Exhaust gas purification device and method for manufacturing exhaust gas purification device

Abstract

An exhaust gas purification device is provided, which exhibits high OSC performance and can efficiently remove NOx even after exposure to high-temperature environments. The exhaust gas purification device comprises a substrate, a first catalyst layer, and a second catalyst layer. The substrate has an upstream end and a downstream end. The first catalyst layer is formed in a first region between the downstream end and a first position and contains a first rhodium-containing catalyst and a first cerium-containing oxide. The second catalyst layer is formed in a second region between the upstream end and a second position and contains a second rhodium-containing catalyst. The average particle size distribution of the first rhodium particles contained in the first rhodium-containing catalyst is 1.5–18 nm. The cerium content of the first catalyst layer, based on the volume of the substrate in the first region, is greater than the cerium content of the second catalyst layer, based on the volume of the substrate in the second region.

Description

Technical Field

[0001] This invention relates to an exhaust gas purification device and a method for manufacturing the exhaust gas purification device. Background Technology

[0002] Exhaust gases from internal combustion engines used in automobiles and other vehicles contain harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Restrictions on the emission of these harmful components are being strengthened year by year. To remove these harmful components, precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are used as catalysts.

[0003] On the other hand, from the perspective of resource risk, it is necessary to reduce the amount of precious metals used. In exhaust gas purification devices, one known method for reducing the amount of precious metals used is to support precious metals as fine particles on a carrier. For example, Patent Document 1 discloses a method for manufacturing an exhaust gas purification material, which includes: a step of preparing a precious metal-supported catalyst by supporting precious metal particles on an oxide carrier; and a step of heating the precious metal-supported catalyst in a reducing atmosphere to control the particle size of the precious metals within a predetermined range.

[0004] Furthermore, Patent Document 2 discloses an exhaust gas purification catalyst device capable of efficiently purifying NOx under both oxygen-deficient and oxygen-excess atmospheres. The exhaust gas purification catalyst device disclosed in Patent Document 2 comprises a substrate, a front catalyst coating, and a rear catalyst coating on the substrate. The front catalyst coating contains a catalyst noble metal and inorganic oxide particles that substantially do not contain OSC (Oxygen Storage Capacity) materials. The rear catalyst coating contains a catalyst noble metal and inorganic oxide particles containing OSC materials. Furthermore, the catalyst noble metal contained in both the front and rear catalyst coatings contains Rh and substantially does not contain any catalyst noble metals other than Rh.

[0005] Existing technical documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-147256

[0007] Patent Document 2: Japanese Patent Application Publication No. 2021-126636 Summary of the Invention

[0008] According to the inventor's careful research, the exhaust gas purification catalyst device described in Patent Document 2 tends to have reduced NOx purification performance under high temperature conditions.

[0009] Therefore, the present invention provides an exhaust gas purification device and a method for manufacturing the same, wherein the exhaust gas purification device has high OSC performance and can efficiently remove NOx even after exposure to a high-temperature environment.

[0010] As an example of the present invention, the following items can be cited.

[0011] [Project 1]

[0012] An exhaust gas purification device comprises a substrate, a first catalyst layer, and a second catalyst layer.

[0013] The substrate has an upstream end for exhaust gas inflow and a downstream end for exhaust gas discharge, the length between the upstream end and the downstream end being Ls.

[0014] The first catalyst layer is formed in a first region and contains a first rhodium-containing catalyst and a first cerium-containing oxide. The first region is located between the downstream end and a first position separated by a first distance La from the downstream end to the upstream end. The first rhodium-containing catalyst contains a first metal oxide support and first rhodium particles supported on the first metal oxide support, wherein the average particle size distribution of the first rhodium particles is 1.5–18 nm.

[0015] The second catalyst layer is formed in the second region and contains a second rhodium-containing catalyst. The second region is located between the upstream end and a second position separated by a second distance Lb from the upstream end to the downstream end. The second rhodium-containing catalyst contains a second metal oxide support and second rhodium particles supported on the second metal oxide support.

[0016] The cerium content of the first catalyst layer, based on the volume of the substrate in the first region, is greater than the cerium content of the second catalyst layer, based on the volume of the substrate in the second region.

[0017] [Project 2]

[0018] According to the exhaust purification device described in Project 1, the standard deviation of the particle size distribution of the first rhodium particles is less than 1.6 nm.

[0019] [Project 3]

[0020] According to the exhaust purification device described in Project 1 or 2, the average particle size distribution of the first rhodium particles is greater than 4 nm and less than 14 nm.

[0021] [Project 4]

[0022] According to any one of Projects 1 to 3, the exhaust purification device contains 0.01 to 2% by weight of the first rhodium particles based on the total weight of the first metal oxide support and the first rhodium particles.

[0023] [Project 5]

[0024] According to any one of Projects 1 to 4, the exhaust gas purification device has an average particle size distribution of 0.1 to 1.0 nm for the second rhodium particles.

[0025] [Project 6]

[0026] The exhaust purification device according to any one of items 1 to 5 further comprises a third catalyst layer, the third catalyst layer being formed in a third region and containing palladium particles, the third region being located between the upstream end and a third position separated by a third distance Lc from the upstream end to the downstream end.

[0027] [Project 7]

[0028] According to any one of items 1 to 6, in the exhaust purification device, the length Ls, the first distance La, and the second distance Lb satisfy Ls <La+Lb≤1.2Ls。

[0029] [Project 8]

[0030] According to any one of items 1 to 7, in the exhaust gas purification device, the cerium content of the first catalyst layer, based on the volume of the substrate in the first region, is more than twice the cerium content of the second catalyst layer, based on the volume of the substrate in the second region.

[0031] [Project 9]

[0032] According to any one of items 1 to 8, in the exhaust purification device, at least one of the first metal oxide carrier or the second metal oxide carrier is a composite oxide containing alumina and zirconium oxide as main components.

[0033] [Project 10]

[0034] A method for manufacturing an exhaust gas purification device according to any one of items 1 to 9 includes the following steps:

[0035] A first rhodium-containing catalyst is prepared, wherein the first rhodium-containing catalyst contains a first metal oxide support and first rhodium particles supported on the first metal oxide support, wherein the average particle size distribution of the first rhodium particles is 1.5 to 18 nm.

[0036] A second rhodium-containing catalyst is prepared, wherein the second rhodium-containing catalyst contains a second metal oxide support and second rhodium particles supported on the second metal oxide support;

[0037] A first catalyst layer is formed in a first region located between a downstream end of a substrate and a first position separated by a first distance La from the downstream end to the upstream end. The first catalyst layer contains the first rhodium-containing catalyst and the first cerium-containing oxide.

