Catalyst composition for exhaust gas purification and catalyst for exhaust gas purification

Abstract

Disclosed is a catalyst composition for exhaust gas purification, which comprises Ce-based oxide particles, Ce-Zr-based composite oxide particles, Al-based oxide particles, and a noble metal element, wherein the amount of Ce in the Ce-based oxide particles, based on the mass of the Ce-based oxide particles, is 90% by mass or greater in terms of the CeO2 equivalent amount, the amount of Ce in the Ce-Zr-based composite oxide particles, based on the mass of the Ce-Zr-based composite oxide particles, is 5% by mass or greater and 90% by mass or less in terms of the CeO2 equivalent amount, the average particle diameter of the Ce-based oxide particles is 0.10 μm or greater and 15 μm or less, and the amount of the Ce-based oxide particles in the catalyst composition for exhaust gas purification, based on the mass of the catalyst composition for exhaust gas purification, is 2.0% by mass or greater and 30% by mass or less.

Description

Technical Field

[0001] This invention relates to a catalyst composition for waste gas purification and a catalyst for waste gas purification. Background Technology

[0002] The exhaust gases emitted by internal combustion engines in automobiles, motorcycles, etc., contain hydrocarbons (THC), carbon monoxide (CO), and nitrogen oxides (NOx). x Harmful components such as THC are removed. A three-way catalyst is used as a catalyst for purifying waste gas to render these harmful components harmless. This catalyst possesses catalytic activity that oxidizes THC into water and carbon dioxide, oxidizes CO into carbon dioxide, and reduces NOx into nitrogen.

[0003] In catalysts used for waste gas purification, such as three-way catalytic converters, Al-based oxides such as alumina (Al2O3) and Ce-Zr composite oxides are used as supports for loading catalytically active components (such as precious metal particles like Pt, Pd, and Rh) (e.g., Patent Documents 1 and 2). It should be noted that in this specification, "Al-based oxides" refers to Al-containing oxides in which the Al2O3 content (based on the mass of the oxide) is 70% or more by mass; "Ce-Zr composite oxides" refers to composite oxides containing Ce and Zr in which the CeO2 content (based on the mass of the composite oxide) is 5% or more and 90% or less by mass.

[0004] Ce-Zr composite oxides are materials with oxygen storage capacity (OSC), which can mitigate fluctuations in oxygen concentration in exhaust gas and thus expand the working window of the catalyst. Other Ce-based oxides, such as cerium oxide (CeO2), can also be used as OSC materials (e.g., Patent Document 2). However, due to its low oxygen storage capacity, CeO2 is generally not used as a support for the catalytically active component of a three-way catalyst. It should be noted that in this specification, "Ce-based oxides" refers to Ce-containing oxides in which the CeO2 content (based on the mass of the oxide) is 90% or more by mass.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-039069

[0008] Patent Document 2: Japanese Patent Application Publication No. 2006-297372 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] While Ce-based oxides exhibit high affinity for catalytically active components (such as noble metal particles like Pt, Pd, and Rh), they suffer from low heat resistance. Conversely, Al-based oxides and Ce-Zr composite oxides, while possessing high heat resistance, exhibit relatively low affinity for catalytically active components. Therefore, by combining Ce-based oxides, Ce-Zr composite oxides, and Al-based oxides as supports for catalytically active components, the weaknesses of Ce-based oxides can be mitigated by using Ce-Zr composite oxides and Al-based oxides, and vice versa. However, even with this combined approach, a decrease in exhaust gas purification performance can still occur.

[0011] For example, when CeO2 is used as a support for catalytically active components, its low heat resistance can sometimes lead to CeO2 aggregation and the disappearance of its micropores (i.e., a decrease in specific surface area). These issues can cause the catalytically active components to become buried, resulting in a decline in exhaust gas purification performance. Since CeO2 aggregation and a decrease in specific surface area are more likely to occur at high temperatures, exhaust gas purification performance is prone to decline after exposure to high temperatures. It should be noted that in this specification, "high temperature" refers to temperatures such as 800°C or higher, especially 900°C or higher.

[0012] Therefore, the object of the present invention is to provide a catalyst composition and a catalyst for exhaust gas purification using Ce-based oxides, Ce-Zr composite oxides and Al-based oxides, wherein the catalyst composition and the catalyst for exhaust gas purification improve the exhaust gas purification performance (especially the exhaust gas purification performance after exposure to high temperature environment).

[0013] Solution for solving the problem

[0014] The inventors have discovered that by adjusting the average particle size and content of Ce-based oxides in a catalyst composition for exhaust gas purification and an exhaust gas purification catalyst using Ce-based oxides, Ce-Zr composite oxides and Al-based oxides, the exhaust gas purification performance (especially the exhaust gas purification performance after exposure to high-temperature environments) can be improved.

[0015] This invention is based on the above understanding and includes the following technical solutions.

[0016] [1] A catalyst composition for purifying waste gas, comprising Ce-based oxide particles, Ce-Zr-based composite oxide particles, Al-based oxide particles, and noble metal elements.

[0017] Based on the mass of the Ce-based oxide particles, the CeO2 equivalent content of Ce in the Ce-based oxide particles is 90% or more by mass.

[0018] Based on the mass of the Ce-Zr composite oxide particles, the CeO2 conversion content of Ce in the Ce-Zr composite oxide particles is more than 5% by mass and less than 90% by mass.

[0019] The average particle size of the Ce-based oxide particles is greater than 0.10 μm and less than 15 μm.

[0020] Based on the mass of the catalyst composition for waste gas purification, the amount of Ce-based oxide particles in the catalyst composition for waste gas purification is 2.0% by mass or more and 30% by mass or less.

[0021] [2] A catalyst for purifying waste gas, comprising a substrate and a catalyst layer disposed on the substrate.

[0022] The catalyst layer is composed of the catalyst composition for waste gas purification described in [1].

[0023] The effects of the invention

[0024] According to the present invention, a catalyst composition and a catalyst for exhaust gas purification using Ce-based oxides, Ce-Zr composite oxides and Al-based oxides can be provided, wherein the catalyst composition and the catalyst for exhaust gas purification improve the exhaust gas purification performance (especially the exhaust gas purification performance after exposure to high temperature environment). Attached Figure Description

[0025] Figure 1 This is a partial cross-sectional view showing the state in which the exhaust gas purification catalyst according to the first embodiment of the present invention is disposed in the exhaust passage of an internal combustion engine.

[0026] Figure 2 for Figure 1 AA-line cross-section view.

[0027] Figure 3 for Figure 2 An enlarged map of the region indicated by the symbol R in the figure.

[0028] Figure 4 for Figure 1 BB line cross-section.

[0029] Figure 5 This is a cross-sectional view (and) of the catalyst for exhaust gas purification according to the second embodiment of the present invention. Figure 4 (Corresponding cross-sectional view). Detailed Implementation

[0030] Catalyst Compositions for Waste Gas Purification

[0031] The catalyst composition for purifying waste gas of the present invention will be described below.

[0032] <Ce-based oxide particles>

[0033] The catalyst composition for exhaust gas purification of the present invention comprises Ce-based oxide particles. It should be noted that, unless otherwise specified, in this specification, "Ce-based oxide particles" refers to the Ce-based oxide particles contained in the catalyst composition for exhaust gas purification of the present invention, and is distinguished from the Ce-based oxide particles used as raw materials in the catalyst composition for exhaust gas purification of the present invention (hereinafter referred to as "Ce-based oxide particles as raw materials").

