JP4868384B2 - Rare earth-noble metal composite material and rare earth-noble metal composite oxide - Google Patents

Description

  The present invention relates to a novel rare earth-noble metal composite material and a rare earth-noble metal composite oxide. Furthermore, it is related with the manufacturing method of these composite materials and composite oxides.

LaCoO _{3 and the} like contained in the perovskite oxide represented by the general formula ABO ₃ are various catalysts and air-side electrode materials for solid oxide fuel cells (SOFC) because of their catalytic action and electronic conductivity. It is being considered.

As a method for synthesizing LaCoO ₃ , there is a solid phase reaction method of La ₂ O ₃ and CoO constituting this oxide. As a liquid phase reaction method, a sol-gel method, an alkoxide method, and the like are known in addition to a coprecipitation reaction method obtained as a precipitate from a solution containing La and Co. However, these methods have problems such as uniformity of dispersion at the atomic level of La and Co in the obtained oxide.

  As one method for solving the problems and the like, a method for synthesizing rare earth-heterogeneous complex oxides (JP-A-6-135722) has been proposed.

  In addition, Pd (palladium), Rh (rhodium) are used as catalytic active components of a three-way catalyst capable of simultaneously removing hydrocarbons (HC), nitrogen oxides (NOx) and carbon monoxide (CO) contained in automobile exhaust gas. ), Noble metals such as Pt (platinum) are widely used.

  However, these precious metals have the following advantages: 1) Pd excels in HC oxidation from low temperature, 2) Rh excels in NOx reduction, 3) Pt excels in CO oxidation from low temperature, but heat resistance Has the problem of being inferior.

Therefore, attempts have been made to improve heat resistance by impregnating and supporting Pd, Rh, or Pt on a composite oxide having a perovskite structure represented by the general formula ABO ₃ . Furthermore, if Pd, Rh, or Pt is contained as a constituent element of the composite oxide, it is possible to further improve heat resistance and exhaust gas purification performance compared to impregnating and supporting Pd, Rh, or Pt. Are known.

For example, as Pd, La _0.9 Ce _0.1 Fe _0.57 Co _0.38 Pd _0.05 O ₃ , La _0.9 Ce _0.1 Mn _0.57 Co _0.38 Pd _0.05 O ₃ , Nd _0.6 Ca _0.4 Fe _0.52 Mn _0.36 Pd _0.12 O ₃ , Pr _0.8 Sr _0.2 Mn _0.9 Pd _0.1 O ₃ (JP-A-8-217461), La _0.9 Ce _0.1 Fe _0.56 Co _0.38 Pd _0.06 O ₃ (JP-A 8-224446), Sr _0.9 Ba _0.1 Co _0.85 Pd _0.15 O ₃ (JP 7-116519 _{discloses), La 0.8 Sr 0.2 Fe 0.95} Pd 0.05 O 3, Sr 0.9 Ba 0.1 Co 0.85 Pd 0.15 O 3 ( _{JP-A-6-100319), Sr 0.9 Ba 0.1 Co} 0.85 Pd 0.15 O 3 ( JP No. 6-304449 and La _0.4 Sr _0.6 Co _0.95 Pd _0.05 O ₃ (Japanese Patent Laid-Open Nos. 5-76762 and 5-245372) are known.

As Rh, for example, La _0.8 Ba _0.2 Ni _0.48 Co _0.50 Rh _0.02 O ₃ (Japanese Patent Laid-Open No. 8-217461), La _0.4 Sr _0.6 Co _0.95 Rh _0.05 O ₃ (Japanese Patent Laid-Open No. 5-76762) and the like are known. ing.

