Method for manufacturing exhaust gas purification material and method for manufacturing exhaust gas purification device

Abstract

Provided are a method for producing an exhaust gas purification material capable of efficiently removing harmful components even after exposure to a high-temperature environment, and a method for producing an exhaust gas purification device. A method for producing an exhaust gas purification material, comprising, in order: (a) impregnating a metal oxide support with a rhodium compound solution; (b) drying the metal oxide support impregnated with the rhodium compound solution to obtain a rhodium-containing catalyst comprising the metal oxide support and rhodium particles supported on the metal oxide support; (c) heating the rhodium-containing catalyst to a temperature range of 700 to 900°C under an inert atmosphere; and (d) mixing the rhodium-containing catalyst with a material having a basicity higher than that of the metal oxide support.

Description

Technical Field

[0001] This invention relates to a method for manufacturing exhaust purification materials and a method for manufacturing exhaust purification devices. 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] Existing technical documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-147256 Summary of the Invention

[0006] Through in-depth research, the inventors discovered that the catalytic activity of exhaust purification materials obtained by the manufacturing method described in Patent Document 1 decreases when used in high-temperature environments.

[0007] Therefore, the purpose of this invention is to provide a method for manufacturing an exhaust gas purification material and an exhaust gas purification device, wherein the exhaust gas purification material can efficiently remove harmful components even after exposure to a high-temperature environment.

[0008] As an example of the present invention, the following items can be cited.

[0009] [Project 1]

[0010] A method for manufacturing an exhaust purification material, comprising the following steps:

[0011] Step (a): Impregnate the metal oxide support with a rhodium compound solution;

[0012] Step (b): The metal oxide support impregnated with the rhodium compound solution is dried to obtain a rhodium-containing catalyst comprising the metal oxide support and rhodium particles supported on the metal oxide support;

[0013] Step (c): Heating the rhodium-containing catalyst to a temperature range of 700–900°C under an inert atmosphere; and

[0014] Step (d): Mix the rhodium-containing catalyst with a material that is more basic than the metal oxide support.

[0015] [Project 2]

[0016] According to the manufacturing method of the exhaust purification material described in Project 1, in the rhodium-containing catalyst after step (c), the average particle size distribution of the rhodium particles is 1.5 to 18 nm, and the standard deviation of the particle size distribution is less than 1.6 nm.

[0017] [Project 3]

[0018] According to the method for manufacturing exhaust purification materials described in Project 2, in the rhodium-containing catalyst after step (c), the average particle size distribution of the rhodium particles is 4 to 14 nm.

[0019] [Project 4]

[0020] According to the method for manufacturing exhaust purification materials described in Project 2, in the rhodium-containing catalyst after step (c), the average particle size distribution of the rhodium particles is 2 to 8 nm.

[0021] [Project 5]

[0022] According to the method for manufacturing exhaust purification material according to any one of items 1 to 4, the rhodium-containing catalyst contains 0.01 to 2% by weight of the rhodium particles based on the total weight of the metal oxide support and the rhodium particles.

[0023] [Project 6]

[0024] According to any one of Projects 1 to 5, the manufacturing method of the exhaust purification material, wherein the metal oxide carrier is an oxide containing zirconium oxide as the main component, a composite oxide containing zirconium oxide and aluminum oxide as the main components, or a composite oxide containing zirconium oxide, aluminum oxide and cerium oxide as the main components.

[0025] [Project 7]

[0026] According to any one of Projects 1 to 6, in the method for manufacturing exhaust purification materials, the metal oxide carrier is a composite oxide containing zirconium oxide, aluminum oxide and cerium oxide as main components, and the material with higher alkalinity than the metal oxide carrier is a composite oxide containing cerium oxide and zirconium oxide as main components.

[0027] [Project 8]

[0028] In the method for manufacturing exhaust purification material according to any one of items 1 to 7, the inert atmosphere is a nitrogen atmosphere.

[0029] [Project 9]

[0030] A method for manufacturing an exhaust gas purification device, comprising:

[0031] The exhaust purification material is obtained by the manufacturing method of any one of items 1 to 8; and

[0032] The exhaust purification material is disposed on a substrate.

[0033] The exhaust purification materials and devices manufactured by the method of the present invention can efficiently remove harmful components even after exposure to high-temperature environments. Detailed Implementation

[0034] The embodiments of this disclosure will be described below. This invention is not limited to the following embodiments, and various design changes can be made without departing from the spirit of the invention as described in the patent claims. In this application, the numerical range indicated by the symbol "~" includes the values ​​before and after the symbol "~" as the lower limit and upper limit, respectively. The upper and lower limits of the numerical ranges described in this application can be arbitrarily combined.

[0035] (1) Exhaust gas purification materials

[0036] First, the exhaust gas purification material manufactured using the method described in the embodiment will be explained. The exhaust gas purification material is a mixture of a metal oxide support, an Rh-containing catalyst containing Rh particles supported on the metal oxide support, and a material with a higher alkalinity than the metal oxide support.

