Catalyst metal particles and catalyst

Abstract

The objective is to provide catalyst metal particles containing Rh as the main component, which can improve catalytic activity, and a catalyst containing the same. [Solution] The catalyst metal particles of the present invention are of formula Rh x Ir y Pt z It is characterized by being expressed as follows: (where x+y+z=100, 40≦x≦80, 10≦y≦40, and 10≦z≦40).

Description

[Technical Field]

[0001] The present invention relates to catalyst metal particles and catalysts, and more particularly to catalyst metal particles containing Rh as a main component and catalysts containing the same. [Background technology]

[0002] Conventionally, catalyst metal particles containing platinum group metals such as Pt, Pd, and Rh have been used as catalysts for exhaust gas purification, such as those used to remove harmful components like NOx from exhaust gas, and 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 effective for carrying out ternary conversion is known, comprising platinum group metal nanoparticles (e.g., nanoparticles of Pt, Pd, Au, Ru, Rh, and their alloys and mixtures thereof), wherein the average particle size of the nanoparticles is about 15 nm to about 50 nm, and the nanoparticles are dispersed on a heat-resistant metal oxide component (Patent Document 1). Also, the following formula: Pd x Ru y M z A multicomponent solid solution nanoparticle represented by (M is at least one selected from the group consisting 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) and a supported catalyst containing the same are known (Patent Document 2). Furthermore, a ternary alloy nanoparticle containing a platinum group metal alloyed with at least two transition metal elements and a catalyst containing the same are known (Patent Document 3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2020-508845 [Patent Document 2] International Publication No. 2017 / 150596 [Patent Document 3] International Publication No. 2023 / 237734 [Overview of the project] [Problems that the invention aims to solve]

[0005] Catalyst metal particles containing Rh as the main component, among platinum group metals, exhibit excellent catalytic activity, for example, in the reduction of NOx in exhaust gas purification catalysts, and these characteristics are utilized. In recent years, the price of Rh, in particular, has soared, making the reduction of its use an urgent issue. On the other hand, even with a reduction in Rh usage, there is a demand for achieving even better catalytic activity than before.

[0006] This invention has been made in view of these points, and its object is to provide catalyst metal particles containing Rh as the main component, which can improve catalytic activity, and a catalyst containing the same. [Means for solving the problem]

[0007] To solve the above problems, the catalyst metal particles of the present invention are of the formula Rh x Ir y Pt z It is characterized by being expressed as follows: (where x+y+z=100, 40≦x≦80, 10≦y≦40, and 10≦z≦40).

[0008] Furthermore, the catalyst of the present invention is characterized by comprising the catalyst metal particles described above and a carrier on which the catalyst metal particles are supported. [Effects of the Invention]

[0009] According to the present invention, catalytic activity can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic perspective view of an exhaust gas purification device using a catalyst according to one embodiment. [Figure 2]It is a schematic cross-sectional view showing a cross-section perpendicular to the stretching direction of the cells of the exhaust gas purification device shown in FIG. 1, and an enlarged view of the cross-section of the catalyst layer is also shown. [Figure 3] (a) to (c) are STEM images of the catalyst pellets of Examples 5, 8, and 12, respectively. [Figure 4] (a) to (e) are, respectively, the STEM image of the catalyst pellet of Example 8, the elemental mapping images of Rh, Ir, and Pt, the elemental mapping image of Rh, the elemental mapping image of Ir, and the elemental mapping image of Pt. [Figure 5] (a) to (c) are diagrams showing, respectively, the fixed-bed flow reactor used for the catalyst activity evaluation, the temperature program used for the catalyst activity evaluation, and the mixed gas used for the catalyst activity evaluation. [Figure 6] It is a graph showing the NO50% purification temperature of the samples of Examples 1 to 12 and Comparative Examples 1 to 6.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the catalyst metal particles and the catalyst according to the present invention will be described. First, the outline of the catalyst metal particles and the catalyst according to the embodiment will be exemplified and described with the catalyst metal particles and the catalyst according to one embodiment. FIG. 1 is a schematic perspective view of an exhaust gas purification device in which a catalyst according to one embodiment is used. FIG. 2 is a schematic cross-sectional view showing a cross-section perpendicular to the stretching direction of the cells of the exhaust gas purification device shown in FIG. 1, and an enlarged view of the cross-section of the catalyst layer is also shown.

