Composite oxide and method for producing the same

Abstract

The present application aims at providing a CeO2-ZrO2-based composite oxide sufficiently micronized and a method for producing the same, and a composite oxide containing a zirconium element and a cerium element and, as occasion demands, other rare earth metal elements, and having a D 50 and a D 90 of 0.5 μm or less and 1 μm or less, respectively.

Description

Technical Field

[0001] This invention relates to a composite oxide containing cerium and zirconium (hereinafter sometimes referred to as "CeO2-ZrO2 composite oxide") and a method for manufacturing the composite oxide. Background Technology

[0002] Exhaust gases emitted from internal combustion engines such as automobiles and motorcycles contain harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). A three-way catalyst is used as a catalyst to purify these harmful components and render them harmless. This catalyst possesses catalytic activity that oxidizes HC and CO to water and carbon dioxide, and reduces NOx to nitrogen.

[0003] In order to mitigate fluctuations in oxygen concentration in exhaust gas and efficiently purify HC, CO, NOx, etc., materials with oxygen storage capacity (OSC) are used as constituent materials of three-way catalysts, such as CeO2-ZrO2 composite oxides.

[0004] For example, Patent Document 1 describes a method for manufacturing CeO2-ZrO2-based composite oxides. In Patent Document 1, after mixing cerium chloride, zirconium oxychloride, praseodymium chloride, and water, ammonium persulfate is added to obtain a slurry containing sulfates. Ammonia water is then added to the obtained slurry to obtain a slurry containing hydroxides. The obtained slurry is filtered and washed to obtain a filter cake, and the obtained filter cake is calcined to manufacture CeO2-ZrO2-based composite oxides.

[0005] It is known that exhaust gases contain harmful components such as HC, CO, and NOx, as well as particulate matter (PM), contributing to air pollution. For example, it is known that gasoline direct injection (GDI) engines in vehicles equipped with gasoline engines have low fuel consumption and high power output, but compared to conventional port injection engines, they emit significantly more PM in their exhaust. To address PM-related environmental control measures, vehicles equipped with GDI or other gasoline engines are required to have gas-permeable filters (GPFs) with PM-capturing capabilities, similar to those equipped with diesel engines.

[0006] As a gas permeable powder (GPF), a substrate having a structure known as a wall-flow type is used. The wall-flow type substrate includes an inflow-side unit extending in the exhaust gas flow direction, an outflow-side unit extending in the exhaust gas flow direction, and a porous partition wall separating the inflow-side unit and the outflow-side unit. In the inflow-side unit, the end of the exhaust gas inflow side in the exhaust gas flow direction is open, and the end of the exhaust gas outflow side in the exhaust gas flow direction is closed. In the outflow-side unit, the end of the exhaust gas inflow side in the exhaust gas flow direction is closed, and the end of the exhaust gas outflow side in the exhaust gas flow direction is open. Exhaust gas flowing into the wall-flow type substrate from the exhaust gas inflow side end (opening) of the inflow-side unit flows out from the exhaust gas outflow side end (opening) of the outflow-side unit through the porous partition wall. As the exhaust gas passes through the porous partition wall, particulate matter (PM) in the exhaust gas is captured within the pores of the partition wall.

[0007] Typically, the space available for catalysts used in exhaust gas purification is limited. Therefore, this study investigated the use of precious metal catalysts such as Pt, Pd, and Rh loaded onto GPFs to purify harmful components such as HC, CO, and NOx while capturing PM.

[0008] For example, Patent Document 2 describes forming a catalyst layer within the porous partition wall of a wall-flow substrate. In Patent Document 2, a slurry containing Pd-loaded alumina powder, Rh-loaded zirconium oxide-lanthanum modified alumina powder, and CeO2-ZrO2 composite oxide powder is pulverized using a ball mill to obtain D. 90 The slurry is 3.0 μm thick, and the resulting slurry is impregnated into the porous partition wall to form a catalyst layer.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2018-047425

[0012] Patent Document 2: Japanese Patent Application Publication No. 2019-198838 Summary of the Invention

[0013] The problem the invention aims to solve

[0014] For CeO2-ZrO2 composite oxides to infiltrate into the porous partition wall, the CeO2-ZrO2 composite oxides need to be micronized. This is because if insufficiently micronized CeO2-ZrO2 composite oxides are allowed to infiltrate into the porous partition wall, the pores of the porous partition wall will be blocked, and the pressure loss will increase.

[0015] However, in the method described in Patent Document 1, sintering occurs through a firing process, thus making it impossible to obtain sufficiently micronized CeO2-ZrO2 composite oxides.

[0016] Furthermore, as described in Patent Document 2, even with dry or wet pulverization of CeO2-ZrO2 composite oxides, only a few μm level of D can typically be achieved. 90 It is impossible to obtain fully micronized CeO2-ZrO2 composite oxides.

[0017] Furthermore, even when CeO2-ZrO2 composite oxides are graded using sieves, fully micronized CeO2-ZrO2 composite oxides cannot be obtained.

[0018] Therefore, the object of the present invention is to provide a fully micronized CeO2-ZrO2 composite oxide and a method for manufacturing the CeO2-ZrO2 composite oxide.

[0019] Solution for solving the problem

[0020] To address the aforementioned issues, this invention provides a composite oxide comprising zirconium and cerium, and, where appropriate, other rare earth metal elements. The Dx of the aforementioned composite oxide is determined by laser diffraction scattering particle size distribution measurement. 50 and D 90 They are below 0.5μm and below 1μm, respectively.

[0021] In addition, the present invention provides a method for manufacturing a composite oxide, which includes the following steps:

[0022] (a) The process of preparing a feed solution containing water, zirconium salt and cerium salt and, where appropriate, other rare earth metal salts;

[0023] (b) A first precipitant selected from an aqueous solution containing sulfate ions and a compound that can dissolve in water to generate sulfate ions is added to the aforementioned raw material liquid to form a first precipitate containing zirconium, thereby obtaining a first slurry containing the aforementioned first precipitate.

[0024] (c) The process of wet pulverizing the aforementioned first slurry;

[0025] (d) Adding a second precipitant selected from an aqueous solution containing hydroxide ions and a compound that can dissolve in water to generate hydroxide ions to the first slurry after the aforementioned wet pulverization treatment, forming a second precipitate containing zirconium and cerium and, depending on the circumstances, other rare earth metal elements, to obtain a second slurry containing the aforementioned second precipitate.

[0026] (e) The process of obtaining filter cake from the aforementioned second slurry; and

[0027] (f) A process of firing the aforementioned filter cake to produce a composite oxide containing zirconium and cerium, and, where appropriate, other rare earth metal elements.

[0028] The effects of the invention

[0029] According to the present invention, a fully micronized CeO2-ZrO2 composite oxide and a method for manufacturing the CeO2-ZrO2 composite oxide can be provided. Detailed Implementation

[0030] The present invention will now be described. It should be noted that, unless otherwise specified, in this specification, "other rare earth metal elements" refers to rare earth metal elements other than cerium, "other rare earth metal ions" refers to rare earth metal ions other than cerium ions, "other rare earth metal salts" refers to rare earth metal salts other than cerium salts, and "other water-soluble rare earth metal salts" refers to water-soluble rare earth metal salts other than water-soluble cerium salts.

[0031] Composite Oxides

[0032] The composite oxide of the present invention contains zirconium and cerium, and may contain other rare earth metal elements as appropriate.

[0033] From the viewpoint of improving the heat resistance of composite oxides, the amount of zirconium oxide (ZrO2) contained in the composite oxides of the present invention, based on the mass of the composite oxides of the present invention, is preferably 20% by mass or more and 90% by mass or less, more preferably 30% by mass or more and 80% by mass or less, and even more preferably 40% by mass or more and 70% by mass or less.

[0034] From the viewpoint of improving the oxygen storage capacity of composite oxides, the amount of cerium oxide (CeO2) contained in the composite oxides of the present invention, based on the mass of the composite oxides of the present invention, is preferably 5% by mass or more and 70% by mass or less, more preferably 10% by mass or more and 50% by mass or less, and even more preferably 15% by mass or more and 40% by mass or less.

[0035] From the perspective of achieving a balance between the oxygen storage capacity and heat resistance of composite oxides, the ratio (mass ratio) of the zirconium oxide equivalent of zirconium element to the cerium oxide equivalent of cerium element is preferably 0.5 or more and 8 or less, more preferably 1 or more and 7 or less, and even more preferably 1.1 or more and 5 or less.

[0036] From the viewpoint of improving the heat resistance of composite oxides, the composite oxides of the present invention preferably contain one, two, or three or more other rare earth metal elements. These other rare earth metal elements can be selected from, for example, yttrium, praseodymium, scandium, lanthanum, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, etc., and are preferably selected from lanthanum, neodymium, and praseodymium. The composite oxides of the present invention may contain, for example, one, two, or three rare earth metal elements selected from lanthanum, neodymium, and praseodymium.

