Oxygen storage material

Abstract

To provide an inexpensive oxygen storage material having excellent oxygen release performance at low temperature.SOLUTION: The present disclosure relates to an oxygen storage material containing a composite oxide. The composite oxide contains cerium and / or europium and silicon and / or phosphorus. The composite oxide has an apatite-type crystalline structure.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an oxygen storage material.

Background Art

[0002] Exhaust gas discharged from internal combustion engines such as automobiles contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO x ), and these harmful components are purified by an exhaust gas purification catalyst and then released into the atmosphere. Conventionally, a three-way catalyst that simultaneously oxidizes CO and HC and reduces NO x has been used as the exhaust gas purification catalyst. As the three-way catalyst, those in which noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on a porous oxide carrier such as alumina (Al 2 O 3 ), silica (SiO 2 ), zirconia (ZrO 2 ), and titania (TiO 2 ) are widely used.

[0003] In recent years, in order to enhance the exhaust gas purification ability of the three-way catalyst against fluctuations in the oxygen concentration in the exhaust gas, an oxygen storage material, which is an inorganic material having an oxygen storage capacity (OSC capacity), has been used in the exhaust gas purification catalyst. Cerium oxide (CeO 2 ) is known to have excellent OSC capacity, and is widely used as an oxygen storage material in the form of a ceria-zirconia composite oxide (CeO 2 -ZrO 2 ).

[0004] As such an oxygen storage material of a ceria-zirconia composite oxide, for example, Patent Document 1 describes a composite oxide containing ceria and zirconia, in which a pyrochlore phase-type regular arrangement phase is formed by cerium ions and zirconium ions in the composite oxide, and the pyrochlore phase-type regular arrangement phase remains at 50% or more after heating at 1000 °C for 5 hours in the atmosphere as compared with before heating. A ceria-zirconia-based composite oxide is described.

[0005] In addition, Patent Document 2 discloses an oxide having a merilite-type structure, represented by the general formula A X B 2-X CD 2 E 7+δ having a composition, wherein A is cerium (Ce), B is one or more elements selected from the group consisting of an alkali metal element, an alkaline earth metal element, magnesium (Mg), indium (In), and a rare earth metal element (excluding cerium), C and D are one or more elements selected from the group consisting of a transition metal element, a Group 12 element, a Group 13 element, a Group 14 element, and a Group 15 element, E is oxygen (O), x is 0 or more and 2.0 or less, δ is -1.0 or more and 1.0 or less, and the oxide is a merilite-type oxide having an oxygen absorption and release function that maintains electrical neutrality.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in a ceria-zirconia composite oxide in which a pyrochlore-phase type regular array phase as in Patent Document 1 is formed, the use of zirconium (Zr), which is a rare metal, can increase the cost. Furthermore, in the composite oxide, there is a problem that the activation energy for releasing excess oxygen from the crystal structure is high and the temperature required for oxygen release is high.

[0008] On the one hand, oxides having a merilite-type structure such as those in Patent Document 2 are composed of abundant elements such as calcium and aluminum. In addition, there are many spaces in the crystal structure of the oxide that can incorporate excess oxygen, and the temperature required for oxygen release is low. However, in this oxide, since the composition in which excess oxygen is incorporated into all of the spaces is unstable, there is a problem that the oxygen storage amount is small.

[0009] Therefore, an object of the present invention is to provide an inexpensive oxygen storage material having excellent oxygen release performance at low temperatures.

Means for Solving the Problems

[0010] As a result of various studies on means for solving the above problems, the present inventors have found that a composite oxide having an apatite-type crystal structure containing Ce and / or europium (Eu) and silicon (Si) and / or phosphorus (P) has a pyrochlore-type crystal structure containing Ce and Zr, which are useful as existing oxygen storage materials. 2 Zr 2 O 7 has a smaller activation energy and is excellent in oxygen storage and oxygen release properties at low temperatures, and thus completed the present invention.

[0011] That is, the gist of the present invention is as follows. (1) An oxygen storage material containing a composite oxide, wherein the composite oxide contains cerium and / or europium and silicon and / or phosphorus, and the composite oxide has an apatite-type crystal structure. (2) The composite oxide is represented by the following 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 each represent a molar ratio, α is 9.33 to 10, β is 6, and γ is 24 to 30.) The oxygen storage material according to (1). (3) The oxygen storage material according to (2), wherein A contains cerium. (4) The oxygen storage material according to (2) or (3), wherein A contains europium. (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 based on the total amount of A. (6) The oxygen storage material according to any one of (2) to (5), wherein A further contains one or more elements selected from the group consisting of an alkali metal, an alkaline earth metal, and rare earth elements other than cerium and europium. (7) The oxygen storage material according to (6), wherein 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). (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. (9) The oxygen storage material according to (8), wherein T further contains boron (B). (10) The oxygen storage material according to any one of (1) to (9), further containing a catalyst metal, wherein the catalyst metal is supported on the composite oxide. (11) The oxygen storage material according to (10), wherein the content of the catalyst metal is 0.01% by weight to 5% by weight based on the total weight of the oxygen storage material. (12) The oxygen storage material according to (10) or (11), wherein the catalyst metal contains a platinum group element. (13) The oxygen storage material according to (12), wherein the platinum group element is one or more elements selected from the group consisting of rhodium (Rh), palladium (Pd), and platinum (Pt). (14) An exhaust gas purification catalyst containing the oxygen storage material according to any one of (1) to (13). (15) An oxidation-reduction catalyst containing the oxygen storage material according to any one of (1) to (13). (16) An oxygen storage method using the oxygen storage material according to any one of (1) to (13). (17) The oxygen enrichment method using the oxygen storage material according to any one of (1) to (13). (18) The oxygen removal method using the oxygen storage material according to any one of (1) to (13). (19) The heating and cooling method using the oxygen storage material according to any one of (1) to (13).

