Exhaust gas purification catalyst for straddle-type vehicles

Abstract

The present invention provides an exhaust gas purification catalyst which is for a saddle riding-type vehicle, has a simple and low-cost structure in which only a singled layered catalyst layer is provided, and has excellent purification performance for CO, HC, and NOx and excellent low-temperature purification performance for the same. The exhaust gas purification catalyst, which is for a saddle riding-type vehicle and is provided in an exhaust gas passage of an internal combustion engine, comprises a metal substrate and a single-layered catalyst layer provided on the metal substrate, wherein the catalyst layer contains: first composite catalyst particles having at least zirconia-based host particles and Rh and CeO2 particles co-supported on the surface of the zirconia-based host particles; second composite catalyst particles having alumina host particles and Pd supported on the surface of the alumina host particles; and / or third composite catalyst particles having ceria alumina host particles and Pd supported on the surface of the ceria alumina host particles.

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas purification catalyst for straddle-type vehicles such as motorcycles and a method for producing the same, and more particularly to an exhaust gas purification catalyst for straddle-type vehicles having only one catalyst layer. [Background technology]

[0002] Exhaust gas from gasoline-fueled automobiles and motorcycles contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Purifying these components requires the use of catalysts to purify each of these harmful components, such as by oxidizing hydrocarbons (HC) to water and carbon dioxide, oxidizing carbon monoxide (CO) to carbon dioxide, and reducing nitrogen oxides (NOx) to nitrogen. Three-way catalysts (TWCs) capable of oxidizing and reducing CO, HC, and NOx are used as catalysts for treating such exhaust gases (hereinafter referred to as "exhaust gas purification catalysts"). Widely known examples of such three-way catalysts include those in which catalytically active components such as platinum group metals (PGMs) (e.g., ruthenium, rhodium, palladium, osmium, iridium, and platinum) are supported on alumina matrix particles with a high specific surface area, and the catalysts are then supported on a substrate, such as a monolithic substrate with a refractory ceramic or metal honeycomb structure.

[0003] In internal combustion engines, such as those described above, the fuel-to-air ratio (A / F) varies significantly depending on engine operating conditions, such as acceleration, deceleration, low-speed driving, and high-speed driving. With the stoichiometric air-fuel ratio of 14.7 in exhaust gases, an oxygen-rich atmosphere (a lean atmosphere) favoring oxidation reactions and a fuel-rich atmosphere (a rich atmosphere) favoring reduction reactions alternate depending on driving conditions. Therefore, exhaust gas catalysts must exhibit a certain level of catalytic performance under both lean and rich-fuel conditions. In particular, motorcycles tend to operate at higher engine speeds in a fuel-rich atmosphere to increase power output, so excellent catalytic performance in a fuel-rich atmosphere is required. For this reason, the air-fuel ratio (A / F) has traditionally been controlled, but A / F alone is insufficient for catalysts to fully demonstrate their catalytic performance. Therefore, the catalyst layer itself must also be able to control the air-fuel ratio (A / F).

[0004] Therefore, catalysts that combine a platinum group element, which is a catalytically active component, with a promoter are used to prevent the deterioration of catalyst purification performance caused by changes in the air-fuel ratio through the chemical action of the catalyst itself. One such promoter, known as a promoter with oxygen storage capacity (OSC), is one that releases oxygen in a reducing atmosphere and absorbs oxygen in an oxidizing atmosphere (hereinafter referred to as "OSC material"). Specifically, ceria (cerium oxide, CeO2) and ceria-zirconia composite oxide are known as OSC materials with oxygen storage capacity. These OSC materials function as buffers that reduce the change between the oxidizing and reducing properties of exhaust gases, thereby maintaining the purification performance of the catalyst. Furthermore, ceria-zirconia composite oxide, which is a solid solution of ceria with zirconia, has even better OSC capacity and is therefore added to many catalysts as an OSC material.

[0005] Exhaust gas purification catalysts for motorcycles face unique challenges different from those for automobiles. For example, because the space available for installing a catalyst is limited compared to that for automobiles, exhaust gas purification catalysts for motorcycles must be small in volume yet exhibit high purification capabilities. Furthermore, motorcycles tend to have relatively short exhaust gas flow paths and use large amounts of fuel to prioritize power output, which means that catalysts are easily exposed to high temperatures. Furthermore, the oxygen concentration in the exhaust gas decreases accordingly, often resulting in an exhaust gas air-fuel ratio (A / F) below the stoichiometric air-fuel ratio of 14.7. Therefore, catalysts must have excellent heat resistance and excellent exhaust gas purification efficiency, even in a fuel-rich atmosphere with an air-fuel ratio (A / F) below 14.7.

[0006] For example, Patent Document 1 discloses a catalytic material for purifying exhaust gas from an internal combustion engine, characterized by having a carrier made of a cerium-zirconium composite oxide containing 45 to 70 mass% CeO2, 20 to 45 mass% ZrO2, 2 to 20 mass% Nd2O3, and 1 to 10 mass% La2O3, and a catalytic component made of metal Pd or Pd oxide supported on the carrier.

[0007] Patent Document 2 also describes a catalyst having a first catalytic layer formed on the surface of a carrier made of a ceramic or metal material and a second catalytic layer formed on the first catalytic layer, the first catalytic layer having a carrier made of a cerium-zirconium composite oxide in which the amount of CeO2 is 45 to 70 mass%, the amount of ZrO2 is 20 to 45 mass%, the amount of Nd2O3 is 2 to 20 mass%, and the amount of La2O3 is 1 to 10 mass%, and a catalytic component made of metal Pd or Pd oxide supported on the carrier, and the second catalytic layer having ZrO2 is 45 to 70 mass%. Disclosed is an exhaust gas purification catalyst for straddle-type vehicles, characterized by having a carrier made of a zirconium-based composite oxide in which the amount of rO2 is 50 to 95 mass %, the amount of CeO2 is 0 to 40 mass %, the amount of Nd2O3 is 2 to 20 mass %, and the amount of La2O3 is 1 to 10 mass %, and a catalytic component made of metallic Rh or Rh oxide supported on the carrier, or having a catalytic component made of metallic Rh or Rh oxide and a catalytic component made of metallic Pt or Pt oxide supported on the carrier.

