JP2008273781A - Ceria-zirconia multiple oxide and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a ceria-zirconia multiple oxide which is capable of efficiently and surely manufacturing a ceria-zirconia multiple oxide having sufficiently high solid solution quantity and mono-dispersion rate of zirconia and sufficiently high heat resistance. <P>SOLUTION: The method of manufacturing the ceria-zirconia multiple oxide includes: a step for obtaining a reaction solution containing hydroxide of zirconium and cerium by neutralizing a raw material solution containing cerium salt and zirconium salt to prepare the hydroxide of cerium and zirconium; a step for supplying hot water to the reaction solution; and a step for obtaining the multiple oxide of ceria and zirconia by hydrothermally reacting hydroxides in the reaction solution using subcritical water or supercritical water as a reaction field after the hot water is supplied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ceria-zirconia composite oxide and a method for producing the same.

  In a catalyst carrier for exhaust gas purification, ceria is an indispensable material as a functional oxide capable of rapidly absorbing and releasing oxygen according to the partial pressure of oxygen in the atmosphere (the capacity of such ceria is generally OSC (oxygen storage capacity). )). However, when such a ceria is used alone, the heat resistance is insufficient in a practical use environment. Therefore, when ceria is used for the exhaust gas purification catalyst carrier, zirconia is dissolved in ceria to improve heat resistance as a ceria-zirconia composite oxide.

On the other hand, it is conventionally known that various metal particles can be synthesized by hydrothermal synthesis using water in a subcritical or supercritical state as a reaction field. For example, in Japanese Patent Application Laid-Open No. 2006-282503 (Patent Document 1), a method of organically modifying the surface of ceria nanoparticles by hydrothermal synthesis using supercritical water as a reaction field and fine particles obtained by the method are disclosed. It is disclosed. In JP-A-2006-255450 (Patent Document 2), a method for producing zirconia crystal particles in which a zirconium compound is hydrothermally reacted using subcritical or supercritical water as a medium, and zirconia obtained by the method. Crystal particles are disclosed. However, the particles of ceria-zirconia composite oxide obtained by adopting the conventional hydrothermal synthesis method under supercritical or subcritical conditions as described in Patent Documents 1 and 2 are the usual coprecipitation methods and the like. Compared with the ceria-zirconia composite oxide obtained by the method, ceria and zirconia were not sufficiently dissolved. Therefore, the particles of ceria-zirconia composite oxide obtained by adopting the conventional hydrothermal synthesis method under supercritical or subcritical conditions do not always have sufficient heat resistance, and the exhaust gas purifying catalyst. When used as a carrier, OSC was not always fully exhibited.
JP 2006-282503 A JP 2006-255450 A

  The present invention has been made in view of the above-described problems of the prior art, and it is possible to efficiently produce a ceria-zirconia composite oxide having a sufficiently high solid solution amount and monodispersion rate of zirconium and sufficiently high heat resistance. It is another object of the present invention to provide a method for producing a ceria-zirconia composite oxide that can be reliably produced, and a ceria-zirconia composite oxide obtained by employing the method.

  As a result of intensive studies to achieve the above object, the present inventors first neutralize a raw material solution containing a cerium salt and a zirconium salt, and contain cerium and zirconium hydroxides. After preparing a reaction solution and then supplying hot water to the reaction solution, the hydroxide in the reaction solution is hydrothermally reacted using water in a subcritical or supercritical state as a reaction field, thereby solidifying zirconium. The present inventors have found that it is possible to efficiently and reliably produce a ceria-zirconia composite oxide having a sufficiently high solubility and a monodispersion rate and sufficiently high heat resistance, and has completed the present invention. .

That is, the method for producing a ceria-zirconia composite oxide of the present invention comprises preparing a hydroxide of cerium and zirconium by neutralizing a raw material solution containing a cerium salt and a zirconium salt. Obtaining a reaction solution containing:
Supplying hot water to the reaction solution;
A step of obtaining a composite oxide of ceria and zirconia by hydrothermally reacting the hydroxide in the reaction solution after the hot water supply with water in a subcritical or supercritical state as a reaction field;
It is the method characterized by including.

  In the method for producing a ceria-zirconia composite oxide of the present invention, the temperature of the hot water is preferably 250 to 350 ° C.

  Moreover, in the manufacturing method of the said ceria-zirconia complex oxide of this invention, it is preferable to further include the process of supplying 500-650 degreeC high hot water to the reaction solution after the said hot water supply.

  In the method for producing a ceria-zirconia composite oxide of the present invention, the subcritical or supercritical water is preferably water having a pressure of 20 to 50 MPa and a temperature of 350 to 450 ° C.

  Furthermore, in the method for producing a ceria-zirconia composite oxide of the present invention, the content ratio of the cerium salt and the zirconium salt in the raw material solution is a molar ratio (Ce: Zr) in terms of metal of cerium and zirconium. It is preferably in the range of 2: 8 to 8: 2.

The ceria-zirconia composite oxide of the present invention is a composite oxide of ceria and zirconia,
Following formula (1):
[Solubility amount (%)] = {(5.425- [Lattice constant]) / 0.3297} × 100 (1)
(In formula (1), [lattice constant] is a value of a lattice constant calculated based on diffraction line position data belonging to the (3, 1, 1) plane when the composite oxide is subjected to X-ray diffraction measurement. Is shown.)
The solid solution amount of zirconium determined by the above is within a range of ± 12% with respect to the value of the molar fraction of zirconium contained in the composite oxide, and
Following formula (2):
[Monodispersion rate (%)] = ([actual value of specific surface area] / [theoretical value of specific surface area]) × 100 (2)
{In Formula (2), the specific surface area actual measurement value is a value measured by the BET (Brunauer Emmet Teller) one-point method, and the specific surface area theoretical value (m ² / g) is the following formula (3):
[Theoretical specific surface area] = 6 × 10 ³ / ([Density] × [Particle diameter]) (3)
(In formula (3), the particle diameter (nm) indicates the average particle diameter calculated by X-ray diffraction measurement, and the density (g / cm ³ ) is determined by the mixing ratio of cerium and zirconium, and the JCPDS-ICDD card. (Theoretical density value obtained from the ceria and zirconia density values described is shown.)
Indicates the value obtained by. }
The monodispersity (unit:%) of the complex oxide obtained by the above is 80% or more,
It is characterized by satisfying the following condition.

