阅读说明：本技术 废气净化催化剂 (Exhaust gas purifying catalyst ) 是由 栗原广树 樱田雄 永井祐乔 远藤庆德 锅本岳史 秋田真吾 于 2019-03-19 设计创作，主要内容包括：废气净化催化剂(10)中的基材(11)具有流入侧室(21)、流出侧室(22)和分隔两室(21、22)的多孔质的分隔壁(23)。具有：第一催化剂部(14),其在分隔壁(23)的面对流入侧室(21)的面中设置于废气流通方向的上游侧的至少一部分；以及第二催化剂部(15),其在分隔壁的面对流出侧室的面中设置于下游侧的至少一部分。关于孔径为10μm以上且18μm以下的孔容,将在设置有第一催化剂部(14)的部位中以第一催化剂部(14)和分隔壁(23)为对象的测定值设为第一孔容、将在设置有第二催化剂部的部位中以第二催化剂部(15)和分隔壁(23)为对象的测定值设为第二孔容时,第一孔容大于第二孔容,第一催化剂部(14)中的孔径的峰顶处于20nm以上且500nm以下。(A substrate (11) in an exhaust gas purification catalyst (10) has an inflow side chamber (21), an outflow side chamber (22), and a porous partition wall (23) that partitions the two chambers (21, 22). Comprising: a first catalyst section (14) that is provided on at least a portion of the upstream side in the exhaust gas flow direction on the surface of the partition wall (23) that faces the inflow-side chamber (21); and a second catalyst portion (15) provided on at least a part of the downstream side in a surface of the partition wall facing the outflow-side chamber. The pore volume has a pore diameter of 10 [ mu ] m to 18 [ mu ] m, wherein when a measured value for the first catalyst portion (14) and the partition wall (23) in a portion where the first catalyst portion (14) is provided is a first pore volume and a measured value for the second catalyst portion (15) and the partition wall (23) in a portion where the second catalyst portion is provided is a second pore volume, the first pore volume is larger than the second pore volume, and the peak top of the pore diameter in the first catalyst portion (14) is 20nm to 500 nm.)

1. An exhaust gas purifying catalyst comprising a base material and a catalyst portion provided on the base material,

the substrate has: an inflow side chamber having an inflow side opening in an exhaust gas flow direction and a space closed at an outflow side; an outlet side chamber having a space in which an inlet side in an exhaust gas flow direction is closed and an outlet side is open; and a porous partition wall for partitioning the inflow side chamber and the outflow side chamber,

the catalyst portion has: a first catalyst portion provided on at least a part of an upstream side in the flow direction in a surface of the partition wall facing the inflow side chamber; and a second catalyst portion provided on at least a part of a downstream side in the flow direction in a surface of the partition wall facing the outflow-side chamber,

the pore volume has a pore diameter of 10 [ mu ] m or more and 18 [ mu ] m or less, and when a value measured with respect to the first catalyst portion and the partition wall in a portion where the first catalyst portion is provided is a first pore volume and a value measured with respect to the second catalyst portion and the partition wall in a portion where the second catalyst portion is provided is a second pore volume, the first pore volume is larger than the second pore volume,

the peak top of the pore diameter of the catalyst portion is 20nm to 500 nm.

2. The exhaust gas purification catalyst according to claim 1, wherein a ratio of the second pore volume to the first pore volume is 0.95 or less.

3. The exhaust gas purification catalyst according to claim 1 or 2, wherein D90 of the metal oxide particles constituting the first catalyst portion is 3 μm or more.

Technical Field

The present invention relates to an exhaust gas purifying catalyst.

Background

In order to meet a strict fuel consumption standard year after year, a Direct Injection engine (hereinafter also referred to as GDI) is widely used for an internal combustion engine including a diesel engine or a Gasoline engine, particularly for a Gasoline engine. GDI is known to have low fuel consumption and high output, but the amount of Particulate Matter (hereinafter also referred to as PM. including soot) in exhaust gas is 5 to 10 times or more as large as that of a conventional port injection engine. In order to meet the environmental regulations relating to the PM emission, it is necessary to provide a Filter (hereinafter also referred to as GPF) having a PM trapping function as in a diesel engine also in a vehicle equipped with a Gasoline engine such as a GDI.

Since the mounting space of the exhaust gas purification catalyst is generally limited, in recent years, a three-way catalyst in which a precious metal such as Pd, Pt, and Rh is supported on the filter is used to collect PM and perform Nitrogen Oxide (NO) at the same time_x) And catalysts for purifying carbon monoxide (CO), Hydrocarbons (HC), and the like.