Advantages of the Invention

[0012] The present invention provides an inexpensive oxygen storage material having excellent oxygen release performance at low temperatures.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

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Figure 5

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Figure 10

Figure 11

Mode for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the oxygen storage material of the present invention is not limited to the following embodiments, and can be implemented in various forms with modifications, improvements, etc. that can be made by those skilled in the art without departing from the gist of the present invention.

[0015] The present invention relates to an oxygen storage material containing a composite oxide, wherein the composite oxide contains cerium and / or europium and silicon and / or phosphorus, and the composite oxide has an apatite-type crystal structure.

[0016] In the present invention, the crystal structure of the composite oxide containing cerium and / or europium and 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 silicon and / or phosphorus has an apatite-type crystal structure.

[0017] The basic XRD spectrum of the apatite-type crystal structure is known in the art. For example, when the composite oxide is Ce 9.33 Si 6 O 26 in the case of using copper Kα radiation in the XRD spectrum, 2θ has peaks at four or more positions selected from the group consisting of 27.3° ± 0.5°, 28.2° ± 0.5°, 31.0° ± 0.5°, and 32.1° ± 0.5°.

[0018] Incidentally, it is well known in the art that the basic XRD spectrum of the apatite-type crystal structure changes the peak position based on the composition of the composite oxide.

[0019] Figure 1 schematically shows the apatite-type crystal structure of an example of the composite oxide included in the present invention. In the composite oxide containing cerium and / or europium and silicon and / or phosphorus of the present invention, the apatite-type crystal structure has a structure in which a path through which oxide ions (O 2- ) are conductive is surrounded by trivalent cerium ions (Ce 3+ ) and / or divalent europium ions (Eu 2+ ). Incidentally, the conduction path (storage space) of oxide ions is one-dimensional. Therefore, the oxygen storage capacity of the composite oxide of the present invention is considered to be exhibited when Ce 3+ is oxidized to Ce 4+ and Eu 2+ is oxidized to Eu 3+ at the same time as the size of the cerium ions and / or europium ions contracts and O 2- is introduced into the crystal structure.

[0020] The composite oxide containing cerium and / or europium and silicon and / or phosphorus of the present invention has the following formula A α T β X γ (wherein A contains cerium and / or europium, T contains silicon and / or phosphorus, X contains oxygen, α, β and γ each represent a molar ratio, α is 9.33 to 10.0, β is 6, and γ is 24 to 30).) It can also be represented by.

[0021] In one embodiment, A contains cerium. In one embodiment, A contains europium. In one embodiment, A contains cerium and europium.

[0022] In addition to Ce and / or Eu, A may further contain one or more metal elements selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals other than Ce and Eu. In one embodiment, in addition to Ce and / or Eu, A further contains one or more metal elements selected from the group consisting of 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 one embodiment, in addition to Ce and / or Eu, A further contains one or more elements selected from the group consisting of Ca, Sr, Y, La, Pr, Sm, Yb, and Lu. In one embodiment, when A contains Ce, A further contains one or more elements selected from the group consisting of 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.

[0023] The content of Ce in A is usually 20 mol% or more, in one embodiment 78 mol% or more, and in one embodiment 80 mol% or more, based on the total amount of substances (mol) of A. The content of Ce in A may be 100 mol% based on A (total mol).

[0024] The content of Eu in A is usually 20 mol% or more, in one embodiment 78 mol% or more, and in one embodiment 80 mol% or more, based on the total amount of substances (mol) of A. The content of Eu in A may be 100 mol% based on A (total mol).

[0025] By the content of Ce and / or Eu in A being within the above range, sufficient oxygen storage capacity can be ensured.

[0026] 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 to compensate for the charges of the included Ce and / or Eu, as will be described in detail below.

[0027] In addition to Si and / or P, T may further contain one or more elements selected from the group consisting of group 13 elements, group 14 elements other than Si, and group 15 elements other than P. In one embodiment, in addition to Si and / or P, T further contains one or more elements selected from the group consisting of boron (B), aluminum (Al), gallium (Ga), and germanium (Ge). In one embodiment, in addition to Si and / or P, T further contains B.

[0028] The content of Si or P in T is usually 66 mol% or more, and in one embodiment 83 mol% or more, based on the total amount of substances (mol) of T. The content of Si or P in T may be 100 mol% based on T (total mol).

