-purifying property for a long term.SOLUTION: A catalyst 10 for purifying exhaust gas includes: a base material 11 in which a plurality of cells 15 are partitioned by partition walls 16; a catalyst layer 30 formed on a partition wall 16 surface of the base material 11; and a phosphorous collection layer 20 provided on the catalyst layer 30. The phosphorous collection layer 20 has a phosphorous collection component containing at least one selected from La, Fe, Zr, Ce, Ti, Sr, Ca, Mg, Pr and Y. When the phosphorous collection layer is 100% in an electron microscope image of the cross section of the phosphorous collection layer 20, large pores whose equivalent circle diameter is larger than 5 μm occupy 45% or more.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an exhaust gas purifying catalyst. More specifically, the present invention relates to an exhaust gas purifying catalyst that purifies harmful components in exhaust gas discharged from an internal combustion engine.

The exhaust gas discharged from the internal combustion engine contains harmful components such as particulate matter (PM), carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NO _x ). In order to purify these harmful components, an exhaust gas purifying catalyst is provided in the exhaust system of the internal combustion engine. Such an exhaust gas purifying catalyst includes, for example, a base material having a plurality of flow paths (cells) and a catalyst layer formed inside the base material. The catalyst layer of the exhaust gas purifying catalyst contains a metal catalyst that purifies the harmful components and a carrier that supports the metal catalyst.

  By the way, the phosphorus component derived from engine oil may be mixed in the exhaust gas discharged | emitted from the above-mentioned internal combustion engine. If such a phosphorus component adheres to the metal catalyst in the catalyst layer, the catalytic function of the metal catalyst is hindered, and so-called phosphorus poisoning may occur, in which the exhaust gas purification ability of the exhaust gas purification catalyst is significantly reduced.

  In order to suppress the occurrence of such phosphorus poisoning, various techniques have been conventionally proposed. For example, Patent Documents 1 to 3 disclose a technique for providing a layer for collecting a phosphorus component (phosphorus collection layer) on the catalyst layer so that the phosphorus component does not contact the metal catalyst in the catalyst layer. ing. Specifically, Patent Document 1 describes a technique for coating a catalyst layer with a layer containing a phosphorus scavenger, and Patent Document 2 describes an alkaline earth metal phosphate compound having low reactivity with a phosphorus component. Describes a technique for coating a catalyst layer. Patent Document 3 discloses a technique in which a layer not containing a metal catalyst (or having a low metal catalyst content) is provided on the catalyst layer.

  As another example of a technique for suppressing phosphorus poisoning, a technique has been proposed in which the composition of the catalyst layer is different between the upstream side and the downstream side in the exhaust gas supply direction. For example, Patent Document 4 discloses a technique in which a metal catalyst is not disposed on the upstream side of a base material to which a phosphorus component is easily supplied, but a metal catalyst is mainly disposed on the downstream side. Further, in Patent Document 5, by providing a wash coat having a high specific surface area and supporting a large amount of noble metal on the upstream side of the base material, the phosphorus component is collected in the wash coat, and the downstream side A technique for preventing the phosphorus component from accumulating in the catalyst layer is disclosed.

Japanese Patent Laid-Open No. 61-274746 Japanese Patent No. 4161722 Japanese Patent No. 5,504,834 Japanese Patent No. 5619091 Special table 2016-516617

However, each of the above conventional techniques has some problems, and further development of a more suitable technique has been desired.
For example, when a phosphorus collection layer is provided on the catalyst layer as in Patent Documents 1 to 3, gas permeability may be reduced by the newly provided phosphorus collection layer. In this case, since it becomes difficult to efficiently bring the harmful components in the exhaust gas into contact with the metal catalyst, the exhaust gas purification ability of the exhaust gas purification catalyst may be reduced. In particular, in the case of an exhaust gas purification catalyst having a wall flow type base material that allows exhaust gas to pass through a porous partition wall, when a phosphorus collection layer is provided on the partition wall of the base material, a phosphorus component is present in the phosphorus collection layer. As a result of deposition, the gas permeability is further lowered, and the pressure loss is rapidly increased, so that the exhaust gas purification ability may be further greatly reduced.

  On the other hand, in the case of the technique such as Patent Document 4, the occurrence of phosphorus poisoning can be suitably suppressed for a predetermined period from the start of use. However, if such an exhaust gas purification catalyst is continuously used, phosphorus poisoning also starts to occur in the metal catalyst disposed on the downstream side, so that it is difficult to maintain sufficient exhaust gas purification performance for a long period of time. Met. Further, the technique described in Patent Document 5 has a problem in that the product cost is significantly increased because a large amount of noble metal is required to maintain a sufficient exhaust gas purification capacity over a long period of time. .

  The present invention has been created to solve such problems, and its purpose is to appropriately suppress phosphorus poisoning of a metal catalyst and to maintain sufficient exhaust gas purification performance over a long period of time. It is to provide a catalyst for use at low cost.

The exhaust gas purifying catalyst disclosed here is disposed in an exhaust passage of an internal combustion engine, and purifies harmful components in the exhaust gas discharged from the internal combustion engine. Such an exhaust gas purifying catalyst includes a base material in which a plurality of cells are partitioned by partition walls, a catalyst layer formed on at least one of the partition wall surface of the base material and the inside of the partition walls of the base material, and a phosphor provided on the catalyst layer. And a collection layer.
And the phosphorus collection layer of this exhaust gas purification catalyst has a phosphorus collection component containing at least one of La, Fe, Zr, Ce, Ti, Sr, Ca, Mg, Pr, and Y. In the electron microscope observation image of the cross section of the phosphorus collection layer, when the phosphorus collection layer is 100%, large pores having an equivalent circle diameter larger than 5 μm occupy 45% or more.

In the exhaust gas purifying catalyst disclosed herein, a phosphorus collection layer having a phosphorus collection component containing La or the like is provided on the catalyst layer. Thereby, the phosphorus component in the exhaust gas can be collected and detoxified before reaching the catalyst layer. For this reason, the fall of the exhaust gas purification capability by the phosphorus poisoning of a metal catalyst can be suppressed suitably.
And the phosphorus collection layer of the catalyst for exhaust gas purification disclosed here is formed such that large pores having an equivalent circle diameter larger than 5 μm occupy 45% or more of the volume of the phosphorus collection layer. Since such a phosphorus collection layer has relatively large pores at a high ratio as compared with the phosphorus collection layer described in Patent Documents 1 to 3, it is remarkably high. It has gas permeability. For this reason, the harmful component in exhaust gas can be made to contact a metal catalyst efficiently, and the high exhaust gas purification capability can be exhibited.
Moreover, since the phosphorus collection layer of the exhaust gas purifying catalyst functions as a filtration layer, it is possible to prevent phosphorus and PM in the exhaust gas from entering the catalyst layer. And this phosphorus collection layer has many large pores, and has remarkably high gas permeability. Therefore, by applying the exhaust gas purifying catalyst disclosed herein to an exhaust gas purifying catalyst having a wall flow type base material, even when used continuously for a long period of time, the increase in pressure loss is reduced. Can be suppressed. Moreover, pressure loss hysteresis can be reduced.
Furthermore, in the exhaust gas purifying catalyst disclosed here, the catalyst layer is covered with the phosphorus trapping layer. Therefore, unlike the technique of Patent Document 4, even when the metal catalyst is used for a long period of time, phosphorus poisoning of the metal catalyst is prevented. It can suppress suitably and can maintain sufficient exhaust gas purification performance for a long period of time. In addition, since it is not necessary to use a large amount of noble metal as in Patent Document 5, a significant increase in product cost can be prevented.

  As described above, according to the exhaust gas purifying catalyst disclosed herein, the exhaust gas purifying catalyst capable of suitably suppressing phosphorus poisoning of the metal catalyst and maintaining sufficient exhaust gas purifying performance over a long period of time. Can be provided at low cost.

  In another preferred embodiment of the exhaust gas purifying catalyst disclosed herein, the porosity of the phosphorus collection layer is 70% or more in the electron microscope observation image of the cross section of the phosphorus collection layer. Thereby, the fall of the gas permeability accompanying formation of a phosphorus collection layer can be suppressed more, and the harmful component in exhaust gas can be made to contact a metal catalyst efficiently. Further, when a wall flow type substrate is used, an increase in pressure loss due to deposition of phosphorus, PM, or the like can be suppressed more effectively. Therefore, the effect of the present invention can be exhibited at a high level.

  In another preferred embodiment of the exhaust gas purifying catalyst disclosed herein, the phosphorus trapping layer has a first pore having a pore diameter of 1 μm or more and less than 10 μm, and a pore diameter of 0.5 μm or more and 1 μm. A multi-pore structure having second pores that are less than Thereby, since the phosphorus collection layer has a structure having multistage pore sizes (openings), harmful components in the exhaust gas can be suitably brought into contact with the metal catalyst, and the phosphorus collection layer 20 can provide a phosphorus component. Can be suitably collected. In addition, when a wall flow type substrate is used, it is possible to highly suppress the intrusion of phosphorus into the catalyst layer and to better suppress the pressure loss hysteresis. Therefore, the effect of the present invention can be exhibited at a high level.

  In another preferred embodiment of the exhaust gas purifying catalyst disclosed herein, in the pore distribution measurement of a mercury porosimeter, the pore volume of the first pore is the pore volume of the second pore. 4 times or more. Thereby, since the gas permeability of a phosphorus collection layer becomes still more favorable, the effect of this invention can be exhibited at a still higher level.

  In another preferred embodiment of the exhaust gas purifying catalyst disclosed herein, the surface aperture ratio is 25% or more in the electron microscope observation image of the surface of the skeleton portion of the phosphorus trapping layer. Thereby, the phosphorus collection efficiency to the phosphorus collection layer can be increased, and the phosphorus poisoning of the metal catalyst can be more suitably suppressed, and the harmful components in the exhaust gas can be efficiently brought into contact with the metal catalyst. . In addition, when a wall flow type substrate is used, an increase in pressure loss accompanying the formation of the phosphorus trapping layer can be dramatically reduced.

In another preferred embodiment of the exhaust gas purifying catalyst disclosed herein, in the electron microscope observation image of the surface of the skeleton portion of the phosphorus trapping layer, the pore diameter P corresponding to 5% cumulative from the small pore side ₅ is 0.03 μm or more, and the pore diameter P ₉₅ corresponding to a cumulative 95% from the small pore side is 1.5 μm or more. Thereby, the phosphorus collection efficiency and mechanical strength in the phosphorus collection layer can be made compatible at a high level.

It is a figure which shows typically the exhaust gas purification apparatus which concerns on one Embodiment. 1 is a perspective view schematically showing an exhaust gas purifying catalyst according to an embodiment. It is a figure which shows typically the cross section along the cylinder axial direction of the catalyst for exhaust gas purification which concerns on one Embodiment. It is a figure which shows typically the cross section along the cylinder axis direction of the catalyst for exhaust gas purification which concerns on other one Embodiment. 2 is an SEM observation image (magnification: 200 times) of a cross section perpendicular to the cylinder axis direction of the exhaust gas purifying catalyst of Example 1. 6 is an SEM observation image (magnification: 200 times) of a cross section perpendicular to the cylinder axis direction of the exhaust gas purifying catalyst of Example 2. 3 is an SEM observation image (magnification: 200 times) of a cross section perpendicular to the cylinder axis direction of the exhaust gas purifying catalyst of Reference Example 1. It is a SEM observation image (magnification: 200 times) of a section perpendicular to the cylinder axis direction of the exhaust gas purifying catalyst of Reference Example 2. 2 is a SEM observation image (magnification: 2000 times) of the surface of a phosphorus collection layer of the exhaust gas purifying catalyst of Example 1. FIG. It is a SEM observation image (magnification: 2000 times) of the surface of the phosphorus collection layer of the exhaust gas purification catalyst of Reference Example 2. It is an enlarged image (magnification: 1000 times) of the SEM observation image of FIG. 12 is an image after image processing is performed on the pores of the phosphorus collection layer shown in FIG. 12 is an image after image processing is performed on pores having an equivalent circle diameter of 5 μm or more among the pores of the phosphorus collection layer shown in FIG. 11. It is a graph which shows the measurement result of the pore distribution of the phosphorus collection layer of Example 1 and Reference Example 2 by a mercury porosimeter. 4 is a surface SEM observation image (magnification 20000 times) of the skeleton portion of the catalyst layer of Example 1. FIG. FIG. 16 is an image after image processing is performed on the surface opening portion in FIG. 15. FIG. It is a graph which shows the relationship between the phosphorus supply amount in Example 1, Reference example 1 and Reference example 2, and 90% purification temperature (T90) of HC. Example 1 is a graph showing the measurement results of the 90% purification temperature (T90) of the decane _(C 10 _{H 22)} in Reference Examples 1 and 2. It is a graph which shows the relationship between the La carrying | support density in Reference Example 1 and Examples 3-5, and 90% purification temperature (T90) of HC. 18 is an SEM observation image (magnification: 1000 times) of a cross section perpendicular to the cylinder axis direction of the exhaust gas purifying catalyst of Example 17. 18 is a SEM observation image (magnification: 2000 times) of the surface of the phosphorus collection layer of the exhaust gas purifying catalyst of Example 17. 19 is a SEM observation image (magnification: 1000 times) of a cross section perpendicular to the cylinder axis direction of the exhaust gas purifying catalyst of Example 18. 19 is a SEM observation image (magnification: 2000 times) of the surface of the phosphorus collection layer of the exhaust gas purifying catalyst of Example 18. 20 is an SEM observation image (magnification: 1000 times) of a cross section perpendicular to the cylinder axis direction of the exhaust gas purifying catalyst of Example 19. 20 is a SEM observation image (magnification: 2000 times) of the surface of the phosphorus collection layer of the exhaust gas purifying catalyst of Example 19. It is a SEM observation image (magnification: 1000 times) of the cross section perpendicular | vertical to the cylinder axis direction of the exhaust gas purification catalyst of Example 20. It is a SEM observation image (magnification: 2000 times) of the surface of the phosphorus collection layer of the exhaust gas purification catalyst of Example 20.

