Catalyst metal particles and catalysts

Abstract

The present invention relates to a catalyst metal particle and a catalyst. Provided is a catalyst metal particle and a catalyst containing the same, which can improve catalytic activity, the catalyst metal particle containing Rh as a main component. The catalyst metal particle of the present invention is characterized in that the catalyst metal particle is represented by the formula Rh x Ir y Pt z (wherein, x+y+z=100, 40≤x≤80, 10≤y≤40, and 10≤z≤40).

Description

Technical Field

[0001] This invention relates to catalyst metal particles and catalysts, and particularly to catalyst metal particles containing Rh as a main component and catalysts containing such catalyst metal particles. Background Technology

[0002] Previously, catalyst metal particles containing platinum group metals such as Pt, Pd, and Rh were used as catalysts for exhaust purification to remove harmful components such as NOx from exhaust gas, as well as electrode catalysts for fuel cells. Various technologies related to such catalyst metal particles and catalysts have been developed.

[0003] As such catalyst metal particles and catalysts, for example, a catalyst composition known is a catalyst composition effective for ternary conversion comprising platinum group metal nanoparticles (e.g., Pt, Pd, Au, Ru, Rh, and nanoparticles of their alloys and mixtures thereof), the nanoparticles having an average particle size of about 15 nm to about 50 nm, the nanoparticles being dispersed on a heat-resistant metal oxide component (Patent Document 1). Additionally, a catalyst using the following formula is known: Pd x Ru y M z (M is selected from at least one of Rh, Pt, Cu, Ag, Au, and Ir. x+y+z=1, x+y=0.01~0.99, z=0.99~0.01, x:y=0.1:0.9~0.9:0.1) represents multi-component solid solution microparticles, and supported catalysts containing such multi-component solid solution microparticles (Patent Document 2). Furthermore, a ternary alloy nanoparticle containing platinum group metals alloyed with at least two transition metal elements, and a catalyst containing such ternary alloy nanoparticles are known (Patent Document 3).

[0004] [Existing Technical Documents]

[0005] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-508845

[0007] [Patent Document 2] International Publication No. 2017 / 150596

[0008] [Patent Document 3] International Publication No. 2023 / 237734 Summary of the Invention

[0009] Among platinum group metals, especially catalytic metal particles containing Rh as the main component, excellent catalytic activity has been achieved, for example, in NOx reduction based on exhaust gas purification catalysts, and this advantage has been utilized. In recent years, due to the high price of Rh, particularly among platinum group metals, reducing its usage has become an urgent issue. On the other hand, even with reduced Rh usage, there is a need to achieve even better catalytic activity than before.

[0010] The present invention was made in view of the following circumstances, and its object is to provide catalyst metal particles capable of improving catalytic activity and catalysts containing the catalyst metal particles, said catalyst metal particles containing Rh as a main component.

[0011] To address the aforementioned issues, the catalyst metal particles of the present invention are characterized by using the formula Rh x Ir y Pt z (where x+y+z=100, 40≤x≤80, 10≤y≤40, and 10≤z≤40.) represents this.

[0012] Furthermore, the catalyst of the present invention is characterized by comprising the above-described catalyst metal particles and a support for supporting the above-described catalyst metal particles.

[0013] According to the present invention, catalytic activity can be improved. Attached Figure Description

[0014] Figure 1 This is a schematic perspective view of an exhaust gas purification device using a catalyst according to one embodiment.

[0015] Figure 2 It means Figure 1 The diagram shows a schematic cross-sectional view of the exhaust gas purification device perpendicular to the direction of the chamber extension, while an enlarged view of the catalyst layer cross-section is also shown.

[0016] Figure 3 (a) to (c) are STEM images of the catalyst particles of Examples 5, 8 and 12, respectively.

[0017] Figure 4 (a) to (e) are STEM images of the catalyst particles of Example 8, elemental mapping images of Rh, Ir and Pt, elemental mapping images of Rh, elemental mapping images of Ir and elemental mapping images of Pt, respectively.

[0018] Figure 5 (a) to (c) are graphs representing the fixed-bed flow reactor used in the catalytic activity evaluation, the temperature program used in the catalytic activity evaluation, and the mixed gas used in the catalytic activity evaluation, respectively.

[0019] Figure 6 This is a graph showing the NO 50% purification temperature of samples from Examples 1-12 and Comparative Examples 1-6.

