JP2012223694A - Exhaust gas purifying catalyst, method for producing the catalyst, and exhaust gas purifying method using the catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying catalyst which has CO oxidizing performance and can purify CO even in low temperature conditions.SOLUTION: In the exhaust gas purifying catalyst which is made of a particulate metal oxide, the metal oxide includes a hollandite type crystal phase having a one dimensional pore structure expressed by AMnO[A is a metal element other than Ag and a mono- or di-valent cation, x meets an unequality: x≤1.65 when A is a monovalent cation and an unequality: x≤0.825 when A is a divalent cation, and when a monovalent cation as A and a divalent cation as A coexist, the value xof x regarding A to be a monovalent cation and the value xof x regarding a metal element A to be a divalent cation meet a condition indicated by the unequality: (x+2×x)≤1.65], and the average length in the c axis direction of the crystal structure of the one dimensional particle of the metal oxide is 10-120 nm.

Description

  The present invention relates to an exhaust gas purification catalyst, a method for producing the same, and an exhaust gas purification method using the same.

  Conventionally, in order to purify harmful components (for example, carbon monoxide (CO), etc.) contained in gas discharged from internal combustion engines such as diesel engines and lean burn engines with low fuel consumption rate Various types of exhaust gas purification catalysts have been studied. Further, it has been studied to use a metal oxide having a specific crystal structure such as a hollandite type for such an exhaust gas purifying catalyst.

For example, Chem. Mater. Vol. 17 (Non-patent Document 1), pages 4335 to 4343 of Liyu Li et al. In the author's “Synthesis and Characterization of Silver Holland Application in Emission Control” with formula: Ag _1.8 Mn ₈ O ₁₆ It describes that CO is oxidized and purified using a metal oxide catalyst. However, the catalyst as described in Non-Patent Document 1 does not always have sufficient CO oxidation performance under low temperature conditions.

On the other hand, it is conventionally known to use a metal oxide having a specific crystal structure such as a hollandite type as a material (NOx adsorbent) for adsorbing NOx. For example, in JP 2002-085968 (Patent Document 1), has a crystal structure of hollandite type, the general _{formula: A x M y N 8-} y O 16 ( wherein, A represents K, Na, Rb Or Ca, M is Fe, Ga, Zn, In, Cr, Co, Mg, Al, or Ni, N is a tetravalent metal element, Sn or Ti, and 0 <x ≦ 2, 0 <y ≦ 2)), a NOx adsorbent comprising a metal oxide represented by And in patent document 1, after mixing these raw materials as a raw material as a method of manufacturing such a metal oxide, oxides and carbonates (for example, K ₂ CO ₃ , Ga ₂ O ₃ , SnO ₂ ), A method for heat treatment at 1375 ° C. or higher for 24 hours is disclosed. Further, in Japanese Patent Application Laid-Open No. 2002-301364 (Patent Document 2), NOx adsorption composed of a hollandite (OMS2 × 2 type) type metal oxide including an octahedron MO whose structure is connected so as to generate micropores having a pore shape. A material is disclosed. And in patent document 2, as a manufacturing method of such a metal oxide, a solution containing 165 g of manganese acetate dissolved in 600 ml of distilled water and 75 ml of acetic acid was added to 2.250 liters of distilled water. A solution containing 100 g of potassium acid is added, the resulting mixture is heated at reflux for 24 hours, the resulting precipitate is filtered, washed and then dried at 100 ° C. in a drying oven and at 600 ° C. in the presence of air. A method for firing is disclosed. However, in Patent Documents 1 and 2, there is no description of using a metal oxide to oxidize CO or the like, and such a metal oxide is used as an exhaust gas purifying catalyst for oxidizing CO or the like. Even so, the CO oxidation performance under low temperature conditions is not always sufficient.

JP 2002-085968 A JP 2002-301364 A

Liyu Li and David L. King, “Synthesis and Characterization of Silver Holland Application in Emission Control”, Chem. Mater. 2005, vol. 17, pages 4335-4343

  The present invention has been made in view of the above-described problems of the prior art, and an exhaust gas purifying catalyst having excellent CO oxidation performance capable of sufficiently oxidizing and purifying CO even under low temperature conditions, and An object of the present invention is to provide an exhaust gas purification method using the same.

  As a result of intensive studies to achieve the above object, the present inventors have found that the metal oxide is a monovalent or divalent in the oxide in an exhaust gas purification catalyst comprising a particulate metal oxide. Metal containing a hollandite-type crystal phase which is a cation and contains a metal element A which is a metal element other than Ag and manganese (Mn) and has a one-dimensional pore structure represented by the following general formula (1) The average length in the c-axis direction of the crystal structure of the primary particles of the metal oxide is 10 to 120 nm, and the length in the c-axis direction of the crystal structure of the primary particles of the metal oxide is Excellent CO oxidation performance that allows the exhaust gas purification catalyst to oxidize and purify CO even under low temperature conditions by setting the ratio of primary particles in the range of 20 to 100 nm (based on the number of particles) to 50 to 100%. From It found that it becomes possible to, and have completed the present invention.

That is, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst comprising a particulate metal oxide,
The metal oxide has the following general formula (1):
A _x Mn ₈ O ₁₆ (1)
[In Formula (1), A is a metal element other than Ag, and is a metal element that becomes a monovalent or divalent cation in the oxide,
x represents a numerical value satisfying the condition shown in the inequality: x ≦ 1.65 when A is a monovalent cation in the oxide, while x is a divalent cation. Represents a numerical value satisfying the condition shown in the inequality: x ≦ 0.825,
In the case where a metal element that becomes a monovalent cation and a metal element that becomes a divalent cation coexist in the oxide as A, the value x ₁ of x relating to the metal element A that becomes a monovalent cation and , divalent and value _{x 2} of x about the metal element a comprising a cation _{inequality: (x 1 + 2 × x} 2) satisfies the conditions shown in ≦ 1.65. ]
A metal oxide containing a hollandite-type crystal phase having a one-dimensional pore structure represented by:
The average length in the c-axis direction of the crystal structure of the primary particles of the metal oxide is 10 to 120 nm, and
Of the primary particles of the metal oxide, the proportion of primary particles having a length in the c-axis direction of the crystal structure in the range of 20 to 100 nm is 50 to 100% based on the number of particles,
It is characterized by.

  In the exhaust gas purifying catalyst of the present invention, the metal element A is at least one element selected from the group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba. Is preferable, and K is particularly preferable.

Further, the first method for producing an exhaust gas purifying catalyst of the present invention includes a first compound containing a metal element A other than Ag, the metal element A being a monovalent or divalent cation in the compound, and Mn. A step of physically mixing the second compound containing in a dry process to obtain a mixture;
Heating the mixture at a temperature of 30 to 150 ° C. for 1 to 8 hours, and calcining at 200 to 550 ° C. to obtain the exhaust gas purifying catalyst of the present invention;
It is the method characterized by including.

Furthermore, the second method for producing an exhaust gas purifying catalyst of the present invention includes a first compound containing a metal element A that is a metal element other than Ag and becomes a monovalent or divalent cation in the compound, and Mn. Ball milling a second compound containing to obtain a pulverized mixture;
Calcining the pulverized mixture at 200 to 550 ° C. to obtain the exhaust gas purifying catalyst of the present invention;
It is the method characterized by including.

  In such a second method for producing an exhaust gas purifying catalyst of the present invention, it is preferable to use a ball made of any one material of zirconia, alumina, agate and silicon nitride for the ball mill.

  The exhaust gas purification method of the present invention is a method characterized in that the exhaust gas containing carbon monoxide is brought into contact with the exhaust gas purification catalyst of the present invention to oxidize and purify the carbon monoxide.