[0037] From the viewpoint of improving the heat resistance of the composite oxide, the oxide equivalent of other rare earth metal elements contained in the composite oxide of the present invention (when the composite oxide of the present invention contains two or more other rare earth metal elements, it is the total amount of oxides of the two or more other rare earth metal elements) is preferably 5% by mass or more and 35% by mass or less, more preferably 7% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 25% by mass or less, based on the mass of the composite oxide of the present invention. It should be noted that the oxides of other rare earth metal elements, except for praseodymium and terbium, are sesquioxides (Ln₂O₃, where Ln represents a rare earth metal element), and praseodymium oxide is typically Pr₆O₃. 11 Terbium oxide is usually Tb4O7.

[0038] When the composite oxide of the present invention contains lanthanum, from the viewpoint of improving the heat resistance of the composite oxide, the amount of lanthanum oxide (La2O3) contained in the composite oxide of the present invention, based on the mass of the composite oxide of the present invention, is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.5% by mass or more and 25% by mass or less, and even more preferably 1% by mass or more and 20% by mass or less.

[0039] When the composite oxide of the present invention contains neodymium, from the viewpoint of improving the heat resistance of the composite oxide, the amount of neodymium oxide (Nd2O3) contained in the composite oxide of the present invention, based on the mass of the composite oxide of the present invention, is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.5% by mass or more and 25% by mass or less, and even more preferably 1% by mass or more and 20% by mass or less.

[0040] In the case where the composite oxide of the present invention contains praseodymium, from the viewpoint of improving the heat resistance of the composite oxide, the praseodymium oxide (Pr6O) contained in the composite oxide of the present invention... 11The conversion amount, based on the mass of the composite oxide of the present invention, is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.5% by mass or more and 25% by mass or less, and even more preferably 1% by mass or more and 20% by mass or less.

[0041] In the composite oxide of the present invention, cerium oxide and zirconium oxide can form separate phases (cerium oxide separate phase or zirconium oxide separate phase) on the basis of forming a solid solution phase.

[0042] In the composite oxide of the present invention, other rare earth metal elements or their oxides may form a solid solution phase together with cerium oxide and / or zirconium oxide, or they may form a separate phase.

[0043] The main composition of the composite oxide of the present invention (mass %) of each metal element in the composite oxide as a whole can be analyzed by fluorescence X-ray diffraction. The main composition analysis based on fluorescence X-ray diffraction is preferably performed according to the conditions described in the examples.

[0044] The composite oxide of the present invention is preferably in powder form.

[0045] From the viewpoint of suppressing the clogging of the pores in the porous partition wall and the resulting increase in pressure loss when the composite oxide is impregnated into the porous partition wall of the wall-flow substrate, the composite oxide of the present invention has D 50 Preferably, it is 0.5 μm or less, more preferably 0.45 μm or less, and even more preferably 0.4 μm or less. The lower limit is preferably 0.05 μm, and more preferably 0.1 μm.

[0046] From the viewpoint of suppressing the clogging of the pores in the porous partition wall and the resulting increase in pressure loss when the composite oxide is impregnated into the porous partition wall of the wall-flow substrate, the composite oxide of the present invention has D 90 Preferably, it is 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.7 μm or less. The lower limit is preferably 0.2 μm, and more preferably 0.3 μm.

[0047] The composite oxide of the present invention has D 50 and D 90 The cumulative volume of the composite oxide of the present invention in the particle size distribution, obtained by laser diffraction scattering particle size distribution measurement method, is 50% and 90% of the particle size, respectively. The laser diffraction scattering particle size distribution measurement method is preferably performed according to the conditions described in the examples.

[0048] The composite oxide of the present invention preferably maintains its specific surface area even when exposed to high-temperature exhaust gas. The specific surface area of ​​the composite oxide of the present invention, measured by the BET method after heat treatment at 1000°C for 3 hours in the atmosphere, is preferably 20 m². 2 / g or more, further preferably 22m 2 / g or more, and more preferably 25m 2 / g or more. The upper limit is preferably 90m. 2 / g, further preferably 80m 2 / g.

[0049] The determination of specific surface area based on the BET method is preferably carried out according to the conditions described in the examples.

[0050] When the composite oxide of the present invention contains other rare earth metal elements, from the viewpoint of improving the heat resistance of the composite oxide and maintaining the specific surface area of ​​the composite oxide even when exposed to high-temperature exhaust gas, the mass percentage of the oxides of other rare earth metal elements at the surface of the composite oxide of the present invention is preferably greater than the mass percentage of the oxides of other rare earth metal elements in the entire composite oxide of the present invention. That is, the oxides of other rare earth metal elements are preferably present in large quantities on the surface of the composite oxide of the present invention. The other rare earth metal elements present on the surface of the composite oxide can improve the heat resistance of the composite oxide and maintain the specific surface area of ​​the composite oxide by inhibiting the growth of CeO2 crystals that occur when the composite oxide is exposed to high-temperature exhaust gas. It can be considered that the other rare earth metal elements present on the surface of the composite oxide will become an obstacle to the growth of CeO2 crystals and inhibit the growth of CeO2 crystals. It can be considered that the larger the ionic radius of the lanthanum element, the greater this effect becomes.

[0051] When the composite oxide of the present invention contains other rare earth metal elements, from the viewpoint of improving the heat resistance of the composite oxide and maintaining the specific surface area of ​​the composite oxide even when exposed to high-temperature exhaust gas, the mass percentage of the other rare earth metal elements at the surface of the composite oxide of the present invention, converted from oxides, is preferably 0.80 times or more, more preferably 0.83 times or more, and even more preferably 0.85 times or more. The upper limit is preferably 3.0 times, more preferably 2.0 times.

[0052] The mass percentage of oxides of other rare earth metal elements on the surface of the composite oxide of the present invention can be determined by X-ray photoelectron spectroscopy. X-ray photoelectron spectroscopy is preferably performed according to the conditions described in the examples. It should be noted that the mass percentage of oxides of other rare earth metal elements on the surface of the composite oxide of the present invention is based on the total mass percentage of oxides of metal elements on the surface of the composite oxide of the present invention (the total mass percentage of oxides of metal elements on the surface of the composite oxide of the present invention is 100% by mass). Furthermore, when the composite oxide of the present invention contains two or more other rare earth metal elements, the mass percentage of oxides of the other rare earth metal elements is the sum of the mass percentages of oxides of the two or more other rare earth metal elements.

[0053] The mass percentage of other rare earth metal elements converted to oxides in the composite oxide of the present invention can be determined by fluorescence X-ray diffraction analysis. Fluorescence X-ray diffraction analysis is preferably performed according to the conditions described in the examples. It should be noted that the mass percentage of other rare earth metal elements converted to oxides in the composite oxide of the present invention is based on the total mass percentage of the metal elements converted to oxides in the composite oxide of the present invention (the total mass percentage of the metal elements converted to oxides in the composite oxide of the present invention is 100% by mass). Furthermore, when the composite oxide of the present invention contains two or more other rare earth metal elements, the mass percentage of the other rare earth metal elements converted to oxides is the sum of the mass percentages of the oxides of those two or more other rare earth metal elements.

[0054] The composite oxide of the present invention can be used as a component of a catalyst for waste gas purification.

[0055] In one embodiment, the catalyst for waste gas purification comprises the composite oxide of the present invention and one or more noble metal elements supported on the composite oxide. The amounts of the composite oxide and noble metal elements of the present invention contained in the catalyst for waste gas purification can be appropriately adjusted.

[0056] The precious metal element can be selected from, for example, palladium, platinum, rhodium, etc. The precious metal element is loaded onto the composite oxide of the present invention in a form capable of functioning as a catalytic active ingredient, such as a precious 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). From the viewpoint of improving exhaust gas purification performance, the catalytic active ingredient is preferably in particulate form.

[0057] Catalysts for waste gas purification may include a support component for loading noble metal elements. The support component is preferably porous. The support component can be selected from, for example, alumina, silica, silica-alumina, aluminosilicates, alumina-zirconia, alumina-chromium oxide, alumina-cerium oxide, etc.

[0058] Catalysts for exhaust gas purification may contain stabilizers, binders, and other components.

[0059] "Loading" refers to the state in which noble metal elements are physically or chemically adsorbed or retained on the outer surface or the inner surface of the pores of the composite oxide of the present invention. The presence of noble metal elements loaded on the composite oxide of the present invention can be confirmed, for example, by analyzing the cross-section of a catalyst for exhaust gas purification using an EDS (energy dispersive spectrometer), through which the presence of the composite oxide and the noble metal elements in the same region can be confirmed.

[0060] In one embodiment, the catalyst for waste gas purification is a shaped body having a granular or similar form. The catalyst for waste gas purification described in this embodiment can be manufactured, for example, by drying and calcining a catalyst composition for waste gas purification. The drying temperature, drying time, calcination temperature, and calcination time can be appropriately adjusted. Calcination can be carried out, for example, in an atmospheric atmosphere.