  Several preferred embodiments of the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not necessarily reflect the actual dimensional relationship. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, general matters relating to the arrangement of the exhaust gas purifying catalyst in an automobile) are the prior art in this field. It can be grasped as a design matter of those skilled in the art based on the above. The present invention can be implemented based on the contents disclosed in the present specification and technical knowledge in the field.

<Exhaust gas purification device 1>
First, the structure of the exhaust gas purification apparatus 1 in which the exhaust gas purification catalyst according to one embodiment of the present invention is used will be described. Drawing 1 is a mimetic diagram of exhaust gas purification device 1 concerning one embodiment. The exhaust gas purification device 1 is provided in the exhaust system of the internal combustion engine 2.

The internal combustion engine (engine) 2 is supplied with a mixture containing oxygen and fuel gas. The internal combustion engine 2 burns this air-fuel mixture and converts the combustion energy into mechanical energy. The air-fuel mixture combusted at this time becomes exhaust gas and is discharged to the exhaust system. The internal combustion engine 2 is supplied with engine oil containing a phosphorus compound in order to prevent seizure due to friction. For this reason, the exhaust gas discharged from the internal combustion engine 2 contains a phosphorus component derived from engine oil.
The internal combustion engine 2 having the configuration shown in FIG. 1 is mainly composed of an automobile gasoline engine. However, the exhaust gas purifying apparatus 1 described later can of course be applied to an engine other than a gasoline engine (for example, a diesel engine). It is.

The exhaust gas purification device 1 includes an exhaust passage (exhaust manifold 3 and exhaust pipe 4), an ECU 5, a first exhaust gas purification catalyst A, and a second exhaust gas purification catalyst B. The exhaust gas purification device 1 purifies harmful components (for example, carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO _x )) contained in the exhaust gas discharged from the internal combustion engine 2, and converts the exhaust gas into the exhaust gas. Collect particulate matter (PM) contained.

  One end of the exhaust manifold 3 is connected to an exhaust port (not shown) that communicates the internal combustion engine 2 and the exhaust system. The other end of the exhaust manifold 3 is connected to the exhaust pipe 4. In addition, the arrow in FIG. 1 has shown the distribution direction of exhaust gas. Here, the exhaust manifold 3 and the exhaust pipe 4 constitute an exhaust gas exhaust passage. A first exhaust gas purification catalyst A and a second exhaust gas purification catalyst B are arranged in the exhaust pipe 4. The first exhaust gas purification catalyst A is an exhaust gas temperature raising catalyst provided on the upstream side of the exhaust gas purification catalyst B. When the second exhaust gas purification catalyst B is regenerated, the second exhaust gas purification catalyst B is used. It has a function to raise the temperature of the exhaust gas flowing into the.

  The ECU 5 is an engine control unit that controls the internal combustion engine 2 and the exhaust gas purification device 1. The ECU 5 includes a digital computer, for example, like a general control device. The ECU 5 further includes a central processing unit (CPU) that executes instructions of the control program, a ROM (read only memory) that stores a control program executed by the CPU, and a working area for developing the control program. A random access memory (RAM) to be used and a storage device (recording medium) such as a memory for storing various data may be provided.

  The ECU 5 is provided with an input port (not shown). The ECU 5 is electrically connected to sensors (for example, a pressure sensor 8) installed in each part of the internal combustion engine 2 and the exhaust gas purification device 1. Thereby, the information detected by each sensor is transmitted to the ECU 5 as an electrical signal through the input port. The ECU 5 is provided with an output port (not shown). The ECU 5 controls the internal combustion engine 2 and the exhaust gas purification device 1 by transmitting a control signal via the output port.

  As an example, the ECU 5 estimates how much PM has been collected by the second exhaust gas purification catalyst B (PM accumulation amount) based on the pressure loss value of the pressure sensor 8. When the pressure loss value exceeds a predetermined value, the ECU 5 raises the second exhaust gas purification catalyst B to a predetermined temperature, and burns and removes PM.

  The exhaust gas purifying catalyst according to the present embodiment may be used for either the first exhaust gas purifying catalyst A or the second exhaust gas purifying catalyst B of the exhaust gas purifying apparatus 1. For example, in the exhaust gas purification apparatus 1 shown in FIG. 1, the first exhaust gas purification catalyst A disposed on the upstream side is more likely to deteriorate in performance due to phosphorus poisoning. The exhaust gas-purifying catalyst 10 (see FIG. 3) is preferably used for the first exhaust gas-purifying catalyst A in FIG.

  Further, the exhaust gas purifying catalyst 10 having the wall flow type substrate 11 as shown in FIG. 4 can be preferably used as the second exhaust gas purifying catalyst B. As a result, it is possible to more suitably suppress the performance degradation due to phosphorus poisoning and to suppress the pressure loss hysteresis in the second exhaust gas purification catalyst B to a small value. For this reason, the PM accumulation amount is accurately estimated based on the pressure loss value of the pressure sensor 8, and the regeneration controllability of the second exhaust gas purification catalyst B is excellent. The purification apparatus 1 can be provided.

  The structure of the exhaust gas purification device 1 described above does not limit the present invention. For example, the exhaust gas temperature raising catalyst (first exhaust gas purification catalyst A) may not necessarily be provided in the exhaust gas purification device. In the case of an exhaust gas purifying apparatus not provided with such an exhaust gas temperature raising catalyst (first exhaust gas purifying catalyst A), a wall flow type as shown in FIG. The exhaust gas-purifying catalyst 10 having the base material 11 can be preferably used.

<Exhaust gas purification catalyst 10>
Next, the exhaust gas-purifying catalyst 10 will be described.
FIG. 2 is a perspective view of the exhaust gas purifying catalyst 10 according to one embodiment. FIG. 3 is a view schematically showing a cross section along the cylinder axis direction of the exhaust gas purifying catalyst 10 according to one embodiment. In FIGS. 2 and 3, the exhaust gas flow direction is depicted by the arrow direction. That is, the left side of FIGS. 2 and 3 is the upstream side of the exhaust passage (exhaust pipe 4), and the right side is the downstream side of the exhaust path (exhaust pipe 4).

The exhaust gas purifying catalyst 10 has a function of purifying harmful components (CO, HC, NO _x ) contained in the exhaust gas discharged from the internal combustion engine 2 (see FIG. 1). The exhaust gas purifying catalyst 10 of the present embodiment is provided on a base material 11 in which a plurality of cells 15 are partitioned by partition walls 16, a catalyst layer 30 formed on the surface of the partition walls 16 of the base material 11, and the catalyst layer 30. And a phosphorus collection layer 20 formed. Hereinafter, each member which comprises this exhaust gas purification catalyst 10 is demonstrated.

(1) Base material The base material 11 constitutes the framework of the exhaust gas purifying catalyst 10. As the base material 11, various materials and forms conventionally used for this type of application can be appropriately employed. For example, the material of the base material 11 is preferably made of a highly heat-resistant material typified by ceramics such as cordierite, aluminum titanate, silicon carbide (SiC), and alloys such as stainless steel. Can be adopted. Moreover, the external shape of the base material 11 can be made into a cylindrical shape, an elliptical cylinder shape, a polygonal cylinder shape, etc. As an example, in FIG. 2, a base material 11 having a cylindrical outer shape is employed. Moreover, the shape of the base material 11 can be, for example, a honeycomb shape, a foam shape, a pellet shape, and the like. In the embodiment of FIG. 2, the honeycomb-shaped base material 11 is employed. In addition, the property (for example, the capacity | capacitance of the base material 11 and the full length Lw of the extending direction X of the partition 16) of the base material 11 is not specifically limited.

  And in this embodiment, the flow-through type base material 11 is used. As shown in FIG. 3, the flow-through-type base material 11 has a plurality of cells 15 that are open at both ends of the exhaust gas inflow side and the exhaust gas outflow side, and a partition wall 16 that partitions adjacent cells 15. ing. The shape of each cell 15 may be various geometric shapes such as a square, a parallelogram, a rectangle such as a rectangle and a trapezoid, a triangle, another polygon (for example, a hexagon, an octagon), and a circle. it can. In the exhaust gas purifying catalyst 10 provided with such a flow-through type substrate 11, the exhaust gas flowing into the cell 15 from the end on the exhaust gas inflow side passes through the cell 15 and flows out from the end on the exhaust gas outflow side. .

(2) Catalyst Layer The catalyst layer 30 is provided on the surface of the partition wall 16 of the substrate 11 as described above. The catalyst layer 30 is formed along the extending direction X of the partition wall 16 from the vicinity of the end portion on the exhaust gas inflow side, and is purified by the exhaust gas passing through the cell 15 contacting the catalyst layer 30 on the surface of the partition wall 16. The
The catalyst layer 30 includes a carrier that forms a skeleton of the catalyst layer 30 and a metal catalyst supported on the carrier. As the metal catalyst, various materials that can be used for a general exhaust gas purification catalyst can be used. Such a metal catalyst, for example, to oxidize CO and HC in exhaust gases, and include a three-way catalyst for reducing NO _x. Specific examples of the three-way catalyst include platinum group elements such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), iridium (Ir), or silver (Ag). ), Gold (Au), and the like. By using at least one of these noble metals can be efficiently purify CO contained in the exhaust gas, HC, each of NO _x. Among these, any of platinum, palladium, and rhodium having high oxidation activity can be preferably used. The content of such a metal catalyst is not particularly limited, but is preferably about 0.01 to 8% by mass, for example, about 0.1 to 5% by mass with respect to the total mass of the support contained in the catalyst layer 30, for example.
As described above, the metal catalyst included in the catalyst layer 30 is not limited to the above-described three-way catalyst. For example, an SCR catalyst that reduces NO _x in an atmosphere in which a predetermined reducing agent (such as urea) is present. Can also be used. As such an SCR catalyst, a transition metal ion exchange zeolite in which a transition metal (such as Cu or Fe) is supported on zeolite can be used.

In addition, a metal oxide having a large specific surface area and high durability (particularly heat resistance) is preferably used for the carrier supporting the metal catalyst. Examples of the metal oxide used in such a carrier include alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), titania (TiO ₂ ), and the like. By using these metal oxides as a support, the catalytic action of the metal catalyst supported on the support can be appropriately exhibited.

The catalyst layer 30 may contain various additives in addition to the metal catalyst and the carrier. For example, when the above three-way catalyst is used as a metal catalyst, an OSC material can be used as the additive. Such an OSC material has a function of occluding and releasing oxygen, and the exhaust gas atmosphere inside the catalyst layer 30 can be stably maintained in the vicinity of stoichiometric (theoretical air-fuel ratio). Can be exhibited stably. Examples of such OSC materials include ceria-zirconia composite oxide. Another example of additives contained in the catalyst layer 30 is, like _the NO _x adsorbing agent and stabilizer with _the NO _x storage capacity.

(3) Phosphorus Collection Layer As shown in FIG. 3, the exhaust gas purifying catalyst 10 according to this embodiment includes a phosphorus collection layer 20 containing a phosphorus collection component. By providing the phosphorus collection layer 20 on the catalyst layer 30, it is possible to collect the phosphorus component in the exhaust gas before reaching the catalyst layer 30 and detoxify the exhaust gas. Poisoning can be suitably suppressed.
And this phosphorus collection layer 20 has a high gas permeability, since the large pores are formed in a high ratio. For this reason, the harmful component in exhaust gas can be made to contact a metal catalyst efficiently, and the high exhaust gas purification capability can be exhibited.

