Zirconia-based composite oxides and methods for their production.

Abstract

DEPCT65 The purpose of this invention is to provide a zirconia-based composite oxide. In order to create a layer of catalyst that, although thinner, still contains a high amount of catalyst. Sufficient for the function of treating exhaust gases on the walls of the honeycomb structure; the purpose of... This invention also provides a method for the production of zirconia-based composite oxides. Furthermore, this invention involves a zirconia-based composite oxide. Its characteristic features include a bulk density after tapping of 0.75 g / ml or more and an area... Its specific surface area after heat treatment for three hours at 1000 degrees Celsius is 45. Square meters / gram or more. -----------------------------------------------------------

Description

Zirconia-based composite oxide and method for producing zirconia-based composite oxide

[0001] The present invention relates to a zirconia-based composite oxide and a method for producing a zirconia-based composite oxide.

[0002] Exhaust gases emitted from internal combustion engines such as automobiles and combustion engines such as boilers contain harmful substances such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), which cause air pollution, etc. Efficiently purifying these harmful substances is an important issue from the perspective of preventing environmental pollution, and active research is being conducted into exhaust gas purification technologies that can simultaneously purify the above three harmful substances.

[0003] Furthermore, with the recent tightening of exhaust gas regulations, development is underway for honeycomb structures that have three-way catalytic performance to purify carbon monoxide, hydrocarbons, and nitrogen oxides in filters that capture particulate matter (for example, GPFs (gasoline particulate filters) and DPFs (diesel particulate filters)). The catalyst material is used by coating the honeycomb structure in a slurried state.

[0004] Patent Document 1 discloses a zirconia-based porous body having peaks at pore diameters of 8 to 20 nm and 30 to 100 nm in a pore distribution based on the BJH method and a total pore volume of 0.4 cc / g or more, and a zirconia-based porous body having peaks at pore diameters of 20 to 110 nm in a pore distribution based on the BJH method and a total pore volume of 0.4 cc / g or more (see claim 1 in particular). Patent Document 1 also discloses a zirconia-based porous body having a specific surface area of ​​at least 30 m after firing at 1000°C for 3 hours. ２ / g (see especially claim 6).

[0005] Patent Document 2 discloses a zirconia-based porous body having a total pore volume of at least 0.75 ml / g after heat treatment at 1000°C for 3 hours, and in which the pore volume of pores having a diameter of 10 to 100 nm after heat treatment at 1000°C for 3 hours is at least 30% of the total pore volume (see especially claim 1). Patent Document 2 also discloses a zirconia-based porous body having a specific surface area of ​​at least 35 m after heat treatment at 1000°C for 3 hours. ２ / g (see especially claim 2).

[0006] Patent Document 3 describes a method for producing a pore-forming material having a peak at a pore diameter of 20 to 100 nm in a pore distribution based on the BJH method, a P / W ratio of 0.05 or more, where W is the half-width of the peak obtained from the measured pore distribution curve and P is the height of the peak, and a total pore volume of 0.5 cm ３ / g or more, (2) after heat treatment at 1000°C for 12 hours, the pore diameter has a peak of 20 to 100 nm, the P / W ratio is 0.03 or more, and the pore diameter is at least 40 m ２ / g and a total pore volume of 0.3 cm ３ / g or more (see especially claim 1). In addition, Patent Document 3 discloses a zirconia-based porous body having a porosity of at least 20 m after heat treatment at 1100°C for 12 hours. ２ / g (see especially claim 2).

[0007] JP 2006-036576 A JP 2008-081392 A JP 2015-189655 A

[0008] The zirconia-based porous bodies disclosed in Patent Documents 1 to 3 have a high specific surface area even after heat treatment. Therefore, when these zirconia-based porous bodies are used as catalyst supports, the catalysts can be said to have high catalytic performance even after exposure to high temperatures. In Patent Documents 1 to 3, in order to obtain a high specific surface area even after heat treatment, the pore volumes of the mesopores (diameter 2 to 50 nm) to macropores (diameter 50 nm or more) of the zirconia-based porous bodies are increased.

[0009] When the zirconia-based porous bodies described in Patent Documents 1 to 3 are used, they maintain high catalytic performance even after exposure to high temperatures, but in order to form an amount of catalyst sufficient to function in exhaust gas treatment on the wall of the honeycomb structure, the catalyst layer needs to be made to a certain thickness. However, an increase in the thickness of the catalyst layer causes exhaust gas pressure loss, reducing the amount of exhaust gas passing through the honeycomb structure, which leads to problems such as a decrease in engine output and a decrease in exhaust gas purification performance.

[0010] Although studies have been conducted to reduce the pressure loss by reducing the thickness of the catalyst layer, there is a limit to how thin the thickness can be because it is necessary to maintain a certain level of exhaust gas purification performance. Even in Patent Documents 1 to 3, there is room for improvement in terms of achieving both exhaust gas purification performance and reduced pressure loss.

[0011] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a zirconia-based composite oxide that enables a sufficient amount of catalyst to function for exhaust gas treatment to be formed on the wall of a honeycomb structure even when the thickness of the catalyst layer is thin, and to provide a method for producing the zirconia-based composite oxide.

[0012] The present inventors have conducted extensive research into zirconia-based composite oxides, and have surprisingly discovered that by using a zirconia-based composite oxide that has a high specific surface area even after heat treatment and a high tapped bulk density, it is possible to form a sufficient amount of catalyst on the wall of a honeycomb structure to function effectively in exhaust gas treatment even when the catalyst layer is thin, thereby completing the present invention.

[0013] That is, the zirconia composite oxide according to the present invention has a tapped bulk density of 0.75 g / ml or more, and a specific surface area of ​​45 m2 or more after heat treatment at 1000°C for 3 hours. ２ / g or more.

[0014] Generally, in the manufacture of catalytic converters, a honeycomb structure is coated with a slurry of a composite oxide carrying a catalyst such as a precious metal, followed by drying and firing processes to form a catalyst layer. The inventors focused on tap bulk density and thought that increasing the tap bulk density would allow the thickness of the catalyst layer to be reduced. According to the above configuration, since the tap bulk density is 0.75 g / ml or more, when the slurry is made into a slurry and applied to the honeycomb structure, it is possible to reduce the coating thickness while increasing the amount of catalyst support per unit volume. As a result, even a thin catalyst layer has sufficient exhaust gas purification ability. Furthermore, according to the above configuration, a specific surface area of ​​45 m after heat treatment at 1000°C for 3 hours is achieved. ２ / g or more, it can be said that the specific surface area is high even after heat treatment. Therefore, it can be said that the catalytic performance is high even after exposure to high temperatures. As described above, with the above configuration, it is possible to form an amount of catalyst on the wall of the honeycomb structure that functions sufficiently for exhaust gas treatment even if the thickness of the catalyst layer is thin.

[0015] In the above-described configuration, the tapped bulk density is preferably 0.8 g / ml or more and 1.3 g / ml or less.

[0016] In the above-described configuration, the tapped bulk density is preferably 0.83 g / ml or more and 1.27 g / ml or less.

[0017] In the above-mentioned structure, the specific surface area after the heat treatment at 1000°C for 3 hours is 47m ２ / g or more 100m ２ / g or less is preferable.

[0018] In the above-mentioned structure, the specific surface area after heat treatment at 1100°C for 3 hours is 15m ２ / g or more 70m ２ / g or less is preferable.

[0019] The specific surface area after heat treatment at 1100°C for 3 hours is 15m ２ / g or more, it can be said that the catalyst has high catalytic performance even after being exposed to a higher temperature.

[0020] In the above configuration, the specific surface area is 45 m ２ / g or more 150m ２ / g or less is preferable.

