JP2012196653A - Catalyst carrier, catalyst for purifying exhaust gas using the same, and method of purifying exhaust gas using the catalyst - Google Patents

Abstract

A catalyst carrier capable of purifying CO even under low temperature conditions.
The invention relates to a catalyst carrier comprising a metal oxide, the metal oxide is the general formula _{(1): A x M y} Ti (8-y) O 16 (1) [A monovalent in the oxide Or a metal element that becomes a divalent cation, M is a metal element other than Ti and can be a trivalent cation in the oxide, and x is a monovalent cation in the oxide. Time is inequality: 0 <x ≦ 2 in numerical range, A is divalent cation, inequality: 0 <x ≦ 1 in numerical range, A is monovalent in oxide When a metal element that becomes a cation of a metal and a metal element that becomes a divalent cation coexist, the value x ₁ of the metal element A that becomes a monovalent cation and the metal that becomes a divalent cation x value _{x 2} and the inequality of the elements a: 0 <a _{(x 1 + 2 × x 2} ) ≦ 2 to indicate conditions satisfied, y is inequality: A numerical value within a range of 0 <y ≦ 2 is indicated. And has a one-dimensional pore structure.
[Selection figure] None

Description

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

  Conventionally, various exhaust gas purification catalysts have been used to purify harmful components such as carbon monoxide (CO) contained in gas discharged from an internal combustion engine or the like. As such an exhaust gas purification catalyst, a catalyst utilizing a metal oxide having a specific crystal structure such as a hollandite type is known.

For example, in Japanese Patent Application Laid-Open No. 2001-198440 (Patent Document 1), a substance having a cryptomelane, hollandite, romanite or todorokite structure containing an octahedron represented by the formula: MO ₆ and an alkali element, alkaline earth Comprising at least one element selected from the group consisting of group elements, rare earths, transition metals, Group IIIA and Group IVA, and a noble metal, and the octahedron is Group IIIB, Group IVB, Group VB , A catalyst comprising at least one element M selected from Group VIB, Group VIIB, Group VIII, Group IB, Group IIB and Group IIIA. However, in Patent Document 1, although it is described that the catalyst is used for NOx purification, it is not described at all that the catalyst is used for oxidizing CO, and the catalyst is used for oxidizing CO. However, CO oxidation performance under low temperature conditions was not always sufficient.

In addition, 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 A catalyst comprising a metal oxide is described. However, even in the catalyst as described in Non-Patent Document 1, the CO oxidation performance under low temperature conditions is not always sufficient.

JP 2001-198440 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. The exhaust gas purifying catalyst obtained by using in combination with the catalyst component is sufficiently oxidized and purified even under low temperature conditions. Catalyst carrier capable of exhibiting sufficiently high CO oxidation performance, exhaust gas purification catalyst having sufficiently high CO oxidation performance using the same, and exhaust gas purification method using the exhaust gas purification catalyst The purpose is to provide.

  As a result of intensive studies to achieve the above object, the present inventors have used, as a catalyst support, a metal oxide belonging to the cryptomelan group represented by the following general formula (1) and having a one-dimensional pore structure. As a result, the inventors have found that the exhaust gas purifying catalyst provided with the catalyst carrier can sufficiently oxidize and purify CO under low temperature conditions, and have completed the present invention.

That is, the catalyst carrier of the present invention is a catalyst carrier made of a metal oxide,
The metal oxide has the following general formula (1):
_{A x M y Ti (8-} y) O 16 (1)
[In the formula (1), A represents a metal element that becomes a monovalent or divalent cation in the oxide,
M represents a metal element other than Ti and can be a trivalent cation in the oxide;
x represents a numerical value in the range of 0 <x ≦ 2 when A is a monovalent cation in the oxide, while x is a divalent cation. Inequality: indicates a numerical value in the range of 0 <x ≦ 1,
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 of the metal element A that becomes a monovalent cation x ₁ And the value x ₂ of the metal element A that is a divalent cation satisfies the condition shown by the inequality: 0 <(x ₁ + 2 × x ₂ ) ≦ 2,
y represents a numerical value within the range of inequality: 0 <y ≦ 2. ]
And a metal oxide belonging to the cryptomelan group having a one-dimensional pore structure.

  In the catalyst carrier of the present invention, the metal oxide is preferably a hollandite-type metal oxide.

  In the catalyst carrier of the present invention, the metal element A is preferably at least one selected from the group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba. .

  In the catalyst carrier of the present invention, the metal element M is at least one selected from the group consisting of Sc, Y, V, Nb, Cr, Mo, W, Re, Fe, Ga, Al, In, and La. It is preferable that

  Furthermore, in the catalyst carrier of the present invention, the metal element A is at least one selected from the group consisting of Ba and Na, and the metal element M is selected from the group consisting of Al and Fe. It is more preferable that

The exhaust gas purifying catalyst of the present invention comprises the catalyst carrier of the present invention,
Metal particles containing at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Mo, W, Ag, Pt, Au, Pd, Rh, Ir and Ru and / or Or catalyst component particles comprising metal oxide particles containing the element;
It is characterized by providing.

  In the exhaust gas purifying catalyst of the present invention, the catalyst component particles are preferably supported on the catalyst carrier.

  Furthermore, in the exhaust gas purifying catalyst of the present invention, the element contained in the catalyst component particles is at least one selected from the group consisting of V, Cu, Pt, Au, Pd, Rh, Ir, and Ru. It is preferable that it is an element of these.

  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.

  According to the present invention, an exhaust gas purifying catalyst obtained by using in combination with a catalyst component exhibits sufficiently high CO oxidation performance that can sufficiently oxidize and purify CO even under low temperature conditions. It is possible to provide an exhaust gas purification catalyst having a sufficiently high CO oxidation performance using the catalyst carrier, and an exhaust gas purification method using the exhaust gas purification catalyst.

It is a graph which shows the CO purification rate of the exhaust gas purification catalysts (A) to (J) obtained in Examples 1 to 5 and Comparative Examples 1 to 5.