[0012] As shown in FIGS. 1 and 2, an exhaust gas purification apparatus 1 using a catalyst (exhaust gas purification catalyst) 6 according to one embodiment is an apparatus for purifying exhaust gas discharged from an internal combustion engine in an automobile or the like. The exhaust gas purification apparatus 1 is a so-called straight flow type three-way catalyst, and includes a honeycomb substrate (substrate) 10 and a catalyst layer 20 provided on the honeycomb substrate 10. The honeycomb substrate 10 is a substrate in which a cylindrical frame portion 11 and a partition wall 14 that partitions the space inside the frame portion 11 in a honeycomb shape are integrally formed. The partition wall 14 is a porous body that defines a plurality of cells 12 extending from the inflow side end face 10Sa to the outflow side end face 10Sb of the honeycomb substrate 10. The shape of the partition wall 14 includes a plurality of wall portions 14L that are spaced apart from each other and arranged in parallel so that a cross section perpendicular to the extending direction of the plurality of cells 12 is square, and a plurality of wall portions 14S that are perpendicular to the plurality of wall portions 14L and spaced apart from each other and arranged in parallel. The cross section perpendicular to the extending direction is in a lattice shape. The plurality of cells 12 are adjacent to each other with the partition wall 14 interposed therebetween, and the inflow side end 12a and the outflow side end 12b are open. Note that the extending direction of the partition wall 14 is substantially the same as the axial direction of the honeycomb substrate 10, and the extending direction of the cell 12 is substantially the same as the extending direction of the partition wall 14.

[0013] As shown in FIG. 2, the catalyst layer 20 is provided on the surface 14s on the cell 12 side of the partition wall 14 so as to occupy the entire axial direction (extending direction of the partition wall 14) of the honeycomb substrate 10. As shown in the enlarged view of FIG. 2, the catalyst layer 20 contains the powder of the catalyst 6 according to one embodiment. The powder of the catalyst 6 contains the powder of the catalyst metal particles 2 according to one embodiment and the powder of the carrier particles (carrier) 4 on which the catalyst metal particles 2 are supported. The catalyst metal particles 2 are ternary alloy nanoparticles whose composition in 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). In the catalyst metal particles 2, the surface layer 2b is richer in Rh than the central portion 2a.

[0014] Conventionally, catalyst metal particles containing Rh as the main component, such as Rh elemental catalyst metal particles (hereinafter sometimes referred to as "Rh-containing catalyst metal particles"), have been utilized to achieve superior catalytic activity, for example, in the reduction of NOx by exhaust gas purification catalysts, compared to catalyst metal particles containing Pd or Pt as the main component. On the other hand, in such conventional Rh-containing catalyst metal particles, there is a need to reduce the amount of Rh used in order to suppress the high costs caused by the soaring price of Rh. In response to this, catalyst metal particles 2 according to one embodiment contain Ir and Pt in addition to Rh, and the composition is adjusted so that the total content of catalyst metal particles 2 (sum of Rh, Ir, and Pt content) is 100 atomic%, with Rh content being 40 atomic% to 80 atomic%, Ir content being 10 atomic% to 40 atomic%, and Pt content being 10 atomic% to 40 atomic%. Furthermore, these Rh, Ir, and Pt are alloyed. As a result, in the catalyst metal particle 2 according to one embodiment, the catalytic activity in applications such as the reduction of NOx by an exhaust gas purification catalyst can be improved by changing the electronic state of Rh to a different state compared to conventional Rh-containing catalyst metal particles. Furthermore, since the surface layer 2b is Rh-richer than the central part 2a, catalytic activity can be improved more effectively.

[0015] Therefore, according to the catalyst metal particles 2 of one embodiment, catalytic activity can be improved compared to conventional Rh-containing catalyst metal particles, for example, in the reduction of NOx by an exhaust gas purification catalyst. Furthermore, catalytic activity can be improved by including Ir and Pt in addition to Rh in amounts of 10 atomic% to 40 atomic% each, thereby reducing the amount of Rh used. The catalyst 6 of one embodiment can achieve similar effects by including the catalyst metal particles 2. As a result, the exhaust gas purification device 1 using catalyst 6 can improve purification performance and reduce the amount of Rh used. Next, the details of the configuration of the catalyst metal particles and catalyst according to the embodiment will be described.