[0038] A second catalyst layer is formed in a second region, the second region being located between the upstream end of the substrate and a second position separated by a second distance Lb from the upstream end to the downstream end, the second catalyst layer containing the second rhodium-containing catalyst.

[0039] [Project 11]

[0040] According to the manufacturing method of the exhaust gas purification device described in Project 10, the step of preparing the first rhodium-containing catalyst includes the following steps:

[0041] The first metal oxide carrier is impregnated with the first rhodium compound solution;

[0042] The first metal oxide support impregnated with the first rhodium compound solution is dried; and

[0043] The dried first metal oxide support was heated to a temperature range of 700–900°C under an inert atmosphere to obtain the first rhodium-containing catalyst.

[0044] [Project 12]

[0045] According to the manufacturing method of the exhaust purification device described in Project 11, the inert atmosphere is a nitrogen atmosphere.

[0046] [Project 13]

[0047] According to the manufacturing method of the exhaust gas purification device described in item 11 or 12, the step of preparing the second rhodium-containing catalyst includes the following steps:

[0048] Impregnate the second metal oxide support with the second rhodium compound solution; and

[0049] The second metal oxide support impregnated with the second rhodium compound solution is dried to obtain the second rhodium-containing catalyst.

[0050] [Project 14]

[0051] The method of manufacturing an exhaust gas purification device according to any one of items 11 to 13 further comprises: forming a third catalyst layer in a third region, the third region being located between the upstream end of the substrate and a third position spaced apart by a third distance Lc from the upstream end to the downstream end, the third catalyst layer containing palladium particles.

[0052] The exhaust gas purification device of the present invention has high OSC performance and can efficiently remove harmful components even after exposure to high temperature environments. Attached Figure Description

[0053] Figure 1 This is an enlarged end view of the exhaust purification device of the embodiment, cut off with a plane parallel to the flow direction of the exhaust, schematically showing the structure near the partition wall of the substrate.

[0054] Figure 2 This is a perspective view schematically representing an example of a substrate.

[0055] Figure 3 This is an enlarged end view of the main part of the modified exhaust purification device, cut off by a plane parallel to the exhaust flow direction, schematically showing the structure near the partition wall of the substrate.

[0056] Figure 4 This is a coordinate graph showing the OSC performance (Cmax) of the exhaust gas purification devices of the embodiments and comparative examples after aging at high temperatures.

[0057] Figure 5 This is a coordinate graph showing the NOx purification performance (NOx-T50) of the exhaust gas purification devices of the embodiments and comparative examples after aging at high temperature.

[0058] Explanation of reference numerals in the attached figures

[0059] 10 Substrate, 12 Frame, 14 Chamber, 16 Partition, 20 First Catalyst Layer, 30 Second Catalyst Layer, 40 Third Catalyst Layer, 100, 200 Exhaust Gas Purification Device, I First End (Upstream End), J Second End (Downstream End), La First Distance, Lb Second Distance, Lc Third Distance, Ls Total Length of Substrate, P First Position, Q Second Position, R Third Position, X First Region, Y Second Region, Z Third Region Detailed Implementation

[0060] The embodiments will now be described with appropriate reference to the accompanying drawings. In the drawings referred to below, the same reference numerals are used to label the same components or components with the same function, and repeated descriptions are sometimes omitted. Additionally, for ease of explanation, the dimensional ratios in the drawings may differ from the actual ratios, and some components may be omitted from the drawings. In this application, the numerical range indicated by the symbol "~" includes the values ​​before and after the symbol "~", which are respectively the lower and upper limits. The upper and lower limits of the numerical ranges described in this application can be arbitrarily combined.

[0061] I. Exhaust gas purification device

[0062] Reference Figure 1 , 2 The exhaust gas purification device 100 of the embodiment will be described. The exhaust gas purification device 100 of the embodiment includes a substrate 10, a first catalyst layer 20, a second catalyst layer 30 and a third catalyst layer 40.

[0063] (1) Substrate 10

[0064] There are no particular limitations on the substrate 10; any substrate suitable for use as a substrate in an exhaust purification device can be used. For example... Figure 2 As shown, the substrate 10 can be composed of a frame portion 12 and a partition wall 16, with the partition wall 16 separating the inner space of the frame portion 12 to divide it into multiple chambers 14. The frame portion 12 and the partition wall 16 can be integrally formed. The frame portion 12 can be any shape, such as cylindrical, elliptical, or polygonal. The partition wall 16 extends between the first end (first end face) I and the second end (second end face) J of the substrate 10, and divides it into multiple chambers 14 extending between the first end I and the second end J. The cross-sectional shape of each chamber 14 can be any shape, such as square, parallelogram, rectangle, trapezoid, triangle, other polygons (e.g., hexagon, octagon), or circle. Each of the multiple chambers 14 can be closed at either the first end I or the second end J, or it can be open at both the first end I and the second end J.

[0065] Examples of materials for the base material 10 include cordierite (2MgO·2Al2O3·5SiO2), aluminum titanate, silicon carbide, silicon oxide, aluminum oxide, and aluminum-rich andalusite ceramics, as well as metals such as stainless steel containing chromium and aluminum. With these materials, the exhaust purification device 100 can maintain high exhaust purification performance even under high-temperature conditions. From a cost-reduction perspective, the base material 10 can also be made of cordierite.

[0066] exist Figure 1 , 2In the diagram, the dashed arrows indicate the direction of exhaust flow in the exhaust purification device 100 and the substrate 10. Exhaust flows into the exhaust purification device 100 through the first end I and exits through the second end J. Therefore, the first end I is appropriately referred to as the upstream end I, and the second end J as the downstream end J. In this specification, the length between the upstream end I and the downstream end J, i.e., the total length of the substrate 10, is denoted as Ls.

[0067] (2) First catalyst layer 20

[0068] The first catalyst layer 20 is disposed on the substrate 10 in a first region X, which is located between the downstream end J and a first position P separated by a first distance La from the downstream end J to the upstream end I (i.e., in the direction opposite to the flow direction of the exhaust gas). The first distance La can be 40% to 65% of the total length Ls of the substrate 10.

[0069] The first catalyst layer 20 contains a first rhodium-containing catalyst. The first rhodium-containing catalyst contains a first metal oxide support and first rhodium (Rh) particles supported on the first metal oxide support.

