JP5288261B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Description

  The present invention relates to an exhaust gas purifying 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 internal combustion engines such as automobiles. Has been used. As such an exhaust gas purifying catalyst, for example, a catalyst in which a noble metal such as platinum (Pt) or rhodium (Rh) is supported on a carrier made of γ-Al ₂ O ₃ or the like is known. Further, as a method for producing such an exhaust gas purifying catalyst, a method in which a solution containing a noble metal salt is brought into contact with a carrier and then calcined to carry the noble metal on the carrier has been adopted. In recent years, various methods for producing exhaust gas purifying catalysts have been studied in order to obtain a catalyst having higher catalytic activity.

  For example, in Japanese Patent Application Laid-Open No. 2006-55807 (Patent Document 1), a multinuclear complex composed of a plurality of organic polydentate ligands and a plurality of noble metal atoms is deposited on an oxide carrier, and then an organic polydentate ligand is formed. A method for producing a catalyst is disclosed in which a catalyst carrying a noble metal cluster is obtained by removing. However, in the method for producing a catalyst as described in Patent Document 1, it is not always possible to obtain a catalyst having sufficient catalytic activity. In particular, the catalyst obtained by such a method for producing a catalyst has been used for a long time. In some cases, the catalyst activity was not always sufficient.

JP 2006-55807 A

  The present invention has been made in view of the above-mentioned problems of the prior art, and even when exposed to a high temperature atmosphere for a long time, the rhodium grain growth can be sufficiently suppressed and sufficient catalytic activity is maintained. It is an object of the present invention to provide an exhaust gas purifying catalyst and a method for producing an exhaust gas purifying 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 rhodium carbonyl polynuclear complex when supporting rhodium on a carrier, so that even when exposed to a high temperature atmosphere for a long time, The inventors have found that it is possible to obtain an exhaust gas purifying catalyst that can sufficiently suppress grain growth and maintain sufficient catalytic activity, and has completed the present invention.

That is, the exhaust gas purifying catalyst of the present invention includes a carrier and rhodium supported on the carrier in an atomic state using a rhodium carbonyl polynuclear complex, and 50 at% or more of the rhodium is composed of a plurality of rhodium atoms. those characterized that you have been supported on the support as clusters.

Furthermore, in the exhaust gas purifying catalyst of the present invention, the rhodium carbonyl polynuclear complex is represented by the following general formula (1):
[Rh _x H _y (CO) _z ] (1)
[In Formula (1), x represents an integer of 2 or more, y represents an integer of 0 or more, and z represents an integer of 1 or more. ]
It is preferable that it is a rhodium carbonyl polynuclear complex represented by these.

In the method for producing an exhaust gas purifying catalyst of the present invention, a rhodium carbonyl polynuclear complex and a rhodium-containing liquid containing chloroform as a solvent are brought into contact with a carrier, the rhodium carbonyl polynuclear complex is supported on the carrier, and calcined. In the method, rhodium is supported in an atomic state on the carrier, and an exhaust gas purifying catalyst is obtained in which 50 at% or more of the rhodium is supported on the carrier as a cluster composed of a plurality of rhodium atoms .

