Oxygen absorption / release material

Abstract

The present invention provides an oxygen absorbing / releasing material made of an Fe-based composite oxide, which can increase the amount of oxygen absorbed and released. The oxygen storage / release material of the present invention is characterized by containing a compound in which part of La in LaFeO3 is substituted with Ca.

Description

[Technical Field]

[0001] The present invention relates to an oxygen absorbing / releasing material containing a transition metal composite oxide. [Background technology]

[0002] In recent years, from the perspective of global environmental conservation, there has been a demand for higher performance in exhaust gas purification catalysts used in automobiles and other vehicles. Catalysts such as three-way catalysts for gasoline engines use oxygen-absorbing / releasing materials to fully demonstrate their purification capabilities when the air-fuel ratio fluctuates. When the air-fuel ratio fluctuates, the oxygen-absorbing / releasing material adsorbs and desorbs oxygen through a redox reaction of cations within the solid, thereby adjusting the oxidizing and reducing components in the exhaust gas to a stoichiometric ratio that allows the catalyst to function. Ceria (CeO2) has traditionally been used as an oxygen-absorbing / releasing material, and in recent years, its composite oxides have been studied, leading to the development of ceria-zirconia (CeO2-ZrO2) composite oxides. However, the oxygen absorption / release capacity of ceria-zirconia solid solutions is approaching its theoretical limit. Ce in ceria-zirconia solid solutions 4+ The cation species that can exceed the limit of (cerium ion) is Ce 4+ Examples of suitable oxygen absorbing / releasing materials include metal ions of first transition elements with smaller atomic weights than those of the first transition elements. For this reason, transition metal composite oxides containing first transition elements have been developed. Among these, Fe-based composite oxides have been developed due to their advantages such as low cost, ease of procurement, and the use of the ubiquitous element Fe. For example, Patent Document 1 discloses an oxygen absorbing / releasing material that is made of an Fe-based composite oxide containing Fe (iron), Zr (zirconia), and a rare earth element, and that can exhibit excellent oxygen absorbing / releasing capacity due to the high dispersion of Fe2O3 (iron (III) oxide). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-241328 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the oxygen absorption and release capacity of oxygen-absorbing and releasing materials made of Fe-based composite oxides was not sufficient. 3+ (trivalent Fe ion) is Ce 4+ Compared to ceria, Fe2O3 is less susceptible to chemical reduction. Furthermore, due to these differences in chemical properties, Fe2O3 generally has a higher oxygen absorption / release capacity operating temperature than ceria. Since Fe-based composite oxides utilize the redox reaction of Fe ions, there is a need to improve these issues and increase oxygen absorption / release capacity. Furthermore, from the perspective of protecting the global environment and realizing a sustainable society, there is an increasing need to further improve the performance of oxygen absorption / release materials made from Fe-based composite oxides and to use general-purpose elements.

[0005] The present invention has been made in consideration of these points, and its object is to provide an oxygen absorbing / releasing material made of an Fe-based composite oxide, which can increase the amount of oxygen absorbed and released. [Means for solving the problem]

[0006] In order to solve the above problems, the oxygen storage / release material of the present invention is characterized by containing a compound in which part of La in LaFeO3 is substituted with Ca. [Effects of the Invention]

[0007] According to the present invention, the amount of oxygen absorbed and released can be increased. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a crystal structure of an oxygen absorbing / releasing material according to one embodiment. [Figure 2](a) is a graph showing the XRD patterns of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 (Pd / La1-xCaxFeO3-δ (0 ≦ x ≦ 1 and 0 ≦ δ ≦ 0.5)), and (b) is an enlarged view of the range of 31 to 34 deg. in the XRD pattern of (a). (c) is a graph showing the change in the oxygen absorption and release amount with respect to the molar ratio x of Ca to the total of La and Ca for the samples of Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 3] (a) is a graph showing the Fe-K absorption edge XANES spectra of the samples of Examples 1 to 5 and Comparative Examples 1 and 2. (b) is a graph showing the three component spectra (spectral components 1 to 3) and the residual spectrum obtained by separating the Fe-K absorption edge XANES spectra of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 by Self-Modeling Curve Resolution (SMCR). (c) is a graph showing the Fe-K absorption edge XANES spectra of the samples of Comparative Examples 1 and 2 and Example 3. (d) is a graph showing the change in the component ratios of spectral components 1 to 3 with respect to the molar ratio x of Ca to the total of La and Ca for the samples of Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 4] (a) is a graph showing the Fe-K absorption edge FT-EXAFS spectra of the samples of Examples 1 to 5 and Comparative Examples 1 and 2. (b) is a schematic diagram of the crystal structures of the sample of Comparative Example 1 (LaFeO3), the samples of Examples 1 to 5 (La1-xCaxFeO3-δ (0 < x < 1)), and the sample of Comparative Example 2 (Ca2Fe2O5). [Figure 5] (a) is a graph showing the XRD patterns of the reduced samples of Examples 1 to 5 and Comparative Examples 1 and 2, and (b) is an enlarged view of the range of 31 to 34 deg. in the XRD pattern of (a). (c) is a graph showing the Fe-K absorption edge XANES spectra of the reduced samples of Examples 1 to 3 and Comparative Examples 1 and 2. [Figure 6] It is a graph showing the results of analyzing the change in the H2 consumption amount during the temperature increase process in the H2-TPR test for the samples of Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 7](a) is a graph showing the XRD patterns of the samples of Examples 6 to 8, and (b) is an enlarged view of the range of 31 to 34 deg. in the XRD pattern of (a). [Figure 8] (a) is a graph showing the XRD patterns of the samples of Examples 9 to 14 together with the XRD pattern of the sample of Example 3, and (b) is an enlarged view of the range of 31 to 34 deg. in the XRD pattern of (a).