[0061] In other embodiments, the catalyst for purifying exhaust gas includes a substrate and a catalyst layer formed on the substrate, the catalyst layer comprising the composite oxide of the present invention and one or more noble metal elements supported on the composite oxide of the present invention.

[0062] The substrate can be appropriately selected from those known for use in catalysts for waste gas purification. The material of the substrate can be selected from ceramics such as alumina (Al2O3), mullite (3Al2O3-2SiO2), cordierite (2MgO-2Al2O3-5SiO2), aluminum titanate (Al2TiO5), silicon carbide (SiC), and stainless steel. The shape of the substrate can be selected from, for example, honeycomb, granular, or spherical shapes.

[0063] The substrate is preferably a wall-flow type substrate. The wall-flow type substrate includes an inflow-side unit extending in the exhaust gas flow direction, an outflow-side unit extending in the exhaust gas flow direction, and a porous partition wall separating the inflow-side unit and the outflow-side unit. In the inflow-side unit, the end of the exhaust gas inflow side in the exhaust gas flow direction is open, and the end of the exhaust gas outflow side in the exhaust gas flow direction is closed. In the outflow-side unit, the end of the exhaust gas inflow side in the exhaust gas flow direction is closed, and the end of the exhaust gas outflow side in the exhaust gas flow direction is open. Exhaust gas flowing into the wall-flow type substrate from the exhaust gas inflow side end (opening) of the inflow-side unit passes through the porous partition wall and flows out from the exhaust gas outflow side end (opening) of the outflow-side unit. When the exhaust gas passes through the porous partition wall, PM in the exhaust gas is captured within the pores of the partition wall.

[0064] In the case of a wall-flow substrate, from the viewpoint of suppressing the increase in pressure loss, the catalyst layer is preferably formed in the porous partition wall of the wall-flow substrate.

[0065] The catalyst layer can be formed by coating a catalyst composition for waste gas purification onto a substrate, followed by drying and firing. The drying temperature, drying time, firing temperature, and firing time can be adjusted appropriately. Firing can be carried out, for example, in an atmospheric atmosphere.

[0066] The catalyst composition for manufacturing a catalyst for exhaust gas purification is, for example, a slurry containing the composite oxide of the present invention and a salt of a noble metal element. The salt of the noble metal element can be selected from, for example, nitrates, ammonium complexes, chlorides, etc. The solvent contained in the dispersion can be selected from, for example, water, organic solvents, etc.

[0067] Manufacturing Methods of Composite Oxides

[0068] The composite oxide of the present invention can be manufactured by a method including steps (a) to (f). Hereinafter, steps (a) to (f) will be described.

[0069] Process (a)

[0070] Step (a) is the process of preparing a feed solution containing water, zirconium salt and cerium salt, and, where appropriate, other rare earth metal salts.

[0071] The water contained in the feed solution is preferably pure water such as ion-exchanged water. The feed solution may contain solvents other than water. Solvents other than water may be selected from organic solvents such as alcohols, acetone, dimethyl sulfoxide, and dimethylformamide. The amount of organic solvent contained in the feed solution is not particularly limited as long as zirconium salts, cerium salts, and other rare earth metal salts, as appropriate, can be dissolved in the feed solution. Based on the volume of the feed solution, it is usually 20 vol% or less, preferably 10 vol% or less.

[0072] The zirconium salt, cerium salt, and other rare earth metal salts contained in the raw material solution are all water-soluble salts. It should be noted that the present invention also includes an embodiment in which the raw material solution prepared in step (a) does not contain other rare earth metal salts. In the embodiment in which the raw material solution prepared in step (a) does not contain other rare earth metal salts, "the zirconium salt, cerium salt, and other rare earth metal salts are all water-soluble salts" means that both cerium salt and zirconium salt are water-soluble salts.

[0073] The solubility of the water-soluble salt relative to water at 20°C (the mass of the water-soluble salt that can dissolve in 100g of water at 20°C) is preferably 1.0g or more, more preferably 2.0g or more, and even more preferably 5.0g or more. The solubility of the water-insoluble salt relative to water at 20°C (the mass of the water-insoluble salt that can dissolve in 100g of water at 20°C) is preferably less than 1.0g, more preferably less than 0.5g, and even more preferably less than 0.1g.

[0074] The water-soluble zirconium salt can be selected from, for example, zirconium oxychloride, zirconium chloride, zirconium oxynitrate, zirconium nitrate, zirconium oxyacetate, etc. From the viewpoints of preventing a decrease in the heat resistance of the composite oxide due to the contamination of nitrate ions, etc., and from the viewpoints of easy availability, zirconium oxychloride or zirconium chloride is preferred, and zirconium oxychloride is more preferred. The feed solution can contain two or more water-soluble zirconium salts. The amount of water-soluble zirconium salt contained in the feed solution is appropriately adjusted in such a way that the zirconium oxide equivalent of the zirconium element contained in the composite oxide manufactured in step (f) is within the desired range.

[0075] Water-soluble cerium salts can be selected from, for example, cerium chloride, cerium nitrate, cerium(III) sulfate, cerium acetate, etc. From the viewpoints of preventing a decrease in the heat resistance of the composite oxide due to the contamination of nitrate ions, etc., and from the viewpoints of easy availability, cerium chloride is preferred. The feed solution may contain two or more types of water-soluble cerium salts. The amount of water-soluble cerium salts contained in the feed solution is appropriately adjusted in such a way that the amount of cerium oxide equivalent of the cerium element contained in the composite oxide produced in step (f) is within the desired range.

[0076] Other water-soluble rare earth metal salts can be selected from, for example, chlorides, nitrates, sulfates, and acetates of rare earth metals other than cerium. From the viewpoints of preventing a decrease in the heat resistance of the composite oxide due to the contamination of nitrates, etc., and from the viewpoints of easy availability, chlorides of rare earth metals other than cerium (e.g., lanthanum chloride, neodymium chloride, praseodymium chloride, etc.) are preferred. Sulfates of rare earth metals are preferably sulfates of trivalent rare earth metals. The feed solution may contain two or more other water-soluble rare earth metal salts. The types and amounts of other water-soluble rare earth metal salts contained in the feed solution are appropriately adjusted in a way that the equivalent amount of other rare earth metal oxides contained in the composite oxide produced in step (f) is within the desired range.

[0077] Process (b)

[0078] Step (b) is a step in which a first precipitant, selected from an aqueous solution containing sulfate ions and a compound that can dissolve in water to generate sulfate ions, is added to the raw material liquid prepared in step (a) to form a first precipitate containing zirconium, thereby obtaining a first slurry containing the first precipitate.

[0079] The feed solution contains metal ions (zirconium ions, cerium ions, and other rare earth metal ions, depending on the case) generated by the ionization of water-soluble salts. The first precipitant added to the feed solution is a precipitant that causes zirconium ions to precipitate as basic zirconium sulfate, selected from aqueous solutions containing sulfate ions and compounds that can dissolve in water to generate sulfate ions. Compounds that can dissolve in water to generate sulfate ions can be selected from, for example, ammonium sulfate, sulfuric acid, alkali metal sulfates (e.g., sodium sulfate, potassium sulfate, etc.), cerium(III) sulfate, rare earth metal sulfates, etc. From the viewpoint of improving the homogeneity of the solid solution phase formed by cerium, zirconium, and oxygen (e.g., a solid solution phase of cerium oxide and zirconium oxide) and from the viewpoint of easy availability, ammonium sulfate, sulfuric acid, or alkali metal sulfate are preferred, and ammonium sulfate is more preferred. Rare earth metal sulfates are preferably trivalent rare earth metal sulfates. The aqueous solution containing sulfate ions can be obtained, for example, by dissolving a compound that can dissolve in water to generate sulfate ions in water (e.g., pure water such as ion-exchanged water).

[0080] If a first precipitant is added to the feed solution, a first precipitate containing zirconium is formed, resulting in a first slurry containing the first precipitate. The zirconium is contained in the first precipitate in the form of basic zirconium sulfate. Basic zirconium sulfate is a water-insoluble zirconium salt formed using the first precipitant.

[0081] From the viewpoint of suppressing the formation of aggregated particles caused by the delayed formation reaction of basic zirconium sulfate, the temperature of the feed liquid when the first precipitant is added is preferably 70°C or higher and 100°C or lower, more preferably 80°C or higher and 100°C or lower, and even more preferably 85°C or higher and 100°C or lower.

[0082] From the viewpoint of precipitating basic zirconium sulfate and suppressing the adverse effects caused by excessive sulfate ions, and improving the heat resistance of the composite oxide manufactured in step (f), it is preferable to add the first precipitant to the feed solution in such a way that the molar amount of sulfate ions in the feed solution is 0.4 times or more and 2 times or less of the molar amount of zirconium in the feed solution. More preferably, the molar amount of sulfate ions in the feed solution is 0.45 times or more and 2 times or less of the molar amount of zirconium in the feed solution, and even more preferably, 0.5 times or more and 1.5 times or less.

