JP5062060B2 - Catalyst for purifying automobile exhaust gas and method for producing the same - Google Patents

Description

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

Conventionally, various catalysts have been used to sufficiently purify components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained in exhaust gas discharged from automobile internal combustion engines. Has been. As one of such catalysts, a catalyst in which ruthenium (Ru) is supported on a support made of γ-Al ₂ O ₃ or the like is known. As a method for producing such a catalyst, a method is disclosed in which a solution containing RuCl ₃ , Ru ₃ (CO) ₁₂ or the like is supported on a carrier and then calcined to carry a noble metal on the carrier to obtain a catalyst. I came.

For example, in “Applied Catalysis A: General, vol. 123 (Non-patent Document 1)” published in 1995, pages 145 to 159, γ-Al ₂ O ₃ modified with KOH is replaced with Ru ₃ as a ruthenium precursor. A method is disclosed in which a solution containing γ-Al ₂ O ₃ on which Ru is supported is obtained by bringing a solution containing (CO) ₁₂ or RuCl ₃ into contact and drying, followed by heating. Also, pages 23-32 of “Applied Catalysis A: General, vol. 283 (Non-patent Document 2)” issued in 2005, and “Applied Catalysis A: General, vol. 325 (Non-patent Document 3)” published in 2007 are also included. Pp. 57-67, an aqueous solution containing Ru (NO) (NO ₃ ) ₃ or RuCl ₃ or the like is brought into contact with Al ₂ O ₃ and dried, followed by firing to obtain Al ₂ on which Ru is supported. A method for obtaining a catalyst comprising O ₃ is disclosed. However, in the conventional catalyst production methods as described in Non-Patent Documents 1 to 3, it has not always been possible to obtain a catalyst having sufficient catalytic activity.
Pietro Moggi, Giancarlo Albanesi, Giovanni Predieri, Giuseppe Spoto, “Ruthenium cluster-derived catalysts for Amoniasis”, Applied G. 123, 1995, pages 145-159. A. Maroto-Valiente, M.M. Cerro-Alarcon, A.M. Guerrero-Ruiz, I .; Rodriguez-Ramos, “Effect of the metal preparation on the surface site distribution of Al2O3-supplied RU catalysts: catalytic effect. 283, 2005, pp. 23-32. R. Lanza, S .; G. Jaras, P.A. Canu, “Partial oxidation of methane over supported ruthenium catalysts”, Applied Catalysis A: General, vol. 325, 2007, pp. 57-67

  The present invention has been made in view of the above-described problems of the prior art, and is used for purifying automobile exhaust gas in which ruthenium in an atomic state is supported in a sufficiently highly dispersed state and has a sufficiently high catalytic activity. It is an object of the present invention to provide a catalyst and a method for producing an automobile exhaust gas purification catalyst capable of efficiently and reliably producing the catalyst.

  As a result of intensive studies to achieve the above object, the present inventors have used a ruthenium carboxylate binuclear complex when supporting ruthenium on a carrier, thereby sufficiently dispersing ruthenium in an atomic state. As a result, it was found that the obtained catalyst had a sufficiently high catalytic activity, and the present invention was completed.

  That is, the automobile exhaust gas purification catalyst of the present invention comprises a carrier and ruthenium supported in an atomic state on the carrier using a ruthenium carboxylate binuclear complex, and 50 at% or more of the ruthenium is ruthenium 2. It is supported on the carrier as atomic clusters.

  Further, in the method for producing an automobile exhaust gas purification catalyst of the present invention, a ruthenium-containing liquid containing a ruthenium carboxylate binuclear complex is brought into contact with a carrier, and the ruthenium carboxylate binuclear complex is supported on the carrier and calcined. Thus, ruthenium is supported on the carrier in an atomic state to obtain an automobile exhaust gas purification catalyst.

In such a method for producing an automobile exhaust gas purification catalyst of the present invention, the ruthenium carboxylate dinuclear complex has the following general formula (1):
Ru ₂ (R-COO) ₄ · X ^m _n (1)
[In the formula (1), R represents an alkyl group having 1 to 5 carbon atoms, X represents a counter anion, m represents an ionic value of the counter anion, and represents a numerical value of −1 to −4, and n represents The numerical value which changes according to the electrical neutral principle according to the value of m is shown. ]
It is preferable that it is at least 1 type of complex selected from the compound represented by these, and its solvate.