The carrier constituting the skeleton portion of the phosphorus collection layer 20 mainly contains a metal oxide. As the metal oxide, a material having predetermined heat resistance and strength can be preferably used. For example, alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ) A material formed of a heat-resistant material such as titania (TiO ₂ ) can be preferably used. The shape of the carrier of the phosphorus collection layer 20 is preferably a needle shape having a high aspect ratio. In addition, the “needle shape” in the present specification is a concept including a shape called a long bar shape, a wire shape, a scale shape, or the like. The average aspect ratio of such acicular metal oxide particles (value obtained by dividing the length in the major axis direction by the length in the minor axis direction (typically the diameter)) is approximately 3 or more, preferably Is preferably 5 or more, for example, about 10 to 50. The average length of the metal oxide particles in the major axis direction is generally about 0.1 μm or more, preferably 0.5 μm or more, for example, 1 to 10 μm. The average length (typically the diameter) of the metal oxide particles in the minor axis direction is generally about 0.01 μm or more, preferably 0.05 μm or more, for example, 0.1 to 1 μm.

  The phosphorus trapping component 20 is carried on the carrier of the phosphorus trapping layer 20. A compound containing at least one element of La, Fe, Zr, Ce, Ti, Sr, Ca, Mg, Pr, and Y is used as the phosphorus collecting component. The compound containing La or the like collects phosphorus components in the exhaust gas and detoxifies the exhaust gas. Specific examples of such phosphorus collecting components include lanthanum oxide, lanthanum carbonate, lanthanum sulfate, iron (II) oxide, iron (III) oxide, iron (II) carbonate, iron (II) sulfate, iron (III) sulfate, Examples thereof include oxides such as cerium oxide, cerium sulfate, calcium oxide, calcium carbonate, calcium sulfate, magnesium oxide, magnesium carbonate, and magnesium sulfate, carbonates, sulfates, and the like.

  The loading density (wt%) of the phosphorus collection component with respect to the carrier is generally 1 wt% or more, preferably 5 wt%, for example, 10 wt% or more. Since the phosphorus component collection efficiency improves as the loading density of the phosphorus collection component increases, it is possible to suitably prevent a reduction in exhaust gas purification ability due to phosphorus poisoning. However, from the viewpoint of suitably dispersing and supporting the phosphorus collecting component and increasing the utilization efficiency of the phosphorus collecting component, the loading density of the phosphorus collecting component is approximately 50 wt% or less, preferably 40 wt% or less, for example 30 wt. % Or less is preferable.

  Further, the width of the phosphorus collection layer 20 (arrangement area on the catalyst layer 30) is not particularly limited. For example, the phosphorus collection layer 20 may be provided on the entire surface of the catalyst layer 30 or may be provided only on a part thereof. Specifically, when the flow-through type substrate 11 is used as in the exhaust gas purifying catalyst 10 according to the present embodiment, the phosphorus collection layer 20 is formed on almost the entire surface of the catalyst layer 30 as shown in FIG. Although it may be provided, the phosphorus collection layer 20 may be provided in a concentrated manner at the end portion on the gas inflow side. When the phosphorus collection layer 20 is provided in a concentrated manner on the end portion on the gas inflow side, the phosphorus component in the exhaust gas can be suitably collected at the end portion on the gas inflow side where the influence of phosphorus poisoning becomes large. Further, the exhaust gas purification ability in the catalyst layer 30 can be more suitably maintained.

  The average thickness of the phosphorus collection layer 20 (length perpendicular to the extending direction X of the partition walls 16) is not particularly limited, but is generally 1 to 300 μm, typically 5 from the viewpoint of exhibiting the effect of the present invention at a high level. It is good to be about 100 μm, for example, about 10 to 50 μm. Further, the coating amount per 1 L of the volume of the substrate 11 of the phosphorus collection layer 20 is not particularly limited, but from the viewpoint of bringing the harmful component into contact with the metal catalyst more efficiently, it is generally 100 g / L or less, preferably 50 g / L. L or less, for example, 30 g / L or less is preferable.

  And in the phosphorus collection layer 20 in this embodiment, the ratio for which the support | carrier which makes the substantial part, especially the frame | skeleton part of the phosphorus collection layer 20 occupies is restrained small. In other words, the phosphorus collection layer 20 has a high porosity and structural characteristics excellent in gas permeability. The porosity of the phosphorus collection layer 20 calculated based on observation with an electron microscope (that is, the ratio of pores in the phosphorus collection layer 20) Va is approximately 60% or more, preferably 70% or more, It may be 90% or less, typically 85% or less, for example 80% or less. By setting the porosity Va to a predetermined value or more, the gas permeability of the phosphorus collection layer 20 becomes better, and harmful components in the exhaust gas can be efficiently brought into contact with the metal catalyst. Further, in the case of the phosphorus collection layer 20 having such a large porosity Va, the contact point between the phosphorus component in the exhaust gas and the phosphorus collection component in the phosphorus collection layer 20 is increased, so that the phosphorus component is more efficiently performed. Can be collected. Therefore, phosphorus poisoning of the metal catalyst can be suitably prevented. Moreover, the mechanical strength of the phosphorus collection layer 20 can be improved by making the said porosity Va into a predetermined value or less. The porosity Va can be adjusted, for example, by controlling the mixing ratio of the carrier and the pore-forming agent in the slurry and the size (particle size) of the carrier and / or the pore-forming agent in the production method described later. .

The porosity Va of the phosphorus collection layer 20 can be calculated as follows.
(1) First, a sample piece including the phosphorus collection layer 20 is embedded with a resin, and the cross section of the phosphorus collection layer 20 is cut out.
(2) Next, the cross section of the cut specimen is observed with a scanning electron microscope (SEM) to obtain a cross-sectional SEM observation image (reflection electron image, observation magnification 1000 times) (see FIG. 11). The observation visual field is set so that approximately 20 or more, for example, 50 or more pores partitioned by the skeleton portion of the phosphorus collection layer 20 are included, and a cross-sectional SEM observation image is obtained.
(3) Next, using the two-dimensional image analysis software winroof (registered trademark), the processing range is set in the phosphorus collection layer 20, and the portion occupied by the pores is extracted by automatic binarization (discriminant analysis method) Then, a binary image is obtained (see FIG. 12).
(4) Next, expansion / contraction processing is performed twice on the binary image.
(5) Next, each pore is separated into a circular shape by circular separation measurement (automatic processing).
(6) Then, in the analyzed image, the ratio (area%) of the area occupied by the pores when the area of the catalyst layer is 100% is measured, and the porosity Va is calculated.

Moreover, in the phosphorus collection layer 20, the porosity of the large pores calculated based on observation with an electron microscope (that is, the ratio of pores having an equivalent circle diameter larger than 5 μm in the phosphorus collection layer 20) Vb is It is generally 45% or more, for example, 50% or more, and is not more than Va, and is generally 85% or less, typically 80% or less, preferably 70% or less, for example 60% or less. By setting the porosity Vb of the large pores to a predetermined value or more, the gas permeability of the phosphorus collection layer 20 is improved, so that harmful components in the exhaust gas can be efficiently brought into contact with the metal catalyst. Moreover, the mechanical strength of the phosphorus collection layer 20 can be improved by making said Vb below a predetermined value. The porosity Vb of the large pores is obtained by controlling the mixing ratio of the carrier and the pore-forming agent in the slurry and the size (particle size) of the carrier and / or the pore-forming agent in the production method described later. Can be adjusted.
In addition, the porosity Vb of the large pores of the phosphorus collection layer 20 is a pore portion having an equivalent circle diameter of 5 μm or less from the porosity (the porosity calculated in (6) above) Va of the entire phosphorus collection layer 20. After obtaining an image excluding the image (see FIG. 13), the ratio (area%) of the area occupied by the pores can be measured and calculated.

  In the phosphorus collection layer 20, the ratio (Vb / Va) of the porosity Vb of the large pores to the porosity Va is approximately 60% or more, preferably 65% or more, and approximately 99% or less, typically It may be 98% or less, for example 90% or less, and in one example 80% or less. Thereby, the effect of this invention and maintenance of mechanical strength can be made compatible at a high level.

  Further, as described above, a needle-like carrier is preferably used as the carrier of the phosphorus collection layer 20. When a needle-like carrier is used in this way, it is preferable to form a three-dimensional network-like phosphorus collection layer having a multi-pore structure. As an example of the phosphorus collection layer 20 having such a multi-element pore structure, a first pore that is partitioned by a skeleton portion and a first pore that is formed inside the skeleton portion and communicates with the first pore. Examples thereof include a phosphorus trapping layer 20 having a binary pore structure having two pores. In the case of such a phosphorus collection layer 20, exhaust gas can be passed through the skeleton portion to collect phosphorus components and PM. Further, in the case of the phosphorus collection layer 20 having such a multi-pore structure, the average pore diameter of the first pores is 1 μm or more and less than 10 μm, and the average pore diameter of the second pores is 0.5 μm or more and less than 1 μm. Is preferable. Thus, harmful components in the exhaust gas can be suitably brought into contact with the metal catalyst, and the phosphorus component can be suitably collected by the phosphorus collection layer 20.

The phosphorus collection layer 20 has first pores partitioned by a skeleton portion, and is configured in a three-dimensional network. The arbitrary cross section of the phosphorus collection layer 20 may have a plurality of divided parts by dividing the skeleton part. It is considered that the greater the number of divided parts (number of divisions), the higher the pore connectivity. That is, the number of divisions can be an index indicating the connectivity of the pores in the phosphorus collection layer 20. In the cross section of the phosphorus collection layer 20, from the viewpoint of improving gas permeability, the number of divisions per unit cross-sectional area (0.01 mm ² ) is approximately 20 or more, typically 40 or more, preferably 60. One or more, more preferably 80 or more, for example 90 or more, and in one example 100 or more. From the viewpoint of improving the mechanical strength, the number of divisions per unit cross-sectional area is approximately 200 or less, preferably 180 or less, more preferably 160 or less, for example 150 or less. However, the number of divisions per unit cross-sectional area is not necessarily 200 or less, and may be more than 2000, for example. Even in this case, the phosphorus collection layer 20 having suitable gas permeability can be obtained.

Note that the number of divisions per unit cross-sectional area of the skeleton portion can be calculated as follows.
(1) First, a sample piece including the phosphorus collection layer 20 is embedded with a resin, and the cross section of the phosphorus collection layer 20 is cut out.
(2) Next, the cross section of the cut specimen is observed with a scanning electron microscope (SEM) to obtain a cross-sectional SEM observation image (reflection electron image, observation magnification 1000 times) (see FIG. 11).
(3) Next, using the two-dimensional image analysis software winroof (registered trademark), the processing range is set in the phosphorus collection layer 20, and the skeleton part is extracted by automatic binarization (discriminant analysis method). Get a value image.
(4) Next, after the dilation / reduction process is performed twice on the binary image, points whose area is smaller than 0.9 μm ² are deleted to remove noise.
(5) Then, the number of divisions of the skeleton portion is read in the analyzed image and converted per unit sectional area (0.01 mm ² ).

The average thickness of the skeleton portion is approximately 5 μm or less, typically 4 μm or less, preferably 3.5 μm or less, for example, 3 μm or less. Thereby, although the phosphorus collection layer 20 is formed, high gas permeability can be exhibited, and the phosphorus component collection effect by the proximity of the phosphorus component and the phosphorus collection component described above can be obtained. You can play at a higher level. The lower limit of the average thickness is not particularly limited, but from the viewpoint of improving the mechanical strength, it is generally about 0.1 μm or more, typically 0.5 μm or more, for example, 1 μm or more.
The average thickness of the skeleton part is the same as the calculation of the number of divisions described above, and after performing (1) to (4), the length of the shortest part (minimum length passing through the center of gravity) is determined for each divided part. It is obtained by calculating and arithmetically averaging the values.

  On the surface of the phosphorus collection layer 20, the surface opening ratio of the skeleton portion is approximately 20% or more, typically 25% or more, preferably 30% or more, and generally 60% or less, typically 50%. Hereinafter, for example, it may be 40% or less. Thereby, harmful components in the exhaust gas can be efficiently brought into contact with the metal catalyst. However, the surface aperture ratio of the skeleton portion may exceed 60%. Even in this case, harmful components in the exhaust gas can be efficiently brought into contact with the metal catalyst.

