JPWO2010010714A1 - Oxygen storage material, exhaust gas purification catalyst, and honeycomb catalyst structure for exhaust gas purification - Google Patents

Abstract

Oxygen storage material with high oxygen storage capacity even with a small oxidation-reduction range, and low-cost three-way catalyst that suppresses the amount of expensive noble metals, and has the same or higher catalytic activity as before A catalyst is provided. Specifically, an oxide containing an alkaline earth metal and (Fe1-sTis) or Co or (Fe1-sTis) and Co is included, and the oxide has an average particle size of 0.1 μm or more and 5 μm or less. An oxygen storage material (A2), wherein the oxide particles are composed of at least two crystal phases, the average size of the crystal phases is 5 nm or more and 80 nm or less, and S is 0 or more and 0.31 or less. provide. Further, oxide M {Co1-x (Fe1-sTis) x} yO4-δ (A1) or (A2) supporting one or more noble metals and oxide (B) supporting one or more noble metals ((B) is an oxide different from (A1) and (A2)), and provides an exhaust gas purifying catalyst having oxygen storage capacity.

Description

The present invention relates to an oxygen storage material capable of occluding and releasing oxygen. The present invention also relates to a catalyst and a honeycomb catalyst structure for purifying carbon monoxide (CO), nitrogen oxide (NO _x ), and unburned hydrocarbon (HC) in combustion exhaust gas. In particular, the present invention relates to a catalyst for purifying carbon monoxide (CO), nitrogen oxide (NO _x ), and unburned hydrocarbon (HC) discharged from an internal combustion engine such as an automobile engine, and a honeycomb catalyst structure.

Oxygen storage capacity (OSC) is an oxygen source for promoters for engine exhaust gas purification catalysts, oxygen storage such as oxygen cylinder replacement, oxygen separation by PSA (Pressure Swing Adsorption), and oxygen source for oxidation and combustion Can be used for etc. Ceria-zirconia (cerium oxide-zirconium oxide, CeO ₂ -ZrO ₂ ) is well known as an oxide having an oxygen storage capacity, and is widely used as a co-catalyst for engine exhaust gas purification catalysts (non-patent) Reference 1). The reason why the oxide having the OSC function is used as the promoter is that the exhaust gas of the engine is rich (when the air-fuel ratio A / F is smaller than the theoretical value 14.6) and the promoter is oxygen in the gas phase. The exhaust gas of the engine has a lean atmosphere (when the air-fuel ratio A / F is larger than the theoretical value of 14.6), and the promoter occludes oxygen in the gas phase, and changes the atmosphere in the vicinity of the noble metal. It is for suppressing. As a result, the purification activity is maintained with a wide A / F. That is, the A / F window showing the purification action is widened.

Various improvements have been made with respect to the promoter, ceria-zirconia.
For example, in Patent Documents 1 to 4, various elements such as rare earth elements and alkaline earth elements are added to ceria-zirconia in order to improve heat resistance at 800 ° C. or higher. At higher temperatures, ceria-zirconia grain growth occurs, which reduces the specific surface area, thus solving the problem of lower OSC.

  Moreover, in patent document 5, in order to suppress sulfur poisoning of ceria and improve durability, it is disclosed that a phosphoric acid compound is mixed. When ceria-zirconia is used as a co-catalyst, ceria-zirconia particles are generally impregnated with a noble metal serving as a catalyst metal.

  In Patent Document 6, a catalyst metal such as Rh is arranged between crystal lattices or lattice points of a double oxide containing Ce and Zr, and a large number of fine pores are distributed in the double oxide. . With the above improvements, the catalyst metal is exposed on the pore surface, and the exhaust gas easily diffuses into the oxygen storage material, increasing the chance of contact between the catalyst metal and the exhaust gas, and improving the exhaust gas purification performance as a catalyst. It can be made to. Arranging the catalyst metal Rh in the crystal lattice of the double oxide means that it is in the form of RhMOx (M is another metal atom, x is the number of oxygen atoms) and is strongly bonded to the double oxide. It is said.

As described above, in order to improve the performance of existing ceria-zirconia oxides, attempts have been made to find OSCs using oxides different from the above oxides. In Patent Document 7, the perovskite double oxide represented by ABO ₃ (where A is La and Sr, and B is at least one of Fe and Co) has a high OSC. It is disclosed. Specifically, a perovskite double oxide represented by La _0.6 Sr _0.4 FeO ₃ or La _0.6 Sr _0.4 CoO ₃ is disclosed. In Patent Document 8, a compound represented by a composition formula ATO ₃ (where T is a transition element) is disclosed as an oxide having OSC even in a low temperature range of about 400 ° C. Specifically, it is a perovskite complex oxide represented by a composition formula SrFeO ₃ or CaFeO ₃ .

Further, oxides having OSC have been studied in addition to the use as a promoter as described above. In Patent Document 9, an oxide containing ZnO as a main component and Bi ₂ O ₃ as an additive for use as a substitute for an oxygen cylinder is disclosed for oxygen storage.

The gas discharged from an internal combustion engine such as an automobile engine contains CO, NO _x , and HC, which are converted into carbon dioxide (CO ₂ ), nitrogen (N ₂ ), and water (H ₂ O). Thus, a catalyst technology for reducing CO, NO _x , and HC emissions is generally known. Such a catalyst technology is used not only for exhaust gas from an internal combustion engine but also for other combustion exhaust gas.

As a three-way catalyst that simultaneously purifies CO, NO _x , and HC in automobile exhaust gas, a catalyst that combines noble metals such as Pt, Pd, and Rh is widely used. These noble metals are supported as fine particles on the surface of activated alumina (γ-alumina, ρ-alumina, χ-alumina, η-alumina, δ-alumina, κ-alumina, θ-alumina, amorphous alumina, etc.) oxide particles. Further, it is used after being coated on a honeycomb of metal or ceramic.

  The three-way catalyst works effectively near the stoichiometric air-fuel ratio, but in order to expand the effective air-fuel ratio width (window), oxygen storage materials such as cerium oxide are included to improve the catalyst performance. It has been broken. For example, Patent Document 10 discloses a method of adding an appropriate amount of ceria to a noble metal / activated alumina oxide catalyst. However, although the catalyst performance is improved by providing oxygen storage capacity by ceria, the amount of noble metals has not been reduced. This is because the oxygen storage capacity of the ceria-based oxide is not always sufficient.

As oxides other than ceria, composite oxides are also being studied, and in particular, composite oxides having a perovskite structure containing rare earth elements have been studied. For example, in Patent Document 11, for the purpose of improving the activity of a three-way catalyst, a perovskite-type complex oxide of LaAl _1-x M _x O ₃ (M: group 1 to group 5, group 12 to group 14) containing La is used. A catalyst carrying Pd is disclosed. In Patent Document 12, a noble metal element is supported on a perovskite complex oxide containing a rare earth element such as (La, Sr) FeO ₃ or (La, Sr) MnO ₃ in order to obtain similarly high catalytic activity. It is disclosed. Further, in Patent Document 13, the composition and additive elements of the (La, Sr) FeO ₃ and (La, Sr) MnO ₃ are studied, and the durability and heat resistance are improved. Further, Patent Documents 14 and 15 disclose composite oxides such as La (Fe, Rh) O _{3 in} which the noble metal Rh is incorporated into the perovskite lattice in order to improve the durability of the catalytic activity of the noble metal. . As described above, in the perovskite complex oxide, a rare earth element such as La is essential to effectively improve the catalytic performance of the three-way catalyst.

Further, when an AM _x O _y (A: alkali metal or alkaline earth metal, M: Fe, Co, or Ni) composite oxide not containing a rare earth element, particularly a spinel-type AM _x O _y composite oxide is combined with a noble metal. Patent Document 16 discloses that it is effective for removing particulate carbon materials and nitrogen oxides in exhaust gas such as diesel engines. However, as in exhaust gas purification of gasoline engines and the like, CO, HC , And performance as a three-way catalyst capable of simultaneously purifying NO _x is not suggested.

Patent Document 17 discloses that calcium ferrite having a composition formula of CaFe ₂ O ₄ is used as an oxidation catalyst. However, the performance as a three-way catalyst that catalyzes both the oxidation reaction of CO and HC and the reduction reaction of NO _x as in exhaust gas purification of a gasoline engine or the like is not suggested. Patent Document 18 discloses that magnesium ferrite having a composition formula of MgFe ₂ O ₄ is used as an oxidation catalyst. However, the performance as a three-way catalyst that catalyzes both the oxidation reaction of CO and HC and the reduction reaction of NO _x as in exhaust gas purification of a gasoline engine or the like is not suggested.

JP-A-9-175822 JP-A-9-175823 Japanese Patent Laid-Open No. 10-216509 JP-A-10-218620 JP 2000-12537 A JP 2007-196150 A JP 2004-41946 A JP 2006-176346 A JP 2007-15903 A JP 54-159391 A JP-A-2005-205280 JP 2006-36558 A JP 2003-175337 A JP 2004-41866 A JP 2004-41867 A JP 2005-66559 A JP 2006-255679 A JP 2007-229546 A

Masakazu Ozawa, Norio Kimura, Hideo Sugawa, Koji Yokota, Toyota Central R & D Review Vo.27, No.3, 43-53 (1992)

  As described above, the OSC-containing oxide is useful in various applications including a cocatalyst for exhaust gas purification. In any application, higher OSC is preferable, and further improvement is desired. In the ceria-zirconia-based oxide, the improvement of durability and heat resistance is more popular than the improvement of OSC. On the other hand, in the oxides other than the ceria-zirconia-based oxide, a search is further made for the purpose of an excellent OSC.

The OSC of ceria-zirconia is usually the highest with a ZrO ₂ content of 50 mol%, with a redox width of 50% O ₂ / N ₂ -20% H ₂ / N ₂ at 500 ° C., 825 μmol-O ₂ / g. (Non-Patent Document 1). On the other hand, Patent Document 8 shows OSCs of 718 μmol-O ₂ / g and 597 μmol-O ₂ / g in SrFeO ₃ and CaFeO ₃ with a redox width of 100% O _{2 to} 100% H ₂ at 400 ° C., respectively. Has been. The oxide disclosed in Patent Document 8 is an oxide exhibiting excellent OSC at a low temperature of 400 ° C., but has a wide redox width of 100% O ₂ -100% H ₂ . Even in the ceria-zirconia OSC of Non-Patent Document 1, when the oxidation-reduction width is further narrowed, the OSC becomes 825 μmol-O ₂ / g.

  Thus, conventionally, an oxygen storage material having a high OSC has been developed under a condition where the oxidation-reduction width is wide. However, there is a problem that the OSC becomes small when the oxidation-reduction width is reduced. In order to obtain an excellent oxygen storage material that can be applied to a wide range of uses, an oxide having a high OSC is desired even under a narrow redox range.

On the other hand, conventional three-way catalyst, CO in the exhaust gas, HC, and NO _x to purify efficiently, consisting mainly of noble metal (other than Pt is, Rh, Pd) Pt is used. As described above, when a large amount of noble metal is used, the catalyst performance is improved, but the cost is also increased. That is, the ratio of exhaust gas purification converters is increasing due to the price structure of engine systems such as automobiles. Therefore, as described above, improvement in performance of a three-way catalyst has been studied by combining a cerium-based oxide or a perovskite complex oxide with a noble metal. However, although the above-described oxides that have been studied so far have improved catalyst performance, the amount of noble metal used cannot always be reduced so as to reduce the cost of the exhaust gas purification converter.

Further, as described in Patent Documents 16 to 18 above, complex oxides not containing rare earth elements have also been developed as exhaust gas purification catalysts. However, these are those that remove particulate carbon materials and nitrogen oxides in exhaust gas such as diesel engines, or are oxidation catalysts that promote only the oxidation reaction, such as CO, HC, and As a three-way catalyst that simultaneously purifies NO _x , sufficient catalytic activity cannot be obtained even when combined with a noble metal. Wherein in the composite oxide, the oxidation of particulate carbonaceous material, adsorption accumulation of NO _x, none of the reductive decomposition of adsorbed NO _x, it is estimated that is happening in the surface of one oxide. However, according to detailed investigations by the inventors, it is extremely difficult to simultaneously perform both oxidation and reduction reactions on the surface of one catalyst, and when one catalyst activity is improved, the other catalyst activity is not sufficiently improved. I know. It has been found that if AM _x O _y is used as it is as a three-way catalyst, CO, HC and NO _x cannot be purified at the same time.