[0034] Ce-based oxide particles are composed of Ce-based oxides. Based on the mass of the Ce-based oxide particles, the CeO2 conversion content of Ce in the Ce-based oxide particles is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. This increases the affinity of the Ce-based oxide particles for the catalytically active components, suppressing the sintering of the catalytically active components loaded on the Ce-based oxide particles. Therefore, the dispersion of the catalytically active components is improved, and the exhaust gas purification performance of the catalyst composition for exhaust gas purification is enhanced. This effect is particularly significant in catalyst compositions for exhaust gas purification after exposure to high-temperature environments. This is because sintering of the catalytically active components loaded on the Ce-based oxide particles is more likely to occur after exposure to high-temperature environments. It should be noted that although theoretically the upper limit is 100% by mass, considering the unavoidable presence of impurities, the actual value may be less than 100% by mass.

[0035] The CeO2 conversion of Ce in Ce-based oxide particles can be determined by analyzing a sample obtained from the catalyst composition for exhaust gas purification of the present invention using energy-dispersive X-ray spectroscopy (EDS (also known as EDX)). The determination is based on the elemental mapping obtained therefrom and the EDS elemental analysis of the specified particles. Specifically, by using elemental mapping, Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles are qualitatively identified (color-coded), and the compositional analysis (elemental analysis) of the specified particles is performed to determine the oxide conversion of the specified elements in the specified particles.

[0036] From the perspective of further improving the affinity of Ce-based oxide particles for catalytically active components and more efficiently suppressing the sintering of catalytically active components loaded on Ce-based oxide particles, based on the mass of Ce-based oxide particles, the ZrO2 conversion content of Zr in Ce-based oxide particles is preferably less than 10% by mass, more preferably less than 5% by mass, more preferably less than 3% by mass, and even more preferably less than 1% by mass. The lower limit is zero. The ZrO2 conversion content of Zr in Ce-based oxide particles is smaller than that of Zr in Ce-Zr composite oxide particles, which distinguishes Ce-based oxide particles from Ce-Zr composite oxide particles. The method for determining the ZrO2 conversion content of Zr in Ce-based oxide particles is the same as the method for determining the CeO2 conversion content of Ce in Ce-based oxide particles.

[0037] When the average particle size of Ce-based oxide particles is too small, a solid-state reaction occurs at the interface between Ce-based oxide particles and Ce-Zr composite oxide particles, preventing the Ce-based oxide particles from existing in particulate form. This solid-state reaction at the interface between Ce-based oxide particles and Ce-Zr composite oxide particles is prone to occur after exposure to high-temperature environments. Conversely, when the average particle size of Ce-based oxide particles is too large, their dispersibility decreases, and their contact with the catalytically active components also decreases. Therefore, in the exhaust gas purification catalyst composition of the present invention, by adjusting the average particle size and amount of Ce-based oxide particles, the exhaust gas purification performance (especially the exhaust gas purification performance after exposure to high-temperature environments) of the catalyst composition is improved.

[0038] From the perspective of improving the exhaust gas purification performance of the catalyst composition for exhaust gas purification (especially the exhaust gas purification performance after exposure to high temperature environment), the average particle size of Ce-based oxide particles is preferably 0.10 μm or more and 15 μm or less, more preferably 0.50 μm or more and 12 μm or less, even more preferably 1.0 μm or more and 10 μm or less, and even more preferably 2.0 μm or more and 7.0 μm or less.

[0039] The method for determining the average particle size of Ce-based oxide particles is as follows: A sample obtained from the catalyst composition for exhaust gas purification of the present invention is observed using a scanning electron microscope. The fixed-direction diameter (Ferret diameter) of 100 randomly selected Ce-based oxide particles within the field of view is measured, and the average value is taken as the average particle size of the Ce-based oxide particles. It should be noted that the average particle size of the Ce-based oxide particles used as raw materials is kept constant during the manufacture of the catalyst composition for exhaust gas purification of the present invention; therefore, the average particle size of the Ce-based oxide particles is usually the same as that of the Ce-based oxide particles used as raw materials.

[0040] The average particle size of Ce-based oxide particles can be adjusted using known pulverizing methods such as ball milling, or it can be adjusted during the manufacturing of Ce-based oxide particles using granulation methods such as spray drying.

[0041] From the perspective of improving the exhaust gas purification performance of the catalyst composition for exhaust gas purification (especially the exhaust gas purification performance after exposure to high temperature environment), based on the mass of the catalyst composition for exhaust gas purification of the present invention, the amount of Ce-based oxide particles in the catalyst composition for exhaust gas purification of the present invention is preferably 2.0% by mass or more and 30% by mass or less, more preferably 3.0% by mass or more and 30% by mass or less, even more preferably 5.0% by mass or more and 25% by mass or less, and even more preferably 10% by mass or more and 20% by mass or less.

[0042] The method for determining the amount of Ce-based oxide particles in the catalyst composition for exhaust gas purification of the present invention is carried out according to the following steps (A) to (D).

[0043] (A) For the sample obtained from the catalyst composition for exhaust gas purification, elemental analysis was performed using inductively coupled plasma atomic emission spectrometry (ICP), X-ray fluorescence analysis (XRF), scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) to determine the types of constituent elements of the entire sample, and the content of each element was calculated by oxide conversion.

[0044] (B) For samples obtained from catalyst compositions for exhaust gas purification, elemental mapping based on SEM observation and SEM-EDX was performed to determine the types of particles contained in the samples (including Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles).

[0045] (C) For each type of particle, elemental analysis was performed on any selected number (e.g., 50) particles using SEM-EDX to determine the constituent elements of the particles, and the content of each element was calculated by oxide conversion. For each type of particle, the average content of each element was taken as the content of each element.

[0046] (D) By constructing and solving equations that express the relationship between the content of each element in the sample, the content of each element in each type of particle, and the content of each type of particle in the sample, the content of each type of particle in the sample can be calculated.

[0047] For example, when the Ce source, Zr source and Al source in the catalyst composition for exhaust gas purification of the present invention are composed of only three types of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles, the amount of Ce-based oxide particles is calculated as follows.

[0048] First, for the sample obtained from the catalyst composition for exhaust gas purification of the present invention, SEM-EDX analysis was performed on 5 randomly selected fields of view (each field of view contains more than 20 particles) to determine the types of constituent elements of the entire sample, and the content (average value) of each element was calculated by oxide conversion.

[0049] Next, for the samples obtained from the catalyst composition for exhaust gas purification, elemental mapping based on SEM observation and SEM-EDX was performed to determine the types of particles contained in the samples (including Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles).

[0050] Next, for each type of particle, elemental analysis was performed on 50 randomly selected particles using SEM-EDX to determine the types of elements constituting the particles, and the content (average value) of each element was calculated by oxide conversion.

[0051] By following the steps above, the following content rates can be obtained.

[0052] • The percentage of Ce in the entire sample as converted to CeO2 (hereinafter referred to as "P") T ")

[0053] • The Ce content in Ce-based oxide particles, calculated as CeO2 (hereinafter referred to as "P1").

[0054] • The Ce content in Ce-Zr composite oxide particles, calculated as CeO2 (hereinafter referred to as "P2").

[0055] • The Ce content in Al-based oxide particles, calculated as CeO2 (hereinafter referred to as "P3").

[0056] • The Zr content in the entire sample, converted to ZrO2 (hereinafter referred to as "Q") T ")

[0057] • The Zr content in Ce-based oxide particles, calculated as ZrO2 (hereinafter referred to as "Q1").

[0058] • The Zr content in Ce-Zr composite oxide particles, calculated as ZrO2 (hereinafter referred to as "Q2").

[0059] • The Zr content in Al-based oxide particles, calculated as ZrO2 (hereinafter referred to as "Q3").

[0060] • The percentage of Al in the entire sample as Al2O3 (hereinafter referred to as "R") T ")

[0061] • The content of Al in Ce-based oxide particles, calculated as Al₂O₃ (hereinafter referred to as "R₁").

[0062] • The Al content in Ce-Zr composite oxide particles, calculated as Al2O3 (hereinafter referred to as "R2").