In the ceria-zirconia composite oxide of the present invention, it is preferable that the actual measured specific surface area of the composite oxide is 150 m ² / g or more. Furthermore, in the ceria-zirconia composite oxide of the present invention, the actual measured specific surface area of the composite oxide is preferably 40 m ² / g or more after heating at 700 ° C. for 5 hours.

  In addition, according to the method for producing a ceria-zirconia composite oxide of the present invention, a ceria-zirconia composite oxide having a sufficiently high solid solution amount and monodispersion rate of zirconium and sufficiently high heat resistance can be efficiently and reliably obtained. Although the reason why it is possible to manufacture is not necessarily clear, the present inventors infer as follows. That is, in the method for producing a ceria-zirconia composite oxide of the present invention, first, a raw material solution containing a cerium salt and a zirconium salt is neutralized to form a cerium and zirconium hydroxide (coprecipitate). After forming the particles, hot water is supplied to the reaction solution containing the hydroxide particles. It is inferred that the step of supplying hot water dissolves the hydroxide once, and the particles of the hydroxide become finer particles and uniformly dispersed in the reaction solution. The In the present invention, using the reaction solution in which such fine hydroxide particles are uniformly dispersed, the hydroxide is hydrothermally reacted using water in a subcritical or supercritical state as a reaction field. Therefore, the uniformity of the particles is improved and fine primary particles are obtained, and the monodispersity of the obtained composite oxide is sufficiently improved. Further, in such a method for producing a ceria-zirconia composite oxide of the present invention, cerium particles and zirconium particles are present in a more uniform proximity in the reaction solution. And fully dissolve. Therefore, according to the present invention, the inventors speculate that a ceria-zirconia composite oxide having a sufficiently high solid solution amount and monodispersion rate of zirconium and sufficiently high heat resistance can be obtained.

  According to the present invention, a ceria-zirconia composite capable of efficiently and reliably producing a ceria-zirconia composite oxide having a sufficiently high solid solution amount and monodispersion rate of zirconium and sufficiently high heat resistance. It becomes possible to provide an oxide manufacturing method and a ceria-zirconia composite oxide obtained by adopting the method.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

First, the method for producing the ceria-zirconia composite oxide of the present invention will be described. That is, the method for producing a ceria-zirconia composite oxide of the present invention comprises preparing a hydroxide of cerium and zirconium by neutralizing a raw material solution containing a cerium salt and a zirconium salt. A first step of obtaining a reaction solution containing
A second step of supplying hot water to the reaction solution;
A third step of obtaining a composite oxide of ceria and zirconia by hydrothermally reacting the hydroxide in the reaction solution after the supply of hot water with water in a subcritical or supercritical state as a reaction field;
It is the method characterized by including. Hereinafter, the first to third steps will be described separately.

  First, the first step will be described. In the first step, a raw material solution containing a cerium salt and a zirconium salt is neutralized to prepare a hydroxide of cerium and zirconium to obtain a reaction solution containing the hydroxide.

  Such a cerium salt is not particularly limited, and cerium nitrate, sulfate, acetate, halide and the like can be appropriately used. As such a cerium salt, nitrate or acetate is more preferably used from the viewpoint of cost and relatively easy removal of components remaining in the composite oxide during synthesis.

  The zirconium salt is not particularly limited, and zirconium nitrate, sulfate, acetate, halide and the like can be appropriately used. As such zirconium salt, nitrate or acetate is more preferably used from the viewpoint of cost and relatively easy removal of components remaining in the composite oxide during synthesis.

  The content ratio of the cerium salt and the zirconium salt in the raw material solution is a molar ratio (Ce: Zr) of cerium and zirconium contained in the solution in the range of 2: 8 to 8: 2. It is preferable that the ratio is in the range of 3: 7 to 7: 3. When the content ratio of the cerium salt is less than the lower limit, sufficient OSC tends not to be obtained. On the other hand, when the content exceeds the upper limit, heat resistance tends to decrease.

  The concentration of the raw material solution is not particularly limited, but the total amount of cations (cerium ions and zirconium ions) is preferably 0.005 to 1.0 mol / L, and 0.01 to 0.5 mol / L. More preferably, it is L. When the concentration of the raw material solution is less than the lower limit, the composite oxide synthesis efficiency tends to decrease. On the other hand, when the upper limit is exceeded, the reactor particles tend to be clogged with the generated particles. It is in.

  Furthermore, it is preferable to add an aqueous hydrogen peroxide solution as a solid solution accelerator to the raw material solution. When the aqueous hydrogen peroxide solution is added in this way, the molar content of hydrogen peroxide is preferably 0.5 to 2.0 times the molar amount of cerium ions in the raw material solution, More preferably, the ratio is 0.8 to 1.5 times. If the ratio of the molar content of hydrogen peroxide relative to cerium ions is less than the lower limit, the effect as a solid solution accelerator tends to be insufficient. On the other hand, if the upper limit is exceeded, the effect as a solid solution accelerator Tend to saturate.

  The method for preparing the raw material solution is not particularly limited, and examples thereof include a method of mixing an aqueous solution containing a cerium salt, an aqueous solution containing a zirconium salt, and the hydrogen peroxide aqueous solution.

Examples of the method of neutralizing the raw material solution include a method of mixing the raw material solution and the neutralizing solution. Such a neutralizing solution is not particularly limited as long as it can generate hydroxides of cerium and zirconium by neutralizing the raw material solution, such as ammonia water, aqueous sodium hydroxide solution, etc. Is mentioned. Moreover, as the addition amount of such a neutralization liquid, 0.9% of the hydroxide ion (OH < ^- >) in a neutralization liquid is neutralization equivalent with respect to the total amount of the cerium ion and zirconium ion in a raw material solution. It is preferable to set it as the quantity which becomes -1.5 times, and it is more preferable to set it as the quantity which becomes 1.0-1.2 times. If the added amount of such a neutralizing solution is less than the lower limit, sufficient neutralization reaction tends not to occur. On the other hand, if the upper limit is exceeded, excess neutralizing agent remains, and cerium and zirconium are dissolved. Tend to affect.

  Next, the second step will be described. In the second step, hot water is supplied to the reaction solution.

  As such hot water, the temperature is preferably 250 to 350 ° C, and more preferably 270 to 320 ° C. When the temperature of the hot water is less than the lower limit, it tends to be difficult to uniformly disperse the hydroxide in the reaction solution. On the other hand, when the temperature exceeds the upper limit, the hydroxide does not sufficiently dissolve. It is in.