Examples of Pt include La _0.4 Sr _0.6 Co _0.95 Pt _0.05 O ₃ (Japanese Patent Laid-Open No. 5-76762), La _0.9 Ce _0.1 Co _0.98 Pt _0.02 O ₃ , La _1.0 Co _0.9 Pt _0.1 O ₃ , La _1.0 Co _0.8 Pt _0.2 O ₃ (Japanese Patent Laid-Open No. 6-100319), La _0.8 Sr _0.2 Cr _0.95 Pt _0.05 O ₃ , La _1.0 Ni _0.98 Pt _0.02 O ₃ , La _1.0 Co _0.9 Pt _0.1 O ₃ , La _1.0 Fe _0.8 Pt _0.2 O ₃ , La _0.8 Sr _0.2 Cr _0.95 Pt _0.05 O ₃ (JP-A-6-304449), La _1.0 Co _0.9 Pt _0.1 O ₃ , La _1.0 Fe _0.8 Pt _0.2 O ₃ , La _1.0 Mn _0.98 Pt _0.02 O ₃ , La _0.8 Sr _0.2 Cr _0.95 Pt _0.05 O ₃ , La _1.0 Co _0.95 Pt _0.05 O ₃ , La _1.0 Mn _0.98 Pt _0.02 O ₃ (Japanese Unexamined Patent Publication No. 7-116519), La _0.2 Ba _0.7 Y _0.1 Cu _0.48 Cr _0.48 Pt _0.04 O ₃ , La _{0.9 e 0.1 Co 0.9 Pt 0.05 Ru 0.05} O 3 ( JP-A-8-217461) have been proposed.

  Furthermore, recently, an improvement of these techniques has been proposed. For example, JP 2004-41866 A is known as Pd, JP 2004-41867 A is known as Rh, and JP 2004-41868 A is known as Pt.

  However, in the method for obtaining the composite oxide described above, there is room for further improvement in terms of uniformity of dispersion of the obtained composite oxide at the atomic level. On the other hand, a method for synthesizing a rare earth-heterogeneous element complex oxide (Japanese Patent Laid-Open No. 6-135722) in which the obtained complex oxide is excellent in dispersion uniformity at the atomic level has been proposed. It is actually difficult to support noble metals such as Rh or Pt.

  Therefore, the main object of the present invention is to provide a highly homogeneous oxide in which noble metal elements are uniformly dispersed.

  As a result of intensive studies in view of the problems of the prior art, the present inventor produces an oxide using a material containing a hexacyano polynuclear complex crystal and a specific element or a compound thereof as a precursor. The present inventors have found that the above object can be achieved and have completed the present invention.

  That is, the present invention relates to the following rare earth-noble metal composite materials and rare earth-noble metal composite oxides.

1. General formula Ln [M (CN) ₆ ] · nH ₂ O (where Ln represents at least one rare earth element, M represents at least one trivalent transition metal element, and n is from 0 to 10) A rare-earth-noble metal-based composite material comprising: a hexacyano polynuclear complex crystal represented by the formula: and a second component of a noble metal element different from M and a compound thereof.

  2. Item 2. The rare earth-noble metal composite material according to Item 1, wherein the second component is present in at least a surface region of the hexacyanopolynuclear complex crystal.

  3. Item 3. The rare earth-noble metal composite material according to Item 1 or 2, wherein a part or all of the second component is chemically bonded to the crystal.

  4). Item 4. The rare earth-noble metal-based composite material according to any one of Items 1 to 3, wherein the molar ratio of Ln to the second component (Ln: second component) is 1: 0.001 to 0.2.

5. General formula Ln [M (CN) ₆ ] · nH ₂ O (where Ln represents at least one rare earth element, M represents at least one trivalent transition metal element, and n is from 0 to 10) And a solution containing a noble metal element ion is brought into contact with the hexacyano polynuclear complex crystal represented by the following formula.

  6). A rare earth-noble metal-based composite oxide obtained by heat-treating the composite material according to any one of Items 1 to 4 in an oxidizing atmosphere.

7). Item 7. The rare earth-noble metal-based composite oxide according to Item 6 , wherein the heat treatment is performed at 300 ° C or higher.

8). The composite oxide has the general formulas LnMO ₃ · mM ′, LnMM′O _{3 + m} and LnMO ₃ · mM′Ox (in any general formula, Ln represents at least one rare earth element, and M is trivalent. And M ′ represents at least one kind of noble metal element different from M. m is not less than 0.001 and not more than 0.2, x is the valence of M ′ n The rare earth-noble metal-based composite oxide according to any one of Items 6 to 7, comprising at least one composite oxide represented by n / 2).