[0063] • The percentage of Al in Al-based oxide particles, calculated as Al₂O₃ (hereinafter referred to as "R₃").

[0064] Next, by constructing and solving equations that express the relationship between the content of each element in the sample, the content of each element in each type of particle, and the content of each type of particle in the sample, the content of each type of particle in the sample is calculated.

[0065] Specifically, when the content (mass basis) of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in the catalyst composition for exhaust gas purification of the present invention is set as X, Y and Z, the following formulas (1) to (3) are valid.

[0066] P T =X×P1+Y×P2+Z×P3···(1)

[0067] Q T =X×Q1+Y×Q2+Z×Q3···(2)

[0068] R T =X×R1+Y×R2+Z×R3···(3)

[0069] X, Y and Z are obtained from the above formulas (1) to (3), and the amount of Ce-based oxide particles in the catalyst composition for exhaust gas purification of the present invention is obtained from X.

[0070] The crystallite diameter of CeO2 in Ce-based oxide particles is preferably 7 nm or more, more preferably 10 nm or more, even more preferably 20 nm or more, and even more preferably 30 nm or more. This suppresses the aggregation of Ce-based oxide particles, the disappearance of the micropores of Ce-based oxide particles (i.e., a decrease in specific surface area), and the burial of catalytically active components within the Ce-based oxide particles. Therefore, the dispersion of catalytically active components and the specific surface area of ​​the catalyst composition for exhaust gas purification are increased, thereby improving the exhaust gas purification performance of the catalyst composition for exhaust gas purification. This effect is particularly significant in catalyst compositions for exhaust gas purification after exposure to high-temperature environments. This is because the aggregation of Ce-based oxide particles, the decrease in the specific surface area of ​​Ce-based oxide particles, and the burial of catalytically active components within the Ce-based oxide particles tend to occur after exposure to high-temperature environments. It should be noted that the upper limit of the crystallite diameter of CeO2 in Ce-based oxide particles is, for example, 200 nm, preferably 100 nm, and more preferably 55 nm. These upper limits can be combined with any of the aforementioned lower limits.

[0071] The method for determining the crystallite diameter of CeO2 in Ce-based oxide particles is as follows. X-ray diffraction (XRD) is performed using a powder sample obtained from the catalyst composition for exhaust gas purification of the present invention and a commercially available X-ray diffraction apparatus. In the obtained XRD pattern, peaks originating from CeO2 at 2θ = 55–58° and peaks at 2θ = 46–49° are identified. The crystallite diameter is determined using the Scherrer equation for the identified peaks. The specific determination method is as described in the examples. The crystallite diameter determined from the peak at 2θ = 55–58° and the crystallite diameter determined from the peak at 2θ = 46–49° are compared, and the larger crystallite diameter is selected as the crystallite diameter of CeO2 in the Ce-based oxide particles. In the obtained XRD pattern, if either the peak at 2θ = 55–58° or the peak at 2θ = 46–49° originating from CeO2 cannot be determined because it originates from other components besides CeO2, the crystallite diameter obtained from the determined peak shall be taken as the crystallite diameter of CeO2 in the Ce-based oxide particles.

[0072] The crystallite diameter of CeO2 in Ce-based oxide particles can be adjusted, for example, by adjusting the firing conditions during the manufacture of Ce-based oxide particles, or by setting a crystallization process (e.g., exposure under hydrothermal conditions) during the manufacture of Ce-based oxide particles.

[0073] Ce-based oxide particles are used as supports for catalytically active components. From the perspective of improving the loading capacity of catalytically active components, Ce-based oxide particles are preferably porous. Ce-based oxide particles are distinguished from cerium oxide used as a binder (hereinafter referred to as "cerium oxide binder"). Cerium oxide binders are derived from cerium oxide sol used as materials in catalyst compositions, or water-soluble cerium salts such as cerium nitrate and cerium nitrate.

[0074] Ce-based oxide particles contain one or more metallic elements other than Ce. Examples of metallic elements other than Ce include rare earth elements such as Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; and transition metal elements such as Fe, Mn, Ni, and Zr. These metallic elements can form solid solution phases with Ce and O, or they can form single phases as crystalline or amorphous phases (e.g., oxide phases of metallic elements other than Ce), or both solid solution and single phases.

[0075] <Ce-Zr composite oxide particles>

[0076] The catalyst composition for exhaust gas purification of the present invention comprises Ce-Zr composite oxide particles. It should be noted that, unless otherwise specified, in this specification, "Ce-Zr composite oxide particles" refers to the Ce-Zr composite oxide particles contained in the catalyst composition for exhaust gas purification of the present invention, and is distinguished from the Ce-Zr composite oxide particles used as raw materials in the catalyst composition for exhaust gas purification of the present invention (hereinafter referred to as "Ce-Zr composite oxide particles as raw materials").

[0077] Ce-Zr composite oxide particles possess oxygen storage capacity (i.e., the ability to absorb oxygen when the oxygen concentration in the exhaust gas is high and release oxygen when the oxygen concentration in the exhaust gas is low), which can mitigate fluctuations in the oxygen concentration in the exhaust gas and expand the operating window of the catalytically active components. Therefore, the exhaust gas purification capacity of the catalyst composition for exhaust gas purification is improved.

[0078] Ce-Zr composite oxide particles are composed of Ce-Zr composite oxides. From the perspective of improving the oxygen storage capacity of Ce-Zr composite oxide particles, based on the mass of the Ce-Zr composite oxide particles, the CeO2 conversion content of Ce in the Ce-Zr composite oxide particles is preferably 5% by mass or more and 90% by mass or less, more preferably 5% by mass or more and 70% by mass or less, further preferably 7% by mass or more and 60% by mass or less, and even more preferably 10% by mass or more and 50% by mass or less. The method for determining the CeO2 conversion content of Ce in Ce-Zr composite oxide particles is the same as the method for determining the CeO2 conversion content of Ce in Ce-based oxide particles.

[0079] From the perspective of further improving the heat resistance of Ce-Zr composite oxide particles and further improving the waste gas purification capacity of catalyst compositions for waste gas purification (especially the waste gas purification capacity after exposure to high-temperature environments), based on the mass of Ce-Zr composite oxide particles, the ZrO2 conversion content of Zr in Ce-Zr composite oxide particles is preferably 10% by mass or more and 95% by mass or less, more preferably 20% by mass or more and 95% by mass or less, more preferably 40% by mass or more and 95% by mass or less, and even more preferably 50% by mass or more and 90% by mass or less. The method for determining the ZrO2 conversion content of Zr in Ce-Zr composite oxide particles is the same as the method for determining the CeO2 conversion content of Ce in Ce-based oxide particles.

[0080] From the perspective of further improving the oxygen storage capacity and heat resistance of Ce-Zr composite oxide particles, and further improving the waste gas purification capacity of catalyst compositions for waste gas purification (especially the waste gas purification capacity after exposure to high-temperature environments), based on the mass of Ce-Zr composite oxide particles, the sum of the CeO2 conversion amount of Ce and the ZrO2 conversion amount of Zr in the Ce-Zr composite oxide particles is preferably 70% by mass or more, more preferably 75% by mass or more, more preferably 80% by mass or more, and more preferably 85% by mass or more. The upper limit is 100% by mass.

[0081] From the perspective of more efficiently utilizing the aforementioned effects of Ce-Zr composite oxide particles, based on the mass of the catalyst composition for waste gas purification of the present invention, the amount of Ce-Zr composite oxide particles in the catalyst composition for waste gas purification of the present invention is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 30% by mass or more. Furthermore, from the perspective of relatively increasing the amount of Ce-based oxide particles and more efficiently utilizing the aforementioned effects of Ce-based oxide particles, based on the mass of the catalyst composition for waste gas purification of the present invention, the amount of Ce-Zr composite oxide particles in the catalyst composition for waste gas purification of the present invention is preferably 97% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. These upper limits can be combined with any of the aforementioned lower limits. The method for determining the amount of Ce-Zr composite oxide particles in the catalyst composition for waste gas purification of the present invention is the same as the method for determining the amount of Ce-based oxide particles in the catalyst composition for waste gas purification of the present invention.