In addition, the surface aperture ratio of the skeleton part of the phosphorus collection layer 20 can be calculated as follows.
(1) First, the sample piece including the phosphorus collection layer 20 is fixed to the surface of the sample table so that the extending direction X of the substrate 11 and the surface of the sample table are parallel to each other.
(2) Next, the surface of the sample piece was observed with a field emission scanning electron microscope (FE-SEM), and a surface SEM observation image (secondary electron image, observation magnification 20000 times) from the outermost surface side of the phosphorus collection layer 20. ) (See FIG. 15).
(3) Next, using a two-dimensional image analysis software winroof (registered trademark), a surface opening is extracted by automatic binarization (discriminant analysis method) to obtain a binary image (see FIG. 16).
(4) Next, after performing the shrinkage process twice and the hole filling process on the binary image, a point having an area of 0.001 μm ² or less is deleted to remove noise.
(5) Then, in the analyzed image, the ratio (area%) of the area occupied by the surface opening when the area of the phosphorus trapping layer is 100% is measured, and the surface opening ratio is calculated.

The average pore diameter of the second pores formed in the skeleton portion of the phosphorus collection layer 20 is typically smaller than the average pore diameter of the first pores, for example, less than 5 μm. Further, the pore diameter P ₅ corresponding to a cumulative 5% from the small pore side having a smaller pore diameter is, for example, 0.01 μm or more, preferably 0.02 μm or more, typically 0.03 μm or more, for example, 0.035 μm or more. In general, it is preferably 0.1 μm or less, typically 0.07 μm or less, for example 0.05 μm or less. In addition, the pore diameter P ₉₅ corresponding to 95% cumulative from the small pore side having a small pore diameter is generally 1 μm or more, typically 1.5 μm or more, for example, 1.7 μm or more, and generally 5 μm or less, preferably Is 4 μm or less, typically 3.5 μm or less, preferably 2.5 μm or less. As for the relationship between the pore diameter _{P 5} and the pore diameter _{P 95,} the pore diameter _{P 5} is not less than 0.03 .mu.m, and may pore diameter _{P 95} is at 1.5μm or more. Thereby, a phosphorus collection function and mechanical strength can be made compatible at a high level, and the effect of the present invention can be exhibited at a higher level.

  Note that the average pore diameter of the second pores was measured by measuring the shape characteristics in the analyzed image after performing steps (1) to (4) in the same procedure as the calculation of the surface aperture ratio. It is obtained by measuring the equivalent diameter.

  As described above, the pores formed in the phosphorus collection layer 20 have pores that are equal to or smaller than the pore size of the catalyst layer 30. In one typical example, in the differential pore distribution curve obtained by measurement with a mercury porosimeter, the phosphorus collection layer 20 has two pore peaks in a pore diameter range of 0.5 to 10 μm. For example, the peak A may have a peak A in a range of 1 μm or more and less than 10 μm, and the peak B may have a peak B in a range of a pore size of 0.5 μm or more and less than 1 μm. The two peaks A and B are the first pores defined by the skeleton portion of the phosphorus collection layer 20 and the first pores formed inside the skeleton portion and communicating with the first pores. 2 pores may be suggested.

Although it may vary depending on the type of the substrate 11 or the like, the pore volume (V1) of the peak A derived from the first pore is approximately 0.03 cm ³ / g or more, preferably 0.04 cm ³ / g or more, More preferably, it is 0.05 cm ³ / g or more. Thereby, since the gas permeability of the phosphorus collection layer 20 improves, the harmful component in exhaust gas can be efficiently contacted with a metal catalyst. In view of improving the mechanical strength, V1 is approximately 0.1 cm ³ / g or less, for example, may is 0.08 cm ³ / g or less.
Although it may vary depending on the type of the substrate 11 or the like, the pore volume (V2) of the peak B derived from the second pore is typically smaller than the peak A and becomes a gentle peak. From the viewpoint of exhibiting the effect of the present invention at a high level, it is generally 0.001 cm ³ / g or more, preferably 0.002 cm ³ / g or more. In view of improving the aspect and mechanical strength to ensure the V1, V2 is approximately 0.02 cm ³ / g or less, for example, it is 0.015 cm ³ / g or less may.

  The ratio (V1 / V2) of the pore volume of the first pore to the pore volume of the second pore is approximately 3 or more, preferably 4 or more, more preferably 5 or more, for example 6 or more. . Thereby, since the gas permeability of the phosphorus collection layer 20 improves by this, the harmful component in waste gas can be made to contact a metal catalyst efficiently. Although an upper limit is not specifically limited, From a viewpoint of improving mechanical strength, it is generally 30 or less, preferably 20 or less, for example, 10 or less.

The pore distribution of the phosphorus collection layer 20 can be calculated as follows. First, a sample piece of the substrate 11 provided with the phosphorus collection layer 20 and the catalyst layer 30 is prepared, and the pore distribution of the sample piece is measured in a pressure range of 1 to 60000 psi using a commercially available mercury porosimeter. To do. Thereby, the pore distribution curve which shows the relationship between pore diameter and pore volume is obtained. By comparing the obtained pore distribution curve with the pore distribution curve of only the base material, the state of the pores formed in the phosphorus collection layer 20 is confirmed.
Moreover, the pore volume of each peak can be calculated | required from the obtained pore distribution curve. Specifically, the integrated pore volume (cm ³ / g) of each peak of the sample piece including the phosphorus collection layer 20 is calculated from the integrated pore volume distribution curve, and the pores of only the base material 11 in the same range are calculated. By subtracting the volume, the pore volume (cm ³ / g) per unit mass of the phosphorus collection layer 20 can be obtained.

<Description of exhaust gas supplied to exhaust gas purification catalyst>
As shown in FIG. 2, the exhaust gas discharged from the internal combustion engine 2 (see FIG. 1) flows into the cell 15 of the exhaust gas purification catalyst 10 from the end of the base material 11 on the exhaust gas inflow side. The exhaust gas flowing into the cell 15 passes through the porous phosphorus trapping layer 20 and then passes through the cell 15 toward the end on the exhaust gas outflow side while contacting the catalyst layer 30, and the exhaust gas purifying catalyst. 10 is discharged to the outside.

At this time, when the exhaust gas passes through the phosphorus collection layer 20, the phosphorus component in the exhaust gas is collected by the phosphorus collection component of the phosphorus collection layer 20. Thereby, since it is possible to prevent the phosphorus component from entering the catalyst layer 30, phosphorus poisoning of the metal catalyst in the catalyst layer 30 can be suitably suppressed.
And the phosphorus collection layer 20 which concerns on this embodiment has a large pore in a relatively high ratio compared with the conventional phosphorus collection layer (a large pore whose circle equivalent diameter is larger than 5 micrometers). More than 45%). By providing such a phosphorus trapping layer 20 having high gas permeability, harmful components in the exhaust gas can be efficiently brought into contact with the metal catalyst. For this reason, harmful components in the exhaust gas can be efficiently brought into contact with the catalyst layer 30 and high exhaust gas purification ability can be exhibited.
Moreover, in the phosphorus collection layer 20 which has such a large pore in a high ratio, since the contact point of a phosphorus component and a phosphorus collection component is increasing, a phosphorus component is collected more efficiently, The phosphorus poisoning of the metal catalyst can be more suitably prevented.
Furthermore, since the phosphorus collection layer 20 according to the present embodiment has a multi-element pore structure (for example, a binary pore structure) including the first pores and the second pores, the skeleton portion is Has phosphorus collection function. Therefore, an excellent phosphorus collecting function can be exhibited.

<Method for Producing Exhaust Gas Purification Catalyst 10>
The exhaust gas-purifying catalyst 10 having the above-described configuration can be produced, for example, based on the following procedure.

When producing the exhaust gas purifying catalyst 10 having the above-described configuration, first, the catalyst layer 30 is formed on the surface of the partition wall 16 of the substrate 11.
Specifically, a mixed liquid is prepared by mixing a metal oxide serving as a support and a compound serving as a metal catalyst supply source at a predetermined ratio. And the composite material for the catalyst layer 30 by which the metal catalyst was carry | supported by the support | carrier was produced by baking after the prepared liquid mixture was dried at predetermined temperature and time. Then, the composite material is mixed with an appropriate solvent (for example, ion-exchanged water) together with a desired additive (for example, OSC material) to prepare a slurry for forming a catalyst layer.
Next, after the slurry for forming the catalyst layer is applied to the surface of the partition wall 16 of the substrate 11, the catalyst layer 30 is formed by drying. Specifically, first, the catalyst layer forming slurry is supplied into the cell 15 from the end of the base material 11 on the gas inflow side, and the cell 15 is sucked from the end of the gas outflow side. As a result, slurry is applied to the surface of the partition 16. The catalyst layer 30 can be formed on the surface of the partition wall 16 by drying the substrate 11 in this state.

In the present embodiment, next, the phosphorus collection layer 20 is formed on the catalyst layer 30.
Specifically, first, a mixed material is prepared by mixing a powder material serving as a carrier of the phosphorus collection layer 20 and a compound serving as a supply source of the phosphorus collection component at a predetermined ratio. And the composite material for the phosphorus collection layers 20 by which the phosphorus collection component was carry | supported by the support | carrier was produced by baking at the predetermined temperature and time after drying the prepared liquid mixture. And this composite material, a pore making material, and a suitable solvent (for example, ion exchange water) are mixed by a predetermined ratio, and the slurry for phosphorus collection layer formation is prepared.
Next, the phosphorus collection layer forming slurry is supplied into the cell 15 of the substrate 11, and the phosphorus collection layer forming slurry is applied onto the catalyst layer 30. The phosphorus collection layer 20 is formed on the catalyst layer 30 by drying and baking the base material 11 in this state.
At this time, the pore-forming agent contained in the phosphorus collection layer forming slurry is thermally decomposed and removed during firing, and the portions where the pore-forming agent was present become pores. Accordingly, the porous phosphorus collection layer 20 in which large pores having an equivalent circle diameter larger than 5 μm occupy 45% or more of the volume of the phosphorus collection layer can be formed.

  Thus, the above-described exhaust gas-purifying catalyst 10 can be produced simply by adding a pore-forming agent to the phosphorus collection layer forming slurry. For this reason, the exhaust gas purifying catalyst 10 according to the present embodiment can be provided at a significantly lower cost compared to the conventional technology that requires a large amount of noble metal.

  In the preparation of the above-described slurry for forming the phosphorus collection layer, any pore forming agent may be used as long as it can be thermally decomposed and removed during firing. Examples include starch, carbon powder, activated carbon, and polymer organic materials (for example, polyethylene, polypropylene, melamine resin, polymethyl methacrylate (PMMA) resin) and the like. The average particle diameter of the pore former is approximately 2 μm or more, preferably 5 μm or more, for example, about 5 to 20 μm.

  Further, in the preparation of the slurry for forming the phosphorus collection layer, the mixing ratio of the carrier powder and the pore forming agent can be an important factor from the viewpoint of realizing the phosphorus collection layer 20 described above. The mixing ratio of the carrier powder and the pore former may vary depending on, for example, the physical properties of the carrier powder (for example, the aspect ratio and the length in the major axis direction), but the volume of the pore former is approximately three times the volume of the carrier powder. It is good to adjust so that it may be about 15 times or less, for example, 10 times or less. Thereby, the phosphorus collection layer 20 with good gas permeability can be better realized. As a result, harmful components in the exhaust gas can be efficiently brought into contact with the metal catalyst, and the purification performance of harmful components (for example, high carbon number HC) by the catalyst layer 30 can be maintained in a high state.

In the preparation of the phosphorus collection layer forming slurry, the viscosity of the slurry can also be an important factor from the viewpoint of realizing the phosphorus collection layer 20 described above. The viscosity of the slurry for forming the phosphorus collection layer is approximately 30 mPa · s or more, preferably 50 mPa · s or more and approximately 500 mPa · s or less when the measurement temperature is 25 ° C. and the shear rate is 300 to 500 s ^−1. It is good to adjust so that it becomes. The slurry viscosity can be measured with a commercially available viscometer (for example, a dynamic viscoelasticity measuring device). By using the slurry having such a viscosity, the phosphorus collection layer 20 can be favorably formed on the surface of the catalyst layer.

  Various additives such as a thickener, a surfactant, and a dispersant can be used to adjust the viscosity of the slurry for forming the phosphorus collection layer. Examples of the thickener include cellulose polymers such as hydroxyethyl cellulose (HEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), and hydroxyethyl methyl cellulose (HEMC). Moreover, as surfactant, a nonionic (nonionic) thing is mentioned, for example.

  Moreover, in the manufacturing process described above, the conditions for drying and firing each slurry are not particularly limited. For example, after drying at about 80 to 300 ° C. for about 1 to 10 hours, about 2 to 4 at about 400 to 1000 ° C. It is good to perform baking for about an hour.

<Other forms of exhaust gas purification catalyst>
Note that the exhaust gas purifying catalyst disclosed herein is not limited to the above-described embodiment. For example, in the exhaust gas purifying catalyst according to the above-described embodiment, a flow-through type base material is used, but a wall flow type base material can also be used. FIG. 4 is a view showing an example of an exhaust gas purifying catalyst using such a wall flow type base material.