[0037] Examples of 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 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.

[0038] The metal oxide support can 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 metal oxide support can 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 can have the function of maintaining the catalytic activity of Rh particles. Cerium oxide can function as an OSC (Oxygen Storage Capacity) material, absorbing oxygen in an oxygen-excess atmosphere and releasing oxygen in an oxygen-deficient atmosphere. Aluminum oxide can inhibit the diffusion of Rh particles. The metal oxide support can contain aluminum oxide, cerium oxide, and zirconium oxide as the main components, and also contain yttrium oxide (Y₂O₃), lanthanum oxide (La₂O₃), neodymium oxide (Nd₂O₃), and praseodymium oxide (Pr₆O₃). 11 The composite oxide contains particles of at least one of the following: yttrium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide. Yttrium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide improve the heat resistance of the composite oxide. Furthermore, in this application, "containing as a main component" means that the content of that component is 50% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more of the total weight. In the case of multiple main components, it means that the total content of these components is 50% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0039] Metal oxide supports can be granular and can have any particle size depending on the purpose.

[0040] Rh particles supported on a metal oxide carrier function as a catalyst for removing harmful components from exhaust gas. The average particle size distribution of Rh particles can range from 1.5 to 18 nm. Generally, the smaller the particle size of Rh particles, the larger their specific surface area, thus exhibiting high catalytic performance. However, excessively small Rh particles are prone to coarsening at high temperatures due to Ostwald ripening and agglomeration, which tends to degrade catalytic performance. When the average particle size distribution of Rh particles is above 1.5 nm, Rh particle coarsening at high temperatures can be suppressed, preventing a decrease in catalytic performance. Furthermore, when the average particle size distribution of Rh particles is below 18 nm, the specific surface area of ​​Rh particles becomes sufficiently large, allowing them to exhibit high catalytic performance. The average particle size distribution of Rh particles can range from 3 to 17 nm, or from 4 nm to 14 nm. Alternatively, the average particle size distribution of Rh particles can range from 2 to 8 nm.

[0041] Furthermore, the standard deviation of the Rh particle size distribution can be less than 1.6 nm. By achieving a standard deviation of less than 1.6 nm in the Rh particle size distribution, as shown in the reference example described later, harmful components can be efficiently removed even after the exhaust gas purification material is exposed to a high-temperature environment. By reducing the standard deviation of the Rh particle size distribution to less than 1.6 nm, the number of large Rh particles and the number of small Rh particles that tend to coarsen under high-temperature conditions are reduced. Therefore, even after the exhaust gas purification material is exposed to a high-temperature environment, the Rh particles can still have a sufficiently large specific surface area, resulting in high catalytic performance. The standard deviation of the Rh particle size distribution can be less than 1 nm.

[0042] Furthermore, in this application, the particle size distribution of Rh particles is based on the number of particles obtained by measuring the equivalent circle diameter of the projected area of ​​more than 50 Rh particles from images obtained by transmission electron microscopy (TEM).

[0043] The loading of Rh particles, i.e., the ratio of Rh particles based on the total weight of the metal oxide support and Rh particles, can range from 0.01% to 2% by weight. By ensuring the Rh particle ratio is 0.01% by weight or more, a sufficient amount of Rh particles is present, thus effectively removing harmful components from exhaust gas. By ensuring the Rh particle ratio is 2% by weight or less, the amount of Rh used can be reduced. Furthermore, since the Rh particles are sufficiently loosely loaded on the metal oxide support, Rh particle coarsening at high temperatures can be suppressed, exhibiting sufficient durability against high temperatures. The Rh particle ratio based on the total weight of the metal oxide support and Rh particles can range from 0.2% to 1.8% by weight.

[0044] Materials with a higher alkalinity than the metal oxide carrier (hereinafter appropriately referred to as "high-alkalinity materials") can be in granular form. High-alkalinity materials can, for example, function as oxygen storage materials (OSCs). Examples include cerium oxide and cerium-containing composite oxides (e.g., composite oxides containing cerium oxide as the main component, composite oxides containing cerium oxide and zirconium oxide as the main components (Ce-Zr composite oxides), and composite oxides containing aluminum oxide, cerium oxide, and zirconium oxide as the main components (Al-Ce-Zr composite oxides)). Ce-Zr composite oxides are particularly preferred due to their high oxygen storage capacity and relatively low cost. In addition to the main component, cerium-containing composite oxides may also contain at least one of praseodymium oxide, lanthanum oxide, yttrium oxide, and neodymium oxide as additives, which can form composite oxides together with the main component. When exhaust gas purification materials contain materials that function as OSCs, the exhaust gas purification materials exhibit good exhaust gas purification performance under both oxygen-excess and oxygen-deficient atmospheres.

[0045] Highly alkaline materials can be granular and can have any particle size depending on the purpose.