For example, patent document 1 describes a filter catalyst having a PM trapping function for a diesel engine, in which a plurality of chambers having openings at both ends thereof which are alternately sealed are partitioned by chamber walls, and the chamber walls have a catalyst support base having a plurality of continuous pores, a first catalyst portion formed on the surface of the chamber walls is provided on the upstream side of the chambers, and a second catalyst portion formed on the surface of the inside of the chamber walls is provided on the downstream side of the chambers. In this document, after catalyst support layers are provided on the upstream side and the downstream side of a substrate, respectively, the substrate is immersed in a liquid containing a catalytically active component, and dried and calcined, so that 2 catalyst support layers support the same catalytically active component, thereby producing a filter catalyst.

Patent document 2 describes, as a catalyst device for purifying particulates in exhaust gas by combustion using a catalyst for a diesel engine, an exhaust gas purification oxidation catalyst device including: a porous filter base material provided with an inflow chamber, an outflow chamber, and a chamber partition wall; and a catalyst supported on the substrate, the catalyst comprising a 1 st catalyst layer supported on the surface of the inflow chamber side of the chamber partition walls and a 2 nd catalyst layer supported on the wall surface of the pores of the chamber partition walls.

Disclosure of Invention

The above-mentioned patent documents are all filter designs related to diesel engines. A diesel engine is assumed to be used in a temperature environment of at most about 800 ℃, and is not suitable for the design content of a gasoline engine having a combustion temperature exceeding 1000 ℃. These documents have problems in removal of PM and exhaust gas purification performance, but have not been designed to exhibit sufficient exhaust gas purification performance even during high-speed operation.

The present invention addresses the problem of providing an exhaust gas purification catalyst that has high heat resistance and high exhaust gas purification performance during high-speed operation.

The present inventors have intensively studied a structure having high heat resistance and high exhaust gas purification performance at high-speed operation in a filter catalyst having a wall-flow structure. As a result, by setting the main peak of the pore diameter of the catalyst layer disposed on the upstream side in the exhaust gas flow direction to fall within a specific range and setting the pore volumes of the 2 catalyst layer forming portions of the chamber partition walls in a specific relationship, it is possible to obtain a PM trapping filter catalyst which is excellent in heat resistance and has high exhaust gas purification performance even under high space velocity conditions such as high-speed operation.

Accordingly, the present invention provides an exhaust gas purifying catalyst comprising a base material and a catalyst portion provided on the base material,

the substrate has: an inflow side chamber having an inflow side opening in an exhaust gas flow direction and a space closed at an outflow side; an outlet side chamber having a space in which an inlet side in an exhaust gas flow direction is closed and an outlet side is open; and a porous partition wall for partitioning the inflow side chamber and the outflow side chamber,

the catalyst portion has: a first catalyst portion provided on at least a part of an upstream side in the flow direction in a surface of the partition wall facing the inflow side chamber; and a second catalyst portion provided on at least a part of a downstream side in the flow direction in a surface of the partition wall facing the outflow-side chamber,

the pore volume has a pore diameter of 10 [ mu ] m or more and 18 [ mu ] m or less, and when a value measured with respect to the first catalyst portion and the partition wall in a portion where the first catalyst portion is provided is a first pore volume and a value measured with respect to the second catalyst portion and the partition wall in a portion where the second catalyst portion is provided is a second pore volume, the first pore volume is larger than the second pore volume,

the peak top of the pore diameter of the catalyst portion is 20nm to 500 nm.

Drawings

Fig. 1 shows a schematic diagram of an exhaust gas purifying catalyst as an embodiment of the present invention.

Fig. 2 is a cross-sectional view of a portion surrounded by a quadrangle in fig. 1, the cross-sectional view being taken along the axial direction of the base material.

Fig. 3 is an enlarged view showing a portion surrounded by a quadrangle in fig. 2.

Fig. 4 is a graph for measuring the pore volume of the first catalyst portion in the exhaust gas purifying catalysts of example 2 and comparative example 1.

Detailed Description

The present invention will be described below based on preferred embodiments, but the present invention is not limited to the embodiments described below.

Fig. 1 to 3 show an example of an exhaust gas purifying catalyst 10 according to the present embodiment. These drawings show only one illustrative example of an exhaust gas purifying catalyst, and do not limit the present invention in any way.

The exhaust gas purifying catalyst 10 is provided in an exhaust path of an internal combustion engine such as a diesel engine, a gasoline engine, and particularly a GDI engine of a vehicle. The exhaust gas purifying catalyst 10 is used as GPF, for example.

As shown in fig. 1, the exhaust gas purifying catalyst 10 includes a substrate 11 having a so-called wall-flow structure. Various materials can be used for the substrate 11, and for example, a substrate made of ceramics such as cordierite and silicon carbide (SiC) or an alloy such as stainless steel can be preferably used. The base material generally has a cylindrical outer shape as shown in fig. 1, and is disposed in the exhaust gas flow path such that the axial direction of the cylindrical outer shape substantially coincides with the exhaust gas flow direction X. Fig. 1 illustrates a substrate having a cylindrical outer shape. However, the overall outer shape of the base material may be an elliptical cylinder or a polygonal cylinder instead of the cylindrical shape.