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

First, the catalyst carrier of the present invention will be described. That is, the catalyst carrier of the present invention is a catalyst carrier made of a metal oxide,
The metal oxide has the following general formula (1):
_{A x M y Ti (8-} y) O 16 (1)
[In the formula (1), A represents a metal element that becomes a monovalent or divalent cation in the oxide,
M represents a metal element other than Ti and can be a trivalent cation in the oxide;
x represents a numerical value in the range of 0 <x ≦ 2 when A is a monovalent cation in the oxide, while x is a divalent cation. Inequality: indicates a numerical value in the range of 0 <x ≦ 1,
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 of the metal element A that becomes a monovalent cation x ₁ And the value x ₂ of the metal element A that is a divalent cation satisfies the condition shown by the inequality: 0 <(x ₁ + 2 × x ₂ ) ≦ 2,
y represents a numerical value within the range of inequality: 0 <y ≦ 2. ]
And a metal oxide belonging to the cryptomelan group having a one-dimensional pore structure.

  A in the general formula (1) is a metal element that becomes a monovalent or divalent cation in the metal oxide. Such metal element A is not particularly limited as long as it is a metal element that becomes a monovalent or divalent cation in the metal oxide, but Li, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba are preferable, Li, Na, K, Ca, and Ba are more preferable, and Ba and Na are particularly preferable. In addition, as such a metal element A, 1 type can be used individually or in combination of 2 or more types.

  Further, M in the general formula (1) is a metal element other than Ti, and is a metal element that can be a trivalent cation in the oxide. Such a metal element M may be any metal element other than Ti and can be a trivalent cation in the oxide, and is not particularly limited. Sc, Y, V, Nb, Cr, Mo, W, Re, Fe, Ga, Al, In, La are preferable, and V, Nb, Cr, Fe, Ga, Al and In are more preferable, and Al and Fe are particularly preferable. In addition, as such a metal element M, 1 type can be used individually or in combination of 2 or more types.

  Furthermore, as the metal element A and the metal element M in the metal oxide represented by the general formula (1), the metal element can be used from the viewpoint that higher CO oxidation performance can be exhibited. Preferably, A is at least one selected from the group consisting of Ba and Na, and the metal element M is at least one selected from the group consisting of Al and Fe.

  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: 0 <x ≦ 2 On the other hand, when the metal element A is a divalent cation, the numerical value is in the range of inequality: 0 <x ≦ 1. When the value of x is equal to or greater than the above upper limit, the amount of the metal element that can be filled in the entire pores of the metal oxide belonging to the cryptomelan group (preferably a metal oxide having a hollandite structure) Since A is supported, a metal oxide belonging to the single-phase cryptomelan group (particularly a single-phase hollandite structure metal oxide) cannot be obtained. Further, such a value of x may be in a range satisfying the inequality (a value in a range in which a metal oxide belonging to a single-phase cryptomelan group can be produced), and a preferable range thereof is: It differs depending on the type of metal element A and metal element M to be used, and cannot be generally stated. However, when used as an exhaust gas purification catalyst, a higher CO oxidation performance tends to be obtained. When the metal element A is a monovalent cation, the inequality is preferably a numerical value in the range of 0.5 ≦ x ≦ 2, and from the same viewpoint, the value of x is When the metal element A is a divalent cation, the numerical value is more preferably in the range of inequality: 0.25 ≦ x ≦ 1.

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 the case of considering a formula represented by _{M y Ti (8-y)} O 16, and the value of x of the metal element a to be the monovalent cation present in the metal oxide and x _1, metal oxide the value of x of the respective metal elements a to be the divalent cations present in the object in the case of the x _2, inequality: 0 <must satisfy the condition shown in _{(x 1 + 2 × x 2} ) ≦ 2 . When the value of (x ₁ + 2 × x ₂ ) represented by such a formula exceeds the upper limit, the entire pores of the metal oxide belonging to the cryptomelan group (preferably a metal oxide having a hollandite structure) are filled. A larger amount of the metal element A is supported, and a metal oxide belonging to the cryptomelan group (particularly, a metal oxide having a single-phase hollandite structure) 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 preferred range of the values of x ₁ and x ₂ is the metal used. Although it differs depending on the type of element A and metal element M, etc., it cannot be generally stated, but when used as an exhaust gas purification catalyst, a higher degree of CO oxidation performance tends to be obtained. It is more preferable that the condition shown by 0.5 ≦ (x ₁ + 2 × x ₂ ) ≦ 2 is satisfied.

  Moreover, y in the general formula (1) is a value indicating the abundance ratio (concentration) of the metal element M in the metal oxide. Such a value of y is a numerical value in the range of inequality: 0 <y ≦ 2. When the value of y exceeds the upper limit, a metal oxide belonging to a single-phase cryptomelan group (particularly a single-phase hollandite structure metal oxide) cannot be obtained. Further, such a preferable range of the value of y varies depending on the types of the metal element A and the metal element M to be used, and cannot be generally described, but the inequality: 0.5 ≦ y ≦ 2 A numerical value within the range is preferable. In addition, the value calculated | required based on the density | concentration measured by an inductively coupled plasma (ICP) analysis is employ | adopted for numerical values, such as the value of x in such General formula (1), and the value of y.

  Moreover, the metal oxide represented by General formula (1) concerning this invention contains titanium (Ti) as an essential component so that it may become clear also from the value of y in the said General formula (1). In the present invention, since titanium is contained in the metal oxide as an essential component in this way, metal oxide crystals are formed by different kinds of metal elements such as metal elements M and Ti. Since the oxidation number of the constituent metal elements can be made different, it is possible to efficiently express the acid sites locally in the metal oxide, and thus when used in combination with the catalyst component In addition, the electronic state of the catalyst component can be controlled, and the dispersibility of the catalyst component particles can be maintained at a high level from the physical structure of the particles due to the one-dimensional pore structure. It is presumed that oxidation performance can be obtained.