  Moreover, it is preferable to set it as 300-500 mass parts with respect to 100 mass parts of said reaction solutions (mixture of a raw material solution and a neutralization liquid) as supply_amount | feed_rate of such hot water. When the amount of hot water added is less than the lower limit, the amount of hot water tends to be insufficient and the hydroxide does not sufficiently dissolve. On the other hand, when the upper limit is exceeded, the hydroxide concentration in the liquid is reduced. It is too low and solid solution tends not to proceed sufficiently.

  Next, the third step will be described. In the third step, a complex oxide of ceria and zirconia is obtained by hydrothermally reacting the hydroxide in the reaction solution after the hot water supply with subcritical or supercritical water as a reaction field. .

  The reaction field of such a hydrothermal reaction is subcritical or supercritical water. By setting it as such a reaction field, a unique reaction environment is provided, the hydrothermal reaction of the said hydroxide advances, and it becomes possible to precipitate an oxide rapidly. Examples of such subcritical or supercritical water include water having a temperature of 350 ° C. or higher and a pressure of 20 Mpa or higher, and water having a pressure of 20 to 50 MPa (particularly preferably 22 to 40 MPa) and a temperature of 350 to 450 ° C. It is preferable that When such pressure and temperature are less than the lower limit, water cannot be brought into a subcritical or supercritical state, and a composite oxide having a sufficiently high monodispersion rate and solid solubility cannot be generated. On the other hand, if the upper limit is exceeded, the durability limit of the device may be exceeded.

  The reaction apparatus for forming such a reaction field is not particularly limited as long as it can achieve conditions of high temperature and high pressure, and for example, either a batch type apparatus or a flow type apparatus can be used. In addition, the time for the hydrothermal reaction in such a reaction field is not particularly limited, and is preferably about 0.01 to 1 minute.

  Further, the third step includes a step of supplying high-temperature water at 500 to 650 ° C. (more preferably 510 to 600 ° C.) to the reaction solution after the supply of hot water to form the reaction field. Is preferred. By supplying the hot water to the reaction solution after the hot water is supplied, the reaction solution can be brought into a supercritical state more efficiently. When the temperature of such hot water is less than the lower limit, it tends to be difficult to efficiently bring the reaction solution into a supercritical state or a subcritical state. On the other hand, when the upper limit is exceeded, the apparatus piping is corroded. , Impurities tend to be mixed.

  In addition, after forming and recovering the complex oxide of ceria and zirconia by hydrothermal reaction, it is preferable to dry and calcine it. Such firing conditions are not particularly limited, but firing at a temperature of 300 to 700 ° C. for 1 to 5 hours is preferable. When the heating temperature and time during firing are less than the lower limit, impurities remaining during the reaction tend not to be sufficiently removed, and when the upper limit is exceeded, the specific surface area tends to decrease.

In the present invention, the following formula (1):
[Solubility amount (%)] = {(5.425- [Lattice constant]) / 0.3297} × 100 (1)
(In formula (1), [lattice constant] is a value of a lattice constant calculated based on diffraction line position data belonging to the (3, 1, 1) plane when the composite oxide is subjected to X-ray diffraction measurement. Is shown.)
The solid solution amount of zirconium determined by the above is within a range of ± 12% with respect to the value of the molar fraction of zirconium contained in the composite oxide, and
Following formula (2):
[Monodispersion rate (%)] = ([actual value of specific surface area] / [theoretical value of specific surface area]) × 100 (2)
{In Formula (2), the specific surface area actual measurement value is a value measured by the BET (Brunauer Emmet Teller) one-point method, and the specific surface area theoretical value (m ² / g) is the following formula (3):
[Theoretical specific surface area] = 6 × 10 ³ / ([Density] × [Particle diameter]) (3)
(In formula (3), the particle diameter (nm) indicates the average particle diameter calculated by X-ray diffraction measurement, and the density (g / cm ³ ) is determined by the mixing ratio of cerium and zirconium, and the JCPDS-ICDD card. (Theoretical density value obtained from the ceria and zirconia density values described is shown.)
Indicates the value obtained by. }
The monodispersity (unit:%) of the complex oxide obtained by the above is 80% or more,
A ceria-zirconia composite oxide satisfying the condition can be produced. Such conditions will be described in detail in the ceria-zirconia composite oxide of the present invention described later.

  Hereinafter, in order to explain the production method of the ceria-zirconia composite oxide of the present invention in more detail, it is preferably used for carrying out the production method of the ceria-zirconia composite oxide of the present invention with reference to the drawings. An embodiment of a manufacturing apparatus capable of the above will be described. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

  FIG. 1 is a schematic diagram showing an outline of a production apparatus suitable for carrying out the method for producing a ceria-zirconia composite oxide of the present invention.

  1 includes a raw material solution storage container 10, a neutralization liquid storage container 11, an ion exchange water storage container 12 for supplying hot water, an ion exchange water storage container 13 for hot water, and a supply pipe. 14, a pump 15, a heating furnace 16 for producing hot water, a heating furnace 17 for forming hot water, a reaction furnace 18, a cooling water storage container 19, a cooler 20, and a solid-liquid separation and recovery unit 21 The pressure regulator 22 and the waste liquid storage container 23 are provided, and each container, reaction furnace, and the like are connected via a supply pipe. In such a manufacturing apparatus, the pressure in the system can be adjusted by a pressure regulator 22 (for example, a back pressure regulator).

  Such containers 10, 11, 12, 13, 19, and 23 are not particularly limited as long as they can store a raw material solution, a neutralizing solution, and the like, and are not particularly limited. Can be used as appropriate. The pump 15 is not particularly limited as long as it can flow the raw material solution or the like into the supply pipe at a predetermined flow rate, and a known pump can be appropriately used. Furthermore, the heating furnace 16 is not particularly limited as long as it can produce the hot water, and a known heating furnace can be appropriately used. Moreover, as the heating furnace 17, what is necessary is just what can manufacture 500-650 degreeC hot water, and it does not restrict | limit, A well-known heating furnace can be utilized suitably. The reactor 18 is not particularly limited as long as the temperature of water can be controlled and maintained at 350 ° C. or higher, and a known reactor can be appropriately used. Furthermore, the cooler 20 is not particularly limited, and a known cooling device can be used as appropriate. For example, a device (such as a water jacket) that can cool the inside of the reaction tube 14 by circulating cooling water can be used. Further, the solid-liquid separation / recovery unit 21 is not particularly limited, and a known apparatus capable of collecting solid components by solid-liquid separation can be used as appropriate. In the present embodiment, the solid-liquid separation and recovery unit 21 is connected to the waste liquid storage container 23. As mentioned above, although the manufacturing apparatus suitable for enforcing the manufacturing method of the ceria-zirconia complex oxide of this invention of this invention was demonstrated, the manufacturing apparatus which can be used for this invention is not restrict | limited.

