Exhaust gas clarification equipment and method for manufacturing exhaust gas clarification equipment

Abstract

To provide exhaust gas clarification equipment that has high OSC, and can highly efficiently remove harmful components even after being exposed to high temperature environment, and a method for manufacturing the exhaust gas clarification equipment.SOLUTION: Exhaust gas clarification equipment comprises: base material having an upstream end and a downstream end; a first catalyst layer formed in a first area between the downstream end and a first position; and a second catalyst layer including second rhodium particles that are formed in a second area between the upstream end and a second position. The first catalyst layer includes a first rhodium-containing catalyst and a first cerium-containing oxide. An average of particle size distribution of the first rhodium particles included in the first rhodium-containing catalyst is 2 to 10 nm. An amount of rhodium, which is solidly dissolved in a first metal oxide carrier, based on a total weight of rhodium included in the first rhodium-containing catalyst is less than 17 wt%. A cerium content (g / L) of the first catalyst layer is one time or more of a cerium content (g / L) of the second catalyst layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an exhaust gas purification device and a method for manufacturing the exhaust gas purification device.

Background Art

[0002] Exhaust gas discharged from internal combustion engines used in vehicles such as automobiles contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Regulations on the emission amounts of these harmful components have been strengthened year by year, and noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are used as catalysts to remove these harmful components.

[0003] The exhaust gas purification device needs to purify NOx with high efficiency in both an oxygen-deficient atmosphere and an oxygen-excess atmosphere. Therefore, a material having the ability to absorb and release oxygen to mitigate atmospheric fluctuations, that is, an oxygen storage capacity (OSC), is used in the exhaust gas purification device.

[0004] Patent Document 1 describes an exhaust gas purification catalyst disposed in an exhaust pipe of an internal combustion engine for purifying exhaust gas discharged from the internal combustion engine. The exhaust gas purification catalyst includes a base material and a catalyst layer formed on the surface of the base material. The catalyst layer has a laminated structure of at least two layers. The first layer includes an upstream catalyst layer formed from the exhaust gas inflow side end of the exhaust gas purification catalyst toward the exhaust gas outflow side, and a downstream catalyst layer formed from the exhaust gas outflow side end of the exhaust gas purification catalyst toward the exhaust gas inflow side. The upstream catalyst layer and the downstream catalyst layer each contain at least Pd and / or Rh as a catalyst metal and an OSC material containing Ce. The second layer contains at least Pt as a catalyst metal and a NOx storage material. In the first layer, when the amount of CeO2 contained in the upstream catalyst layer is C1 and the amount of CeO2 contained in the downstream catalyst layer is C2, the relationship C1 < C2 is satisfied.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-134093 Summary of the Invention [Problem to be solved by the invention]

[0006] The NOx purification performance of the exhaust gas purification catalyst device described in Patent Document 1 tends to decrease in high-temperature environments. Therefore, the present disclosure provides an exhaust gas purification device that has a high OSC and can remove harmful components with high efficiency even after being exposed to a high-temperature environment, and a manufacturing method thereof. [Means for solving the problem]

[0007] Aspects of the present disclosure include the following. [Aspect 1] An exhaust gas purification device, a substrate having an upstream end into which exhaust gas flows and a downstream end from which the exhaust gas is discharged; a first catalyst layer formed in a first region between the downstream end and a first position spaced a first distance from the downstream end toward the upstream end, the first catalyst layer comprising a first rhodium-containing catalyst and a first cerium-containing oxide, the first rhodium-containing catalyst comprising a first metal oxide support and first rhodium particles supported on the first metal oxide support, the first rhodium particles having an average particle size distribution of 2 to 10 nm, and an amount of rhodium dissolved in the first metal oxide support being less than 17 wt % based on the total weight of rhodium contained in the first rhodium-containing catalyst; a second catalyst layer including second rhodium particles formed in a second region between the upstream end and a second position spaced a second distance from the upstream end toward the downstream end; Equipped with an exhaust gas purification device, wherein the cerium content of the first catalytic layer, based on the volume of the substrate in the first region, is at least one time the cerium content of the second catalytic layer, based on the volume of the substrate in the second region. [Aspect 2] 2. The exhaust gas purification device according to claim 1, wherein the amount of rhodium dissolved in the first metal oxide support is 3% by weight or less, based on the total weight of rhodium contained in the first rhodium-containing catalyst. [Aspect 3] 3. The exhaust gas purification device according to claim 1, wherein the cerium content of the first catalytic layer, based on the volume of the substrate in the first region, is 1 to 9 times the cerium content of the second catalytic layer, based on the volume of the substrate in the second region. [Aspect 4] The exhaust gas purification device according to any one of Aspects 1 to 3, wherein the second catalyst layer comprises a second rhodium-containing catalyst comprising a second metal oxide support and the second rhodium particles supported on the second metal oxide support. [Aspect 5] A method for manufacturing an exhaust gas purification device, (a) preparing a first rhodium-containing catalyst comprising a first metal oxide support and first rhodium particles supported on the first metal oxide support; (b) forming a first catalyst layer including the first rhodium-containing catalyst and a first cerium-containing oxide in a first region between a downstream end of a substrate and a first position spaced a first distance from the downstream end toward the upstream end; (c) forming a second catalyst layer including second rhodium particles in a second region of the substrate between the upstream end and a second position spaced a second distance from the upstream end toward the downstream end; Including, Preparing the first rhodium-containing catalyst comprises: (i) impregnating the first metal oxide support with a rhodium compound solution; (ii) drying the first metal oxide support impregnated with the rhodium compound solution to obtain a first rhodium-supported metal oxide; (iii) heating the first rhodium-supported metal oxide to a temperature in the range of 850 to 1000°C in an atmosphere containing carbon monoxide at a concentration of 0.01 to 5% by volume and the remainder being an inert gas, to obtain the first rhodium-containing catalyst; Including, a cerium content of the first catalytic layer, based on the volume of the substrate in the first region, is at least one time a cerium content of the second catalytic layer, based on the volume of the substrate in the second region. [Effects of the Invention]

[0008] The exhaust gas purification device of the present disclosure has a high OSC and can remove harmful components with high efficiency even after being exposed to a high-temperature environment. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an enlarged end view of a main part of an exhaust gas purification device according to an embodiment, cut along a plane parallel to the flow direction of exhaust gas, and schematically shows the configuration of the vicinity of the partition walls of the substrate. [Figure 2] FIG. 2 is a perspective view schematically illustrating an example of the substrate. [Figure 3] FIG. 3 is an enlarged end view of a main part of an exhaust gas purification device according to a modified embodiment, cut along a plane parallel to the flow direction of exhaust gas, and schematically shows the configuration of the vicinity of the partition walls of the substrate. [Figure 4] FIG. 4 is a graph showing Cmax of the exhaust gas purifying devices of the examples and comparative examples after aging at high temperatures. [Figure 5] FIG. 5 is a graph showing the NOx-T50 of the exhaust gas purification devices of the example and the comparative example after aging at high temperature. [Figure 6] FIG. 6 is a graph showing the relationship between the dissolved Rh content and NOx-T50 for Reference Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the drawings referred to in the following description, the same components or components having similar functions are designated by the same reference numerals, and repeated explanations may be omitted. For convenience of explanation, the dimensional ratios and shapes of each part in the drawings may be exaggerated and may differ from the actual dimensional ratios and shapes.

