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, and a noble metal element, the Ce-based oxide particles containing at least one additional element selected from Al, Mg, La, Pr, Y, and Nd, the amount of the at least one additional element in the Ce-based oxide particles being 0.1 to 20 mass% based on the mass of the Ce-based oxide particles.

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 used in waste gas purification. A three-way catalyst is used as a catalyst to purify these harmful components and render them harmless. This catalyst has the ability to oxidize THC into water and carbon dioxide, oxidize CO into carbon dioxide, and oxidize NO... x Catalytic activity that reduces and converts nitrogen.

[0003] In three-way catalytic converters and other catalysts used for waste gas purification, 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, meaning oxides with an Al2O3 conversion weight of 70% or more based on the mass of the oxide; "Ce-Zr composite oxides" refers to composite oxides containing Ce and Zr, meaning composite oxides with a CeO2 conversion weight of 5% or more but less than 90% based on the mass of the composite oxide.

[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 components of three-way catalysts. It should be noted that in this specification, "Ce-based oxides" refers to Ce-containing oxides, meaning oxides with a CeO2 conversion content of 80% or more by mass, based on the mass of the oxide.

[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, Ce-Zr composite oxides, while possessing high heat resistance, exhibit relatively low affinity for catalytically active components. Therefore, combining Ce-based oxides and Ce-Zr composite oxides as supports for catalytically active components can compensate for the weaknesses of one over the other. 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] In addition, when CeO2 is used as a carrier for the catalytically active component, the exhaust gas purification performance may sometimes decrease due to the low oxygen storage capacity of CeO2.

[0013] Therefore, the object of the present invention is to provide a catalyst composition and a catalyst for exhaust gas purification using Ce-based oxides and Ce-Zr composite 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).

[0014] Solution for solving the problem

[0015] The inventors have discovered that by adding at least one additional element selected from Al, Mg, La, Pr, Y, and Nd to the Ce-based oxides in the catalyst composition and catalyst for exhaust gas purification using Ce-based oxides and Ce-Zr composite oxides, the exhaust gas purification performance (especially the exhaust gas purification performance after exposure to high-temperature environments) is improved.

[0016] This invention is based on the above understanding and includes the following technical solutions.

[0017] [1] A catalyst composition for purifying waste gas, comprising Ce-based oxide particles, Ce-Zr-based composite oxide particles, and noble metal elements.

[0018] The Ce-based oxide particles contain at least one additional element selected from Al, Mg, La, Pr, Y, and Nd.

[0019] Based on the mass of the Ce-based oxide particles, the CeO2 equivalent content of Ce in the Ce-based oxide particles is 80% or more by mass.

[0020] Based on the mass of the Ce-based oxide particles, the oxide equivalent of the at least one additional element in the Ce-based oxide particles is 0.1% by mass or more and 20% by mass or less.

[0021] Based on the mass of the Ce-Zr composite oxide particles, the CeO2 conversion amount of Ce in the Ce-Zr composite oxide particles is more than 5% by mass and less than 90% by mass.

[0022] [2] A catalyst for purifying waste gas, comprising a substrate and a catalyst layer disposed on the substrate.

[0023] The catalyst layer is composed of the catalyst composition for waste gas purification described in [1].

[0024] The effects of the invention

[0025] According to the present invention, a catalyst composition for exhaust gas purification and a catalyst for exhaust gas purification using Ce-based oxides and Ce-Zr-based composite oxides can be provided, wherein the catalyst composition for exhaust gas purification 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

[0026] 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.

[0027] Figure 2 for Figure 1 AA-line cross-section view.

[0028] Figure 3 for Figure 2 An enlarged map of the region indicated by the symbol R in the figure.

[0029] Figure 4 for Figure 1 BB line cross-section.

[0030] 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

[0031] <<Catalyst Composition for Exhaust Gas Purification>>

[0032] The catalyst composition for exhaust gas purification of the present invention will be described below.

[0033] <Ce-based oxide particles>

[0034] The catalyst composition for exhaust gas purification of the present invention contains Ce-based oxide particles. It should be noted that in this specification, unless otherwise specified, "Ce-based oxide particles" refers to the Ce-based oxide particles contained in the catalyst composition for exhaust gas purification of the present invention, which is distinguished from the Ce-based oxide particles used as raw materials for the catalyst composition for exhaust gas purification of the present invention (hereinafter referred to as "Ce-based oxide particles as raw materials").

[0035] The Ce-based oxide particles are composed of a Ce-based oxide. Based on the mass of the Ce-based oxide particles, the CeO2 conversion amount of Ce in the Ce-based oxide particles is preferably 80% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more. Thereby, the affinity of the Ce-based oxide particles for the catalytic active components is improved, and sintering between the catalytic active components supported by the Ce-based oxide particles can be suppressed. Therefore, the dispersion degree of the catalytic active components is improved, and the exhaust gas purification performance of the catalyst composition for exhaust gas purification is improved. This effect is particularly remarkable in the catalyst composition for exhaust gas purification after exposure to a high-temperature environment. This is because sintering between the catalytic active components supported by the Ce-based oxide particles is likely to occur after exposure to a high-temperature environment. It should be noted that the upper limit is the value obtained by subtracting the oxide conversion amount of the additional element from 100% by mass.

[0036] The CeO2 conversion amount of Ce in the Ce-based oxide particles can be measured as follows: Analyze a specimen obtained from the catalyst composition for exhaust gas purification of the present invention by energy dispersive X-ray spectroscopy (EDS (also called EDX)), and perform the measurement based on the element mapping and EDS element analysis of the specified particles obtained therefrom. Specifically, through element mapping, qualitative identification (color differentiation) of Ce-based oxide particles, Ce-Zr composite oxide particles, and other particles (such as Al-based oxide particles) is performed, and composition analysis (element analysis) of the specified particles is performed, so that the oxide conversion amount of the specified element in the specified particles can be measured.

[0037] 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.

[0038] Ce-based oxide particles contain at least one additional element selected from Al, Mg, La, Pr, Y, and Nd. That is, Ce-based oxide particles are composite oxides containing Ce and at least one additional element selected from Al, Mg, La, Pr, Y, and Nd. It should be noted that "additional element" refers to elements other than Ce and O.

[0039] Added elements can form solid solution phases together with Ce and O, or they can form single phases as crystalline or amorphous phases (e.g., oxide phases of added elements), or both solid solution phases and single phases.

