Exhaust gas purification catalyst

Abstract

To provide a catalyst for purification of exhaust gas for achieving both warming performance and high load performance.SOLUTION: There is provided a catalyst for purification of exhaust gas which comprises a substrate and a catalyst coat layer. The catalyst coat layer has a front stage portion and a rear stage portion. The content X1 of alumina per substrate volume of the front stage portion is smaller than the content X2 of alumina per substrate volume of the rear stage portion. The ratio (Y2 / Y1) of the coating amount Y2 per substrate volume of the rear stage portion to the coating amount Y1 per substrate volume of the front stage portion satisfies the following expression: 1.0<(Y2 / Y1)≤2.0.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] Exhaust gas discharged from an internal combustion engine of a vehicle or the like contains harmful components such as nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO). Among the harmful components, NOx has a negative effect on the human body and also causes acid rain, so that emission regulations are becoming particularly strict. In order to efficiently react and remove these harmful components from exhaust gas, exhaust gas purification catalysts have been used. One typical configuration of an exhaust gas purification catalyst is one in which a catalyst coating layer containing a precious metal such as Pt (platinum), Pd (palladium), or Rh (rhodium) and a carrier such as alumina is formed on a highly heat-resistant substrate such as ceramics. Patent documents 1 to 5 are listed as prior art documents related to exhaust gas purification catalysts.

[0003] One of the performances required for an exhaust gas purification catalyst is the ability to quickly activate and exhibit good purification performance even in a low-temperature state such as immediately after starting an engine (warm-up performance). In this regard, for example, Patent Document 1 discloses an exhaust gas purification catalyst including a substrate, an upstream catalyst coating layer formed on the exhaust gas upstream side of the substrate, and a downstream catalyst coating layer formed on the exhaust gas downstream side of the substrate. Patent Document 1 describes that the low-temperature oxidation activity of the upstream catalyst coating layer can be improved by making the heat capacity of the downstream catalyst coating layer larger than that of the upstream catalyst coating layer and forming a high-loading portion with a higher loading concentration of precious metal than other portions of the upstream catalyst coating layer in the upstream portion of the upstream catalyst coating layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-285605 A [Patent Document 2] JP 2007-038072 A [Patent Document 3] JP 2017-100073 A [Patent Document 4] JP 2017-104825 A [Patent Document 5] JP 2016-185531 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the number of vehicles with small-displacement engines has been increasing due to the downsizing of internal combustion engines and the growing demand for light vehicles. Such vehicles are typically equipped with only one exhaust gas purification catalyst. Therefore, one exhaust gas purification catalyst is required to satisfy not only warm-up performance but also high-load performance. For example, even in high-load environments where the vehicle accelerates rapidly when overtaking or entering a highway, resulting in a large displacement, it is required to appropriately purify harmful components in exhaust gas.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas purifying catalyst which achieves both good warm-up performance and good high load performance.

[0007] The present invention provides a catalyst for purifying exhaust gas, which is disposed in an exhaust passage of an internal combustion engine and purifies exhaust gas discharged from the internal combustion engine. The catalyst for purifying exhaust gas includes a substrate and a catalyst coating layer formed on the substrate and containing a precious metal catalyst and alumina. The catalyst coating layer has a front stage portion located upstream in the flow direction of the exhaust gas and a rear stage portion located downstream of the front stage portion. The alumina content X1 (g / L) per substrate volume of the front stage portion is equal to or less than the alumina content X2 (g / L) per substrate volume of the rear stage portion, and the ratio (Y2 / Y1) of the coating amount Y2 (g / L) per substrate volume of the rear stage portion to the coating amount Y1 (g / L) per substrate volume of the front stage portion satisfies the following formula: 1.0<(Y2 / Y1)≦2.0.

[0008] By making the alumina content of the front stage equal to or less than that of the rear stage and by appropriately setting the coating amount ratio (Y2 / Y1) within the above ratio range, it is possible to achieve both warm-up performance and high load performance. In other words, the front stage warms up easily, and excellent warm-up performance can be achieved. In addition, by increasing the heat capacity of the rear stage, harmful components in the exhaust gas (especially NOx) can be effectively purified even when the exhaust volume is large, and excellent high load performance can be achieved.

[0009] In a preferred embodiment, the ratio (X2 / X1) of the alumina content X2 to the alumina content X1 satisfies the following formula: 1.0≦(X2 / X1)≦2.0. This provides a favorable balance between the alumina ratios in the front and rear stages, thereby achieving both warm-up performance and high load performance at a higher level.

[0010] In a preferred embodiment, the alumina content X1 is 20 g / L or more and 50 g / L or less, which increases the heat resistance of the front stage and improves the warm-up performance, thereby achieving a higher level of balance between the warm-up performance and the high load performance.

[0011] In a preferred embodiment, the coating amount Y2 is 100 g / L or more and 160 g / L or less, which increases the heat resistance of the rear stage and improves the high-load performance, thereby achieving a higher level of balance between warm-up performance and high-load performance.

[0012] In a preferred embodiment, the front-stage portion includes a front-stage lower layer formed on a surface of the base material and a front-stage upper layer formed on the front-stage lower layer, the front-stage upper layer containing rhodium, thereby achieving a higher level of balance between warm-up performance and high load performance.

[0013] In a preferred embodiment, the alumina content in the front upper layer is 5 g / L or more and 25 g / L or less, thereby making it possible to further improve the warm-up performance and achieve a higher level of balance between the warm-up performance and the high load performance.

[0014] In a preferred embodiment, the rear section includes a rear lower layer formed on a surface of the base material and a rear upper layer formed on the rear lower layer, the front upper layer and the rear upper layer containing rhodium, and the front lower layer and the rear lower layer containing palladium, thereby achieving a higher level of balance between warm-up performance and high load performance. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of an exhaust gas purification system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view that typically illustrates the exhaust gas purifying catalyst of FIG. [Diagram 3] FIG. 2 is a schematic diagram showing the configuration of a rib wall portion of the exhaust gas purifying catalyst of FIG. 1. [Figure 4] 1 is a graph showing the relationship between the coating amount ratio (Y2 / Y1) and NOx-WU (warm-up performance). [Diagram 5] 1 is a graph showing the relationship between the coating amount ratio (Y2 / Y1) and NOx-T50 (high load performance) during temperature reduction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Matters other than those specifically mentioned in this specification and necessary for carrying out the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the relevant field. In addition, in the following drawings, the same reference numerals are used for members and parts that perform the same function, and duplicated explanations may be omitted or simplified. In addition, the expression "A to B" (A and B are arbitrary numbers) indicating a range in this specification includes the meaning of A or more and B or less, as well as "preferably greater than A" and "preferably smaller than B".

[0017] <Exhaust gas purification system> FIG. 1 is a schematic diagram of an exhaust gas purification system 1. The exhaust gas purification system 1 includes an internal combustion engine 2, an exhaust gas purification device 3, and an engine control unit (Engine Control Unit: ECU) 4. The exhaust gas purification system 1 is configured to purify harmful components, such as NOx, HC, and CO, contained in exhaust gas discharged from the internal combustion engine 2 using the exhaust gas purification device 3. Note that the arrows in FIG. 1 indicate the flow direction of exhaust gas. In the following description, the side closer to the internal combustion engine 2 is referred to as the upstream side, and the side farther from the internal combustion engine 2 is referred to as the downstream side along the flow of exhaust gas.

[0018] Here, the internal combustion engine 2 is mainly configured as a gasoline engine of a vehicle. However, the internal combustion engine 2 may be an engine other than gasoline, such as a diesel engine or an engine mounted on a hybrid vehicle. The internal combustion engine 2 has a plurality of combustion chambers (not shown). Each combustion chamber is connected to a fuel tank (not shown). Gasoline is stored in the fuel tank here. However, the fuel stored in the fuel tank may be diesel fuel (light oil) or the like. In the combustion chamber, fuel gas supplied from the fuel tank is burned. The combustion chamber communicates with an exhaust port 2a. The exhaust port 2a communicates with an exhaust gas purification device 3. The burned fuel gas becomes exhaust gas and is discharged to the exhaust gas purification device 3.