[0046] In this application, "material with higher basicity than metal oxide support" refers to a material with a lower average electronegativity than the metal oxide support. "Average electronegativity" is a value obtained by weighted averaging of the polarization electronegativity (hereinafter referred to as "electronegativity") of the constituent elements based on the quantity of each element per unit weight. For example, the average electronegativity of composite oxide particles (ACZ particles) containing Al2O3, CeO2, ZrO2, La2O3, Y2O3, and Nd2O3 in the following weight fractions is calculated as follows.

[0047] The average electronegativity of ACZ particles

[0048] = Electronegativity of Al × Weight fraction of Al2O3 / Formula weight of Al2O3 × 2

[0049] +Electronegativity of Ce × Weight fraction of CeO2 / Formula weight of CeO2

[0050] +Zr electronegativity × ZrO2 weight fraction / ZrO2 formula weight

[0051] +Electronegativity of La × Weight fraction of La₂O₃ / Formula weight of La₂O₃ × 2

[0052] +Electronegativity of Y × Weight fraction of Y₂O₃ / Formula weight of Y₂O₃ × 2

[0053] +Nd electronegativity × Nd₂O₃ weight fraction / Nd₂O₃ formula weight × 2

[0054] +O electronegativity × (weight fraction of Al2O3 / formula weight of Al2O3 × 3 + weight fraction of CeO2 / formula weight of CeO2 × 2 + weight fraction of ZrO2 / formula weight of ZrO2 × 2 + weight fraction of La2O3 / formula weight of La2O3 × 3 + weight fraction of Y2O3 / formula weight of Y2O3 × 3 + weight fraction of Nd2O3 / formula weight of Nd2O3 × 3)

[0055] = 1.61 × 0.3 / 101.9 × 2

[0056] +1.12×0.2 / 172.1

[0057] +1.33×0.44 / 123.2

[0058] +1.10×0.02 / 325.8×2

[0059] +1.22×0.02 / 225.8×2

[0060] +1.14×0.02 / 336.4×2

[0061] +3.44×(0.3 / 101.9×3+0.2 / 172.1×2+0.44 / 123.2×2+0.02 / 325.8×3+0.02 / 225.8×3+0.02 / 336.4×3)

[0062] =0.081

[0063] In addition, CeO2, ZrO2 and Pr6O 11 Contains CeO2: 51.4 wt%, ZrO2: 45.6 wt%, and Pr6O2 in the following weight fractions. 11 The average electronegativity of 3.0% by weight of composite oxide particles (CZ particles) is calculated as follows.

[0064] The average electronegativity of CZ particles

[0065] = Electronegativity of Ce × Weight fraction of CeO2 / Formula weight of CeO2

[0066] +Zr electronegativity × ZrO2 weight fraction / ZrO2 formula weight

[0067] +Pr's electronegativity × Pr6O 11 weight fraction / Pr6O 11 formula quantity × 6

[0068] +O electronegativity × (weight fraction of CeO2 / formula weight of CeO2 × 2) + weight fraction of ZrO2 / formula weight of ZrO2 × 2 + Pr6O 11 weight fraction / Pr6O 11 (formula quantity × 11)

[0069] = 1.12 × 0.514 / 172.1

[0070] +1.33×0.456 / 123.2

[0071] +1.13×0.03 / 1021.4×6

[0072] +3.44×(0.514 / 172.1×2+0.456 / 123.2×2+0.03 / 1021.4×11)

[0073] =0.056

[0074] Based on the above calculations, the average electronegativity of the CZ particles in the above composition is lower than that of the ACZ particles in the above composition, and therefore the basicity is higher than that of the ACZ particles in the above composition.

[0075] (2) Manufacturing method of exhaust purification materials

[0076] The manufacturing method of the above-mentioned exhaust gas purification material includes the following steps in sequence: impregnating a metal oxide support with a rhodium compound solution (step S1); drying the metal oxide support impregnated with the rhodium compound solution to obtain a Rh-containing catalyst containing the metal oxide support and Rh particles supported on the metal oxide support (step S2); heating the Rh-containing catalyst to a temperature range of 700-900°C under an inert atmosphere (step S3); and mixing the Rh-containing catalyst with a highly alkaline material (step S4). Each step is described in turn.

[0077] First, the metal oxide support is impregnated with a rhodium compound solution (step S1). Examples of rhodium compound solutions include aqueous solutions of rhodium hydroxide and rhodium nitrate. The impregnation method is not particularly limited. For example, the rhodium compound solution can be impregnated into the metal oxide support by adding distilled water while stirring.

[0078] Next, the metal oxide support impregnated with the rhodium compound solution is dried (step S2). This yields an Rh-containing catalyst containing a metal oxide support and Rh particles supported on the metal oxide support. Calcination may be performed after drying if necessary. In the Rh-containing catalyst, the proportion of Rh particles can be 0.01–2% by weight, particularly in the range of 0.2–1.8% by weight, based on the total weight of the Rh-containing catalyst (i.e., the combined weight of the metal oxide support and Rh particles).