[0008] On the other hand, Patent Document 3 discloses an exhaust gas purification catalyst for saddle-type vehicles that is provided in the exhaust passage of an internal combustion engine and that aims to reduce costs by not using Pt or Rh, which are relatively expensive among precious metals. The catalyst comprises a substrate, palladium as a catalytically active component, an inorganic porous body such as porous γ-alumina as a catalyst support, and a catalyst layer as a single layer containing ceria (CeO) particles and barium as promoter components. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-227739 [Patent Document 2] WO2010 / 109734 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-208578 Summary of the Invention [Problem to be solved by the invention]

[0010] In the above-mentioned Patent Document 1, a catalyst material (Pd-supported cerium-zirconium composite oxide) is used in which Pd is supported on the surface of a cerium-zirconium composite oxide of a specific composition as a base particle. However, this catalyst material alone still has insufficient purification performance (see Examples 1 and 2).

[0011] Furthermore, exhaust gases emitted from internal combustion engines of automobiles and the like emit large amounts of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) when the catalyst temperature is low, such as during startup. To improve purification performance, it is important to quickly increase the temperature of the catalyst and improve the low-temperature purification performance of the catalyst. However, the catalyst material described in Patent Document 1 alone still has insufficient low-temperature catalytic activity (see Examples 1 and 2).

[0012] Meanwhile, Ce is an important rare earth metal that is used in applications other than catalytic materials, such as phosphors and glass substrate polishing agents, but due to recent overseas circumstances, the supply has been in crisis, supply has been severely restricted, and international prices have skyrocketed. Therefore, new catalytic materials that use less Ce are in demand, but the catalytic material described in Patent Document 1 still uses a relatively large amount of Ce, and from this perspective, it does not meet recent demands.

[0013] The exhaust gas purification catalyst described in Patent Document 2 has a laminated structure in which a first catalyst layer containing the Pd-supported cerium-zirconium composite oxide described in Patent Document 1 as a catalytic component is provided on the surface of a substrate, and a second catalyst layer containing Rh or Pt-supported cerium-zirconium composite oxide as a catalytic component is further provided on the first catalyst layer. Providing two or more catalyst layers in this manner requires a series of processes for each catalyst layer: coating the catalyst slurry, calcining, supporting the PGM, drying, and calcining. This increases production costs, resulting in expensive exhaust gas purification catalysts. Furthermore, the exhaust gas purification catalyst described in Patent Document 2 has a laminated catalyst layer structure, which results in poor gas diffusion, and insufficient purification performance and low-temperature catalytic activity (see Tables 3 and 5).

[0014] On the other hand, Patent Document 3 describes an exhaust gas purification catalyst provided with a single-layer catalyst containing a relatively small amount of Ce, but the purification performance was extremely low (see Tables 2 and 3).

[0015] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an exhaust gas purification catalyst for a straddle-type vehicle, which has a simple and low-cost structure with only one catalyst layer, but is excellent in purification performance for CO, HC, and NOx, and in their low-temperature purification performance. [Means for solving the problem]

[0016] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have discovered a single-layer catalyst that uses a combination of predetermined Rh-supported composite catalyst particles and predetermined Pd-supported composite catalyst particles, and have found that the above-mentioned problems can be solved by using such a single-layer catalyst, which has led to the completion of the present invention.

[0017] That is, the present invention provides various specific embodiments as shown below. [1] An exhaust gas purification catalyst for a saddle-ride type vehicle that is provided in an exhaust gas passage of an internal combustion engine, the catalyst comprising: a metal substrate; and a single-layer catalyst layer provided on the metal substrate, the catalyst layer containing first composite catalyst particles having at least zirconia-based matrix particles and Rh and CeO particles co-supported on the surfaces of the zirconia-based matrix particles; second composite catalyst particles including alumina matrix particles and Pd supported on the surfaces of the alumina matrix particles; and / or third composite catalyst particles having at least ceria-alumina matrix particles and Pd supported on the surfaces of the ceria-alumina matrix particles.

[0018] [2] The exhaust gas purification catalyst for a saddle-type vehicle according to [1], wherein the zirconia-based base particles are rare-earth solid-doped zirconia base particles in which at least one rare-earth element selected from the group consisting of Ce, Nd, and La is solid-solved.

[0019] [3] The exhaust gas purification catalyst for straddle-type vehicles according to [1] or [2], wherein the zirconia-based base particles contain, in oxide equivalent, 65 to 85 mass % of ZrO2 and 15 to 35 mass % of an oxide of a rare earth element.

[0020] [4] The exhaust gas purification catalyst for a saddle-type vehicle according to any one of [1] to [3], wherein the second composite catalyst particles contain the alumina matrix particles and Pd and Ba supported on the surfaces of the alumina matrix particles.

[0021] [5] The exhaust gas purification catalyst for a saddle-type vehicle according to any one of [1] to [4], wherein the ceria-alumina base particles of the third composite catalyst particles contain, in oxide equivalent, 70 to 90 mass % of Al2O3 and 10 to 30 mass % of CeO2.

[0022] [6] The exhaust gas purification catalyst for a saddle-type vehicle according to any one of [1] to [5], wherein the catalyst layer further contains fourth composite catalyst particles containing ceria-alumina base particles and Rh supported on the surfaces of the ceria-alumina base particles.

[0023] [7] The exhaust gas purifying catalyst for straddle-type vehicles according to any one of [1] to [6], wherein the coating amount of the catalyst layer is 1 to 200 g / L per 1 L of the metal substrate. [Effects of the Invention]

[0024] According to the present invention, it is possible to realize a high-performance exhaust gas purification catalyst for saddle-riding type vehicles, which has excellent CO, HC, and NOx purification performance and low-temperature purification performance, and which is excellent in productivity and economy, even though it has a simple and low-cost configuration with only one catalyst layer. Based on its composition and structure, the exhaust gas purification catalyst for saddle-riding type vehicles of the present invention can be particularly suitably used as a three-way catalyst (TWC) that reduces NOx, CO, HC, and the like in exhaust gas. In particular, the exhaust gas purification catalyst for saddle-riding type vehicles of the present invention can be preferably used in fields such as motorcycles, which require high heat resistance in a small volume and high exhaust gas purification efficiency even in a fuel-rich atmosphere. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic cross-sectional view showing an exhaust gas purification catalyst 100 for a straddle-type vehicle according to an embodiment. [Figure 2] 2 is a schematic cross-sectional view showing the general configuration of a first composite catalyst particle 31. FIG. [Figure 3] 2 is a schematic cross-sectional view showing the general configuration of a second composite catalyst particle 41. FIG. [Figure 4] 3 is a schematic cross-sectional view showing the general configuration of a third composite catalyst particle 51. FIG. [Figure 5] 3 is a schematic cross-sectional view showing the general configuration of a fourth composite catalyst particle 61. FIG. [Figure 6] FIG. 1 is a graph showing the purification performance (C450 purification rate) of an example and a comparative example. [Figure 7] FIG. 1 is a graph showing low-temperature purification performance (T50) of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the following embodiments are merely examples for explaining the present invention, and the present invention is not limited thereto. That is, the present invention can be implemented with any modifications within the scope of the gist thereof. In this specification, for example, a numerical range such as "1 to 100" includes both the lower limit "1" and the upper limit "100". The same applies to other numerical ranges. In addition, in this specification, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to the ratios shown in the drawings.

