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Definitions

• the present invention relates to a composite oxide containing cerium element and zirconium element (hereinafter sometimes referred to as “CeO 2 —ZrO 2 -based composite oxide”) and a method for producing the composite oxide.
• 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).
• HC hydrocarbons
• CO carbon monoxide
• NOx nitrogen oxides
• a three-way catalyst that oxidizes HC and CO and converts them to water and carbon dioxide and reduces NOx to nitrogen is used. in use.
• a material having an oxygen storage capacity is used as a constituent material of a three-way catalyst (OSC material).
• OSC material for example, a CeO 2 —ZrO 2 -based composite oxide is used.
• Patent Document 1 describes a method for producing a CeO 2 —ZrO 2 based composite oxide.
• Patent Document 1 after cerium chloride, zirconium oxychloride, praseodymium chloride and water are mixed, ammonium peroxodisulfate is added to obtain a slurry containing a sulfate, and aqueous ammonia is added to the obtained slurry to obtain a hydroxide.
• the resulting slurry is filtered and washed to obtain a cake, and the obtained cake is calcined to produce a CeO 2 —ZrO 2 -based composite oxide.
• Exhaust gas contains particulate matter (PM) along with harmful components such as HC, CO, and NOx, and is known to cause air pollution.
• PM particulate matter
• the direct injection engine (GDI: Gasoline Direct Injection engine), which is used in vehicles equipped with gasoline engines, has low fuel consumption and high output, but compared to conventional port injection engines, PM emissions in the exhaust gas are is known to be large.
• GDI Gasoline Direct Injection engine
• PM emissions in the exhaust gas are known to be large.
• vehicles equipped with gasoline engines such as GDI are also required to install a filter (GPF: Gasoline Particulate Filter) having a PM collection function, like vehicles equipped with diesel engines.
• GPF Gasoline Particulate Filter
• the wall-flow type substrate includes inflow-side cells extending in the exhaust gas flow direction, outflow-side cells extending in the exhaust gas flow direction, and porous partition walls separating the inflow-side cells and the outflow-side cells.
• the inflow-side cell the end on the exhaust gas inflow side in the exhaust gas flow direction is open, and the end on the exhaust gas outflow side in the exhaust gas flow direction is closed.
• the outflow-side cell the end on the exhaust gas inflow side in the exhaust gas flow direction is closed, and the end on the exhaust gas outflow side in the exhaust gas flow direction is open.
• Exhaust gas that has flowed into the wall-flow substrate from the end (opening) of the inflow-side cell on the exhaust gas inflow side passes through the porous partition wall and flows through the end (opening) of the outflow-side cell on the exhaust gas outflow side. flow out from When the exhaust gas passes through the porous partition wall, PM in the exhaust gas is trapped in the pores of the partition wall.
• the mounting space for catalysts for purifying exhaust gas is limited, so precious metal catalysts such as Pt, Pd, and Rh are supported on GPF to trap PM and purify harmful components such as HC, CO, and NOx. are being considered to do so.
• Patent Literature 2 describes forming a catalyst layer within porous partition walls in a wall flow type substrate.
• a slurry containing Pd-supported alumina powder, Rh-supported zirconia-lanthanum-modified alumina powder, and CeO 2 —ZrO 2 -based composite oxide powder is pulverized with a ball mill to obtain a slurry having a D 90 of 3.0 ⁇ m.
• the porous partition walls are impregnated with the obtained slurry to form a catalyst layer.
• the CeO 2 —ZrO 2 -based composite oxide In order to impregnate the porous partition walls with the CeO 2 —ZrO 2 -based composite oxide, the CeO 2 —ZrO 2 -based composite oxide must be finely divided. This is because impregnation of the CeO 2 —ZrO 2 -based composite oxide, which is insufficiently atomized, into the porous partition walls clogs the pores of the porous partition walls, increasing the pressure loss.
• an object of the present invention is to provide sufficiently finely divided CeO 2 —ZrO 2 -based composite oxide and a method for producing the CeO 2 —ZrO 2 -based composite oxide.
• the present invention provides a composite oxide containing zirconium element, cerium element, and optionally other rare earth metal elements, which is measured by a laser diffraction scattering particle size distribution measurement method.
• the composite oxide is provided, wherein D50 and D90 of the composite oxide are 0.5 ⁇ m or less and 1 ⁇ m or less, respectively.
• the present invention also provides the following steps: (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 generating sulfate ions by dissolving in water to the raw material solution to form a first precipitate containing elemental zirconium; obtaining a first slurry comprising said first precipitate; (c) subjecting the first slurry to a wet pulverization process; (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-grinding treatment; forming a second precipitate containing elemental zirconium, elemental cerium and optionally other rare earth metal elements to obtain a second slurry containing said second precipitate; (e
• a sufficiently finely divided CeO 2 —ZrO 2 -based composite oxide and a method for producing the CeO 2 —ZrO 2 -based composite oxide are provided.
• other rare earth metal elements refer to rare earth metal elements other than cerium elements
• other rare earth metal ions refer to rare earth metal ions other than cerium ions
• other rare earth metal salts means rare earth metal salts other than cerium salts
• “Other water-soluble rare earth metal salts” mean water-soluble rare earth metal salts other than water-soluble cerium salts.
• the composite oxide of the present invention contains zirconium element, cerium element, and optionally other rare earth metal elements.
• the zirconium oxide (ZrO 2 ) equivalent amount of the zirconium element contained in the composite oxide of the present invention is preferably 20 mass based on the mass of the composite oxide of the present invention from the viewpoint of improving the heat resistance of the composite oxide. % or more and 90 mass % or less, more preferably 30 mass % or more and 80 mass % or less, and even more preferably 40 mass % or more and 70 mass % or less.
• the amount of cerium element contained in the composite oxide of the present invention in terms of cerium oxide (CeO 2 ) is preferably 5 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. % 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.