Mode for Carrying Out the Invention

[0009] Hereinafter, the oxygen absorption and release material according to an embodiment of the present invention will be described. First, the oxygen absorption and release material according to one embodiment will be exemplified and described. FIG. 1 is a schematic diagram of the crystal structure of the oxygen absorption and release material according to one embodiment.

[0010] The oxygen absorption and release material according to one embodiment contains a compound in which a part of La (lanthanum) is substituted with Ca (calcium) in LaFeO3. In this compound, a part of Fe (iron) may be substituted with at least one selected from the group consisting of Co (cobalt), Mn (manganese), and Ni (nickel). Further, in this compound, a part of La may be further substituted with at least one selected from the group consisting of Ce (cerium), Pr (praseodymium), Eu (europium), Nd (neodymium), Sm (samarium), and Y (yttrium). That is, the oxygen absorption and release material according to one embodiment, as the compound, for example, La 1-x-z Ca x RE z (Fe 1-y M y )O 3-δ (However, x is a number satisfying 0 < x < 1. Further, RE is at least one selected from the group consisting of Ce, Pr, Eu, Nd, Sm, and Y, and z is a number satisfying 0 ≦ z < 1. And x and z are numbers satisfying 0 < x + z < 1. Further, M is at least one selected from the group consisting of Co, Mn, and Ni, and y is a number satisfying 0 ≦ y < 1. Further, δ represents oxygen deficiency, and is a number satisfying 0 < δ ≦ 0.5.) and contains a compound represented by.

[0011] Conventional La(Fe) such as LaFeO3 1-y M y )O3 (where y is a number satisfying 0≦y<1), as shown in FIG. 1, all Fe ions occupy hexacoordinate octahedral sites. In contrast, in the compound (for example, the above-mentioned La 1-x-z Ca x RE z (Fe 1-y M y )O 3-δ ), as shown in Figure 1, the conventional La(Fe 1-y M y It is believed that, due to the substitution of a part of La in )O3 with Ca, the occupancy rate of the hexacoordinated octahedral sites of Fe ions decreases while the occupancy rate of the tetracoordinated tetrahedral sites of Fe ions increases, resulting in oxygen deficiency. Therefore, it is believed that the crystal structure of the compound contained in the oxygen absorbing / releasing material according to one embodiment is a crystal structure of an oxygen-deficient perovskite oxide. In addition, in the compound of such an oxygen absorbing / releasing material (a derivative of a perovskite oxide), La is present at the A site of the crystal structure. 3+ (La ions) together with La 3+ Part of Ca was substituted 2+ To compensate for the charge caused by the coexistence of (Ca ions), the Fe ions have a valence higher than 3. As a result, in the oxygen-absorbing / releasing material according to one embodiment, a redox reaction of the Fe ions is possible due to the specific chemical properties of the Fe ions, and the amount of oxygen absorbed and released can be increased.

[0012] In addition, the compound contained in the oxygen absorbing / releasing material according to one embodiment is a compound in which part of Fe is substituted with at least one selected from the group consisting of Co, Mn, and Ni (for example, the above-mentioned La 1-x-z Ca x RE z (Fe 1-y M y )O 3-δWhen it is a compound in which y satisfies 0 < y among them, it is considered that the oxygen absorption and release amount of the oxygen absorption and release material can be further increased by a mechanism such as a multi-electron reaction by at least one ion selected from Co, Mn, and Ni or a structural change favorable for oxygen absorption and desorption.

[0013] Furthermore, when the compound contained in the oxygen absorption and release material according to one embodiment is a compound in which a part of La is substituted with at least one selected from the group consisting of Ce, Pr, Eu, Nd, Sm, and Y (for example, the above La 1-x-z Ca x RE z (Fe 1-y M y )O 3-δ in which z satisfies 0 < z among them), in the compound of the oxygen absorption and release material according to one embodiment, Ca 2+ and La 3+ and ions of rare earth elements RE (at least one selected from the group consisting of Ce, Pr, Eu, Nd, Sm, and Y) having a different ionic radius from RE 3+ ) are further introduced, and the oxygen absorption and release amount of the oxygen absorption and release material can be increased. Furthermore, if such rare earth elements are at least one selected from the group consisting of Ce, Pr, and Eu, due to reasons such as a local oxide structural change favorable for oxygen absorption and desorption occurring in the crystal structure of the compound of the oxygen absorption and release material, it is considered that the oxygen absorption and release amount of the oxygen absorption and release material can be further increased. Subsequently, the configuration of the oxygen absorption and release material according to the embodiment will be described in more detail.

[0014] The oxygen absorption and release material contains a compound in which a part of La in LaFeO3 is substituted with Ca. The compound is not particularly limited, and for example, La 1-x Ca x FeO 3-δ (where x is a number satisfying 0 < x < 1, and δ represents oxygen deficiency and is a number satisfying 0 < δ ≦ 0.5).) and the like.

[0015] As the oxygen absorption and release material, for example, the molar ratio of Ca to the total of La and Ca in the above compound (for example, x in the above La 1-x Ca x FeO 3-δ is preferably 0.2 to 0.8, and among them, the molar ratio is preferably 0.4 to 0.6. This is because the oxygen absorption and release amount of the oxygen absorption and release material can be particularly increased.

[0016] As the oxygen absorption and release material, for example, a part of the above Fe in the above compound (for example, a part of the above Fe in the above La 1-x Ca x FeO 3-δ is preferably substituted with at least one selected from the group consisting of Co, Mn, and Ni. This is because the oxygen absorption and release amount of the oxygen absorption and release material can be further increased. In this specification, the compound represented by the above La 1-x Ca x FeO 3-δ and the compound in which a part of the above Fe in the above La 1-x Ca x FeO 3-δ is substituted with at least one selected from the group consisting of Co, Mn, and Ni is represented by La' 1-x Ca x (Fe 1-y M y )O 3-δ (However, x is a number satisfying 0 < x < 1, and δ represents oxygen deficiency and is a number satisfying 0 < δ ≤ 0.5. Further, M is at least one selected from the group consisting of Co, Mn, and Ni, and y is a number satisfying 0 ≤ y < 1.)