In Patent Document 17, a long-term durability test is simulated by assuming a practical use as an exhaust gas purification catalyst for a motorcycle, but only propylene decomposition (oxidation reaction) and NO _x is reduced. It is not shown whether it is reduced, ie the performance of the three-way catalyst. Furthermore, Patent Document 17 and Patent Document 18 describe that compositions other than CaFe ₂ O ₄ and MgFe ₂ O ₄ may be included. Patent Document 17 also discloses an oxidation catalyst including two phases of CaFe ₂ O ₄ and Ca ₂ Fe ₂ O ₅ , but it is merely a manufacturing reason that it is expensive to produce a single phase. It is.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an oxygen storage material capable of obtaining a high OSC even when the redox width is small. The present invention also provides a low-cost three-way catalyst that suppresses the amount of expensive noble metal used or does not use Pt, and has a catalytic activity equal to or higher than that of conventional catalysts and an exhaust gas purifying catalyst. It is to provide a honeycomb catalyst structure.

  The inventors of the present invention used a plurality of (at least two) fine particles of an oxide containing an alkaline earth metal M and (Fe, Ti) or Co, or both (Fe, Ti) and Co. It was found that a high OSC can be obtained even when the redox width is small by using particles composed of a simple crystal phase, and the oxygen storage material of the present invention was completed.

Further, the present inventors have found that in the case of oxides supporting the noble metal which does not contain _{Pt M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ (s = 0, M (Co _{1-x Fe x) y O} 4-δ) (A1), or the oxygen storage material and (A2), the oxygen storage capacity of a different oxide and the oxide (a) and oxygen storage material (A2) It has been found that a catalytic activity higher than the catalytic activity of a single substance is expressed by supporting a noble metal not containing Pt on the oxide (B) having a catalyst, and the exhaust gas purifying catalyst and the exhaust gas purifying catalyst of the present invention. A honeycomb catalyst structure was completed.

That is, the present invention has the following gist.
[1] An oxygen storage material comprising an oxide containing an alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or (Fe _1-s Ti _s ) and Co,
The oxide is a particle having an average particle diameter of 0.1 μm or more and 5 μm or less,
The oxide particles are composed of a plurality of crystal phases, and the average size of the crystal phases is 5 nm or more and 80 nm or less,
The oxygen storage material, wherein s is 0 ≦ s ≦ 0.31.
[2] In the oxide, the molar ratio between the alkaline earth metal M and the total amount of (Fe _1-s Ti _s ) and Co is 0.1 ≦ M / {(Fe _1-s Ti _s ) + Co } ≦ 0.9, wherein the oxygen storage material according to [1].
[3] An oxygen storage material comprising an alkaline earth metal M and an oxide containing Fe or Co, or both Fe and Co,
The oxide is a particle having an average particle diameter of 0.1 μm or more and 5 μm or less,
The oxide particles are composed of a plurality of crystal phases,
The oxygen storage material according to [1] or [2], wherein an average size of the crystal phase is 5 nm or more and 80 nm or less.
[4] The oxide is characterized in that the molar ratio of the alkaline earth metal M and the total amount of Fe and Co is 0.1 ≦ M / (Fe + Co) ≦ 0.9 [3] 2. The oxygen storage material according to 1.
[5] The oxygen storage material according to any one of [1] to [4], wherein the alkaline earth metal M is Sr.
[6] The oxygen storage material according to any one of [1] to [4], wherein the alkaline earth metal M contains Ca.
[7] The oxygen storage material according to any one of [1] to [6], wherein a noble metal is supported on the oxide.
[8] The oxygen storage material according to [7], wherein the noble metal is at least one selected from the group consisting of Pt, Pd, and Rh.
[9] The oxygen storage material according to [7], wherein the noble metal is at least one selected from the group consisting of Ag and Ru.
[10] The oxygen according to [7], wherein the noble metal is one or more selected from the group consisting of Pt, Pd, and Rh and one or more selected from the group consisting of Ag and Ru. Storage material.

[11] Containing alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or both (Fe _1-s Ti _s ) and Co, used for exhaust gas purification of carburetor-type motorcycles An oxygen storage material containing oxides,
The oxide is a particle having an average particle diameter of 0.1 μm or more and 5 μm or less,
The oxygen storage material, wherein s is 0 ≦ s ≦ 0.31.
[12] The oxygen storage material according to any one of [1] to [10], which is contained in an exhaust gas purification catalyst of a carburetor type motorcycle.

[13] Pd, oxide carrying one or more noble metals selected from the group consisting of Ag and _{Rh M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ ( where M is one or more elements substantially selected from the group consisting of Ca, Sr and Ba, x is 0 to 1, y is 1 to 2, s is 0 to 0.31, and δ is in the charge. (A1) or the oxygen storage material (A2) according to any one of claims 1 to 10, and
An oxide (B) supporting one or more noble metals selected from the group consisting of Pd, Ag and Rh,
The catalyst for purifying exhaust gas, wherein the oxide (B) is an oxide different from the oxide (A1) and the oxygen storage material (A2) and has an oxygen storage capacity.
[14] Oxide M (Co _1-x Fe _x ) _y O _4-δ supporting one or more noble metals selected from the group consisting of Pd, Ag, and Rh (where M is substantially Ca, One or more elements selected from the group consisting of Sr and Ba, x is 0 to 1, y is 1 to 2, and δ is a value determined to satisfy the charge neutrality condition) (A1), or Oxygen storage material (A2) according to any of [1] to [10],
An oxide (B) supporting one or more noble metals selected from the group consisting of Pd, Ag and Rh,
The catalyst for purifying exhaust gas, wherein the oxide (B) is an oxide different from the oxide (A1) and the oxygen storage material (A2) and has an oxygen storage capacity.
[15] The exhaust gas purifying catalyst according to [13] or [14], wherein the oxide (B) has an oxygen storage capacity of 50 μmol-O ₂ / g or more at 500 ° C.
[16] The exhaust gas-purifying catalyst according to any one of [13] to [15], wherein the oxide (B) contains cerium.
[17] The oxide (B) is an oxide containing cerium and zirconium _{(Ce z Zr 1-z)} O 2-δ, z is 0.4 to 1.0 [13] - [ [16] The exhaust gas-purifying catalyst according to any one of [16].
[18] The exhaust gas purifying apparatus according to any one of [13] to [17], wherein the noble metal supported on the oxide (A) is Pd and the noble metal supported on the oxide (B) is Rh. catalyst.
[19] and the noble metal oxide carrying _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ (A1) or the oxygen storage material (A2), carrying the precious metal oxide The mass ratio to the product (B) is 0.1 to 10 in terms of the mass ratio of A / B (where A is the mass of A1 or A2 and B is the mass of B) [13]. To [18] The exhaust gas-purifying catalyst according to any one of [18].
[20] oxide carrying the noble metal _{M (Co 1-x Fe x} ) y O 4-δ (A1), or the oxygen storage material (A2), the oxide carrying the precious metal (B) Any of [13] to [18] in which the mass ratio is 0.1 to 10 in terms of the mass ratio of A / B (where A is the mass of A1 or A2 and B is the mass of B). An exhaust gas purifying catalyst according to claim 1.
[21] The exhaust gas-purifying catalyst according to any one of [13] to [20], wherein the value of x is 0.2 to 1.
[22] The exhaust gas purification catalyst according to any one of [13] to [21], which is an exhaust gas purification catalyst for a carburetor type motorcycle.
[23] Pd, oxide carrying one or more noble metals selected from the group consisting of Ag and _{Rh M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ ( where M is one or more elements substantially selected from the group consisting of Ca, Sr and Ba, x is 0 to 1, y is 1 to 2, s is 0 to 0.31, and δ is in the charge. (A1) or the oxygen storage material (A2) according to any one of [1] to [10],
An oxide (B) supporting one or more noble metals selected from the group consisting of Pd, Ag, and Rh.
A catalyst for exhaust gas purification, which is a catalyst for exhaust gas purification of a carburetor type motorcycle.
[24] An exhaust gas-purifying honeycomb catalyst structure, wherein the exhaust gas-purifying catalyst according to any one of [13] to [23] is wash-coated on a ceramic or metal honeycomb.

  According to the present invention, compared to conventional ceria-zirconia and other known OSC oxides, an excellent oxygen storage material having a high OSC even when the oxidation-reduction width is narrow can be provided. In addition, according to the present invention, it is possible to provide a catalyst for exhaust gas purification that can reduce the amount of noble metal used and that is excellent in purification performance. Further, according to the present invention, since it is not necessary to use Pt, the amount of noble metal used is reduced, and the cost of the exhaust gas purification converter can be greatly reduced.

1 is a conceptual diagram in which a catalyst for exhaust gas purification of the present invention is applied to a honeycomb substrate and a conceptual diagram illustrating an exhaust gas purification reaction.

As described above, a perovskite composite oxide is known as an oxide exhibiting OSC other than ceria-zirconia, and further, perovskite oxide ATO ₃ exhibiting excellent OSC even at a low temperature is disclosed in Patent Document 8. Yes. That is, until now, in order to improve the OSC, it is desirable to use a crystal phase (single phase) represented by a specific composition formula such as ATO ₃ , and the search and development have been made. For example, Patent Document 8 specifically states that a single phase of SrFeO ₃ or CaFeO ₃ is excellent in low-temperature OSC.

Also, for ceria-zirconia, it is desirable that it is not a two oxides of ceria and zirconia, but a solid solution that becomes (Ce, Zr) O ₂ and is a single phase that does not contain other crystal phases. . Furthermore, in order to obtain a higher OSC, it has been common knowledge in the art that the particles are small and the specific surface area is large. Therefore, until now, the device which suppresses grain growth and a specific surface area does not become small has been made | formed (patent documents 1-4).

  However, the present inventors are convinced that, in order to design a material having a higher OSC, the conventional technical idea as described above is limited, and it is necessary to design the material with a new idea. Thus, the oxygen storage material of the present invention has been found out with such a technical idea.

That is, the present invention relates to an oxide containing an alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or (Fe _1-s Ti _s ) and Co, not a single phase, Rather, by using oxide particles in which at least two types of crystal phases form a domain structure with a size of 5 to 80 nm, a high OSC is obtained even when the redox width is narrow.

Here, when S is 0, the following can be said. That is, the present invention relates to an oxide containing an alkaline earth metal M and Fe or Co, or both Fe and Co, and is not a single phase, but rather, at least two crystal phases are 5 to 80 nm. By using oxide particles having a domain structure in size, a high OSC can be obtained even when the redox width is narrow. Thereby, the oxide of the present invention has a higher OSC than the single phase of SrFeO ₃ and CaFeO ₃ of Patent Document 8. In addition, if the oxide particles of the present invention are composed of the plurality of fine crystal phases, the average particle size of 0.1 mm can be obtained without reducing the particle size or the high specific surface area such as a porous structure. Large particles of 1-5 μm with high OSC.

In order for the oxide particles to absorb oxygen, oxygen ions need to diffuse from the particle surface to the inside of the particles, but the particles are in one crystal phase such as (Ce, Zr) O ₂ , SrFeO ₃ , CaFeO _3. Is formed, a concentration gradient of oxygen ions is generated in one crystal phase particle. However, the concentration gradient is hardly generated in the particle, and particularly, a large concentration gradient is not easily generated. Therefore, in the case of such particles, the concentration gradient becomes a driving force for diffusion of oxygen ions, so that there is a problem that the particles do not diffuse to the center of the particles. In particular, when the oxidation-reduction width is narrow, the above problem becomes remarkable, and as a result, high OSC cannot be obtained. In addition, when oxygen ions enter or exit the crystal lattice, the crystal lattice extends or contracts in a specific orientation. When the oxide particles have a single phase, the stress concentration due to the expansion and contraction of the crystal lattice increases, and conversely, oxygen ions do not easily enter and exit the entire particle.

  However, as in the present invention, when the oxide particles are composed of a plurality of (at least two kinds) fine crystal phases, even if the oxide particles are large, the crystal phases and crystal phases in the particles The crystal interface becomes a diffusion channel of oxygen ions, and oxygen ions can be easily diffused to the center of the particle. Therefore, the whole particle works effectively and can store a lot of oxygen. Even if the oxidation-reduction width is narrow, oxygen ions can diffuse to the center of the particle, so that high OSC is exhibited. In addition, since one oxide particle is composed of a fine crystal phase having a size of 5 to 80 nm, stress due to expansion and contraction of the crystal lattice caused by the entry and exit of oxygen ions is relieved at the crystal interface. In addition, since the direction of expansion and contraction differs depending on each crystal phase, stress concentration does not occur in a specific direction, so that the expansion and contraction of each crystal lattice due to the entry and exit of oxygen ions is facilitated. As a result, the entry and exit of oxygen ions is facilitated throughout the oxide particles. Therefore, the crystal phases constituting the oxide particles have a crystal interface and are in contact with each other.