[0027] Fig. 1 is a schematic cross-sectional view showing an exhaust gas purification catalyst 100 for a saddle-ride type vehicle according to this embodiment. Also, Figs. 2 to 5 are schematic cross-sectional views showing the general configurations of a first composite catalyst particle 31, a second composite catalyst particle 41, a third composite catalyst particle 51, and a fourth composite catalyst particle 61.

[0028] The exhaust gas purification catalyst 100 for a saddle-riding type vehicle of this embodiment includes a metal substrate 11 and a single-layer catalyst layer 21 provided on the metal substrate 11, and the catalyst layer 21 contains first composite catalyst particles 31, and second composite catalyst particles 41 and / or third composite catalyst particles 51. The exhaust gas purification catalyst 100 for a saddle-riding type vehicle of this embodiment is provided in an exhaust gas passage of an internal combustion engine, and purifies carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and the like that pass through the system.

[0029] The metal substrate 11 is a support that supports the single-layer catalyst layer 21 described above. The metal substrate 11 can be appropriately selected from those known in the art, and the type is not particularly limited. Examples of the metal substrate 11 include, but are not limited to, metal honeycomb substrates made of stainless steel or the like, wire mesh substrates made of stainless steel or the like, and steel wool-like knitted wire substrates. The shape of the metal substrate 11 is also not particularly limited, and any shape can be selected, such as a prismatic shape, a cylindrical shape, a spherical shape, a honeycomb shape, a sheet shape, or a pellet shape. These may be used alone or in appropriate combination of two or more types.

[0030] The catalyst layer 21 is a single catalyst layer provided on the metal substrate 11. The catalyst layer 21 contains first composite catalyst particles 31, second composite catalyst particles 41 and / or third composite catalyst particles 51, and, if necessary, fourth composite catalyst particles 61.

[0031] The first composite catalyst particle 31 is a composite particle having at least zirconia-based base particles 32 and Rh and CeO2 particles 33 co-supported on the surfaces 32a of the zirconia-based base particles 32. In the first composite catalyst particle 31, by co-supporting the Rh and CeO2 particles 33 on the surfaces 32a of the zirconia-based base particles 32, a decrease in catalytic activity due to Rh particle growth is suppressed. Furthermore, the support of the CeO2 particles 33 provides high purification performance over a wide A / F window for exhaust gases from saddle-ride vehicles, which have drastic changes in the concentrations of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), and also improves low-temperature purification performance. Note that the first composite catalyst particle 31 can be used singly or in appropriate combination of two or more types.

[0032] The zirconia-based base particles 32 are zirconia (ZrO2), a composite oxide in which zirconia (ZrO2) is doped with other elements, or a solid solution thereof. Specific examples of the zirconia-based base particles 32 include zirconium (IV) oxide, zirconium-rare earth element composite oxide, zirconium-transition element composite oxide, and zirconium-rare earth element-transition element composite oxide. Examples of rare earth elements include, but are not limited to, cerium, neodymium, praseodymium, lanthanum, and yttrium. The rare earth elements may be used singly or in appropriate combination of two or more. When a rare earth element is contained, its content is not particularly limited, but may be in the range of 0.1 to 1.0% by weight, based on the total amount of the zirconia-based base particles 32, in terms of the oxides of the rare earth elements (e.g., La2O3, Nd2O3, Pr5O). 11The transition element content (total of elements such as Fe2O3, TiO2, etc.) is preferably 0.1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Examples of transition elements include, but are not limited to, chromium, cobalt, iron, nickel, titanium, manganese, and copper. The transition elements may be used singly or in appropriate combinations of two or more. When a transition element is included, its content is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, in terms of the oxides of the transition elements, relative to the total amount of the zirconia-based base particles 32. The zirconia-based base particles 32 may be used singly or in appropriate combinations of two or more.

[0033] The zirconia-based base particles 32 are preferably zirconia-based composite oxides containing, in oxide equivalent, 65 to 85 mass % ZrO2 and 15 to 35 mass % of an oxide of a rare earth element, and more preferably zirconia-based composite oxides containing, in oxide equivalent, 70 to 80 mass % ZrO2 and 20 to 30 mass % of an oxide of a rare earth element.

[0034] In the zirconia-based base particles 32, a portion of the zirconium may be substituted with an alkali metal element such as lithium, sodium, or potassium, or an alkaline earth metal element such as beryllium, magnesium, calcium, strontium, or barium. The alkali metal element and alkaline earth metal element may be used alone or in any combination and ratio of two or more. The zirconia-based base particles 32 may also contain hafnium (Hf), which is typically contained in zirconia ore in an amount of about 1 to 2 mass %, as an inevitable impurity.

[0035] Average particle diameter D of zirconia-based base material particles 32 50The average particle diameter D of the zirconia-based base particles 32 is set to 1 / 2 mm, and can be appropriately set depending on the desired performance. 50 is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and is preferably 30 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less. 50 means the median diameter measured by a laser diffraction particle size distribution analyzer (for example, the laser diffraction particle size distribution analyzer SALD-3100 manufactured by Shimadzu Corporation).

[0036] Rh and CeO2 particles 33 are co-supported in a highly dispersed manner on the surfaces 32a of the zirconia-based base particles 32. Here, Rh functions as a catalytically active component, and the CeO2 particles 33 function as a catalytically active component or a promoter having oxygen storage capacity (OSC). By co-supporting Rh and CeO2 particles 33 on the surfaces 32a of the zirconia-based base particles 32, heat resistance is improved and a decrease in catalytic performance when exposed to high temperatures can be suppressed, thereby improving purification performance and low-temperature purification performance. In addition, since the CeO2 particles 33 are supported on the surfaces 32a of the zirconia-based base particles 32, the interaction between Rh and Ce is promoted, which also improves purification performance and low-temperature purification performance.