[0017] As the oxygen absorption and release material, for example, a part of the above La in the above compound (for example, the above La 1-x Ca ' x (Fe 1-y M y [[ID=(part of the above-mentioned La) is preferably replaced by at least one selected from the group consisting of Ce, Pr, Eu, Nd, Sm, and Y. Among them, those replaced by at least one selected from the group consisting of Ce, Pr, and Eu are preferred. This is because even when ions of such rare earth elements are further introduced into the La site in the compound of the oxygen absorption and release material, the oxygen absorption and release amount of the oxygen absorption and release material can be increased. Furthermore, if such a rare earth element is at least one selected from the group consisting of Ce, Pr, and Eu, the oxygen absorption and release amount of the oxygen absorption and release material can be further increased. In this specification, the above-mentioned La 1-x Ca x (Fe 1-y M y )O 3-δ The compounds represented by, and the above-mentioned La 1-x Ca x (Fe 1-y M y )O 3-δ where a part of the above-mentioned La is further replaced by at least one selected from the group consisting of Ce, Pr, Eu, Nd, Sm, and Y are all La 1-x-z Ca x RE z (Fe 1-y M y )O 3-δ (However, x is a number satisfying 0 < x < 1. Also, RE is at least one selected from the group consisting of Ce, Pr, Eu, Nd, Sm, and Y, and z is a number satisfying 0 ≦ z < 1. And x and z are numbers satisfying 0 < x + z < 1. Also, M is at least one selected from the group consisting of Co, Mn, and Ni, and y is a number satisfying 0 ≦ y < 1. Furthermore, δ represents oxygen deficiency and is a number satisfying 0 < δ ≦ 0.5.) are represented by.

Examples

[0018] Hereinafter, the oxygen absorption and release material according to the embodiment will be described more specifically with reference to examples and comparative examples.

[0019] 1. Synthesis of oxygen absorption and release material and production of Pd-supported oxygen absorption and release material After synthesizing the oxygen-absorbing and releasing materials of the examples and comparative examples, Pd (palladium) was supported on these oxygen-absorbing and releasing materials to produce Pd-supported oxygen-absorbing and releasing materials. Each example will be described below.

[0020] Example 1: Pd / La 0.8 Ca 0.2 FeO 3-δ ] First, we used the complex polymerization method to 0.8 Ca 0.2 FeO 3-δ Powder (oxygen absorbing / releasing material) was synthesized. First, 800 mmol of citric acid (4.55 equivalents relative to the total amount of metal salts) was placed in a beaker, and 180 mL of methanol was added to dissolve it. 88 mmol of Fe(NO3)3·9H2O (iron nitrate nonahydrate), 18 mmol of Ca(NO3)2·4H2O (calcium nitrate tetrahydrate), and 70 mmol of La(NO3)3·6H2O (lanthanum nitrate hexahydrate) were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, yielding a gelled sample. Next, the gelled sample was pre-baked at 350°C for 3 hours. This resulted in the formation of La 0.8 Ca 0.2 FeO 3-δ The precursor powder was then subjected to a final firing at 1250°C for 5 hours. 0.8 Ca 0.2 FeO 3-δ The powder was synthesized.

[0021] Next, acetone was added to another beaker and (CH3COO)2Pd (palladium acetate) powder was dissolved. 0.8 Ca 0.2 FeO 3-δ After adding the powder, the mixture was heated and stirred to remove the solvent. After the solvent was removed, the sample was dried overnight at 120°C, and the resulting solid was crushed in a mortar and sintered at 500°C for 2 hours. 0.8 Ca 0.2 FeO 3-δ Pd / La powder (oxygen absorbing / releasing material) supported by Pd powder0.8 Ca 0.2 FeO 3-δ In this manufacturing method, the amount of Pd supported was 1 part by weight per 100 parts by weight of the oxygen absorbing / releasing material.