[0070] Examples of first metal oxide supports include oxides of at least one metal selected from Groups 3, 4, and 13 of the periodic table, as well as lanthanide metals. When the first metal oxide support contains two or more metal elements, it can be a mixture of oxides of these two or more metal elements, a composite oxide containing these two or more metal elements, or a mixture of an oxide of at least one metal element and at least one composite oxide.

[0071] The first metal oxide support may be, for example, an oxide of at least one metal selected from 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 Y, La, Ce, Ti, Zr, and Al, and more preferably an oxide of at least one metal selected from Al, Ce, and Zr. The first metal oxide support may be an oxide containing zirconium oxide (ZrO2) as the main component, a composite oxide containing zirconium oxide and aluminum oxide (Al2O3) as the main components (Al-Zr composite oxide), or a composite oxide containing zirconium oxide, aluminum oxide, and cerium oxide (CeO2) as the main components (Al-Ce-Zr composite oxide). Zirconia may have the function of maintaining the catalytic activity of the first Rh particles. Cerium oxide can function as an OSC (Oxygen Storage Capacity) material, capable of absorbing oxygen in an oxygen-excess atmosphere and releasing oxygen in an oxygen-deficient atmosphere. However, the Rh particles on cerium oxide tend to increase in size at high temperatures; therefore, the first metal oxide support may not contain Ce. Aluminum oxide can suppress the diffusion of the first Rh particles. The first metal oxide support may contain at least one of aluminum oxide, cerium oxide, and zirconium oxide as its main components, and also contains yttrium oxide (Y₂O₃), lanthanum oxide (La₂O₃), neodymium oxide (Nd₂O₃), and praseodymium oxide (Pr₆O₃). 11 A composite oxide comprising at least one of the following: yttrium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide. The heat resistance of the composite oxide is improved by yttrium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide.

[0072] Furthermore, in this application, "containing as a main component" means that the content of the component is 50% or more, 70% or more, 80% or more, or 90% or more of the total weight. In the case of multiple main components, it means that the total content of these components is 50% or more, 70% or more, 80% or more, or 90% or more.

[0073] The first metal oxide support can be granular, and its particle size can be appropriately set.

[0074] The first Rh particles supported on a first metal oxide carrier function as a catalyst for removing harmful components from exhaust gas, primarily acting as a catalyst for NOx reduction. The average particle size distribution of the first Rh particles can range from 1.5 to 18 nm. Generally, the smaller the particle size, the larger the specific surface area, thus exhibiting high catalytic performance. However, Rh particles with excessively small particle sizes (e.g., less than about 1 nm) are prone to coarsening at high temperatures due to Ostwald ripening and agglomeration, which tends to degrade catalytic performance. By having an average particle size distribution of 1.5 nm or more, fewer Rh particles are prone to coarsening, thus suppressing the decrease in catalytic performance of the first Rh particles at high temperatures. Furthermore, by having an average particle size distribution of 18 nm or less, the specific surface area of ​​the first Rh particles becomes sufficiently large, allowing them to exhibit high catalytic performance. The average particle size distribution of the first Rh particles can be in the range of 3 to 17 nm, greater than 4 nm but less than 14 nm, or greater than 4 nm but less than 8 nm.

[0075] Furthermore, the standard deviation of the particle size distribution of the first Rh particles can be less than 1.6 nm. By making the standard deviation of the particle size distribution of the first Rh particles less than 1.6 nm, the number of coarse particles and the number of tiny Rh particles that easily coarsen under high-temperature environments are reduced. Therefore, even when the exhaust gas purification device is exposed to a high-temperature environment, the first Rh particles can still have a sufficiently large specific surface area, resulting in high catalyst performance. The standard deviation of the particle size distribution of the first Rh particles can be less than 1 nm.

[0076] Furthermore, in this application, the particle size distribution of the first Rh particles is a number-based particle size distribution obtained by measuring the equivalent circle diameter of the projected area of ​​more than 50 first Rh particles based on images obtained by transmission electron microscopy (TEM).

[0077] The loading amount of the first Rh particles, 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, can be in the range of 0.01 to 2% by weight. By making the proportion of the first Rh particles 0.01% by weight or more, a sufficient amount of first Rh particles is present, thus enabling effective removal of harmful components from the exhaust gas. By making the proportion of the first Rh particles 2% by weight or less, the amount of Rh used can be reduced. In addition, since the first Rh particles are sufficiently loosely supported on the metal oxide support, the coarsening of the first Rh particles under high-temperature environments can be suppressed, demonstrating sufficient durability against high temperatures. The proportion of the first Rh particles based on the total weight of the first metal oxide support and the first Rh particles can be in the range of 0.2 to 1.8% by weight.

[0078] The content of the first Rh particles in the first catalyst layer 20 is, based on the substrate volume in the first region X, for example, 0.05 to 5 g / L, 0.08 to 2 g / L, or 0.1 g / L to 1 g / L. Thereby, the exhaust gas purification device 100 can have a sufficiently high exhaust gas purification performance.

[0079] The first catalyst layer 20 further contains a first cerium-containing oxide. The first cerium-containing oxide functions as an OSC material. The first cerium-containing oxide may be cerium oxide or a composite oxide containing cerium oxide (for example, a composite oxide containing cerium oxide as a main component, a composite oxide containing cerium oxide and zirconium oxide as main components (Ce-Zr-based composite oxide), a composite oxide containing alumina, cerium oxide, and zirconium oxide as main components (Al-Ce-Zr-based composite oxide)). In particular, due to its high oxygen storage capacity and relatively low cost, the Ce-Zr-based composite oxide is preferred. The Ce-Zr-based composite oxide may also have a pyrochlore-type crystal structure. The composite oxide containing cerium oxide may contain at least one of lanthanum oxide, yttrium oxide, neodymium oxide, and praseodymium oxide as an additive in addition to the main component, and these additives may form a composite oxide together with the main component. The OSC material may be granular, and its particle size may be appropriately set.

[0080] The Ce content (converted to Ce atoms) in the first catalyst layer 20 is, based on the substrate volume in the first region X, for example, greater than 0 g / L and 20 g / L or less, preferably 5 to 20 g / L. Thereby, the exhaust gas purification device 100 can have a high OSC performance.

[0081] The first catalyst layer 20 may further contain other optional components. Examples of other optional components include adhesives and additives.