9. An exhaust gas purifying catalyst comprising the rare earth-noble metal-based composite oxide according to any one of Items 6 to 8.

10. A dehydrogenation catalyst comprising the rare earth-noble metal-based composite oxide according to any one of Items 6 to 8.

11. 9. A hydrocracking catalyst comprising the rare earth-noble metal-based composite oxide according to any one of Items 6 to 8.

  According to the method for producing a composite material of the present invention, in particular, a composite material in which a noble metal element or a compound thereof is distributed in the surface region of a hexacyano polynuclear complex crystal can be obtained. Then, the composite material can be heat-treated in an oxidizing atmosphere to obtain a homogeneous oxide (particularly, a uniform dispersed state at the atomic level).

  Thus, according to the composite material, it is possible to provide a uniform oxide at the atomic level by a simple method of heat-treating the composite material at a relatively low temperature. Moreover, if it is the said method via the said composite material, it is also possible to design the composition, a surface area, etc. freely. The oxide of the present invention can be widely used for various applications. For example, it can be suitably used as an electrode material in addition to a catalyst for removing nitrogen oxide (NOx), CO, hydrocarbon (HC), etc., a dehydrogenation catalyst, a hydrocracking catalyst, and the like.

1. Rare earth-noble metal composite material and method for producing the same
Composite Material The rare earth-noble metal composite material of the present invention has a general formula Ln [M (CN) ₆ ] .nH ₂ O (where Ln represents at least one rare earth element, and M represents at least a trivalent transition metal). 1 is a type, wherein n is 0 or more and 10 or less), and includes at least one second component of a noble metal element different from M and a compound thereof.

The hexacyano polynuclear complex crystal has the general formula Ln [M (CN) ₆ ] · nH ₂ O (where Ln represents at least one rare earth element and M represents at least one trivalent transition metal). N is 0 or more and 10 or less).
Ln may be any of rare earth elements, specifically, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. Can be mentioned. Among these, at least one of La, Ce, Pr, Nd, Sm, and Yb is desirable. M is a trivalent transition metal. For example, Cr, Mo, W, Mn, Fe, Ru, Co, Rh, Ir, etc. are mentioned. Among these, at least one of Cr, Mn, Fe and Co is particularly desirable.

  This hexacyano polynuclear complex crystal may be either an anhydride or a hydrate. In the case of a hydrate, n is generally 10 or less.

  The second component is at least one of a noble metal element different from M and a compound thereof. Examples of the noble metal element include Pd, Rh, Pt, Os, Ag, Au, Ir, and the like. Among these, at least one of Pd, Rh, and Pt is preferable. Any form may be sufficient as said compound. Examples thereof include inorganic acid salts such as nitrates, hydrochlorides, sulfates and carbonates, organic acid salts such as oxalates and acetates, hydroxides and oxides, and the like. Among these, it is desirable to use inorganic acid salts, particularly nitrates.

  The second component may be present anywhere in the composite material of the present invention, but is desirably present in the surface region of the hexacyano polynuclear complex crystal. When the composite material having such a configuration is used as a catalyst material, an electrode material, or the like, more excellent catalyst characteristics, electrode characteristics, and the like can be efficiently obtained.

  Part or all of the second component is desirably chemically bonded to the hexacyano polynuclear complex crystal. In particular, when the second component is present in the surface region of the hexacyanopolynuclear complex crystal, the second component is firmly fixed by chemical bonding, and more excellent heat resistance when used as a catalyst material or the like. , Durability and the like can be exhibited.

  The content ratio of the second component may be appropriately set according to the use of the material of the present invention, desired characteristics, etc. In general, the above-mentioned Ln: second component = 1: 0.001-0. It is desirable to set it to about 2 (particularly 1: 0.01 to 0.2).