[0037] The content of Rh is not particularly limited and may be set appropriately according to the desired performance, taking into consideration the material and pore size of the zirconia-based base particles 32. However, from the viewpoint of catalytic activity, the content of Rh is preferably 0.001 to 5 mass%, more preferably 0.01 to 3 mass%, and even more preferably 0.1 to 1 mass%, in terms of metal Rh relative to the total amount of the first composite catalyst particles 31.

[0038] The content of the CeO2 particles 33 is not particularly limited and may be set appropriately according to the desired performance, taking into consideration the material and pore size of the zirconia-based base particles 32. However, from the viewpoint of catalytic activity, the content is preferably 5 to 20 mass % in oxide equivalent relative to the total amount of the first composite catalyst particles 31 (excluding the amount of precious metal), more preferably 7 to 18 mass %, and even more preferably 10 to 15 mass %.

[0039] The second composite catalyst particles 41 are composite particles having at least an alumina matrix particle 42 and Pd supported on the surface 42a of the alumina matrix particle 42. The second composite catalyst particles 41 can be used singly or in appropriate combination of two or more types.

[0040] The alumina matrix particles 42 are matrix particles containing alumina (Al2O3) as a main component. Here, "containing alumina as a main component" means that the alumina content is more than 90 mass % and 100 mass % or less of the total amount of the alumina matrix particles 42. Specific examples of the alumina matrix particles 42 include, but are not limited to, alumina, silica-alumina, aluminosilicates, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-magnesium oxide, alumina-barium oxide, and alumina-lanthanum oxide. The alumina matrix particles 42 can be used singly or in appropriate combination of two or more types.

[0041] Average particle diameter D of alumina base material particles 42 50 The average particle diameter D of the alumina base particles 42 is set to 1 / 2 mm, and is not particularly limited. 50 is preferably 0.1 μm or more, more preferably 1 μm or more, even more preferably 3 μm or more, and is preferably 50 μm or less, more preferably 45 μm or less, even more preferably 40 μm or less.

[0042] Pd is co-loaded in a highly dispersed state on the surfaces 42a of the alumina matrix particles 42. Here, Pd functions as a catalytically active component. By loading Pd on the surfaces 42a of the alumina matrix particles 42, the purification performance and low-temperature purification performance are improved.

[0043] The Pd content is not particularly limited and may be set appropriately according to the desired performance, taking into consideration the material and pore size of the alumina base particles 42. However, from the viewpoint of catalytic activity, the total amount of Pd, calculated as metal, relative to the total amount of the second composite catalyst particles 41 is preferably 0.001 to 5 mass%, more preferably 0.01 to 3 mass%, and even more preferably 0.1 to 1 mass%.

[0044] The second composite catalyst particles 41 may further support a Ba component, which is an alkaline earth metal, on the surfaces 42a of the alumina matrix particles 42. These components are known as NOx storage components. The Ba component can be supported on the surfaces 42a of the alumina matrix particles 42, for example, as barium carbonate or barium sulfate. The Ba component stores NOx in a lean environment with a high oxygen content and releases the stored NOx in a rich environment with a low oxygen content. The content of the Ba component is not particularly limited and may be appropriately set in accordance with the desired performance, taking into account the material and pore size of the alumina matrix particles 42. From the viewpoint of catalytic activity, the Ba component content is preferably 0.1 to 10 mass %, more preferably 0.5 to 8 mass %, and even more preferably 1 to 5 mass %, calculated as oxide, of the total amount of the second composite catalyst particles 41 (excluding the amount of precious metals).

[0045] The third composite catalyst particles 51 are composite particles having at least ceria-alumina matrix particles 52 and Pd supported on surfaces 52a of the ceria-alumina matrix particles 52. The third composite catalyst particles 51 can be used singly or in appropriate combination of two or more types.

[0046] The ceria-alumina base particles 52 are a composite oxide of ceria (CeO2) and alumina (Al2O3). The content ratio of ceria and alumina can be appropriately set depending on the desired performance and is not particularly limited. However, the content ratio of ceria to alumina, calculated as oxides, is preferably 10-30% by mass:70-90% by mass, and more preferably 15-25% by mass:75-85% by mass. In addition to ceria and alumina, the ceria-alumina base particles 52 may contain the above-mentioned rare earth elements, transition elements, alkali metal elements, alkaline earth metal elements, etc. Furthermore, the ceria-alumina base particles 52 may be used singly or in appropriate combination of two or more types.

[0047] Average particle diameter D of ceria-alumina matrix particles 52 50 The average particle diameter D of the ceria-alumina base particles 52 is set to 1 / 2 mm, and is not particularly limited. 50 is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, and is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less.

[0048] Pd is co-loaded in a highly dispersed state on the surfaces 52a of the ceria-alumina base particles 52. Here, Pd functions as a catalytically active component. By loading Pd on the surfaces 52a of the ceria-alumina base particles 52, high heat resistance and OSC performance can be maintained, thereby improving purification performance and low-temperature purification performance.

[0049] The Pd content is not particularly limited and may be set appropriately according to the desired performance, taking into consideration the material and pore size of the ceria-alumina base particles 52. From the viewpoint of catalytic activity, the Pd content is preferably 0.001 to 15 mass %, more preferably 0.1 to 5 mass %, and even more preferably 0.3 to 3 mass %, in terms of Pd metal, relative to the total amount of the third composite catalyst particles 51.

[0050] The fourth composite catalyst particles 61 are composite particles having at least ceria-alumina matrix particles 62 and Rh supported on surfaces 62a of the ceria-alumina matrix particles 62. The fourth composite catalyst particles 61 can be used singly or in appropriate combination of two or more types.

[0051] The ceria-alumina matrix particles 62 are a composite oxide of ceria (CeO2) and alumina (Al2O3). The content ratio of ceria and alumina can be appropriately set depending on the desired performance and is not particularly limited. However, the content ratio of ceria to alumina, calculated as oxides, is preferably 10-30% by mass:70-90% by mass, and more preferably 15-25% by mass:75-85% by mass. In addition to ceria and alumina, the ceria-alumina matrix particles 62 may contain the above-mentioned rare earth elements, transition elements, alkali metal elements, alkaline earth metal elements, etc. Furthermore, the ceria-alumina matrix particles 62 may be used singly or in appropriate combination of two or more types.

[0052] Average particle diameter D of ceria-alumina matrix particles 62 50 The average particle diameter D of the ceria-alumina base particles 62 is set to 1 / 2 mm, and is not particularly limited. 50 is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, and is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less.