As described above, in the present invention, the oxide particles containing the alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or both (Fe _1-s Ti _s ) and Co, or The oxide particles (in the case of S = 0) containing the alkaline earth metal M and Fe or Co, or both Fe and Co are particles composed of at least two crystal phases. The average size of the crystal phase is 5 nm or more and 80 nm or less. The structure of the crystal phase can be determined by X-ray diffraction or neutron diffraction. Further, the presence of at least two types of crystal phases in one particle can be determined from a crystal lattice image and a diffraction image obtained by a transmission electron microscope.

  The average size of the crystal phase is an average size of single crystal regions (hereinafter referred to as crystal domains) that maintain the same crystal structure included in one oxide crystal grain in a sample cross section. The shape and size of the crystal domain can be easily determined by observing a high-magnification atomic image with a transmission electron microscope and specifying a portion where the atomic arrangement changes. The average size of the crystal phase is the number average size of 50 values of the projected area equivalent circle diameter of the crystal phase obtained from observation (the diameter of a circle having the same area as the projected area of the crystal phase). At this time, the average size is obtained by averaging the sizes of the selected 50 crystal phases regardless of the types of crystal phases.

  When the average size is less than 5 nm, the proportion of the crystal phase interface in one particle is too large, and thus high OSC cannot be obtained. On the other hand, if the average size exceeds 80 nm, the crystal phase becomes too large and oxygen ions cannot easily enter and exit to the center of the crystal phase, so that a high OSC cannot be obtained.

  Moreover, it is preferable that a plurality of (at least two) crystal phases constituting the oxide particles exist as five or more domains in one oxide particle. This is because there are more crystal interfaces and more oxygen ion diffusion channels. In addition, although the upper limit of the kind of crystal phase is 5 types, it is 2-3 types as a more preferable range. If the number of constituent crystal phases exceeds 5, complicated phase separation or the like accompanying element diffusion between phases proceeds, and it may be difficult to obtain stable characteristics. The range in which more stable characteristics can be expected is 2 to 3 types.

  Moreover, the upper limit of the number of domains is about 100,000, More preferably, it is 20-70000. If the number of domains is less than 5, the oxygen diffusion path is limited, and there is a possibility that it cannot be used effectively to the inside of the crystal phase. When the number of domains is more than 100,000, oxygen diffusion tends to be rate-determined, the crystal phase inside the oxide particles may not be effectively used, and the mechanical strength of the oxide particles may increase, which is not preferable.

Oxides containing alkaline earth metal M and (Fe _1-s Ti _s ) or Co or both (Fe _1-s Ti _s ) and Co according to the invention, in particular S = 0 In some cases, the oxide containing the alkaline earth metal M and Fe or Co, or both Fe and Co is a particle having an average particle size of 0.1 μm or more and 5 μm or less. When the particle size is small, the distance to the center of the particle is small and it can withstand distortion of the crystal lattice due to the entry and exit of oxygen ions, so that a high OSC can be easily obtained. However, since a long time is required for pulverization or the like, the lower limit of the average particle diameter is set to 0.1 μm. On the other hand, if the average particle diameter exceeds 5 μm, the particles are too large, so even if a crystal interface that serves as a diffusion channel for oxygen ions exists in the particles, the oxygen ions will not diffuse quickly to the center of the particles. . Here, the particle diameter of the oxide particles can be measured by a usual method, but is measured by, for example, a laser diffraction method, a centrifugal sedimentation method, or the like. Moreover, an average particle diameter is a 50% diameter of mass accumulation particle size distribution.

Oxide particles containing alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or both (Fe _1-s Ti _s ) and Co, when S = 0, alkaline earth With respect to the average particle size of the oxide particles containing the metal M and Fe or Co, or both Fe and Co, the average size of the crystal phase constituting the oxide particles is 1/10 to 1 / More preferably, it is 100. That is, when the average particle diameter of the oxide particles is Do (nm) and the average size of the crystal phase is Dc (nm), the relationship is 1/100 ≦ Dc / Do ≦ 1/10. A high OSC is obtained. This is because, in the above relationship, an appropriate number of crystal phases constituting the oxide particles are contained, and a large number of crystal phase interfaces in which oxygen ions diffuse are formed in the oxide particles. When Dc / Do is less than 1/100, the ratio of the crystal phase interface in the oxide particles increases and the ratio of the crystal phase decreases, so that high OSC may not be obtained. In addition, when Dc / Do is more than 1/10, the ratio of the crystal phase (crystal domain) in the oxide particles is reduced, the diffusion channel necessary for oxygen diffusion is insufficient, and oxygen ions enter and exit. There is a case where the ability to relax the effect concentration is insufficient.

Regarding the oxide containing the alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or (Fe _1-s Ti _s ) and Co, the alkaline earth metal M and the (Fe _When the molar ratio of _1-s Ti _s ) and the total amount of Co is 0.1 ≦ M / ((Fe _1-s Ti _s ) + Co) ≦ 0.9, the redox width is narrow, Since higher OSC is obtained, it is preferable. If the molar ratio of M / ((Fe _1-s Ti _s ) + Co) is less than 0.1, high OSC may not be obtained when the redox width is narrowed. On the other hand, even if the molar ratio of M / ((Fe _1-s Ti _s ) + Co) exceeds 0.95, high OSC may not be obtained if the redox width is narrowed. Here, in the case of S = 0, with respect to the oxide containing the alkaline earth metal M and Fe or Co, or both Fe and Co, the alkaline earth metal M and the Fe and Co It is preferable that the molar ratio with respect to the total amount is 0.1 ≦ M / (Fe + Co) ≦ 0.9 because a higher OSC can be obtained even if the redox width is narrow. If the molar ratio of M / (Fe + Co) is less than 0.1, high OSC may not be obtained when the redox width becomes narrow. On the other hand, even if the molar ratio of M / (Fe + Co) exceeds 0.95, a high OSC may not be obtained if the redox width is narrowed.

In addition, the oxide containing the alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or both (Fe _1-s Ti _s ) and Co contains Ti (that is, And S> 0 and S ≦ 0.31), it was found that the high temperature durability (OSC reduction degree after exposure to high temperature, heat resistance) related to the OSC ability is more excellent. In particular, when used by being mixed together with an acidic oxide, if Ti is contained within the above range, the effect of improving the high-temperature durability appears remarkably. On the other hand, if the value of S exceeds 0.31, sufficient OSC cannot be obtained.

The at least two crystal phases constituting the oxide containing the alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or (Fe _1-s Ti _s ) and Co, for example, _{M l {Co, (Fe 1} -s Ti s)} by the formula expressed as m _{O n,} is at least two crystal phases l and m is different from the composition formula. In the case of S = 0, the alkaline earth metal M and at least two crystal phases constituting the oxide containing Fe or Co, or both Fe and Co are, for example, represented by the general formula: M _l (Co, _Fe) expressed as m _{O n,} l and m is at least 2 kinds of crystal phase comprising a different composition formula.

Specific _{examples, M {Co 1-z (} Fe 1-s Ti s) z} O 3-δ, M {Co 1-z (Fe 1-s Ti s) z} 2 O 4-δ, _{M 7 {Co 1-z (} Fe 1-s Ti s) z} 10 O 22-δ, M 5 {Co 1-z (Fe 1-s Ti s) z} 2 O 8-δ, M 2 {Co _{1-z (Fe 1-s} Ti s) z} O 4-δ, M 3 {Co 1-z (Fe 1-s Ti s) z} 2 O 6-δ, M 5 {Co 1-z (Fe _{1-s Ti s) z}} 14 O 26-δ, M 2 {Co 1-z (Fe 1-s Ti s) z} 6 O 11-δ, M {Co 1-z (Fe 1-s Ti s _{) z} 4 O 7-δ} , M 2 {Co 1-z (Fe 1-s Ti s) z} 14 O 22-δ, M 3 {Co 1-z (Fe 1-s Ti s) _{} 32 O 51-δ, M} 4 {Co 1-z (Fe 1-s Ti s) z} 9 O 17-δ, M {Co 1-z (Fe 1-s Ti s) z} 3 O 5- _{δ, M 3 {Co 1-} z (Fe 1-s Ti s) z} 15 O 25-δ, M 3 {Co 1-z (Fe 1-s Ti s) z} 4 O 9-δ, and M _{{Co 1-z (Fe 1} -s Ti s) z} 12 O 19-δ ( where, z is 0 to 1, [delta] is a value determined in the charge neutrality condition is satisfied.) at least, such A combination of the two.

Specific examples of the case of S = 0 _{is, M (Co 1-z Fe} z) O 3-δ, M (Co 1-z Fe z) 2 O 4-δ, M 7 (Co 1-z Fe _{z) 10 O 22-δ,} M 5 (Co 1-z Fe z) 2 O 8-δ, M 2 (Co 1-z Fe z) O 4-δ, M 3 (Co 1-z Fe z) 2 _{O 6-δ, M 5 (} Co 1-z Fe z) 14 O 26-δ, M 2 (Co 1-z Fe z) 6 O 11-δ, M (Co 1-z Fe z) 4 O 7- _{δ, M 2 (Co 1-} z Fe z) 14 O 22-δ, M 3 (Co 1-z Fe z) 32 O 51-δ, M 4 (Co 1-z Fe z) 9 O 17-δ, _{M (Co 1-z Fe z} ) 3 O 5-δ, M 3 (Co 1-z Fe z) 15 O 25-δ, M 3 (Co 1-z Fe z) 4 O 9-δ And _{M (Co 1-z Fe z} ) 12 O 19-δ ( where, z is 0 to 1, [delta] is a value determined in the charge neutrality condition is satisfied.) At least two combinations of such is there.

  Examples of the alkaline earth metal M include Be, Mg, Ca, Sr, Ba, and Ra. The alkaline earth metal can be used alone or in combination of two or more. Mg, Ca, Sr, and Ba that can easily form a complex oxide with Fe and Co are preferable. In particular, when the alkaline earth metal M is Ba or Sr, a high OSC is obtained, and Sr is preferred. Moreover, when Ca is contained in the alkaline earth metal M, the high temperature durability (the degree of OSC reduction after being exposed to a high temperature, heat resistance) is further enhanced. In particular, when the oxygen storage material of the present invention is coated on a honeycomb substrate using activated alumina as an adhesive, the improvement in the high-temperature durability is remarkable. The Ca content is a molar ratio Ca / M with respect to the total amount of the alkaline earth metal M, preferably in the range of 0.1 to 1.0, and more preferably in the range of 0.4 to 1.0.

As more preferred oxygen storage material, the crystal phase constituting the _{oxide, (Ba 1-y Sr y} ) {Co 1-z (Fe 1-s Ti s) z} O 3-δ, (Ba 1 _{-y Sr y) {Co 1-} z (Fe 1-s Ti s) z} 2 O 4-δ, (Ba 1-y Sr y) 7 {Co 1-z (Fe 1-s Ti s) z} ₁₀ O _22-δ or (Ba _{1-y S r y} ) {Co _1-z (Fe _1-s Ti _s ) _z } ₁₂ O _19-δ (where y and z are each 0 to 1, δ is a value determined so as to satisfy the charge neutrality condition).

As more preferred oxygen storage material in the case of S = 0, the crystal phase constituting the _{oxide, (Ba 1-y Sr y} ) (Co 1-z Fe z) O 3-δ, (Ba 1- _{y Sr y) (Co 1-} z Fe z) 2 O 4-δ, (Ba 1-y Sr y) 7 (Co 1-z Fe z) 10 O 22-δ, or _(Ba 1-y _Sr y) In the case of containing one or more kinds of (Co _1-z Fe _z ) ₁₂ O _19-δ (where y and z are each 0 to 1, and δ is a value determined so as to satisfy the charge neutrality condition). It is.

  Here, the range of y is not particularly limited. However, when the operation time in the rich atmosphere is long and it is desired to further improve the durability against the reducing atmosphere, 0.3 ≦ y ≦ 0.8. To. Further, the range of z is set to satisfy 0 ≦ z ≦ 0.3 in order to obtain a higher OSC. On the other hand, in order to obtain higher OSC repetition durability, 0.3 <z ≦ 1.0.