[0029] When the content of Si or P in T is within the above range, the small cations (Si 4 or P 4+ ) located at the center of the TO tetrahedron required to form the apatite-type structure can be ensured. 5+ ) can be ensured.

[0030] In addition, the content of elements other than Si and P in T can also be determined to compensate for the charges of the included Ce and / or Eu and Si and / or P, as will be described in detail below.

[0031] In the apatite-type crystal structure of the composite oxide included in the present invention, Ce is included as Ce 3+ , and Eu is included as Eu 2+ . In the crystal structure, Ce 3+ and Eu 2+Although they have different valences, they occupy the same site. Therefore, it is not possible to create an apatite in which Ce and Eu are simply replaced in the complex oxide. Thus, when changing the ions present in the complex oxide to ions having a valence different from that of the said ions, other ions separately present in the complex oxide, for example, ions that do not contribute to the oxygen storage amount, that is, ions having a fixed valence, are also changed in the same way to enable charge compensation. For example, in the complex oxide, when Ce 3+ is replaced with Eu 2+ , this change in charge of -1 can be compensated for by, for example, changing Ca 2+ (Sr 2+ ) that can occupy the same site as Ce and Eu to La 3+ , and by a change in charge of +1 due to replacing Si 4+ that can occupy a site different from that of Ce and Eu with P 5+ . For example, when it is desired to confirm the difference in the effects of Ce 3+ and Eu 2+ in the complex oxide, it can be carried out by comparing 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).

[0032] Furthermore, in the apatite-type crystal structure of the complex oxide included in the present invention, when Ce 8 A 2 T 6 O 26 (A = Ca or Sr, T = Si) in the complex oxide is replaced with Eu 3+ with Eu 2+ , the Ca or Sr of A is changed to Ce, and charge compensation is carried out by replacing Si 4+ with P 5+ to produce Eu 8 A 2 T 6 O 26 (A = Ce, T = P).

[0033] X contains O and is usually composed of O. In X, O may optionally be present in the state of OH.

[0034] The content of O in X is usually 92 mol% or more, and in one embodiment 99 mol% or more, based on the total amount of substances (mol) of X. The content of O in X may be 100 mol% based on X (total mol).

[0035] By the content of O in X being within the above range, sufficient oxygen storage capacity can be ensured.

[0036] In one embodiment, the composite oxide containing cerium, silicon and / or phosphorus of the present invention has the following formula (Ce, A’) α (Si, P, T’) β O γ (wherein A’ is one or more metal elements selected from the group consisting of Ca, Sr, Y, La, Pr, Sm, Eu, Yb, and Lu, T’ is B, α, β and γ each represent a molar ratio, α is 9.33 to 10, β is 6, and γ is 24 to 30.) It is represented by. 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.

[0037] In one embodiment, the composite oxide containing cerium, silicon and / 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 2 Si 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 represented by

[0038] In one embodiment, the europium and phosphorus-containing composite oxide of the present invention has the following formula (Eu, A’) α (P) β O γ (wherein A’ is one or more metal elements selected from the group consisting of Ce, La, and Pr, α, β, and γ each represent a molar ratio, α is 9.33 to 10, β is 6, and γ is 24 to 30.) represented by

[0039] In one embodiment, the europium and phosphorus-containing composite oxide of the present invention is Eu 8 Ce 2 P 6 O 26 , Eu 8 La 2 P 6 O 26 , or Eu 8 La 2 P 6 O 26 represented by

[0040] The oxygen storage material of the present invention may further contain a catalytic metal. The catalytic metal is supported on the composite oxide described above. Examples of the catalytic metal include noble metals. The noble metals include, but are not limited to, platinum group noble metals. Examples of the platinum group noble metals include ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). In one embodiment, the noble metal is one or more selected from the group consisting of Rh, Pt, and Pd. The supported amount of the noble metal is the same as that of conventional exhaust gas purification catalysts and is not limited, but is 0.01% by weight to 5% by weight based on the total weight of the oxygen storage material, and in one embodiment, it is 0.5% by weight to 2% by weight.

[0041] The oxygen storage material of the present invention is excellent in oxygen release at low temperatures. Therefore, the present invention also relates to an exhaust gas purification catalyst and / or an oxidation-reduction catalyst containing the oxygen storage material of the present invention.

[0042] The exhaust gas purification catalyst and / or the oxidation-reduction catalyst of the present invention may contain a carrier material other than the oxygen storage material of the present invention. Examples of the carrier material other than the oxygen storage material of the present invention include metal oxides that are porous and have excellent heat resistance. For example, aluminum oxide (alumina: Al 2 O 3 ), zirconium oxide (zirconia: ZrO 2 ), silicon oxide (silica: SiO 2 ), or composite oxides mainly composed of these metal oxides can be used. In the exhaust gas purification catalyst, conventional loading methods such as the adsorption loading method and the water absorption loading method can be used.

[0043] The exhaust gas purification catalyst and / or the oxidation-reduction catalyst of the present invention can exhibit excellent regular structure durability and OCS ability over 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.