[0020] [Explanation of reference numerals in the attached figures]

[0021] 1: Exhaust gas purification device; 2: Catalyst metal particles; 4: Carrier particles (carrier); 6: Catalyst (exhaust gas purification catalyst); 10: Honeycomb substrate (substrate); 20: Catalyst layer. Detailed Implementation

[0022] The following describes embodiments of the catalyst metal particles and catalyst of the present invention.

[0023] First, to provide a general overview of the catalyst metal particles and catalyst involved in the embodiments, an example of catalyst metal particles and catalyst involved in one embodiment will be described. Figure 1 This is a schematic perspective view of an exhaust gas purification device using a catalyst according to one embodiment. Figure 2 It means Figure 1 The diagram shows a schematic cross-sectional view of the exhaust gas purification device perpendicular to the direction of the chamber extension, while an enlarged view of the catalyst layer cross-section is also shown.

[0024] like Figure 1 and Figure 2 As shown, an exhaust purification device 1 using a catalyst (exhaust purification catalyst) 6 according to one embodiment is a device for purifying exhaust gas emitted from an internal combustion engine in a vehicle or the like. The exhaust purification device 1 is a so-called direct-flow three-way catalyst, comprising a honeycomb substrate (substrate) 10 and a catalyst layer 20 disposed on the honeycomb substrate 10. The honeycomb substrate 10 is a substrate integrally formed with a cylindrical frame portion 11 and partition walls 14 dividing the space inside the frame portion 11 into a honeycomb pattern. The partition walls 14 are porous materials that delineate multiple chambers 12 extending from the inflow-side end face 10Sa of the honeycomb substrate 10 to the outflow-side end face 10Sb. The shape of the partition walls 14 includes multiple wall portions 14L arranged parallel to each other with a square cross-section perpendicular to the extension direction of the multiple chambers 12, and multiple wall portions 14S arranged parallel to each other and orthogonal to these multiple wall portions 14L, with a lattice-like cross-section perpendicular to the extension direction. Multiple cells 12 are adjacent to each other separated by partition walls 14, with inflow side 12a and outflow side 12b openings. Furthermore, the extension direction of partition walls 14 is approximately the same as the axial direction of the honeycomb substrate 10, and the extension direction of cells 12 is approximately the same as the extension direction of partition walls 14.

[0025] Catalyst layer 20, such as Figure 2As shown, the catalyst layer 20 is disposed integrally on the surface 14s of the pore 12 side of the cellular substrate 10 in an axial direction (extending direction of the cellular substrate 10). Figure 2 The enlarged view shows a powder containing a catalyst 6 according to one embodiment. The catalyst 6 powder comprises a powder of catalyst metal particles 2 according to one embodiment and a powder of support particles (support) 4 supporting the catalyst metal particles 2. The catalyst metal particles 2 are composed of the formula Rh based on atomic ratio. x Ir y Pt z (where x+y+z=100, 40≤x≤80, 10≤y≤40, and 10≤z≤40.) represents ternary alloy nanoparticles. Furthermore, in the catalyst metal particles 2, the surface layer 2b is rich in Rh compared to the central portion 2a.

[0026] Conventionally, catalyst metal particles containing Rh as the main component, such as elemental Rh catalyst metal particles (hereinafter sometimes referred to as "Rh-containing catalyst metal particles"), have achieved superior catalytic activity, for example, in NOx reduction based on exhaust gas purification catalysts, compared to catalyst metal particles containing Pd, Pt, etc. Therefore, this advantage has been utilized. On the other hand, in such conventional Rh-containing catalyst metal particles, to mitigate the high cost caused by the soaring price of Rh, it is required to reduce the amount of Rh used. In contrast, catalyst metal particles 2 according to one embodiment contain Ir and Pt in addition to Rh. The overall composition of catalyst metal particles 2 (the total content of Rh, Ir, and Pt) is set to 100 atomic%, with the Rh content being 40 atomic% or more and 80 atomic% or less, the Ir content being 10 atomic% or more and 40 atomic% or less, and the Pt content being 10 atomic% or more and 40 atomic% or less. Furthermore, these Rh, Ir, and Pt are alloyed. Therefore, in the catalyst metal particles 2 according to one embodiment, compared with conventional Rh-containing catalyst metal particles, by changing the electronic state of Rh to a different state, catalytic activity in NOx reduction based on exhaust gas purification catalysts can be improved, for example. Furthermore, by enriching the surface layer 2b with Rh compared to the central portion 2a, catalytic activity can be improved more effectively.