  Next, a preferred example of a method for producing a ceria-zirconia composite oxide using the production apparatus shown in FIG. 1 will be described. First, the inside of the system is held at 25 MPa by the pressure regulator 22. Then, the raw material solution is supplied from the raw material solution storage container 10 into the supply pipe 14 at a flow rate of 5 mL / min using the pump 15, and at the same time, the flow rate of 5 mL / min from the neutralization solution storage container 11 using the pump 15. Then, the neutralizing liquid is supplied into the supply pipe 14. As a result, the raw material solution and the neutralizing liquid are mixed in the connection portion 14 a of the supply pipe 14, and a reaction solution is formed in the supply pipe 14. In such a reaction solution, hydroxides of cerium and zirconia are formed.

  Next, ion exchange water is supplied into the supply pipe 14 from the ion exchange water storage container 12 for supplying hot water at a flow rate of 40 mL / min using the pump 15, heated to 300 ° C. by the heating furnace 16, and supplied to the supply pipe. Hot water is formed within 14. And the hot water formed in this way is supplied to the reaction solution which flows in the supply pipe 14 in the connection part 14b. Further, ion-exchanged water is supplied from the ion-exchanged water storage container 13 for supplying hot water into the supply pipe 14 at a flow rate of 40 mL / min using the pump 15, and heated to 550 ° C. by the heating furnace 17 to generate hot water. It is formed. The hot water thus formed is supplied to the reaction solution after the hot water is supplied flowing in the supply pipe 14 at the connection portion 14c. The reaction solution supplied with the hot water flows into the reaction furnace 18 whose temperature is controlled at 400 ° C. Note that the reaction solution becomes supercritical at once when hot water is supplied. Therefore, in the reaction furnace 18, a hydrothermal reaction proceeds using water in a supercritical state as a reaction field, and a ceria-zirconia composite oxide is generated. Next, the solution after the hydrothermal reaction flows into the supply pipe 14 from the reaction furnace 18, and cooling water at 20 to 30 ° C. is supplied from the cooling water storage container 19 at the connection portion 14 d. When cooling water is supplied in this way, the reaction solution is rapidly cooled and the reaction stops. The cooling water is supplied at a flow rate of 50 mL / min using the pump 15. Thereafter, the solution supplied with the cooling water flows into the portion where the cooler 20 is installed and is cooled to 25 to 35 ° C. Then, the solid and the liquid are separated by the solid-liquid separator, and the ceria-zirconia composite oxidation is performed. Is recovered. Then, the ceria-zirconia composite oxidation recovered in this way may be dried and then fired.

  As mentioned above, although an example of the method of manufacturing a ceria-zirconia composite oxide was demonstrated using the manufacturing apparatus shown in FIG. 1, the manufacturing method of the ceria-zirconia composite oxide of this invention is limited to the said embodiment. It is not a thing. For example, the supply speed of the raw material solution and the neutralization liquid is not limited to the speed employed in the above embodiment, and in the present invention, the supply speed can be appropriately changed according to the concentration of the raw material solution and the like. Further, the temperature of the hot water is not particularly limited to the temperature adopted in the above embodiment, and in the present invention, the temperature of the hot water may be adjusted to the above suitable temperature range. Moreover, in the said embodiment, although the inside of a reaction furnace is controlled by 400 degreeC, in this invention, what is necessary is just to control temperature so that a reaction field may be subcritical or supercritical water. Further, in the above embodiment, the pressure in the system is adjusted to 25 MPa. However, in the present invention, the pressure may be controlled so that the reaction field becomes water in a subcritical or supercritical state.

  As mentioned above, although the manufacturing method of the ceria-zirconia composite oxide of this invention was demonstrated, next, the ceria-zirconia composite oxide of this invention is demonstrated.

The ceria-zirconia composite oxide of the present invention is a composite oxide of ceria and zirconia,
Following formula (1):
[Solubility amount (%)] = {(5.425- [Lattice constant]) / 0.3297} × 100 (1)
(In formula (1), [lattice constant] is a value of a lattice constant calculated based on diffraction line position data belonging to the (3, 1, 1) plane when the composite oxide is subjected to X-ray diffraction measurement. Is shown.)
The solid solution amount of zirconium determined by the above is within a range of ± 12% with respect to the value of the molar fraction of zirconium contained in the composite oxide, and
Following formula (2):
[Monodispersion rate (%)] = ([actual value of specific surface area] / [theoretical value of specific surface area]) × 100 (2)
{In Formula (2), the specific surface area actual measurement value is a value measured by the BET (Brunauer Emmet Teller) one-point method, and the specific surface area theoretical value (m ² / g) is the following formula (3):
[Theoretical specific surface area] = 6 × 10 ³ / ([Density] × [Particle diameter]) (3)
(In formula (3), the particle diameter (nm) indicates the average particle diameter calculated by X-ray diffraction measurement, and the density (g / cm ³ ) is determined by the mixing ratio of cerium and zirconium, and the JCPDS-ICDD card. (Theoretical density value obtained from the ceria and zirconia density values described is shown.)
Indicates the value obtained by. }
The monodispersity (unit:%) of the complex oxide obtained by the above is 80% or more,
It is characterized by satisfying the following condition.

The ceria-zirconia composite oxide of the present invention has the following formula (1):
[Solubility amount (%)] = {(5.425- [Lattice constant]) / 0.3297} × 100 (1)
The amount of zirconium solid solution determined by the above is in the range of ± 12% (more preferably ± 10%) with respect to the value of the molar fraction of zirconium contained in the composite oxide. If such a solid solution amount is less than the lower limit, the heat resistance tends to decrease, and if it exceeds the upper limit, OSC tends to decrease.