As shown in fig. 1, the substrate 11 has: an inflow side chamber 21 extending in the exhaust gas flow direction X and having a space whose inflow side in the flow direction X is open and whose outflow side is closed; and an outlet side chamber 22 extending in the flow direction X and having a space in which the inlet side in the flow direction X is closed and the outlet side is open.

The inflow side chamber 21 has an exhaust gas outflow side end located at the downstream side end R2 in the exhaust gas flow direction X closed by the sealing portion 24, and an exhaust gas inflow side end located at the upstream side end R1 opened. The exhaust gas inflow side end of the outflow side chamber 22 located at the upstream side end R1 is closed by the seal 25, and the exhaust gas outflow side end located at the downstream side end R2 is open. The inflow side chamber 21 and the outflow side chamber 22 can circulate gas, liquid, and the like from the open end portions, and the circulation of the exhaust gas is blocked at the closed seal portions 24 and 25. The inflow side chamber 21 and the outflow side chamber 22 are bottomed-hole-shaped spaces extending in the axial direction of the substrate 11. The shape of the cross section perpendicular to the axial direction of the base material 11 may be a square, a parallelogram, a rectangle, a trapezoid, or the like; polygons such as triangle, hexagon, octagon, etc.; circular, elliptical, and the like.

A porous partition wall 23 is formed between the inflow side chamber 21 and the adjacent outflow side chamber 22 to partition them. The inflow side chamber 21 and the outflow side chamber 22 are partitioned by the partition wall 23. The partition wall 23 forms the inner walls of the inflow side chamber 21 and the outflow side chamber 22 in the shape of a bottomed hole. The partition wall 23 has a porous structure through which gas such as exhaust gas can pass. The thickness of the partition 23 is preferably 150 to 400 μm, for example.

A catalyst portion having a catalytically active component is supported on the substrate 11. As shown in fig. 2, the catalyst portion includes: a first catalyst portion 14 (hereinafter, also referred to as a first catalyst layer 14) having a layered shape provided at least on the upstream side in the exhaust gas flow direction X (hereinafter, also referred to as the X direction) of the surfaces of the partition walls 23 facing the inflow side chamber 21; and a second catalyst portion 15 (hereinafter also referred to as a second catalyst layer 15) having a layer shape provided at least on the downstream side in the exhaust gas flow direction X, on the surface of the partition wall 23 facing the outlet side chamber 22.

From the viewpoint of reducing the pressure loss and improving the exhaust gas purification performance, and from the viewpoint of suitable trapping performance of PM, the length L1 (see fig. 2) of the first catalyst layer 14 in the X direction is preferably 20% to 60%, and more preferably 30% to 50%, of the length L (see fig. 2) of the substrate 11 in the X direction. From the viewpoint of reducing the pressure loss and improving the exhaust gas purification performance and the appropriate PM trapping performance, the length L2 (see fig. 2) of the second catalyst layer 15 in the X direction is preferably 50% to 90%, more preferably 60% to 80%, of the length L of the substrate 11 in the X direction. The first catalyst layer 14 is preferably formed from an upstream end in the exhaust gas flow direction, and the second catalyst layer 15 is preferably formed from a downstream end.

From the viewpoint of improving the exhaust gas purification performance, the total length L1+ L2 of the length L1 of the first catalyst layer 14 in the X direction and the length L2 of the second catalyst layer 15 in the X direction is preferably greater than the length L of the substrate 11 in the X direction, and is preferably (L1+ L2)/L ═ 1.05 or more. The upper limit of (L1+ L2)/L is preferably 1.40 or less, more preferably 1.35 or less, and still more preferably 1.30 or less, from the viewpoint of reducing the pressure loss.

The lengths of the first catalyst layer 14 and the second catalyst layer 15 can be measured as follows. That is, it is preferable to determine the length of the exhaust gas-purifying catalyst 10 by visually measuring the length at any 10 points in the cross section cut along the axial direction of the substrate 11 and taking the average value of the lengths. When the boundaries of the first catalyst layer 14 and the second catalyst layer 15 in the exhaust gas flow direction cannot be judged by visual observation, the composition in a plurality of (for example, 8 to 16) positions in the exhaust gas purification catalyst in the exhaust gas flow direction can be analyzed and determined based on the concentration of the catalytically active component in each position. The concentration of the catalytic active component in each site can be determined by, for example, fluorescent X-ray analysis (XRF) or ICP-emission spectroscopy (ICP-AES).

From the viewpoint of achieving both ease of manufacture and exhaust gas purification performance, the first catalyst layer 14 is preferably formed to extend downstream from the upstream end R1 in the X direction of the substrate 11. Similarly, the second catalyst layer 15 is preferably formed to extend from the downstream side end R2 in the X direction of the substrate 11 to the upstream side.

