Composite oxide and method for producing the same

Abstract

The purpose of the present invention is to provide: a sufficiently pulverized CeO2-ZrO2-based composite oxide; and a method for producing said CeO2-ZrO2-based composite oxide. Provided are: a composite oxide comprising a zirconium element, a cerium element, and optionally, other rare-earth metal elements, wherein the D50 and D90 of said composite oxide, as measured by a laser diffraction and scattering-type particle size distribution measurement method, are at most 0.5 μm and at most 1 μm, respectively; and a method for producing said composite oxide.

Description

[Technical Field]

[0001] The present invention relates to a composite oxide containing cerium and zirconium elements (hereinafter sometimes referred to as "CeO2-ZrO2-based composite oxide") and a method for producing the composite oxide. [Background technology]

[0002] Exhaust gases emitted from internal combustion engines of automobiles, motorcycles, etc. contain harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Three-way catalysts are used to purify exhaust gases and neutralize these harmful components. They have the catalytic activity of oxidizing HC and CO to convert them into water and carbon dioxide, and reducing NOx to convert them into nitrogen.

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

[0004] For example, Patent Document 1 describes a method for producing a CeO2-ZrO2-based composite oxide. In Patent Document 1, cerium chloride, zirconium oxychloride, praseodymium chloride, and water are mixed, and then ammonium peroxodisulfate is added to obtain a slurry containing sulfate, ammonia water is added to the obtained slurry to obtain a slurry containing hydroxide, the obtained slurry is filtered and washed to obtain a cake, and the obtained cake is fired to produce a CeO2-ZrO2-based composite oxide.

[0005] Exhaust gas contains particulate matter (PM) along with harmful components such as HC, CO, and NOx, and is known to cause air pollution. For example, gasoline direct injection (GDI) engines used in gasoline-powered vehicles are known to have low fuel consumption and high power output, but emit larger amounts of PM in their exhaust gases than conventional port-injection engines. In order to comply with environmental regulations regarding PM, vehicles equipped with gasoline engines such as GDI are required to be equipped with a gasoline particulate filter (GPF) that has a PM-collecting function, just like diesel-powered vehicles.

[0006] For example, a substrate having a structure known as a wall-flow type is used as a GPF. The wall-flow type substrate includes inlet cells extending in the exhaust gas flow direction, outlet cells extending in the exhaust gas flow direction, and porous partition walls separating the inlet and outlet cells. The inlet cells have an open end on the exhaust gas inlet side in the exhaust gas flow direction and a closed end on the exhaust gas outlet side in the exhaust gas flow direction. The outlet cells have a closed end on the exhaust gas inlet side in the exhaust gas flow direction and an open end on the exhaust gas outlet side in the exhaust gas flow direction. Exhaust gas that flows into the wall-flow type substrate from the exhaust gas inlet side end (opening) of the inlet cell passes through the porous partition walls and flows out from the exhaust gas outlet side end (opening) of the outlet cell. As the exhaust gas passes through the porous partition walls, PM in the exhaust gas is captured in the pores of the partition walls.

[0007] Since the space available for installing exhaust gas purification catalysts is usually limited, consideration has been given to supporting precious metal catalysts such as Pt, Pd, and Rh on GPFs to capture PM as well as purify harmful components such as HC, CO, and NOx.

[0008] For example, Patent Document 2 describes the formation of a catalyst layer inside the porous partition walls of a wall-flow type substrate. In Patent Document 2, a slurry containing Pd-supported alumina powder, Rh-supported zirconia-lanthanum modified alumina powder, and CeO2-ZrO2-based composite oxide powder is pulverized in a ball mill, and D 90 A slurry having a particle size of 3.0 μm was obtained, and the obtained slurry was impregnated into the porous partition walls to form a catalyst layer. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2018-047425 [Patent Document 2] Japanese Patent Application Publication No. 2019-198838 Summary of the Invention [Problem to be solved by the invention]

[0010] In order to impregnate the porous partition walls with the CeO2-ZrO2-based composite oxide, the CeO2-ZrO2-based composite oxide needs to be atomized. If the porous partition walls are impregnated with an insufficiently atomized CeO2-ZrO2-based composite oxide, the pores of the porous partition walls will be blocked, resulting in an increase in pressure loss.

[0011] However, in the method described in Patent Document 1, sintering occurs during the firing process, and therefore it is not possible to obtain a CeO2-ZrO2-based composite oxide that is sufficiently finely divided.

[0012] Furthermore, as described in Patent Document 2, even if the CeO2-ZrO2 composite oxide is dry- or wet-pulverized, the D 90 However, it is not possible to obtain a sufficiently finely divided CeO2-ZrO2 composite oxide.

[0013] Furthermore, even if the CeO2-ZrO2-based composite oxide is classified using a sieve, it is not possible to obtain a CeO2-ZrO2-based composite oxide that is sufficiently finely divided.

[0014] Therefore, an object of the present invention is to provide a CeO2-ZrO2-based composite oxide that has been sufficiently atomized and a method for producing the CeO2-ZrO2-based composite oxide. [Means for solving the problem]

[0015] In order to solve the above problems, the present invention provides a composite oxide containing zirconium element, cerium element, and optionally other rare earth metal element, wherein the D of the composite oxide measured by a laser diffraction scattering particle size distribution measurement method is 50 and D 90 are 0.5 μm or less and 1 μm or less, respectively.

[0016] The present invention also provides a method for producing a pharmaceutical composition comprising the steps of: (a) preparing a raw material liquid containing water, a zirconium salt, a cerium salt, and optionally other rare earth metal salts; (b) adding a first precipitant selected from an aqueous solution containing sulfate ions and a compound capable of dissolving in water to generate sulfate ions to the raw material liquid to form a first precipitate containing elemental zirconium, thereby obtaining a first slurry containing the first precipitate; (c) subjecting the first slurry to a wet milling process; (d) adding a second precipitating agent selected from an aqueous solution containing hydroxide ions and a compound capable of dissolving in water to generate hydroxide ions to the first slurry after the wet-pulverization treatment, to form a second precipitate containing elemental zirconium, elemental cerium, and optionally other rare earth metal elements, thereby obtaining a second slurry containing the second precipitate; (e) obtaining a cake from the second slurry; and (f) A step of calcining the cake to produce a composite oxide containing zirconium, cerium, and optionally other rare earth metal elements. The present invention provides a method for producing a complex oxide, comprising: [Effects of the Invention]

[0017] According to the present invention, there are provided a CeO2-ZrO2-based composite oxide that has been sufficiently atomized and a method for producing the CeO2-ZrO2-based composite oxide. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described below. In this specification, unless otherwise specified, "other rare earth metal elements" means rare earth metal elements other than cerium, "other rare earth metal ions" means rare earth metal ions other than cerium ions, "other rare earth metal salts" means rare earth metal salts other than cerium salts, and "other water-soluble rare earth metal salts" means water-soluble rare earth metal salts other than water-soluble cerium salts.

[0019] <Complex oxide> The composite oxide of the present invention contains zirconium element, cerium element, and optionally other rare earth metal elements.

[0020] From the viewpoint of improving the heat resistance of the composite oxide, the amount of zirconium element contained in the composite oxide of the present invention, calculated as zirconium oxide (ZrO), 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, based on the mass of the composite oxide of the present invention.

[0021] The amount of cerium element contained in the composite oxide of the present invention, converted into cerium oxide (CeO), 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, based on the mass of the composite oxide of the present invention, from the viewpoint of improving the oxygen storage capacity of the composite oxide.

[0022] The ratio (mass ratio) of the amount of zirconium element converted into zirconium oxide to the amount of cerium element converted into cerium oxide 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, from the viewpoint of achieving a balance between the oxygen storage capacity and heat resistance of the composite oxide.

[0023] From the viewpoint of improving the heat resistance of the composite oxide, the composite oxide of the present invention preferably contains one, two, or three or more other rare earth metal elements. The 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., but are preferably selected from lanthanum, neodymium, and praseodymium. The composite oxide of the present invention can contain, for example, one, two, or three rare earth metal elements selected from lanthanum, neodymium, and praseodymium.

[0024] The amount of other rare earth metal elements contained in the composite oxide of the present invention in terms of oxide (when the composite oxide of the present invention contains two or more other rare earth metal elements, the total amount of the two or more other rare earth metal elements in terms of oxide) 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, from the viewpoint of improving the heat resistance of the composite oxide. Note 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 usually Pr6O 11 and terbium oxide is usually Tb4O7.