As shown in FIG. 4, the wall flow type base material 11 includes an inlet cell 12 having an end on the exhaust gas inflow side, an exit cell 14 having an end on the exhaust gas outflow side, and an inlet cell. 12 and a partition wall 16 that partitions the outlet cell 14. And the sealing part 12a is arrange | positioned and sealed at the edge part by the side of the exhaust gas outflow of the entrance side cell 12. FIG. Further, a sealing portion 14a is disposed and sealed at the end of the outlet cell 14 on the exhaust gas inflow side.
The partition wall 16 of the wall flow type substrate 11 has a porous structure through which exhaust gas can pass, and the catalyst layer 30 is formed inside the partition wall 16. In this case, the phosphorus collection layer 20 is formed on the surface of the catalyst layer 30 formed inside the partition wall 16 (in other words, the surface of the partition wall 16).

  In the exhaust gas-purifying catalyst 10, exhaust gas discharged from the internal combustion engine 2 (see FIG. 1) is supplied to the inlet cell 12, passes through the partition wall 16, and is discharged to the outlet cell 14. At this time, since the phosphorus collection layer 20 collects the phosphorus component in the exhaust gas, the detoxified exhaust gas is supplied to the catalyst layer 30. For this reason, it can prevent suitably that phosphorus poisoning arises in the metal catalyst in the catalyst layer 30. And since the large pore is formed in the phosphorus collection layer 20 by the high ratio similarly to above-described embodiment, high gas permeability can be exhibited. For this reason, harmful components in the exhaust gas can be suitably brought into contact with the metal catalyst of the catalyst layer 30 to prevent a reduction in exhaust gas purification ability due to an increase in pressure loss.

  Even in the case of the exhaust gas purifying catalyst 10 using the wall flow type substrate 11 as shown in FIG. 4, the phosphorus collection layer having the pore structure basically similar to the above-described embodiment. 20 is formed. However, in the case of the exhaust gas purifying catalyst 10 using the wall flow type base material 11, not only the effect of improving the exhaust gas purifying ability by bringing the harmful component into contact with the metal catalyst more efficiently, but also the increase in pressure loss. The effect that it can suppress is also acquired.

  Specifically, in the wall flow type substrate 11, the porosity Va of the phosphorus collection layer 20 is 50% or more, preferably 60% or more, more preferably 70% or more, and generally 90% or less. Typically, by setting it to 85% or less, for example 80% or less, not only can the harmful components in the exhaust gas be brought into contact with the metal catalyst efficiently, but also the effect of better suppressing the pressure loss hysteresis is exhibited. Can be made.

Even when the wall flow type substrate 11 is used, the phosphorus collection layer 20 preferably has a multi-pore structure. When the wall flow type substrate 11 is used, the average pore diameters of the first pores and the second pores formed in the phosphorus trapping layer 20 having a multi-element pore structure are determined by the phosphorus trapping. The average pore diameter of the pores of the catalyst layer 30 provided in the lower layer of the layer 20 is preferably equal to or smaller than the average pore diameter of the catalyst layer 30.
In a preferred embodiment at this time, the size relationship of the average pore diameter satisfies the second pore <the first pore <the pore of the catalyst layer 30. By relatively reducing the pore diameter of the second pores formed in the skeleton part, the mechanical strength and durability of the skeleton part can be improved. Moreover, according to the said structure, since the phosphorus collection layer 20 becomes a structure which has a multistage pore diameter (for example, two-stage pore diameter), a much more superior collection function can be exhibited. As a result, it is possible to suppress the pressure loss hysteresis better by suppressing the deposition of phosphorus and PM in the pores inside the catalyst layer 30.

  Further, the surface opening ratio of the skeleton portion of the phosphorus collection layer 20 is also approximately 20% or more, typically 25% or more, preferably 30% or more, as in the case of using a flow-through type substrate. Therefore, it may be set to approximately 60% or less, typically 50% or less, for example, 40% or less. As a result, in addition to the effect that harmful components in the exhaust gas can be efficiently contacted with the metal catalyst, the effect that the increase in pressure loss accompanying the formation of the phosphorus trapping layer can be drastically reduced can also be obtained.

As for the pore volume (V1) of the peak A derived from the first pores, as in the case of flow-through of the substrate, generally 0.03 cm ³ / g or more, preferably 0.04 cm ³ / g or more, more preferably 0.05 cm ³ / g or more. In this case as well, an effect that an increase in pressure loss accompanying the formation of the phosphorus collection layer 20 can be suppressed can be obtained.

  Further, the ratio of the pore volume of the first pore to the pore volume of the second pore (V1 / V2) is also generally about 3 or more, as in the case of using the flow-through type substrate. Is 4 or more, more preferably 5 or more, for example 6 or more. Also in this case, not only the purification efficiency of harmful components is improved, but also an effect of suppressing an increase in pressure loss due to the formation of the phosphorus collection layer 20 is obtained.

  In the case of producing an exhaust gas purifying catalyst using a wall flow type base material, the volume of the pore forming agent is approximately three times or more the volume of the carrier powder when preparing the phosphorus collection layer forming slurry. And it is good to adjust so that it may be about 15 times or less, for example, 10 times or less. As a result, the rate of increase in pressure loss due to the formation of the phosphorus collection layer 20 can be suppressed to approximately 1.6 times or less that of the base material 11 alone.

  In the exhaust gas purifying catalyst 10 using the wall flow type base material 11 as shown in FIG. 4, when the total length Lw of the partition wall 16 in the extending direction X (in the exhaust gas flowing direction) is 100%, phosphorus trapping is performed. The length of the collecting layer 20 is approximately 70% or more, typically 80% or more, and preferably 90% or more. For example, the length is preferably the same as the total length Lw of the partition wall 16 in the extending direction X. Thereby, phosphorus poisoning of the metal catalyst in the catalyst layer 30 can be suitably prevented. Further, when 90% or more of the total surface area of the catalyst layer 30 is covered with the phosphorus collection layer 20, it is difficult for the phosphorus component and PM to enter the catalyst layer 30. Therefore, it is possible to suppress the phosphorus loss and PM from accumulating inside the catalyst layer 30 and to significantly reduce the pressure loss hysteresis. The phosphorus collection layer 20 may be provided continuously on the surface of the catalyst layer 30 or may be provided intermittently.

  Hereinafter, some test examples related to the present invention will be described, but the present invention is not intended to be limited to those shown in the test examples.

[First test]
In this test, an exhaust gas purification catalyst having a catalyst layer formed on the surface of a partition wall of a flow-through base material and a phosphorus collection layer formed on the catalyst layer was produced, and the performance of the exhaust gas purification catalyst was evaluated. evaluated.

1. Preparation of Exhaust Gas Purification Catalyst (Example 1) In Example 1, a flow-through honeycomb substrate (manufactured by Cordierite, cell number 400 cpsi, partition wall thickness 6 mil) manufactured by Nippon Choshi Co., Ltd. was prepared.
In this test, first, a catalyst layer containing metal catalysts (Pt and Pd) was formed on the surface of the partition walls of the base material.
Specifically, a mixture of a dinitrodiammine platinum nitric acid solution and a palladium nitrate solution is impregnated with Al ₂ O ₃ powder as a carrier, dried and fired, and Pt / Pd supported-Al ₂ O ₃ A powder was obtained.
Then, the resulting Pt / Pd supported _-Al 2 _{O 3} powder (1130 g), and acicular TiO ₂ powder (33 g), and acetic acid (150 g), and aluminum hydroxide (37 g), deionized water (3430G And a wet pulverization to prepare a slurry.
To this slurry, 20 g of citric acid and 5 g of HEC (hydroxyethyl cellulose) were added and thickened to obtain a slurry for forming a catalyst layer.
The catalyst layer forming slurry is introduced into the cell from the end portion on the exhaust gas inflow side of the base material, and sucked from the end portion on the exhaust gas outflow side, so that the length of the partition wall in the extending direction of the partition wall surface is reduced. The slurry was applied over a 100% area. This was dried at 90 ° C. and then fired at 500 ° C. to form a catalyst layer on the partition wall surface.

Next, a phosphorus collection layer containing a phosphorus collection component (La) and having a large proportion of large-diameter pores was formed on the catalyst layer described above.
Specifically, an aqueous lanthanum nitrate solution is impregnated with needle-like titania powder (average fiber diameter φ = 0.2 μm, average fiber length L = 3 μm), dried and fired to obtain La-supported TiO ₂ powder. Obtained.
Then, a La-carrying -TiO ₂ powder obtained (75 g), TiO ₂ content was mixed with 6% TiO ₂ sol (520 g), to prepare a slurry by wet milling.
To this slurry, a melamine resin (90 g) having an average particle diameter of 5 μm was added as a pore-forming agent, and then 3 g of CMC was added to increase the viscosity, thereby obtaining a slurry for forming a phosphorus collection layer. The amount (90 g) of the pore-forming agent (melamine resin) described above was adjusted so that 36 g of the pore-forming agent was included per 1 L of catalyst volume.
The phosphorus trapping layer forming slurry is introduced into the cell from the end of the base material on the exhaust gas inflow side, and sucked from the end of the exhaust gas outflow side, so that the surface of the catalyst layer has a partition wall extending direction. The slurry was applied over a region of 100% length. The input amount of the slurry at this time was adjusted so that a phosphorus collection layer having an amount of 30 g per 1 L of the substrate volume was formed by firing described later.
After drying this at 90 degreeC, the phosphorus collection layer was formed on the catalyst layer by baking at 500 degreeC. The pore-forming agent in the slurry is pyrolyzed and removed by the heat of firing at this time, and pores are formed where the pore-forming agent was present. Phosphorus traps with a large proportion of large-diameter pores formed A stratification was formed.

(Example 2) The carrier used for the phosphorus collection layer was changed from needle-like titania powder to needle-like alumina powder (average fiber diameter φ = 0.3 μm, average fiber length L = 8 μm), and La-supported-Al _The above example except that ₂ O ₃ powder (75 g) and Al ₂ O ₃ sol (390 g) having an Al ₂ O ₃ content of 15% were mixed to prepare a slurry for forming a phosphorus collection layer. An exhaust gas purifying catalyst was prepared under the same conditions as in 1.

Reference Example 1 In Reference Example 1, an exhaust gas purifying catalyst in which only a catalyst layer was formed on a partition wall of a base material without forming a phosphorus collection layer was produced. The base material structure and the catalyst layer forming method were set to the same conditions as in Example 1 described above.

(Reference Example 2) An exhaust gas purifying catalyst was produced under the same conditions as in Example 1 above, except that a pore-forming agent (polymethyl methacrylate resin) was not added to the slurry when forming the phosphorus collection layer. did.

2. Evaluation of Exhaust Gas Purification Catalyst Next, various evaluations were performed on the exhaust gas purification catalyst of each example described above. The evaluations performed in this test are listed below.

(1) SEM observation In each of the above examples, a sample piece including a phosphorus collection layer and a catalyst layer is embedded in a resin, and after a cross section of the phosphorus collection layer is cut out, a cross section perpendicular to the cylinder axis direction is scanned. Observation with a scanning electron microscope (SEM) gave a cross-sectional SEM observation image (reflected electron image, observation magnification 200 times). 5 to 8 are SEM observation images (magnification: 200 times) of a cross section perpendicular to the cylinder axis direction of the exhaust gas purifying catalyst of each example described above, FIG. 5 is Example 1, FIG. 6 is Example 2, and FIG. Shows Reference Example 1 and FIG. 8 shows Reference Example 2. 9 is an SEM observation image (magnification: 2000 times) of the surface of the phosphorus collection layer of Example 1, and FIG. 10 is an SEM observation image (magnification: 2000 times) of the surface of the phosphorus collection layer of Reference Example 2. .

As shown in FIGS. 5 and 6, it can be confirmed that in Example 1 and Example 2 in which the pore-forming agent was added to the slurry for forming the phosphorus collection layer, the phosphorus collection layer 20 was formed on the catalyst layer 30. It was. From the SEM observation images of FIGS. 5, 6, and 9, it was confirmed that relatively large pores were formed at a high ratio in the phosphorus collection layers 20 of Examples 1 and 2.
On the other hand, as shown in FIG. 7, in the exhaust gas purifying catalyst of Reference Example 1, no phosphorus collection layer was formed on the catalyst layer 130. As shown in FIG. 8, in the exhaust gas purifying catalyst of Reference Example 2, the phosphorus collection layer 120 was formed on the catalyst layer 130. However, as shown in FIGS. 8 and 10, unlike Example 1 and Example 2, the phosphorus collection layer 120 of Reference Example 2 was a dense layer in which large pores were hardly formed.