[0082] (3) The second catalyst layer 30

[0083] The second catalyst layer 30 is formed on the substrate 10 in the second region Y, and the second region Y is located between the upstream end I and the second position Q which is separated from the upstream end I by a second distance Lb in the downstream direction (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. In addition, the length Ls of the substrate, the first distance La, and the second distance Lb may satisfy Ls < La + Lb ≤ 1.2Ls. That is, the length of the overlapping region of the first catalyst layer 20 and the second catalyst layer 30 may be more than 0% and 20% or less of the full length Ls of the substrate 10. Thereby, the exhaust gas purification device 100 can have a high OSC performance. Furthermore, in the overlapping region of the first catalyst layer 20 and the second catalyst layer 30, Figure 1The second catalyst layer 30 is formed on the first catalyst layer 20, but the first catalyst layer 20 can also be formed on the second catalyst layer 30.

[0084] The second catalyst layer 30 contains a second rhodium-containing catalyst. The second rhodium-containing catalyst contains a second metal oxide support and second rhodium (Rh) particles supported on the second metal oxide support.

[0085] As the second metal oxide support, a material that can be used as the first metal oxide support described above can be used.

[0086] The second Rh particles supported on the second metal oxide carrier function as a catalyst for removing harmful components from exhaust gas, primarily acting as a catalyst for NOx reduction. As described later, the Ce content in the second catalyst layer 30, which promotes the formation of coarse Rh particles under high-temperature conditions, is lower than the Ce content in the first catalyst layer 20. Therefore, the second Rh particles are less likely to be coarse compared to the first Rh particles. Thus, the average particle size distribution of the second Rh particles is not particularly limited. From the viewpoint of ease of manufacturing, the average particle size distribution of the second Rh particles can, for example, be in the range of 0.1 to 1.0 nm. The standard deviation of the particle size distribution of the second Rh particles can be in the range of 0.01 to 0.3 nm.

[0087] Furthermore, in this application, the particle size distribution of the second Rh particles is a number-based particle size distribution obtained by measuring the equivalent circle diameter of the projected area of ​​more than 50 second Rh particles based on images obtained by transmission electron microscopy (TEM).

[0088] The loading of the second Rh particles, i.e., the proportion of Rh particles based on the total weight of the second metal oxide support and the second Rh particles, can range from 0.01% to 2% by weight. By ensuring the proportion of second Rh particles is 0.01% by weight or more, a sufficient amount of second Rh particles is present, thus effectively removing harmful components from the exhaust gas. By ensuring the proportion of second Rh particles is 2% by weight or less, the amount of Rh used can be reduced. Furthermore, since the second Rh particles are sufficiently loosely loaded on the metal oxide support, the coarsening of the second Rh particles under high-temperature environments can be suppressed, exhibiting sufficient durability against high temperatures. The proportion of second Rh particles based on the total weight of the second metal oxide support and the second Rh particles can range from 0.2% to 1.8% by weight.

[0089] The content of the second Rh particles in the second catalyst layer 30 is based on the volume of the substrate in the second region Y, and can be, for example, 0.05–5 g / L, 0.08–2 g / L, or 0.1–1 g / L. Therefore, the exhaust gas purification device 100 can have sufficiently high exhaust gas purification performance.

[0090] The second catalyst layer 30 may also contain a second cerium oxide. As the second cerium oxide, a material that can be used as the above-mentioned first cerium oxide can be used.

[0091] The Ce content (converted to Ce atoms) in the second catalyst layer 30 is, for example, 0 to 30 g / L based on the substrate volume in the second region Y. In addition, the Ce content (converted to Ce atoms) of the second catalyst layer 30 based on the substrate volume in the second region Y is smaller than the Ce content (converted to Ce atoms) of the first catalyst layer 20 based on the substrate volume in the first region X. By containing a higher concentration of cerium oxide acting as an OSC material in the first catalyst layer 20 located downstream of the second catalyst layer 30 in the exhaust flow direction, the OSC performance of the exhaust gas purification device 100 is improved. The Ce content of the first catalyst layer 20 based on the substrate volume in the first region X can be 2 times or more, particularly 5 times or more, the Ce content of the second catalyst layer 30 based on the substrate volume in the second region Y. Thereby, the OSC performance of the exhaust gas purification device 100 is further improved.

[0092] The second catalyst layer 30 may also contain other optional components. As other optional components, for example, binders and additives can be cited.

[0093] (4) The third catalyst layer 40

[0094] The third catalyst layer 40 is formed on the substrate 10 in the third region Z, and the third region Z is located between the upstream end I and the third position R that is separated from the upstream end I by a third distance Lc in the downstream direction (i.e., in the exhaust flow direction) to the downstream end J. The third distance Lc can be 15 to 35% of the total length Ls of the substrate 10. In addition, the length Ls of the substrate, the first distance La, and the third distance Lc can satisfy La + Lc < Ls. That is, there may be no region where the first catalyst layer 20 and the third catalyst layer 40 overlap. Thereby, the exhaust gas purification device 100 can have higher NOx purification performance. In Figure 1 In this case, the third catalyst layer 40 is formed on the second catalyst layer 30, but the second catalyst layer 30 may also be formed on the third catalyst layer 40.

[0095] The third catalyst layer 40 contains palladium (Pd) particles. Pd particles function as a catalyst for removing harmful components from exhaust gas, primarily acting as a catalyst for oxidizing HC. Similar to Rh particles, smaller Pd particle sizes exhibit higher catalytic performance; however, they tend to coarsen at high temperatures. Even if the average particle size distribution of Pd particles is kept in the same range as the first Rh particles (1.5–18 nm), coarsening of Pd particles cannot be suppressed. Therefore, the average particle size distribution of Pd particles is not particularly limited. From a manufacturing perspective, the average particle size distribution of Pd particles can, for example, be in the range of 0.5–10 nm, and the standard deviation of the particle size distribution can be in the range of 0.1–3.0 nm.

[0096] Furthermore, in this application, the particle size distribution of Pd particles is a number-based particle size distribution obtained by measuring the equivalent circle diameter of the projected area of ​​more than 50 Pd particles based on images obtained by transmission electron microscopy (TEM) or scanning electron microscopy (SEM).

[0097] The Pd particle content in the third catalyst layer 40 is based on the volume of the substrate in the third region Z, and can be, for example, 0.1 to 20 g / L, preferably 1 to 15 g / L, and more preferably 3 to 9 g / L. Therefore, the exhaust gas purification device 100 can have sufficiently high exhaust gas purification performance.

[0098] The third catalyst layer 40 may also contain other components such as a support for carrying Pd particles, OSC material, and barium compounds.

[0099] Metal oxide supports can be used as carriers for Pd particles, but are not limited to them. Pd particles can be supported on the carrier using any method, such as impregnation, adsorption, or water absorption.

[0100] As a metal oxide support, materials that can be used as the first metal oxide support described above can be used.