Furthermore, such a metal oxide represented by the general formula (1) is a metal oxide belonging to the cryptomelan group having a one-dimensional pore structure. That is, such a metal oxide represented by the general formula (1) is a single-phase metal having a crystal structure belonging to the cryptomelan group (for example, a hollandite-type, predelite-type, or Freudenbergite-type crystal structure). It is an oxide and has a one-dimensional pore structure derived from its crystal structure. Here, “having a single-phase crystal structure” means that no other crystal phase other than the crystal phase belonging to the cryptomelan group is confirmed in the X-ray diffraction (XRD) measurement. When the product is a hollandite-type metal oxide, it means that no other crystal phase other than the hollandite-type crystal phase is confirmed in the X-ray diffraction (XRD) measurement. In addition, the “metal oxide belonging to the cryptomelan group” means a tetragonal system, a monoclinic system or a monoclinic system represented by the above general formula (1) represented by a hollandite type, a predelite type or a Freuden bargeite type. A pseudo-tetragonal metal oxide, whose basic unit is an octahedron represented by the formula: BO ₆ (wherein B represents the metal element M or Ti), and is represented by I2 / m, I4, I4 / It refers to a metal oxide having a crystal phase belonging to any one of the space groups m and C2 / m. In addition, in such a metal oxide belonging to the cryptomelan group (for example, a hollandite-type, predelite-type, or Freudenbergite-type metal oxide), a tunnel-like shape parallel to the c-axis is derived from the crystal structure. A pore is formed. That is, such a metal oxide belonging to the cryptomelan group has a one-dimensional pore structure parallel to the c-axis. Such a crystal structure can be confirmed from its X-ray diffraction pattern. In the present invention, the presence or absence of the “one-dimensional pore structure” of the metal oxide is determined based on whether or not the crystal structure belonging to the cryptomelan group is confirmed from the X-ray diffraction pattern, and belongs to the cryptomelan group. When the crystal structure is confirmed, the metal oxide can be recognized as having a one-dimensional pore structure.

  As the metal oxide represented by the general formula (1), a particulate oxide is preferable. Moreover, as such primary particles of the metal oxide, the average particle size (average particle size) is preferably 1-1000 nm, more preferably 2-500 nm, and 3-100 nm. Is more preferable. If the average value of the particle diameter of such primary particles is less than the lower limit, sintering (grain growth) tends to be easy. On the other hand, if the upper limit is exceeded, the pores become longer. There is a tendency that the surface area cannot be obtained. In addition, the average value (average particle diameter) of the particle diameters of such primary particles is obtained by measuring the particle diameter of any 100 or more primary particles with a transmission electron microscope (TEM) and obtaining the particle diameter of each particle. Can be obtained by averaging. Moreover, the particle diameter of such a primary particle means the maximum diameter of the cross section of the particle. When the cross section of the particle is not circular, the diameter is the maximum circumscribed circle of the cross section of the particle.

As the primary particles of metal oxide represented by the general formula (1), it is preferable that a specific surface area of 1~300m ² / g, and more preferably 5 to 200 m ² / g . If the specific surface area is less than the lower limit, it tends to be difficult to support the catalyst component having an appropriate amount of oxidizing ability in order to exhibit sufficient catalytic activity, and on the other hand, exceeds the upper limit. And, the specific surface area tends to decrease due to thermal degradation. In addition, such a specific surface area can be calculated | required as a BET specific surface area using a BET isotherm adsorption formula from an adsorption isotherm.

  Further, in the metal oxide represented by the general formula (1), since the basic skeleton contains Ti as an essential component in a sufficient ratio, the average pore size obtained as a theoretical value from the crystal structure The pore diameter is a value in the vicinity of 0.47 nm (basically a value in the range of 0.47 nm ± 0.1 nm). Such a metal oxide having an average pore diameter outside the above range is obtained as a metal oxide represented by the general formula (1) of a single phase belonging to the cryptomelan group containing Ti as an essential component. Tend to be difficult. Such a theoretical value of the average pore diameter basically agrees 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 represented by the general formula (1), the metal element A is present in the pores. If the crystal structure of the metal oxide belongs to the cryptomelan group (for example, hollandite type, predelite type, or Freudenbergite type), the metal oxide that the metal element A exists in the pores due to the crystal structure. Since the structure of the product is achieved, the presence of the metal element A in the pores can be confirmed by measuring the crystal structure of the metal oxide by XRD measurement.

In addition, as such a metal oxide represented by the general formula (1), when used as an exhaust gas purifying catalyst, it is possible to exhibit higher CO oxidation performance under low temperature conditions. Therefore, a hollandite-type metal oxide is preferable. Note that the “hollandite-type” crystal phase suitable for the present invention is an octahedral basic unit represented by the formula: BO ₆ (wherein B represents the metal element M or Ti). This is a phase in which two units are arranged in the unit and laterally and a one-dimensional pore (tunnel-like pore parallel to the c-axis) is formed in the center. Such a hollandite crystal phase is a phase whose space group belongs to I4 / m and I2 / m.

  Moreover, it does not restrict | limit especially as a method for manufacturing the metal oxide represented by such General formula (1), For example, manufacturing conditions according to the said metal element A, the kind of said metal element M, etc. The crystal structure belonging to the cryptomelan group (for example, a hollandite type, predelite type, or Freudenbergite type crystal structure) can also be suitably used to produce the crystal structure as appropriate. . Moreover, as a method for producing such a metal oxide represented by the general formula (1), for example, a first compound containing the metal element A, a second compound containing the metal element M, After obtaining a mixture by mixing with a third compound containing Ti, the method (I) for producing the metal oxide represented by the general formula (1) may be used by firing the mixture. . Hereinafter, such method (I) will be described.

  In the method (I), first, a first compound containing the metal element A, a second compound containing the metal element M, and a third compound containing Ti are mixed to obtain a mixture.

  The first compound containing the metal element A is not particularly limited as long as it contains the metal element A, and a compound containing the metal element M together with the metal element A may be used. Examples of such a first compound include nitrates, carbonates, sulfates, and organic acid salts (for example, acetates and citrates) of the metal element A. In addition, you may use such a 1st compound individually by 1 type or in combination of 2 or more types. The form of the first compound is not particularly limited, and may be a hydrate.

  The second compound containing the metal element M is not particularly limited as long as it contains the metal element M. For example, the nitrate, carbonate, sulfate, organic acid salt (for example, acetate) of the metal element M Citrate) and the like. In addition, you may use such a 2nd compound individually by 1 type or in combination of 2 or more types. The form of the second compound is not particularly limited, and may be a hydrate.

  Furthermore, the third compound containing Ti is not particularly limited as long as it contains Ti. For example, Ti nitrate, carbonate, sulfate, organic acid salt (for example, acetate, citrate), and the like. Can be mentioned. In addition, you may use such a 3rd compound individually by 1 type or in combination of 2 or more types. The form of the third compound is not particularly limited, and may be a hydrate. Furthermore, as such first to third compounds, commercially available products may be used as appropriate.

  The method of mixing the first to third compounds (mixing method) is not particularly limited, and a method of physically mixing the powders of the first to third compounds may be employed, or A method of mixing the first to third compounds in a solvent may be employed. In addition, it is preferable to employ | adopt the method of mixing said 1st-3rd compound in a solvent from a viewpoint of the uniformity of mixing as such a mixing method.