The first catalyst layer 14 and the second catalyst layer 15 may contain the same or different catalytically active components. As such a catalytically active component, platinum group metals are exemplified, and specifically, any 1 or 2 or more of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) are exemplified. From the viewpoint of exhaust gas purification performance, the catalytically active components contained in the first catalyst layer 14 and the second catalyst layer 15 are each preferably contained in an amount of 0.001 mass% or more, more preferably 0.01 mass% or more, and most preferably 0.05 mass% or more, of the total amount of components contained in the catalyst layers. On the other hand, from the viewpoint of balancing the exhaust gas purification performance and the cost, the upper limit is preferably 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less.

Among them, the catalytically active components contained in the first catalyst layer 14 and the second catalyst layer 15 are more preferably different from each other. In particular, from the fact that NO can be purified efficiently_xFrom the viewpoint of harmful components of exhaust gas such as CO and HC, it is particularly preferable that the first catalyst layer 14 contains a noble metal selected from platinum (Pt), palladium (Pd) and rhodium (Rh), and the second catalyst layer 15 contains a noble metal selected from platinum (Pt), palladium (Pd), rhodium (Rh) and other noble metals than the noble metal contained in the first catalyst layer 14.

From the viewpoint of further improving the heat resistance of the exhaust gas purification catalyst 10, the content of the catalytically active component contained in the first catalyst layer 14 is preferably about 0.1g or more and 15g or less, and more preferably 1g or more and 8g or less, relative to 1L of the volume of the substrate. The content of the catalytically active component contained in the second catalyst layer 15 is preferably about 0.01g to 5g, more preferably 0.1g to 1g, based on 1L of the volume of the substrate.

From the viewpoint of improving the exhaust gas purification performance at the time of startup, the mass of the catalytically active component contained in the first catalyst layer 14 relative to the volume 1L of the substrate is preferably greater than the mass of the catalytically active component contained in the second catalyst layer 15, more preferably 1.1 times or more, particularly preferably 1.3 times or more and 20 times or less, and even more preferably 1.5 times or more and 15 times or less, the mass of the catalytically active component contained in the second catalyst layer 15.

The volume of the substrate referred to herein is a volume including not only the substrate portion but also the first catalyst layer 14 and the second catalyst layer 15, the pores in the partition wall 23, and the spaces inside the chambers 21 and 22.

In the exhaust gas purification catalyst 10, when a value measured with respect to the first catalyst portion 14 and the partition wall 23 in a portion where the first catalyst portion 14 is provided is a first pore volume and a value measured with respect to the second catalyst portion 15 and the partition wall 23 in a portion where the second catalyst portion 15 is provided is a second pore volume, the first pore volume is larger than the second pore volume, with respect to a pore volume having a pore diameter of 10 μm or more and 18 μm or less.

In general, the wall-flow substrate for GPF has a substrate-derived pore size peak in the range of 10 to 18 μm or in the vicinity thereof. Thus, the first pore volume being larger than the second pore volume means that the second catalyst layer 15 intrudes into the interior of the partition wall to a greater extent than the first catalyst layer 14 in the partition wall portion. The present inventors have found that by providing the catalyst with such a configuration, the exhaust gas purification performance during high-speed operation is improved. One of the reasons for this is that the catalyst layer easily contacts both the first catalyst layer 14 and the second catalyst layer 15 without obstructing the flow of the exhaust gas, and the contact property with the catalytically active component becomes appropriate.

The first pore volume may be measured by the following method, in which a portion of the partition wall 23 where the first catalyst layer 14 is formed and the second catalyst layer 15 is not formed is cut out as a sample. The second pore volume may be measured by the following method, in which a portion of the partition wall 23 where the second catalyst layer 15 is formed but the first catalyst layer 14 is not formed is cut out as a sample.

Specific methods for preparing the sample are described below, for example. In the cutting, it is preferable to cut the partition wall in a cross section perpendicular to the axial direction of the substrate 11.

Preparation of a first sample for pore volume measurement: 1cm was cut at a distance of 10% from the upstream end R1 of the base material with respect to the full length L³(1 side is a cube of 1 cm).

Preparation of a second sample for pore volume determination: 1cm was cut at a distance of 10% from the downstream end R2 of the base material with respect to the entire length L³(1 side is a cube of 1 cm).

Number of samples: 5 for each of the first and second volumes.

Pore volume was measured according to JIS R1655: 2003 was measured by mercury intrusion method. Specifically, the cut sample was dried at 150 ℃ for 1 hour, and the pore volume of the sample was measured at room temperature (20 ℃) using a mercury intrusion porosimeter (AutoPore IV9520, product of Micromeritics). The mercury intrusion pressure was initially set to 0.0048MPa, and the maximum pressure was set to 255.1060 MPa. The pore volume was measured at a pressure of 131 points in total, which contained these values. Each pressure was held for 10 seconds.