• the ratio (mass ratio) of the zirconium oxide equivalent amount of the zirconium element to the cerium oxide equivalent amount of the cerium element is preferably 0.5 or more and 8 or less from the viewpoint of balancing the oxygen storage capacity and heat resistance in the composite oxide. , more preferably 1 or more and 7 or less, and still more preferably 1.1 or more and 5 or less.
• the composite oxide of the present invention preferably contains one, two, or three or more other rare earth metal elements.
• Other rare earth metal elements include, for example, yttrium element, praseodymium element, scandium element, lanthanum element, neodymium element, samarium element, europium element, gadolinium element, terbium element, dysprosium element, holmium element, erbium element, thulium element, ytterbium element , lutetium, etc., preferably 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.
• the amount of other rare earth metal elements contained in the composite oxide of the present invention in terms of oxide is preferably 5% by mass or more and 35% by mass or less, more preferably 7% by mass, based on the mass of the composite oxide of the present invention. % or more and 30 mass % or less, more preferably 10 mass % or more and 25 mass % or less.
• rare earth metal elements are sesquioxides (Ln 2 O 3 , Ln represents a rare earth metal element) except praseodymium element and terbium element, and praseodymium oxide is usually Pr 6 O 11 .
• terbium oxide is usually Tb4O7 .
• the lanthanum oxide (La 2 O 3 ) equivalent amount of the lanthanum element contained in the composite oxide of the present invention is from the viewpoint of improving the heat resistance of the composite oxide.
• the mass of the composite oxide of the invention 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, still more preferably 1% by mass or more and 20% by mass or less is.
• the neodymium oxide (Nd 2 O 3 ) equivalent amount of the neodymium element contained in the composite oxide of the present invention is the present invention from the viewpoint of improving the heat resistance of the composite oxide.
• the mass of the composite oxide of the invention 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, still more preferably 1% by mass or more and 20% by mass or less is.
• the praseodymium oxide (Pr 6 O 11 ) conversion amount of the praseodymium element contained in the composite oxide of the present invention is the present invention from the viewpoint of improving the heat resistance of the composite oxide.
• the mass of the composite oxide of the invention 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, still more preferably 1% by mass or more and 20% by mass or less is.
• cerium oxide and zirconium oxide may each form a single phase (cerium oxide single phase or zirconium oxide single phase) in addition to the solid solution phase.
• other rare earth metal elements or oxides thereof may form a solid solution phase together with cerium oxide and/or zirconium oxide, or may form a single phase.
• the bulk composition of the composite oxide of the present invention (mass% of each metal element in terms of oxide in the entire composite oxide of the present invention) can be analyzed by fluorescent X-ray analysis.
• Bulk composition analysis by fluorescent X-ray analysis is preferably performed according to the conditions described in Examples.
• the composite oxide of the present invention is preferably powdery.
• the D 50 of the composite oxide of the present invention indicates that when the composite oxide is impregnated into the porous partition walls of the wall flow type substrate, the pores of the porous partition walls are clogged and the pressure loss caused thereby increases.
• the lower limit is preferably 0.05 ⁇ m, more preferably 0.1 ⁇ m.
• the D 90 of the composite oxide of the present invention indicates that when the composite oxide is impregnated into the porous partition walls of the wall flow type substrate, the pores of the porous partition walls are clogged and the pressure loss caused thereby increases.
• the lower limit is preferably 0.2 ⁇ m, more preferably 0.3 ⁇ m.
• the D 50 and D 90 of the composite oxide of the present invention are, respectively, the cumulative volume of 50% and 90% in the volume-based particle size distribution of the composite oxide of the present invention obtained by the laser diffraction scattering particle size distribution measurement method. is the particle size.
• the laser diffraction scattering particle size distribution measurement method is preferably performed according to the conditions described in Examples.
• the composite oxide of the present invention can maintain its specific surface area even when exposed to high-temperature exhaust gas.
• the surface area is preferably 20 m 2 /g or greater, more preferably 22 m 2 /g or greater, and even more preferably 25 m 2 /g or greater.
• the upper limit is preferably 90 m 2 /g, more preferably 80 m 2 /g.
• Measurement of the specific surface area by the BET method is preferably carried out according to the conditions described in the Examples.
• the composite oxide of the present invention improves the heat resistance of the composite oxide and maintains the specific surface area of the composite oxide even when exposed to high-temperature exhaust gas. It is preferable that the mass % of the other rare earth metal element in terms of oxide on the surface of the oxide is larger than the mass % of the other rare earth metal element in terms of oxide in the entire composite oxide of the present invention. That is, it is preferable that the oxides of other rare earth metal elements are abundantly present on the surface of the composite oxide of the present invention. Other rare earth metal elements present on the surface of the composite oxide improve the heat resistance of the composite oxide by suppressing the growth of CeO2 crystals that occur when the composite oxide is exposed to high-temperature exhaust gas.
• the specific surface area of the oxide can be maintained.
• Other rare earth metal elements present on the surface of the composite oxide are thought to act as barriers to CeO2 crystal growth and suppress CeO2 crystal growth. This effect is considered to be greater for elements with larger ionic radii, such as lanthanum elements.
• the composite oxide of the present invention improves the heat resistance of the composite oxide and maintains the specific surface area of the composite oxide even when exposed to high-temperature exhaust gas.
• the mass% of the other rare earth metal element in terms of oxide on the surface of the oxide is 0.80 times or more the mass% of the other rare earth metal element in terms of oxide in the entire composite oxide of the present invention. It is 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.
• the mass% of other rare earth metal elements in terms of oxides on the surface of the composite oxide of the present invention can be measured by X-ray photoelectron spectroscopy. X-ray photoelectron spectroscopy is preferably performed according to the conditions described in Examples.
• the mass% of other rare earth metal elements in terms of oxides on the surface of the composite oxide of the present invention is based on the total mass of metal elements in terms of oxides on the surface of the composite oxide of the present invention ( is 100% by mass in terms of metal elements on the surface of the composite oxide). Further, when the composite oxide of the present invention contains two or more kinds of other rare earth metal elements, the mass% of the other rare earth metal elements in terms of oxide is the two or more kinds of other rare earth metal elements in terms of oxide is the sum of mass % of
• the mass% of other rare earth metal elements in terms of oxides in the entire composite oxide of the present invention can be measured by fluorescent X-ray analysis.