[0019] The exhaust gas purification device 3 includes an exhaust passage 5 communicating with the internal combustion engine 2, an oxygen sensor 8, and an exhaust gas purification catalyst 10. The exhaust passage 5 is an exhaust gas flow path through which exhaust gas flows. The exhaust passage 5 includes an exhaust manifold 5a and an exhaust pipe 5b. An upstream end of the exhaust manifold 5a is connected to an exhaust port 2a of the internal combustion engine 2. A downstream end of the exhaust manifold 5a is connected to an exhaust pipe 5b. An exhaust gas purification catalyst 10 is disposed in the middle of the exhaust pipe 5b. The exhaust gas purification device 3 is configured to purify harmful components in the exhaust gas by a single exhaust gas purification catalyst 10. However, the number of exhaust gas purification catalysts 10 is not particularly limited, and a plurality of exhaust gas purification catalysts 10 may be provided. In that case, the configurations and functions of the plurality of exhaust gas purification catalysts 10 may be different from each other. The configuration and the like of the exhaust gas purification catalyst 10 will be described in detail later.

[0020] The ECU 4 controls the internal combustion engine 2 and the exhaust gas purification device 3. The ECU 4 is electrically connected to the internal combustion engine 2 and the exhaust gas purification device 3. The ECU 4 is electrically connected to sensors (e.g., the oxygen sensor 8) installed at various locations in the exhaust gas purification device 3. The configuration of the ECU 4 may be the same as that of a conventional device, and is not particularly limited. The ECU 4 is, for example, a processor or an integrated circuit. The ECU 4 has an input port (not shown) and an output port (not shown). The ECU 4 receives information such as the operating state of the vehicle, the amount of exhaust gas discharged from the internal combustion engine 2, the temperature of the exhaust gas, and the pressure of the exhaust gas via the input port. The ECU 4 receives information detected by a sensor (e.g., the amount of oxygen measured by the oxygen sensor 8) via the input port.

[0021] The ECU 4 transmits a control signal via an output port based on, for example, the received information. The ECU 4 controls, for example, the operation of the internal combustion engine 2, such as fuel injection control, ignition control, and intake air amount adjustment control. The ECU 4 controls the driving and stopping of the exhaust gas purification device 3 based on, for example, the operating state of the internal combustion engine 2.

[0022] <Exhaust gas purification catalyst> FIG. 2 is a perspective view showing the catalyst 10 for purifying exhaust gas. The arrows in FIG. 2 indicate the flow of exhaust gas. In FIG. 2, the upstream side of the exhaust path 5 relatively close to the internal combustion engine 2 is shown on the left side, and the downstream side of the exhaust path relatively far from the internal combustion engine 2 is shown on the right side. Also, in FIG. 2, the symbol X indicates the cylinder axis direction of the catalyst 10 for purifying exhaust gas. The catalyst 10 for purifying exhaust gas is installed in the exhaust path 5 so that the cylinder axis direction X is along the flow direction of the exhaust gas. The cylinder axis direction X is the flow direction of the exhaust gas. Hereinafter, one direction Xa of the cylinder axis direction X may be referred to as the upstream side (also referred to as the exhaust gas inflow side or front side), and the other direction Xb may be referred to as the downstream side (also referred to as the exhaust gas outflow side or rear side). However, these are merely directions for convenience of explanation, and do not limit the installation form of the catalyst 10 for purifying exhaust gas in any way.

[0023] The exhaust gas purifying catalyst 10 has a function of purifying NOx in exhaust gas. An end of the exhaust gas purifying catalyst 10 in one direction Xa is an exhaust gas inlet 10a, and an end of the exhaust gas purifying catalyst 10 in the other direction Xb is an exhaust gas outlet 10b. The outer shape of the exhaust gas purifying catalyst 10 here is cylindrical. However, the outer shape of the exhaust gas purifying catalyst 10 is not particularly limited, and may be, for example, an elliptical cylindrical shape, a polygonal cylindrical shape, a pipe shape, a foam shape, a pellet shape, a fiber shape, or the like. The exhaust gas purifying catalyst 10 includes a straight-flow type substrate 11 and a catalyst coating layer 20 (see FIG. 3).

[0024] <Base material> The substrate 11 constitutes the framework of the exhaust gas purification catalyst 10. The substrate 11 is not particularly limited, and various materials and shapes used in the conventional use of this type can be used. The substrate 11 may be, for example, a ceramic carrier made of ceramics such as cordierite, aluminum titanate, and silicon carbide, or a metal carrier made of stainless steel (SUS), Fe-Cr-Al alloy, Ni-Cr-Al alloy, and the like. As shown in FIG. 2, the substrate 11 of this embodiment has a honeycomb structure. The substrate 11 includes a plurality of cells (cavities) 12 regularly arranged in the cylindrical axis direction X, and partition walls (rib walls) 14 separating the plurality of cells 12. Although not particularly limited, the volume of the substrate 11 may be about 0.1 to 10 L, for example, 1 to 5 L. The length (total length) of the substrate 11 along the cylindrical axis direction X may be about 10 to 500 mm, for example, 50 to 300 mm. In this specification, the "volume of the substrate 11" refers to the apparent volume (bulk volume) including the volume of the substrate 11 itself (net volume) and the volume of the cells 12 inside.

[0025] The cells 12 are flow paths for exhaust gas. The cells 12 extend in the cylinder axis direction X. The cells 12 are through-holes that penetrate the substrate 11 in the cylinder axis direction X. The shape, size, number, etc. of the cells 12 may be designed, for example, in consideration of the flow rate and components of the exhaust gas supplied to the exhaust gas purification catalyst 10. The shape of the cross section of the cells 12 perpendicular to the cylinder axis direction X is not particularly limited. The cross-sectional shape of the cells 12 may be, for example, a quadrangle such as a square, parallelogram, rectangle, or trapezoid, or other polygonal shape (e.g., a triangle, hexagon, or octagon), a corrugated shape, a circle, or various other geometric shapes. The rib wall 14 faces the cells 12 and separates the adjacent cells 12. Although not particularly limited, the thickness of the rib wall 14 (the dimension in the direction perpendicular to the surface; the same applies below) may be approximately 0.1 to 10 mils (1 mil is approximately 25.4 μm), for example 0.2 to 5 mils, from the viewpoint of improving mechanical strength and reducing pressure loss.

[0026] <Catalyst coating layer> The catalyst coating layer 20 is a site for purifying exhaust gas. The catalyst coating layer 20 is a porous body having a large number of interconnected pores. The exhaust gas that has flowed into the exhaust gas purification catalyst 10 comes into contact with the catalyst coating layer 20 while flowing through the flow paths (cells 12) of the exhaust gas purification catalyst 10. This purifies harmful components in the exhaust gas.

[0027] In this embodiment, the catalyst coating layer 20 contains at least a precious metal catalyst and alumina. The precious metal catalyst is a catalyst that oxidizes and / or reduces harmful components in exhaust gas. The precious metal catalyst is not particularly limited, and one or more of various precious metals conventionally used for this type of application can be appropriately used. For example, platinum group metals such as rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), osmium (Os), iridium (Ir), silver (Ag), gold (Au), etc. can be mentioned. Among them, it is preferable to use at least one of Pd and Pt, which have high oxidation activity, in combination with Rh, which has high reduction activity.

