CERIA-ZIRCONIA COMPOSITE OXIDE, METHOD FOR THE PRODUCTION OF THE SAME, AND CATALYST FOR PURIFICATION

专利摘要:
ceria-zirconia composite oxide, method for its production, and catalyst for purification of exhaust gas using ceria-zirconia composite oxide. a cerium-zirconia composite oxide includes at least one of lanthanum, yttrium and praseodymium. a ratio of a total content of at least one rare earth element to a total content of cerium and zirconium is 0.1 at% to 4.0 at%. a content of the rare earth element present in regions close to the surface, which are at a distance less than 50 nm from the surfaces of primary particles of the cerium-zirconia composite oxide, responsible for 90 at% or more of the total content of the earth element rare. an average particle size of the primary particles of the ceria-zirconia composite oxide is 2.2 (mi) m to 4.5 (mi) m. after a predetermined durability test, the intensity ratio i (14/29) of a diffraction line at 2 (theta) = 14.5 ° for a diffraction line at 2 (theta) = 29 ° and the intensity ratio i (28/29) of a diffraction line at 2 (theta) = 28.5 ° for the diffraction line at 2 (theta) = 29 ° respectively satisfy the following conditions: i (14/29) ¿0.02 , hey (28/29) = 0.08.
公开号:BR112016007140B1
申请号:R112016007140-9
申请日:2014-10-02
公开日:2021-03-30
发明作者:Akira Morikawa；Kae Konishi；Toshitaka Tanabe；Akihiko Suda；Masahide Miura；Isao Chinzei；Hiromasa Suzuki；Akiya Chiba；Kosuke IIZUKA
申请人:Toyota Jidosha Kabushiki Kaisha；Cataler Corporation；
IPC主号:

专利说明:

BACKGROUND OF THE INVENTION 1. Field of the Invention
[001] The present invention relates to a ceria-zirconia composite oxide, a method for producing it, and a catalyst for purifying exhaust gas using the ceria-zirconia composite oxide. 2. Description of Related Technique
[002] In the related description, composite oxides containing various metal oxides were used as a support, a cocatalyst, and the like for an exhaust gas purification catalyst. As a metal oxide in such a composite oxide, ceria is favorably used because ceria is capable of storing and releasing oxygen (that is, it has an oxygen storage capacity) according to the partial pressure of oxygen in the atmosphere. In addition, recently, several species of ceria-containing composite oxides have been studied, and various ceria-zirconia composite oxides and methods for producing the same have been described.
[003] Japanese Patent Application Publication No. 2011 219329 (JP 2011-219329 A) describes an example of a ceria-zirconia composite oxide containing a ceria and zirconia composite oxide. According to this related technique, a ratio of cerium to zirconia content in the composite oxide is fixed in the range of 43:57 to 48:52 by molar ratio ([cerium]: [zirconium]). In addition, an intensity ratio 1 (14/29) of a diffraction line at 20 = 14.5 ° for a diffraction line at 20 = 29 ° and an intensity ratio I (28/29) of a line of diffraction. diffraction at 2θ = 28.5 ° for the diffraction line at 2θ = 29 °, whose intensity ratios I (14/29) and I (28/29) are calculated from an X-ray diffraction pattern obtained by an X-ray diffraction evaluation using CuKα after heating under a temperature condition of 1100 ° C in air for 5 hours, respectively, satisfying the following conditions: I (14/29)> 0.015; and I (28/29) <0.08. According to this related technique, it is possible to provide a ceria-zirconia composite oxide having high heat resistance and being able to exhibit excellent oxygen storage capacity even after exposure to a high temperature for a long period of time. However, recently, the demand characteristics for an exhaust gas purification catalyst have increased. Consequently, a ceria-zirconia composite oxide having sufficiently greater oxygen storage capacity (OSC) and sufficiently greater heat resistance at the same time and capable of exhibiting excellent oxygen storage capacity (OSC) more sufficiently excellent even after exposure to a high temperature for a long period of time.
[004] In addition, International Publication No. WO2012 / 105454 describes an exhaust gas purification catalyst including: a ceria-zirconia composite oxide (A) having a pyrochlorine structure; and a ceria-zirconia composite oxide (B) having a crystal structure. At least a part of the cerium-zirconia composite oxide (A) is composed with the ceriazirconia composite oxide (B). However, in the exhaust gas purification catalyst described in International Publication No. WO2012 / 105454, the surface structures of primary particles of ceria-zirconia composite oxide (A) having a pyrochlorine structure are unstable, a suppression effect deterioration of an oxygen storage material is not enough, oxygen absorbing and releasing performance after exposure to a high temperature is not always enough, and durability is not enough. SUMMARY OF THE INVENTION
[005] The invention provides a ceriazirconia composite oxide, a method for producing it, and a catalyst for purifying exhaust gas using the ceriazirconia composite oxide, the ceria composite oxide -zirconia having sufficiently excellent oxygen storage capacity (OSC) and sufficiently excellent heat resistance at the same time and being able to exhibit sufficiently excellent oxygen storage capacity (OSC) even after exposure to a high temperature for a long period of time time.
[006] The present inventors studied carefully to obtain the object described above and it was discovered that, by adding a specific rare earth element, which is capable of suppressing the phase transformation of a pyrochlorine structure of CeO2-ZrO2 in the oxide of ceria-zirconia composite, to regions close to the surface of primary particles of a ceria-zirconia composite oxide in such a way that the specific conditions are met, the following effects can be obtained: the oxygen storage capacity and resistance to heat of the cerium-zirconia composite oxide obtained are sufficiently excellent and highly well balanced; and sufficiently excellent oxygen storage capacity can be displayed even after being exposed to a high temperature for a long period of time. Based on the above finding, the invention has been completed.
[007] A first aspect of the invention is a ceria-zirconia composite oxide containing a ceria-zirconia composite oxide. Cerium-zirconia composite oxide includes at least one rare earth element selected from the group consisting of lanthanum, yttrium and praseodymium. A ratio of a total content of at least one rare earth element to a total content of cerium and zirconium in the cerium-zirconia composite oxide is 0.1% on an atomic basis to 4.0% on an atomic basis. A content of the rare earth element present in regions close to the surface responsible for 90% on atomic basis or more of the total content of the rare earth element, the regions close to the surface being at a distance less than 50 nm from the surfaces of primary oxide particles of ceria-zirconia composite. A ratio of ceria to zirconia content in the ceria-zirconia composite oxide is in a range of 43:57 to 48:52 per molar ratio. A particle size of the primary particles of ceriazirconia composite oxide is 2.2 μm to 4.5 μm. An intensity ratio I (14/29) of a diffraction line at 20 = 14.5 ° for a diffraction line at 20 = 29 ° and an intensity ratio I (28/29) of a diffraction line at 20 = = 28.5 ° for the diffraction line at 20 = 29 ° respectively satisfies the following conditions: I (14/29) ^ 0.02; and I (28/29) <0.08, in which the intensity ratio I (14/29) and the intensity ratio I (28/29) are calculated from an X-ray diffraction pattern of the oxide of ceria-zirconia composite, the X-ray diffraction pattern obtained by an X-ray diffraction evaluation using CuK α after heating the ceria-zirconia composite oxide under a temperature condition of 1100 ° C in air for 5 hours.
[008] A second aspect of the invention is a method for producing a ceria-zirconia composite oxide containing a ceria-zirconia composite oxide. The method includes: preparing ceria-zirconia composite oxide powder in which a ratio of ceria content to zirconia is in a range of 43:57 to 48:52 per molar ratio and an average particle size of primary particles of the powder of ceria-zirconia composite oxide is 2.2 μm to 4.5 μm; allowing at least one rare earth element selected from the group consisting of lan- tanium, yttrium and praseodymium to be supported in the cerium-zirconia composite oxide powder; and burning the cerium-zirconia composite oxide powder in which the rare earth element is supported at 600 ° C to 1200 ° C to obtain cerium-zirconia composite oxide according to the first aspect of the invention.
[009] A catalyst for purifying exhaust gas according to a third aspect of the invention includes the cerium-zirconia composite oxide according to the first aspect of the invention.
[0010] The intensity ratio I (14/29) and the intensity ratio of I (28/29) described in the aspects of the invention, each, refer to an intensity ratio of a diffraction line at 20 = 14 , 5 ° for a diffraction line at 20 = 29 ° and an intensity ratio of a diffraction line at 20 = 28.5 ° for the diffraction line at 20 = 29 °, whose intensity ratios are calculated from an X-ray diffraction pattern obtained by an X-ray diffraction evaluation using CuKa after heating a ceria-zirconia composite oxide, which is a measurement target, under a temperature condition of 1100 ° C in air for 5 hours. X-ray diffraction measurement is performed with CuKa rays using "RINT 2100" (trade name, manufactured by Rigaku Corporation) as a measurement device under 40 kV, 30 mA, and 20 = 2 ° / min.