[0044] Furthermore, in the oxygen storage material of the present invention, by utilizing the property of absorbing and releasing oxygen and the property that the energy states in the state of adsorbing oxygen and the state of releasing oxygen are different, it is possible to store oxygen (oxygen storage method), enrich oxygen (oxygen enrichment method), remove oxygen (oxygen removal method), and / or heat and / or cool (heating and cooling method) using the oxygen storage material of the present invention.

[0045] The oxygen storage material of the present invention can be produced by ordinary methods such as the solid phase method, the liquid phase method, and the alkoxide method. For example, an aqueous solution of a cerium compound, a europium compound, a silicon compound, a phosphorus compound, and optionally a compound containing an element other than Ce, Eu, Si, and P as described above (hereinafter also referred to as "cerium compound and silicon compound, etc.") and an aqueous solution of a complexing agent are mixed, dried to precipitate a product containing Ce and / or Eu and Si and / or P, and then fired in a reducing atmosphere. The cerium compound and the silicon compound, etc. can also be used as a solution in a non-aqueous solvent, for example, alcohol or organic carboxylic acid ester.

[0046] As the cerium compound, for example, water-soluble compounds such as nitrates such as cerium nitrate and cerium diammonium nitrate, sulfates such as cerium sulfate, chlorides such as cerium chloride, and compounds soluble in alcohol such as alkoxides such as cerium isopropoxide can be used.

[0047] 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 compounds soluble in alcohol such as alkoxides such as europium isopropoxide can be used.

[0048] As the silicon compound, alkoxides such as tetraethyl orthosilicate and tetraisopropyl orthosilicate can be used.

[0049] As the phosphorus compound, ammonium dihydrogen phosphate or the like can be used.

[0050] As the compound containing elements other than Ce and Si, water-soluble or alcohol-soluble compounds such as nitrates, sulfates, chlorides, alkoxides and the like can be used.

[0051] The complexing agent is not particularly limited, and examples thereof include polyvalent carboxylic acids, amino acids and the like. Examples of the polyvalent carboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, citric acid, tartaric acid and the like. In one embodiment, the complexing agent is citric acid. Examples of the amino acid include glycine, alanine, asparagine, aspartic acid and the like.

[0052] When a precipitate is formed by mixing an aqueous solution of a cerium compound and a silicon compound or the like with an aqueous solution of a complexing agent, the precipitate may be filtered and then dried.

[0053] The drying of the mixed solution of the aqueous solution of the cerium compound and the silicon compound or the like and the aqueous solution of the complexing agent can usually be carried out at 50°C to 150°C for usually 5 hours to 48 hours.

[0054] The firing of the product containing Ce and / or Eu and Si and / or P can usually be carried out by heating and holding at 600°C to 1500°C for 2 hours 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 a reducing gas such as H 2 , CO or the like. Thereby, an apatite-type oxygen storage material can be obtained.

Examples

[0055] Hereinafter, some examples related to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples. 1. Production of oxygen storage material 1-1. Reagents Cerium(III) nitrate hexahydrate (Ce(NO 3 ) 3 ·6H 2 O) (manufactured by Nacalai Tesque, Inc.): ≥ 35.0 wt% (as CeO 2 ) Ammonium cerium(IV) nitrate (NH 4 ) 2 Ce(NO 3 ) 6 (manufactured by Tokyo Chemical Industry Co., Ltd.): > 98.0 wt% Yttrium(III) nitrate hexahydrate (Y(NO 3 ) 3 ·6H 2 O) (manufactured by Kanto Chemical Co., Inc.): > 99.99 wt% Lanthanum(III) nitrate hexahydrate (La(NO 3 ) 3 ·6H 2 O) (manufactured by Nacalai Tesque, Inc.): ≥ 99.9 wt% Praseodymium(III) nitrate hexahydrate (Pr(NO 3 ) 3 ·6H 2 O) (manufactured by Kanto Chemical Co., Inc.): > 99.95 wt% Neodymium(III) nitrate hexahydrate (Nd(NO 3 ) 3 ·6H 2 O) (manufactured by FUJIFILM Wako Pure Chemical Corporation): 99.5 wt% Samarium(III) nitrate hexahydrate (Sm(NO 3 ) 3 ·6H 2 O) (manufactured by FUJIFILM Wako Pure Chemical Corporation) 99.5 wt% Europium(III) nitrate hexahydrate (Eu(NO 3 ) 3 ·6H 2 O) (manufactured by Kanto Chemical Co., Inc.): > 99.95 wt% Gadolinium(III) nitrate hexahydrate (Gd(NO 3 ) 3 ·6H 2 O) (manufactured by FUJIFILM Wako Pure Chemical Corporation): 99.5 wt% Terbium(III) nitrate hexahydrate (Tb(NO 3 )3 ·6H 2 O) (manufactured by Kanto Chemical Co., Inc.): >99.95 wt% Ytterbium(III) nitrate pentahydrate (Yb(NO 3 ) 3 ·5H 2 O) (manufactured by Sigma-Aldrich): 99.9% Lutetium(III) nitrate tetrahydrate (Lu(NO 3 ) 3 ·4H 2 O) (manufactured by Kanto Chemical Co., Inc.): >99.95 wt% Calcium nitrate tetrahydrate (Ca(NO 3 ) 2 ·4H 2 O) (manufactured by FUJIFILM Wako Pure Chemical Corporation): 98.5+ wt% Strontium nitrate (Sr(NO 3 ) 2 ) (manufactured by FUJIFILM Wako Pure Chemical Corporation): 98.0~102.0 wt% Tetraethyl orthosilicate (Si(OEt) 4 ) (manufactured by Tokyo Chemical Industry Co., Ltd.): >98.0 wt% Ammonium dihydrogen phosphate ((NH 4 )H 2 PO 4 ) (manufactured by FUJIFILM Wako Pure Chemical Corporation): 99.0+ wt% Boric acid (H 3 BO 3 ) (manufactured by FUJIFILM Wako Pure Chemical Corporation): 99.5+ wt% Aluminum nitrate nonahydrate (Al(NO 3 ) 3 ·9H 2 O) (manufactured by FUJIFILM Wako Pure Chemical Corporation): 98.0+ wt% Zirconium oxynitrate dihydrate (ZrO(NO 3 ) 2 ·2H 2 O) (manufactured by Kanto Chemical Co., Inc.): >99.0 wt% Citric acid (manufactured by FUJIFILM Wako Pure Chemical Corporation): 98.0+ wt% Ethylene glycol (manufactured by Nacalai Tesque, Inc.): 99.5 wt% Palladium(II) nitrate (Pd(NO3 ) 2 )(manufactured by FUJIFILM Wako Pure Chemical Corporation): 97.0 + wt% Palladium(II) acetate (Pd(OAc) 2 )(manufactured by FUJIFILM Wako Pure Chemical Corporation): 97.0 + wt%