[0011] In this application, unless otherwise specified, numerical ranges expressed using the symbol "~" include the numerical values ​​written before and after the symbol "~" as the lower and upper limits, respectively. The upper and lower limits described in this application can be used alone or in any combination.

[0012] In this application, unless otherwise specified, "comprising" means that additional components or elements may be included, and includes "consisting essentially of" and "consisting of." "Consisting essentially of" means that additional components or elements may be included that do not have a substantial adverse effect. "Consisting of" means that the material or element is included only, but does not exclude the further inclusion of unavoidable impurities.

[0013] Furthermore, in this application, unless otherwise specified in the context, "on" encompasses both "directly on" and "indirectly on."

[0014] I. Exhaust gas purification equipment An exhaust gas purification device 100 according to an embodiment will be described with reference to Figures 1 and 2. The exhaust gas purification device 100 according to the embodiment includes a substrate 10, a first catalyst layer 20, a second catalyst layer 30, and a third catalyst layer 40.

[0015] (1) Base material 10 The substrate 10 is not particularly limited, and any substrate that can be used as a substrate for an exhaust gas purification device can be used. For example, as shown in FIG. 2, the substrate 10 may be composed of a frame 12 and partition walls 16 that divide the space surrounded by the frame 12 to define a plurality of cells 14. The frame 12 and the partition walls 16 may be integrally formed. The frame 12 may have any shape, such as a cylindrical, elliptical cylindrical, or polygonal cylindrical shape. The partition walls 16 extend between a first end (first end face) I and a second end (second end face) J of the substrate 10, and define a plurality of cells 14 extending between the first end I and the second end J. The cross-sectional shape of each cell 14 may be any shape, such as a square, parallelogram, rectangle, trapezoid, or other rectangular shape, a triangle, other polygonal shapes (e.g., hexagon, octagon), or a circle. Each of the plurality of cells 14 may be sealed at either the first end I or the second end J, or may be open at both the first end I and the second end J.

[0016] In the present application, the "volume of the substrate" means the total volume of the frame 12, the partition walls 16 and the cells 14, that is, the total volume of the frame 12 and the space surrounded by the frame 12.

[0017] Examples of materials for the substrate 10 include ceramics such as cordierite (2MgO·2Al2O3·5SiO2), aluminum titanate, silicon carbide, silica, alumina, and mullite, and metals such as stainless steel containing chromium and aluminum. These materials enable the exhaust gas purification device 100 to exhibit high exhaust gas purification performance even under high-temperature conditions. From the perspective of cost reduction, the substrate 10 may be made of cordierite.

[0018] 1 and 2, dashed arrows indicate the flow direction of exhaust gas in the exhaust gas purification device 100 and the substrate 10. Exhaust gas flows into the exhaust gas purification device 100 through the first end I and is discharged from the exhaust gas purification device 100 through the second end J. Therefore, hereinafter, the first end I will also be referred to as the upstream end I and the second end J as the downstream end J, as appropriate. In this specification, the length between the upstream end I and the downstream end J, i.e., the total length of the substrate 10, will be represented as Ls.

[0019] (2) First catalyst layer 20 The first catalyst layer 20 is disposed on the substrate 10 in a first region X between the downstream end J and a first position P separated by a first distance La from the downstream end J toward the upstream end I (i.e., in the direction opposite to the flow direction of the exhaust gas). The first distance La may be 40% to 65% of the entire length Ls of the substrate 10.

[0020] The first catalyst layer 20 includes a first Rh-containing catalyst. The first Rh-containing catalyst includes a first metal oxide support and first Rh particles supported on the first metal oxide support.

[0021] Examples of the first metal oxide support include an oxide of at least one metal selected from the group consisting of metals in Groups 3, 4, and 13 of the periodic table and lanthanoid metals. When the first metal oxide support contains two or more metal elements, the first metal oxide support may be a mixture of oxides of the two or more metal elements, a composite oxide containing the two or more metal elements, or a mixture of an oxide of at least one metal element and at least one composite oxide.

[0022] The first metal oxide support may be, for example, an oxide of at least one metal selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), lutetium (Lu), titanium (Ti), zirconium (Zr), and aluminum (Al), preferably an oxide of at least one metal selected from the group consisting of Y, La, Ce, Ti, Zr, and Al, more preferably an oxide of at least one metal selected from the group consisting of Al, Ce, and Zr. The first metal oxide support may be an oxide containing zirconia (ZrO) as a major component, a composite oxide containing zirconia and alumina (AlO) as major components (Al-Zr composite oxide), or a composite oxide containing zirconia, alumina, and ceria (CeO) as major components (Al-Ce-Zr composite oxide). Zirconia can have the function of maintaining the catalytic activity of the first Rh particles. Ceria can function as an oxygen storage material that absorbs oxygen in an oxygen-rich atmosphere and releases oxygen in an oxygen-deficient atmosphere. However, since the particle size of Rh particles on ceria is likely to increase in a high-temperature environment, the first metal oxide support preferably does not contain Ce. Alumina can have the function of suppressing the diffusion of the first Rh particles. The first metal oxide support contains at least one of alumina, ceria, and zirconia as a main component, and further contains yttria (YO), lanthana (LaO), neodymia (NdO), or praseodymia (PrO). 11 Yttria, lanthana, neodymia, and praseodymia improve the heat resistance of the composite oxide.

[0023] In this application, "containing as a main component" means that the content of the component is 50% by weight or more of the total weight, and when there are multiple main components, the total content of those components is 50% by weight or more. The content of a component described as a main component may be 70% by weight or more, 80% by weight or more, or 90% by weight or more of the total weight.

[0024] The first metal oxide support may be in the form of particles and may have any particle size depending on the purpose.

[0025] The first Rh particles supported on the first metal oxide support function as a catalyst for removing harmful components contained in exhaust gas, primarily for reducing NOx. The average particle size distribution of the first Rh particles may be within a range of 2 to 10 nm. Generally, the smaller the particle size of Rh particles, the larger the specific surface area and therefore the higher the catalytic performance. However, Rh particles with excessively small particle sizes tend to coarsen in high-temperature environments due to Ostwald ripening and aggregation, resulting in a deterioration of catalytic performance. When the average particle size distribution of the first Rh particles is 2 nm or more, the coarsening of the Rh particles in high-temperature environments is suppressed, and the deterioration of catalytic performance is suppressed. Furthermore, when the average particle size distribution of the first Rh particles is 10 nm or less, the specific surface area of ​​the first Rh particles is sufficiently large, allowing the first Rh particles to exhibit high catalytic performance. The average particle size distribution of the first Rh particles may be within a range of 3 to 6 nm or 4 to 6 nm.