[0011] Here, the diffraction line at 20 = 14.5 ° is a diffraction line derived from the (111) plane of the ordered phase (phase K). The diffraction line at 20 = 29 ° is a diffraction line derived from the (222) plane of the ordered phase and the overlap of a diffraction line derived from the (111) plane of the cubic crystal phase of the solid ceria-zirconia solution ( Solid CZ solution). Thus, by calculating the intensity ratio I (14/29), which is the intensity ratio between the two diffraction lines, an index indicating the relationship (remaining ratio) of the maintained ordered phase is defined. When the diffraction line intensity is calculated, an average diffraction line intensity at 2θ = 10 ° to 12 ° which is an antecedent value is subtracted from a value of each diffraction line intensity. In addition, a K phase (Ce2Zr2O8) that is completely charged with oxygen and a pyrochlor phase (Ce2Zr2O7) from which oxygen is completely removed are each completely ordered phase. The intensity ratio I (14/29) of the K phase and the intensity ratio I (14/29) of the pyrochlor phase are respectively 0.04 and 0.05, whose intensity ratios are calculated from the PDF cards corresponding (PDF2: 01-070-4048 for the k phase, PDF2: 01-075-2694 for the pyrochlor phase). In addition, the ordered phase, that is, a crystal phase having an ordered structure formed from cerium ions and zirconium ions, has an ordered structure-type ordered phase (Φ phase (which is the same phase as the k phase)) : a super lattice structure that occurs in a fluorite structure) of a crystal that has peaks at 2θ angle positions of 14.5 °, 28 °, 37 °, 44.5 ° and 51 ° in a radius diffraction pattern X obtained by an X-ray diffraction evaluation using CuKa. The "peak" here refers to the one having a height of 30 cps or more, the height being from the reference line to the top of the peak.
[0012] In addition, the diffraction line at 2θ = 28.5 ° is a diffraction line derived from the (111) CeO2 plane only. Thus, by calculating the intensity ratio I (28/29) which is the intensity ratio of the diffraction line at 2θ = 28.5 ° for the diffraction line at 2θ = 29, an index indicating the degree of separation of CeO2 phase of a composite oxide is defined.
[0013] The present inventors assume that the reason why the object described above can be obtained by the ceria-zirconia composite oxide according to the aspects of the invention is as follows. In the pyrochlor phase (Ce2Zr2O7) of CeO2-ZrO2 in the cerium-zirconia composite oxide, the phase change with the Kocorre phase according to the partial oxygen pressure in the gas phase, and the oxygen storage capacity (OSC ) is displayed. When a ceria-zirconia composite oxide having this Ce2Zr2O7 pyrochlor phase is exposed to an oxidation atmosphere at a high temperature, since the Ce2Zr2O7 pyrochlor phase is the metastable phase, its structure returns to the fluorite structure starting from the surfaces of primary particles. As a result, the oxygen storage capacity (OSC) deteriorates. According to the aspects, the cerium-zirconia composite oxide contains at least one rare earth element (RE) selected from the group consisting of lanthanum (La), yttrium (Y) and praseodymium (Pr). Using rare earth element (RE) ions and zirconium ions, a pyrochlor structure like RE2Zr2O7 can be formed, and a crystal phase having an ordered structure can be obtained. This pyrochlor structure type RE2Zr2O7 is the stable phase and has greater heat resistance than that of the pyrochlor structure type Ce2Zr2O7. According to aspects of the invention, an ordered phase having a pyrochlor structure type RE2Zr2O7 is formed in regions close to the surface of primary particles of the ceria-zirconia composite oxide. Consequently, the phase transformation of the CeO2-ZrO2 pyrochlorine structure is suppressed, the heat resistance at high temperature is improved, and the sufficiently high oxygen absorption and release capacity is displayed even after exposure to a high temperature. Based on this discovery, the present inventors assume that: the oxygen storage capacity and heat resistance of the cerium-zirconia composite oxide are sufficiently excellent and highly well balanced; and the sufficiently excellent oxygen storage capacity can be displayed even after being exposed to a high temperature for a long period of time.
[0014] According to aspects of the invention, it is possible to provide a ceria-zirconia composite oxide, a method for producing it, and a catalyst for purifying exhaust gas using the ceria-zirconia composite oxide , ceria-zirconia composite oxide having sufficiently excellent oxygen storage capacity (OSC) and sufficiently excellent heat resistance at the same time and being able to exhibit sufficiently excellent oxygen storage capacity (OSC) even after exposure to a high temperature over a long period of time. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The aspects, advantages, and technical and industrial significance of exemplary modalities of the invention will be described below with reference to the accompanying drawings, in which similar numerals denote similar elements and in which:
[0016] FIGURE 1 is a graph illustrating the results of the EDX analyzes of a La-CZ composite oxide (subjected to the duration test 1) prepared in Example 2 according to the invention;
[0017] FIGURE 2 is a high resolution transmission electron microscopy (HR-TEM) image of the La-CZ oxide and composite (subjected to the duration test 1) prepared in Example 2 according to the invention;
[0018] FIGURE 3 is a graph illustrating the results of the EDX analyzes of a La-CZ composite oxide (subjected to the duration test 1) prepared in Example 5 according to the invention;
[0019] FIGURE 4 is a high resolution transmission electron microscopy (HR-TEM) image of the La-CZ oxide and composite (subjected to the duration test 1) prepared in Example 5 according to the invention;
[0020] FIGURE 5 is a graph illustrating the results of the EDX analyzes of a La-CZ composite oxide (subjected to the duration test 1) prepared in Example 7 according to the invention;
[0021] FIGURE 6 is a high resolution transmission electron microscopy (HR-TEM) image of the La-CZ oxide and composite (subjected to the duration test 1) prepared in Example 7 according to the invention;
[0022] FIGURE 7 is a graph illustrating the results of EDX analyzes of a ceria-zirconia composite oxide (subjected to the duration 1 test) for comparison prepared in Comparative Example 1; and
[0023] FIGURE 8 is a high resolution transmission electron microscopy (HR-TEM) image of the ceria-zirconia composite oxide (subjected to the duration 1 test) for comparison prepared in Comparative Example 1. DETAILED DESCRIPTION OF MODALITIES
[0024] Hereinafter, the invention will be described in detail using preferred embodiments thereof.
[0025] First, a ceria-zirconia composite oxide according to one embodiment of the invention will be described. It is necessary that the cerium-zirconia composite oxide according to the modality contains at least one rare earth element selected from the group consisting of lanthanum (La), yttrium (Y) and praseodymium (Pr). In addition, a ratio of a total content of at least one rare earth element to a total content of cerium and zirconium in the cerium-zirconia composite oxide is necessarily 0.1% on an atomic basis to 4.0% on an atomic basis and preferably 0.25% on an atomic basis to 2.5% on an atomic basis. When the content ratio of at least one rare earth element selected from the group consisting of lanthanum (La), yttrium (Y) and praseodymium (Pr) is less than the lower limit, a function of maintaining I (14/29) and OSC after a durability test tends to decrease, and thus an effect of obtaining excellent OSC and high heat resistance at the same time and exhibiting excellent OSC even after exposure to a high temperature for a long period of time cannot sufficiently obtained. On the other hand, when the content ratio of the rare earth element is greater than the upper limit, the function of maintaining I (14/29) and OSC after a durability test tends to decrease, and thus an effect of exhibiting excellent OSC cannot be sufficiently achieved. These rare earth elements can be used alone or in a combination of two or more species. In addition, in the cerium-zirconia composite oxide, different additive elements can be added to regions close to the surface and to other regions.
[0026] In addition, in the cerium-zirconia composite oxide according to the modality, this rare earth element may be present in the state of solid solution, state of dispersion, or the like. In particular, to allow the rare earth element to have the effects of the modality more significantly, it is preferable that at least a part of the rare earth element is solubilized solid in the cerium-zirconia composite oxide.
[0027] Furthermore, in the cerium-zirconia composite oxide according to the modality, it is necessary that the content of at least one rare earth element selected from the group consisting of lanthanum, yttrium and praseodymium present in regions close to the surface that they are at a distance less than 50 nm from the primary particle surfaces of the ceria-zirconia composite oxide responsible for 90% on an atomic basis or more of the total content of the rare earth element. It is more preferable that the content of the rare earth element present in regions close to the surface that are at a distance less than 30 nm from the surfaces responsible for 80% on atomic basis or more than the total content of the rare earth element. When a distortion of the rare earth element is outside the above described limitation, a sufficient structure stabilizing effect cannot be exhibited. In the cerium-zirconia composite oxide according to the modality, when the content of the rare earth element present in the regions close to the surface responsible for 90% on atomic basis or more of the total content of the rare earth element, the morphology and dispersion of the element rare earthquakes are not particularly limited. That is, although it is preferable that substantially all primary particles of the cerium-zirconia composite oxide present in the regions close to the surface have the rare earth element, some primary particles may not contain the rare earth element within a range that does not impair the effects of the modality.