• the fluorescent X-ray analysis method is preferably performed according to the conditions described in Examples.
• the mass% of other rare earth metal elements in terms of oxides in the entire composite oxide of the present invention is based on the total mass of metal elements in terms of oxides in the entire composite oxide of the present invention ( is 100% by mass in terms of the metal elements in the entire composite oxide).
• the mass% of the other rare earth metal elements in terms of oxide is the two or more kinds of other rare earth metal elements in terms of oxide is the sum of mass % of
• the composite oxide of the present invention can be used as a component of an exhaust gas purification catalyst.
• the exhaust gas purifying catalyst contains 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 the noble metal element of the present invention contained in the exhaust gas purifying catalyst can be appropriately adjusted.
• the noble metal element can be selected from, for example, palladium element, platinum element, rhodium element, and the like.
• 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, for example, in the form of a noble metal, an alloy containing a noble metal element, a compound containing a noble metal element (e.g., an oxide of a noble metal element), or the like.
• the catalytically active component is preferably particulate from the viewpoint of improving exhaust gas purification performance.
• the exhaust gas purifying catalyst may contain a carrier component for supporting the noble metal element.
• the carrier component is preferably a porous body.
• the carrier component can be selected from, for example, alumina, silica, silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia, alumina-ceria, and the like.
• the exhaust gas purification catalyst may contain other components such as stabilizers and binders.
• “Supported” means a state in which the noble metal element is physically or chemically adsorbed or retained on the outer surface or inner surface of pores of the composite oxide of the present invention.
• the fact that the noble metal element is supported on the composite oxide of the present invention can be confirmed, for example, by elemental mapping obtained by analyzing the cross section of the exhaust gas purification catalyst with an EDS (energy dispersive spectrometer). It can be confirmed by the presence of the substance and the noble metal element in the same region.
• the exhaust gas purifying catalyst is a molded body having a shape such as a pellet.
• the exhaust gas purifying catalyst according to this embodiment can be produced, for example, by drying and calcining the exhaust gas purifying catalyst composition. The drying temperature, drying time, baking temperature and baking time can be adjusted as appropriate. Firing can be performed, for example, in an air atmosphere.
• an exhaust gas purifying catalyst comprises a substrate and a catalyst layer formed on the substrate, the catalyst layer comprising the composite oxide of the present invention and supported on the composite oxide of the present invention. and one or more noble metal elements.
• the substrate can be appropriately selected from substrates used in known exhaust gas purification catalysts.
• the material of the substrate is, for example, alumina (Al 2 O 3 ), mullite (3Al 2 O 3 -2SiO 2 ), cordierite (2MgO-2Al 2 O 3 -5SiO 2 ), aluminum titanate (Al 2 TiO 5 ). , ceramics such as silicon carbide (SiC), metal materials such as stainless steel, and the like.
• the shape of the substrate can be selected from, for example, honeycomb, pellet, spherical, and the like.
• the base material is preferably a wall-flow type base material.
• the wall-flow type substrate includes inflow-side cells extending in the exhaust gas flow direction, outflow-side cells extending in the exhaust gas flow direction, and porous partition walls separating the inflow-side cells and the outflow-side cells.
• the inflow-side cell the end on the exhaust gas inflow side in the exhaust gas flow direction is open, and the end on the exhaust gas outflow side in the exhaust gas flow direction is closed.
• the outflow-side cell the end on the exhaust gas inflow side in the exhaust gas flow direction is closed, and the end on the exhaust gas outflow side in the exhaust gas flow direction is open.
• Exhaust gas that has flowed into the wall-flow substrate from the end (opening) of the inflow-side cell on the exhaust gas inflow side passes through the porous partition wall and flows through the end (opening) of the outflow-side cell on the exhaust gas outflow side. flow out from When the exhaust gas passes through the porous partition wall, PM in the exhaust gas is trapped in the pores of the partition wall.
• the catalyst layer is preferably formed within the porous partition walls of the wall-flow type base material from the viewpoint of suppressing an increase in pressure loss.
• the catalyst layer can be formed by applying the exhaust gas purifying catalyst composition to the base material, drying it, and firing it.
• the drying temperature, drying time, baking temperature and baking time can be adjusted as appropriate. Firing can be performed, for example, in an air atmosphere.
• the exhaust gas purifying catalyst composition used for manufacturing the exhaust gas purifying catalyst is, for example, a slurry containing the composite oxide of the present invention and a salt of a noble metal element.
• Salts of noble metal elements can be selected from, for example, nitrates, ammine complex salts, chlorides, and the like.
• the solvent contained in the dispersion can be selected from, for example, water, organic solvents, and the like.
• the composite oxide of the present invention can be produced by a method including steps (a) to (f). Steps (a) to (f) will be described below.
• 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.
• the water contained in the raw material liquid is preferably pure water such as ion-exchanged water.
• the raw material liquid may contain a solvent other than water.
• Solvents other than water can be selected from organic solvents such as alcohol, acetone, dimethylsulfoxide, and dimethylformamide.
• the amount of the 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 it is usually 20 vol% or less based on the volume of the raw material solution. , preferably 10 vol % or less.
• the zirconium salts, cerium salts and other rare earth metal salts contained in the raw material solution are all water-soluble salts.
• the present invention also includes an embodiment in which the raw material liquid prepared in step (a) does not contain other rare earth metal salts, and the raw material liquid prepared in step (a) does not contain other rare earth metal salts.
• "the zirconium salt, the cerium salt and the other rare earth metal salt are all water-soluble salts” means that both the cerium salt and the zirconium salt are water-soluble salts.
• 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.
• the solubility of the poorly water-soluble salt in water at 20°C is preferably less than 1.0 g, more preferably 0.5 g or less, and even more preferably is 0.1 g or less.
