Oxygen storage material

Abstract

The invention relates to an oxygen storage material. Provided is an inexpensive oxygen storage material having excellent oxygen release performance at low temperatures. The oxygen storage material according to the present invention is an oxygen storage material containing a composite oxide, the composite oxide containing cerium and / or europium and silicon and / or phosphorus, and the composite oxide having an apatite-type crystal structure.

Description

Technical Field

[0001] The present invention relates to oxygen storage materials. Background Art

[0002] The exhaust gas emitted from internal combustion engines such as automobiles contains carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO x ) and other harmful components, which are purified by the exhaust gas purification catalyst and then released into the atmosphere. In the past, the exhaust gas purification catalyst used simultaneously oxidized CO and HC and NO x As a three-way catalyst, a catalyst in which a noble metal such as platinum (Pt), palladium (Pd), or rhodium (Rh) is supported on alumina (Al 2 O 3 ), silicon dioxide (SiO 2 )、ZrO 2 ), titanium dioxide (TiO 2 ) etc.

[0003] In recent years, in order to improve the exhaust gas purification ability of the three-way catalyst in response to the fluctuation of the oxygen concentration in the exhaust gas, oxygen storage materials, which are inorganic materials having oxygen storage capacity (OSC capacity), have been used in exhaust gas purification catalysts. 2 ) has excellent OSC capability, which is based on ceria-zirconia composite oxide (CeO 2 -ZrO 2 ) is widely used as an oxygen storage material.

[0004] As an oxygen storage material of such a ceria-zirconia composite oxide, for example, Patent Document 1 describes a ceria-zirconia composite oxide, which is characterized in that it contains a composite oxide of ceria and zirconia, in which an ordered array phase of a pyrochlore phase is formed by cerium ions and zirconium ions, and after heating at a temperature of 1000° C. in the atmosphere for 5 hours, more than 50% of the ordered array phase of the pyrochlore phase remains compared to before heating.

[0005] In addition, Patent Document 2 describes a melilite-type oxide having an oxygen absorption and release function, which is an oxide having a melilite-type structure and has a general formula A X B 2-X CD 2 E 7+δThe composition represented by the invention is as follows: A is cerium (Ce), B is one or more elements selected from alkali metal elements, alkaline earth metal elements, magnesium (Mg), indium (In) and rare earth metal elements (but excluding cerium), C and D are one or more elements selected from transition metal elements, Group 12 elements (elements in the 12th column of the periodic table), Group 13 elements (elements in the 13th column of the periodic table), Group 14 elements (elements in the 14th column of the periodic table) and Group 15 elements (elements in the 15th column of the periodic table), E is oxygen (O), x is greater than 0 and less than 2.0, δ is greater than -1.0 and less than 1.0, and the oxide maintains electrical neutrality.

[0006] Prior Art Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2009-84061

[0008] Patent Document 2: Japanese Patent Application Publication No. 2023-55681 Summary of the invention

[0009] However, in the ceria-zirconia composite oxide forming a pyrochlore phase-type ordered array phase as in Patent Document 1, the use of zirconium (Zr) which is a rare metal may lead to an increase in cost. In addition, in this composite oxide, the activation energy when releasing excess oxygen from the crystal structure is high, and there is a problem that the temperature required for releasing oxygen is high.

[0010] On the other hand, an oxide having a pyroxene-type structure such as Patent Document 2 is composed of calcium, aluminum, and the like, which are abundant elements. In addition, the oxide has many spaces in the crystal structure that can accommodate excess oxygen, and the temperature required to release oxygen is low. However, in the oxide, a composition in which excess oxygen is accommodated in all of the spaces is unstable, and thus there is a problem of a small oxygen storage capacity.

[0011] Therefore, an object of the present invention is to provide an inexpensive oxygen storage material having excellent oxygen release performance at low temperatures.

[0012] The present inventors have made various studies on means for solving the above-mentioned problems and have found that a composite oxide having an apatite type crystal structure containing Ce and / or europium (Eu) and containing silicon (Si) and / or phosphorus (P) is more effective than a conventional composite oxide having a pyrochlore type crystal structure containing Ce and Zr which is useful as an oxygen storage material. 2 Zr 2 O 7 The present invention has been completed because the activation energy is small and the oxygen storage and release properties at low temperatures are excellent.

[0013] That is, the gist of the present invention is as follows.

[0014] (1) An oxygen storage material is an oxygen storage material comprising a composite oxide, the composite oxide comprising cerium and / or europium and silicon and / or phosphorus, the composite oxide having an apatite type crystal structure.

[0015] (2) The oxygen storage material according to (1), wherein the composite oxide is represented by the general formula A α T β X γ (In the formula, A contains cerium (Ce) and / or europium (Eu), T contains silicon (Si) and / or phosphorus (P), X contains oxygen (O), α, β and γ represent molar ratios, α is 9.33 to 10, β is 6, and γ is 24 to 30.)

[0016] (3) The oxygen storage material according to (2), wherein A contains cerium.

[0017] (4) The oxygen storage material according to (2) or (3), wherein A contains europium.

[0018] (5) The oxygen storage material according to any one of (2) to (4), wherein the content of cerium and / or europium is 20 mol% or more relative to the total amount of A.

[0019] (6) The oxygen storage material according to any one of (2) to (5), wherein A further contains one or more elements selected from alkali metals, alkaline earth metals, and rare earth elements other than cerium and europium.

[0020] (7) In the oxygen storage material according to (6), A further contains one or more elements selected from the group consisting of calcium (Ca), strontium (Sr), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), ytterbium (Yb) and lutetium (Lu).

[0021] (8) The oxygen storage material according to any one of (2) to (7), wherein T further contains one or more elements selected from the group consisting of Group 13 elements, Group 14 elements, and Group 15 elements.

[0022] (9) The oxygen storage material according to (8), wherein T further contains boron (B).

[0023] (10) The oxygen storage material according to any one of (1) to (9), further comprising a catalyst metal, wherein the catalyst metal is supported on the composite oxide.

[0024] (11) The oxygen storage material according to (10), wherein the content of the catalyst metal is 0.01 wt% to 5 wt% relative to the total weight of the oxygen storage material.