[0021] Specific surface area is 45m ２ / g or more, it can be said that the specific surface area is relatively high before heat treatment (before exposure to high temperature).

[0022] In the above-mentioned structure, in the pore distribution based on mercury intrusion porosimetry, the ratio of the pore volume of pores having a diameter of 100 nm or more and 1000 nm or less to the total pore volume is preferably 17% or less of the total pore volume.

[0023] In the pore distribution based on mercury intrusion porosimetry, when the ratio of the pore volume of pores having a diameter of 100 nm or more and 1000 nm or less to the total pore volume is 17% or less of the total pore volume, the tapped bulk density is 0.75 g / ml or more and the specific surface area after heat treatment at 1000°C for 3 hours is 45 m ２ / g or more can be easily achieved. This is due to the following discovery by the present inventors.

[0024] The present inventors have discovered the following regarding the relationship between the pore size and physical properties of zirconia-based composite oxides: (1) Pores with a diameter of 10-100 nm are formed by the aggregation of primary particles. (2) By increasing the volume of pores with a diameter of 10-100 nm, the specific surface area after heat treatment can be increased. (3) The volume of pores with a diameter of 100 nm or more has little effect on the specific surface area after heat treatment. (4) The volume of pores with a diameter of 100 nm or more has a significant effect on the tapped bulk density of zirconia-based composite oxides.

[0025] Based on the above findings, the present inventors believed that the tapped bulk density could be increased by reducing the volume of pores with diameters of 100 nm or more. In other words, they believed that by increasing the volume of pores with diameters of 10-100 nm in a zirconia-based composite oxide and decreasing the volume of pores with diameters of 100 nm or more, it would be possible to maintain a high specific surface area after heat treatment of the zirconia-based composite oxide and increase the tapped bulk density. As a result, they found that if the pore volume of pores with diameters of 100 nm or more and 1000 nm or less accounts for 17% or less of the total pore volume in the pore distribution based on mercury intrusion porosimetry, the tapped bulk density would be 0.75 g / ml or more and the specific surface area after heat treatment at 1000°C for 3 hours would be 45 m ２ / g or more can be easily achieved.

[0026] In the above-mentioned configuration, the particle diameter D ５０ is preferably 5 μm or more and 25 μm or less.

[0027] Particle diameter D ５０ When the particle size is 5 μm or more and 25 μm or less, the tap bulk density can be easily increased.

[0028] In the above-mentioned composition, when the entire zirconia-based composite oxide is taken as 100 mass %, the zirconia content is preferably 30 mass % or more and 95 mass % or less.

[0029] When the zirconia content is 30% by mass or more and 95% by mass or less, the carrier can be suitably used as a catalyst carrier.

[0030] In the above-mentioned composition, it is preferable to contain one or more oxides selected from rare earth elements other than Pm.

[0031] The inclusion of one or more oxides selected from rare earth elements other than Pm can improve the thermal stability of the specific surface area, i.e., it can reduce the amount of change in the specific surface area before and after exposure to high temperatures, thereby preventing a significant decrease in catalytic performance.

[0032] The present invention also provides a method for producing a zirconia-based composite oxide, characterized in that it comprises: a first step including a step of adding a sulfating agent to a zirconium salt solution at a temperature of 100°C or higher while stirring at a stirring Reynolds number of 400 or higher and 2000 or lower, and a step of cooling the solution to 60°C or lower after adding the sulfating agent; and a second step including a step of heating the cooled solution obtained in the first step to a temperature of 100°C or higher while stirring at a stirring Reynolds number of 10 or higher and 350 or lower.

[0033] In the above-described configuration, in the first step, a sulfating agent is added to a zirconium salt solution at a temperature of 100°C or higher while stirring at a stirring Reynolds number of 400 to 2000. The first step controls the generation and aggregation of primary particles, in other words, the volume of pores with diameters of 10-100 nm. Therefore, the reaction conditions in the first step significantly affect the heat resistance of the specific surface area (specific surface area after heat treatment). The aggregation state of primary particles is governed by chemical factors such as reaction temperature and physical factors such as shear stress due to turbulence. In the first step, the aggregation state of primary particles is controlled by controlling the temperature to 100°C or higher and the stirring Reynolds number to 400 to 2000, thereby controlling the volume of pores with diameters of 10-100 nm to fall within a suitable range (to increase the volume). In the above-described configuration, in the second step, the cooled solution obtained in the first step is heated to a temperature of 100°C or higher while stirring at a stirring Reynolds number of 10 to 350. The second step is a step of further controlling the aggregation state of the basic zirconium sulfate slurry obtained in the first step. In the second step, the size of secondary particles or higher-order particles is controlled by stirring the slurry in a laminar flow with a stirring Reynolds number of 10 or more and 350 or less, and the volume of pores having a diameter of 100 nm or more is controlled to be within a suitable range (to be small). As described above, according to the method for producing a zirconia-based composite oxide, a zirconia-based composite oxide having a large volume of pores having a diameter of 10-100 nm and a small volume of pores having a diameter of 10-100 nm can be easily produced, and therefore, a tapped bulk density of 0.75 g / ml or more and a specific surface area of ​​45 m after heat treatment at 1000°C for 3 hours can be obtained. ２ This makes it possible to easily produce a zirconia-based composite oxide having a zirconia content of 1 / g or more.

[0034] In the above-described configuration, it is preferable that the stirring Reynolds number in the second step is 50 or more and 300 or less.

[0035] In the above-described configuration, it is preferable that the stirring Reynolds number in the first step is 600 or more and 1800 or less.

[0036] In the above-described configuration, the temperature during stirring in the first step is preferably 105° C. or higher and 200° C. or lower.

[0037] In the above-described configuration, the temperature during stirring in the second step is preferably 105° C. or higher and 180° C. or lower.

[0038] According to the present invention, it is possible to provide a zirconia-based composite oxide that enables a sufficient amount of catalyst to function for exhaust gas treatment to be formed on the wall of a honeycomb structure even when the thickness of the catalyst layer is thin, and a method for producing the zirconia-based composite oxide.

[0039] FIG. 2 is a diagram showing the pore distribution of the zirconia-based composite oxides of Example 1 and Comparative Example 1.

[0040] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments. In this specification, zirconia is a general term and contains 10 mass % or less of impurity metal compounds including hafnia.

[0041] [Zirconia-based composite oxide] The zirconia-based composite oxide according to this embodiment, which will be described in detail later, is a composite oxide containing zirconia as an essential component and containing oxides other than zirconia (other metal oxides). The use of the zirconia-based composite oxide according to this embodiment is not particularly limited, but it is useful as a catalyst support for exhaust gas purification. When used as a catalyst support for exhaust gas purification, examples of catalysts that can be supported include noble metal catalysts.

[0042] <Tap Bulk Density> The zirconia-based composite oxide according to this embodiment has a tap bulk density of 0.75 g / ml or more. Because the tap bulk density is 0.75 g / ml or more, when the zirconia-based composite oxide is slurried and applied to a honeycomb structure, the coating thickness can be reduced while increasing the amount of catalyst support per unit volume. As a result, even a thin catalyst layer has sufficient exhaust gas purification capacity. The inventors have confirmed that the amount of catalyst support per unit volume in the catalyst layer after applying the zirconia-based composite oxide as a slurry is proportional to the tap bulk density of the zirconia-based composite oxide. The tap bulk density is preferably 0.8 g / ml or more, more preferably 0.83 g / ml or more, even more preferably 0.85 g / ml or more, and particularly preferably 0.9 g / ml or more. The upper limit of the tapped bulk density is not particularly limited, but is preferably 1.3 g / ml or less, more preferably 1.27 g / ml or less, even more preferably 1.25 g / ml or less, particularly preferably 1.2 g / ml or less, and especially preferably 1.15 g / ml or less.