[0026] The standard deviation of the particle size distribution of the first Rh particles may be 4 nm or less. When the standard deviation of the particle size distribution of the first Rh particles is 4 nm or less, the number of coarse particles and the number of fine particles that tend to coarsen in a high-temperature environment are reduced, allowing the first Rh particles to have a sufficiently large specific surface area even after being exposed to a high-temperature environment, and as a result, to exhibit high catalytic performance.

[0027] In the present application, the particle size distribution of the first Rh particles is a particle size distribution based on the number, which is obtained by measuring the projected area circle equivalent diameter of 50 or more first Rh particles based on images obtained by a transmission electron microscope (TEM).

[0028] The amount of the first Rh particles supported, i.e., the proportion of the first Rh particles based on the total weight of the first metal oxide support and the first Rh particles, may be within the range of 0.01 to 5 wt %. When the proportion of the first Rh particles is 0.01 wt % or more, a sufficient amount of the first Rh particles is present, making it possible to effectively remove harmful components in exhaust gas. When the proportion of the first Rh particles is 5 wt % or less, it is possible to reduce the amount of Rh used. Furthermore, because the first Rh particles are supported sufficiently sparsely on the first metal oxide support, coarsening of the first Rh particles in high-temperature environments is suppressed, and sufficient durability against high temperatures can be exhibited.

[0029] The content of the first Rh particles in the first catalyst layer 20 may be, for example, 0.05 to 5 g / L, 0.08 to 2 g / L, or 0.1 to 1 g / L based on the volume of the substrate in the first region X. This allows the exhaust gas purification device 100 to have sufficiently high exhaust gas purification performance.

[0030] The amount of Rh dissolved in the first metal oxide support may be less than 17% by weight, based on the total weight of Rh contained in the first Rh-containing catalyst. As a result, highly efficient removal of harmful components is possible even after the first Rh-containing catalyst is exposed to a high-temperature environment, as shown in the Reference Examples described below. The amount of Rh dissolved in the first metal oxide support may be 3% by weight or less, based on the total weight of Rh contained in the first Rh-containing catalyst. In this case, particularly highly efficient removal of harmful components is possible even after the first Rh-containing catalyst is exposed to a high-temperature environment, as shown in the Reference Examples described below.

[0031] The amount of Rh dissolved in the first metal oxide support, based on the total weight of Rh contained in the first Rh-containing catalyst, can be determined as follows. The X-ray absorption spectrum Sm(x) of a standard sample of pure Rh metal and the X-ray absorption spectrum Sox(x) of a standard sample of Rh2O3 are measured using an X-ray absorption fine structure (XAFS) measurement device. The first Rh-containing catalyst is placed in a hydrogen atmosphere at 400°C, and the X-ray absorption spectrum S(x) at the K-absorption edge of Rh is measured using the XAFS measurement device. The obtained X-ray absorption spectra Sm(x), Sox(x), and S(x) are used to calculate the following equation: S(x)=a·Sm(x)+b·Sox(x) The values ​​of a and b are determined by least-squares fitting using a and b as parameters. In a hydrogen atmosphere at 400°C, Rh present on the surface of the first metal oxide support (i.e., Rh not dissolved in the first metal oxide support) is reduced to a metallic (zero valent) state, while Rh dissolved in the first metal oxide support is not reduced and exists in an oxide (trivalent) state bonded to oxygen in the first metal oxide support. Therefore, the ratio of a to b determined by least-squares fitting corresponds to the ratio of the amount of Rh present on the surface of the first metal oxide support to the amount of Rh dissolved in the first metal oxide support in the first Rh-containing catalyst. Therefore, the amount of Rh dissolved in the first metal oxide support, based on the total weight of Rh contained in the first Rh-containing catalyst, can be determined by calculating b / (a+b).

[0032] The first catalyst layer 20 further includes a first Ce-containing oxide. The first Ce-containing oxide functions as an oxygen storage material. The first Ce-containing oxide may be ceria or a composite oxide containing ceria (e.g., a composite oxide containing ceria as a main component, a composite oxide containing ceria and zirconia as main components (Ce-Zr composite oxide), or a composite oxide containing alumina, ceria, and zirconia as main components (Al-Ce-Zr composite oxide)). Ce-Zr composite oxides are particularly preferred because they have high oxygen storage capacity and are relatively inexpensive. The Ce-Zr composite oxide may have a fluorite or pyrochlore crystal structure, or these may be used in combination. In the fluorite-type Ce-Zr composite oxide, Ce ions and Zr ions are arranged on a fluorite-type superlattice. In the pyrochlore-type CZ particles, Ce ions and Zr ions are arranged on a pyrochlore-type superlattice. The ceria-containing composite oxide may contain, in addition to the main component, at least one of lanthana, yttria, neodymia, and praseodymia as an additive, and these additives may form a composite oxide together with the main component. The oxygen storage material may be in a particulate form and may have any particle size depending on the purpose.

[0033] The Ce content (in terms of Ce atoms) in the first catalyst layer 20 may be, for example, more than 10 g / L and not more than 25 g / L, or 15 to 25 g / L, based on the volume of the substrate in the first region X. This allows the exhaust gas purification device 100 to have a high OSC.

[0034] The first catalyst layer 20 may further contain other optional components, such as a binder and an additive.

[0035] (3) Second catalyst layer 30 The second catalytic layer 30 is formed on the substrate 10 in a second region Y between the upstream end I and a second position Q separated by a second distance Lb from the upstream end I toward the downstream end J (i.e., in the exhaust gas flow direction). The second distance Lb may be 40 to 70% of the total length Ls of the substrate 10. The length Ls of the substrate, the first distance La, and the second distance Lb may satisfy the relationship Ls≦La+Lb≦1.2Ls. That is, the length of the region where the first catalytic layer 20 and the second catalytic layer 30 overlap may be 0% or more and 20% or less of the total length Ls of the substrate 10. This allows the exhaust gas purification device 100 to have a high OSC. In the region where the first catalytic layer 20 and the second catalytic layer 30 overlap, although the second catalytic layer 30 is formed on the first catalytic layer 20 in FIG. 1 , the first catalytic layer 20 may be formed on the second catalytic layer 30.

[0036] The second catalyst layer 30 includes second Rh particles. The second Rh particles may be supported on a second metal oxide support. That is, the second catalyst layer 30 may include a second Rh-containing catalyst including a second metal oxide support and second Rh particles supported on the second metal oxide support.

[0037] As the second metal oxide support, the materials usable as the first metal oxide support described above can be used.