[0040] When Ce-based oxide particles contain at least one additional element selected from Al and Mg, the heat resistance of the Ce-based oxide particles is improved, and the decrease in specific surface area and the accompanying burial of catalytically active components within the Ce-based oxide particles are suppressed. Therefore, the specific surface area of ​​the catalyst composition for exhaust gas purification is increased, the dispersion of 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. The decrease in specific surface area of ​​Ce-based oxide particles and the accompanying burial of catalytically active components within the Ce-based oxide particles are more likely to occur after exposure to high-temperature environments.

[0041] When Ce-based oxide particles contain at least one additional element selected from La, Pr, Y, and Nd, the 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) of the Ce-based oxide particles loaded with noble metal elements is improved. Therefore, fluctuations in the oxygen concentration in the exhaust gas can be mitigated, thereby expanding the operating window of the catalytically active components and improving the exhaust gas purification capacity of the catalyst composition for exhaust gas purification.

[0042] From the perspective of more efficiently leveraging the aforementioned effects of the added elements, based on the mass of Ce-based oxide particles, the oxide conversion amount of the added elements in the Ce-based oxide particles is preferably 0.1% by mass or more and 20% by mass or less. "Oxide conversion amount of the added elements" refers to the Al₂O₃ conversion amount for Al, the MgO conversion amount for Mg, the La₂O₃ conversion amount for La, and the Pr₆O₃ conversion amount for Pr. 11 The conversion amount includes the conversion amount of Y₂O₃ involving Y and the conversion amount of Nd₂O₃ involving Nd. Additionally, "the conversion amount of oxides of additional elements" refers to the oxide conversion amount of that single additional element when Ce-based oxide particles contain one additional element, and the sum of the oxide conversion amounts of two or more additional elements when Ce-based oxide particles contain two or more additional elements.

[0043] From the perspective of improving the heat resistance of Ce-based oxide particles, the sum of the CeO2 conversion amount of Ce and the oxide conversion amount of the added elements in the Ce-based oxide particles, based on the mass of the Ce-based oxide particles, is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. It should be noted that the upper limit is 100% by mass.

[0044] Hereinafter, the additional elements selected from Al and Mg will be referred to as "the first additional element", and the additional elements selected from La, Pr, Y and Nd will be referred to as "the second additional element".

[0045] In one embodiment, the Ce-based oxide particles contain at least one first additional element and do not contain a second additional element. In this embodiment, from the perspective of more efficiently utilizing the aforementioned effects of the first additional element, it is preferable that, based on the mass of the Ce-based oxide particles, the oxide equivalent of the first additional element in the Ce-based oxide particles is 0.1% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 15% by mass or less, even more preferably 0.1% by mass or more and 12% by mass or less, and even more preferably 0.1% by mass or more and 10% by mass or less. "Oxide equivalent of the first additional element" refers to the oxide equivalent of that single first additional element when the Ce-based oxide particles contain one first additional element; when the Ce-based oxide particles contain two first additional elements, it refers to the sum of the oxide equivalents of the two first additional elements.

[0046] In other embodiments, the Ce-based oxide particles contain at least one second additional element and do not contain the first additional element. In this embodiment, to more efficiently utilize the aforementioned effects of the second additional element, based on the mass of the Ce-based oxide particles, the oxide conversion amount of the second additional element in the Ce-based oxide particles is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 15% by mass or less, further preferably 0.1% by mass or more and 12% by mass or less, and even more preferably 0.1% by mass or more and 10% by mass or less. "Oxide conversion amount of the second additional element" refers to the oxide conversion amount of that single second additional element when the Ce-based oxide particles contain one second additional element, and refers to the sum of the oxide conversion amounts of the two or more second additional elements when the Ce-based oxide particles contain two or more second additional elements.

[0047] In yet another embodiment, the Ce-based oxide particles contain at least one first additional element and at least one second additional element. In this embodiment, to more efficiently utilize the aforementioned effects of the first and second additional elements, based on the mass of the Ce-based oxide particles, the oxide equivalent of the first additional element in the Ce-based oxide particles is preferably 0.1% by mass or more and 19.9% ​​by mass or less, more preferably 0.1% by mass or more and 14.9% by mass or less, further preferably 0.1% by mass or more and 11.9% by mass or less, and even more preferably 0.1% by mass or more and 9.9% by mass or less; based on the mass of the Ce-based oxide particles, the oxide equivalent of the second additional element in the Ce-based oxide particles is preferably 0.1% by mass or more. The content of the first and second added elements in the Ce-based oxide particles is preferably 0.1% to 14.9% by mass or less, more preferably 0.1% to 11.9% by mass or less, and even more preferably 0.1% to 9.9% by mass or less, based on the mass of the Ce-based oxide particles. The total amount of oxide equivalents of the first and second added elements in the Ce-based oxide particles is preferably 0.2% to 20% by mass or less, more preferably 0.5% to 15% by mass or less, even more preferably 1% to 12% by mass or less, and even more preferably 2% to 10% by mass or less. The meanings of "oxide equivalent of the first added element" and "oxide equivalent of the second added element" are the same as described above.

[0048] 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 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 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.

[0049] 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.

[0050] 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 to hydrothermal conditions) during the manufacture of Ce-based oxide particles.

[0051] From the perspective of more efficiently utilizing the aforementioned effects of Ce-based oxide particles, 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 1.0% by mass or more, more preferably 2.0% by mass or more, further preferably 3.0% by mass or more, further preferably 5.0% by mass or more, and further preferably 10% by mass or more. Furthermore, from the perspective of relatively increasing the amount of components other than Ce-based oxide particles (e.g., the amount of Ce-Zr composite oxide particles, the amount of other particles, etc.) to further increase the specific surface area of ​​the catalyst composition for exhaust gas purification (especially the specific surface area after exposure to a 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 50% by mass or less, more preferably 30% by mass or less, further preferably 25% by mass or less, further preferably 20% by mass or less, and further preferably 15% by mass or less. These upper limits can be combined with any of the lower limits mentioned above.

[0052] 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).

[0053] (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.

[0054] (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 other particles (e.g., Al-based oxide particles)).

[0055] (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.

[0056] (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.

[0057] 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.

[0058] 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.

[0059] 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).

[0060] 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.

[0061] By following the steps above, the following content rates can be obtained.

[0062] • The percentage of Ce in the entire sample as converted to CeO2 (hereinafter referred to as "P") T ”)

[0063] • The Ce content in Ce-based oxide particles, calculated as CeO2 (hereinafter referred to as "P1").