[0027] Therefore, the catalyst metal particles 2 according to one embodiment can improve catalytic activity in NOx reduction and other processes based on exhaust gas purification catalysts compared to conventional Rh-containing catalyst metal particles. Furthermore, even if Ir and Pt are contained in quantities ranging from 10 atomic% to 40 atomic% respectively, in addition to Rh, catalytic activity can still be improved, thus reducing the amount of Rh used. The catalyst 6 according to one embodiment achieves the same effect by including the catalyst metal particles 2. As a result, in the exhaust gas purification device 1 using the catalyst 6, purification performance can be improved, and the amount of Rh used can be reduced. Next, details regarding the composition of the catalyst metal particles and the catalyst according to the embodiments will be explained.

[0028] 1. Catalyst metal particles

[0029] The catalyst metal particles involved in the implementation method are composed of the formula Rh based on atomic ratio. x Ir y Pt z (where x+y+z=100, 40≤x≤80, 10≤y≤40, and 10≤z≤40.) represents ternary alloy particles.

[0030] The contents of Rh, Ir, and Pt in the catalyst metal particles are explained. The total contents of Rh, Ir, and Pt are set at 100 atomic%. The Rh content is not particularly limited as long as it is 40 atomic% or more and 80 atomic% or less, but preferably 45 atomic% or more and 75 atomic% or less, more preferably 50 atomic% or more and 70 atomic% or less, and particularly preferably 55 atomic% or more and 65 atomic% or less. This is because when the Rh content is above the lower limit of these ranges, it becomes easier to improve the catalytic activity, and when the Rh content is below the upper limit of these ranges, the amount of Rh used can be particularly reduced.

[0031] The total content of Rh, Ir, and Pt is set to 100 atomic%. The content of Ir is not particularly limited as long as it is 10 atomic% or more and 40 atomic% or less, but preferably 15 atomic% or more and 35 atomic% or less, more preferably 20 atomic% or more and 30 atomic% or less, and particularly preferably 22.5 atomic% or more and 27.5 atomic% or less. This is because when the content of Ir is above the lower limit of these ranges, it becomes easier to reduce the amount of Rh used, and when the content of Ir is below the upper limit of these ranges, it becomes easier to improve the catalytic activity. The total content of Rh, Ir, and Pt is set to 100 atomic%. The content of Pt is not particularly limited as long as it is 10 atomic% or more and 40 atomic% or less, but preferably 15 atomic% or more and 35 atomic% or less, more preferably 20 atomic% or more and 30 atomic% or less, and particularly preferably 22.5 atomic% or more and 27.5 atomic% or less. This is because when the Pt content is above the lower limit of these ranges, it becomes easier to reduce the amount of Rh used, and when the Pt content is below the upper limit of these ranges, it becomes easier to increase the catalytic activity.

[0032] The catalyst metal particles are not particularly limited to any particles as described above, and are generally present in the form of powdered catalyst metal particles. For example, catalyst metal particles rich in Rh in the surface layer compared to the central portion are preferred (catalyst metal particles with a larger atomic ratio of Rh content to the combined content of Rh, Ir, and Pt in the surface layer compared to the central portion). This is because it allows for more effective improvement in catalytic activity.

[0033] The average particle size of the catalyst metal particles is not particularly limited, but is, for example, 1 nm or more and 120 nm or less, preferably 1 nm or more and 30 nm or less, and more preferably 1 nm or more and 10 nm or less, and particularly preferably 1 nm or more and 5 nm or less. Here, "average particle size of catalyst metal particles" refers to the average particle size obtained by observing the powder of catalyst metal particles contained in the powder of the catalyst described below using a method such as STEM (scanning transmission electron microscope) or TEM (transmission electron microscope). For example, it is the calculated average of the equivalent circle diameters of 30 or more catalyst metal particles with an equivalent circle diameter of 1 nm or more randomly selected in the TEM image.

[0034] There are no particular limitations on the method for manufacturing catalyst metal particles; for example, methods using polyol reduction can be cited. The polyol reduction method involves reducing metal ions with a polyol, causing nanoscale metal particles to precipitate. In this method, for example, metal salts of Rh, Ir, and Pt are dissolved in polyols (reducing agents) such as ethylene glycol, glycerol, diethylene glycol, and triethylene glycol. The mixture is heated at a specified temperature (e.g., 120°C) for a specified time (e.g., 24 hours) to allow the reaction to proceed. After natural cooling, a reaction solution containing powder of catalyst metal particles in a solid solution state (Rh, Ir, and Pt) is obtained. The powder is then separated from the reaction solution by centrifugation or similar methods, thus manufacturing catalyst metal particles in powder form. In this method, by adding a metal salt along with a protective agent such as polyvinylpyrrolidone or polyethylene glycol, the aggregation of the catalyst metal particles can be suppressed. Furthermore, by adding a metal salt to a polyol along with a particle size modifier such as sodium hydroxide or nitric acid, the average particle size of the catalyst metal particles can be controlled.