[0028] The content and content ratio of the rare earth element present in the regions close to the surface of the ceriazirconia composite oxide can be confirmed by performing the composition analysis using, for example, EDX (X-ray spectrometer) dispersive energy) or SIMS (secondary ion mass spectrometer) and comparing the relationships of content of additive elements between the regions close to the surface of the primary particles and the other regions. Alternatively, the content and content ratio of the rare earth element present in the regions close to the surface can be confirmed with a method using the elution of the added rare earth element. Specifically, the rare earth element added to regions close to the surface is eluted when it comes in contact with an acidic solution such as an aqueous acidic nitric solution. Consequently, the content of the rare earth element present in the regions close to the surface can be confirmed by measuring the content of the rare earth element eluted in an acidic nitric aqueous solution when the cerium-zirconia composite oxide is brought into contact with the aqueous solution. of citric acid. More specifically, the content of the rare earth element present in the regions close to the surface can be confirmed, for example, by adding 10 ml of 1N aqueous nitric acid solution to 0.1 g of the ceriazirconia composite oxide, stirring the solution at room temperature for 2 hours to allow the additive elements present in the regions close to the surface to be eluted, and by measuring the content of the additive elements eluted by chemical analysis.
[0029] Furthermore, in the ceria-zirconia composite oxide according to the modality, a ratio of ceria content to zirconia is necessarily in a range of 43:57 to 48:52 per molar ratio and preferably in a range of 44:56 to 48:52. When the ratio of cerium content is less than the lower limit, a decrease in oxygen storage capacity caused by the zirconium-rich composition exceeds the stability improvement effect of the composite oxide obtained by ceria phase separation being suppressed. Consequently, the oxygen storage capacity after a high temperature durability test is insufficient. On the other hand, when the ratio of cerium content is greater than the upper limit, the effect of improving the stability of the composite oxide obtained by the phase separation of ceria being suppressed cannot be obtained. Consequently, the oxygen storage capacity after a high temperature durability test is insufficient.
[0030] Furthermore, in the modality, an average particle size of the primary particles of the ceria-zirconia composite oxide is necessarily 2.2 μm to 4.5 μm, preferably 2.5 μm to 4.5 μm, and more preferably 2.5 μm to 4.0 μm. When the average particle size of the primary particles is less than the lower limit, the heat resistance of the CeO2-ZrO2 pyrochlor structure tends to decrease. On the other hand, when the average particle size of the primary particles is greater than the upper limit, the time required for the elution of oxygen tends to increase excessively.
[0031] The average particle size of the primary particles of the cerium-zirconia composite oxide according to the modality can be obtained by measuring the particle sizes of 50 arbitrary primary particles by observing an electron microscope image of (SEM) and calculating an average particle size value. If a cross-section of a particle is not circular, the diameter of a minimum circumscribed circle is measured.
[0032] In addition, the starting sizes of the primary particles, the composition and structure of each particle, the aggregate state of secondary particles, and the like can be confirmed by observing or analyzing the ceria-zirconia composite oxide using a appropriate combination of SEM (scanning electron microscope), TEM (transmission electron microscope), FE-STEM (field emission scanning electron microscope), HR-TEM (high resolution transmission electron microscope), EDX ( dispersive energy X-ray spectrometer), XPS (X-ray photoelectron spectrometer) and the like.
[0033] Furthermore, the intensity ratio described above I (14/29) of the ceria-zirconia composite oxide according to the embodiment is necessarily 0.02 or more, preferably 0.030 or more, and more preferably 0.033 or more. When the ratio of intensity I (14/29) is less than the lower limit, the ratio of the maintained ordered phase is low, and the oxygen storage capacity after a high temperature durability test is insufficient. The upper limit of the intensity ratio described above I (14/29) is not particularly limited, but is preferably 0.05 or less from the point of view that the intensity ratio I (14/29) of the pyroclore phase calculated from the PDF card (01-075-2694) is established as an upper limit.
[0034] In addition, the intensity ratio described above I (28/29) of the ceria-zirconia composite oxide according to the modality is necessarily 0.08 or less, preferably 0.06 or less, and more preferably 0, 04 or less. When the ratio of intensity I (28/29) is greater than the upper limit, the phase separation of ceria is not sufficiently suppressed, and the oxygen storage capacity after a high temperature durability test is insufficient. The lower limit of the intensity ratio I (28/29) is not particularly limited, and the lower the lower limit, the better.
[0035] In ceria-zirconia composite oxide according to the modality, the content ratio of the ordered phase (the pyrochlor phase type Ce2Zr2O7 and the pyrochlor phase type RE2Zr2O7) for all crystal phases which is determined by the relationship peak intensity of the X-ray diffraction pattern is preferably 50% to 100% and more preferably 80% to 100%. When the ratio of the content of the ordered phase is less than the lower limit, the effect of suppressing the deterioration of the oxygen storage capacity of the composite oxide and the resistance to heat tend to decrease. In the ordered phase, the content ratio of the RE2Zr2O7 type pyrochlor structure is preferably 0.1% to 8.0% and more preferably 0.8% to 5.0%. When the content ratio of the RE2Zr2O7 type pyrochlorine structure in the ordered phase is less than the lower limit, the deterioration suppression effect and heat resistance tend to decrease. On the other hand, when the content ratio of the RE2Zr2O7 type pyrochlor structure is greater than the upper limit, the oxygen storage capacity tends to decrease.
[0036] In addition, the cerium-zirconia composite oxide according to the modality may also contain at least one element selected from the group consisting of rare earth elements different from cerium, lanthanum, yttrium and praseodymium and elements alkaline earth. Containing such an element, ceriazirconia composite oxide according to the modality tends to exhibit greater exhaust gas purification capacity when used as a catalyst support for exhaust gas purification. Examples of the rare earth element other than cerium, lanthanum, yttrium and praseodymium include scandium (Sc), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), ytterbium (Yb) and lutetium (Lu). Among these, Nd or Sc is preferable and Nd is more preferable from the point of view that, when the noble metal is supported therein, the interaction with the noble metal increases and the affinity to it tends to increase. In addition, examples of alkaline earth metals include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). Among these, Mg, Ca, or Ba is preferable from the point of view that, when the noble metal is supported on it, the interaction with the noble metal increases and its affinity tends to increase. Rare earth elements other than cerium, lanthanum, yttrium and praseodymium and alkaline earth metals having low electronegativity interact strongly with a noble metal, and, consequently, bind to the noble metal by means of oxygen in an oxidizing atmosphere, and vaporization and sintering of the noble metal are suppressed. In this way, there is a tendency that the deterioration of the noble metal, which is an active site during exhaust gas purification, can be sufficiently suppressed.
[0037] In addition, when the cerium-zirconia composite oxide according to the modality also contains at least one element selected from the group consisting of rare earth elements other than cerium, lanthanum, yttrium and praseodymium and alkaline earth elements, content thereof in the cerium-zirconia composite oxide is preferably 1 wt% to 20 wt% and more preferably 3 wt% to 7 wt%. When the content of the element is less than the lower limit, and when the noble metal is supported on the obtained composite oxide, it tends to be difficult to sufficiently improve the interaction with the noble element. On the other hand, when the element content is greater than the upper limit, the oxygen storage capacity tends to decrease.
[0038] In addition, the specific surface area of the ceria-zirconia composite oxide is not particularly limited, but is preferably 0.01 m2 / g to 20 m2 / g and more preferably 0.05 m2 / g to 10 m2 / g. When the specific surface area is less than the lower limit, the interaction with a noble metal decreases, and the oxygen storage capacity tends to decrease. When the specific surface area is greater than the upper limit, the number of particles having a smaller particle size increases, and the heat resistance tends to decrease. The specific surface area can be calculated from an absorption isotherm with a specific BET surface area using a BET isotherm absorption equation.
[0039] Next, a method according to one embodiment of the invention for producing the ceria-zirconia composite oxide according to the embodiment will be described. In the method for producing a ceria-zirconia composite oxide according to the modality, ceria-zirconia composite oxide powder in which a ratio of ceria to zirconia content is in a range of 43:57 to 48:52 per molar ratio and an average particle size of primary particles is 2.2 μm to 4.5 μm is produced (stage of preparation of ceria-zirconia composite oxide powder).