Production method of composite material The production method of the composite material of the present invention is not particularly limited as long as the above-described constitution can be obtained, but it is particularly desirable to produce the composite material by the following production method . That is, the general formula Ln [M (CN) ₆ ] .nH ₂ O (where Ln represents at least one rare earth element, M represents at least one trivalent transition metal, and n is 0 to 10). According to the method for producing a rare earth-noble metal-based composite material, the hexacyano polynuclear complex crystal represented by the following formula is contacted with a solution containing ions of a noble metal element. The composite material can be manufactured.

  The hexacyano polynuclear complex crystal may have the same structure as the hexacyano polynuclear complex crystal shown in the description of the composite material of the present invention. This crystal can be produced according to a known production method. For example, a method disclosed in JP-A-6-135722 may be followed. That is, a hexacyano polynuclear complex crystal can be obtained by an ion exchange reaction (the following formula (1)) between an alkali metal salt or ammonium salt of the hexacyano complex and a salt of a rare earth element.

A ₃ [M (CN) ₆ ] + LnX ₃ + aq.
= Ln [M (CN) ₆ ] · nH ₂ O + 3AX
... (1)
More specifically, K ₃ [Fe (CN) ₆ ] is used as the alkali metal salt of the hexacyano complex, La (NO ₃ ) ₃ is used as the rare earth element salt, and both are subjected to an ion exchange reaction to form La. [Fe (CN) ₆ ] · nH ₂ O can be obtained. This is expressed by the following equation (2).

K ₃ [Fe (CN) ₆ ] + La (NO ₃ ) ₃ + aq.
= La [Fe (CN) ₆ ] .nH ₂ O + 3KNO ₃ (2)
On the other hand, a solution containing noble metal element ions can be prepared, for example, by dissolving a noble metal compound in a suitable solvent. Preferably, an aqueous solution obtained by dissolving a water-soluble compound (especially a water-soluble salt) of a noble metal element in water can be suitably used. For example, a noble metal element nitrate or the like can be preferably used as the compound.

  The concentration of the above solution is not particularly limited, but is usually set appropriately within a range of about 0.1 to 5 mol / L.

  The method of bringing the solution into contact with the hexacyanopolynuclear complex crystal is not limited. Any of the method of immersing the hexacyanopolynuclear complex crystal in the solution, the method of spraying or impregnating the solution with the hexacyanopolynuclear complex crystal, etc. Can be adopted. In this case, the mixing ratio of the two is not particularly limited, and the ratio of the two in the obtained composite material is appropriately set so as to be the above ratio (Ln: second component = 1: 0.001-0.2 in molar ratio). Adjust it.

  Moreover, the temperature conditions etc. in the case of making both contact are not specifically limited, Generally, what is necessary is just to implement at normal temperature and a normal pressure.

2. Rare earth-noble metal-based composite oxide and method for producing the same The rare-earth-noble metal-based composite oxide of the present invention is obtained by heat-treating the above-described composite material in an oxidizing atmosphere.

  The composite material is subjected to heat treatment without mechanical processing such as cutting and pulverization in order to maintain such a structure, particularly when the second component is present in the surface region. It is desirable.

  The heat treatment temperature varies depending on the composition of the raw material, desired characteristics, and the like, but is generally a temperature at which an organic component in the hexacyano complex disappears and a desired oxide is formed. Generally, it is desirable to set it to 300 ° C. or more (particularly 500 to 800 ° C.). The heat treatment time can be appropriately determined according to the heat treatment temperature and the like.

  The heat treatment atmosphere may be an oxidizing atmosphere as described above. For example, any of air, oxygen gas atmosphere, mixed gas atmosphere of oxygen gas and inert gas may be used.

  By performing the heat treatment, the rare earth-noble metal composite oxide of the present invention can be obtained. In general, the reaction represented by the following formula (3) proceeds by heat treatment (wherein Y represents M ′ or a compound thereof, and p represents the number of moles of oxygen necessary for the following reaction).