  Furthermore, in the method for producing an automobile exhaust gas purification catalyst of the present invention, the ruthenium-containing liquid solvent is preferably an alcohol.

The reason why the above object is achieved by the automobile exhaust gas purification catalyst and the method for producing the automobile exhaust gas purification catalyst of the present invention is not necessarily clear, but the present inventors speculate as follows. That is, first, in the conventional method for producing a catalyst, ruthenium is supported on a carrier using a ruthenium salt such as ruthenium chloride. Ruthenium chloride or the like that has been used in such a conventional method for producing a catalyst forms a weak electrostatic bond with the carrier. For this reason, when a reduction treatment (calcination) is performed after ruthenium chloride or the like is supported on the carrier, the ruthenium chloride or the like is easily separated from the carrier, and aggregation of ruthenium atoms cannot be sufficiently suppressed. Therefore, in the conventional catalyst manufacturing method, it is assumed that ruthenium particles grow on the support due to the reduction treatment (calcination), and the ruthenium cannot be sufficiently dispersed and supported in an atomic state. Is done. Actually, for example, in Non-Patent Document 1 described above, regarding a catalyst prepared from Ru ₃ (CO) ₁₂ , the metal particles (Ru) supported on the support are elliptical, and the average diameter of the metal particles. Is about 2 nm, and that the metal particles are aggregates of about 50 ruthenium atoms. Further, in the above-described Non-Patent Document 1, with respect to catalyst prepared from RuCl _3, it carrier supported metal particles (Ru) are heterogeneous, that there is a range of the particle size, the aggregates of metal particles It is described that the size is 10 nm or more.

  In contrast, in the present invention, ruthenium is supported on the carrier using a ruthenium carboxylate binuclear complex. Since such a ruthenium carboxylate binuclear complex has an unsaturated coordination site, it can form a coordination bond with a hydroxyl group on the carrier. When such a coordination bond is formed, the complex is supported on the carrier in a state of excellent stability due to the strong binding force. When such a ruthenium carboxylate dinuclear complex is supported on a carrier and then baked, the ligand can be removed while sufficiently suppressing ruthenium aggregation. Therefore, by using such a ruthenium carboxylate binuclear complex, ruthenium can be supported on the carrier in an atomic state and in a sufficiently dispersed state. In the present invention, ruthenium is supported as a diatomic cluster depending on the structure of the ruthenium carboxylate binuclear complex. Since ruthenium is supported on the carrier as a two-atom cluster as described above, the number of active sites of the obtained catalyst is sufficient. In addition, by supporting as a two-atom cluster, the mass is doubled compared to the case of supporting as a single atom, so that the thermal stability of ruthenium atoms on the support is improved, and the catalyst is used repeatedly. Further, unnecessary aggregation of ruthenium atoms is sufficiently suppressed. Thus, in the catalyst for purification of automobile exhaust gas according to the present invention, ruthenium is stably supported on the carrier in an atomic state and in a sufficiently dispersed state, and therefore has a sufficient amount of active points and is excellent. The present inventors infer that the catalyst activity can be sufficiently exhibited.

  According to the present invention, ruthenium in an atomic state is supported in a sufficiently highly dispersed state, and an automobile exhaust gas purification catalyst having a sufficiently high catalytic activity and the catalyst can be produced efficiently and reliably. It is possible to provide a method for producing a possible automobile exhaust gas purification catalyst.

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

  First, the automobile exhaust gas purification catalyst of the present invention will be described. That is, the automobile exhaust gas purification catalyst of the present invention comprises a carrier and ruthenium supported in an atomic state on the carrier using a ruthenium carboxylate binuclear complex, and 50 at% or more of the ruthenium is ruthenium 2. It is supported on the carrier as atomic clusters.