[0043] <Specific Surface Area> The zirconia composite oxide had a specific surface area of ​​45 m after heat treatment at 1000°C for 3 hours. ２ / g or more. After heat treatment at 1000°C for 3 hours, the specific surface area is 45m ２ / g or more, it can be said that the catalyst has a high specific surface area even after heat treatment. In other words, it can suppress deterioration (aggregation and enlargement) of the precious metal supported on the zirconia-based composite oxide as a support. Therefore, it can be said that the catalyst has high catalytic performance even after being exposed to high temperatures.

[0044] The specific surface area after the heat treatment at 1000°C for 3 hours is preferably 47m ２ / g or more, more preferably 50m ２ / g or more, more preferably 53m ２ The upper limit of the specific surface area after heat treatment at 1000°C for 3 hours is not particularly limited, but it is preferably 100 m ２ / g or less, more preferably 95m ２ / g or less, more preferably 90m ２The specific surface area after the heat treatment at 1000° C. for 3 hours is generally lower than the specific surface area before the heat treatment.

[0045] The zirconia composite oxide has a specific surface area of ​​15 m after heat treatment at 1100°C for 3 hours. ２ / g or more. After heat treatment at 1100°C for 3 hours, the specific surface area is preferably 15m ２ / g or more, it can be said that the catalyst has high catalytic performance even after being exposed to a higher temperature.

[0046] The specific surface area after the heat treatment at 1100°C for 3 hours is more preferably 17m ２ / g or more, more preferably 20m ２ / g or more, particularly preferably 23m ２ The upper limit of the specific surface area after the heat treatment at 1100°C for 3 hours is not particularly limited, but it is preferably 70 m ２ / g or less, more preferably 65m ２ / g or less, more preferably 60m ２ The specific surface area after the heat treatment at 1100°C for 3 hours is generally lower than the specific surface area before the heat treatment and the specific surface area after the heat treatment at 1000°C for 3 hours.

[0047] The zirconia composite oxide has a specific surface area (initial specific surface area) of 45 m ２ / g or more 150m ２ / g or less. ２ / g or more 150m ２ / g or less, it can be said that the zirconia-based composite oxide has a relatively high specific surface area before heat treatment (before exposure to high temperatures). Here, the specific surface area (initial specific surface area) refers to the specific surface area before heat treatment, pulverization, etc. are performed after production of the zirconia-based composite oxide.

[0048] The specific surface area (initial specific surface area) is preferably 45 m ２ / g or more, more preferably 50m ２ / g or more, more preferably 55m ２ The upper limit of the specific surface area is not particularly limited, but is preferably 150 m ２ / g or less, more preferably 145m ２ / g or less, more preferably 140m ２ / g or less, particularly preferably 135m ２ / g or less, particularly preferably 130m ２ / g or less.

[0049] The specific surface area after heat treatment at 1000°C for 3 hours, the specific surface area after heat treatment at 1100°C for 3 hours, and the specific surface area (initial specific surface area) refer to values ​​obtained by the method described in the Examples.

[0050] <Pore Volume> In the zirconia-based composite oxide according to this embodiment, the ratio of the pore volume of pores having a diameter of 100 nm or more and 1000 nm or less to the total pore volume (hereinafter also referred to as "pore volume ratio A") is preferably 17% or less of the total pore volume. When the pore volume ratio A is 17% or less of the total pore volume, the tapped bulk density is 0.75 g / ml or more, and the specific surface area after heat treatment at 1000°C for 3 hours is 45 m ２ / g or more can be easily achieved, as is clear from the examples.

[0051] The pore volume ratio A is more preferably 15% or less, even more preferably 12% or less, and particularly preferably 10% or less. There is no particular limitation on the lower limit of the pore volume ratio A, but it is preferably 0.1% or more, more preferably 0.3% or more.

[0052] The total pore volume is preferably 0.5 ml / g or more, more preferably 0.7 ml / g or more, and even more preferably 0.8 ml / g or more. The total pore volume is preferably 2.0 ml / g or less, more preferably 1.9 ml / g or less, and even more preferably 1.8 ml / g or less.

[0053] The pore volume of pores having a diameter of 100 nm or more and 1000 nm or less is preferably 0.01 ml / g or more, more preferably 0.02 ml / g or more, and even more preferably 0.03 ml / g or more. The pore volume of pores having a diameter of 100 nm or more and 1000 nm or less is preferably 0.20 ml / g or less, more preferably 0.19 ml / g or less, and even more preferably 0.18 ml / g or less.

[0054] The pore volume of pores having a diameter of 10 nm or more and less than 100 nm is preferably 0.20 ml / g or more, more preferably 0.25 ml / g or more, and even more preferably 0.30 ml / g or more. When the pore volume of pores having a diameter of 10 nm or more and less than 100 nm is 0.20 ml / g or more, the specific surface area after heat treatment at 1000°C for 3 hours can be further increased. The pore volume of pores having a diameter of 10 nm or more and less than 100 nm is preferably 1.00 ml / g or less, more preferably 0.95 ml / g or less, and even more preferably 0.90 ml / g or less.

[0055] The details of how to determine the total pore volume, the pore volume of the pores having a diameter of 10 nm or more and less than 100 nm, and the pore volume of the pores having a diameter of 100 nm or more and 1000 nm or less are according to the methods described in the Examples.

[0056] <Particle diameter> Particle diameter D of the zirconia-based composite oxide ５０ is preferably 5 μm to 100 μm, more preferably 8 μm to 90 μm, and even more preferably 10 μm to 80 μm. ５０ When the particle diameter D is 5 μm or more and 100 μm or less, the tap bulk density can be easily increased. ５０ If the particle diameter D is too small, the tapped bulk density tends to be low. ５０ By making the particle diameter D relatively large (for example, 5 μm to 100 μm), it becomes easy to increase the tap bulk density. ５０ The smaller the particle diameter D, the more densely packed the particles are. On the contrary, since zirconia-based composite oxides are porous, their mass per unit volume is light, and their shape is not spherical. ５０ The smaller the particle diameter D, the smaller the tapped bulk density tends to be. ５０ The particle size of the zirconia-based composite oxide is measured before it is crushed or heat-treated after it is produced. The term "crushing" as used herein means to crush the material into small particles, and refers to crushing by a general method such as a planetary mill, a ball mill, or a jet mill.

[0057] The particle diameter D ５０ refers to the value obtained by the method described in the Examples.

[0058] <Composition> The zirconia-based composite oxide contains zirconia. The zirconia content is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and particularly preferably 45% by mass or more, when the entire zirconia-based composite oxide is taken as 100% by mass. There is no particular upper limit for the zirconia content, but the zirconia content is preferably 95% by mass or less, more preferably 92% by mass or less, even more preferably 90% by mass or less, and particularly preferably 85% by mass or less. When the zirconia content is 30% by mass or more but 95% by mass or less, the zirconia can be suitably used as a catalyst support.

[0059] The zirconia-based composite oxide preferably contains one or more oxides selected from rare earth elements.

[0060] The rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. However, it is preferable that the zirconia-based composite oxide does not contain Pm. In other words, it is more preferable that the zirconia-based composite oxide contains one or more oxides selected from rare earth elements other than Pm.

[0061] The inclusion of one or more oxides selected from rare earth elements other than Pm can improve the thermal stability of the specific surface area, i.e., it can reduce the amount of change in the specific surface area before and after exposure to high temperatures, thereby preventing a significant decrease in catalytic performance.

