Exhaust gas purifying catalyst

Abstract

To provide an exhaust gas purifying catalyst capable of reducing the emission amount of paraffin, and further improving warm-up performance while using a relatively small amount of noble metals.SOLUTION: An exhaust gas purifying catalyst comprises at least a substrate 11 and a catalyst layer provided on the substrate. The catalyst layer includes a first catalyst layer 21 provided on a substrate and containing Pd, a second catalyst layer 31 provided on the first catalyst layer and containing Rh, and a third catalyst layer 41 provided on the second catalyst layer. The third catalyst layer includes an upstream-side third catalyst layer 41a containing Pd and Pt on the upstream side, and a downstream-side third catalyst layer 41b provided downstream in an exhaust gas flow path and spaced a distance Lc from the upstream-side third catalyst layer and containing Rh. The distance Lc is 0.5 to 15% of the total length of the substrate, and the Pt content (g / L) in the upstream-side third catalyst layer is 3% to 30% relative to the Pd content (g / L) in the same layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas purification catalyst, and more particularly to an exhaust gas purification catalyst having a catalyst layer with a laminated structure, which uses platinum, palladium and rhodium as essential components. [Background technology]

[0002] Three-way catalysts (TWCs) that use platinum group metals (PGMs), such as ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt), as catalytically active components are widely used to purify hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emitted from internal combustion engines of automobiles and other vehicles.

[0003] Conventionally, in order to reduce the amount of relatively expensive PGM used while ensuring high catalytic activity, exhaust gas purification catalysts with a composite particle structure in which catalytically active components are supported on a substrate in the form of fine particles have been widely used. Specific examples include exhaust gas purification catalysts having base particles made of metal oxides such as alumina, zirconia, and ceria, and PGM supported on these base particles.

[0004] This type of exhaust gas purification catalyst is often installed directly below the engine to shorten the warm-up time by supplying high-temperature exhaust gas and quickly raising the temperature to the catalyst activation temperature, thereby achieving highly efficient purification performance. However, for example, the exhaust gas temperature is low at the initial stage of engine start, making it difficult to achieve the desired catalytic activity. In addition, in recent years, the number of vehicles in which the engine is frequently stopped and started has increased. Therefore, there is a demand for improved catalyst warm-up performance and low-temperature purification performance. One possible approach to improving the low-temperature purification performance of a catalyst is to increase the amount of catalytic precious metal supported, but this has the potential problem of increasing costs.

[0005] To address this issue, various proposals have been made, including the development of exhaust gas purification catalysts that include a catalyst layer with a laminated structure using Pd and Rh as essential components. Specifically, Patent Documents 1 and 2 disclose exhaust gas purification catalysts that include a catalyst layer with a three-layer laminated structure that includes a Pd catalyst layer, a Rh catalyst layer, and a Pd catalyst layer in this order on a honeycomb substrate.

[0006] Zone-coated catalysts have also been developed, in which separate catalyst layers are arranged on a honeycomb substrate on the upstream and downstream sides of the exhaust gas flow path. For example, Patent Document 3 discloses an exhaust gas purification catalyst comprising a catalyst layer having a Pd region and an Rh region arranged adjacent to the Pd region on the surface of a honeycomb substrate or the like. Patent Document 4 also discloses an exhaust gas purification catalyst comprising a lower catalyst layer containing at least one of Pd and Pt formed on the surface of a honeycomb substrate or the like, a front-stage upper catalyst layer containing Pd that coats the surface of the lower catalyst layer on the upstream side in the exhaust gas flow direction, and a rear-stage upper catalyst layer containing Rh that coats the surface of the lower catalyst layer on the downstream side in the gas flow direction of the front-stage upper catalyst layer, with the Pd loading density, coating length, and coating amount of the catalyst layers adjusted.

[0007] Furthermore, in Patent Document 5, the present applicants have proposed a zone-coated catalyst in which separate catalyst layers are arranged on an OSC (Oxygen Storage Capacity) layer on a honeycomb substrate on the upstream and downstream sides of an exhaust gas flow path. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2010-501337 [Patent Document 2] Publication number 2012-525955 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-093266 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-026112 [Patent Document 5] Japanese Patent Publication No. 2020-032305 Summary of the Invention [Problem to be solved by the invention]

[0009] Exhaust gases emitted from internal combustion engines of automobiles, etc., 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 heat up the catalyst and improve its low-temperature purification performance. In other words, by improving the catalyst's temperature rise performance, or in other words, its warm-up performance, the catalyst can be activated more quickly. Furthermore, by improving its low-temperature purification performance, harmful substances in exhaust gases can be purified with high efficiency.

[0010] However, Patent Documents 1 and 2 merely disclose that the purification performance of a three-way catalyst is improved, and do not fully consider the low-temperature purification performance or warm-up performance of exhaust gas emitted from an internal combustion engine of an automobile or the like.

[0011] Patent Document 3 discloses that zone coating of a catalyst layer improves exhaust gas purification performance. Furthermore, Patent Document 4 discloses that optimizing the coating length of the catalyst layer improves the catalyst's ease of warming up, which is important for the catalyst's low-temperature purification performance, i.e., warm-up performance, thereby improving exhaust gas purification performance. However, neither Patent Document 3 nor Patent Document 4 fully considers the effects of overlapping zone coatings.

[0012] On the other hand, Patent Document 5 discloses an exhaust gas purification catalyst and the like in which the warm-up performance and low-temperature purification performance are improved by separating and zone-coating the catalyst layers. However, from the viewpoint of further reducing the amount of PGM used, which is relatively expensive, there is still room for improvement in Patent Document 5. Furthermore, it is easily conceivable that simply reducing the amount of PGM used would result in a decrease in low-temperature purification performance and further deterioration of warm-up performance.

[0013] Furthermore, none of Patent Documents 1 to 5 pays any attention to reducing the amount of paraffin emissions. The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a catalyst for purifying exhaust gases, etc., which is capable of reducing the amount of paraffin emissions. Another object of the present invention is to provide a catalyst for purifying exhaust gases, etc., which has further improved warm-up performance despite using a relatively small amount of precious metal. [Means for solving the problem]

[0014] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by employing a zone-coated catalyst having a predetermined layered structure including a first catalyst layer, a second catalyst layer, and a third catalyst layer (an upstream-side third catalyst layer, and a downstream-side third catalyst layer), thereby completing the present invention.