[0101] As an OSC material, materials that can be used as the first cerium-containing oxide mentioned above can be used.

[0102] Barium compounds can inhibit the poisoning of Pd particles. Examples of barium compounds include barium sulfate, barium carbonate, barium oxide, and barium nitrate. Barium compounds can be granular, and their particle size can be appropriately set.

[0103] The third catalyst layer 40 may also contain other optional components. Examples of other optional components include binders and additives.

[0104] II. Manufacturing Method of Exhaust Gas Purification Device

[0105] An example of a method for manufacturing the exhaust gas purification device 100 according to the above embodiment will be described. The method for manufacturing the exhaust gas purification device 100 includes: preparing a first rhodium-containing catalyst; preparing a second rhodium-containing catalyst; forming a first catalyst layer 20 in a first region X of a substrate 10; forming a second catalyst layer 30 in a second region Y of the substrate 10; and forming a third catalyst layer 40 in a third region Z of the substrate 10. The first catalyst layer 20, the second catalyst layer 30, and the third catalyst layer 40 can be formed in any order.

[0106] An example of the steps for preparing the first rhodium-containing catalyst is described. The first rhodium-containing catalyst can be prepared by the following steps: impregnating a first metal oxide support with a first rhodium compound solution; drying the first metal oxide support impregnated with the first rhodium compound solution; and heating the dried first metal oxide support to a temperature range of 700–900°C under an inert atmosphere.

[0107] Examples of the first rhodium compound solution include aqueous solutions of rhodium hydroxide and rhodium nitrate. The impregnation method is not particularly limited. For example, the first rhodium compound solution can be impregnated into the first metal oxide support by adding distilled water while stirring.

[0108] Next, the first metal oxide support impregnated with the first rhodium compound solution is dried. Firing may be performed after drying if necessary. Then, the first metal oxide support is heated to a temperature range of 700–900°C under an inert atmosphere. This yields a first rhodium-containing catalyst containing the first metal oxide support and first Rh particles supported on the first metal oxide support. Examples of inert atmospheres include nitrogen and argon. The heating time can be appropriately set, for example, 1–5 hours. By heating under an inert atmosphere, the particle size distribution of the first Rh particles in the first rhodium-containing catalyst can be appropriately controlled. Specifically, the average particle size distribution of the first Rh particles can be in the range of 1.5–18 nm, 3–17 nm, greater than 4 nm and less than 14 nm, or greater than 4 nm and less than 8 nm, and the standard deviation of the particle size distribution of the first Rh particles can be less than 1.6 nm or less than 1 nm.

[0109] Furthermore, heating in a reducing atmosphere such as hydrogen makes it difficult to produce sufficiently large first Rh particles, resulting in the aforementioned particle size distribution. Heating in an oxidizing atmosphere such as air may cause Rh to dissolve into the first metal oxide support, reducing the number of first Rh particles on the surface of the first metal oxide support.

[0110] An example of the steps for preparing a second rhodium-containing catalyst is described. The second rhodium-containing catalyst can be prepared by the following steps: impregnating a second metal oxide support with a solution of a second rhodium compound; and drying the second metal oxide support impregnated with the solution of the second rhodium compound. Firing may be performed after drying if necessary. After drying and optional firing, it is not necessary to heat the first metal oxide support under an inert atmosphere. That is, the second rhodium-containing catalyst can be prepared in the same manner as the first rhodium-containing catalyst, except that heating under an inert atmosphere is not required.

[0111] A third catalyst layer 40 containing palladium particles is formed in the third region Z 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. Suitable inorganic acid salts of Pd, such as hydrochlorides, nitrates, phosphates, sulfates, borates, hydrofluoric acids, etc., can be used as the Pd particle precursor. Alternatively, the third slurry may contain a carrier powder pre-loaded with Pd particles. Furthermore, the third slurry may also contain optional components such as OSC materials, binders, and additives. The properties of the third slurry, such as viscosity and particle size of the solid components, can be appropriately adjusted. The prepared third slurry is then coated onto the third region Z of the substrate 10. For example, the third region Z of the substrate 10 is immersed in the third slurry, and after a predetermined time, the substrate 10 is lifted from the third slurry, thereby coating the third slurry onto the third region Z of the substrate 10. Alternatively, the third slurry can flow into the substrate 10 from the upstream end I, and a blower can be used to blow air towards the upstream end I, causing the third slurry to spread and extend towards the downstream end J, thereby coating the third slurry onto the third region Z of the substrate 10. Then, the third slurry is dried and fired at a predetermined temperature and time. Thus, a third catalyst layer 40 is formed in the third region Z of the substrate 10.

[0112] A first catalyst layer 20 containing the prepared first Rh-containing catalyst and the first cerium-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 the first Rh-containing catalyst and the first cerium-containing oxide is prepared. The first slurry may also contain optional components such as binders and additives. The properties of the first slurry, such as viscosity and particle size of the solid components, can be appropriately adjusted. The prepared first slurry is then coated onto the first region X of the substrate 10. For example, the first region X of the substrate 10 is immersed in the first slurry, and after a predetermined time, the substrate 10 is lifted from the first slurry, thereby coating the first slurry onto the first region X of the substrate 10. Alternatively, the first slurry can flow into the substrate 10 from the downstream end J, and air is blown towards the downstream end J using a blower, causing the first slurry to spread towards the upstream end I, thereby coating the first slurry onto the first region X of the substrate 10. Next, the first slurry is dried and calcined at a predetermined temperature and time. Thus, the first catalyst layer 20 is formed in the first region X of the substrate 10.

[0113] A second catalyst layer 30 containing a second Rh-containing catalyst is formed in 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 is prepared. The second slurry may also contain optional components such as OSC materials, binders, and additives. The properties of the second slurry, such as viscosity and particle size of solid components, can be appropriately adjusted. The prepared second slurry is then coated onto the second region Y of the substrate 10. For example, the second region Y of the substrate 10 is immersed in the second slurry, and after a predetermined time, the substrate 10 is lifted from the second slurry, thereby coating the second slurry onto the second region Y of the substrate 10. Alternatively, the second slurry can flow into the substrate 10 from the upstream end I, and air is blown towards the upstream end I using a blower to spread the second slurry towards the downstream end J, thereby coating the second slurry onto the second region Y of the substrate 10. Next, the second slurry is dried and fired at a predetermined temperature and time. Thus, the second catalyst layer 30 is formed in the second region Y of the substrate 10.

[0114] The exhaust purification device described in this embodiment is applicable to various vehicles equipped with internal combustion engines.