[0079] The Rh-containing catalyst is heated to a temperature range of 700–900°C under an inert atmosphere (step S3). Examples of inert atmospheres include nitrogen and argon. The heating time can be appropriately set, for example, 1–8 hours.

[0080] By heating under an inert atmosphere, the average value and standard deviation of the particle size distribution of Rh particles containing Rh catalyst can be appropriately controlled. Specifically, the average value of the Rh particle size distribution can be in the range of 1.5–18 nm, 3–17 nm, 4–14 nm, or 2–8 nm, and the standard deviation of the Rh particle size distribution can be less than 1.6 nm or less than 1 nm.

[0081] Furthermore, as shown in the embodiments described later, heating in a reducing atmosphere such as hydrogen cannot produce sufficiently large Rh particles, making it difficult to obtain the particle size distribution described above. Heating in an oxidizing atmosphere such as air causes Rh particles to dissolve into the metal oxide support, thus reducing the number of Rh particles on the surface of the metal oxide support.

[0082] Then, the Rh-containing catalyst is mixed with a highly alkaline material (step S4). The mixing method is not particularly limited; for example, the Rh-containing catalyst and the highly alkaline material can be pulverized and mixed. This yields a powdered exhaust gas purification material. It can also be molded into granules or any other shape using methods such as stamping.

[0083] Typically, when fine Rh particles with a diameter of several nm are exposed to high-temperature environments (e.g., above 1000°C), Ostwald curing occurs, resulting in larger Rh particles. The inventors have discovered that Rh on highly basic materials is more stable in its trivalent (oxide) state compared to its 0-valent (metal) state. Furthermore, Rh in its oxide state is prone to evaporation and migration. Therefore, due to the high collision frequency of Rh atoms on highly basic materials, coarser Rh particles are more easily formed compared to those on metal oxide supports. When exhaust gas purification materials containing both an Rh-containing catalyst and a highly basic material are used in high-temperature environments, Rh atoms from the tiny Rh particles on the metal oxide support migrate to the highly basic material, forming coarser Rh particles on the highly basic material. Therefore, when an Rh-containing catalyst is used in conjunction with a highly basic material, the Rh particles become coarser compared to using the Rh-containing catalyst alone, leading to a potential decrease in purification performance. However, in the manufacturing method of the embodiment, as described above, the average value and standard deviation of the particle size distribution of Rh particles on the metal oxide support are controlled by heating under an inert atmosphere, thereby reducing the number of excessively small Rh particles. This prevents or reduces the migration of Rh atoms to highly alkaline materials and the formation of coarse Rh particles caused by Ostwald curing when the exhaust gas purification material is exposed to a high-temperature environment. Therefore, the exhaust gas purification material manufactured using the manufacturing method of the embodiment does not easily experience a decrease in exhaust gas purification performance even under high-temperature environments.

[0084] Furthermore, in the manufacturing method of this embodiment, Rh particles with appropriately controlled particle size are formed by using an impregnation method with a rhodium compound solution and a simple process of heating under an inert atmosphere. Therefore, the manufacturing method of this embodiment has high production efficiency and is suitable for mass production.

[0085] (3) Manufacturing method of exhaust purification device

[0086] An exhaust purification device can be manufactured by configuring the above-mentioned exhaust purification material on a substrate.

[0087] Exhaust purification materials can be formulated together with adhesives, additives, etc. on a substrate.

[0088] There are no particular limitations on the substrate material; for example, a monolithic substrate with a honeycomb structure can be used. The substrate can be formed from ceramic materials with high heat resistance, such as cordierite (2MgO·2Al2O3·5SiO2), alumina, zirconium oxide, and silicon carbide, or from metallic materials made of metal foil such as stainless steel. From a cost perspective, cordierite is preferred as the substrate material.

[0089] When the substrate is a porous body with multiple pores, the exhaust purification material can be disposed on the inner surface of the substrate that defines the pores. That is, in this application, "disposed on the substrate" includes disposed on the outer surface of the substrate and disposed on the inner surface of the substrate.

[0090] Exhaust gas purification materials can be configured onto a substrate, for example, as follows: First, a slurry containing the exhaust gas purification material is prepared. The slurry may also contain binders, additives, etc. The properties of the slurry, such as viscosity and particle size of solid components, can be appropriately adjusted. The prepared slurry is then applied to a predetermined area of ​​the substrate. For example, the predetermined area of ​​the substrate is immersed in the slurry, and after a predetermined time, the substrate is lifted out of the slurry, thereby coating the predetermined area of ​​the substrate with the slurry. Alternatively, the slurry can be applied to the substrate by flowing it into the substrate and blowing it with a blower to spread the slurry. Next, the slurry is dried and fired at a predetermined temperature and time. Thus, the exhaust gas purification material is configured onto the substrate.