[0082] From the perspective of balancing the above-mentioned effects of Ce-based oxide particles and Ce-Zr-based composite oxide particles, and further improving the exhaust gas purification performance (especially the exhaust gas purification performance after exposure to high-temperature environments) of the catalyst composition for exhaust gas purification of the present invention, the ratio of the amount of Ce-Zr-based composite oxide particles to the amount of Ce-based oxide particles, by mass ratio, is preferably 0.5 or more and 32 or less, more preferably 1.0 or more and 25 or less, and even more preferably 1.5 or more and 15 or less.

[0083] The average particle size of the Ce-Zr composite oxide particles is preferably 0.1 μm or more and 15 μm or less, more preferably 0.5 μm or more and 12 μm or less, and even more preferably 1 μm or more and 10 μm or less. The method for determining the average particle size of the Ce-Zr composite oxide particles is the same as the method for determining the average particle size of Ce-based oxide particles. The average particle size of the Ce-Zr composite oxide particles can be adjusted in the same way as the average particle size of Ce-based oxide particles. It should be noted that when manufacturing the catalyst composition for exhaust gas purification of the present invention, the average particle size of the Ce-Zr composite oxide particles used as raw materials is kept constant, therefore, the average particle size of the Ce-Zr composite oxide particles is usually the same as the average particle size of the Ce-Zr composite oxide particles used as raw materials.

[0084] Ce-Zr composite oxides are used as supports for catalytically active components. From the perspective of improving the loading capacity of catalytically active components, Ce-Zr composite oxide particles are preferably porous.

[0085] In Ce-Zr composite oxide particles, Ce, Zr, and O preferably form a solid solution phase. Ce, Zr, and O can also form single phases (CeO2 phase and / or ZrO2 phase) as crystalline or amorphous phases based on the solid solution phase.

[0086] Ce-Zr composite oxide particles can contain one or more metallic elements other than Ce and Zr. Examples of metallic elements other than Ce include rare earth elements other than Ce. Examples of rare earth elements other than Ce include Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Metallic elements other than Ce and Zr can form solid solution phases with Ce, Zr, and O, or they can form single phases as crystalline or amorphous phases, or both.

[0087] <Al-based oxide particles>

[0088] The catalyst composition for exhaust gas purification of the present invention comprises Al-based oxide particles. It should be noted that, unless otherwise specified, in this specification, "Al-based oxide particles" refers to the Al-based oxide particles contained in the catalyst composition for exhaust gas purification of the present invention, and is distinguished from the Al-based oxide particles used as raw materials in the catalyst composition for exhaust gas purification of the present invention (hereinafter referred to as "Al-based oxide particles as raw materials").

[0089] Generally speaking, Al-based oxide particles have higher heat resistance than Ce-based oxide particles and Ce-Zr composite oxide particles. Therefore, the specific surface area of ​​the catalyst composition for waste gas purification (especially the specific surface area after exposure to high-temperature environments) is increased, and the waste gas purification performance of the catalyst composition for waste gas purification (especially the waste gas purification performance after exposure to high-temperature environments) is improved.

[0090] Al-based oxide particles are composed of Al-based oxides. Al-based oxide particles may or may not contain elements other than Al and O.

[0091] Elements other than Al and O can be selected from, for example, B, Si, rare earth elements (such as Y, Ce, La, Nd, Pr, Sm, Gd, etc.), Zr, Cr, alkaline earth metal elements (such as Mg, Ca, Sr, Ba, etc.). From the perspective of improving the heat resistance of Al-based oxide particles, elements selected from Ce, La, Sr, Ba, etc. are preferred.

[0092] Examples of Al-based oxides include alumina particles (oxides formed solely of Al and O), oxides obtained by modifying the surface of alumina with elements other than Al and O, and oxides obtained by dissolving elements other than Al and O in alumina. Specific examples of Al-based oxides containing elements other than Al and O include alumina-silica, alumina-silicate, alumina-zirconium oxide, alumina-chromium oxide, alumina-cerium oxide, and alumina-lanthanum oxide.

[0093] In Al-based oxide particles, elements other than Al and O can form solid solution phases together with Al and O, or they can form single phases as crystalline or amorphous phases (e.g., oxide phases of elements other than Al and O), or both solid solution phases and single phases.

[0094] When Al-based oxide particles contain elements other than Al and O, from the perspective of improving heat resistance, based on the mass of Al-based oxide particles, the Al2O3 conversion amount of Al in the Al-based oxide particles is preferably 70% or more and 99.9% or less by mass, more preferably 80% or more and 99.5% or less by mass, and even more preferably 90% or more and 99% or less by mass.

[0095] From the perspective of increasing specific surface area (especially specific surface area after exposure to high-temperature environments) and ensuring sufficient amount of co-catalyst (e.g., Ce-based oxide particles, Ce-Zr composite oxide particles, etc.), based on the mass of the catalyst composition for exhaust gas purification of the present invention, the amount of Al-based oxide particles in the catalyst composition for exhaust gas purification of the present invention is preferably 10% by mass or more and 90% by mass or less, more preferably 15% by mass or more and 70% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less. The method for determining the amount of Al-based oxide particles in the catalyst composition for exhaust gas purification of the present invention is the same as the method for determining the amount of Ce-based oxide particles in the catalyst composition for exhaust gas purification of the present invention.

[0096] From the perspective of increasing the specific surface area (especially the specific surface area after exposure to high temperature environment) and ensuring a sufficient amount of co-catalyst, in the catalyst composition for exhaust gas purification of the present invention, the ratio of the amount of Al-based oxide particles to the amount of Ce-based oxide particles, by mass ratio, is preferably 0.1 or more and 10 or less, more preferably 0.2 or more and 5 or less, and even more preferably 0.3 or more and 3 or less.

[0097] From the perspective of balancing the heat resistance of Al-based oxide particles and their coatability on substrates, the average particle size of the Al-based oxide particles is preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 30 μm or less, and even more preferably 4 μm or more and 20 μm or less. The method for determining the average particle size of the Al-based oxide particles is the same as the method for determining the average particle size of Ce-based oxide particles. The average particle size of the Al-based oxide particles can be adjusted in the same way as the average particle size of the Ce-based oxide particles. It should be noted that when manufacturing the catalyst composition for exhaust gas purification of the present invention, the average particle size of the Al-based oxide particles used as raw materials remains unchanged; therefore, the average particle size of the Al-based oxide particles is usually the same as the average particle size of the Al-based oxide particles used as raw materials.

[0098] Al-based oxide particles are used as supports for catalytically active components. From the perspective of improving the loading capacity of catalytically active components, porous Al-based oxide particles are preferred. Al-based oxide particles are distinguished from alumina used as a binder (hereinafter referred to as "alumina binder"). Alumina binders are derived from alumina sol used as a material in catalyst compositions.

[0099] <Precious Metal Elements>

[0100] The catalyst composition for exhaust gas purification of the present invention contains at least one noble metal element. The noble metal element may be selected from, for example, Au, Ag, Pt, Pd, Rh, Ir, Ru, Os, etc., and is preferably selected from Rh and Pt.

[0101] The precious metal element is included in the catalyst composition for exhaust gas purification of the present invention in a form that can function as a catalytic active ingredient, such as a metal, an alloy containing a precious metal element, or a compound containing a precious metal element (e.g., an oxide of a precious metal element).