[0022] Example 2: Pd / La 0.6 Ca 0.4 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. 88 mmol of Fe(NO3)3·9H2O, 35 mmol of Ca(NO3)2·4H2O, and 53 mmol of La(NO3)3·6H2O were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.6 Ca 0.4 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0023] Example 3: Pd / La 0.5 Ca 0.5 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. 88 mmol of Fe(NO3)3·9H2O, 44 mmol of Ca(NO3)2·4H2O, and 44 mmol of La(NO3)3·6H2O were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.5 Ca 0.5 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0024] Example 4: Pd / La 0.4 Ca0.6 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. 88 mmol of Fe(NO3)3·9H2O, 53 mmol of Ca(NO3)2·4H2O, and 35 mmol of La(NO3)3·6H2O were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.4 Ca 0.6 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0025] Example 5: Pd / (La 0.2 Ca 0.8 )2Fe2O5] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker, and 180 mL of methanol was added to dissolve it. 88 mmol of Fe(NO3)3·9H2O, 70 mmol of Ca(NO3)2·4H2O, and 18 mmol of La(NO3)3·6H2O were added, followed by 800 mmol of ethylene glycol, which was stirred at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, yielding a gelled sample. A Pd / (La 0.2 Ca 0.8 )2Fe2O5 powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0026] Example 6: Pd / La 0.5 Ca 0.5 Fe 0.8 Co 0.2 O 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. 70 mmol of Fe(NO3)3·9H2O, 18 mmol of Co(NO3)2·6H2O (cobalt nitrate hexahydrate), 44 mmol of Ca(NO3)2·4H2O, and 44 mmol of La(NO3)3·6H2O (lanthanum nitrate hexahydrate) were then added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, yielding a gelled sample. A Pd / La ion ... 0.5 Ca 0.5 Fe 0.8 Co 0.2 O 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0027] Example 7: Pd / La 0.5 Ca 0.5 Fe 0.8 Mn 0.2 O 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. 70 mmol of Fe(NO3)3·9H2O, 18 mmol of Mn(NO3)2·6H2O (manganese nitrate hexahydrate), 44 mmol of Ca(NO3)2·4H2O, and 44 mmol of La(NO3)3·6H2O (lanthanum nitrate hexahydrate) were then added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, yielding a gelled sample. A Pd / La ion ... 0.5 Ca 0.5 Fe 0.8 Mn 0.2 O 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0028] Example 8: Pd / La 0.5 Ca 0.5 Fe 0.8 Ni 0.2 O3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. 70 mmol of Fe(NO3)3·9H2O, 18 mmol of Ni(NO3)2·6H2O (nickel nitrate hexahydrate), 44 mmol of Ca(NO3)2·4H2O, and 44 mmol of La(NO3)3·6H2O (lanthanum nitrate hexahydrate) were then added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, yielding a gelled sample. La was prepared using the same manufacturing method as in Example 1, except that the conditions for obtaining the gelled sample were as described above. 0.5 Ca 0.5 Fe 0.8 Ni 0.2 O 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0029] Example 9: Pd / La 0.4 Ca 0.5 Ce 0.1 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. To this, 88 mmol of Fe(NO3)3·9H2O, 44 mmol of Ca(NO3)2·4H2O, 35 mmol of La(NO3)3·6H2O, and 8.8 mmol of Ce(NO3)3·6H2O (cerium nitrate hexahydrate) were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.4 Ca 0.5 Ce 0.1 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0030] Example 10: Pd / La 0.4 Ca 0.5 Pr 0.1 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. To this, 88 mmol of Fe(NO3)3·9H2O, 44 mmol of Ca(NO3)2·4H2O, 35 mmol of La(NO3)3·6H2O, and 8.8 mmol of Pr(NO3)3·6H2O (praseodymium nitrate hexahydrate) were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.4 Ca 0.5 Pr 0.1 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0031] Example 11: Pd / La 0.4 Ca 0.5 EU 0.1 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. To this, 88 mmol of Fe(NO3)3·9H2O, 44 mmol of Ca(NO3)2·4H2O, 35 mmol of La(NO3)3·6H2O, and 8.8 mmol of Eu(NO3)3·6H2O (europium nitrate hexahydrate) were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.4 Ca 0.5 EU 0.1 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0032] Example 12: Pd / La 0.4 Ca 0.5 Nd 0.1 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. To this, 88 mmol of Fe(NO3)3·9H2O, 44 mmol of Ca(NO3)2·4H2O, 35 mmol of La(NO3)3·6H2O, and 8.8 mmol of Nd(NO3)3·6H2O (neodymium nitrate hexahydrate) were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.4 Ca 0.5 Nd 0.1 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0033] Example 13: Pd / La 0.4 Ca 0.5 Sm 0.1 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. To this, 88 mmol of Fe(NO3)3·9H2O, 44 mmol of Ca(NO3)2·4H2O, 35 mmol of La(NO3)3·6H2O, and 8.8 mmol of Sm(NO3)3·6H2O (samarium nitrate hexahydrate) were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.4 Ca 0.5 Sm 0.1 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0034] Example 14: Pd / La 0.4 Ca 0.5 Y 0.1 FeO 3-δ ] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. To this, 88 mmol of Fe(NO3)3·9H2O, 44 mmol of Ca(NO3)2·4H2O, 35 mmol of La(NO3)3·6H2O, and 8.8 mmol of Y(NO3)3·6H2O (yttrium nitrate hexahydrate) were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / La ion ... 0.4 Ca 0.5 Y 0.1 FeO 3-δ The powder (Pd-supported oxygen absorbing / releasing material) was produced.

[0035] [Comparative example 1: Pd / LaFeO3] To obtain the gelled sample, first, 800 mmol of citric acid was placed in a beaker and 180 mL of methanol was added to dissolve it. 88 mmol of Fe(NO3)3·9H2O and 88 mmol of La(NO3)3·9H2O were added, followed by 800 mmol of ethylene glycol and stirring at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, obtaining a gelled sample. A Pd / LaFeO3 powder (Pd-loaded oxygen storage / release material) was produced using the same manufacturing method as in Example 1, except that the conditions for obtaining the gelled sample were as described above.

[0036] [Comparative example 2: Pd / Ca2Fe2O5] To obtain the gelled sample, 800 mmol of citric acid was first placed in a beaker and 180 mL of methanol was added to dissolve it. 88 mmol of Fe(NO3)3·9H2O and 88 mmol of Ca(NO3)2·4H2O were then added, followed by 800 mmol of ethylene glycol, and the mixture was stirred at room temperature for 30 minutes. After stirring, the mixture was aged at 100°C for 3 hours to gel, yielding a gelled sample. A Pd / Ca2Fe2O5 powder (Pd-loaded oxygen storage / release material) was produced using the same manufacturing method as in Example 1, except that the gelled sample was obtained under the above conditions.

[0037] [Comparative example 3: Pd / Ce 0.7 Zr 0.3 O2] First, distilled water was added to a beaker and Pd(NO3)2 (palladium nitrate) powder was dissolved. Commercially available ceria-zirconia powder (CeO2 / ZrO2 = 67 / 33 in molar ratio in oxide equivalent) was then added, and the mixture was heated and stirred to remove the solvent. Next, the sample after solvent removal was dried overnight at 120°C, and the resulting solid was crushed in a mortar and fired at 500°C for 2 hours. As a result of the above, Ce 0.7 Zr 0.3 Pd / Ce, in which Pd powder is supported on O2 (ceria-zirconia) powder (oxygen absorbing / releasing material) 0.7 Zr 0.3 A powder of O2 (Pd-supported oxygen absorbing / releasing material) was produced. Note that in this production method, the amount of Pd supported was set to 1 part by weight per 100 parts by weight of the oxygen absorbing / releasing material.