[0025] When the composite oxide of the present invention contains lanthanum, the amount of lanthanum contained in the composite oxide of the present invention, calculated as lanthanum oxide (La2O3), is preferably 0.1 mass % or more and 30 mass % or less, more preferably 0.5 mass % or more and 25 mass % or less, and even more preferably 1 mass % or more and 20 mass % or less, based on the mass of the composite oxide of the present invention, from the viewpoint of improving the heat resistance of the composite oxide.

[0026] When the composite oxide of the present invention contains neodymium element, the amount of neodymium element contained in the composite oxide of the present invention, calculated as neodymium oxide (Nd2O3), is preferably 0.1 mass % or more and 30 mass % or less, more preferably 0.5 mass % or more and 25 mass % or less, and even more preferably 1 mass % or more and 20 mass % or less, based on the mass of the composite oxide of the present invention, from the viewpoint of improving the heat resistance of the composite oxide.

[0027] When the composite oxide of the present invention contains praseodymium element, the praseodymium element contained in the composite oxide of the present invention is praseodymium oxide (PrO 11 From the viewpoint of improving the heat resistance of the composite oxide, the amount converted into SiO 2 is preferably 0.1 mass % or more and 30 mass % or less, more preferably 0.5 mass % or more and 25 mass % or less, and even more preferably 1 mass % or more and 20 mass % or less, based on the mass of the composite oxide of the present invention.

[0028] In the composite oxide of the present invention, cerium oxide and zirconium oxide may each form a single phase (a cerium oxide single phase or a zirconium oxide single phase) in addition to a solid solution phase.

[0029] In the composite oxide of the present invention, the other rare earth metal element or its oxide may form a solid solution phase together with cerium oxide and / or zirconium oxide, or may form a single phase.

[0030] The bulk composition of the composite oxide of the present invention (mass % of each metal element in the entire composite oxide of the present invention, calculated as the oxide) can be analyzed by X-ray fluorescence analysis. Bulk composition analysis by X-ray fluorescence analysis is preferably carried out under the conditions described in the Examples.

[0031] The composite oxide of the present invention is preferably in the form of a powder.

[0032] D of the composite oxide of the present invention 50 is preferably 0.5 μm or less, more preferably 0.45 μm or less, and even more preferably 0.4 μm or less, from the viewpoint of suppressing blockage of pores in the porous partition walls and the resulting increase in pressure loss when the composite oxide is impregnated into the porous partition walls of a wall-flow type substrate. The lower limit is preferably 0.05 μm, and more preferably 0.1 μm.

[0033] D of the composite oxide of the present invention 90 is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.7 μm or less, from the viewpoint of suppressing blockage of pores in the porous partition walls and the resulting increase in pressure loss when the composite oxide is impregnated into the porous partition walls of a wall-flow type substrate. The lower limit is preferably 0.2 μm, and more preferably 0.3 μm.

[0034] D of the composite oxide of the present invention 50 and D 90 are the particle sizes at which the cumulative volume is 50% and 90%, respectively, in the volume-based particle size distribution of the composite oxide of the present invention obtained by a laser diffraction / scattering particle size distribution measurement method. The laser diffraction / scattering particle size distribution measurement method is preferably carried out under the conditions described in the Examples.

[0035] The composite oxide of the present invention is preferably capable of maintaining its specific surface area even when exposed to high-temperature exhaust gas, and the specific surface area of ​​the composite oxide of the present invention measured by the BET method after heat treatment in air at 1000°C for 3 hours is preferably 20 m 2 / g or more, more preferably 22m 2 / g or more, and even more preferably 25m 2 / g or more. The upper limit is preferably 90m 2 / g, more preferably 80m 2 / g.

[0036] The specific surface area is preferably measured by the BET method under the conditions described in the Examples.

[0037] When the composite oxide of the present invention contains other rare earth metal elements, the mass % of the other rare earth metal elements, calculated as oxides, on the surface of the composite oxide of the present invention is preferably greater than the mass % of the other rare earth metal elements, calculated as oxides, in the entire composite oxide of the present invention, 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. That is, it is preferable that the oxides of the other rare earth metal elements are abundantly present 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 suppress CeO2 crystal growth that occurs when the composite oxide is exposed to high-temperature exhaust gas, thereby improving the heat resistance of the composite oxide and maintaining the specific surface area of ​​the composite oxide. The other rare earth metal elements present on the surface of the composite oxide are thought to act as a barrier to CeO2 crystal growth and suppress CeO2 crystal growth. This effect is thought to be greater for elements with larger ionic radii, such as lanthanum.

[0038] 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 % of the other rare earth metal elements, calculated as oxides, on the surface of the composite oxide of the present invention is preferably at least 0.80 times, more preferably at least 0.83 times, and even more preferably at least 0.85 times, the mass % of the other rare earth metal elements, calculated as oxides, in the entire composite oxide of the present invention. The upper limit is preferably 3.0 times, and more preferably 2.0 times.

[0039] The mass % of other rare earth metal elements on the surface of the composite oxide of the present invention, calculated as oxides, can be measured by X-ray photoelectron spectroscopy. X-ray photoelectron spectroscopy is preferably performed under the conditions described in the Examples. The mass % of other rare earth metal elements on the surface of the composite oxide of the present invention, calculated as oxides, is based on the total mass of metal elements on the surface of the composite oxide of the present invention, calculated as oxides (the total mass % of metal elements on the surface of the composite oxide of the present invention, calculated as oxides, is 100 mass %). When the composite oxide of the present invention contains two or more types of other rare earth metal elements, the mass % of other rare earth metal elements on the surface of the composite oxide of the present invention, calculated as oxides, is the total mass % of the two or more types of other rare earth metal elements on the surface of the composite oxide of the present invention, calculated as oxides.

[0040] The mass% of other rare earth metal elements in the entire composite oxide of the present invention, calculated as oxides, can be measured by X-ray fluorescence analysis. X-ray fluorescence analysis is preferably performed under the conditions described in the Examples. The mass% of other rare earth metal elements in the entire composite oxide of the present invention, calculated as oxides, is based on the total mass of metal elements in the entire composite oxide of the present invention, calculated as oxides (the total mass% of metal elements in the entire composite oxide of the present invention, calculated as oxides, is 100 mass%). When the composite oxide of the present invention contains two or more other rare earth metal elements, the mass% of other rare earth metal elements in terms of oxides is the sum of the mass% of the two or more other rare earth metal elements in terms of oxides.

[0041] The composite oxide of the present invention can be used as a component of a catalyst for purifying exhaust gases.

[0042] In one embodiment, the exhaust gas purifying catalyst comprises the composite oxide of the present invention and one or more precious metal elements supported on the composite oxide. The amounts of the composite oxide of the present invention and the precious metal elements contained in the exhaust gas purifying catalyst can be adjusted as appropriate.

[0043] The noble metal element can be selected from, for example, palladium, platinum, rhodium, etc. The noble metal element is supported on the composite oxide of the present invention in a form capable of functioning as a catalytically active component, such as a noble metal, an alloy containing the noble metal element, or a compound containing the noble metal element (for example, an oxide of the noble metal element). The catalytically active component is preferably in the form of particles from the viewpoint of enhancing exhaust gas purification performance.

[0044] The exhaust gas purification catalyst may contain a carrier component for supporting a precious metal element. The carrier component is preferably a porous material. The carrier component can be selected from, for example, alumina, silica, silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia, alumina-ceria, etc.

[0045] The exhaust gas purifying catalyst may contain other components such as a stabilizer and a binder.

[0046] "Supported" means a state in which a precious metal element is physically or chemically adsorbed or held on the outer surface or the inner surface of a pore of the composite oxide of the present invention. Support of a precious metal element on the composite oxide of the present invention can be confirmed, for example, by the presence of the composite oxide of the present invention and the precious metal element in the same region in element mapping obtained by analyzing a cross section of an exhaust gas purification catalyst with an EDS (energy dispersive spectroscopy).

[0047] In one embodiment, the exhaust gas purification catalyst is a molded body having a shape such as a pellet. The exhaust gas purification catalyst according to this embodiment can be produced, for example, by drying and calcining the exhaust gas purification catalyst composition. The drying temperature, drying time, calcination temperature, and calcination time can be appropriately adjusted. Calcination can be carried out, for example, in an air atmosphere.