  It is preferable that a noble metal is supported on the oxide because an oxygen storage rate and an oxygen release rate are increased and an OSC start temperature is decreased. The supported noble metal is considered to promote the dissociation of oxygen molecules or cause the action of separating the absorption point and the release point of oxygen on the surface of the oxide particles, so that the above effect is considered to be obtained.

  Examples of the noble metal include Pt, Pd, Rh, Ag, Ir, In, Au, Ru, Os and the like. Among the noble metals, Pt, Pd or Rh is preferable in that a high OSC can be obtained. Moreover, it is preferable to contain Ag or Ru in the said noble metal at the point of making OSC start temperature low. Further, when one or more selected from the group consisting of Pt, Pd and Rh and one or more selected from the group consisting of Ag and Ru are mixed and supported, high OSC can be obtained while lowering the OSC start temperature. It is done.

  The particle size of the noble metal to be supported is more preferably in the range of 1 to 10 nm in terms of number average particle diameter. This is because more excellent effects can be obtained. The amount of the noble metal supported is not particularly limited, but is preferably 0.01 to 10.0% by mass with respect to the total mass of the oxide and the noble metal.

The oxygen storage material is preferably contained in an exhaust gas purification catalyst of a carburetor-type motorcycle, can effectively exhibit a high OSC function, and can obtain excellent exhaust gas purification performance. Further, oxygen storage materials used for exhaust gas purification of carburetor type motorcycles are alkaline earth metal M, (Fe _1-s Ti _s ) or Co, or both (Fe _1-s Ti _s ) and Co. An oxygen storage material containing an oxide containing the oxide, wherein the oxide is a particle having an average particle size of 0.1 μm or more and 5 μm or less, and the s is an oxygen storage material satisfying 0 ≦ s ≦ 0.31 It works effectively and exhibits excellent purification performance when incorporated in the exhaust gas purification catalyst.

An oxide containing an alkaline earth metal M and (Fe _1-s Ti _s ) or Co or both (Fe _1-s Ti _s ) and Co; and an alkaline earth metal M and Fe or Co or Both of the oxides containing both Fe and Co (corresponding to the case of S = 0) are solid phase reaction methods, liquid phase methods such as coprecipitation methods and sol-gel methods, chemical vapor deposition methods, It can be manufactured by any method such as a laser ablation method. A production method by a solid phase reaction method and a coprecipitation method will be described below.

  In the production by the solid-phase reaction method, as starting materials, oxides, hydroxides, carbonates, nitrates, organic acid salts, sulfates, etc. of alkaline earth metals M, oxides of Co and Fe, hydroxides, nitrates, Sulfates and Ti oxides can be used. The starting material powder of M and the starting material of Co and Fe (when Ti is included, Ti starting material) are weighed and mixed so as to have a desired composition, and then in the range of 700 to 1300 ° C. Calcination inside. Mixing of the starting materials may be either wet or dry, and any existing method such as mortar mixing, ball mill, planetary ball mill or the like may be used. The oxide obtained by calcination is used after being pulverized and classified in some cases.

  In the production by the coprecipitation method, M nitrates, sulfates, organic acid salts, etc., Co, Fe and Ti nitrates, sulfates, hydroxides, chlorides, chelate complexes, organic acid salts, etc. can be used as starting materials. . The M starting material and the Co and Fe starting materials (when Ti is included, Ti starting materials) are weighed to have a desired composition and dissolved in water. A pH adjuster is added to coprecipitate the dissolved M, Co, Fe, and Ti ions with a neutral to basic pH of the solution. The coprecipitate is separated and washed by filtration or centrifugation, dried, and calcined in the range of 700 to 1300 ° C. The oxide obtained by calcination is used after being pulverized and classified as necessary.

In order for the oxide particles to have at least two crystal phases, the composition of the starting material is set to a composition ratio different from the stoichiometric composition of the crystal phase. For example, M: {Co + (Fe _1-s Ti _s )} = 1: 2, 7:10, 5: 2, 2: 1, 3: 2, 5:14, 2: 6, 1: 4, 1: 7, 3:32, 4: 3, 1: 3, 1: 5, 3: 4, 1:12, or when S = 0, M: (Co + Fe) = 1: 2, 7:10, 5: 2, 2: 1, 3: 2, 5:14, 2: 6, 1: 4, 1: 7, 3:32, 4: 3, 1: 3, 1: 5, 3: 4, 1:12 Because of the stoichiometric ratio, the composition ratio is different from these. Here, the composition ratio different from the stoichiometric ratio is a composition deviating by 10% or more from the composition of the stoichiometric ratio.

  As described above, when the starting materials are mixed at a composition ratio different from the stoichiometric ratio and the rate of temperature increase to the calcining temperature is 1 ° C./min to 20 ° C./min, one oxide particle is included. At least two kinds of crystal phases are easily formed with an average size of 5 nm or more and 80 nm or less.

In the above production method, the composition range of the starting material is such that the molar ratio of the alkaline earth metal M and the total amount of (Fe _1-s Ti _s ) and Co is 0.09 ≦ M / {(Fe ₁ More preferably, _−s Ti _s ) + Co} ≦ 0.95. In the case of S = 0, it is more preferable that the molar ratio between the alkaline earth metal M and the total amount of Fe and Co is 0.09 ≦ M / (Fe + Co) ≦ 0.95.

Oxide particles containing alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or (Fe _1-s Ti _s ) and Co, or an alkali in the case of S = 0 The method for supporting the noble metal on the oxide particles containing the earth metal M and Fe or Co, or both Fe and Co is not particularly limited, but for example, it can be supported by the following method. A water-soluble noble metal salt (for example, nitrate, chloride, acetate, sulfate, etc.) is dissolved in water. In the obtained solution, the alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or an oxide containing both (Fe _1-s Ti _s ) and Co, or the alkali An oxide powder containing the earth metal M and Fe or Co, or both Fe and Co is added and dispersed by stirring, ultrasonic dispersion, or the like. After removing the water from the suspension and drying, the catalyst metal can be supported by heat treatment in the range of 400 to 900 ° C. A more preferable range of the heat treatment temperature is 450 to 700 ° C. Further, a colloidal solution of a noble metal can be used instead of using the solution of the noble metal salt.

  The OSC may be measured by an oxygen pulse method using TPR (Temperature Programmed Reduction) and measured by an ordinary TG-DTA (Thermogravimetry-Differential Thermal Analysis). Also good.

  In the oxygen pulse method, oxygen is released in a reducing atmosphere (for example, a mixed gas of hydrogen and argon) while heating the sample from room temperature to the measurement temperature, and the atmosphere is once replaced with an inert gas such as argon. Can measure OSC by mixing oxygen in a pulsed manner with argon and determining the total amount of oxygen introduced up to the breakthrough point. On the other hand, in TG-DTA, oxygen is released from the sample at each temperature first in a reducing atmosphere, and the convergence value of the sample mass is obtained. Then, this time, it switches to oxidizing atmosphere (atmosphere, mixed gas of oxygen and argon), the convergence value of a sample mass is again calculated | required, and OSC can be calculated | required from the difference of these two masses.

  In measuring the OSC durability of a sample, evaluation can be performed by repeating the above-described reduction and oxidation cycles while maintaining the sample temperature constant, and determining the change in OSC with the number of cycles.

As shown in the conceptual diagram of FIG. 1, the exhaust gas purifying catalyst of the present invention has M {Co _1-x (Fe _1-s Ti) supporting one or more kinds of noble metals selected from the group consisting of Pd, Ag and Rh. (case of _{s = 0, M (Co 1} -x Fe x) s) x} y O 4-δ and y _{O 4-δ)} composite oxide (A1) or the above oxygen storage material (A2), And an oxide (B) having an oxygen storage capacity and supporting one or more kinds of noble metals selected from the group consisting of Pd, Ag and Rh. Even with the composite oxide (A1) supporting a precious metal not containing Pt, the oxidation reaction of CO and HC proceeds sufficiently, but the reduction reaction of NO _x is slight. Also, only the above-mentioned oxygen storage material (A2), it may not obtain a high catalytic activity as a three-way catalyst, especially if high promoting effect can not be obtained for the reduction reaction of NO _x (NO _x purification) There is. On the other hand, all of the oxidation reaction of CO, the oxidation reaction of HC, and the NO _x reduction reaction proceed even with the oxide (B) having an oxygen storage ability that supports a noble metal that does not use Pt, but the space velocity ( If the SV) is increased, it cannot be sufficiently purified and the catalytic activity is insufficient. However, the catalyst of the present invention including both of them has a catalyst performance higher than the performance obtained by simply adding the performances of both catalysts, and exhibits a high purification performance equal to or higher than the conventional three-way catalyst performance level.

Such synergistic high catalytic performance is achieved by the oxidation reaction of CO to CO ₂ and the partial oxidation reaction of HC on the surface of the composite oxide (A1) supporting the noble metal or the oxygen storage material (A2). It is presumed that the partially oxidized HC (HCO _x ) mainly reduces NO _x on the surface of the oxide (B) having the ability to store oxygen and supporting the noble metal.

In other words, acts as the oxide (B) alone three-way catalyst having an oxygen storage capacity supporting the noble _{metal, M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ (s = If _0, the _{M (Co 1-x Fe x} ) y O 4-δ) composite oxide (A1) and the oxygen storage material (A2) is present, by the action of the following (i) ~ (iii) efficiently CO, it is estimated that can purify HC, and NO _x.
(I) producing a large amount of partially oxidized HC effective in reducing NO _x ;
(Ii) CO and oxidation reaction of the HC _{M {Co 1-x (Fe} 1-s Ti s) x} For _{y O 4-δ (s =} 0, M (Co 1-x Fe x) y O 4 since occurs on the surface of the composite oxide of _-δ) (A1) and oxygen storage material (A2) in the oxide (B) surface reduces the load on the oxidation reaction, it can be widely used in _the NO _x reduction reaction;
(Iii) In addition to the composite oxide (A1) or the oxygen storage material (A2), the oxide (B) also has an oxygen storage capacity, and has different temperature characteristics and atmosphere dependence. Work more effectively while complementarily complementing each other.

It is one or more elements in the oxide _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ, where M is selected from the group consisting of Ca, Sr and Ba of the present invention , X is 0 to 1, and y is 1 to 2. s is 0 to 0.31, and δ is a value determined so as to satisfy the charge neutrality condition. Here, the composition formula represents the ratio of metal elements, and the ratio of oxygen (4-δ) is determined by the charge neutrality condition. That is, here, the value of | δ | may exceed 1 depending on the ratio of metal elements. Therefore, where the oxygen ratio (4-δ) is w and the composition formula is M {Co _1-x (Fe _1-s Ti _s ) _x } _y O _w (w is determined to satisfy the charge neutrality condition. Value)).

  x is preferably in the range of 0.2 to 1 and more preferably in the range of 0.9 to 1 in terms of catalyst activity. This is because the durability of the catalyst tends to increase as the proportion of Fe increases, and in particular, a decrease in catalyst activity after durability can be suppressed.

  The heat resistance improves as the substitution ratio s with Ti increases. In particular, when mixed with an acidic oxide and used, if the above-mentioned proportion of Ti is contained, the effect of improving high-temperature durability appears remarkably. If the substitution ratio s by Ti becomes too large, the catalyst performance (particularly the oxidation catalyst performance) tends to decrease, so the upper limit of the substitution ratio s is set to 0.31. From the viewpoint of heat resistance and catalyst performance, the value of s is more preferably from 0.01 to 0.15, and even more preferably from 0.02 to 0.1.

  Since y tends to be superior in oxygen storage capacity at high temperatures as it is large, and tends to be excellent in oxygen storage capacity at low temperatures as y is small, it is appropriately selected within the range of 1-2 depending on the application. If y is smaller than 1, the oxygen storage capacity becomes small, and an excellent exhaust gas purification capacity cannot be obtained. On the other hand, when y exceeds 1, the oxygen storage ability at a low temperature is remarkably lowered, so that an excellent exhaust gas purification ability cannot be obtained. Further, when y is within the above range, the synergistic effect in combination with the oxide (B) becomes remarkable.