[0028] Alumina (Al2O3) is a porous material that constitutes the framework of the catalyst coat layer 20. Alumina is typically a support material that supports a precious metal catalyst. Alumina has high heat resistance and durability. By including alumina in the catalyst coat layer 20, the thermal stability and durability of the catalyst coat layer 20 can be improved. The specific heat of alumina is about 0.75 to 0.85 kJ / (kg·K). Alumina generally has a high specific heat compared to other support materials that have been used in the past for this type of application, such as cerium oxide (ceria), zirconium oxide (zirconia), silicon oxide (silica), titanium oxide (titania), etc. In other words, it is difficult to heat up. Therefore, as will be described in detail later, by adjusting the content of alumina with respect to the flow direction of the exhaust gas (preferably, changing it along the flow direction of the exhaust gas), the warm-up performance and high load characteristics of the catalyst coat layer 20 can be suitably adjusted.

[0029] In addition to the precious metal catalyst and alumina, the catalyst coating layer 20 may contain an optional component as appropriate. Examples of such optional components include OSC materials having oxygen storage capacity, such as ceria and composite oxides containing ceria (e.g., ceria-zirconia composite oxide); porous carriers (non-OSC materials) other than the above-mentioned alumina, such as rare earth metal oxides, such as zirconia, silica, and titania; alkaline earth metal elements, such as calcium (Ca) and barium (Ba); rare earth metal elements, such as yttrium (Y), lanthanum (La), and neodymium (Nd); and various additives, such as NOx adsorbents having NOx storage capacity. In the catalyst coating layer 20, the content ratio of each optional component may be, for example, equal to or less than the content ratio of alumina, on a mass basis. The total content ratio of the optional components may be, for example, lower than the content ratio of alumina.

[0030] FIG. 3 is a schematic diagram showing the structure of the rib wall 14 of the exhaust gas purification catalyst 10. FIG. 3 shows a part of a cross section cut along the cylinder axis direction X. The arrow in FIG. 3 shows the flow direction of the exhaust gas. The catalyst coating layer 20 is provided on the surface of the substrate 11, specifically on the rib wall 14. However, the catalyst coating layer 20 may be partially or entirely permeated into the catalyst coating layer 20. The catalyst coating layer 20 may be provided continuously or intermittently on the rib wall 14. The entire coating width (average length) of the catalyst coating layer 20 in the cylinder axis direction X may be approximately 50% or more, typically 80% or more, and preferably 90% or more of the total length L of the substrate 11, and may be, for example, approximately the same length as the total length L of the substrate 11. The overall coating thickness of the catalyst coating layer 20 (average length in the direction perpendicular to the cylinder axis direction X) is preferably about 1 to 300 μm, typically 5 to 100 μm, for example about 10 to 50 μm.

[0031] The catalyst coating layer 20 in FIG. 3 includes a front stage 21 located upstream in the flow direction of exhaust gas (the direction of the arrow in FIG. 3), and a rear stage 22 located downstream of the front stage 21. Here, the front stage 21 and the rear stage 22 each contain a precious metal catalyst and alumina. The front stage 21 and the rear stage 22 each have a laminated structure in which two catalyst coating layers having different configurations are laminated in the thickness direction. However, the front stage 21 and / or the rear stage 22 may have a single layer structure. The front stage 21 and / or the rear stage 22 may have a laminated structure of three or more layers. Each part will be described in order below.

[0032] <front section> The front section 21 is formed along the cylinder axis direction X from the exhaust gas inlet 10a towards the downstream side. The coating width (average length) L1 in the cylinder axis direction X of the front section 21 may be designed in consideration of, for example, the size of the substrate 11 and the flow rate of the exhaust gas flowing through the exhaust gas purification catalyst 10. In some embodiments, the coating width L1 in the cylinder axis direction X of the front section 21 satisfies 0.2L ≦ L1, preferably 0.25L ≦ L1 ≦ 0.6L, more preferably L1 ≦ 0.5L, for example, 0.3L ≦ L1 ≦ 0.5L. Thereby, the warm-up performance and the high-load performance can be balanced at a higher level. In FIG. 3, the front section 21 is formed in a portion corresponding to 50% of the total length L of the substrate 11. That is, L1 = 0.5L.

[0033] The front section 21 preferably contains at least Rh as a noble metal catalyst, and more preferably contains Rh and Pd. The total content M1 of the noble metal catalyst in the front section 21 is preferably more than the content M2 of the noble metal catalyst in the rear section 22 on a mass basis. That is, it is preferable that M2 < M1. Although not particularly limited, the content (mass) M1 of the noble metal catalyst in the front section 21 is generally 0.1 to 10 g, preferably 1 to 5 g, for example, 1.5 to 3 g per liter of the volume of the substrate, in terms of oxide, from the viewpoint of improving the warm-up performance and the like. Thereby, the warm-up performance and the high-load performance can be balanced at a higher level.

[0034] In this embodiment, the alumina content X1 (g / L) per unit volume of the base material in the front stage portion 21 is equal to or less than the alumina content X2 (g / L) per unit volume of the base material in the rear stage portion 22. That is, X1 ≦ X2. For example, X1 < X2. Although not particularly limited, the alumina content X1 in the front stage portion 21 is generally 100 g / L or less, 70 g / L or less, preferably 50 g / L or less, more preferably 45 g / L or less, from the viewpoints of enhancing the heat resistance of the front stage portion 21, making the front stage portion 21 easier to warm up and improving the warm-up performance better, etc. Also, from the viewpoints of balancing the warm-up performance and the high-load performance, etc., it is generally 5 g / L or more, 10 g / L or more, preferably 20 g / L or more, more preferably 30 g / L or more, for example 34 g / L or more.

[0035] In this embodiment, the coating amount Y1 (g / L) per unit volume of the base material in the front stage portion 21 is less than the coating amount Y2 (g / L) per unit volume of the base material in the rear stage portion 22. That is, Y1 < Y2. Although not particularly limited, the coating amount (forming amount) Y1 in the front stage portion 21 is generally 40 g / L or more, 60 g / L or more, preferably 70 g / L or more, for example 74 g / L or more, from the viewpoints of enhancing the heat resistance of the front stage portion 21, balancing the warm-up performance and the high-load performance at a high level, etc. Also, from the viewpoints of increasing the noble metal loading density in the front stage portion 21 to make the front stage portion 21 easier to warm up, improving the warm-up performance better, and reducing the pressure loss when the exhaust gas flows into the cell 12, etc., it is generally 200 g / L or less, 150 g / L or less, preferably 110 g / L or less, for example 105 g / L or less.

[0036] Here, the front section 21 includes a front lower layer 21B formed on the surface of the base material 11 (specifically, the rib wall 14) and a front upper layer 21A formed on the front lower layer 21B. From the viewpoint of improving warm-up performance, the ratio (Tb / Ta) of the thickness Tb of the front lower layer 21B to the thickness Ta of the front upper layer 21A is preferably 1 or more, more preferably 1.5 or more, and even more preferably 2 or more, for example, 2 to 5, although it is not particularly limited thereto. Note that a third layer (intermediate layer) may be further provided between the front upper layer 21A and the front lower layer 21B. The front section 21 may include the front lower layer 21B, one or more intermediate layers, and the front upper layer 21A.

[0037] <First stage upper layer> The front upper layer 21A is a portion located farthest from the substrate 11 in the thickness direction of the front section 21. The front upper layer 21A is a portion of the catalyst coating layer 20 that first comes into contact with the exhaust gas flowing in from the exhaust gas inlet 10a. The front upper layer 21A constitutes the surface layer (surface portion) of the front section 21. The front upper layer 21A contains at least a precious metal catalyst and alumina. The front upper layer 21A may further contain the optional components described above. The front upper layer 21A preferably contains at least Rh as a precious metal catalyst. This allows a higher level of balance between warm-up performance and high load performance.