[0048] In another embodiment, the exhaust gas purification catalyst comprises a substrate and a catalytic layer formed on the substrate, and the catalytic layer contains the composite oxide of the present invention and one or more types of precious metal elements supported on the composite oxide of the present invention.

[0049] The substrate can be appropriately selected from substrates used in known exhaust gas purification catalysts. 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 metal materials such as stainless steel. The shape of the substrate can be selected from honeycomb, pellet, spherical, and the like.

[0050] The substrate is preferably a wall-flow substrate. The wall-flow substrate includes inlet cells extending in the exhaust gas flow direction, outlet cells extending in the exhaust gas flow direction, and porous partition walls separating the inlet and outlet cells. The inlet cells have an open end on the exhaust gas inlet side in the exhaust gas flow direction and a closed end on the exhaust gas outlet side in the exhaust gas flow direction. The outlet cells have a closed end on the exhaust gas inlet side in the exhaust gas flow direction and an open end on the exhaust gas outlet side in the exhaust gas flow direction. Exhaust gas that flows into the wall-flow substrate from the exhaust gas inlet side end (opening) of the inlet cell passes through the porous partition walls and flows out from the exhaust gas outlet side end (opening) of the outlet cell. As the exhaust gas passes through the porous partition walls, PM in the exhaust gas is captured in the pores of the partition walls.

[0051] When the substrate is a wall-flow type substrate, the catalyst layer is preferably formed inside the porous partition walls of the wall-flow type substrate from the viewpoint of suppressing an increase in pressure loss.

[0052] The catalyst layer can be formed by applying the catalyst composition for exhaust gas purification to a substrate, drying it, and calcining it. The drying temperature, drying time, calcination temperature, and calcination time can be appropriately adjusted. Calcination can be carried out, for example, in an air atmosphere.

[0053] The exhaust gas purification catalyst composition used in the production of the exhaust gas purification catalyst is, for example, a slurry containing the composite oxide of the present invention and a salt of a precious metal element. The salt of the precious metal element can be selected from, for example, nitrates, ammine complex salts, chlorides, etc. The solvent contained in the dispersion can be selected from, for example, water, organic solvents, etc.

[0054] <Method for producing composite oxide> The composite oxide of the present invention can be produced by a method including steps (a) to (f), which will be explained below.

[0055] Engineering (a) Step (a) is a step of preparing a raw material liquid containing water, a zirconium salt, a cerium salt, and optionally other rare earth metal salts.

[0056] The water contained in the raw material solution is preferably pure water such as ion-exchanged water. The raw material solution may contain a solvent other than water. The solvent other than water can be selected from organic solvents such as alcohol, acetone, dimethyl sulfoxide, and dimethylformamide. The amount of organic solvent contained in the raw material solution is not particularly limited as long as the zirconium salt, cerium salt, and optionally other rare earth metal salts can be dissolved in the raw material solution, but is usually 20 vol% or less, preferably 10 vol% or less, based on the volume of the raw material solution.

[0057] The zirconium salt, cerium salt, and other rare earth metal salts contained in the raw material solution are all water-soluble salts. Note that the present invention also encompasses an embodiment in which the raw material solution prepared in step (a) does not contain other rare earth metal salts, and 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 the cerium salt and the zirconium salt are water-soluble salts.

[0058] The solubility of the water-soluble salt in water at 20°C (the mass of the water-soluble salt that can be dissolved in 100 g of water at 20°C) is preferably 1.0 g or more, more preferably 2.0 g or more, and even more preferably 5.0 g or more, and the solubility of the poorly water-soluble salt in water at 20°C (the mass of the poorly water-soluble salt that can be dissolved in 100 g of water at 20°C) is preferably less than 1.0 g, more preferably 0.5 g or less, and even more preferably 0.1 g or less.

[0059] The water-soluble zirconium salt can be selected from, for example, zirconium oxychloride, zirconium chloride, zirconium oxynitrate, zirconium nitrate, zirconium oxyacetate, etc., but from the viewpoints of preventing a decrease in the heat resistance of the composite oxide due to contamination with nitrate radicals, etc., and of easy availability, zirconium oxychloride or zirconium chloride is preferred, and zirconium oxychloride is more preferred. The raw material liquid may contain two or more types of water-soluble zirconium salts. The amount of water-soluble zirconium salt contained in the raw material liquid is appropriately adjusted so that the amount of zirconium element contained in the composite oxide produced in step (f) converted into zirconium oxide falls within a desired range.

[0060] The water-soluble cerium salt can be selected from, for example, cerium chloride, cerium nitrate, cerium (III) sulfate, cerium acetate, etc., but cerium chloride is preferred from the viewpoints of preventing a decrease in the heat resistance of the composite oxide due to contamination with nitrate ions, etc., and from the viewpoints of ease of availability. The raw material solution may contain two or more types of water-soluble cerium salts. The amount of water-soluble cerium salt contained in the raw material solution is appropriately adjusted so that the amount of cerium element contained in the composite oxide produced in step (f) converted into cerium oxide falls within a desired range.

[0061] The other water-soluble rare earth metal salts can be selected from, for example, chlorides, nitrates, sulfates, acetates, etc. of rare earth metal elements other than cerium. However, from the viewpoint of preventing a decrease in the heat resistance of the composite oxide due to contamination with nitrate ions, etc., and from the viewpoint of easy availability, chlorides of rare earth metal elements other than cerium (e.g., lanthanum chloride, neodymium chloride, praseodymium chloride, etc.) are preferred. The sulfates of rare earth metal elements are preferably sulfates of trivalent rare earth metal elements. The raw material solution may contain two or more types of other water-soluble rare earth metal salts. The type and amount of the other water-soluble rare earth metal salts contained in the raw material solution are appropriately adjusted so that the amount of the other rare earth metal elements contained in the composite oxide produced in step (f) in terms of oxide is within the desired range.

[0062] Engineering (b) Step (b) is a step of adding a first precipitant selected from an aqueous solution containing sulfate ions and a compound that can dissolve in water to produce sulfate ions to the raw material liquid prepared in step (a), thereby forming a first precipitate containing elemental zirconium and obtaining a first slurry containing the first precipitate.

[0063] The raw material solution contains metal ions (zirconium ions, cerium ions, and possibly other rare earth metal ions) generated by ionization of the water-soluble salt. The first precipitant added to the raw material solution is a precipitant that precipitates zirconium ions as basic zirconium sulfate and is selected from aqueous solutions containing sulfate ions and compounds that can dissolve in water to generate sulfate ions. Examples of compounds that can dissolve in water to generate sulfate ions include ammonium sulfate, sulfuric acid, alkali metal sulfates (e.g., sodium sulfate, potassium sulfate, etc.), cerium (III) sulfate, and rare earth metal sulfates. However, from the viewpoints of improving the uniformity of the solid solution phase formed by cerium, zirconium, and oxygen elements (e.g., a solid solution phase of cerium oxide and zirconium oxide) and of easy availability, ammonium sulfate, sulfuric acid, or alkali metal sulfates is preferred, and ammonium sulfate is more preferred. The rare earth metal sulfate is preferably a trivalent rare earth metal sulfate. An 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 (for example, pure water such as ion-exchanged water).

[0064] Adding a first precipitant to the raw material solution forms a first precipitate containing elemental zirconium, resulting in a first slurry containing the first precipitate. The elemental zirconium is contained in the first precipitate in the form of basic zirconium sulfate. Basic zirconium sulfate is a poorly water-soluble zirconium salt formed by the first precipitant.

[0065] From the viewpoint of suppressing the generation of aggregated particles due to a delay in the reaction for forming basic zirconium sulfate, the temperature of the raw material 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.

[0066] From the viewpoints of sufficiently precipitating basic zirconium sulfate, suppressing the adverse effects of excess sulfate ions, and improving the heat resistance of the composite oxide produced in step (f), it is preferable to add the first precipitant to the raw material solution so that the molar amount of sulfate ions in the raw material solution is 0.4 to 2 times the molar amount of elemental zirconium in the raw material solution. The molar amount of sulfate ions in the raw material solution is more preferably 0.45 to 2 times, and even more preferably 0.5 to 1.5 times the molar amount of elemental zirconium in the raw material solution.

[0067] From the viewpoint of uniformly forming the precipitate, it is preferable to add the first precipitant dropwise to the raw material liquid while stirring the raw material liquid.

[0068] From the viewpoint of aging the precipitate uniformly, it is preferable to age the first precipitate while stirring the first slurry. The ageing time is preferably from 0.5 hours to 12 hours, more preferably from 1 hour to 4 hours, and even more preferably from 1 hour to 2 hours.