[0062] Among the rare earth elements, Y (yttrium), La (lanthanum), Ce (cerium), Nd (neodymium), and Pr (praseodymium) are preferred. Among these, Y, La, and Ce are more preferred, La and Ce are even more preferred, and Ce is particularly preferred. That is, the zirconia-based composite oxide preferably contains one or more oxides selected from the group consisting of lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide, and yttrium oxide.

[0063] In addition to zirconia and the oxides of rare earth elements, the zirconia-based composite oxide may contain oxides of one or more elements selected from the group consisting of: A) one or more oxides selected from the group consisting of In, Si, Sn, Bi, and Zn; B) transition metal oxides (excluding oxides of rare earth elements and precious metal elements); and C) alkaline earth metal oxides. Hereinafter, the elements indicated as A) to C) are referred to as "other elements" in this specification. When the zirconia-based composite oxide contains oxides of the other elements, the content of the oxides of the other elements may be 0.1% by mass or more, calculated as oxide, when the entire zirconia-based composite oxide is taken as 100% by mass. The content of the oxides of the other elements is not particularly limited, but may be 20% by mass or less, 10% by mass or less, 7% by mass or less, 5% by mass or less, etc. Examples of the transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Ta, and W. Examples of the alkaline earth metals include Mg, Ca, Sr, and Ba.

[0064] Preferable composition ratios of the zirconia-based composite oxide include the following combinations (1) to (4) of which the total does not exceed 100%. (1) Zirconia: 30% to 95%; Ceria: 0% to 70%; Rare earth oxides other than ceria: 0% to 30%; Oxides of other elements: 0% to 20%. (2) Zirconia: 35% to 92%; Ceria: 5% to 65%; Rare earth oxides other than ceria: 0% to 25%; Oxides of other elements: 0% to 10%. (3) Zirconia: 40% to 90%; Ceria: 10% to 60%; Rare earth oxides other than ceria: 0% to 20%; Oxides of other elements: 0% to 7%. (4) Zirconia: 45% to 85%; Ceria: 10% to 55%; Rare earth oxides other than ceria: 0% to 20%; Oxides of other elements: 0% to 5%.

[0065] The composition of the zirconia-based composite oxide is determined by the method described in the Examples.

[0066] The zirconia-based composite oxide according to this embodiment has a tapped bulk density of 0.75 g / ml or more, and a specific surface area of ​​45 m after heat treatment at 1000°C for 3 hours. ２ / g or more, it is possible to form an amount of catalyst on the wall of the honeycomb structure that functions sufficiently for exhaust gas treatment even if the thickness of the catalyst layer is thin. As a result, the pressure loss caused by the thickness of the catalyst layer can be reduced, and the fuel efficiency of automobiles, etc. can be improved. In addition, since the amount of catalyst that can be coated per unit volume increases, the oxygen storage capacity (OSC) per unit volume can be improved. By improving the OSC per unit volume, the catalyst performance can be improved.

[0067] [Method for producing zirconia-based composite oxide] An example of a method for producing a zirconia-based composite oxide will be described below, although the method for producing a zirconia-based composite oxide of the present invention is not limited to the following example.

[0068] The method for producing a zirconia-based composite oxide according to this embodiment includes a first step including a step of adding a sulfating agent to a zirconium salt solution at a temperature of 100°C or higher while stirring at a stirring Reynolds number of 400 or higher and 2000 or lower, and a step of cooling the solution to 60°C or lower after adding the sulfating agent; and a second step including a step of heating the cooled solution obtained in the first step to a temperature of 100°C or higher while stirring at a stirring Reynolds number of 10 or higher and 350 or lower.

[0069] <First Step> In the method for producing a zirconia-based composite oxide according to this embodiment, first, a sulfating agent is added to a zirconium salt solution at a temperature of 100°C or higher while stirring at a stirring Reynolds number of 400 or more and 2000 or less (first step 1-1).

[0070] Here, the stirring Reynolds number (Re ｄ The stirring Reynolds number (Re ｄ ) is expressed by the following formula: ｄ =ρnd ２ / μ d: Blade diameter [m] n: Blade rotation speed [s －１ ] ρ: Density [kg / m ３ ] μ: Viscosity [Pas]

[0071] Normally, when the mixing Reynolds number is 10 or less, the mixed liquid is in a strictly laminar flow state, with flow mainly occurring in the rotational direction. When the mixing Reynolds number exceeds 10, a discharge flow from the impeller gradually occurs, and a circulating flow occurs within the vessel. Furthermore, when the mixing Reynolds number exceeds 400, turbulent flow begins to occur. A mixing Reynolds number in the range of several hundred to several thousand is considered to be in a transition state, where turbulent flow begins to occur near the impeller, while laminar flow remains near the vessel wall and vessel bottom, away from the impeller.

[0072] Step 1-1 is a step for controlling the generation and aggregation of primary particles, in other words, a step for controlling the volume of pores with diameters of 10-100 nm. Therefore, the reaction conditions in Step 1 have a significant effect on the heat resistance of the specific surface area (specific surface area after heat treatment). The aggregation state of the primary particles is governed by chemical factors such as the reaction temperature and physical factors such as shear stress caused by turbulent flow. In Step 1, the aggregation state of the primary particles is controlled by controlling the temperature to 100°C or higher and the stirring Reynolds number to 400 or higher and 2000 or lower, and the volume of pores with diameters of 10-100 nm is controlled to be within a suitable range (to be large).

[0073] As described above, in Step 1-1, a sulfating agent is added to a zirconium salt solution at a temperature of 100°C or higher while stirring at a stirring Reynolds number of 400 or higher and 2000 or lower, which creates a turbulent flow so as to easily generate fine primary particles. The stirring Reynolds number in Step 1-1 is preferably 500 or higher, more preferably 600 or higher, even more preferably 700 or higher, and particularly preferably 800 or higher. The stirring Reynolds number in Step 1-1 is preferably 1900 or lower, more preferably 1800 or lower, even more preferably 1700 or lower, and particularly preferably 1600 or lower.

[0074] The stirring temperature in Step 1-1 is preferably 105°C or higher, more preferably 110°C or higher, and even more preferably 115°C or higher. The stirring temperature in Step 1-1 is preferably 200°C or lower, more preferably 195°C or lower, and even more preferably 190°C or lower. The zirconium salt solution and the sulfating agent usually react at a temperature of 65°C or higher to produce basic zirconium sulfate. Therefore, in this embodiment, the stirring temperature in Step 1 is set to 100°C or higher, thereby appropriately promoting the sulfation reaction and facilitating the formation of fine primary particles. If the stirring temperature in Step 1 is too low, the sulfation reaction will be slow, and large aggregated particles will tend to be more likely to be produced.

[0075] The pressure in the step 1-1 is not particularly limited, but is preferably 1.0×10 ５ Pa or more, more preferably 1.2 × 10 ５ The pressure is not particularly limited, but is preferably 1.5×10 ６ Pa or less, more preferably 1.4 × 10 ６ Pa or less.

[0076] The sulfating agent is preferably added after the temperature is brought to the same temperature as the zirconium salt solution, and the zirconium salt solution reacts with the sulfating agent to produce basic zirconium sulfate.

[0077] The zirconium salt may be any salt capable of supplying zirconium ions, such as zirconium oxynitrate, zirconium oxychloride, zirconium nitrate, etc. These may be used alone or in combination of two or more. Among these, zirconium oxychloride is preferred because of its high productivity on an industrial scale.

[0078] The solvent for preparing the zirconium salt solution may be selected depending on the type of zirconium salt, and water (pure water, ion-exchanged water, the same applies below) is usually preferred.

[0079] The concentration of the zirconium salt solution is not particularly limited, but generally, zirconium oxide (ZrO ２It is desirable that the amount of the soluble fiber contained in the water is 5 to 250 g (particularly 20 to 150 g).