[0038] Although not particularly limited, the loading density of the precious metal catalyst (e.g., Rh) in the front upper layer 21A is preferably 0.01 g or more, more preferably 0.05 g or more, and even more preferably 0.1 g or more per 1 L of substrate volume from the viewpoint of improving warm-up performance, etc. Also, from the viewpoint of suppressing sintering of the precious metal and enhancing catalytic reactivity, etc., the loading density is preferably 3 g or less, more preferably 2 g or less, and even more preferably 1 g or less per 1 L of substrate volume.

[0039] Although not particularly limited, the alumina content A of the front upper layer 21A is AlFrom the viewpoint of improving heat resistance and warm-up performance, the alumina content A of the front upper layer 21A is about 50 g or less, 30 g or less, preferably 25 g or less, for example 20 g or less per 1 L of the base material volume. Al From the viewpoint of balancing warm-up performance and high-load performance, the amount is generally 1 g or more, preferably 3 g or more, more preferably 5 g or more, for example 10 g or more, per 1 L of base material volume, and from the viewpoint of achieving excellent NOx purification performance even under high load, the amount is preferably 5 to 30 g, more preferably 10 to 30 g, for example 15 to 25 g.

[0040] It is preferable that the front upper layer 21A contains an OSC material (for example, a ceria-zirconia composite oxide) as an optional component. This makes it possible to more stably achieve excellent warm-up performance. Although not particularly limited, the content A of the OSC material in the front upper layer 21A is OSC The content A of the OSC material is generally 1 to 50 g, preferably 5 to 45 g, more preferably 10 to 40 g, for example 20 to 30 g per 1 L of the volume of the base material. OSC From the viewpoint of more appropriately enhancing the OSC ability, the alumina content A Al Above (i.e., A Al ≦A OSC In some embodiments, the alumina content A Al OSC material content A OSC Mass ratio (A OSC / A Al ) may be preferably 0.1 to 10, and more preferably 1 to 5, from the viewpoint of further improving warm-up performance.

[0041] Although not particularly limited, the coating amount A of the first upper layer 21A coat From the viewpoint of improving heat resistance and balancing warm-up performance and high load performance, the amount of the filler per 1 L of base material volume is generally 20 g or more, preferably 30 g or more, more preferably 35 g or more, and generally 100 g or less, preferably 80 g or less, more preferably 60 g or less, for example 55 g or less.

[0042] <First stage lower layer> The front lower layer 21B is a portion of the front section 21 that comes into contact with the rib wall 14. Here, the front lower layer 21B contains at least a precious metal catalyst and alumina. The front lower layer 21B may further contain the optional components described above. When the front upper layer 21A contains Rh as a precious metal catalyst, it is preferable that the front lower layer 21B contains at least Pd. This makes it possible to achieve a higher level of balance between warm-up performance and high load performance.

[0043] Although not particularly limited, the supporting density of the precious metal catalyst (e.g., Pd) in the first lower layer 21B is preferably 0.1 g or more, more preferably 0.2 g or more, even more preferably 0.5 g or more, for example 1 g or more, and preferably 10 g or less, more preferably 5 g or less, even more preferably 3 g or less, for example 2 g or less, per 1 L of the base material volume, from the viewpoint of improving the warm-up performance. In some embodiments, the supporting density of the precious metal catalyst (e.g., Pd) in the first lower layer 21B is preferably larger than the supporting density of the precious metal catalyst (e.g., Rh) in the first upper layer 21A, and is preferably approximately 2 times or more, for example 3 times or more, 5 times or more, or 10 times or more, and approximately 50 times or less, for example 30 times or less, or 20 times or less, of the supporting density in the first upper layer 21A. This allows the warm-up performance and the high load performance to be balanced at a higher level.

[0044] Although not particularly limited, the alumina content B of the front lower layer 21B Al From the viewpoint of improving heat resistance and warm-up performance, the alumina content B of the front lower layer 21B is preferably about 50 g or less, 30 g or less, and more preferably 25 g or less, for example 20 g or less, per 1 L of the base material volume. Al From the viewpoint of balancing warm-up performance and high-load performance, the amount is generally 1 g or more, preferably 3 g or more, more preferably 5 g or more, for example 10 g or more, per 1 L of base material volume, and from the viewpoint of achieving excellent NOx purification performance even under high load, the amount is further preferably 10 to 30 g, for example 15 to 25 g.

[0045] In some embodiments, the alumina content B of the front lower layer 21B Al is the alumina content A of the front upper layer 21A Al The following, namely, B Al ≦A Al The alumina content B may be Al is the alumina content A of the front upper layer 21A Al Approximately the same as B Al ≒A Al (Manufacturing errors and the like are acceptable.) Alumina Content B Al is 0.5A Al ≦B coat ≦1.5A Al , preferably 0.8A Al ≦B Al ≦1.2A Al In some embodiments, the alumina content B Al is 1.2B Al ≦A Al This can improve the heat resistance and durability of the front stage section 21, and can provide stable warm-up performance and high load performance for a long period of time.

[0046] It is preferable that the front lower layer 21B contains an OSC material (for example, a ceria-zirconia composite oxide) as an optional component. This makes it possible to more stably achieve excellent warm-up performance. Although not particularly limited, the content B of the OSC material in the front lower layer 21B is OSC The content of the OSC material B is generally 1 to 50 g, preferably 5 to 40 g, more preferably 7 to 30 g, for example 10 to 20 g, per 1 L of the volume of the base material. OSC is the alumina content B Al The following (i.e., B OSC ≦B Al The alumina content B may be Al OSC material content B OSC Mass ratio (B OSC / B Al ) may be preferably 0.1 to 0.9, and more preferably 0.5 to 0.8.

[0047] In some embodiments, the OSC material content B of the front lower layer 21B OSC is the content A of the OSC material in the front upper layer 21A OSC The following, namely, B OSC ≦A OSC Content B OSC is preferably B OSC ≦0.8A OSC , more preferably B OSC ≦0.7A OSC For example, B OSC ≦0.6A OSC This makes it possible to achieve a higher level of balance between warm-up performance and high load performance.

[0048] Although not particularly limited, the coating amount B of the front lower layer 21B coat From the viewpoint of improving heat resistance and balancing warm-up performance and high load performance, the amount of the filler per 1 L of base material volume is generally 20 g or more, preferably 30 g or more, and more preferably 35 g or more, and generally 100 g or less, preferably 80 g or less, and more preferably 50 g or less.

[0049] In some embodiments, the coating amount B of the front lower layer 21B coat is the coating amount A of the upper layer 21A of the first stage coat Approximately the same as B coat ≒A coat (Manufacturing errors and the like are acceptable.) Coating amount B coat is 0.5A coat ≦B coat ≦1.5A coat , preferably 0.8A coat ≦B coat ≦1.2A coat This can reduce pressure loss and achieve a higher level of balance between warm-up performance and high load performance. Also, the durability and heat resistance of the front stage portion 21 can be improved.

[0050] <Later part> The rear stage 22 is formed along the cylinder axis direction X from the exhaust gas outlet 10b toward the upstream side. The coat width (average length) L2 of the rear stage 22 in the cylinder axis direction X may be designed in consideration of, for example, the size of the substrate 11 and the flow rate of exhaust gas flowing through the exhaust gas purification catalyst 10. In some embodiments, the coat width L2 of the rear stage 22 in the cylinder axis direction X is equal to or greater than the coat width L1 of the front stage 21 in the cylinder axis direction X. The coat width L2 typically satisfies 0.3L≦L2, preferably 0.4L≦L2≦0.8L, and more preferably 0.5L≦L2≦0.7L. This allows the warm-up performance and the high load performance to be balanced at a higher level. In FIG. 3, the rear stage 22 is formed in a portion corresponding to 50% of the total length L of the substrate 11. That is, L2=0.5L.