  The reason why the exhaust gas purifying catalyst of the present invention makes it possible to sufficiently oxidize and purify CO even under low temperature conditions is not necessarily clear, but the present inventors speculate as follows. That is, first, in a metal oxide containing a hollandite-type crystal phase, a one-dimensional pore is formed in a direction parallel to the c-axis of the crystal, and the metal element A is monovalent and / or A structure that exists as a divalent cation is formed. In such a catalyst composed of a metal oxide containing a hollandite-type crystal phase, when the average length in the c-axis direction of the crystal structure of the primary particle of the metal oxide is shortened, a crystal having high oxidation activity as a surface in contact with the gas The existence ratio of the plane perpendicular to the c-axis direction of the structure (the (110) plane of the crystal) is high, and it is assumed that advanced oxidation of CO or the like is possible when the exhaust gas comes into contact. From such a viewpoint, in the present invention, the average length in the c-axis direction of the crystal structure of the primary particles of the metal oxide is 10 to 120 nm, and among the primary particles of the metal oxide, the c-axis direction of the crystal structure The ratio of primary particles in the range of 20 to 100 nm (based on the number of particles) is set to 50 to 100%, whereby the aspect ratio (the length of the particles in the c-axis direction and the direction perpendicular to the c-axis) (110) plane of the crystal which is a plane perpendicular to the c-axis direction in which the metal oxide in the catalyst is present in a high proportion and has a high oxidation activity. The present inventors infer that the present invention can exhibit an excellent oxidation performance such as CO, because the abundance ratio can be made sufficiently high. In addition, in the manufacturing method of the conventional metal oxide as described in the said nonpatent literature 1 and patent documents 1-2, since the growth to a c-axis direction will be promoted at the time of manufacture of a metal oxide, it is obtained. While the average length in the c-axis direction of the crystal structure of the primary particles of the metal oxide is 10 to 120 nm, among the primary particles of the metal oxide, the length in the c-axis direction of the crystal structure is in the range of 20 to 100 nm. The proportion of certain primary particles could not be 50 to 100% based on the number of particles, and a metal oxide having a high aspect ratio was formed. Therefore, in the conventional exhaust gas purifying catalyst, the abundance ratio of the (110) plane of the crystal, which is a plane perpendicular to the c-axis direction of the metal oxide having high oxidation activity, is reduced. The present inventors infer that the oxidation performance such as that was not obtained.

  According to the present invention, it is possible to provide an exhaust gas purification catalyst having excellent CO oxidation performance that can sufficiently oxidize and purify CO even under low temperature conditions, and an exhaust gas purification method using the same. It becomes possible.

2 is a transmission electron microscope (TEM) photograph of the metal oxide obtained in Example 1. FIG. 2 is a transmission electron microscope (TEM) photograph of the metal oxide obtained in Example 1. FIG. 2 is a transmission electron microscope (TEM) photograph of the metal oxide obtained in Example 1. FIG. 2 is a transmission electron microscope (TEM) photograph of the metal oxide obtained in Comparative Example 1. 2 is a transmission electron microscope (TEM) photograph of the metal oxide obtained in Comparative Example 1. 2 is a transmission electron microscope (TEM) photograph of the metal oxide obtained in Comparative Example 1. It is a graph which shows the CO purification rate of the exhaust gas purification catalyst (A)-(O) obtained in Examples 1-10 and Comparative Examples 1-5.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

First, the exhaust gas purifying catalyst of the present invention will be described. That is, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst comprising a particulate metal oxide,
The metal oxide has the following general formula (1):
A _x Mn ₈ O ₁₆ (1)
[In Formula (1), A is a metal element other than Ag, and is a metal element that becomes a monovalent or divalent cation in the oxide,
x represents a numerical value satisfying the condition shown in the inequality: x ≦ 1.65 when A is a monovalent cation in the oxide, while x is a divalent cation. Represents a numerical value satisfying the condition shown in the inequality: x ≦ 0.825,
In the case where a metal element that becomes a monovalent cation and a metal element that becomes a divalent cation coexist in the oxide as A, the value x ₁ of x relating to the metal element A that becomes a monovalent cation and , divalent and value _{x 2} of x about the metal element a comprising a cation _{inequality: (x 1 + 2 × x} 2) satisfies the conditions shown in ≦ 1.65. ]
A metal oxide containing a hollandite-type crystal phase having a one-dimensional pore structure represented by:
The average length in the c-axis direction of the crystal structure of the primary particles of the metal oxide is 10 to 120 nm, and
Of the primary particles of the metal oxide, the proportion of primary particles having a length in the c-axis direction of the crystal structure in the range of 20 to 100 nm is 50 to 100% based on the number of particles,
It is characterized by.

  A in the general formula (1) is a metal element other than Ag, and is a metal element that becomes a monovalent or divalent cation in the metal oxide. Such a metal element A may be any metal element other than Ag and can be a monovalent or divalent cation, and is not particularly limited, but from the viewpoint that it can exhibit higher CO oxidation performance. Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba are preferable, Li, Na, K, Ca and Ba are more preferable, and K is particularly preferable. In addition, as such a metal element A, 1 type can be used individually or in combination of 2 or more types. In addition, when Ag is used as such a metal element A, sufficient CO oxidation performance cannot be obtained.

  Moreover, the metal oxide represented by the general formula (1) contains manganese (Mn) as an essential component, as is apparent from the general formula. As described above, since the metal oxide according to the present invention contains Mn, the valence can be easily changed, and sufficiently high CO oxidation performance can be exhibited.

  Further, x in the general formula (1) is a value indicating the abundance ratio (concentration) of the metal element A in the metal oxide. Such a value of x differs depending on the valence of the cation of the metal element A. When the metal element A is a monovalent cation, the inequality: x ≦ 1.65 On the other hand, when the metal element A becomes a divalent cation, the numerical value satisfies the condition shown in the inequality: x ≦ 0.825. If the value of x exceeds the above upper limit, the entire pore of the hollandite structure is filled with the cation of the metal element A, the defect sites are reduced, and the valence change of Mn hardly occurs. Therefore, a sufficiently high CO oxidation performance cannot be obtained.

  In addition, the value of x in the general formula (1) is inequality: 0.5 ≦ x ≦ 1.60 (more preferably 0.6 ≦ when the metal element A is a monovalent cation). More preferably, the numerical value is within the range of x ≦ 1.50). The value of x is shown in the inequality: 0.25 ≦ x ≦ 0.8 (more preferably 0.3 ≦ x ≦ 0.75) when the metal element A is a divalent cation. It is more preferable that the numerical value satisfies the condition. If the value of x is less than the lower limit, it tends to be thermally unstable. On the other hand, if it exceeds the upper limit, CO oxidation activity tends to be low. In addition, the value calculated | required based on the density | concentration measured by inductively coupled plasma (ICP) analysis with respect to a metal oxide is employ | adopted for numerical values, such as x in such General formula (1). Moreover, if the molar ratio ([A] / [Mn]) of the metal element A and Mn is expressed using x in the general formula (1), the molar ratio is x / 8. Therefore, the molar ratio ([A] / [Mn]) between the metal element A and Mn in the metal oxide is 0.206 or less when the metal element A becomes a monovalent cation. On the other hand, when the metal element A is a divalent cation, the value is 0.103 or less.

In the case where a metal element that becomes a monovalent cation and a metal element that becomes a divalent cation coexist as the metal element A, the general formula (1): A _x for each valence of the metal element A In consideration of the formula represented by Mn ₈ O ₁₆ , the value of x of the metal element A that becomes a monovalent cation existing in the metal oxide is x _1, and the divalent that exists in the metal oxide the value of x of the respective metal elements a comprising a cation when a _{x 2, inequality: (x 1 + 2 × x} 2) must satisfy the condition shown in ≦ 1.65. When the value of (x ₁ + 2 × x ₂ ) represented by such a formula exceeds the upper limit, the entire pore of the hollandite structure is filled with the cation of the metal element A, and the number of defect sites is reduced. Since it becomes difficult for the valence of Mn to change, a sufficiently high CO oxidation performance cannot be obtained. The value of the x ₁ is the sum of the monovalent value of x for all monovalent becomes cationic metal element A in the case of the metal element A comprising a cation coexist plural kinds. Similarly, the value of x _2, the metal element A to be the divalent cations when the coexisting multiple species, the sum of the values of x for all divalent become cationic metal element A.

Further, in the case where a metal element that becomes a monovalent cation and a metal element that becomes a divalent cation coexist as the metal element A, the values of x ₁ and x ₂ are 0.5 ≦ (x ₁ + 2 × x ₂ ) ≦ 1.60 (more preferably 0.6 ≦ (x ₁ + 2 × x ₂ ) ≦ 1.50) is more preferable. If such a value of (x ₁ + 2 × x ₂ ) is less than the lower limit, it tends to be thermally unstable, whereas if it exceeds the upper limit, the CO oxidation activity tends to be low.

Furthermore, such a metal oxide includes a hollandite-type crystal phase. The “hollandite-type” crystal phase here has an octahedron represented by the formula: MnO ₆ as a basic unit, and such basic units are arranged in two vertical units and two horizontal units, and a one-dimensional pore in the center. This is a phase in which (tunnel-like pores and pores parallel to the c-axis) are formed. Further, such a hollandite crystal phase is a phase whose space group belongs to I4 / m and I2 / m. Further, in such a hollandite-type crystal phase, a structure in which the cation of the metal element A is arranged in the one-dimensional pore is formed. The existence of such a hollandite-type crystal phase can be confirmed from an X-ray diffraction pattern.