[0015] That is, the present invention provides various specific embodiments as shown below. (1) An exhaust gas purification catalyst comprising: a substrate defining a gas flow path through which exhaust gas passes; and a catalyst layer provided on the substrate, the catalyst layer comprising: a first catalyst layer provided on the substrate and containing Pd; a second catalyst layer provided on the first catalyst layer and containing Rh; and a third catalyst layer provided on the second catalyst layer, the third catalyst layer comprising: an upstream third catalyst layer provided upstream of the exhaust gas flow path and containing Pd and Pt; and a downstream third catalyst layer provided downstream of the exhaust gas flow path and spaced a distance Lc from the upstream third catalyst layer and containing Rh, wherein the distance Lc is within a range of 0.5 to 15% of the total length of the substrate in a cross-sectional view in the flow direction of the exhaust gas; and a Pt content (g / L) in the upstream third catalyst layer per 1 L of substrate in the upstream third catalyst layer is within a range of 3% to 30% of the Pd content (g / L) in the upstream third catalyst layer per 1 L of substrate. (2) The exhaust gas purifying catalyst according to (1), wherein the upstream third catalytic layer is provided so as to cover the second catalytic layer within a range of 30 to 70% of the total length of the substrate in a cross-sectional view in the flow direction of the exhaust gas, and the downstream third catalytic layer is provided so as to cover the second catalytic layer within a range of 70 to 30% of the total length of the substrate in a cross-sectional view in the flow direction of the exhaust gas. (3) The exhaust gas purifying catalyst according to (1) or (2), wherein the Rh content (g / L) in the downstream-side third catalytic layer per 1 L of the substrate is greater than the Rh content (g / L) in the second catalytic layer per 1 L of the substrate. (4) The catalyst for purifying exhaust gas according to any one of (1) to (3), wherein the catalyst amount of the first catalytic layer per 1 L of the substrate is 10 to 100 (g / L). (5) The exhaust gas purifying catalyst according to any one of (1) to (4), wherein the upstream third catalyst layer contains fourth base particles containing Ce and Zr, and Pt is supported on the fourth base particles.

[0016] (6) The exhaust gas purifying catalyst according to any one of (1) to (5), wherein the first catalyst layer contains at least first base particles and first composite catalyst particles having the Pd supported on the first base particles. (7) The exhaust gas purifying catalyst according to (6), wherein the first base particles are an oxygen occlusion / release material. (8) The exhaust gas purifying catalyst according to (6) or (7), wherein the first catalyst layer further contains alumina.

[0017] (9) The exhaust gas purifying catalyst according to any one of (1) to (8), wherein the second catalyst layer contains at least second composite catalyst particles having second base particles and the Rh supported on the second base particles. (10) The exhaust gas purifying catalyst according to (9), wherein the second base particles contain alumina. (11) The exhaust gas purifying catalyst according to (9) or (10), wherein the second catalyst layer further contains an oxygen occlusion / release material.

[0018] (12) The exhaust gas purifying catalyst according to any one of (1) to (11), wherein the upstream-side third catalyst layer contains at least third base particles and third composite catalyst particles having the Pd supported on the third base particles. (13) The exhaust gas purifying catalyst according to (12), wherein the third base particles contain alumina. (14) The exhaust gas purifying catalyst according to (12) or (13), wherein the upstream third catalyst layer further contains an oxygen occlusion / release material. (15) The exhaust gas purifying catalyst according to any one of (1) to (14), wherein the upstream-side third catalyst layer contains at least fourth base particles and fourth composite catalyst particles having the Pt supported on the fourth base particles. (16) The exhaust gas purifying catalyst according to (15), wherein the fourth base particles are an oxygen occlusion / release material.

[0019] (17) The exhaust gas purifying catalyst according to any one of (1) to (16), wherein the downstream-side third catalyst layer contains at least fifth composite catalyst particles having fifth base particles and the Rh supported on the fifth base particles. (18) The exhaust gas purifying catalyst according to (17), wherein the fifth base particles contain alumina. (19) The exhaust gas purifying catalyst according to (17) or (18), wherein the downstream third catalyst layer further contains an oxygen storage / release material. [Effects of the Invention]

[0020] According to the present invention, it is possible to reduce paraffin emissions. Furthermore, it is possible to realize an exhaust gas purification catalyst or the like that exhibits improved warm-up performance while using a relatively small amount of precious metal. Based on its composition and structure, the exhaust gas purification catalyst or the like of the present invention can be particularly suitably used as a three-way catalyst (TWC) that reduces NOx, CO, HC, and other contaminants in exhaust gas. This three-way catalyst can exhibit excellent purification performance during low start-up temperatures, when the air-fuel ratio (A / F) fluctuates, during warm-up, and other conditions. Furthermore, the exhaust gas purification catalyst or the like of the present invention can be installed in a direct-behind-engine catalytic converter or a tandem-arranged direct-behind catalytic converter, thereby reducing canning costs and other costs. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an exhaust gas purifying catalyst according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 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 those shown. However, the following embodiments are merely examples for explaining the present invention, and the present invention is not limited thereto. In other words, the present invention can be implemented with any modifications within the scope of the gist of the present invention. 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.

[0023] 1 is a schematic cross-sectional view showing the general configuration of an exhaust gas purifying catalyst 100 according to one embodiment of the present invention. The exhaust gas purifying catalyst 100 includes at least a catalyst substrate 11 serving as a base material defining a gas flow path through which exhaust gas passes, a first catalyst layer 21 provided on at least one surface of the catalyst substrate 11, a second catalyst layer 31 provided on the upper surface of the first catalyst layer 21, and a third catalyst layer 41 provided on the upper surface of the second catalyst layer 31. That is, in this embodiment, a laminated structure including at least the first catalyst layer 21, the second catalyst layer 31, and the third catalyst layer 41, in this order, is provided on the catalyst substrate 11. The third catalyst layer 41 includes an upstream-side third catalyst layer 41a provided on the upstream side of the gas flow path and a downstream-side third catalyst layer 41b provided on the downstream side of the gas flow path, and the upstream-side third catalyst layer 41a and the downstream-side third catalyst layer 41b are arranged in parallel and spaced a distance Lc apart. The arrows in the figure indicate the flow direction of the exhaust gas. Each component will be described in detail below.

[0024] The catalyst substrate 11 is a catalyst member for supporting the above-mentioned laminated structure (laminate). By using the catalyst substrate 11 as an integrally structured catalyst member with a catalyst layer provided thereon, it becomes easier to incorporate into devices, and the applicability to various applications increases. For example, in exhaust gas purification applications, a honeycomb structured substrate or the like is used as the catalyst substrate 11, and this integrally structured catalyst member is placed in the flow path through which the gas flow passes, and the gas flow passes through the cells of the honeycomb structured substrate, thereby enabling highly efficient exhaust gas purification.

[0025] The catalyst substrate 11 used here can be appropriately selected from those known in the art. Representative examples include ceramic monolith substrates such as cordierite, silicon carbide, and silicon nitride, metal honeycomb substrates made of stainless steel, wire mesh substrates made of stainless steel, and steel wool-like knitted wire substrates, but are not particularly limited to these. The shape 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, or a sheet shape. These can be used alone or in appropriate combination of two or more types.

[0026] Here, in this specification, "provided on at least one side of the catalyst substrate 11" means both an embodiment in which the stacked catalyst is provided only on the upper surface (or lower surface) of the catalyst substrate 11 as shown in Fig. 1, and an embodiment in which the stacked catalyst is provided on both the upper and lower surfaces of the catalyst substrate 11. In this case, "provided on one side" is used to mean both an embodiment in which the catalyst substrate 11 and the stacked catalyst are directly placed on each other, and an embodiment in which the catalyst substrate 11 and the stacked catalyst are spaced apart by any other layer. In other words, any other layer (e.g., a primer layer, an adhesive layer, etc.) may be interposed between the catalyst substrate 11 and the stacked catalyst.