[0051] The rear stage 22 preferably contains at least Pd as a precious metal catalyst, and more preferably contains Rh and Pd. Although not particularly limited, the content (mass) M2 of the precious metal catalyst in the rear stage 22 is, in terms of oxide, about 0.1 to 5 g, preferably 0.2 to 3 g, for example 0.5 to 2 g per 1 L of the base material, from the viewpoint of improving high-load performance. This makes it possible to achieve a higher level of balance between warm-up performance and high-load performance.

[0052] In this embodiment, the alumina content X2 (g / L) per base material volume of the rear stage 22 is equal to or greater than the alumina content X1 (g / L) per base material volume of the front stage 21. Although not particularly limited, the alumina content X1 of the rear stage 22 may be approximately 5 g / L or more, 10 g / L or more, preferably 30 g / L or more, for example 40 g / L or more, 45 g / L or more, and more preferably 50 g / L or more, from the viewpoint of improving the heat resistance of the rear stage 22 and improving the heat retention of the rear stage 22 to further improve the high-load performance. Also, from the viewpoint of balancing the warm-up performance and the high-load performance, the alumina content X1 may be approximately 100 g / L or less, preferably 80 g / L or less, 70 g / L or less, and more preferably 65 g / L or less.

[0053] In some embodiments, the ratio (X2 / X1) of the alumina content X2 to the alumina content X1 satisfies the following formula: 1.0≦(X2 / X1)≦2.0. The alumina content ratio (X2 / X1) may be approximately 1.05 or more, for example 1.1 or more, and approximately 1.9 or less, preferably 1.5 or less. By including a large amount of alumina having a high specific heat in the rear stage portion 22, the heat capacity of the rear stage portion 22 can be increased. This improves the heat retention performance, and allows both warm-up performance and high load performance to be achieved at a high level.

[0054] In this embodiment, the coating amount Y2 (g / L) per base material volume of the rear stage section 22 is greater than the coating amount Y1 (g / L) per base material volume of the front stage section 21. Although not particularly limited, the coating amount (molding amount) Y2 of the rear stage section 22 may be approximately 50 g / L or more, 70 g / L or more, preferably 100 g / L or more, and more preferably 110 g / L or more, from the viewpoints of increasing the heat resistance of the rear stage section 22 and improving the high-load performance by increasing the heat retention of the rear stage section 22. Also, from the viewpoints of reducing pressure loss, increasing the loading density of the precious metal in the rear stage section 22 to improve the catalytic reactivity in the rear stage section 22, and balancing the warm-up performance and the high-load performance at a high level, the coating amount may be approximately 200 g / L or less, 170 g / L or less, preferably 160 g / L or less, 150 g / L or less, 140 g / L or less, and more preferably 135 g / L or less.

[0055] In this embodiment, the ratio (Y2 / Y1) of the coating amount Y2 of the rear stage section 22 to the coating amount Y1 of the front stage section 21 satisfies the following formula: 1.0<(Y2 / Y1)≦2.0. The coating amount ratio (Y2 / Y1) is generally 1.02 or more, preferably 1.05 or more, more preferably 1.1 or more, and even more preferably 1.2 or more, and generally 1.9 or less, preferably 1.8 or less, and more preferably 1.5 or less. This makes it possible to achieve a higher level of balance between warm-up performance and high load performance.

[0056] Here, the rear section 22 includes a rear lower layer 22D formed on the surface of the substrate 11 (specifically, the rib wall 14) and a rear upper layer 22C formed on the rear lower layer 22D. Although not particularly limited, the ratio (Td / Tc) of the thickness Td of the rear lower layer 22D to the thickness Tc of the rear upper layer 22C is preferably 1 or more, more preferably 1.5 or more, and even more preferably 2 or more, for example, 2 to 5. Note that a third layer (intermediate layer) may be further provided between the rear upper layer 22C and the rear lower layer 22D. The rear section 22 may include the rear lower layer 22D, one or more intermediate layers, and the rear upper layer 22C.

[0057] <Upper level back> The rear upper layer 22C is a portion located farthest from the substrate 11 in the thickness direction of the rear section 22. The rear upper layer 22C constitutes a surface layer (surface portion) of the rear section 22. Here, the rear upper layer 22C contains at least a precious metal catalyst and alumina. The rear upper layer 22C may further contain the optional components described above. The rear upper layer 22C preferably contains at least Rh as a precious metal catalyst. This allows a higher level of balance between warm-up performance and high load performance.

[0058] Although not particularly limited, the supporting density of the precious metal catalyst (e.g., Rh) in the rear upper layer 22C is preferably 0.01 g or more, more preferably 0.05 g or more, and even more preferably 0.1 g or more, and is preferably 3 g or less, more preferably 2 g or less, and even more preferably 1 g or less, per 1 L of the substrate volume, from the viewpoint of suppressing sintering of the precious metal to enhance the catalytic reactivity in the rear section 22 and improving the high load performance. In some embodiments, the supporting density of the precious metal catalyst (e.g., Rh) in the rear upper layer 22C may be approximately equal to the supporting density of the precious metal catalyst (e.g., Rh) in the front upper layer 21A. For example, the absolute difference between the supporting densities of the two may be approximately 0.2 g or less, for example 0.1 g or less, per 1 L of the substrate volume.

[0059] Although not particularly limited, the alumina content C of the rear upper layer 22C is AlFrom the viewpoint of improving heat resistance and high load performance, the amount of the carbon black per 1 L of base material is generally 1 g or more, 5 g or more, preferably 10 g or more, 20 g or more, for example 25 g or more, and generally 100 g or less, 50 g or less, preferably 40 g or less, and from the viewpoint of achieving excellent NOx purification performance even under high load, the amount is more preferably 25 to 35 g.

[0060] In some embodiments, the alumina content C of the rear upper layer 22C Al is the alumina content A of the front upper layer 21A Al That is, A Al ≦C Al The alumina content C may be Al is the alumina content A of the front upper layer 21A Al Approximately the same as C Al ≒A Al (Manufacturing errors and the like are acceptable.) Alumina Content C Al is 0.5A Al ≦C Al ≦1.5A Al , preferably 0.8A Al ≦C Al ≦1.2A Al In some embodiments, the alumina content C Al is preferably 1.2A Al ≦C Al , more preferably 1.4A Al ≦C Al , for example, 1.5A Al ≦B Al ≦3A Al This can favorably improve the heat retention of the rear stage section 22, and can achieve a higher level of balance between warm-up performance and high load performance.

[0061] The rear upper layer 22C preferably contains an OSC material (for example, a ceria-zirconia composite oxide) as an optional component. This can suitably improve the heat retention of the rear section 22, and can more stably achieve excellent high-load performance. Although not particularly limited, the content C of the OSC material in the rear upper layer 22C is OSCThe content of the OSC material C is generally 1 to 100 g, preferably 5 to 70 g, more preferably 10 to 50 g, for example 15 to 35 g, per 1 L of the volume of the substrate. OSC From the viewpoint of more appropriately enhancing the OSC ability, the alumina content C Al Above (i.e., C Al ≦C OSC In some embodiments, the content C of the OSC material in the subsequent upper layer 22C may be OSC is the content A of the OSC material in the front upper layer 21A OSC For example, the absolute difference between the contents of the two may be within about 5 g, for example, within 2 g, or within 1 g.

[0062] Although not particularly limited, the coating amount C of the rear upper layer 22C coat From the viewpoint of improving heat resistance and balancing warm-up performance and high load performance, the amount of the filler per 1 L of base material volume is generally 30 g or more, preferably 40 g or more, and more preferably 50 g or more, and generally 100 g or less, preferably 80 g or less, and more preferably 70 g or less, for example 65 g or less.