[0091] The exhaust purification device described in this embodiment is applicable to various vehicles equipped with internal combustion engines.

[0092] Example

[0093] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments.

[0094] Examples 1-5

[0095] (1) Preparation of test samples

[0096] As a metal oxide support, composite oxide particles containing Al2O3, CeO2, and ZrO2 as main components, and also containing La2O3, Y2O3, and Nd2O3 (hereinafter appropriately referred to as "ACZ particles"). The weight fractions of each component in the ACZ particles are: Al2O3: 30 wt%, CeO2: 20 wt%, ZrO2: 44 wt%, La2O3: 2 wt%, Y2O3: 2 wt%, and Nd2O3: 2 wt%.

[0097] While stirring distilled water, 10 g of ACZ particles and 8.0 g of rhodium hydroxide aqueous solution (0.5 wt%) were added sequentially, and the mixture was stirred for 10 minutes. The resulting mixture was dried and calcined by heating in an electric furnace at 500°C for 2 hours in air atmosphere. This yielded a Rh-containing catalyst containing ACZ particles and rhodium (Rh) particles supported on the ACZ particles. Based on the total weight of ACZ and Rh particles, the Rh-containing catalyst contained 0.34 wt% Rh particles.

[0098] The Rh-containing catalyst was heated for 5 hours under a nitrogen atmosphere at the temperatures shown in Table 1. After heating, the Rh-containing catalyst was observed using a transmission electron microscope (TEM) to determine the particle size distribution of the Rh particles (initial Rh particles) supported on the ACZ particles. The mean and standard deviation of the initial Rh particle size distribution are shown in Table 1.

[0099] In the heated Rh-containing catalyst, 10g of a catalyst containing CeO2 and ZrO2 as main components, and also containing Pr6O, was added. 11 The composite oxide particles (hereinafter appropriately referred to as "CZ particles"). The weight fractions of each component in the CZ particles are: CeO2: 51.4 wt%, ZrO2: 45.6 wt%, Pr6 ... 11 (3.0% by weight), pulverize and mix in a mortar. Measure 2g of the obtained powder, shape it, and obtain particles.

[0100] (2) Determination of the average particle size of Rh particles after aging treatment

[0101] The particles were heated to 1100°C and alternately exposed to a stoichiometric mixture (air-fuel ratio A / F = 14.6) and a lean mixture (A / F > 14.6) at a time ratio of 1:1 for 5 hours. Then, the average particle size of the Rh particles in the particles of Examples 2 and 4 was determined using the carbon monoxide pulse method. The results are shown in Table 1.

[0102] (3) Evaluation of exhaust gas purification performance

[0103] While circulating the aged particles through a gas of the composition listed in Table 2 at a flow rate of 15 L / min, the particles were heated to 600°C and maintained for 5 minutes, then cooled to 150°C. Then, while continuing gas circulation, the particles were heated to 600°C at a rate of 20°C / min, and the particle temperature at which 50% of the NOx in the gas was removed was measured (hereinafter appropriately denoted as "NOx"). X -T50"。The results are shown in Table 1.

[0104] Comparative Example 1

[0105] The Rh-containing catalyst was not heated under a nitrogen atmosphere; otherwise, the particles were prepared in the same manner as in Example 1. The mean and standard deviation of the initial Rh particle size distribution are shown in Table 1. The particles underwent aging treatment and exhaust gas purification performance evaluation in the same manner as in Example 1. The results are shown in Table 1.

[0106] Comparative Examples 2-3

[0107] The Rh-containing catalyst was heated to the temperature listed in Table 1 under a nitrogen atmosphere, and the particles were prepared in the same manner as in Example 1. The average and standard deviation of the initial Rh particle size distribution are shown in Table 1. The particles were aged and their exhaust gas purification performance was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0108] Comparative Example 4

[0109] The Rh-containing catalyst was heated in an air atmosphere instead of a nitrogen atmosphere, and the particles were prepared in the same manner as in Example 3. When the heated Rh-containing catalyst was observed with TEM, no Rh particles supported on the ACZ particles were identified. It is believed that Rh was dissolved in the ACZ particles by heating in an air atmosphere. The particles underwent aging treatment and exhaust gas purification performance evaluation in the same manner as in Example 1. The results are shown in Table 1.

[0110] Comparative Example 5

[0111] The Rh-containing catalyst was heated in a hydrogen atmosphere instead of a nitrogen atmosphere, and the particles were prepared in the same manner as in Example 3. The mean and standard deviation of the initial Rh particle size distribution are shown in Table 1. The particles were aged and their exhaust gas purification performance was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0112] Comparative Example 6

[0113] The particles were prepared in the same manner as in Example 4, except that ACZ particles were used instead of CZ particles. The particles underwent aging treatment and their exhaust gas purification performance was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0114] Comparative Example 7

[0115] The Rh-containing catalyst was not heated under a nitrogen atmosphere, and the particles were prepared in the same manner as in Comparative Example 6. The particles underwent aging treatment and exhaust gas purification performance evaluation in the same manner as in Example 1. The results are shown in Table 1.