  According to the present invention, it is possible to obtain an exhaust gas purifying catalyst that can sufficiently suppress the growth of rhodium particles and maintain sufficient catalytic activity even when exposed to a high temperature atmosphere for a long time. The reason why the catalyst can be produced efficiently and reliably is not necessarily clear, but the present inventors speculate as follows. That is, in the present invention, rhodium is supported on the carrier using a rhodium carbonyl polynuclear complex. Among rhodium carbonyl polynuclear complexes, for example, in the rhodium carbonyl hexanuclear complex, a structure in which the C atom of the carbonyl group, which is a ligand, is coordinated to the Rh atom and an O atom exists outside the complex. (See FIG. 1). In such a rhodium carbonyl polynuclear complex, rhodium chloride or the like used in the conventional method for producing a catalyst forms an electrostatic weak bond with a carrier, whereas as shown in FIG. It is possible to form a chemical bond between the oxygen atom of the carbonyl group and the metal atom (for example, Al atom) constituting the carrier (in FIG. 2 (a), it is chemically bonded to the Al atom). Only the carbonyl groups that are present. When such a coordination bond is formed, it is presumed that the complex is supported on the carrier in an excellent stability state due to the strong binding force. When such a rhodium carbonyl multinuclear complex is baked after being supported on a carrier, the bond between rhodium in the rhodium carbonyl multinuclear complex is easily maintained by the carbonyl group as a ligand. ) In the state in which rhodium in the rhodium carbonyl polynuclear complex is bonded to each other (for example, the state of a 4-atom cluster when the complex is tetranuclear, or the state of a 6-atom cluster when the complex is hexanuclear). As a carrier. In such a case, the ligand can be removed while sufficiently suppressing the aggregation of the complexes. Therefore, the rhodium clusters are supported on the carrier in a sufficiently dispersed state. Thus, in the exhaust gas purifying catalyst of the present invention, clusters composed of a plurality of rhodium atoms are supported on the carrier in a state where the clusters are sufficiently dispersed. And since such clusters are heavier than rhodium atoms, they are difficult to move on the support, and even when exposed to a high temperature atmosphere for a long time, rhodium does not grow easily, so the catalytic activity is maintained. Inferred. Further, since the clusters are supported on the carrier in a sufficiently dispersed state, it is presumed that they have a sufficient amount of active sites and can exhibit a sufficient catalytic activity.

  According to the present invention, an exhaust gas purifying catalyst capable of sufficiently suppressing rhodium grain growth and maintaining sufficient catalytic activity even when exposed to a high temperature atmosphere for a long time, and the catalyst are efficiently produced. It is possible to provide a method for producing an exhaust gas purifying catalyst that can be reliably produced.

It is a schematic diagram which shows the rhodium carbonyl hexanuclear complex which is one of the rhodium carbonyl polynuclear complexes concerning this invention. FIG. 2 (a) is a schematic diagram showing a state in which the rhodium carbonyl multinuclear complex according to the present invention is chemically bonded to the carrier, and FIG. 2 (b) shows the rhodium carbonyl multinuclear complex according to the present invention. It is a schematic diagram which shows the state which carried | supported in an atomic state. 2 is a graph showing a mass spectrum of electrospray ionization mass spectrometry in a rhodium-containing liquid used in Example 1. FIG. 2 is a scanning transmission electron microscope (STEM) photograph of the exhaust gas purifying catalyst powder obtained in Example 1. FIG. 4 is a scanning transmission electron microscope (STEM) photograph of the exhaust gas purifying catalyst powder obtained in Example 2. FIG. 3 is a scanning transmission electron microscope (STEM) photograph of the exhaust gas purifying catalyst powder obtained in Comparative Example 1. FIG. It is a graph which shows the rhodium dispersion degree after the endurance test of the catalyst for exhaust gas purification obtained in Example 4 and Comparative Example 2. It is a graph which shows the rhodium dispersion degree after the endurance test of the catalyst for exhaust gas purification obtained in Examples 5-6 and Comparative Example 3. It is a graph which shows the rhodium dispersion degree after the endurance test of the catalyst for exhaust gas purification obtained in Examples 7-8 and Comparative Example 4. It is a graph which shows the 50% purification temperature after the endurance test of the catalyst for exhaust gas purification obtained in Examples 5-8 and Comparative Examples 3-4. It is a graph which shows NO purification rate after the endurance test of the catalyst for exhaust gas purification obtained in Examples 4-8 and Comparative Examples 2-4.

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

  First, the exhaust gas purifying catalyst of the present invention will be described. That is, the exhaust gas purifying catalyst of the present invention comprises a carrier and rhodium supported in an atomic state on the carrier using a rhodium carbonyl polynuclear complex.