[0027] The above-described laminate structure (laminate) has a laminate structure including at least a first catalyst layer 21, a second catalyst layer 31, and a third catalyst layer 41 in this order. Here, in this specification, "including at least in this order" means that the first catalyst layer 21, the second catalyst layer 31, and the third catalyst layer 41 are arranged in this order, and as long as they are arranged in this order, any other layer (for example, a primer layer, an adhesive layer, etc.) may be interposed between these layers. That is, the stacked structure of the stacked catalyst may be any of the following: a configuration in which the first catalyst layer 21, the second catalyst layer 31, and the third catalyst layer 41 are directly placed on top of each other (first catalyst layer 21 / second catalyst layer 31 / third catalyst layer 41); or a configuration in which the first catalyst layer 21, the second catalyst layer 31, and the third catalyst layer 41 are spaced apart with any other layer interposed therebetween (for example, first catalyst layer 21 / other layer / second catalyst layer 31 / other layer / third catalyst layer 41; first catalyst layer 21 / other layer / second catalyst layer 31 / third catalyst layer 41; or first catalyst layer 21 / second catalyst layer 31 / other layer / third catalyst layer 41).

[0028] In this embodiment, the first catalyst layer 21 is a catalyst layer containing Pd. The first catalyst layer 21 preferably contains at least first composite catalyst particles having first base particles and Pd supported on the first base particles, and more preferably the first base particles are an oxygen storage / release material. By providing such a first catalyst layer 21 on the catalyst substrate 11, the oxygen storage / release capacity (hereinafter sometimes abbreviated as "OSC capacity") of the exhaust gas purification catalyst 100 can be improved, and the desired purification performance can be achieved. The oxygen storage / release material used here has oxygen storage capacity. Specific examples include ceria-based oxygen storage / release materials (e.g., ceria-based (composite) oxides) and zirconia-based high heat-resistant materials (e.g., zirconia-based (composite) oxides), but are not particularly limited thereto. The oxygen storage / release materials can be used alone or in appropriate combinations of two or more.

[0029] In this specification, the term "ceria-based (composite) oxide" is used as a term that encompasses both ceria-based oxides and ceria-based composite oxides, and more specifically, it is used as a concept that encompasses ceria (CeO) or composite oxides or solid solutions thereof doped with other elements. Similarly, the term "zirconia-based (composite) oxide" is used as a term that encompasses both zirconia-based oxides and zirconia-based composite oxides, and more specifically, it is used as a concept that encompasses zirconia (ZrO) or composite oxides or solid solutions thereof doped with other elements other than cerium. Note that a cerium-zirconium-based composite oxide containing both cerium and zirconium is treated as falling under the former ceria-based composite oxide but not the latter zirconia-based composite oxide.

[0030] Specific examples of ceria-based (composite) oxides include cerium (IV) oxide, cerium-rare earth element composite oxides other than cerium, cerium-transition element composite oxides, and cerium-rare earth element-transition element composite oxides other than cerium. Among these, ceria-based oxygen storage-release materials are preferably ceria-zirconia-based composite oxides, which have an excellent balance between oxygen storage-release capacity and heat resistance, and more preferably ceria-zirconia-based composite oxides in which rare earth elements other than cerium and zirconium are solid-dissolved. Note that ceria-based (composite) oxides preferably have a total mass ratio of Ce and Zr of 50% by mass or more and 95% by mass or less, calculated as oxides (CeO2 and ZrO2).

[0031] Specific examples of zirconia-based (composite) oxides include zirconium (IV) oxide, zirconium-cerium and rare earth element composite oxides excluding zirconium, zirconium-transition element composite oxides, and zirconium-cerium and rare earth element-transition element composite oxides excluding zirconium. Among these, as the zirconia-based highly heat-resistant material, zirconia-based composite oxides in which rare earth elements other than cerium and zirconium are dissolved are more preferred from the viewpoint of a balance between heat resistance, toughness, etc. Note that, as the zirconia-based (composite) oxide, one having a mass proportion of Zr of 50% by mass or more and 80% by mass or less, calculated as oxide (ZrO2), is preferably used.

[0032] Here, the ceria-based (composite) oxide and the zirconia-based (composite) oxide may contain rare earth elements other than cerium and zirconium (hereinafter, sometimes referred to as "other rare earth elements"), such as scandium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Among these, yttrium, lanthanum, praseodymium, and neodymium are preferred. The other rare earth elements may be used alone or in appropriate combination of two or more. When other rare earth elements are contained, their content ratio is not particularly limited, but is preferably the total amount of the oxides of the above-mentioned other rare earth elements (for example, La2O3, Nd2O3, Pr5O) relative to the total amount of the base material particles. 11 etc.), is preferably 0.1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and is preferably 55% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less.

[0033] Furthermore, the ceria-based (composite) oxide and the zirconia-based (composite) oxide may contain transition elements such as chromium, cobalt, iron, nickel, titanium, manganese, and copper. The transition elements may be used singly or in appropriate combination of two or more. When a transition element is contained, its content is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, based on the total amount of the base particles, in terms of the oxides of the transition elements (for example, the sum of Fe2O3, TiO2, etc.). 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0034] In the above-mentioned ceria-based (composite) oxides and zirconia-based (composite) oxides, a portion of the cerium and 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. Furthermore, the above-mentioned ceria-based (composite) oxides and zirconia-based (composite) oxides may contain hafnium (Hf), which is usually contained in zirconia ore in an amount of about 1 to 2 mass%, as an inevitable impurity.

[0035] The oxygen storage / release material may be commercially available in various grades. For example, base particles having the above-described composition may be produced by methods known in the art. While the production method is not particularly limited, the coprecipitation method and the alkoxide method are preferred.

[0036] A preferred coprecipitation method involves adding an alkaline substance to an aqueous solution of a cerium salt and / or zirconium salt, optionally containing other rare earth metal elements or transition elements, in a predetermined stoichiometric ratio, to hydrolyze the mixture or co-precipitate 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, etc. are preferred. The type of alkaline substance is also not particularly limited. Generally, an aqueous ammonia solution is preferred. A preferred alkoxide method involves hydrolyzing a mixture of a cerium alkoxide and / or zirconium alkoxide, optionally containing 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 ethylene oxide adducts thereof are preferred. The rare earth metal element may be blended as a metal alkoxide or as any of the above-mentioned salts.

[0037] The firing conditions for the subsequent firing treatment may be conventional and are not particularly limited. The firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and an air atmosphere. The firing temperature and treatment time vary depending on the desired composition and its stoichiometric ratio, but from the viewpoint of productivity, they are generally preferably 150°C or higher and 1300°C or lower for 1 to 12 hours, and more preferably 350°C or higher and 800°C or lower for 2 to 4 hours. Prior to the high-temperature firing, it is preferable to perform reduced-pressure drying using a vacuum dryer or the like, and then perform a drying treatment at 50°C or higher and 200°C or lower for approximately 1 to 48 hours.