In such a metal oxide, the index of the existence ratio of the hollandite-type crystal phase is preferably 60% by mass or more, and preferably 70% by mass to 100% by mass. When the index of the abundance ratio of such hollandite-type crystal phase is less than the lower limit, the effect derived from the hollandite-type metal oxide cannot be fully utilized, and a sufficiently high CO oxidation performance cannot be obtained. There is a tendency. The crystal phase other than the hollandite-type crystal phase that can be included in the metal oxide according to the present invention is not particularly limited, and examples thereof include a Mn ₂ O ₃ -type crystal phase and a Mn ₃ O ₄ -type crystal phase. Is mentioned. The presence of such other crystal phases can also be confirmed from the X-ray diffraction pattern. The “index of the abundance ratio of the hollandite-type crystal phase” in the metal oxide is the crystal of each peak in the X-ray diffraction pattern after measuring the X-ray diffraction pattern and using software such as Rietan-2000. Identify the phase, determine the peak area of the main peak of each crystal phase present in the metal oxide, and the main peak peak of the hollandite-type crystal phase with respect to the total peak area of the main peak of each crystal phase (total area) The area ratio can be calculated, and the value can be obtained as “an index of the abundance ratio of the hollandite-type crystal phase”. The “main peak” in the X-ray diffraction pattern referred to here is the peak of each crystal phase that has the highest height to the peak top.

  Such metal oxides preferably have a single-phase crystal structure from the viewpoint of obtaining higher CO oxidation activity. Here, “having a single-phase crystal structure” means that no other crystal phase other than one specific type of crystal phase is confirmed in the X-ray diffraction (XRD) measurement. It means that no other crystal phase other than the hollandite type crystal phase is confirmed in the line diffraction (XRD) measurement. Thus, in the metal oxide according to the present invention, the abundance ratio of the hollandite-type crystal phase is particularly preferably 100% by mass.

  Such metal oxides are in the form of particles. Such metal oxide primary particles have an average length (average length) of 10 to 120 nm in the c-axis direction of the crystal structure. If the average length of such primary particles in the c-axis direction is less than 10 nm, sintering (grain growth) is likely to occur, and sufficient CO oxidation performance cannot be exhibited. On the other hand, it exceeds 120 nm. Then, since the abundance ratio of the (110) plane of the crystal, which is a plane perpendicular to the c-axis direction, of the metal oxide having high oxidation activity is lowered, sufficient CO oxidation performance cannot be obtained. Further, from the same viewpoint, since higher CO oxidation performance can be obtained, the average value of the length of the primary particles of such metal oxide in the c-axis direction is more preferably 10 to 110 nm, More preferably, it is 10-100 nm. In addition, such “average value of the length of the crystal structure of the primary particles in the c-axis direction” is determined by the transmission electron microscope (TEM) in the c-axis direction ((110) plane of any 100 or more primary particles. And the average value of these values can be obtained. In the metal oxide according to the present invention, the average value of the length of the crystal structure of the primary particle of the metal oxide in the c-axis direction is 10 to 120 nm, so that the (110) plane of the crystal with high oxidation activity is obtained. Since it is possible to make the gas and the gas (exhaust gas) contact with each other more efficiently, it is presumed that very high CO oxidation performance can be obtained.

  Further, as the primary particles of such a metal oxide, the proportion of primary particles having a length in the c-axis direction of the crystal structure of the primary particles in the range of 20 to 100 nm (more preferably 20 to 80 nm). , 50 to 100% on the basis of the number of particles. If the ratio of such primary particles is less than the lower limit, the abundance ratio of the (110) plane of the crystal having high oxidation activity is lowered, so that a sufficiently high CO oxidation performance cannot be obtained. From the same viewpoint, the proportion of particles having a crystal structure length in the c-axis direction of primary particles in the range of 20 to 100 nm (more preferably 20 to 80 nm) is 60 to 100 based on the number of particles. %, And more preferably 70 to 100%. In addition, such “ratio of primary particles” is obtained by measuring the length in the c-axis direction of arbitrary 100 or more primary particles with a transmission electron microscope (TEM), and based on the measured value. It can be determined by calculating the number of primary particles whose length in the c-axis direction of the crystal structure is in the range of 20 to 100 nm (more preferably 20 to 80 nm) with respect to the measured number of all primary particles.

  Further, as described above, such a metal oxide has a one-dimensional structure derived from a hollandite crystal phase. In addition, in the metal oxide concerning this invention, since Mn is contained in the basic skeleton of a crystal | crystallization, the average pore diameter calculated | required as a theoretical value from the crystal structure will be 0.46 nm. Such a theoretical value of the average pore diameter basically coincides with the actually measured value. Moreover, as a method of actually measuring such an average pore diameter, for example, a nitrogen adsorption method can be mentioned.

  Further, in the metal oxide containing a hollandite-type crystal phase, as described above, the pores become tunnel-like pores and become pores parallel to the c-axis. Therefore, in a metal oxide containing a hollandite-type crystal phase, the “average value of the length in the c-axis direction of the crystal structure of the primary particles” can be simulated with the average length of the pores of the metal oxide. In the present invention, the “average value of the length of the primary particles in the c-axis direction” obtained by the above-described measuring method of “average value of the length of the primary particles in the c-axis direction” is used as the metal oxide The average length of the pores is adopted. Therefore, the metal oxide according to the present invention satisfies the condition that the average length of the pores is 10 to 120 nm. Further, the preferable range of the average length of the pores of the metal oxide is the same as the preferable range of “the average value of the length of the crystal structure of the primary particles in the c-axis direction”.

  Further, as the primary particle of such a metal oxide, the average diameter of the maximum circumscribed circle in the plane perpendicular to the c-axis of the particle is preferably 1 to 100 nm, and more preferably 3 to 50 nm. . When the average diameter of the circumscribed circle is less than the lower limit, sintering tends to be easy. On the other hand, when the upper limit is exceeded, the specific surface area tends to be small, and the CO oxidation performance tends to be insufficient. In addition, such an average diameter can be calculated | required by measuring the magnitude | size in the surface perpendicular | vertical to the c-axis of 100 or more primary particles with a transmission electron microscope (TEM).

  In addition, the exhaust gas purifying catalyst of the present invention only needs to be composed of primary particles of a metal oxide containing the hollandite type crystal phase as described above, and other known metal oxides that can be used for exhaust gas purification. Or a combination of metals and the like may be used as appropriate. Further, the form of such an exhaust gas purification catalyst is not particularly limited, and may be used, for example, by being molded into a pellet, or a known base material (for example, made of ceramics) that can be used for an exhaust gas purification catalyst. May be used by being supported on a honeycomb substrate or the like) or a carrier.

  The exhaust gas purification catalyst of the present invention has been described above. Next, the first exhaust gas purification catalyst of the present invention that can be suitably used as a method for producing the exhaust gas purification catalyst of the present invention. The manufacturing method will be described.

The first method for producing an exhaust gas purifying catalyst of the present invention is a dry physical mixing of a first compound containing a metal element A that becomes a monovalent or divalent cation in a compound and a second compound containing Mn. To obtain a mixture (i),
Step (ii) of heating the mixture at a temperature of 30 to 150 ° C. for 1 to 8 hours and then calcining at 200 to 550 ° C. to obtain the exhaust gas purifying catalyst of the present invention,
It is the method characterized by including. According to the first method for producing an exhaust gas purification catalyst of the present invention, the exhaust gas purification catalyst of the present invention can be efficiently produced. Hereinafter, steps (i) to (ii) will be described separately.

  First, step (i) will be described. In the step (i), the first compound containing the metal element A that becomes a monovalent or divalent cation in the compound and the second compound containing Mn are physically mixed in a dry manner to obtain a mixture.

Such a metal element A is the same as that described in the exhaust gas purifying catalyst of the present invention. The first compound containing the metal element A is not particularly limited as long as it contains the metal element A. For example, a compound containing manganese (Mn) together with the metal element A may be used. . Examples of the first compound include permanganate, nitrate, carbonate, sulfate, organic acid salt (for example, acetate) of metal element A, and the like. As the first compound containing such a metal element A, KMnO ₄ , Ca (MnO ₄ ) ₂ , LiMnO ₄ , NaMnO ₄ , Ba (MnO ₄ ) _{2 are used} from the viewpoint of easy availability and high reactivity. CH ₃ COOK is preferred, and KMnO ₄ (potassium permanganate) is particularly preferred. In addition, you may use such a 1st compound individually by 1 type or in combination of 2 or more types. Moreover, you may use a commercially available 1st compound suitably. The form of the first compound is not particularly limited, and may be a hydrate.