[0038] [Comparative Example 4: Pd / Ce 0.3 Zr 0.7 O2] First, distilled water was added to a beaker and Pd(NO3)2 powder was dissolved. Commercially available ceria-zirconia powder (CeO2 / ZrO2 = 33 / 67 in terms of oxide molar ratio) was then added, and the mixture was heated and stirred to remove the solvent. Next, the sample after the solvent removal was dried overnight at 120°C, and the resulting solid was crushed in a mortar and sintered at 500°C for 2 hours. As a result of the above, Ce 0.3 Zr 0.7 Pd / Ce, in which Pd powder is supported on O2 (ceria-zirconia) powder (oxygen absorbing / releasing material) 0.3 Zr 0.7 A powder of O2 (Pd-supported oxygen absorbing / releasing material) was produced. Note that in this production method, the amount of Pd supported was set to 1 part by weight per 100 parts by weight of the oxygen absorbing / releasing material.

[0039] 2. Evaluation Various analyses and tests were carried out on the Pd-supported oxygen storage / release materials obtained in Examples 1 to 14 and Comparative Examples 1 to 4, and the results were evaluated. The results are explained below.

[0040] [Powder XRD (X-ray diffraction)] For each sample of the Pd-supported oxygen absorbing / releasing material of Examples 1 to 5, 6 to 8, and 9 to 14, and Comparative Examples 1 to 4, the intensity of diffracted X-rays was measured in the range of 10 to 90 degrees using a powder X-ray diffractometer (SmartLab manufactured by Rigaku Corporation) with CuKα radiation (λ=1.5418 nm) as the X-ray source and a step width of 0.02 degrees / 0.12 seconds. This resulted in the acquisition of an XRD pattern for each sample.

[0041] Furthermore, the samples of Examples 1 to 5 and Comparative Examples 1 and 2 were introduced into a sample tube, and reduced under the conditions of heating the sample to 500°C and maintaining that temperature for 30 minutes while a gas containing 1% by volume of H2 (hydrogen) and the remainder of N2 (nitrogen) was circulated through the tube, and XRD patterns were obtained for the reduced samples in the same manner as above.

[0042] [XAFS (X-ray absorption fine structure) analysis] XAFS (X-ray absorption fine structure) analysis was performed on the Pd-loaded oxygen storage / release material samples of Examples 1 to 5 and Comparative Examples 1 and 2 at the BL12C experimental station of the Photon Factory, Energy Accelerator Research Organization. The XAFS analysis was performed using a Si(111)2 crystal spectrometer to analyze the Fe-K absorption edge. The XAFS analysis was performed using a transmission method, with X-rays detected using an ion chamber. The XAFS analysis was performed on each sample in this manner, and the X-ray absorbance was normalized to obtain XANES (X-ray absorption near edge structure) spectra with normalized X-ray absorbance, and EXAFS (extended X-ray absorption fine structure) spectra with normalized X-ray absorbance.

[0043] Furthermore, in order to investigate the component ratios of Fe ion species contained in the samples of Examples 1 to 5 and Comparative Examples 1 and 2, the Fe K-edge XANES spectra of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 were separated by SMCR (self-modeling curve resolution). As a result, the spectra were separated into three component spectra (spectral components 1 to 3) and a residue spectrum. SMCR is described, for example, in W.H. Lawton and E.A. Sylvestre, "Self Modeling Curve Resolution," TECHNOMETRICS, vol. 13, pp. 617-633.

[0044] Furthermore, when the Fe-K absorption edge XANES spectrum of each sample of Examples 1 to 5 and Comparative Examples 1 and 2 was synthesized from the above three component spectra (spectral components 1 to 3), the ratio of spectral components 1 to 3 added was calculated as the component ratio of spectral components 1 to 3 in the sample of each example.

[0045] Furthermore, in order to investigate the coordination structure of the Fe ion species contained in each sample of Examples 1 to 5 and Comparative Examples 1 and 2, the Fe K-edge EXAFS spectrum of each sample was Fourier transformed to obtain an Fe K-edge FT-EXAFS (Fourier transform extended X-ray absorption fine structure) spectrum, which is a radial distribution function.

[0046] Furthermore, for the samples of Examples 1 to 3 and Comparative Examples 1 and 2, XAFS analysis was performed on the samples after reduction under the same conditions as those described in the above [Powder X-ray diffraction (XRD)], and Fe K-edge XANES spectra were obtained in the same manner as above.

[0047] [H2-TPR (Hydrogen Temperature Programmed Reduction) Test] For the Pd-loaded oxygen storage / release materials of Examples 1 to 5 and Comparative Examples 1 and 2, a hydrogen temperature-programmed reduction (H2-TPR) test was performed using a Belcat A (Microtrac-Bell Corporation). In the H2-TPR test, 50 mg of sample was weighed and introduced into a sample tube. Next, the sample was heated to 500°C while a gas containing 20% ​​by volume of O2 (oxygen) and the remainder of He (helium) was circulated through the tube at a flow rate of 30 mL / min. This temperature was maintained for 10 minutes, and then the sample was cooled. The atmosphere inside the tube was then replaced with Ar (argon) gas. Then, the sample was heated to 600°C or higher at 10°C / min while a gas containing 5% by volume of H2 and the remainder of Ar was circulated through the tube at a flow rate of 30 mL / min. The H2 consumption of the sample was analyzed during this process. The analysis was performed using a thermal conductivity detector (TCD), and the amount of H2 consumed by each sample (TCD signal [mV]) was quantified by placing a desiccant in front of the TCD to trap the water produced.