Such a carrier is not particularly limited as long as it is a carrier that can be used for an exhaust gas purification catalyst. For example, a carrier made of a metal oxide can be used as appropriate. Examples of such metal oxides include activated alumina, alumina-ceria-zirconia, ceria-zirconia, zirconia, and lanthanum-stabilized activated alumina. Examples of such metal oxides include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), and gadolinium (Gd). Terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y), zirconium (Zr), aluminum (Al) And at least one selected from the group consisting of oxides of magnesium (Mg) and vanadium (V), solid solutions thereof, and composite oxides thereof. Among such metal oxides, CeO ₂ , ZrO ₂ , Y ₂ O ₃ , TiO ₂ , Al ₂ O ₃ , solid solutions thereof, and composite oxides thereof are obtained from the viewpoint that higher catalytic activity can be obtained. What contains at least 1 type selected from the group which consists of a thing is more preferable.

In addition, the shape of such a carrier is not particularly limited, but is preferably a powder from the viewpoint of obtaining a sufficient specific surface area. Further, the specific surface area of such a carrier is not particularly limited, but is more preferably 30 m ² / g or more from the viewpoint of obtaining higher catalytic activity.

  The ruthenium supported on the carrier is one supported on the carrier in an atomic state using the ruthenium carboxylate dinuclear complex. In the automobile exhaust gas purification catalyst of the present invention, ruthenium is supported on the support in an atomic state using the ruthenium carboxylate binuclear complex, so that the dispersibility of the ruthenium atoms becomes sufficiently high, and the activity of the catalyst Since the number of points is sufficient, a sufficiently high catalytic activity can be obtained. Such a ruthenium carboxylate binuclear complex is the same as the ruthenium carboxylate binuclear complex used in the method for producing the automobile exhaust gas purification catalyst of the present invention described later. Furthermore, such a supported state (atomic state) of ruthenium can be achieved by employing the method for producing a catalyst for purifying automobile exhaust gas according to the present invention described later.

  In the present invention, 50 at% or more (more preferably 70 at%) of the ruthenium is supported on the support as a ruthenium diatomic cluster. The “two-atom cluster” as used herein refers to the accumulation of two ruthenium atoms at a distance (preferably a distance of 2 to 3 mm) approximately equal to the bond length of the Ru—Ru bond in the precursor ruthenium carboxylate dinuclear complex. It is an aggregate that is doing. Such diatomic clusters can be confirmed by observing with a scanning transmission electron microscope (STEM). When the ratio of ruthenium atoms supported in such a two-atom cluster state is in the above range, ruthenium is sufficiently dispersed and supported, so that the number of active sites of the catalyst is sufficient, High catalytic activity is obtained. On the other hand, if the ratio of ruthenium existing as a diatomic cluster is less than the lower limit, sufficiently high catalytic activity cannot be obtained. As a method for obtaining the ratio (at%) of the ruthenium atoms present as such a two-atom cluster, a spherical aberration correction device using an arbitrary region of 12 nm in the vertical direction and 12 nm in the horizontal direction on the carrier of the automobile exhaust gas purification catalyst as a converging lens. The total number of atoms of ruthenium existing in the region and the number of atoms of ruthenium existing as a two-atom cluster are determined based on the obtained STEM image, respectively, by a scanning transmission electron microscope (STEM) provided with A method of calculating the ratio of the number of atoms existing as a two-atom cluster to the total number of ruthenium atoms is adopted. As the scanning transmission electron microscope (STEM), for example, a trade name “JEM-2100F” manufactured by JEOL Ltd. can be used.

  Further, the amount of ruthenium supported is not particularly limited, but is preferably 0.005 to 5.000% by mass with respect to the total amount of the carrier and ruthenium, and 0.008 to 0.300% by mass. More preferably. If the amount is less than the lower limit, it tends to be difficult to obtain sufficient catalytic activity, and if it exceeds the upper limit, the performance tends to be saturated.