[0063] In some embodiments, the coating amount C of the rear upper layer 22C coat is the coating amount A of the upper layer 21A of the first stage coat That is, A coat ≦C coat The coating amount C of the rear upper layer 22C may be coat is the coating amount A of the upper layer 21A of the first stage coat Approximately the same as C coat ≒A coat (Manufacturing errors and the like are acceptable.) Coating amount C coat is 0.5A coat ≦C coat ≦1.5A coat , preferably 0.8A coat ≦C coat ≦1.2A coat In some embodiments, the coating amount C coat is preferably 1.2A coat ≦C coat, more preferably 1.4A coat ≦C coat , for example, 1.5A coat ≦C coat ≦3A coat This can improve the heat retention of the rear stage section 22 and achieve a higher level of balance between the warm-up performance and the high load performance.

[0064] <Lower level> The rear lower layer 22D is a portion of the rear section 22 that comes into contact with the rib wall 14. Here, the rear lower layer 22D contains at least a precious metal catalyst and alumina. The rear lower layer 22D may further contain the optional components described above. When the rear upper layer 22C contains Rh as a precious metal catalyst, it is preferable that the rear lower layer 22D contains at least Pd. This makes it possible to achieve both warm-up performance and high load performance at a higher level.

[0065] Although not particularly limited, the supporting density of the precious metal catalyst (e.g., Pd) in the rear lower layer 22D is preferably 0.01 g or more, more preferably 0.05 g or more, and even more preferably 0.1 g or more, and preferably 3 g or less, more preferably 2 g or less, and even more preferably 1 g or less, per 1 L of the volume of the base material, from the viewpoint of improving the heat retention performance of the rear section 22 and improving the high load performance. In some embodiments, the supporting density of the precious metal catalyst (e.g., Pd) in the rear lower layer 22D is preferably larger than the supporting density of the precious metal catalyst (e.g., Rh) in the rear upper layer 22C, and is preferably approximately 2 times or more, for example 3 times or more, 5 times or more, and approximately 20 times or less, for example 10 times or less, of the supporting density in the rear upper layer 22C. This allows the warm-up performance and the high load performance to be balanced at a higher level.

[0066] Although not particularly limited, the alumina content D of the rear lower layer 22D is AlFrom the viewpoint of improving heat resistance and high load performance, the amount of the carbon black per 1 L of base material volume is approximately 1 g or more, preferably 3 g or more, and more preferably 5 g or more, for example 10 g or more or 20 g or more, and approximately 50 g or less, 40 g or less, and preferably 30 g or less, and from the viewpoint of achieving excellent NOx purification performance even under high load, the amount is preferably 20 to 30 g.

[0067] In some embodiments, the alumina content D of the rear lower layer 22D Al is the alumina content C of the rear upper layer 22C Al That is, C Al ≦D Al The alumina content D Al is the alumina content C of the rear upper layer 22C Al Approximately the same as C Al ≒D Al (Manufacturing errors and the like are acceptable.) Alumina Content D Al is 0.5C Al ≦D Al ≦1.5C Al , preferably 0.8C Al ≦D Al ≦1.2C Al In some embodiments, the alumina content D Al is preferably 1.2C Al ≦D Al , e.g., 1.3C Al ≦D Al ≦3C Al This can improve the heat resistance and durability of the rear stage portion 22, and can provide stable warm-up performance and high load performance for a long period of time. Al is the alumina content B of the front lower layer 21B Al That is, B Al ≦D Al This can improve the heat retention of the rear section 22.

[0068] The rear lower layer 22D preferably contains an OSC material (for example, a ceria-zirconia composite oxide) as an optional component. This can suitably improve the heat retention of the rear section 22, and can more stably achieve excellent high-load performance. Although not particularly limited, the content D of the OSC material in the rear lower layer 22D can be OSC The content D of the OSC material is generally 1 to 50 g, preferably 5 to 45 g, more preferably 10 to 40 g, for example 20 to 30 g, per 1 L of the volume of the substrate. OSC is the alumina content D Al The following (i.e., D OSC ≦D Al ) may also be used.

[0069] In some embodiments, the content D of the OSC material in the subsequent lower layer 22D OSC is the content C of the OSC material in the rear upper layer 22C OSC For example, the absolute difference between the contents of the two may be within about 5 g, for example, within 2 g, or within 1 g. In some embodiments, the content D of the OSC material in the rear lower layer 22D is OSC is the content C of the OSC material in the rear upper layer 22C OSC The following, namely, D OSC ≦C OSC Content D OSC is preferably D OSC ≦0.8C OSC , more preferably D OSC ≦0.7C OSC , for example, D OSC ≦0.6C OSC This makes it possible to achieve a higher level of balance between warm-up performance and high load performance.

[0070] Although not particularly limited, the coating amount D of the rear lower layer 22D coatFrom the viewpoint of improving heat resistance and balancing warm-up performance and high load performance, the amount of the filler per 1 L of base material volume is generally 30 g or more, preferably 40 g or more, more preferably 50 g or more, for example 60 g or more, and generally 200 g or less, preferably 150 g or less, more preferably 100 g or less, for example 80 g or less, 75 g or less.

[0071] In some embodiments, the coat amount D of the rear lower layer 22D coat is the coat amount C of the rear upper layer 22C coat That is, C coat ≦D coat The coating amount D coat is preferably D coat ≦1.1C coat , e.g., 1.2C coat ≦D coat ≦2C coat This can improve the durability and heat resistance of the rear stage portion 22, and can balance the warm-up performance and the high load performance at a higher level. coat is the coating amount B of the first lower layer 21B coat That is, B coat ≦D coat This can improve the heat retention of the rear section 22.

[0072] The catalyst coating layer 20 having the above-mentioned configuration can be manufactured, for example, by the following method. That is, first, the substrate 11 and a slurry for forming the catalyst coating layer 20 are prepared. A slurry is prepared for each layer to be formed. Here, four types of slurries are prepared, specifically, a slurry (for forming the front upper layer) for forming the front lower layer 21B, a slurry (for forming the front lower layer) for forming the rear upper layer 22C, and a slurry (for forming the rear lower layer) for forming the rear lower layer 22D. Each slurry contains a precious metal source (for example, a solution containing a precious metal ion) and alumina as essential raw material components, and may be prepared by dispersing other optional components, such as a binder and various additives, in a dispersion medium. For example, alumina sol, silica sol, etc. can be used as the binder. For example, water or an aqueous solvent can be used as the dispersion medium. The properties of the slurry, such as the viscosity and solid content, may be appropriately adjusted depending on, for example, the size and structure of the substrate 11, the properties required for the catalyst coating layer 20, and the like.

[0073] Next, the prepared slurry is made to flow into the cell 12 from the end of the substrate 11, and is supplied to a predetermined length along the cylinder axis direction X. Here, the slurry for forming the front lower layer and the slurry for forming the front upper layer are made to flow in this order from the inlet 10a. Also, the slurry for forming the rear upper layer and the slurry for forming the rear lower layer are made to flow in this order from the outlet 10b. Each time the slurry is supplied, the substrate 11 to which the slurry has been supplied may be fired at a predetermined temperature and time. The firing method may be the same as in the past. As a result, the raw material components are sintered, and the catalyst coating layer 20 including the front upper layer 21A, the front lower layer 21B, the rear upper layer 22C, and the rear lower layer 22D can be formed on the substrate 11.

[0074] Test examples relating to the present invention will be described below, but it is not intended that the present invention be limited to those shown in the following test examples.

[0075] Here, exhaust gas purification catalysts (Comparative Examples 1 and 2, Examples 1 to 5) having a catalyst coating layer as shown in FIG. 3 were produced. In this test example, the front section 21 has a front upper layer 21A and a front lower layer 21B. The rear section 22 has a rear upper layer 22C and a rear lower layer 22D. The ratio of the coating width L1 of the front section 21 to the coating width L2 of the rear section 22 is 50:50. Here, the coating amounts Y1 and Y2 were changed to confirm the effects on warm-up performance and NOx purification performance. In the following description, "L-cat" refers to the solid content per 1 L of the volume of the base material of the exhaust gas purification catalyst.