[0069] Engineering (c) Step (c) is a step of subjecting the first slurry obtained in step (b) to a wet grinding treatment.

[0070] When the first slurry is subjected to the wet grinding treatment, the first precipitate contained in the first slurry is ground, and a ground product of the first precipitate is obtained.

[0071] The composite oxide produced in step (f) has a desired D 50 and D 90 In order to effectively achieve this, the wet grinding process is carried out to obtain the D 50 It is preferable that the D of the pulverized product of the first precipitate is 0.5 μm or more and 1.5 μm or less. 50 The diameter of the first precipitate before the wet-pulverization treatment is more preferably 0.5 μm or more and 1.3 μm or less, and even more preferably 0.5 μm or more and 1.2 μm or less. 50is usually 10 μm or more and 40 μm or less, preferably 10 μm or more and 30 μm or less.

[0072] The composite oxide produced in step (f) has a desired D 50 and D 90 From the viewpoint of effectively realizing this, the D of the first precipitate before the wet grinding treatment 50 D of the crushed product of the first precipitate 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.

[0073] The composite oxide produced in step (f) has a desired D 50 and D 90 In order to effectively achieve this, the wet grinding process is carried out to obtain the D 90 It is preferable that the D of the pulverized product of the first precipitate is 1 μm or more and 2.5 μm or less. 90 The diameter of the first precipitate before the wet grinding treatment is more preferably 1 μm or more and 2.3 μm or less, and even more preferably 1 μm or more and 2 μm or less. 90 is usually 10 μm or more and 100 μm or less, preferably 20 μm or more and 50 μm or less.

[0074] The composite oxide produced in step (f) has a desired D 50 and D 90 From the viewpoint of effectively realizing this, the D of the first precipitate before the wet grinding treatment 90 D of the crushed product of the first precipitate 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.

[0075] First precipitate crushed product D 50 and D 90are particle sizes at which the cumulative volume is 50% and 90%, respectively, in the volume-based particle size distribution of the pulverized product of the first precipitate obtained by the laser diffraction scattering particle size distribution measurement method. The laser diffraction scattering particle size distribution measurement method is preferably performed under the conditions described in the Examples. D of the first precipitate before the wet-pulverization treatment 50 and D 90 The same is true.

[0076] The desired D 50 and D 90 From the viewpoint of effectively realizing the above, it is preferable to carry out the wet grinding treatment using beads. The diameter of the beads is usually 0.015 mm or more and 2.0 mm or less. 50 and D 90 From the viewpoint of effectively realizing this, the diameter of the beads 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.

[0077] The desired D 50 and D 90 From the viewpoint of effectively realizing this, it is preferable that the wet grinding treatment be carried out so that the acceleration applied to the beads exceeds 1 G. The acceleration applied to the beads is usually 2 G or more and 1000 G or less, and preferably 40 G or more and 1000 G or less. The desired acceleration can be applied to the beads, for example, by centrifugal force generated by the high-speed rotation of a paint shaker, which is a paint disperser.

[0078] The desired D 50 and D 90 From the viewpoint of effectively achieving this, the wet milling treatment using beads is preferably carried out for 0.5 hours or more, more preferably 1 hour or more, with the upper limit being preferably 10 hours, more preferably 5 hours.

[0079] In step (c), the first slurry obtained in step (b) may be used for wet-pulverization as is, or the first slurry obtained in step (b) may be diluted and then used for wet-pulverization. Dilution can be performed using a solvent such as water (e.g., pure water such as ion-exchanged water) or a solvent other than water (e.g., an organic solvent). Specific examples of the organic solvent are the same as those described above.

[0080] Engineering (d) Step (d) is a step of adding a second precipitating agent 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 wet-milling treatment, thereby forming a second precipitate containing elemental zirconium, elemental cerium, and optionally other rare earth metal elements, and obtaining a second slurry containing the second precipitate.

[0081] When a second precipitant is added to the first slurry after the wet milling treatment, a second precipitate containing zirconium, cerium, and optionally other rare earth metal elements is formed, and a second slurry containing the second precipitate is obtained. The pH of the second slurry is usually 9 or more and 14 or less, preferably 11 or more and 14 or less.

[0082] The zirconium element is contained in the second precipitate in the form of zirconium hydroxide, a poorly water-soluble zirconium salt formed by the second precipitating agent. Note that basic zirconium sulfate formed by the first precipitating agent is converted to zirconium hydroxide by the second precipitating agent.

[0083] The cerium element is contained in the second precipitate in the form of cerium hydroxide, which is a sparingly water-soluble cerium salt formed by the second precipitating agent.

[0084] Other rare earth metal elements (e.g., lanthanum, neodymium, praseodymium, etc.) are contained in the second precipitate in the form of hydroxides (e.g., lanthanum hydroxide, neodymium hydroxide, praseodymium hydroxide, etc.). The hydroxides of other rare earth metal elements are sparingly water-soluble rare earth metal salts formed by the second precipitating agent. The hydroxides of other rare earth metal elements formed by the second precipitating agent are coprecipitated with cerium hydroxide formed by the second precipitating agent.

[0085] The second precipitate includes composite salt particles containing zirconium hydroxide, cerium hydroxide, and optionally hydroxides of other rare earth metal elements. The second precipitate may include zirconium hydroxide particles, cerium hydroxide particles, hydroxide particles of other rare earth metal elements, etc. in addition to the composite salt particles. The composite salt particles are formed, for example, by the adhesion and growth of cerium hydroxide and / or hydroxides of other rare earth metal elements formed by the second precipitating agent on the surface of basic zirconium sulfate formed by the first precipitating agent (the basic zirconium sulfate is converted to zirconium hydroxide by the second precipitating agent).

[0086] From the viewpoint of suppressing a decrease in oxygen storage capacity due to phase separation between cerium oxide and zirconium oxide in the composite oxide produced in step (f), the temperature of the first slurry when the second precipitating agent 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.

[0087] From the viewpoint of sufficiently precipitating zirconium hydroxide, cerium hydroxide, and hydroxides of other rare earth metal elements, it is preferable to add the second precipitant to the first slurry so that the molar amount of hydroxide ions in the first slurry is at least twice the molar amount of oxygen necessary to convert zirconium, cerium, and other rare earth metal elements in the first slurry into oxides. The molar amount of hydroxide ions in the first slurry is more preferably at least 2 times but not more than 10 times, even more preferably at least 2 times but not more than 5 times, and even more preferably at least 2 times but not more than 3 times the molar amount of oxygen necessary to convert zirconium, cerium, and other rare earth metal elements in the first slurry into oxides.

[0088] The molar amount of oxygen required to convert zirconium, cerium, and other rare earth metal elements in the first slurry into oxides can be calculated by [(molar amount of zirconium) × 2] + [(molar amount of cerium) × 2] + [(molar amount of rare earth metal elements other than cerium, praseodymium, and terbium) × 3 / 2] + [(molar amount of praseodymium) × 11 / 6] + [(molar amount of terbium) × 7 / 4].

[0089] Engineering (e) Step (e) is a step of obtaining a cake from the second slurry.

[0090] The cake can be obtained by subjecting the second slurry to solid-liquid separation. Examples of solid-liquid separation methods include filtration, centrifugation, and decantation, with filtration being preferred. The solvent is removed by solid-liquid separation to obtain a cake, but the solvent is not completely removed, so some of the solvent remains in the cake.

[0091] In step (e), it is preferable to obtain a first cake from the second slurry, treat the first cake with an alcohol-containing liquid, and obtain a second cake having an alcohol concentration of 90 vol% or more. This makes it possible to suppress the aggregation of the second precipitate contained in the cake, and to obtain a desired D in the composite oxide produced in step (f). 50 and D 90 can be effectively realized.

[0092] The first cake can be obtained by subjecting the second slurry to solid-liquid separation, the explanation of which is as above.

[0093] Before treating the first cake with the alcohol-containing liquid, the first cake may be washed with a washing liquid. As the washing liquid, water (e.g., pure water such as ion-exchanged water) is preferably used. By washing the first cake with the washing liquid, a part or all of the solvent in the first cake is replaced with the washing liquid.