  Further, the automobile exhaust gas purifying catalyst of the present invention may be provided with the carrier and ruthenium supported in an atomic state on the carrier using the ruthenium carboxylate binuclear complex, and the form is not particularly limited. For example, it may be in the form of a honeycomb-shaped monolith catalyst in which the catalyst is supported on a base material, a pellet-shaped pellet catalyst, or the like. The base material used here is not particularly limited, and a particulate filter base material (DPF base material), a monolithic base material, a pellet base material, a plate base material, and the like can be suitably employed. Also, the material of such a base material is not particularly limited, but a base material made of a ceramic such as cordierite, silicon carbide, mullite, or a base material made of a metal such as stainless steel including chrome and aluminum is preferably used. can do. Further, the method for supporting the catalyst on such a substrate is not particularly limited, and a known method can be appropriately employed. In addition, in such an automobile exhaust gas purification catalyst, other components (for example, NOx occlusion material) that can be used for the exhaust gas purification catalyst may be appropriately supported as long as the effects of the present invention are not impaired. Moreover, the automobile exhaust gas purification catalyst of the present invention can be manufactured by employing the method for manufacturing the automobile exhaust gas purification catalyst of the present invention described later.

  Next, a method for producing the automobile exhaust gas purification catalyst of the present invention capable of suitably producing the automobile exhaust gas purification catalyst of the present invention will be described. That is, in the method for producing an automobile exhaust gas purification catalyst of the present invention, a ruthenium-containing liquid containing a ruthenium carboxylate binuclear complex is brought into contact with a carrier, the ruthenium carboxylate binuclear complex is supported on the carrier, and calcined. Thus, ruthenium is supported on the carrier in an atomic state to obtain an automobile exhaust gas purification catalyst.

  Such a ruthenium-containing liquid contains a ruthenium carboxylate dinuclear complex. Such a ruthenium carboxylate binuclear complex is a binuclear complex in which a bridged ligand containing a carboxyl group is coordinated to two ruthenium atoms as a nucleus. By using such a ruthenium carboxylate binuclear complex, it becomes possible to form a coordinate bond between the complex and the carrier, and the carrier can be supported on the carrier with sufficiently high thermal stability. In addition, it is possible to carry ruthenium as a two-atom cluster on the carrier by firing the carrier carrying the complex.

Moreover, as a bridge | crosslinking type ligand containing such a carboxyl group, general formula (i):
R ¹ -COO (i)
[Wherein R ¹ represents an alkyl group. ]
The bridge | crosslinking type ligand represented by these is mentioned. Such an alkyl group in formula (i) preferably has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms. When the carbon number of such an alkyl group exceeds the upper limit, the solubility becomes insufficient and the supporting efficiency tends to decrease.

Moreover, as such a ruthenium carboxylate binuclear complex, the following general formula (1):
Ru ₂ (R-COO) ₄ · X ^m _n (1)
[In the formula (1), R represents an alkyl group having 1 to 5 carbon atoms (more preferably 1 to 3), X represents a counter anion, m represents an ionic value of the counter anion, and 4 represents a numerical value, and n represents a numerical value that varies according to the electrical neutral principle according to the value of m. ]
And at least one complex selected from the compounds represented by formula (I) and solvates thereof are preferred.

In such formulas (i) and (1), the alkyl group represented by R ¹ or R may be linear or branched, and may be a methyl group or an ethyl group. Propyl group, isopropyl group, butyl group, tert-butyl group, pentyl group and the like. The alkyl group may have a substituent. Such substituents include halogen atoms, hydroxyl groups, acyl groups, aldehyde groups, carbonyl groups, amino groups, imino groups, cyano groups, azo groups, azi groups, thiol groups, sulfo groups, nitro groups, and derivatives thereof. Is mentioned. Examples of the alkyl group having such a substituent include a trifluoromethyl group, a tribromomethyl group, a dicyanomethyl group, a difluoromethyl group, and a dibromomethyl group.

Further, the counter anion represented by X in the formula (1) is not particularly limited, but those having a charge of -1 (having a monovalent negative charge) are preferable, for example, BF ₄ ⁻ , PO ₄ ⁻ , SbCl ₆ ⁻ , FeCl ₄ ⁻ , AlCl ₄ ⁻ , PF ₆ ⁻ , F ⁻ , Cl ⁻ , Br ⁻ , I ^{− and the} like can be mentioned. Moreover, m in the said Formula (1) is an ionic value of the said counter anion, and shows the numerical value of -1 to -4. Further, n in the formula (1) indicates a numerical value that changes according to the electric neutral principle according to the value of m, and indicates the number of counter anions in the ruthenium carboxylate dinuclear complex. In the case where the ionic value of the counter anion is -1, when the ruthenium oxidation number is +3 for convenience, 2 is indicated, and when the ruthenium oxidation number is +2.5 for convenience, 1 is indicated, and the ruthenium oxidation number is +2 In this case, 0 is indicated. That is, when the ruthenium oxidation number is +2, the counter anion does not exist.