Examples of specific _{compositions, M {Co 1-x (} Fe 1-s Ti s) x} O 3-δ (M {Co 1-x (Fe 1-s Ti s) x} O w), _{M {Co 1-x (Fe} 1-s Ti s) x} 2 O 4-δ (M {Co 1-x (Fe 1-s Ti s) x} 2 O w), M 7 {Co 1-x _{(Fe 1-s Ti s)} x} 10 O 22-δ (M 7 {Co 1-x (Fe 1-s Ti s) x} 10 O w), M 5 {Co 1-x (Fe 1-s _{Ti s) x} 14 O 26} -δ (M 5 {Co 1-x (Fe 1-s Ti s) x} 14 O w), M 2 {Co 1-x (Fe 1-s Ti s) x} _{6 O 11-δ (M 2} {Co 1-x (Fe 1-s Ti s) x} 6 O w), M {Co 1-x (Fe 1-s Ti s) x} 3 O _{-Δ (M {Co 1-x} (Fe 1-s Ti s) x} 3 O w), and _{M 3 {Co 1-x (} Fe 1-s Ti s) x} 4 O 9-δ (M 3 _{{Co 1-x (Fe 1} -s Ti s) w} 4 O z) and the like are included. _Furthermore, the structure of the _{M {Co 1-x (Fe} 1-s Ti s) x} composite oxide of y _{O 4-δ} is not particularly limited, it has a perovskite structure is at least partially Is preferred.

In the case of S = 0, the oxide _is represented as _{M (Co 1-x Fe x} ) y O 4-δ. Similar to the _above, in the _{M (Co 1-x Fe x} ) y O 4-δ, a least one element M is selected from the group consisting of Ca, Sr and Ba, x is 0-1, y is 1-2. δ is a value determined so as to satisfy the charge neutrality condition. Here, the composition formula represents the ratio of the metal element, and the ratio of oxygen (4-δ) is determined by the charge neutrality condition. That is, here, the value of | δ | may exceed 1 depending on the ratio of metal elements. Therefore, the oxygen ratio of (4-[delta]) as w, the composition formula _{M (Co 1-x Fe x} ) y O w (w is a value determined in the charge neutrality condition is satisfied.) Expressed as You can also

  x is particularly preferably in the range of 0.2 to 1 and more preferably in the range of 0.9 to 1 in terms of catalyst activity. Since y tends to be superior in oxygen storage capacity at high temperature as it is large, and tends to be excellent in oxygen storage capacity at low temperature as y is small, it can be appropriately selected within the above range depending on the application. If y is smaller than 1, the oxygen storage capacity is reduced, and thus an excellent exhaust gas purification ability cannot be obtained. On the other hand, if y exceeds 1, the oxygen storage capacity at low temperatures is significantly reduced, so that an excellent exhaust gas purification capacity cannot be obtained. Further, when y is within the above range, the synergistic effect in combination with the oxide (B) becomes remarkable.

Examples of specific _{composition, M (Co 1-x Fe} x) O 3-δ (M (Co 1-x Fe x) O w), M (Co 1-x Fe x) 2 O 4-δ _{(M (Co 1-x Fe} x) 2 O w), M 7 (Co 1-x Fe x) 10 O 22-δ (M 7 (Co 1-x Fe x) 10 O w), M 5 (Co _{1-x Fe x) 14 O} 26-δ (M 5 (Co 1-x Fe x) 14 O w), M 2 (Co 1-x Fe x) 6 O 11-δ (M 2 (Co 1-x _{Fe x) 6 O w),} M (Co 1-x Fe x) 3 O 5-δ (M (Co 1-x Fe x) 3 O w), and _{M 3 (Co 1-x Fe} x) 4 O _{9-δ (M 3 (Co} 1-x Fe x) 4 O w) are included, and the like. Further, the structure of the composite oxide of M (Co _1-x Fe _x ) _y O _4-δ is not particularly limited, but it is preferable that at least a part thereof has a perovskite structure.

Wherein _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ, and the case for S = 0 _M of _{(Co 1-x Fe x)} y O 4-δ complex oxide The particle size is preferably in the range of 0.5 to 5.0 μm in average particle size in order to effectively support the noble metal. If it becomes smaller than this, it will become easy to sinter by use at high temperature, and there exists a possibility that an oxide particle and a noble metal may become coarse easily. On the other hand, if the particle size is too large, the fixing strength of the catalyst layer is lowered, and there is a possibility that the particles are easily peeled off. The average particle diameter is measured, for example, using a laser diffraction particle size distribution measuring device, and is obtained from the median value (median).

Wherein _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ, and the case for S = 0 _M of _{(Co 1-x Fe x)} y O 4-δ complex oxide The specific surface area of the particles is preferably in the range of 1 to ²⁰ m ² / g. If the specific surface area is smaller than this, the precious metal is difficult to disperse and may not function effectively. Moreover, if the specific surface area is about 20 m ² / g, a large oxygen storage capacity can be exhibited. Considering the concern of sintering too much and sintering too much, this level is considered sufficient. The specific surface area is determined by, for example, the BET method using nitrogen gas adsorption.

Wherein _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ, and the case for _{S = 0 M (Co 1-} x Fe x) composite oxides y _{O 4-δ} The noble metal supported on is one or more kinds of noble metals selected from the group consisting of Pd, Ag and Rh, more preferably Pd. When these noble metals are supported on an oxide, the physical properties of the oxide surface change due to the interaction between the two, and the oxygen storage capacity is further improved. In particular, it was confirmed that the oxide (A1) has a large effect by supporting Pd. The particle size of the noble metal to be supported is preferably in the range of 1 to 3 nm in terms of average particle size. If the particle size is to be made smaller than this, a technically special operation is required, which may increase the cost. On the other hand, if the particle size is larger than this, the surface area of the noble metal may be reduced and the activity may be reduced. The average particle diameter is determined by the method described above.

  The amount of the noble metal supported is not particularly limited, but is preferably 0.1 to 2.0 parts by mass with respect to 100 parts by mass of the composite oxide. If the supported amount is less than this, the volume of the oxide becomes unnecessarily large, and the gas to be purified may not reach the depth of the catalyst layer, so there is a possibility that all precious metals cannot be used effectively. There is a case. Further, if the loading amount is larger than this, aggregation between the noble metals is likely to occur, and there is a possibility that the activity of the noble metal is easily reduced.

The oxide (B) has an oxygen storage capacity. The oxygen storage capacity of the oxide (B) is preferably 50 μmol-O ₂ / g or more at 500 ° C., but does not necessarily have a large oxygen storage capacity. This is because the composite oxide (A1) and the oxygen storage material (A2) already have an oxygen storage capacity, and the oxide (B) only needs to compensate for this, and the burden is light.

  As described above, the oxygen storage capacity may be measured by an oxygen pulse method using TPR (Temperature Programmed Reduction), or by an ordinary thermobalance method. In the case of the thermobalance method, the sample atmosphere can be switched alternately between air and a reducing atmosphere such as 4% hydrogen-containing argon, and the stable mass can be measured in each atmosphere for about 1 hour, and the mass difference can be obtained. . Since the oxygen storage capacity varies depending on the temperature, it is preferable to measure the oxygen storage capacity at several points by changing the measurement temperature in the expected temperature range of use of the catalyst.

From the above circumstances, materials that can be selected as the oxide (B) having oxygen storage ability are relatively wide. Examples of materials that can be used as the oxide (B) include cerium-containing oxides such as Ce—ZrO, Ce—CaO, Ce—rare earth (Sm, Gd, Y, La), Ce—Zr—rare earth, and the like. Zr-rare earth (Y, Sc, Yb, Nd, Sm, Gd), Zr-CaO, etc. which are zirconium-containing oxides; Bi-rare earth (Y, Gd), Bi-Nb ₂ O ₅ which are bismuth-containing oxides , Bi-WO _3, etc.; pyrochlore type oxide _{(La 2 Zr 2 O 7,} Sm 2 Zr 2 O 7, Gd 2 Zr 2 O 7, Gd 2 (Zr, Ti) 2 O 7, Y 2 (Zr, Ti ) ₂ O ₇ ) and the like.

Among these, in particular, an oxide containing cerium has a region having a higher oxygen storage capacity than the composite oxide (A1) in a low temperature region of 300 ° C. or lower when a noble metal is supported. Therefore, since it acts complementarily with the composite oxide (A1), it is preferable as the oxide (B). A more preferred oxide (B), oxide containing cerium and zirconium a _{(Ce z Zr 1-z)} O 2-δ, is z oxide is 0.4 to 1.0 .

  The particle diameter of the oxide (B) is not particularly limited, but is an average particle diameter, for example, 0.01 to 5.0 μm, and preferably 0.5 to 5.0 μm. When the average particle size is smaller than this, sintering at high temperatures is likely to cause sintering, and the oxide particles and the noble metal are likely to be coarsened. On the other hand, when the average particle size is larger than this, the fixing strength of the catalyst layer is lowered, and there is a possibility that it is easily peeled off. The average particle diameter is determined by the method described above.

The specific surface area of the oxide (B) is not particularly limited as long exhibit sufficient oxygen storage capacity, usually from 1~80m ² / g, it is preferably in the range of 1-20 m ² / g. If the specific surface area is smaller than this, the dispersion of the noble metal may be deteriorated, and there is a possibility that it will not function effectively. In addition, even if the specific surface area is about 20 m ² / g, since a large oxygen storage capacity can be exhibited, this level is considered to be sufficient in consideration of the concern that the sintering may proceed too much due to being too large. The specific surface area is determined by the method described above.

  The noble metal supported on the oxide (B) having the oxygen storage ability is selected from the group consisting of Pd, Ag and Rh, and more preferably Rh. When these noble metals are supported on an oxide, the physical properties of the oxide surface change due to the interaction between the two, and the oxygen storage capacity is further improved. Further, as shown in the conceptual diagram of the purification mechanism shown in FIG. 1, it is presumed that there is a role sharing of the oxide, and it is preferable to support Pd on the oxide (A1). Therefore, it was confirmed from the combination effect that it is more effective to carry Rh.

  The particle size of the noble metal to be supported is preferably in the range of 1 to 3 nm in terms of average particle size. If the particle size is to be made smaller than this, a technically special operation is required, which may increase the cost. On the other hand, if the particle size is larger than this, the surface area of the noble metal may be reduced and the activity may be reduced.

  The amount of the noble metal supported is not particularly limited, but is preferably 0.1 to 1.5 parts by mass with respect to 100 parts by mass of the oxide (B). If the supported amount is smaller than this, the volume of the oxide becomes excessively large, and the gas to be purified may not reach the depth of the catalyst layer, so there is a possibility that a part of the noble metal cannot be used effectively. There is. Further, if the loading amount is larger than this, aggregation between the noble metals may easily occur, and the activity of the noble metal may be easily reduced.

In particular, (in the case of _{S = 0, M (Co 1} -x Fe x) y O 4-δ) carrying _{Pd M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ complex The combination of the oxide (A1) and the oxide (B) supporting Rh clarifies the role of catalytic activity as shown in FIG. 1, and the catalytic activity for each reaction becomes higher, that is, , (A1) and (B) have higher catalytic selectivity, and the overall catalytic activity for exhaust gas purification becomes higher.

(For _{S = 0, M (Co 1} -x Fe x) y O 4-δ) M {Co 1-x (Fe 1-s Ti s) x} y O 4-δ supporting the noble metal composite oxide The mass ratio of (A1) or the oxygen storage material (A2) to the oxide (B) having an oxygen storage capacity supporting a noble metal is A / B (where A is the mass of A1 or A2, and B Is the mass of B.) The mass ratio is preferably 0.1 to 10. In the mass ratio is less than 0.1, the precious metal was supported _{M {Co 1-x (Fe} 1-s Ti s) x} For _{y O 4-δ (S =} 0, M (Co 1-x Fe x _{) y} O _3-δ) to the composite oxide (A1) or oxygen storage material (A2) is reduced, in some cases higher catalytic activity can not be obtained. On the other hand, when the mass ratio exceeds 10, since the oxide supporting the noble metal (B) is reduced, there is a case where _the NO _x purification is reduced.

  The catalyst of the present invention has a sufficient purification performance even when a catalyst material such as activated alumina supporting a noble metal, which is well known, is not included. Therefore, it is suggested that it has a mechanism different from the catalyst mechanism of the conventional catalyst material. Of course, the catalyst of the present invention may be used by including activated alumina supporting a noble metal.

Of the present invention _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ, and the case for _{S = 0 M (Co 1-} x Fe x) y O 4-δ complex oxide The product can be produced by an arbitrary method such as a solid phase reaction method, a liquid phase method such as a coprecipitation method or a sol-gel method, a chemical vapor deposition method, or a laser ablation method. A production method by a solid phase reaction method and a coprecipitation method will be described below.