From the viewpoint of improving the exhaust gas purification performance at the time of high-speed operation, the ratio of the second pore volume V2 to the first pore volume V1(V2/V1) in the exhaust gas purification catalyst 10 is preferably 0.95 or less, more preferably 0.8 or less, and particularly preferably 0.7 or less. On the other hand, from the viewpoint of reducing the pressure loss, the ratio of the second pore volume V2 to the first pore volume V1(V2/V1) is preferably 0.4 or more, more preferably 0.5 or more, and particularly preferably 0.6 or more.

In order to make the first pore volume larger than the second pore volume, the particle diameter of the metal oxide particles constituting the first catalyst layer 14 and the second catalyst layer 15, the coating amount of the first catalyst layer 14 and the second catalyst layer 15, the calcination temperature for producing the first catalyst layer 14 and the second catalyst layer 15, the slurry viscosity, and/or the presence or absence of a pore-forming material may be adjusted. Note that, by setting the particle diameter of the metal oxide constituting the first catalyst layer 14 to a particle diameter that is less likely to enter the pores of the partition walls 23 and setting the particle diameter of the metal oxide constituting the second catalyst layer 15 to a particle diameter that is more likely to enter the pores of the partition walls 23, the first pore volume can be easily made larger than the second pore volume, and the value of V2/V1 can be made to be in the above range. The particle diameter of the metal oxide particles constituting the first catalyst layer 14 and the second catalyst layer, and the coating amount of the first catalyst layer 14 and the second catalyst layer 15 may be adjusted to the value range of V2/V1. However, the present invention is not limited to this configuration.

From the viewpoint of heat resistance, the peak top of the pore diameter measured with respect to the first catalyst layer 14 in the portion where the first catalyst layer 14 is provided is preferably 20nm or more and 500nm or less, and more preferably 20nm or more and 100nm or less.

"the peak top of the pore diameter of the first catalyst layer 14 is 20nm or more and 500nm or less" means that when a graph in which the pore volume is plotted on the vertical axis and the pore diameter is plotted on the horizontal axis is plotted for the first catalyst layer 14 and the partition wall in the portion where the first catalyst layer 14 is provided, the peak having the highest peak height is observed in the range of the pore diameter of 500nm or less and in the range of the pore diameter of 20nm or more and 500nm or less. Since the peak of the pore diameter of the partition wall derived from the substrate is larger than 500nm, it can be understood that the peak is directed to the first catalyst layer 14 when the peak is not more than the upper limit.

In order to set the peak top of the pore diameter of the first catalyst layer 14 to 20nm or more and 500nm or less, for example, in a preferred method for producing the exhaust gas purifying catalyst 10 described below, the particle diameter of the metal oxide particles used may be set to a preferred range described below, or the coating amounts of the first catalyst layer 14 and the second catalyst layer 15, the calcination temperatures for producing the first catalyst layer 14 and the second catalyst layer 15, the slurry viscosity, the presence or absence of pore-forming materials, the amounts thereof, and the like may be appropriately adjusted.

A preferred composition of the first catalyst layer 14 will be further described. From the viewpoint of efficiently exhibiting the exhaust gas purification performance by the catalytically active component, it is preferable that the first catalyst layer 14 further contains a supported component supporting the catalytically active component or a component serving as a co-catalyst. As the supported component and the component serving as a co-catalyst, a metal oxide is mentioned, and specifically, an inorganic oxide as an oxygen storage component (also referred to as an OSC material, OSC is an abbreviation of oxygen storage capacity) and an inorganic oxide other than the oxygen storage component are mentioned. In the first catalyst layer 14, it is preferable that both the inorganic oxide as the oxygen storage component and the inorganic oxide other than the oxygen storage component support the catalytically active component.

In the present specification, "loaded" means a state of being physically or chemically adsorbed or held on an outer surface or an inner surface of a pore. Specifically, in the case where one particle carries another particle, for example, it is confirmed from an element map image of a cross section of the exhaust gas purifying catalyst 10 analyzed by energy dispersive X-ray analysis (EDS) that an element constituting one particle and an element constituting another particle exist in the same region, and it can be judged as "carried".

The inorganic oxide as the oxygen storage component may be any metal oxide having a multivalent state and an oxygen storage ability, and examples thereof include CeO₂Cerium oxide-zirconium oxide composite oxide (hereinafter also referred to as CeO)₂-ZrO₂) Iron oxide, copper oxide. In addition to these, from the viewpoint of thermal stability and the like, it is also preferable to use an oxide of a rare earth element other than Ce. Examples of the oxide of a rare earth element other than Ce include Sc₂O₃、Y₂O₃、La₂O₃、Pr₆O₁₁、Nd₂O₃、Sm₂O₃、Eu₂O₃、Gd₂O₃、Tb₄O₇、Dy₂O₃、HO₂O₃、Er₂O₃、Tm₂O₃、Yb₂O₃And Lu₂O₃. Note that CeO₂-ZrO₂Is CeO₂And ZrO₂A solid solution of (2). CeO (CeO)₂And ZrO₂The solid solution can be formed by using an X-ray diffraction apparatus (XRD) according to whether or not CeO-derived material is formed₂-ZrO₂Is confirmed by the single phase of (2).