The solvate of the compound represented by the general formula (1) is a solvent used at the time of production, storage, use, etc. of the ruthenium carboxylate dinuclear complex represented by the general formula (1). Is solvated. The solvated molecule in such a solvate is not particularly limited, and H ₂ O, (CH ₃ ) ₂ O, CH ₃ OH depending on the type of solvent used during production, storage, use, etc. And various molecules. Moreover, as a solvate of such a ruthenium carboxylate binuclear complex, the following general formula (2):
_{[Ru 2 (R-COO)} 4 (solv) l] · X m n
[Wherein, R, X, m, and n have the same meanings as R, X, m, and n in formula (1), solv represents a solvent molecule, and l is an integer from 0 to 2. Indicates. ]
The thing represented by these is preferable.

  Moreover, the synthesis | combining method in particular of such a ruthenium carboxylate binuclear complex and its solvate is not restrict | limited, A well-known method is employable suitably. Further, as such a ruthenium carboxylate dinuclear complex, a commercially available product may be used.

  Moreover, the solvent for the ruthenium-containing liquid is not particularly limited, and water, an organic solvent, or the like that can dissolve the ruthenium carboxylate dinuclear complex can be appropriately used. As the solvent of such a ruthenium-containing liquid, an organic solvent is preferably used from the viewpoint of the stability of the complex in the solvent, and at least one organic solvent selected from the group consisting of alcohol and acetone is used. More preferably, among these, alcohol is particularly preferable from the viewpoint of solubility. Moreover, as such alcohol, C1-C3 alcohol is more preferable. When the carbon number of such alcohol exceeds the upper limit, the solubility is lowered and the viscosity is increased, so that dispersibility is lowered and uniform support tends to be impossible. Among these alcohols, methanol is particularly preferable from the viewpoint that a catalyst having higher catalytic activity can be obtained.

  Furthermore, the content ratio of ruthenium (metal) in such a ruthenium-containing liquid is not particularly limited, but is preferably 0.0001 to 1% by mass in terms of metal. When the content ratio of ruthenium is less than the lower limit, it is difficult to efficiently support the ruthenium carboxylate dinuclear complex on the support, and the performance tends to be insufficient.On the other hand, when the upper limit is exceeded, It is difficult to selectively adsorb, and it tends to be difficult to uniformly support the ruthenium carboxylate dinuclear complex. In addition, the preparation method in particular of such a ruthenium containing liquid is not restrict | limited, For example, the well-known method which can melt | dissolve the said ruthenium carboxylate binuclear complex in the said solvent is employable suitably.

  The carrier used in the method for producing the automobile exhaust gas purification catalyst of the present invention is the same as the carrier described in the automobile exhaust gas purification catalyst of the present invention.

  Further, the method for bringing the ruthenium-containing liquid into contact with the carrier and supporting the ruthenium carboxylate dinuclear complex on the carrier is not particularly limited, and the carrier can carry the ruthenium carboxylate binuclear complex. Such a known method can be appropriately employed. For example, a method of supporting the ruthenium carboxylate binuclear complex on the carrier by immersing the carrier in the ruthenium-containing liquid may be employed. Further, when the ruthenium carboxylate binuclear complex is supported on the surface of the carrier by immersing the carrier in the ruthenium-containing liquid, the pressure of 1 to 10 atm, 0 ° C. or higher, and the ruthenium-containing liquid It is preferable to stir for about 0.5 to 24 hours under the condition of the temperature below the boiling point of the solvent (more preferably about room temperature). If the pressure and temperature conditions for supporting the ruthenium carboxylate dinuclear complex on the surface of the support are less than the lower limit, the supporting efficiency tends to decrease, while if the upper limit is exceeded, excessive stirring is continued. Manufacturing costs tend to increase.