  Moreover, it is preferable that such a 1st compound is a powdery thing. Although it does not restrict | limit especially as a particle | grain of such a 1st compound, It is preferable that an average particle diameter is 0.01-2000 micrometers, and it is more preferable that it is 0.1-1000 micrometers. If the average particle size of the particles of the first compound is less than the lower limit, it tends to be difficult to handle the powder, and if it exceeds the upper limit, mixing tends to be difficult.

Moreover, as a 2nd compound containing Mn, nitrate, carbonate, sulfate, organic acid salt (for example, acetate) of Mn, etc. are mentioned, for example. As such a second compound containing Mn, Mn (CH ₃ COO) ₂ is preferable from the viewpoint of easy availability and high reactivity. In addition, you may use such a 2nd compound individually by 1 type or in combination of 2 or more types. Moreover, you may use a commercially available 2nd compound suitably. Further, the form of the second compound is not particularly limited, and may be a hydrate (for example, Mn (CH ₃ COO) ₂ .4H ₂ O). As the second compound containing Mn, manganese acetate compound (acetate manganese (e.g. _Mn (CH 3 _{COO) 2} or the like) or a hydrate thereof (e.g., _Mn (CH 3 _COO) 2 · 4H ₂ O, etc. )) Is particularly preferred.

  Moreover, it is preferable that such a 2nd compound is a powdery thing. Although it does not restrict | limit especially as a particle | grain of such a 2nd compound, It is preferable that an average particle diameter is 0.01-2000 micrometers, and it is more preferable that it is 0.1-1000 micrometers. When the average particle size of the particles of the second compound is less than the lower limit, it tends to be difficult to handle the powder. On the other hand, when the average particle size exceeds the upper limit, sufficient mixing tends to be difficult.

In addition, when a mixture is obtained by dry-type physical mixing in this way, when the metal element A is a metal element that becomes a monovalent cation in the mixture, the number of moles of the metal element A [ A] and the number of moles of Mn [Mn] are inequalities: ([A] / [Mn]) ≦ 0.65 (more preferably 0.12 ≦ ([A] / [Mn]) ≦ 0.6) When the metal element A is a metal element that becomes a divalent cation, the number of moles [A] of the metal element A and the number of moles [Mn] of Mn are inequalities: ([A ] / [Mn]) ≦ 0.325 (more preferably 0.06 ≦ ([A] / [Mn]) ≦ 0.3), and the metal element A becomes a monovalent cation. When the metal element and the metal element that becomes a divalent cation coexist, the number of moles of the metal element A that becomes a monovalent cation And A _1], 2-valent moles of metal element A comprising a cation and _{[A 2],} the number of moles of Mn [Mn] and but _{inequality: ([A 1 + 2 ×} A 2] / [Mn]) ≦ 0.65 (more preferably 0.12 ≦ ([A ₁ + 2 × A ₂ ] / [Mn]) ≦ 0.6) The first compound and the second compound are mixed so as to satisfy the condition shown in FIG. It is preferable to do. When the ratio of the number of moles exceeds the above upper limit, the concentration of the metal element A becomes too high and the entire pore is filled with the cation of the metal element A, so that the number of defect sites is reduced. Since the valence change of Mn is difficult to occur, a sufficiently high CO oxidation performance tends to be not obtained. On the other hand, if it is less than the lower limit, a large amount of unreacted product tends to be obtained.

  In the step (i), the first compound and the second compound are physically mixed in a dry manner. Here, “physically mixing in a dry process” means physically mixing the first compound and the second compound in a dry process (in a dry state), for example, a dry process using a mortar. Etc. to be mixed. In addition, in the manufacturing method of the 1st exhaust gas purification catalyst of this invention, the method of mixing said 1st compound and said 2nd compound with a dry type is employ | adopted, and said 1st compound is wet (in presence of a solvent). And the case where the second compound is mixed. This is because, when the mixture is an aqueous solution of the first compound and the second compound, growth in the c-axis direction is promoted in the subsequent heating step, and a metal oxide having a long c-axis length is formed. This is because the metal oxide according to the present invention (primary particles of the metal oxide having an average length in the c-axis direction of 10 to 120 nm) cannot be produced.

  The average particle size of the powder of the mixture is not particularly limited, but is preferably 5 to 1000 nm (more preferably 10 to 500 nm). If the size of the powder is less than the lower limit, the cost for mixing increases, and the economy tends to decrease. On the other hand, when the upper limit is exceeded, the mixture is not sufficiently mixed and unreacted components tend to remain. It is in.

  Next, process (ii) is demonstrated. In step (ii), the mixture is heated at a temperature of 30 to 150 ° C. for 1 to 8 hours and then calcined at 200 to 550 ° C. to obtain the exhaust gas purifying catalyst of the present invention.

  Thus, in step (ii), the mixture is heated (baked) before being baked. The heating temperature in such heat treatment is 30 to 150 ° C. When the heating temperature is lower than the lower limit, a metal oxide containing a hollandite type crystal phase cannot be obtained. On the other hand, when the heating temperature exceeds the upper limit, similarly, a metal oxide containing a hollandite-type crystal phase cannot be obtained. As for the heating temperature of such a mixture, not only can the metal oxide according to the present invention be produced more efficiently, but also a metal oxide having a hollandite-type single phase crystal phase can be produced more reliably. Therefore, the temperature is preferably 60 to 140 ° C, and more preferably 70 to 120 ° C.

  Moreover, the heating time in the said heat processing of the said mixture is 1 to 8 hours. When the heating time is less than the lower limit, the reaction does not proceed sufficiently, the yield of the metal oxide according to the present invention is reduced, and the metal oxide cannot be obtained efficiently, while the upper limit is exceeded. When it exceeds, manufacturing cost will become high and it exists in the tendency for economical efficiency to fall. From the same viewpoint, such heating time is preferably 2 to 7 hours, and more preferably 3 to 6 hours.

  In addition, after such heat treatment, from the viewpoint of removing excess metal element A, the obtained mixture may be washed with water and dried. Moreover, it is preferable to perform the heat processing with respect to such a mixture in the gas atmosphere containing 1 volume% or more of oxygen, and it is more preferable to perform in the air from a viewpoint of the simplicity of a process.

  In the present invention, a hollandite-type crystal phase can be obtained by appropriately aging by performing the heat treatment under the conditions of the heating temperature and time as described above, while sufficiently suppressing crystal growth in the c-axis direction. Since the metal oxide can be synthesized, the length in the c-axis direction of the crystal structure of the metal oxide is appropriate at the time of firing described later, whereby the average value of the length in the c-axis direction of the metal oxide is 10 to 10. The ratio of primary particles in which the length in the c-axis direction of the crystal structure of the obtained metal oxide particles is in the range of 20 to 100 nm among the obtained metal oxide particles is 50 on the basis of the number of particles. It becomes possible to set it as -100%.

  In step (ii), the mixture after the heat treatment is baked. The temperature at the time of such baking is 200-550 degreeC. When the firing temperature is lower than the lower limit, a metal oxide containing a hollandite-type crystal phase cannot be obtained sufficiently. On the other hand, when the upper limit is exceeded, formation of a plurality of crystal phases is promoted. In addition, a metal oxide containing a hollandite-type crystal phase cannot be obtained (in particular, a single-phase metal oxide cannot be obtained). Further, from the same viewpoint, the firing temperature is preferably 300 to 550 ° C, and more preferably 350 to 500 ° C.

  Moreover, as such baking time, it is preferable that it is 1 to 8 hours, and it is more preferable that it is 2 to 6 hours. If the firing time is less than the lower limit, a metal oxide containing a hollandite-type crystal phase tends not to be obtained. On the other hand, if the upper limit is exceeded, the crystal structure grows in the c-axis direction. The metal oxide having an average c-axis length exceeding 120 nm tends to be promoted.