[0040] A method for preparing the ceria-zirconia composite oxide powder according to the modality is not particularly limited. For example, a method may be adopted, the method including: preparing powder of solid ceria-zirconia solution using a co-precipitation method such that the ratio of ceria zirconia content is within the range described above; molding the powder from a solid ceriazirconia solution; and heating the molded article under reduction conditions to obtain ceria-zirconia composite oxide powder according to the modality.
[0041] For example, in the method for preparing the ceria-zirconia composite oxide powder according to the modality, the ceria-zirconia solid solution powder in which a ratio of ceria content to zirconia is in a range of 43:57 to 48:52 by molar ratio is molded by compression under pressure from 400 kgf / cm2 to 3500 kgf / cm2, followed by a reduction treatment under a temperature condition of 1450 ° C to 2000 ° C to obtain powder of cerium-zirconia composite oxide.
[0042] In solid solution powder (ceriazirconia solid solution powder) containing ceria and zirconia according to a specific example of the invention, a ratio of ceria content to zirconia is necessarily in a range of 43:57 to 48: 52 by molar ratio. When the ratio of cerium content in the powder of solid ceria-zirconia solution is less than the lower limit, a decrease in the oxygen storage capacity caused by the zirconium-rich composition of the ceria-zirconia composite oxide obtained exceeds the effect improvement of stability of the composite oxide obtained by separation of ceria phase being suppressed. Consequently, the oxygen storage capacity after a high temperature durability test is insufficient. On the other hand, when the ratio of cerium content is greater than the upper limit, the effect of improving the stability of the composite oxide obtained by the separation of the ceria phase being suppressed cannot be obtained in the cerium-zirconia composite oxide obtained . Consequently, the oxygen storage capacity after a high temperature durability test is insufficient. Like ceria-zirconia solid solution powder, a solid solution in which ceria and zirconia are mixed at an atomic level is preferable from the point of view of sufficiently forming the ordered phase. In addition, an average primary particle size of the powder of solid ceria-zirconia solution is preferably about 2 nm to 100 nm. When the average primary particle size of the ceria-zirconia solid solution powder is less than the lower limit, the solid ceria-zirconia solution in the powder does not progress sufficiently and tends to be difficult to obtain the ordered phase. On the other hand, when the average primary particle size of the ceria-zirconia solid solution powder is greater than the upper limit, the contact state between the primary particles during compression modeling deteriorates and the particle development during the reduction treatment tends to be insufficient.
[0043] Furthermore, a method for producing ceria-zirconia solid solution powder is not particularly limited. For example, a method can be used in which the solid solution powder is produced using a so-called coprecipitation method such that the ratio of cerium zirconia content is within the range described above. In the coprecipitation method, for example, a precipitate is produced in the presence of ammonia using an aqueous solution containing a salt (for example, a nitrate) of cerium and a salt (for example, a nitrate) of zirconium. Then, the precipitate obtained is filtered, washed, and dried, followed by burning and grinding with a crusher such as a ball mill to obtain the powder of a solid solution of ceriazirconia. The aqueous solution containing a cerium salt and a zirconium salt is prepared in such a way that the ratio of ceria to zirconia content in the obtained solid solution powder is within a predetermined range. In addition, optionally, a salt of at least one element selected from the group consisting of rare earth elements and alkaline earth elements, a surfactant (for example, a non-ionic surfactant) and the like can be added to the aqueous solution.
[0044] Then, in the specific example, the powder of solid solution of ceria-zirconia is molded by compression under pressure from 400 kgf / cm2 to 3500 kgf / cm2 (preferably 500 kgf / cm2 to 3000 kgf / cm2). When the pressure during the compression modeling step is less than the lower limit, the packing density of the powder is not sufficiently improved, and therefore, the crystal development during the reduction treatment does not progress sufficiently. As a result, the oxygen storage capacity after a high temperature durability test of the obtained ceria-zirconia composite oxide is insufficient. On the other hand, when the pressure during the compression modeling step is greater than the upper limit, the phase separation of ceria easily progresses. As a result, the oxygen storage capacity after a high temperature durability test of the obtained ceria-zirconia composite oxide is insufficient. An understanding modeling method is not particularly limited, and a well-known compression modeling method such as isostatic pressing can be appropriately adopted.
[0045] Then, in the specific example, after compression modeling, the powder molded article of solid ceriazirconia solution is heated under a reduction condition at a temperature of 1450 ° C to 2000 ° C (preferably 1600 ° C to 1900 ° C) for 0.5 hours to 24 hours (preferably 1 hour to 10 hours) as a reducing treatment. As a result, the ceria-zirconia composite oxide powder according to the modality is obtained. When the temperature of the reduction treatment is less than the lower limit, the stability of the ordered phase is low. As a result, the oxygen storage capacity after a high temperature durability test of the obtained ceria-zirconia composite oxide is insufficient. On the other hand, when the temperature of the reduction treatment is lower than the upper limit, a balance between the energy (for example, electrical energy) required for the reduction treatment and the performance improvement is poor. In addition, when the heating time during the reduction treatment is shorter than the lower limit, the production of the ordered phase tends to be insufficient. On the other hand, when the warm-up time during the reduction treatment is longer than the upper limit, a balance between the energy (for example, electrical energy) required for the reduction treatment and the performance improvement is poor.
[0046] Furthermore, a method for the reduction treatment is not particularly limited, as the powder of the solid solution can be heated in a reduction atmosphere under a predetermined temperature condition. For example, a reduction treatment method can be used, the method including: placing the powder of solid solution in a vacuum heating oven; evacuate the oven; changing the internal atmosphere of the furnace to a reducing atmosphere allowing the reducing gas to flow into the furnace; and heating the oven under a predetermined temperature condition. Alternatively, another reduction treatment method can be used, the method including: placing the powder of solid solution in a graphite furnace; evacuate the oven; heating the oven under a predetermined temperature condition to reduce the gas such as CO or HC from an oven body, a heating fuel, and the like; and changing the internal atmosphere of the furnace to a reducing atmosphere using the reducing gas produced. Alternatively, yet another reduction treatment method can be used, the method including: placing the powder of solid solution in a crucible filled with activated carbon; heating the crucible under a predetermined temperature condition to produce reducing gas such as CO or HC from the activated carbon; and changing the inert atmosphere of the crucible to a reducing atmosphere using the reducing gas produced.
[0047] The reducing gas used to obtain the reducing atmosphere is not particularly limited, and the reducing gas such as CO, HC, H2 or other hydrocarbon gas can be used appropriately. In addition, among the examples of the reducing gas, the reducing gas containing no carbon (C) is most preferably used from the point of view of preventing the production of a by-product such as zirconium carbide (ZrC) when the reducing treatment is performed at a high temperature. When non-carbon reducing gas (C) is used, the reduction treatment can be carried out under a higher temperature condition that is close to a melting point of zirconium or the like. Consequently, the structure stability of the crystal phase can be sufficiently improved.
[0048] In the specific example, after the reduction treatment, it is preferable that the ceria-zirconia composite oxide powder is oxidized. By the ceriazirconia composite oxide powder being oxidized, the oxygen that was lost during the reduction treatment is supplemented, and the stability as the oxide powder tends to increase. A method for treating oxidation is not particularly limited. For example, a method in which the ceriazirconia composite oxide powder is heated in an oxidizing atmosphere (for example, air) can preferably be adopted. In addition, a heating temperature condition during oxidation treatment is not particularly limited, but is preferably about 300 ° C to 800 ° C. In addition, a heating time during the oxidation treatment is not particularly limited, however it is preferably about 0.5 hours to 5 hours.
[0049] Furthermore, in the specific example, after the reduction treatment or the oxidation treatment, it is preferable that the ceria-zirconia composite oxide powder is ground. A method for treating crushing is not particularly limited. For example, a wet shredding method, a dry shredding method, or a shredding and freezing method can preferably be adopted.
[0050] Then, in the method to produce a cerium-zirconia composite oxide according to the modality, at least one rare earth element selected from the group consisting of lanthanum (La), yttrium (Y) and praseodymium (Pr ) is supported on the composite oxide powder obtained in the ceria-zirconia composite oxide powder preparation step (rare earth element support step).
[0051] In the modality, as the rare earth element (RE) that is supported in the cerium-zirconia composite oxide powder, at least one rare earth element selected from lanthanum (La), yttrium (Y) and pseosodymium ( Pr) is necessarily used. That is, a rare earth element or a combination of two or more rare earth elements selected from the group above can be supported in the ceriazirconia composite oxide powder. Using the rare earth element (RE) that is supported in the ceria-zirconia composite oxide powder, the oxygen storage capacity and heat resistance of the ceria-zirconia composite oxide obtained are sufficiently excellent and highly well balanced, and sufficiently excellent oxygen storage capacity can be displayed even after exposure to a high temperature for a long period of time. As the rare earth element (RE) that is supported in the cerium-zirconia composite oxide powder, lanthanum (La) and praseodymium (Pr) are preferably used.