Ln [M (CN) ₆ ] · nH ₂ O · mY + pO ₂
-> LnMO ₃ · mM ′ (or LnMM′O _{3 + m} or LnMO ₃ · mM′Ox) (3)
The double oxide of the present invention is a mixed oxide containing Ln, M and a noble metal element. But it is not limited to the form of specific oxides, in particular the general formula LnMO ₃ · mM ', also in the LnMM'O _{3 + m} and LnMO ₃ · mM'Ox (either general formula, Ln is a rare earth element at least M represents at least one trivalent transition metal, M ′ represents at least one noble metal element different from M. m is from 0.001 to 0.2, and x is When the valence of M ′ is n, it is a value represented by n / 2).

  M is a trivalent transition metal. For example, Cr, Mo, W, Mn, Fe, Ru, Co, Rh, Ir, etc. are mentioned. Among these, at least one of Cr, Mn, Fe and Co is particularly desirable.

  M ′ is at least one kind of noble metal element different from M. Examples of the noble metal element include Pd, Rh, Pt, Os, Ag, Au, and Ir. Among these, at least one of Pd, Rh, and Pt is preferable.

  The content ratio of these composite oxides is not particularly limited, and may be set as appropriate according to the type of M, M ′, etc. used.

  Further, in the oxide of the present invention, other impurities, unreacted substances, and the like may be contained within a range that does not hinder the effects of the present invention. For example, some cyano groups derived from the raw material may remain.

<Action>
Coordination compounds are composed of metal ions and ligands, and form crystals in the solid state. The crystal has a structure in which the same or different metal ions are regularly arranged through ligands, but a coordinated unsaturated field in which the metal ions are missing (not bonded) always occurs at the crystal interface. To do.

  The present invention relates to a method for using this coordinated unsaturated field, and the same or different metal ions or their complexes can be selectively bonded (coordinated bond) to the coordinated unsaturated field.

In a crystal (Ln [M (CN) _x ]) in which the same or different metal ions are regularly arranged by a cyano bridging ligand, Ln is a rare earth metal ion, and here, the valence, type, and number of combinations of metals. Is not limited. [M (CN) x] represents a cyano complex. Here, the valence of metal, the number of types and combinations, and the number of cyano ions are not limited.
For _{example, La x Ce y Nd z [} Co a Mn b Cr c (CN) 6]
(X + y + z = 1, a + b + c = 1)
Co _x Ni _y [Pd _a Pt _b (CN) ₄ ]
(X + y = 1, a + b = 1)
Can be mentioned.

  At this crystal interface, there is a cyano ion that is not bonded to a metal ion as a coordinated unsaturated field. Arbitrary metal ions can be bound here. There are no limitations on the type, valence, number, etc. of the metal ions bound to the coordinated unsaturated field. Further, the metal ion to be bonded to the coordinated unsaturated field is not limited to a normal hydrated ion.

As the simplest example, a result of a system in which Pd ²⁺ ions are bonded to an interface of a La [Co (CN) ₆ ] type crystal is shown. The coupling structure can be schematically shown as in FIG.

  Next, an Example and a comparative example are shown and this invention is demonstrated in detail. However, the present invention is not limited to the scope of the examples. In the following description, the catalyst precursor refers to a substance before being converted to a double oxide by heat treatment regardless of the presence or absence of coating with Pd.

<Example 1>
La ³⁺ and [Co (CN) ₆ ] ^3- are equivalent to an aqueous solution of about 0.5 to 1 M of La (NO ₃ ) ₃ and an aqueous solution of about 0.5 to 1 M of K ₃ [Co (CN) ₆ ]. The mixture was mixed to make a mole. The produced La [Co (CN) ₆ ] .nH ₂ O crystals were filtered off, washed thoroughly with water and dried.

La [Co (CN) ₆ ] · nH ₂ O was immersed in a Pd (NO ₃ ) ₂ aqueous solution having a metal-converted Pd concentration of 4.3% by weight to cover the coating limit of Pd. As a result, a Pd (NO ₃ ) ₂ coated La [Co (CN) ₆ ] .nH ₂ O composite material having a metal element molar ratio of La: Co: Pd = 1.0: 1.0: 0.195 was obtained. In order to confirm that Pd (NO ₃ ) ₂ is coated on La [Co (CN) ₆ ] · nH ₂ O, the crystals before and after the coating treatment are identified by X-ray diffraction and infrared absorption spectroscopy. It was. The observation result by X-ray diffraction method is shown in FIG. 2 (upper figure), and the measurement result by infrared absorption spectroscopy is shown in FIG. This confirmed that La [Co (CN) ₆ ] · nH ₂ O was coated with Pd (NO ₃ ) ₂ .