Such a carrier is not particularly limited, and a known carrier that can be used as a catalyst for exhaust gas purification can be appropriately used. For example, a carrier made of a metal oxide can be suitably used. Examples of the metal oxide used for such a carrier include activated alumina, alumina-ceria-zirconia, ceria-zirconia, zirconia, lanthanum stabilized activated alumina, and the like. Lanthanum (La), cerium (Ce) , Praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er) , Oxides of thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y), zirconium (Zr), aluminum (Al), magnesium (Mg) and vanadium (V), solid solutions thereof, and these At least selected from the group consisting of complex oxides of Seed is preferred. 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 rhodium is supported on a carrier in an atomic state using the rhodium carbonyl polynuclear complex. In the present invention, rhodium is supported on the carrier in an atomic state using the rhodium carbonyl polynuclear complex, and clusters composed of a plurality of rhodium atoms are supported on the carrier in a state where the clusters are sufficiently dispersed. In the present invention, since the clusters are heavier than the rhodium atoms, it is difficult for them to move on the support. Therefore, even when exposed to a high temperature atmosphere for a long time, rhodium is less likely to grow. Since they are supported on the carrier in a sufficiently dispersed state, they have a sufficient amount of active sites and can exhibit a sufficient catalytic activity. The supported state of rhodium using such a rhodium carbonyl polynuclear complex can be achieved by employing the method for producing an exhaust gas purifying catalyst of the present invention described later.

The rhodium carbonyl polynuclear complex according to the present invention is a complex in which a ligand having two or more rhodium atoms and a carbonyl group on the rhodium atom is coordinated. When rhodium is one atom in one molecule of the complex, rhodium grain growth cannot be sufficiently suppressed in the obtained catalyst. Moreover, in such a rhodium carbonyl polynuclear complex, what is necessary is just to have the ligand which has at least 1 carbonyl group as a ligand, and you may have another ligand. As such a rhodium carbonyl polynuclear complex, for example, the following general formula (1):
[Rh _x H _y (CO) _z ] (1)
The complex represented by these is mentioned. The complex represented by the general formula (1) may be charged as plus (+) or minus (−) as a complex molecule, or may not be charged. In addition, when charged as a complex molecule, it is solvated by a solvent used at the time of manufacture, storage, use, etc. of the complex (for example, water when the solvent at the time of manufacture or use is water). May be).

  In the general formula (1), x represents an integer of 2 or more. Further, from the viewpoint of further suppressing the catalytic activity and rhodium grain growth in the obtained catalyst, x is more preferably an integer in the range of 2 to 17, and particularly preferably an integer in the range of 4 to 6. . Y represents an integer of 0 or more. Furthermore, although z shows an integer greater than or equal to 1, it is more preferable that it is an integer of the range of 1-32, and it is especially preferable that it is an integer of the range of 12-16.

Examples of such a rhodium carbonyl polynuclear complex include a rhodium carbonyl tetranuclear complex represented by a composition formula: [Rh ₄ (CO) ₁₂ ] and a rhodium carbonyl represented by a composition formula: [Rh ₆ (CO) ₁₆ ]. Examples include hexanuclear complexes. The method for synthesizing such a rhodium carbonyl polynuclear complex is not particularly limited, and a known method can be appropriately employed. Furthermore, as such a rhodium carbonyl polynuclear complex, a commercially available product may be used.

  Furthermore, in the present invention, it is preferable that 50 at% or more (more preferably 70 at% or more) of all rhodium atoms are supported on the carrier as clusters composed of a plurality of rhodium atoms. If the ratio of rhodium supported in such a state is in the above range, the clusters are sufficiently dispersed and supported, so that the number of active sites of the catalyst is sufficient, and a more advanced catalyst. Activity tends to be obtained. Further, when the proportion of rhodium existing as a cluster composed of a plurality of rhodium atoms is less than the lower limit, a sufficiently high catalytic activity tends to be not obtained. In the present invention, since the rhodium carbonyl polynuclear complex having a plurality of rhodium atoms is supported on the carrier, the cluster is composed of rhodium atoms having the same number as the number of nuclei of the rhodium carbonyl multinuclear complex. It is guessed. In the present invention, a method for determining the ratio (at%) of rhodium atoms present as a cluster composed of a plurality of rhodium atoms is obtained by using an arbitrary region of 12 nm in length and 12 nm on the support of the exhaust gas purifying catalyst as a spherical surface on a converging lens Measured with a scanning transmission electron microscope (STEM) equipped with an aberration corrector, and based on the obtained STEM image, the total number of rhodium atoms present in the region and the rhodium existing as a cluster composed of a plurality of rhodium atoms. A method is adopted in which the number of atoms is determined and the ratio of the number of atoms to the total number of rhodium atoms is calculated. As the scanning transmission electron microscope (STEM), for example, a trade name “JEM-2100F” manufactured by JEOL Ltd. can be used.