[0102] From the perspective of balancing exhaust gas purification performance and cost, based on the mass of the catalyst composition for exhaust gas purification of the present invention, the amount of precious metal elements in the catalyst composition for exhaust gas purification of the present invention is preferably 0.010% by mass or more and 20% by mass or less, more preferably 0.050% by mass or more and 10% by mass or less, and even more preferably 0.10% by mass or more and 5.0% by mass or less. It should be noted that, in this specification, "amount of precious metal elements" refers to the metal equivalent of that single precious metal element when the catalyst composition contains one such element; and refers to the sum of the metal equivalents of the two or more precious metal elements when the catalyst composition contains two or more such elements.

[0103] The amount of precious metal elements in the catalyst composition for exhaust gas purification of the present invention can be determined by analyzing a sample obtained from the catalyst composition for exhaust gas purification of the present invention using EDS or WDS (wavelength dispersive X-ray fluorescence spectrometer), and determining the amount by the obtained elemental mapping and EDS elemental analysis of the specified particles.

[0104] Precious metal elements are preferably loaded onto Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles. Under low to medium temperature conditions, the exhaust gas purification performance of the precious metal elements loaded onto Ce-based oxide particles is readily exhibited; under high temperature conditions, the exhaust gas purification performance of the precious metal elements loaded onto Ce-Zr-based composite oxide particles and Al-based oxide particles is readily exhibited. Therefore, by loading precious metal elements onto Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles, excellent exhaust gas purification performance can be achieved over a wide temperature range. In particular, the catalyst composition for exhaust gas purification of the present invention exhibits excellent exhaust gas purification performance under low to medium temperature conditions after exposure to a high-temperature environment. It should be noted that, in this specification, "low to medium temperature" refers to temperatures, for example, above 50°C and below 400°C, preferably above 100°C and below 350°C. "Loading" refers to the state in which catalytically active components such as precious metals are physically or chemically adsorbed or retained on the outer surface or inner surface of the pores of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles. For example, when analyzing a sample obtained from the catalyst composition for exhaust gas purification of the present invention using SEM-EDX, if the catalytically active component and Ce-based oxide particles are present in the same area, it can be determined that the catalytically active component is loaded on the Ce-based oxide particles; if the catalytically active component and Ce-Zr-based composite oxide particles are present in the same area, it can be determined that the catalytically active component is loaded on the Ce-Zr-based composite oxide particles; if the catalytically active component and Al-based oxide particles are present in the same area, it can be determined that the catalytically active component is loaded on the Al-based oxide particles. Based on the mass of the Ce-based oxide particles, the amount of precious metal elements loaded on the Ce-based oxide particles is preferably 0.05% by mass or more, more preferably 0.10% by mass or more. The upper limit is, for example, 20% by mass. Based on the mass of Ce-Zr composite oxide particles, the amount of noble metal elements loaded on the Ce-Zr composite oxide particles is preferably 0.05% by mass or more, more preferably 0.10% by mass or more. The upper limit is, for example, 20% by mass. Based on the mass of Al oxide particles, the amount of noble metal elements loaded on the Al oxide particles is preferably 0.05% by mass or more, more preferably 0.10% by mass or more. The upper limit is, for example, 20% by mass.

[0105] <Other Ingredients>

[0106] The catalyst composition for waste gas purification of the present invention may contain one or more inorganic oxide particles other than Ce-based oxide particles, Ce-Ze-based composite oxide particles, and Al-based oxide particles (hereinafter referred to as "other inorganic oxide particles"), binders, stabilizers, and other components. Examples of other inorganic oxide particles include, for example, zirconium oxide particles, silica particles, and titanium dioxide particles. Examples of binders include, for example, inorganic oxide-based binders such as alumina sol, zirconium oxide sol, titanium dioxide sol, and silica sol. Examples of stabilizers include, for example, nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (e.g., Sr, Ba).

[0107] <The morphology of catalyst compositions for waste gas purification>

[0108] The catalyst composition for waste gas purification of the present invention is in the form of, for example, powder, shaped body, or layer.

[0109] <Method for Manufacturing Catalyst Composition for Waste Gas Purification>

[0110] The catalyst composition for waste gas purification of the present invention can be manufactured by, for example, the following method: A solution containing a noble metal salt is mixed with Ce-based oxide particles, Ce-Zr-based composite oxide particles, Al-based oxide particles, and other components (e.g., binders, stabilizers, etc.) as raw materials, followed by drying and calcination. The calcined product can be pulverized as needed. Examples of noble metal salts include nitrates, ammonium complexes, and chlorides. The solvent of the solution containing the noble metal salt is, for example, water (e.g., deionized water). The solution containing the noble metal salt may contain organic solvents such as alcohols. The drying temperature is, for example, 50°C or higher and 150°C or lower, and the drying time is, for example, 1 hour or higher and 3 hours or lower. The calcination temperature is, for example, 300°C or higher and 700°C or lower, and the calcination time is, for example, 1 hour or higher and 3 hours or lower. Calcination can be carried out, for example, in an atmospheric atmosphere.

[0111] From the perspective of adjusting the crystallite diameter of CeO2 in Ce-based oxide particles to a desired range, it is preferable to apply a heat load to the Ce-based oxide particles used as raw materials to adjust the crystallite diameter of CeO2 in the Ce-based oxide particles used as raw materials. The heat load can be applied, for example, by firing at 1000°C for 1 hour in an atmospheric atmosphere. The crystallite diameter of CeO2 in the Ce-based oxide particles used as raw materials is preferably 7 nm or more, more preferably 10 nm or more, further preferably 20 nm or more, and even more preferably 30 nm or more. The upper limit of the crystallite diameter of CeO2 in the Ce-based oxide particles used as raw materials is, for example, 200 nm, preferably 100 nm, and more preferably 55 nm. These upper limits can be combined with any of the lower limits mentioned above. The method for determining the crystallite diameter of CeO2 in the Ce-based oxide particles used as raw materials is the same as the method for determining the crystallite diameter of CeO2 in Ce-based oxide particles used as raw materials, except that the determination is performed on the Ce-based oxide particles used as raw materials.

[0112] Catalysts for Waste Gas Purification

[0113] The catalyst for purifying waste gas according to the present invention will be described below.

[0114] The catalyst for purifying exhaust gas of the present invention comprises a substrate and a catalyst layer of the present invention disposed on the substrate. The catalyst for purifying exhaust gas of the present invention may have a catalyst layer other than the catalyst layer of the present invention at one or more locations selected from the lower side, upper side, downstream side, and upstream side of the catalyst layer of the present invention.

[0115] <Substrate>

[0116] The substrate can be appropriately selected from conventionally used substrates for catalysts used in waste gas purification. Examples of substrates include wall-flow substrates and flow-through substrates.

[0117] The material constituting the substrate can be appropriately selected from materials conventionally used as substrates for catalysts used in exhaust gas purification. Preferably, the material constituting the substrate is one whose shape remains stable when exposed to exhaust gas at temperatures, for example, above 400°C. Examples of substrate materials include, for instance, cordierite, silicon carbide (SiC), aluminum titanate ceramics, and alloys such as stainless steel.

[0118] <Catalyst Layer>

[0119] The catalyst layer of the present invention is composed of the catalyst composition for exhaust gas purification of the present invention. That is, the catalyst layer of the present invention comprises Ce-based oxide particles, Ce-Zr-based composite oxide particles, Al-based oxide particles, and noble metal elements. The descriptions of <Ce-based oxide particles>, <Ce-Zr-based composite oxide particles>, <Al-based oxide particles>, <noble metal elements>, and <other components> above also apply to the catalyst layer of the present invention. Where applicable, "catalyst composition for exhaust gas purification of the present invention" shall be replaced with "catalyst layer of the present invention".