[0038] The second Rh particles function as a catalyst for removing harmful components contained in exhaust gas, primarily for reducing NOx. As described below, the second catalytic layer 30 contains Ce, which promotes coarsening of Rh particles in high-temperature environments, in an amount equal to or less than the Ce content of the first catalytic layer 20. Therefore, the second Rh particles are less likely to coarsen than the first Rh particles. Therefore, the average particle size distribution of the second Rh particles is not particularly limited. From the viewpoint of ease of preparation, the average particle size distribution of the second Rh particles may be within a range of 0.1 to 1 nm. From the viewpoint of further suppressing coarsening of the second Rh particles in high-temperature environments, the average particle size distribution of the second Rh particles may be within a range of 2 to 10 nm. The standard deviation of the particle size distribution of the second Rh particles may be 4 nm or less, 1 nm or less, or 0.5 nm or less.

[0039] In the present application, the particle size distribution of the second Rh particles is a particle size distribution based on the number, which is obtained by measuring the projected area circle equivalent diameter of 50 or more second Rh particles based on images obtained by a transmission electron microscope (TEM).

[0040] The amount of the second Rh particles supported, i.e., the proportion of the second Rh particles based on the total weight of the second metal oxide support and the second Rh particles, may be in the range of 0.01 to 2 wt %. When the proportion of the second Rh particles is 0.01 wt % or more, a sufficient amount of the second Rh particles is present, making it possible to effectively remove harmful components in exhaust gas. When the proportion of the second Rh particles is 2 wt % or less, it is possible to reduce the amount of Rh used. Furthermore, because the second Rh particles are sufficiently sparsely supported on the second metal oxide support, coarsening of the second Rh particles in high-temperature environments is suppressed, and sufficient durability against high temperatures can be exhibited.

[0041] The content of the second Rh particles in the second catalyst layer 30 may be, for example, 0.05 to 5 g / L, 0.08 to 2 g / L, or 0.1 to 1 g / L based on the volume of the substrate in the second region Y. This allows the exhaust gas purification device 100 to have sufficiently high exhaust gas purification performance.

[0042] The amount of Rh dissolved in the second metal oxide support may be less than 17% by weight, or 3% by weight or less, based on the total weight of Rh contained in the second Rh-containing catalyst. The proportion of Rh dissolved in the second metal oxide support can be determined in the same manner as the proportion of Rh dissolved in the first metal oxide support described above.

[0043] The second catalyst layer 30 may optionally contain a second Ce-containing oxide. As the second Ce-containing oxide, the above-mentioned materials that can be used as the first Ce-containing oxide can be used.

[0044] The Ce content (in Ce atom equivalent) in the second catalytic layer 30 may be, for example, 0 to 20 g / L or 5 to 16 g / L, based on the volume of the substrate in the second region Y. Furthermore, the Ce content (in Ce atom equivalent) in the second catalytic layer 30 based on the volume of the substrate in the second region Y is not more than one time the Ce content (in Ce atom equivalent) in the first catalytic layer 20 based on the volume of the substrate in the first region X. In other words, the Ce content in the first catalytic layer 20 based on the volume of the substrate in the first region X is not less than one time the Ce content in the second catalytic layer 30 based on the volume of the substrate in the second region Y. By incorporating a higher concentration of oxygen storage material in the first catalytic layer 20, which is located downstream of the second catalytic layer 30 in the exhaust gas flow direction, the OSC of the exhaust gas purification device 100 is improved. The Ce content of the first catalytic layer 20 based on the volume of the substrate in the first region X may be 1 to 9 times, 2 to 9 times, or 4 to 9 times the Ce content of the second catalytic layer 30 based on the volume of the substrate in the second region Y.

[0045] The second catalyst layer 30 may further contain other optional components, such as a binder and an additive.

[0046] (4) Third catalyst layer 40 The third catalyst layer 40 is formed in the entire region between the upstream end I and the downstream end J, between the substrate 10 and the first catalyst layer 20 and between the substrate 10 and the second catalyst layer 30 .

[0047] The third catalyst layer 40 contains Pd particles. The Pd particles function as a catalyst for removing harmful components contained in exhaust gas, and mainly function as a catalyst for oxidizing HC.

[0048] The content of Pd particles in the third catalyst layer 40 may be, for example, 0.1 to 10 g / L, 1 to 5 g / L, or 1 to 3 g / L based on the total volume of the substrate, which allows the exhaust gas purification device 100 to have sufficiently high exhaust gas purification performance.

[0049] The third catalyst layer 40 may further contain other components such as a support for supporting the Pd particles, an oxygen storage material, a barium compound, and the like.

[0050] The Pd particles can be supported on a carrier, for example, a metal oxide carrier, by any method such as impregnation, adsorption, or water absorption.

[0051] As the metal oxide support, the materials usable as the first metal oxide support described above can be used.

[0052] As the oxygen storage material, the above-mentioned material that can be used as the first Ce-containing oxide can be used.

[0053] The barium compound can suppress the poisoning of Pd particles. Examples of the barium compound include barium sulfate, barium carbonate, barium oxide, and barium nitrate. The barium compound may be in a particulate form and may have any particle size depending on the purpose.

[0054] The third catalyst layer 40 may further contain other optional components, such as a binder and an additive.

[0055] The exhaust gas purification device according to the embodiment can be applied to various vehicles equipped with an internal combustion engine. The exhaust gas purification device according to the embodiment can be used as a start-up converter (S / C) disposed immediately below the internal combustion engine in the direction of exhaust gas flow, or as an underfloor converter (UF / C) disposed downstream of the S / C in the direction of exhaust gas flow.

[0056] II. Manufacturing method of exhaust gas purification device An example of a manufacturing method for the exhaust gas purification device 100 according to the above embodiment will be described. The manufacturing method for the exhaust gas purification device 100 includes preparing a first Rh-containing catalyst, preparing a second Rh-containing catalyst, forming a third catalyst layer 40 over the entire area of ​​the substrate 10, forming the first catalyst layer 20 in the first area X of the substrate 10, and forming a second catalyst layer 30 in the second area Y of the substrate 10. The first catalyst layer 20 and the second catalyst layer 30 may be formed in any order. Furthermore, preparing the second Rh-containing catalyst and forming the third catalyst layer 40 are not essential steps.

[0057] (a) First Preparation of Rh-Containing Catalyst The first Rh-containing catalyst can be prepared by the following steps: impregnating a first metal oxide support with a first Rh compound solution; drying the first metal oxide support impregnated with the first Rh compound solution to obtain a first Rh-supported metal oxide; and heating the first Rh-supported metal oxide to a temperature in the range of 850 to 1000°C in an atmosphere containing carbon monoxide (CO) at a concentration of 0.01 to 5% by volume, the remainder being an inert gas, to obtain the first Rh-containing catalyst.

[0058] Examples of the first Rh compound solution include an aqueous rhodium hydroxide solution and an aqueous rhodium nitrate solution. The impregnation method is not particularly limited. For example, the first metal oxide support can be impregnated with the first Rh compound solution by adding the first metal oxide support and the first Rh compound solution to stirred distilled water.

[0059] Next, the first metal oxide support impregnated with the first Rh compound solution is dried to obtain the first Rh-supported metal oxide, which may be calcined after drying, if necessary.