  Further, the exhaust gas purifying catalyst of the present invention may be provided with the carrier and rhodium supported in an atomic state on the carrier using the rhodium carbonyl polynuclear complex, and the form thereof is not particularly limited. It may be in the form of a honeycomb-shaped monolith catalyst in which the catalyst is supported on a substrate, 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 such an exhaust gas purifying catalyst, other components (for example, NOx occlusion material) that can be used for the exhaust gas purifying catalyst may be appropriately supported within a range not impairing the effects of the present invention.

  Next, the manufacturing method of the exhaust gas purifying catalyst of the present invention will be described. That is, in the method for producing an exhaust gas purifying catalyst of the present invention, a rhodium-containing liquid containing a rhodium carbonyl polynuclear complex is brought into contact with a carrier, the rhodium carbonyl polynuclear complex is supported on the carrier, and calcined. And obtaining an exhaust gas purifying catalyst in which rhodium is supported in an atomic state.

  Such a rhodium-containing liquid contains the aforementioned rhodium carbonyl polynuclear complex. In the present invention, by using such a rhodium carbonyl polynuclear complex, when this is supported on a carrier, it becomes possible to form a coordinate bond between the complex and the carrier. It becomes possible to support the cluster of atoms on the carrier in a state where the clusters are sufficiently dispersed.

  The solvent for the rhodium-containing liquid is not particularly limited, and a solvent capable of dissolving the rhodium carbonyl polynuclear complex can be used as appropriate, but an organic solvent can be used from the viewpoint of selective adsorption efficiency on the carrier. It is particularly preferable to use chloroform, diethyl ether, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, toluene, or pyridine.

  Further, the content ratio of rhodium (metal) in such a rhodium-containing liquid is not particularly limited, but is preferably 0.001 to 1% by mass in terms of metal. If the ratio of rhodium is less than the lower limit, it tends to be difficult to efficiently support the rhodium carbonyl polynuclear complex on the support. On the other hand, if the upper limit is exceeded, selective adsorption is difficult, and the rhodium carbonyl polynuclear complex is reduced. It tends to be difficult to carry uniformly. The method for preparing such a rhodium-containing liquid is not particularly limited, and for example, a method capable of dissolving the rhodium carbonyl polynuclear complex in the solvent may be adopted as appropriate.

  In the method for producing an exhaust gas purifying catalyst of the present invention, the rhodium-containing liquid is brought into contact with the carrier, and the rhodium carbonyl polynuclear complex is supported on the carrier. The method is not particularly limited, and a known method capable of supporting the rhodium carbonyl polynuclear complex on the carrier can be appropriately employed. For example, by immersing the carrier in the rhodium-containing liquid. A method of supporting the rhodium carbonyl polynuclear complex on the carrier may be adopted. When the rhodium carbonyl polynuclear complex is supported on the surface of the carrier by immersing the carrier in the rhodium-containing liquid, the pressure is 1 to 10 atm, the freezing point of the rhodium-containing liquid is higher than the freezing point. It is preferable to stir for about 0.1 to 24 hours under the following temperature conditions (more preferably about room temperature). If the pressure and temperature conditions for supporting the rhodium carbonyl polynuclear complex on the surface of the support are less than the lower limit, the supporting efficiency tends to decrease. Tend to increase.