[0052] Regarding the quantity of the rare earth element (RE) supported, a ratio of a total content of the rare earth element (RE) in the cerium-zirconia composite oxide obtained to a total content of cerium and zirconium in the oxide of Cerium-zirconia composite is necessarily 0.1% on an atomic basis to 4.0% and preferably 0.25% on an atomic basis to 2.5% on an atomic basis. When the content ratio of the rare earth element (RE) is less than the lower limit, the function of maintaining I (14/29) and OSC after a durability test tends to decrease. Consequently, an effect of obtaining excellent OSC and high heat resistance at the same time and exhibiting excellent OSC even after being exposed to a high temperature for a long period of time cannot be sufficiently achieved. On the other hand, when the content ratio of the rare earth element is greater than the upper limit, the function of maintaining I (14/29) and OSC after a durability test tends to decrease, and the effect of exhibiting excellent OSC does not it is sufficiently obtained.
[0053] A method of allowing at least one rare earth element selected from the group consisting of lanthanum (La), yttrium (Y) and praseodymium (Pr) to be supported in the cerium-zirconia composite oxide powder is not particularly limited. This support method is not particularly limited, as the rare earth element (RE) can be supported in the cerium-zirconia composite oxide powder, and a well-known method can be appropriately adopted. For example, a liquid phase method, a solid phase method, and a gas phase method that are commonly used can be used without any particular limitation, the liquid phase method including a support impregnation method, an exchange method ion (for example, an absorption support method), a water-absorption support method, a sol-gel method, and a precipitation support method (for example, a coprecipitation method); the solid phase method including a powder mixing method and a solid ion exchange method; and the gas phase method including a CVD method. Among these, a support impregnation method, a water absorption method, and an ion exchange method are preferably used from the point of view of the availability of raw materials of additive elements.
[0054] The rare earth element (RE) support method is not particularly limited, and it is preferable that the rare earth element is supported in the cerium-zirconia composite oxide in such a way that the content of the rare earth element present in regions close to the surface that is at a distance less than 50 nm from the surfaces of primary particles of the cerium-zirconia composite oxide obtained responsible for 90% on atomic basis or more of the total content of the rare earth element. For this purpose, a water absorption method is preferably used because the additive elements can be prevented from being diffused into the particles by measuring the amount of water absorption of the powder, in advance, and allowing the powder to absorb a solution of crude material in which the necessary quantities of the additive elements are dissolved.
[0055] A raw material (source of rare earth element) of the rare earth element (RE) that is supported in the cerium-zirconia composite oxide according to the modality is not particularly limited, and a salt, a complex, a simple substance, an oxide, or similar to the rare earth element can be used. This rare earth element (RE) source can be appropriately selected according to the support method, conditions, and the like. Specifically, a supported rare earth element (RE) salt is used. For example, an inorganic acid salt such as a nitrate, a sulfate, or a hydrochloride or an organic acid salt such as an acetate can be used. The source of the rare earth element (RE) can be soluble or insoluble in a dispersion medium.
[0056] For example, for the support of the rare earth element (RE), firstly, an aqueous solution in which a salt or similar of the rare earth element (RE) is dissolved (for example, an aqueous lanthanum nitrate solution, a aqueous yttrium nitrate solution, or aqueous praseodymium nitrate solution) is prepared. Then, the cerium-zirconia composite oxide powder is mixed with the aqueous solution containing the rare earth element (RE), followed by stirring at a predetermined temperature for a predetermined time to be impregnated with the rare earth element (RE) . Then, the ceria-zirconia composite oxide powder impregnated with the rare earth element (ER) is filtered, washed, and dried. As a result, the cerium-zirconia composite oxide impregnated with the rare earth element (RE) according to the modality is obtained.
[0057] Alternatively, for the support of the rare earth element (RE), first, a dispersion of the ceria-zirconia composite oxide powder is prepared. For example, the ceria-zirconia composite oxide powder is suspended in ion exchange water to obtain the dispersion. Then, an aqueous solution of a rare earth element (RE) compound (eg, lanthanum nitrate) is prepared, and the ceriazirconia composite oxide powder dispersion is mixed with the aqueous solution to prepare a dispersion. mixture of the cerium-zirconia composite oxide powder and the rare earth element (RE) compound. Then, the mixed dispersion is spray dried, washed, and dried. As a result, the ceria-zirconia composite oxide impregnated with the rare earth element (RE) according to the modality is obtained.
[0058] The conditions of such drying and the like are not particularly limited, and the well-known conditions can be appropriately adopted. For example, as a drying condition, a condition of heating at 100 ° C to 400 ° C for 1 hour to 12 hours can be adopted.
[0059] Then, in the method to produce a ceria-zirconia composite oxide according to the modality, the ceria-zirconia composite oxide powder in which the rare earth element is supported, which is obtained in the rare earth element support, it is burned at 600 ° C to 1200 ° C to obtain ceriazirconia composite oxide according to the modality (firing step).
[0060] In the firing step of ceriazirconia composite oxide powder in which the rare earth element is supported, a firing temperature is necessarily at a temperature of 600 ° C to 1200 ° C, preferably 800 ° C to 1100 ° C, and more preferably 900 ° C to 1100 ° C. When the firing temperature is lower than the lower limit, the rare earth element supported tends not to be sufficiently reactive. On the other hand, when the firing temperature is higher than the upper limit, the CeO2-ZrO2 pyrochlor structure tends to deteriorate.
[0061] Furthermore, in the firing stage, the conditions (for example, a heat treatment time and atmosphere) of the firing treatment other than a firing method, a firing device, and a firing temperature are not particularly limited, and a well-known method, device and conditions can be appropriately adopted. For example, as the firing device, a fluidized bed oven, a muffle furnace, or a kiln (kiln) can be used. In addition, the heating time in the firing step is preferably 3 hours to 20 hours and more preferably 4 hours to 10 hours, although it varies depending on the firing temperature. In addition, as the heat-treating atmosphere, a well-known condition, for example, air, an inert gas atmosphere containing air or oxygen, or an inert gas atmosphere such as argon gas can be adopted. Alternatively, an oxidation atmosphere (for example, air) is preferably adopted.
[0062] As described above, the ceriazirconia composite oxide according to the modality can be obtained using the method to produce a ceriazirconia composite oxide according to the modality.
[0063] Here above, the cerium-zirconia composite oxide according to the modality and the method for its production have been described. Hereinafter, an exhaust gas purification catalyst according to an embodiment of the invention in which the cerium-zirconia composite oxide is used will be described.
[0064] The exhaust gas purification catalyst according to the modality contains the ceria-zirconia composite oxide according to the modality. The exhaust gas purification catalyst according to the modality has sufficiently excellent oxygen storage capacity (OSC) and sufficiently high heat resistance at the same time and exhibits sufficiently excellent oxygen storage capacity (OSC) even after exposure to a high temperature over a long period of time.
[0065] As a preferable example of the exhaust gas purification catalyst according to the modality, an exhaust gas purification catalyst can be used, the catalyst including: a support containing the cerium-zirconia composite oxide of according to the modality; and a noble metal that is supported on the support. Examples of noble metal include platinum, rhodium, palladium, osmium, iridium, gold, and silver. In addition, a method of supporting the noble metal in the support is not particularly limited, and a well-known method can be appropriately adopted. For example, a method can be adopted, the method including: immersing the powder (support) of the ceria-zirconia composite oxide in a solution in which a salt (for example, a nitrate, a chlorine, or an acetate) of the noble metal or a complex of the noble metal is dissolved in a solvent such as water or alcohol; solvent removal; and burning the dust. In addition, the amount of the noble metal supported on the support is not particularly limited, since the required amount of the noble metal is appropriately supported, however it is preferably 0.01% by weight.
[0066] In addition, as another preferable example of the exhaust gas purification catalyst according to the modality, an exhaust gas purification catalyst can be used, the catalyst being obtained having the cerium-zirconia composite oxide according to the embodiment around a first catalyst that includes catalyst support particles and a noble metal supported on the fine catalyst support particles. The catalyst support particles are not particularly limited, and a support (for example, alumina particles, alumina and ceria particles, or alumina, ceria, and zirconia particles) including a metal oxide or a metal oxide composite which can be used as a catalyst support for exhaust gas purification can be used appropriately. In addition, as a method of allowing the noble metal to be supported on the catalyst support particles, the methods described above can be adopted. In addition, the amount of the noble metal supported in the catalyst support particles is not particularly limited, since a necessary amount of the noble metal is suitably supported, however it is preferably 0.01% by weight. In addition, a method of disposing the cerium-zirconia composite oxide according to the embodiment around the first catalyst is not particularly limited. For example, a method of mixing the first catalyst and the cerium-zirconia composite oxide according to the modality can be adopted. In addition, from the point of view of obtaining greater catalyst activity, it is preferable that the cerium-zirconia composite oxide according to the modality is disposed around the first catalyst in a state that can be highly dispersed.