[0056] 1 - 2. Production of Composite Oxide Example 1 (Ce 9.33 Si 6 O 26 ) (1) A stir bar was placed in a 500 mL glass beaker, and 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) as an additive, ethylene glycol (6.21 g, 100 mmol), distilled water (18 mL) as a solvent, and ethanol (200 mL) were added. (2) The solution was heated with stirring using a hot stirrer and evaporated to dryness. (3) The contents were recovered, the stir bar was removed, and the mixture was pulverized and mixed in a mortar. (4) The powder was transferred to an alumina crucible and calcined in air at 500 °C for 6 hours using a muffle furnace. (5) The powder was transferred to an alumina boat, activated carbon was placed on it, and it was fired at 1200 °C for 16 hours under an Ar gas flow of 0.5 L / min. (6) The activated carbon was removed from the alumina boat, and the product was recovered.

[0057] Comparative Example 1 (CeCaAl 3 O 7 ) (1) A stir bar was placed in a 500 mL glass beaker, and as raw materials, (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(NO3 ) 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 were added. (2) The solution was heated with stirring using a hot stirrer and evaporated to dryness. (3) The content was recovered, the stir bar was removed, and it was pulverized and mixed in a mortar. (4) The powder was transferred to an alumina boat and calcined at 1000 °C for 16 hours under a 10% H 2 / Ar gas flow at 5 L / min, and the product was recovered.

[0058] Comparative Example 2 (Ce 2 Zr 2 O 7 ) (1) A stir bar was placed in a 1 L glass beaker, and Ce(NO 3 ) 3 ·6H 2 O (8.68 g, 20.0 mmol), ZrO(NO 3 ) 2 ·6H 2 O (5.35 g, 20.0 mmol) were added as raw materials, and distilled water (100 mL) was added as a solvent and stirred until dissolved. (2) 28% aqueous ammonia (32 mL) was diluted with distilled water (900 mL), and the solution from (1) was added, and stirring was continued at room temperature for one day and night. (3) The resulting solution and precipitate were transferred to a centrifuge tube and centrifuged at 3,000 rpm for 5 minutes, and the supernatant was removed. (4) Distilled water (500 mL) was added to the resulting precipitate to redisperse the precipitate, and the centrifugation operation was repeated twice for washing. (5) The resulting precipitate was calcined at 250 °C for 2 hours and pulverized in a mortar. (6) The resulting powder was calcined at 800 °C for 5 hours, and the resulting powder was press-molded at 2 t. (7) The molded body was calcined at 1400 °C for 5 hours under a 10% H 2 / N 2 gas flow at 5 L / min, and the product was recovered.

[0059] Comparative Example 3 (La9.33 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to La(NO 3 ) 3 ·6H 2 O (6.59 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol), and the product was recovered in the same manner as in Example 1 except for the change.

[0060] Comparative Example 4 (Pr 9.33 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to Pr(NO 3 ) 3 ·6H 2 O (6.62 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol), and the product was recovered in the same manner as in Example 1 except for the change.

[0061] Comparative Example 5 (Nd 9.33 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to Nd(NO 3 ) 3 ·6H 2 O (6.67 g, 15.2 mmol) and Si(OEt) 4The product was recovered in the same manner as in Example 1, except that it was changed to (2.04 g, 9.78 mmol).

[0062] Comparative Example 6 (Sm 9.33 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to Sm(NO 3 ) 3 ·6H 2 O (6.76 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol). The product was recovered in the same manner as in Example 1, except for the above change.