[0094] The alcohol-containing liquid contains one or more types of alcohol. Examples of alcohol include methyl alcohol, ethyl alcohol, n-propyl alcohol, 2-propanol, 1-propanol, n-butyl alcohol, s-butyl alcohol, t-butyl alcohol, pentyl alcohol, and hexyl alcohol. Among these, methyl alcohol, ethyl alcohol, n-propyl alcohol, 2-propanol, and 1-propanol are preferred, and methyl alcohol, ethyl alcohol, and n-propyl alcohol are more preferred. When the alcohol-containing liquid contains one type of alcohol, the one type of alcohol is preferably ethyl alcohol. When the alcohol-containing liquid contains two or more types of alcohol, the two or more types of alcohol are preferably ethyl alcohol and one or more other alcohols.

[0095] The alcohol concentration of the alcohol-containing liquid is adjusted appropriately depending on the alcohol concentration of the second cake to be realized. The alcohol concentration of the alcohol-containing liquid may be equal to or higher than the alcohol concentration of the second cake to be realized. Therefore, the alcohol concentration of the alcohol-containing liquid may be the same as or higher than the alcohol concentration of the second cake to be realized. The upper limit of the alcohol concentration of the alcohol-containing liquid is not particularly limited. Note that when the alcohol-containing liquid contains two or more types of alcohol, the alcohol concentration of the alcohol-containing liquid is the total concentration of the two or more types of alcohol.

[0096] When the alcohol-containing liquid contains ethyl alcohol, the ethyl alcohol concentration is preferably 51 vol% or more, more preferably 65 vol% or more, and even more preferably 90 vol% or more, based on the volume of the alcohol-containing liquid. The upper limit of the ethyl alcohol concentration is not particularly limited, but is usually 100 vol%.

[0097] The alcohol-containing liquid 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 carbons (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.).

[0098] As the alcohol-containing liquid, for example, commercially available denatured alcohol (industrial alcohol) can be used as is or after diluting with water such as ion-exchanged water.

[0099] The treatment of the first cake with the alcohol-containing liquid is not particularly limited as long as the first cake is brought into contact with the alcohol-containing liquid and the liquid in the first cake (e.g., a solvent for the raw material liquid, a cleaning liquid, etc.) can be replaced with the alcohol-containing liquid. Examples include a method of immersing the first cake in the alcohol-containing liquid and a method of mixing the first cake with the alcohol-containing liquid. The second cake is obtained by solid-liquid separation after contacting the first cake with the alcohol-containing liquid (e.g., after immersing the first cake in the alcohol-containing liquid or after mixing the first cake with the alcohol-containing liquid). Examples of solid-liquid separation methods include filtration, centrifugation, and decantation, with centrifugation being preferred. The alcohol-containing liquid is removed by the solid-liquid separation method to obtain the second cake, but the alcohol-containing liquid is not completely removed, so the alcohol-containing liquid remains in the second cake. By repeatedly treating the first cake with the alcohol-containing liquid, the alcohol concentration of the second cake approaches and eventually becomes the same as the alcohol concentration of the alcohol-containing liquid. Therefore, if the alcohol concentration of the alcohol-containing liquid is the same as the alcohol concentration of the second cake to be realized, the treatment of the first cake with the alcohol-containing liquid is repeated until the alcohol concentration of the second 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 alcohol concentration of the second cake to be realized, the treatment of the first cake with the alcohol-containing liquid is repeated until the alcohol concentration of the second cake reaches the target alcohol concentration.

[0100] The composite oxide produced in step (f) has a desired D 50 and D 90 From the viewpoint of effectively realizing this, the alcohol concentration of the second 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%.

[0101] The alcohol concentration of the second cake is defined by the alcohol concentration of the alcohol-containing liquid after it has been used to treat the first cake. That is, after the first cake is brought into contact with the alcohol-containing liquid (for example, after the first cake is immersed in the alcohol-containing liquid or after the first cake is mixed with the alcohol-containing liquid), the alcohol concentration of the filtrate, supernatant, or effluent obtained by solid-liquid separation is measured, and the measured alcohol concentration of the filtrate, supernatant, or effluent is defined as the alcohol concentration of the second cake.

[0102] The alcohol concentration can be measured according to a conventional method. For example, a conversion table between the alcohol concentration of an alcohol-containing liquid and the specific gravity of the alcohol-containing liquid can be prepared in advance, the specific gravity of the alcohol-containing liquid can be measured, and the alcohol concentration of the alcohol-containing liquid can be calculated based on the measured specific gravity. The specific gravity of the alcohol-containing liquid can be measured, for example, using a hydrometer-type hydrometer. The temperature of the alcohol-containing liquid when measuring the specific gravity is, for example, 15°C. Regarding the measurement of specific gravity and the conversion of specific gravity to alcohol concentration, JIS B 7548:2009 (Alcohol Hydrometer) Annex A (Regulations) "International Alcohol Tables" can be referenced.

[0103] It is preferable to dry the second cake before subjecting it to step (f). Drying can be carried out according to a conventional method. The drying temperature is usually 60°C or higher and 200°C or lower, preferably 80°C or higher and 130°C or lower, and the drying time is usually 1 hour or higher and 24 hours or lower, preferably 2 hours or higher and 12 hours or lower.

[0104] Engineering (f) Step (f) is a step of calcining the cake obtained in step (e) to produce a composite oxide containing elemental zirconium, elemental cerium, and optionally other rare earth metal elements.

[0105] In step (e), a first cake is obtained from the second slurry, and the first cake is treated with an alcohol-containing liquid to obtain a second cake having an alcohol concentration of 90 vol% or more. In this case, the second cake is baked in step (f).

[0106] The precipitate can be calcined according to a conventional method. Calcination is usually carried out in an air atmosphere. The calcination temperature is usually 600°C to 1100°C, preferably 600°C to 1000°C, and more preferably 600°C to 950°C. The calcination time is usually 2 hours to 20 hours, preferably 2 hours to 10 hours, and even more preferably 2 hours to 5 hours.

[0107] In step (c), the first slurry is subjected to a wet-milling treatment to atomize the first precipitate (basic zirconium sulfate). In step (d), a second precipitant is added to the first slurry after the wet-milling treatment, and cerium hydroxide and, in some cases, hydroxides of other rare earth metal elements are precipitated around the crushed first precipitate as a nucleus (however, basic zirconium sulfate is converted to zirconium hydroxide by the second precipitant). The second precipitate thus obtained is sufficiently atomized. Therefore, in step (f), the desired D 50 and D 90 In particular, in step (e), a first cake is obtained from the second slurry, the first cake is treated with an alcohol-containing liquid to obtain a second cake having an alcohol concentration of 90 vol% or more, and in step (f), the second cake is baked, whereby aggregation of the second precipitate contained in the cake can be suppressed, and the composite oxide produced in step (f) has a desired D 50 and D 90 can be effectively realized.

[0108] When the raw material solution contains other rare earth metal salts, in step (d), a second precipitant is added to the first slurry after wet milling. This causes cerium hydroxide and hydroxides of other rare earth metal elements to precipitate around the pulverized first precipitate as nuclei (however, basic zirconium sulfate is converted to zirconium hydroxide by the second precipitant). Therefore, in the composite oxide obtained in step (f), the mass % of the other rare earth metal elements on the surface of the composite oxide, calculated as oxides, is greater than the mass % of the other rare earth metal elements in the entire composite oxide. In other words, the oxides of the other rare earth metal elements are abundantly present on the surface of the composite oxide. The other rare earth metal elements present on the surface of the composite oxide suppress the CeO crystal growth that occurs when the composite oxide is exposed to high-temperature exhaust gas, thereby improving the heat resistance of the composite oxide and maintaining the specific surface area of ​​the composite oxide. It is believed that other rare earth metal elements present on the surface of the composite oxide act as a barrier to CeO2 crystal growth, suppressing it. This effect is believed to be greater for elements with a larger ionic radius, such as lanthanum.

[0109] The composite oxide obtained in step (f) may be subjected to a pulverization treatment, if necessary. The pulverization treatment can be carried out in a dry or wet manner using, for example, a mortar, a hammer mill, a ball mill, a bead mill, a jet mill, a roller mill, or the like.

[0110] However, if the composite oxide obtained in step (f) is subjected to volumetric pulverization using a pulverizer having a "compression" or "impact" pulverization mechanism, the particles may generally break into several pieces, not from the particle surface but from the entire particle. For this reason, volumetric pulverization is not preferable as a fine pulverization process, and the product D of the present invention is not suitable. 50 and D 90 It becomes difficult to obtain a composite oxide having a particle size of 0.50 μm or less and 1.0 μm or less, respectively. Examples of crushers having a "compression" or "impact" crushing mechanism include a hammer mill, a pin mill, and a dry ball mill.