• the water-soluble zirconium salt can be selected from, for example, zirconium oxychloride, zirconium chloride, zirconium oxynitrate, zirconium nitrate, zirconium oxyacetate, etc., and prevents deterioration of the heat resistance of the composite oxide due to contamination with nitrate radicals.
• Zirconium oxychloride or zirconium chloride is preferred, and zirconium oxychloride is more preferred, from the viewpoint of compatibility and availability.
• the raw material liquid may contain two or more water-soluble zirconium salts. The amount of the water-soluble zirconium salt contained in the raw material liquid is appropriately adjusted so that the zirconium oxide-equivalent amount of the zirconium element contained in the composite oxide produced in step (f) falls within a desired range.
• the water-soluble cerium salt can be selected from, for example, cerium chloride, cerium nitrate, cerium (III) sulfate, cerium acetate, etc., from the viewpoint of preventing deterioration of the heat resistance of the composite oxide due to contamination with nitrate radicals and the like.
• Cerium chloride is preferred from the viewpoint of easy availability.
• the raw material liquid may contain two or more water-soluble cerium salts. The amount of the water-soluble cerium salt contained in the raw material solution is appropriately adjusted so that the cerium oxide-equivalent amount of the cerium element contained in the composite oxide produced in step (f) is within the desired range.
• 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 the cerium element. Chlorides of rare earth metal elements other than cerium (for example, lanthanum chloride, neodymium chloride, praseodymium chloride, etc.) are preferred from the viewpoint of preventing a decrease in the content and being readily available.
• the rare earth metal sulfate is preferably a trivalent rare earth metal sulfate.
• the raw material liquid may contain two or three or more other water-soluble rare earth metal salts. The type and amount of the other water-soluble rare earth metal salt contained in the raw material solution are such that the oxide conversion amount of the other rare earth metal element contained in the composite oxide produced in step (f) is within the desired range. is adjusted accordingly.
• step (b) In the step (b), a first precipitant selected from an aqueous solution containing sulfate ions and a compound that can be dissolved in water to generate sulfate ions is added to the raw material liquid prepared in the step (a), and zirconium element and obtaining a first slurry containing the first precipitate.
• the raw material liquid contains metal ions (zirconium ions, cerium ions, and possibly other rare earth metal ions) generated by the ionization of water-soluble salts.
• the first precipitant added to the raw material solution is a precipitant that precipitates zirconium ions as basic zirconium sulfate, and is selected from an aqueous solution containing sulfate ions and a compound that can be dissolved in water to generate sulfate ions.
• Compounds that can be dissolved 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, and the like.
• alkali metal sulfates e.g., sodium sulfate, potassium sulfate, etc.
• cerium (III) sulfate e.g., rare earth metal sulfates, and the like.
• ammonium sulfate, sulfuric acid or alkali Metal sulfates are 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 be dissolved in water to generate sulfate ions in water (for example, pure water such as ion-exchanged water).
• a first precipitate containing elemental zirconium is formed, and a first slurry containing the first precipitate is obtained.
• Elemental zirconium is contained in the first precipitate in the form of basic zirconium sulfate.
• Basic zirconium sulfate is a sparingly water soluble zirconium salt formed by the first precipitant.
• the temperature of the raw material liquid when adding the first precipitant is preferably 70° C. or higher and 100° C. or lower, more preferably 70° C. or higher and 100° C. or lower. is 80° C. or higher and 100° C. or lower, more preferably 85° C. or higher and 100° C. or lower.
• the molar amount of sulfate ions in the raw material solution is It is preferable to add the first precipitant to the raw material solution such that the molar amount of the zirconium element in the raw material solution is 0.4 times or more and 2 times or less.
• the molar amount of sulfate ions in the raw material solution is more preferably 0.45 to 2 times, more preferably 0.5 to 1.5 times, the molar amount of zirconium element in the raw material solution. Even more preferred.
• the first precipitant into the raw material liquid while stirring the raw material liquid.
• the aging 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.
• Step (c) is a step of subjecting the first slurry obtained in step (b) to wet pulverization.
• the first precipitate contained in the first slurry is pulverized to obtain a pulverized first precipitate.
• the wet pulverization treatment is performed so that the pulverized product of the first precipitate has a D50 of 0.5 ⁇ m or more.
• 0.5 ⁇ m or less is preferable.
• the D50 of the pulverized material of the first precipitate is more preferably 0.5 ⁇ m or more and 1.3 ⁇ m or less, and even more preferably 0.5 ⁇ m or more and 1.2 ⁇ m or less.
• the D50 of the first precipitate before wet pulverization is usually 10 ⁇ m or more and 40 ⁇ m or less, preferably 10 ⁇ m or more and 30 ⁇ m or less.
• the pulverized material of the first precipitate relative to the D 50 of the first precipitate before the wet pulverization treatment 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.
• the wet pulverization treatment is performed so that the pulverized product of the first precipitate has a D90 of 1 ⁇ m or more and 2.5 ⁇ m. It is preferable to do so as follows. More preferably, the D90 of the pulverized material of the first precipitate is 1 ⁇ m or more and 2.3 ⁇ m or less, and even more preferably 1 ⁇ m or more and 2 ⁇ m or less.
• the D90 of the first precipitate before wet pulverization is usually 10 ⁇ m or more and 100 ⁇ m or less, preferably 20 ⁇ m or more and 50 ⁇ m or less.
• the pulverized material of the first precipitate with respect to the D 90 of the first precipitate before the wet pulverization treatment 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.
• the D 50 and D 90 of the pulverized first precipitate are respectively the cumulative volume of 50% in the volume-based particle size distribution of the pulverized first precipitate obtained by the laser diffraction scattering particle size distribution measurement method. and 90%.
• the laser diffraction scattering particle size distribution measurement method is preferably performed according to the conditions described in Examples. The same is true for the D 50 and D 90 of the first precipitate before wet milling.
• the wet pulverization treatment is preferably carried out using beads.
• the diameter of the beads is usually 0.015 mm or more and 2.0 mm or less.