[0038] The average particle diameter (D 50 ) can be appropriately set depending on the desired performance and is not particularly limited, but from the viewpoint of maintaining a large specific surface area, improving heat resistance, and increasing the number of catalytically active sites, it is preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 3 μm or more, preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. In this specification, the average particle diameter D of the oxygen storage-release material 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).

[0039] The first catalyst layer 21 may contain other components as long as it contains the above-mentioned Pd. Examples of other components include, but are not limited to, various additives known in the art, such as base particles such as alumina; binders such as boehmite and alumina sol; dispersion stabilizers such as nonionic surfactants and anionic surfactants; pH adjusters; viscosity adjusters; and PGMs such as Rh and Pt. Details of these various known additives will be described later in the sections for each catalyst layer. The first catalyst layer 21 may also contain other components such as catalysts and co-catalysts known in the art.

[0040] The content of the oxygen storage / release material in the first catalytic layer 21 can be set appropriately depending on the desired performance and is not particularly limited, but is preferably 50 mass% or more and 100 mass% or less, more preferably 70 mass% or more, even more preferably 90 mass% or more, more preferably 95 mass% or less, and even more preferably 90 mass% or less, relative to the total amount of the first catalytic layer 21.

[0041] On the other hand, the second catalyst layer 31 is a catalyst layer containing Rh. By providing this second catalyst layer 31 on the first catalyst layer 21, the purification performance of the exhaust gas purification catalyst 100 during A / F fluctuations can be improved, and the desired purification performance can be achieved.

[0042] In this embodiment, the second catalyst layer 31 preferably contains at least second composite catalyst particles having second matrix particles and Rh as catalytically active particles supported on the second matrix particles. From the viewpoint of improving purification performance during A / F fluctuations, at least rhodium is essential as the PGM contained in the second catalyst layer 31. In this embodiment, an oxygen storage / release material such as a ceria-based composite oxide is used as the second matrix particles, and a Rh-supported oxygen storage / release material is used as the second composite catalyst particles. Here, the second matrix particles are matrix particles that support catalytically active particles in a highly dispersed state.

[0043] On the other hand, the third catalytic layer 41 is a zone-coated layer having an upstream-side third catalytic layer 41a provided on the upstream side of the gas flow path and a downstream-side third catalytic layer 41b provided on the downstream side of the upstream-side third catalytic layer 41a. By employing a zone-coated layer in which the upstream-side third catalytic layer 41a containing Pd and Pt and the downstream-side third catalytic layer 41b containing Rh are arranged in this manner, it is possible to improve warm-up performance.

[0044] In this embodiment, the upstream-side third catalytic layer 41a is a catalytic layer containing Pd and Pt. The PGM contained in the upstream-side third catalytic layer 41a must contain at least Pd and Pt to improve warm-up performance. The upstream-side third catalytic layer 41a preferably contains at least third composite catalyst particles having third matrix particles and Pd as catalytically active particles supported on the third matrix particles, and fourth composite catalyst particles having fourth matrix particles and Pt as catalytically active particles supported on the fourth matrix particles. In this embodiment, alumina is used as the third matrix particles, and Pd-supported alumina is used as the third composite catalyst particles. Here, the third matrix particles are matrix particles that support catalytically active particles in a highly dispersed state. In addition, in this embodiment, an oxygen storage-release material such as a ceria-based composite oxide is used as the fourth matrix particles, and a Pt-supported oxygen storage-release material is used as the fourth composite catalyst particles. The fourth base particles are base particles that support catalytically active particles in a highly dispersed state, and the oxygen storage / release material used here is preferably the catalytically active particles described in the section on the first base particles, and a duplicated description will be omitted here.

[0045] In this embodiment, the downstream-side third catalytic layer 41b is a catalytic layer containing Rh. From the viewpoint of improving low-temperature conversion performance, at least Rh is essential as the PGM contained in the downstream-side third catalytic layer 41b. The downstream-side third catalytic layer 41b preferably contains at least fifth composite catalyst particles having fifth base particles and Rh as catalytically active particles supported on the fifth base particles. In this embodiment, an oxygen storage-release material such as a ceria-based composite oxide is used as the fifth base particles, and a Rh-supported oxygen storage-release material is used as the fifth composite catalyst particles. Here, the fifth base particles are base particles that support the catalytically active particles in a highly dispersed state.

[0046] The first to fifth base particles supporting the PGM described above can be appropriately selected from those known in the art depending on the required performance, and the type is not particularly limited. Examples include, but are not limited to, silica; boehmite; alumina (α-Al2O3, δ-Al2O3, γ-Al2O3, δ-Al2O3, η-Al2O3, θ-Al2O3); composite oxides containing alumina such as silica-alumina, silica-alumina-zirconia, and silica-alumina-boria; metal oxides or composite metal oxides such as lanthanum oxide, neodymium oxide, and praseodymium oxide; perovskite-type oxides; barium compounds, anatase-type titania, and zeolites. Among these, porous particles with a large BET specific surface area are preferred as the substrate. Specific examples include alumina, silica, boehmite, and silica-alumina. Examples of alumina include γ-alumina, δ-alumina, and θ-alumina. Silica includes crystalline silica with various different phase transformations, as well as amorphous, glassy, ​​and colloidal silica. Silica generally has a higher BET specific surface area than alumina, and PGMs are highly dispersed in it. Silica-alumina is available in crystalline and amorphous forms. The Si / Al ratio in silica-alumina varies and is appropriately set depending on the application. An example of titania is anatase-type titania. Examples of crystalline zeolites include ZSM-type zeolite and β-type zeolite. The base particles can be used alone or in appropriate combination of two or more types.

[0047] The average particle diameter of the first to fifth base material particles (D 50 ) can be appropriately set depending on the desired performance and is not particularly limited, but from the viewpoint of maintaining a large specific surface area and increasing the number of catalytically active sites by improving heat resistance, it is preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 3 μm or more, preferably 30 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. In this specification, the average particle diameter D of the first to fifth base material particles 50means the median diameter measured by a laser diffraction particle size analyzer (e.g., a laser diffraction particle size analyzer SALD-3100 manufactured by Shimadzu Corporation). Commercially available products of various grades can be used as the first to fifth base particles described above. For example, base particles having the above-described compositions can also be produced by methods known in the art.

[0048] Each of the catalyst layers 21, 31, 41a, and 41b may contain, in addition to the first to fifth base particles described above, base particles capable of supporting the above-described PGMs and precious metal elements (hereinafter, sometimes referred to as "other base particles"). Examples of other base particles include, but are not limited to, silica; alumina; stabilized composite oxides containing alumina, such as silica-alumina, silica-alumina-zirconia, and silica-alumina-boria; zeolites; metal oxides or metal composite oxides, such as cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, praseodymium oxide, titania, ceria-zirconia, and composite oxides such as zirconia and ceria-zirconia doped with rare earth elements and / or transition elements, or stabilized composite oxides obtained by doping these with rare earth elements, transition elements, etc. These materials can be used alone or in appropriate combinations of two or more. Among these, those having a specific surface area of ​​50 to 300 m 2 / g, preferably 100 to 200m 2 / g γ-alumina is preferably used. The other base particles may or may not support the above-mentioned PGM.