[0060] The first Rh-supported metal oxide is heated to a temperature in the range of 850 to 1000°C in an atmosphere containing carbon monoxide (CO) at a concentration of 0.01 to 5% by volume, the remainder being an inert gas, thereby obtaining a first Rh-containing catalyst containing the first metal oxide support and the first Rh particles supported on the first metal oxide support.

[0061] Examples of inert gases include nitrogen and argon. The heating time may be set appropriately, for example, for 1 to 30 hours. By heating in an atmosphere containing CO and an inert gas, it is possible to appropriately control the particle size distribution of the first Rh particles while preventing or reducing the dissolution of Rh into the first metal oxide support. For example, it is possible to control the average particle size distribution of the first Rh particles to within a range of 2 to 10 nm, 3 to 6 nm, or 4 to 6 nm, and the standard deviation of the particle size distribution of the first Rh particles to 4 nm or less.

[0062] Heating in an inert atmosphere such as a nitrogen atmosphere or an oxidizing atmosphere such as an air atmosphere induces solid solution of Rh in the first metal oxide support, resulting in a decrease in the first Rh particles on the surface of the first metal oxide support, making it difficult to exhibit high catalytic performance.

[0063] (b) Preparation of the second Rh-containing catalyst The second Rh-containing catalyst can be prepared by the following steps: impregnating a second metal oxide support with a second Rh compound solution, and drying the second metal oxide support impregnated with the second Rh compound solution. If necessary, calcination may be performed after drying. After drying and optional calcination, heating may be performed at a temperature in the range of 850 to 1000°C in an atmosphere containing CO at a concentration of 0.01 to 5% by volume, with the remainder being an inert gas, but this heating is not essential. That is, the second Rh-containing catalyst can be prepared in the same manner as the first Rh-containing catalyst, except that heating in an atmosphere consisting of CO and an inert gas is not essential.

[0064] (c) Formation of the third catalyst layer A third catalyst layer 40 containing Pd particles is formed on the entire surface of the substrate 10. The third catalyst layer 40 can be formed, for example, as follows. First, a slurry (third slurry) containing a Pd particle precursor is prepared. The Pd particle precursor can be an appropriate inorganic acid salt of Pd, such as hydrochloride, nitrate, phosphate, sulfate, borate, or hydrofluoride. Alternatively, the third slurry may contain a support powder on which Pd particles are pre-supported. The third slurry may further contain optional components such as an oxygen storage material, a binder, or an additive. The properties of the third slurry, such as viscosity and particle size of the solid components, may be adjusted as appropriate. The prepared third slurry is applied to the entire surface of the substrate 10. For example, the entire surface of the substrate 10 can be immersed in the third slurry, and after a predetermined time has elapsed, the substrate 10 is removed from the third slurry, thereby applying the third slurry to the entire surface of the substrate 10. Alternatively, the third slurry may be applied to the entire area of ​​the substrate 10 by pouring the third slurry into the substrate 10 from the upstream end I and then blowing air onto the upstream end I with a blower to spread the third slurry toward the downstream end J. Next, the third slurry is dried and fired at a predetermined temperature for a predetermined time. As a result, the third catalyst layer 40 is formed on the entire area of ​​the substrate 10.

[0065] (d) Formation of the first catalyst layer A first catalyst layer 20 containing a first Rh-containing catalyst and a first Ce-containing oxide is formed in a first region X of the substrate 10. The first catalyst layer 20 can be formed, for example, as follows. First, a first slurry containing a first Rh-containing catalyst and a first Ce-containing oxide is prepared. The first slurry may further contain optional components such as a binder and additives. The properties of the first slurry, such as viscosity and particle size of the solid components, may be adjusted as appropriate. The prepared first slurry is applied to the first region X of the substrate 10. For example, the first region X of the substrate 10 can be applied to the first region X of the substrate 10 by immersing the first region X of the substrate 10 in the first slurry and then lifting the substrate 10 from the first slurry after a predetermined time has elapsed. Alternatively, the first slurry may be applied to the first region X of the substrate 10 by pouring the first slurry into the downstream end J of the substrate 10 and blowing air at the downstream end J with a blower to spread the first slurry toward the upstream end I. Next, the first slurry is dried and fired at a predetermined temperature for a predetermined time, thereby forming a first catalyst layer 20 on the first region X of the substrate 10.

[0066] (e) Formation of the second catalyst layer A second catalyst layer 30 containing second Rh particles is formed on the second region Y of the substrate 10. The second catalyst layer 30 can be formed, for example, as follows. First, a second slurry containing a second Rh-containing catalyst or an Rh particle precursor is prepared. The Rh particle precursor may be an appropriate inorganic salt of Rh, such as hydrochloride, nitrate, phosphate, sulfate, borate, or hydrofluoride. The second slurry may further contain optional components such as an oxygen storage material, a binder, or an additive. The properties of the second slurry, such as viscosity and particle size of the solid components, may be adjusted as appropriate. The prepared second slurry is applied to the second region Y of the substrate 10. For example, the second region Y of the substrate 10 may be immersed in the second slurry, and after a predetermined time has elapsed, the substrate 10 is pulled out of the second slurry, thereby applying the second slurry to the second region Y of the substrate 10. Alternatively, the second slurry may be applied to the second region Y of the substrate 10 by pouring the second slurry into the substrate 10 from the upstream end I and then blowing air onto the upstream end I with a blower to spread the second slurry toward the downstream end J. Next, the second slurry is dried and fired at a predetermined temperature for a predetermined time. As a result, the second catalyst layer 30 is formed in the second region Y of the substrate 10.

[0067] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments, and various design modifications can be made without departing from the technical scope of the claims. For example, the exhaust gas purification device does not need to include the third catalyst layer 40 described above. In other words, an exhaust gas purification device 200 that does not include the third catalyst layer 40, as shown in FIG. 3, is also included in the technical scope of the present disclosure. [Example]

[0068] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0069] (1) Materials used in the examples and comparative examples a) Base material (honeycomb base material) Material: Cordierite Volume: 875cc Length: 10.5cm Wall thickness: 2 mil (50.8 μm) Cell density: 600 cells per square inch Cell cross-sectional shape: hexagonal

[0070] b)AZ particles The AZ particles were composite oxide particles containing Al2O3 and ZrO2 as the main components, and further containing La2O3 and Y2O3. The weight fractions of each component in the AZ particles were Al2O3: 30 wt%, ZrO2: 60 wt%, La2O3: 5 wt%, and Y2O3: 5 wt%.

[0071] c)Al2O3 particles The Al2O3 particles were composite oxide particles containing Al2O3 as the main component and La2O3 as well. The weight fractions of the components in the Al2O3 particles were Al2O3: 99 wt % and La2O3: 1 wt %.

[0072] d) ACZ particles The ACZ particles were composite oxide particles containing Al2O3, CeO2, and ZrO2 as the main components, as well as La2O3 and Y2O3. The weight fractions of each component in the ACZ particles were 30 wt% Al2O3, 20 wt% CeO2, 40 wt% ZrO2, 5 wt% La2O3, and 5 wt% Y2O3.