[0080] The sulfating agent is not limited as long as it reacts with zirconium ions to produce sulfate (i.e., a sulfating reagent), and examples thereof include sodium sulfate, potassium sulfate, and ammonium sulfate. The sulfating agent may be in any form, such as a powder or a solution, but a solution (particularly an aqueous solution) is preferred. When a solution is used, the concentration of the solution can be appropriately set.

[0081] The sulfating agent is sulfate (SO ４ ２－ ) / ZrO ２ It is preferable to add the acid so that the weight ratio of the acid to the acid mixture is 0.3 to 0.6. The free acid concentration in the mixed solution is preferably 0.2 to 2.2 N (normal). Examples of free acids include sulfuric acid, nitric acid, and hydrochloric acid. There are no limitations on the type of free acid, but hydrochloric acid is preferred because of its high productivity on an industrial scale.

[0082] After adding the sulfating agent (after step 1-1), it is preferable to hold the reaction solution for 10 to 60 minutes to mature the produced basic zirconium sulfate (step 1-2). The basic zirconium sulfate is not limited, but examples thereof include ZrOSO ４ ZrO ２ , 5ZrO ２ ・3 SO ３ , 7ZrO ２ ・3 SO ３ The basic zirconium sulfate may be one of these or a mixture of two or more of these.

[0083] During the step of holding the reaction solution for 10 to 60 minutes (step 1-2), it is preferable to continue stirring as in step 1-1.

[0084] Thereafter (after the above-mentioned step 1-2), the reaction solution is cooled to 60° C. or less (step 1-3).

[0085] The cooling is preferably 50°C or lower, more preferably 40°C or lower. There is no particular limitation on the lower limit temperature of the cooling, but it is preferably to a temperature at which the reaction liquid does not freeze, such as 10°C or higher, 20°C or higher, etc. The cooling rate does not need to be particularly controlled, and the reaction liquid may be allowed to cool naturally. However, when the scale is large, natural cooling takes time, so cooling may be performed using a heat exchanger or the like. In this case, the cooling rate may be appropriately set, for example, within the range of 0.1°C / min or higher and 20°C / min or lower.

[0086] The first step has been described above.

[0087] <Second Step> After the first step, the cooled solution obtained in the first step is heated to a temperature of 100° C. or higher while being stirred at a stirring Reynolds number of 10 or more and 350 or less (2-1 step).

[0088] Step 2-1 is a step of further controlling the aggregation state of the basic zirconium sulfate slurry obtained in Step 1. In Step 2, the size of secondary particles or higher-order particles is controlled by stirring the slurry in a laminar flow with a stirring Reynolds number of 10 or more and 350 or less, and the volume of pores with diameters of 100 nm or more is controlled to fall within a suitable range (to be small).

[0089] As described above, in the 2-1 step, in order to promote particle aggregation, the mixture is heated to a temperature of 100°C or higher while being stirred at a stirring Reynolds number of 10 or more and 350 or less so that only laminar flow occurs without generating turbulence.

[0090] The heating rate is not particularly limited, but may be set appropriately within the range of 0.1° C. / min to 10° C. / min.

[0091] The stirring Reynolds number in the step 2-1 is 10 or more, preferably 20 or more, more preferably 50 or more, and even more preferably 100 or more. The stirring Reynolds number in the step 2-1 is 350 or less, preferably 300 or less, more preferably 250 or less, and even more preferably 220 or less. In the step 2-1, stirring at a stirring Reynolds number of 10 or more and 350 or less can create a laminar flow in the reaction vessel and promote aggregation in the sulfation reaction. As a result, the volume of pores with a diameter of 100 nm or more can be reduced, resulting in a powder with a high tapped bulk density.

[0092] The heating temperature in the step 2-1 is preferably 105° C. or higher, more preferably 110° C. or higher, and even more preferably 115° C. or higher. The stirring temperature in the step 2-1 is preferably 180° C. or lower, more preferably 175° C. or lower, and even more preferably 170° C. or lower.

[0093] The pressure in the 2-1 step is not particularly limited, but is preferably 1.0×10 ５ Pa or more, more preferably 1.2 × 10 ５ The pressure is not particularly limited, but is preferably 1.5×10 ６ Pa or less, more preferably 1.4 × 10 ６ Pa or less.

[0094] After the temperature reaches 100° C. or higher, the reaction solution is preferably maintained for 10 to 60 minutes to age the produced basic zirconium sulfate (step 2-2).

[0095] During the step of holding the reaction solution for 10 to 60 minutes (step 2-2), it is preferable to continue stirring as in step 2-1.

[0096] Thereafter (after the step 2-2), the reaction solution is cooled to 50° C. or less (step 2-3). By the above steps, a basic zirconium sulfate slurry is obtained.

[0097] The cooling may be carried out in the same manner as in the step 1-2.

[0098] The second step has been described above.

[0099] Thereafter, when one or more oxides selected from the group consisting of rare earth elements and other elements are to be contained in the zirconia-based composite oxide, a predetermined amount of a salt solution or compound of one or more metals selected from the group consisting of rare earth elements and other elements is added to the basic zirconium sulfate-containing slurry after the second step and before the neutralization step described below.

[0100] The first step and the second step (particularly the first-1 step and the second-1 step) are preferably carried out in an autoclave, which allows easy control of temperature and pressure.

[0101] Next, the basic zirconium sulfate is neutralized to produce zirconium hydroxide. Specifically, zirconium hydroxide is produced by neutralizing the basic zirconium sulfate with an alkali. The alkali is not limited, and examples that can be used include ammonium hydroxide, ammonium bicarbonate, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide is preferred from the viewpoint of industrial cost.

[0102] The amount of alkali to be added is not particularly limited as long as it can produce zirconium hydroxide as a precipitate from the basic zirconium sulfate solution. Usually, the alkali is added so that the pH of the solution becomes 11 or higher, preferably 12 or higher.

[0103] After the neutralization reaction, the zirconium hydroxide-containing solution is preferably kept at 35 to 60° C. for at least 1 hour, which allows the produced precipitate to mature and makes it easier to filter.

[0104] Next, the zirconium hydroxide is recovered by solid-liquid separation, such as filtration, centrifugation, or decantation.

[0105] After the zirconium hydroxide is recovered, it is preferable to wash the zirconium hydroxide with water to remove any adhering impurities.

[0106] The zirconium hydroxide may be dried by natural drying or by heating.

[0107] Next, the zirconium hydroxide is heat-treated (calcined) to obtain a zirconia-based composite oxide. The heat treatment temperature is not particularly limited, but is preferably about 400 to 900°C for about 1 to 5 hours. The heat treatment atmosphere is preferably air or an oxidizing atmosphere.

[0108] The obtained zirconia-based composite oxide may be subjected to a treatment for deflocculating the agglomerates, if necessary, for the purpose of improving the handling properties.

[0109] The method for producing a zirconia-based composite oxide according to this embodiment has been described above.

[0110] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. The zirconia-based composite oxides obtained in the examples and comparative examples contain 1.3 to 2.5 mass % of hafnium oxide as an unavoidable impurity relative to zirconium oxide (calculated using the following formula (X)). <Formula (X)> ([mass of hafnium oxide] / ([mass of zirconium oxide]+[mass of hafnium oxide]))×100(%)

[0111] [Preparation of Zirconia-Based Composite Oxide] (Example 1) 144 g of zirconium oxychloride octahydrate (ZrO ２ The resulting solution (55 g) was dissolved in ion-exchanged water, and then 35% by mass hydrochloric acid and ion-exchanged water were added to adjust the acid concentration to 0.67N and ZrO ２ The concentration was adjusted to 4 w / v % (mass volume percent concentration) to obtain a zirconium salt solution.