[0049] The coating amount (coat amount) of Pd in ​​the first catalyst layer 21 can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 0.001 to 0.10 (g / L), more preferably 0.003 to 0.07 (g / L), and even more preferably 0.005 to 0.04 (g / L) in terms of the amount of precious metal per unit volume (1 L) of the catalyst base 11. Even with such a small amount of Pd used, the oxygen adsorption / release capacity of the exhaust gas purifying catalyst 100 can be improved, and the desired purification performance can be achieved.

[0050] Herein, "per unit volume (1 L) of the catalytic substrate 11 (per 1 L of substrate)" means "per 1 L of the total bulk volume, including not only the net volume of the catalytic substrate 11 (substrate) but also the volume of voids formed inside the substrate." Furthermore, when cells are partitioned and formed inside the catalytic substrate 11 (substrate), it means "the total bulk volume, 1 L, including the net volume of the catalytic substrate 11 (substrate), the volume of voids, and the volume of the cells." Hereinafter, the coating amount (coat amount) of each component per 1 L of substrate may be expressed in this unit (g / L).

[0051] On the other hand, the coating amount (coat amount) of Rh in the second catalyst layer 31 can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 0.01 to 0.40 (g / L), more preferably 0.03 to 0.30 (g / L), and even more preferably 0.05 to 0.20 (g / L) in terms of the amount of precious metal per unit volume (1 L) of the catalyst base 11. Even with such a small amount of Rh used, it is possible to raise the purification performance of the exhaust gas purification catalyst 100 when the A / F varies, and it is possible to provide the desired purification performance.

[0052] The coating amount (coating amount) of Pd in ​​the upstream-side third catalyst layer 41a can be set appropriately depending on the desired performance and is not particularly limited. It is preferably 0.5 to 5.0 g / L, more preferably 1.0 to 4.0 g / L, and even more preferably 1.2 to 3.0 g / L, in terms of the amount of precious metal per unit volume (1 L) of the catalyst substrate 11. The coating amount (coating amount) of Pt in the upstream-side third catalyst layer 41a can be set appropriately depending on the desired performance and is not particularly limited. It is preferably 0.01 to 3.0 g / L, more preferably 0.03 to 2.0 g / L, and even more preferably 0.05 to 1.0 g / L, in terms of the amount of precious metal per unit volume (1 L) of the catalyst substrate 11. By providing the upstream-side third catalyst layer 41a containing Pd and Pt in this manner, warm-up performance can be improved.

[0053] On the other hand, the coating amount (coat amount) of Rh in the downstream-side third catalytic layer 41b can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 0.01 to 1.50 (g / L), more preferably 0.02 to 0.50 (g / L), and even more preferably 0.03 to 0.30 (g / L) in terms of the amount of precious metal per unit volume (1 L) of the catalytic base 11. By disposing the downstream-side third catalytic layer 41b containing Rh in this manner, it is possible to improve warm-up performance.

[0054] Here, the content of Pt contained in the catalyst layers (each of the catalyst layers 21, 31, 41a, and 41b) of the exhaust gas purification catalyst 100 can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 0.001 to 1.00 (g / L) in total, more preferably 0.01 to 0.50 (g / L), and even more preferably 0.02 to 0.30 (g / L) in terms of the amount of precious metal per unit volume (1 L) of the catalyst base 11.

[0055] Furthermore, the content of Pd contained in the catalyst layers (each of the catalyst layers 21, 31, 41a, 41b) of the exhaust gas purification catalyst 100 can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 0.20 to 1.80 (g / L) in total, more preferably 0.30 to 1.50 (g / L), and even more preferably 0.40 to 1.20 (g / L) in terms of the amount of precious metal per unit volume (1 L) of the catalyst base 11.

[0056] Furthermore, the content of Rh contained in the catalyst layers (each of the catalyst layers 21, 31, 41a, and 41b) of the exhaust gas purification catalyst 100 can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 0.01 to 1.50 (g / L), more preferably 0.02 to 0.50 (g / L), and even more preferably 0.03 to 0.30 (g / L) in terms of the amount of precious metal per unit volume (1 L) of the catalyst base 11.

[0057] Here, the mass proportion of Rh contained in each of the catalyst layers 31, 41b can be appropriately set depending on the desired performance and is not particularly limited, but from the viewpoint of reducing the amount of paraffin emissions, keeping the amount of PGM used relatively low, and obtaining high catalytic performance, it is preferable that the Rh content in the downstream-side third catalyst layer 41b be higher than the Rh content in the second catalyst layer 31. Specifically, the ratio of the Rh content in the downstream-side third catalyst layer 41b to the Rh content in the second catalyst layer 31 is preferably 1 or more and 5 or less, more preferably 1.1 or more and 4 or less, and even more preferably 1.2 or more and 3 or less.

[0058] Here, the ratio of the Pt content (g / L) to the Pd content (g / L) in the upstream-side third catalytic layer 41a can be set appropriately depending on the desired performance and is not particularly limited. However, from the viewpoint of reducing the amount of paraffin emissions, keeping the amount of PGM used relatively low, and obtaining high catalytic performance, the ratio is preferably 3% or more and 30% or less, more preferably 3% or more and 25% or less, and even more preferably 4% or more and 25% or less, expressed as a percentage of the Pt content (g / L) / Pd content (g / L).

[0059] Each of the catalyst layers 21, 31, 41a, and 41b may contain other components as long as it contains the aforementioned essential PGMs and the first to fifth base particles, which are blended as necessary. Examples of other components include, but are not limited to, various additives known in the art, such as binders, dispersion stabilizers such as nonionic surfactants and anionic surfactants, pH adjusters, viscosity adjusters, PGMs other than the essential Pd, Rh, and Pt, alkali metals, and alkaline earth metal elements.

[0060] Examples of binders include various sols such as boehmite, 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, but is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass, and even more preferably 0.1 to 8% by mass, based on the total weight of each catalyst layer 21, 31, 41a, and 41b. Each catalyst layer 21, 31, 41a, and 41b may contain, in addition to the above-mentioned components, catalysts, co-catalysts, and various additives known in the art.

[0061] A Ba-containing compound can also be used as an additive. Adding a Ba-containing compound is expected to improve heat resistance and activate catalytic performance. Examples of Ba-containing compounds include, but are not limited to, sulfates, carbonates, composite oxides, and oxides. More specific examples include BaO, Ba(CH3COO)2, BaO2, BaCO3, BaZrO3, and BaAl2O4. The amount of Ba-containing compound used is not particularly limited, but is preferably 1 to 20 mass% in total, more preferably 2 to 15 mass%, and even more preferably 3 to 13 mass%, based on the total amount of each catalyst layer 21, 31, 41a, and 41b.