[0083] From the perspective of uniformly generating precipitate, it is preferable to add the first precipitant dropwise to the feed liquid while stirring it.

[0084] From the viewpoint of ensuring uniform maturation of the precipitate, it is preferable to mature the first precipitate while stirring the first slurry. The maturation time is preferably 0.5 hours or more and 12 hours or less, more preferably 1 hour or more and 4 hours or less, and even more preferably 1 hour or more and 2 hours or less.

[0085] Process (c)

[0086] Step (c) is a wet pulverization process for the first slurry obtained in step (b).

[0087] If the first slurry is subjected to wet pulverization, the first precipitate contained in the first slurry will be pulverized to obtain a pulverized product of the first precipitate.

[0088] The composite oxide manufactured in process (f) effectively achieves the desired D. 50 and D 90 From the perspective of wet grinding, the preferred method is to use the first precipitate as the basis for grinding the D-type material. 50 The process is carried out in a manner that results in particles larger than 0.5 μm and smaller than 1.5 μm. The D of the pulverized first precipitate... 50 Further preferably, the micrometer size is 0.5 μm or larger and 1.3 μm or smaller, and even more preferably 0.5 μm or larger and 1.2 μm or smaller. It should be noted that the D of the first precipitate before wet pulverization... 50 Typically, the size is 10μm or larger and 40μm or smaller, preferably 10μm or larger and 30μm or smaller.

[0089] The composite oxide manufactured in process (f) effectively achieves the desired D. 50 and D 90 From the perspective of the first precipitate pulverized material D 50 D relative to the first precipitate before wet grinding treatment 50 The ratio is preferably 0.02 or more and 0.12 or less, more preferably 0.02 or more and 0.1 or less, and even more preferably 0.03 or more and 0.08 or less.

[0090] The composite oxide manufactured in process (f) effectively achieves the desired D. 50 and D 90 From the perspective of wet grinding, the preferred method is to use the first precipitate as the basis for grinding the D-type material. 90 The process involves reducing the particle size to between 1 μm and 2.5 μm. The first precipitate is pulverized (D...). 90 Further preferably, the particle size is 1 μm or larger and 2.3 μm or smaller, and even more preferably, 1 μm or larger and 2 μm or smaller. It should be noted that the D of the first precipitate before wet pulverization... 90 Typically, the size is 10μm or larger and 100μm or smaller, preferably 20μm or larger and 50μm or smaller.

[0091] The composite oxide manufactured in process (f) effectively achieves the desired D. 50 and D 90 From the perspective of the first precipitate pulverized material D90 D relative to the first precipitate before wet grinding treatment 90 The ratio is preferably 0.02 or more and 0.12 or less, more preferably 0.02 or more and 0.1 or less, and even more preferably 0.03 or more and 0.09 or less.

[0092] The first precipitate of pulverized material D 50 and D 90 The cumulative volume of the pulverized material of the first precipitate, obtained by laser diffraction scattering particle size distribution determination method, is the 50% and 90% of the particle size, respectively. The laser diffraction scattering particle size distribution determination method is preferably performed according to the conditions described in the examples. The D of the first precipitate before wet pulverization treatment... 50 and D 90 The same applies.

[0093] The pulverized material from the first precipitate effectively achieves the desired D. 50 and D 90 From this perspective, wet grinding is preferably performed using beads. The diameter of the beads is typically between 0.015 mm and 2.0 mm. This ensures that the ground material effectively achieves the desired D... 50 and D 90 From this perspective, the diameter of the bead is preferably 0.3 mm or less, more preferably 0.1 mm or less. The lower limit is preferably 0.01 mm or more, more preferably 0.03 mm or more.

[0094] The pulverized material from the first precipitate effectively achieves the desired D. 50 and D 90 From this perspective, wet grinding is preferably carried out in a manner that applies an acceleration to the beads exceeding 1G. The acceleration applied to the beads is typically 2G or more and 1000G or less, preferably 40G or more and 1000G or less. The desired acceleration can be applied to the beads by, for example, using the centrifugal force generated by the high-speed rotation of a paint agitator used as a paint disperser.

[0095] The pulverized material from the first precipitate effectively achieves the desired D. 50 and D 90 From this perspective, it is preferable to use beads for wet pulverization for at least 0.5 hours, and more preferably for at least 1 hour. The upper limit is preferably 10 hours, and more preferably 5 hours.

[0096] In step (c), the first slurry obtained in step (b) can be used directly for wet grinding, or the first slurry obtained in step (b) can be diluted before being used for wet grinding. Dilution can be performed using solvents such as water (e.g., deionized water, or other pure water) or solvents other than water (e.g., organic solvents). Specific examples of organic solvents are the same as described above.

[0097] Process (d)

[0098] Step (d) is to add a second precipitant selected from an aqueous solution containing hydroxide ions and a compound that can dissolve in water to generate hydroxide ions to the first slurry after wet grinding, to form a second precipitate containing zirconium and cerium and, depending on the case, other rare earth metal elements, to obtain a second slurry containing the second precipitate.

[0099] If a second precipitant is added to the first slurry after wet grinding, a second precipitate containing zirconium and cerium, and other rare earth metals as appropriate, is formed, resulting in a second slurry containing the second precipitate. The pH of the second slurry is typically 9 or higher and 14 or lower, preferably 11 or higher and 14 or lower.

[0100] Zirconium is contained in the second precipitate as zirconium hydroxide. Zirconium hydroxide is a water-insoluble zirconium salt formed using the second precipitant. It should be noted that the basic zirconium sulfate formed using the first precipitant is converted into zirconium hydroxide by the second precipitant.

[0101] Cerium is contained in the second precipitate as cerium hydroxide. Cerium hydroxide is a water-insoluble cerium salt formed using the second precipitant.

[0102] Other rare earth metals (such as lanthanum, neodymium, and praseodymium) are contained in the second precipitate as hydroxides (such as lanthanum hydroxide, neodymium hydroxide, and praseodymium hydroxide). These hydroxides are water-insoluble rare earth metal salts formed using the second precipitant. The hydroxides of these rare earth metals formed using the second precipitant co-precipitate with cerium hydroxide formed using the second precipitant.

[0103] The second precipitate comprises composite salt particles containing zirconium hydroxide and cerium hydroxide, and, depending on the circumstances, hydroxides of other rare earth metal elements. The second precipitate may, in addition to containing composite salt particles, also contain zirconium hydroxide particles, cerium hydroxide particles, hydroxide particles of other rare earth metal elements, etc. The composite salt particles are formed by attaching and growing cerium hydroxide and / or hydroxides of other rare earth metal elements formed using a second precipitant onto the surface of, for example, basic zirconium sulfate formed using a first precipitant (which is converted to zirconium hydroxide by a second precipitant).

[0104] From the viewpoint of suppressing the reduction in oxygen storage capacity caused by the phase separation of cerium oxide and zirconium oxide in the composite oxide manufactured in process (f), the temperature of the first slurry when the second precipitant is added is preferably 35°C or higher and 60°C or lower, more preferably 35°C or higher and 55°C or lower, and even more preferably 35°C or higher and 45°C or lower.

[0105] From the viewpoint of fully extracting hydroxides of zirconium hydroxide, cerium hydroxide, and other rare earth metals, it is preferable to add a second precipitant to the first slurry in such a way that the molar amount of hydroxide ions in the first slurry is at least twice the molar amount of oxygen required to form oxides of zirconium, cerium, and other rare earth metals in the first slurry. More preferably, the molar amount of hydroxide ions in the first slurry is at least twice and less than ten times the molar amount of oxygen required to form oxides of zirconium, cerium, and other rare earth metals in the first slurry; even more preferably, it is at least twice and less than five times; and even more preferably, it is at least twice and less than three times.

[0106] The molar amount of oxygen required to convert zirconium, cerium, and other rare earth metals in the first slurry into oxides can be calculated as [(molar amount of zirconium) × 2] + [(molar amount of cerium) × 2] + [(molar amount of rare earth metals other than cerium, praseodymium, and terbium) × 3 / 2] + [(molar amount of praseodymium) × 11 / 6] + [(molar amount of terbium) × 7 / 4].

[0107] Process (e)

[0108] Step (e) is the process of obtaining filter cake from the second slurry.

[0109] Filter cake can be obtained by feeding a second slurry into a solid-liquid separation process. Examples of solid-liquid separation processes include filtration, centrifugation, and decantation, among which filtration is preferred. While the solvent is removed by the solid-liquid separation process to obtain a filter cake, the solvent is not completely removed, and therefore, solvent residues remain in the filter cake.

[0110] In step (e), a first filter cake is preferably obtained from a second slurry, and the first filter cake is treated with an alcohol-containing liquid to obtain a second filter cake with an alcohol concentration of 90 vol% or higher. This suppresses the aggregation of the second precipitate contained in the filter cake, enabling the composite oxide manufactured in step (f) to effectively achieve the desired D. 50 and D 90 .