[0112] <First Step> The obtained zirconium salt solution was placed in an autoclave and heated to 120°C while stirring so that the stirring Reynolds number was 1000. During this time, the pressure was reduced to 2 × 10 ５ The temperature at the start of the temperature increase was room temperature (25°C), and the time from the start of the temperature increase until the temperature reached 120°C was 1.5 hours.

[0113] Immediately after reaching 120°C, 120°C, 2 x 10 ５In the autoclave, 828 g of 5% sodium sulfate (sulfating agent) was added and the mixture was maintained at 100 Pa for 15 minutes. Stirring (stirring Reynolds number: 1000) was continued during this time.

[0114] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 1000) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours.

[0115] This is the first step.

[0116] <Second Step> After allowing to cool naturally, the stirring conditions were changed so that the stirring Reynolds number was 200, and the temperature was raised to 120°C while stirring. During this time, the pressure was 2 x 10 ５ The time from the start of temperature increase until the temperature reached 120°C was 1.5 hours.

[0117] After the temperature reached 120°C, the mixture was maintained at this temperature for 15 minutes, during which stirring (Reynolds number of stirring: 200) was continued.

[0118] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 200) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours. In this manner, a basic zirconium sulfate slurry was obtained.

[0119] This is the second step.

[0120] The obtained basic zirconium sulfate-containing slurry was added with 400 g of cerium nitrate solution (CeO ２ Conversion: 40g), lanthanum nitrate solution 50g (La ２ O ３ Equivalent: 5 g) was added.

[0121] Further, 25% sodium hydroxide (alkali for neutralization) was added until the pH reached 13 or higher, thereby forming a hydroxide precipitate (zirconium hydroxide-containing slurry).

[0122] The obtained hydroxide precipitate was filtered and thoroughly washed with water, and the obtained hydroxide was dried at 105°C for 24 hours. The dried hydroxide was heat-treated (calcined) in air at 600°C for 5 hours. The obtained calcined product was broken up with a hammer head (manufactured by IKA, MF 10.2 hammer head) to obtain the zirconia-based composite oxide according to Example 1.

[0123] Example 2 A zirconia-based composite oxide according to Example 2 was obtained in the same manner as in Example 1, except that the stirring conditions in the second step were changed to a stirring Reynolds number of 100.

[0124] (Example 3) 155 g of zirconium oxychloride octahydrate (ZrO ２ The resulting solution (60 g) was dissolved in ion-exchanged water, and then 35% by mass hydrochloric acid and ion-exchanged water were added to adjust the acid concentration to 0.67N and ZrO ２ The concentration was adjusted to 4 w / v % (mass volume percent concentration) to obtain a zirconium salt solution.

[0125] <First Step> The obtained zirconium salt solution was placed in an autoclave and heated to 120°C while stirring so that the stirring Reynolds number was 1000. During this time, the pressure was reduced to 2 × 10 ５ The temperature at the start of the temperature increase was room temperature (25°C), and the time from the start of the temperature increase until the temperature reached 120°C was 1.5 hours.

[0126] Immediately after reaching 120°C, 120°C, 2 x 10 ５ In the autoclave, 888 g of 5% sodium sulfate (sulfating agent) was added and the mixture was maintained at 100 Pa for 15 minutes. During this time, stirring (Reynolds number of stirring: 1000) was continued.

[0127] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 1000) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours.

[0128] This is the first step.

[0129] <Second Step> After allowing to cool naturally, the stirring conditions were changed so that the stirring Reynolds number was 200, and the temperature was raised to 120°C while stirring. During this time, the pressure was 2 x 10 ５ The time from the start of temperature increase until the temperature reached 120°C was 1.5 hours.

[0130] After the temperature reached 120°C, the mixture was maintained at this temperature for 15 minutes, during which stirring (Reynolds number of stirring: 200) was continued.

[0131] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 200) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours. In this manner, a basic zirconium sulfate slurry was obtained.

[0132] This is the second step.

[0133] To the obtained basic zirconium sulfate-containing slurry, 250 g of cerium nitrate solution (CeO ２ Conversion: 25g), lanthanum nitrate solution 50g (La ２ O ３ Conversion: 5 g) and 100 g of yttrium nitrate solution (Y ２ O ３ (equivalent to 10 g) was added.

[0134] Further, 25% sodium hydroxide (alkali for neutralization) was added until the pH reached 13 or higher, thereby forming a hydroxide precipitate (zirconium hydroxide-containing slurry).

[0135] The obtained hydroxide precipitate was filtered and thoroughly washed with water, and the obtained hydroxide was dried at 105°C for 24 hours. The dried hydroxide was heat-treated (calcined) in air at 500°C for 5 hours. The obtained calcined product was broken up with a hammer head (manufactured by IKA, MF 10.2 hammer head) to obtain the zirconia-based composite oxide according to Example 3.

[0136] (Example 4) 126 g of zirconium oxychloride octahydrate (ZrO ２ The resulting solution (48 g) was dissolved in ion-exchanged water, and then 35% by mass hydrochloric acid and ion-exchanged water were added to adjust the acid concentration to 0.67N and ZrO ２The concentration was adjusted to 4 w / v % (mass volume percent concentration) to obtain a zirconium salt solution.

[0137] <First Step> The obtained zirconium salt solution was placed in an autoclave and heated to 120°C while stirring so that the stirring Reynolds number was 1500. During this time, the pressure was reduced to 2 × 10 ５ The temperature at the start of the temperature increase was room temperature (25°C), and the time from the start of the temperature increase until the temperature reached 120°C was 1.5 hours.

[0138] Immediately after reaching 120°C, 120°C, 2 x 10 ５ In the autoclave, 696 g of 5% sodium sulfate (sulfating agent) was added and the mixture was maintained at 100 Pa for 15 minutes. Stirring (Stirring Reynolds number: 1500) was continued during this time.

[0139] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 1500) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours.

[0140] This is the first step.

[0141] <Second Step> After allowing to cool naturally, the stirring conditions were changed so that the stirring Reynolds number was 200, and the temperature was raised to 120°C while stirring. During this time, the pressure was 2 x 10 ５ The time from the start of temperature increase until the temperature reached 120°C was 1.5 hours.

[0142] After the temperature reached 120°C, the mixture was maintained at this temperature for 15 minutes, during which stirring (Reynolds number of stirring: 200) was continued.

[0143] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 200) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours. In this manner, a basic zirconium sulfate slurry was obtained.

[0144] This is the second step.

[0145] To the obtained basic zirconium sulfate-containing slurry, 480 g of cerium nitrate solution (CeO ２ Conversion: 48g), lanthanum nitrate solution 40g (La ２ O ３ Equivalent: 4 g) was added.

[0146] Further, 25% sodium hydroxide (alkali for neutralization) was added until the pH reached 13 or higher, thereby forming a hydroxide precipitate (zirconium hydroxide-containing slurry).

[0147] The obtained hydroxide precipitate was filtered and thoroughly washed with water, and the obtained hydroxide was dried at 105°C for 24 hours. The dried hydroxide was heat-treated (calcined) in air at 600°C for 5 hours. The resulting calcined product was broken up with a hammer head (manufactured by IKA, MF 10.2 hammer head) to obtain the zirconia-based composite oxide according to Example 4.

[0148] (Example 5) 209 g of zirconium oxychloride octahydrate (ZrO ２ The resulting solution (80 g) was dissolved in ion-exchanged water, and then 35% by mass hydrochloric acid and ion-exchanged water were added to adjust the acid concentration to 0.67N and ZrO ２ The concentration was adjusted to 4 w / v % (mass volume percent concentration) to obtain a zirconium salt solution.