[0062] Here, each of the catalyst layers 31, 41a, 41b preferably contains, in addition to the second to fifth base particles described above, an oxygen storage / release material having oxygen storage capacity as another base particle or as a non-base particle. By containing an oxygen storage / release material in each of the catalyst layers 31, 41a, 41b, the OSC function of the exhaust gas purification catalyst 100 can be reinforced, and purification performance tends to be improved even when the A / F fluctuates. Note that, as the oxygen storage / release material that can be used in combination, a ceria-based oxygen storage / release material or a zirconia-based high heat-resistant material is preferably used. Here, specific examples of the oxygen storage / release material that can be used in combination are the same as those described for the first catalyst layer 21 described above, and therefore, a duplicated description will be omitted here.

[0063] Furthermore, when each catalyst layer 31, 41a, 41b contains other base material particles or non-base material particles, the content ratio of these can be set appropriately depending on the desired performance and is not particularly limited, but is preferably 1 mass% or more and 45 mass% or less, more preferably 3 mass% or more and 40 mass% or less, and even more preferably 5 mass% or more and 35 mass% or less, of the total amount of each catalyst layer 31, 41a, 41b.

[0064] Furthermore, the coating amount (coat amount) of the first catalyst layer 21 can be appropriately set depending on the desired performance and is not particularly limited. However, taking into consideration the influence of pressure loss, engine output, fuel consumption, etc., the coating amount per unit volume (1 L) of the catalyst substrate 11 is preferably 10 to 100 (g / L), more preferably 12 to 80 (g / L), and even more preferably 15 to 60 (g / L).

[0065] The coating amount (coat amount) of the second catalyst layer 31 can be appropriately set depending on the desired performance and is not particularly limited. However, taking into consideration the influence of pressure loss, engine output, fuel consumption, etc., the coating amount per unit volume (1 L) of the catalyst substrate 11 is preferably 10 to 80 (g / L), more preferably 20 to 70 (g / L), and even more preferably 30 to 60 (g / L).

[0066] The coating amount (coat amount) of the upstream-side third catalyst layer 41a can be appropriately set depending on the desired performance and is not particularly limited. However, taking into consideration the influence of pressure loss, engine output, fuel consumption, etc., the coating amount per unit volume (1 L) of the catalyst substrate 11 is preferably 20 to 120 (g / L), more preferably 30 to 100 (g / L), and even more preferably 40 to 100 (g / L).

[0067] The coating amount (coat amount) of the downstream-side third catalyst layer 41b can be appropriately set depending on the desired performance and is not particularly limited. However, taking into consideration the influence of pressure loss, engine output, fuel consumption, etc., the coating amount per unit volume (1 L) of the catalyst base 11 is preferably 20 to 120 (g / L), more preferably 30 to 100 (g / L), and even more preferably 40 to 100 (g / L).

[0068] The total coating amount (total coat amount) of the catalyst layers 21, 31, 41a, and 41b can be set appropriately depending on the desired performance and is not particularly limited, but considering the influences of pressure loss, engine output, fuel economy, etc., the total amount is preferably 100 to 200 (g / L), more preferably 120 to 190 (g / L), and even more preferably 140 to 180 (g / L) per unit volume (1 L) of the catalyst substrate 11. In this case, since the upper layer of the laminated structure is more likely to come into contact with exhaust gas components, the coating amount of the second catalyst layer 31 is preferably greater than that of the first catalyst layer 21, and also preferably greater than that of the third catalyst layer 41.

[0069] The exhaust gas purification catalyst 100 of this embodiment employs a zone-coated laminated catalyst having the above-described laminated structure, with the uppermost layer (outermost layer) being a zone-coated layer of the upstream-side third catalyst layer 41a and the downstream-side third catalyst layer 41b. By employing this configuration, the amount of paraffin emissions is reduced, and the exhaust gas purification catalyst 100 is realized with improved warm-up performance, even while using a relatively small amount of precious metal. It is presumed that the upstream-side third catalyst layer 41a ensures the warm-up performance of quickly warming up the catalyst, the downstream-side third catalyst layer 41b provides excellent low-temperature purification performance, and furthermore, the second catalyst layer 31 is responsible for purification performance during A / F fluctuations, and the first catalyst layer 21 is responsible for raising the OSC capacity, all of which contribute to the excellent exhaust gas purification performance.

[0070] The coating ratios of the upstream-side third catalytic layer 41a and the downstream-side third catalytic layer 41b are not particularly limited and can be set appropriately depending on the desired performance. From the viewpoints of reducing paraffin emissions, keeping the amount of precious metal used relatively low, fully demonstrating the warm-up performance of the upstream-side third catalytic layer 41a, and ensuring sufficient installation space for the downstream-side third catalytic layer 41b to achieve excellent low-temperature conversion performance and A / F characteristics, the coating length La of the upstream-side third catalytic layer 41a, as viewed in cross section in the exhaust gas flow direction, is preferably in the range of 30 to 69%, more preferably 35 to 64%, and even more preferably 37 to 54%, of the total length L of the catalytic substrate 11. The coating length Lb of the downstream-side third catalytic layer 41b, as viewed in cross section in the exhaust gas flow direction, is preferably in the range of 69 to 30%, more preferably 64 to 35%, and even more preferably 62 to 45%, of the total length L of the catalytic substrate 11. Hereinafter, the application lengths La and Lb may also be expressed as a ratio (%) to the total length L of the catalyst substrate 11.

[0071] Here, we found that if the upstream-side third catalytic layer 41a and the downstream-side third catalytic layer 41b are formed so as to overlap in the thickness direction of the layers, the overlapping region becomes a raised portion in the thickness direction, resulting in a localized increase in catalyst amount, resulting in a decrease in catalyst temperature rise. Furthermore, if there is a raised portion in the thickness direction between the upstream-side third catalytic layer 41a and the downstream-side third catalytic layer 41b, the gas flow distribution to the downstream-side third catalytic layer 41b is also impaired. On the other hand, if the upstream-side third catalytic layer 41a and the downstream-side third catalytic layer 41b are too far apart, the catalyst coating length in the gas flow direction becomes shorter, resulting in a decrease in gas distribution to the catalyst and a decrease in purification performance. Therefore, from the perspectives of catalyst temperature rise and gas distribution to the catalyst, it is preferable that the upstream-side third catalytic layer 41a and the downstream-side third catalytic layer 41b, which are arranged in parallel on the second catalytic layer 31, be separated by a predetermined distance Lc. In this case, the distance Lc is preferably in the range of 0.5 to 15% of the total length L of the catalyst substrate 11, more preferably in the range of 1.0 to 10.5%, even more preferably in the range of 1.5 to 8.5%, and particularly preferably in the range of 2.0 to 6.0%.