[0076] (Comparative Example 1) First, a cordierite honeycomb substrate (volume: 1.083 L, substrate total length L: 130 mm, number of cells: 600 cells, cell cross-sectional shape: square, partition wall thickness: 2 mil) was prepared. Then, four types of slurries (slurries 1 to 4) were wash-coated on the honeycomb substrate as follows to form a catalyst coating layer.

[0077] First, a Pd nitrate solution, alumina, ceria-zirconia composite oxide, and water were mixed to prepare a slurry 1 for forming the front lower layer. Next, the slurry 1 was poured into the cells from the upstream end of the honeycomb substrate, and a wash coat was applied to a portion corresponding to 50% of the total length of the honeycomb substrate from the upstream end toward the downstream side. The wash coat was performed so that the coating amount was 50 g / L-cat, and Pd was 2 g / L-cat, alumina was 25 g / L-cat, and ceria-zirconia composite oxide was 15 g / L-cat. Then, the mixture was dried at 250°C for 1 hour, and then fired at 500°C for 1 hour to form the front lower layer 21B.

[0078] First, a Pd nitrate solution, alumina, ceria-zirconia composite oxide, and water were mixed to prepare a slurry 2 for forming the rear lower layer. Next, the slurry 2 was poured into the cells from the downstream end of the honeycomb substrate, and a wash coat was applied to a portion corresponding to 50% of the total length of the honeycomb substrate from the downstream end toward the upstream side. The wash coat was performed so that the coating amount was 50 g / L-cat, and Pd was 0.5 g / L-cat, alumina was 25 g / L-cat, and ceria-zirconia composite oxide was 15 g / L-cat. Then, the mixture was dried at 250°C for 1 hour, and then fired at 500°C for 1 hour to form the rear lower layer 22D.

[0079] First, a slurry 3 for forming the front upper layer was prepared by mixing a Rh nitrate solution, alumina, a ceria-zirconia composite oxide, and water. Next, the slurry 3 was poured into the cells from the upstream end of the honeycomb substrate, and a wash coat was applied on the front lower layer 21B. The wash coat was performed so that the coating amount was 52 g / L-cat, and Rh was 0.1 g / L-cat, alumina was 25 g / L-cat, and ceria-zirconia composite oxide was 25 g / L-cat. Then, the mixture was dried at 250°C for 1 hour, and then fired at 500°C for 1 hour to form the front upper layer 21A.

[0080] First, a slurry 4 for forming the rear upper layer was prepared by mixing a Rh nitrate solution, alumina, a ceria-zirconia composite oxide, and water. Next, the slurry 4 was poured into the cells from the downstream end of the honeycomb substrate, and a wash coat was applied on the rear lower layer 22D. The wash coat was performed so that the coating amount was 52 g / L-cat, and Rh was 0.1 g / L-cat, alumina was 25 g / L-cat, and ceria-zirconia composite oxide was 25 g / L-cat. Then, the mixture was dried at 250°C for 1 hour, and then fired at 500°C for 1 hour to form the rear upper layer 22C.

[0081] Finally, the catalyst was dried at 120°C for 2 hours, and then calcined at 500°C for 2 hours to produce an exhaust gas purification catalyst (Comparative Example 1). In Comparative Example 1, the total coating amount (Y1) of the front stage portion 21 was 102 g / L-cat, and the total alumina content (X1) of the front stage portion 21 was 50 g / L-cat. The total coating amount (Y2) of the rear stage portion 22 was the same as that of the front stage portion 21, 102 g / L-cat, and the total alumina content (X2) of the rear stage portion 22 was the same as that of the front stage portion 21, 50 g / L-cat.

[0082] (Example 1) The washcoat of the slurry 1 for forming the front lower layer was performed so that the alumina content was 20 g / L-cat and the ceria-zirconia composite oxide content was 20 g / L-cat (i.e., the amount of the ceria-zirconia composite oxide was increased by the amount of the alumina reduced). The washcoat of the slurry 2 for forming the rear lower layer was performed. ,Ko An exhaust gas purification catalyst (Example 1) was produced in the same manner as in Comparative Example 1, except that the coating amount was increased to 60 g / L-cat (the coating amount was increased). In Example 1, the total alumina content (X1) of the front portion 21 was 45 g / L-cat. The total coating amount (Y2) of the rear portion 22 was 112 g / L-cat, and the total alumina content (X2) of the rear portion 22 was 50 g / L-cat.

[0083] (Example 2) Wash coat of slurry 2 for forming the rear lower layer, Contains 30g / L-cat alumina, and An exhaust gas purification catalyst (Example 2) was produced in the same manner as in Example 1, except that the coating amount was increased to 73 g / L-cat and the wash coating of the slurry 4 for forming the rear upper layer was performed to 62 g / L-cat (the coating amount was increased). In Example 2, the total coating amount (Y2) of the rear portion 22 was 135 g / L-cat, and the total alumina content (X2) of the rear portion 22 was 55 g / L-cat.

[0084] (Example 3) An exhaust gas purifying catalyst (Example 3) was produced in the same manner as in Comparative Example 1, except that the wash coating of the slurry 2 for forming the rear lower layer was performed so that the coating amount was 73 g / L-cat (the coating amount was increased). In Example 3, the total coating amount (Y2) of the rear portion 22 was 125 g / L-cat.

[0085] (Example 4) An exhaust gas purification catalyst (Example 4) was produced in the same manner as in Comparative Example 1, except that the wash coating of the slurry 1 for forming the front lower layer was carried out so that it contained 18 g / L-cat of alumina and had a coating amount of 40 g / L-cat (the coating amount was reduced), the wash coating of the slurry 3 for forming the front upper layer was carried out so that it contained 21 g / L-cat of alumina and had a coating amount of 44 g / L-cat (the coating amount was reduced), the wash coating of the slurry 2 for forming the rear lower layer was carried out so that it contained 24 g / L-cat of alumina and had a coating amount of 68 g / L-cat (the coating amount was increased), and the wash coating of the slurry 4 for forming the rear upper layer was carried out so that it contained 32 g / L-cat of alumina and had a coating amount of 57 g / L-cat (the coating amount was increased). In Example 4, the total coating amount (Y1) of the front stage 21 is 84 g / L-cat, and the total alumina content (X1) of the front stage 21 is 39 g / L-cat. The total coating amount (Y2) of the rear stage 22 is 125 g / L-cat, and the total alumina content (X2) of the rear stage 22 is 56 g / L-cat.

[0086] (Example 5) An exhaust gas purification catalyst (Example 5) was produced in the same manner as in Comparative Example 1, except that the wash coating of the slurry 1 for forming the front lower layer was carried out so that it contained 15 g / L-cat of alumina and had a coating amount of 35 g / L-cat (the coating amount was reduced), the wash coating of the slurry 3 for forming the front upper layer was carried out so that it contained 19 g / L-cat of alumina and had a coating amount of 39 g / L-cat (the coating amount was reduced), the wash coating of the slurry 2 for forming the rear lower layer was carried out so that it contained 29 g / L-cat of alumina and had a coating amount of 73 g / L-cat (the coating amount was increased), and the wash coating of the slurry 4 for forming the rear upper layer was carried out so that it contained 35 g / L-cat of alumina and had a coating amount of 62 g / L-cat (the coating amount was increased). In Example 5, the total coating amount (Y1) of the front stage 21 is 74 g / L-cat, and the total alumina content (X1) of the front stage 21 is 34 g / L-cat. The total coating amount (Y2) of the rear stage 22 is 135 g / L-cat, and the total alumina content (X2) of the rear stage 22 is 64 g / L-cat.