[0063] Comparative Example 7 (Gd 9.33 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to Gd(NO 3 ) 3 ·6H 2 O (6.87 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol). The product was recovered in the same manner as in Example 1, except for the above change.

[0064] Comparative Example 8 (Tb 9.33 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to Tb(NO 3 )3 ·6H 2 O (6.89 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed, and the product was recovered in the same manner as in Example 1.

[0065] Example 2 (Ce 2 Ca 8 P 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to Ce(NO 3 ) 3 ·6H 2 O (1.36 g, 3.12 mmol), Ca(NO 3 ) 3 ·4H 2 O (2.95 g, 12.5 mmol), and (NH 4 )H 2 PO 4 (1.08 g, 9.38 mmol), and the product was recovered in the same manner as in Example 1.

[0066] Example 3 (Ce 9.33 Si 5 BO 25.5 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed 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 the product was recovered in the same manner as in Example 1.

[0067] Example 4 (Ce 7.33 Y 2 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed 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). The product was recovered in the same manner as in Example 1 except for the above changes.

[0068] Example 5 (Ce 7.33 La 2 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were 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 (2.04 g, 9.78 mmol). The product was recovered in the same manner as in Example 1 except for the above changes.

[0069] Example 6 (Ce 7.33 Pr 2 Si 6 O 26 ) In Example 1, Ce(NO 3 )3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol), except that 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 (2.04 g, 9.78 mmol) were changed, the product was recovered in the same manner as in Example 1.

[0070] Example 7 (Ce 7.33 Sm 2 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were 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 (2.04 g, 9.78 mmol) were changed, the product was recovered in the same manner as in Example 1.

[0071] Example 8 (Ce 7.33 Lu 2 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to Ce(NO 3 ) 3 ·6H 2O (5.19 g, 12.0 mmol), Lu(NO 3 ) 3 ·4H 2 O (1.41 g, 3.26 mmol), and Si(OEt) 4 (2.04 g, 9.78 mmol) except for the change, the product was recovered in the same manner as in Example 1.

[0072] Example 9 (Ce 8 Ca 2 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were changed to Ce(NO 3 ) 3 ·6H 2 O (5.43 g, 12.5 mmol), Ca(NO 3 ) 2 ·4H 2 O (0.738 g, 3.12 mmol), and Si(OEt) 4 (1.95 g, 9.38 mmol) except for the change, the product was recovered in the same manner as in Example 1.

[0073] Example 10 (Ce 8 Sr 2 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were 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) 4The product was recovered in the same manner as in Example 1, except that it was changed to (1.95 g, 9.38 mmol).

[0074] Example 11 (Ce 8 Eu 2 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were 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 (1.95 g, 9.38 mmol). The product was recovered in the same manner as in Example 1.

[0075] Example 12 (Ce 8 Yb 2 Si 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were 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 (1.95 g, 9.38 mmol). The product was recovered in the same manner as in Example 1.

[0076] Example 13 (Eu 8 La 2 P6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were 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 (1.08 g, 9.38 mmol), and the product was recovered in the same manner as in Example 1 except for the change.

[0077] Example 14 (Eu 8 Ce 2 P 6 O 26 ) In Example 1, Ce(NO 3 ) 3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were 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 (1.08 g, 9.38 mmol), and the product was recovered in the same manner as in Example 1 except for the change.

[0078] Example 15 (Eu 8 Pr 2 P 6 O 26 ) In Example 1, Ce(NO 3 )3 ·6H 2 O (6.61 g, 15.2 mmol) and Si(OEt) 4 (2.04 g, 9.78 mmol) were used, and 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 (1.08 g, 9.38 mmol) were changed. Otherwise, the product was recovered in the same manner as in Example 1.

[0079] 2. Analysis and Evaluation of the Product 2-1. X-ray Diffraction Measurement (Confirmation of the Crystal Structure of the Product) For the products of Examples 1 to 15 and Comparative Examples 1 to 8, X-ray diffraction (XRD) measurements were performed respectively. The measuring apparatus and measuring conditions are shown below. · Measuring Apparatus: RINT RAPID II (manufactured by Rigaku Corporation) · Measuring Conditions: Voltage 50 V, Current 100 mA, Collimator Diameter φ0.3 mm, Sample Angle ω 15°

[0080] 2-2. For apatite-type Ce 9.33 Si 6 O 26 , merilite-type CeCaAl 3 O 7 , pyrochlore-type Ce 2 Zr 2 O 7 respectively The X-ray diffraction patterns predicted from the crystal structures were calculated and compared with the X-ray diffraction patterns of each product. Figure 2 shows the X-ray diffraction patterns of the products of Example 1 and Comparative Examples 1 to 2. From Figure 2, it was found that the product of Example 1 has an apatite-type crystal structure, the product of Comparative Example 1 has a merilite-type crystal structure, and the product of Comparative Example 2 has a pyrochlore-type crystal structure.