[0064] • The Ce content in Ce-Zr composite oxide particles, calculated as CeO2 (hereinafter referred to as "P2").

[0065] • The Ce content in Al-based oxide particles, calculated as CeO2 (hereinafter referred to as "P3").

[0066] • The Zr content in the entire sample, converted to ZrO2 (hereinafter referred to as "Q") T ")

[0067] • The Zr content in Ce-based oxide particles, calculated as ZrO2 (hereinafter referred to as "Q1").

[0068] • The Zr content in Ce-Zr composite oxide particles, calculated using ZrO= (hereinafter referred to as "Q2").

[0069] • The Zr content in Al-based oxide particles, calculated as ZrO2 (hereinafter referred to as "Q3").

[0070] • The percentage of Al in the entire sample as Al2O3 (hereinafter referred to as "R") T ")

[0071] • The content of Al in Ce-based oxide particles, calculated as Al₂O₃ (hereinafter referred to as "R₁").

[0072] • The Al content in Ce-Zr composite oxide particles, calculated as Al2O3 (hereinafter referred to as "R2").

[0073] • The percentage of Al in Al-based oxide particles, calculated as Al₂O₃ (hereinafter referred to as "R₃").

[0074] 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.

[0075] Specifically, when the content (mass basis) of Ce-based oxide particles, Ce-Zr-based composite oxide particles and other 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.

[0076] P T =X×P1+Y×P2+Z×P3 (1)

[0077] Q T =X×Q1+Y×Q2+Z×Q3 (2)

[0078] R T =X×R1+Y×R2+Z×R3 (3)

[0079] 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.

[0080] 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. On the other hand, when the average particle size of Ce-based oxide particles is too large, the dispersibility of the Ce-based oxide particles decreases, and the contact between the Ce-based oxide particles and the catalytically active components decreases. Therefore, from the perspective of more efficiently utilizing the aforementioned effects of Ce-based oxide particles, 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] The Ce-based oxide particles may contain one or more metal elements other than Ce, Al, Mg, La, Pr, Y, and Nd. Examples of the metal elements other than Ce, Al, Mg, La, Pr, Y, and Nd include rare earth elements such as Sc, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; transition metal elements such as Fe, Mn, Ni, and Zr, etc. The metal elements other than Ce, Al, Mg, La, Pr, Y, and Nd may form a solid solution phase together with Ce and O, may form a single phase (such as an oxide phase of a metal element) as a crystalline phase or an amorphous phase, or may form both a solid solution phase and a single phase.

[0085] <Ce-Zr composite oxide particles>

[0086] The catalyst composition for exhaust gas purification of the present invention contains Ce-Zr composite oxide particles. It should be noted that in this specification, unless otherwise specified, "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, which is distinguished from the Ce-Zr composite oxide particles (hereinafter referred to as "Ce-Zr composite oxide particles as raw materials") used as raw materials of the catalyst composition for exhaust gas purification of the present invention.

[0087] The Ce-Zr composite oxide particles have an oxygen storage capacity (that is, 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), and can slow down the fluctuation of the oxygen concentration in the exhaust gas and expand the working window of the catalytic active component. Therefore, the exhaust gas purification ability of the catalyst composition for exhaust gas purification is improved.

[0088] The Ce-Zr composite oxide particles are composed of a Ce-Zr composite oxide. From the perspective of improving the oxygen storage capacity of the Ce-Zr composite oxide particles, based on the mass of the Ce-Zr composite oxide particles, the CeO2 conversion amount 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 further preferably 10% by mass or more and 50% by mass or less. The measurement method of the CeO2 conversion amount of Ce in the Ce-Zr composite oxide particles is the same as the measurement method of the CeO2 conversion amount of Ce in the Ce-based oxide particles.

[0089] 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.

[0090] 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.

[0091] 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 oxide particles and more efficiently utilizing the aforementioned effects of Ce 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 98.99% 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 oxide particles in the catalyst composition for waste gas purification of the present invention.

[0092] 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 70 or less, more preferably 1.0 or more and 25 or less, and even more preferably 1.5 or more and 15 or less.

[0093] 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.

[0094] Ce-Zr composite oxide particles are used as supports for catalytically active components. From the perspective of improving the loading capacity of catalytically active components, porous materials are preferred for Ce-Zr composite oxide particles.

[0095] 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.

[0096] 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.

[0097] <Precious Metal Elements>

[0098] 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.

[0099] 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).

[0100] 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.

[0101] 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.

[0102] Precious metal elements are preferably loaded onto Ce-based oxide particles and Ce-Zr-based composite 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 is readily exhibited. Therefore, by loading precious metal elements onto Ce-based oxide particles and Ce-Zr-based composite 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 a temperature, 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 and Ce-Zr-based composite 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 region, it can be determined that the catalytically active component is loaded onto the Ce-based oxide particles; if the catalytically active component and Ce-Zr-based composite oxide particles are present in the same region, it can be determined that the catalytically active component is loaded onto the Ce-Zr-based composite oxide particles. Based on the mass of the Ce-based oxide particles, the amount of noble metal element loaded onto 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 the Ce-Zr-based composite oxide particles, the amount of noble metal element loaded onto the Ce-Zr-based 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.

[0103] <Other Ingredients>

[0104] The catalyst composition for exhaust gas purification of the present invention may contain one or more inorganic oxide particles other than Ce-based oxide particles and Ce-Zr-based composite oxide particles (hereinafter referred to as "other particles"). It should be noted that, unless otherwise specified, in this specification, "other particles" refers to other particles contained in the catalyst composition for exhaust gas purification of the present invention, and is distinguished from other particles used as raw materials for the catalyst composition for exhaust gas purification of the present invention (hereinafter referred to as "other particles as raw materials").

[0105] Other particles are composed of oxides of metallic elements other than Ce and Zr. Examples of other particles include: Al-based oxide particles, zirconium oxide particles, silicon dioxide particles, titanium dioxide particles, etc.

[0106] 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.

[0107] 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.

[0108] 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 oxides, elements selected from Ce, La, Sr, Ba, etc. are preferred.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] Other particles are used as supports for the catalytically active ingredients. From the perspective of improving the loading capacity of the catalytically active ingredients, these other particles are preferably porous. Al-based oxide particles are distinguished from alumina used as a binder (hereinafter referred to as "alumina binder"). Alumina binder is derived from alumina sol used as a material in the catalyst composition.