[0116] NO in Examples 1-5 and Comparative Examples 1-5 X A comparison with T50 shows that heating the Rh-containing catalyst to a temperature range of 700–900°C under a nitrogen atmosphere improves NOx reduction performance. As shown in Table 1, in Examples 1-5, heating to a temperature range of 700–900°C under a nitrogen atmosphere resulted in an average Rh particle size distribution ranging from 1.5 to 18 nm, and a standard deviation of the particle size distribution becoming less than 1.6 nm. This indicates that the coarsening of Rh particles during aging treatment was suppressed, as was the reduction in the specific surface area of ​​Rh particles, resulting in high NOx reduction performance. This is particularly evident in the NOx reduction of Examples 2 and 4. XWhen comparing -T50, it was found that heating at 850°C under a nitrogen atmosphere resulted in superior NOx reduction performance compared to heating at 750°C under a nitrogen atmosphere. It was concluded that in Example 4, where the heating temperature was 850°C, the average particle size of the aged Rh particles was smaller than that in Example 2, and the Rh particles had a larger specific surface area, thus resulting in higher NOx reduction performance. Furthermore, the NOx reduction performance of Examples 3 and Comparative Examples 4-5 was also compared. X A comparison with T50 shows that, in order to properly control the particle size distribution of Rh particles, heating of the Rh-containing catalyst is required under a nitrogen atmosphere.

[0117] Compare NO in Example 6 X -T50 compared to NO in Example 7 X -T50 is higher. This indicates that heating under a nitrogen atmosphere in Comparative Example 6 did not improve NOx reduction performance. In Comparative Examples 6-7, it is believed that since the particles do not contain materials with a higher alkalinity than the ACZ particles used as catalyst supports, significant coarsening of Rh particles does not occur during aging treatment even without controlling the particle size distribution of Rh particles.

[0118] Table 1

[0119]

[0120] Table 2

[0121] Element Proportion CO 0.52% by volume <![CDATA[O2]]> 0.50% by volume <![CDATA[C3H6]]> 3000ppmC NO 0.32% by volume <![CDATA[CO2]]> 14% by volume <![CDATA[H2]]> 3% by volume <![CDATA[N2]]> margin

[0122] The following reference examples illustrate the results of experiments conducted to determine an initial Rh particle size distribution suitable for preventing or reducing the degradation of exhaust gas purification performance under high-temperature environments. It is understood that the preferred initial Rh particle size distribution obtained from the reference examples, which employs a method different from the embodiments described above to load Rh particles onto ACZ particles, can also prevent or reduce the degradation of exhaust gas purification performance under high-temperature environments in exhaust gas purification materials manufactured by the methods of the embodiments.

[0123] Reference Example 1

[0124] (1) Preparation of test samples

[0125] Polyvinylpyrrolidone and rhodium chloride were dissolved in ethylene glycol. Sodium hydroxide was added to the resulting solution. The solution was then heated at 200°C overnight. This yielded a rhodium particle dispersion (Rh particle dispersion).

[0126] Rh particle dispersion and ACZ particles were added to distilled water, and the resulting mixture was heated and dried while stirring. The resulting particles were placed in a dryer maintained at 120°C for 2 hours to further remove moisture, and then calcined in an electric furnace at 500°C for 2 hours in an air atmosphere.

[0127] TEM observation of the sintered particles confirmed the presence of Rh particles loaded onto the ACZ particles. Furthermore, based on the TEM images, the particle size distribution of the Rh particles loaded onto the ACZ particles (initial Rh particles) was determined. The mean and standard deviation of the initial Rh particle size distribution are shown in Table 3. Additionally, the weight ratio of Rh particles in the sintered particles (i.e., the weight ratio of Rh particles based on the total weight of ACZ particles and Rh particles) is also shown in Table 3.

[0128] Add an equal weight of CeO2 and ZrO2 composite oxide particles (hereinafter appropriately referred to as "CZ-2 particles") to the calcined particles, and pulverize and mix them in a mortar. Take 2g of the obtained powder, shape it, and obtain granules.

[0129] (2) Determination of the average particle size of Rh particles after aging treatment

[0130] The average particle size of the Rh particles after aging treatment was determined in the same manner as in Example 2. The results are shown in Table 3.

[0131] (3) Evaluation of exhaust gas purification performance

[0132] The exhaust gas purification performance of the aged particles was measured in the same manner as in Example 1. The results are shown in Table 3.

[0133] See Example 2

[0134] The particles were prepared in the same manner as in Reference Example 1, except that an aqueous solution of rhodium nitrate was used instead of the Rh particle dispersion. The mean and standard deviation of the initial Rh particle size distribution, and the weight ratio of Rh particles in the calcined particles are shown in Table 3.