[0073] e) Fluorite type ZC particles The fluorite-type ZC particles were composite oxide particles containing CeO2 and ZrO2 as the main components, as well as La2O3 and Y2O3. The weight fractions of each component in the fluorite-type ZC particles were CeO2: 20 wt%, ZrO2: 70 wt%, La2O3: 5 wt%, and Y2O3: 5 wt%.

[0074] f) Pyrochlore-type CZ particles Pyrochlore-type CZ particles contain CeO2 and ZrO2 as the main components, and also contain Pr6O 11 The weight fractions of the components in the pyrochlore-type CZ particles were CeO2: 51.7 wt%, ZrO2: 46.6 wt%, PrO 11 : 1.7% by weight.

[0075] g) Rhodium nitrate aqueous solution

[0076] h) Aqueous rhodium hydroxide solution

[0077] i) Palladium nitrate aqueous solution

[0078] j) Barium sulfate particles

[0079] (2) Fabrication of exhaust gas purification device Examples 1 to 3 a) Preparation of the first Rh-containing catalyst The AZ particles and the rhodium nitrate aqueous solution were added sequentially to stirred distilled water. The resulting mixture was dried and calcined in an electric furnace in an air atmosphere at 500°C for 2 hours. This yielded a first Rh-supported metal oxide. The first Rh-supported metal oxide was then heated at 950°C for 20 hours in an atmosphere containing 1% by volume of CO and the remainder N. This yielded a first Rh-containing catalyst.

[0080] The first Rh-containing catalyst was observed with a transmission electron microscope (TEM) to determine the particle size distribution (initial particle size distribution) of the Rh particles (first Rh particles) supported on the AZ particles. The average and standard deviation of the initial particle size distribution of the first Rh particles are shown in Table 1.

[0081] The proportion of Rh dissolved in the AZ particles based on the total weight of Rh contained in the first Rh-containing catalyst was determined by measuring the X-ray absorption spectrum at the K absorption edge of Rh using an XAFS measurement device. The results are shown in Table 1.

[0082] b) Preparation of the second Rh-containing catalyst The AZ particles and the rhodium nitrate aqueous solution were added in that order to the distilled water under stirring. The resulting mixture was dried and calcined in an electric furnace in an air atmosphere at 500°C for 2 hours. This produced a second Rh-containing catalyst containing AZ particles and Rh particles supported on the AZ particles.

[0083] c) Preparation of the slurry A first Rh-containing catalyst, Al2O3 particles, fluorite-type ZC particles, pyrochlore-type CZ particles, and an Al2O3-based binder were added to stirred distilled water to prepare a first suspended slurry. A second Rh-containing catalyst, Al2O3 particles, fluorite-type ZC particles, pyrochlore-type CZ particles, and an Al2O3-based binder were added to stirred distilled water to prepare a second suspended slurry. A third suspended slurry was prepared by adding Al2O3 particles, ACZ particles, a palladium nitrate aqueous solution, barium sulfate particles, and an Al2O3-based binder to stirred distilled water.

[0084] d) Formation of the third catalyst layer The third slurry was poured into the substrate from the upstream end, and excess third slurry was blown away with a blower. This coated the partition walls of the substrate over the entire area between the upstream and downstream ends of the substrate, forming a third slurry layer. The substrate was placed in a dryer with an internal temperature maintained at 120°C for 2 hours to evaporate the water in the third slurry layer. The substrate was then calcined in an electric furnace in an air atmosphere at 500°C for 2 hours. This formed a third catalyst layer.

[0085] The contents of Al2O3 particles, ACZ particles, Pd particles derived from the aqueous palladium nitrate solution, and barium sulfate particles in the third catalytic layer were 10 g / L, 15 g / L, 2 g / L, and 5 g / L, respectively, based on the total volume of the substrate.

[0086] e) Formation of the first catalyst layer The first slurry was poured into the downstream end of the substrate, and excess first slurry was blown away with a blower. This coated the third catalyst layer with the first slurry in a first region between the downstream end of the substrate and a first position spaced 50% of the substrate's overall length from the downstream end toward the upstream end, forming a first slurry layer. The substrate was placed in a dryer with an internal temperature maintained at 120°C for two hours to evaporate water from the first slurry layer. The substrate was then calcined in an electric furnace in an air atmosphere at 500°C for two hours, forming a first catalyst layer.

[0087] The contents of Rh, AZ particles, Al2O3 particles, fluorite-type ZC particles, and pyrochlore-type CZ particles in the first catalyst layer were as shown in Table 1. The contents of each material shown in Table 1 are based on the volume of the substrate in the first region.

[0088] f) Formation of the second catalyst layer The second slurry was poured into the substrate from the upstream end, and excess second slurry was blown away with a blower. This resulted in a third catalyst layer being coated with the second slurry in a second region between the upstream end of the substrate and a second position spaced 50% of the substrate's overall length from the upstream end toward the downstream end of the substrate, forming a second slurry layer. The substrate was placed in a dryer with an internal temperature maintained at 120°C for two hours to evaporate the water in the second slurry layer. The substrate was then calcined in an electric furnace in an air atmosphere at 500°C for two hours, thereby forming a second catalyst layer.

[0089] The contents of Rh, AZ particles, Al2O3 particles, fluorite-type ZC particles, and pyrochlore-type CZ particles in the second catalyst layer were as shown in Table 1. The contents of each material shown in Table 1 are based on the volume of the substrate in the second region.

[0090] In this way, the exhaust gas purification devices of Examples 1 to 3 were obtained. The ratios (Ce content ratios) of the Ce content of the first catalytic layer based on the volume of the substrate in the first region to the Ce content of the second catalytic layer based on the volume of the substrate in the second region were as shown in Table 1.

[0091] Comparative Example 1 The exhaust gas purification device of Comparative Example 1 was obtained in the same manner as in Example 1, except that the contents of Rh, AZ particles, Al2O3 particles, fluorite-type ZC particles, and pyrochlore-type CZ particles in the first catalytic layer, and the contents of Rh, AZ particles, Al2O3 particles, fluorite-type ZC particles, and pyrochlore-type CZ particles in the second catalytic layer were as shown in Table 1.

[0092] Example 4 An exhaust gas purification device of Example 4 was obtained in the same manner as in Example 2, except that the second Rh-containing catalyst was prepared as follows.

[0093] Preparation of a second Rh-containing catalyst The AZ particles and the rhodium nitrate aqueous solution were added sequentially to stirred distilled water. The resulting mixture was dried and calcined in an electric furnace in an air atmosphere at 500°C for 2 hours. This yielded a second Rh-supported metal oxide. The second Rh-supported metal oxide was then heated at 950°C for 20 hours in an atmosphere containing 1% by volume of CO and the remainder N. This yielded a second Rh-containing catalyst.

[0094] Comparative Examples 2 to 5 Exhaust gas purification devices of Comparative Examples 2 to 5 were obtained in the same manner as in Examples 1 to 3 and Comparative Example 1, respectively, except that the first Rh-containing catalyst was prepared as follows.