[0116] When the catalyst composition for exhaust gas purification of the present invention contains other particles, the precious metal element can be loaded onto the other particles. The meaning of "loaded" is the same as described above. At high temperatures, the exhaust gas purification performance of the precious metal element loaded onto the other particles is readily realized. Therefore, by loading the precious metal element onto Ce-based oxide particles, Ce-Zr-based composite oxide particles, and other particles, the exhaust gas purification performance over a wide temperature range is improved. Based on the mass of the other particles, the amount of precious metal element loaded onto the other particles is preferably 0.05% by mass or more, more preferably 0.10% by mass or more. It should be noted that the upper limit is, for example, 20% by mass.

[0117] The catalyst composition for waste gas purification of the present invention may contain stabilizers, binders, etc. Examples of binders include inorganic oxide-based binders such as alumina sol, zirconium oxide sol, titanium dioxide sol, and silica sol. Examples of stabilizers include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (e.g., Sr, Ba).

[0118] <The morphology of catalyst compositions for waste gas purification>

[0119] The catalyst composition for waste gas purification of the present invention is in the form of, for example, powder, shaped body, or layer.

[0120] <Method for Manufacturing Catalyst Compositions for Waste Gas Purification>

[0121] 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 composite oxide particles, and other components added as needed (e.g., other particles as raw materials, binders, stabilizers, etc.), 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.

[0122] 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 it is performed using Ce-based oxide particles used as raw materials.

[0123] Catalysts for Waste Gas Purification

[0124] The catalyst for purifying waste gas according to the present invention will be described below.

[0125] 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.

[0126] <Substrate>

[0127] 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.

[0128] 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.

[0129] <Catalyst Layer>

[0130] The catalyst layer of the present invention is composed of the catalyst composition for waste gas purification of the present invention. That is, the catalyst layer of the present invention contains Ce-based oxide particles, Ce-Zr composite oxide particles, and noble metal elements. The descriptions of the above <Ce-based oxide particles>, <Ce-Zr composite oxide particles>, <noble metal elements>, and <other components> also apply to the catalyst layer of the present invention. When applicable, replace "the catalyst composition for waste gas purification of the present invention" with "the catalyst layer of the present invention".

[0131] From the perspective of considering the balance between waste gas purification performance and cost, the mass of the catalyst layer of the present invention per unit volume of the substrate (the mass after drying and firing) 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 further preferably 50 g / L or more and 150 g / L or less. It should be noted that the volume of the substrate refers to the apparent volume of the substrate. For example, when the substrate is a cylindrical shape with an outer diameter of 2r, the volume of the substrate is represented by the formula: volume of the substrate = π × r 2 × (length of the substrate).

[0132] <First Embodiment>

[0133] Based on the following Figures 1-4 the waste gas purification catalyst 1A according to the first embodiment of the present invention will be described.

[0134] As Figure 1 shown, the waste gas purification catalyst 1A is disposed in the exhaust passage in the exhaust pipe P of the internal combustion engine. The internal combustion engine is, for example, a gasoline engine or the like. The waste gas discharged from the internal combustion engine flows through the exhaust passage in the exhaust pipe P from one end to the other end of the exhaust pipe P, and is purified by the waste gas purification catalyst 1A disposed in the exhaust pipe P. In the drawings, the waste gas flow direction is represented by the symbol X. In this specification, sometimes the upstream side of the waste gas flow direction X is referred to as the "waste gas inflow side", and the downstream side of the waste gas flow direction X is referred to as the "waste gas outflow side".

[0135] The exhaust passage in the exhaust pipe P may be configured with other waste gas purification catalysts while being configured with the waste gas purification catalyst 1A. For example, the waste gas purification catalyst 1A may be disposed on the upstream side of the exhaust passage in the exhaust pipe P, and other waste gas purification catalysts may be disposed on the downstream side of the exhaust passage in the exhaust pipe P. As other waste gas purification catalysts, for example, the waste gas purification catalyst 1B described later can be cited.

[0136] As Figures 2-4 shown, the waste gas purification catalyst 1A includes a substrate 10 and a catalyst layer 20 provided on the substrate 10.

[0137] The above description of the substrate also applies to the substrate 10.

[0138] 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, and noble metal elements. The above description of the catalyst layer of the present invention also applies to the catalyst layer 20.

[0139] 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.

[0140] like Figure 2 As shown, the cylindrical part 11 is cylindrical, but it can also be elliptical, polygonal, or other shapes.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] like Figure 4 As shown, the catalyst layer 20 is disposed on the partition wall portion 12 of the substrate 10.

[0147] like Figure 4As 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.

[0148] 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, and other components added as needed (e.g., other particles as raw materials, binders, stabilizers, etc.). 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.

[0149] <Second Implementation Method>

[0150] 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.

[0151] like Figure 5 As shown, catalyst 1B for waste gas purification differs from catalyst 1A for waste gas purification in the following ways:

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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, 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] Example

[0162] The present invention will be further described in detail below based on embodiments and comparative examples.

[0163] Prepare cerium oxide powder for use in the following examples, comparative examples, and comparative examples. The CeO2 equivalent of Ce in the cerium oxide powder is approximately 100% by mass (>99% by mass).

[0164] [Example 1]

[0165] (1) Preparation of Ce-based oxides

[0166] Cerium oxide powder (CeO2 equivalent: 95.0 g) was added to an aqueous aluminum nitrate solution (Al2O3 equivalent: 5.0 g), stirred at room temperature for 2 hours, and then evaporated to dryness to obtain a dry powder. The obtained dry powder was calcined at 1000°C for 1 hour in air to obtain the Ce-based oxide powder of Example 1 (CeO2 equivalent: 95.0 wt%, Al2O3 equivalent: 5.0 wt%).

[0167] (2) Preparation of catalyst composition for waste gas purification

[0168] To prepare 100 parts by weight of the catalyst composition, 61.0 parts by weight of Ce-Zr composite oxide powder (CeO2 equivalent of Ce: 40% by weight, ZrO2 equivalent of Zr: 50% by weight, La2O3 equivalent of La: 10% by weight), 28.0 parts by weight of Al oxide powder (Al2O3 equivalent of Al: 99% by weight, La2O3 equivalent of La: 1% by weight), and 10.0 parts by weight of Ce oxide powder from Example 1 (CeO2 equivalent of Ce: 95.0% by weight, Al2O3 equivalent of Al: 5.0% by weight) were added sequentially to a dinitrodiamineplatinum nitric acid aqueous solution (Pt metal conversion: 1.0 parts by weight), and 10.0 parts by weight of Ce oxide powder from Example 1 (CeO2 equivalent of Ce: 95.0% by weight, Al2O3 equivalent of Al: 5.0% by weight). After standing for 1 hour, the dinitrodiamineplatinum nitric acid aqueous solution was allowed to impregnate and load the Ce-Zr composite oxide powder, Al oxide powder, and Ce 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.