[0120] From the perspective of balancing exhaust gas purification performance and cost, the mass of the catalyst layer of the present invention per unit volume of the substrate (mass after drying and calcination) is preferably 10 g / L or more and 300 g / L or less, more preferably 30 g / L or more and 200 g / L or less, and even more preferably 50 g / L or more and 150 g / L or less. It should be noted that the volume of the substrate refers to its apparent volume. For example, when the substrate is a cylinder with an outer diameter of 2r, the volume of the substrate is expressed by the formula: Volume of substrate = π × r 2 It is expressed as × (length of the substrate).

[0121] <First Embodiment>

[0122] The following is based on Figures 1-4 The first embodiment of the present invention relates to a catalyst 1A for purifying waste gas.

[0123] like Figure 1 As shown, a catalyst 1A for exhaust gas purification is disposed in the exhaust passage within the exhaust pipe P of an internal combustion engine. The internal combustion engine is, for example, a gasoline engine. Exhaust gas discharged from the internal combustion engine flows from one end of the exhaust pipe P to the other end within the exhaust passage of the exhaust pipe P, and is purified by the catalyst 1A disposed within the exhaust pipe P. In the attached diagram, the direction of exhaust gas flow is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas inflow side," and the downstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas outflow side."

[0124] The exhaust passage within the exhaust pipe P can be equipped with other exhaust gas purification catalysts in addition to the exhaust gas purification catalyst 1A. For example, the exhaust gas purification catalyst 1A can be installed upstream of the exhaust passage within the exhaust pipe P, while other exhaust gas purification catalysts can be installed downstream of the exhaust passage within the exhaust pipe P. Examples of other exhaust gas purification catalysts include, for instance, the exhaust gas purification catalyst 1B, which will be described later.

[0125] like Figures 2-4 As shown, the catalyst 1A for exhaust gas purification includes a substrate 10 and a catalyst layer 20 disposed on the substrate 10.

[0126] The above description of the substrate also applies to substrate 10.

[0127] The catalyst layer 20 is composed of the catalyst composition for exhaust gas purification of the present invention. That is, the catalyst layer 20 comprises Ce-based oxide particles, Ce-Zr-based composite oxide particles, Al-based oxide particles, and noble metal elements. The above description of the catalyst layer of the present invention also applies to the catalyst layer 20.

[0128] like Figures 2-4 As shown, the substrate 10 has: a cylindrical portion 11 defining the shape of the substrate 10, a partition portion 12 disposed within the cylindrical portion 11, and a small chamber 13 separated by the partition portion 12.

[0129] like Figure 2 As shown, the cylindrical part 11 is cylindrical, but it can also be elliptical, polygonal, or other shapes.

[0130] like Figures 2-4 As shown, adjacent chambers 13 are separated by partition walls 12. The partition walls 12 are preferably porous. The thickness of the partition walls 12 is, for example, 20 μm or more and 1500 μm or less.

[0131] like Figure 4 As shown, the chamber 13 extends in the exhaust gas flow direction X and has an end on the exhaust gas inflow side and an end on the exhaust gas outflow side.

[0132] like Figure 4 As shown, both the exhaust gas inlet end and the exhaust gas outlet end of the chamber 13 are open. Therefore, the exhaust gas that flows in from the exhaust gas inlet end (opening) of the chamber 13 flows out from the exhaust gas outlet end (opening) of the chamber 13. This configuration is called a flow-through type.

[0133] like Figure 2 and 3 As shown, the top view shape of the exhaust gas inflow end (opening) of the chamber 13 is quadrilateral, but it can also be hexagonal, octagonal, or other shapes. The top view shape of the exhaust gas outflow end (opening) of the chamber 13 is the same.

[0134] The cell density per square inch of substrate 10 is, for example, more than 300 cells and less than 900 cells. It should be noted that the cell density per square inch of substrate 10 is the total number of cells 13 per square inch in the cross-section obtained by cutting substrate 10 with a plane perpendicular to the exhaust gas flow direction X.

[0135] like Figure 4 As shown, the catalyst layer 20 is disposed on the partition wall portion 12 of the substrate 10.

[0136] like Figure 4 As shown, the catalyst layer 20 extends along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inflow side to the end of the partition wall 12 on the exhaust gas outflow side. The catalyst layer 20 may also extend along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inflow side, but not reach the end of the partition wall 12 on the exhaust gas outflow side; or it may extend in the opposite direction to the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas outflow side, but not reach the end of the partition wall 12 on the exhaust gas inflow side.

[0137] The catalyst 1A for exhaust gas purification can be manufactured by forming a catalyst layer 20 on the partition wall portion 12 of the substrate 10. For example, a slurry is prepared by mixing a solution containing a noble metal salt, Ce-based oxide particles as raw materials, Ce-Zr composite oxide particles as raw materials, Al-based oxide particles as raw materials, and other components (e.g., binders, stabilizers, etc.) added as needed. The slurry is then coated onto the partition wall portion 12 of the substrate 10, dried, and calcined, thereby forming the catalyst layer 20 on the partition wall portion 12 of the substrate 10. The noble metal salt, the solvent of the solution containing the noble metal salt, the drying conditions, the calcination conditions, and the crystallite diameter of CeO2 in the Ce-based oxide particles as raw materials are the same as those in the manufacturing method of the catalyst composition for exhaust gas purification of the present invention.

[0138] <Second Implementation>

[0139] The following is based on Figure 5 The second embodiment of the present invention relates to a catalyst 1B for exhaust gas purification. In the catalyst 1B, components identical to those in the catalyst 1A for exhaust gas purification are indicated by the same designations as those in the catalyst 1A. Unless otherwise stated below, the above description concerning the catalyst 1A for exhaust gas purification also applies to the catalyst 1B for exhaust gas purification.

[0140] like Figure 5 As shown, catalyst 1B for waste gas purification differs from catalyst 1A for waste gas purification in the following ways:

[0141] The substrate 10 is provided with a first sealing portion 14 for sealing the exhaust gas outflow end of a portion of the chamber 13 and a second sealing portion 15 for sealing the exhaust gas inflow end of the remaining chambers 13. Thus, the substrate 10 forms an inflow-side chamber 13a with an end opening on the exhaust gas inflow side and the exhaust gas outflow end blocked by the first sealing portion 14, and an outflow-side chamber 13b with its end blocked by the second sealing portion 15 and the exhaust gas outflow end open.

[0142] A catalyst layer 20a is provided on the inflow side chamber 13a side of the partition wall portion 12 of the substrate 10, and a catalyst layer 20b is provided on the outflow side chamber 13b side of the partition wall portion 12 of the substrate 10.

[0143] like Figure 5 As shown, a plurality of (e.g., four) outflow side chambers 13b are arranged adjacent to an inflow side chamber 13a, and the inflow side chamber 13a and the outflow side chambers 13b adjacent to the inflow side chamber 13a are separated by a porous partition 12.

[0144] like Figure 5 As shown, the catalyst layer 20a extends from the end of the partition wall 12 on the exhaust gas inflow side along the exhaust gas flow direction X, but does not reach the end of the partition wall 12 on the exhaust gas outflow side. Alternatively, the catalyst layer 20a may extend from the end of the partition wall 12 on the exhaust gas inflow side to the end of the partition wall 12 on the exhaust gas outflow side.

[0145] like Figure 5 As shown, the catalyst layer 20b extends from the end of the partition wall 12 on the exhaust gas outflow side in a direction opposite to the exhaust gas flow direction X, but does not reach the end of the partition wall 12 on the exhaust gas inflow side. Alternatively, the catalyst layer 20b may extend from the end of the partition wall 12 on the exhaust gas outflow side to the end of the partition wall 12 on the exhaust gas inflow side.