[0053] Rh is highly dispersed and co-loaded on the surfaces 62a of the ceria-alumina base particles 62. Here, Rh functions as a catalytically active component. By loading Rh on the surfaces 62a of the ceria-alumina base particles 62, it is possible to maintain high heat resistance and OSC performance, and also to suppress the degradation of catalytic performance when exposed to high temperatures, thereby improving purification performance and low-temperature purification performance.

[0054] The content of Rh is not particularly limited and may be appropriately set according to the desired performance taking into consideration the material and pore size of the ceria-alumina base particles 62, but from the viewpoint of catalytic activity, etc., the content of Rh is preferably 0.001 to 15 mass% in total, more preferably 0.1 to 5 mass%, and even more preferably 0.3 to 3 mass%, in terms of metal Rh relative to the total amount of the fourth composite catalyst particles 61.

[0055] In the catalyst layer 21 of this embodiment, the Rh and Pd supported on each composite catalyst particle 31, 41, 51, and 61 can change into a metal element or a metal oxide depending on the external environment. Therefore, it is sufficient that the Rh and Pd supported on each composite catalyst particle 31, 41, 51, and 61 be confirmed at least in a reducing atmosphere, and the properties of Rh and Pd in ​​an oxidizing atmosphere or a stoichiometric atmosphere are not particularly limited to a metal element. Here, in this specification, a reducing atmosphere means a state in which the Rh and Pd are left to stand in a hydrogen gas atmosphere at 400°C for 0.5 hours or more. The presence of Rh and Pd can be confirmed by various measurement methods such as observation with a scanning transmission electron microscope (STEM), powder X-ray diffraction (XRD), electron probe micro analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), or electron spectroscopy for chemical analysis (ESCA).

[0056] The method for producing each composite catalyst particle 31, 41, 51, 61 is not particularly limited as long as it can provide the Rh, Pd, or CeO particles 33 or barium component supported on the surfaces 32a, 42a, 52a, 62a of each base particle 32, 42, 52, 62. From the viewpoint of producing composite particles simply and at low cost, an evaporation-to-dryness method (impregnation method) or the like is preferred.

[0057] The base particles 32, 42, 52, and 62 used as raw materials can be commercially available products of various grades or can be produced by methods known in the art. While there are no particular limitations on the production methods, for example, the coprecipitation method or alkoxide method is preferred for the zirconia-based base particles 32. A preferred coprecipitation method involves adding an alkaline substance to an aqueous solution containing a cerium salt and / or a zirconium salt, optionally mixed with other rare earth metal elements or transition elements, in a predetermined stoichiometric ratio, to hydrolyze the mixture or coprecipitate a precursor, and then calcining the hydrolysis product or coprecipitate. The types of salts used are not particularly limited. Generally, hydrochlorides, oxyhydrochlorides, nitrates, oxynitrates, carbonates, phosphates, acetates, oxalates, citrates, and the like are preferred. The type of alkaline substance is also not particularly limited. Generally, an aqueous ammonia solution is preferred. A preferred example of the alkoxide method involves hydrolyzing a mixture of cerium alkoxide and / or zirconium alkoxide with, if necessary, other rare earth metal elements or transition elements in a predetermined stoichiometric ratio, followed by calcination. The type of alkoxide used is not particularly limited. Generally, methoxide, ethoxide, propoxide, isopropoxide, butoxide, or their ethylene oxide adducts are preferred. The rare earth metal elements may be compounded as metal alkoxides or as the various salts described above. Calcination conditions are not particularly limited and may be conventional. The calcination atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, or air. The calcination temperature and treatment time vary depending on the desired composition and its stoichiometric ratio. However, from the standpoint of productivity, they are generally preferably 150°C to 1300°C for 1 to 12 hours, and more preferably 350°C to 800°C for 2 to 4 hours. Prior to the high-temperature firing, it is preferable to carry out reduced-pressure drying using a vacuum dryer or the like at 50° C. or higher and 200° C. or lower for about 1 to 48 hours.

[0058] A preferred evaporation-to-dryness method involves impregnating each of the base particles 32, 42, 52, and 62 with an aqueous solution containing the Rh or Pd ions, Ce ions, Ba ions, and the like to be supported, followed by a heat treatment or chemical treatment. This impregnation process results in the Rh or Pd ions, Ce ions, Ba ions, and the like being adsorbed (attached) in a highly dispersed state onto the surfaces 32a, 42a, 52a, and 62a of each of the base particles 32, 42, 52, and 62. The Rh and Pd ions can be incorporated into the aqueous solution as various Rh and Pd salts. The types of salts used are not particularly limited. Generally, sulfates, hydrochlorides, oxyhydrochlorides, nitrates, oxynitrates, carbonates, oxycarbonates, phosphates, acetates, oxalates, citrates, chlorides, oxides, composite oxides, complex salts, and the like are preferred. Furthermore, the content ratio of Rh and Pd ions in the aqueous solution is not particularly limited and can be appropriately adjusted so that the desired content ratio of Rh and Pd is achieved in each of the resulting composite catalyst particles 31, 41, 51, 61 or catalyst layer 21. Furthermore, it goes without saying that the aqueous solution used here may contain the above-mentioned optional components, for example, other rare earth elements and transition elements, and further, inevitable impurities.

[0059] After the impregnation treatment, if necessary, solid-liquid separation, water washing, and drying treatment, such as drying in the air at a temperature of approximately 50°C to 200°C for approximately 1 to 48 hours to remove moisture, can be performed according to conventional methods. The drying treatment can be natural drying, or a drying device such as a drum dryer, a vacuum dryer, or a spray dryer can be used. The drying atmosphere can be air, a vacuum, or an inert gas atmosphere such as nitrogen gas. Before or after drying, further treatments such as pulverization and classification can be performed as needed. Chemical treatments can also be performed. For example, after the impregnation treatment in the evaporation-to-dryness method, a basic component can be used to hydrolyze Rh or Pd ions on each base material particle 32, 42, 52, and 62. The basic component used here is preferably ammonia, amines such as ethanolamine, caustic soda, alkali metal hydroxides such as strontium hydroxide, or alkaline earth metal hydroxides such as barium hydroxide. By these heat treatments and chemical treatments, Rh, Pd, etc. highly dispersed to nano-order size, and further CeO 2 particles 33 and barium components as required, are generated on each of the base material particles 32 , 42 , 52 , 62 .