[Lattice constant] in the above formula (1) can be obtained as follows. First, X-ray diffraction (XRD) measurement of ceria-zirconia composite oxide is performed. And the data of the position which belongs to (3,1,1) plane is read from the obtained diffraction line, and it calculates and calculates based on this data. The peak top method is adopted for such calculation. In addition, the lattice constant calculated from the data of the position of the diffraction line attributed to the (3, 1, 1) plane of the ceria-zirconia composite oxide is the solid solution amount of zirconium (Zr) in the ceria-zirconia composite oxide. It is known that there is a linear relationship with (Vegard law). Therefore, by plotting the lattice constants of ceria (CeO ₂ ), zirconia (ZrO ₂ ) and ceria-zirconia composite oxide described in the JCPDS-ICDD card against the solid capacity of Zr, a straight line is derived. The above equation (1) for calculating the solid volume of Zr is derived. When the Ce / Zr content ratio (mixing ratio) is 50/50, the zirconium solid solution amount is 50% in an ideal solid solution state, and the Ce / Zr mixing ratio is 80/50. If it is 20, the solid solution amount of zirconium is 20% in an ideal solid solution state.

The ceria-zirconia composite oxide of the present invention has the following formula (2):
[Monodispersion rate (%)] = ([actual value of specific surface area] / [theoretical value of specific surface area]) × 100 (2)
The monodispersion rate (unit:%) of the complex oxide obtained by the above is 80% or more (more preferably 85% or more, and still more preferably 88% or more). When the monodispersion rate is less than the lower limit, the uniformity of the particles is insufficient and the secondary agglomeration is progressing, so that the catalyst metal cannot be sufficiently dispersed when used as a catalyst support. , It tends to be difficult to develop sufficient catalytic activity.

  The specific surface area actual measurement value in the above formula (2) is a value actually measured by a BET (Brunauer Emmet Teller) one-point method. In this invention, the following conditions are employ | adopted as measurement conditions of such a BET 1 point method.

〔Measurement condition〕
Pretreatment atmosphere: N ₂
Pretreatment temperature: 200 ° C., 15 minutes Pretreatment gas flow rate: 25 ml / min per reaction tube
Adsorbed gas: Flow rate of mixed gas adsorbed gas of N ₂ (30% by volume) and He (70% by volume): 25 ml / min per reaction tube
Adsorption temperature: -196 ° C (using liqN ₂ ).

Moreover, the specific surface area theoretical value (m ² / g) in the above formula (2) is the following formula (3):
[Theoretical specific surface area] = 6 × 10 ³ / ([Density] × [Particle diameter]) (3)
(In formula (3), the particle diameter (nm) indicates the average particle diameter calculated by X-ray diffraction measurement, and the density (g / cm ³ ) is determined by the mixing ratio of cerium and zirconium, and the JCPDS-ICDD card. (Theoretical density value obtained from the ceria and zirconia density values described is shown.)
Is a value obtained by That is, the [specific surface area theoretical value] assumes that the ceria-zirconia composite oxide is spherical particles and the primary particles are completely monodispersed, and the density of each ceria and zirconia monooxide is It is a specific surface area calculated by allocating according to the content ratio (mixing ratio).

As a method for determining the particle size in the formula (3), X-ray diffraction (XRD) measurement of ceria-zirconia composite oxide is performed, and the half width of the peak is derived from the obtained diffraction line data, A method of calculating by half-width data is adopted. As a method for such XRD measurement, a method of measuring by the 2θ / θ method using a trade name “RINT-TTR” manufactured by Rigaku Corporation as a measuring instrument can be employed. In the present invention, the following measurement conditions are adopted as measurement conditions for X-ray diffraction (XRD) measurement, and the particle diameter (T) is expressed by the following formula:
T = (0.89 × λ × 180) / {(B ² −Be ² ) ^1/2 × π × cos θ}
(Wherein T represents the particle diameter (unit: Å), λ represents 1.54056 (unit: Å), B represents a half-value (unit: °), and Be represents a correction value unique to the apparatus. (0.103 °) and θ represents a diffraction angle (unit: °).)
It can ask for.
[XRD measurement conditions]
Radiation source: Cu-Kα, 50 kV, 300 mA
Measurement range: 20-80 °
Scanning speed (2θ): 2 ° / min.

[Density] in the above formula (3) is the theoretical value of the density obtained from the mixing ratio of cerium (Ce) and zirconium (Zr) and the density values of ceria and zirconia described in the JCPDS-ICDD card. It is. The theoretical value of the density is that of ceria (CeO ₂ : No. 43-1002) described in the JCPDS-ICDD card is 7.22 g / cm ³ , and zirconia (ZrO ₂ : No. 27-0097). Since the density is 6.21 g / cm ³ , the following formula (4):
[Theoretical density] = 7.22 × [Ce mixing ratio] + 6.21 × [Zr mixing ratio] (4)
Is a value obtained by calculating.

  Further, the ceria-zirconia composite oxide of the present invention is in the form of particles having an average particle diameter of 3 to 8 nm (more preferably 4 to 7 nm) calculated from the half width of the peak of the X-ray diffraction line. preferable. When the average particle size is less than the lower limit, aggregation of primary particles is not suppressed and the monodispersion rate tends to decrease. On the other hand, when the upper limit is exceeded, the specific surface area decreases and the catalyst is used as a catalyst carrier. It tends to be insufficient.

Moreover, as a specific surface area actual value of the ceria-zirconia composite oxide of this invention, it is preferable that it is 150 m < ² > / g or more. If the measured value of the specific surface area is less than the lower limit, sufficient catalytic activity tends not to be obtained when the ceria-zirconia composite oxide of the present invention is used as a catalyst carrier for exhaust gas purification.

Further, the ceria-zirconia composite oxide of the present invention preferably has a measured specific surface area of 40 m ² / g or more (more preferably 45 m ² / g or more) after heating at 700 ° C. for 5 hours. If the measured value of the specific surface area is less than the lower limit, the heat resistance of the ceria-zirconia composite oxide is not sufficient, and sufficient catalytic activity tends not to be obtained when used as a catalyst carrier for exhaust gas purification. It is in.

  In addition, as the ceria-zirconia composite oxide of the present invention, the content ratio (mixing ratio) of ceria and zirconia contained in the composite oxide is a molar ratio (Ce: Zr) in terms of metal of cerium and zirconium. It is preferably in the range of 2: 8 to 8: 2, and more preferably in the range of 3: 7 to 7: 3.