[0146] At least one of catalyst layers 20a and 20b is a catalyst layer of the present invention comprising Ce-based oxide particles, Ce-Zr-based composite oxide particles, Al-based oxide particles, and noble metal elements, and the above description regarding the catalyst layers of the present invention applies. The compositions of catalyst layers 20a and 20b may be the same or different.

[0147] In the catalyst 1B for exhaust gas purification, exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the inflow side chamber 13a passes through the porous partition 12 and flows out from the end (opening) of the exhaust gas outflow side of the outflow side chamber 13b. This pattern is called wall flow type.

[0148] In the exhaust gas purification catalyst 1B, when exhaust gas flows in from the exhaust gas inflow side end (opening) of the inflow side chamber 13a and passes through the porous partition wall 12, particulate matter (PM) in the exhaust gas is captured in the fine pores of the partition wall 12. Therefore, the exhaust gas purification catalyst 1B can be used as a gasline particulate filter for gasoline engines or a diesel particulate filter for diesel engines.

[0149] The catalyst 1B for exhaust gas purification can be manufactured by the following method: The exhaust gas inflow end of the substrate 10 is immersed in a slurry for forming catalyst layer 20a, the slurry is drawn from the opposite side and dried to form a precursor layer for catalyst layer 20a. The exhaust gas outflow end of the substrate 10 is immersed in a slurry for forming catalyst layer 20b, the slurry is drawn from the opposite side and dried to form a precursor layer for catalyst layer 20b. After forming the precursor layers for catalyst layer 20a and catalyst layer 20b, catalyst layer 20a and catalyst layer 20b are formed by firing, thus producing catalyst 1B for exhaust gas purification. The manufacturing conditions for catalyst 1B are the same as those for catalyst 1A for exhaust gas purification.

[0150] Example

[0151] The present invention will be further described in detail below based on embodiments and comparative examples.

[0152] [Example 1]

[0153] (1) Determination of the average particle size of Ce-based oxide powder and the crystallite diameter of CeO2 in Ce-based oxide powder

[0154] Ce-based oxide powders were prepared as raw materials. The CeO2 content of Ce in the Ce-based oxide powders was approximately 100% by mass (>99% by mass). The average particle size of the Ce-based oxide powders used as raw materials and the crystallite diameter of CeO2 in the Ce-based oxide powders were measured.

[0155] The method for determining the average particle size of Ce-based oxide powder is as follows. Ce-based oxide powder was observed using a scanning electron microscope (Miniscope TM3000, Hitachi High-Tech Co., Ltd.). The fixed-direction diameter (Ferret diameter) of 100 randomly selected particles within the field of view was measured, and the average value was taken as the average particle size of the Ce-based oxide powder. The average particle size of the Ce-based oxide powder was 5.0 μm.

[0156] The method for determining the crystallite diameter of CeO2 in Ce-based oxide powder is as follows. X-ray diffraction (XRD) was performed using Ce-based oxide powder and a commercially available powder X-ray diffractometer (Rigaku Corporation, "MiniFlex 600") under the following conditions: X-ray source: CuKα; operating axis: 2θ / θ; measurement method: continuous; counting unit: cps; start angle: 5°; end angle: 90°; sampling width: 0.02°; scan speed: 10° / min; voltage: 40kV; current: 150mA. In the obtained XRD pattern, peaks originating from CeO2 at 2θ = 55–58° and 2θ = 46–49° were identified. Using analytical software (Rigaku Corporation, "PDXL version 2"), the Scherrer formula was applied to the identified peaks to automatically calculate the crystallite diameter. The crystallite diameters obtained from the peaks at 2θ = 55–58° and 2θ = 46–49° were compared, and the larger crystallite diameter was selected as the crystallite diameter of CeO2 in the Ce-based oxide powder. The crystallite diameter of CeO2 in the Ce-based oxide powder is 7.2 nm.

[0157] (2) Preparation of catalyst composition

[0158] To prepare 100 parts by weight of the catalyst composition, 33.5 parts by weight of Al-based oxide powder (Al2O3 equivalent of Al: 99% by weight, La2O3 equivalent of La: 1% by weight), 35 parts by weight of Ce-Zr composite oxide powder (CeO2 equivalent of Ce: 20% by weight, ZrO2 equivalent of Zr: 70% by weight, Nd2O3 equivalent of Nd: 10% by weight), and 30 parts by weight of Ce-based oxide powder (CeO2 equivalent of Ce: approximately 100% by weight (>99% by weight); average particle size: 5.0 μm; crystallite diameter: 7.2 nm) were added to a rhodium nitrate aqueous solution (Rh metal equivalent: 1.5 parts by weight). After standing for 1 hour, the rhodium nitrate aqueous solution was allowed to impregnate and load the Al-based oxide powder, Ce-Zr composite oxide powder, and Ce-based oxide powder. Then, the mixture was evaporated and dried to obtain a dry powder. The obtained dry powder was calcined at 500°C for 1 hour in an atmospheric atmosphere to obtain a powdered catalyst composition.

[0159] (3) Determination of the dispersion of precious metals

[0160] The catalyst composition obtained in (2) above was subjected to heat treatment at 1000°C for 30 hours in a quartz tubular furnace under an atmosphere of 0.5 vol.% O2 gas, 10 vol.% H2O in the form of water vapor, and N2 as background gas. The amount of CO adsorbed in the noble metal was measured by CO pulse method using a metal dispersion measuring device (BELMETAL3 manufactured by MicrotracBEL Co., Ltd.) after heat treatment of the catalyst composition, and the noble metal dispersion was calculated. Here, the noble metal dispersion refers to the ratio of the number B of noble metal atoms exposed on the surface of noble metal particles to the total number A of noble metal atoms in the catalyst composition (Rh in Examples 1-7 and Comparative Examples 1-13, and Pt in Examples 8 and Comparative Example 14), and is calculated by noble metal dispersion (%) = (B / A) × 100. Based on the premise that the noble metal atoms exposed on the surface of the noble metal particles adsorb CO at a 1:1 ratio, the number B of noble metal atoms exposed on the surface of the noble metal particles was calculated from the amount of CO adsorption measured by the CO pulse method. The results are shown in Table 2. It should be noted that in Examples 1-7 and Comparative Examples 1-13, a noble metal dispersion of 3.5 or higher was evaluated as "A", and a noble metal dispersion of less than 3.5 was evaluated as "B". In Example 8 and Comparative Example 14, a noble metal dispersion of 0.2 or higher was evaluated as "A", and a noble metal dispersion of less than 0.2 was evaluated as "B".

[0161] (4) Determination of BET specific surface area

[0162] The catalyst composition obtained in (2) was subjected to heat treatment in the same manner as in (3) above. The BET specific surface area of ​​the heat-treated catalyst composition was determined by N2 gas adsorption using QUADRASORB SI (Kunta Chemicals). The results are shown in Table 2. It should be noted that the BET specific surface area is 45 m². 2 A rating of "A" is given when the content is above / g, and the BET specific surface area is less than 45m². 2 The rating is "B" when the weight is / g.

[0163] (5) Evaluation of exhaust gas purification performance

[0164] The catalyst composition obtained in (2) above was subjected to heat treatment at 1000°C for 30 hours in a quartz tubular furnace under an atmosphere of 0.5 vol.% O2 gas, 10 vol.% H2O in water vapor state as background gas, and N2. The heat-treated catalyst composition was filled into a reaction tube, and the exhaust gas purification performance of the heat-treated catalyst composition was measured using a fixed-bed flow-through reaction device. Specifically, 0.1 g of the heat-treated catalyst composition was filled into a reaction tube, and simulated exhaust gas (CO: 3000 ppm, C3H6: 1000 ppm, NO: 500 ppm, O2: 0.28%, CO2: 14%, H2O: 10%, N2: balance) was introduced into the reaction tube at a heating rate of 10°C / min, an air-fuel ratio (A / F): 14.6, and a total flow rate of 1000 mL / min. It should be noted that "A / F" is an abbreviation for Air / Fuel, representing the ratio of air to fuel. The temperature was increased to 600°C at a rate of 10°C / min and held for 10 minutes for pretreatment. Then, after a brief cooling, the temperature was increased from 100°C to 600°C at a rate of 10°C / min. The amount of NO in the simulated exhaust gas flowing from the outlet of the reaction tube was measured using Fourier transform infrared spectroscopy (FT-IR), and the purification rate was calculated based on the following formula. It should be noted that in the following formula, X represents the detection amount without the catalyst composition, and Y represents the detection amount with the catalyst composition.