[0060] The firing conditions may be conventional and are not particularly limited. The heating means is not particularly limited, and known equipment such as an electric furnace or a gas furnace can be used. The firing atmosphere may be an oxidizing atmosphere, an air atmosphere, or a reducing atmosphere, with an oxidizing atmosphere or an air atmosphere being preferred. The firing temperature and treatment time vary depending on the desired performance, but from the perspective of Rh and Pd production and productivity, they are generally preferably 300°C or higher and 1100°C or lower for 0.1 to 12 hours, and more preferably 400°C or higher and 800°C or lower for 0.5 to 6 hours.

[0061] In addition to the above-mentioned components, the catalyst layer 21 can be used by mixing with catalysts, co-catalysts, base particles, and the like known in the art. Examples of known catalysts, co-catalysts, and base particles that can be used in combination include, but are not limited to, metal oxides or metal composite oxides such as silica, alumina, lanthanum oxide, neodymium oxide, and praseodymium oxide; perovskite-type oxides; composite oxides containing alumina such as silica-alumina, silica-alumina-zirconia, and silica-alumina-boria; barium compounds; and zeolites. The proportions of the catalysts, co-catalysts, and base particles used in combination can be appropriately determined depending on the required performance, but are not particularly limited. The total amount of the catalysts, co-catalysts, and base particles is preferably 0.01% by mass to 20% by mass, more preferably 0.05% by mass to 10% by mass, and even more preferably 0.1% by mass to 8% by mass.

[0062] In addition to the above-mentioned components, the catalyst layer 21 can be used by mixing with additives known in the art. Examples of additives that can be used in combination include, but are not limited to, various binders, dispersion stabilizers such as nonionic surfactants and anionic surfactants, pH adjusters, and viscosity adjusters. Examples of binders include, but are not limited to, various sols such as alumina sol, titania sol, silica sol, and zirconia sol. Soluble salts such as aluminum nitrate, aluminum acetate, titanium nitrate, titanium acetate, zirconium nitrate, and zirconium acetate can also be used as binders. Acids such as acetic acid, nitric acid, hydrochloric acid, and sulfuric acid can also be used as binders. The amount of binder used is not particularly limited, and can be any amount necessary to maintain the molded body. The proportion of the above-mentioned additives can be appropriately determined depending on the required performance, and is not particularly limited. However, a total of 0.01 to 20 mass% of the total amount is preferably 0.05 to 10 mass%, more preferably 0.1 to 8 mass%.

[0063] In the exhaust gas purification catalyst 100 for saddle-ride type vehicles of this embodiment, the above-mentioned catalyst layer 21 is provided on at least one surface side of the metal substrate 11. By adopting such a configuration, a low-cost catalyst configuration with a small manufacturing load can be realized, and the catalyst can be easily incorporated into an apparatus during manufacturing, thereby increasing the applicability to various uses. For example, by using a metal honeycomb structure carrier or the like as the metal substrate 11, and installing this exhaust gas purification catalyst 100 for saddle-ride type vehicles in a flow path through which a gas flow passes, and passing the gas flow through the cells of the honeycomb structure carrier, it is possible to purify exhaust gases with high efficiency.

[0064] In this specification, the term "single-layer catalyst" refers to a catalyst having only one catalyst layer. Furthermore, the term "provided on at least one surface of the metal substrate 11" encompasses an embodiment in which any layer other than the catalyst layer is interposed between the one surface of the metal substrate 11 and the catalyst layer.

[0065] Such an exhaust gas purification catalyst 100 for a saddle-ride type vehicle can be obtained, for example, by providing the catalyst layer 21 on the above-mentioned metal substrate 11. The method for forming the catalyst layer 21 may be performed according to a conventional method, and is not particularly limited. For example, the exhaust gas purification catalyst 100 for a saddle-ride type vehicle of this embodiment can be obtained by applying a slurry mixture containing each of the components of the above-mentioned catalyst layer 21 to the metal substrate 11 by applying any of various known coating methods, washcoating methods, etc., and then drying, baking, etc. as necessary.

[0066] As a specific example, each of the above-mentioned composite catalyst particles 31, 41, 51, 61, an aqueous medium, and, if necessary, binders known in the art, other catalysts, co-catalysts, OSC materials, various base material particles, additives, etc. are mixed in a desired mixing ratio to prepare a slurry mixture, and the obtained slurry mixture is applied to the surface of the metal substrate 11, dried and fired, thereby obtaining an exhaust gas purification catalyst 100 for a saddle-type vehicle in which a catalyst layer 21 is provided on the metal substrate 11.

[0067] The aqueous medium used in preparing the slurry mixture may be in an amount that allows each main component to be uniformly dispersed in the slurry. If necessary, an acid or base may be added to adjust the pH, or a surfactant or dispersion resin may be added to adjust the viscosity or improve the dispersibility of the slurry. From the viewpoint of firmly adhering or bonding the resulting catalyst layer 21 to the metal substrate 11, it is preferable to use the binders described above. The slurry can be mixed using known grinding or mixing methods, such as grinding and mixing using a ball mill.

[0068] After the slurry mixture is applied to the metal substrate 11, it can be dried and fired according to a conventional method. The drying temperature is not particularly limited, but is preferably, for example, 70 to 200°C, and more preferably 80 to 150°C. The firing temperature is also not particularly limited, but is preferably, for example, 300 to 650°C, and more preferably 400 to 600°C. The heating means used in this step can be, for example, a known heating means such as an electric furnace or a gas furnace.

[0069] The total coating amount of the catalyst layer 21 described above is not particularly limited, but from the viewpoint of the balance between catalytic performance and pressure loss, it is preferably 1 to 200 g / L (excluding the amount of precious metal) per 1 L of the capacity of the metal substrate 11, and more preferably 50 to 180 g / L (excluding the amount of precious metal).

[0070] The total coating amount of Rh and Pd is not particularly limited, but is preferably 0.05 to 1.5 g / L, more preferably 0.1 to 1.0 g / L, in terms of metal, from the viewpoint of the balance between catalytic performance and pressure drop. The total coating amount of Rh is not particularly limited, but is preferably 0.02 to 0.6 g / L, more preferably 0.04 to 0.4 g / L, in terms of metal, from the viewpoint of the balance between catalytic performance and pressure drop. The total coating amount of Pd is not particularly limited, but is preferably 0.03 to 0.9 g / L, more preferably 0.06 to 0.6 g / L, in terms of metal, from the viewpoint of the balance between catalytic performance and pressure drop. The mass ratio of the coating amounts of Pd and Rh (Pd / Rh) is preferably 10 / 1 to 10 / 9, more preferably 10 / 2 to 10 / 8, in terms of metal.