[0081] Figure 3A shows the X-ray diffraction patterns of the products of Examples 1 to 3 and Comparative Examples 3 to 8, and Figure 3B shows the X-ray diffraction patterns of the products of Examples 4 to 12. From Figure 3, the products of Examples 1 to 12 and Comparative Examples 3 to 8 had an apatite-type crystal structure.

[0082] Figure 8 shows the X-ray diffraction patterns of the products of Examples 13 to 15. From Figure 8, the products of Examples 13 to 15 had an apatite-type crystal structure.

[0083] 2-3. Confirmation of the oxygen desorption temperature under a reducing atmosphere (confirmation of the oxygen storage capacity of the product containing Ce) For the products of Example 1 and Comparative Examples 1 to 2, hydrogen temperature-programmed reduction (H 2 TPR) was performed respectively. The measuring device is shown below.

[0084] · Measuring device: BELCAT A (manufactured by Microtrac BEL Co., Ltd.)

[0085] Figure 4A and the measurement conditions are shown below. · Pretreatment conditions: After introducing the product (about 50 mg) into the sample tube, it was heated to 500 °C at a rate of 30 mL / min under a 20% O 2 / He flow for 10 minutes for pretreatment and then cooled. · Measurement conditions: After replacement with Ar, it was heated at a rate of 10 °C / min under a 5% H 2 / Ar flow, and the hydrogen (H 2 ) consumption was analyzed. The analysis was performed by TCD, and a drying material was placed in front of the TCD to trap the generated water.

[0086] For the products of Example 1 and Comparative Examples 1 to 2 with Pd supported, H 2 TPR was also performed in the same manner. The Pd loading conditions are shown below.

[0087] · 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 ) 2Pd was added to the product to a concentration of 1 wt%, and the mixture was stirred and dissolved at room temperature. Then, the product was added and the mixture was heated to evaporate to dryness. The obtained solid was dried at 120 °C overnight, ground in a mortar, and calcined at 500 °C for 3 hours to obtain a product supporting Pd. · Pd loading conditions (Comparative Example 1): In the Pd loading conditions (Example 1 and Comparative Example 2), 30 mL of distilled water was added to 30 mL of acetone, and Pd(NO 3 ) 2 was changed to Pd(OAc) 2 . A product supporting Pd was obtained in the same manner as in the Pd loading conditions (Example 1 and Comparative Example 2) except for this change.

[0088] Figure 4B shows the H 2 TPR results of the products before and after Pd loading in Example 1 and Comparative Examples 1 - 2. The peak ([[]] * ) appearing at a low temperature after Pd loading in Figure 4B is considered to be due to the reduction of the supported Pd. In the products without Pd loading, in Example 1 and Comparative Example 1, the peak of hydrogen consumption appears at a lower temperature than in Comparative Example 2, indicating that oxygen is released at a lower temperature. Also, in Comparative Example 1, two peaks are generated. When Pd is loaded, the peak of hydrogen consumption shifts to the low temperature side in all products, but still, in Example 1 and Comparative Example 1, the peak of hydrogen consumption appears on the lower temperature side than in Comparative Example 2, indicating that oxygen is released at a lower temperature.

[0089] Subsequently, regarding the H 2 TPR results of the products after Pd loading in Example 1 and Comparative Examples 1 - 2, since the large hydrogen consumption peak at 150 °C - 250 °C is considered to be due to the oxygen release of the oxygen storage material, the position of the hydrogen consumption peak was taken as the oxygen release temperature, and the oxygen storage amount was determined from the total hydrogen consumption amount excluding the hydrogen consumption amount derived from Pd. Figure 5 shows the oxygen release temperature and oxygen storage amount of the products after Pd loading in Example 1 and Comparative Examples 1 - 2.

[0090] From Figure 5, it was found that Example 1 has an oxygen storage amount comparable to that of Comparative Example 2, while also having the characteristic of releasing oxygen from a temperature as low as that of Comparative Example 1.

[0091] ​2-4. Confirmation of weight change in an oxidizing atmosphere (confirmation of oxygen storage capacity of products having an apatite-type crystal structure) For the products of Examples 1 to 15 and Comparative Examples 3 to 8, oxidation was carried out at 500 °C in air for 2 hours, and the oxygen storage amount was determined from the weight change (OSC = ((weight after oxidation - weight before oxidation) / weight before oxidation) × 100). Fig. 6 shows the oxygen storage amounts of the products of Examples 1 to 12 and Comparative Examples 3 to 8. Fig. 9 shows the oxygen storage amounts of the products of Examples 1, 2, and 13 to 15. Table 1 summarizes the compositions, crystal structures, H 2 TPR (Pd-supported), and oxygen storage amounts by oxidation in air of the composite oxides of Examples 1 to 15 and Comparative Examples 1 to 8.

[0092]

Table 1

[0093] From Fig. 6 and Table 1, it was confirmed that the products of Examples 1 to 12 containing Ce showed a remarkable weight change due to oxidation and had oxygen storage capacity. The products of Comparative Examples 3 to 8 containing rare earth elements other than Ce did not show a remarkable weight change due to oxidation. From this result, it was found that among the compounds having an apatite-type crystal structure, those containing Ce have oxygen storage capacity.