[0067] Hereinafter, the invention will be described in more detail using the examples and comparative examples, however it is not limited to the following examples.
[0068] (Example 1), the powder of solid solution of ceria-zirconia in which a ratio of ceria content to zirconia was 46:54 per molar ratio was prepared as follows. That is, first, 452 g of an aqueous solution containing cerium nitrate in an amount of 28% by weight in terms of CeO2, 590 g of an aqueous solution containing zirconium oxinitrate in an amount of 18% by weight in terms of ZrO2 , and 200 g of an aqueous solution containing hydrogen peroxide in an amount 1.1 times the molar amount of cerium to be contained were added to 321 g of an aqueous solution containing ammonia in an amount 1.2 times the equivalent neutralization to produce a coprecipitate. The obtained coprecipitate was centrifuged and washed (with ion exchange water). Then, the co-precipitate obtained was air-dried at 110 ° C for 10 hours or more and burned in air at 400 ° C for 5 hours to obtain a solid solution (solid solution CeO2-ZrO2) of cerium and zirconium . Then, the solid solution was ground to a particle size of 75 μm or less using a sieve with a grinder (manufactured by AS ONE Corporation, product name "Wonder Blender") to obtain the powder of solid solution of ceria-zirconia .
[0069] Then, a polyethylene bag (volume: 0.05 L) was packed with 20 g of the powder of solid solution of ceria-zirconia obtained, the inside of it was degassed, and the mouth of the bag was heated to be sealed. The bag was then molded by cold isostatic pressing (CIP) using an isostatic press machine (manufactured by Nikkiso Co., Ltd., product name: "CK4-22-60") under a pressure (modeling pressure) of 2000 kgf / cm2 for 1 minute. As a result, an article molded from the powder of a solid solution of ceria-zirconia was obtained. The size of the molded article was as follows: a length of 4 cm; a width of 4 cm; and an average thickness of 7 mm, and the weight of the molded article was about 20 g.
[0070] Then, the molded articles obtained (two molten articles) were placed inside a crucible (internal volume: a diameter of 8 cm, a height of 7 cm) loaded with 70 g of activated carbon, and the crucible has been converted with a lid. The crucible was placed in an electric high-speed heating oven, heated to 1000 ° C over a heating time of 1 hour, heated to 1700 ° C over a heating time of 4 hours and maintained at this temperature for 5 hours , was cooled to 1000 ° C over a cooling time of 4 hours, and allowed to cool to room temperature. As a result, the molded article subjected to the reduction treatment was obtained.
[0071] Then, the molded article subjected to the reduction treatment was heated and oxidized in the air at a temperature condition of 500 ° C for 5 hours. As a result, a cerium-zirconia composite oxide in which a ratio of ceria to zirconia content was 46:54 per molar ratio was obtained. The obtained ceriazirconia composite oxide was ground to a particle size of 75 μm or less using a sieve.
[0072] Next, a solution of aqueous lanthanum nitrate containing lanthanum (La) in an amount of 0.25% on an atomic basis with respect to a total amount of cerium and zirconium in the obtained cerium-zirconia composite oxide . Then, 10 g of the cerium-zirconia composite oxide obtained were placed in the aqueous lanthanum nitrate solution, followed by stirring at room temperature for 1 hour. A predetermined amount of lananium was supported in the cerium-zirconia composite oxide using a water-absorbing support method. Then, the La support powder was filtered off, followed by drying in air at 110 ° C for 12 hours.
[0073] Then, the obtained ceria-zirconia composite oxide La obtained was burned in the air at 900 ° C for 5 hours. As a result, a ceria-zirconia composite oxide containing particulate La was obtained.
[0074] Regarding the cerium-zirconia composite oxide containing the particulate La obtained, the structure and shape of the particles were measured using HR-TEM (high-resolution transmission electron microscope), composition analysis and nearby regions of the particle surface were analyzed using EDX (dispersive energy X-ray spectrometer) and the average particle size of primary particles was measured using a scanning electron microscopy (SEM) image. The average particle size of the primary particles was obtained by measuring the particle sizes of 50 arbitrary primary particles by observing a scanning electron microscope (SEM) image and calculating an average value of the particle sizes. If a cross-section of a particle was not circular, the diameter of a minimum circumscribed circle was measured. As a result, a ratio of the lanthanum content to the total content of cerium and zirconium in the ceria-zirconia composite oxide containing La was 0.25% on an atomic basis. In addition, the lanthanum content present in regions close to the surface that were at a distance less than 50 nm from the surfaces of primary particles of a ceria-zirconia composite oxide supported by La is responsible for 100% in atomic basis of the total lanthanum content in the cerium-zirconia composite oxide supporting La. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide containing La obtained was 3.0 μm.
[0075] <Durability test 1> The ceriazirconia composite oxide containing La obtained (La-CZ composite oxide) was heated in the air under conditions of 1100 ° C and 5 hours to perform a high durability test temperature (1100 ° C air).
[0076] <Durability test 2> The ceriazirconia composite oxide containing La obtained (La-CZ composite oxide) was heated while allowing the model gas to flow under conditions of 1050 ° C and 5 hours to perform a high temperature durability test (1050 ° C RL). As a flow condition of the model gas, rich gas (R) containing 8% by volume of CO in nitrogen and lean gas (L) containing 20% by volume of O2 in nitrogen were alternately supplied on a 15 minute basis.
[0077] <X-Ray Diffraction Measurement (XRD)> With respect to a La-CZ composite oxide (Fresco) obtained without performing any durability test on the ceria-zirconia composite oxide containing La obtained, an oxide of La-CZ composite subjected to durability test 1 (1100 ° C air) and a La-CZ composite oxide subjected to durability test 2 (1050 ° C RL), one crystal phase of each composite oxide of La-CZ was measured using an X-ray diffraction method. Using "RINT-2100" (manufactured by Rigaku Corporation, product name: "RINT-2100") as an X-ray diffractometer, a standard X-ray diffraction was measured under conditions (X-ray source: Cu-Kα ray (À = 0.15418 nm), tube voltage: 40 kV, tube current: 30 mA) to obtain the intensity ratio I ( 14/29) and the intensity ratio I (28/29). The results obtained are shown in Table 1, respectively.
[0078] <Oxygen Absorption Measurement and Release Quantity Test: OSC Evaluation> With respect to a La-CZ (Fresco) composite oxide obtained without performing any durability tests on the ceria-zirconia composite oxide containing La obtained, a La-CZ composite oxide subjected to durability test 1 (1100 ° C air) and a La-CZ composite oxide subjected to durability test 2 (1050 ° C RL), 3 g of each La-CZ composite oxide and 1 g of Pd / Al2O3 catalyst on which the Pd (0.25% by weight) was supported were physically mixed using a mortar, followed by compression molding and crushing. As a result, an exhaust gas purification catalyst having a pellet shape with a diameter of 0.5 mm to 1 mm was obtained.
[0079] 15 mg of the obtained catalyst was weighed, and the oxygen absorption and the amount of its release were measured using a thermogravimetric analyzer. Oxygen absorption and release amount indicate that the amount (O2-mg / CZ-g) of oxygen absorbed and released at 400 ° C per 1 g of CZ in the catalyst and was obtained from a reversible weight change using a thermogravimetric analyzer (TG, manufactured by Ohkurariken Co., Ltd.) placing the catalyst sample in a sample cell of the thermogravimetric analyzer and allowing the gas containing H2 (10% by volume) and N2 (90% by volume) and gas containing Air (O2: 21% by volume, N2: 78% by volume) alternatively flow under a temperature condition of 400 ° C on a 20 minute basis for 120 minutes at a flow rate of 200 ml / minute with respect to 15 mg of the catalyst. For evaluation, an oxygen release side (reduction side) value was used. In this case, a theoretical limit value for the amount of oxygen released was 0.4 mg. The results obtained are shown in Table 1.
[0080] (Example 2) A ceria-zirconia composite oxide containing La particulate was obtained with the same method as that of Example 1, except that a solution of aqueous lanthanum nitrate con-tendolanthanum (La) in an amount of 0.5% on an atomic basis with respect to a total amount of cerium and zirconium in the cerium-zirconia composite oxide was prepared and used in the rare earth element support step.