[0165] Purification rate (%) = (XY) / X × 100

[0166] The gas temperature at the inlet of the reaction tube when the NO purification rate reached 50% was taken as the ignition temperature T50 (°C). It should be noted that the ignition temperature T50 was determined during heating. The results are shown in Table 2. It should be noted that in Examples 1-7 and Comparative Examples 1-13, a T50 below 230°C was rated "A", a T50 above 230°C but below 235°C was rated "B", and a T50 above 235°C was rated "C"; in Example 8 and Comparative Example 14, a T50 below 400°C was rated "A", and a T50 above 400°C was rated "C".

[0167] [Examples 2-5]

[0168] Except for varying the amounts of Al-based oxide powder, Ce-Zr composite oxide powder, and Ce-based oxide powder as shown in Table 1, the same procedures as in Example 1 were performed. The results are shown in Table 2.

[0169] [Examples 6 and 7]

[0170] Except for varying the average particle size of the Ce-based oxide powder, the crystallite diameter of CeO2 in the Ce-based oxide powder, the amount of Al-based oxide powder added, the amount of Ce-Zr composite oxide powder added, and the amount of Ce-based oxide powder added, as shown in Table 1, the same procedures as in Example 1 were performed. The results are shown in Table 2. It should be noted that in Example 6, after applying a heat load to the Ce-based oxide powder, the average particle size of the Ce-based oxide powder and the crystallite diameter of CeO2 in the Ce-based oxide powder were measured. The heat load was applied by firing at 1000°C for 1 hour in an atmospheric atmosphere.

[0171] [Example 8]

[0172] To prepare 100 parts by mass of the catalyst composition, 39 parts by mass of Al-based oxide powder (Al₂O₃ equivalent of Al: 99% by mass, La₂O₃ equivalent of La: 1% by mass), 39 parts by mass of Ce-Zr composite oxide powder (CeO₂ equivalent of Ce: 20% by mass, ZrO₂ equivalent of Zr: 70% by mass, Nd₂O₃ equivalent of Nd: 10 parts by mass) and 10 parts by mass of Nd₂O₃ were added to a dinitrodiamine platinum nitric acid aqueous solution (Pt metal equivalent: 1.0 parts by mass). 40 parts by weight of Al-based oxide powder (CeO2 equivalent of Ce: approximately 100% by weight (>99% by weight); average particle size: 5.0 μm; crystallite diameter: 7.2 nm) and 20 parts by weight of Ce-based oxide powder (CeO2 equivalent of Ce: approximately 100% by weight (>99% by weight); average particle size: 5.0 μm; crystallite diameter: 7.2 nm) were placed for 1 hour to allow the dinitrodiamineplatinum nitric acid aqueous solution to impregnate and load the Al-based oxide powder, Ce-Zr composite oxide powder, and Ce-based oxide powder. The mixture was then evaporated and dried to obtain a dry powder. Otherwise, the same procedures as in Example 1 were performed. The results are shown in Table 2.

[0173] [Comparative Examples 1-5]

[0174] Except for changing the amounts of Al-based oxide powder, Ce-Zr-based composite oxide powder, and Ce-based oxide powder to the amounts shown in Table 1, the same procedures as in Example 1 were performed. The results are shown in Table 2.

[0175] [Comparative Examples 6-10]

[0176] The composition of the Ce-based oxide powder was changed as follows: In Comparative Example 6, the CeO2 equivalent of Ce was 85% by mass, and the BaO equivalent of Ba was 15% by mass; in Comparative Example 7, the CeO2 equivalent of Ce was 85% by mass, and the Nd2O3 equivalent of Nd was 15% by mass; in Comparative Example 8, the CeO2 equivalent of Ce was 85% by mass, and the La2O3 equivalent of La was 15% by mass; in Comparative Example 9, the CeO2 equivalent of Ce was 85% by mass, and the Si2O3 equivalent of Si2O3 was 15% by mass. The SiO2 equivalent amount was 15% by mass. In Comparative Example 10, the CeO2 equivalent amount of Ce was 85% by mass, and the ZrO2 equivalent amount of Zr was 15% by mass. The average particle size of the Ce-based oxide powder, the crystallite diameter of CeO2 in the Ce-based oxide powder, the amount of Al-based oxide powder, the amount of Ce-Zr composite oxide powder, and the amount of Ce-based oxide powder were varied as shown in Table 1, except that the same operations as in Example 1 were performed. The results are shown in Table 2.

[0177] [Comparative Examples 11-13]

[0178] Except for varying the average particle size of the Ce-based oxide powder, the crystallite diameter of CeO2 in the Ce-based oxide powder, the amount of Al-based oxide powder added, the amount of Ce-Zr composite oxide powder added, and the amount of Ce-based oxide powder added, as shown in Table 1, the same procedures as in Example 1 were performed. The results are shown in Table 2.

[0179] [Comparative Example 14]

[0180] Except for changing the amounts of Al-based oxide powder, Ce-Zr composite oxide powder, and Ce-based oxide powder to the amounts shown in Table 1, the same procedures were performed as in Example 8. The results are shown in Table 2.

[0181] [Table 1]

[0182]

[0183] [Table 2]

[0184]

[0185] Explanation of reference numerals in the attached figures

[0186] 1A, 1B Catalysts for Waste Gas Purification

[0187] 10 Substrate

[0188] 11 cylindrical part

[0189] 12. Adjacent Department

[0190] 13 cabins

[0191] 20, 20a, 20b: Catalyst layer

Claims

1. A catalyst composition for waste gas purification, comprising Ce-based oxide particles, Ce-Zr-based composite oxide particles, Al-based oxide particles, and noble metal elements. Based on the mass of the Ce-based oxide particles, the CeO2 equivalent content of Ce in the Ce-based oxide particles is 90% or more by mass. Based on the mass of the Ce-Zr composite oxide particles, the CeO2 conversion content of Ce in the Ce-Zr composite oxide particles is more than 5% by mass and less than 90% by mass. The average particle size of the Ce-based oxide particles is greater than 1.0 μm and less than 15 μm. Based on the mass of the catalyst composition for waste gas purification, the amount of Ce-based oxide particles in the catalyst composition for waste gas purification is 2.0% by mass or more and 30% by mass or less.

2. The catalyst composition for waste gas purification according to claim 1, wherein, Based on the mass of the Ce-Zr composite oxide particles, the Zr content of Zr in the Ce-Zr composite oxide particles is more than 10% by mass and less than 95% by mass.

3. The catalyst composition for waste gas purification according to claim 1 or 2, wherein, The noble metal element is loaded onto the Ce-based oxide particles, the Ce-Zr-based composite oxide particles, and the Al-based oxide particles.

4. The catalyst composition for waste gas purification according to claim 1 or 2, wherein, The precious metal element is selected from Rh and Pt.

5. The catalyst composition for waste gas purification according to claim 1 or 2, wherein, The CeO2 crystallites in the Ce-based oxide particles have a crystallite diameter of 10 nm or more.

6. A catalyst for purifying waste gas, comprising a substrate and a catalyst layer disposed on the substrate. The catalyst layer is composed of the catalyst composition for waste gas purification as described in any one of claims 1 to 5.

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