[0115] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. Various design changes can be made without departing from the spirit of the present invention as described in the patent claims. For example, the exhaust gas purification device may not include the third catalyst layer 40 described above. That is, as... Figure 3 The exhaust purification device 200 shown, which does not include the third catalyst layer 40, is also within the scope of the present invention.

[0116] Example

[0117] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments.

[0118] (1) Materials used in the examples and comparative examples

[0119] a) Substrate (Cellular Substrate)

[0120] Material: Iolite

[0121] Capacity: 875cc

[0122] Length: 10.5cm

[0123] The thickness of the partition wall: 2 mil (50.8 μm)

[0124] Pore ​​density: 600 per square inch

[0125] Hole cross-sectional shape: hexagonal

[0126] b) AZ particles

[0127] AZ particles are composite oxide particles containing Al2O3 and ZrO2 as main components, and also La2O3, Y2O3, and Nd2O3. The weight fractions of each component in AZ particles are: Al2O3: 30 wt%, ZrO2: 60 wt%, La2O3: 4 wt%, Y2O3: 4 wt%, and Nd2O3: 2 wt%.

[0128] c) Al2O3 particles

[0129] Al2O3 particles are composite oxide particles containing Al2O3 as the main component and also containing La2O3. The weight fractions of each component in the Al2O3 particles are Al2O3: 96 wt% and La2O3: 4 wt%.

[0130] d) ACZ particles

[0131] ACZ particles are composite oxide particles containing Al2O3, CeO2, and ZrO2 as main components, and also La2O3, Y2O3, and Nd2O3. The weight fractions of each component in ACZ particles are: Al2O3: 30 wt%, CeO2: 20 wt%, ZrO2: 44 wt%, La2O3: 2 wt%, Y2O3: 2 wt%, and Nd2O3: 2 wt%.

[0132] e)CZ particles

[0133] CZ particles are composite oxide particles containing CeO2 and ZrO2 as main components, as well as La2O3 and Y2O3. The weight fractions of each component in CZ particles are: CeO2: 40 wt%, ZrO2: 50 wt%, La2O3: 5 wt%, and Y2O3: 5 wt%.

[0134] f) Pyrochlore-type CZ particles

[0135] Pyrochlore-type CZ particles contain CeO2 and ZrO2 as main components, and also contain Pr6O. 11 Composite oxide particles. The weight fractions of each component in the pyrochlore-type CZ particles are CeO2: 51.4 wt%, ZrO2: 45.6 wt%, Pr6O... 11 3% by weight. In pyrochlore-type CZ particles, cerium and zirconium ions have a regular arrangement structure of pyrochlore type, and a portion of the cerium and zirconium ions are replaced by praseodymium. Pyrochlore-type CZ particles are prepared according to the following steps.

[0136] 129.7 g of cerium nitrate hexahydrate, 99.1 g of zirconium oxynitrate dihydrate, 5.4 g of praseodymium nitrate hexahydrate, and 36.8 g of 18% hydrogen peroxide aqueous solution were dissolved in 500 g of ion-exchange water. Hydroxide precipitate was obtained by reverse co-precipitation using 340 g of 25% ammonia solution. The precipitate was separated by filter paper, dried in a drying oven at 150°C for 7 hours to remove moisture, calcined in an electric furnace at 500°C for 4 hours, and then pulverized.

[0137] Using a Wet-CIP compression molding machine, apply 2000 kgf / cm². 2 The pressure is used to shape the resulting powder.

[0138] The resulting molded body was placed in a graphite crucible containing activated carbon and reduced at 1700°C for 5 hours under an Ar atmosphere. Then, it was fired in an electric furnace at 500°C for 5 hours.

[0139] The product was ground using a vibratory mill. This yielded pyrochlore-type CZ particles.

[0140] g) Rhodium nitrate aqueous solution (concentration 2.8% by weight)

[0141] h) Palladium nitrate aqueous solution (concentration 8.0% by weight)

[0142] i) Barium sulfate particles

[0143] (2) Fabrication of exhaust purification device

[0144] Examples 1 and 2

[0145] a) Preparation of the first rhodium-containing catalyst

[0146] While stirring distilled water, AZ particles and an aqueous solution of rhodium nitrate were added sequentially. The resulting mixture was dried and calcined by heating in an electric furnace at 500°C for 2 hours in air. The resulting particles were then heated at 850°C for 5 hours in a nitrogen atmosphere. This yielded a first Rh-containing catalyst containing AZ particles and rhodium (Rh) particles supported on the AZ particles. The first Rh-containing catalyst contained 0.60% by weight of Rh particles based on the total weight of the AZ particles and Rh particles.

[0147] The first Rh-containing catalyst was observed using a transmission electron microscope (TEM), and the particle size distribution (initial particle size distribution) of the Rh particles (first Rh particles) supported on AZ particles was determined. The mean and standard deviation of the initial particle size distribution of the first Rh particles are shown in Table 1.

[0148] b) Preparation of the second rhodium-containing catalyst

[0149] While stirring distilled water, AZ particles and an aqueous solution of rhodium nitrate were added sequentially. The resulting mixture was dried and calcined by heating in an electric furnace at 500°C for 2 hours in air. This yielded a second Rh-containing catalyst containing AZ particles and rhodium (Rh) particles supported on the AZ particles. The second Rh-containing catalyst contained 0.94% by weight of Rh particles based on the total weight of the AZ and Rh particles.

[0150] The second Rh-containing catalyst was observed using transmission electron microscopy (TEM) to determine the particle size distribution (initial particle size distribution) of the Rh particles (second Rh particles) supported on AZ particles. The mean and standard deviation of the initial particle size distribution of the second Rh particles are shown in Table 1.

[0151] c) Slurry preparation

[0152] While stirring distilled water, a first Rh-containing catalyst, Al₂O₃ particles, ACZ particles, pyrochlore-type CZ particles, and an Al₂O₃-based binder were added to prepare a first suspension. While stirring distilled water, a second Rh-containing catalyst, Al₂O₃ particles, ACZ particles, pyrochlore-type CZ particles, and an Al₂O₃-based binder were added to prepare a second suspension. While stirring distilled water, Al₂O₃ particles, CZ particles, palladium nitrate aqueous solution, barium sulfate particles, and an Al₂O₃-based binder were added to prepare a third suspension.

[0153] d) Formation of the third catalyst layer

[0154] The third slurry is allowed to flow in from the upstream end of the substrate, and unwanted portions are blown away using a blower. This forms a third slurry layer on the substrate in a third region, located between the upstream end of the substrate and a third position at a distance equal to 30% of the total length of the substrate from the upstream end to the downstream end. Next, the substrate is placed in a dryer maintained at 120°C for 2 hours to evaporate the water in the third slurry layer. Then, the substrate is heated in an electric furnace at 500°C in air for 2 hours to calcine the third slurry layer. This forms the third catalyst layer.

