US20080009410A1 - Cerium oxide-zirconium oxide-based mixed oxide and method for producing the same - Google Patents

Cerium oxide-zirconium oxide-based mixed oxide and method for producing the same Download PDF

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US20080009410A1
US20080009410A1 US11/819,557 US81955707A US2008009410A1 US 20080009410 A1 US20080009410 A1 US 20080009410A1 US 81955707 A US81955707 A US 81955707A US 2008009410 A1 US2008009410 A1 US 2008009410A1
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oxide
cerium
zirconium
salt
zirconium oxide
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Hiroshi Okamoto
Masatoshi Maruki
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Daiichi Kigenso Kagaku Kogyo Co Ltd
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Daiichi Kigenso Kagaku Kogyo Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G25/00—Compounds of zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/40—Mixed oxides
    • B01D2255/407—Zr-Ce mixed oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/908—O2-storage component incorporated in the catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/42—Platinum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B01J37/038—Precipitation; Co-precipitation to form slurries or suspensions, e.g. a washcoat
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to a cerium oxide-zirconium oxide-based mixed oxide and a production process thereof.
  • cerium oxide has an oxygen storage capacity (OSC), and is used as a co-catalyst or catalyst support of automotive three-way catalysts.
  • OSC oxygen storage capacity
  • the dispersibility thereof is extremely good in the case of loading with a precious metal, and particularly platinum. Namely, it is a known fact that the cerium oxide has the superior characteristic of being able to inhibit aggregation of platinum particles at high temperatures.
  • Japanese Examined Patent Publication No. H06-74145 describes a “composition mainly consisting of ceric oxide having a stabilized specific surface area, comprising ceric oxide and at least one type of additive at a ratio of 1 to 20% by weight, wherein the additive is an oxide of one or more types of other metal elements A selected from the group consisting of silicon, zirconium and thorium”.
  • Japanese Patent No. 3623517 describes a “composition composed of cerium oxide and zirconium oxide having an atomic ratio of cerium/zirconium of at least 1 and demonstrating a specific surface area of at least 35 m 2 /g after being calcined for 6 hours at 900° C. and an oxygen storage capacity of at least 1.5 ml/g O 2 at 400° C.”.
  • Japanese Patent Application Publication No. 2002-177781 describes an “exhaust gas purification catalyst comprising a mixed oxide (B) comprised of cerium oxide loaded onto a solid solution oxide (A) containing zirconium and cerium”.
  • this catalyst has a unique structure in which cerium oxide is loaded around a solid solution oxide (A) containing zirconium and cerium, and what is more, there are no descriptions whatsoever regarding the OSC and platinum dispersibility thereof.
  • Japanese Patent Application Publication No. 2005-314134 describes “metal oxide particles having a core portion containing a comparatively large amount of a ceria-zirconia solid solution and a shell portion containing a comparatively large amount of a second metal oxide”, and a “production process of metal oxide particles having a core portion containing a comparatively large amount of a ceria-zirconia solid solution and a shell portion containing a comparatively large amount of a second metal oxide that provides a sol containing colloidal particles of a ceria-zirconia solid solution and colloidal particles of a second metal oxide each having different isoelectric points, comprising making the pH of the sol closer to the isoelectric point of the colloidal particles of the ceria-zirconia solid solution than the isoelectric point of the colloidal particles of the second metal oxide, aggregating the colloidal particles of the ceria-zirconia solid solution, making the pH of the sol closer to the isoelectric point of the colloidal particles of the second metal oxide than
  • the shell portion and core portion are characterized by both being in the form of ceria-zirconia solid solutions, and the production process is extremely unique.
  • an object of the present invention is to provide a cerium oxide-zirconium oxide-based mixed oxide having superior platinum dispersibility and a suitable OSC, and a simple production process thereof.
  • the inventors of the present invention unexpectedly found that by adding a cerium salt and a zirconium salt to a slurry containing a cerous sulfate-alkali metal mixed salt, adding an alkali thereto to obtain a mixed hydroxide containing cerium hydroxide and zirconium hydroxide, followed by subjecting this to heat treatment to obtain a mixed oxide comprising cerium oxide and tetragonal or cubic zirconium oxide as a mixture, the zirconium oxide is composed of a solid solution containing cerium, a cerium oxide-zirconium oxide-based mixed oxide is obtained having superior platinum dispersibility and a suitable OSC.
  • the present invention provides the following on the basis of this finding.