(2) Measurement of porosity Next, using the cross-sectional SEM observation image (600 times magnification) of the catalyst layer, the ratio of the entire void (porosity Va) to the entire phosphorus collection layer and the phosphorus collection layer The ratio of voids (pore ratio Vb of large pores) of large pores (pores having an equivalent circle diameter larger than 5 μm) was calculated. The results are shown in Table 1. The calculation method has already been described above.
As representative examples, SEM observation and analysis results according to Example 1 are shown in FIGS. FIG. 11 is an enlarged image (magnification: 1000 times) of the SEM observation image of FIG. FIG. 12 shows an image after image processing is performed on the pores of the phosphorus collection layer 20 shown in FIG. FIG. 13 shows an image after image processing is performed on pores having an equivalent circle diameter of 5 μm or more among the pores of the phosphorus collection layer 20 shown in FIG. 11.

As shown in Table 1, in Examples 1 and 2, a high porosity Va of 70% or more was confirmed for the phosphorus collection layer. Further, the porosity Vb of the large pores accounted for 45% or more (for example, 50% or more) of the entire catalyst layer. In Examples 1 and 2, the ratio of the porosity Vb of the large pores to the porosity Va (Vb / Va) occupied 60% or more (for example, 65% or more). On the other hand, although the phosphorus collection layer was formed also in the reference example 2, since this phosphorus collection layer was formed densely, the porosity Va and the porosity Vb of a large pore were not able to be measured. .
From these analysis results, the phosphorus collection layers of Examples 1 and 2 have relatively large pores at a high ratio as compared to the general phosphorus collection layer as shown in Reference Example 2. It was confirmed that It is expected that the phosphorus trapping layer having such large pores at a high ratio has high gas permeability.

(3) Measurement of pore distribution Next, with respect to the exhaust gas purifying catalyst of each example, the pore distribution of the phosphorus collection layer was measured using a mercury porosimeter. The measurement results of Example 1 and Reference Example 2 are shown in FIG. As shown in FIG. 14, in Example 1, many large pores (holes) having a pore diameter of 1 μm or more are formed, while in Reference Example 2, almost 1 μm or more of pores are formed. The result was not obtained. Based on the measurement result of the mercury porosimeter, the volume of the first pore (pore volume) of 1 μm or more and less than 10 μm and the volume of the second pore of 0.5 μm or more and less than 1 μm for each example. (Phosphorus trapping layer skeleton pore volume) was calculated. The results are shown in Table 2.

  From the above Table 2 and FIG. 14, it was confirmed that the phosphorus collection layer of the exhaust gas purifying catalyst of Example 1 and Example 2 has a multi-pore structure having two kinds of pores having different diameters. It was. In addition, regarding the volume ratio of the first pore and the second pore constituting the multi-pore structure, in Example 1 and Example 2, the volume of the first pore is 4 of the volume of the second pore. It was more than twice. It is presumed that the phosphorus collection layers of Examples 1 and 2 having such structural features have excellent gas permeability and can exhibit an excellent phosphorus collection function.

(4) Measurement of the number of divisions and the thickness of the skeleton portion Using a cross-sectional SEM observation image (magnification 1000 times) of the phosphorus collection layer as shown in FIG. 11, the number of divisions per unit cross-sectional area of the phosphorus collection layer ( Piece / 0.01 mm ² ) and the average thickness (μm) of the skeleton portion were calculated. Image processing was performed with N = 5 for each example, and the obtained values were averaged. The results are shown in Table 3. The calculation method has already been described above. The “number of divisions” indicates the number per unit cross-sectional area (0.01 mm ² ) of the phosphorus collection layer, and the larger the number of divisions, the more the pores in the phosphorus collection layer communicate with each other. It can be said.

As described above, in Example 1 and Example 2, the number of divisions of the phosphorus collection layer was larger than that in Reference Example 2, and the respective pores formed in the phosphorus collection layer were connected to each other. Also from this point, it was confirmed that Example 1 and Example 2 have high gas permeability.
In Examples 1 and 2, the average thickness of the skeleton part was clearly smaller than that in Reference Example 2. From these results, in Examples 1 and 2, phosphorus is preferably obtained by efficiently bringing the phosphorus-collecting component (La) supported on the carrier forming the skeleton of the phosphorus-trapping layer into contact with the phosphorus component in the exhaust gas. It was confirmed that it can be collected.
From these results, it was confirmed that the phosphorus collection layers of Examples 1 and 2 have high gas permeability and can efficiently collect the phosphorus component in the exhaust gas.

(5) Measurement of surface opening ratio and pore diameter Using the surface SEM observation image of the skeleton portion of the catalyst layer, the surface opening ratio (area%) and the pore diameter (μm) of the skeleton portion were calculated. The results are shown in Table 4 below. The calculation method has already been described above. Further, “pore diameter P ₅ ” refers to a pore diameter corresponding to 5% cumulative from the small pore side, and “pore diameter P ₉₅ ” refers to a pore diameter corresponding to 95% cumulative from the small pore side. ing.
15 and 16 show the SEM observation / analysis results according to Example 1 as representative examples of the surface SEM observation images used in this evaluation. 15 is a surface SEM observation image (magnification of 20000 times) of the skeleton portion of the catalyst layer of Example 1. FIG. FIG. 16 shows an image after image processing is performed on the surface opening portion in FIG.

As shown in Table 1, in Example 1 and Example 2, the surface area ratio of the skeleton portion was 30% or more, and the surface area ratio was higher than that of Reference Example 2. In Examples 1 and 2, the pore diameter (P ₅ ) corresponding to 5% cumulative from the small pore side is 0.03 μm or more, and the pore diameter corresponding to 95% cumulative from the small pore side ( P ₉₅ ) was 1.5 μm or more. Also from such structural characteristics, it was confirmed that the phosphorus collection layers of Examples 1 and 2 have high gas permeability.

(6) Phosphorus poisoning test In this evaluation, after the phosphorous poisoning treatment was performed on the exhaust gas purifying catalysts of Example 1, Reference Example 1 and Reference Example 2, the model gas was used after the phosphorous poisoning treatment. The exhaust gas purification ability was evaluated.
In the phosphorous poisoning treatment in this evaluation, first, the exhaust gas outflow side end of the exhaust gas purification catalyst of each example was immersed in a triammonium phosphate aqueous solution (0.61 wt%). Aspiration was performed. Next, a hot air of 90 ° C. was supplied into the substrate and dried, followed by a baking treatment of 500 ° C.

And model gas A of the composition shown below was supplied to each exhaust gas purification catalyst after phosphorus poisoning treatment, and exhaust gas purification ability was evaluated. Specifically, the temperature of the exhaust gas purification catalyst is raised from 100 ° C. to 350 ° C. at a rate of temperature increase of 20 ° C./min, and the temperature at which the hydrocarbon (HC) purification rate reaches 90% (90 % Purification temperature (T90)).
In this evaluation, the exhaust gas purifying catalyst of each example was 90% purified in the respective states before the phosphorous poisoning treatment, the first phosphorous poisoning treatment, the second phosphorous poisoning treatment, and the third phosphorous poisoning treatment. The temperature (T90) was measured. The results are shown in Table 5 and FIG.

(Composition of model gas A)
CO: 800 ppm
CO ₂ : 7%
O ₂ : 10%
NO: 150ppm
C ₃ H ₆ : 1000 ppmC
H ₂ O: 10%
SV: 50000h-1

  As shown in Table 5 and FIG. 17, it is confirmed that Example 1 has a lower 90% purification temperature (T90) than Reference Example 1 and Reference Example 2, that is, has a high exhaust gas purification capability. It was. The exhaust gas purifying catalyst of Example 1 has a 90% purification temperature (T90) of about 175 ° C. without greatly reducing the exhaust gas purification capability even when the phosphorous poisoning treatment is performed a plurality of times. It was maintained. Therefore, as in Example 1, when a phosphorus collection layer having a large proportion of large pores is provided on the catalyst layer, generation of phosphorus poisoning of the metal catalyst in the catalyst layer is suppressed, and high exhaust gas purification is achieved. It was confirmed that the ability could be suitably maintained.

(7) High carbon number HC purification performance In this test, the high carbon number HC purification performance was added to each exhaust gas purification catalyst with respect to the exhaust gas purification catalysts of Example 1, Reference Example 1 and Reference Example 2. I investigated. Specifically, the following model gas B containing decane (C ₁₀ H ₂₂ ) having a high carbon number HC was supplied. Then, the temperature of the exhaust gas purification catalyst was raised from 100 ° C. to 350 ° C. at a rate of temperature increase of 20 ° C./min, and the 90% purification temperature (T90) of decane was examined. The results are shown in Table 6 and FIG. In addition, the specific composition of the used model gas B is as follows.

(Composition of model gas B)
CO: 800 ppm
CO ₂ : 7%
O ₂ : 10%
NO: 150ppm
C ₁₀ H ₂₂ : 1000 ppmC
H ₂ O: 10%
SV: 50000h-1

As shown in Table 6 and FIG. 18, in Reference Example 2, it was confirmed that the 90% purification temperature (T90) of decane was higher than that of Reference Example 1, and the purification ability of decane was lowered. This is because, in Reference Example 2, as shown in FIGS. 8 and 10, since a dense phosphorus collection layer in which large pores are hardly formed is formed, gas permeability in the phosphorus collection layer is lowered. Therefore, it is understood that decane (C ₁₀ H ₂₂ ) having a high carbon number HC could not suitably pass through the phosphorus collection layer and did not contact the metal catalyst in the catalyst layer.
On the other hand, in Example 1, a 90% purification temperature (T90) comparable to that in Reference Example 1 in which no phosphorus collection layer was formed was measured. Therefore, the exhaust gas purifying catalyst of Example 1 having a phosphorus collection layer in which large pores are formed at a high ratio has a remarkably high gas permeability. Therefore, the phosphorus collection layer is provided. Nevertheless, it has been found that high carbon number HC such as decane can be suitably purified.

(8) Evaluation of content of phosphorus-collecting component (La) In this evaluation, first, three types of exhaust gas purification are performed according to the same procedure as Example 1 except that the loading density of the phosphorus-collecting component (La) is different. Catalysts (Examples 3 to 5) were prepared. The exhaust gas purification catalysts of Examples 3 to 5 and Reference Example 1 were subjected to phosphorus poisoning treatment in the same procedure as described above so that the phosphorus poisoning amount was 5.8 g / L. And the model gas A mentioned above was supplied, and 90% purification temperature (T90) of hydrocarbon (HC) was measured. The results are shown in Table 7 and FIG. Table 7 below also lists the La support density in each example.

  As shown in Table 7 and FIG. 19, it was confirmed that the 90% purification temperature of HC decreased (the exhaust gas purification ability improved) as the La carrying density in the phosphorus collection layer increased. From these results, it was found that the exhaust gas purification ability can be improved by setting the La support density in the phosphorus collection layer within a range of 1 wt% to 10 wt%.

[Second test]
In this test, the structure of the base material was changed from the flow-through type to the wall flow type, and the performance when the wall flow type base material was used in the exhaust gas purification catalyst of the present invention was evaluated.

1. Preparation of Exhaust Gas Purifying Catalyst (Example 6) In Example 6, a wall flow type honeycomb substrate (made of silicon carbide, cell number 300 cpsi, partition wall thickness 12 mil) manufactured by Nippon Choshi Co., Ltd. was prepared.
In this test, first, a catalyst layer containing metal catalysts (Pt and Pd) was formed inside the partition walls of the wall flow type substrate.
Specifically, a solution obtained by mixing a dinitrodiammine platinum nitric acid solution and a palladium nitrate solution is impregnated with a powder of γ-Al ₂ O ₃ as a carrier, dried and baked to obtain Pt / Pd supported-Al ₂ O. _Three powders were obtained.
Then, the resulting Pt / Pd supported _-Al 2 _{O 3} powder (1130 g), and acicular TiO ₂ powder (33 g), and acetic acid (150 g), aluminum hydroxide (37 g), deionized water (3430g) Were mixed and wet pulverized to prepare a slurry containing powder having a median diameter of about 0.5 μm.
To this slurry, 20 g of citric acid and 5 g of HEC (hydroxyethyl cellulose) were added and thickened to obtain a slurry for forming a catalyst layer.
Next, the end of the base material on the exhaust gas inflow side was immersed in the catalyst layer forming slurry and sucked from the end of the exhaust gas outflow side. As a result, slurry was applied to the inside of the porous partition wall. After drying this at 90 degreeC, the catalyst layer was formed in the partition by baking at 500 degreeC.

  Next, a slurry for forming a phosphorus collection layer containing a pore-forming agent having the same composition as in Example 1 is prepared, and the slurry for forming a phosphorus collection layer is entered from the end of the exhaust gas inflow side of the substrate. After throwing into the cell, the outlet cell was sucked to give slurry to the surface of the catalyst layer. After drying this at 90 degreeC, the phosphorus collection layer was formed in the surface (surface of a partition) of the catalyst layer by baking at 500 degreeC.