  FIG. 2 is a view showing the results of X-ray diffraction analysis of the precursor obtained in Example 1, and shows that there is no difference before and after the coating treatment with Pd. That is, the coated Pd is not incorporated into the cyano complex crystal lattice observed by X-ray diffraction analysis.

3 is an FT-IR spectrum before and after the Pd coating treatment of La [Co (CN) ₆ ] · 5H ₂ O in Example 1. FIG. The spectrum before coating is the lower curve, and the spectrum after coating is the upper curve. According to the upper curve (La [Co (CN) ₆ ] · 5H ₂ O + Pd), the coordination bond portion of the Pd atom cannot be confirmed because it overlaps with the peak indicating the bond between the metal of La and Co and the CN group. A peak of NO ₃ group bonded to the surface via Pd was confirmed.

Next, this composite material was heat-treated at 600 ° C. in an oxidizing atmosphere in the air to obtain a composite oxide having a molar ratio of La: Co: Pd: O = 1.0: 1.0: 0.195: 3.20. The specific surface area of the obtained oxide powder was 24.6 m ² / g. The crystallinity in the bulk of the oxide particles was confirmed by X-ray diffraction and lattice observation with a transmission electron microscope. The result of the analysis by the X-ray diffraction method is shown in FIG. Observation with a transmission electron microscope confirmed that the oxide crystallites of the coated and non-coated oxides were LaCoO ₃ crystal lattices, and the coated Pd was not dissolved in the LaCoO ₃ crystals. . Further, it was confirmed that the coated Pd was present on the surface of LaCoO _{3 in} a state where it was not crystallized and was not a particle.

  As described above, it was confirmed that Pd coated on the precursor covered the surface of the composite oxide.

  Further, as an effect of high dispersion of Pd on the surface, the obtained composite oxide was heated in a 5% hydrogen-95% argon stream as a reducing gas, and the desorption behavior of oxygen was examined. The results are shown in Table 1. From the temperature-programmed desorption spectrum, oxygen desorption started at 247 ° C and had a maximum near 400 ° C, and oxygen desorption started at 491 ° C and had a maximum near 600 ° C.

<Example 2>
La [Co (CN) ₆ ] · nH ₂ O obtained in the same manner as in Example 1 was immersed in a Pd (NO ₃ ) ₂ aqueous solution having a metal-converted Pd concentration of 0.43% by weight, and the metal element molar ratio was La: Co. : Pd = 1.0: 1.0: 0.104 Pd (NO ₃ ) ₂ coated La [Co (CN) ₆ ] · nH ₂ O composite material was obtained. In the same manner as in Example 1, the crystals before and after the coating treatment were identified by X-ray diffraction and infrared absorption spectroscopy, whereby Pd (NO ₃ ) ₂ was added to La [Co (CN) ₆ ] · nH ₂ O. It was confirmed that was coated.

Next, the composite material was heat-treated at 600 ° C. in an oxidizing atmosphere in the air to obtain a composite oxide having a molar ratio of La: Co: Pd: O = 1.0: 1.0: 0.104: 3.12. The specific surface area of the obtained oxide powder was 25.3 m ² / g. In the same manner as in Example 1, the temperature programmed desorption spectrum of oxygen was measured. The results are shown in Table 1. The temperature-programmed desorption spectrum showed a desorption behavior starting at 253 ° C. and having a maximum near 400 ° C., and desorption behavior starting at 493 ° C. and having a maximum near 600 ° C.