  • a cerium oxide-zirconium oxide-based mixed oxide comprising cerium oxide and zirconium oxide, wherein (1) the weight ratio of CeO 2 :ZrO 2 is 60:40 to 90:10, and (2) the cerium oxide and the zirconium oxide are present as a mixture, the zirconium oxide being composed of a solid solution in which tetragonal or cubic zirconium oxide contains cerium.
  • cerium oxide-zirconium oxide-based mixed oxide according to above 1, wherein the ratio of the cerium oxide as calculated from the X-ray diffraction peak intensity after heat treatment for 3 hours at 1000° C. in air is 50% by volume or more.
  • cerium oxide-zirconium oxide-based mixed oxide according to above 1 or 2, wherein the mixed oxide contains 1 to 20 wt % of one type or two or more types of oxides selected from rare earth elements excluding cerium, transition metal elements, aluminum and silicon.
  • a method for producing a cerium oxide-zirconium oxide-based mixed oxide comprising: a first step of adding a sulfating agent to a cerous salt to obtain a slurry containing a cerous sulfate-alkali metal mixed salt; a second step of adding a cerium salt and a zirconium salt to the slurry; a third step of adding an alkali to the mixture obtained in the second step to obtain a mixed hydroxide containing cerium hydroxide and zirconium hydroxide; and a fourth step of heat-treating the mixed hydroxide to obtain a mixed oxide containing cerium oxide and zirconium oxide.
  • cerium oxide-zirconium oxide-based mixed oxide according to above 4, wherein one type or two or more types of metal salt selected from rare earth elements excluding cerium, transition metal elements, aluminum and silicon is added in the second step.
  • a cerium oxide-zirconium oxide-based mixed oxide and a simple production process thereof, having superior platinum dispersibility and a suitable OSC, can be provided which can be preferably used in the relevant art as a co-catalyst or catalyst support and the like of an automotive three-way catalyst.
  • FIG. 1 shows the X-ray diffraction results of powders obtained by heat-treating oxides obtained in Example 1 and Comparative Example 1 for 3 hours at 1000° C.;
  • FIG. 2 shows the X-ray diffraction results of powders obtained by loading the oxides obtained in Example 1 and Comparative Example 1 with 1 wt % Pt followed by heat treating for 3 hours at 900° C.;
  • FIG. 3 shows an SEM image of a powder obtained by loading the oxide obtained in Example 1 with 1 wt % Pt followed by heat treating for 3 hours at 900° C.
  • FIG. 4 shows an SEM image of a powder obtained by loading the oxide obtained in Comparative Example 1 with 1 wt % Pt followed by heat-treating for 3 hours at 900° C.
  • the zirconia referred to in the present invention refers to ordinary zirconia, and includes that containing impurity metal compounds, including hafnia, up to 10% by weight.
  • % refers to percent by weight.
  • the cerium oxide-zirconium oxide-based mixed oxide of the present invention is a cerium oxide-zirconium oxide-based mixed oxide comprising cerium oxide and zirconium oxide, wherein (1) the weight ratio of CeO 2 :ZrO 2 is 60:40 to 90:10, and (2) the cerium oxide and the zirconium oxide are present as a mixture, the zirconium oxide being composed of a solid solution in which tetragonal or cubic zirconium oxide contains cerium.
  • the cerium oxide and the zirconium oxide are present as a mixture, the zirconium oxide being composed of a solid solution in which tetragonal or cubic zirconium oxide contains cerium” indicates that, in terms of crystal chemistry, (1) cerium oxide phase and (2) tetragonal or cubic zirconium oxide phase which forms a solid solution containing cerium, namely the two peaks of cerium oxide and tetragonal or cubic zirconium oxide, are clearly recognized.
  • cerium oxide phase and (2) tetragonal or cubic zirconium oxide phase which is composed of a solid solution containing cerium are equally mixed each other (as defined in the original Japanese in the Kojien, 2nd revised edition, Oct. 15, 1979, 4th printing).
  • the zirconium oxide phase is dispersed in the cerium oxide phase basically in the present invention.
  • the “mixed oxide (B) comprised of cerium oxide merely loaded onto a solid solution oxide (A) containing zirconium and cerium” described in Japanese Patent Application Publication No. 2002-177781, and the “metal oxide particles having a core portion containing a comparatively large amount of a ceria-zirconia solid solution and a shell portion containing a comparatively large amount of a second metal oxide” described in Japanese Patent Application Publication No. 2005-314.134 are not included in the present invention.