In the production by the solid phase reaction method, as starting materials, oxides of M, hydroxides, carbonates, nitrates, organic acid salts, sulfates, oxides of Co and Fe, hydroxides, nitrates, sulfates, Ti Oxide etc. are used. The starting material powder of M and the starting material of Co and Fe (when Ti is included, Ti starting material) are weighed and mixed so as to have a desired composition, and then within a range of 600 to 1200 ° C. Calcinate with. Mixing of the starting materials may be either wet or dry, and may be performed by any existing method such as mortar mixing, ball mill, planetary ball mill and the like. (For _{S = 0, M (Co 1} -x Fe x) y O 4-δ) calcining obtained _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ complex The oxide is used after being pulverized and optionally classified.

In the production by the coprecipitation method, M nitrates, sulfates, organic acid salts, etc., Co, Fe and Ti nitrates, sulfates, hydroxides, chlorides, chelate complexes, organic acid salts, etc. can be used as starting materials. . The M starting material and the Co and Fe starting materials (when Ti is included, Ti starting materials) are weighed to have a desired composition and dissolved in water. A pH adjuster is added to make the pH of the solution neutral to basic, so that dissolved M, Co, Fe, and Ti ions are co-precipitated. The coprecipitate is separated and washed by filtration or centrifugation, dried, and calcined in the range of 600 to 1200 ° C. (For _{S = 0, M (Co 1} -x Fe x) y O 4-δ) calcining obtained _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ complex The oxide is used after being pulverized and classified as necessary.

Noble _{metal, M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ complex oxide, and a case of _{S = 0 M (Co 1-} x Fe x) y O 4- _The method for supporting the _δ composite oxide is not particularly limited. For example, it can be supported by the following method. Water-soluble noble metal salts such as nitrates, chlorides, acetates, sulfates, etc. are dissolved in water. To the resulting _{solution, M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ ( For _{S = 0, M (Co 1} -x Fe x) y O 4-δ) The composite oxide powder is added and dispersed by stirring, ultrasonic dispersion or the like. After removing the water from the suspended solution and drying it, heat treatment was performed in the range of 400 to 900 ° C., and M {Co _1-x (Fe _1-s Ti _s ) _x } _y O ₄₋ supporting noble metal was supported. (for _{S = 0, M (Co 1} -x Fe x) y O 4-δ) δ complex oxide (A1) can be produced.

The method for supporting the noble metal on the oxide (B) is not particularly limited. For example, the _{M {Co 1-x (Fe} 1-s Ti s) x} ( For _{S = 0, M (Co 1} -x Fe x) y O 4-δ) y O 4-δ complex oxide It can be produced by the same method as in the case.

Noble metal _{carrying, M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ, or a case of _{S = 0 M (Co 1-} x Fe x) y O 4-δ The composite oxide (A1) and the oxide (B) having an oxygen storage capacity supporting a noble metal can be mixed to obtain the exhaust gas purifying catalyst of the present invention. The mixing may be either wet or dry, and any existing method such as mortar mixing, ball mill, planetary ball mill, etc. may be used.

  The exhaust gas-purifying catalyst of the present invention can be made into a honeycomb catalyst structure for exhaust gas purification by wash-coating a ceramic or metal honeycomb. The ceramic honeycomb that can be used in the present invention is not particularly limited, and examples thereof include cordierite honeycombs and silicon carbide honeycombs. The metal honeycomb that can be used in the present invention is not particularly limited, and examples thereof include a stainless honeycomb.

  When the exhaust gas-purifying catalyst of the present invention is wash-coated on a honeycomb, first, a slurry in which the catalyst, the binder and the like are dispersed is prepared, and the honeycomb is immersed therein. Examples of the binder include aluminum nitrate, colloidal alumina, and an organic binder. Next, excess slurry on the honeycomb surface is removed by a method such as blowing off, and after drying, heat treatment is performed in the atmosphere at a temperature of 500 to 900 ° C. for several hours. The slurry may be sucked up by devising a jig for mounting the honeycomb so that the slurry is applied only to the inner wall of the honeycomb.

  The exhaust gas purifying catalyst is more preferably used for exhaust gas purification of a carburetor type motorcycle. Excellent exhaust gas purification performance is exhibited by the complementary action of the composite oxide (A1) or oxygen storage material (A2) and the oxide (B). In a carburetor type motorcycle, a fuel valve and an air valve are opened and closed in accordance with a throttle opening to adjust the speed. Since the air-fuel ratio A / F greatly fluctuates depending on the running pattern, there are cases where the conventional catalyst purification window deviates for a relatively long time. That is, the conventional three-way catalyst has a small apparent purification window because the oxygen storage capacity of a carburetor type motorcycle is not sufficient.

  As described above, in the conventional three-way catalyst, it is difficult to widen the purification window in the carburetor type motorcycle, whereas in the catalyst of the present invention, the oxygen storage capacity is sufficient and the composite oxide (A1 ) Or the oxygen storage material (A2) and the oxide (B) as a complementary action, the purification window in the carburetor type motorcycle can be widened, and excellent exhaust gas purification performance can be obtained.

An exhaust gas purification catalyst used for exhaust gas purification of a carburetor-type motorcycle is an oxide M {Co _1-x (Fe) supporting one or more precious metals selected from the group consisting of Pd, Ag, and Rh. _1-s Ti _s ) _x } _y O _4-δ (A1), or an oxide carrying one or more noble metals selected from the group consisting of the oxygen storage material (A2) and Pd, Ag, and Rh Even a catalyst containing (B) works effectively, and when it is incorporated in the exhaust gas purification catalyst, it exhibits better purification performance.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

[Example 1]
An oxide having oxygen storage capacity was produced by the following method.
Carbonates were used as the raw materials for Ca, Sr, and Ba, and oxides were used as the raw materials for Mg, Co, and Fe. The raw material was weighed at a predetermined molar ratio, added to isopropyl alcohol (dispersion medium), and wet-mixed while pulverizing with a ball mill to obtain a slurry. The slurry was separated from the slurry by a suction filter and dried at approximately 120 ° C. for 1 hour. The obtained dried product was pulverized and then heated at the rate of temperature increase shown in Tables 1 to 4 up to the calcination temperature shown in Table 1 with an electric furnace.

  After maintaining the furnace temperature at the calcining temperature for 5 hours and calcining, the heater of the electric furnace was stopped and the furnace was cooled to room temperature. The above calcination was performed in an air atmosphere. The fired product was pulverized and then dry-pulverized with an automatic mortar to obtain an oxide having the composition shown in Table 1. The composition indicates the amount charged in the production, and it was confirmed by chemical analysis that the amount of the metal element in the raw material compound and the amount of the metal element in the product coincided.

  The powder X-ray diffraction pattern of the obtained sample was measured, and the crystal phase contained in the sample was identified and the content of each crystal phase was calculated. Next, the sample was observed with a transmission electron microscope (TEM), and the average particle diameter of the oxide particles and the average size of the crystal phase were measured. In this measurement, 40 or more oxide particles are selected from different positions of the powder sample, and a high-magnification atomic image observation is performed by TEM, and the size and number of crystal domains are determined by specifying the portion where the atomic arrangement changes. Were determined. The average number of crystal domains contained in one oxide particle was calculated from the average size of the obtained crystal phase and the average particle size of the oxide particles. No. For the 1-1 oxide particles, direct observation of the domains by TEM and estimation of the intragranular domains confirmed that it had 26 domains on average, which was almost the same as the above calculation results. It was.

[Example 2]
Next, a noble metal was supported on the oxide as follows. A predetermined amount of each noble metal nitrate shown in Tables 5 and 6 was weighed and dissolved in pure water to make an aqueous solution of about 100 mL. The aqueous solution and 100 g of the oxide powder were placed in a rotary evaporator and subjected to defoaming while rotating and stirring at room temperature and under reduced pressure. Furthermore, after returning to normal pressure and heating to about 60-70 ° C., the pressure was reduced, followed by dehydration and drying. After cooling to room temperature, the pressure was returned to normal pressure, the solid was taken out, and dried at about 180 ° C. for 2 hours. The obtained product was heat treated in the atmosphere at 650 ° C. for 5 hours, and then crushed into granules. By the above operation, an oxide sample carrying a noble metal was obtained. It should be noted that no significant change in the particle size of the oxide particles, the composition of the oxide crystal phase, or the size was observed by this operation.

  The OSC of the sample was measured by the following method using TG-DTA. 20 mg of a sample was weighed and placed in a platinum sample pan. Moreover, (alpha)-alumina was put into the platinum dish as a standard sample, and it adjusted so that the mass difference with a sample might be less than 1 mg. A sample and a standard sample were set in the apparatus, and heated to 500 ° C. at 10 ° C. per minute while flowing air as an atmospheric gas. When the temperature reached 500 ° C., the atmosphere gas was switched to an argon mixed gas containing 4% hydrogen or nitrogen gas, and the sample mass was measured by holding for 1 hour. Subsequently, the atmosphere gas was switched to air, and the sample mass was measured while maintaining the same for 1 hour, and the OSC was obtained from the difference between the two measured masses. The atmospheric gas was controlled by a mass flow controller at a flow rate of 200 mL per minute. In addition, after repeating this cycle in an oxidizing / reducing atmosphere 100 times, the 100th OSC was determined. The results are shown in Tables 7-10.

From the results of Tables 1 to 10, the following was clearly understood, and the effects of the present invention were confirmed.
(1) The oxide phase containing an alkaline earth metal M and Fe or Co, or both Fe and Co has an average particle diameter of 0.1 μm or more and 5 μm or less, and the oxide particles are at least 2 When the particles were composed of seed crystal phases, and the average size of the crystal phases was 5 nm or more and 80 nm or less, the OSC showed a high value. It is considered that oxygen enters and exits effectively because there are a plurality of crystal phases having different structures present in the oxide grains and the average size thereof is in an appropriate range.

  (2) When the oxide is such that the molar ratio of the alkaline earth metal M and the total amount of Fe and Co is 0.1 ≦ M / (Fe + Co) ≦ 0.9, the OSC further increases. Show. This is probably because a higher OSC was obtained even when the redox width was narrow due to the balance of the functions of the alkaline earth metal M, Fe and Co.

  (3) When noble metal is supported on the oxide, OSC shows a higher value. This is presumably because when the noble metal was supported on the oxide, the oxygen storage rate and oxygen release rate increased, and the OSC start temperature decreased.

  (4) Furthermore, if the noble metal is one or more selected from the group consisting of Pt, Pd, and Rh, the OSC further shows a high value. This is probably because these elements in the noble metal increase the oxygen storage rate and the oxygen release rate. Moreover, even if the noble metal contains one or more selected from the group consisting of Ag and Ru, OSC shows a high value at 300 ° C. This is probably because these elements in the noble metal lower the OSC start temperature.

[Example 3]
Carbonates were used as raw materials for Ca, Sr, and Ba, and oxides were used as raw materials for Mg, Co, Fe, and Ti. The raw materials were weighed at a predetermined molar ratio, added to isopropyl alcohol (dispersion medium), and wet-mixed while pulverizing with a ball mill to obtain a slurry. The solid content was separated from the obtained slurry by a suction filter and dried at about 120 ° C. for 1 hour. The obtained dried product was pulverized, and then heated to the calcination temperature at the heating rate shown in Tables 11 to 13 in an electric furnace. After maintaining the furnace temperature at the calcining temperature for 5 hours and calcining, the heater of the electric furnace was stopped and the furnace was cooled to room temperature. The above calcination was performed in an air atmosphere. The fired product was pulverized and then dry-pulverized with an automatic mortar to obtain oxides having the compositions shown in Tables 11 to 13. As the composition, the amount charged in the production was used, and it was confirmed by chemical analysis that the amount of the metal element in the compound charged and that in the product coincided with each other.

  The powder X-ray diffraction pattern of the obtained sample was measured, and the crystal phase contained in the sample was identified and the content of each crystal phase was calculated. Next, the sample was observed with a transmission electron microscope (TEM), and the average particle diameter of the oxide particles and the average size of the crystal phase were measured. In this measurement, 40 or more oxide particles are selected from different positions of the powder sample, and a high-magnification atomic image observation is performed by TEM, and the size and number of crystal domains are determined by specifying the portion where the atomic arrangement changes. Were determined. The average number of crystal domains contained in one oxide particle was calculated from the average size of the obtained crystal phase and the average particle size of the oxide particles. In addition, No. With respect to the oxide particles of 3-1, direct observation of the domains was performed with TEM, and the domains in the grains were counted. As a result, it was confirmed that the particles had an average of 25 domains, which was consistent with the above calculation results.