[0035] As metal salts of Rh, there are no particular limitations as long as they can produce catalyst metal particles; examples include rhodium chloride (RhCl3), rhodium acetate, and rhodium nitrate. As metal salts of Ir, there are no particular limitations as long as they can produce catalyst metal particles; examples include iridium chloride (IrCl3), iridium acetylacetone, potassium iridium cyanide, and potassium iridiumate. As metal salts of Pt, there are no particular limitations as long as they can produce catalyst metal particles; examples include chloroplatinic acid (H2PtCl6), chloroplatinic acid (H2PtCl4), potassium tetrachloroplatinate (K2PtCl4), ammonium hexachloroplatinate ((NH4)2PtCl6), and sodium hexachloroplatinate (Na2PtCl6).

[0036] 2. Catalyst

[0037] The catalyst involved in the embodiments is a catalyst comprising the catalyst metal particles involved in the embodiments and a support carrying the catalyst metal particles.

[0038] The support is not particularly limited as long as it can support catalyst metal particles, and it usually exists in the form of support particles (supports). The average particle size of the support particles is not particularly limited, for example, it is 1 nm or more and 500 nm or less. Here, "average particle size of support particles" refers to the average particle size obtained by observing the powder of support particles using a method such as STEM or TEM, for example, the calculated average of the equivalent circle diameters of 30 or more support particles with an equivalent circle diameter of 1 nm or more randomly selected in the TEM image.

[0039] The material of the support is not particularly limited as long as it can support the aforementioned catalyst metal particles. For example, it can be an inorganic compound. Specifically, alumina (Al₂O₃), zirconium oxide (ZrO₂), cerium dioxide (CeO₂), silicon dioxide (SiO₂), titanium dioxide (TiO₂), their solid solutions (e.g., cerium dioxide-zirconium oxide composite oxides), and combinations thereof are preferred. Among these, alumina and zirconium oxide are preferred because they have a large specific surface area and high heat resistance.

[0040] The catalyst, as described above, is not particularly limited and typically exists in the form of a catalyst powder comprising powdered catalyst metal particles and powdered support particles (carriers) carrying the catalyst metal particles. As a catalyst, exhaust gas purification catalysts are preferred, for example. This is because excellent catalytic activity and a reduction in the amount of Rh used can be achieved in exhaust gas purification catalysts.

[0041] The application of the exhaust gas purification catalyst is not particularly limited. For example, it can be used in an exhaust gas purification device that uses the catalyst described in one embodiment, such as an exhaust gas purification device having a substrate and a catalyst layer disposed on the substrate, wherein the catalyst layer contains the exhaust gas purification catalyst. The exhaust gas purification device can be either a direct-flow type or a wall-flow type, but a direct-flow type is preferred, and a three-way catalyst is particularly preferred. Examples of wall-flow types include GPF (gasoline particulate filter) and DPF (diesel particulate filter).

[0042] There are no particular limitations on the method for manufacturing the catalyst. For example, a method can be given by preparing a catalyst slurry by impregnating powdered support particles in a reaction solution containing powdered catalyst metal particles, followed by drying and calcining of the catalyst slurry. The reaction solution is obtained by using a polyol reduction method to manufacture catalyst metal particles.

[0043] [Example]

[0044] The following examples and comparative examples are provided to further illustrate the catalyst metal particles and catalysts involved in the implementation.

[0045] 1. Manufacturing of catalyst metal particle powder, catalyst powder, and catalyst granules.

[0046] [Example 1]

[0047] The composition formula Rh based on atomic ratio was created. 80 Ir 10 Pt 10After producing powder of catalyst metal particles and powder of catalyst (exhaust gas purification catalyst) containing the powder of catalyst metal particles, catalyst particles are produced by granulating the catalyst powder.