[0155] The contents of Al₂O₃ particles, C₂ particles, Pd particles from the palladium nitrate aqueous solution, and barium sulfate particles in the third catalyst layer, based on the volume of the substrate in the third region, were 25 g / L, 75 g / L, 7 g / L, and 5 g / L, respectively. Furthermore, the particle size distribution of the Pd particles was determined by observing the third catalyst layer using transmission electron microscopy (TEM). The average particle size distribution of the Pd particles was 8.7 nm, with a standard deviation of 2.1 nm.

[0156] e) Formation of the first catalyst layer

[0157] The first slurry is allowed to flow into the substrate from one end (downstream), and unwanted portions are blown away using a blower. This forms a first slurry layer on the substrate in a first region located between the downstream end of the substrate and a first position at a distance equal to 65% of the total length of the substrate from the downstream end to the upstream end. Next, the substrate is placed in a dryer maintained at 120°C for 2 hours to evaporate the water in the first slurry layer. Then, the substrate is heated in an electric furnace at 500°C in air for 2 hours to calcine the first slurry layer. This forms the first catalyst layer.

[0158] The contents of the first Rh-containing catalyst and Al2O3 particles in the first catalyst layer, based on the volume of the substrate in the first region, are 20.12 g / L (of which the content of AZ particles is 20 g / L and the content of Rh particles is 0.12 g / L) and 20 g / L, respectively. The contents of ACZ particles and pyrochlore-type CZ particles in the first catalyst layer, based on the volume of the substrate in the first region, are shown in Table 1.

[0159] f) Formation of the second catalyst layer

[0160] The second slurry is allowed to flow in from the upstream end of the substrate, and unwanted portions are blown away using a blower. This forms either a first catalyst layer on the substrate in the second region, or a second slurry layer on the third catalyst layer. The second region is located between the upstream end of the substrate and a second position at a distance equal to 55% of the total length of the substrate from the upstream end to the downstream end. Next, the substrate is placed in a dryer maintained at 120°C for 2 hours to evaporate the water in the second slurry layer. Then, the substrate is heated in an electric furnace at 500°C in air for 2 hours to calcine the second slurry layer. This forms the second catalyst layer.

[0161] The contents of the second Rh-containing catalyst and Al2O3 particles in the second catalyst layer, based on the substrate volume in the second region, are 40.38 g / L (of which the content of AZ particles is 40 g / L and the content of Rh particles is 0.38 g / L) and 40 g / L, respectively. The contents of ACZ particles and pyrochlore-type CZ particles in the second catalyst layer, based on the substrate volume in the second region, are shown in Table 1.

[0162] Thus, the exhaust purification devices of Examples 1 and 2 are obtained.

[0163] Example 3

[0164] The heating temperature under a nitrogen atmosphere was set to 750°C, and the first Rh-containing catalyst was prepared in the same manner as in Example 1. Using the obtained first Rh-containing catalyst, an exhaust gas purification device was fabricated in the same manner as in Example 1. The average value and standard deviation of the initial particle size distribution of the first Rh particles in Example 3 are shown in Table 1.

[0165] Example 4

[0166] The heating temperature under a nitrogen atmosphere was set to 900°C, and the first Rh-containing catalyst was prepared in the same manner as in Example 1. Using the obtained first Rh-containing catalyst, an exhaust gas purification device was fabricated in the same manner as in Example 1. The average value and standard deviation of the initial particle size distribution of the first Rh particles in Example 4 are shown in Table 1.

[0167] Example 5

[0168] After drying and calcination, the second Rh-containing catalyst was prepared by heating at 850°C for 5 hours under a nitrogen atmosphere, otherwise in the same manner as in Example 2. Using the obtained second Rh-containing catalyst, an exhaust gas purification device was fabricated in the same manner as in Example 1. The average value and standard deviation of the initial particle size distribution of the second Rh particles are shown in Table 1.

[0169] Comparative Examples 1 and 2

[0170] The contents of ACZ particles and pyrochlore-type CZ particles in the first catalyst layer based on the substrate volume in the first region, and the contents of ACZ particles and pyrochlore-type CZ particles in the second catalyst layer based on the substrate volume in the second region are shown in Table 1. Otherwise, the exhaust purification device was manufactured in the same manner as in Example 1.

[0171] Comparative Examples 3-5

[0172] The first Rh-containing catalyst was prepared in the same manner as in Example 1, except that heating under a nitrogen atmosphere was not performed. Using the obtained first Rh-containing catalyst, exhaust gas purification devices for Comparative Examples 3-5 were prepared in the same manner as Comparative Examples 2 and Examples 1 and 2. The average value and standard deviation of the initial particle size distribution of the first Rh particles in Comparative Examples 3-5 are shown in Table 1.

[0173] (3) Aging treatment and subsequent determination of the average particle size of Rh particles

[0174] Each exhaust purification device was connected to the exhaust system of a V8 engine. A mixture of air-fuel ratio (A / F = 14.6) and excess oxygen (lean: A / F > 14.6) was alternately and repeatedly introduced into the engine at a time ratio of 3:1. The bed temperature of the exhaust purification device was maintained at 950°C for 50 hours. This process was then used to age the exhaust purification devices.

[0175] (4) OSC performance evaluation

[0176] An aged exhaust purification device was connected to the exhaust system of an L-type 4-cylinder engine. The engine was alternately supplied with an air-fuel mixture with an A / F ratio of 14.1 and an A / F ratio of 15.1. The maximum oxygen storage capacity (Cmax) was calculated using the formula: Cmax(g) = 0.23 × ΔA / F × injected fuel quantity. Furthermore, ΔA / F represents the difference between the theoretical mixture ratio and the A / F sensor output. The results are shown in Table 1 and... Figure 4 .

[0177] like Figure 4 As shown, regardless of the initial particle size distribution of the first Rh particles, the higher the ratio of Ce content in the first catalyst layer to Ce content in the second catalyst layer, the greater the increase in Cmax (i.e., improved OSC performance). This demonstrates that high OSC performance can be obtained by distributing a large amount of cerium oxide, which functions as an OSC material, in the downstream region of the exhaust gas purification device.