  Here, regarding the mixing method, first, a case where a method of physically mixing the powders of the first to third compounds will be described. As a method of physically mixing such powders of the first to third compounds, for example, a method of mixing using a mortar or a method of pulverizing and mixing by ball milling can be appropriately employed. Thus, when the powders of the first to third compounds are physically mixed, the average particle diameters of the powders (particles) of the first to third compounds are 0.01 to 2000 μm, respectively. It is preferable that it is 0.1-1000 micrometers. If the average particle size of the particles of the first to third compounds is less than the lower limit, it tends to be difficult to handle the powder. On the other hand, if the average particle size exceeds the upper limit, mixing tends to be difficult. .

  The average particle size of the powder of the mixture obtained by physically mixing in this way 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. In addition, according to the particle diameter after such mixing, mixing conditions can be changed suitably.

  Next, the case where the method of mixing the first to third compounds in a solvent is adopted as the mixing method will be described. Although it does not restrict | limit especially as a solvent which can be utilized for such a mixing method, From an industrial viewpoint, it is preferable to use water (ion-exchange water). Moreover, as a method of mixing the first to third compounds in a solvent, an aqueous solution (A) in which the first compound is dissolved, an aqueous solution (B) in which the second compound is dissolved, and the third compound are dissolved. You may employ | adopt the method of stirring and mixing a 1st-3rd compound in aqueous solution using any 1 or more types in aqueous solution (C). As a method using such an aqueous solution, for example, a mixed solution of an aqueous solution (B) and an aqueous solution (C) is prepared, and a third compound is added thereto and mixed to obtain a mixed solution ( Examples thereof include i) and a method (ii) in which the powder of the second compound and the third compound is added to and mixed with the aqueous solution (A). Further, when adopting the method (i) using such an aqueous solution, the salt of the metal element M and the salt of Ti in the aqueous solution (B) and (C) are from the viewpoint of safety during firing. It is preferable to use the same type of salt (for example, both citrates).

  Furthermore, in the case of adopting a method of mixing the first to third compounds in a solvent, the solvent is removed from the liquid mixture obtained by the mixing method (for example, the solvent is evaporated, etc.) to obtain the solid content. A mixture of the first compound, the second compound and the third compound may be obtained, or the mixture obtained by the mixing method may be refluxed to obtain a mixture as a precipitate. In addition, when obtaining a mixture as a deposit, the mixture can be easily recovered by filtration after the precipitation has occurred. Moreover, the conditions (time etc.) of such a recirculation | reflux process can be suitably changed according to the design (a particle diameter, the length of a pore, etc.) of the target metal oxide.

  Furthermore, the amount of the first to third compounds used to obtain the mixture varies depending on the type of mixing method used and the like, and cannot be generally stated. What is necessary is just to set it as the ratio which can form the metal oxide represented by (1), and it can change suitably according to the design of the target metal oxide. Thus, the amount of the first to third compounds used is not particularly limited, but the total number of moles of metal element A in the resulting mixture, the total number of moles of metal element M in the mixture, and the mixture When the ratio of the total number of moles of titanium (Ti) in the inside is expressed as [total number of moles of A]: [total number of moles of M]: [total number of moles of Ti], A is a monovalent metal element In this case, [total number of moles of A], [total number of moles of M], and [total number of moles of Ti] as the ratio values are respectively 0 <[total number of moles of A] ≦ 3, It is preferable to adjust so that 0 <[total number of moles of M] ≦ 2, 8> [total number of moles of Ti] ≧ 6, and when A is a divalent metal element, The total number of moles of A, the total number of moles of M, and the total number of moles of Ti are 0 <[total number of moles of A], respectively. 1.5, 0 <[total number of moles of M] ≦ 2,8> [total number of moles of Ti] is preferably adjusted so that the numerical ranges shown in ≧ 6. When a monovalent metal element and a divalent metal element coexist as A, the converted value of the number of moles of A in the mixture ([total number of moles of monovalent A] + 2 × [2 The total number of moles of metal A in the mixture] and the total number of moles of titanium (Ti) in the mixture ([total number of moles of monovalent A] ] + 2 × [total number of moles of divalent A]): [total number of moles of M]: [total number of moles of Ti] Number] + 2 × [total number of moles of divalent A]) ≦ 3, 0 <[total number of moles of M] ≦ 2, 8> [total number of moles of Ti] ≧ 6 It is preferable to adjust. When the number of moles of A and M exceeds the upper limit, a metal oxide having a crystal structure belonging to the cryptomelan group tends not to be obtained in a single phase.

  Moreover, in the process of obtaining such a mixture, before performing the below-mentioned baking process, you may perform a drying process suitably with respect to the obtained mixture. Such a drying process is not particularly limited, and a known method can be appropriately used.

  Moreover, in the said method (I), after obtaining a mixture as mentioned above, the said mixture is baked and the metal oxide represented by General formula (1) is obtained.

  Such firing conditions vary depending on the type of metal element A and metal element M to be used, the preparation method of the mixture, and the like, and are not particularly limited. The conditions are not limited to crystals belonging to the cryptomelan group. What is necessary is just to set suitably on conditions that can obtain the metal oxide which has a structure (For example, a hollandite type, a predelite type, or a Freudenbergite type crystal structure). Hereinafter, suitable conditions for firing will be described according to the type of mixing method employed in obtaining the mixture.

  When the mixing method employed in obtaining the mixture is a method of physically mixing the powders of the first to third compounds, the firing temperature is 500 to 1400 ° C. (more preferably 600 to 1200). And the firing time is preferably 1 to 24 hours (more preferably 2 to 12 hours). If the firing temperature and time are less than the lower limit, a metal oxide having sufficient crystallinity tends not to be obtained. On the other hand, if the upper limit is exceeded, a single-phase metal oxide tends not to be obtained. .

  Moreover, when the said mixing method employ | adopted when obtaining the said mixture is the method of mixing said 1st-3rd compound in a solvent, baking temperature is 500-1200 degreeC (more preferably 600-1000 degreeC). More preferably, the mixture is fired at 700 to 900 ° C. and the firing time is 1 to 12 hours (more preferably 2 to 10 hours). When the firing temperature and time are less than the lower limit, a metal oxide having sufficient crystallinity tends not to be obtained. On the other hand, when the upper limit is exceeded, a single-phase metal oxide tends not to be obtained. is there.