[0169] The obtained catalyst composition was analyzed using electron probe microanalysis (EPMA), and Al2O3 was detected at the same positions as CeO2. This confirms that the Ce-based oxide particles in the catalyst composition are composed of oxides containing both Ce and Al.

[0170] [Example 2]

[0171] (1) Preparation of Ce-based oxides

[0172] Except that an aqueous solution of magnesium nitrate (MgO equivalent of Mg: 5.0 g) was used instead of an aqueous solution of aluminum nitrate, the Ce-based oxide powder of Example 2 (CeO2 equivalent of 95.0 wt%, MgO equivalent of 5.0 wt%) was obtained in the same manner as in Example 1.

[0173] (2) Preparation of catalyst composition for waste gas purification

[0174] Except that the Ce-based oxide powder of Example 2 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0175] Analysis of the obtained catalyst composition using EPMA revealed the presence of MgO at the same positions as CeO2. This confirms that the Ce-based oxide particles in the catalyst composition consist of oxides containing both Ce and Mg.

[0176] [Example 3]

[0177] (1) Preparation of Ce-based oxides

[0178] Except that an aqueous solution of lanthanum nitrate (La equivalent to La2O3: 5.0 g) was used instead of an aqueous solution of aluminum nitrate, the Ce-based oxide powder of Example 3 (Ce equivalent to CeO2: 95.0 wt%, La equivalent to La2O3: 5.0 wt%) was obtained in the same manner as in Example 1.

[0179] (2) Preparation of catalyst composition for waste gas purification

[0180] Except that the Ce-based oxide powder of Example 3 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0181] EPMA analysis of the obtained catalyst composition revealed the presence of La2O3 at the same positions as CeO2. This confirms that the Ce-based oxide particles in the catalyst composition consist of oxides containing both Ce and La.

[0182] [Example 4]

[0183] (1) Preparation of Ce-based oxides

[0184] In addition to using praseodymium nitrate aqueous solution (Pr of Pr6O) 11 Except for replacing the aqueous solution of aluminum nitrate, Ce-based oxide powder (CeO2 conversion: 95.0% by mass, Pr6O) of Example 4 was obtained in the same manner as in Example 1. 11 Conversion quantity: 5.0% by mass.

[0185] (2) Preparation of catalyst composition for waste gas purification

[0186] Except that the Ce-based oxide powder of Example 4 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0187] The obtained catalyst composition was analyzed by EPMA, and Pr6O was detected at the same position as CeO2. 11 This confirms that the Ce-based oxide particles in the catalyst composition are composed of oxides containing Ce and Pr.

[0188] [Example 5]

[0189] (1) Preparation of Ce-based oxides

[0190] Except that an aqueous solution of yttrium nitrate (Y2O3 equivalent of Y: 5.0 g) was used instead of an aqueous solution of aluminum nitrate, the Ce-based oxide powder of Example 5 (CeO2 equivalent of 95.0 wt%, Y2O3 equivalent of 5.0 wt%) was obtained in the same manner as in Example 1.

[0191] (2) Preparation of catalyst composition for waste gas purification

[0192] Except that the Ce-based oxide powder of Example 5 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0193] Analysis of the obtained catalyst composition using EPMA revealed the presence of Y₂O₃ at the same positions as CeO₂. This confirms that the Ce-based oxide particles in the catalyst composition consist of oxides containing both Ce and Y.

[0194] [Example 6]

[0195] (1) Preparation of Ce-based oxides

[0196] Except that a neodymium nitrate aqueous solution (Nd2O3 equivalent: 5.0 g) was used instead of an aluminum nitrate aqueous solution, the Ce-based oxide powder of Example 6 (CeO2 equivalent: 95.0 wt%, Nd2O3 equivalent: 5.0 wt%) was obtained in the same manner as in Example 1.

[0197] (2) Preparation of catalyst composition for waste gas purification

[0198] Except that the Ce-based oxide powder of Example 6 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0199] EPMA analysis of the obtained catalyst composition revealed the presence of Nd₂O₃ at the same positions as CeO₂. This confirms that the Ce-based oxide particles in the catalyst composition consist of oxides containing both Ce and Nd.

[0200] [Comparative Example 1]

[0201] To prepare 100 parts by mass of the catalyst composition, 66.0 parts by mass of Ce-Zr composite oxide powder (CeO2 equivalent: 40% by mass, ZrO2 equivalent: 50% by mass, La2O3 equivalent: 10% by mass) and 33.0 parts by mass of Al oxide powder (Al2O3 equivalent: 99% by mass, La2O3 equivalent: 1% by mass) were added sequentially to a dinitrodiamineplatinum nitric acid aqueous solution (Pt metal conversion: 1.0 parts by mass). The mixture was allowed to stand for 1 hour to allow the dinitrodiamineplatinum nitric acid aqueous solution to impregnate and load the Ce-Zr composite oxide powder and the Al oxide powder. The mixture was then evaporated and dried to obtain a dry powder. The dried powder was calcined at 500°C for 1 hour under atmospheric atmosphere to obtain the powdered catalyst composition.

[0202] [Comparative Example 2]

[0203] To prepare 100 parts by mass of the catalyst composition, 61.0 parts by mass of Ce-Zr composite oxide powder (CeO2 equivalent of Ce: 40% by mass, ZrO2 equivalent of Zr: 50% by mass, La2O3 equivalent of La: 10% by mass), 28.0 parts by mass of Al oxide powder (Al2O3 equivalent of Al: 99% by mass, La2O3 equivalent of La: 1% by mass), and 10.0 parts by mass of cerium oxide powder (CeO2 equivalent of Ce: approximately 100% by mass (>99% by mass)) were added sequentially to a dinitrodiamineplatinum nitric acid aqueous solution (Pt metal equivalent: 1.0 parts by mass). After standing for 1 hour, the dinitrodiamineplatinum nitric acid aqueous solution was allowed to impregnate and load the Ce-Zr composite oxide powder, Al oxide powder, and cerium 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.

[0204] The obtained catalyst composition was analyzed by EPMA, and the results showed that Al2O3, which exists in the same position as CeO2, was not detected.