[0025] (12) The oxygen storage material according to (10) or (11), wherein the catalyst metal contains a platinum group element.

[0026] (13) The oxygen storage material according to (12), wherein the platinum group element is one or more elements selected from rhodium (Rh), palladium (Pd) and platinum (Pt).

[0027] (14) An exhaust gas purification catalyst comprising the oxygen storage material according to any one of (1) to (13).

[0028] (15) A redox catalyst comprising the oxygen storage material according to any one of (1) to (13).

[0029] (16) An oxygen storage method using the oxygen storage material described in any one of (1) to (13).

[0030] (17) An oxygen enrichment method using the oxygen storage material described in any one of (1) to (13).

[0031] (18) An oxygen removal method using the oxygen storage material described in any one of (1) to (13).

[0032] (19) A heating and cooling method using the oxygen storage material described in any one of (1) to (13).

[0033] According to the present invention, it is possible to provide an inexpensive oxygen storage material having excellent oxygen release performance at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram schematically showing an apatite-type crystal structure of an example of the composite oxide included in the present invention.

[0035] Figure 2 It is the X-ray diffraction diagram of the product of Example 1 and Comparative Examples 1-2.

[0036] Figure 3 A is an X-ray diffraction pattern of the products of Examples 1 to 3 and Comparative Examples 3 to 8, and B is an X-ray diffraction pattern of the products of Examples 4 to 12.

[0037] Figure 4 A is the measurement condition of the hydrogen temperature reduction test, and B is the H of the products before and after Pd loading in Example 1 and Comparative Examples 1 to 2. 2 TPR results.

[0038] Figure 5 This is a graph showing the oxygen release temperature and oxygen storage amount of the products of Example 1 and Comparative Examples 1 and 2 after Pd was loaded.

[0039] Figure 6This is a graph showing the oxygen storage amounts of the products of Examples 1 to 12 and Comparative Examples 3 to 8.

[0040] Figure 7 1 and 2 are X-ray diffraction patterns of the product of Example 1 before and after oxidation.

[0041] Figure 8 This is the X-ray diffraction pattern of the products of Examples 13 to 15.

[0042] Fig. 9 This is a graph showing the oxygen storage amounts of the products of Examples 1-2 and 13-15.

[0043] Fig.10 This is a diagram schematically showing an apatite-type crystal structure of an example of the composite oxide included in the present invention.

[0044] Fig.11 This is a graph showing the oxygen storage amounts of the products of Examples 9 to 10 and 13. DETAILED DESCRIPTION

[0045] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0046] In this specification, the features of the present invention are described with reference to the drawings as appropriate. In the drawings, the sizes and shapes of the various parts are exaggerated for clarity, and the actual sizes and shapes are not accurately depicted. Therefore, the technical scope of the present invention is not limited to the sizes and shapes of the various parts shown in these drawings. Furthermore, the oxygen storage material of the present invention is not limited to the following embodiments, and can be implemented in various ways without departing from the scope of the gist of the present invention by implementing changes, improvements, etc. that can be made by those skilled in the art.

[0047] The present invention relates to an oxygen storage material, which is an oxygen storage material containing a composite oxide. The composite oxide contains cerium and / or europium, silicon and / or phosphorus, and has an apatite type crystal structure.

[0048] In the present invention, the crystal structure of the composite oxide containing cerium and / or europium and containing silicon and / or phosphorus can be determined by X-ray diffraction (XRD) analysis. In the present invention, the composite oxide containing cerium and / or europium and containing silicon and / or phosphorus has an apatite-type crystal structure.

[0049] The basic XRD spectrum of apatite type crystal structure is well known in the art. 9.33 Si 6 O 26In the case of , in an XRD spectrum using copper Kα rays, it has peaks at four or more positions selected from 27.3°±0.5°, 28.2°±0.5°, 31.0°±0.5°, and 32.1°±0.5° with respect to 2θ.

[0050] It is well known in the technical field that the peak position of the basic XRD spectrum of the apatite type crystal structure changes depending on the composition of the composite oxide.

[0051] Figure 1 The apatite crystal structure of an example of the composite oxide contained in the present invention is schematically shown. In the composite oxide containing cerium and / or europium and containing silicon and / or phosphorus of the present invention, the apatite crystal structure has a structure capable of conducting oxygen ions (O 2- ) is blocked by trivalent cerium ions (Ce 3+ ) and / or divalent europium ions (Eu 2+ ) surrounded by Ce. Furthermore, the oxygen ion conduction path (storage space) is one-dimensional. Therefore, it is believed that the oxygen storage capacity of the composite oxide of the present invention is achieved by 3+ Oxidized to Ce 4+ 、Eu 2+ Oxidized to Eu 3+ When the size of the cerium ions and / or europium ions shrinks, O 2- It is introduced into the crystal structure to play its role.

[0052] The composite oxide containing cerium and / or europium and containing silicon and / or phosphorus of the present invention can also be represented by the following formula:

[0053] A α T β X γ

[0054] (In the formula, A contains cerium and / or europium, T contains silicon and / or phosphorus, X contains oxygen, α, β and γ represent molar ratios, α is 9.33 to 10.0, β is 6, and γ is 24 to 30.)

[0055] In one embodiment, A contains cerium. In one embodiment, A contains europium. In one embodiment, A contains cerium and europium.

[0056] A may also contain one or more metal elements selected from alkali metals, alkaline earth metals and rare earth metals other than Ce and Eu in addition to Ce and / or Eu. In one embodiment, A contains one or more metal elements selected from lithium (Li), sodium (Na), potassium (K), calcium (Ca), strontium (Sr), barium (Ba), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), terbium (Tb), ytterbium (Yb) and lutetium (Lu) in addition to Ce and / or Eu. In one embodiment, A contains one or more elements selected from Ca, Sr, Y, La, Pr, Sm, Yb and Lu in addition to Ce and / or Eu. In one embodiment, when A contains Ce, A also contains one or more elements selected from Ca, Sr, Y, La, Pr, Sm, Eu, Yb and Lu. In one embodiment, when A contains Eu, A further contains one or more elements selected from the group consisting of Ce, La and Pr.