[0149] <First Step> The obtained zirconium salt solution was placed in an autoclave and heated to 120°C while stirring so that the stirring Reynolds number was 1000. During this time, the pressure was reduced to 2 × 10 ５ The temperature at the start of the temperature increase was room temperature (25°C), and the time from the start of the temperature increase until the temperature reached 120°C was 1.5 hours.

[0150] Immediately after reaching 120°C, 120°C, 2 x 10 ５ In the autoclave, 1200 g of 5% sodium sulfate (sulfating agent) was added and the mixture was maintained at 100 Pa for 15 minutes. Stirring (stirring Reynolds number: 1000) was continued during this time.

[0151] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 1000) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours.

[0152] This is the first step.

[0153] <Second Step> After allowing the mixture to cool naturally, the stirring conditions were changed so that the stirring Reynolds number was 300, and the temperature was raised to 120°C while stirring. During this time, the pressure was reduced to 2 x 10 ５ The time from the start of temperature increase until the temperature reached 120°C was 1.5 hours.

[0154] After the temperature reached 120°C, the mixture was maintained at this temperature for 15 minutes, during which stirring (Reynolds number of stirring: 300) was continued.

[0155] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 300) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours. In this manner, a basic zirconium sulfate slurry was obtained.

[0156] This is the second step.

[0157] The obtained basic zirconium sulfate-containing slurry was added with 100 g of neodymium nitrate solution (Nd ２ O ３ Conversion: 10g), praseodymium nitrate solution 100g (Pr ６ O １１ (equivalent to 10 g) was added.

[0158] Further, 25% sodium hydroxide (alkali for neutralization) was added until the pH reached 13 or higher, thereby forming a hydroxide precipitate (zirconium hydroxide-containing slurry).

[0159] The obtained hydroxide precipitate was filtered and thoroughly washed with water, and the obtained hydroxide was dried at 105°C for 24 hours. The dried hydroxide was heat-treated (calcined) in air at 500°C for 5 hours. The resulting calcined product was broken up with a hammer head (manufactured by IKA, MF 10.2 hammer head) to obtain the zirconia-based composite oxide of Example 5.

[0160] (Example 6) 84 g of zirconium oxychloride octahydrate (ZrO ２ The resulting solution (32 g) was dissolved in ion-exchanged water, and then 35% by mass hydrochloric acid and ion-exchanged water were added to adjust the acid concentration to 0.67N and ZrO ２ The concentration was adjusted to 4 w / v % (mass volume percent concentration) to obtain a zirconium salt solution.

[0161] <First Step> The obtained zirconium salt solution was placed in an autoclave and heated to 120°C while stirring so that the stirring Reynolds number was 500. During this time, the pressure was reduced to 2 × 10 ５ The temperature at the start of the temperature increase was room temperature (25°C), and the time from the start of the temperature increase until the temperature reached 120°C was 1.5 hours.

[0162] Immediately after reaching 120°C, 120°C, 2 x 10 ５ In the autoclave, 475 g of 5% sodium sulfate (sulfating agent) was added and the mixture was maintained at 100 Pa for 15 minutes. Stirring (stirring Reynolds number: 500) was continued during this time.

[0163] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 500) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours.

[0164] This is the first step.

[0165] <Second Step> After allowing to cool naturally, the stirring conditions were changed so that the stirring Reynolds number was 200, and the temperature was raised to 120°C while stirring. During this time, the pressure was 2 x 10 ５ The time from the start of temperature increase until the temperature reached 120°C was 1.5 hours.

[0166] After the temperature reached 120°C, the mixture was maintained at this temperature for 15 minutes, during which stirring (Reynolds number of stirring: 200) was continued.

[0167] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 200) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours. In this manner, a basic zirconium sulfate slurry was obtained.

[0168] This is the second step.

[0169] To the obtained basic zirconium sulfate-containing slurry, 500 g of cerium nitrate solution (CeO ２ Conversion: 50g), lanthanum nitrate solution 60g (La ２ O ３ Conversion: 6 g) and 120 g of yttrium nitrate solution (Y ２ O ３ Equivalent: 12 g) was added.

[0170] Further, 25% sodium hydroxide (alkali for neutralization) was added until the pH reached 13 or higher, thereby forming a hydroxide precipitate (zirconium hydroxide-containing slurry).

[0171] The obtained hydroxide precipitate was filtered and thoroughly washed with water, and the obtained hydroxide was dried at 105°C for 24 hours. The dried hydroxide was heat-treated (calcined) in air at 500°C for 5 hours. The resulting calcined product was broken up with a hammer head (manufactured by IKA, MF 10.2 hammer head) to obtain the zirconia-based composite oxide of Example 6.

[0172] Example 7 A zirconia-based composite oxide according to Example 7 was obtained in the same manner as in Example 1, except that the temperature in the first step was increased to 150°C.

[0173] Example 8 A zirconia-based composite oxide according to Example 8 was obtained in the same manner as in Example 1, except that the temperature in the second step was increased to 150°C.

[0174] (Comparative Example 1) 145 g of zirconium oxychloride octahydrate (ZrO ２ The resulting solution (56 g in terms of ZrO) was dissolved in ion-exchanged water, and then 35% by mass hydrochloric acid and ion-exchanged water were added to adjust the acid concentration to 0.67N. ２ The concentration was adjusted to 4 w / v % (mass volume percent concentration) to obtain a zirconium salt solution.

[0175] <First Step> The obtained zirconium salt solution was placed in an autoclave and heated to 120°C while stirring so that the stirring Reynolds number was 1000. During this time, the pressure was reduced to 2 × 10 ５ The temperature at the start of the temperature increase was room temperature (25°C), and the time from the start of the temperature increase until the temperature reached 120°C was 1.5 hours.

[0176] Immediately after reaching 120°C, 120°C, 2 x 10 ５ In the autoclave, 828 g of 5% sodium sulfate (sulfating agent) was added and the mixture was maintained at 100 Pa for 15 minutes. Stirring (stirring Reynolds number: 1000) was continued during this time.

[0177] Thereafter, the mixture was allowed to cool naturally to 50° C. Stirring (stirring Reynolds number: 1000) was continued during this period. The time required for the mixture to cool naturally to 50° C. was 6 hours.

[0178] This is the first step.

[0179] Up to this point, the process was the same as in Example 1. Thereafter, the following steps were carried out without carrying out the second step.

[0180] The obtained basic zirconium sulfate-containing slurry was added with 400 g of cerium nitrate solution (CeO ２ Conversion: 40g), lanthanum nitrate solution 40g (La ２ O ３ Equivalent: 4 g) was added.

[0181] Further, 25% sodium hydroxide (alkali for neutralization) was added until the pH reached 13 or higher, thereby forming a hydroxide precipitate (zirconium hydroxide-containing slurry).

[0182] The obtained hydroxide precipitate was filtered and thoroughly washed with water, and the obtained hydroxide was dried at 105°C for 24 hours. The dried hydroxide was heat-treated (calcined) in air at 600°C for 5 hours. The obtained calcined product was broken up with a hammer head (manufactured by IKA, MF 10.2 hammer head) to obtain the zirconia-based composite oxide according to Comparative Example 1.

[0183] Comparative Example 2 A zirconia-based composite oxide according to Comparative Example 2 was obtained in the same manner as in Example 3, except that the second step was not carried out.

[0184] Comparative Example 3 A zirconia-based composite oxide according to Comparative Example 3 was obtained in the same manner as in Example 4, except that the second step was not carried out.

[0185] Comparative Example 4 A zirconia-based composite oxide according to Comparative Example 4 was obtained in the same manner as in Example 1, except that the stirring conditions in the second step were changed to a stirring Reynolds number of 1,000.