[0095] First, preparation of Rh-containing catalysts The AZ particles and the rhodium hydroxide aqueous solution were added sequentially to stirred distilled water. The resulting mixture was dried and calcined in an electric furnace by heating at 500°C for 2 hours in an air atmosphere. This yielded a first Rh-supported metal oxide. The first Rh-supported metal oxide was then heated at 850°C for 5 hours in a nitrogen atmosphere. This yielded a first Rh-containing catalyst.

[0096] The first Rh-containing catalyst was observed with a transmission electron microscope (TEM) to determine the particle size distribution (initial particle size distribution) of the Rh particles (first Rh particles) supported on the AZ particles. The average and standard deviation of the initial particle size distribution of the first Rh particles are shown in Table 1.

[0097] The proportion of Rh dissolved in the AZ particles based on the total weight of Rh contained in the first Rh-containing catalyst was determined in the same manner as in Examples 1 to 3. The results are shown in Table 1.

[0098] Comparative Example 6 An exhaust gas purification device of Comparative Example 6 was obtained in the same manner as in Comparative Example 3, except that the second Rh-containing catalyst was prepared as follows.

[0099] Preparation of a second Rh-containing catalyst The AZ particles and the rhodium hydroxide aqueous solution were added sequentially to stirred distilled water. The resulting mixture was dried and calcined in an electric furnace by heating at 500°C for 2 hours in an air atmosphere. This yielded a second Rh-supported metal oxide. The second Rh-supported metal oxide was then heated at 850°C for 5 hours in a nitrogen atmosphere. This yielded a second Rh-containing catalyst.

[0100] Comparative Example 7 An exhaust gas purification device of Comparative Example 7 was obtained in the same manner as in Example 3, except that the first Rh-containing catalyst was prepared as follows.

[0101] First, preparation of Rh-containing catalysts The AZ particles and the rhodium nitrate aqueous solution were added in that order to the distilled water under stirring. The resulting mixture was dried and calcined in an electric furnace in an air atmosphere at 500°C for 2 hours. This produced a first Rh-containing catalyst containing AZ particles and Rh particles supported on the AZ particles.

[0102] The first Rh-containing catalyst was observed with a transmission electron microscope (TEM) to determine the particle size distribution (initial particle size distribution) of the Rh particles (first Rh particles) supported on the AZ particles. The average and standard deviation of the initial particle size distribution of the first Rh particles are shown in Table 1.

[0103] The proportion of Rh dissolved in the AZ particles based on the total weight of Rh contained in the first Rh-containing catalyst was determined in the same manner as in Examples 1 to 3. The results are shown in Table 1.

[0104] (3) Aging treatment Each exhaust gas purification device was connected to the exhaust system of a V8 engine, and a stoichiometric (air-fuel ratio A / F = 14.6) and oxygen-rich (lean: A / F > 14.6) mixture was repeatedly flowed into the engine, alternating at a fixed time ratio of 3:1, while the bed temperature of the exhaust gas purification device was maintained at 950°C for 50 hours. This aging treatment was performed on the exhaust gas purification device.

[0105] (4) OSC evaluation The aged exhaust gas purification device was connected to the exhaust system of an L-type four-cylinder engine, and an air-fuel mixture with an air-fuel ratio A / F of 14.1 and an air-fuel mixture with an air-fuel ratio A / F of 15.1 were alternately supplied to the engine. Exhaust gas at a temperature of 600°C was introduced into the exhaust gas purification device. The oxygen surplus or deficiency was calculated from the difference between the stoichiometric point and the A / F sensor output using the formula 0.23 x ΔA / F x injected fuel amount, and the maximum oxygen storage capacity (Cmax) was determined. The results are shown in Table 1 and Figure 4. Cmax was large when the Ce content ratio was 1 or higher. In other words, OSC was high when the Ce content ratio was 1 or higher.

[0106] (5) NOx purification performance evaluation The aged exhaust gas purification device was connected to the exhaust system of an L-type four-cylinder engine, and an air-fuel mixture with an air-fuel ratio A / F of 14.4 was supplied to the engine at an air flow rate of 30 g / s. The bed temperature of the exhaust gas purification device was increased from 200°C to 500°C at a rate of 20°C / min, and the bed temperature at which 50% of the NOx in the gas was removed (hereinafter referred to as "NOx-T50") was measured. The results are shown in Table 1 and Figure 5.

[0107] The exhaust gas purification devices using the first Rh-containing catalyst prepared by heat treatment in a CO2-containing atmosphere (Examples 1 to 4 and Comparative Example 1) exhibited lower NOx-T50 values ​​than the exhaust gas purification devices using the first Rh-containing catalyst prepared by heat treatment in a nitrogen atmosphere (Comparative Examples 2 to 6) and the exhaust gas purification device using the first Rh-containing catalyst prepared without heat treatment (Comparative Example 7). This indicates that the first Rh-containing catalyst prepared by heat treatment in a CO2-containing atmosphere improved NOx reduction performance. In the first Rh-containing catalyst that underwent heat treatment in a CO2-containing atmosphere, the average particle size distribution of the initial Rh particles was as large as 4.68 to 5.75 nm. This is thought to have suppressed coarsening of the Rh particles during the aging treatment and suppressed a decrease in the specific surface area of ​​the Rh particles, resulting in high NOx reduction performance. In the first Rh-containing catalyst that was not heat-treated, the average particle size distribution of the Rh particles was as small as 0.7 nm, and therefore the Rh particles coarsened during the aging treatment, reducing their specific surface area, which is thought to have resulted in reduced NOx reduction performance.In the first Rh-containing catalyst that was heat-treated in a nitrogen atmosphere, more than 17.1 wt% of the Rh contained in the first Rh-containing catalyst was solid-dissolved in the AZ particles, which is thought to have resulted in reduced NOx reduction performance.

[0108] The exhaust gas purification device of Example 4, which used the second Rh-containing catalyst prepared by heat treatment in a CO-containing atmosphere, exhibited a lower NOx-T50 than the exhaust gas purification device of Example 2, which used the second Rh-containing catalyst prepared without heat treatment. This demonstrates that the second Rh-containing catalyst prepared by heat treatment in a CO-containing atmosphere improved the NOx reduction performance. However, the improvement in NOx reduction performance achieved by the first Rh-containing catalyst prepared by heat treatment in a CO-containing atmosphere was far greater than the improvement in NOx reduction performance achieved by the second Rh-containing catalyst prepared by heat treatment in a CO-containing atmosphere. This demonstrates that preparing the first Rh-containing catalyst by heat treatment in a CO-containing atmosphere is particularly useful.

[0109] [Table 1]

[0110] Reference examples 1~6 In Reference Examples 1 to 6, experiments were carried out to examine the effect of the proportion of Rh dissolved in the AZ particles on the NOx reduction performance.