[0111] On the other hand, if the composite oxide obtained in step (f) is subjected to surface pulverization using a pulverizer having a "grinding" or "shear" pulverization mechanism, a compressive force or shear force is applied to the particles by friction, and fine powder is formed from the particle surface. For this reason, surface pulverization is generally suitable for fine pulverization and is preferred. Examples of pulverizers having a "grinding" pulverization mechanism include a bead mill and a force mill. When the composite oxide obtained in step (f) is subjected to pulverization, the D of the pulverized composite oxide is 50 and D 90 From the viewpoint of easier control of the surface pulverization, it is preferable to carry out the surface pulverization using these pulverizers. [Example]

[0112] The present invention will be described in more detail below based on examples and comparative examples.

[0113] [D 50 and D 90 Measurement of D of the target powder 50 and D 90 The particle sizes at which the cumulative volume is 50% and 90%, respectively, are measured in the volume-based particle size distribution of the target powder obtained by laser diffraction / scattering particle size distribution measurement. Laser diffraction / scattering particle size distribution measurement was performed by dispersing the target powder in a 0.2% by mass aqueous solution of sodium hexametaphosphate and ultrasonicating it (output: 30 W, treatment time: 360 seconds) using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3000II, manufactured by Microtrac-Bell). The measurement conditions were particle refractive index: 1.81, particle shape: aspherical, solvent refractive index: 1.33, set zero: 30 seconds, measurement time: 60 seconds, and measurement range: 0.01 to 10,000 μm.

[0114] [Measurement of specific surface area] The specific surface area was measured in accordance with "(3.5) Single-point method" in "6.2 Flow Method" of JIS R1626:1996 "Measurement of specific surface area of ​​fine ceramic powders by gas adsorption BET method." Specifically, a nitrogen-helium mixed gas containing 30% by volume of nitrogen as the adsorption gas and 70% by volume of helium as the carrier gas was used as the gas, and a Mountec fully automatic specific surface area meter, Macsorbmodel-1201, was used as the BET specific surface area measuring device, and measurements were made using the BET single-point method.

[0115] [Bulk composition analysis of complex oxides] Bulk composition analysis of the composite oxides was carried out using X-ray fluorescence spectroscopy (XRF). The conditions for the XRF analysis are as follows: XRF analyzer: Rigaku ZSX Primus II Accelerating voltage: 50 kV Current: 50mA Atmosphere: Vacuum 1.4Pa Target: Rh 4.0kW Filter: Ni400 Diaphragm: 30mm Slit: S2 Spectroscopic crystal: LiF(200) Detector: SC Attenuator: 1 / 1 PHA:LL50, UL400 PR gas: 4.7 mL / min Constant temperature: 36.5℃

[0116] [Surface composition analysis of complex oxides] The surface composition of the composite oxide was analyzed using X-ray photoelectron spectroscopy (XPS).

[0117] The conditions for the XPS analysis are as follows: XPS analyzer: PHI Quantes manufactured by ULVAC-PHI, Inc. Excitation X-ray: Monochromated Al-Kα line (1486.7 eV) Output: 50W Accelerating voltage: 15 kV X-ray irradiation diameter: 200μmφ Measurement area: 1000×300μm 2 Detection angle: 15° Pass energy: 26.0 eV Energy step: 0.1 eV / step Measured elements / orbitals (semi-quantitative calculated elements): C 1s, O 1s, Zr 3d, La 3d5 / 2, Ce 3d, Pr 3d5 / 2, Nd 3d5 / 2

[0118] XPS data were analyzed using data analysis software (ULVAC-PHI Multipack Ver. 9.9). Iterated Shirley was used as the background mode.

[0119] [Calculation of the degree of deviation of the surface composition from the bulk composition] In calculating the degree of deviation of the surface composition from the bulk composition, a cerium-zirconium composite oxide prepared by the following method was used as a reference sample. Cerium nitrate, zirconium oxynitrate, lanthanum nitrate, neodymium nitrate, and praseodymium nitrate were dissolved in water to obtain 500 g of a raw material solution. The amounts of cerium nitrate, zirconium oxynitrate, lanthanum nitrate, neodymium nitrate, and praseodymium nitrate were adjusted so that the mass of elemental cerium (calculated as cerium oxide), the mass of elemental zirconium (calculated as zirconium oxide), the mass of elemental lanthanum (calculated as lanthanum oxide), the mass of elemental neodymium (calculated as neodymium oxide), and the mass of elemental praseodymium (calculated as praseodymium oxide) were 40 mass%, 50 mass%, 2 mass%, 4 mass%, and 4 mass%, respectively, based on the total mass of these.

[0120] The temperature of 10% by mass ammonia water was raised to 40°C, and the raw material liquid was added dropwise with stirring until the pH of the ammonia water fell below 9.5, forming a precipitate, which was then filtered and washed by suction filtration to obtain a cake.

[0121] The cake was air-dried, 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.

[0122] The reference sample was subjected to bulk composition analysis by XRF and surface composition analysis by XPS using the above-mentioned methods. The results are shown in Tables 2 and 3. In Table 2, "CeO2," "ZrO2," "La2O3," "Nd2O3," and "Pr6O 11 " represents the XRF analysis values ​​of cerium, zirconium, lanthanum, neodymium, and praseodymium elements converted to oxides. In Table 3, "CeO2", "ZrO2", "La2O3", "Nd2O3", and "Pr6O 11 " respectively represent the XPS analysis values ​​(semi-quantitative values) of the elements cerium, zirconium, lanthanum, neodymium, and praseodymium in terms of oxide.

[0123] Based on the following formulas, correction factor C1 for the XPS analysis value of cerium element converted into cerium oxide, correction factor C2 for the XPS analysis value of zirconium element converted into zirconium oxide, correction factor C3 for the XPS analysis value of lanthanum element converted into lanthanum oxide, correction factor C4 for the XPS analysis value of neodymium element converted into neodymium oxide, and correction factor C5 for the XPS analysis value of praseodymium element converted into neodymium oxide were calculated. The correction factors are shown in Table 4.

[0124] Correction coefficient C1 = XRF analysis value of cerium element in the reference sample converted to cerium oxide / XPS analysis value of cerium element in the reference sample converted to cerium oxide Correction coefficient C2 = XRF analysis value of zirconium element in the reference sample converted to zirconium oxide / XPS analysis value of zirconium element in the reference sample converted to zirconium oxide Correction coefficient C3 = XRF analysis value of lanthanum element in the reference sample converted to lanthanum oxide / XPS analysis value of lanthanum element in the reference sample converted to lanthanum oxide Correction factor C4 = XRF analysis value of neodymium element in reference sample converted to neodymium oxide / XPS analysis value of neodymium element in reference sample converted to neodymium oxide Correction factor C5 = XRF analysis value of praseodymium element in the reference sample converted to praseodymium oxide / XPS analysis value of praseodymium element in the reference sample converted to praseodymium oxide

[0125] For each composite oxide in the Examples and Comparative Examples, the XPS measurement value of cerium element converted into cerium oxide is multiplied by the correction factor C1 to obtain V1, the XPS analysis value of zirconium element converted into zirconium oxide is multiplied by the correction factor C2 to obtain V2, the XPS analysis value of lanthanum element converted into lanthanum oxide is multiplied by the correction factor C3 to obtain V3, the XPS analysis value of neodymium element converted into neodymium oxide is multiplied by the correction factor C4 to obtain V4, and the XPS analysis value of praseodymium element converted into neodymium oxide is multiplied by the correction factor C5 to obtain V6. The analytical value was multiplied by a correction coefficient C5 to calculate a value V5, and a corrected value CV1 for the XPS analytical value of cerium element, converted into cerium oxide; a corrected value CV2 for the XPS analytical value of zirconium element, converted into zirconium oxide; a corrected value CV3 for the XPS analytical value of lanthanum element, converted into lanthanum oxide; a corrected value CV4 for the XPS analytical value of neodymium element, converted into neodymium oxide; and a corrected value CV5 for the XPS analytical value of praseodymium element, converted into praseodymium oxide, were calculated based on the following formulas.