[0016] 1.Catalytic metal particles The catalyst metal particles according to the embodiment have an atomic ratio composition of the formula Rh x Ir y Pt z These are ternary alloy particles represented by (where x+y+z=100, 40≦x≦80, 10≦y≦40, and 10≦z≦40).

[0017] The content of Rh, Ir, and Pt in the catalyst metal particles will be explained. The Rh content is not particularly limited as long as it is between 40 atomic% and 80 atomic% when the total content of Rh, Ir, and Pt is taken as 100 atomic%, but it is preferably between 45 atomic% and 75 atomic% and more preferably between 50 atomic% and 70 atomic% and particularly preferably between 55 atomic% and 65 atomic%. This is because if the Rh content is above the lower limit of these ranges, it is easy to improve catalytic activity, and if the Rh content is below the upper limit of these ranges, the amount of Rh used can be particularly reduced.

[0018] The Ir content is not particularly limited as long as it is between 10 atomic% and 40 atomic% when the total content of Rh, Ir, and Pt is taken as 100 atomic%, but it is preferably between 15 atomic% and 35 atomic%, more preferably between 20 atomic% and 30 atomic%, and especially preferably between 22.5 atomic% and 27.5 atomic%. This is because if the Ir content is above the lower limit of these ranges, it is easy to reduce the amount of Rh used, and if the Ir content is below the upper limit of these ranges, it is easy to improve the catalytic activity. The Pt content is not particularly limited as long as it is between 10 atomic% and 40 atomic% when the total content of Rh, Ir, and Pt is taken as 100 atomic%, but it is preferably between 15 atomic% and 35 atomic%, more preferably between 20 atomic% and 30 atomic%, and especially preferably between 22.5 atomic% and 27.5 atomic%. This is because if the Pt content is above the lower limit of these ranges, it becomes easier to reduce the amount of Rh used, and if the Pt content is below the upper limit of these ranges, it becomes easier to improve catalytic activity.

[0019] The catalyst metal particles are not particularly limited as long as they are as described above, but they usually exist as a powder. For example, catalyst metal particles that are Rh-rich at the surface rather than in the center (i.e., those with a higher atomic ratio of Rh content to the total content of Rh, Ir, and Pt at the surface than in the center) are preferred because they can more effectively improve catalytic activity.

[0020] The average particle size of the catalyst metal particles is not particularly limited, but for example, it is 1 nm to 120 nm, preferably 1 nm to 30 nm, more preferably 1 nm to 10 nm, and especially preferably 1 nm to 5 nm. Here, "average particle size of catalyst metal particles" refers to the average particle size obtained by observing the catalyst metal particle powder contained in the catalyst powder described later using a TEM (transmission electron microscope) such as a STEM (scanning transmission electron microscope). For example, it is the calculated average of the equivalent circle diameters of 30 or more catalyst metal particles randomly selected from the TEM image, each having an equivalent circle diameter of 1 nm or more.

[0021] There are no particular limitations on the method for producing catalyst metal particles, but examples include a method using the polyol reduction method. The polyol reduction method is a method in which metal ions are reduced by the reducing action of a polyhydric alcohol (polyol), and nano-sized metal particles are precipitated. In a method for producing catalyst metal particles using the polyol reduction method, for example, metal salts of Rh, Ir, and Pt are dissolved in a polyhydric alcohol (reducing agent) such as ethylene glycol, glycerin, diethylene glycol, or triethylene glycol, and the reaction is carried out by heating at a predetermined temperature (e.g., 120°C, etc.) for a predetermined time (e.g., 24 hours, etc.), and then cooled to obtain a reaction solution containing a powder of catalyst metal particles containing Rh, Ir, and Pt in a solid solution state. After that, the catalyst metal particles are separated from the reaction solution by centrifugation or the like to produce catalyst metal particles as a powder. In this production method, aggregation of catalyst metal particles can be suppressed by adding a protective agent such as polyvinylpyrrolidone or polyethylene glycol to the polyhydric alcohol along with the metal salt. Furthermore, by adding a particle size modifier such as sodium hydroxide or nitric acid to the polyhydric alcohol along with the metal salt, the average particle size of the catalyst metal particles can be controlled.