[0048] [Oxygen absorption / release test] Oxygen absorption / release tests were conducted on the Pd-supported oxygen absorption / release materials of Examples 1 to 5, 6 to 8, and 9 to 14, as well as Comparative Examples 1 to 4. In the oxygen absorption / release tests, 2 g of the sample was placed in a fixed-bed flow reactor, and the conversion behavior of each gas was investigated using an FT-IR analyzer (SESAM-HL, manufactured by Best Instruments Co., Ltd.) and an oxygen meter (Bex, manufactured by the same company). The sample was heated to 500°C while flowing a gas containing 10% by volume of O2 and the remainder of N2 at a flow rate of 10 L / min. Subsequently, a gas containing 1% by volume of O2 and the remainder of N2 and a gas containing 2% by volume of CO2 and the remainder of N2 were introduced alternately at the same flow rate and temperature for 120 seconds each in six cycles. The average of the CO2 generation rate during the CO introduction period over two to five cycles was calculated as the oxygen absorption / release rate.

[0049] [evaluation] (Samples of Pd-supported oxygen absorbing / releasing materials of Examples 1 to 5) FIG. 2(a) shows the results of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 (Pd / La 1-x Ca x FeO 3-δ2(b) is a graph showing the XRD pattern of the samples of Examples 1 to 5 and Comparative Examples 1 to 4 (0≦x≦1 and 0≦δ≦0.5), and FIG. 2(b) is an enlarged view of the range of 31 to 34 degrees in the XRD pattern of FIG. 2(a). Table 1 below shows the oxygen absorption and release amounts of the samples of Examples 1 to 5 and Comparative Examples 1 to 4. FIG. 2(c) is a graph showing the change in the oxygen absorption and release amount with respect to the molar ratio x of Ca to the total of La and Ca for the samples of Examples 1 to 5 and Comparative Examples 1 and 2.

[0050] [Table 1]

[0051] As shown in FIG. 2(a), the XRD patterns of the samples of Comparative Example 1 and Examples 1 to 4 are consistent with those of orthorhombic perovskite-type LaFeO3. As shown in FIG. 2(b), the XRD patterns of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 (Pd / La 1-x Ca x FeO 3-δ In the XRD pattern of the sample (0≦x≦1 and 0≦δ≦0.5), the diffraction peak with the highest intensity shifts to the higher angle side as x increases. This indicates that Ca ions with a smaller ionic radius are introduced into the La site. On the other hand, the sample of Example 5 (La 0.2 Ca 0.8 The XRD patterns of the samples (Pd / La)2Fe2O5) and Comparative Example 2 (Ca2Fe2O5) are consistent with those of orthorhombic brownmillerite-type Ca2Fe2O5, and are therefore considered to have the same structure. 1-x Ca x FeO 3-δIn the samples (0≦x≦1 and 0≦δ≦0.5), the oxygen absorption / release capacity was ranked in a mountain shape with the sample of Example 3 where x was 0.5 being the largest. That is, the sample of Example 3 where x was 0.5 had the largest oxygen absorption / release capacity, and as x decreased or increased from 0.5 as the reference, the oxygen absorption / release capacity decreased. In addition, in the samples of Examples 2 to 4 where x was 0.4 to 0.6, the sample of Comparative Example 3 (Pd / Ce 0.7 Zr 0.3 O2) and the sample of Comparative Example 4 (Pd / Ce 0.3 Zr 0.7 O2), a higher oxygen absorption / release capacity was obtained.

[0052] FIG. 3(a) is a graph showing the Fe-K absorption edge XANES spectra of the samples of Examples 1 to 5 and Comparative Examples 1 and 2, with the horizontal axis representing X-ray energy and the vertical axis representing normalized X-ray absorbance. FIG. 3(b) is a graph showing three component spectra (spectral components 1 to 3) and residue spectra obtained by separating the Fe-K absorption edge XANES spectra of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 using SMCR. FIG. 3(c) is a graph showing the Fe-K absorption edge XANES spectra of the samples of Comparative Examples 1 and 2 and Example 3. FIG. 3(d) is a graph showing the change in the component ratio of spectral components 1 to 3 with respect to the molar ratio x of Ca to the total of La and Ca for the samples of Examples 1 to 5 and Comparative Examples 1 and 2.

[0053] As shown in FIG. 3(a), the Fe-K absorption edge energies of the sample of Comparative Example 1 (Pd / LaFeO3) and the sample of Comparative Example 2 (Pd / Ca2Fe2O5) are consistent with that of Fe2O3, and therefore the Fe ions contained in the samples of Comparative Examples 1 and 2 correspond to trivalent ions. On the other hand, the samples of Examples 1 to 5 (Pd / La 1-x Ca x FeO 3-δThe Fe-K absorption edge energy of (0 < x < 1 and 0 < δ ≤ 0.5)) is shifted to the higher energy side compared to that of Fe2O3, and the shift width is maximized in the sample of Example 3 where the molar ratio x of Ca to the total of La and Ca is 0.5. This is because La 3+ and Ca 2+ coexist in the A site of the crystal structure, which causes the valence of Fe ions to be higher than trivalent, and x = 0.5 results in the highest valence of Fe ions. Generally, the oxidation number of Fe in Fe compounds is 2 or 3, and its most stable oxidation number is 3. On the other hand, in Sr3Fe2O 7-δ found by K. Beppu, S. Hosokawa, K. Teramura, T. Tanaka, Journal of Materials Chemistry A, 2015, 3(25), 13540-13545., the oxidation number of Fe is greater than 3, and it is known that this abnormally high-valent Fe exhibits high oxygen absorption and release ability. For the samples of Examples 1 to 5 (Pd / La 1-x Ca x FeO 3-δ (0 < x < 1 and 0 < δ ≤ 0.5)), similarly, it is considered that the fact that the oxidation number of Fe is higher than 3 is related to the expression of excellent oxygen desorption characteristics.

[0054] As shown in FIGS. 3(b) and 3(c), spectral components 1 to 3 faithfully reproduce the XANES spectra of the samples of Comparative Example 1 (Pd / LaFeO3), Comparative Example 2 (Pd / Ca2Fe2O5), and Example 3 (Pd / La 0.5 Ca 0.5 FeO 3-δ ), respectively. This indicates that Fe in the samples of Examples 1 to 5 and Comparative Examples 1 and 2 (Pd / La 1-x Ca x FeO 3-δ ) with different molar ratios x of Ca to the total of La and Ca is composed of the components of three kinds of Fe ion species contained in the samples of Comparative Example 1, Comparative Example 2, and Example 3, respectively.