[0094] From Fig. 9 and Table 1, it was confirmed that the products of Examples 13 to 15 containing Eu showed a remarkable weight change due to oxidation and had oxygen storage capacity. Also, the products of Examples 13 to 15 containing Eu showed a large oxygen storage amount even when compared with Examples 1 to 2 containing Ce.

[0095] Ce (Ce 3+ )-containing apatite does not show the oxygen storage amount expected when all Ce 3+ is oxidized to Ce 4+ , that is, it is known that not all Ce 3+ contained in the structure is oxidized to Ce 4+ . On the other hand, in apatite containing Eu 3+ , which is more easily oxidized than Ce 2+ , Eu2+ from Eu 3+ to is easily oxidized, and it is considered that more oxygen (O 2 ) can be incorporated into the structure.

[0096] 2-5. Consideration of oxygen storage mechanism (relationship between crystal structure and oxygen storage capacity) Figure 1 shows the crystal structure of apatite-type (Ce 9.33 Si 6 O 26 ). Compounds containing rare earth metals such as La and having an apatite-type crystal structure are, for example, J.E.H.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 ", and 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 single crystals grown by floating zone method", are studied as oxide ion (O 2- ) conductors. As shown in Figure 1, the apatite-type crystal structure has an O 2- conduction path and is surrounded by rare earth metal sites. When the rare earth metal is Ce (Ce 9.33 Si 6 O 26 etc.), when the compound is oxidized in air or an oxidizing atmosphere, Ce 3+ becomes Ce 4+ , and O 2-The ionic radius of the rare earth metal sites surrounding the conduction path becomes smaller. As a result, O 2- it is considered that the conduction path expands and O 2- functions as a storage space.

[0097] Fig. 7 shows the X-ray diffraction patterns of the product of Example 1 before and after oxidation, and Table 2 shows the lattice constants and unit cell volumes of Example 1.

[0098]

Table 2

[0099] From Table 2, although oxygen is incorporated into the crystal structure by oxidation (oxygen storage) and the weight increases, and the number of atoms per unit cell increases, the volume of the unit cell hardly changes. This is because, upon oxidation, Ce changes from Ce 3+ to Ce 4+ and at the same time, O 2- is inserted. The a-axis and b-axis directions are expanded and inflated by O 2- , but as Ce 3+ becomes Ce 4+ , there is a slight contraction in the c-axis direction, so it is considered that the change in the volume of the unit cell is very small.

[0100] 2-6. Explanation of why the apatite containing Eu (Eu 2+ ) has a better oxygen storage capacity than the apatite containing Ce (Ce 3+ ) The apatite of the present invention is synthesized in a reducing atmosphere, and Ce is contained as Ce 3+ , and Eu is contained as Eu 2+ . The standard electrode potential of the ion is 1.61 eV for Ce 3+ →Ce 4+ + e - , and -0.35 eV for Eu 2+ →Eu 3+ + e - . Therefore, as an ion, Eu 3+ is more easily oxidized and more likely to store oxygen than Ce 2+ . In the crystal structure, Ce3+ and Eu 2+ occupy the same site, but since their valences are different, it is difficult to conduct experiments with all elements and amounts other than Ce and Eu perfectly matched. However, it is possible to perform charge compensation without affecting the oxygen storage amount by using ions with unchanged valences. Figure 10 shows the sites occupied by Ce 3+ and Eu 2+ and the ions Ca 2+ 、Sr 2+ 、and La 3+ that have the same valence as Ce and Eu, as well as the sites occupied by Si 4+ and P 5+ .

[0101] 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 ) differ somewhat in the elements and amounts other than Ce and Eu, but this is for charge compensation and has no effect on the oxygen storage amount. Those skilled in the art can recognize that this is the effect of replacing Ce with Eu. Subsequently, Tables 3 and 11 show the compositions, the ratios of Ce and Eu, and the oxygen storage amounts of Examples 9 to 10 and 13.

[0102]

Table 3

[0103] From Table 3 and Figure 11, when the composition of the apatite of the present invention is represented as A 10 T 6 O 26 , compared with Examples 9 and 10 where 80 mol% of A is Ce 3+ , 80 mol% of A is Eu 2+It was found that Example 13, which is [as described], exhibits a larger oxygen storage capacity. From this result as well, it was found that the apatite with europium (Eu) as the main component has a superior oxygen storage capacity compared to the apatite with cerium (Ce) as the main component.

Claims

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

2. The composite oxide has the following general formula: α T β X γ (wherein A contains cerium and / or europium, T contains silicon and / or phosphorus, X contains oxygen, and α, β, and γ each represent a molar ratio, α is 9.33 to 10, β is 6, and γ is 24 to 30.

3. The oxygen storage material of claim 2 , wherein A comprises cerium.

4. The oxygen storage material of claim 2 , wherein A comprises europium.

5. 3. The oxygen storage material according to claim 2, wherein the content of cerium and / or europium is 20 mol % or more based on the total amount of substance 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.

6. The oxygen storage material of claim 2 , wherein T further comprises boron.

7. 7. The oxygen storage material according to claim 1, further comprising a catalytic metal, the catalytic metal being supported on the composite oxide.

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