[0022] Examples of metal salts of Rh include rhodium chloride (RhCl3), rhodium acetate, and rhodium nitrate, as long as catalyst metal particles can be produced. Examples of metal salts of Ir include iridium chloride (IrCl3), iridium acetylacetonate, potassium iridium cyanate, and potassium iridate, as long as catalyst metal particles can be produced. Examples of metal salts of Pt include chloroplatinic acid (H2PtCl6), chloroplatinic acid (H2PtCl4), potassium tetrachlorideplatinate (K2PtCl4), ammonium hexachloroplatinate ((NH4)2PtCl6), and sodium hexachloroplatinate (Na2PtCl6), as long as catalyst metal particles can be produced.

[0023] 2. Catalyst The catalyst according to the embodiment includes catalyst metal particles according to the embodiment and a carrier on which the catalyst metal particles are supported.

[0024] The carrier is not particularly limited as long as it can support the catalyst metal particles, but it usually exists as a powder of carrier particles. The average particle size of the carrier particles is not particularly limited, but for example, it is between 1 nm and 500 nm. Here, "average particle size of carrier particles" refers to the average particle size obtained by observing the carrier particle powder using a method such as STEM, for example, and is the calculated average of the equivalent circle diameters of 30 or more carrier particles randomly selected from a TEM image, each having an equivalent circle diameter of 1 nm or more.

[0025] The material of the support is not particularly limited as long as it can support the catalyst metal particles mentioned above, but examples include inorganic compounds, specifically aluminum oxide (Al2O3), zirconia (ZrO2), ceria (CeO2), silica (SiO2), titania (TiO2), solid solutions thereof (e.g., ceria-zirconia composite oxide), and combinations thereof, with aluminum oxide and zirconia being particularly preferred because they have a large specific surface area and high heat resistance.

[0026] The catalyst is not particularly limited as long as it is one of the above-mentioned types, but it usually exists as a catalyst powder containing a powder of catalyst metal particles and a powder of carrier particles (carrier) on which the catalyst metal particles are supported. As a catalyst, for example, exhaust gas purification catalysts used for purifying exhaust gas are preferred. This is because they can achieve excellent catalytic activity and a reduction in the amount of Rh used in exhaust gas purification catalysts.

[0027] The applications of the exhaust gas purification catalyst are not particularly limited, but an exhaust gas purification device that uses the catalyst according to one embodiment is preferred, for example, an exhaust gas purification device comprising a base material and a catalyst layer provided on the base material, wherein the catalyst layer contains the exhaust gas purification catalyst. The exhaust gas purification device may be of the straight-flow type or the wall-flow type, but the straight-flow type is preferred, and among these, a three-way catalyst is preferred. Examples of wall-flow type devices include GPF (gasoline particulate filter) and DPF (diesel particulate filter).

[0028] The method for producing the catalyst is not particularly limited, but examples include preparing a catalyst slurry by immersing a carrier particle powder in a reaction solution containing catalyst metal particle powder obtained by a method using polyol reduction to produce catalyst metal particles, and then drying and calcining the catalyst slurry. [Examples]

[0029] The catalyst metal particles and catalyst according to the embodiment will be described in more detail below with reference to examples and comparative examples.

[0030] 1. Production of catalyst metal particle powder, catalyst powder, and catalyst pellets [Example 1] The composition in atomic ratio is given by formula Rh 80 Ir 10 Pt 10 After producing a powder of catalyst metal particles represented by [the formula] and a powder of a catalyst (exhaust gas purification catalyst) containing the catalyst metal particle powder, catalyst pellets were produced by pelletizing the catalyst powder.