  In addition, as a method of firing after supporting the rhodium carbonyl polynuclear complex on the carrier, a method of firing for about 1 to 5 hours at a temperature of 200 to 700 ° C. (more preferably 300 to 600 ° C.) is adopted. Is preferred. 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, rhodium is supported when rhodium is supported on the support. The atoms tend to aggregate.

  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, as a rhodium precursor, 51.8 mg of hexadecacarbonyl hexarhodium which is a rhodium carbonyl hexanuclear complex (manufactured by Aldrich, composition formula: [Rh ₆ (CO) ₁₆ ]) is dissolved in 1 L of chloroform to prepare a rhodium-containing liquid. After the preparation, 10 g of EMS (compositional formula: MgAl ₂ O ₄ , specific surface area: 100 m ² / g) was added to the rhodium-containing liquid to obtain a mixed solution (supporting liquid). The rhodium-containing liquid was subjected to mass spectrometry using an electrospray ionization mass spectrometer (ESIMS, manufactured by Micro Mass). The obtained results are shown in FIG. As is clear from the results shown in FIG. 3, it was confirmed that the rhodium-containing liquid was present as a rhodium carbonyl hexanuclear complex.

  Next, the obtained mixed solution is stirred for 12 hours under a condition of about 30 ° C. using a hot stirrer, and then the powder is taken out from the mixed solution by filtration, and placed in the atmosphere at 400 ° C. for 3 hours. Then, an exhaust gas purifying catalyst having rhodium supported on γ-alumina was obtained. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP (high frequency inductively coupled plasma analysis), and the value is shown in Table 1.

(Example 2)
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that 10 g of γ-alumina (“AKP-G0-01” manufactured by Sumitomo Chemical Co., Ltd.) was used instead of EMS. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Example 3)
Instead of the rhodium carbonyl hexanuclear complex, dodecacarbonyl tetrarhodium (Aldrich, composition formula: [Rh ₄ (CO) ₁₂ ]) 54.5 mg, which is a rhodium carbonyl tetranuclear complex, was used in the same manner as in Example 2. Thus, an exhaust gas purification catalyst was obtained. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

Example 4
Exhaust gas purification catalyst was obtained in the same manner as in Example 2 except that the addition amount of hexadecacarbonyl hexarhodium, which is a rhodium carbonyl hexanuclear complex, was 25.9 mg and the calcination temperature was 500 ° C. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Example 5)
Except for using 10 g of AZL (composition: Al ₂ O ₃ (200 mol) / ZrO ₂ (95 mol) / La ₂ O ₃ (2.5 mol), specific surface area: 110 m ² / g) instead of γ-alumina. Obtained an exhaust gas purifying catalyst in the same manner as in Example 4. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Example 6)
Instead of rhodium carbonyl hexanuclear complex, dodecacarbonyl tetrarhodium which is a rhodium carbonyl tetranuclear complex (manufactured by Aldrich, composition formula: [Rh ₄ (CO) ₁₂ ]) 27.25 mg was used in the same manner as in Example 5. Thus, an exhaust gas purification catalyst was obtained. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Example 7)
The same as Example 4 except that 10 g of Nd-AZL (composition: Nd ₂ O ₃ (2% by mass) / AZL (98% by mass), specific surface area: 105 m ² / g) was used instead of γ-alumina. An exhaust gas purification catalyst was obtained. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Example 8)
Instead of rhodium carbonyl hexanuclear complex, dodecacarbonyl tetrarhodium (Aldrich, composition formula: [Rh ₄ (CO) ₁₂ ]) 27.25 mg, which is a rhodium carbonyl tetranuclear complex, was used in the same manner as in Example 7. Thus, an exhaust gas purification catalyst was obtained. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Comparative Example 1)
First, 1.09 g of rhodium nitrate (composition formula: Rh ₂ (NO ₃ ) ₃ ) aqueous solution (“Rh-10H” manufactured by Tanaka Kikinzoku, rhodium content: 2.75 mass%) as a rhodium precursor is added to 1 L of ion-exchanged water. After preparing the solution by dissolving in, 10 g of γ-alumina (“AKP-G0-01” manufactured by Sumitomo Chemical Co., Ltd.) was added to the solution to obtain a mixed solution. Next, the obtained mixed solution is stirred for 12 hours under a condition of about 30 ° C. using a hot stirrer, and then the powder is taken out from the mixed solution by filtration, and is then placed in the atmosphere at a temperature of 300 ° C. for 3 hours. Then, an exhaust gas purifying catalyst for comparison in which rhodium was supported on γ-alumina was obtained. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Comparative Example 2)
An exhaust gas purifying catalyst for comparison in which rhodium was supported on γ-alumina was obtained in the same manner as in Comparative Example 1 except that the amount of rhodium nitrate added was 0.545 g and the firing temperature was 500 ° C. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Comparative Example 3)
Except for using 10 g of AZL (composition: Al ₂ O ₃ (200 mol) / ZrO ₂ (95 mol) / La ₂ O ₃ (2.5 mol), specific surface area: 110 m ² / g) instead of γ-alumina. Obtained an exhaust gas purification catalyst in the same manner as in Comparative Example 2. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