In particular, CeO is preferable in the first catalyst layer 14 from the viewpoint of balancing heat resistance and OSC₂The amount of the (B) is 10 to 45% by mass, and more preferably 15 to 35% by mass. Preferred ZrO in the first catalyst layer 14₂The amount of the (B) is 20 to 55% by mass, and more preferably 25 to 45% by mass. Preferred CeO as used herein₂And ZrO₂The amount of (C) includes CeO as a solid solution₂、ZrO₂The amount of (c).

As the inorganic oxide other than the oxygen storage component that can be contained in the first catalyst layer 14, metal oxides other than the oxygen storage component are exemplified, and alumina, silica-alumina, titania, and aluminosilicates are exemplified. From the viewpoint of heat resistance, alumina is particularly preferably used. The content of alumina in the first catalyst layer 14 is preferably 8 to 30 mass%, and more preferably 10 to 25 mass%.

A preferred composition of the second catalyst layer 15 will be further described. From the viewpoint of efficiently exhibiting the exhaust gas purification performance by the catalytically active component, it is preferable that the second catalyst layer 15 further contains a carrier component for carrying the catalytically active component. Examples of the supporting component include those similar to the metal oxides listed for the first catalyst layer 14.

Examples of the inorganic oxide as the oxygen storage component include the same inorganic oxides as the oxygen storage component described in the first catalyst layer 14. Among them, the exhaust gas purifying catalyst has a high OSC, and particularly preferably contains cerium oxide or a cerium oxide-zirconium oxide composite oxide. Particularly, CeO is preferable in the second catalyst layer 15 from the viewpoint of balancing heat resistance and OSC₂The amount of (B) is 3 to 30% by mass, and more preferably 5 to 20% by mass. Preferred ZrO in the second catalyst layer 15₂The amount of the (B) is 35 to 75% by mass, and more preferably 40 to 70% by mass. Preferred CeO as used herein₂And ZrO₂The amount of (C) includes CeO as a solid solution₂、ZrO₂The amount of (c).

Examples of the inorganic oxide other than the oxygen storage component that can be contained in the second catalyst layer 15 include the same inorganic oxides as those listed in the first catalyst layer 14. Alumina is particularly preferable from the viewpoint of high heat resistance. The amount of alumina in the second catalyst layer 15 is preferably 5 to 40 mass%, and more preferably 5 to 25 mass%.

The first catalyst layer 14 may be formed in either the inside or the surface of the partition wall 23, but is preferably formed on the surface of the partition wall 23 because the exhaust gas purification performance during high-speed operation can be further improved. The first catalyst layer 14 is formed on the surface of the partition wall 23 means that it is mainly present on the surface, not inside the partition wall 23. More specifically, for example, the presence of the main surface can be confirmed by a method of observing a cross section of the partition wall provided with the first catalyst layer 14 with a scanning electron microscope (JEM-ARM 200F, manufactured by JE Electron corporation), analyzing by Energy dispersive X-ray analysis (EDS), and analyzing by line analysis of a boundary between an element (e.g., Si, Mg, etc.) present only in the substrate and an element (e.g., Ce, Zr, etc.) present only in the catalyst layer, and analyzing by Electron Probe Microanalyzer (EPMA).

The main presence on the surface means that the mass of the first catalyst layer 14 present on the surface per unit cross section of the partition wall 23 is greater than the mass of the first catalyst layer 14 present inside the same unit cross section of the partition wall 23 when viewed by cutting the exhaust gas purification catalyst 10 along a plane perpendicular to the axial direction. The unit cross section means, for example, an area of 5mm × 5 mm.

The second catalyst layer 15 may be formed on either the surface or the inside of the partition wall 23, but it is preferable that at least a part of the second catalyst layer 15 is present inside the partition wall 23. In the second catalyst layer 15, when the coating amount is 100 mass% as a whole in a range of a length (0.1L) 1/10 where the distance from the downstream end R2 to the upstream side in the exhaust gas flow direction X to the downstream end is the length L of the substrate, from the viewpoint of reducing the pressure loss, the exhaust gas purification performance during high-speed operation, and the like, the mass of the second catalyst layer 15 present inside the partition wall 23 is preferably larger than the mass of the first catalyst layer 14 present on the partition wall surface in 100 mass% of the coating amount.