[0111] The first filter cake can be obtained by feeding the second slurry into a solid-liquid separation process. The explanation related to the solid-liquid separation process is shown above.

[0112] Before treating the first filter cake with an alcohol-containing liquid, the first filter cake can be washed with a washing solution. Water (e.g., pure water such as ion-exchanged water) is preferably used as the washing solution. By washing the first filter cake with the washing solution, some or all of the solvent in the first filter cake is replaced by the washing solution.

[0113] The alcohol-containing liquid contains one or more alcohols. Examples of alcohols include methanol, ethanol, n-propanol, 2-propanol, 1-propanol, n-butanol, sec-butanol, tert-butanol, pentanol, and hexanol. Among these, methanol, ethanol, n-propanol, 2-propanol, and 1-propanol are preferred, and methanol, ethanol, and n-propanol are more preferred. When the alcohol-containing liquid contains one alcohol, ethanol is preferred. When the alcohol-containing liquid contains two or more alcohols, ethanol and one or more other alcohols are preferred.

[0114] The alcohol concentration of the alcohol-containing liquid can be adjusted appropriately based on the desired alcohol concentration of the second filter cake. The alcohol concentration of the alcohol-containing liquid only needs to be higher than the desired alcohol concentration of the second filter cake. Therefore, the alcohol concentration of the alcohol-containing liquid can be the same as or exceed the desired alcohol concentration of the second filter cake. There is no specific upper limit to the alcohol concentration of the alcohol-containing liquid. It should be noted that when the alcohol-containing liquid contains two or more alcohols, the alcohol concentration of the alcohol-containing liquid is the total concentration of those two or more alcohols.

[0115] When the alcohol-containing liquid contains ethanol, the ethanol concentration, based on the volume of the alcohol-containing liquid, is preferably 51 vol% or more, more preferably 65 vol% or more, and even more preferably 90 vol% or more. There is no particular upper limit to the ethanol concentration, and it is typically 100 vol%.

[0116] Alcohol-containing liquids may contain one or more components other than alcohol. Examples of components other than alcohol include water, ketones (acetone, methyl ethyl ketone (MEK), cyclohexanone, methyl isobutyl ketone, diacetone alcohol, cycloheptanone, diethyl ketone, etc.), ethers (1,4-dioxane, dioxolane, diisopropyl ether dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, etc.), alicyclic hydrocarbons (cyclohexane, etc.), aromatic hydrocarbons (toluene, xylene, etc.), halogenated hydrocarbons (dichloromethane, dichloroethane, etc.), esters (methyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl lactate, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, butyl cellosolve, etc.), cellosolve acetates, sulfoxides (dimethyl sulfoxide, etc.), and amides (dimethylformamide, dimethylacetamide, etc.).

[0117] As an alcohol-containing liquid, it can be directly diluted with, for example, commercially available modified alcohols (industrial alcohols) or with water such as ion-exchanged water.

[0118] The treatment of the first filter cake based on the alcohol-containing liquid is not particularly limited as long as it allows the first filter cake to come into contact with the alcohol-containing liquid and replace the liquid (e.g., solvent of the feed liquid, washing liquid, etc.) in the first filter cake with the alcohol-containing liquid. Examples include methods such as immersing the first filter cake in the alcohol-containing liquid or mixing the first filter cake with the alcohol-containing liquid. The second filter cake is obtained by solid-liquid separation after contacting the first filter cake with the alcohol-containing liquid (e.g., after immersing the first filter cake in the alcohol-containing liquid or after mixing the first filter cake with the alcohol-containing liquid). Examples of solid-liquid separation methods include filtration, centrifugation, and decantation, among which centrifugation is preferred. The alcohol-containing liquid is removed by solid-liquid separation to obtain the second filter cake, but the alcohol-containing liquid is not completely removed, so alcohol-containing liquid remains in the second filter cake. By reusing the alcohol-containing liquid to treat the first filter cake, the alcohol concentration of the second filter cake is made close to the alcohol concentration of the alcohol-containing liquid, ultimately achieving consistency. Therefore, if the alcohol concentration of the alcohol-containing liquid is the same as the desired alcohol concentration of the second filter cake, the treatment of the first filter cake using the alcohol-containing liquid is repeated until the alcohol concentration of the second filter cake matches the alcohol concentration of the alcohol-containing liquid. On the other hand, if the alcohol concentration of the alcohol-containing liquid exceeds the desired alcohol concentration of the second filter cake, the treatment of the first filter cake using the alcohol-containing liquid is repeated until the alcohol concentration of the second filter cake reaches the target alcohol concentration.

[0119] The composite oxide manufactured in process (f) effectively achieves the desired D. 50 and D 90 From this perspective, the alcohol concentration of the second filter cake is preferably 90 vol% or more, more preferably 95 vol% or more, and even more preferably 99 vol% or more. The upper limit is 100 vol%.

[0120] The alcohol concentration of the second filter cake is defined based on the alcohol concentration of the alcohol-containing liquid after use in the treatment of the first filter cake. That is, the alcohol concentration of the filtrate, supernatant, or drain obtained by solid-liquid separation after the first filter cake is contacted with the alcohol-containing liquid (e.g., after the first filter cake is immersed in the alcohol-containing liquid or after the first filter cake is mixed with the alcohol-containing liquid) is measured, and the measured alcohol concentration of the filtrate, supernatant, or drain is taken as the alcohol concentration of the second filter cake.

[0121] Alcohol concentration can be determined using conventional methods. For example, a conversion table between alcohol concentration and specific gravity of the alcohol-containing liquid can be prepared beforehand. The specific gravity of the alcohol-containing liquid can be measured, and the alcohol concentration can be calculated from the measured specific gravity. The specific gravity of the alcohol-containing liquid can be measured using, for example, a float-type hydrometer. The temperature of the alcohol-containing liquid during specific gravity measurement is, for example, 15°C. For information on specific gravity measurement and conversion from specific gravity to alcohol concentration, refer to Annex A (Specification) of JIS B 7548:2009 (Alcohol Floats), "International Alcohol Table".

[0122] Before feeding the second filter cake to step (f), it is preferable to dry the second filter cake. Drying can be carried out by conventional methods. The drying temperature is usually above 60°C and below 200°C, preferably above 80°C and below 130°C, and the drying time is usually above 1 hour and below 24 hours, preferably above 2 hours and below 12 hours.

[0123] Process (f)

[0124] Step (f) is to sinter the filter cake obtained in step (e) to produce a composite oxide containing zirconium and cerium, and, depending on the circumstances, other rare earth metal elements.

[0125] In step (e), a first filter cake is obtained from the second slurry. The first filter cake is then treated with an alcohol-containing liquid to obtain a second filter cake with an alcohol concentration of 90 vol% or more. In step (f), the second filter cake is then calcined.

[0126] The calcination of the precipitate can be carried out using conventional methods. Calcination is typically performed in an atmospheric atmosphere. The calcination temperature is typically 600°C or higher and 1100°C or lower, preferably 600°C or higher and 1000°C or lower, and more preferably 600°C or higher and 950°C or lower. The calcination time is typically 2 hours or higher and 20 hours or lower, preferably 2 hours or higher and 10 hours or lower, and more preferably 2 hours or higher and 5 hours or lower.

[0127] In step (c), the first precipitate (basic zirconium sulfate) is micronized by wet pulverizing the first slurry. In step (d), a second precipitant is added to the wet-pulverized first slurry, causing cerium hydroxide and hydroxides of other rare earth metals (if applicable) to precipitate around the pulverized first precipitate as a core (wherein, basic zirconium sulfate is converted to zirconium hydroxide by the second precipitant). The second precipitate obtained in this manner is sufficiently micronized. Therefore, in step (f), it is possible to manufacture D with the desired properties. 50 and D 90 The composite oxide. In particular, by obtaining a first filter cake from a second slurry in step (e), treating the first filter cake with an alcohol-containing liquid to obtain a second filter cake with an alcohol concentration of 90 vol% or more, and calcining the second filter cake in step (f), the aggregation of the second precipitate contained in the filter cake can be suppressed, and the composite oxide produced in step (f) can effectively achieve the desired D. 50 and D 90 .

[0128] When the raw material liquid contains other rare earth metal salts, by adding a second precipitant to the first slurry after wet grinding in step (d), cerium hydroxide and hydroxides of other rare earth metal elements are precipitated around the pulverized material of the first precipitate (wherein, basic zirconium sulfate is converted to zirconium hydroxide due to the second precipitant). Therefore, in the composite oxide obtained in step (f), the mass percentage of oxides of other rare earth metal elements on the surface of the composite oxide is greater than the mass percentage of oxides of other rare earth metal elements in the overall composite oxide. That is, oxides of other rare earth metal elements are abundant on the surface of the composite oxide. The other rare earth metal elements present on the surface of the composite oxide can improve the heat resistance of the composite oxide and maintain its specific surface area by inhibiting the growth of CeO2 crystals when the composite oxide is exposed to high-temperature exhaust gas. It can be considered that the other rare earth metal elements present on the surface of the composite oxide will hinder the growth of CeO2 crystals and inhibit CeO2 crystal growth. It can be considered that the larger the ionic radius of the lanthanum element, the greater this effect becomes.