[0087] In this way, the exhaust gas purifying catalyst according to each example was prepared. Table 1 shows the coating amount Y1 of the front stage portion 21, the alumina content X1 of the front stage portion 21, the coating amount Y2 of the rear stage portion 22, and the alumina content X2 of the rear stage portion 22. The coating amount Y1 of the front stage portion 21 was obtained by the sum of the slurry 1 for forming the front stage lower layer and the slurry 3 for forming the front stage upper layer, and the coating amount Y2 of the rear stage portion 22 was obtained by the sum of the slurry 2 for forming the rear stage lower layer and the slurry 4 for forming the rear stage upper layer. The alumina content X1 of the front stage portion 21 and the alumina content X2 of the rear stage portion 22 were also obtained in the same manner. Then, the exhaust gas purifying catalyst of each example prepared above was evaluated as follows.

[0088] [Table 1]

[0089] <Durability test> Each example of the exhaust gas purification catalyst was attached to the exhaust system of a gasoline engine with a displacement of 4.6 L. The engine was then operated at an average engine speed of 3500 rpm and a durability test was carried out for 50 hours at an inlet gas temperature of 1000°C.

[0090] <Warm-up performance evaluation test - Warm-up (WU) performance> After the durability test, each example of the exhaust gas purification catalyst was attached to the exhaust system of a 2.5L gasoline engine. The inlet gas temperature to the exhaust gas purification catalyst was kept constant at 500°C, and the time (warm-up time, NOx-WU) until the NOx purification rate reached 50% was measured. The results are shown in Table 1 and Figure 4. Figure 4 shows the relationship between the ratio (Y2 / Y1) of the coating amount Y2 of the rear stage 22 to the coating amount Y1 of the front stage 21, and the warm-up time. The smaller the warm-up time value (lower in Figure 4), the better the warm-up performance.

[0091] As shown in Table 1 and Fig. 4, Examples 1 to 5, in which the alumina content ratio (X2 / X1) was 1.0 < (X2 / X1) and the coating amount ratio (Y2 / Y1) was 1.0 < (Y2 / Y1) < 2.0, had better warm-up performance than Comparative Example 1. The reason for this is considered to be that by making the ratio 1.0 < (Y2 / Y1), in other words, by making the coating amount of the front stage section 21 less than the coating amount of the rear stage section 22, the precious metal density of the front stage section 21 was increased, making it easier for the catalyst to warm up. In addition, although the detailed mechanism is unknown, a comparison between Comparative Example 1 and Example 3 suggests that the properties of the rear stage section 22 (e.g., the coating amount) also have some effect on the warm-up performance.

[0092] <High-load performance evaluation test> After the durability test, the exhaust gas purification catalyst of each example was attached to the exhaust system of a gasoline engine with a displacement of 2.5L. Then, the high load performance was evaluated using a catalyst evaluation device. Specifically, the exhaust gas purification catalyst of each example was installed in a catalyst evaluation device, and while supplying simulated exhaust gas with a theoretical air-fuel ratio (A / F) of 14.6 at an average engine speed of 2600 rpm, the inlet gas temperature was lowered from 500°C to room temperature (25°C), and the NOx purification rate at the time of temperature drop was measured. The NOx purification rate was measured from the ratio of the NOx concentrations in the inflow gas and the outflow gas at this time. Then, the temperature (NOx-T50) at which the NOx purification rate became 50% was obtained. The results are shown in Table 1 and FIG. 5. FIG. 5 shows the relationship between the ratio (Y2 / Y1) of the coating amount Y2 of the rear stage 22 to the coating amount Y1 of the front stage 21 and the NOx-T50 at the time of temperature drop.

[0093] 5, Examples 1 to 5 in which the alumina content ratio (X2 / X1) was 1.0≦(X2 / X1) and the coating amount ratio (Y2 / Y1) was 1.0<(Y2 / Y1)≦2.0 had superior high load performance compared to Comparative Example 1. The reasons for this are considered to be that (1) 1.0≦(X2 / X1) increased the heat capacity of the rear stage section 22 and improved the heat retention of the rear stage section 22; (2) 1.0<(Y2 / Y1) increased the precious metal density in the front stage section 21 and improved the catalytic reactivity in the front stage section 21; and (3) (Y2 / Y1) ≦2.0 suppressed sintering of the precious metal.

[0094] In particular, at least one, preferably two or more of the following: (1): 1.1≦(Y2 / Y1)≦1.8, especially 1.2≦(Y2 / Y1)≦1.5; (2): 70g / L≦Y1≦105g / L; (3): 110g / L≦Y2≦135g / L; (4): 1.0≦(X2 / X1)≦2.0; (5): X1≦50g / L, particularly 34g / L-cat≦X1≦45g / L-cat; (6): X2≦65g / L, particularly 50g / L-cat≦X2≦65g / L-cat; By satisfying these requirements, it was possible to achieve a higher level of balance between warm-up performance and high-load performance.

[0095] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples exemplified above. For example, it is possible to replace a part of the above-mentioned embodiment with another modified embodiment, and it is also possible to add another modified embodiment to the above-mentioned embodiment. Furthermore, if a technical feature is not described as essential, it is also possible to delete it as appropriate. [Explanation of symbols]

[0096] 10. Exhaust gas purification catalysts 11 Base material 20 Catalyst coating layer 21 Front section 21A Upper front stage 21B Lower front stage 22 Rear section 22C upper layer 22D Lower layer

Claims

1. An exhaust gas purifying catalyst that is disposed in an exhaust passage of an internal combustion engine and purifies exhaust gas discharged from the internal combustion engine, A substrate and a catalyst coating layer formed on the substrate, the catalyst coating layer including a precious metal catalyst and alumina, the catalyst coating layer has a front stage portion located on the upstream side in a flow direction of the exhaust gas, and a rear stage portion located on the downstream side of the front stage portion, The alumina content X1 (g / L) per volume of the substrate in the front stage portion is equal to or less than the alumina content X2 (g / L) per volume of the substrate in the rear stage portion, The alumina content X1 is 5 g / L or more and 100 g / L or less, The alumina content X2 is 5 g / L or more and 100 g / L or less, The ratio (Y2 / Y1) of the coating amount Y2 (g / L) per base material volume of the rear stage portion to the coating amount Y1 (g / L) per base material volume of the front stage portion is The following formula is satisfied: 1.0<(Y2 / Y1)≦2.0; The coating amount Y1 is 40 g / L or more and 200 g / L or less, The coating amount Y2 is 50 g / L or more and 200 g / L or less, The front section includes a front lower layer formed on a surface of the base material and a front upper layer formed on the front lower layer, The rear section includes a rear lower layer formed on a surface of the base material and a rear upper layer formed on the rear lower layer, The coating amount of the rear lower layer is greater than the coating amount of the front lower layer. Catalyst for purifying exhaust gas.

2. The ratio (X2 / X1) of the alumina content X2 to the alumina content X1 is The following formula is satisfied: 1.0≦(X2 / X1)≦2.0; The exhaust gas purifying catalyst according to claim 1.

3. The alumina content X1 is 20 g / L or more and 50 g / L or less. The exhaust gas purifying catalyst according to claim 1 or 2.

4. The coating amount Y2 is 100 g / L or more and 160 g / L or less. The exhaust gas purifying catalyst according to any one of claims 1 to 3.

5. The first upper layer contains rhodium. The exhaust gas purifying catalyst according to any one of claims 1 to 4.

6. The content of the alumina in the first upper layer is 5 g / L or more and 25 g / L or less. The exhaust gas purifying catalyst according to claim 5 .

7. the front upper layer and the rear upper layer contain rhodium; the front lower layer and the rear lower layer contain palladium; The exhaust gas purifying catalyst according to claim 5 or 6.

8. The coating amount of the first lower layer is 50 g / L or less, The coating amount of the rear lower layer is 60 g / L or more. The exhaust gas purifying catalyst according to any one of claims 1 to 7.

Images