[0031] First, a powder of catalyst metal particles was produced using the polyol reduction method. Specifically, rhodium chloride (RhCl3), iridium chloride (IrCl3), and chloroplatinic acid (H2PtCl6) were dissolved in ethylene glycol, a reducing agent, as metal salts, so that the atomic ratios of Rh, Ir, and Pt were in the ratios of the above formula (80:10:10). Polyvinylpyrrolidone was then dissolved as a protective agent, and the mixture was heated at 120°C for 24 hours. This produced a powder of catalyst metal particles and obtained a reaction solution containing the catalyst metal particle powder. At this time, a particle size modifier was added to the ethylene glycol along with these metal salts. Next, a catalyst slurry was prepared by immersing powder of carrier particles composed of aluminum oxide in the obtained reaction solution. Then, the catalyst slurry was applied to a substrate and dried and calcined to produce a catalyst powder containing the catalyst metal particle powder and the carrier particle powder on which the catalyst metal particles were supported. In this case, the amounts of catalyst metal particle powder and carrier particle powder were adjusted during the preparation of the catalyst slurry so that the amount of catalyst metal particles supported per gram of carrier particle powder was 20 μmol / g. Subsequently, catalyst pellets were produced by pelletizing the resulting catalyst powder.

[0032] [Examples 2-12 and Comparative Examples 1-3] A catalyst metal particle powder whose atomic composition is represented by the formula shown in Table 1 below, and a catalyst (exhaust gas purification catalyst) powder containing the catalyst metal particle powder were manufactured, and then catalyst pellets were produced by pelletizing the catalyst powder. In this case, the catalyst metal particle powder and catalyst powder were manufactured in the same manner as in Example 1, except that when manufacturing the catalyst metal particle powder, rhodium chloride, iridium chloride, and chloroplatinic acid were dissolved in ethylene glycol so that the atomic ratios of Rh, Ir, and Pt matched the atomic ratios of the formula shown in Table 1 below.

[0033] [Comparative Example 4] A powder of Rh elemental catalyst metal particles and a powder of a catalyst (exhaust gas purification catalyst) containing the catalyst metal particle powder were manufactured, and then catalyst pellets were produced by pelletizing the catalyst powder. In this case, the catalyst metal particle powder and catalyst powder were manufactured in the same manner as in Example 1, except that only rhodium chloride was dissolved as a metal salt in ethylene glycol during the production of the catalyst metal particle powder, and then catalyst pellets were manufactured.

[0034] [Comparative Example 5] In this case, catalyst metal particle powder of elemental Ir and catalyst powder (exhaust gas purification catalyst) containing the catalyst metal particle powder were manufactured, and then catalyst pellets were produced by pelletizing the catalyst powder.

[0035] [Comparative Example 6] A powder of Pt catalyst metal particles and a powder of a catalyst (exhaust gas purification catalyst) containing the catalyst metal particle powder were manufactured, and then catalyst pellets were produced by pelletizing the catalyst powder. In this case, the catalyst metal particle powder and catalyst powder were manufactured in the same manner as in Example 1, except that only chloroplatinic acid was dissolved as a metal salt in ethylene glycol during the production of the catalyst metal particle powder, and then catalyst pellets were manufactured.

[0036] 2. Evaluation [STEM observation and EDX compositional analysis] In Examples 1-12 and Comparative Examples 1-4, the average particle size of the catalyst metal particles in the reaction solution was measured by taking a sample of the reaction solution containing the catalyst metal particle powder obtained during the production process and observing it with a TEM. In this process, 30 or more catalyst metal particles with an equivalent circle diameter of 1 nm or more were randomly selected from the TEM image, and the calculated average of their equivalent circle diameters was obtained as the average particle size of the catalyst metal particle powder. The results are shown in Table 1 below. Furthermore, samples taken from the catalyst pellets produced in Examples 5, 8, and 12 were observed with a STEM. Figures 3(a) to 3(c) show the STEM images of the catalyst pellets from Examples 5, 8, and 12, respectively. The particle size of the catalyst metal particles in the catalyst pellet of Example 5 shown in Figure 3(a) is in the range of 2.8 ± 1.0 nm, the particle size of the catalyst metal particles in the catalyst pellet of Example 8 shown in Figure 3(b) is in the range of 4.0 ± 0.7 nm, and the particle size of the catalyst metal particles in the catalyst pellet of Example 12 shown in Figure 3(c) is in the range of 3.3 ± 0.6 nm. The particle sizes of the catalyst metal particles in the catalyst pellets of Examples 5, 8, and 12 shown in these STEM images are almost the same as the average particle size of the catalyst metal particle powder in the reaction solutions of Examples 5, 8, and 12 shown in Table 1 below.