[0178] (5) NOx purification performance evaluation

[0179] An aged exhaust gas purification device was connected to the exhaust system of an L-type 4-cylinder engine. 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. The bed temperature at which 50% of the NOx in the gas was removed was measured (hereinafter appropriately referred to as "NO"). X -T50"。The results are shown in Table 1 and Figure 5 .

[0180] like Figure 5 As shown, when the ratio of Ce content in the first catalyst layer to Ce content in the second catalyst layer is 0.5 or higher, regardless of the initial particle size distribution of the first Rh particles, the larger the ratio of Ce content in the first catalyst layer to Ce content in the second catalyst layer, the higher the NO content. X The higher the T50 (i.e., the lower the NOx purification performance), the better. However, compared to exhaust gas purification devices with an average initial particle size distribution of 0.70 nm for the first Rh particles, exhaust gas purification devices with an average initial particle size distribution of 5.49 nm for the first Rh particles show an increase in NOx emissions associated with an increase in the ratio of Ce content in the first catalyst layer to Ce content in the second catalyst layer. XThe increase in -T50 is small. Therefore, when the ratio of Ce content in the first catalyst layer to Ce content in the second catalyst layer exceeds 1, especially 2.5 or higher, exhaust gas purification devices with an average initial particle size distribution of 5.49 nm for the first Rh particles show significantly higher NOx purification performance compared to exhaust gas purification devices with an average initial particle size distribution of 0.70 nm for the first Rh particles. Furthermore, exhaust gas purification devices with an average initial particle size distribution of 3.36–7.85 nm for the first Rh particles show even higher NOx purification performance compared to exhaust gas purification devices with an average initial particle size distribution of 0.70 nm for the first Rh particles.

[0181] An exhaust gas purification device with an average initial particle size distribution of 5.45 nm for the second Rh particles showed lower NO emissions compared to an exhaust gas purification device with an average initial Rh particle size distribution of 0.68 nm. X -T50 (i.e., higher NOx purification performance). However, its difference (4.6℃) is smaller than that of exhaust gas purification devices with an average initial particle size distribution of 5.49 nm for the first Rh particles and exhaust gas purification devices with an average initial particle size distribution of 0.70 nm for the first Rh particles. X The difference in T50 (10.1℃) indicates that controlling the initial particle size of the first Rh particles is particularly effective in improving NOx purification performance.

[0182] Table 1

[0183]

Claims

1. An exhaust gas purification device, comprising a substrate, a first catalyst layer, and a second catalyst layer. The substrate has an upstream end for exhaust gas inflow and a downstream end for exhaust gas discharge, the length between the upstream end and the downstream end being Ls. The first catalyst layer is formed in a first region and contains a first rhodium-containing catalyst and a first cerium-containing oxide. The first region is located between the downstream end and a first position separated by a first distance La from the downstream end to the upstream end. The first rhodium-containing catalyst contains a first metal oxide support and first rhodium particles supported on the first metal oxide support, wherein the average particle size distribution of the first rhodium particles is 3~18 nm. The second catalyst layer is formed in the second region and contains a second rhodium-containing catalyst. The second region is located between the upstream end and a second position separated by a second distance Lb from the upstream end to the downstream end. The second rhodium-containing catalyst contains a second metal oxide support and second rhodium particles supported on the second metal oxide support. The cerium content of the first catalyst layer, based on the volume of the substrate in the first region, is more than twice the cerium content of the second catalyst layer, based on the volume of the substrate in the second region.

2. In the exhaust purification device according to claim 1, the standard deviation of the particle size distribution of the first rhodium particles is less than 1.6 nm.

3. In the exhaust purification device according to claim 1 or 2, the average particle size distribution of the first rhodium particles is greater than 4 nm and less than 14 nm.

4. The exhaust purification device according to claim 1 or 2, wherein the first rhodium-containing catalyst contains 0.01 to 2% by weight of the first rhodium particles based on the total weight of the first metal oxide support and the first rhodium particles.

5. The exhaust purification device according to claim 1 or 2, wherein the average particle size distribution of the second rhodium particles is 0.1~1.0 nm.

6. The exhaust purification device according to claim 1 or 2, further comprising a third catalyst layer, the third catalyst layer being formed in a third region and containing palladium particles, the third region being located between the upstream end and a third position separated by a third distance Lc from the upstream end to the downstream end.

7. The exhaust purification device according to claim 1 or 2, wherein the length Ls, the first distance La, and the second distance Lb satisfy Ls <La+Lb≤1.2Ls。 8. The exhaust purification device according to claim 1 or 2, wherein at least one of the first metal oxide carrier or the second metal oxide carrier is a composite oxide containing alumina and zirconium oxide as main components.

9. A method for manufacturing the exhaust gas purification device according to claim 1 or 2, comprising the following steps: A first rhodium-containing catalyst is prepared, wherein the first rhodium-containing catalyst contains a first metal oxide support and first rhodium particles supported on the first metal oxide support, wherein the average particle size distribution of the first rhodium particles is 3~18 nm. A second rhodium-containing catalyst is prepared, wherein the second rhodium-containing catalyst contains a second metal oxide support and second rhodium particles supported on the second metal oxide support; A first catalyst layer is formed in a first region located between a downstream end of a substrate and a first position separated by a first distance La from the downstream end to the upstream end. The first catalyst layer contains the first rhodium-containing catalyst and the first cerium-containing oxide. A second catalyst layer is formed in a second region, the second region being located between the upstream end of the substrate and a second position separated by a second distance Lb from the upstream end to the downstream end, the second catalyst layer containing the second rhodium-containing catalyst.

10. The method for manufacturing the exhaust gas purification device according to claim 9, wherein the step of preparing the first rhodium-containing catalyst comprises the following steps: The first metal oxide carrier is impregnated with the first rhodium compound solution; The first metal oxide support impregnated with the first rhodium compound solution is dried; and The dried first metal oxide support was heated to a temperature range of 700~900℃ under an inert atmosphere to obtain the first rhodium-containing catalyst.

11. The method for manufacturing the exhaust gas purification device according to claim 10, wherein the inert atmosphere is a nitrogen atmosphere.

12. The method for manufacturing the exhaust gas purification device according to claim 10, wherein the step of preparing the second rhodium-containing catalyst comprises the following steps: Impregnate the second metal oxide support with the second rhodium compound solution; and The second metal oxide support impregnated with the second rhodium compound solution is dried to obtain the second rhodium-containing catalyst.

13. The method for manufacturing the exhaust gas purification device according to claim 10 further comprises: A third catalyst layer is formed in a third region, the third region being located between the upstream end of the substrate and a third position separated by a third distance Lc from the upstream end to the downstream end, the third catalyst layer containing palladium particles.

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