  Moreover, as a method of baking after carrying | supporting the said ruthenium carboxylate binuclear complex on the said support | carrier, the method of baking for about 1 to 5 hours by the temperature conditions of 200-600 degreeC (more preferably 300-500 degreeC) is employ | adopted. It is preferable. When the firing temperature and time are less than the lower limit, it tends to be difficult to efficiently and sufficiently remove the ligand. On the other hand, when the upper limit is exceeded, ruthenium is supported when ruthenium is supported on the support. The atoms tend to aggregate.

  In addition, according to the manufacturing method of the automobile exhaust gas purification catalyst of the present invention, it is possible to support ruthenium on the carrier in an atomic state and in a sufficiently highly dispersed state. The reason why it is possible to carry ruthenium in an atomic state and in a sufficiently highly dispersed state is not necessarily clear, but the present inventors infer as follows. That is, first, when the ruthenium-containing liquid is brought into contact with the carrier, the coordination site of the ruthenium carboxylate binuclear complex forms a coordinate bond with the hydroxyl group on the carrier. Therefore, the ruthenium carboxylate binuclear complex is supported on the carrier with a sufficiently strong binding force. Further, when the ruthenium carboxylate binuclear complex is supported on the carrier in this way, the nuclei in each complex are arranged on the carrier in a state of being separated from each other due to the presence of the ligand, and each complex on the carrier surface. A state in which nuclei are dispersed and arranged in an island shape is formed. Next, when a carrier carrying such a ruthenium carboxylate binuclear complex is calcined, the thermal stability of the bond between the carrier and the complex is high, so that aggregation of atoms (ruthenium atoms) in the nucleus of the complex is sufficiently prevented. However, since the ligand is removed, the ruthenium atoms are supported on the support while maintaining the state of being dispersed in an island shape. Since ruthenium is supported on the support in this way, ruthenium is supported on the support in the atomic state and in the form of a two-atom cluster depending on the number of ruthenium atoms contained in the nucleus of the complex used. Therefore, according to the method for producing a catalyst for purification of automobile exhaust gas of the present invention, it is presumed that ruthenium atoms can be supported in a sufficiently dispersed state.

  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, a ruthenium acetate dinuclear complex ([Ru ₂ (CH ₃ CO ₂ ) ₄ (H ₂ O) ₂ ] · BF ₄ : 83.9 mg) was dissolved in methanol (1000 mL) to prepare a ruthenium-containing liquid. Next, γ-alumina (trade name “AKP-G0-01” manufactured by Sumitomo Chemical Co., Ltd .: 10.0 g) was added to the ruthenium-containing liquid to obtain a mixture. Next, the mixture was stirred for 12 hours under a temperature condition of 30 ° C., and then evaporated to dryness. The obtained solid was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours to obtain an automobile exhaust gas purification catalyst. It was. The supported amount of ruthenium in the obtained catalyst was 0.3% by mass.

(Example 2)
First, a ruthenium acetate dinuclear complex ([Ru ₂ (CH ₃ CO ₂ ) ₄ (H ₂ O) ₂ ] · BF ₄ : 83.9 mg) was dissolved in acetone (1000 mL) to prepare a ruthenium-containing liquid. Next, γ-alumina (trade name “AKP-G0-01” manufactured by Sumitomo Chemical Co., Ltd .: 10.0 g) was added to the ruthenium-containing liquid to obtain a mixture. Next, the mixture was stirred for 12 hours under a temperature condition of 30 ° C., and then evaporated to dryness. The obtained solid was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours to obtain an automobile exhaust gas purification catalyst. It was. The supported amount of ruthenium in the obtained catalyst was 0.3% by mass.

(Example 3)
First, a ruthenium acetate dinuclear complex ([Ru ₂ (CH ₃ CO ₂ ) ₄ (H ₂ O) ₂ ] · BF ₄ : 83.9 mg) was dissolved in ion-exchanged water (1000 mL) to prepare a ruthenium-containing liquid. . Next, γ-alumina (trade name “AKP-G0-01” manufactured by Sumitomo Chemical Co., Ltd .: 10.0 g) was added to the ruthenium-containing liquid to obtain a mixture. Next, the mixture was stirred for 12 hours under a temperature condition of 30 ° C., and then evaporated to dryness. The obtained solid was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours to obtain an automobile exhaust gas purification catalyst. It was. The supported amount of ruthenium in the obtained catalyst was 0.3% by mass.