[0057] The Ce content in A is usually 20 mol% or more, in one embodiment 78 mol% or more, and in one embodiment 80 mol% or more relative to the total amount (moles) of A. The Ce content in A may also be 100 mol% relative to A (total moles).

[0058] The content of Eu in A is usually 20 mol% or more, 78 mol% or more, and 80 mol% or more in one embodiment relative to the total amount (moles) of A. The content of Eu in A may also be 100 mol% relative to A (total moles).

[0059] When the content of Ce and / or Eu in A is within the above range, sufficient oxygen storage capacity can be ensured.

[0060] The content of elements other than Ce and Eu in A is not limited. The content of elements other than Ce and Eu in A can be determined so as to compensate for the charges of Ce and / or Eu contained, as described in detail below.

[0061] T may contain one or more elements selected from Group 13 elements, Group 14 elements other than Si, and Group 15 elements other than P in addition to Si and / or P. In one embodiment, T contains one or more elements selected from boron (B), aluminum (Al), gallium (Ga), and germanium (Ge) in addition to Si and / or P. In one embodiment, T contains B in addition to Si and / or P.

[0062] The content of Si or P in T is usually 66 mol% or more, and in one embodiment, 83 mol% or more relative to the total amount (moles) of T. The content of Si or P in T may be 100 mol% relative to T (total moles).

[0063] When the content of Si or P in T is within the above range, it is possible to ensure that the TO required for forming the apatite structure is located 4 The small cation at the center of the tetrahedron (Si 4+ or P 5+ ).

[0064] The content of elements other than Si and P in T can also be determined so as to compensate for the charges of Ce and / or Eu contained, and Si and / or P contained, as described in detail below.

[0065] In the apatite crystal structure of the composite oxide contained in the present invention, Ce is Ce 3+ Contains in the form of Eu 2+ In this crystal structure, although Ce 3+ and Eu 2+ The valences of the ions are different, but they occupy the same site. Therefore, it is not possible to form apatite in which Ce and Eu are simply substituted in the composite oxide. Therefore, when the ions present in the composite oxide are changed to ions having a valence different from that of the ions, charge compensation can be performed by similarly changing other ions present in the composite oxide, for example, ions having a fixed valence that do not contribute to the oxygen storage capacity. For example, when Ce is replaced in the composite oxide, Eu is replaced by Ce. 3+ Replaced by Eu 2+ In the case of , this -1 charge change can be achieved by, for example, replacing Ca which can occupy the same site as Ce and Eu. 2+ (Sr 2+ ) is replaced by La 3+ , and Si that can occupy different sites from Ce and Eu 4+ Replace with P 5+ For example, if you want to confirm the Ce content in a composite oxide, 3+ and Eu 2+ In the case of a difference in the effect of Ce 8 A 2 T 6 O 26 (A=Ca or Sr, T=Si) and Eu 8 A 2 T 6 O 26 (A=La, T=P) is used for implementation.

[0066] Furthermore, in the apatite-type crystal structure of the composite oxide contained in the present invention, the composite oxide Ce 8 A 2 T 6 O 26 Ce in (A=Ca or Sr, T=Si) 3+ Replaced by Eu 2+ In the case of 4+ Replace with P 5+ To perform charge compensation to produce Eu 8 A 2 T 6 O 26 (A=Ce, T=P).

[0067] X contains O and is usually composed of O. In X, O may exist in the state of OH depending on the situation.

[0068] The content of O in X is usually 92 mol% or more, and in one embodiment, 99 mol% or more, relative to the total amount (moles) of X. The content of O in X may be 100 mol% relative to X (total moles).

[0069] When the content of O in X is within the above range, sufficient oxygen storage capacity can be ensured.

[0070] In one embodiment, the composite oxide containing cerium and silicon or phosphorus of the present invention is represented by the formula (Ce, A'): α (Si, P, T') β O γ (wherein A' is one or more metal elements selected from Ca, Sr, Y, La, Pr, Sm, Eu, Yb and Lu, T' is B, α, β and γ represent molar ratios, α is 9.33 to 10, β is 6, and γ is 24 to 30.) Here, the molar ratio of Ce to A' (Ce:A') is usually 1:0 to 1:4, and the molar ratio of Si or P to T' (Si, P:T') is usually 1:0 to 5:1.

[0071] In one embodiment, the composite oxide containing cerium and silicon or phosphorus of the present invention is Ce 9.33 Si 6 O 26 、Ce 2 Ca 8 P 6 O 26 、Ce 9.33 Si 5 BO 25.5 、Ce 7.33 Y 2Si 6 O 26 、Ce 7.33 La 2 Si 6 O 26 、Ce 7.33 Pr 2 Si 6 O 26 、Ce 7.33 Sm 2 Si 6 O 26 、Ce 7.33 Lu 2 Si 6 O 26 、Ce 8 Ca 2 Si 6 O 26 、Ce 8 Sr 2 Si 6 O 26 、Ce 8 Eu 2 Si 6 O 26 or Ce 8 Yb 2 Si 6 O 26 express.

[0072] In one embodiment, the composite oxide containing europium and phosphorus of the present invention is represented by the formula (Eu, A'): α (P) β O γ (wherein A' is one or more metal elements selected from Ce, La and Pr, α, β and γ represent molar ratios, α is 9.33 to 10, β is 6, and γ is 24 to 30.)

[0073] In one embodiment, the composite oxide containing europium and phosphorus of the present invention is Eu 8 Ce 2 P 6 O 26 、Eu 8 La 2 P 6 O 26 or Eu 8 Pr 2 P 6 O 26 express.

[0074] The oxygen storage material of the present invention may also contain a catalyst metal. The catalyst metal is supported on the composite oxide described above. As the catalyst metal, a noble metal can be mentioned. As the noble metal, it is not limited, including platinum group noble metals. As platinum group noble metals, ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt) can be mentioned. In one embodiment, the noble metal is one or more selected from Rh, Pt and Pd. The loading amount of the noble metal can be the same as that of the conventional exhaust purification catalyst, and is not limited, but it can be 0.01 weight% to 5 weight% relative to the total weight of the oxygen storage material, and in one embodiment, it is 0.5 weight% to 2 weight%.