[0048] First, a powder of catalyst metal particles was prepared using a polyol reduction method. Specifically, rhodium chloride (RhCl3), iridium chloride (IrCl3), and chloroplatinic acid (H2PtCl6), as metal salts, were dissolved in ethylene glycol, a reducing agent, with the atomic ratio of Rh, Ir, and Pt being 80:10:10 as described above. Polyvinylpyrrolidone, as a protective agent, was then dissolved, and the mixture was heated at 120°C for 24 hours. This produced a powder of catalyst metal particles, yielding a reaction solution containing the powder. Furthermore, a particle size modifier was added to the ethylene glycol along with these metal salts. Next, a catalyst slurry was prepared by impregnating a powder of alumina-supported particles into the obtained reaction solution. Then, by coating the catalyst slurry onto a substrate and subjecting it to drying and calcination, a catalyst powder containing both the powder of catalyst metal particles and the powder of the support particles supporting the catalyst metal particles was produced. In this case, the amounts of catalyst metal particle powder and support particle powder during catalyst slurry preparation were adjusted so that the catalyst metal particle loading per 1g of support particle powder was 20μmol / g. Next, catalyst particles were manufactured by granulating the obtained catalyst powder.

[0049] [Examples 2-12 and Comparative Examples 1-3]

[0050] After manufacturing a powder of catalyst metal particles whose composition by atomic ratio is expressed by the formula shown in Table 1 below, and a powder of catalyst (exhaust gas purification catalyst) containing the powder of catalyst metal particles, catalyst particles were manufactured by granulating the catalyst powder. In this case, when manufacturing the powder of catalyst metal particles, rhodium chloride, iridium chloride, and chloroplatinic acid were dissolved in ethylene glycol in an atomic ratio of Rh, Ir, and Pt such that the atomic ratios expressed by the formulas shown in Table 1 below were used. Otherwise, the powder of catalyst metal particles and the powder of catalyst were manufactured in the same manner as in Example 1, and catalyst particles were manufactured.

[0051] [Comparative Example 4]

[0052] After producing powdered catalyst metal particles of elemental Rh and powdered catalyst (exhaust gas purification catalyst) containing the powdered catalyst metal particles, catalyst particles were produced by granulating the catalyst powder. In this case, when producing the powdered catalyst metal particles, only rhodium chloride was dissolved in ethylene glycol as a metal salt. Apart from this, the powdered catalyst metal particles and the powdered catalyst were produced in the same manner as in Example 1, and catalyst particles were produced.

[0053] [Comparative Example 5]

[0054] After producing powdered catalyst metal particles of elemental Ir and powdered catalyst (exhaust gas purification catalyst) containing the powdered catalyst metal particles, catalyst particles were produced by granulating the catalyst powder. In this case, when producing the powdered catalyst metal particles, only iridium chloride was dissolved in ethylene glycol as a metal salt. Apart from this, the powdered catalyst metal particles and the powdered catalyst were produced in the same manner as in Example 1, and catalyst particles were produced.

[0055] [Comparative Example 6]

[0056] After producing powdered catalyst metal particles of elemental Pt and powdered catalyst (exhaust gas purification catalyst) containing the powdered catalyst metal particles, catalyst particles were produced by granulating the catalyst powder. In this case, when producing the powdered catalyst metal particles, only chloroplatinic acid was dissolved in ethylene glycol as a metal salt. Apart from this, the powdered catalyst metal particles and the powdered catalyst were produced in the same manner as in Example 1, and catalyst particles were produced.

[0057] 2. Evaluation

[0058] [STEM observation and EDX composition analysis]

[0059] The average particle size of the catalyst metal particle powder in the reaction solution was determined by observing it using TEM. Specifically, at least 30 catalyst metal particles with an equivalent circular diameter of 1 nm or more were randomly selected from the TEM image, and the calculated average of their equivalent circular diameters was used as the average particle size of the catalyst metal particle powder. The results are shown in Table 1 below. Furthermore, samples taken from the particles of the catalysts prepared in Examples 5, 8, and 12 were observed using STEM. Figure 3 (a) ~ Figure 3 (c) are STEM images of the catalyst particles of Examples 5, 8 and 12, respectively. Figure 3 (a) The catalyst metal particles in the catalyst particles of Example 5 shown have a particle size in the range of 2.8 ± 1.0 nm. Figure 3 (b) The catalyst metal particles in the catalyst particles of Example 8 shown have a particle size in the range of 4.0 ± 0.7 nm. Figure 3 (c) The particle size of the catalyst metal particles in the catalyst particles of Example 12 shown is in the range of 3.3 ± 0.6 nm. The particle size of the catalyst metal particles in the catalyst particles of Examples 5, 8 and 12 shown in such STEM images is almost the same as the average particle size of the catalyst metal particle powder in the reaction solution of Examples 5, 8 and 12 shown in Table 1 below.