[0205] [Comparative Example 3]

[0206] (1) Preparation of Ce-based oxides

[0207] Except that an aqueous solution of zirconium nitrate (ZrO2 equivalent of Zr: 5.0 g) was used instead of an aqueous solution of aluminum nitrate, the Ce-based oxide powder of Comparative Example 3 (CeO2 equivalent of Ce: 95.0 wt%, ZrO2 equivalent of Zr: 5.0 wt%) was obtained in the same manner as in Example 1.

[0208] (2) Preparation of catalyst composition for waste gas purification

[0209] Except that the Ce-based oxide powder of Comparative Example 3 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0210] Analysis of the obtained catalyst composition using EPMA revealed the presence of ZrO2 at the same positions as CeO2. This confirms that the Ce-based oxide particles in the catalyst composition consist of oxides containing both Ce and Zr.

[0211] [Comparative Example 4]

[0212] (1) Preparation of Ce-based oxides

[0213] Besides using phosphoric acid aqueous solution (P of P4O) 10 Except for replacing the aqueous aluminum nitrate solution, Ce-based oxide powder (CeO2 conversion: 95.0 wt%, P4O) of Comparative Example 4 was obtained in the same manner as in Example 1. 10 Conversion quantity: 5.0% by mass.

[0214] (2) Preparation of catalyst composition for waste gas purification

[0215] Except that the Ce-based oxide powder of Comparative Example 4 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0216] The obtained catalyst composition was analyzed by EPMA, and P4O was detected at the same position as CeO2. 10 This confirms that the Ce-based oxide particles contained in the catalyst composition are composed of oxides containing Ce and P.

[0217] [Comparative Example 5]

[0218] (1) Preparation of Ce-based oxides

[0219] Except that an aqueous solution of tin nitrate (SnO equivalent of Sn: 5.0 g) was used instead of an aqueous solution of aluminum nitrate, the Ce-based oxide powder of Comparative Example 5 (CeO2 equivalent of Ce: 95.0 wt%, SnO equivalent of Sn: 5.0 wt%) was obtained in the same manner as in Example 1.

[0220] (2) Preparation of catalyst composition for waste gas purification

[0221] Except that the Ce-based oxide powder of Comparative Example 5 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0222] Analysis of the obtained catalyst composition using EPMA revealed the presence of SnO at the same positions as CeO2. This confirms that the Ce-based oxide particles in the catalyst composition consist of oxides containing both Ce and Sn.

[0223] [Comparative Example 6]

[0224] (1) Preparation of Ce-based oxides

[0225] Except that an aqueous solution of indium nitrate (equivalent to 5.0 g of In₂O₃ in In) was used instead of an aqueous solution of aluminum nitrate, the Ce-based oxide powder of Comparative Example 6 (equivalent to 95.0% by mass of CeO₂ and 5.0% by mass of In₂O₃ in In) was obtained in the same manner as in Example 1.

[0226] (2) Preparation of catalyst composition for waste gas purification

[0227] Except that the Ce-based oxide powder of Comparative Example 6 was used instead of the Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0228] EPMA analysis of the obtained catalyst composition revealed the presence of In₂O₃ at the same positions as CeO₂. This confirms that the Ce-based oxide particles in the catalyst composition consist of oxides containing both Ce and In.

[0229] [Experimental Example 1]

[0230] (1) Determination of the average particle size of Ce-based oxide powders

[0231] The average particle size of each Ce-based oxide powder obtained in Examples 1-6 and Comparative Examples 1-6 was determined as follows: The Ce-based oxide powder was observed using a scanning electron microscope (JEOL JCM-7000), and the fixed-direction diameter (Ferret diameter) of 100 randomly selected particles within the field of view was measured. The average value was taken as the average particle size of the Ce-based oxide powder.

[0232] (2) Determination of crystallite diameter using Ce-based oxide powder

[0233] Using the Ce-based oxide powders obtained in Examples 1-6 and Comparative Examples 1-6, the crystallite diameter of CeO2 in the Ce-based oxide particles was determined as follows. X-ray diffraction (XRD) was performed using Ce-based oxide powder and a commercially available powder X-ray diffractometer (Rigyaku Corporation "MiniFlex600") 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 at 2θ = 55–58° and 2θ = 46–49° originating from CeO2 were identified. The crystallite diameter was automatically calculated using analytical software (Rigyaku Corporation "PDXL version 2") by applying the Scherrer formula to the identified peaks. The crystallite diameters obtained from the peaks at 2θ = 55–58° and the peaks at 2θ = 46–49° were compared, and the larger crystallite diameter was selected as the crystallite diameter of CeO2 in the Ce-based oxide powder.

[0234] (3) Determination of crystallite diameter using catalyst composition

[0235] Using the catalyst compositions obtained in Examples 1-6 and Comparative Examples 1-6, the crystallite diameter of CeO2 in Ce-based oxide particles was determined in the same manner as described in (2) above.

[0236] (4) Determination of the dispersion of precious metals

[0237] The catalyst compositions obtained in Examples 1-6 and Comparative Examples 1-6 were heat-treated at 1000°C for 20 hours in a quartz tubular furnace under an atmosphere of 0.5 vol.% O2, 10 vol.% H2O in the form of water vapor, and N2 as a background gas. The amount of CO adsorbed in the noble metal was measured using a CO pulse method with the heat-treated catalyst composition and a metal dispersion measuring device (BELMETAL3, manufactured by MicrotracBEL Co., Ltd.), 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 the noble metal particles to the total number A of noble metal atoms (Pt in Examples 1-6 and Comparative Examples 1-6), calculated using the formula: noble metal dispersion (%) = (B / A) × 100. The number B of noble metal atoms exposed on the surface of the noble metal particles is calculated from the amount of CO adsorbed by the CO pulse method, based on the premise that the noble metal atoms exposed on the surface of the noble metal particles and CO are adsorbed at a 1:1 ratio.

[0238] (5) Measurement of OSC levels

[0239] The OSC of each catalyst composition obtained in Examples 1-6 and Comparative Examples 1-6 was determined using a metal dispersion measuring device (BELMETAL3 manufactured by MicrotracBEL Co., Ltd.) by CO pulse method.