[Example 4]
Next, a noble metal was supported on the oxide as follows. A predetermined amount of each noble metal nitrate shown in Table 14 and Table 15 was weighed and dissolved in pure water to make an aqueous solution of about 100 mL. The aqueous solution and 100 g of the oxide powder were put in a rotary evaporator, and first, defoamed while rotating and stirring at room temperature and under reduced pressure. After returning to normal pressure and heating to about 60-70 ° C., the pressure was reduced and dewatered and dried. After cooling to room temperature, the pressure was returned to normal pressure, the solid was taken out, and dried at about 180 ° C. for 2 hours. The obtained product was heat treated in the atmosphere at 650 ° C. for 5 hours, and then crushed into granules. By the above operation, an oxide sample carrying a noble metal was obtained. Note that no change in the particle size of the oxide particles, the composition of the crystal phase of the oxide, or the size was observed by this operation.

  The OSC of the sample was measured in the same manner as described above. The results are shown in Tables 16-19.

From the results shown in Tables 16 to 19, the following was clearly understood, and the effects of the present invention were confirmed.
(1) Oxidation containing an alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or both (Fe _1-s Ti _s ) and Co, when Ti of S> 0 is contained The average particle diameter of the physical phase is 0.1 μm or more and 5 μm or less, the oxide particles are particles composed of at least two crystal phases, and the average size of the crystal phase is 5 nm or more and 80 nm or less, If the Ti content is S ≦ 0.31, the OSC shows a high value. It is considered that oxygen enters and exits effectively because there are a plurality of crystal phases having different structures present in the oxide grains and the average size thereof is in an appropriate range.

(2) The oxide has a molar ratio of the alkaline earth metal M and the total amount of (Fe _1-s Ti _s ) and Co of 0.1 ≦ M / {(Fe _1-s Ti _s ) + Co } ≦ 0.9 indicates a higher OSC value. This is probably because a higher OSC was obtained even when the redox width was narrow due to the balance of the functions of the alkaline earth metal M, (Fe _1-s Ti _s ), and Co.

  (3) When noble metal is supported on the oxide, OSC shows a higher value. This is presumably because when the noble metal was supported on the oxide, the oxygen storage rate and oxygen release rate increased, and the OSC start temperature decreased.

  (4) Furthermore, if the noble metal is one or more selected from the group consisting of Pt, Pd, and Rh, the OSC further shows a high value. This is probably because these elements in the noble metal increase the oxygen storage rate and the oxygen release rate. Moreover, even if the noble metal contains one or more selected from the group consisting of Ag and Ru, OSC shows a high value at 300 ° C. This is probably because these elements in the noble metal lower the OSC start temperature.

[Example 5]
Furthermore, even after heat-treating the samples of Examples 1 to 4 in air at 1050 ° C. for 85 hours, OSC measurement was performed by the same method as described above to evaluate high-temperature heat resistance. Table 20 shows a representative example of the results. In Table 20, the OSC value repeated 100 times with Air-4% H ₂ is defined as 100, and the decrease rate of the OSC is shown as a percentage. It can be seen that the rate of decrease in OSC is smaller in the case of containing Ti even after the heat treatment exceeding 1000 ° C. Similar trends were observed for the other samples.

[Example 6]
_{M (Co 1-x Fe x} ) y O 4-δ complex oxide was prepared by the following procedure.
Carbonates were used as raw materials for Ca, Sr, and Ba, and oxides were used as raw materials for Co and Fe. The raw material was weighed at a predetermined molar ratio, added to isopropyl alcohol (dispersion medium), and wet-mixed while pulverizing with a ball mill to obtain a slurry. The solid content was separated from the obtained slurry by a suction filter and dried at about 120 ° C. for 1 hour. The obtained dried product was pulverized and then baked in an electric furnace at 950 ° C. for 5 hours in the air to obtain a porous massive baked product. Fired product disintegrated, dry milled by an automatic mortar, the composition of Table _{21 M (Co 1-x Fe} x) was y _{O 4-δ} complex oxide. The oxide was pulverized so as to have an average particle size of 1.2 μm. The specific surface area at this time was about 2.2 m ² / g. For measurement of the specific surface area, Belsorb manufactured by Nippon Bell Co., Ltd. was used, and the specific surface area was determined by the BET method by nitrogen gas adsorption. The particle size was measured using a laser diffraction particle size distribution measuring device manufactured by Shimadzu Corporation. As the composition, the amount used in the production was used, and it was confirmed by chemical analysis that the amount of the metal element in the charged compound coincided with the amount of the metal element in the product.

Next, Pd, Ag, and Rh were supported on the M (Co _1-x Fe _x ) _y O _4-δ composite oxide as follows. Predetermined amounts of nitrates of Pd, Ag, and Rh were weighed and dissolved in pure water to make an aqueous solution of about 100 mL. The aqueous solution and 100 g of the oxide powder were placed in a rotary evaporator and subjected to defoaming while rotating and stirring at room temperature and under reduced pressure. Next, after returning to normal pressure and heating to about 60-70 ° C., the pressure was reduced, followed by dehydration and drying. After cooling to room temperature, the pressure was returned to normal pressure, the solid was taken out, and dried at about 180 ° C. for 2 hours. The obtained product was heat treated in the atmosphere at 650 ° C. for 5 hours, and then crushed into granules. By the above operation, M (Co ₁₎ in which one or more kinds of noble metals of Pd, Ag or Rh, which is one of the catalysts of the present invention, are supported at a supported amount of 1.2 parts by mass with respect to 100 parts by mass of the composite oxide. _{-x Fe x) y O 4-} δ oxide (A1) was obtained.

Containing cerium and zirconium _{(Ce z Zr 1-z)} O 2-δ complex oxide was prepared by the same method as the above _{M (Co 1-x Fe x} ) y O 4-δ complex oxide The oxide was used as a raw material for Ce and Zr, and the firing temperature of the obtained solid product was 1500 ° C. in the atmosphere for 5 hours. As a result, a porous massive fired product was obtained. Fired product disintegrated, by an automatic mortar dry milled to obtain a composition as shown in Table _{21 (Ce z Zr 1-z} ) O 2-δ complex oxide. The average particle diameter of the pulverized oxide was 1.0 μm, and the specific surface area was 2.0 m ² / g.

Next, Pd, Ag, or Rh was supported on the cerium-based oxide or alumina by the following method. A predetermined amount of commercially available ceria, ceria zirconia-based oxide or commercially available alumina was weighed and dispersed in pure water to obtain a dispersion solution having a volume of about 100 mL. Pd, Ag, or Rh nitrate or finely dispersed Pd, Ag, or Rh is mixed with this solution, and one or more kinds of noble metals such as Pd, Ag, or Rh are supported on 100 parts by mass of oxide in an amount of 0.6 mass. The oxide (B) which is a ceria, a ceria zirconia-based oxide or alumina supported on the part was obtained. The average particle diameter of the commercially available ceria used here or commercially available alumina was 1.4 μm, and the specific surface area was 90.6 m ² / g.

Table 21 summarizes the catalysts constructed using the various noble metal-supported oxides prepared by the above procedure. In addition, the composition formula described in the composition column of the oxide (A1) shown in Table 21 indicates the ratio of the metal element as described above. Thus, for example, No. 6-1 CaFeO _4-δ can also be expressed as CaFeO _w or CaFeO _3-δ . No. The same applies to 6-2 to 6-8, 6-12, 6-13, 6-22, 6-32, and 6-34. For example, No. 6-9 CaF ₂ O _4-δ can also be expressed as CaFe ₂ O _w . No. The same applies to 6-10, 6-11, 6-14 to 6-30, 6-33, and 6-35.

  A cylindrical stainless steel honeycomb having a predetermined shape diameter of 25 cm, a height of 60 cm, and a cell pore size of 1 mm × 2 mm in the cross section of the honeycomb was used as the honeycomb to wash coat the catalyst. The honeycomb was held vertically, and a slurry in which an excessive amount of catalyst, binder, etc. was dispersed was uniformly deposited on the upper end face thereof, sucked from the lower end face of the honeycomb and applied to the inner wall of the honeycomb, and the excess slurry was removed. When the slurry adhered to the outer surface of the honeycomb, the adhered slurry was wiped before drying. While continuing the suction, the upper end face of the honeycomb was air blown and dried. The honeycomb was turned upside down, and the slurry was applied to the inner wall of the honeycomb and dried again. Thereafter, a heat treatment was performed in the atmosphere at 650 ° C. for 1 hour to obtain a stainless steel honeycomb catalyst structure obtained by wash-coating the catalyst of the present invention. The total amount of noble metals fixed to the honeycomb was 0.5 g / L.

The catalyst performance of the honeycomb catalyst structure was evaluated by the following method. The used evaluation apparatus is a flow type reaction apparatus composed of stainless steel pipes. A model gas having the composition shown in Table 22 is introduced from the inlet side, and this is circulated to the exhaust gas purification reaction section. To be discharged. The purification reaction part is heated by heating the model gas with an external heater and sending it to the exhaust gas purification reaction part. In the temperature range from 100 ° C. to 450 ° C., the gas composition on the outflow side (after passing through the catalyst portion) was analyzed, and the change rates of the CO, HC, and NO concentrations were determined to evaluate the respective purification characteristics. The space velocity (SV) was set to 50,000 hr ⁻¹ . In the evaluation apparatus of the present invention, the measurement was performed 100 seconds after switching the inlet gas composition, and the operation of switching to another inlet gas composition after 180 seconds was repeated.

Table 23 shows the results of the catalyst performance evaluation performed by supporting the catalyst shown in Table 21 on the honeycomb. In Table 23, ◎ indicates T ₅₀ (Note 1) of 220 ° C. or less, ◯ indicates the same 220-250 ° C., Δ indicates the same 250-350 ° C., and x indicates the same above 350 ° C. The calculation of T ₅₀ used for the determination was the average value of the results measured under lean and stoichiometric conditions for CO and HC, and the average value of the results measured under rich and stoichiometric conditions for NO _x .
(Note 1) T ₅₀ is the temperature (° C.) when the gas concentrations of CO, HC, and NO _x are reduced by half due to catalytic action, and the lower the value, the higher the activity.

  As can be seen from Table 23, all of the catalyst configurations according to the present invention (6-1 to 6-28: Examples) were judged as good or better, but the catalyst configurations according to the present invention (6-29 to 6) were not used. In -35: Comparative Example), it was found that the purification performance was lower than this.

  Next, the oxygen storage capacity of the oxide (B) supporting one or more noble metals selected from the group consisting of Pd, Ag, and Rh was evaluated. The precious metals each supported 0.6 parts by mass with respect to 100 parts by mass of the carrier oxide (two types supported each supported 0.6 parts by mass). A thermobalance method was used for the evaluation. The sample atmosphere was alternately switched between a reducing atmosphere of air and 4% hydrogen-containing argon, and a stable weight was measured in each atmosphere for about 1 hour, and the oxygen storage capacity was determined from the weight difference. The measurement temperature was three points of 200 ° C, 500 ° C, and 900 ° C. The results are shown in Table 24.

The oxide (B) shown in Table 24 (an oxide having an oxygen storage ability not supporting a noble metal or an oxide not supporting a noble metal even if supporting a noble metal) is 50 μm-O at 500 ° C. It was found to have a low oxygen storage capacity of ₂ / g or less. This result is considered to be a cause of a decrease in purification performance as shown in the comparative example of Table 23.

[Example 7]
_{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ oxide (s> 0), was prepared by the following procedure. Carbonates were used as raw materials for Ca, Sr, and Ba, and oxides were used as raw materials for Co, Fe, and Ti. The raw material was weighed at a predetermined molar ratio, added to isopropyl alcohol (dispersion medium), and wet-mixed while pulverizing with a ball mill to obtain a slurry. The solid content was separated from the obtained slurry by a suction filter and dried at about 120 ° C. for 1 hour. The obtained dried product was pulverized and then baked in an electric furnace at 950 ° C. for 5 hours in the air to obtain a porous massive baked product. Fired product disintegrated, by an automatic mortar dry milled to obtain a composition of _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ oxide shown in Table 25. The oxide was pulverized so as to have an average particle size of 1.2 μm. The specific surface area at this time was about 2.2 m ² / g. For measurement of the specific surface area, Belsorb manufactured by Nippon Bell Co., Ltd. was used, and the specific surface area was determined by the BET method by nitrogen gas adsorption. The particle size was measured using a laser diffraction particle size distribution measuring device manufactured by Shimadzu Corporation. The described composition is determined from the amount charged in the production, and it was confirmed by chemical analysis that the amount of the metal element in the charged compound coincides with the amount of the metal element in the product.