[0081] Regarding the cerium-zirconia composite oxide containing the particulate La obtained, the observation of HR-TEM, the analysis of EDX and the observation of SEM were carried out with the same method as that of Example 1. The result was that the rate of lanthanum content in the ceria-zirconia composite oxide containing La was 0.5% on an atomic basis with respect to the total content of cerium and zirconium. In addition, the lanthanum content present in regions close to the surface that were at a distance less than 50 nm from the primary particle surfaces of a ceria-zirconia composite oxide supported by La is responsible for 100% on an atomic basis of the total content of lantanium in the cerium-zirconia composite oxide supporting La. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide containing La obtained was 3.2 μm.
[0082] In addition, regarding the ceriazirconia composite oxide containing La obtained, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release amount were carried out with the same method than that of Example 1. The results obtained are shown in Table 1.
[0083] FIGURE 1 illustrates the results of the EDX analysis of the primary particles of the ceria-zirconia composite oxide containing La subjected to the durability test 1 (1100 ° C air) and FIGURE 2 illustrates the results of the HR observation -TEM (high resolution transmission electron microscope) of the same. It was clearly confirmed from FIGURES 1 and 2 that, in the ceria-zirconia composite oxide containing La from the example according to the invention, the particle surfaces were changed from the CeO2-ZrO2 pyrochlorine structure to the CeO2-ZrO2 cubic crystal at a depth of 3 nm to 7 nm.
[0084] (Example 3) A ceria-zirconia composite oxide containing particulate Y was obtained with the same method as that of Example 1, except that an aqueous yttrium nitrate solution containing yttrium (Y) in an amount of 0, 5% atomic basis with respect to a total amount of cerium and zirconium in the cerium-zirconia composite oxide was prepared and used in the rare earth element support step.
[0085] Regarding the cerium-zirconia composite oxide containing the particulate Y obtained, the observation of HR-TEM, the analysis of EDX and the observation of SEM were carried out with the same method as that of Example 1. The result was that the ratio of yttrium content in the cerium-zirconia composite oxide containing Y was 0.5% on an atomic basis with respect to the total content of cerium and zirconium. In addition, the content of yttrium present in regions close to the surface that were at a distance less than 50 nm from the surfaces of primary particles of the ceria-zirconia composite oxide supporting Y is responsible for 95% on an atomic basis of the total content of Yttrium in the Y-containing ceria-zirconia composite oxide. In addition, the average primary particle size of the Y-containing ceria-zirconia composite oxide was 3.1 μm.
[0086] In addition, regarding the ceriazirconia composite oxide containing Y obtained, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release amount were carried out with the same method than that of Example 1. The results obtained are shown in Table 1.
[0087] (Example 4) A cerium-zirconia composite oxide containing particulate Pr was obtained with the same method as that of Example 1, except that an aqueous praseodymium nitrate solution containing praseodymium (Pr) in an amount of 0.5% on an atomic basis with respect to a total amount of cerium and zirconium in the cerium-zirconia composite oxide was prepared and used in the rare earth element support step.
[0088] Regarding the ceria-zirconia composite oxide containing the obtained particulate Pr, the observation of HR-TEM, the analysis of EDX and the observation of SEM were carried out with the same method as that of Example 1. The result was that the rate of praseodymium content in the ceria-zirconia composite oxide containing Pr was 0.5% on an atomic basis with respect to the total cerium and zirconium content. In addition, the content of praseodymium present in regions close to the surface that were at a distance less than 50 nm from the surfaces of primary particles of the ceria-zirconia composite oxide supporting Pr is responsible for 100% on an atomic basis of the total content of praseodymium in the cerium-zirconia composite oxide supporting Pr. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide containing Pr obtained was 3.3 μm.
[0089] In addition, regarding the ceriazirconia composite oxide containing Pr obtained, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release amount were carried out with the same method than that of Example 1. The results obtained are shown in Table 1.
[0090] (Example 5) A ceria-zirconia composite oxide containing La particulate was obtained with the same method as that of Example 1, except that a solution of aqueous lanthanum nitrate containing lanthanum (La) in an amount of 0, 5% atomic base with respect to a total amount of cerium and zirconium in the cerium-zirconia composite oxide was prepared and used in the rare earth element support step and the firing temperature was set at 1100 ° C in the firing step .
[0091] Regarding the cerium-zirconia composite oxide containing the particulate La obtained, the observation of HR-TEM, the analysis of EDX and the observation of SEM were carried out with the same method as that of Example 1. The result was that the rate of lanthanum content in the ceria-zirconia composite oxide containing La was 0.5% on an atomic basis with respect to the total content of cerium and zirconium. In addition, the lanthanum content present in regions close to the surface that were at a distance less than 50 nm from the primary particle surfaces of a ceria-zirconia composite oxide supported by La is responsible for 100% on an atomic basis of the total content of lantanium in the cerium-zirconia composite oxide supporting La. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide containing La obtained was 3.4 μm.
[0092] In addition, regarding the ceriazirconia composite oxide containing La obtained, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release amount were carried out with the same method than that of Example 1. The results obtained are shown in Table 1.
[0093] FIGURE 3 illustrates the results of the EDX analysis of the primary particles of the ceria-zirconia composite oxide containing La subjected to the durability test 1 (1100 ° C air) and FIGURE 4 illustrates the results of the HR observation -TEM (high resolution transmission electron microscope) of the same. It was clearly confirmed from FIGURES 3 and 4 that, in the cerium-zirconia composite oxide containing La from the example according to the invention, the particle surfaces were changed from the CeO2-ZrO2 pyrochlorine structure to the CeO2-ZrO2 cubic crystal at a depth of 1 nm to 3 nm.
[0094] (Example 6) A cerium-zirconia composite oxide containing La particulate was obtained with the same method as that of Example 1, except that a solution of aqueous lanthanum nitrate containing lanthanum (La) in an amount of 1, 0% on atomic basis with respect to a total amount of cerium and zirconium in the cerium-zirconia composite oxide was prepared and used in the rare earth element support step.
[0095] Regarding the ceria-zirconia composite oxide containing the particulate La obtained, the observation of HR-TEM, the analysis of EDX and the observation of SEM were carried out with the same method as that of Example 1. The result was that the rate of lanthanum content in the cerium-zirconia composite oxide containing La was 1.0% on an atomic basis with respect to the total content of cerium and zirconium. In addition, the lanthanum content present in regions close to the surface that were at a distance less than 50 nm from the primary particle surfaces of a ceria-zirconia composite oxide supported by La is responsible for 100% on an atomic basis of the total content of lantanium in the cerium-zirconia composite oxide supporting La. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide containing La obtained was 3.3 μm.
[0096] In addition, regarding the ceriazirconia composite oxide containing La obtained, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release amount were carried out with the same method than that of Example 1. The results obtained are shown in Table 1.
[0097] (Example 7) A ceria-zirconia composite oxide containing La particulate was obtained with the same method as that of Example 1, except that a solution of aqueous lanthanum nitrate containing lanthanum (La) in an amount of 2, 5% atomic basis with respect to a total amount of cerium and zirconium in the cerium-zirconia composite oxide was prepared and used in the rare earth element support step.
[0098] Regarding the cerium-zirconia composite oxide containing the particulate La obtained, the observation of HR-TEM, the analysis of EDX and the observation of SEM were carried out with the same method as that of Example 1. The result was that the rate of lanthanum content in the cerium-zirconia composite oxide containing La was 2.5% on an atomic basis with respect to the total content of cerium and zirconium. In addition, the lanthanum content present in regions close to the surface that were at a distance less than 50 nm from the primary particle surfaces of a ceria-zirconia composite oxide supported by La is responsible for 100% on an atomic basis of the total content of lantanium in the cerium-zirconia composite oxide supporting La. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide containing La obtained was 3.6 μm.
[0099] In addition, regarding the ceriazirconia composite oxide containing La obtained, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release amount were performed with the same method than that of Example 1. The results obtained are shown in Table 1.
[00100] FIGURE 5 illustrates the results of the EDX analysis of the primary particles of the ceria-zirconia composite oxide containing La subjected to the durability test 1 (1100 ° C air) and FIGURE 6 illustrates the results of the HR observation -TEM (high resolution transmission electron microscope) of the same. It was clearly confirmed from FIGURES 5 and 6 that, in the ceria-zirconia composite oxide containing La from the example according to the invention, the particle surfaces were changed from the CeO2-ZrO2 pyrochlorine structure to the CeO2-ZrO2 cubic crystal at a depth of 1 nm to 3 nm.
[00101] (Comparative Example 1) the ceriazirconia composite oxide (in which lanthanum was not supported and which was not filtered) obtained in Example 1 was prepared as a particulate ceriazirconia composite oxide for comparison.