[0111] (1) Preparation of exhaust gas purification materials As a metal oxide support, composite oxide particles containing Al2O3 and ZrO2 as main components, and further containing La2O3, Y2O3, and Nd2O3 (hereinafter referred to as "AZ particles" where appropriate. The weight fractions of each component in the AZ particles were Al2O3: 30 wt%, ZrO2: 60 wt%, La2O3: 4 wt%, Y2O3: 4 wt%, and Nd2O3: 2 wt%) were prepared.

[0112] 6 g of AZ particles and 4 g of a rhodium hydroxide aqueous solution (Rh concentration 1 wt%) were added to the stirred distilled water in that order and stirred for 10 minutes. The resulting mixture was dried and calcined in an electric furnace in an air atmosphere at 500°C for 2 hours. This yielded Rh-supported metal oxide a.

[0113] The Rh-supported metal oxide a was heated at 850° C. for 5 hours in an atmosphere containing CO at a concentration of 1% by volume and the remainder being N2, thereby obtaining an exhaust gas purification material a.

[0114] 6 g of AZ particles and 1.45 g of a rhodium nitrate aqueous solution (Rh concentration 2.75 wt%) were added to the stirred distilled water in that order and stirred for 10 minutes. The resulting mixture was dried and calcined in an electric furnace in an air atmosphere at 500°C for 2 hours. This yielded Rh-supported metal oxide b.

[0115] The Rh-supported metal oxide b was heated in an air atmosphere at 1000° C. for 5 hours, thereby obtaining an exhaust gas purifying material b.

[0116] An exhaust gas purifying material was obtained by mixing exhaust gas purifying material a and exhaust gas purifying material b in the amounts shown in Table 2. The proportion of Rh dissolved in the AZ particles based on the total weight of Rh contained in the exhaust gas purifying material was determined by measuring the X-ray absorption spectrum at the K absorption edge of Rh using an XAFS measurement device. The results are shown in Table 2.

[0117] (2) Preparation of pellets for evaluating exhaust gas purification performance 6g of exhaust gas purification material and CeO2 and ZrO2 as main components, and Pr6O 11 Composite oxide particles containing CeO2 (hereinafter referred to as "CZ particles" in the Reference Examples as appropriate). The weight fractions of the components in the CZ particles are CeO2: 51.4 wt%, ZrO2: 45.6 wt%, PrO 11 4 g of ACZ particles (3.0 wt%) and 10 g of composite oxide particles (hereinafter referred to as "ACZ particles" as appropriate in the Reference Examples) containing Al2O3, CeO2, and ZrO2 as main components, and further containing La2O3, Y2O3, and Nd2O3, respectively, were added. Hydroxyethyl cellulose (HEC) and citric acid were added to adjust the viscosity, and the mixture was stirred for 6 hours to obtain a slurry. The slurry was fired in an electric furnace in an air atmosphere at 500°C for 2 hours. The fired product was crushed to a predetermined size to obtain pellets.

[0118] (3) Pellets aging treatment The pellets were heated to 1000°C and exposed to alternate fuel-rich (rich, air-fuel ratio A / F<14.6) and oxygen-rich (lean, A / F>14.6) mixtures every 5 minutes for 5 hours.

[0119] (4) Evaluation of exhaust gas purification performance after aging treatment After the aging treatment, a gas having the composition shown in Table 3 was passed through the pellet at a flow rate of 15 L / min. The pellet was heated to 600°C, maintained at this temperature for 5 minutes, and then cooled to 150°C. Then, while continuing to pass the gas, the pellet was heated to 600°C at a rate of 20°C / min, and the temperature of the pellet when 50% of the NOx in the gas was removed (hereinafter referred to as "NOx-T50") was measured. The results are shown in Table 2.

[0120] [Table 2]

[0121] [Table 3]

[0122] The relationship between the solute Rh fraction and NOx-T50 is shown in Figure 6. Figure 6 shows that the smaller the solute Rh fraction, the lower the NOx-T50 (i.e., the higher the NOx reduction performance). When the solute Rh fraction was less than 17 wt%, high NOx reduction performance was achieved. When the solute Rh fraction was 3 wt% or less, particularly high NOx reduction performance was achieved.

Claims

1. An exhaust gas purification device, a substrate having an upstream end into which exhaust gas flows and a downstream end from which the exhaust gas is discharged; a first catalytic layer formed in a first region between the downstream end and a first position spaced a first distance from the downstream end toward the upstream end, the first catalytic layer comprising a first rhodium-containing catalyst and a first cerium-containing oxide, the first rhodium-containing catalyst comprising a first metal oxide support and first rhodium particles supported on the first metal oxide support, the first rhodium particles having an average particle size distribution of 2 to 10 nm, and an amount of rhodium dissolved in the first metal oxide support being less than 17 wt % based on the total weight of rhodium contained in the first rhodium-containing catalyst; a second catalyst layer including second rhodium particles formed in a second region between the upstream end and a second position spaced a second distance from the upstream end toward the downstream end; Equipped with an exhaust gas purification device, wherein a cerium content of the first catalytic layer, based on the volume of the substrate in the first region, is at least one time a cerium content of the second catalytic layer, based on the volume of the substrate in the second region.

2. 2. The exhaust gas purification device according to claim 1, wherein the amount of rhodium dissolved in the first metal oxide support is 3% by weight or less, based on the total weight of rhodium contained in the first rhodium-containing catalyst.

3. 2. The exhaust gas purification device according to claim 1, wherein a cerium content of the first catalytic layer, based on a volume of the substrate in the first region, is 1 to 9 times a cerium content of the second catalytic layer, based on a volume of the substrate in the second region.

4. 2. The exhaust gas purification device according to claim 1, wherein the second catalyst layer comprises a second rhodium-containing catalyst comprising a second metal oxide support and the second rhodium particles supported on the second metal oxide support.

5. A method for manufacturing an exhaust gas purification device, (a) preparing a first rhodium-containing catalyst comprising a first metal oxide support and first rhodium particles supported on the first metal oxide support; (b) forming a first catalyst layer including the first rhodium-containing catalyst and a first cerium-containing oxide in a first region between a downstream end of a substrate and a first position spaced a first distance from the downstream end toward the upstream end; (c) forming a second catalyst layer including second rhodium particles in a second region of the substrate between the upstream end and a second position spaced a second distance from the upstream end toward the downstream end; Including, Preparing the first rhodium-containing catalyst comprises: (i) impregnating the first metal oxide support with a rhodium compound solution; (ii) drying the first metal oxide support impregnated with the rhodium compound solution to obtain a first rhodium-supported metal oxide; (iii) heating the first rhodium-supported metal oxide to a temperature in the range of 850 to 1000°C in an atmosphere containing carbon monoxide at a concentration of 0.01 to 5% by volume and the remainder being an inert gas, to obtain the first rhodium-containing catalyst; Including, a cerium content of the first catalytic layer, based on the volume of the substrate in the first region, is at least one time a cerium content of the second catalytic layer, based on the volume of the substrate in the second region.

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