[0240] In the OSC determination, the catalyst composition was heated to 800°C under He flow, pretreated at this temperature for 40 minutes, and then cooled to 300°C. Next, while maintaining the catalyst composition at 300°C, O2 gas was injected in four pulses for oxidation treatment. Then, a test gas containing CO was injected in ten pulses. The total amount of CO gas consumed was used to determine the OSC amount (μmol / g) per unit weight of the catalyst composition using a thermal conductivity detector (TCD) built into a metal dispersion measuring device (BELMETAL3, manufactured by MicrotracBEL Co., Ltd.).

[0241] (6) Evaluation of exhaust gas purification performance

[0242] The catalyst compositions obtained in Examples 1-6 and Comparative Examples 1-6 were heat-treated 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 compositions were then packed into a reaction tube, and the exhaust gas purification performance of the heat-treated catalyst compositions was measured using a fixed-bed flow-through reactor. Specifically, 0.1 g of the heat-treated catalyst composition was packed 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.

[0243] Purification rate (%) = (XY) / X × 100

[0244] The gas temperature at the inlet of the reaction tube when the NO purification rate reaches 50% is taken as the ignition temperature T50 (°C). It should be noted that the ignition temperature T50 is determined during the heating process.

[0245] The average particle size of Ce-based oxide powders and the crystallite diameter of CeO2 determined using Ce-based oxide powders are shown in Table 1. The crystallite diameter, noble metal dispersion, OSC content, and T50 of CeO2 determined using the catalyst composition are shown in Table 2. Table 1 also shows the composition and amount of Ce-based oxide powders used as materials in the catalyst compositions of Examples 1-6 and Comparative Examples 1-6. In Table 1, “CeO2” represents the CeO2 equivalent of Ce (mass %), “Al2O3” represents the Al2O3 equivalent of Al (mass %), “MgO” represents the MgO equivalent of Mg (mass %), “La2O3” represents the La2O3 equivalent of La (mass %), and “Pr6O” represents the Pr6O3 equivalent of Pr6O3. 11 "Indicates Pr6O" 11 Conversion quantity (mass%), "Y2O3" represents the Y2O3 conversion quantity (mass%) of Y, "Nd2O3" represents the Nd2O3 conversion quantity (mass%) of Nd, "ZrO2" represents the ZrO2 conversion quantity of Zr, "P4O" represents the ZrO2 conversion quantity (mass%) of P4O3. 10 "P represents P4O" 10 Conversion amount (mass%), "SnO" indicates the SnO conversion amount (mass%) of Sn, "In2O3" indicates the In2O3 conversion amount (mass%) of In.

[0246] [Table 1]

[0247]

[0248] [Table 2]

[0249] Table 2

[0250]

[0251] As shown in Table 2, the T50 of the catalyst compositions of Examples 1 to 6 is lower than that of the catalyst compositions of Comparative Examples 1 to 6, and the exhaust gas purification performance of the catalyst compositions of Examples 1 to 6 is improved compared with that of the catalyst compositions of Comparative Examples 1 to 6.

[0252] As shown in Table 2, the noble metal dispersion of the catalyst compositions of Examples 1 and 2 is higher than that of the catalyst compositions of Examples 3-6. On the other hand, the OSC content of the catalyst compositions of Examples 3-6 is greater than that of the catalyst compositions of Examples 1 and 2. From these results, it is clear that the mechanism by which the catalyst compositions of Examples 1 and 2 improve the exhaust gas purification performance is different from that of the catalyst compositions of Examples 3-6.

[0253] It is believed that when Ce-based oxide particles contain a first additional element selected from Al and Mg, the heat resistance of Ce-based oxide particles is improved, the decrease in specific surface area of ​​Ce-based oxide particles and the accompanying burial of catalytically active components in Ce-based oxide particles are suppressed. As a result, the specific surface area of ​​the catalyst composition for exhaust gas purification is increased, the dispersion of catalytically active components is improved, and the exhaust gas purification performance of the catalyst composition for exhaust gas purification is improved.

[0254] Furthermore, it is believed that when Ce-based oxide powder contains a second additional element selected from La, Pr, Y and Nd, the oxygen storage capacity of Ce-based oxide particles loaded with noble metal elements is improved, thereby improving the exhaust gas purification capacity of the catalyst composition for exhaust gas purification.

[0255] [Experimental Example 2]

[0256] In Experiment 2, an experiment was conducted to determine the appropriate range of the content of the first additional element selected from Al and Mg.

[0257] (1) Experimental Example 2A

[0258] Except for the addition of cerium oxide powder (CeO2 equivalent: 99.9 g) to an aqueous aluminum nitrate solution (Al2O3 equivalent: 0.1 g for Al), Ce oxide powder (CeO2 equivalent: 99.9 wt% for Ce and Al2O3 equivalent: 0.1 wt% for Al) was obtained in the same manner as in Example 1.

[0259] (2) Experimental Example 2B

[0260] Except for the addition of cerium oxide powder (CeO2 equivalent: 97.5 g) to an aqueous aluminum nitrate solution (Al2O3 equivalent: 2.5 g for Al), Ce oxide powder (CeO2 equivalent: 97.5 wt% for Ce and Al2O3 equivalent: 2.5 wt% for Al) was obtained in the same manner as in Example 1.

[0261] (3) Experimental Example 2C

[0262] The Ce-based oxide powder obtained in Example 1 (Ce O2 equivalent: 95.0% by mass, Al Al2O3 equivalent: 5.0% by mass) was used as the Ce-based oxide powder in Test Example 2C.

[0263] (4) Experimental Example 2D

[0264] Except for the addition of cerium oxide powder (CeO2 equivalent: 90.0 g) to an aqueous aluminum nitrate solution (Al2O3 equivalent: 10.0 g for Al), Ce-based oxide powder (CeO2 equivalent: 90.0 wt% for Ce and Al2O3 equivalent: 10.0 wt% for Al) was obtained in the same manner as in Example 1.

[0265] (5) Experimental Example 2E

[0266] Except for the addition of cerium oxide powder (CeO2 equivalent: 80.0 g) to an aqueous aluminum nitrate solution (Al2O3 equivalent: 20.0 g for Al), Ce-based oxide powder (CeO2 equivalent: 80.0 wt% for Ce and Al2O3 equivalent: 20.0 wt% for Al) was obtained in the same manner as in Example 1.

[0267] (6) Experimental Example 2F

[0268] Cerium oxide powder was calcined in the atmosphere at 1000°C for 1 hour to obtain Ce-based oxide powder of Experimental Example 2F (Ce O2 conversion: approximately 100% by mass (>99% by mass)).