  In the case where the mixing method employed when obtaining the mixture is a method of mixing the first to third compounds in a solvent, the firing step is performed from the viewpoint of decomposition of the organic acid in the raw material. You may perform temporary baking before implementing. As such pre-baking conditions, it is preferable to employ a condition of heating at a temperature of 100 to 600 ° C. (more preferably 200 to 500 ° C.) for 1 to 10 hours (more preferably 2 to 8 hours).

  The catalyst carrier of the present invention made of a metal oxide belonging to the cryptomelan group represented by the above general formula (1) and having a one-dimensional pore structure has been described above. Hereinafter, the exhaust gas purifying catalyst of the present invention will be described. To do.

The exhaust gas purifying catalyst of the present invention comprises the catalyst carrier of the present invention,
Metal particles containing at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Mo, W, Ag, Pt, Au, Pd, Rh, Ir and Ru and / or Or catalyst component particles comprising metal oxide particles containing the element;
It is characterized by providing.

  The particles of the catalyst component are at least one selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Mo, W, Ag, Pt, Au, Pd, Rh, Ir, and Ru. And / or selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Mo, W, Ag, Pt, Au, Pd, Rh, Ir and Ru. It consists of metal oxide particles containing at least one element. The element forming the catalyst component particles is not particularly limited, but V, Cu, Pt, Au, Pd, Rh, Ir, and Ru are preferable from the viewpoint of obtaining higher CO oxidation performance. Cu, Pt, Au, and Pd are more preferable, and Pt and Pd are particularly preferable. These elements forming the catalyst component particles can be used singly or in combination of two or more.

  In addition, as an element for forming such catalyst component particles, Pt and an element of a catalyst component other than Pt (more preferably other than Pt) from the viewpoint that it is possible to exhibit higher CO oxidation performance. In combination with Pt and Pd.

  In the exhaust gas purifying catalyst of the present invention, the catalyst component (V, Cr, Mn, Fe, Co, Ni, Cu, Mo, etc.) is added to the catalyst carrier made of the metal oxide represented by the general formula (1). , W, Ag, Pt, Au, Pd, Rh, Ir, and Ru, a metal containing at least one element selected from the group consisting of at least one element and / or a metal oxide containing the element) is supported in the form of particles. It is preferable. That is, in the present invention, it is preferable that the catalyst component particles are supported on a catalyst carrier made of a metal oxide represented by the general formula (1) and belonging to the cryptomelan group. Thus, the catalyst component particles are supported on the catalyst carrier, so that a higher CO oxidation activity can be obtained.

  Furthermore, the average particle diameter of such catalyst component particles is more preferably 100 nm or less, and more preferably 1 to 50 nm. When the average particle diameter of the catalyst component particles exceeds the upper limit, it tends to be difficult to obtain a sufficiently high CO oxidation activity. The particle diameter of such catalyst component particles can be confirmed by measurement by X-ray diffraction (XRD).

  In the exhaust gas purifying catalyst of the present invention, the total amount of the catalyst components in the catalyst is preferably 0.01 to 10% by mass, and more preferably 0.1 to 5% by mass. If the total amount of such catalyst component particles is less than the lower limit, a sufficiently high level of CO oxidation performance tends not to be obtained. On the other hand, if the upper limit is exceeded, the cost increases and the catalyst component particles Grain growth tends to occur easily.

  Further, in such an exhaust gas purifying catalyst, when Pt and an element of a catalyst component other than Pt are used in combination, the amount of Pt in the catalyst is 0.01 to 5% by mass (more preferably, 0.1%). It is preferable that the amount of the element of the catalyst component other than Pt is 0.01 to 5% by mass (more preferably 0.1 to 2% by mass). By supporting Pt or the like at such a ratio, higher CO oxidation performance tends to be obtained.

  In addition, as a method of loading the catalyst component particles on the catalyst carrier, the catalyst component elements (V, Cr, Mn, Fe, Co, Ni, Cu, Mo, W, Ag, Pt, Au, Pd, A method in which an aqueous solution containing a salt of Rh, Ir, Ru) (for example, a dinitrodiamine salt) or a complex (for example, a tetraammine complex) is brought into contact with the catalyst carrier and then dried and fired can be employed. Thus, the method of bringing the aqueous solution containing the element salt or complex of the catalyst component into contact with the catalyst carrier is not particularly limited, and a known method such as an immersion method or an impregnation method can be appropriately used. . The drying and firing conditions after contacting the aqueous solution are not particularly limited as long as the catalyst components can be supported on the catalyst carrier, and known conditions can be appropriately employed. For example, conditions for heating at 80 to 140 ° C. for about 1 to 48 hours as drying conditions and conditions for heating at 200 to 700 ° C. for about 0.5 to 5 hours may be employed as drying conditions, respectively.

  Further, the exhaust gas purifying catalyst of the present invention only needs to include the catalyst carrier of the present invention made of the metal oxide represented by the general formula (1) and particles of the catalyst component. Is not particularly limited, and a carrier containing other known metals that can be used for purification of exhaust gas may be used in appropriate combination. The form of the exhaust gas purifying catalyst of the present invention is not particularly limited, and may be used, for example, by being molded into a pellet shape, or supported on a known substrate (for example, a ceramic honeycomb substrate). May be used.

  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.

  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
<Process for preparing metal oxide>
First, titanium citric acid is added by adding 0.3 mol of titanium tetraisopropoxide to a solution obtained by dissolving 0.93 mol of citric acid in 165 ml of ion-exchanged water, and stirring under a temperature condition of 80 ° C. An aqueous titanium citrate solution containing a salt at a concentration of 0.91 mol / L was prepared. Next, 0.3 mol of basic aluminum acetate was added to a solution obtained by dissolving 0.93 mol of citric acid in 165 ml of ion-exchanged water, and the mixture was stirred at a temperature of 80 ° C. to thereby obtain aluminum citrate. Was prepared at a concentration of 0.83 mol / L.

  Next, 51.1 ml of the titanium citrate aqueous solution and 16.3 ml of the aluminum citrate aqueous solution were mixed to obtain a first mixed solution, and then 0.0075 mol of the first mixed solution was added. Barium acetate was added to obtain a second mixture. Thereafter, moisture was removed from the second mixed solution by evaporation to obtain a solid content. Next, after the solid content was dried, it was calcined in the atmosphere at 400 ° C. for 5 hours. And the solid content after temporary baking was baked on the heating conditions of 800 degreeC and 5 hours in air | atmosphere, and the metal oxide (particulate form) was obtained.