[0060] Furthermore, samples taken from the particles of the catalyst manufactured in Example 8 were observed using STEM and elemental mapping was performed based on EDX (energy-dispersive X-ray diffraction). Figure 4 (a) ~ Figure 4 (e) are, respectively, STEM images of the catalyst particles of Example 8, elemental mapping images of Rh, Ir, and Pt, elemental mapping images of Rh, Ir, and Pt. Figure 4 (b) ~ Figure 4 The elemental mapping shown in (e) confirms that Rh, Ir, and Pt are alloyed in the catalyst metal particles of the catalyst particles of Example 8. Furthermore, it is known that the surface layer of these catalyst metal particles is rich in Rh compared to the central portion (the atomic ratio of Rh content in the surface layer relative to the combined content of Rh, Ir, and Pt is greater than that in the central portion).

[0061] [Catalytic Activity Evaluation]

[0062] use Figure 5 (a) shows a fixed-bed flow reactor, using Figure 5 (b) shows the temperature program (temperature conditions for pretreatment and activity evaluation) and in Figure 5 (c) shows the composition of the mixed gas to evaluate the catalytic activity of the catalyst particles in Examples 1-12 and Comparative Examples 1-6.

[0063] In this case, firstly, a 0.3g sample taken from the catalyst particles is loaded into the furnace of the fixed-bed flow reactor. Next, while the mixed gas is circulated within the furnace at a flow rate of 1L / min, the temperature of the mixed gas flowing into the sample (hereinafter sometimes simply referred to as the "inflow gas") is controlled using the furnace's heater according to... Figure 5(b) The pretreatment temperature conditions were raised from room temperature to 600°C over approximately 1400 seconds, then lowered to room temperature over approximately 1400 seconds and maintained at room temperature for approximately 900 seconds, thus performing the pretreatment. Next, while the mixed gas continued to flow through the furnace at a flow rate of 1 L / min, the temperature of the incoming gas was controlled using the furnace's heater according to... Figure 5 (b) During the activity evaluation process, the temperature conditions were increased from room temperature to 600°C over approximately 1400 seconds. The concentrations [volume %] of each component in the gas effluent from the sample (hereinafter sometimes simply referred to as "effluent gas") were measured using an FT-IR (Fourier Transform Infrared Spectrometry) analyzer and an MPD (Magnetic Pressure Detection) analyzer in a fixed-bed flow-through reactor. In particular, the NO50% purification temperature [°C] was determined by converting 50% of the NO in the influent gas to N2. The results are shown in Table 1 below. Figure 6 This is a graph showing the NO 50% purification temperature of samples from Examples 1-12 and Comparative Examples 1-6.

[0064]

[0065] As shown in Table 1 above and Figure 6 As shown, the composition, expressed in terms of atomic ratio, is represented by the formula Rh. x Ir y Pt z (Where x+y+z=100, 40≤x≤80, 10≤y≤40, and 10≤z≤40.) The catalyst particles of Examples 1-12, which represent catalyst metal particles, show a lower NO 50% purification temperature and improved catalytic activity compared to the catalyst particles of Comparative Example 1 containing elemental Rh. It is believed that through alloying of Rh, Ir, and Pt in the catalyst metal particles, the electronic state of Rh changes to different states, thereby demonstrating the low-temperature activity of the catalyst. Furthermore, it is known that even the catalyst particles of Examples 10-12, which have an Rh content of 40 atomic%, show improved catalytic activity despite the low Rh content. This result is believed to be due to the same reason as the results shown in the EDX-based elemental mapping image as described above: even the catalyst metal particles of Examples 10-12 are rich in Rh in the surface layer compared to the central portion.

[0066] The above describes in detail the catalyst metal particles and embodiments of the catalyst involved in this invention. However, this invention is not limited to the embodiments described above, and various design changes can be made without departing from the spirit of the invention as set forth in the claims.

Claims

1. A catalyst metal particle, characterized in that, Composition based on atomic ratio using the formula Rh x Ir y Pt z It is expressed that, where x+y+z=100, 40≤x≤80, 10≤y≤40, and 10≤z≤40.

2. A catalyst, characterized in that, It comprises the catalyst metal particles as described in claim 1 and the support carrying the catalyst metal particles.

3. The catalyst according to claim 2, characterized in that, It is an exhaust purification catalyst.

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