[0129] The composite oxide obtained in step (f) may be pulverized as needed. Pulverization can be carried out using, for example, a mortar and pestle mill, hammer mill, ball mill, bead mill, jet mill, roller mill, etc., and can be performed in a dry or wet manner.

[0130] If a pulverizer with a "compression" or "impact" pulverizing mechanism is used to perform volumetric pulverization on the composite oxide obtained in step (f), the particles typically do not break from the surface; instead, they may break into multiple fragments. Therefore, volumetric pulverization is not preferred as a micro-pulverization process, making it difficult to obtain the product of the present invention, namely D. 50 and D 90 These are composite oxides with diameters below 0.50 μm and 1.0 μm, respectively. Examples include hammer mills, pin mills, dry ball mills, and other pulverizers that employ "compression" or "impact" pulverizing mechanisms.

[0131] On the other hand, if the composite oxide obtained in step (f) is surface-milled using a pulverizer with a "grinding" or "shearing" mechanism, compressive or shearing forces are applied frictionally to the particles, forming micropowder from the particle surface. Therefore, surface milling is generally suitable for micro-pulverization and is preferred. For example, bead mills, force mills, and other pulverizers with a "grinding" mechanism are suitable. In the case of pulverizing the composite oxide obtained in step (f), the D of the pulverized composite oxide is easier to control. 50 and D 90 From this perspective, these shredders are preferred for surface shredding.

[0132] Example

[0133] The present invention will now be described in more detail with reference to embodiments and comparative examples.

[0134] [D] 50 and D 90 [Determination]

[0135] D of the target powder 50 and D 90 The cumulative volume of the particle size distribution of the target powder obtained by laser diffraction scattering particle size distribution measurement is defined as the 50% and 90% particle sizes, respectively. The laser diffraction scattering particle size distribution measurement was performed as follows: the target powder was dispersed in a 0.2% (w / w) sodium hexametaphosphate aqueous solution, subjected to ultrasonic treatment (output power: 30W, treatment time: 360 seconds), and then measured using a laser diffraction scattering particle size distribution measuring device (MICROTRAC MT3000II, manufactured by MICROTRAC BELL). The measurement conditions were set as follows: particle refractive index: 1.81, particle shape: non-spherical, solvent refractive index: 1.33, zeroing: 30 seconds, measurement time: 60 seconds, measurement range: 0.01–10,000 μm.

[0136] [Determination of specific surface area]

[0137] The specific surface area was determined according to the "(3.5) Single-point method" in "6.2 Flow method" of JIS R1626:1996 "Determination of specific surface area of ​​fine ceramic powders based on gas adsorption BET method". Specifically, a nitrogen-helium mixed gas containing 30% by capacity nitrogen as the adsorbent gas and 70% by capacity helium as the carrier gas was used as the BET specific surface area measuring device. A fully automatic specific surface area meter Macsorb model-1201 manufactured by MOUNTEC was used, and the determination was performed by the BET single-point method.

[0138] [Main Composition Analysis of Composite Oxides]

[0139] The bulk composition analysis of the composite oxides was performed using X-ray fluorescence (XRF).

[0140] The conditions for XRF analysis are as follows.

[0141] XRF analysis device: Rigaku Corporation ZSX Primus II

[0142] Accelerating voltage: 50kV

[0143] Current: 50mA

[0144] Atmosphere: Vacuum 1.4 Pa

[0145] Palladium: Rh 4.0kW

[0146] Filter: Ni400

[0147] Diaphragm: 30mm

[0148] Slit: S2

[0149] Spectroscopic crystallization: LiF(200)

[0150] Detector: SC

[0151] Attenuator: 1 / 1

[0152] PHA: LL50, UL400

[0153] PR gas: 4.7 mL / min

[0154] Isothermalization temperature: 36.5℃

[0155] [Surface composition analysis of composite oxides]

[0156] The surface composition analysis of the composite oxides was performed using X-ray photoelectron spectroscopy (XPS).

[0157] The conditions for XPS analysis are as follows.

[0158] XPS analysis device: PHIQuantes manufactured by ULVAC-PHI.

[0159] Excitation X-rays: Monochromatic Al-Kα rays (1486.7 eV)

[0160] Output power: 50W

[0161] Accelerating voltage: 15kV

[0162] X-ray irradiation diameter: 200μmφ

[0163] Measurement area: 1000×300μm 2

[0164] Detection angle: 15°

[0165] Energy consumption: 26.0 eV

[0166] Energy step size: 0.1 eV / step

[0167] Element / orbital determination (semi-quantitative element calculation): C 1s, O 1s, Zr 3d, La 3d5 / 2, Ce 3d, Pr 3d5 / 2, Nd 3d5 / 2

[0168] XPS data was analyzed using data analysis software (MULTI-PACK, Ver9.9, manufactured by ULVAC-PHI). Iterated Shirley was used as the background mode.

[0169] [Calculation of the degree of deviation between surface composition and body composition]

[0170] When calculating the degree of deviation of the surface composition from the bulk composition, a cerium-zirconium composite oxide prepared using the following method is used as a reference sample.

[0171] Cerium nitrate, zirconium oxynitrate, lanthanum nitrate, neodymium nitrate, and praseodymium nitrate were dissolved in water to obtain 500g of raw material solution. The amounts of cerium nitrate, zirconium oxynitrate, lanthanum nitrate, neodymium nitrate, and praseodymium nitrate were prepared in the following manner, based on their total mass, as follows: 40% by mass (converted to cerium oxide), 50% by mass (converted to zirconium oxide), 2% by mass (converted to lanthanum oxide), 4% by mass (converted to neodymium oxide), and 4% by mass (converted to praseodymium oxide).

[0172] Heat 10% (w / w) ammonia solution to 40°C and add the raw material solution dropwise while stirring. Continue adding the raw material solution until the pH of the ammonia solution is less than 9.5, causing it to form a precipitate. Filter and wash the precipitate by vacuum filtration to obtain a filter cake.

[0173] After air-drying the filter cake, it was dried overnight at 90°C and then calcined in a muffle furnace. After calcination, it was pulverized to obtain a powdered composite oxide, which was used as a reference sample.

[0174] For the reference sample, XRF-based bulk composition analysis and XPS-based surface composition analysis were performed using the methods described above. The results are shown in Tables 2 and 3. In Table 2, “CeO2”, “ZrO2”, “La2O3”, “Nd2O3”, and “Pr6O” are listed. 11 "CeO2", "ZrO2", "La2O3", "Nd2O3", and "Pr6O3" represent the XRF analysis values ​​converted from oxides of cerium, zirconium, lanthanum, neodymium, and praseodymium, respectively. In Table 3, "CeO2", "ZrO2", "La2O3", "Nd2O3", and "Pr6O3" are respectively... 11 "These represent the XPS analysis values ​​(semi-quantitative values) converted from oxides of cerium, zirconium, lanthanum, neodymium, and praseodymium, respectively."

[0175] The relevant correction coefficients C1, C2, C3, C4, and C5 for the XPS analysis values ​​converted from cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide are calculated according to the following formulas. The correction coefficients are shown in Table 4.

[0176] Correction factor C1 = XRF analysis value converted from cerium oxide in the reference sample / XPS analysis value converted from cerium oxide in the reference sample

[0177] Correction factor C2 = (XRF analysis value converted from zirconium oxide in the reference sample) / (XPS analysis value converted from zirconium oxide in the reference sample)

[0178] Correction factor C3 = XRF analysis value converted from lanthanum oxide in the reference sample / XPS analysis value converted from lanthanum oxide in the reference sample

[0179] Correction factor C4 = XRF analysis value of neodymium oxide converted from neodymium in the reference sample / XPS analysis value of neodymium oxide converted from neodymium in the reference sample

[0180] Correction factor C5 = XRF analysis value of praseodymium oxide converted from praseodymium in the reference sample / XPS analysis value of praseodymium oxide converted from praseodymium in the reference sample

[0181] For each composite oxide in the Examples and Comparative Examples, the following values ​​were calculated: V1 (calculated by multiplying the XPS measurement value of cerium oxide converted to cerium oxide by correction factor C1), V2 (calculated by multiplying the XPS analysis value of zirconium oxide converted to zirconium oxide by correction factor C2), V3 (calculated by multiplying the XPS analysis value of lanthanum oxide converted to lanthanum oxide by correction factor C3), V4 (calculated by multiplying the XPS analysis value of neodymium oxide converted to neodymium oxide by correction factor C4), and V5 (calculated by multiplying the XPS analysis value of praseodymium oxide converted to praseodymium oxide by correction factor C5). The following correction values ​​were then used to calculate: CV1 (calculated by cerium oxide), CV2 (calculated by zirconium oxide), CV3 (calculated by lanthanum oxide), CV4 (calculated by neodymium oxide), and CV5 (calculated by praseodymium oxide).