[0072] The separation state and separation distance Lc between the upstream-side third catalytic layer 41a and the downstream-side third catalytic layer 41b can be confirmed, for example, by a transmission X-ray device. Specifically, X-rays are irradiated from the side or circumferential direction of the exhaust gas purifying catalyst 100 to obtain an image, and the separation state and separation distance Lc can be confirmed in the image. The separation distance Lc was calculated as the average value of three points: a 1 / 4 position, a 1 / 2 position (center axis), and a 3 / 4 position when the image is divided into four in the width direction from one side or outer peripheral side surface to the other side or outer peripheral side surface.

[0073] The exhaust gas purifying catalyst 100 having the layer structure described above can be manufactured, for example, by providing each of the catalyst layers 21, 31, 41a, and 41b on a catalyst substrate 11, such as the ceramic monolith substrate described above, in a conventional manner. For example, the exhaust gas purifying catalyst 100 of this embodiment can be obtained by sequentially coating (supporting) a slurry mixture of each of the catalyst layers 21, 31, 41a, and 41b on the surface of the catalyst substrate 11. The method for applying the slurry mixture to the catalyst substrate 11 may be performed in a conventional manner and is not particularly limited. Various known coating methods, washcoating methods, and zone coating methods can be applied. After the slurry mixture is applied, it can be dried and fired in a conventional manner.

[0074] As a specific example, the first to fifth composite catalyst particles described above, an aqueous medium, and, if necessary, binders, Ba-containing compounds, other base particles, other catalysts, co-catalysts, OSC materials, binders, various additives, etc., are mixed in desired proportions to prepare slurry mixtures for the catalyst layers 21, 31, 41a, and 41b, and the resulting slurry mixture for the first catalyst layer 21 is applied to the surface of the catalyst substrate 11, such as a honeycomb structure substrate, and then dried and fired to provide the first catalyst layer 21 on the catalyst substrate 11. Next, the slurry mixtures for the catalyst layers 31, 41a, and 41b are applied in the same manner, and then dried and fired to provide the first catalyst layer 21, second catalyst layer 31, and third catalyst layer 41 (upstream third catalyst layer 41a and downstream third catalyst layer 41b) on the catalyst substrate 11. In this case, the above-mentioned zone coating can be performed by, for example, applying the slurry mixture for the upstream third catalytic layer 41a by a coating length La from the upstream side of the exhaust gas flow path of the catalytic substrate 11, and applying the slurry mixture for the downstream third catalytic layer 41b by a coating length Lb from the downstream side of the exhaust gas flow path of the catalytic substrate 11. Then, by making the following relationship, where L is the total length L of the catalytic substrate 11, the coating length La of the upstream third catalytic layer 41a + the coating length Lb of the downstream third catalytic layer 41b < the total length L of the catalytic substrate 11, the above-mentioned distance Lc can be set.

[0075] The aqueous medium used in preparing the slurry mixture may be in an amount that allows each component to be uniformly dispersed or dissolved in the slurry. If necessary, an acid or base may be added to adjust the pH, or a surfactant or dispersing resin may be added to adjust the viscosity or improve the dispersibility of the slurry. From the viewpoint of firmly adhering or bonding the first to fifth composite catalyst particles, it is preferable to use the binders described above. Furthermore, known pulverizing or mixing methods, such as pulverizing and mixing using a ball mill, can be used as a method for mixing the slurry.

[0076] After the slurry mixture is applied to the catalyst 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.

[0077] The exhaust gas purifying catalyst 100 of this embodiment can be used as a catalyst for purifying exhaust gas from, for example, diesel engines, gasoline engines, jet engines, boilers, gas turbines, etc., and is useful as a catalyst for purifying exhaust gas from internal combustion engines, particularly as a three-way catalyst for purifying exhaust gas from automobiles. The exhaust gas purifying catalyst 100 of this embodiment can be disposed in the exhaust system of various engines. The number and location of the catalysts can be appropriately designed depending on exhaust gas regulations. For example, when exhaust gas regulations are strict, two or more catalysts can be disposed in the underfloor position immediately behind the catalyst directly below the exhaust system. The exhaust gas purifying catalyst 100 of this embodiment can exhibit excellent effects in the purification reactions of CO, HC, and NOx not only during start-up at low temperatures but also under various driving conditions, including high-speed driving at high temperatures. [Example]

[0078] The features of the present invention will be explained in more detail below with reference to test examples, examples, and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing 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 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.

[0079] Example 1 First, a ceria-zirconia composite oxide (CeO: 40% by mass) was impregnated with a palladium (II) nitrate solution (containing 20% ​​by mass in terms of Pd) and then fired at 600°C for 30 minutes to obtain first composite catalyst particles of Example 1. Thereafter, the obtained first composite catalyst particles were mixed with γ-alumina powder and boehmite, and the mixture was diluted with pure water to prepare a slurry mixture for the first catalyst layer of Example 1.

[0080] The obtained slurry mixture for the first catalyst layer was applied to a cordierite honeycomb substrate by washcoating at a coating amount of 40 g / L and dried to produce a first catalyst layer (Pd coating amount: 0.01 g / L).

[0081] Next, the γ-alumina powder and the above-mentioned ceria-zirconia composite oxide were impregnated with a rhodium (III) nitrate solution (containing 10% by mass in terms of Rh) and fired at 600°C for 30 minutes to obtain second composite catalyst particles of Example 1. Thereafter, the obtained second composite catalyst particles were mixed with boehmite and diluted with pure water to prepare a slurry mixture for the second catalyst layer of Example 1.

[0082] The obtained slurry mixture for the second catalyst layer was applied to the first catalyst layer 21 of a cordierite honeycomb substrate by a washcoating method at a coating amount of 50 g / L and dried to produce a second catalyst layer (Rh coating amount: 0.06 g / L).

[0083] Next, the above-mentioned γ-alumina powder and the above-mentioned ceria-zirconia composite oxide were impregnated with a palladium (II) nitrate solution (containing 20 mass% in terms of Pd) and calcined at 600°C for 30 minutes to obtain third composite catalyst particles of Example 1. Furthermore, the above-mentioned ceria-zirconia composite oxide was impregnated with a platinum (II) acetate solution (containing 20 mass% in terms of Pt) to obtain fourth composite catalyst particles of Example 1. Thereafter, the obtained third and fourth composite catalyst particles were mixed with a Ba compound and boehmite, and the mixture was diluted with pure water to prepare a slurry mixture for the upstream third catalyst layer of Example 1.

[0084] The obtained slurry mixture for the upstream third catalyst layer was applied by wash coating to the second catalyst layer 31 on the exhaust gas inlet side of a cordierite honeycomb substrate at a coating amount of 80 g / L and dried to prepare an upstream third catalyst layer (Pd coating amount: 1.94 g / L, Pt coating amount: 0.10 g / L). When the total length L of the substrate is 100%, the coating length La of the upstream third catalyst layer is 39.0% from the end face on the exhaust gas inlet side.