<Process for preparing exhaust gas purification catalyst>
5 g of the metal oxide obtained as described above was added to an aqueous solution in which 0.107 g of Pt (NO ₂ ) ₂ (NH ₃ ) ₂ and 0.0704 g of Pd (NO ₃ ) ₂ were dissolved. After stirring for a time to obtain a mixture, the mixture was subjected to a drying treatment in the atmosphere at 110 ° C. for 24 hours to obtain a catalyst precursor. Next, the obtained catalyst precursor was calcined in the atmosphere at 300 ° C. for 3 hours to obtain an exhaust gas purifying catalyst (A). The exhaust gas-purifying catalyst (A) thus obtained was one in which Pt and Pd were supported on the metal oxide at a ratio of 1.3 wt% (Pt) and 0.65 wt% (Pd), respectively. It was.

[Evaluation of metal oxide properties]
Inductively coupled plasma (ICP) analysis was performed on the metal oxide obtained when the exhaust gas purifying catalyst was formed in Example 1. As a result of such measurement, it was confirmed that the metal oxide was a metal oxide represented by the formula: BaAl _1.8 Ti _6.2 O ₁₆ .

Further, X-ray diffraction (XRD) analysis was performed on such a metal oxide. As a result of such measurement, from the X-ray diffraction pattern obtained by XRD measurement, in the obtained metal oxide, a hollandite-type crystal phase was confirmed, and the presence of other crystal phases was not confirmed. That is, from the results of such XRD measurement, it was confirmed that the obtained metal oxide was a single-phase metal oxide and a metal oxide having a hollandite-type crystal structure. Further, from these results, it was found that a one-dimensional pore structure derived from a hollandite type crystal structure was formed in the metal oxide. Furthermore, when the average pore diameter of the metal oxide was determined by calculating from the measured value of the lattice constant by X-ray diffraction, the average pore diameter was 0.47 nm. Further, when the specific surface area was determined from the adsorption isotherm using the BET isotherm adsorption equation, the specific surface area (BET) of the metal oxide particles was 22 m ² / g.

(Example 2)
Instead of preparing the aluminum citrate aqueous solution, 96.3 g of triammonium iron (III) trioxalate trihydrate was added to a solution obtained by dissolving 0.98 mol of citric acid in 180 ml of ion-exchanged water. In addition, an aqueous iron citrate solution containing iron ammonium citrate at a concentration of 0.60 mol / L was prepared by stirring under a temperature condition of 80 ° C., and in place of the second mixed solution In addition to using a mixed solution prepared by adding 51.1 ml of the titanium citrate aqueous solution and 11.8 ml of the iron ammonium citrate aqueous solution and then adding 0.0075 mol of barium acetate, Example 1 was employed to obtain an exhaust gas purifying catalyst (B). In the exhaust gas purifying catalyst (B) thus obtained, Pt and Pd are supported on the metal oxide (particulate) at a ratio of 1.3 wt% (Pt) and 0.65 wt% (Pd), respectively. It was.

[Evaluation of metal oxide properties]
The characteristics of the metal oxide obtained when forming the exhaust gas-purifying catalyst (B) in Example 2 were evaluated by adopting the same method as the method for evaluating the characteristics of the metal oxide in Example 1. The obtained metal oxide was confirmed to be a metal oxide represented by the formula: BaFeTi ₇ O ₁₆ and having a hollandite-type crystal structure (single phase) having a one-dimensional pore structure. Further, such a metal oxide had an average pore diameter of 0.47 nm and a specific surface area (BET) of 18 m ² / g.

(Example 3)
A hollandite-type metal oxide (particulate) represented by the formula: BaAl _1.8 Ti _6.2 O ₁₆ by adopting the same method as the “process for preparing a metal oxide” employed in Example 1 Then, the step of preparing the following exhaust gas purification catalyst was carried out, and Pt was supported on the metal oxide to obtain the exhaust gas purification catalyst (C).

<Process for preparing exhaust gas purification catalyst>
5 g of the metal oxide was added to an aqueous solution in which 0.0823 g of Pt (NO ₂ ) ₂ (NH ₃ ) ₂ was dissolved, and the mixture was stirred for 1 hour to obtain a mixture. A drying treatment was performed under heating conditions of 24 ° C. for 24 hours to obtain a catalyst precursor. Next, the obtained catalyst precursor was calcined in the atmosphere at 300 ° C. for 3 hours to obtain an exhaust gas purifying catalyst (C). The exhaust gas-purifying catalyst (C) thus obtained was supported on the metal oxide at a ratio of 1.0 wt% Pt.

Example 4
<Process for preparing metal oxide>
First, after preparing an aqueous solution in which 24 g of sodium hydroxide was dissolved in 250 ml of ion exchange water, 0.00625 mol of triammonium iron oxalate (III) trihydrate and 20 g of titanium oxide ( Particulate, average particle diameter: 6.8 nm) were sequentially added to obtain a mixed solution. Next, after the mixed liquid was refluxed for 24 hours, the formed precipitate was collected by filtration to obtain a solid (precipitate). Next, the obtained solid content was washed 5 times with distilled water and dried in the air at 110 ° C. for 24 hours. Then, the dried solid content was baked in the air at 800 ° C. for 5 hours to obtain a metal oxide (particulate).

<Process for preparing exhaust gas purification catalyst>
5 g of the metal oxide was added to an aqueous solution in which 0.0823 g of Pt (NO ₂ ) ₂ (NH ₃ ) ₂ was dissolved, and the mixture was stirred for 1 hour to obtain a mixture. A drying treatment was performed under heating conditions of 110 ° C. for 24 hours to obtain a catalyst precursor. Next, the obtained catalyst precursor was calcined in the atmosphere at 300 ° C. for 3 hours to obtain an exhaust gas purifying catalyst (D). The exhaust gas-purifying catalyst (D) thus obtained was one in which Pt was supported on the metal oxide at a ratio of 1.0 wt%.

[Evaluation of metal oxide properties]
When the characteristics of the metal oxide obtained when forming the exhaust gas purification catalyst in Example 4 were evaluated by adopting the same method as the method for evaluating the characteristics of the metal oxide employed in Example 1, The obtained metal oxide is a metal oxide represented by the formula: NaFe _0.2 Ti _7.8 O ₁₆ and having a hollandite-type crystal structure (single phase) having a one-dimensional pore structure. Was confirmed. Moreover, such a metal oxide had an average pore diameter of 0.47 nm and a specific surface area (BET) of 24 m ² / g.