  By such firing treatment, a metal oxide containing a hollandite-type crystal phase can be synthesized while sufficiently suppressing crystal growth in the c-axis direction, and the average value of the c-axis direction length of the metal oxide is 10 The ratio of primary particles having a length in the c-axis direction of the crystal structure of the obtained metal oxide particles in the range of 20 to 100 nm among the obtained metal oxide particles is based on the number of particles. Thus, the exhaust gas purifying catalyst of the present invention comprising the metal oxide represented by the above general formula (1) can be obtained.

  As mentioned above, although the manufacturing method of the 1st catalyst for exhaust gas purification of this invention was demonstrated, next, it can utilize suitably as a method for manufacturing the catalyst for exhaust gas purification of this invention. A method for producing a second exhaust gas purifying catalyst will be described.

The second method for producing a catalyst for exhaust gas purification according to the present invention comprises ball milling and grinding a first compound containing a metal element A that becomes a monovalent or divalent cation in a compound and a second compound containing Mn. Obtaining a mixture (I);
A step (II) of obtaining the exhaust gas purifying catalyst of the present invention by calcining the pulverized mixture at 200 to 550 ° C .;
It is the method characterized by including. According to the second method for producing an exhaust gas purification catalyst of the present invention, the exhaust gas purification catalyst of the present invention can be efficiently produced. Hereinafter, step (I) and step (II) will be described separately.

First, step (I) will be described. In step (I), the first compound and the second compound are ball milled to obtain a pulverized mixture. The metal element A, the first compound, and the second compound are the same as those described in the first method for producing an exhaust gas purifying catalyst of the present invention. Moreover, the suitable conditions of the ratio ([A] / [Mn] and [A ₁ + 2 × A ₂ ] / [Mn]) of the number of moles of metal element A and the number of moles of Mn in the pulverized mixture are as described above. The ratio between the number of moles of metal element A and the number of moles of Mn in the mixture described in the first method for producing an exhaust gas purification catalyst of the present invention ([A] / [Mn] and [A ₁ + 2 × A ₂ ] / [Mn]) is the same as the preferred conditions.

  Further, the ball mill method employed in the step (I) is not particularly limited, and a known ball mill method such as a rotating ball mill method, a vibrating ball mill method, a planetary ball mill method, and a stirring ball mill method (also referred to as an attritor) is used. It can be adopted as appropriate. Among such ball mill methods, it is particularly preferable to use the rotating ball mill method and the planetary ball mill method from the viewpoint of providing sufficient kinetic energy.

  In such a ball mill, the first compound and the second compound are placed in a container (pot) together with a ball for mixing and grinding, and the container is rotated, etc. The second compound is mixed with a dry method and pulverized to obtain a pulverized mixture. In such a ball mill, it is preferable to perform ball milling so that the average particle size of the powder of the pulverized mixture is 5 to 1000 nm (more preferably 10 to 500 nm). If the size of the powder is less than the lower limit, the cost and time for mixing tend to increase. On the other hand, if the upper limit is exceeded, the first compound and the second compound are not sufficiently mixed. , Unreacted components tend to remain after the reaction.

  As a ball used for such a ball mill, it is preferable to use a ball made of any one material of zirconia, alumina, agate and silicon nitride from the viewpoint of poor reactivity with the raw material. In addition, as for the size of such a ball, since a suitable one varies depending on the capacity of the container to be used, etc., it cannot be generally stated, but from the viewpoint that the size of the powder of the pulverized mixture is in the above range. It is preferable to use one having a diameter of about 1 to 50 mm.

  Further, the container (pot) used for such a ball mill is not particularly limited, and a known container can be used as appropriate, and its size, material, shape, etc. can be changed as appropriate according to the amount of metal oxide to be produced. (For example, a stainless steel container or PP container having a capacity of 50 to 10,000 ml may be used). Furthermore, in such a ball mill, a commercially available ball mill apparatus may be used as appropriate.

  In addition, since the rotation speed and milling time of the container vary depending on the type of balls used and the average particle size of the target pulverized mixture powder, the first compound to be used cannot be generally stated. What is necessary is just to determine suitably according to the kind etc. of these. From the viewpoint of ball milling so that the average particle size of the powder of the pulverized mixture falls within the above range, for example, a method of ball milling for 1 to 10 hours at a rotation speed of the container of 100 to 1000 rpm may be employed. . In addition, after such a ball mill, from the viewpoint of removing excess metal element A, the obtained pulverized mixture is washed with water and dried, and then used for a firing treatment (step (II)) described later. Also good.

  Further, in the present invention, by performing the ball mill as described above, a metal oxide containing a hollandite type crystal phase can be synthesized while sufficiently suppressing crystal growth in the c-axis direction. The length in the c-axis direction of the crystal structure of the oxide becomes appropriate, which makes it possible to make the average value of the length in the c-axis direction of the metal oxide within the range of 10 to 130 nm. The proportion of primary particles having a crystal structure length in the range of 20 to 100 nm among the primary particles of the metal oxide to be produced can be 50 to 100% on the basis of the number of particles.

  Next, process (II) is demonstrated. In step (II), the pulverized mixture is calcined at 200 to 550 ° C. to obtain the exhaust gas purification positive catalyst of the present invention.

  Such a calcination temperature is 200-550 degreeC. When the firing temperature is lower than the lower limit, a metal oxide containing a hollandite-type crystal phase cannot be obtained sufficiently. On the other hand, when the upper limit is exceeded, formation of a plurality of crystal phases is promoted. In addition, a metal oxide containing a hollandite-type crystal phase cannot be obtained (in particular, a single-phase metal oxide cannot be obtained). Further, from the same viewpoint, the firing temperature is preferably 300 to 550 ° C, and more preferably 350 to 500 ° C.

  Moreover, as such baking time, it is preferable that it is 1 to 8 hours, and it is more preferable that it is 2 to 6 hours. If the firing time is less than the lower limit, a metal oxide containing a hollandite-type crystal phase tends not to be obtained. On the other hand, if the upper limit is exceeded, the crystal structure grows in the c-axis direction. The metal oxide having an average c-axis length exceeding 120 nm tends to be promoted.

  By such firing treatment, a metal oxide containing a hollandite-type crystal phase can be synthesized while sufficiently suppressing crystal growth in the c-axis direction, and the average value of the c-axis direction length of the metal oxide is 10 The ratio of primary particles having a length in the c-axis direction of the crystal structure of the obtained metal oxide particles in the range of 20 to 100 nm among the obtained metal oxide particles is based on the number of particles. Thus, the exhaust gas purifying catalyst of the present invention comprising the metal oxide represented by the above general formula (1) can be obtained.

  As described above, the first and second exhaust gas purification catalyst manufacturing methods of the present invention that can be suitably used as a method for manufacturing the exhaust gas purification catalyst of the present invention have been described. The method for producing the purification catalyst is not limited to the first and second exhaust gas purification catalyst production methods of the present invention, and the exhaust gas purification catalyst of the present invention can be produced. Any method can be used as appropriate.

As another method capable of producing such an exhaust gas purifying catalyst of the present invention, for example, a solution in which a first compound containing a metal element A that becomes a monovalent or divalent cation in a compound is dissolved. (For example, an aqueous solution) is contacted with a Mn compound (more preferably, an oxide (MnO ₂ )) and then evaporated to dryness to obtain a metal oxide precursor in which the first compound is supported on the Mn compound. Thereafter, the metal oxide precursor may be calcined at 200 to 550 ° C. to obtain the exhaust gas purification positive catalyst of the present invention. Such metal element A and the first compound are the same as those described in the first method for producing an exhaust gas purifying catalyst of the present invention. In addition, what is necessary is just to change suitably the usage-amount of the oxide of a 1st compound or Mn so that the metal oxide represented by the said General formula (1) may be obtained. Moreover, the conditions in particular at the time of evaporating to dryness are not restrict | limited, You may dry by heating for 1 to 12 hours on 60-120 degreeC temperature conditions. The conditions for calcining the mixture thus obtained can be the same as the calcining conditions employed in the first method for producing an exhaust gas purifying catalyst of the present invention. It is possible to produce the exhaust gas purifying catalyst of the present invention also by such a method.

  Further, by carrying out the method for producing the exhaust gas purifying catalyst of the present invention as described above (including the first and second exhaust gas purifying catalysts of the present invention), the above general formula ( The exhaust gas purifying catalyst comprising the metal oxide represented by 1) can be obtained, and the obtained metal oxide has a structure in which the cations of the metal element A are arranged in the pores. The Thus, after manufacturing the metal oxide represented by the general formula (1), a compound (for example, nitric acid or the like) that can react with the metal element A to form a salt of A is used. In addition, by adding the metal oxide to a solution (for example, an aqueous solution) in which such a compound is dissolved and reacting, it is possible to remove a part of the metal element A from the pores as a salt, The concentration of the metal element A arranged in the pores of the metal oxide can be easily adjusted.