  Moreover, as a method for producing the ceria-zirconia composite oxide of the present invention, the above-mentioned method for producing a ceria-zirconia composite oxide of the present invention can be suitably employed.

Such a ceria-zirconia composite oxide of the present invention has a sufficiently high monodispersion rate and a sufficiently high heat resistance, and can be suitably used as a catalyst carrier for exhaust gas purification. The catalytic activity of the resulting catalyst can be sufficiently improved. Although the reason why excellent catalytic activity is obtained when the ceria-zirconia composite oxide of the present invention is used as a catalyst carrier for exhaust gas purification is not necessarily clear, the present inventors speculate as follows. . That is, first, the cation of CeO ₂ contained in the ceria-zirconia composite oxide changes in valence according to the exposed atmosphere (Ce ⁴⁺ ⇔ Ce ³⁺ ), and in accordance with the principle of electrical neutrality, the gas phase It has the characteristic of occluding or releasing oxygen in the lattice or oxygen in the lattice. This is a characteristic generally referred to as Oxygen Storage Capacity (OSC), and OSC is greatly affected by a catalyst metal (for example, a noble metal) supported in a composite oxide. And since the active point of oxygen absorption / release is the interface between CeO ₂ and the noble metal to be supported, if the catalyst metal is supported in a highly dispersed state on CeO ₂ (or CZ), more oxygen will be absorbed. Presumed to be released quickly. On the other hand, as an effective tool for removing hydrocarbons at low temperatures, which is the most important issue in exhaust gas purification of automobiles, it has been proposed to utilize oxygen in the lattice released from low temperatures. . Oxygen released from the lattice has a strong oxidizing power and decomposes harmful components such as aldehyde, as is known in TiO ₂ photocatalysts. Therefore, a catalyst using an oxide capable of supplying more lattice oxygen from a low temperature as a support reacts with hydrocarbon and lattice oxygen at a low temperature on the noble metal that is the active site, and has a lower temperature oxidation activity than conventional. Is expected to develop. When used as a catalyst support, the ceria-zirconia composite oxide of the present invention is composed of fine primary particles that are almost monodisperse and can support catalyst metals (for example, precious metals) in a highly dispersed state. Therefore, it is assumed that more oxygen can be released quickly and oxygen in the lattice can be supplied, so that the low-temperature oxidation activity is improved.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
A ceria-zirconia composite oxide was manufactured using the same apparatus and method as the manufacturing apparatus shown in FIG. 1 and the ceria-zirconia composite oxide manufacturing method using the same. In this example, the ceria-zirconia composite oxide recovered in the solid-liquid separation and recovery unit 21 was dried at 120 ° C. for 6 hours and then calcined in the atmosphere at 400 ° C. for 5 hours. Moreover, the preparation method of the raw material solution and neutralization liquid used for manufacture, and manufacturing conditions are collectively shown below.

<Method for preparing raw material solution>
After obtaining a mixed solution in which an equal amount of a 0.025M cerium nitrate aqueous solution and a 0.025M zirconyl oxynitrate aqueous solution was mixed, a 25% by mass aqueous hydrogen peroxide solution was added to the mixed solution to contain hydrogen peroxide. The raw material solution was prepared by adding so that the amount was 1.1 times the amount of cerium ions in the mixed solution.

<Preparation method of neutralization liquid>
When 25% by mass of an aqueous ammonia solution (manufactured by Wako Pure Chemical Industries, Ltd.) is diluted with ion-exchanged water and is the same amount as the raw material solution, hydroxide ions with respect to cerium ions and zirconium ions in the raw material solution The concentration was adjusted so that the amount of the solution was 1.2 times the neutralization equivalent to obtain a neutralized solution.

<Production conditions>
In-system pressure: 25 MPa, raw material solution supply rate: 5 mL / min, neutralization solution supply rate: 5 mL / min, hot water supply rate: 40 mL / min, heating furnace 16 set temperature: 470 ° C., hot water Supply rate: 40 mL / min, set temperature of heating furnace 17: 600 ° C., set temperature of reaction furnace: 400 ° C., supply rate of cooling water: 50 mL / min, temperature of cooling water: 10-30 ° C. Temperature of experimental water to be circulated: 10 to 30 ° C., drying conditions after recovery: 6 hours at 120 ° C. in the atmosphere, firing conditions after recovery: 400 ° C. in the atmosphere for 5 hours.

(Comparative Example 1)
First, using the raw material solution and the neutralized solution prepared in Example 1, the raw material solution was added to the neutralized solution while stirring with a mechanical stirrer to obtain a hydroxide. Next, the obtained hydroxide was dried in the atmosphere at 110 ° C. for 6 hours, and further calcined in the atmosphere at 400 ° C. for 5 hours to obtain a ceria-zirconia composite oxide for comparison (both Sink method).

(Comparative Example 2)
A ceria-zirconia composite oxide for comparison was obtained in the same manner as in Example 1 except that the neutralized solution was not used and the hot water was not supplied.

[Characteristic evaluation of ceria-zirconia composite oxide obtained in Example 1 and Comparative Examples 1-2]
<X-ray diffraction measurement>
X-ray diffraction measurement was performed on the ceria-zirconia composite oxide obtained in Example 1 and Comparative Examples 1-2. In the X-ray diffraction measurement, a trade name “RINT-TTR” manufactured by Rigaku Corporation was used as a measuring instrument. Graphs of the obtained diffraction lines are shown in FIG. 2 (Example 1), FIG. 3 (Comparative Example 1), and FIG. 4 (Comparative Example 2). The graphs shown in FIGS. 2 to 4 are in the range of 2θ = 56 to 62 °.

  As is clear from the results shown in FIGS. 2 to 4, in the diffraction line data near the (3, 1, 1) plane, the ceria-zirconia composite oxide obtained in Example 1 (FIG. 2) and Comparative Example 1 are used. The ceria-zirconia composite oxide (FIG. 3) obtained in Example 1 has one diffraction line, but in the ceria-zirconia composite oxide (FIG. 4) obtained in Comparative Example 2, 2θ = 57.11 °. In addition to the main diffraction lines, it was confirmed that a plurality of diffraction lines overlap and the peak itself is broad ring. From these results, in the ceria-zirconia composite oxide obtained in Example 1 and Comparative Example 1, one type of solid solution was formed, whereas in the ceria-zirconia composite oxide obtained in Comparative Example 2, the ceria-zirconia obtained in Comparative Example 2 was formed. It was suggested that the composite oxide is a mixture of a plurality of solid solutions.