(Example 5)
The same method as described in Example 4 except that in the step of preparing the metal oxide, the addition amount of triammonium iron (III) trioxalate trihydrate was changed from 0.00625 mol to 0.0125 mol. To obtain an exhaust gas purifying catalyst (E). The exhaust gas-purifying catalyst (E) thus obtained was supported by the metal oxide (particulate) at a rate of 1.0 wt%.

[Evaluation of metal oxide properties]
When the characteristics of the metal oxide obtained when forming the exhaust gas purification catalyst in Example 5 were evaluated by adopting the same method as the method for evaluating the characteristics of the metal oxide employed in Example 1, The obtained metal oxide is a metal oxide represented by the formula: NaFe _0.4 Ti _7.6 O ₁₆ and having a hollandite crystal structure (single phase) having a one-dimensional pore structure. Was confirmed. Moreover, such a metal oxide had an average pore diameter of 0.47 nm and a specific surface area (BET) of 15 m ² / g.

(Comparative Example 1)
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 at 110 ° C. for 24 hours. Thereafter, the dried solid was calcined at 500 ° C. for 4 hours to obtain an exhaust gas purifying catalyst (F) made of a metal oxide for comparison.

[Evaluation of characteristics of metal oxide (exhaust gas purification catalyst (F))]
When the characteristics of the metal oxide (catalyst for exhaust gas purification (F)) obtained in Comparative Example 1 were evaluated using the same method as the method for evaluating the characteristics of the metal oxide employed in Example 1, The obtained metal oxide was confirmed to be a metal oxide represented by the formula: AgMn ₈ O ₁₆ and having a hollandite crystal structure (single phase) having a one-dimensional pore structure. Moreover, such a metal oxide had an average pore diameter of 0.46 nm and a specific surface area (BET) of 5 m ² / g.

(Comparative Example 2)
12.5 ml of acetic acid was added to the first 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. The second solution was added to obtain a mixed solution. Next, after the mixed liquid was refluxed for 24 hours, the formed precipitate was collected by filtration to obtain a solid (precipitate). Next, the obtained solid content was washed 5 times with distilled water. Thereafter, the solid content was left to dry in the atmosphere for 12 hours. Next, the dried solid was calcined at 500 ° C. for 4 hours to obtain an exhaust gas purifying catalyst (G) made of a metal oxide for comparison.

[Evaluation of characteristics of metal oxide (exhaust gas purification catalyst (G))]
When the characteristics of the metal oxide obtained in Comparative Example 2 (exhaust gas purifying catalyst (G)) were evaluated using the same method as the method for evaluating the characteristics of the metal oxide employed in Example 1, The obtained metal oxide was confirmed to be a metal oxide represented by the formula: KMn ₈ O ₁₆ and having a hollandite crystal structure (single phase) having a one-dimensional pore structure. Moreover, such a metal oxide had an average pore diameter of 0.46 nm and a specific surface area (BET) of 83 m ² / g.

(Comparative Example 3)
<Process for preparing metal oxide>
A metal oxide (KMn ₈ O ₁₆ ) was obtained by employing the same method as the method for producing the metal oxide (exhaust gas purifying catalyst (G)) employed in Comparative Example 2.

<Process for preparing exhaust gas purification catalyst>
After adding 5 g of the metal oxide to an aqueous solution in which 0.107 g of Pt (NO ₂ ) ₂ (NH ₃ ) ₂ and 0.0704 g of Pd (NO ₃ ) ₂ were dissolved, the mixture was stirred for 1 hour to obtain a mixture The mixture was dried in the atmosphere at 110 ° C. for 24 hours to obtain a catalyst precursor. Next, the obtained catalyst precursor was calcined in the atmosphere at 300 ° C. for 3 hours to obtain an exhaust gas purifying catalyst (H). The exhaust gas-purifying catalyst (H) thus obtained was one in which Pt and Pd were supported at a ratio of 1.3 wt% (Pt) and 0.65 wt% (Pd), respectively.

(Comparative Example 4)
<Process for preparing metal oxide>
A metal oxide (KMn ₈ O ₁₆ ) was obtained by employing the same method as the method for producing the metal oxide (exhaust gas purifying catalyst (G)) employed in Comparative Example 2.

<Process for preparing exhaust gas purification catalyst>
5 g of the metal oxide was added to an aqueous solution in which 0.0082 g of Pt (NO ₂ ) ₂ (NH ₃ ) ₂ was dissolved, and the mixture was stirred for 1 hour to obtain a mixture. Then, a drying treatment was performed under heating conditions for 24 hours to obtain a catalyst precursor. Next, the obtained catalyst precursor was calcined in the atmosphere at 300 ° C. for 3 hours to obtain an exhaust gas purifying catalyst (I). The exhaust gas-purifying catalyst (H) thus obtained was supported at a rate of 1.0 wt% Pt.

(Comparative Example 5)
In an aqueous solution in which 0.0119 g of Pt (NO ₂ ) ₂ (NH ₃ ) ₂ was dissolved, 0.92 g of aluminum oxide (particulate, average particle size: 17 μm, trade name “MI307” manufactured by Rhodia) and 4 .95 g of titanium oxide (particulate, average particle size: 6.8 nm, trade name “ST-01” manufactured by Ishihara Sangyo Co., Ltd.) and 0.1 mol of barium acetate were added and stirred for 1 hour, and then evaporated to dryness. Solidification was performed to obtain a powdery solid. Next, the obtained solid was subjected to a drying treatment in the atmosphere at 110 ° C. for 24 hours to obtain a catalyst precursor. Next, the obtained catalyst precursor was calcined in the atmosphere at 300 ° C. for 3 hours to obtain an exhaust gas purifying catalyst (J). The exhaust gas-purifying catalyst (J) thus obtained was a catalyst in which Ba and Pt were supported on a carrier made of a mixed powder of alumina and titania. Further, the exhaust gas-purifying catalyst (J) was one in which Pt was supported on the mixed powder at a rate of 1.0 wt%. In addition, although the exhaust gas purification catalyst (J) and the exhaust gas purification catalyst (C) obtained in Example 3 are different in form, the composition ratios of the constituent components are the same.