[0126] Correction value CV1 = value V1 x 100 / (total value of values ​​V1 to V5) Correction value CV2 = value V2 x 100 / (total value of values ​​V1 to V5) Correction value CV3 = value V3 x 100 / (total value of values ​​V1 to V5) Correction value CV4 = value V4 x 100 / (total value of values ​​V1 to V5) Correction value CV5 = value V5 x 100 / (total value of values ​​V1 to V5)

[0127] For each of the composite oxides in the Examples and Comparative Examples, the degree of deviation of the surface composition from the bulk composition was calculated based on the following formula, and this value was used as an index of the surface concentrations of the elements lanthanum, neodymium, and praseodymium in each composite oxide.

[0128] Deviation of surface composition from bulk composition = (corrected value CV3 + corrected value CV4 + corrected value CV5) / (XRF analysis value of lanthanum converted to lanthanum oxide + XRF analysis value of neodymium converted to neodymium oxide + XRF analysis value of praseodymium converted to praseodymium oxide)

[0129] Example 1 (1) Preparation of the first slurry Cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were dissolved in water to obtain 480 g of a 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 so that the mass of elemental cerium (calculated as cerium oxide), the mass of elemental zirconium (calculated as zirconium oxide), the mass of elemental lanthanum (calculated as lanthanum oxide), the mass of elemental neodymium (calculated as neodymium oxide), and the mass of elemental praseodymium (calculated as praseodymium oxide) were 40 mass%, 50 mass%, 2 mass%, 4 mass%, and 4 mass%, respectively, based on the total mass of these elements.

[0130] The temperature of the raw material solution was raised to 85°C, and while stirring the raw material solution, a 25% by mass aqueous solution of ammonium sulfate was added dropwise so that the molar amount of sulfate ions was 0.5 times the molar amount of zirconium element, forming a precipitate to obtain a first slurry. After the dropwise addition was completed, the precipitate was aged at 85°C while stirring the first slurry.

[0131] (2) Wet grinding of the first slurry After the precipitate had aged, the first slurry was cooled to 40°C. After cooling, the first slurry was added to a 1 L polyethylene container filled with 300 g of 0.1 mm diameter ZrO2 beads, and the first slurry was subjected to a wet-milling process at room temperature for 1 hour using a paint shaker (Asada Iron Works Paint Shaker PS-08). In the wet-milling process, the centrifugal force generated by the high-speed rotation of the paint shaker applies an acceleration of more than 1 G (usually between 50 G and 500 G), which crushes the precipitate.

[0132] (3)D 50 and D 90 Measurement of The first slurry before or after the crushing process is used to measure the D of the precipitate before or after the crushing process. 50 and D 90 was measured by the above method, and the results are shown in Table 1.

[0133] (4) Preparation of the second slurry The ground first slurry was transferred to a beaker and heated to 40°C while stirring. A 24% by mass aqueous solution of sodium hydroxide was then added dropwise so that the molar amount of hydroxide ions was 2.5 times the molar amount of oxygen required to convert cerium, zirconium, lanthanum, neodymium, and praseodymium into oxides. A precipitate was formed, yielding a second slurry. The pH of the second slurry was 13.5. After the addition, the precipitate was aged at 40°C while stirring the second slurry.

[0134] (5) Preparation of the first cake After aging the precipitate, the second slurry was filtered and washed using ion-exchanged water to obtain a first cake.

[0135] (6) Preparation of the second cake The denatured alcohol used was CS Sorb NM-85 manufactured by China Oil Refining Co., Ltd. The composition of the denatured alcohol used was 85.4% by mass of ethyl alcohol, 5% by mass of methyl alcohol, and 9.6% by mass of n-propyl alcohol.

[0136] Several types of alcohol-containing liquids with different alcohol concentrations (volume percent concentration) were prepared using denatured alcohol and ion-exchanged water, and the specific gravity (15 / 15°C) of the alcohol-containing liquids was measured using a hydrometer, and a conversion table between specific gravity (15 / 15°C) and alcohol concentration (vol%) was created.

[0137] 20 g of the washed first cake was treated with denatured alcohol to replace the water content of the first cake. Specifically, the first cake was suspended in denatured alcohol and then centrifuged (8000 rpm x 5 minutes). The specific gravity (15°C / 15°C) of the supernatant was measured using a hydrometer. The alcohol concentration of the supernatant was calculated from the specific gravity using a conversion table between specific gravity (15°C / 15°C) and alcohol concentration (vol%). The alcohol concentration of the supernatant was defined as the alcohol concentration of the cake. The above process was repeated three times until the alcohol concentration of the supernatant (i.e., the alcohol concentration of the cake) reached 99 vol%, resulting in a second cake with an alcohol concentration of 99 vol%.

[0138] (7) Preparation of composite oxides The second cake was air-dried, dried overnight at 90°C, and then fired in a muffle furnace. After firing, the cake was pulverized with a hand mixer (Force Mill FM-1 manufactured by Osaka Chemical Co., Ltd.) and sieved through a 100 mesh screen to obtain a powdered composite oxide.

[0139] (8) Characterization of complex oxides [D 50 and D 90 Measurement of D of the composite oxide obtained in (7) above 50 and D 90 was measured by the above method, and the results are shown in Table 1.

[0140] [Measurement of specific surface area] The composite oxide obtained in (7) above was heat-treated in air at 1000°C for 3 hours, and then the specific surface area of ​​the heat-treated composite oxide was measured by the above-mentioned method. The results are shown in Table 1.

[0141] [Bulk composition analysis] The bulk composition of the composite oxide obtained in (7) above was analyzed by XRF using the method described above. The results are shown in Table 2. In Table 2, "CeO2", "ZrO2", "La2O3", "Nd2O3" and "Pr6O 11" respectively represent the XRF analysis values ​​of cerium, zirconium, lanthanum, neodymium and praseodymium elements converted to oxides.

[0142] Example 2 A composite oxide was prepared in the same manner as in Example 1, except that the amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were adjusted so that the mass of cerium in terms of cerium oxide, the mass of zirconium in terms of zirconium oxide, the mass of lanthanum in terms of lanthanum oxide, the mass of neodymium in terms of neodymium oxide, and the mass of praseodymium in terms of praseodymium oxide were 40 mass%, 46 mass%, 2 mass%, 8 mass%, and 4 mass%, respectively, based on the total mass of these.

[0143] The composite oxide obtained in Example 2 was subjected to the same procedure as in Example 1 to obtain D 50 and D 90 The results are shown in Tables 1 and 2.

[0144] [Surface composition analysis] The surface composition of the composite oxide obtained in Example 2 was analyzed by XPS using the method described above. The results are shown in Table 3. In Table 3, "CeO2", "ZrO2", "La2O3", "Nd2O3" and "Pr6O 11 " respectively represent the XPS analysis values ​​(semi-quantitative values) of the elements cerium, zirconium, lanthanum, neodymium, and praseodymium in terms of oxide.

[0145] [Calculation of the degree of deviation of the surface composition from the bulk composition] For the composite oxide obtained in Example 2, the degree of deviation of the surface composition from the bulk composition was calculated by the above-mentioned method based on the bulk composition analysis results (Table 2) and the surface composition analysis results (Table 3). The results are shown in Tables 4 and 5. In Table 4, "CeO2", "ZrO2", "La2O3", "Nd2O3" and "Pr6O 11" respectively represent the degree of deviation for cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide.

[0146] Example 3 A composite oxide was prepared in the same manner as in Example 1, except that the amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were adjusted so that the mass of cerium in terms of cerium oxide, the mass of zirconium in terms of zirconium oxide, the mass of lanthanum in terms of lanthanum oxide, the mass of neodymium in terms of neodymium oxide, and the mass of praseodymium in terms of praseodymium oxide were 40 mass%, 46 mass%, 2 mass%, 4 mass%, and 8 mass%, respectively, based on the total mass of these.

[0147] The composite oxide obtained in Example 3 was subjected to the same procedure as in Example 1 to obtain D 50 and D 90 The results are shown in Tables 1 and 2.

[0148] Furthermore, for the composite oxide obtained in Example 3, surface composition analysis by XPS and calculation of the degree of deviation of the surface composition from the bulk composition were carried out in the same manner as in Example 2. The results are shown in Tables 3 to 5.

[0149] Comparative Example 1 (1) Preparation of the first slurry Cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were dissolved in water to obtain 107 kg of a raw material solution. The amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride were adjusted so that the mass of elemental cerium in terms of cerium oxide, the mass of elemental zirconium in terms of zirconium oxide, the mass of elemental lanthanum in terms of lanthanum oxide, the mass of elemental neodymium in terms of neodymium oxide, and the mass of elemental praseodymium in terms of praseodymium oxide were 40 mass%, 50 mass%, 2 mass%, 4 mass%, and 4 mass%, respectively, based on the total mass of these.