(Reference Example 3) An exhaust gas purifying catalyst was produced under the same conditions as in Example 6 above, except that a slurry for forming a phosphorus collection layer to which no pore-forming agent was added was used.

2. Evaluation of Exhaust Gas Purification Catalyst For the exhaust gas purification catalyst of Example 6 and Reference Example 3 described above, the following items were evaluated. Hereinafter, each evaluation will be described.

(1) Product pressure loss Pressure loss (product pressure loss) after formation of the catalyst layer was measured. The results are shown in Table 8. The “product pressure loss” in Table 8 indicates the ratio when the pressure loss of the base material itself on which the catalyst layer and the phosphorus collection layer are not formed is 1.

  As shown in Table 8, in Example 6, the pressure loss was suppressed to 1.5 times or less that of the substrate. This is presumably because the phosphorus trapping layer of Example 6 has structural characteristics with good gas permeability such as having a large proportion of large pores. On the other hand, in Reference Example 3, the pressure loss was as high as about 2.2 times that of the base material. This is presumably because a structure that covers the pores of the base material is formed by disposing a phosphorus trapping layer having low gas permeability on the catalyst layer.

(2) PM deposition pressure loss An exhaust gas purification filter was installed on the engine bench to deposit PM, and the pressure loss at the time when 5 g of PM was deposited was evaluated as “PM deposition pressure loss”. The pressure loss was standardized by the amount of intake air. The results are shown in Table 9.

As shown in Table 9, in Example 6, the PM deposition pressure loss was as low as about 0.1 kPa / (g / sec). This is presumably because the phosphorus collection layer functions as a filtration layer and the entry of phosphorus and PM into the catalyst layer (partition wall) is suppressed.
On the other hand, in Reference Example 3, the PM deposition pressure loss exceeded 0.25 kPa / (g / sec). In Reference Example 3, since the phosphorus collection layer is disposed on the catalyst layer, an increase in pressure loss due to the deposition of phosphorus and PM inside the catalyst layer can be suppressed, but the phosphorus collection layer is dense. It is considered that the original product pressure loss increased and the PM deposition pressure loss also increased.

(3) Pressure loss hysteresis When the exhaust gas purification filter is installed on the engine bench and PM deposition is started from the state before use (before PM deposition), 5 g of PM after regeneration treatment remains. From this, the post-regeneration deposition pressure loss when PM deposition was started again was measured. Then, the initial and post-regeneration deposition pressure loss values were compared, and the difference in PM deposition amount at the same pressure loss value was defined as the pressure loss hysteresis (g / unit). The results are shown in Table 10.

As shown in Table 10, in Example 6, the pressure loss hysteresis was kept as low as about 1.5 (g / unit). This is thought to be because PM deposition was suppressed in the pores of the substrate because the phosphorus collection layer functioned as a filtration layer.
Also in Reference Example 3, the pressure loss hysteresis was kept as low as about 1.4 (g / unit). However, in Reference Example 3, since the absolute value of the PM deposition pressure loss is increased as shown in Table 9 above, it is expected that the fuel consumption will deteriorate.

(4) Number of exhausted PM particles An exhaust gas purification filter was installed in the exhaust path of the vehicle, and the number of exhausted PM particles (number / km) when traveling in NEDC mode was measured. The results are shown in Table 11.

  As shown in Table 11, Example 6 and Reference Example 3 showed the same number of discharged PM particles in the phosphorus collection layer. From this, the exhaust gas purifying catalyst of Example 6 has a significantly high gas permeability as described above, and suppresses the PM emission amount despite being able to prevent an increase in pressure loss, etc. It was found that it has the same collection performance as the densely formed phosphorus collection layer.

[Third test]
In this test, a plurality of exhaust gas purification catalysts having different phosphorus collection components contained in the phosphorus collection layer were prepared, and the performance of the exhaust gas purification catalyst was evaluated.

1. Production of Exhaust Gas Purification Catalyst (Example 7) In Example 7, an exhaust gas purification catalyst was produced according to the same procedure as “Example 1” in the first test described above. That is, the exhaust gas purification catalyst of Example 7 is an exhaust gas purification catalyst in which a phosphorus collection layer in which large-diameter pores are formed at a high ratio contains lanthanum (La) as a phosphorus collection component and is formed on the catalyst layer. is there.

(Example 8) In Example 8, an exhaust gas purifying catalyst under the same conditions as in Example 7 except that the phosphorus collecting component used in the phosphorus collecting layer was changed from lanthanum (La) to magnesium (Mg). Was made.

(Example 9) In Example 9, an exhaust gas purifying catalyst was used under the same conditions as in Example 7 above, except that the phosphorus collection component used in the phosphorus collection layer was changed from lanthanum (La) to calcium (Ca). Was made.

(Example 10) In Example 10, an exhaust gas purifying catalyst under the same conditions as in Example 7 above, except that the phosphorus collection component used in the phosphorus collection layer was changed from lanthanum (La) to iron (Fe). Was made.

(Example 11) In Example 11, an exhaust gas purifying catalyst under the same conditions as in Example 7 except that the phosphorus collecting component used in the phosphorus collecting layer was changed from lanthanum (La) to yttrium (Y). Was made.

(Example 12) In Example 12, an exhaust gas purifying catalyst under the same conditions as in Example 7 above, except that the phosphorus collecting component used in the phosphorus collecting layer was changed from lanthanum (La) to cerium (Ce). Was made.

(Example 13) In Example 13, the exhaust gas-purifying catalyst was used under the same conditions as in Example 7 above, except that the phosphorus collection component used in the phosphorus collection layer was changed from lanthanum (La) to praseodymium (Pr). Was made.

(Example 14) In Example 14, an exhaust gas purifying catalyst under the same conditions as in Example 7 except that the phosphorus collecting component used in the phosphorus collecting layer was changed from lanthanum (La) to strontium (Sr). Was made.

Reference Example 4 In Reference Example 4, an exhaust gas purification catalyst was produced according to the same procedure as “Reference Example 1” in the first test described above. That is, the exhaust gas purifying catalyst of Reference Example 4 is an exhaust gas purifying catalyst in which no phosphorus collection layer is formed and only the catalyst layer is formed on the partition walls of the base material.

Reference Example 5 In Reference Example 5, an exhaust gas purifying catalyst in which a layer of TiO ₂ to which no phosphorus trapping component was added was formed on the catalyst layer was produced. That is, in Reference Example 5, an exhaust gas purifying catalyst was produced under the same conditions as in Example 7 except that the phosphorus collecting component was not added.

2. Evaluation of Exhaust Gas Purification Catalyst In this test, a “phosphorus poisoning test” was performed on each of the exhaust gas purification catalysts described above. The test results of Examples 7 to 11 are shown in Table 12, and the test results of Examples 12 to 14 and Reference Examples 4 and 5 are shown in Table 13. Note that the test conditions of the “phosphorus poisoning test” are set to the same conditions as the “(6) phosphorus poisoning test” of the first test described above, and thus detailed description thereof is omitted here.

  As shown in Table 12 and Table 13, any of Examples 7 to 14 in which the catalyst layer containing the phosphorus-collecting component is formed has higher exhaust gas purification capacity than Reference Examples 4 and 5. Was confirmed. And it was confirmed that the exhaust gas purification catalysts of Examples 7 to 14 are less likely to have a reduced exhaust gas purification ability even when the phosphorous poisoning treatment is performed a plurality of times. Therefore, even when any of La, Fe, Zr, Ce, Ti, Sr, Ca, Mg, Pr, and Y is used as the phosphorus collection component, the phosphorus capture having a large proportion of large pores. It was confirmed that the effect of providing the layer collecting layer on the catalyst layer can be suitably exhibited.

[Fourth test]
In this test, a plurality of exhaust gas purification catalysts having different formation conditions for the skeleton portion of the phosphorus collection layer were produced, and the structure of the skeleton portion of the phosphorus collection layer after production was evaluated.

1. Production of Exhaust Gas Purification Catalyst (Example 15) In Example 15, an exhaust gas purification catalyst was produced according to the same procedure as “Example 1” in the first test described above.
That is, in Example 15, needle-like titania powder (average fiber diameter φ = 0.2 μm, average fiber length L = 3 μm) was used as a carrier constituting the skeleton portion of the phosphorus collection layer, and the phosphorus collection layer A TiO ₂ sol having a TiO ₂ content of 6% was used as the binder. Then, the above carrier and binder are mixed at a ratio of 75: 520 to prepare a slurry, and a pore-forming agent (melamine resin having an average particle diameter of 5 μm) is added to the slurry at a ratio of 36 g / L, and then 3 g Was added to increase the viscosity, thereby obtaining a slurry for forming a phosphorus collection layer.
Next, a flow-through type base material is prepared, and a catalyst layer containing the same Pt / Pd-supported Al ₂ O ₃ powder and needle-like TiO ₂ powder as in Example 1 is formed on the partition walls of the base material. did. And the phosphorus collection layer was formed on the catalyst layer by providing the slurry for phosphorus collection layer formation on a catalyst layer, and drying and baking. The amount of the slurry at this time was adjusted so that a phosphorus collection layer having an amount of 30 g per 1 L of the substrate volume was formed by firing.

(Example 16) In Example 16, an exhaust gas purification catalyst was produced according to the same procedure as "Example 2" in the first test described above.
That is, in Example 16, the carrier used for the phosphorus collection layer was changed to acicular alumina powder (average fiber diameter φ = 0.3 μm, average fiber length L = 8 μm), and the binder of the phosphorus collection layer was changed to Al. _{The 2} O ₃ content was changed to 15% Al ₂ O ₃ sol. Then, an exhaust gas purifying catalyst was produced under the same conditions as in Example 15 except that the mixing ratio of the carrier and the binder was changed to 75: 390.

(Example 17) In Example 17, an exhaust gas purifying catalyst was produced under the same conditions as in Example 15 except that the average particle diameter of the melamine resin as a pore forming agent was changed to 12 µm.

(Example 18) In Example 18, an exhaust gas purifying catalyst was produced under the same conditions as in Example 15 except that the amount of pore-forming agent (melamine resin) added was changed to 54 g / L.

Example 19 In Example 19, the same conditions as in Example 15 except that the average fiber diameter φ of the needle-like titania powder used as the carrier forming the skeleton portion of the phosphorus collection layer was changed to 0.4 μm. A catalyst for exhaust gas purification was prepared.

(Example 20) In Example 20, as a carrier forming the skeleton portion of the phosphorus collection layer, acicular titania powder (average fiber diameter φ = 0.2 µm, average fiber length L = 3 µm) and granular ceria zirconia (average) Except for the point of using a mixture (particle ratio: 1: 1) with a particle diameter of 14 μm) and the point that the binder of the phosphorus collection layer was changed to an Al ₂ O ₃ sol with an Al ₂ O ₃ content of 15%. Thus, an exhaust gas purifying catalyst was produced under the same conditions as in Example 15.

(Reference Example 6) In Reference Example 6, an exhaust gas purification catalyst was produced according to the same procedure as "Reference Example 1" in the first test described above. That is, the exhaust gas purifying catalyst of Reference Example 6 is an exhaust gas purifying catalyst in which no phosphorus collection layer is formed and only the catalyst layer is formed on the partition walls of the base material.

Reference Example 7 In Reference Example 7, an exhaust gas purification catalyst was produced according to the same procedure as “Reference Example 2” in the first test described above. That is, an exhaust gas purifying catalyst was produced under the same conditions as in Example 15 except that no pore forming agent was added to the slurry when forming the phosphorus collection layer.

2. Evaluation of exhaust gas purification catalyst For each of the above exhaust gas purification catalysts, "SEM observation", "measurement of porosity", "measurement of pore distribution", "measurement of the number of divisions and the thickness of the skeleton", " The measurement of the surface opening ratio and pore diameter, the high carbon number HC purification performance, and the phosphorus poisoning test were conducted to investigate the structure of the phosphorus trapping layer. The conditions for each test were set to the same conditions as described in “(1) SEM observation” to “(5) Measurement of surface opening ratio and pore diameter” in the first test described above. Then, detailed explanation is omitted.

  Of each test described above, the results of “SEM observation” are shown in FIGS. The results of “Measurement of porosity” and “Measurement of pore distribution” are shown in Table 14, and the results of “Measurement of the number of divisions and thickness of the skeleton” and “Measurement of surface opening ratio and pore diameter” are shown. As shown in FIG.