[0075] The oxygen storage material of the present invention is excellent in oxygen release properties at low temperatures. Therefore, the present invention also relates to an exhaust gas purification catalyst and / or a redox catalyst containing the oxygen storage material of the present invention.

[0076] The exhaust gas purification catalyst and / or the oxidation-reduction catalyst of the present invention may also contain a carrier material other than the oxygen storage material of the present invention. As a carrier material other than the oxygen storage material of the present invention, porous metal oxides with excellent heat resistance can be cited, for example, aluminum oxide (aluminum trioxide: Al 2 O 3 ), zirconium oxide (zirconium dioxide: ZrO 2 ), silicon oxide (silicon dioxide: SiO 2 ) or a composite oxide containing these metal oxides as a main component. In the exhaust gas purification catalyst, the supporting method can utilize conventional supporting methods such as adsorption supporting method and water absorption supporting method.

[0077] The exhaust gas purification catalyst and / or redox catalyst of the present invention can exhibit excellent ordered structure durability and OCS capability in a wide temperature range. The exhaust gas purification catalyst of the present invention is usually used in a low temperature range of about 200°C to 600°C.

[0078] In addition, in the oxygen storage material of the present invention, by utilizing the properties of absorbing and releasing oxygen, and the different energy states between the state of adsorbing oxygen and the state of releasing oxygen, the oxygen storage material of the present invention can be used to store oxygen (oxygen storage method), enrich oxygen (oxygen enrichment method), remove oxygen (oxygen removal method), and / or be heated and / or cooled (heating and cooling method).

[0079] The oxygen storage material of the present invention can be manufactured by a common method such as a solid phase method, a liquid phase method, an alkoxide method, etc. For example, an aqueous solution of a cerium compound, a europium compound, a silicon compound, a phosphorus compound, and a compound containing elements other than Ce, Eu, Si and P as described above (hereinafter also referred to as "cerium compound and silicon compound, etc.") is mixed with an aqueous solution of a complex forming agent, and then dried to precipitate a product containing Ce and / or Eu and containing Si and / or P, and then calcined in a reducing atmosphere. The cerium compound and the silicon compound, etc. can also be used in the form of a solution of a non-aqueous solvent such as an alcohol or an organic carboxylic acid ester.

[0080] As the cerium compound, for example, nitrates such as cerium nitrate and diammonium cerium nitrate, sulfates such as cerium sulfate, chlorides such as cerium chloride, and water-soluble compounds such as nitrates such as cerium isopropoxide, and alcohol-soluble compounds such as alkoxides may be used.

[0081] As the europium compound, for example, water-soluble compounds such as nitrates such as europium nitrate, sulfates such as europium sulfate, chlorides such as europium chloride, and alcohol-soluble compounds such as alkoxides such as europium isopropoxide can be used.

[0082] As the silicon compound, alkoxides such as tetraethyl orthosilicate and tetraisopropyl orthosilicate can be used.

[0083] As the phosphorus compound, diammonium phosphate or the like can be used.

[0084] As the compound containing an element other than Ce, Eu, Si, and P, a water-soluble or alcohol-soluble compound such as a nitrate, a sulfate, a chloride, an alkoxide, or the like can be used.

[0085] The complex forming agent is not particularly limited, and examples thereof include polycarboxylic acids, amino acids, and the like. Examples of polycarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, citric acid, and tartaric acid. In one embodiment, the complex forming agent is citric acid. Examples of amino acids include glycine, alanine, asparagine, and aspartic acid.

[0086] When a precipitate is generated by mixing the aqueous solution of the cerium compound, the silicon compound, etc. and the aqueous solution of the complex forming agent, the precipitate may be filtered and then dried.

[0087] The mixed solution of the aqueous solution of the cerium compound, the silicon compound, etc. and the aqueous solution of the complex forming agent can be dried usually at a temperature of 50° C. to 150° C. for 5 to 48 hours.

[0088] The calcination of the product containing Ce and / or Eu and containing Si and / or P can usually be carried out by heating and maintaining it at a temperature of 600° C. to 1500° C. for 2 to 48 hours in a reducing atmosphere. The reducing atmosphere can be an inert gas atmosphere or a non-oxidizing atmosphere. In one embodiment, it can be an atmosphere containing H 2 , CO and other reducing gas atmosphere. Thus, an apatite type oxygen storage material can be obtained.

[0089] Example

[0090] Hereinafter, some embodiments of the present invention will be described, but the present invention is not intended to be limited to the scope shown in these embodiments.

[0091] 1. Manufacture of oxygen storage materials

[0092] 1-1. Reagents

[0093] Cerium(III) nitrate hexahydrate (Ce(NO 3 ) 3 6H 2 O) (manufactured by Norotech Co., Ltd.): ≥35.0% by weight (in CeO 2 count)

[0094] Cerium(IV) ammonium nitrate (NH 4 ) 2 Ce(NO 3 ) 6 (Tokyo Chemical Industry Co., Ltd.): >98.0 wt%

[0095] Yttrium(III) nitrate hexahydrate (Y(NO 3 ) 3 6H 2 O) (manufactured by Kanto Chemical Co., Ltd.): >99.99% by weight

[0096] Lanthanum(III) nitrate hexahydrate (La(NO 3 ) 3 6H 2 O) (manufactured by Nakalaku Co., Ltd.): ≥99.9% by weight

[0097] Praseodymium(III) nitrate hexahydrate (Pr(NO 3 ) 3 6H 2 O) (manufactured by Kanto Chemical Co., Ltd.): >99.95 wt%

[0098] Neodymium(III) nitrate hexahydrate (Nd(NO 3 ) 3 6H 2O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 99.5% by weight

[0099] Samarium(III) nitrate hexahydrate (Sm(NO 3 ) 3 6H 2 O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 99.5 wt%

[0100] Europium(III) nitrate hexahydrate (Eu(NO 3 ) 3 6H 2 O) (manufactured by Kanto Chemical Co., Ltd.): >99.95 wt%

[0101] Gadolinium(III) nitrate hexahydrate (Gd(NO 3 ) 3 6H 2 O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 99.5% by weight

[0102] Terbium(III) nitrate hexahydrate (Tb(NO 3 ) 3 6H 2 O) (manufactured by Kanto Chemical Co., Ltd.): >99.95 wt%