Fig. 3 schematically shows a state where the first catalyst layer 14 is formed on the surface of the partition wall 23 and the second catalyst layer 15 is formed inside the partition wall 23. As shown in fig. 3, even if the catalyst layer is present inside the partition wall 23, it is preferable that the catalyst layer is offset from the coated chamber side in the thickness direction of the partition wall 23. In the embodiment of the present invention, as shown in fig. 3, the first catalyst layer 14 may be formed on the surface of the partition wall 23 and the second catalyst layer 15 may be formed inside the partition wall 23, both the first catalyst layer 14 and the second catalyst layer 15 may be formed on the surface of the partition wall 23, or both the first catalyst layer 14 and the second catalyst layer 15 may be formed inside the partition wall 23. Among them, from the viewpoint of improving the exhaust gas purification performance during high-speed operation, it is preferable to adopt a mode in which the first catalyst layer 14 is formed on the surface of the partition wall 23 and the second catalyst layer 15 is formed inside the partition wall 23.

Next, a preferred method for producing the exhaust gas purifying catalyst of the present invention will be described below.

The production method comprises the following steps (1) to (3). Either of the steps (1) and (2) may be performed first.

Step (1) is a step of applying a slurry for the first catalyst layer 14, which contains a catalytically active component, metal oxide particles, and metal oxide and has a D90 of 3 μm or more, to the partition wall 23 on the inflow side chamber 21 side, and then drying the slurry.

In the step (2), the second catalyst layer 15 having a D90 of 5 μm or less, which contains the catalytically active component and the metal oxide particles, is applied to the partition wall 23 on the outflow-side chamber 22 side with a slurry, and then dried.

And (3) firing the substrate 11 after the steps (1) and (2).

Examples of the metal oxide particles include the above-described inorganic oxide as an oxygen storage component and inorganic oxides other than the oxygen storage component, which are constituent components of the first catalyst layer 14 and the second catalyst layer 15. (1) The catalytically active components of (1) and (2) may be mixed with the metal oxide particles in the form of a water-soluble salt such as a nitrate to obtain a slurry for the first catalyst layer 14 and a slurry for the second catalyst layer 15, respectively, and the slurry may be applied to the substrate 11 and then calcined in (3). Alternatively, the metal oxide particles may be loaded with the catalytically active component in advance, and the loaded metal oxide particles may be made into a slurry. When the catalytically active component is supported in advance, the metal oxide particles are immersed in an aqueous solution of a water-soluble salt of the catalytically active component, and then calcined at 350 to 550 ℃.

In order to bring the metal oxide particles supporting the catalytically active component into close contact with the substrate, the slurry for the first catalyst layer 14 in (1) and the slurry for the second catalyst layer 15 in (2) may contain a binder. Examples of the binder include alumina sol and zirconia sol.

(1) The slurry for the first catalyst layer 14 and the slurry for the second catalyst layer 15 (2) preferably have different metal oxide particles having a particle diameter D90. D90 is a 90% cumulative particle size on a volume basis.

From the viewpoint of smoothly obtaining an exhaust gas purifying catalyst having a pore volume higher on the upstream side than on the downstream side and from the viewpoint of heat resistance, D90 of the metal oxide particles of the slurry for the first catalyst layer 14 is preferably 3 μm or more, more preferably 5 μm or more, still more preferably 10 μm or more, and particularly preferably 15 μm or more. From the viewpoint of improving the dispersibility of the catalytically active component, the D90 of the metal oxide particles in the slurry for the first catalyst layer 14 is preferably 80 μm or less, and more preferably 50 μm or less.

On the other hand, from the viewpoint of smoothly obtaining an exhaust gas purifying catalyst having a first pore volume larger than a second pore volume, the D90 of the metal oxide particles of the slurry for the second catalyst layer 15 is preferably less than 5 μm, more preferably less than 3 μm, and particularly preferably 1 μm or less. From the viewpoint of heat resistance, D90 of the metal oxide particles of the slurry for the second catalyst layer 15 is preferably 0.1 μm or more.

The D90 of the metal oxide particles mentioned herein may be the particle diameter before the catalytic active component is supported even if the particle diameter is the particle diameter in the state where the catalytic active component is supported, and may be not less than the above-mentioned preferable lower limit or not more than the above-mentioned preferable upper limit in any state after the catalytic active component is supported and before the catalytic active component is supported.

The D90 of the metal oxide particles can be measured, for example, as follows. That is, the metal oxide particles were put in an aqueous solvent using an automatic sample feeder for a laser diffraction particle size distribution measuring apparatus ("microtoracdc" manufactured by Microtrac Bell corporation), irradiated with 40W of ultrasonic waves at a flow rate of 40% for 360 seconds, and then measured using a laser diffraction scattering particle size distribution meter ("Microtrac MT3300 EXII" manufactured by Microtrac Bell corporation). The measurement conditions were 1.5 refractive index of the particles, spherical shape of the particles, 1.3 refractive index of the solvent, 30 seconds of zero setting, and 30 seconds of measurement time, and the average value of 2 measurements was obtained. Pure water was used as the aqueous solvent.