In addition, the above-described method for producing the exhaust gas purifying catalyst of the present invention (including the first and second exhaust gas purifying catalyst production methods of the present invention) is carried out to carry out the above general formula (1). After the production of the metal oxide represented by the following formula, a metal element A of a different type from the metal element A present in the pores (for convenience, hereinafter referred to as “metal element A1”) (for convenience, hereinafter referred to as “ By using a compound containing the metal element A2 ")), an ion exchange reaction is allowed to proceed with respect to the obtained metal oxide, whereby at least one of the ions of the metal element A1 present in the pores of the metal oxide. It is also possible to obtain a different kind of metal oxide represented by the general formula (1) by exchanging a part thereof with ions of the metal element A2. The compound containing such a metal element A2 is not particularly limited as long as it can be used for an ion exchange reaction. For example, the above-described first compound can be used as appropriate. The conditions for such an ion exchange reaction are not particularly limited as long as the ions of the metal element A1 existing in the pores can be exchanged for the ions of the metal element A2, and a known ion exchange method is used. It can be used as appropriate. As a method for obtaining different types of metal oxides using the ion exchange reaction as described above, for example, first, using CH ₃ COONH ₄ , a part of the metal element A1 existing in the pores of the metal oxide is used. After ion exchange between NH ₄ and NH ₄ , the metal oxide is added to a solution in which the compound containing the metal element A 2 is dissolved and reacted, so that NH ₄ and ions of the metal element A 2 are present in the pores. A method of obtaining different types of metal oxides by exchanging A2 ions in the pores, or adding the obtained metal oxides to a solution in which a compound containing the metal element A2 is dissolved. Thus, a method of obtaining a different kind of metal oxide by arranging the metal element A2 in the pores and exchanging at least a part of the ions of A1 with the ions of the metal element A2 can be exemplified. In addition, it does not restrict | limit especially as a solvent of the solution used for such reaction, For example, you may use water.

  The exhaust gas purification catalyst of the present invention has been described above. Next, the exhaust gas purification method of the present invention using the exhaust gas purification catalyst of the present invention will be described.

  The exhaust gas purification method of the present invention is a method characterized in that the exhaust gas containing carbon monoxide is brought into contact with the exhaust gas purification catalyst of the present invention to oxidize and purify the carbon monoxide.

  The method for bringing the exhaust gas containing carbon monoxide (CO) into contact with the exhaust gas is not particularly limited. For example, the exhaust gas purification catalyst of the present invention is disposed in an exhaust gas pipe, and the engine of a gasoline vehicle, diesel engine, fuel For example, a method of contacting exhaust gas discharged from an internal combustion engine such as a lean burn engine having a low consumption rate with the exhaust gas purifying catalyst of the present invention in an exhaust gas pipe may be adopted.

  In addition, the exhaust gas purification method of the present invention can be particularly suitably used for a method of purifying CO by contacting exhaust gas containing CO in an oxygen-excess atmosphere. As used herein, “oxygen-excess atmosphere” refers to an atmosphere having a chemical equivalent ratio of oxygen to reducing gas component of 1 or more. As described above, according to the present invention, even an exhaust gas in an oxygen-excess atmosphere discharged from a diesel engine or a lean burn engine having a low fuel consumption rate can be efficiently purified.

  Further, when purifying exhaust gas in this way, the exhaust gas purifying catalyst of the present invention may be used alone or with other materials supported on a base material. Such a substrate is not particularly limited, and a known substrate that can be used for supporting a catalyst for exhaust gas purification can be appropriately used. Further, when purifying the exhaust gas in this manner, the exhaust gas purifying catalyst of the present invention may be used in combination with another catalyst from the viewpoint of more efficiently purifying the exhaust gas. Such other catalyst is not particularly limited, and a known catalyst (for example, NOx reduction catalyst, NOx occlusion reduction type (NSR catalyst), NOx selective reduction catalyst (SCR catalyst), oxidation catalyst, etc.) is appropriately used. Can do.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
First, KMnO ₄ (Wako Pure Chemical Industries Co., Ltd. under the trade name "Potassium permanganate") 4.74 g _{and, Mn (AC) 2 · 4H} 2 O ( Wako Pure Chemical Industries Co., Ltd. under the trade name "manganese acetate (II ) Tetrahydrate ”) 11.01 g was sufficiently mixed in a mortar to obtain a mixture ([molar ratio] K: Mn = 4: 10). Next, the mixture was aged by heating in air at 80 ° C. for 4 hours to obtain a sample. Thereafter, the sample was washed 4 times with 500 mL of distilled water and dried for 12 hours. Next, the dried sample was calcined at 500 ° C. for 4 hours to obtain an exhaust gas purifying catalyst (A) composed of metal oxide particles.

(Example 2)
First, the product name “ANZ-605” manufactured by Nippon Ceramics Co., Ltd. was used as an apparatus for the ball mill, and 4.74 g of KMnO ₄ (trade name “potassium permanganate” manufactured by Wako Pure Chemical Industries, Ltd.) _AC) 2 · _4H 2 O (Wako Pure Chemical Industries Co., Ltd. under the trade name "manganese (II) acetate tetrahydrate" and) 11.01 g, with alumina balls having a diameter of 10 mm (130 pieces are used), the capacity The container was placed in a 1 L polypropylene (PP) container, and the container was rotated at 120 rpm for 6 hours at room temperature and ball milled to obtain a powder of a pulverized mixture ([molar ratio] K: Mn = 4: 10). Next, the pulverized mixture was washed with 500 mL of distilled water four times and dried for 12 hours. Next, the pulverized mixture was calcined at 500 ° C. for 4 hours to obtain an exhaust gas purifying catalyst (B) composed of metal oxide particles.

(Example 3)
First, after obtaining a solution obtained by dissolving 1.42 g of CH ₄ COOK (trade name “potassium acetate” manufactured by Wako Pure Chemical Industries, Ltd.) in 100 mL of distilled water, MnO ₂ (Chuo Electric Industrial Co., Ltd.) was added to the solution. 10 g of company-made trade name “CMD-K200”) was immersed to obtain a mixture ([molar ratio] K: Mn = 13: 100). Next, the mixture was heated at 100 ° C. for 3 hours to evaporate water and obtain a sample. Next, the sample was dried at 110 ° C. under heating conditions for 24 hours, and then calcined at 500 ° C. for 4 hours to obtain an exhaust gas purifying catalyst (C) composed of metal oxide particles.

Example 4
First, metal oxide particles (exhaust gas purifying catalyst (A)) were obtained in the same manner as in Example 1. Next, the obtained metal oxide particles were put into a 200 mL aqueous solution in which nitric acid was dissolved at a concentration of 10% by mass, and heat-treated at 80 ° C. for 5 hours. In addition, by such a process, some K which existed in the pore of the metal oxide before heat processing is removed as a salt (nitrate). Next, the metal oxide particles after the heat treatment were collected from the aqueous solution, washed 4 times with 500 mL of distilled water, and dried for 12 hours. The metal oxide particles thus obtained were used as they were as an exhaust gas purification catalyst (D).

(Example 5)
First, metal oxide particles (exhaust gas purifying catalyst (A)) were obtained in the same manner as in Example 1. Next, the obtained metal oxide particles were put into a 100 mL aqueous solution in which Na ₂ CO ₃ was dissolved at a concentration of 0.05 mol / L, and allowed to stand at room temperature (25 ° C.) for 5 hours. In addition, by such a process, some K in the metal oxide before heat processing is ion-exchanged with Na (ion exchange reaction). Next, the metal oxide particles after the heat treatment were collected from the aqueous solution, washed 4 times with 500 mL of distilled water, and dried for 12 hours. The metal oxide particles thus obtained were directly used as an exhaust gas purifying catalyst (E).

(Example 6)
First, metal oxide particles (exhaust gas purifying catalyst (A)) were obtained in the same manner as in Example 1. Next, the obtained metal oxide particles were put into a 100 mL aqueous solution in which (CH ₃ COOH) ₂ Ba was dissolved at a concentration of 0.2 mol / L, and allowed to stand at room temperature (25 ° C.) for 5 hours. did. In addition, by such a process, some K in the metal oxide before heat processing is ion-exchanged with Ba (ion exchange reaction). Next, the metal oxide particles after the heat treatment were collected from the aqueous solution, washed 4 times with 500 mL of distilled water, and dried for 12 hours. The metal oxide particles thus obtained were used as they were as an exhaust gas purification catalyst (F).