<Zr solid solution amount>
1-3, the solid solution amount (Zr solid solution amount) of zirconium in the ceria-zirconia composite oxide obtained in Example 1 and Comparative Examples 1-2 was determined using the diffraction lines shown in FIGS. That is, in the ceria-zirconia composite oxide obtained in Example 1 and Comparative Example 1, the peak top value of the peak is used, and in Comparative Example 2, the position of 2θ = 57.11 ° which is the main peak is used. Using the values, the respective lattice constants were calculated, and the obtained values were substituted into the above formula (1) to determine the Zr solid solution amount of each composite oxide. The results are shown in Table 1.

<Average particle size>
The average particle diameter of the ceria-zirconia composite oxide obtained in Example 1 and Comparative Examples 1 and 2 was determined using the diffraction lines shown in FIGS. That is, in the ceria-zirconia composite oxide obtained in Example 1 and Comparative Example 1, the half width of the peak was used, and in the ceria-zirconia composite oxide obtained in Comparative Example 2, The particle diameter was calculated from the half width of the main peak (2θ = 57.11 °), and the average particle diameter was determined. The results are shown in Table 1.

<Measured value of specific surface area (initial)>
The specific surface area of the ceria-zirconia composite oxide obtained in Example 1 and Comparative Examples 1 and 2 was measured by the BET 1-point method under the following measurement conditions.

〔Measurement condition〕
Pretreatment atmosphere: N ₂
Pretreatment temperature: 200 ° C., 15 minutes Pretreatment gas flow rate: 25 ml / min per reaction tube
Adsorbed gas: Flow rate of mixed gas adsorbed gas of N ₂ (30% by volume) and He (70% by volume): 25 ml / min per reaction tube
Adsorption temperature: -196 ° C (using liqN ₂ )
<Monodispersion>
In the ceria-zirconia composite oxide obtained in Example 1 and Comparative Examples 1 and 2, since the content ratio (mixing ratio) of cerium and zirconium is 1: 1, the above formula (4) is mixed with cerium and zirconium. A theoretical value of density was obtained by substituting 1/2 for the ratio. As a result, the theoretical density value was 6.72. Next, the specific surface area theoretical value was determined from the obtained theoretical density value and the average particle diameter value of each composite oxide obtained as described above. And the specific surface area actual measurement value and specific surface area theoretical value which were obtained as mentioned above were substituted into the said Formula (2), and the ceria-zirconia complex oxide obtained in Example 1 and Comparative Examples 1-2 was used. The monodispersity was determined. The results are shown in Table 1.

<Measured specific surface area and average particle diameter after heating at 700 ° C. for 5 hours>
The ceria-zirconia composite oxides obtained in Example 1 and Comparative Examples 1-2 were each heated in the atmosphere at 700 ° C. for 5 hours. And using each complex oxide after such a heating, the method similar to the above-mentioned measuring method was employ | adopted, and the specific surface area actual value and average particle diameter were calculated | required. The results are shown in Table 1.

<Evaluation of OSC performance>
A catalyst was produced using the ceria-zirconia composite oxide obtained in Example 1 and Comparative Examples 1-2, and OSC performance was measured. That is, first, 10 g of each ceria-zirconia composite oxide obtained in Example 1 and Comparative Examples 1 and 2 was used, and each composite oxide was mixed with a dinitrodiammine platinum aqueous solution having a platinum content of 0.1 g and 200 ml. In a beaker containing a solution of ion-exchanged water, impregnated respectively, dried under a temperature condition of 110 ° C. for 6 hours, and calcined in the atmosphere for 3 hours. The amount of platinum supported in the catalyst was about 1 A catalyst was produced by supporting platinum so as to be in mass%.

Next, 15 mg of each of the obtained catalysts was used, and for each catalyst, gas A composed of H ₂ (50% by volume) / N ₂ (50% by volume) and O ₂ (20% by volume) / N ₂ ( 80% by volume) was circulated alternately every 5 minutes so that the flow rate of each gas was 20 ml / min, and the increase / decrease in the mass of the catalyst at 300 ° C. was measured. A thermogravimetric analyzer (TG) was used for measuring the mass. Then, from the obtained mass fluctuation value, an average value (mol) of the amount of absorbed and released oxygen molecules per mol of CeO ₂ contained in the catalyst was calculated, and this was used as the OSC value. The results are shown in Table 1.

  As is clear from the results shown in Table 1, the ceria-zirconia composite oxide (Example 1) of the present invention was compared with the ceria for comparison in both cases of the actual measured specific surface area and after heating at 700 ° C. -It was confirmed that it was larger than the zirconia composite oxide (Comparative Examples 1-2). From these results, it is recognized that there is a difference in the characteristics of the composite oxide depending on the synthesis method, and the ceria-zirconia composite oxide (Example 1) of the present invention has a sufficiently high initial specific surface area and is excellent. It was confirmed that it had high heat resistance.

Moreover, since the particle diameter of the ceria-zirconia composite oxide obtained in Example 1 is 4.4 nm, the specific surface area theoretical value calculated from the above formula (3) was 203 m ² / g ¹ . In addition, since the ceria-zirconia composite oxide obtained in Comparative Example 1 has a particle diameter of 5 nm, the specific surface area theoretical value is 179 m ² / g ¹ , and further, the ceria-zirconia obtained in Comparative Example 2 Since the particle diameter of the composite oxide was 6 nm, it was 149 m ² / g ¹ . Therefore, when the specific surface area theoretical value is compared with the initial specific surface area actual measurement value, in the ceria-zirconia composite oxide obtained in Example 1, the difference between the actual measurement value and the theoretical value is 13 m ² / g ^1. In the ceria-zirconia composite oxide obtained in 1-2, the differences were 42 m ² / g ¹ (Comparative Example 1) and 20 m ² / g ¹ (Comparative Example 2), respectively. From these results and the results of the monodispersion rate shown in Table 1, the ceria-zirconia composite oxide (Example 1) of the present invention is more than the ceria-zirconia composite oxide (Comparative Examples 1 and 2) for comparison. Also, it was confirmed that the primary particles have a higher monodispersion rate. Therefore, it is surmised that the ceria-zirconia composite oxide (Example 1) of the present invention can support a noble metal with higher dispersion when used as a catalyst carrier.