[Evaluation of characteristics of exhaust gas purification catalysts (A) to (J)]
Using the exhaust gas purifying catalysts (A) to (J) obtained in Examples 1 to 5 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 1 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 (J) obtained in Examples 1 to 5 and Comparative Examples 1 to 5) are shown in Table 2 and FIG. Shown in In addition, the symbols (A) to (J) in Table 2 and FIG. 1 indicate the types of exhaust gas purification catalysts (A) to (J) obtained in Examples 1 to 5 and Comparative Examples 1 to 5, respectively. Symbol (symbol indicating the type of catalyst).

As is clear from the results shown in Table 2 and FIG. 1, the exhaust gas purification catalysts (Examples 1 to 5) of the present invention all have a CO purification rate of 50.4 even under a low temperature condition of 200 ° C. It was found that it had a very high CO oxidation performance. Further, in the exhaust gas purifying catalyst (Examples 1 to 5) of the present invention, it was confirmed that higher CO purification performance can be obtained when Pt and Pd are supported (Examples 1 and 2). . On the other hand, when the hollandite type metal oxide represented by AgMn ₈ O ₁₆ or KMn ₈ O ₁₆ is used as it is as a catalyst (Comparative Examples 1 and 2), sufficient CO oxidation performance cannot be obtained. It was confirmed. In addition, in the catalyst for purifying exhaust gas for comparison (Comparative Examples 3 to 4) in which a catalyst component is supported on a hollandite-type metal oxide (KMn ₈ O ₁₆ ) that does not contain Ti as an essential component, the CO oxidation performance is still sufficient. It didn't become a thing. In particular, the exhaust gas purification catalyst obtained in Comparative Example 4 carrying only Pt had a very low CO purification rate of 2.4%. From these results, by using the hollandite-type metal oxide obtained in Examples 1 to 5 containing Ti as an essential component as a catalyst support, the resulting catalyst exhibits very high CO oxidation performance. It became clear that it would be possible to

In the exhaust gas purifying catalysts for Comparative Examples 3 to 4, the metal oxide used as a carrier such as Pt is a hollandite-type metal oxide represented by the formula: KMn ₈ O ₁₆ , Since the metal element in the basic unit is only Mn capable of taking a plurality of valences (the basic unit of the crystal is only an octahedron represented by the formula: MnO ₆ ), the Mn valence changes on the support. In this case, local acid sites could not be sufficiently expressed, and metallization of Pt and / or Pd supported on the carrier did not proceed sufficiently, so that sufficient CO oxidation performance could not be obtained. It is guessed. On the other hand, in the exhaust gas purifying catalysts of the present invention obtained in Examples 1 to 5, the metal oxide used as a carrier such as Pt is composed of Ti and Fe or Al as the metal elements constituting the basic unit of the crystal. Since the crystal is composed of different kinds of elements, local acid spots are easily formed in the metal oxide due to the difference in oxidation number, etc. In addition to being able to sufficiently control the electronic state of Pt and / or Pd, it is possible to maintain the dispersibility of the Pt and / or Pd particles sufficiently high from the physical structure of the particles due to the one-dimensional pore structure. Therefore, it is presumed that sufficiently high CO oxidation performance was obtained.

  Further, when the exhaust gas purification catalyst obtained in Example 3 and the exhaust gas purification catalyst obtained in Comparative Example 5 were compared, the composition ratio of the constituent components was the same, but the exhaust gas obtained in Comparative Example 5 was the same. In the purification catalyst, the CO oxidation performance was not sufficient. From the results of the exhaust gas purifying catalyst obtained in Example 3 and Comparative Example 5, it is possible to use a hollandite-type metal oxide represented by the above general formula (1) as a carrier, so that it is sufficiently sophisticated. It was confirmed that CO oxidation performance was obtained.

  As described above, according to the present invention, the exhaust gas purifying catalyst obtained by using in combination with the catalyst component is sufficiently advanced to sufficiently oxidize and purify CO even under low temperature conditions. It is possible to provide a catalyst carrier capable of exhibiting oxidation performance, an exhaust gas purification catalyst having sufficiently high CO oxidation performance using the same, and an exhaust gas purification method using the exhaust gas purification catalyst Become.

  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 (9)

A catalyst carrier comprising a metal oxide,
The metal oxide has the following general formula (1):
_{A x M y Ti (8-} y) O 16 (1)
[In the formula (1), A represents a metal element that becomes a monovalent or divalent cation in the oxide,
M represents a metal element other than Ti and can be a trivalent cation in the oxide;
x represents a numerical value in the range of 0 <x ≦ 2 when A is a monovalent cation in the oxide, while x is a divalent cation. Inequality: indicates a numerical value in the range of 0 <x ≦ 1,
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 of the metal element A that becomes a monovalent cation x ₁ And the value x ₂ of the metal element A that is a divalent cation satisfies the condition shown by the inequality: 0 <(x ₁ + 2 × x ₂ ) ≦ 2,
y represents a numerical value within the range of inequality: 0 <y ≦ 2. ]
And a metal oxide belonging to the cryptomelan group having a one-dimensional pore structure.   The catalyst carrier according to claim 1, wherein the metal oxide is a hollandite-type metal oxide.   The catalyst according to claim 1 or 2, wherein the metal element A is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba. Carrier.   The metal element M is at least one selected from the group consisting of Sc, Y, V, Nb, Cr, Mo, W, Re, Fe, Ga, Al, In, and La. 4. The catalyst carrier according to any one of 3.   The metal element A is at least one selected from the group consisting of Ba and Na, and the metal element M is at least one selected from the group consisting of Al and Fe. 5. The catalyst carrier according to any one of 4 above. A catalyst carrier according to any one of claims 1 to 5;
Metal particles containing at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Mo, W, Ag, Pt, Au, Pd, Rh, Ir and Ru and / or Or catalyst component particles comprising metal oxide particles containing the element;
An exhaust gas purifying catalyst comprising:   The exhaust gas-purifying catalyst according to claim 6, wherein the catalyst component particles are supported on the catalyst carrier.   The element contained in the particles of the catalyst component is at least one element selected from the group consisting of V, Cu, Pt, Au, Pd, Rh, Ir, and Ru. The exhaust gas purifying catalyst according to any one of 7.   An exhaust gas purification method comprising contacting exhaust gas containing carbon monoxide with the exhaust gas purification catalyst according to any one of claims 6 to 8, and oxidizing and purifying the carbon monoxide.

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