[0135] The average particle size of the Rh particles after aging treatment and the exhaust gas purification performance were determined in the same manner as in Reference Example 1. The results are shown in Table 3.

[0136] See Example 3

[0137] The Rh particle dispersion prepared as described below was used instead of the Rh particle dispersion prepared in Reference Example 1, and the particles were prepared in the same manner as in Reference Example 1. 0.2 g of rhodium(III) nitrate was dissolved in 50 mL of ion-exchanged water to prepare an aqueous solution of rhodium nitrate (pH 1.0). Additionally, an aqueous solution of tetraethylammonium hydroxide (pH 14) with a concentration of 175 g / L was prepared. The aqueous solutions of rhodium nitrate and tetraethylammonium hydroxide were reacted using a reactor (microreactor) with two plates as gap adjustment components. Specifically, the Rh particle dispersion was prepared by introducing the aqueous solutions of rhodium nitrate and tetraethylammonium hydroxide at a molar ratio of 18:1 (tetraethylammonium hydroxide:rhodium nitrate) into a reaction field with a gap set to 10 μm. The resulting Rh particle dispersion had a pH of 14.

[0138] The average and standard deviation of the initial Rh particle size distribution, and the weight ratio of Rh particles in the sintered particles are shown in Table 3.

[0139] The average particle size of the Rh particles after aging treatment and the exhaust gas purification performance were determined in the same manner as in Reference Example 1. The results are shown in Table 3.

[0140] See Example 4

[0141] The amount of sodium hydroxide used in the preparation of the Rh particle dispersion was changed, but the particles were prepared in the same manner as in Reference Example 1. The average and standard deviation of the initial Rh particle size distribution, and the weight ratio of Rh particles in the calcined particles are shown in Table 3.

[0142] The average particle size of the Rh particles after aging treatment and the exhaust gas purification performance were determined in the same manner as in Reference Example 1. The results are shown in Table 3.

[0143] See Example 5-7

[0144] The amount of sodium hydroxide used in the preparation of the Rh particle dispersion was changed, but the particles were prepared in the same manner as in Reference Example 1. The average and standard deviation of the initial Rh particle size distribution, and the weight ratio of Rh particles in the calcined particles are shown in Table 3.

[0145] The exhaust gas purification performance of the particles after aging treatment was evaluated in the same manner as in Reference Example 1. The results are shown in Table 3.

[0146] See Example 8

[0147] A mixture of distilled water, Rh particle dispersion, and ACZ particles was prepared in the same manner as in Reference Example 1, and then dried and calcined. The resulting particles were heated to 900°C and then alternately exposed to a mixture of gases with a stoichiometric ratio (air-fuel ratio A / F = 14.6) and a mixture of gases with excess oxygen (lean: A / F > 14.6) for 5 hours at a fixed time ratio of 1:1.

[0148] Next, the particles exposed to the mixed gas were observed using TEM. Based on the TEM images, the particle size distribution of the Rh particles (initial Rh particles) loaded on the ACZ particles was determined. The mean and standard deviation of the initial Rh particle size distribution, as well as the weight ratio of Rh particles in the sintered particles, are shown in Table 3.

[0149] Add an equal weight of CZ-2 particles to the particles exposed to the mixed gas, then pulverize and mix in a mortar. Measure 2g of the resulting powder, shape it into granules.

[0150] The exhaust gas purification performance of the particles after aging treatment was evaluated in the same manner as in Reference Example 1. The results are shown in Table 3.

[0151] See Example 9

[0152] The particles were prepared in the same manner as in Reference Example 1, except that the mixing ratio of the Rh particle dispersion and ACZ particles was changed. The average and standard deviation of the initial Rh particle size distribution, and the weight ratio of Rh particles in the sintered particles are shown in Table 3.

[0153] The particulate exhaust purification performance was evaluated in the same manner as in Reference Example 1. The results are shown in Table 3.

[0154] See Example 10

[0155] The particles were prepared in the same manner as in Reference Example 3, except that the mixing ratio of the Rh particle dispersion and ACZ particles was changed. The average value and standard deviation of the initial Rh particle size distribution, and the weight ratio of Rh particles in the sintered particles are shown in Table 3.

[0156] The particulate exhaust purification performance was evaluated in the same manner as in Reference Example 1. The results are shown in Table 3.