[0186] Comparative Example 5 A zirconia-based composite oxide according to Comparative Example 5 was obtained in the same manner as in Example 1, except that the temperature in the first step was increased to 80°C.

[0187] Comparative Example 6 A zirconia-based composite oxide according to Comparative Example 6 was obtained in the same manner as in Example 1, except that the temperature in the second step was increased to 80°C.

[0188] Comparative Example 7 The first step was carried out in the same manner as in Example 1, except that the stirring conditions in the first step were changed to a stirring Reynolds number of 200. However, a uniform slurry was not obtained, and the target product was not obtained.

[0189] [Composition Measurement of Zirconia-Based Composite Oxides] The compositions (oxide equivalent) of the zirconia-based composite oxides of the examples and comparative examples were analyzed using an ICP-AES ("ULTIMA-2" manufactured by HORIBA). The results are shown in Tables 1 and 2.

[0190] [Measurement of pore volume] For the zirconia-based composite oxides of the examples and comparative examples, the pore size distribution was obtained by mercury intrusion porosimetry using a pore size distribution measurement device (Autopore IV9500, manufactured by Micromeritics). The measurement conditions were as follows. <Measurement conditions> Measurement device: pore size distribution measurement device (Autopore IV9500, manufactured by Micromeritics) Measurement range: 0.0036 to 10.3 μm Number of measurement points: 120 Mercury contact angle: 140 degrees Mercury surface tension: 480 dyne / cm

[0191] Using the obtained pore distribution, the total pore volume, the pore volume of pores having a diameter of 10 nm or more but less than 100 nm, and the pore volume of pores having a diameter of 100 nm or more but less than 1000 nm were determined. The results are shown in Tables 1 and 2. Tables 1 and 2 also show the ratio of the pore volume of pores having a diameter of 100 nm or more but less than 1000 nm to the total pore volume (pore volume ratio). (Pore volume ratio) = [(pore volume of pores having a diameter of 100 nm or more but less than 1000 nm) / (total pore volume)] × 100 (%). Furthermore, for Example 1 and Comparative Example 1, the pore distribution of the obtained zirconia-based composite oxide is shown in Figure 1.

[0192] [Particle diameter D ５０ 0.15 g of the zirconia composite oxide (powder) of each of the Examples and Comparative Examples and 40 ml of a 0.2% aqueous solution of sodium hexametaphosphate were placed in a 50 ml beaker and dispersed for 5 minutes using an ultrasonic homogenizer "Sonifier S-450D" (Emerson Japan, Ltd.), and then the beaker was placed in an apparatus (a laser diffraction particle size distribution analyzer ("SALD-2300" manufactured by Shimadzu Corporation)) and measured. The results are shown in Tables 1 and 2.

[0193] [Measurement of tapped bulk density] A TAP DENSER KYT-3000 (manufactured by Seishin Enterprise Co., Ltd.) was used as a measuring device for tapped bulk density. 15 g of sample powder (zirconia-based composite oxides according to Examples and Comparative Examples) was filled into a tapping cell, and the spacer height was set to 3 cm. The tapping cell was set on a tapping table, and tapping was performed 800 times with the measuring device. After tapping was completed, the scale on the cell was read, and the tapped bulk density was calculated by [(powder weight) / (volume)]. More detailed measurement conditions were as follows. The results are shown in Tables 1 and 2. <Measurement conditions for tapped bulk density> Tapping stroke: 3 cm Tapping speed: 100 times / 50 seconds

[0194] [Measurement of specific surface area before heat treatment] The specific surface areas of the zirconia composite oxides of the examples and comparative examples were measured by the BET method using a specific surface area meter ("Macsorb" manufactured by Mountec). The results are shown in Tables 1 and 2.

[0195] [Measurement of specific surface area after heat treatment at 1000°C for 3 hours] The zirconia-based composite oxides of the examples and comparative examples were heat treated at 1000°C for 3 hours under atmospheric pressure (0.1013 MPa). The specific surface area of ​​the zirconia-based composite oxides after heat treatment at 1000°C for 3 hours was measured in the same manner as in "Measurement of specific surface area before heat treatment." The results are shown in Tables 1 and 2.

[0196] [Measurement of specific surface area after heat treatment at 1100°C for 3 hours] The zirconia-based composite oxides of the examples and comparative examples were heat treated at 1100°C for 3 hours under atmospheric pressure (0.1013 MPa). The specific surface area of ​​the zirconia-based composite oxides after heat treatment at 1100°C for 3 hours was measured in the same manner as in "Measurement of specific surface area before heat treatment." The results are shown in Tables 1 and 2.

[0197]

[0198]

Claims

DEPCT651. Zirconia-based composite oxides with a bulk density after tapping of 0.75 g / ml or more and a specific surface area of ​​45 m³ / g or more after heat conditioning at 1000 °C for 3 hours.

2. Zirconia-based composite oxides according to claim 1 where the bulk density after tapping is 0.8 g / ml or more and 1.3 g / ml or less.

3. Zirconia-based composite oxides according to claim 1 or 2 where the bulk density after tapping is 0.83 g / ml or more and 1.27 g / ml or less.

4. Zirconia-based composite oxides according to any one of claims 1 through 3 where the specific surface area after heat conditioning at 1000 °C for 3 hours is 47 m³ / g or more and 100 m³ / g or less. 5.

6. Zirconia-based composite oxides under any of the claims 1 through 4 in which the zirconia-based composite oxide has a specific surface area of ​​15 m³ / g or more and 70 m³ / g or less after heat conditioning at 1100 °C for 3 hours.

7. Zirconia-based composite oxides under any of the claims 1 through 5 in which the zirconia-based composite oxide has a specific surface area of ​​45 m³ / g or more and 150 m³ / g or less.

8. Zirconia-based composite oxides under any of the claims 1 through 6 in which the ratio of the pore volume of pores with a diameter of 100 nm or more and 1000 nm or less to the total pore volume in the pore distribution by mercury intrusion method is 17% or less of the total pore volume. 9.

9. Zirconia-based composite oxides under any of the claims 1 through 7 where the zirconia-based composite oxide has a particle size of D505 µm or more and 25 µm or less.

10. Zirconia-based composite oxides under any of the claims 1 through 8 where the amount of zirconia is 30% by mass or more and 95% by mass or less on the basis of 100% by mass of the zirconia-based composite oxide.

11. Zirconia-based composite oxides under any of the claims 1 through 9 which are composed of one or more oxides of selected rare earth metals other than PM1.Methods for the production of zirconia-based composite oxides under any of the claims 1 through 10, in which the method includes: a first step which includes the addition of a sulfate-containing substance to a zirconium salt solution at a temperature of 100°C or higher while stirring the zirconium salt solution at a Reynolds stirring number of 400 or more and 2000 or less, and a step which cools the zirconium salt solution to which the sulfate-containing substance has been added to 60°C or lower; and a second step which includes the heating of the cooled solution obtained in the first step to 100°C or higher while stirring the solution at a Reynolds stirring number of 10 or more and 350 or less.

12. Methods for the production of zirconia-based composite oxides under claim 11, in which the Reynolds stirring number in the second step is 50 or more and 300 or less. 13.

14. Methods for the production of zirconia-based compound oxides under any of Reputation 11 or 12 where the Reynolds number of the first step stirring is 600 or more and 1800 or less.

15. Methods for the production of zirconia-based compound oxides under any of Reputation 11 through 13 where the temperature during the first step stirring is 105 °C or higher and 200 °C or less.

16. Methods for the production of zirconia-based compound oxides under any of Reputation 11 through 14 where the temperature during the second step stirring is 105 °C or higher and 180 °C or less.