(Example 7)
First, metal oxide particles (exhaust gas purifying catalyst (A)) were obtained in the same manner as in Example 1. Next, the obtained metal oxide particles were put into a 100 mL aqueous solution in which CH ₃ COONH ₄ was dissolved at a concentration of 0.2 mol / L, and allowed to stand at room temperature (25 ° C.) for 5 hours. One process). Incidentally, such a first process, a portion of the K in the metal oxide before the heat treatment is NH ₄ ion exchange (ion exchange reaction). Subsequently, the metal oxide particles after the first treatment (particles in which part of K was ion-exchanged with NH ₄ ) were collected from the aqueous solution, and then washed with 500 mL of distilled water four times. Then, the washed metal oxide particles are put into an aqueous solution (100 mL) in which Ca (NO ₃ ) ₂ .4H ₂ O is dissolved at a concentration of 0.2 mol / L, and 5 ° C. at room temperature (25 ° C.). Allowed to stand for a second time (second treatment). Incidentally, such a second process, the second process NH ₄ before the metal oxide is Ca ion exchange (ion exchange reaction). Next, after collecting the metal oxide particles after the second treatment from the aqueous solution, the particles were washed 4 times with 500 mL of distilled water and dried for 12 hours. The metal oxide particles thus obtained were used as they were as an exhaust gas purification catalyst (G).

(Example 8)
The aqueous solution used for the second heat treatment is CH ₃ COOLi at a concentration of 0.1 mol / L from an aqueous solution (100 mL) in which Ca (NO ₃ ) ₂ .4H ₂ O is dissolved at a concentration of 0.2 mol / L. Exhaust gas purification positive catalyst (H) composed of metal oxide particles was obtained in the same manner as in Example 7, except that the solution was changed to a dissolved aqueous solution (100 mL). In the metal oxide particles, Li is introduced into the pores by an ion exchange reaction.

Example 9
Exhaust gas purification positive catalyst (I) made of metal oxide particles was obtained in the same manner as in Example 1 except that the heating temperature at the time of obtaining the sample (heating temperature in the aging step) was changed from 80 ° C. to 40 ° C. .

(Example 10)
The amount of KMnO ₄ used was changed from 4.74 g to 7.11 g, and the amount of Mn (AC) ₂ .4H ₂ O was changed from 11.01 g to 7.34 g. Exhaust gas purification positive catalyst (J) made of metal oxide particles was obtained in the same manner as in Example 1 except that the molar ratio was 6:10.

(Comparative Example 1)
First, 12.5 ml of acetic acid was added to a solution obtained by dissolving 27.5 g of Mn (NO ₃ ) ₂ in 50 ml of distilled water, and then 16.6 g of KMnO ₄ was further dissolved in 375 ml of distilled water. An aqueous solution was added and mixed to obtain a mixed solution. The resulting mixture was then heated at reflux for 24 hours. Thereby, a precipitate was formed in the mixed solution. Next, the precipitate was taken out from the mixed solution by filtration, washed 4 times with 500 mL of distilled water, and dried for 12 hours to obtain a sample. Next, the dried sample was calcined at 500 ° C. for 4 hours to obtain an exhaust gas purifying catalyst (K) composed of metal oxide particles for comparison.

(Comparative Example 2)
Exhaust gas purification positive catalyst (L) made of metal oxide particles for comparison in the same manner as in Example 1 except that the heating temperature at the time of obtaining the sample (heating temperature in the aging step) was changed from 80 ° C. to 160 ° C. )

(Comparative Example 3)
The amount of KMnO ₄ used was changed from 4.74 g to 1.19 g, the amount of Mn (AC) ₂ .4H ₂ O used was changed from 11.01 g to 16.51 g, and the moles of K and Mn in the mixture were changed. Exhaust gas purification positive catalyst (M) composed of metal oxide particles for comparison was obtained in the same manner as in Example 1 except that the ratio was 1:10.

(Comparative Example 4)
After adding 3 ml of nitric acid to a solution obtained by dissolving 1.91 g of AgMnO ₄ in 320 ml of distilled water, 2.25 g of Mn (NO ₃ ) ₂ was added and dissolved to obtain a mixed solution. . Next, the obtained mixed solution was aged at 120 ° C. for 6 hours to form a precipitate. Next, the solid (precipitate) was collected by filtration from the mixed solution, and the obtained solid was washed five times with distilled water. Thereafter, the solid content was left to dry in the atmosphere for 12 hours. Thereafter, the dried solid was calcined at 500 ° C. for 4 hours to obtain an exhaust gas purifying catalyst (N) made of metal oxide particles for comparison.

(Comparative Example 5)
MnO ₂ (trade name “CMD-K200” manufactured by Chuo Denki Kogyo Co., Ltd.) was prepared, and the metal oxide particles composed of MnO ₂ were directly used as an exhaust gas purification catalyst (O).

[Evaluation of characteristics of exhaust gas purification catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 5]
<Measurement by transmission electron microscope (TEM)>
Each metal oxide obtained in Examples 1 to 3 and Examples 9 to 10 and Comparative Examples 1 to 4 was measured with a transmission electron microscope (TEM). As a result of such measurement, transmission electron microscope (TEM) photographs of the metal oxide obtained in Example 1 are shown in FIGS. 1 to 3, and a transmission electron microscope of the metal oxide obtained in Comparative Example 1 is shown. (TEM) photographs are shown in FIGS.

  Moreover, based on the result of the transmission electron microscope (TEM) measurement, the average length in the c-axis direction of the crystal structure of the primary particles of the metal oxides obtained in Examples 1 to 10 and Comparative Example 1 was determined. . In addition, the average length in the c-axis direction of the crystal structure of such primary particles is obtained by measuring the length in the c-axis direction of 100 metal oxide primary particles for each measured Example and each Comparative Example. The average value was calculated. The results are shown in Table 1.

  Furthermore, among the primary particles of the metal oxides obtained in Examples 1 to 10 and Comparative Example 1, based on the results of transmission electron microscope (TEM) measurement, the length in the c-axis direction is in the range of 20 to 100 nm. The proportion of particles in In addition, the number of primary particles of the metal oxide measured for obtaining the average value was 100 for each example and each comparative example. The results are shown in Table 1.

  The metal oxide particles obtained in Examples 4 to 8 were prepared by changing the concentration of the metal element in the pores using the metal oxide particles obtained in Example 1 or fine particles. The average length of primary particles in the c-axis direction and the proportion of particles having a length in the c-axis direction in the range of 20 to 100 nm are obtained by performing an ion exchange reaction of metal elements in the pores. The value is the same as that of the metal oxide particles obtained in Example 1. Therefore, the metal oxide particles (exhaust gas purification catalysts (D) to (H)) obtained in Examples 4 to 8 were measured by transmission electron microscope (TEM) of the metal oxide obtained in Example 1. Based on the results, the average length of the primary particles in the c-axis direction and the proportion of particles having a length in the c-axis direction in the range of 20 to 100 nm were determined.

  As is clear from the results shown in Table 1, in the metal oxides obtained in Examples 1 to 10, the average length in the c-axis direction of the primary particles of the metal oxide is 120 nm or less and The proportion of particles having a length in the c-axis direction in the range of 20 to 100 nm was also in the range of 50 to 100%. On the other hand, as is clear from the results shown in Table 1, in the metal oxide obtained in Comparative Example 1, the average value of the lengths of the primary particles in the c-axis direction exceeds 120 nm. It was. In the metal oxide obtained in Comparative Example 1, the proportion of particles having a length in the c-axis direction in the range of 20 to 100 nm was less than 50%. In addition, considering that the final firing conditions are the same in Example 1 and Comparative Example 1, the step of mixing and aging in a wet manner as employed in Comparative Example 1 in the step before firing is performed. When it was adopted, it was found that the growth rate in the c-axis direction was increased in the aging process.

<Inductively coupled plasma (ICP) analysis>
Inductively coupled plasma (ICP) analysis was performed on the metal oxides obtained in Examples 1 to 10 and Comparative Examples 1 to 3, respectively. The results of such measurement are shown in Table 2. In Table 2, the value of x for each metal element A in the general formula (1) is shown. In Examples 6 and 7, since the metal element A that becomes a monovalent cation and the metal element A that becomes a divalent cation coexist, the metal element A that becomes a monovalent cation. The value of x of “x ₁ ” and the value of x of the metal element A that is a divalent cation is x ₂ , and the formula: A _T = (x ₁ + 2 × x ₂ ) was calculated and found. Table 2 shows the values of _AT .