[0182] Correction value CV1 = value V1 × 100 / (total value of values ​​V1 to V5)

[0183] Correction value CV2 = value V2 × 100 / (total value of values ​​V1 to V5)

[0184] Correction value CV3 = value V3 × 100 / (total value of values ​​V1 to V5)

[0185] Correction value CV4 = value V4 × 100 / (total value of values ​​V1 to V5)

[0186] Correction value CV5 = value V5 × 100 / (total value of values ​​V1 to V5)

[0187] For each composite oxide in the examples and comparative examples, the degree of deviation of the surface composition from the bulk composition was calculated according to the following formula, and the value was used as an indicator of the surface concentration of lanthanum, neodymium and praseodymium in each composite oxide.

[0188] The degree of deviation of the surface composition from the bulk composition = (correction value CV3 + correction value CV4 + correction value CV5) / (XRF analysis value converted from lanthanum oxide + XRF analysis value converted from neodymium oxide + XRF analysis value converted from praseodymium oxide)

[0189] [Example 1]

[0190] (1) Preparation of the first slurry

[0191] Cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were dissolved in water to obtain 480 g of raw material solution. Ion-exchanged water was used as the water (the same applies below). The amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were adjusted to 40%, 50%, 2%, 4%, and 4% by mass, respectively, based on their total mass, according to the following conversions: cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide.

[0192] The raw material solution was heated to 85°C. While stirring the solution, a 25% (w / w) ammonium sulfate aqueous solution was added dropwise at a rate where the molar amount of sulfate ions was 0.5 times the molar amount of zirconium, causing a precipitate to form, thus obtaining the first slurry. After the addition was completed, the first slurry was stirred while the precipitate was allowed to mature at 85°C.

[0193] (2) Wet grinding treatment of the first slurry

[0194] After the precipitate has matured, the first slurry is cooled to 40°C. After cooling, the first slurry is added to a 1L polyethylene container filled with 300g of ZrO2 beads with a diameter of 0.1mm. Using a paint agitator (Asada Iron Works PS-08), the first slurry is wet-milled at room temperature for 1 hour. During the wet milling process, the precipitate is milled by applying an acceleration exceeding 1G (typically between 50G and 500G) to the beads using the centrifugal force generated by the high-speed rotation of the paint agitator.

[0195] (3)D 50 and D 90 Measurement

[0196] Using the first slurry before or after pulverization, the D of the precipitate before or after pulverization was determined by the method described above. 50 and D 90 The results are shown in Table 1.

[0197] (4) Preparation of the second slurry

[0198] The first slurry, after being pulverized, was transferred to a beaker. While stirring, the temperature was raised to 40°C. Then, a 24% (w / w) sodium hydroxide aqueous solution was added dropwise, with the molar amount of hydroxide ions being 2.5 times the molar amount of oxygen required to convert cerium, zirconium, lanthanum, neodymium, and praseodymium into oxides. This formed a precipitate, yielding the second slurry. The pH of the second slurry was 13.5. After the addition was complete, the second slurry was stirred while the precipitate was allowed to mature at 40°C.

[0199] (5) Preparation of the first filter cake

[0200] After the precipitate has matured, the second slurry is filtered and washed using ion-exchanged water to obtain the first filter cake.

[0201] (6) Preparation of the second filter cake

[0202] The modified alcohol used was CS SOLVE NM-85 manufactured by China Essential Oil Company. The composition of the modified alcohol used was: 85.4% by mass of ethanol, 5% by mass of methanol, and 9.6% by mass of n-propanol.

[0203] Using modified alcohol and ion-exchanged water, various alcohol-containing liquids with different alcohol concentrations (volume percentage) were prepared. The specific gravity of the alcohol-containing liquids (15 / 15℃) was measured using a float-type hydrometer, and a conversion table between specific gravity (15 / 15℃) and alcohol concentration (vol%) was created.

[0204] 20g of the first filter cake after washing was treated with modified alcohol to replace the water in the first filter cake with modified alcohol. Specifically, the first filter cake was suspended in modified alcohol and then centrifuged (8000 rpm × 5 minutes). The specific gravity of the supernatant (15℃ / 15℃) was measured using a float-type hydrometer. Using a conversion table between specific gravity (15℃ / 15℃) and alcohol concentration (vol%), the alcohol concentration of the supernatant was calculated based on the specific gravity of the supernatant. The alcohol concentration of the supernatant was defined as the alcohol concentration of the filter cake. The above treatment was repeated 3 times until the alcohol concentration of the supernatant (i.e., the alcohol concentration of the filter cake) reached 99 vol%, resulting in a second filter cake with an alcohol concentration of 99 vol%.

[0205] (7) Preparation of composite oxides

[0206] After the second filter cake was air-dried, it was dried overnight at 90°C and then calcined in a muffle furnace. After calcination, it was pulverized using a manual stirrer (Force Mill FM-1 manufactured by Osaka Chemical Co., Ltd.) and then sieved through a 100-mesh sieve to obtain a powdered composite oxide.

[0207] (8) Characterization of composite oxides

[0208] [D] 50 and D 90 [Determination]

[0209] The D of the composite oxide obtained in (7) above was determined using the method described above. 50 and D 90 The results are shown in Table 1.

[0210] [Determination of specific surface area]

[0211] The composite oxide obtained in (7) above was heat-treated at 1000°C for 3 hours in the atmosphere, and the specific surface area of ​​the heat-treated composite oxide was determined using the method described above. The results are shown in Table 1.

[0212] [Analysis of Main Components]

[0213] Regarding the composite oxides obtained in (7) above, XRF-based bulk composition analysis was performed using the above method. The results are shown in Table 2. In Table 2, “CeO2”, “ZrO2”, “La2O3”, “Nd2O3” and “Pr6O” are listed. 11 "These represent the XRF analysis values ​​converted from oxides of cerium, zirconium, lanthanum, neodymium, and praseodymium, respectively."

[0214] [Example 2]

[0215] The amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were adjusted to 40% by mass, 46% by mass, 2% by mass, 8% by mass, and 4% by mass, respectively, based on their total mass. Except for this, the composite oxide was prepared in the same manner as in Example 1.

[0216] Regarding the composite oxide obtained in Example 2, the same procedure as in Example 1 was followed for D... 50 and D 90 The determination of the specific surface area and the bulk composition analysis based on XRF were performed. The results are shown in Tables 1-2.

[0217] [Surface Composition Analysis]

[0218] The composite oxide obtained in Example 2 was subjected to XPS-based surface composition analysis using the method described above. The results are shown in Table 3. In Table 3, “CeO2”, “ZrO2”, “La2O3”, “Nd2O3”, and “Pr6O” are listed. 11 "These represent the XPS analysis values ​​(semi-quantitative values) converted from oxides of cerium, zirconium, lanthanum, neodymium, and praseodymium, respectively."

[0219] [Calculation of the degree of deviation between surface composition and body composition]

[0220] Regarding the composite oxide obtained in Example 2, the degree of deviation of the surface composition from the bulk composition was calculated using the above method based on the bulk composition analysis results (Table 2) and surface composition analysis results (Table 3). The results are shown in Tables 4 and 5. In Table 4, “CeO2”, “ZrO2”, “La2O3”, “Nd2O3”, and “Pr6O” are listed. 11 "These represent the degree of divergence between cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide, respectively."

[0221] [Example 3]

[0222] The amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were adjusted to 40% by mass, 46% by mass, 2% by mass, 4% by mass, and 8% by mass, respectively, based on their total mass. Except for this, the preparation of the composite oxide was carried out in the same manner as in Example 1.

[0223] Regarding the composite oxide obtained in Example 3, the same procedure as in Example 1 was followed for D... 50 and D 90 The determination of the specific surface area and the bulk composition analysis based on XRF were performed. The results are shown in Tables 1-2.

[0224] Furthermore, regarding the composite oxide obtained in Example 3, the same procedure as in Example 2 was performed, including XPS-based surface composition analysis and calculation of the degree of deviation of the surface composition from the bulk composition. The results are shown in Tables 3-5.

[0225] [Comparative Example 1]

[0226] (1) Preparation of the first slurry

[0227] Cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were dissolved in water to obtain 107 kg of raw material solution. The amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were adjusted to 40%, 50%, 2%, 4%, and 4% by mass, respectively, based on their total mass, according to the following conversions: cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide.

[0228] The raw material solution was heated to 85°C. While stirring the solution, a 25% (w / w) ammonium sulfate aqueous solution was added dropwise at a rate where the molar amount of sulfate ions was 1.0 times the molar amount of zirconium, causing a precipitate to form, thus obtaining the first slurry. After the addition was completed, the first slurry was stirred while the precipitate was allowed to mature at 85°C.