[0071] The exhaust gas purification catalyst 100 for a saddle-riding type vehicle of this embodiment described above can be arranged in the exhaust system of various engines of a saddle-riding type vehicle, and the number and locations of the catalysts to be installed can be designed as desired in accordance with exhaust gas regulations. Furthermore, the exhaust gas purification catalyst 100 for a saddle-riding type vehicle of this embodiment has a simple and low-cost configuration with only one catalyst layer, yet can exhibit excellent effects in terms of purification performance for CO, HC, and NOx and low-temperature purification performance. [Example]

[0072] The features of the present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the spirit of the present invention. Furthermore, the values ​​of various production conditions and evaluation results in the following examples represent preferred upper or lower limits in the embodiments of the present invention, and preferred numerical ranges may be defined by combining the above-mentioned upper or lower limits with the values ​​of the following examples or values ​​between the examples.

[0073] Example 1 Zirconia composite oxide base particles containing 75.0 mass% ZrO2 and 25.0 mass% rare earth element oxides in oxide equivalent were placed in a Nauta mixer, and a predetermined amount of cerium nitrate and pure water for dilution were further added. The mixture was stirred for 15 minutes to prepare composite particles in which 12.5 mass% CeO2 particles in oxide equivalent were supported on the surfaces of the zirconia composite oxide base particles.

[0074] Next, a predetermined amount of rhodium nitrate and pure water were added to the stirrer and stirred for 5 minutes, and then the composite particles were added and stirred for an additional 15 minutes, thereby obtaining an Rh catalyst slurry containing first composite catalyst particles in which Rh and CeO particles were co-supported on the surfaces of zirconia composite oxide base particles.

[0075] Next, a predetermined amount of palladium nitrate and pure water were added to the stirrer and stirred for 5 minutes, after which ceria-alumina base particles containing 80.7 mass% Al2O3 and 19.3 mass% CeO2, calculated as oxides for the third composite catalyst particles, were further added and stirred for 15 minutes, thereby obtaining a Pd catalyst slurry containing third composite catalyst particles in which Pd was supported on the surfaces of the ceria-alumina base particles.

[0076] The obtained Rh catalyst slurry and Pd catalyst slurry were each weighed in a predetermined amount, placed in a stirrer, and stirred for 15 minutes. They were then pulverized in a ball mill until the average particle size D90 reached 11 μm. An alumina sol binder and distilled water were added to the resulting mixture, which was then stirred for an additional 10 minutes to obtain a catalyst slurry for washcoating.

[0077] A stainless steel metal honeycomb carrier (300 cpsi / 50 μm, 40 × 90 mmL) was immersed in the washcoat catalyst slurry, after which excess washcoat liquid in the cells was removed with an air blower, dried, and calcined at 500°C for 1 hour to obtain an exhaust gas purification catalyst for straddle-type vehicles. The washcoat amount of this catalyst was 120 g / L (excluding the amount of precious metals) per 1 L of stainless steel metal honeycomb carrier, and the Rh content was 0.2 g / L and the Pd content was 0.3 g / L.

[0078] Example 2 A predetermined amount of rhodium nitrate and pure water were added to a stirrer and stirred for 5 minutes, after which the CeO2 particle-supported composite particles obtained in Example 1 were added and stirred for an additional 15 minutes. Ceria-alumina base particles containing 80.7 mass% Al2O3 and 19.3 mass% CeO2, calculated as oxides, for the fourth composite catalyst particles were further added and stirred for 15 minutes. This yielded an Rh catalyst slurry containing first composite catalyst particles in which Rh and CeO2 particles were co-supported on the surfaces of zirconia composite oxide base particles and fourth composite catalyst particles in which Rh was supported on the surfaces of ceria-alumina base particles.

[0079] Next, a predetermined amount of palladium nitrate and pure water were added to the stirrer and stirred for 5 minutes, after which Al2O3 powder with Ba supported on its surface was added and stirred for an additional 15 minutes. After that, 1N nitric acid was added until the pH reached 4 to 5, and the mixture was stirred for 15 minutes. This yielded a Pd catalyst slurry containing second composite catalyst particles with Pd and Ba supported on the surfaces of alumina particles.

[0080] The resulting Rh catalyst slurry and Pd catalyst slurry were weighed out in predetermined amounts and placed in a stirrer. After stirring for 15 minutes, Ba-supported Al2O3 powder was added and stirred for 15 minutes. The mixture was then pulverized in a ball mill until the average particle size D90 reached 11 μm. An alumina sol binder and distilled water were added to the resulting mixture, which was then stirred for another 10 minutes to obtain a catalyst slurry for washcoating.

[0081] A stainless steel metal honeycomb carrier (300 cpsi / 50 μm, 40 × 90 mmL) was immersed in the washcoat catalyst slurry, after which excess washcoat liquid in the cells was removed with an air blower, dried, and calcined at 500°C for 1 hour to obtain an exhaust gas purification catalyst for straddle-type vehicles. The washcoat amount of this catalyst was 120 g / L (excluding the amount of precious metals) per 1 L of stainless steel metal honeycomb carrier, and the Rh content was 0.2 g / L and the Pd content was 0.3 g / L.

[0082] (Comparative Example 1) A predetermined amount of rhodium nitrate and pure water were added to a stirrer and stirred for 5 minutes, after which ceria-alumina base particles were added and stirred for 15 minutes. This resulted in a mixed slurry containing composite catalyst particles in which Rh was supported on the surface of the ceria-alumina base particles. This mixed slurry was then pulverized in a ball mill until the average particle diameter D90 reached 11 μm. An alumina sol binder and distilled water were added to the resulting mixture, and the mixture was stirred for an additional 10 minutes to obtain an Rh catalyst slurry containing composite catalyst particles in which Rh was supported on the surface of the ceria-alumina base particles.

[0083] Next, a predetermined amount of palladium nitrate and pure water were added to a stirrer and stirred for 5 minutes, after which the ceria-alumina base particles were added and stirred for 15 minutes. This resulted in a mixed slurry containing composite catalyst particles in which Pd was supported on the surface of the ceria-alumina base particles. This mixed slurry was then pulverized in a ball mill until the average particle diameter D90 reached 11 μm. An alumina sol binder and distilled water were added to the resulting mixture, and the mixture was stirred for an additional 10 minutes to obtain a Pd catalyst slurry.