[0103] Ytterbium(III) nitrate pentahydrate (Yb(NO 3 ) 3 ·5H 2 O) (manufactured by Semantec): 99.9% by weight

[0104] Lutetium(III) nitrate tetrahydrate (Lu(NO 3 ) 3 ·4H 2 O) (manufactured by Kanto Chemical Co., Ltd.): >99.95 wt%

[0105] Calcium nitrate tetrahydrate (Ca(NO 3 ) 2 ·4H 2 O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): ≥ 98.5% by weight

[0106] Strontium nitrate (Sr(NO 3 ) 2 ) (Fujifilm Wako Pure Chemical Industries, Ltd.): 98.0 to 102.0% by weight

[0107] Tetraethyl orthosilicate (Si(OEt) 4 ) (Tokyo Chemical Industry Co., Ltd.): >98.0 wt%

[0108] Ammonium dihydrogen phosphate (NH4 )H 2 PO 4 ) (Fujifilm Wako Pure Chemical Industries, Ltd.): ≥ 99.0% by weight

[0109] Boric acid (H 3 BO 3 ) (Fujifilm Wako Pure Chemical Industries, Ltd.): ≥ 99.5% by weight

[0110] Aluminum nitrate nonahydrate (Al(NO 3 ) 3 9H 2 O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): ≥ 98.0 wt %

[0111] Zirconium oxynitrate dihydrate (ZrO(NO 3 ) 2 ·2H 2 O) (manufactured by Kanto Chemical Co., Ltd.): >99.0 wt%

[0112] Citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): ≥ 98.0 wt%

[0113] Ethylene glycol (manufactured by Nakura Co., Ltd.): 99.5% by weight

[0114] Palladium(II) nitrate (Pd(NO 3 ) 2 ) (Fujifilm Wako Pure Chemical Industries, Ltd.): ≥ 97.0 wt%

[0115] Palladium(II) acetate (Pd(OAc) 2 ) (Fujifilm Wako Pure Chemical Industries, Ltd.): ≥ 97.0 wt%

[0116] 1-2. Production of composite oxides

[0117] Example 1 (Ce 9.33 Si 6 O 26 )

[0118] (1) Place a stirrer in a 500 mL glass beaker and add Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol), Si(OEt) 4 (2.04 g, 9.78 mmol), citric acid (19.2 g, 100 mmol) and ethylene glycol (6.21 g, 100 mmol) as additives, and distilled water (18 mL) and ethanol (200 mL) as solvents.

[0119] (2) The solution is heated with a hot stirrer while being stirred to evaporate to dryness.

[0120] (3) The contents were recovered, the stirring bar was removed, and the mixture was crushed and mixed in a mortar.

[0121] (4) The powder was transferred to an alumina crucible and pre-fired in the atmosphere at 500° C. for 6 hours using a muffle furnace.

[0122] (5) The powder was transferred to an alumina boat, activated carbon was placed thereon, and the mixture was calcined at 1200° C. for 16 hours under an Ar gas flow of 0.5 L / min.

[0123] (6) Removing the activated carbon from the alumina boat and recovering the product.

[0124] Comparative Example 1 (CeCaAl 3 O 7 )

[0125] (1) Place a stirring bar in a 500 mL glass beaker and add (NH 4 ) 2 Ce(NO 3 ) 6 (2.74 g, 5.00 mmol), Ca(NO 3 ) 2 ·4H 2 O (1.18 g, 5.00 mmol), Al(NO 3 ) 3 9H 2 O (5.63 g, 15.0 mmol), citric acid (9.6 g, 100 mmol) as an additive, and distilled water (100 mL) as a solvent.

[0126] (2) The solution is heated with a hot stirrer while being stirred to evaporate to dryness.

[0127] (3) The contents were recovered, the stirring bar was removed, and the mixture was crushed and mixed in a mortar.

[0128] (4) The powder was transferred to an alumina boat and heated at 5 L / min with 10% H 2 The mixture was calcined at 1000°C for 16 hours under an Ar flow, and the product was recovered.

[0129] Comparative Example 2 (Ce 2 Zr 2 O 7 )

[0130] (1) Place a stirring bar in a 1 L glass beaker and add Ce(NO 3 ) 3 6H2 O (8.68 g, 20.0 mmol), ZrO (NO 3 ) 2 6H 2 O (5.35 g, 20.0 mmol) and distilled water (100 mL) as a solvent were added and stirred to dissolve.

[0131] (2) 28% aqueous ammonia (32 mL) was diluted with distilled water (900 mL), and the solution of (1) was added, followed by continuous stirring at room temperature for one day and one night.

[0132] (3) The obtained solution and precipitate were transferred to a centrifuge tube, centrifuged at 3000 rpm for 5 minutes, and the supernatant was removed.

[0133] (4) Distilled water (500 mL) was added to the obtained precipitate to redisperse the precipitate and centrifuge it. This operation was repeated twice to wash the precipitate.

[0134] (5) The obtained precipitate was pre-calcined at 250°C for 2 hours and then pulverized in a mortar.

[0135] (6) The obtained powder was calcined at 800°C for 5 hours, and then the powder was compacted at a pressure of 2 tons.

[0136] (7) The molded product was heated at 5 L / min with 10% H 2 / N 2 The product was calcined at 1400°C for 5 hours under air flow and recovered.

[0137] Comparative Example 3 (La 9.33 Si 6 O 26 )

[0138] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to La(NO 3 ) 3 6H 2 O (6.59 g, 15.2 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0139] Comparative Example 4 (Pr 9.33 Si 6 O 26 )

[0140] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Pr(NO 3 ) 3 6H 2 O (6.62 g, 15.2 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0141] Comparative Example 5 (Nd 9.33 Si 6 O 26 )

[0142] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Nd(NO 3 ) 3 6H 2 O (6.67 g, 15.2 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0143] Comparative Example 6 (Sm 9.33 Si 6 O 26 )

[0144] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Sm(NO 3 ) 3 6H 2 O (6.76 g, 15.2 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0145] Comparative Example 7 (Gd 9.33 Si6 O 26 )

[0146] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Gd(NO 3 ) 3 6H 2 O (6.87 g, 15.2 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0147] Comparative Example 8 (Tb 9.33 Si 6 O 26 )

[0148] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Tb(NO 3 ) 3 6H 2 O (6.89 g, 15.2 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0149] Example 2 (Ce 2 Ca 8 P 6 O 26 )

[0150] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (1.36 g, 3.12 mmol), Ca(NO 3 ) 3 ·4H 2O (2.95 g, 12.5 mmol) and (NH 4 )H 2 PO 4 (1.08 g, 9.38 mmol), and otherwise, carried out in the same manner as in Example 1, and the product was recovered.