[0037] Furthermore, samples taken from the catalyst pellets produced in Example 8 were observed using STEM and elemental mapping was performed using EDX (energy-dispersive X-ray analysis). Figures 4(a) to 4(e) show the STEM image, elemental mapping images of Rh, Ir, and Pt of the catalyst pellets in Example 8, an elemental mapping image of Rh, an elemental mapping image of Ir, and an elemental mapping image of Pt, respectively. From the elemental mapping images shown in Figures 4(b) to 4(e), it can be confirmed that Rh, Ir, and Pt are alloyed in the catalyst metal particles of the catalyst pellets in Example 8. Furthermore, it can be seen that the surface layer of these catalyst metal particles is Rh-richer than the center layer (the atomic ratio of Rh content to the total content of Rh, Ir, and Pt is higher at the surface layer than at the center layer).

[0038] [Catalytic activity evaluation] The catalytic activity of the catalyst pellets in each of Examples 1 to 12 and Comparative Examples 1 to 6 was evaluated using a fixed-bed flow reactor as shown in Figure 5(a), with the temperature program (temperature conditions for pretreatment and activity evaluation) shown in Figure 5(b) and the mixed gas composition shown in Figure 5(c).

[0039] In this case, first, a 0.3g sample taken from the catalyst pellet was loaded into the heating furnace of a fixed-bed flow reactor. Next, while the mixed gas was circulated through the heating furnace at a flow rate of 1 L / min, the temperature of the mixed gas flowing into the sample (hereinafter sometimes abbreviated as "inflow gas") was raised from room temperature to 600°C in approximately 1400 seconds using the heater of the heating furnace, as shown in the pretreatment temperature conditions of Figure 5(b), then lowered back to room temperature in approximately 1400 seconds, and maintained at room temperature for approximately 900 seconds to perform the pretreatment. Next, while the mixed gas continued to flow through the heating furnace at a flow rate of 1 L / min, the temperature of the inflowing gas was raised from room temperature to 600°C in approximately 1400 seconds using the heater of the heating furnace, according to the temperature conditions for activity evaluation shown in Figure 5(b). During this process, the activity evaluation was performed by measuring the concentration [volume %] of each component of the gas flowing out of the sample (hereinafter sometimes abbreviated as "flowing gas") using an FT-IR (Fourier transform infrared spectroscopy) analyzer and an MPD (magnetic pressure) analyzer of a fixed-bed flow reactor. In the activity evaluation, in particular, the temperature at which 50% of the NO in the inflowing gas is converted to N2 was determined as the NO 50% purification temperature [°C]. The results are shown in Table 1 below. Figure 6 is a graph showing the NO 50% purification temperatures of the samples for each example of Examples 1 to 12 and Comparative Examples 1 to 6.

[0040] [Table 1]

[0041] As shown in Table 1 and Figure 6 above, the composition in atomic ratio is given by formula Rh x Ir y Pt zIn the catalyst pellets of Examples 1 to 12, which contain catalyst metal particles represented by (where x+y+z=100, 40≦x≦80, 10≦y≦40, and 10≦z≦40), the NO 50% purification temperature is lower and catalytic activity is improved compared to the catalyst pellets containing Rh elemental catalyst metal particles of Comparative Example 1. It is thought that the alloying of Rh, Ir, and Pt in the catalyst metal particles causes a change in the electronic state of Rh, resulting in the low-temperature activity of the catalyst. Furthermore, even in the catalyst pellets of Examples 10 to 12, which have an Rh content of 40 atomic%, catalytic activity is improved despite the low Rh content. This result is thought to be due to the fact that the catalyst metal particles of Examples 10 to 12 are Rh-rich at the surface rather than in the center, similar to the results shown in the elemental mapping images by EDX as described above.

[0042] Although embodiments of the catalyst metal particles and catalyst according to the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of Symbols]

[0043] 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

Claims

1. The composition in atomic ratio is given by formula Rh ｘ Ir ｙ Pt ｚ A catalyst metal particle characterized by being represented as follows: (where x + y + z = 100, 40 ≤ x ≤ 80, 10 ≤ y ≤ 40, and 10 ≤ z ≤ 40).

2. A catalyst comprising catalyst metal particles as described in claim 1 and a carrier on which the catalyst metal particles are supported.

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

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