[0150] The raw material solution was heated to 85°C, and while stirring the raw material solution, a 25% by mass aqueous solution of ammonium sulfate was added dropwise so that the molar amount of sulfate ions was 1.0 times the molar amount of zirconium element, forming a precipitate to obtain a first slurry. After the dropwise addition was completed, the precipitate was aged at 85°C while stirring the first slurry.

[0151] (2) Preparation of the second slurry The temperature of the first slurry was lowered to 40°C, and then a 24% by mass aqueous solution of sodium hydroxide was added dropwise to the first slurry while stirring, so that the molar amount of hydroxide ions was 2.5 times the molar amount of oxygen required to convert elemental cerium, elemental zirconium, elemental lanthanum, elemental neodymium, and elemental praseodymium into oxides, forming a precipitate to obtain a second slurry. The pH of the second slurry was 13.5. After the dropwise addition, the precipitate was aged at 40°C while stirring the second slurry.

[0152] (3) Preparation of cake After the precipitate was aged, the second slurry was filtered and washed using a filter press (TFP-4-8 MKII type manufactured by Ataka Daiki Co., Ltd.) to obtain a cake.

[0153] (4) Preparation of composite oxides The cake was air-dried, dried overnight at 90°C, and then fired in a muffle furnace. After firing, the cake was pulverized in a Glow Mill (MULTI MILL manufactured by Glow Engineering Co., Ltd.) to obtain a powdered composite oxide.

[0154] (5) Characterization of complex oxides The composite oxide obtained in (4) above was subjected to the same procedure as in Example 1 to obtain D 50 and D 90 The results are shown in Tables 1 and 2.

[0155] Furthermore, for the composite oxide obtained in (4) above, surface composition analysis by XPS and calculation of the degree of deviation of the surface composition from the bulk composition were carried out in the same manner as in Example 2. The results are shown in Tables 3 to 5.

[0156] Comparative Examples 2 to 4 4 kg of the composite oxide obtained in Comparative Example 1 was placed in a 100 L container, and 76 kg of ion-exchanged water was added and stirred to obtain a slurry with a composite oxide concentration of 5 mass %. The obtained slurry was transferred using a pump to a bead mill (Ultra Apex Mill UAM-1 manufactured by Hiroshima Metal & Machinery Co., Ltd.), and the process of wet pulverization using the bead mill was repeatedly carried out.

[0157] The conditions for grinding using a bead mill were as follows: Beads used: ZrO2 beads with a diameter of 0.1 mm Bead filling amount: 1.95kg Filling rate: 80% Mill rotation speed: 3200 rpm Number of passes through the bead mill: 1 to 4 Slurry supply rate: 0.89 L / min

[0158] The slurry was sampled after being treated with a bead mill once (Comparative Example 2), twice (Comparative Example 3), or four times (Comparative Example 4). The sampled slurry was filtered and washed with ion-exchanged water to obtain a pulverized composite oxide.

[0159] The crushed composite oxides obtained in Comparative Examples 2 to 4 were subjected to the same procedure as in Example 1. 50 and D 90 The results are shown in Tables 1 and 2.

[0160] Furthermore, for the pulverized composite oxides obtained in Comparative Examples 2 to 4, surface composition analysis by XPS and calculation of the degree of deviation of the surface composition from the bulk composition were carried out in the same manner as in Example 2. The results are shown in Tables 3 to 5.

[0161] [Table 1]

[0162] [Table 2]

[0163] [Table 3]

[0164] [Table 4]

[0165] [Table 5]

[0166] As shown in Table 1, in Examples 1 to 3, the composite oxides containing zirconium, cerium, and other rare earth metal elements (lanthanum, neodymium, and praseodymium) were used, and the D 50 and D 90 It was possible to obtain composite oxides with particle sizes of 0.5 μm or less and 1 μm or less, respectively.

[0167] As shown in Table 1, the composite oxides of Examples 1 to 3 were heat-treated in air at 1000°C for 3 hours, and then the specific surface area measured by the BET method was 20 m 2 / g or more.

[0168] As shown in Table 5, in the composite oxides of Examples 2 and 3, the degree of deviation of the surface composition from the bulk composition (the ratio of the mass % (surface composition) of other rare earth metal elements (lanthanum, neodymium, and praseodymium) measured by X-ray photoelectron spectroscopy in terms of oxides to the mass % (bulk composition) of other rare earth metal elements (lanthanum, neodymium, and praseodymium) measured by X-ray fluorescence analysis in terms of oxides) was 0.91 and 0.86, respectively. From these results, it can be seen that in Examples 2 and 3, the surface concentrations of other rare earth metal elements (lanthanum, neodymium, and praseodymium), which are presumed to contribute to improving the heat resistance of the composite oxide, are higher than the D of the composite oxide. 50 is higher than those of Comparative Examples 3 and 4, which are comparable to those of Examples 2 and 3.

Claims

1. A composite oxide containing zirconium, cerium, and other rare earth metal elements, D of the composite oxide measured by a laser diffraction scattering particle size distribution measurement method ５０ and D ９０ are 0.5 μm or less and 1 μm or less, respectively; The composite oxide, wherein the mass % of the other rare earth metal element on the surface of the composite oxide, calculated as an oxide thereof, is 0.80 times or more the mass % of the other rare earth metal element in the entire composite oxide, calculated as an oxide thereof, as measured by X-ray photoelectron spectroscopy.

2. After heat treatment in air at 1000°C for 3 hours, the specific surface area measured by the BET method is 20 m ２ The composite oxide according to claim 1, wherein the Mo content is 1 / g or more.

3. The following steps: (a) preparing a raw material liquid containing water, a zirconium salt, a cerium salt, and other rare earth metal salts; (b) adding a first precipitant selected from an aqueous solution containing sulfate ions and a compound capable of dissolving in water to generate sulfate ions to the raw material liquid to form a first precipitate containing elemental zirconium, thereby obtaining a first slurry containing the first precipitate; (c) subjecting the first slurry to a wet grinding treatment; (d) adding a second precipitant selected from an aqueous solution containing hydroxide ions and a compound capable of dissolving in water to generate hydroxide ions to the first slurry after the wet-pulverization treatment, thereby forming a second precipitate containing zirconium, cerium, and other rare earth metal elements, and obtaining a second slurry containing the second precipitate; (e) obtaining a cake from the second slurry; and (f) A step of calcining the cake to produce a composite oxide containing zirconium, cerium, and other rare earth metal elements. A method for producing a complex oxide, comprising:

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

5. In step (c), the D of the pulverized product of the first precipitate measured by a laser diffraction scattering particle size distribution measurement method ５０ The method according to claim 3 or 4, wherein the wet grinding treatment is carried out so that the particle size is 0.5 μm or more and 1.5 μm or less.

6. In step (c), the D of the pulverized product of the first precipitate measured by a laser diffraction scattering particle size distribution measurement method ９０ The method according to any one of claims 3 to 5, wherein the wet pulverization treatment is carried out so that the particle size is 1 µm or more and 2.5 µm or less.

7. The method according to any one of claims 3 to 6, wherein in step (c), the wet grinding treatment is carried out using beads.

8. The method according to claim 7 , wherein in step (c), the wet-grinding treatment is carried out so that the acceleration applied to the beads exceeds 1 G.

9. The method according to claim 7 or 8, wherein the beads have a diameter of 0.3 mm or less.

10. The method according to any one of claims 7 to 9, wherein in step (c), the wet grinding treatment is carried out for 1 hour or more.

11. 11. The production method according to claim 3, wherein in step (b), the first precipitate is added to the raw material solution so that a molar amount of sulfate ions in the raw material solution is 0.4 to 2 times a molar amount of zirconium element in the raw material solution.

12. The method according to any one of claims 3 to 11, wherein in the step (b), the temperature of the raw material liquid when the first precipitant is added is 70°C or higher and 100°C or lower.

13. 13. The method according to claim 3, wherein in the step (d), the second precipitating agent is added to the first slurry so that the molar amount of hydroxide ions in the first slurry is at least twice the molar amount of oxygen necessary to convert zirconium element, cerium element, and other rare earth metal elements in the first slurry into oxides.

14. The method according to any one of claims 3 to 13, wherein in the step (d), the temperature of the first slurry when the second precipitate is added is 35°C or higher and 60°C or lower.

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