• 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.
• the wet pulverization treatment is preferably performed so that the acceleration applied to the beads exceeds 1G.
• the acceleration applied to the beads is usually 2 G or more and 1000 G or less, preferably 40 G or more and 1000 G or less. Desired acceleration can be applied to the beads, for example, by centrifugal force generated by high-speed rotation of a paint shaker, which is a dispersing machine for paint.
• the wet pulverization treatment using beads is preferably performed for 0.5 hours or longer, and may be performed for 1 hour or longer. More preferred.
• the upper limit is preferably 10 hours, more preferably 5 hours.
• the first slurry obtained in step (b) may be used as it is for wet pulverization, or the first slurry obtained in step (b) may be diluted and then wet pulverized. It may be used for processing. Dilution can be performed using a solvent such as water (eg, pure water such as ion-exchanged water) or a solvent other than water (eg, organic solvent). Specific examples of the organic solvent are the same as those described above.
• a solvent such as water (eg, pure water such as ion-exchanged water) or a solvent other than water (eg, organic solvent). Specific examples of the organic solvent are the same as those described above.
• Step (d) includes 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-grinding treatment. forming a second precipitate containing elemental zirconium, elemental cerium and optionally other rare earth metal elements to obtain a second slurry containing the second precipitate.
• a second precipitant is added to the wet-milled first slurry to form a second precipitate comprising elemental zirconium, elemental cerium, and optionally other rare earth metal elements, and forming a second precipitate.
• a second slurry is obtained containing the material.
• the pH of the second slurry is usually 9 or more and 14 or less, preferably 11 or more and 14 or less.
• the zirconium element is contained in the second precipitate in the form of zirconium hydroxide.
• Zirconium hydroxide is a sparingly water soluble zirconium salt formed by the second precipitant. Note that the basic zirconium sulfate formed by the first precipitant is converted to zirconium hydroxide by the second precipitant.
• cerium element is contained in the second precipitate in the form of cerium hydroxide.
• Cerium hydroxide is a sparingly water soluble cerium salt formed by the second precipitant.
• rare earth metal elements e.g., lanthanum element, neodymium element, praseodymium element, etc.
• hydroxides e.g., lanthanum hydroxide, neodymium hydroxide, praseodymium hydroxide, etc.
• Hydroxides of other rare earth metal elements are sparingly water-soluble rare earth metal salts formed by the second precipitant.
• Other rare earth metal hydroxides formed by the second precipitant co-precipitate with the cerium hydroxide formed by the second precipitant.
• the second precipitate contains composite salt particles containing zirconium hydroxide, cerium hydroxide, and optionally other hydroxides of rare earth metal elements.
• the second precipitate may contain, in addition to the composite salt particles, zirconium hydroxide particles, cerium hydroxide particles, hydroxide particles of other rare earth metal elements, and the like.
• the composite salt particles are deposited, for example, on the surface of basic zirconium sulfate formed by a first precipitant (the basic zirconium sulfate is converted to zirconium hydroxide by a second precipitant) and subjected to a second precipitation. It is formed by deposition and growth of cerium hydroxide and/or hydroxides of other rare earth metal elements formed by the agent.
• the temperature of the first slurry when adding the second precipitant 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.
• the molar amount of hydroxide ions in the first slurry is the same as the zirconium element, cerium hydroxide, and cerium hydroxide in the first slurry.
• the second precipitant is added to the first slurry in amounts greater than or equal to twice the molar amount of elemental oxygen required to oxidize the element and other rare earth metal elements.
• the molar amount of hydroxide ions in the first slurry is at least twice the molar amount of oxygen element required to convert zirconium element, cerium element and other rare earth metal elements in the first slurry into oxides. It is more preferably 10 times or less, even more preferably 2 times or more and 5 times or less, and even more preferably 2 times or more and 3 times or less.
• the molar amount of oxygen element necessary to convert the zirconium element, cerium element and other rare earth metal elements in the first slurry into oxides is [(molar amount of zirconium element) x 2] + [(cerium element molar amount) ⁇ 2] + [(molar amount of rare earth metal elements other than cerium element, praseodymium element, and terbium element) ⁇ 3/2] + [(molar amount of praseodymium element) ⁇ 11/6] + [(terbium element (molar amount) ⁇ 7/4].
• Step (e) is a step of obtaining a cake from the second slurry.
• a cake can be obtained by subjecting the second slurry to a solid-liquid separation method.
• the solid-liquid separation method include filtration, centrifugation, decantation, etc. Among these, filtration is preferred.
• the solvent is removed by the solid-liquid separation method to obtain a cake, but since the solvent is not completely removed, the solvent remains in the cake.
• 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. Thereby, aggregation of the second precipitate contained in the cake can be suppressed, and the desired D50 and D90 can be effectively achieved in the composite oxide produced in step (f).
• the first cake can be obtained by subjecting the second slurry to a solid-liquid separation method.
• a description of the solid-liquid separation method is given above.
• the first cake may be washed with a washing liquid before treating the first cake with the alcohol-containing liquid.
• a washing liquid it is preferable to use water (for example, pure water such as ion-exchanged water). By washing the first cake with the washing liquid, part or all of the solvent in the first cake is replaced with the washing liquid.
• the alcohol-containing liquid contains one or more alcohols.
• alcohols 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.
• 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.
• the alcohol-containing liquid contains one alcohol
• the one alcohol is preferably ethyl alcohol.
• the two or more alcohols are ethyl alcohol. Alcohol and one or more other alcohols are preferred.
• the alcohol concentration of the alcohol-containing liquid is appropriately adjusted according to the alcohol concentration of the second cake to be achieved.
• 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 the alcohol concentration of the second cake to be achieved, or may exceed the alcohol concentration of the second cake to be achieved.
• the upper limit of the alcohol concentration of the alcohol-containing liquid is not particularly limited. When the alcohol-containing liquid contains two or more alcohols, the alcohol concentration of the alcohol-containing liquid is the total concentration of the two or more alcohols.