[0151] Example 3 (Ce 9.33 Si 5 BO 25.5 )

[0152] Change Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) in Example 1 to Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol), Si(OEt) 4 (1.70 g, 8.15 mmol) and H 3 BO 3 (0.101 g, 1.63 mmol), and otherwise, carried out in the same manner as in Example 1, and the product was recovered.

[0153] Example 4 (Ce 7.33 Y 2 Si 6 O 26 )

[0154] Change Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) in Example 1 to Ce(NO 3 ) 3 ·6H 2 O (5.19 g, 12.0 mmol), Y(NO 3 ) 3 ·6H 2 O (1.24 g, 3.26 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol), and otherwise, carried out in the same manner as in Example 1, and the product was recovered.

[0155] Example 5 (Ce 7.33 La 2 Si 6 O26 )

[0156] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (5.19 g, 12.0 mmol), La (NO 3 ) 3 6H 2 O (1.41 g, 3.26 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0157] Example 6 (Ce 7.33 Pr 2 Si 6 O 26 )

[0158] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (5.19 g, 12.0 mmol), Pr(NO 3 ) 3 6H 2 O (1.42 g, 3.26 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0159] Example 7 (Ce 7.33 Sm 2 Si 6 O 26 )

[0160] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4(2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (5.19 g, 12.0 mmol), Sm (NO 3 ) 3 6H 2 O (1.45 g, 3.26 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0161] Example 8 (Ce 7.33 Lu 2 Si 6 O 26 )

[0162] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (5.19 g, 12.0 mmol), Lu (NO 3 ) 3 ·4H 2 O (1.41 g, 3.26 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g (2.04 g, 9.78 mmol) was 0.24 g (2.04 g, 9.78 mmol), and the product was recovered.

[0163] Example 9 (Ce 8 Ca 2 Si 6 O 26 )

[0164] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (5.43 g, 12.5 mmol), Ca(NO 3 ) 2 ·4H 2O (0.738 g, 3.12 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g, 2.5 g, and 1.5 mmol (1.95 g, 9.38 mmol) was greater than that of 0.1 g (1.95 g, 9.38 mmol), and the product was recovered.

[0165] Example 10 (Ce 8 Sr 2 Si 6 O 26 )

[0166] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (5.43 g, 12.5 mmol), Sr(NO 3 ) 2 (0.661 g, 3.12 mmol), Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g, 2.5 g, and 1.5 mmol (1.95 g, 9.38 mmol) was greater than that of 0.1 g (1.95 g, 9.38 mmol), and the product was recovered.

[0167] Example 11 (Ce 8 Eu 2 Si 6 O 26 )

[0168] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (5.43 g, 12.5 mmol), Eu (NO 3 ) 3 6H 2 O (1.39 g, 3.12 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g, 2.5 g, and 1.5 mmol (1.95 g, 9.38 mmol) was greater than that of 0.1 g (1.95 g, 9.38 mmol), and the product was recovered.

[0169] Example 12 (Ce 8 Yb 2 Si 6 O26 )

[0170] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Ce(NO 3 ) 3 6H 2 O (5.43 g, 12.5 mmol), Yb(NO 3 ) 3 ·5H 2 O (1.40 g, 3.12 mmol) and Si(OEt) 4 The same procedure as in Example 1 was carried out except that the amount of 1.5 g, 2.5 g, and 1.5 mmol (1.95 g, 9.38 mmol) was greater than that of 0.1 g (1.95 g, 9.38 mmol), and the product was recovered.

[0171] Example 13 (Eu 8 La 2 P 6 O 26 )

[0172] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Eu(NO 3 ) 3 6H 2 O (5.58 g, 12.5 mmol), La (NO 3 ) 3 6H 2 O (1.35 g, 3.12 mmol) and (NH 4 )H 2 PO 4 The same procedure as in Example 1 was carried out except that the amount of 1.08 g, 9.38 mmol) was 0.247 g (1.08 g, 9.38 mmol), and the product was recovered.

[0173] Example 14 (Eu 8 Ce 2 P 6 O 26 )

[0174] The Ce(NO 3 ) 3 6H 2O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Eu(NO 3 ) 3 6H 2 O (5.58 g, 12.5 mmol), Ce (NO 3 ) 3 6H 2 O (1.36 g, 3.12 mmol) and (NH 4 )H 2 PO 4 The same procedure as in Example 1 was carried out except that the amount of 1.08 g, 9.38 mmol) was 0.247 g (1.08 g, 9.38 mmol), and the product was recovered.

[0175] Example 15 (Eu 8 Pr 2 P 6 O 26 )

[0176] The Ce(NO 3 ) 3 6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) was changed to Eu(NO 3 ) 3 6H 2 O (5.58 g, 12.5 mmol), Pr(NO 3 ) 3 6H 2 O (1.36 g, 3.12 mmol) and (NH 4 )H 2 PO 4 The same procedure as in Example 1 was carried out except that the amount of 1.08 g, 9.38 mmol) was 0.247 g (1.08 g, 9.38 mmol), and the product was recovered.

[0177] 2. Analysis and evaluation of products

[0178] 2-1. X-ray diffraction measurement (confirmation of crystal structure of product)

[0179] X-ray diffraction (XRD) measurement was performed on the products of Examples 1 to 15 and Comparative Examples 1 to 8. The measurement apparatus and measurement conditions are shown below.