  • Example 1 of the present invention results of X-ray diffraction of a powder obtained in Example 1 of the present invention are shown in FIG. 1 .
  • cerium oxide and (2) tetragonal or cubic zirconium oxide which is composed of a solid solution containing cerium, namely the two peaks of cerium oxide and tetragonal or cubic zirconium oxide can be seen to be clearly observed.
  • the cerium oxide-zirconium oxide-based mixed oxide of the present invention has the characteristics described above, it has the superior platinum dispersibility and suitable OSC described below.
  • the OSC of the cerium oxide-zirconium oxide-based mixed oxide of the present invention is 0.20 mmol-O 2 /g or more and preferably 0.25 mmol-O 2 /g or more. If the OSC is less than 0.20 mmol-O 2 /g, the OSC of ceria actually functioning as an automotive catalyst decreases, thereby making this undesirable.
  • the particle size of platinum is 200 nm or less and preferably 170 nm or less. If the particle size exceeds 200 nm, the number of active sites as a catalyst decreases, thus resulting in the possibility of a decrease in catalyst activity and making this undesirable.
  • the content of cerium oxide as calculated from X-ray diffraction peak intensity of the cerium oxide-zirconium oxide-based mixed oxide of the present invention following heat treatment for 3 hours at 1000° C. in air is preferably 50% by volume or more, more preferably 60% by volume or more and particularly preferably 70% by volume or more. If this ratio of cerium oxide is less than 50% by volume, Pt dispersibility decreases, thereby making this undesirable.
  • the specific surface area of the cerium oxide-zirconium oxide-based mixed oxide of the present invention following heat treatment for 3 hours at 1000° C. in air is preferably 10 m 2 /g or more. If the specific surface area is less than 10 m 2 /g, there is the possibility of promoting sintering of the precious metal serving as the catalyst, thereby making this undesirable.
  • cerium oxide-zirconium oxide-based mixed oxide of the present invention may also contain 1 to 20% by weight of one type or two or more types of oxides selected from the group consisting of oxides of rare earth elements excluding cerium, transition metal elements, aluminum and silicon.
  • rare earth elements other than cerium include lanthanoid elements such as Sc, Y, La, Pr or Nd.
  • transition metal elements include Ti, Cr, Mn, Fe, Co, Ni, Cu, Mo and W. If these metal oxides are contained at less than 1% by weight, there is no effect of improving heat resistance, while if contained in excess of 20% by weight, the ratio of CeO 2 decreases and the cubic crystal ratio of the cerium oxide decreases, thereby making this undesirable.
  • a sulfating agent is added to a cerous salt to obtain a slurry containing a cerous sulfate-alkali metal mixed salt.
  • the cerous salt may be that which provides cerous ion, and for example, one type or two or more types of cerous sulfate, cerous chloride or cerous nitrate can be used.
  • the solvent is suitably selected according to the type of cerium salt used and the like, it is normally desirable to use water (and preferably pure water or ion exchange water).
  • the concentration of the cerium salt solution typically it is preferably 5 to 200 g, and particularly preferably 50 to 100 g, of cerium oxide (CeO 2 ) equivalent in 1000 g of solvent.
  • a sulfating agent that forms a cerous sulfate-alkali metal mixed salt by reacting with cerous ion is preferably used for the sulfating agent, examples of which include sodium sulfate and potassium sulfate.
  • the sulfating agent may be in the form of, for example, a powder or a solution, and is preferably used in the form of a solution (and particularly preferably an aqueous solution).
  • concentration in the case of using as a solvent can be suitably set.
  • the sulfating agent is added so that the weight ratio of Na 2 SO 4 /CeO 2 in the case of using Na 2 SO 4 is 1.5 to 2.5, and the free acid concentration of the mixture is preferably 0.2 to 2.2 N (normal).
  • hydrochloric acid is preferable from the standpoint of having superior productivity on an industrial scale.
  • this solution After having added the sulfating agent to the cerous salt, this solution is heated to 85° C. or higher and held (aged) at that temperature for a fixed period of time to form a cerous sulfate-alkali metal mixed salt.
  • cerous sulfate-alkali metal mixed salt examples include Ce 2 (SO 4 ) 3 ⁇ 2M 2 SO 4 and M 3 [Ce 2 (SO 4 ) 3 ] (wherein M represents an alkali metal) .
  • a slurry can be obtained containing a cerous sulfate-alkali metal mixed salt.
  • cerous sulfate-alkali metal mixed salt may be filtered or rinsed with water and the like for the purpose of solid-liquid separation as necessary, since the present invention comprises a subsequent step, it can normally be used in the next step without filtering.