• the ethyl alcohol concentration is preferably 51 vol% or higher, more preferably 65 vol% or higher, and even more preferably 90 vol% or higher, based on the volume of the alcohol-containing liquid.
• the upper limit of the ethyl alcohol concentration is not particularly limited, it is usually 100 vol %.
• the alcohol-containing liquid may contain one or more components other than alcohol.
• 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.) etc.), esters (methyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethy
• the alcohol-containing liquid for example, commercially available denatured alcohol (industrial alcohol) can be used as it is or diluted with water such as ion-exchanged water.
• the first cake is treated with the alcohol-containing liquid by contacting the first cake with the alcohol-containing liquid, and replacing the liquid in the first cake (for example, the solvent of the raw material liquid, the washing liquid, etc.) with the alcohol-containing liquid. It is not particularly limited as long as it is possible, and examples thereof include a method of immersing the first cake in the alcohol-containing liquid, a method of mixing the first cake and the alcohol-containing liquid, and the like.
• the second cake is prepared after contacting the first cake with the alcohol-containing liquid (for example, after immersing the first cake in the alcohol-containing liquid, or after mixing the first cake and the alcohol-containing liquid after), obtained by solid-liquid separation. Examples of the solid-liquid separation method include filtration, centrifugation, decantation, etc.
• centrifugation is preferred.
• the alcohol-containing liquid is removed by the solid-liquid separation method to obtain a second cake, but since the alcohol-containing liquid is not completely removed, the alcohol-containing liquid remains in the second cake.
• the alcohol concentration of the second cake approaches and eventually matches 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 achieved, the treatment of the first cake with the alcohol-containing liquid is such that the alcohol concentration of the second cake is that of the alcohol-containing liquid. Repeat until the alcohol concentration matches. On the other hand, if the alcohol concentration of the alcohol-containing liquid exceeds the alcohol concentration of the second cake to be achieved, the treatment of the first cake with the alcohol-containing liquid is such that the alcohol concentration of the second cake reaches the target alcohol concentration. is repeated until
• the alcohol concentration of the second cake is preferably 90 vol% or more, more preferably 95 vol% or more, Even more preferably, it is 99 vol % or more.
• the upper limit is 100vol%.
• 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 contacting the first cake with the alcohol-containing liquid (for example, after immersing the first cake in the alcohol-containing liquid, or after mixing the first cake and the alcohol-containing liquid), The alcohol concentration of the filtrate, supernatant or wastewater obtained by the liquid separation is measured, and the measured alcohol concentration of the filtrate, supernatant or wastewater is taken as the alcohol concentration of the second cake.
• the alcohol concentration can be measured according to a standard method. For example, a conversion table between the alcohol concentration of the alcohol-containing liquid and the specific gravity of the alcohol-containing liquid is prepared in advance, the specific gravity of the alcohol-containing liquid is measured, and the alcohol concentration of the alcohol-containing liquid is calculated based on the measured specific gravity. can be calculated.
• the specific gravity of the alcohol-containing liquid can be measured, for example, with a hydrometer.
• the temperature of the alcohol-containing liquid when measuring the specific gravity is, for example, 15°C.
• JIS B 7548: 2009 (sake accuracy floating hail) Annex A (regulation) "International alcohol table" can be referred to.
• drying can be carried out according to a conventional method.
• the drying temperature is generally 60° C. or higher and 200° C. or lower, preferably 80° C. or higher and 130° C. or lower, and the drying time is generally 1 hour or longer and 24 hours or shorter, preferably 2 hours or longer and 12 hours or shorter.
• Step (f) is a step of baking the cake obtained in step (e) to produce a composite oxide containing zirconium element, cerium element, and optionally other rare earth metal elements.
• step (e) when a first cake is obtained from the second slurry, the first cake is treated with an alcohol-containing liquid, and a second cake having an alcohol concentration of 90 vol% or more is obtained, step (f ), bake the second cake.
• Firing of the precipitate can be carried out according to the usual method. Firing is usually performed in an air atmosphere.
• the firing temperature is usually 600° C. or higher and 1100° C. or lower, preferably 600° C. or higher and 1000° C. or lower, more preferably 600° C. or higher and 950° C. or lower.
• the firing time is usually 2 hours or more and 20 hours or less, preferably 2 hours or more and 10 hours or less, more preferably 2 hours or more and 5 hours or less.
• step (c) the first precipitate (basic zirconium sulfate) is pulverized by wet pulverizing the first slurry.
• step (d) by adding a second precipitant to the first slurry after the wet-grinding treatment, the pulverized material of the first precipitate is used as a nucleus around which cerium hydroxide and optionally other Hydroxides of rare earth metal elements are precipitated (but the basic zirconium sulfate is converted to zirconium hydroxide by the second precipitant).
• the second precipitate thus obtained is well atomized. Therefore, in step (f), a composite oxide having desired D50 and D90 can be produced.
• 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 step (f) ), by baking the second cake, aggregation of the second precipitate contained in the cake can be suppressed, and the desired D 50 and D 90 in the composite oxide produced in step (f) can be effectively realized.
• the pulverized material of the first precipitate is used as a nucleus , around which cerium hydroxide and other rare earth metal hydroxides are precipitated (however, the 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 element in terms of oxide on the surface of the composite oxide is is larger than the mass % of That is, oxides of other rare earth metal elements are abundantly present on the surface of the composite oxide.
• rare earth metal elements present on the surface of the composite oxide improve the heat resistance of the composite oxide by suppressing the growth of CeO2 crystals that occur when the composite oxide is exposed to high-temperature exhaust gas. The specific surface area of the oxide can be maintained. Other rare earth metal elements present on the surface of the composite oxide are thought to act as barriers to CeO2 crystal growth and suppress CeO2 crystal growth. This effect is considered to be greater for elements with larger ionic radii, such as lanthanum elements.
• the composite oxide obtained in step (f) may be pulverized as necessary.
• the pulverization treatment can be performed dry or wet using, for example, a mortar, hammer mill, ball mill, bead mill, jet mill, roller mill, or the like.