(1) SEM Observation In Example 15, a phosphorus collection layer having the same structure as “Example 1” in the first test was obtained (see FIGS. 5, 9, and 11). Moreover, in Example 16, the phosphorus collection layer which has the same structure as "Example 2" in a 1st test was obtained (refer FIG. 6). In Example 17, a phosphorus collection layer having a structure as shown in FIGS. 20 and 21 was obtained, and in Example 18, a phosphorus collection layer having a structure as shown in FIGS. 22 and 23 was obtained. Furthermore, in Example 19, a phosphorus collection layer having a structure as shown in FIGS. 24 and 25 was obtained, and in Example 20, a phosphorus collection layer having a structure as shown in FIGS. 26 and 27 was obtained. Further, in Reference Example 6, as in “Reference Example 1” in the first test, an exhaust gas purification catalyst in which a phosphorus collection layer was not formed was obtained (see FIG. 7). In Reference Example 7, a catalyst layer having the same structure as that of “Reference Example 2” in the first test was obtained (see FIG. 8).

Comparing the SEM photographs of the exhaust gas purification catalysts of the above examples, in any of the exhaust gas purification catalysts of Examples 15 to 20, a phosphorus collection layer having a large proportion of large pores is formed on the catalyst layer. It was confirmed that
Then, when examining the detailed structure of the phosphorus trapping layer, in Example 17 (see FIGS. 20 and 21) using a pore-forming agent having an average particle diameter of 12 μm, a large fineness corresponding to the particle diameter of the pore-forming agent is obtained. Holes were formed in the phosphorus collection layer. Furthermore, in Example 18 (see FIGS. 22 and 23) in which the amount of pore-forming agent added was increased to 54 g / L, the proportion of large pores formed was higher than in Examples 15 and 16. Further, as shown in FIGS. 24 to 27, in Example 19 and Example 20 in which the carrier forming the skeleton of the phosphorus collection layer was changed, a phosphorus collection layer having a larger void than in Examples 15 and 16 was formed. .

(2) Measurement of porosity As shown in Table 14, in the exhaust gas purification catalysts of Examples 15 to 20, the porosity Va of the phosphorus collection layer was 50% or more. Moreover, in the phosphorus collection layers in Examples 15 to 20, the porosity Vb of the large pores accounted for 45% or more of the entire catalyst layer. In Examples 15 to 20, the ratio of the porosity Vb of the large pores to the porosity Va (Vb / Va) accounted for 65% or more. From these analysis results, the phosphorus collection layers of Examples 15 to 20 have relatively large pores at a high ratio as compared to the general phosphorus collection layer as shown in Reference Example 7. It was confirmed that

(3) Measurement of pore distribution From Table 14 above, the phosphorus collection layers of the exhaust gas purifying catalysts of Examples 15 to 20 have the first pores having a relatively large volume and the second pores having a relatively small volume. And were confirmed to have a multi-pore structure. In Examples 15 to 20, the volume ratio of the first pores to the second pores was 4 times or more. For this reason, it is estimated that the phosphorus collection layer of the exhaust gas purifying catalyst of Examples 15 to 20 has excellent gas permeability and can exhibit an excellent phosphorus collection function.

(4) Measurement of the number of divisions and the thickness of the skeleton part As shown in Table 15, the exhaust gas purification catalysts of Examples 15 to 20 all have a larger number of divisions of the phosphorus collection layer than Reference Example 7, and phosphorus The respective pores formed in the collection layer were connected to each other. From this point, it was confirmed that Examples 15 to 20 have high gas permeability. In Examples 15 to 20, the average thickness of the skeleton portion was clearly smaller than that of Reference Example 7. From these results, in Examples 15 to 20, the phosphorus collection component supported on the carrier forming the skeleton of the phosphorus collection layer and the phosphorus component in the exhaust gas are efficiently brought into contact with each other to suitably collect phosphorus. It was confirmed that it was possible. From these results, it was confirmed that the phosphorus collection layers of Examples 15 to 20 have high gas permeability and can efficiently collect the phosphorus component in the exhaust gas.

(5) Measurement of surface opening ratio and pore diameter As shown in Table 15, in Examples 15 to 20, the surface opening ratio of the skeleton portion was 25% or more. In Examples 15 to 20, the pore diameter (P ₅ ) corresponding to 5% cumulative from the small pore side is 0.03 μm or more and the pore diameter corresponding to 95% cumulative from the small pore side ( P ₉₅ ) was 1.5 μm or more. Also from such structural characteristics, it was confirmed that the phosphorus collection layers of Examples 15 to 20 have high gas permeability.

(6) Purification performance of high carbon number HC In Examples 15 to 20, a 90% purification temperature (T90) similar to that of Reference Example 6 in which no phosphorus collection layer was formed was measured. From this, the exhaust gas purifying catalysts of Examples 15 to 20 have suitable gas permeability, and thus have a high carbon number HC such as decane even though a phosphorus collection layer is provided. It was confirmed that can be suitably purified.

(7) Phosphorus poisoning test As shown in Table 15, Examples 15 to 20 have higher exhaust gas purification capacity than Reference Example 6 and Reference Example 7 (90% purification temperature (T90) is low). It was confirmed. From this, when the phosphorus collection layer which has a large pore in a high ratio like Example 15-20 was provided on the catalyst layer, generation | occurrence | production of the phosphorus poisoning of the metal catalyst in a catalyst layer is suppressed, It was confirmed that the high exhaust gas purification capability can be suitably maintained.

(8) Summary As described above, Examples 15 to 20 in which the phosphorus collection layer is formed using a predetermined carrier and a pore-forming agent have a phosphorus collection layer in which large pores are formed at a high ratio. An exhaust gas purification catalyst was produced. Such an exhaust gas purification catalyst has high gas permeability and can efficiently collect the phosphorus component in the exhaust gas, thereby suitably suppressing phosphorus poisoning of the catalyst layer and extending the sufficient exhaust gas purification performance. It was confirmed that it can be maintained over a period of time.

[Fifth test]
In the fourth test described above, a flow-through type base material is used. In the fifth test, the base material is changed to a wall flow type, and the performance when the wall flow type base material is used. Evaluated.

1. Production of Exhaust Gas Purification Catalyst (Example 21) In Example 21, an exhaust gas purification catalyst was produced according to the same procedure as "Example 17" in the fourth test except that a wall flow type substrate was used.
That is, in Example 21, needle-like titania powder (average fiber diameter φ = 0.2 μm, average fiber length L = 3 μm) was used as a carrier constituting the skeleton portion of the phosphorus collection layer, and the phosphorus collection layer A TiO ₂ sol having a TiO ₂ content of 6% was used as the binder. Then, the above carrier and binder are mixed at a ratio of 75: 520 to prepare a slurry, and a pore-forming agent (melamine resin having an average particle diameter of 12 μm) is added to the slurry at a ratio of 36 g / L, and then 3 g Was added to increase the viscosity, thereby obtaining a slurry for forming a phosphorus collection layer.
And the phosphorus collection layer was formed on the catalyst layer by giving the slurry for phosphorus collection layer formation to the partition of the wall flow type base material, and drying and baking. The amount of the slurry at this time was adjusted so that a phosphorus collection layer having an amount of 30 g per 1 L of the substrate volume was formed by firing.

(Example 22) In Example 22, an exhaust gas purification catalyst was produced according to the same procedure as "Example 18" in the fourth test except that a wall flow type substrate was used. In other words, in Example 22, the same conditions as in Example 21 except that the average particle diameter of the pore former (melamine resin) was 5 μm and the amount of pore former added was changed to 54 g / L. A catalyst for exhaust gas purification was prepared.

(Example 23) In Example 23, an exhaust gas purification catalyst was produced according to the same procedure as "Example 19" in the fourth test except that a wall flow type substrate was used. In other words, in Example 23, except that the average particle diameter of the pore-forming agent (melamine resin) was 5 μm and the average fiber diameter φ of the acicular titania powder used as the carrier was changed to 0.4 μm. An exhaust gas purifying catalyst was prepared under the same conditions as in Example 21.

(Example 24) In Example 24, an exhaust gas purification catalyst was produced according to the same procedure as "Example 20" in the fourth test except that a wall flow type substrate was used. In other words, in Example 24, the average particle diameter of the pore-forming agent (melamine resin) was 5 μm, needle-shaped titania powder (average fiber diameter φ = 0.2 μm, average fiber length L = 3 μm), and granular The point that the mixture (mixing ratio 1: 1) with ceria zirconia (average particle size: 14 μm) was used as the skeleton part of the phosphorus collection layer, and the binder of the phosphorus collection layer was made of Al ₂ O ₃ sol (Al ₂ O ₃ Exhaust gas purification catalyst was produced under the same conditions as in Example 21 except that the content was changed to 15%.

2. Evaluation of Exhaust Gas Purification Catalyst Evaluation tests of “product pressure loss”, “PM deposition pressure loss”, “pressure loss hysteresis”, and “exhaust PM particle number” were performed on each of the above exhaust gas purification catalysts. The test results are shown in Table 16.
In addition, since the conditions of each test were set to the same conditions as those described in “(1) Product pressure loss” to “(4) Number of discharged PM particles” in the second test described above, detailed description is given here. Is omitted.

(1) Product pressure loss As shown in Table 16, in Examples 21 to 24, the pressure loss was suppressed to 1.6 times or less that of the base material. Therefore, the exhaust gas purifying catalysts of Examples 21 to 24 have structural characteristics with good gas permeability such that the phosphorus collection layer has large pores at a high ratio, and therefore, exhaust gas for diesel engines. It has been confirmed that it is preferably used as a purification catalyst (DPF: Diesel particulate filter).

(2) PM Deposition Pressure Loss and Pressure Loss Hysteresis As shown in Table 16, in Examples 21 to 24, the PM deposition pressure loss is suppressed to as low as about 0.1 kPa / (g / sec) and the pressure loss hysteresis is 1. It was suppressed to about 5 (g / unit). From this, in the exhaust gas purifying catalysts of Examples 21 to 24, it is understood that the phosphorus collection layer functions as a filtration layer, and the penetration of phosphorus and PM into the catalyst layer (partition wall) is suppressed. .

(3) Exhaust PM particle number Moreover, it was confirmed that the exhaust gas purification catalyst of Examples 21 to 24 has an exhaust PM particle number of 5.8E + 09 to 5.9E + 09. From this, the exhaust gas purifying catalysts of Examples 21 to 24 have significantly high gas permeability and can suppress the increase in pressure loss, etc. It was found that PM can be collected.

(4) Summary From the results of the fifth test described above, when a phosphorus trapping layer is formed using a predetermined carrier and a pore-forming agent, a high gas is obtained even when a wall flow type substrate is used. It was confirmed that an exhaust gas purifying catalyst having permeability and capable of efficiently collecting the phosphorus component in the exhaust gas can be produced.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification device 2 Internal combustion engine 3 Exhaust manifold 4 Exhaust pipe 5 ECU
8 Pressure sensor 10 Exhaust gas purification catalyst 11 Base material 12 Incoming cell 12a, 14a Sealing portion 14 Outgoing cell 15 Cell 16, 116 Partition 20, 120 Phosphorus collection layer 30, 130 Catalyst layer A For first exhaust gas purification Catalyst B Second exhaust gas purification catalyst X Partition extending direction Lw Total length of partition extending direction

Claims (6)

An exhaust gas purifying catalyst that is disposed in an exhaust passage of an internal combustion engine and purifies harmful components in exhaust gas discharged from the internal combustion engine,
A base material in which a plurality of cells are partitioned by partition walls, a catalyst layer formed on at least one of the partition wall surface of the base material and inside the partition walls of the base material, and a phosphorus collection layer provided on the catalyst layer, With
The phosphorus collection layer has a phosphorus collection component containing at least one of La, Fe, Zr, Ce, Ti, Sr, Ca, Mg, Pr, and Y.
In the electron microscope observation image of the cross section of the phosphorus collection layer, when the phosphorus collection layer is 100%, large pores having an equivalent circle diameter larger than 5 μm account for 45% or more. catalyst.   The exhaust gas purifying catalyst according to claim 1, wherein a porosity of the phosphorus collection layer is 70% or more in an electron microscope observation image of a cross section of the phosphorus collection layer.   The phosphorus collection layer has a multi-pore structure having a first pore having a pore diameter of 1 μm or more and less than 10 μm and a second pore having a pore diameter of 0.5 μm or more and less than 1 μm. The exhaust gas purifying catalyst according to claim 1 or 2.   4. The exhaust gas purifying catalyst according to claim 3, wherein in the pore distribution measurement of a mercury porosimeter, the pore volume of the first pore is at least four times the pore volume of the second pore.   The catalyst for exhaust gas purification according to any one of claims 1 to 4, wherein a surface aperture ratio is 25% or more in an electron microscope observation image of a surface of a skeleton portion of the phosphorus collection layer. In the electron microscope observation image of the surface of the skeleton part of the phosphorus trapping layer, the pore diameter P ₅ corresponding to 5% cumulative from the small pore side is 0.03 μm or more, and the cumulative 95 from the small pore side. % to the corresponding pore diameter _{P 95} is 1.5μm or more, the exhaust gas purifying catalyst according to any one of claims 1-5.