  • cerous sulfate-alkali metal mixed salt can be used directly as a starting substance, and this case is also included in the scope of the present invention.
  • a cerium salt and a zirconium salt are added to the slurry obtained in the first step.
  • the cerium salt may be either a cerous salt or a ceric salt provided it provides cerium ion.
  • cerium salts such as cerium sulfate, cerium chloride or cerium nitrate can be used.
  • the zirconium salt may be any zirconium salt provided it provides zirconium ion, and for example, one type or two or more types of zirconium salts such as zirconium oxynitrate, zirconium oxychloride or zirconium nitrate can be used.
  • the concentration of the cerium salt typically it is preferably 5 to 200 g, and particularly preferably 50 to 100 g, as cerium oxide (CeO 2 ) in 1000 g of solvent.
  • cerium oxide-zirconium oxide-based mixed metal oxide of the present invention can contain 1 to 20% of one type or two or more types of oxides selected from oxides of rare earth elements excluding cerium, transition metal elements, aluminum and silicon, in this case, this can be accommodated in the present step by adding a prescribed amount of one type or two or more types of a metal salt selected from the group consisting of metal salts of rare earth elements excluding cerium, transition metal elements, aluminum and silicon.
  • An alkali is added to the slurry containing a cerous sulfate-alkali metal mixed salt to which was added a cerium salt and a zirconium salt prepared in the second step to obtain a mixed hydroxide containing cerium hydroxide and zirconium hydroxide.
  • alkali there are no particular limitations on the alkali.
  • alkalis that can be used include ammonium hydroxide, ammonium bicarbonate, sodium hydroxide and potassium hydroxide.
  • sodium hydroxide is preferable for the reason that it can be inexpensively used industrially.
  • the amount of alkali added provided it is able to cause the formation of a precipitate from the aforementioned solution, and is normally such that the pH of the solution is 11 or higher and preferably 12 or higher.
  • This neutralization step namely the neutralization of a solution in which three components consisting of solid cerium salt, ionic cerium salt (cerium ion) and ionic zirconium salt (zirconium ion) are all present, is the major characteristic of the present invention, and the cerium oxide-zirconium oxide-based mixed metal oxide of the present invention, comprising “a mixture of cerium oxide and tetragonal or cubic zirconium oxide which is a solid solution comprising cerium”, can be produced by heat treating the mixed hydroxide containing cerium hydroxide and zirconium hydroxide obtained in this step.
  • the degree of the mixing of the cerium salts and zirconium can be controlled.
  • the (2) ionic cerium salt coprecipitates with ionic zirconium salt in the step comprising addition of alkali resulting in a hydroxide in which Ce and Zr are dispersed well.
  • the (1) solid cerium salt is already in the form of aggregated particles and not in an ionic state, dispersion with zirconium ion is not adequate, resulting in a hydroxide which is difficult to mixed in the neutralization step.
  • the hydroxide formed in the neutralization step is a hydroxide in which cerium hydroxide from (1) and cerium hydroxide and zirconium hydroxide from (2) are dispersed well, and by then undergoing firing, a mixed oxide powder containing cerium oxide is thought to be formed.
  • the solution containing the mixed hydroxide containing cerium hydroxide and zirconium hydroxide at 35 to 60° C. for 1 hour or more from the viewpoint of aging the resulting precipitate to facilitate separation by filtration.
  • the formed precipitate composed of the mixed hydroxide containing cerium hydroxide and zirconium hydroxide is then recovered by a solid-liquid separation method.
  • Solid-liquid separation may be carried out in accordance with known methods such as filtration, centrifugal separation and decantation.
  • the mixed hydroxide containing cerium hydroxide and zirconium hydroxide is preferably washed with water to remove any adhered impurities as necessary.
  • the resulting mixed hydroxide may be further dried as necessary. Drying may be carried out in accordance with a known method such as air drying or heat drying. In addition, the mixed hydroxide may be subjected to grinding treatment, classification treatment and the like as necessary following drying treatment.
  • cerium oxide-zirconium oxide-based mixed oxide is obtained by carrying out heat treatment on the mixed hydroxide containing cerium hydroxide and zirconium hydroxide.
  • heat treatment there are no particular limitations on the heat treatment, and it may be normally carried out at about 400 to 900° C. for 1 to 5 hours.
  • heat treatment atmosphere there are no particular limitations on the heat treatment atmosphere, and heat treatment may be normally carried out in air or an oxidizing atmosphere.