[0084] A stainless steel metal honeycomb carrier (300 cpsi / 50 μm, 40 × 90 mmL) was immersed in the Pd catalyst slurry, after which excess washcoat liquid in the cells was removed with air blowing, followed by drying and firing at 500°C for 1 hour. The Pd catalyst slurry-coated stainless steel metal honeycomb carrier was then immersed in the Rh catalyst slurry, after which excess washcoat liquid in the cells was removed with air blowing, followed by drying and firing at 500°C for 1 hour to obtain a multilayer catalyst for purifying exhaust gases for straddle-type vehicles. The washcoat amount of this catalyst was 120 g / L (excluding the amount of precious metals) per 1 L of stainless steel metal honeycomb carrier, with an Rh content of 0.2 g / L and a Pd content of 0.3 g / L.

[0085] (Comparative Example 2) Predetermined amounts of the Rh catalyst slurry obtained in Comparative Example 1 and the Pd catalyst slurry obtained in Comparative Example 1 were weighed and placed in a stirrer, and an alumina sol binder material and distilled water were added thereto, followed by stirring for 10 minutes to obtain a catalyst slurry for washcoating.

[0086] A stainless steel metal honeycomb carrier (300 cpsi / 50 μm, 40 × 90 mmL) was immersed in the washcoat catalyst slurry, after which excess washcoat liquid in the cells was removed with an air blower, dried, and calcined at 500°C for 1 hour to obtain an exhaust gas purification catalyst for straddle-type vehicles. The washcoat amount of this catalyst was 120 g / L (excluding the amount of precious metals) per 1 L of stainless steel metal honeycomb carrier, and the Rh content was 0.2 g / L and the Pd content was 0.3 g / L.

[0087] <Performance evaluation> The purification characteristics of each catalyst were evaluated using a model gas evaluation device manufactured by Horiba, Ltd. Here, the ratios at which HC, CO, and NO (nitrogen oxide) in the model gas were reduced at 450°C (C450 purification rate) and the temperature at which a 50% purification rate was reached [T50 (°C)] were measured to evaluate the three-way purification performance of each catalyst. In this evaluation, test pieces (25.4 x 50 mmL) were punched out from the exhaust gas purification catalysts for straddle-type vehicles obtained in Examples 1 and 2 and Comparative Examples 1 and 2, and these test pieces were heated at 1050°C for 5 hours in an atmosphere that alternated between a rich atmosphere of 2% CO + 10% H2O + balance N2 and a lean atmosphere of 5% O2 + 10% H2O + balance N2 at 5-minute intervals. The catalysts after durability treatment, which were held for 10 minutes, were used as evaluation samples. The evaluation device used was a flow-type reactor composed of stainless steel piping. A model gas with the following composition was introduced from the inlet, circulated through the exhaust gas purification reaction section, and discharged from the outlet. The purification reaction section was heated by heating the model gas with an external heater and sending it to the exhaust gas purification reaction section. The gas composition on the outlet side (after passing through the catalyst section) was analyzed over a temperature range of 100°C to 450°C, and the rate of change in CO, HC, and NO concentrations was determined. The results are shown in Figures 6 and 7.

[0088] Model gas composition: CO: 0.3%, C3H6: 3000 ppm, NO: 3000 ppm, O2: 0.15%, CO2: 10%, H2O: 10%, N2: balance A / F=14.5 Space velocity (SV): 72,000 / h Evaluation temperature: 100~500℃ Heating rate: 10℃ / min [Industrial Applicability]

[0089] The exhaust gas purification catalyst for straddle-type vehicles of the present invention has a simple and low-cost structure with only one catalyst layer, yet is excellent in purification performance for CO, HC, and NOx and in low-temperature purification performance for these, and is also excellent in productivity and economy, and therefore, based on its composition and structure, can be widely and effectively used as a three-way catalyst (TWC) that reduces NOx, CO, HC, etc. in exhaust gas. In particular, the exhaust gas purification catalyst for straddle-type vehicles of the present invention can be particularly effectively used in fields such as motorcycles, which require high heat resistance in a small volume and high exhaust gas purification efficiency even in a fuel-rich atmosphere. [Explanation of symbols]

[0090] 100 ···Exhaust gas purification catalyst for straddle-type vehicles 11 Metal substrate 21 ···Catalyst layer 31...first composite catalyst particles 32 Zirconia-based matrix particles 32a...Surface 33 CeO2 particles 41...Second composite catalyst particles 42 Alumina matrix particles 42a...Surface 51...Third composite catalyst particles 52 ···Ceria-alumina matrix particles 52a...Surface 61...Fourth composite catalyst particles 62 ···Ceria-alumina matrix grains 62a...Surface

Claims

1. An exhaust gas purification catalyst for a saddle-ride type vehicle, which is provided in an exhaust gas passage of an internal combustion engine, A three-way catalyst including a metal substrate and a single catalyst layer provided on the metal substrate, The catalyst layer is Zirconia-based base particles and Rh and CeO co-supported on the surface of the zirconia-based base particles 2 particles; and The catalyst comprises second composite catalyst particles containing alumina matrix particles and Pd supported on the surfaces of the alumina matrix particles, and / or third composite catalyst particles having at least ceria-alumina matrix particles and Pd supported on the surfaces of the ceria-alumina matrix particles, The zirconia-based base particles contain, in oxide equivalent, 65 to 85 mass % of ZrO 2 and 15 to 35 mass % of an oxide of a rare earth element, the ceria-alumina matrix particles of the third composite catalyst particles contain, in oxide equivalent, 70 to 90 mass % of Al 2 O 3 and 10 to 30 mass % of CeO 2 ; Exhaust gas purification catalyst for saddle-type vehicles.

2. The zirconia-based base particles are rare earth-doped zirconia base particles in which at least one rare earth element selected from the group consisting of Ce, Nd, and La is dissolved. The exhaust gas purifying catalyst for a straddle-type vehicle according to claim 1.

3. The second composite catalyst particles include the alumina matrix particles and Pd and Ba supported on the surfaces of the alumina matrix particles. The exhaust gas purifying catalyst for a straddle-type vehicle according to claim 1 or 2.

4. the catalyst layer further contains fourth composite catalyst particles containing ceria-alumina matrix particles and Rh supported on the surfaces of the ceria-alumina matrix particles; The exhaust gas purifying catalyst for a straddle-type vehicle according to any one of claims 1 to 3.

5. the coating amount of the catalyst layer is 1 to 200 g / L per 1 L of the metal substrate; The exhaust gas purifying catalyst for a straddle-type vehicle according to any one of claims 1 to 4.

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