• the composite oxide obtained in the step (f) is subjected to volume pulverization using a pulverizer having a “compression” or “impact” pulverization mechanism, generally the particle surface Instead, the particles may break apart into several chunks apart from the whole particle. Therefore, volume pulverization is not preferable as a fine pulverization treatment, and it becomes difficult to obtain the composite oxide of the present invention having D50 and D90 of 0.50 ⁇ m or less and 1.0 ⁇ m or less, respectively.
• Pulverizers having a "compression” or “impact” pulverization mechanism include, for example, hammer mills, pin mills, dry ball mills, and the like.
• step (f) when the composite oxide obtained in step (f) is subjected to surface pulverization using a pulverizer having a pulverization mechanism of “grinding” or “shearing”, the particles are frictionally subjected to compressive force or shear. A force is applied to form fines from the particle surface. For this reason, surface milling is generally suitable for the fine milling process and is preferred. For example, a bead mill, a force mill, and the like correspond to the pulverizer having a pulverization mechanism of "grinding".
• surface pulverization is performed with these pulverizers from the viewpoint that the D50 and D90 of the pulverized composite oxide are easier to control. preferably.
• D50 and D90 of the target powder are particle sizes at which the cumulative volume is 50% and 90 %, respectively, in the volume-based particle size distribution of the target powder obtained by laser diffraction scattering particle size distribution measurement.
• the target powder is dispersed in a 0.2% by mass sodium hexametaphosphate aqueous solution, ultrasonically treated (output: 30 W, processing time: 360 seconds), and then laser diffraction scattering particle size distribution measurement is performed.
• An apparatus Microtrac MT3000II manufactured by Microtrac Bell was used. 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, measurement range: 0.01 to 10,000 ⁇ m. .
• the specific surface area was measured according to "(3.5) One-point method" in “6.2 Flow method” of JIS R1626:1996 "Method for measuring specific surface area of fine ceramic powder by gas adsorption BET method”. Specifically, as the gas, a nitrogen-helium mixed gas containing 30% by volume of nitrogen as an adsorption gas and 70% by volume of helium as a carrier gas is used. Using a specific surface area meter Macsorb model-1201, it was measured by the BET one-point method.
• XPS analyzer PHI Quantes manufactured by ULVAC-Phi, Inc.
• Excitation X-ray monochromatic Al-K ⁇ ray (1486.7 eV)
• Output 50W
• Accelerating voltage 15 kV
• X-ray irradiation diameter 200 ⁇ m ⁇
• Measurement area 1000 ⁇ 300 ⁇ m 2
• Detection angle 15°
• Pass energy 26.0 eV
• Energy step 0.1 eV/step
• Measured elements/orbitals (semi-quantitative calculation elements): C 1s, O 1s, Zr 3d, La 3d5/2, Ce 3d, Pr 3d5/2, Nd 3d5/2
• the XPS data was analyzed using data analysis software (ULVAC-PHI Multipack Ver9.9). Iterated Berry was used as the background mode.
• cerium-zirconium composite oxide prepared by the following method was used as a reference sample in calculating the degree of deviation of the surface composition from the bulk composition.
• Cerium nitrate, zirconium oxynitrate, lanthanum nitrate, neodymium nitrate and praseodymium nitrate were dissolved in water to obtain 500 g of a raw material solution.
• cerium nitrate, zirconium oxynitrate, lanthanum nitrate, neodymium nitrate and praseodymium nitrate are the mass of cerium element converted to cerium oxide, the mass of zirconium element converted to zirconium oxide, the mass of lanthanum element converted to lanthanum oxide, and the oxidation of neodymium element. They were prepared so that the mass in terms of neodymium and the mass in terms of praseodymium oxide of the praseodymium element were 40% by mass, 50% by mass, 2% by mass, 4% by mass, and 4% by mass, respectively, based on the total mass.
• the temperature of 10% by mass ammonia water was raised to 40°C, and the raw material liquid was added dropwise while stirring.
• the raw material liquid was added dropwise until the pH of ammonia water fell below 9.5 to form a precipitate, which was filtered and washed by suction filtration to obtain a cake.
• the cake was air-dried, it was dried overnight at 90°C and baked in a muffle furnace. After sintering, the powder was pulverized to obtain a powdered composite oxide, which was used as a reference sample.
• the correction coefficient C1 for the XPS analysis value of cerium oxide converted to cerium element the correction coefficient C2 to the XPS analysis value of zirconium oxide converted to zirconium oxide, and the correction coefficient C3 to the XPS analysis value of lanthanum oxide converted to lanthanum element , a correction coefficient C4 for the XPS analysis value of the neodymium element converted to neodymium oxide, and a correction coefficient C5 for the XPS analysis value of the praseodymium element converted to neodymium oxide.
• Table 4 shows the correction factors.
• Correction coefficient C1 XRF analysis value of the cerium element in the reference sample converted to cerium oxide/XPS analysis value of the cerium element in the reference sample converted to cerium oxide
• Correction coefficient C2 XRF analysis value of the zirconium element in the reference sample converted to zirconium oxide/reference XPS analysis value of zirconium oxide conversion of zirconium element in sample
• Correction coefficient C3 XRF analysis value of lanthanum oxide conversion of lanthanum element in reference sample / XPS analysis value of lanthanum oxide conversion of lanthanum element in reference sample
• Correction coefficient C4 in reference sample XRF analysis value of neodymium oxide equivalent of neodymium element/XPS analysis value of neodymium oxide equivalent of neodymium element in reference sample
• Correction coefficient C5 XRF analysis value of praseodymium oxide equivalent of praseodymium oxide in reference sample/praseodymium oxide of praseodymium element in reference sample Converted XPS
• the value V1 obtained by multiplying the XPS measurement value of the cerium oxide equivalent of the cerium element by the correction factor C1 the value V1 obtained by multiplying the XPS analysis value of the zirconium element converted to the zirconium oxide equivalent by the correction factor C2.