[0269] (7) Determination of the average particle size of Ce-based oxide powders

[0270] The average particle size of Ce-based oxide powders in Examples 2A to 2F was determined in the same manner as in Example 1(1). The results are shown in Table 3.

[0271] (8) Determination of crystallite diameter using Ce-based oxide powder

[0272] The crystallite diameter of CeO2 in Ce oxide particles was determined using Ce oxide powders from Examples 2A to 2F in the same manner as in Example 1(2). The results are shown in Table 3.

[0273] (9) Determination of BET specific surface area

[0274] The BET specific surface area of ​​Ce-based oxide powders in Examples 2A–2F was determined using QUADRASORB SI (Quanta Chrome) by N2 gas adsorption method. The results are shown in Table 3.

[0275] [Table 3]

[0276] Table 3

[0277]

[0278] As shown in Table 3, the BET specific surface area of ​​the Ce-based oxide powders in Test Examples 2A to 2E is greater than that of the Ce-based oxide powder in Test Example 2F. These results clearly indicate that, based on the mass of the Ce-based oxide powder, the appropriate range for the oxide equivalent of the first added element in the Ce-based oxide powder is 0.1% by mass or more and 20% by mass or less.

[0279] [Experimental Example 3]

[0280] In Experiment 3, an experiment was conducted to determine the appropriate range of the content of the second additional element selected from La, Pr, Y and Nd.

[0281] (1) Experimental Example 3A

[0282] Except for the addition of cerium oxide powder (CeO2 equivalent: 99.9 g) to an aqueous solution of lanthanum nitrate (La in La2O3 equivalent: 0.1 g), Ce oxide powder (CeO2 equivalent: 99.9 wt%, La in La2O3 equivalent: 0.1 wt%) was obtained in the same manner as in Example 1.

[0283] Except that Ce-based oxide powder of Experimental Example 3A was used instead of Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0284] (2) Experimental Example 3B

[0285] Except for the addition of cerium oxide powder (CeO2 equivalent: 97.5 g) to an aqueous solution of lanthanum nitrate (La in La2O3 equivalent: 2.5 g), Ce oxide powder (CeO2 equivalent: 97.5 wt% and La in La2O3 equivalent: 2.5 wt%) was obtained in the same manner as in Example 1.

[0286] Except that Ce-based oxide powder of Experimental Example 3B was used instead of Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0287] (3) Experimental Example 3C

[0288] The Ce-based oxide powder obtained in Example 3 (Ce O2 equivalent: 95.0% by mass, La La 2O3 equivalent: 5.0% by mass) was used as the Ce-based oxide powder of Test Example 3C.

[0289] Except that Ce-based oxide powder of Experimental Example 3C was used instead of Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0290] (4) Experimental Example 3D

[0291] Except for the addition of cerium oxide powder (CeO2 equivalent: 90.0 g) to an aqueous solution of lanthanum nitrate (La in La2O3 equivalent: 10.0 g), Ce oxide powder (CeO2 equivalent: 90.0 wt% and La in La2O3 equivalent: 10.0 wt%) was obtained in the same manner as in Example 1.

[0292] Except that Ce-based oxide powder of Experimental Example 3D was used instead of Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0293] (5) Experimental Example 3E

[0294] Except for the addition of cerium oxide powder (CeO2 equivalent: 80.0 g) to an aqueous solution of lanthanum nitrate (La in La2O3 equivalent: 20.0 g), Ce oxide powder (CeO2 equivalent: 80.0 wt% and La in La2O3 equivalent: 20.0 wt%) was obtained in the same manner as in Example 1.

[0295] Except that Ce-based oxide powder of Experimental Example 3E was used instead of Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0296] (6) Experimental Example 3F

[0297] Cerium oxide powder was calcined in the atmosphere at 1000°C for 1 hour to obtain Ce-based oxide powder of Experimental Example 3F (Ce O2 conversion: approximately 100% by mass (>99% by mass)).

[0298] Except that Ce-based oxide powder of Experimental Example 3F was used instead of Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0299] (7) Test Case 3G

[0300] Except for the addition of cerium oxide powder (CeO2 equivalent: 70.0 g) to an aqueous solution of lanthanum nitrate (La in La2O3 equivalent: 30.0 g), Ce oxide powder (CeO2 equivalent: 70.0 wt% and La in La2O3 equivalent: 30.0 wt%) was obtained in the same manner as in Example 1.

[0301] Except that Ce-based oxide powder of Experimental Example 3G was used instead of Ce-based oxide powder of Example 1, the powdered catalyst composition was obtained in the same manner as in Example 1.

[0302] (8) Determination of the average particle size of Ce-based oxide powders

[0303] The average particle size of Ce-based oxide powders in Examples 3A to 3G was determined in the same manner as in Example 1(1). The results are shown in Table 4.

[0304] (9) Determination of crystallite diameter using Ce-based oxide powder

[0305] Using Ce-based oxide powders from Test Examples 3A to 3G, the crystallite diameter of CeO2 in the Ce-based oxide particles was determined in the same manner as in Test Example 1(2). The results are shown in Table 4.

[0306] (10) Measurement of OSC

[0307] The OSC of the catalyst compositions of Examples 3A to 3G were determined by CO pulse method in the same manner as in Example 1(5). The results are shown in Table 4.

[0308] [Table 4]

[0309] Table 4

[0310]

[0311] As shown in Table 4, the OSC content of the catalyst compositions in Test Examples 3A to 3E is greater than that of the catalyst compositions in Test Examples 3F and 3G. These results clearly indicate that, based on the mass of the Ce-based oxide powder, the suitable range for the oxide equivalent of the second additional element in the Ce-based oxide powder is 0.1% by mass or more and 20% by mass or less.

[0312] Explanation of reference numerals in the attached figures

[0313] 1A, 1B: Catalysts for waste gas purification

[0314] 10: Substrate

[0315] 11: Cylindrical part

[0316] 12: The next room

[0317] 13: Small room

[0318] 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, and noble metal elements. The Ce-based oxide particles contain at least one additional element selected from Al, Mg, La, Pr, Y, and Nd. Based on the mass of the Ce-based oxide particles, the CeO2 equivalent content of Ce in the Ce-based oxide particles is 80% or more by mass. Based on the mass of the Ce-based oxide particles, the oxide equivalent of the at least one additional element in the Ce-based oxide particles is 0.1% by mass or more and 20% by mass or less. 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 0.10 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 1.0% by mass or more.

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

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 and the Ce-Zr-based composite 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. 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 4.

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