<Measurement by X-ray diffraction (XRD)>
X-ray diffraction (XRD) analysis was performed on the metal oxides obtained in Examples 1 to 10 and Comparative Examples 1 to 3, and the crystal structure was measured. The results of such measurement are shown in Table 2.

As is clear from the results shown in Table 2, it was confirmed that all of the metal oxides obtained in Examples 1 to 10 and Comparative Examples 1 to 3 were metal oxides containing a hollandite type crystal phase. It was done. In Example 9, the phase of Mn ₂ O ₃ was confirmed. Based on the X-ray diffraction pattern obtained from the X-ray diffraction, the main peak of each hollandite crystal phase was changed from the main peak of each crystal phase. When the index of the area ratio was calculated, the index of the ratio of the hollandite-type crystal phase was 91% by mass. In Examples 1-10, the general formula _{(1): A x Mn 8} O 16 (A is a monovalent or divalent metal element serving as cations in the oxide.) Represented by It is a metal oxide containing a hollandite-type crystal phase, and when A is a monovalent cation, the inequality: x ≦ 1.65 is satisfied, and A is a monovalent cation. When a metal element and a metal element that becomes a divalent cation coexist, the condition shown by the inequality: A _T ≦ 1.65 was satisfied. On the other hand, in the metal oxides obtained in Comparative Examples 2 to 3, the metal element A contains K, but the value of x in the general formula (1) is 1.69 or more, The concentration of the metal element A was high. Since Example 1 and Comparative Example 2 are the same steps except the aging step before firing, when heated at a high temperature (160 ° C.) in the aging step, the metal element A in the pores It turned out that the content rate of (potassium (K)) becomes high and the target metal oxide (metal oxide represented by the said General formula (1)) cannot be formed.

[Evaluation of characteristics of exhaust gas purification catalysts (A) to (O)]
Using the exhaust gas purifying catalysts (A) to (O) obtained in Examples 1 to 10 and Comparative Examples 1 to 5, the CO oxidation performance of each catalyst was measured. In measuring such CO oxidation performance, first, a fixed bed flow reactor was used to fill a reaction tube having an inner diameter of 15 mm with an exhaust gas purification catalyst (1.0 g). Next, a lean gas having a composition shown in Table 3 below is supplied at a flow rate of 5 L / min to the exhaust gas purifying catalyst under a temperature condition of 200 ° C. (constant), and before contacting the exhaust gas purifying catalyst. The CO concentration in the gas (inlet gas: lean gas) and the gas (outgas) after contacting the exhaust gas purifying catalyst was measured using a continuous gas analyzer, and the CO concentration in the input gas in the steady state and the output The CO purification rate was calculated from the CO concentration in the gas.

  The measurement results of such CO oxidation performance (results of CO purification rates of the exhaust gas purification catalysts (A) to (O) obtained in Examples 1 to 10 and Comparative Examples 1 to 5) are shown in FIG. Symbols (A) to (O) in FIG. 7 are symbols (catalysts) indicating the types of exhaust gas purifying catalysts (A) to (O) obtained in Examples 1 to 10 and Comparative Examples 1 to 5, respectively. Is a symbol indicating the type).

As is clear from the results shown in FIG. 7, when the metal element A is a monovalent cation represented by the general formula (1), x is an inequality: x ≦ 1.65 And a metal element which becomes a monovalent cation and a metal element which becomes a divalent cation coexist as A, a hollandite type crystal satisfying the condition represented by the inequality A _T ≦ 1.65 It is a metal oxide containing a phase, and the average length of the crystal structure of the primary particles in the c-axis direction is 10 to 120 nm, and the length of the crystal structure of the primary particles in the c-axis direction is 20 to In the exhaust gas purifying catalyst of the present invention (Examples 1 to 10) comprising a metal oxide in which the proportion of primary particles in the range of 100 nm is 50 to 100% on the basis of the number of particles, CO is sufficiently oxidized. Purifying and advanced CO oxidation It was found to be one having a capacity. On the other hand, the oxidation performance of CO of the exhaust gas purifying catalyst made of the metal oxide obtained in Comparative Examples 2 to 3 in which the value of x in the formula was 1.688 or more was low. It was. In addition, a comparative example in which the average length of primary particles exceeds 120 nm and the proportion of primary particles in the c-axis direction of the crystal structure in the primary particles in the range of 20 to 100 nm is less than 50%. The CO oxidation performance of the exhaust gas purifying catalyst comprising the metal oxide obtained in 1 was not sufficient. From these results, the average length in the c-axis direction of the crystal structure of the primary particles of the metal oxide is 10 to 120 nm, and among the primary particles of the metal oxide, the length in the c-axis direction of the crystal structure is Aspect ratio (ratio of the length in the c-axis direction of the particle to the length in the direction perpendicular to the c-axis) such that the proportion of primary particles in the range of 20 to 100 nm (based on the number of particles) is 50 to 100%. ) Is sufficiently low and the catalyst for exhaust gas purification of the present invention comprising a sufficiently uniform metal oxide has a sufficiently high abundance ratio of the plane (crystal (110) plane) perpendicular to the c-axis having high oxidation activity Therefore, it is presumed that excellent oxidation performance such as CO is exhibited.

  As described above, according to the present invention, an exhaust gas purification catalyst having excellent CO oxidation performance capable of sufficiently oxidizing and purifying CO even under low temperature conditions, and exhaust gas purification using the same It becomes possible to provide a method.

Therefore, the exhaust gas purifying catalyst and the exhaust gas purifying method of the present invention are particularly suitable as a catalyst for purifying exhaust gas containing CO discharged from an internal combustion engine such as an automobile engine and a method for purifying such exhaust gas. Useful.

Claims (7)

An exhaust gas purifying catalyst comprising a particulate metal oxide,
The metal oxide has the following general formula (1):
A _x Mn ₈ O ₁₆ (1)
[In Formula (1), A is a metal element other than Ag, and is a metal element that becomes a monovalent or divalent cation in the oxide,
x represents a numerical value satisfying the condition shown in the inequality: x ≦ 1.65 when A is a monovalent cation in the oxide, while x is a divalent cation. Represents a numerical value satisfying the condition shown in the inequality: x ≦ 0.825,
In the case where a metal element that becomes a monovalent cation and a metal element that becomes a divalent cation coexist in the oxide as A, the value x ₁ of x relating to the metal element A that becomes a monovalent cation and , divalent and value _{x 2} of x about the metal element a comprising a cation _{inequality: (x 1 + 2 × x} 2) satisfies the conditions shown in ≦ 1.65. ]
A metal oxide containing a hollandite-type crystal phase having a one-dimensional pore structure represented by:
The average length in the c-axis direction of the crystal structure of the primary particles of the metal oxide is 10 to 120 nm, and
Of the primary particles of the metal oxide, the proportion of primary particles having a length in the c-axis direction of the crystal structure in the range of 20 to 100 nm is 50 to 100% based on the number of particles,
An exhaust gas purifying catalyst characterized by.   The exhaust gas according to claim 1, wherein the metal element A is at least one element selected from the group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba. Purification catalyst.   The exhaust gas purifying catalyst according to claim 1 or 2, wherein the metal element A is K. A step of physically mixing a first compound containing a metal element A which becomes a monovalent or divalent cation in the compound and a second compound containing Mn to obtain a mixture;
After heating the said mixture at the temperature of 30-150 degreeC for 1 to 8 hours, baking at 200-550 degreeC, and obtaining the catalyst for exhaust gas purification as described in any one of Claims 1-3,
A method for producing an exhaust gas purifying catalyst, comprising: Ball milling a first compound containing a metal element A that becomes a monovalent or divalent cation in the compound and a second compound containing Mn to obtain a pulverized mixture;
Calcining the pulverized mixture at 200 to 550 ° C to obtain the exhaust gas purifying catalyst according to any one of claims 1 to 3,
A method for producing an exhaust gas purifying catalyst, comprising:   6. The method for producing an exhaust gas purification catalyst according to claim 5, wherein a ball made of any one of zirconia, alumina, agate, and silicon nitride is used for the ball mill.   An exhaust gas purification method comprising contacting an exhaust gas containing carbon monoxide with the exhaust gas purification catalyst according to claim 1 to oxidize and purify the carbon monoxide.