(Comparative Example 1)
First, a ruthenium ammine hydrochloride solution (manufactured by Tanaka Kikinzoku Co., Ltd., Lot # 9911-4273: Ru concentration 0.647 wt%, Ru weight 5.00 g / 800 ml, 4.64 mg) was dissolved in ion-exchanged water (1000 mL). A ruthenium solution was prepared. Next, γ-alumina (trade name “AKP-G0-01” manufactured by Sumitomo Chemical Co., Ltd .: 10.0 g) was added to the ruthenium solution to obtain a mixture. Next, the mixture was stirred for 12 hours under a temperature condition of 30 ° C. and then evaporated to dryness. The obtained solid was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours, and the exhaust gas purification for comparison was performed. A catalyst was obtained. The supported amount of ruthenium in the obtained catalyst was 0.3% by mass.

(Comparative Example 2)
Ru (III) nitrosyl nitrate, solution in dilute nitric acid RuHN ₄ O ₁₀ (Aldrich, 373567-25ML: 2.00 g) was dissolved in ion exchange water (1000 mL) to prepare a ruthenium solution. Next, γ-alumina (trade name “AKP-G0-01” manufactured by Sumitomo Chemical Co., Ltd .: 10.0 g) was added to the ruthenium solution to obtain a mixture. Next, the mixture was stirred for 12 hours under a temperature condition of 30 ° C. and then evaporated to dryness. The obtained solid was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours, and the exhaust gas purification for comparison was performed. A catalyst was obtained. The supported amount of ruthenium in the obtained catalyst was 0.3% by mass.

(Comparative Example 3)
Ruthenium chloride RuCl ₃ (trade name “R0074” manufactured by Tokyo Chemical Industry Co., Ltd .: 61.6 mg) was dissolved in acetone (1000 mL) to prepare a ruthenium solution. Next, γ-alumina (trade name “AKP-G0-01” manufactured by Sumitomo Chemical Co., Ltd .: 10.0 g) was added to the ruthenium solution to obtain a mixture. Next, the mixture was stirred for 12 hours under a temperature condition of 30 ° C. and then evaporated to dryness. The obtained solid was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours, and the exhaust gas purification for comparison was performed. A catalyst was obtained. The supported amount of ruthenium in the obtained catalyst was 0.3% by mass.

[Characteristic evaluation of automobile exhaust gas purification catalysts and the like obtained in Examples 1 to 3 and Comparative Examples 1 to 3]
<ESIMS measurement of ruthenium-containing liquid prepared in Examples 1 to 3>
With respect to the ruthenium-containing liquids prepared in Examples 1 to 3, ESIMS measurement was performed using Q-TOF (manufactured by Micromass) as a measuring device. Graphs of mass spectra of the respective ruthenium-containing liquids obtained by such ESIMS measurement are shown in FIG. 1 (Example 1), FIG. 2 (Example 2), and FIG. 3 (Example 3), respectively. The measurement conditions for such ESIMS measurement are shown below.
<Measurement condition>
Ionization method: Electrospray ionization method Ionization mode: Positive ion mode Capillary voltage: 3200V
Cone voltage: 40V
Desolvation temperature: 120 ° C
As is apparent from the results shown in FIGS. 1 to 3, it was confirmed that the ruthenium binuclear complex was dissolved in the ruthenium-containing liquid prepared in Examples 1 to 3.

<Measurement of automobile exhaust gas purification catalyst by scanning transmission electron microscope>
The regions of 12 nm in length and 12 nm in width of the powders of automobile exhaust gas purification catalysts obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were scanned and transmitted with an electron microscope (STEM: trade name “JEM- 2100F "). As a result of such measurement, in the automobile exhaust gas purification catalysts obtained in Examples 1 to 3, the ratio of ruthenium atoms supported as diatomic clusters is based on the total ruthenium atoms supported on γ-alumina. It was confirmed that it was 50 at% or more. On the other hand, in the automobile exhaust gas purification catalysts obtained in Comparative Examples 1 to 3, the ratio of ruthenium atoms supported as diatomic clusters was 50 at% with respect to all ruthenium atoms supported on γ-alumina. It was confirmed that it was less than.