(Comparative Example 4)
In the same manner as in Comparative Example 2, except that 10 g of Nd-AZL (composition: Nd ₂ O ₃ (2% by mass) / AZL (98% by mass), specific surface area: 105 m ² / g) was used instead of γ-alumina. An exhaust gas purification catalyst was obtained. The amount of rhodium supported in the obtained exhaust gas purification catalyst was analyzed by ICP, and the value is shown in Table 1.

[Evaluation of Performance of Exhaust Gas Purification Catalysts Obtained in Examples 1-8 and Comparative Examples 1-4]
<Measurement by Scanning Transmission Electron Microscope (Cs-STEM) with Spherical Aberration Correction Device>
The 12-nm and 12-nm regions of the exhaust gas purifying catalyst powders obtained in Examples 1 and 2 and Comparative Example 1 were observed with a scanning transmission electron microscope (trade name “JEM-2100F” manufactured by JEOL). did. STEM photographs of the exhaust gas purifying catalysts obtained in Examples 1 and 2 and Comparative Example 1 obtained by such observation are shown in FIG. 4 (Example 1), FIG. 5 (Example 2), and FIG. Shown in Comparative Example 1).

  As is clear from the results shown in FIG. 4 and FIG. 5, in the exhaust gas purifying catalyst of the present invention (Examples 1 and 2) in which rhodium is supported on a carrier using a rhodium carbonyl hexanuclear complex, the catalyst is not formed on the carrier. It was confirmed that clusters composed of a plurality of rhodium atoms were dispersed and supported. From the results shown in FIGS. 4 and 5, the rhodium supported on the carrier of the exhaust gas purifying catalyst obtained in Examples 1 and 2 has 70 at% or more of all rhodium atoms supported as 6-atom clusters. (It is noted that, in FIGS. 4 and 5, rhodium is present as a 6-atom cluster in the circled region). On the other hand, as is clear from the results shown in FIG. 6, in the exhaust gas purifying catalyst for comparison (Comparative Example 1), rhodium atoms are dispersed in a monoatomic form, but as a cluster. It was confirmed that some of them were supported, and the number of atoms of these clusters was not fixed, for example, it was confirmed that there were also clusters composed of several tens of rhodium atoms (in FIG. 6, circles). In the region surrounded by, there are clusters of rhodium atoms with undefined number of atoms). From these results, by supporting rhodium on the support using a rhodium carbonyl polynuclear complex, the rhodium atoms are sufficiently dispersed and uniformly supported, and more than 70 at% of all rhodium atoms are formed from a plurality of rhodium atoms. It was confirmed that it can be supported as a cluster.