<Example 3>
La [Co (CN) ₆ ] · nH ₂ O obtained in the same manner as in Example 1 was immersed in a Pd (NO ₃ ) ₂ aqueous solution having a metal-converted Pd concentration of 0.04 wt%, and the metal element molar ratio was La: Co. : Pd = 1.0: 1.0: 0.068 Pd (NO ₃ ) ₂ coated La [Co (CN) ₆ ] · nH ₂ O composite material was obtained. In the same manner as in Example 1, the crystals before and after the coating treatment were identified by X-ray diffraction and infrared absorption spectroscopy, whereby Pd (NO ₃ ) ₂ was added to La [Co (CN) ₆ ] · nH ₂ O. It was confirmed that was coated.

Next, this composite material was heat-treated at 600 ° C. in an oxidizing atmosphere in the air to obtain a composite oxide having a molar ratio of La: Co: Pd: O = 1.0: 1.0: 0.068: 3.10. The specific surface area of the obtained oxide powder was 24.7 m ² / g. When the temperature-programmed desorption spectrum of oxygen was measured in the same manner as in Example 1, it showed a desorption behavior starting from 263 ° C and having a maximum at around 400 ° C, and starting from 498 ° C and having a maximum at around 600 ° C. It was.

By ^adjusting the concentration of Pd ²⁺ ions in this way, the amount of binding to the crystal interface of Pd ²⁺ can be controlled. In addition, the amount of Pd ²⁺ ions bound in each crystal is uniform.

<Comparative Examples 1-3>
As Comparative Example 1, La [Co (CN) ₆ ] · nH ₂ O obtained in the same manner as in Example 1 was heat-treated at 600 ° C. in an oxidizing atmosphere in the air without coating treatment to obtain LaCoO ₃ . The specific surface area of the obtained oxide powder was 24.2 m ² / g.

  With respect to the oxide powder thus obtained, the temperature programmed desorption spectrum of oxygen was measured in the same manner as in Example 1. The results are shown in Table 1. Thermal desorption spectra showed a desorption behavior starting at 322 ° C and having a maximum near 400 ° C, and desorption behavior starting at 520 ° C and having a maximum near 600 ° C.

Further, as Comparative Example 2, the temperature-programmed desorption spectrum of oxygen was measured in the same manner as in Example 1 for LaCoO ₃ synthesized by a solid phase method and 0.2 mol times of Pd supported by a known method. The results are shown in Table 1. Thermal desorption spectra showed a desorption behavior starting at 311 ° C and having a maximum near 400 ° C, and desorption behavior starting at 508 ° C and having a maximum near 600 ° C.

As Comparative Example 3, the temperature programmed desorption spectrum of oxygen was measured in the same manner as in Example 1 for LaCoO ₃ prepared by the coprecipitation method. The results are shown in Table 1. The temperature-programmed desorption spectrum showed a desorption behavior starting at 325 ° C and having a maximum near 400 ° C, and desorption behavior starting at 522 ° C and having a maximum near 600 ° C.

  Thus, by using the present invention, the starting temperature of oxygen desorption, which is an index of the surface activity of various catalysts containing noble metals, is reduced by 50 to 70 ° C., the degree of dispersion of Pd coated on the surface is high, and the activity Is high.

<Example 4>
The transition metal M in Example 1 was changed from cobalt to iron, and an aqueous solution of potassium ferricyanide K ₃ [Fe (CN) ₆ ] and an aqueous solution of lanthanum nitrate (III) were mixed and stirred so that each compound was equimolar. did. The thus produced crystals of La [Fe (CN) ₆ ] · nH ₂ O were filtered off, washed thoroughly with water and dried. This product was immersed in a 20% by weight palladium nitrate aqueous solution in terms of palladium and coated to the palladium coating limit to obtain a composite material. This composite material was heat-treated at 600 ° C. in an oxidizing atmosphere in the air to obtain a composite oxide having a molar ratio of La: Fe: Pd: O = 1: 1: 0.045: 3. The amount of Pd supported in this material corresponds to 2% by weight in terms of noble metal.

Analysis of this composite oxide by X-ray diffraction and observation with a transmission electron microscope confirmed that the coated palladium was not dissolved, crystallized, or coarsened into LaFeO ₃ crystals. . The results obtained by X-ray diffraction are shown in FIG.