<Evaluation of catalytic activity of automobile exhaust gas purification catalyst>
Using 0.5 g of automobile exhaust gas purification catalyst powder obtained in Examples 1 to 3 and Comparative Examples 1 to 3, each powder was molded by a cold isostatic pressure method (CIP: 1000 kg / cm ² ) for 1 minute. Then, each sample for a catalytic activity test was prepared by pulverizing into pellets having a diameter of 0.5 to 1 mm. Next, each of the obtained samples was installed in a fixed-bed flow evaluation device, and the exhaust model gas shown in Table 1 below was supplied at a flow rate of 3.5 L / min for 15 minutes under a temperature condition of 300 ° C. processing). Then, after cooling until the temperature of each sample reaches 100 ° C., the exhaust model gas is heated from 100 ° C. to 300 ° C. at a temperature rising rate of 15 ° C./min while supplying the exhaust model gas at a flow rate of 3.5 L / min. The temperature at which the purification rate of C ₃ H _{6 in} the supplied exhaust model gas reaches 50% (50% purification temperature: hereinafter referred to as “T50”) was measured. The results are shown in FIG.

  As is clear from the results shown in FIG. 4, the automobile exhaust gas purification catalyst (Examples 1 to 3) of the present invention has a lower T50 than the automobile exhaust gas purification catalyst (Comparative Examples 1 to 3) for comparison. It was confirmed that the temperature was excellent and the catalyst activity was excellent. In addition, when alcohol was used as the solvent for the ruthenium-containing liquid (Example 1), it was confirmed that T50 was at a particularly low temperature. By using alcohol as the solvent, the catalyst has higher catalytic activity. It was found that a catalyst was obtained.

  As described above, according to the present invention, ruthenium in an atomic state is supported in a sufficiently dispersed state, and the catalyst for purifying automobile exhaust gas having a sufficiently high catalytic activity and the catalyst are efficiently produced. It is possible to provide a method for producing a catalyst for purifying automobile exhaust gas that can be reliably produced. Such an automobile exhaust gas purification catalyst of the present invention can be used as a three-way catalyst or the like used to purify exhaust gas discharged from an automobile.

4 is a graph of mass spectrum obtained by ESIMS measurement of a ruthenium complex in a ruthenium-containing liquid prepared in Example 1. FIG. It is a graph of the mass spectrum obtained by carrying out ESIMS measurement of the ruthenium complex in the ruthenium containing liquid prepared in Example 2. It is a graph of the mass spectrum obtained by carrying out ESIMS measurement of the ruthenium complex in the ruthenium containing liquid prepared in Example 3. It is a graph showing the 50% purification temperature (T50) of _C 3 _{H 6} of the automobile exhaust gas purifying catalyst obtained in Examples 1-3 and Comparative Examples 1-3.

Claims (4)

  A ruthenium supported on the carrier in an atomic state using a ruthenium carboxylate binuclear complex, and at least 50 at% of the ruthenium is supported on the carrier as a ruthenium diatomic cluster. A catalyst for purifying automobile exhaust gas.   A ruthenium-containing liquid containing a ruthenium carboxylate binuclear complex is brought into contact with a carrier, the ruthenium carboxylate binuclear complex is supported on the carrier, and calcined, whereby ruthenium is supported on the carrier in an atomic state and automobile exhaust gas. A method for producing a catalyst for purification of automobile exhaust gas, comprising obtaining a catalyst for purification. The ruthenium carboxylate dinuclear complex has the following general formula (1):
Ru ₂ (R-COO) ₄ · X ^m _n (1)
[In the formula (1), R represents an alkyl group having 1 to 5 carbon atoms, X represents a counter anion, m represents an ionic value of the counter anion, and represents a numerical value of −1 to −4, and n represents The numerical value which changes according to the electrical neutral principle according to the value of m is shown. ]
The method for producing a catalyst for purifying automobile exhaust gas according to claim 2, wherein the compound is a compound selected from the group consisting of:   The method for producing a catalyst for purifying automobile exhaust gas according to claim 2 or 3, wherein the solvent of the ruthenium-containing liquid is alcohol.

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