<Measurement of degree of rhodium dispersion after endurance test> First, an endurance test was performed on the exhaust gas purifying catalysts obtained in Examples 2 to 8 and Comparative Examples 1 to 4. That is, first, for each exhaust gas purification catalyst, a rich gas composed of H ₂ (2% by volume), CO ₂ (10% by volume), H ₂ O (3% by volume) and N ₂ (remainder), and O ₂ (1% by volume), CO ₂ (10% by volume), H ₂ O (3% by volume), and lean gas consisting of N ₂ (remainder) were alternately supplied for 5 minutes each for 50 hours. The rich gas and the lean gas were supplied so as to pass at a rate of 500 mL / min per 2 g of the catalyst under the condition of a temperature of 1000 ° C., and the durability test of the catalyst was performed.

Next, the rhodium dispersity of the exhaust gas purifying catalysts (Examples 2 to 8 and Comparative Examples 1 to 4) after the durability test was measured. The CO pulse measurement method was adopted for the measurement of such rhodium dispersity. That is, first, the exhaust gas purifying catalyst after the endurance test is heated to 400 ° C. in 40 minutes in a gas atmosphere of O ₂ (100% by volume) and then held for 15 minutes. Next, after changing the gas atmosphere to a gas atmosphere of He (100% by volume), it is held at 400 ° C. for 40 minutes. Next, after changing the gas atmosphere to a gas atmosphere of H ₂ (100% by volume), the gas atmosphere was maintained at 400 ° C. for 15 minutes, and then the gas atmosphere was changed to a gas atmosphere of He (100% by volume) to 400 ° C. And then naturally cooled to 50 ° C. while maintaining a He (100% by volume) gas atmosphere. Thereafter, in a gas atmosphere of He (100% by volume), 1.0 μmol / pulse CO was pulsed with respect to each exhaust gas purifying catalyst until adsorption was saturated. And the amount of CO which was not adsorbed by the catalyst among the pulsed CO was detected using a heat conduction detector, and the amount of CO adsorbed was measured from the number of pulses and the TCD area when the adsorption was saturated. Then, from the obtained CO adsorption amount and the rhodium (Rh) loading amount, the following formula: [Rh dispersity (%)] = ([CO adsorption amount (mol)] / [Rh loading amount (mol)] ) × 100 was calculated to determine the rhodium dispersity. The obtained results are shown in Table 1. Moreover, the rhodium dispersion after the endurance test of the exhaust gas purification catalyst obtained in Example 4 and Comparative Example 2, the rhodium dispersion after the endurance test of the exhaust gas purification catalyst obtained in Examples 5 to 6 and Comparative Example 3 FIG. 7, FIG. 8 and FIG. 9 show the rhodium dispersion degree after the durability test of the exhaust gas purifying catalysts obtained in Examples 7 to 8 and Comparative Example 4, respectively.

As is clear from the results shown in Table 1, the exhaust gas purifying catalyst of the present invention (Examples 2 to 4) has a high degree of rhodium dispersion even after an endurance test and is exposed to a high temperature atmosphere for a long time. Also, it was confirmed that the rhodium grain growth on the support was sufficiently suppressed. On the other hand, in the exhaust gas purification catalyst for comparison (Comparative Example 1), compared with the exhaust gas purification catalyst obtained in Example 2 in which the type of carrier and the amount of rhodium supported are the same as those in Comparative Example 1. It was confirmed that the rhodium dispersity after the durability test was low. Moreover, as shown in FIG. 7, when the rhodium dispersion degree after the durability test of the exhaust gas purifying catalyst obtained in Example 4 and Comparative Example 2 is compared, in the exhaust gas purifying catalyst of the present invention (Example 4), It was confirmed that the degree of rhodium dispersion after the durability test was 71% higher than that of the exhaust gas-purifying catalyst obtained in Comparative Example 2 in which the type of carrier and the amount of rhodium supported were the same as in Example 4. Furthermore, as shown in FIG. 8, when the rhodium dispersion degree after the durability test of the exhaust gas purification catalyst obtained in Example 6 and Comparative Example 3 is compared, in the exhaust gas purification catalyst (Example 6) of the present invention, It was confirmed that the degree of rhodium dispersion after the durability test was increased by 109% as compared with the exhaust gas purifying catalyst obtained in Comparative Example 3 in which the type of carrier and the amount of rhodium supported were the same as in Example 6. Moreover, as shown in FIG. 9, when the rhodium dispersion degree after the durability test of the exhaust gas purifying catalyst obtained in Example 8 and Comparative Example 3 is compared, in the exhaust gas purifying catalyst of the present invention (Example 8), It was confirmed that the degree of rhodium dispersion after the durability test was 96% higher than that of the exhaust gas-purifying catalyst obtained in Comparative Example 4 in which the type of carrier and the amount of rhodium supported were the same as in Example 8.