The above _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ oxide (s> 0) also was supported Pd, Ag, and Rh in the same manner as described above . Predetermined amounts of nitrates of Pd, Ag, and Rh were weighed and dissolved in pure water to make an aqueous solution of about 100 mL. The aqueous solution and 100 g of the oxide powder were placed in a rotary evaporator and subjected to defoaming while rotating and stirring at room temperature and under reduced pressure. Next, after returning to normal pressure and heating to about 60-70 ° C., the pressure was reduced, followed by dehydration and drying. After cooling to room temperature, the pressure was returned to normal pressure, the solid was taken out, and dried at about 180 ° C. for 2 hours. The obtained product was heat treated in the atmosphere at 650 ° C. for 5 hours, and then crushed into granules. By the above operation, M {Co ₁ in which one or more kinds of Pd, Ag, or Rh noble metal, which is one of the catalysts of the present invention, is supported at a supported amount of 1.2 parts by mass with respect to 100 parts by mass of the composite oxide. _{-x (Fe 1-s Ti s} ) x} y O 4-δ oxide (s> 0) was obtained.

Containing cerium and zirconium _{(Ce z Zr 1-z)} O 2-δ oxide other than composite oxide (B), the above _{M {Co 1-x (Fe} 1-s Ti s) x} y O _It was produced by the same method as _4-δ oxide, but using oxides as raw materials for Ce, Zr, Bi, La, Co, and Fe, and carbonates as raw materials for Ca and Sr, The firing temperature was 1200 to 1500 ° C. in the air for 5 hours. The fired product was pulverized and then dry-pulverized with an automatic mortar, and the average particle diameter and specific surface area of the obtained porous massive fired product are summarized in Table 26 together with the firing conditions. Table 26 also summarizes the results obtained by supporting Pd, Ag, or Rh on the oxide (B) obtained above by the method described above and evaluating the oxygen storage capacity of the oxide (B) by the method described above. It was. Table 25 shows catalysts constructed using various noble metal-supported oxides prepared by the above procedure.

Table 27 shows the results of carrying out the catalyst performance evaluation with the catalyst shown in Table 25 supported on the honeycomb. In Table 27, ◎ indicates T ₅₀ (Note 1) of 220 ° C. or less, ○ indicates 220-250 ° C., Δ indicates 250-350 ° C., and x indicates more than 350 ° C. The calculation of the T ₅₀ used for the determination, for CO and HC, the average value of the results of measurement in lean and stoichiometric conditions, averaged value of the results of measurement in the rich and stoichiometric conditions with respect to NO _x .
(Note 1) T ₅₀ is the temperature (° C.) when the gas concentrations of CO, HC, and NO _x are reduced by half due to catalytic action, and the lower the value, the higher the activity.

  As shown in Table 27, all of the catalyst configurations according to the present invention (7-1 to 7-20: Examples) were good determinations of ◯ or more, but the catalyst configurations according to the present invention (7-21 to 21) 7-24: Comparative Example) showed that the purification performance was lower than this.

[Example 8]
Various combinations of the oxide (A2) and the oxide (B) of the present invention were changed to evaluate the catalyst performance.
The oxide (A2) was prepared according to the methods of Examples 1 to 4 and combined with the oxide (B). The method of wash-coating on the honeycomb and the method of evaluating the catalyst were as described above. Table 28 shows the catalyst composed of oxide (A2) and oxide (B), and Table 29 shows the results of catalyst performance evaluation.

  As can be seen from Table 29, when an oxygen storage material composed of a plurality of crystal phases is used, an excellent purification performance is recognized even without a precious metal, and the catalyst configuration (8-1 to 8- 16: Examples) were all good determinations of ◯ or more, but it was confirmed that the catalyst configuration not according to the present invention (8-17 to 8-24: comparative examples) had a purification performance lower than this. .

[Example 9]
A mode running test was conducted using two motorcycles of the carburetor specification and the electronic fuel injection system (FI) specification, and CO, THC and NOx emissions were evaluated. First, a catalyst was coated on a cylindrical stainless steel honeycomb having a diameter of 40 mm, a length of 60 mm, and a cell density of 300 cells per 1 inch (25.4 mm) square of the honeycomb by the method described above. The amount of noble metal supported was 1.0 g / L in total, and in the configuration in which a plurality of noble metals were supported, the amount of each noble metal was equal. Next, the manufactured honeycomb catalyst structure was attached to the muffler by welding. After installation, it was confirmed that there was no gas leakage from the exhaust gas system. The test method was performed according to the test method (TRIAS) established by the Ministry of Land, Infrastructure, Transport and Tourism. The driving mode was the EU motorcycle motorcycle test.

Tables 30 to 31 show the results of the purification rate evaluation of CO, THC, and NOx. Each purification rate is 100% as the amount of exhaust gas component under the same conditions without a catalyst, and the reduction rate of each exhaust gas component amount when a catalyst is installed is evaluated by mass%. The evaluation results are shown.
CO purification rate ×: Less than 60%, ○: 60% or more, ◎ 65% or more
THC purification rate ×: Less than 60%, ○: 60% or more, ◎: 65% or more
NO purification rate ×: Less than 20%, ○: 20% or more, ◎: 25% or more

  As can be seen from Tables 30 and 31, the catalyst according to the present invention works effectively both in the carburetor system and in the FI system, but a remarkable effect was recognized particularly in the carburetor system. This is a result of the development of a material having a high OSC capability and the catalyst configuration, and shows that the catalyst of the present invention is particularly suitable for use in a carburetor type motorcycle.

_{1 M {Co 1-x (} Fe 1-s Ti s) x} ( For _{s = 0, M (Co 1} -x Fe x) y O 4-δ) y O 4-δ complex oxide (A1) Or noble metal supported on the oxygen storage material (A2) 2 M {Co _1-x (Fe _1-s Ti _s ) _x } _y O _4−δ (when s = 0, M (Co _1-x Fe _x ) _y O _4-δ ) composite oxide (A1) or oxygen storage material (A2)
3 Noble metal supported on oxide (B) having oxygen storage ability 4 Oxide (B) having oxygen storage ability
5 Honeycomb substrate

Claims (24)

An oxygen storage material comprising an oxide containing alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or both (Fe _1-s Ti _s ) and Co,
The oxide is a particle having an average particle diameter of 0.1 μm or more and 5 μm or less,
The oxide particles are composed of a plurality of crystal phases,
The average size of the crystal phase is 5 nm or more and 80 nm or less,
The oxygen storage material, wherein s is 0 ≦ s ≦ 0.31. In the oxide, the molar ratio of the alkaline earth metal M and the total amount of (Fe _1-s Ti _s ) and Co is 0.1 ≦ M / {(Fe _1-s Ti _s ) + Co} ≦ 0. The oxygen storage material according to claim 1, which is .9. An oxygen storage material comprising an alkaline earth metal M and an oxide containing Fe or Co, or both Fe and Co,
The oxide is a particle having an average particle diameter of 0.1 μm or more and 5 μm or less,
The oxide particles are composed of a plurality of crystal phases,
The oxygen storage material according to claim 1 or 2, wherein an average size of the crystal phase is 5 nm or more and 80 nm or less.   4. The oxide according to claim 3, wherein a molar ratio between the alkaline earth metal M and the total amount of Fe and Co is 0.1 ≦ M / (Fe + Co) ≦ 0.9. Oxygen storage material.   The oxygen storage material according to any one of claims 1 to 4, wherein the alkaline earth metal M is Sr.   The oxygen storage material according to any one of claims 1 to 4, wherein Ca is contained in the alkaline earth metal M.   The oxygen storage material according to claim 1, wherein a noble metal is supported on the oxide.   The oxygen storage material according to claim 7, wherein the noble metal is at least one selected from the group consisting of Pt, Pd, and Rh.   The oxygen storage material according to claim 7, wherein the noble metal is at least one selected from the group consisting of Ag and Ru.   8. The oxygen storage material according to claim 7, wherein the noble metal is one or more selected from the group consisting of Pt, Pd, and Rh and one or more selected from the group consisting of Ag and Ru. Oxide containing alkaline earth metal M and (Fe _1-s Ti _s ) or Co, or (Fe _1-s Ti _s ) and Co, used for exhaust gas purification of carburetor-type motorcycles An oxygen storage material comprising:
The oxide is a particle having an average particle diameter of 0.1 μm or more and 5 μm or less,
The oxygen storage material, wherein s is 0 ≦ s ≦ 0.31.   The oxygen storage material according to any one of claims 1 to 10, wherein the oxygen storage material is contained in an exhaust gas purification catalyst of a carburetor type motorcycle. Pd, oxide carrying one or more noble metals selected from the group consisting of Ag and _{Rh M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ ( where, M is substantially In particular, it is one or more elements selected from the group consisting of Ca, Sr and Ba, where x is 0 to 1, y is 1 to 2, s is 0 to 0.31, and δ is a charge neutral condition. (A1) or the oxygen storage material (A2) according to any one of claims 1 to 10, and
An oxide (B) supporting one or more noble metals selected from the group consisting of Pd, Ag and Rh,
The catalyst for purifying exhaust gas, wherein the oxide (B) is an oxide different from the oxide (A1) and the oxygen storage material (A2) and has an oxygen storage capacity. Pd, oxide carrying one or more noble metals selected from the group consisting of Ag and _{Rh M (Co 1-x Fe} x) y O 4-δ ( where, M is essentially Ca, Sr and Ba 1 or more elements selected from the group consisting of: x is 0 to 1, y is 1 to 2, and δ is a value determined so as to satisfy the charge neutrality condition) (A1) or claim The oxygen storage material (A2) according to any one of Items 1 to 10,
An oxide (B) supporting one or more noble metals selected from the group consisting of Pd, Ag and Rh,
The catalyst for purifying exhaust gas, wherein the oxide (B) is an oxide different from the oxide (A1) and the oxygen storage material (A2) and has an oxygen storage capacity. The exhaust gas purifying catalyst according to claim 13 or 14, wherein the oxide (B) has an oxygen storage capacity of 50 µmol-O ₂ / g or more at 500 ° C.   The exhaust gas-purifying catalyst according to any one of claims 13 to 15, wherein the oxide (B) contains cerium. The oxide (B) is an oxide containing cerium and zirconium _{(Ce z Zr 1-z)} O 2-δ, it claims 13 to 16 z is 0.4 to 1.0 2. An exhaust gas purifying catalyst according to item 1.   The exhaust gas purifying catalyst according to any one of claims 13 to 18, wherein the noble metal supported on the oxide (A1) is Pd, and the noble metal supported on the oxide (B) is Rh. Wherein the noble metal oxide carrying _{M {Co 1-x (Fe} 1-s Ti s) x} y O 4-δ (A1) or the oxygen storage material (A2), oxide carrying the precious metal (B The mass ratio of A / B (where A is the mass of A1 or A2 and B is the mass of B) is 0.1-10. The exhaust gas purifying catalyst according to claim 1. The mass ratio of the oxide carrying the noble metal _{M (Co 1-x Fe x} ) y O 4-δ (A1) or the oxygen storage material (A2), oxide carrying the noble metal and (B) is, The exhaust gas according to any one of claims 14 to 18, wherein A / B (where A is the mass of A1 or A2 and B is the mass of B) is 0.1 to 10 in mass ratio. Purification catalyst.   21. The exhaust gas purifying catalyst according to any one of claims 13 to 20, wherein the value of x is 0.2 to 1.   The exhaust gas purification catalyst according to any one of claims 13 to 21, wherein the exhaust gas purification catalyst is a carburetor-type motorcycle exhaust gas purification catalyst. Pd, oxide carrying one or more noble metals selected from the group consisting of Ag and _{Rh M {Co 1-x (} Fe 1-s Ti s) x} y O 4-δ ( where, M is substantially In particular, it is one or more elements selected from the group consisting of Ca, Sr and Ba, where x is 0 to 1, y is 1 to 2, s is 0 to 0.31, and δ is a charge neutral condition. (A1), or the oxygen storage material (A2) according to any one of claims 1 to 10,
Including an oxide (B) supporting one or more precious metals selected from the group consisting of Pd, Ag and Rh,
A catalyst for exhaust gas purification, which is a catalyst for exhaust gas purification of a carburetor type motorcycle.   24. A honeycomb catalyst structure for exhaust gas purification, wherein the exhaust gas purification catalyst according to any one of claims 13 to 23 is wash-coated on a ceramic or metal honeycomb.

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