From the viewpoint of smoothly obtaining an exhaust gas purifying catalyst having a first pore volume larger than a second pore volume, it is preferable that the slurry for the first catalyst layer 14 in (1) contains a pore-forming material. The pore-forming material may be, for example, crosslinked polymethyl (meth) acrylate particles, crosslinked polybutyl (meth) acrylate particles, crosslinked polystyrene particles, crosslinked polyacrylate particles, or the like. The average particle diameter D50 of the pore-forming material is preferably 0.1 to 100. mu.m. D50 is a volume-based 50% cumulative particle diameter, and can be determined by the same method as that for D90.

In order to coat the first catalyst layer 14 of (1) with the slurry on the substrate 11, a method of immersing the upstream side of the substrate 11 in the exhaust gas flow direction in the slurry may be mentioned. The slurry may also be sucked from the downstream side while the impregnation is being performed. In this way, the first catalyst layer 14 is coated with the slurry on the face of the partition wall 23 facing the inflow side chamber in the upstream side of the substrate 11 through the inflow side chamber opening in the X direction upstream side. By the particle diameter of the metal oxide particles, most of the metal oxide constituting the first catalyst layer 14 is located on the surface of the partition wall 23.

In order to coat (2) the slurry for the second catalyst layer 15 on the substrate 11, a method of immersing the substrate 11 on the downstream side in the exhaust gas flow direction in the slurry may be mentioned. It is also possible to perform this impregnation while sucking the slurry from the upstream side. In this way, the second catalyst layer 15 is coated with the slurry on the surface of the partition wall 23 facing the outlet side chamber in the downstream side in the X direction of the substrate 11 through the outlet side chamber opening in the downstream side. As described above, the second catalyst layer 15 may be present in either of the inside and the surface of the partition wall 23, but it is preferable that at least a part be present inside the partition wall 23, and it is preferable that the part present inside be greater than the part present on the surface.

From the viewpoint of heat resistance and workability, the drying temperature of the slurry of (1) and (2) is preferably 40 to 120 ℃. (3) The roasting temperature is preferably 350-550 ℃.

From the viewpoint of reducing the pressure loss and the exhaust gas purification performance at the time of high-speed operation, the amount of the first catalyst layer 14 obtained is preferably smaller than the amount of the second catalyst layer 15. The amount of the first catalyst layer 14 to be coated is preferably 50g or less per 1L volume of the substrate from the viewpoint of reducing the pressure loss and the exhaust gas purification performance at the time of high-speed operation, and is preferably 5g or more from the viewpoint of improving the exhaust gas purification performance and the appropriate PM trapping. In particular, more preferably 8g or more and 40g or less.

The coating amount of the second catalyst layer 15 is preferably 80g or less with respect to 1L of the volume of the substrate from the viewpoint of reducing the pressure loss or the like, and is preferably 20g or more from the viewpoint of improving the exhaust gas purification performance. Particularly, 30g or more and 70g or less are more preferable.

When the exhaust gas purifying catalyst obtained in the above-described manufacturing method is used as a particulate filter, as shown in fig. 2, exhaust gas flows from the inflow side chamber 21 of the substrate 11. The exhaust gas flowing from the inflow side chamber 21 reaches the outflow side chamber 22 through the porous partition wall 23. In fig. 2, the path of the exhaust gas flowing from the inflow side chamber 21 to the outflow side chamber 22 through the partition wall 23 is indicated by an arrow. At this time, since the partition wall 23 has a porous structure, PM is trapped on the surface of the partition wall 23 or in the pores inside the partition wall 23 while the exhaust gas passes through the partition wall 23. In addition, since the partition wall 23 is provided with the first catalyst layer 14 and the second catalyst layer 15, harmful components in the exhaust gas are purified during the exhaust gas passes through the inside and the surface of the partition wall 23. The exhaust gas reaching the outflow side chamber 22 through the partition wall 23 is discharged to the outside of the exhaust gas purifying catalyst 10 from the opening on the exhaust gas outflow side.

According to the exhaust gas purifying catalyst 10 produced in this way, the first pore volume is larger than the second pore volume, and the main peak of the pore diameter in the 1 st catalyst portion is within a specific range, so that not only is the heat resistance excellent, but also the exhaust gas purifying performance during high-speed operation is excellent.

In the present invention, the content of the above-mentioned various components, i.e., cerium oxide and zirconium oxide, and the content of the inorganic oxides other than the oxygen storage component, can be determined by measuring the amount of each metal, e.g., cerium, zirconium, and aluminum, in a solution in which each catalyst layer is completely dissolved by ICP-AES measurement. The amount of the catalytically active component relative to the porous substrate 11 can be measured, for example, by measuring the amount of the noble metal in a solution in which the catalyst layer is completely dissolved by ICP-AES.

When the catalyst layer is contained in the partition wall of the substrate, the amount of each metal in the solution in which only the substrate is completely dissolved can be measured by subtracting the amount of each metal in the solution in which each catalyst layer and the substrate are completely dissolved from the amount of each metal in the solution.