[0229] (2) Preparation of the second slurry

[0230] After cooling the first slurry to 40°C, while stirring the first slurry, a 24% (w / w) sodium hydroxide aqueous solution was added dropwise in a manner that the molar amount of hydroxide ions was 2.5 times the molar amount of oxygen required to produce oxides from cerium, zirconium, lanthanum, neodymium, and praseodymium, causing a precipitate to form the second slurry. The pH of the second slurry was 13.5. After the addition was complete, the second slurry was stirred while the precipitate was allowed to mature at 40°C.

[0231] (3) Preparation of filter cake

[0232] After the precipitate has matured, the second slurry is filtered and washed using a filter press (TFP-4-8MKII type manufactured by Daiki Ataka Engineering Co., Ltd.) to obtain a filter cake.

[0233] (4) Preparation of composite oxides

[0234] After air-drying the filter cake, it was dried overnight at 90°C and then calcined in a muffle furnace. After calcination, it was pulverized using a glow discharge mill (a multimill manufactured by Growing Engineering) to obtain a powdered composite oxide.

[0235] (5) Characterization of composite oxides

[0236] Regarding the composite oxide obtained in (4) above, the same procedure as in Example 1 was followed for D. 50 and D 90 The determination of the specific surface area and the bulk composition analysis based on XRF were performed. The results are shown in Tables 1-2.

[0237] Furthermore, regarding the composite oxide obtained in (4) above, the same procedure as in Example 2 was followed to perform XPS-based surface composition analysis and calculate the degree of deviation of the surface composition from the bulk composition. The results are shown in Tables 3-5.

[0238] [Comparative Examples 2-4]

[0239] Four kilograms of the composite oxide obtained in Comparative Example 1 were added to a 100-L container, along with 76 kilograms of ion-exchanged water and stirred to obtain a slurry with a composite oxide concentration of 5% by mass. The resulting slurry was then transferred to a bead mill (Ultra Apex Mill UAM-1, manufactured by HIROSHIMA METAL & MACHINERY) for repeated wet milling.

[0240] The grinding conditions based on the bead mill are shown below.

[0241] Beads used: ZrO2 beads with a diameter of 0.1 mm.

[0242] Bead filling weight: 1.95kg

[0243] Fill rate: 80%

[0244] Mill speed: 3200 rpm

[0245] Number of passes based on bead mill: 1-4

[0246] Slurry supply rate: 0.89 L / min

[0247] Slurries processed by bead milling once (Comparative Example 2), twice (Comparative Example 3), or four times (Comparative Example 4) were sampled. The sampled slurries were filtered and washed with ion-exchanged water to obtain pulverized composite oxides.

[0248] The pulverized composite oxides obtained in Comparative Examples 2-4 were subjected to the same procedure as in Example 1, and D was performed. 50 and D 90 The determination of the specific surface area and the bulk composition analysis based on XRF were performed. The results are shown in Tables 1-2.

[0249] Furthermore, regarding the pulverized composite oxides obtained in Comparative Examples 2-4, the same procedure as in Example 2 was performed, including XPS-based surface composition analysis and calculation of the degree of deviation of the surface composition from the bulk composition. The results are shown in Tables 3-5.

[0250] [Table 1]

[0251] Table 1

[0252]

[0253] [Table 2]

[0254] Table 2

[0255]

[0256] [Table 3]

[0257] Table 3

[0258]

[0259] [Table 4]

[0260] Table 4

[0261]

[0262] [Table 5]

[0263] Table 5

[0264] The degree of deviation between surface composition and body composition Example 1 - Example 2 0.91 Example 3 0.86 Comparative Example 1 0.97 Comparative Example 2 1.05 Comparative Example 3 0.71 Comparative Example 4 0.73

[0265] As shown in Table 1, in Examples 1-3, composite oxides containing zirconium, cerium, and other rare earth metals (lanthanum, neodymium, and praseodymium) were obtained. The D of these composite oxides was determined by laser diffraction scattering particle size distribution method. 50 and D 90 The composite oxides are below 0.5 μm and below 1 μm, respectively.

[0266] As shown in Table 1, the specific surface area of ​​the composite oxides of Examples 1-3, after being heat-treated at 1000°C for 3 hours in the atmosphere and measured by the BET method, was 20 m². 2 / g or more.

[0267] As shown in Table 5, in the composite oxides of Examples 2 and 3, the degree of divergence between the surface composition and the bulk composition (the ratio of the mass percentage (surface composition) of the oxides of other rare earth metal elements (lanthanum, neodymium, and praseodymium) determined by X-ray photoelectron spectroscopy to the mass percentage (bulk composition) of the oxides of other rare earth metal elements (lanthanum, neodymium, and praseodymium) determined by fluorescence X-ray diffraction) was 0.91 and 0.86, respectively. Based on these results, it can be inferred that in Examples 2 and 3, the surface concentration of other rare earth metal elements (lanthanum, neodymium, and praseodymium) that could contribute to improving the heat resistance of the composite oxides was higher than the Do of the composite oxides. 50 Comparative Examples 3 and 4 are of the same degree as Examples 2 and 3.

Claims

1. A composite oxide comprising zirconium, cerium, and other rare earth metals. The D of the composite oxide was determined by laser diffraction scattering particle size distribution method. 50 and D 90 They are below 0.5μm and below 1μm, respectively. The specific surface area, determined by the BET method, was 20 m² after heat treatment at 1000℃ for 3 hours in the atmosphere. 2 / g or more, The mass percentage of other rare earth metal elements at the surface of the composite oxide, as determined by X-ray photoelectron spectroscopy, is more than 0.80 times the mass percentage of other rare earth metal elements in the overall composite oxide. The zirconium oxide content of the composite oxide, calculated based on the mass of the composite oxide, is between 20% and 90% by mass. The amount of cerium oxide contained in the composite oxide, calculated based on the mass of the composite oxide, is more than 5% by mass and less than 70% by mass. The oxide equivalent of the other rare earth metal elements contained in the composite oxide is between 5% and 35% by mass, based on the mass of the composite oxide.

2. A method for manufacturing the composite oxide according to claim 1, comprising the following steps: (a) The process of preparing a raw material solution containing water, zirconium salt, cerium salt and other rare earth metal salts; (b) A first precipitant selected from an aqueous solution containing sulfate ions and a compound that can dissolve in water to generate sulfate ions is added to the raw material liquid to form a first precipitate containing zirconium, thereby obtaining a first slurry containing the first precipitate. (c) The process of wet pulverizing the first slurry; (d) Adding a second precipitant selected from an aqueous solution containing hydroxide ions and a compound that can dissolve in water to generate hydroxide ions to the first slurry after wet pulverization to form a second precipitate containing zirconium, cerium and other rare earth metal elements, and obtaining a second slurry containing the second precipitate. (e) The process of obtaining filter cake from the second slurry; and (f) The process of firing the filter cake to produce a composite oxide containing zirconium, cerium and other rare earth metal elements; In step (b), the first precipitant is added to the raw material solution in such a way that the molar amount of sulfate ions in the raw material solution is more than 0.4 times and less than 2 times the molar amount of zirconium in the raw material solution; In step (c), the D of the pulverized first precipitate, as determined by laser diffraction scattering particle size distribution measurement method, is used. 50 The D of the pulverized material of the first precipitate is 0.5 μm or larger and 1.5 μm or smaller. 90 The wet pulverization process is carried out in a manner that produces particles larger than 1 μm and smaller than 2.5 μm. In step (d), the second precipitant is added to the first slurry in such a way that the molar amount of hydroxide ions in the first slurry is more than twice the molar amount of oxygen required to form oxides of zirconium, cerium and other rare earth metals in the first slurry.

3. The manufacturing method according to claim 2, wherein, In step (e), a first filter cake is obtained from the second slurry, and the first filter cake is treated with an alcohol-containing liquid to obtain a second filter cake with an alcohol concentration of 90 vol% or more. In step (f), the second filter cake is calcined to produce the composite oxide.

4. The manufacturing method according to claim 2 or 3, wherein, In step (c), beads are used to perform the wet pulverization process.

5. The manufacturing method according to claim 4, wherein, In step (c), the wet pulverization process is performed with an acceleration of more than 1G applied to the beads.

6. The manufacturing method according to claim 4, wherein, The diameter of the bead is less than 0.3 mm.

7. The manufacturing method according to claim 4, wherein, In step (c), the wet pulverization process is carried out for more than 1 hour.

8. The manufacturing method according to claim 2 or 3, wherein, In step (b), the temperature of the raw material liquid when the first precipitant is added is above 70°C and below 100°C.

9. The manufacturing method according to claim 2 or 3, wherein, In step (d), the temperature of the first slurry when the second precipitant is added is above 35°C and below 60°C.

Images