[0180] ·Measurement device: RINT RAPID II (manufactured by Rigaku Corporation)

[0181] Measurement conditions: voltage 50V, current 100mA, collimator diameter φ0.3mm, sample angle ω15°

[0182] 2-2. About apatite-type Ce 9.33 Si 6 O 26 , chalcite type CeCaAl 3 O 7 , pyrochlore type Ce 2 Zr 2 O 7

[0183] The X-ray diffraction pattern predicted from the crystal structure was calculated and compared with the X-ray diffraction pattern of each product.

[0184] Figure 2 The X-ray diffraction patterns of the products of Example 1 and Comparative Examples 1 and 2 are shown. Figure 2 It is found that the product of Example 1 has an apatite type crystal structure, the product of Comparative Example 1 has a pyrochlore type crystal structure, and the product of Comparative Example 2 has a pyrochlore type crystal structure.

[0185] Figure 3 A represents the X-ray diffraction patterns of the products of Examples 1 to 3 and Comparative Examples 3 to 8, Figure 3 B shows the X-ray diffraction patterns of the products of Examples 4 to 12. Figure 3 It is found that the products of Examples 1 to 12 and Comparative Examples 3 to 8 have an apatite type crystal structure.

[0186] Figure 8 The X-ray diffraction patterns of the products of Examples 13 to 15 are shown. Figure 8 From the above, it can be seen that the products of Examples 13 to 15 have an apatite type crystal structure.

[0187] 2-3. Confirmation of oxygen desorption temperature in reducing atmosphere (confirmation of oxygen storage capacity of Ce-containing product)

[0188] The products of Example 1 and Comparative Examples 1 and 2 were subjected to hydrogen temperature reduction (H 2 TPR). The measuring apparatus is shown below.

[0189] ·Measuring device: BELCAT A (manufactured by Malikrotech Co., Ltd.)

[0190] exist Figure 4 A and below show the measurement conditions.

[0191] Pretreatment conditions: After the product (about 50 mg) was introduced into a sample tube, it was stirred at 30 mL / min of 20% O 2The temperature was raised to 500°C under a flow of / He, and the pretreatment was performed for 10 minutes, followed by cooling.

[0192] Measurement conditions: After replacement with Ar, 5% H 2 The temperature was raised at 10°C / min under a flow of Ar and hydrogen (H 2 The analysis is performed using TCD, with a desiccant placed in front of the TCD to capture the generated water.

[0193] The products of Example 1 and Comparative Examples 1 and 2 were subjected to H treatment in the same manner as the products loaded with Pd. 2 TPR. The Pd loading conditions are shown below.

[0194] Pd loading conditions (Example 1 and Comparative Example 2): 30 mL of distilled water was placed in a 100 mL beaker, and Pd (NO 3 ) 2 After stirring at room temperature to dissolve, the product was added, heated, and evaporated to dryness. The obtained solid was dried at 120°C for one night, crushed in a mortar, and calcined at 500°C for 3 hours to obtain a product loaded with Pd.

[0195] Pd loading conditions (Comparative Example 1): In the Pd loading conditions (Example 1 and Comparative Example 2), 30 mL of distilled water was replaced with 30 mL of acetone, and Pd(NO 3 ) 2 Changed to Pd(OAc) 2 , except for this, the same Pd-supporting conditions as those in Example 1 and Comparative Example 2 were followed to obtain a product on which Pd was supported.

[0196] Figure 4 B represents H of the products before and after Pd loading in Example 1 and Comparative Examples 1 and 2. 2 TPR results. Figure 4 The peak of the product after Pd loading in B appears at low temperature ( * ) is believed to be caused by the reduction of the loaded Pd. In the product without Pd loading, Example 1 and Comparative Example 1 show hydrogen consumption peaks at low temperatures compared with Comparative Example 2, indicating that oxygen is released at low temperatures. In addition, Comparative Example 1 produces two peaks. When Pd is loaded, in any product, the hydrogen consumption peak moves to the low temperature side, but Example 1 and Comparative Example 1 still show hydrogen consumption peaks on the low temperature side compared with Comparative Example 2, indicating that oxygen is released at a lower temperature.

[0197] Next, the H of the products after Pd loading in Example 1 and Comparative Examples 1 and 2 was analyzed. 2From the TPR results, it is believed that the large hydrogen consumption peak at 150°C to 250°C is caused by the release of oxygen from the oxygen storage material. Therefore, the position of the hydrogen consumption peak is taken as the oxygen release temperature, and the oxygen storage capacity is calculated based on the total hydrogen consumption after deducting the hydrogen consumption caused by Pd. Figure 5 The oxygen release temperature and oxygen storage amount of the products of Example 1 and Comparative Examples 1 and 2 after Pd loading are shown.

[0198] Depend on Figure 5 It is understood that Example 1 has an oxygen storage amount comparable to that of Comparative Example 2, and also has a characteristic of releasing oxygen from a low temperature comparable to that of Comparative Example 1.

[0199] 2-4. Confirmation of weight change in an oxidizing atmosphere (confirmation of oxygen storage capacity of a product having an apatite-type crystal structure)

[0200] The products of Examples 1 to 15 and Comparative Examples 3 to 8 were oxidized in air at 500°C for 2 hours, and the oxygen storage capacity was determined from the weight change (OSC = ((weight after oxidation - weight before oxidation) / weight before oxidation) x 100). Figure 6 The oxygen storage amounts of the products of Examples 1 to 12 and Comparative Examples 3 to 8 are shown. Fig. 9 The oxygen storage capacity of the products of Examples 1, 2, and 13 to 15 is shown. Table 1 summarizes the composition, crystal structure, H 2 TPR (supported Pd) and oxygen storage capacity obtained by oxidation in the atmosphere.

[0201] Table 1 Composition, crystal structure and oxygen storage capacity of the embodiments and comparative examples

[0202]

[0203] from Figure 6 As shown in Table 1, the products of Examples 1 to 12 containing Ce showed a significant weight change due to oxidation, and it can be confirmed that they have oxygen storage capacity. The products of Comparative Examples 3 to 8 containing rare earth elements other than Ce did not show a significant weight change due to oxidation. From this result, it can be seen that among the compounds having an apatite-type crystal structure, the compounds containing Ce have oxygen storage capacity.