  • a mixed oxide obtained in this manner can be crushed as necessary.
  • a crushing machine such as a planetary mill, ball mill or jet mill.
  • Specific surface area was measured according to the BET method using a specific surface area measuring instrument (Flowsorb II, Micromeritics Corp.).
  • H 2 -TPR was determined according to the Temperature Programmed Reduction method (Multitask T.P.R., Bel Japan Inc.).
  • 0.3 g of powder were sufficiently oxidized by heating to 600° C. and holding for 60 minutes in highly pure oxygen gas.
  • the powder was heated to from 100 to 900° C. at a heating rate of 10° C./min in a 5% hydrogen-argon gas flow (100 sccm), and the hydrogen consumed during this time was measured continuously with a quadrupole mass spectrometer to obtain a water vapor generation curve accompanying the rise in temperature.
  • the area under the resulting hydrogen consumption curve for the amount of hydrogen consumed at 600° C. was taken to be amount of oxygen released at 600° C.
  • the cerium oxide ratio was defined in the manner indicated below from powder X-ray diffraction data following heat treatment for 3 hours at 1000° C. when the diffraction intensity of 2 ⁇ :28.55° equivalent to the (111) plane of cubic cerium oxide is defined as I 0 , and the diffraction intensity of 2 ⁇ :30.5° or 30.2° equivalent to the (111) plane of cubic or tetragonal zirconium oxide is defined as I 1 .
  • Cerium oxide ratio (vol %) I 0 /(I 0 +I 1 ) ⁇ 100 (4) Platinum Particle Size
  • Pt particles (white spots in FIGS. 3 and 4 ) observed by SEM-EDX were measured by visualizing under a scanning electron microscope followed by determination of the average value.
  • This solution was then neutralized using 500 g of 25% sodium hydroxide.
  • the pH at this time was 12 or higher.
  • a hydroxide was obtained by filtering and rinsing with water.
  • the resulting hydroxide was then fired for 5 hours at 650° C. in air to obtain an oxide.
  • the X-ray diffraction results for the resulting oxide are shown in FIG. 1 .
  • the specific surface area, specific surface area following heat treatment for 3 hours at 1000° C., the cerium oxide ratio and OSC were determined for this oxide.
  • Pt was loaded onto this oxide followed by determination of platinum particle size.
  • Pt was loaded by dispensing a dinitrodiamine platinum nitrate solution (Pt: 4.5%) into the oxide to 1% by weight followed by impregnating and drying for 5 hours at 500° C.
  • the resulting hydroxide was fired for 5 hours at 650° C. in air to obtain an oxide.
  • This oxide was subjected to the same measurements as Example 1. Those results are shown in Table 1 along with analysis values. Furthermore, X-ray diffraction results for the resulting oxide are shown in FIG. 1 .
  • Example 1 ZrO 2 (wt %) 22.0 22.0 CeO 2 (wt %) 78.0 78.0 SA (m 2 /g) 65.7 69.1
  • Aged SA* 1 (m 2 /g) 14.4 20.2 Cerium oxide ratio (vol %) 80.6 5.5
  • the article of the present invention was determined to have a suitable OSC of 0.25 mmol-O 2 /g, and the cerium oxide ratio of 80.6 vol % was found to be much higher than the comparative example.
  • the platinum particle size of approximately 170 nm following heat treatment for 3 hours at 900° C. was not more than half of that of the comparative example.
  • the product of the present invention is about 8.7 times greater ((350/170)3) in terms of quantity(number of particles) and about 2.1 times greater (350/170) in terms of specific surface area, thus demonstrating extremely superior dispersibility.

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US10232348B2 (en) 2010-12-22 2019-03-19 Pacific Industrial Development Corporation Doped catalyst support materials having oxygen storage capacity (OSC) and method of making thereof
US10610852B2 (en) 2011-06-01 2020-04-07 Rhodia Operations Complex oxide, method for producing same, and exhaust gas purification catalyst
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US10065179B2 (en) 2013-08-09 2018-09-04 Toyota Jidosha Kabushiki Kaisha Ceria-zirconia-based composite oxide and method for producing same, and exhaust gas purification catalyst including ceria-zirconia-based composite oxide
US10913051B2 (en) 2013-08-09 2021-02-09 Toyota Jidosha Kabushiki Kaisha Ceria-zirconia-based composite oxide and method for producing same, and exhaust gas purification catalyst including ceria-zirconia-based composite oxide
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