<Comparative example 4>
Commercially available γ-Al ₂ O ₃ was impregnated with palladium nitrate so that the Pd content was 2% by weight, dried at 100 ° C., calcined at 600 ° C. for 30 minutes, and catalyst (2% by weight Pd / γ-Al ₂ O ₃₎ was prepared.

<Purification test with model gas>
The composite oxides of Example 4 and Comparative Example 4 were aged for 10 hours at 800 ° C. in the atmosphere using an electric furnace.
The composite oxide 100 mg subjected to the aging treatment was placed in a column of the following measuring apparatus, and a model gas having the following conditions was passed through the column.

= Measuring device =
RPD Co., Ltd. TPD-TypeR (Temperature desorption gas analysis system)
= Model gas conditions =
・ Total flow rate of model gas composition: 300cc / min
NO content: 1667ppm
C ₃ H ₆ or C ₃ H ₈ content 5000 ppmC (switched every 200 seconds)
H ₂ O content: 10% by weight
He: balance / model gas temperature: 450 ° C.

The evaluation results of the exhaust gas purification performance for NOx in the obtained model gas are shown in FIG. The NOx removal characteristics were compared at 30 ionic strengths corresponding to NO mass numbers. The vertical axis in FIG. 5 represents the ionic strength of residual NO, and the lower the ionic strength level, the better the NO removal characteristics. From this result, it can be seen that the composite oxide of Example 4 is superior in NO removal characteristics when C ₃ H ₆ and C ₃ H ₈ are introduced as the reducing agent compared to the catalyst of Comparative Example 4.

  Thus, by using the composite oxide of the present invention as a catalyst, it exhibits excellent NOx removal performance in an atmosphere containing propane and propylene, which are hydrocarbon components discharged from internal combustion engines such as gasoline and diesel engines. Recognize.

Pd (NO _{3) 2} is a schematic view of a crystal Pd (NO ₃₎ bound to a cyano ion surfactant ₂ coating La [Co (CN) _6] type crystals. It is a figure which shows the result of the X-ray diffraction analysis of the precursor obtained in Example 1, and complex oxide. _{2 is} an FT-IR spectrum before and after Pd coating of La [Co (CN) ₆ ] · 5H ₂ O in Example 1. FIG. It is a figure by the X ray diffraction method of complex oxide obtained in Example 4. The figure which shows the result of having evaluated the NOx removal characteristic about the model gas of the complex oxide of Example 4, and the catalyst of the comparative example 4. FIG.

Claims (8)

A hexacyano polynuclear complex crystal represented by the general formula Ln [M (CN) ₆ ] · nH ₂ O (where Ln represents La , M represents Co or Fe, and n is 0 or more and 10 or less); And a rare earth-noble metal-based composite material comprising a second component comprising at least one of Pd and a compound thereof covering the surface of the crystal . Wherein some or all of the second component, is chemically bonded to said crystal, rare earth according to claim 1 - precious metal-based composite material. The rare earth-noble metal-based composite material according to claim 1 or 2 , wherein the molar ratio of Ln to the second component (Ln: second component) is 1: 0.001 to 0.2. A hexacyano polynuclear complex crystal represented by the general formula Ln [M (CN) ₆ ] · nH ₂ O (where Ln represents La , M represents Co or Fe, and n is 0 or more and 10 or less). A method for producing a rare earth-noble metal-based composite material, comprising contacting a solution containing Pd ions. A rare earth-noble metal composite oxide obtained by heat-treating the composite material according to claim 1 in an oxidizing atmosphere. The rare earth-noble metal-based composite oxide according to claim 5 , wherein the heat treatment is performed at 300 ° C or higher. The composite oxide has the general formulas LnMO ₃ · mM ′ and LnMO ₃ · mM′Ox (in any general formula, Ln represents La , M represents Co or Fe , and M ′ represents Pd . m is 0.001 to 0.2 .x, when the valence of Pd is n, at least one composite oxide represented by a value expressed by n / 2.) The rare earth-noble metal-based composite oxide according to claim 5 or 6 . Rare earth according to any one of claims 5-7 - the exhaust gas purifying catalyst comprising a noble metal composite oxide.

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