[0157] Reference Examples 1 and 4-6, where the initial Rh particle average size distribution is in the range of 1.5–18 nm, show NO. X -T50 is higher than NO in reference examples 2, 3, and 7. XThe low T50 indicates that the particles in Reference Examples 1 and 4-6 have higher NOx reduction performance. The measurement results of the average particle size of Rh particles after aging treatment in Reference Examples 1 and 4 and Reference Examples 2 and 3 show that in Reference Examples 1 and 4, where the average initial Rh particle size distribution is 1.5 nm or more, the coarsening of Rh particles caused by aging treatment is suppressed compared to Reference Examples 2 and 3, where the average initial Rh particle size distribution is less than 1.5 nm. Therefore, it is believed that in Reference Examples 1 and 4-6, where the average initial Rh particle size distribution is 1.5 nm or more, Rh particle coarsening is suppressed, thereby suppressing the reduction of the specific surface area of ​​Rh particles, thus resulting in high NOx reduction performance. Furthermore, it is believed that in Reference Example 7, where the average initial Rh particle size distribution exceeds 18 nm, the NOx reduction performance is poor because the specific surface area of ​​the Rh particles is small before aging treatment.

[0158] In Reference Example 8, similar to Reference Examples 1 and 4-6, the average particle size distribution of the initial Rh particles ranged from 1.5 to 18 nm. However, the standard deviation of the initial Rh particle size distribution was greater than 1.6 nm, which was larger than that of Reference Examples 1 and 4-6. This indicates that the particles in Reference Example 8 contained more tiny Rh particles compared to those in Reference Examples 1 and 4-6. It is believed that in Reference Example 8, due to the aging treatment, the tiny Rh particles became coarser, resulting in a smaller specific surface area of ​​the Rh particles after aging compared to Reference Examples 1 and 4-6. Consequently, the NOx reduction performance was lower than that of Reference Examples 1 and 4-6.

[0159] Similarly, the particles of Reference Example 9, with an initial Rh particle size distribution average in the range of 1.5–18 nm, showed lower NO content compared to the particles of Reference Example 10, with an initial Rh particle size distribution average of less than 1.5 nm. X -T50, i.e., higher NOx reduction performance. Furthermore, the difference in NOx reduction performance between Reference Example 9 and Reference Example 10 is smaller than the difference in NOx reduction performance between Reference Example 1 and Reference Example 3. This indicates that when the weight proportion of Rh particles in the calcined particles is in the range of 0.01 to 2 wt%, particularly 0.2 to 1.8 wt%, sufficient improvement in NOx reduction performance can be obtained by setting the average particle size distribution of the initial Rh particles to 1.5 nm or more. However, when the weight proportion of Rh particles in the calcined particles is larger (e.g., exceeding 2 wt%), even setting the average particle size distribution of the initial Rh particles to 1.5 nm or more may not result in sufficient improvement in NOx reduction performance.

[0160] Table 3

[0161]

Claims

1. A method for manufacturing an exhaust purification material, comprising the following steps: Step (a): Impregnate the metal oxide support with a rhodium compound solution; Step (b): The metal oxide support impregnated with the rhodium compound solution is dried to obtain a rhodium-containing catalyst comprising the metal oxide support and rhodium particles supported on the metal oxide support; Step (c): The rhodium-containing catalyst is heated to a temperature range of 700~900℃ under an inert atmosphere, controlling the average particle size distribution of the rhodium particles to be 1.5~18nm, and the standard deviation of the particle size distribution to be less than 1.6nm; and Step (d): The rhodium-containing catalyst is mixed with a material whose basicity is higher than that of the metal oxide support. The metal oxide support is an oxide containing zirconium oxide as the main component, a composite oxide containing zirconium oxide and aluminum oxide as the main components, or a composite oxide containing zirconium oxide, aluminum oxide, and cerium oxide as the main components. The material with higher alkalinity than the metal oxide carrier is cerium oxide, a composite oxide containing cerium oxide as the main component, a composite oxide containing cerium oxide and zirconium oxide as the main components, or a composite oxide containing aluminum oxide, cerium oxide and zirconium oxide as the main components.

2. In the method for manufacturing exhaust purification material according to claim 1, in the rhodium-containing catalyst after step (c), the average particle size distribution of the rhodium particles is 4~14 nm.

3. In the method for manufacturing exhaust purification material according to claim 1, in the rhodium-containing catalyst after step (c), the average particle size distribution of the rhodium particles is 2~8 nm.

4. The method for manufacturing exhaust purification material according to any one of claims 1 to 3, wherein the rhodium-containing catalyst contains 0.01 to 2% by weight of the rhodium particles based on the total weight of the metal oxide support and the rhodium particles.

5. The method for manufacturing exhaust purification material according to any one of claims 1 to 3, wherein the metal oxide carrier is a composite oxide containing zirconium oxide, aluminum oxide and cerium oxide as main components, and the material with higher alkalinity than the metal oxide carrier is a composite oxide containing cerium oxide and zirconium oxide as main components.

6. The method for manufacturing the exhaust purification material according to any one of claims 1 to 3, wherein the inert atmosphere is a nitrogen atmosphere.

7. A method for manufacturing an exhaust gas purification device, comprising: The exhaust purification material is obtained by the manufacturing method of the exhaust purification material according to any one of claims 1 to 3; and The exhaust purification material is disposed on a substrate.

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