<Evaluation of NO purification rate after endurance test>
The NO purification rate of the exhaust gas purifying catalysts (Examples 4 to 8 and Comparative Examples 2 to 4) after the durability test was evaluated. That is, the exhaust gas purifying catalyst after the endurance test was used as a sample and installed in a normal pressure fixed bed flow type reactor (manufactured by Best Sokki). Then, CO (0.7 _volume%), H 2 (0.23 volume%), NO (0.12 _{volume%), C 3 H 6 (} 0.16 _volume%), C 2 (0.64 volume %), CO ₂ (10% by volume), H ₂ O (3% by volume), and N ₂ (the balance) are supplied at a gas flow rate of 3500 mL / min so that the gas temperature with catalyst becomes 100 ° C. And the NO concentration of the catalyst-containing gas was measured. Then, while raising the temperature of the gas containing the catalyst to 500 ° C. at a rate of temperature increase of 15 ° C./min, the NO concentration of the catalyst outgas is measured, and NO The purification rate was calculated.

  The temperature at which the NO purification rate in the supplied model gas reaches 50% (NO 50% purification temperature) was measured. The obtained result is shown in FIG. As is apparent from the results shown in FIG. 10, the exhaust gas purifying catalyst (Examples 5 to 8) of the present invention has 50 as compared with the exhaust gas purifying catalyst (Comparative Examples 3 to 4) for comparison. % Purification temperature was confirmed to be low.

  Further, the NO purification rate at temperatures of 400 ° C. and 500 ° C. was measured. The obtained results are shown in FIG. As is clear from the results shown in FIG. 11, in the exhaust gas purifying catalysts (Examples 4 to 8) of the present invention, NO purification is performed in comparison with the exhaust gas purifying catalysts (Comparative Examples 2 to 4) for comparison. The rate was high and it was confirmed that the catalyst had sufficient catalytic activity.

  As described above, according to the present invention, an exhaust gas purifying catalyst capable of sufficiently suppressing rhodium grain growth and maintaining sufficient catalytic activity even when exposed to a high temperature atmosphere for a long time, In addition, it is possible to provide a method for producing an exhaust gas purifying catalyst capable of efficiently and reliably producing the catalyst. Such an exhaust gas purifying catalyst of the present invention can be used as a three-way catalyst used for purifying exhaust gas discharged from automobiles.

Claims (3)

And carrier, by using a rhodium carbonyl multinuclear complex and a supported rhodium atomic state on the support, the Rukoto than 50at% of the rhodium is supported on the support as clusters of a plurality of rhodium atoms A catalyst for exhaust gas purification. The rhodium carbonyl polynuclear complex has the following general formula (1):
[Rh _x H _y (CO) _z ] (1)
[In Formula (1), x represents an integer of 2 or more, y represents an integer of 0 or more, and z represents an integer of 1 or more. ]
The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is a rhodium carbonyl multinuclear complex represented by the formula: The rhodium-containing liquid containing chloroform as a rhodium carbonyl multinuclear complex and a solvent into contact with a carrier, the rhodium carbonyl polynuclear complex allowed supported on the support, by firing, rhodium is supported in an atomic state on the support A method for producing an exhaust gas purifying catalyst, comprising obtaining an exhaust gas purifying catalyst supported on the carrier as a cluster in which 50 at% or more of the rhodium is composed of a plurality of rhodium atoms .