[00102] Regarding the cerium-zirconia composite oxide obtained for comparison, the observation of HR-TEM, the analysis of EDX and the observation of SEM were performed with the same method as that of Example 1. The result was that content rate of the rare earth element in the cerium-zirconia composite oxide for comparison was 0.0% on an atomic basis with respect to the total content of cerium and zirconium. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide obtained for comparison was 3.2 μm.
[00103] In addition, regarding the ceriazirconia composite oxide obtained for comparison, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release amount were performed with the same method than that of Example 1. The results obtained are shown in Table 1.
[00104] FIGURE 7 illustrates the results of the EDX analysis of the primary particles of the ceria-zirconia composite oxide for comparison to the durability test 1 (1100 ° C air) and FIGURE 8 illustrates the results of the observation of HR- TEM (high resolution transmission electron microscope) of them. It was clearly confirmed from FIGURES 7 and 8 that, in the cerium-zirconia composite oxide for comparison, the particle surfaces were changed from the CeO2-ZrO2 pyrochlorine structure to the CeO2-ZrO2 cubic crystal at a depth of 8 nm at 10 nm.
[00105] (Comparative Example 2) A ceriazirconia composite oxide containing particulate La was obtained with the same method as that of Example 1, except that an aqueous lanthanum nitrate solution containing lanthanum (La) in an amount of 5 , 0% on atomic basis with respect to a total amount of cerium and zirconium in the cerium-zirconia composite oxide was prepared and used in the rare earth element support step.
[00106] Regarding the cerium-zirconia composite oxide containing La particulate obtained, the observation of HR-TEM, the analysis of EDX and the observation of SEM were carried out with the same method as that of Example 1. The result was that the rate of lanthanum content in the cerium-zirconia composite oxide containing La was 5.0% on an atomic basis with respect to the total content of cerium and zirconium. In addition, the lanthanum content present in regions close to the surface that were at a distance less than 50 nm from the primary particle surfaces of a ceria-zirconia composite oxide supported by La is responsible for 89% on an atomic basis of the total content of lanthanum in the cerium-zirconia composite oxide supporting La. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide containing La obtained was 3.5 μm.
[00107] In addition, regarding the ceriazirconia composite oxide containing La obtained, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release quantity were performed with the same method than that of Example 1. The results obtained are shown in Table 1.
[00108] (Comparative Example 3) A ceriazirconia composite oxide containing particulate Fe was obtained with the same method as that of Example 1, except that iron was used instead of the lanthanum support step in the rare earth element ( lanthanum) and a solution of aqueous iron nitrate containing iron (Fe) in an amount of 2.5% on an atomic basis with respect to a total amount of cerium and zirconium in the cerium-zirconia composite oxide was prepared and used.
[00109] Regarding the cerium-zirconia composite oxide containing the particulate Fe obtained, the observation of HR-TEM, the analysis of EDX and the observation of SEM were carried out with the same method as that of Example 1. The result was that the rate of iron content in the cerium-zirconia composite oxide containing Fe was 2.5% on an atomic basis with respect to the total content of cerium and zirconium. In addition, the iron content present in regions close to the surface that were at a distance less than 50 nm from the surfaces of primary particles of the ceria-zirconia composite oxide supporting Fe is responsible for 92% on an atomic basis of the total content of iron in the ceria-zirconia composite oxide supporting Fe. In addition, the average particle size of primary particles of the ceria-zirconia composite oxide containing Fe obtained was 3.1 μm.
[00110] In addition, regarding the ceriazirconia composite oxide containing Fe obtained, the durability tests, the measurement of X-ray diffraction, and the measurement of oxygen absorption and release amount were performed with the same method than that of Example 1. The results obtained are shown in Table 1.

[00111] <Results of Evaluation Tests> From the comparison of the results of examples 1 to 7 and the results of comparative examples 1 to 3 shown in Table 1, the following can be confirmed, clearly: when a rate of the content of rare earth element added for the total content of cerium and zirconium in the cerium-zirconia composite oxide containing rare earth element is in a range of 0.1% on atomic basis to 4.0% on atomic base, and when the content of rare earth element present in regions close to the surface that are at a distance less than 50 nm from the surfaces of primary particles of the cerium-zirconia composite oxide containing a rare earth element responsible for 90% on atomic basis or more of the content total of the rare earth element (Examples 1 to 7), sufficiently excellent oxygen storage capacity (OSC) and sufficiently high heat resistance can be obtained at the same time, and sufficient oxygen storage capacity excellent (OSC) can be displayed even after exposure to a high temperature for a long period of time,
[00112] It can also be confirmed that when the content of the rare earth element added is out of range (comparative examples 1 and 2), the ratio of intensity I (14/29) and oxygen storage capacity (OSC) after the tests of durability are bad.
[00113] Furthermore, it can also be confirmed that in the cerium-zirconia composite oxide (Comparative Example 3) containing Fe instead of a specific rare earth element, the intensity ratio I (14/29) which is the ratio of the maintained ordered phase of pyrochlor tends to be retained, however the ratio of intensity I (28/29) which is the index that indicates the degree of phase separation of CeO2 from a composite oxide is large and the deterioration of OSC is great .
[00114] As described above, according to the modalities, it is possible to provide a ceria-zirconia composite oxide, a method for producing it, and a catalyst for purifying the exhaust gas using the ceria- zirconia, the cerium-zirconia composite oxide having sufficiently excellent oxygen storage capacity (OSC) and sufficiently excellent heat resistance at the same time and being able to exhibit sufficiently excellent oxygen storage capacity (OSC) even after exposure to a high temperature for a long period of time,
[00115] In this way, the cerium-zirconia composite oxide according to the modality has sufficiently excellent oxygen storage capacity (OSC) and sufficiently high heat resistance at the same time and, therefore, can be desirably used as a support, a cocatalyst, a catalyst atmosphere control material, and the like for a catalyst for exhaust gas purification.

权利要求:
Claims (3)
[0001]
1. Cerium-zirconia composite oxide that contains a cerium-zirconia composite oxide, characterized by the fact that it comprises lanthanum, in which a ratio between the total content of lanthanum and the total content of cerium and zirconium in the composite oxide of ceria-zirconia is 0.25% to 2.5% on atomic basis, a content of lanthanum present in regions close to the surface is responsible for 90% on atomic basis or more of the total content of lanthanum, the regions close to the surface being less than 50 nm from the surfaces of the primary particles of the cerium-zirconia composite oxide, a ratio of cerium to zirconium content in the cerium-zirconia compositive oxide is in the range of 43:57 to 48 : 52 for molar reason, an average particle size of the primary particles of the ceria-zirconia composite oxide is 2.2 μm to 4.5 μm, and an intensity ratio I (14/29) of a diffraction line at 2θ = 14.5 ° for a diffraction line at 2θ = 29 ° and an intensity ratio I (28/29) of a line diffraction at 2θ = 28.5 ° in relation to the diffraction line at 2θ = 29 ° satisfies the following conditions, respectively: I (14/29)> 0.032; and I (28/29) <0.08, in which the intensity ratio I (14/29) and the intensity ratio I (28/29) are calculated from an X-ray diffraction pattern of the ceria-zirconia composite oxide, the X-ray diffraction pattern being obtained by an X-ray diffraction measurement using CuKα after heating the ceria-zirconia composite oxide under a temperature condition of 1100 ° C in the air for 5 hours .
[0002]
2. Method for producing a ceria-zirconia composite oxide that contains a ceria-zirconia composite oxide, characterized by the fact that it comprises: preparing ceria-zirconia composite oxide powder, in which the ratio of cerium to zirconium ranges from 43:57 to 48:52 by molar ratio and an average particle size of primary particles of ceria-zirconia oxide powder is 2.2 μm to 4.5 μm; allow the lanthanum to be supported in the cerium-zirconia composite oxide powder; and burning ceria-zirconia composite oxide powder in which lanthanum is supported from 600 ° C to 1200 ° C to obtain ceria-zirconia compositive oxide, as defined in claim 1.
[0003]
3. Catalyst for purification of exhaust gases, characterized by the fact that it comprises ceriazirconia composite oxide, as defined in claim 1.

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法律状态:
2019-11-12| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2020-09-01| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application [chapter 6.1 patent gazette]|

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2021-02-02| B09A| Decision: intention to grant|

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2021-03-30| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 02/10/2014, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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JP2013-209190|2013-10-04|

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JP2013209190A|JP5883425B2|2013-10-04|2013-10-04|Ceria-zirconia composite oxide, production method thereof, and exhaust gas purification catalyst using the ceria-zirconia composite oxide|

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PCT/IB2014/001995|WO2015049575A1|2013-10-04|2014-10-02|Ceria-zirconia composite oxide, method for producing the same, and catalyst for purifying exhaust gas using the ceria-zirconia composite oxide|

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