[0204] from Fig. 9 As shown in Table 1, the products of Examples 13 to 15 containing Eu showed a significant weight change due to oxidation, and it can be confirmed that they have oxygen storage capacity. In addition, the products of Examples 13 to 15 containing Eu also showed a greater oxygen storage capacity than Examples 1 to 2 containing Ce.

[0205] Known to contain Ce (Ce 3+) is not shown in Ce 3+ All oxidized to Ce 4+ The expected oxygen storage capacity under the condition of 3+ All are oxidized to Ce 4+ On the other hand, it is believed that 3+ Eu easily oxidized 2+ In apatite, from Eu 2+ To Eu 3+ is easily oxidized and can convert more oxygen (O 2 ) into the structure.

[0206] 2-5. Investigation of oxygen storage mechanism (relationship between crystal structure and oxygen storage capacity)

[0207] Figure 1 Indicates apatite type (Ce 9.33 Si 6 O 26 ) crystal structure. Compounds containing rare earth metals such as La and having an apatite-type crystal structure are described, for example, in JEH Sansom et al., Solid State Ionics, 139, 205-210 (2001), "A powder neutron diffraction study of the oxide-ion-conducting apatite-type phases, La 9.33 Si 6 O 26 and La 8 Sr 2 Si 6 O 26 ", Y.Masubuchi et al., Solid State Ionics, 166, 213~217 (2004), "Oxide ion conduction in Nd 9.33 (SiO 4 ) 6 O 2 and Sr 2 Nd 8 (SiO 4 ) 6 O 2 In the "single crystals grown by floating zone method", oxygen ions (O 2 -) conductors have been studied. Figure 1 As shown, in the apatite crystal structure, there is O 2-conduction path, which is surrounded by rare earth metal sites. In the case where the rare earth metal is Ce (Ce 9.33 Si 6 O 26 If the compound is oxidized in the atmosphere or in an oxidizing atmosphere, Ce 3+ Change to Ce 4+ , surrounded by O 2- The ionic radius of the rare earth metal site in the conduction path becomes smaller. It is believed that the result is 2 - The conduction path is enlarged, thereby acting as O 2- Storage space comes into play.

[0208] Figure 7 X-ray diffraction patterns of the product of Example 1 before and after oxidation are shown. Table 2 shows the lattice constant and unit cell volume of Example 1.

[0209] Table 2 Lattice constants and unit cell volumes of the product of Example 1 before and after oxidation

[0210]

[0211] From Table 2, we can see that although oxygen is incorporated into the crystal structure through oxidation (oxygen storage), the weight increases, and the number of atoms per unit cell increases, the volume of the unit cell hardly changes. This is because Ce is converted from Ce to Ce through oxidation. 3+ Change to Ce 4+ At the same time, O 2 -, it is believed that the unit cell is in the a-axis and b-axis directions due to O 2 - and expands and thus expands, but because Ce 3+ Change to Ce 4+ It shrinks slightly in the c-axis direction, so the volume change of the unit cell is very small.

[0212] 2-6. Containing Eu (Eu 2+ ) and apatite containing Ce(Ce 3+ ) has a better oxygen storage capacity than apatite

[0213] The apatite of the present invention is synthesized in a reducing atmosphere, and Ce is Ce 3+ Contains in the form of Eu 2+ Contains in the form of. Regarding the standard electrode potential of ions, Ce 3+ →Ce 4+ +e- is 1.61eV, Eu 2+ →Eu 3+ +e- is -0.35eV, so it is considered that as an ion, it is similar to Ce. 3+ In comparison, Eu 2+ It is easy to be oxidized and easy to store oxygen. In the crystal structure, Ce 3+and Eu 2+ Since they occupy the same site but have different valences, it is difficult to conduct experiments to make the elements other than Ce and Eu and their contents completely consistent. However, it is possible to use ions with the same valence to perform charge compensation without affecting the oxygen storage capacity. Fig.10 Ce 3+ and Eu 2+ and the ion Ca with unchanged valence 2+ , Sr 2+ and La 3+ Occupied sites, and Si 4+ and P 5+ Occupied position.

[0214] For example, Example 9 (Ce 8 Ca 2 Si 6 O 26 ) and Example 10 (Ce 8 Sr 2 Si 6 O 26 ) and Example 13 (Eu 8 La 2 P 6 O 26 ), except for Ce and Eu, the elements and their contents are slightly different, but this is for charge compensation and has no effect on the oxygen storage capacity. Anyone skilled in the art will recognize that it is the effect of replacing Ce with Eu. Fig.11 The compositions, ratios of Ce and Eu, and oxygen storage capacities of Examples 9 to 10 and 13 are shown.

[0215] Table 3 Composition, Ce, Eu ratio and oxygen storage capacity of Examples 9, 10 and 13

[0216]

[0217] From Table 3 and Fig.11 It can be seen that when the composition of the apatite of the present invention is changed to A 10 T 6 O 26 In the case of A, 80 mol% is Ce 3+ Compared with Example 9 and Example 10, 80 mol% of A is Eu 2+ Example 13 shows a greater oxygen storage capacity. From this result, it can be seen that the apatite mainly composed of europium (Eu) has a superior oxygen storage capacity compared to the apatite mainly composed of cerium (Ce).

Claims

1. An oxygen storage material, comprising a composite oxide, The composite oxide contains cerium and / or europium, and contains silicon and / or phosphorus. The composite oxide has an apatite type crystal structure.

2. The oxygen storage material according to claim 1, The composite oxide is represented by the general formula A α T β X γ It represents that, in the formula, A contains cerium and / or europium, T contains silicon and / or phosphorus, X contains oxygen, α, β and γ represent molar ratios, α is 9.33-10, β is 6, and γ is 24-30. The oxygen storage material according to claim 2 , wherein A contains cerium. The oxygen storage material according to claim 2 , wherein A contains europium.

5. The oxygen storage material according to claim 2, The content of cerium and / or europium is 20 mol% or more based on the total amount of A, and A further contains one or more elements selected from the group consisting of calcium, strontium, yttrium, lanthanum, praseodymium, samarium, ytterbium and lutetium. The oxygen storage material according to claim 2 , wherein T further contains boron. 7 . The oxygen storage material according to claim 1 , further comprising a catalyst metal, wherein the catalyst metal is supported on the composite oxide.

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