• V2 value V3 obtained by multiplying the XPS analysis value of lanthanum oxide converted to lanthanum oxide by correction factor C3, value V4 obtained by multiplying the XPS analysis value of neodymium element converted to neodymium oxide by correction factor C4, and praseodymium element converted to neodymium oxide
• the value V5 is calculated by multiplying the XPS analysis value of by the correction coefficient C5, and based on the following formula, the correction value CV1 of the XPS analysis value of cerium oxide conversion of cerium element, the correction of the XPS analysis value of zirconium oxide conversion of zirconium element.
• Correction value CV1 value V1 x 100/(total value of values V1 to V5)
• Correction value CV2 value V2 ⁇ 100 / (total value of values V1 to V5)
• Correction value CV3 value V3 ⁇ 100 / (total value of values V1 to V5)
• Correction value CV4 value V4 ⁇ 100 / (total value of values V1 to V5)
• Correction value CV5 value V5 ⁇ 100 / (total value of values V1 to V5)
• 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 the surface concentration of the lanthanum element, the neodymium element, and the praseodymium element in each composite oxide. as an indicator of
• Example 1 (1) Preparation of 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. As water, ion-exchanged water was used (same below).
• the amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride are the mass of cerium element in terms of cerium oxide, the mass of zirconium element in terms of zirconium oxide, the mass of lanthanum in terms of lanthanum oxide, and the oxidation of neodymium element.
• the neodymium-equivalent mass and the praseodymium oxide-equivalent mass of the praseodymium element were adjusted to 40% by mass, 50% by mass, 2% by mass, 4% by mass, and 4% by mass, respectively, based on the total mass.
• the temperature of the raw material solution was raised to 85° C., and while stirring the raw material solution, a 25% by mass ammonium sulfate aqueous solution was added dropwise so that the molar amount of sulfate ions was 0.5 times the molar amount of zirconium element, and the precipitate was removed. formed to obtain a first slurry. After the dropwise addition was completed, the precipitate was aged at 85° C. while stirring the first slurry.
• the amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride are the mass of the cerium element in terms of cerium oxide, the mass of the zirconium element in terms of zirconium oxide, the mass of the lanthanum element in terms of lanthanum oxide, and the oxidation of the neodymium element.
• Example 2 As in Example 1, the composite oxide obtained in Example 2 was subjected to D50 and D90 measurements, specific surface area measurement, and bulk composition analysis by XRF. The results are shown in Tables 1-2.
• Example 2 The composite oxide obtained in Example 2 was subjected to surface composition analysis by XPS by the method described above. Table 3 shows the results.
• Table 3 “CeO 2 ”, “ZrO 2 ”, “La 2 O 3 ”, “Nd 2 O 3 ” and “Pr 6 O 11 ” are cerium element, zirconium element, lanthanum element, neodymium element and The XPS analysis value (semi-quantitative value) of the praseodymium element in terms of oxide is shown.
• the amounts of cerium chloride, zirconium oxychloride, lanthanum chloride, neodymium chloride, and praseodymium chloride are the mass of the cerium element in terms of cerium oxide, the mass of the zirconium element in terms of zirconium oxide, the mass of the lanthanum element in terms of lanthanum oxide, and the oxidation of the neodymium element.
• Example 2 As in Example 1, the composite oxide obtained in Example 3 was subjected to D50 and D90 measurements, specific surface area measurement, and bulk composition analysis by XRF. The results are shown in Tables 1-2.
• Example 3 In addition, regarding the composite oxide obtained in Example 3, in the same manner as in Example 2, the surface composition analysis by XPS and the degree of divergence of the surface composition from the bulk composition were calculated. The results are shown in Tables 3-5.
• the neodymium-equivalent mass and the praseodymium oxide-equivalent mass of the praseodymium element were adjusted to 40% by mass, 50% by mass, 2% by mass, 4% by mass, and 4% by mass, respectively, based on the total mass.
• the temperature of the raw material solution was raised to 85° C., and while stirring the raw material solution, a 25% by mass ammonium sulfate aqueous solution was added dropwise so that the molar amount of sulfate ions was 1.0 times the molar amount of zirconium element, and the precipitate was removed. formed to obtain a first slurry. After the dropwise addition was completed, the precipitate was aged at 85° C. while stirring the first slurry.
• Comparative Examples 2 to 4 4 kg of the composite oxide obtained in Comparative Example 1 was placed in a 100 L container, 76 kg of ion-exchanged water was added, and the mixture was stirred to obtain a slurry having a composite oxide concentration of 5% by mass. The resulting slurry was transferred to a bead mill (Ultra Apex Mill UAM-1 manufactured by Hiroshima Metal & Machinery Co., Ltd.) using a pump, and subjected to wet pulverization by the bead mill, which was repeated.
• a bead mill Ultra Apex Mill UAM-1 manufactured by Hiroshima Metal & Machinery Co., Ltd.
• the grinding conditions by the bead mill were as follows. Beads used: ZrO2 beads with a diameter of 0.1 mm Bead loading: 1.95 kg Filling rate: 80% Mill rotation speed: 3200 rpm Number of bead mill treatments (passes): 1 to 4 Slurry supply rate: 0.89 L/min
• Example 2 As in Example 1, the pulverized composite oxides obtained in Comparative Examples 2 to 4 were subjected to D 50 and D 90 measurement, specific surface area measurement, and bulk composition analysis by XRF. The results are shown in Tables 1-2.
• the composite oxides of Examples 1 to 3 had a specific surface area of 20 m 2 /g or more as measured by the BET method after heat treatment at 1000° C. for 3 hours in air.
• the degree of deviation of the surface composition from the bulk composition (other rare earth metal elements (lanthanum element, neodymium element and praseodymium element) measured by fluorescent X-ray analysis ) of other rare earth metal elements (lanthanum element, neodymium element and praseodymium element) measured by X-ray photoelectron spectroscopy (lanthanum element, neodymium element and praseodymium element) in terms of oxide mass% (surface composition) ratio) were 0.91 and 0.86, respectively.

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