[0055] As shown in Fig. 3(d), in the samples of Examples 1 to 5 and Comparative Examples 1 and 2 (Pd / La 1-x Ca x FeO 3-δ ), the component ratio of spectral component 3 showed a mountain-shaped sequence with the sample of Example 3 where x = 0.5 being the maximum, similar to the oxygen absorption and release amount shown in Fig. 2(c) described above. This indicates that the oxygen absorption and release ability of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 is borne by the component of Fe ion species corresponding to spectral component 3, that is, Fe in the phase where Ca and La equally occupy the A site of the crystal structure.

[0056] Fig. 4(a) is a graph showing the Fe-K absorption edge FT-EXAFS spectra of the samples of Examples 1 to 5 and Comparative Examples 1 and 2. The horizontal axis represents the interatomic distance R [Å], and the vertical axis represents the Fourier transform magnitude FT [a.u.]. Fig. 4(b) is a schematic diagram of the crystal structures of the sample of Comparative Example 1 (LaFeO3), the samples of Examples 1 to 5 (La 1-x Ca x FeO 3-δ (0 < x < 1)), and the sample of Comparative Example 2 (Ca2Fe2O5).

[0057] As shown in Fig. 4(a), in the Fe-K absorption edge FT-EXAFS spectrum of the sample of Comparative Example 1 (Pd / LaFeO3), the vibration appearing near R = 1.6 Å is attributed to the vibration based on the coordination bond between Fe ions and the nearest oxygen. In the samples of Examples 1 to 5 and Comparative Examples ۱ and ۲ (Pd / La 1-x Ca x FeO 3-δIn the FT-EXAFS spectrum of 1-x Ca x FeO 3-δ , the decrease in the vibration intensity with an increase in the molar ratio x of Ca to the total of La and Ca indicates a decrease in the number of Fe-O coordination bonds between Fe ions and the nearest oxygen. In the Fe-K absorption edge XANES spectra of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 shown in Fig. 1-x Ca x FeO 3-δ 3(a) described above, correspondingly, the absorbance of the pre-edge appearing near 7111 eV increases with an increase in x. This pre-edge is an absorption based on 1s-3d transition, and it is known that it becomes a forbidden transition when Fe ions occupy a 6-coordinate octahedral site and an allowed transition when Fe ions occupy a 4-coordinate tetrahedral site (Takashi YAMAMOTO, Adv. X-Ray. Chem. Anal., Japan 38, pp.45-65 (2007)). These results suggest that in the sample of Comparative Example 1 (Pd / LaFeO3), all Fe ions occupy 6-coordinate octahedral sites, and in the sample (Pd / La 1-x Ca x FeO 3-δ ), with an increase in x, the occupancy ratio of 6-coordinate octahedral sites of Fe ions decreases and the occupancy ratio of 4-coordinate tetrahedral sites of Fe ions increases. It is considered that in the sample of Comparative Example 2 (Pd / Ca2Fe2O5), a change occurs such that half of the Fe ions occupy 6-coordinate octahedral sites. Also, from these results, as shown in Fig. 3+ Ca [[ID=2^1]] 2+ 4(b), in the samples of Examples 1 to 5 (La 3-δ (0 < x < 1)), the coordination structure of Fe ions is considered to be the coordination structure of oxygen-deficient perovskite-type oxides, which is an intermediate structure between Comparative Examples 1 and 2. And in the samples of Examples 1 to 5 (La 1-x Ca x FeO 3-δ (0 < x < 1)), for charge compensation for the coexistence of La 3+ and Ca 2+ which are ions at the A site of the crystal structure, Fe ions become higher valent than trivalent, and it is considered that the valence of Fe ions is the highest in the sample of Example 3 where x = 0.5. As a result, it is considered that the amount of oxygen absorption and release can be increased significantly.

[0058] Fig. 5(a) is a graph showing the XRD patterns (solid lines) of the post-reduction samples of Examples 1 to 5 and Comparative Examples 1 and 2 superimposed on the XRD patterns (dashed lines) of the pre-reduction samples of Examples 1 to 5 and Comparative Examples 1 and 2 shown in Fig. 2(a), and Fig. 5(b) is an enlarged view of the range from 31 to 34 degrees in the XRD pattern of Fig. 5(a). Fig. 5(c) is a graph showing the Fe K-edge XANES spectra of the post-reduction samples of Examples 1 to 3 and Comparative Examples 1 and 2, with the horizontal axis representing the X-ray energy and the vertical axis representing the normalized X-ray absorbance.

[0059] As shown in FIG. 5(a), no significant change was observed in the XRD patterns of the reduced samples of Examples 1 to 5 and Comparative Examples 1 and 2 compared to the samples before reduction. This suggests that the oxide skeletal structures of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 are maintained under the reduction conditions. Furthermore, as shown in FIG. 5(b), the XRD patterns of the samples of Examples 1 to 5 and Comparative Examples 1 and 2 (Pd / La 1-x Ca x FeO 3-δ Among the samples (0≦x≦1 and 0≦δ≦0.5), the sample of Example 3, where x is 0.5, exhibits a particularly large shift in the diffraction peak of the reduced sample relative to the corresponding diffraction peak of the sample before reduction toward lower angles. This is thought to be the result of the largest number of Fe ions being reduced in the sample of Example 3, where x is 0.5, among the samples of Examples 1 to 5 and Comparative Examples 1 and 2, and the largest reflection of lattice expansion due to the increase in the radius of the Fe ions. Furthermore, as shown in Figure 5(c), all of the reduced samples of Examples 1 to 3 and Comparative Examples 1 and 2 exhibit the same Fe K-absorption edge energy as the Fe2O3 standard sample. This suggests that the valence of Fe ions is trivalent in all of the reduced samples of Examples 1 to 3 and Comparative Examples 1 and 2. Therefore, it is thought that the adsorption and desorption of oxygen in the samples of Examples 1 to 3 occurs through a redox reaction between Fe ions with a valence higher than trivalent and Fe ions with a valence of trivalent.