  Further, as is apparent from the results shown in Table 1, when the ceria-zirconia composite oxide obtained in Example 1 is used, the Zr solid solution amount and the OCS performance may be sufficiently high. confirmed. Such a result is presumed to be due to a synergistic effect in which the dispersion state of the noble metal and the Zr solid solution amount are improved. On the other hand, in Comparative Example 1, since supercritical water was not used as a reaction field, the monodispersion rate was low and the OSC was also small. Furthermore, in Comparative Example 2, although supercritical water was used as a reaction field, neutralization and hot water supply were not performed. Therefore, the monodispersion rate was higher than that in Comparative Example 1, but the Zr solid solution amount was extremely low. The OSC was also getting smaller. From such a result, the raw material is neutralized as in the manufacturing method employed in Example 1 to once form a hydroxide, then hot water is supplied to improve the mixed state of Ce and Zr, and By using supercritical water as the reaction field, it is confirmed that the solid solution amount of zirconium can be improved over the conventional coprecipitation method (Comparative Example 1) and the method employed in Comparative Example 2, It was found that the ceria-zirconia composite oxide obtained in Example 1 can be suitably used as a catalyst carrier for exhaust gas purification.

  From the above results, according to the method for producing a ceria-zirconia composite oxide of the present invention, a ceria-zirconia composite oxide having both high Zr solid solution amount and improved monodispersity and sufficiently high heat resistance. It was confirmed that it was possible to manufacture the product efficiently and reliably. Moreover, it was confirmed that the ceria-zirconia composite oxide of the present invention obtained by adopting such a method has excellent characteristics as a catalyst carrier.

  As described above, according to the present invention, it is possible to efficiently and reliably produce a ceria-zirconia composite oxide having sufficiently high solid solution amount and monodispersion rate of zirconium and sufficiently high heat resistance. It is possible to provide a method for producing a possible ceria-zirconia composite oxide and a ceria-zirconia composite oxide obtained by adopting the method.

  Therefore, the method for producing a ceria-zirconia composite oxide of the present invention is a method for producing a ceria-zirconia composite oxide that can be suitably used as a ceria-zirconia-based carrier used as a catalyst for purifying exhaust gas of automobiles and the like. As particularly useful.

It is a schematic diagram which shows the outline of the manufacturing apparatus suitable for enforcing the manufacturing method of the ceria-zirconia complex oxide of this invention. 2 is a graph showing diffraction lines by X-ray diffraction of ceria-zirconia composite oxide obtained in Example 1. FIG. 5 is a graph showing diffraction lines by X-ray diffraction of ceria-zirconia composite oxide obtained in Comparative Example 1. FIG. 6 is a graph showing diffraction lines by X-ray diffraction of ceria-zirconia composite oxide obtained in Comparative Example 2. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Raw material solution storage container, 11 ... Neutralization liquid storage container, 12 ... Ion exchange water storage container for hot water supply, 13 ... Ion exchange water storage container for high hot water, 14 ... Supply pipe, 15 ... Pump, 16 DESCRIPTION OF SYMBOLS ... Heating furnace for hot water production, 17 ... Heating furnace for hot water formation, 18 ... Reaction furnace, 19 ... Cooling water storage container, 20 ... Cooler, 21 ... Solid-liquid separation and recovery part, 22 ... Pressure regulator, 23: Waste liquid container.

Claims (8)

Neutralizing a raw material solution containing a cerium salt and a zirconium salt to prepare a hydroxide of cerium and zirconium, and obtaining a reaction solution containing the hydroxide;
Supplying hot water to the reaction solution;
A step of obtaining a composite oxide of ceria and zirconia by hydrothermally reacting the hydroxide in the reaction solution after the hot water supply with water in a subcritical or supercritical state as a reaction field;
A method for producing a ceria-zirconia composite oxide, comprising:   The method for producing a ceria-zirconia composite oxide according to claim 1, wherein the temperature of the hot water is 250 to 350 ° C.   The method for producing a ceria-zirconia composite oxide according to claim 1, further comprising a step of supplying high-temperature water at 500 to 650 ° C. to the reaction solution after the supply of hot water.   The ceria-zirconia composite oxidation according to any one of claims 1 to 3, wherein the subcritical or supercritical water is water having a pressure of 20 to 50 Mpa and a temperature of 350 to 450 ° C. Manufacturing method.   The content ratio of a cerium salt and a zirconium salt in the raw material solution is in a range of 2: 8 to 8: 2 in terms of a molar ratio of cerium and zirconium in terms of metal (Ce: Zr). Item 5. The method for producing a ceria-zirconia composite oxide according to any one of Items 1 to 4. A complex oxide of ceria and zirconia,
Following formula (1):
[Solubility amount (%)] = {(5.425- [Lattice constant]) / 0.3297} × 100 (1)
(In formula (1), [lattice constant] is a value of a lattice constant calculated based on diffraction line position data belonging to the (3, 1, 1) plane when the composite oxide is subjected to X-ray diffraction measurement. Is shown.)
The solid solution amount of zirconium determined by the above is within a range of ± 12% with respect to the value of the molar fraction of zirconium contained in the composite oxide, and
Following formula (2):
[Monodispersion rate (%)] = ([actual value of specific surface area] / [theoretical value of specific surface area]) × 100 (2)
{In Formula (2), the specific surface area actual measurement value is a value measured by the BET (Brunauer Emmet Teller) one-point method, and the specific surface area theoretical value (m ² / g) is the following formula (3):
[Theoretical specific surface area] = 6 × 10 ³ / ([Density] × [Particle diameter]) (3)
(In formula (3), the particle diameter (nm) indicates the average particle diameter calculated by X-ray diffraction measurement, and the density (g / cm ³ ) is determined by the mixing ratio of cerium and zirconium, and the JCPDS-ICDD card. (Theoretical density value obtained from the ceria and zirconia density values described is shown.)
Indicates the value obtained by. }
The monodispersity (unit:%) of the complex oxide obtained by the above is 80% or more,
A ceria-zirconia composite oxide characterized by satisfying the following condition. The ceria-zirconia composite oxide according to claim 6, wherein a measured specific surface area of the composite oxide is 150 m ² / g or more. The ceria-zirconia composite oxide according to claim 6 or 7, wherein the actual measured specific surface area of the composite oxide is 40 m ² / g or more after heating at 700 ° C for 5 hours.

Images