[0060] FIG. 6 is a graph showing the results of analyzing the change in H2 consumption amount during the temperature rise process in the H2-TPR test for the samples of Examples 1 to 5 and Comparative Examples 1 and 2.

[0061] As shown in Figure 6, the H2 consumption detected below 300°C during the temperature rise process is attributed to H2 consumption resulting from the reduction of Fe ions and supported Pd. In the samples of Examples 1 to 5 and Comparative Examples 1 and 2, the peak values ​​of H2 consumption below 300°C during the temperature rise process were in a mountain-shaped order, with the sample of Example 3, where x was 0.5, being the highest. In addition, the integrated value of H2 consumption up to 300°C during the temperature rise process of the sample of Example 3 was 1.16 mmol g -1 and the above-mentioned oxygen absorption / release amount (1.07 mmol g) of the sample of Example 3 -1 ) is roughly consistent with the above. From the integrated value of the H consumption amount and the Fe content of the sample of Example 3, the number of reactive electrons per Fe ion is determined to be 0.47. In addition, considering that the valence number of the Fe ions contained in the sample of Example 3 after reduction is 3 as described above, it is believed that in the sample of Example 3, redox reactions are repeated with the valence number of the Fe ions being between about 3.5 and about 3.

[0062] (Samples of Pd-supported oxygen absorbing / releasing materials of Examples 6 to 8) Fig. 7(a) is a graph showing the XRD patterns of the samples of Examples 6 to 8 together with the XRD pattern of the sample of Example 3, and Fig. 7(b) is an enlarged view of the range of 31 to 34 degrees in the XRD pattern of Fig. 7(a). Table 2 below shows the oxygen absorption and release amounts of the samples of Examples 6 to 8.

[0063] [Table 2]

[0064] As shown in FIG. 7(a), the XRD patterns of the samples of Examples 6 to 8, like the sample of Example 3, are consistent with those of orthorhombic perovskite-type LaFeO3. Furthermore, as shown in FIG. 7(b), the angles of the maximum intensity diffraction peaks in the XRD patterns of the samples of Examples 6 to 8 are shifted relative to the angles of the corresponding diffraction peaks in the sample of Example 3. This indicates that in the samples of Examples 6 to 8, Co, Mn, and Ni ions with different ionic radii are introduced into the Fe sites of the sample of Example 3. Furthermore, as shown in Table 2, the oxygen absorption and release amounts of the samples of Examples 6 to 8 were greater than those of the samples of Comparative Examples 3 and 4 and Example 3 described above.

[0065] (Samples of Pd-supported oxygen absorbing / releasing materials of Examples 9 to 14) Fig. 8(a) is a graph showing the XRD patterns of the samples of Examples 9 to 14 together with the XRD pattern of the sample of Example 3, and Fig. 8(b) is an enlarged view of the range of 31 to 34 degrees in the XRD pattern of Fig. 8(a). Table 3 below shows the oxygen absorption and release amounts of the samples of Examples 9 to 14 together with the oxygen absorption and release amounts of the samples of Example 3 and Comparative Examples 1 to 4.

[0066] [Table 3]

[0067] As shown in Fig. 8(a), the XRD patterns of the samples of Examples 9 to 14 are identical to those of orthorhombic perovskite-type LaFeO3, as with the sample of Example 3. As shown in Fig. 8(b), the angles of the diffraction peaks with maximum intensity in the XRD patterns of the samples of Examples 9 to 14 are shifted relative to the angles of the corresponding diffraction peaks of the sample of Example 3. This indicates that in the samples of Examples 9 to 14, Ca is present at the La site of the compound of the oxygen absorbing / releasing material in the sample of Example 3. 2+ and La 3+The results show that ions of rare earth elements (at least one selected from the group consisting of Ce, Pr, Eu, Nd, Sm, and Y) having an ionic radius different from that of La were introduced. Furthermore, as shown in Table 3, the oxygen absorption / release amounts of the samples of Examples 9 to 14 were greater than those of the samples of Comparative Examples 3 and 4. The oxygen absorption / release amounts of the samples of Examples 9 to 11 were greater than that of the sample of Example 3. An increase in the oxygen absorption / release amount was observed due to partial substitution of the La site with any of Ce, Pr, and Eu. This effect of increasing the oxygen absorption / release amount is presumed to be due to the introduction of ions of a rare earth element (at least one selected from the group consisting of Ce, Pr, and Eu) into the La site in the compound of the oxygen-absorbing / releasing material in the sample, which caused a local oxide structural change in the crystal structure of the compound that is favorable for oxygen absorption / desorption.

[0068] The above describes in detail the embodiments of the oxygen absorbing and releasing material according to the present invention, but the present invention is not limited to the embodiments described above, and various design modifications can be made within the scope of the spirit of the present invention as set forth in the claims.

Claims

1. LaFeO ３ 1. An oxygen absorbing / releasing material comprising a compound in which part of La is substituted with Ca.

2. 2. The oxygen-absorbing material according to claim 1, wherein the molar ratio of Ca to the total of La and Ca in the compound is 0.4 to 0.

6.

3. 3. The oxygen-absorbing material according to claim 1, wherein a portion of the Fe in the compound is substituted with at least one element selected from the group consisting of Co, Mn, and Ni.

4. 3. The oxygen absorbing / releasing material according to claim 1, wherein a portion of the La in the compound is further substituted with at least one element selected from the group consisting of Ce, Pr, Eu, Nd, Sm, and Y.

5. 5. The oxygen-absorbing material according to claim 4, wherein a portion of the La in the compound is substituted with at least one element selected from the group consisting of Ce, Pr, and Eu.

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