[0085] Next, the above-mentioned γ-alumina powder and the above-mentioned ceria-zirconia composite oxide were impregnated with a rhodium (III) nitrate solution (containing 10% by mass in terms of Rh) and fired at 600°C for 30 minutes to obtain fifth composite catalyst particles of Example 1. Thereafter, the obtained fifth composite catalyst particles were mixed with boehmite and diluted with pure water to prepare a slurry mixture for the downstream-side third catalyst layer of Example 1.

[0086] The obtained slurry mixture for the downstream-side third catalyst layer was applied by wash coating to the second catalyst layer 31 on the exhaust gas outlet side of a cordierite honeycomb substrate at a coating amount of 90 g / L and dried to prepare a downstream-side third catalyst layer (Rh coating amount: 0.08 g / L). When the total length L of the substrate is 100%, the coating length Lb of the downstream-side third catalyst layer is 56.9% from the end face on the exhaust gas outlet side.

[0087] As a result, the first catalyst layer, the second catalyst layer, and the third catalyst layer (the upstream-side third catalyst layer and the downstream-side third catalyst layer) were provided in this order on the cordierite honeycomb substrate, and when the total length L of the substrate was taken as 100%, the upstream-side third catalyst layer and the downstream-side third catalyst layer were arranged on the second catalyst layer at a distance Lc = 4.1% apart, thereby obtaining an integrally structured laminated catalyst of Example 1 having the layer configuration shown in Figure 1.

[0088] Next, the obtained monolithic structure type laminated catalysts were individually stored in converters, and the converters were then attached downstream of the exhaust port of a gasoline engine. Thereafter, durability treatment was carried out under engine (3UZ-FE) exhaust gas at a bed temperature of 960°C for 40 hours, to obtain the monolithic structure type laminated catalyst of Example 1 after durability treatment.

[0089] (Comparative Examples 1 to 3) The integrally structured laminated catalysts of Comparative Examples 1 to 3 after durability treatment were obtained in the same manner as in Example 1, except that the amount of precious metal in the slurry mixture for the upstream third catalyst layer was changed as shown in Table 1 so that the total amount of precious metal did not change.

[0090] <Performance evaluation> [Vehicle performance measurement] Using an FTIR exhaust gas analyzer (FAST-3200) manufactured by Iwata Electric Industry Co., Ltd., the amount of paraffin emitted when driving in the low phase (0 to 589 seconds) of the WLTC mode was measured in real time by FT-IR, and the emission ratios of Comparative Examples 2 and 3 and Example 1 were calculated based on the emission amount of Comparative Example 1.

[0091] Table 1 shows the formulations and configurations of the exhaust gas purifying catalysts of Example 1 and Comparative Examples 1 to 3, as well as the performance evaluation results of each catalyst.

[0092] [Table 1]

[0093] As shown in Table 1, it was confirmed that the monolithic laminated catalyst of Example 1, in which the upstream third catalyst layer and the downstream third catalyst layer are spaced apart, had lower paraffin emissions than the monolithic laminated catalysts of Comparative Examples 1 to 3.

[0094] (Examples 2 and 3) The integrally structured laminated catalysts of Examples 2 to 3 after durability treatment were obtained in the same manner as Example 1, except that the amount of precious metal in the slurry mixture for the upstream third catalyst layer was changed as shown in Table 2 so that the total amount of precious metal did not change.

[0095] The above-mentioned γ-alumina powder and the above-mentioned ceria-zirconia composite oxide were impregnated with a palladium (II) nitrate solution (containing 20 mass % in terms of Pd) and calcined at 600°C for 30 minutes to obtain the third composite catalyst particles of Example 1. The above-mentioned ceria-zirconia composite oxide was also impregnated with a platinum (II) acetate solution (containing 20 mass % in terms of Pt) to obtain the fourth composite catalyst particles of Example 1. Thereafter, the obtained third and fourth composite catalyst particles were mixed with a Ba compound and boehmite, and the mixture was diluted with pure water to prepare slurry mixtures for the upstream third catalyst layers of Comparative Examples 4 to 6. The integrally structured laminated catalysts of Comparative Examples 4 to 6 after durability treatment were obtained in the same manner as in Example 1, except that the slurry mixture for the upstream third catalyst layer of Example 1 was replaced with the slurry mixture for the upstream third catalyst layer of Comparative Examples 4 to 6, and the amount of precious metal in the slurry mixture for the upstream third catalyst layer was changed as shown in Table 2 so that the total amount of precious metal did not change.

[0096] <Performance evaluation> The warm-up performance and A / F characteristics of each of the exhaust gas purifying catalysts obtained after durability treatment were evaluated under the following evaluation conditions.

[0097] [Measurement of warm-up performance] Warm-up performance was measured using each exhaust gas purification catalyst, which had been allowed to cool to room temperature after durability testing. A 2-liter engine was used, with an engine speed of 2500 rpm, a boost pressure of -380 mmHg, and an air-fuel ratio of 14.6 ± 0.1 / 2.5 Hz. A temperature sensor was attached one inch from the catalyst inlet end, and exhaust gas maintained at 500°C was introduced by bypass switching. Measurements were taken as the temperature rose from a starting temperature of 50°C. The gas composition at the catalyst inlet and outlet was analyzed to determine the HC purification rate. The time required for the HC purification rate to reach 50% (50% HC purification time) was calculated and used as the warm-up performance. A shorter 50% HC purification time indicates a better catalyst.

[0098] [A / F characteristic measurement] After durability testing, each exhaust gas purification catalyst was allowed to cool to room temperature and then its A / F characteristics were measured. A 2L engine was used, with the engine speed at 2500 rpm and boost pressure at -300 mmHg. The catalyst inlet gas temperature was fixed at 500°C, and the A / F was oscillated at ±1.0 A / F and 1 Hz while the average air-fuel ratio was continuously varied. The gas compositions at the catalyst inlet and outlet were analyzed, and the CO, HC, and NOx reduction efficiencies were calculated for average air-fuel ratios (A / F) ranging from 13.5 to 15.5. The CO, HC, and NOx reduction efficiencies versus the inlet air-fuel ratio were plotted on a graph to create a ternary characteristic curve. The A / F characteristics were determined by the reduction efficiencies at the crossover point (COP) between the CO and NOx reduction curves. A higher COP indicates a better catalyst.

[0099] Table 2 shows the formulations and configurations of the exhaust gas purifying catalysts of Examples 1 to 3 and Comparative Examples 4 to 6, as well as the performance evaluation results of each catalyst.

[0100] [Table 2]

[0101] As shown in Table 2, it was confirmed that the monolithic laminated catalysts of Examples 1 to 3, in which the upstream third catalyst layer and the downstream third catalyst layer are spaced apart, are superior in warm-up performance and A / F characteristics compared to the monolithic laminated catalysts of Comparative Examples 4 to 6. In particular, it can be seen that the monolithic laminated catalysts of Examples 1 to 3 are excellent in A / F characteristics and have further improved warm-up performance, despite using an extremely small total amount of precious metals. [Industrial Applicability]

[0102] The exhaust gas purifying catalyst 100 of the present invention can be widely and effectively used as a three-way catalyst for reducing NOx, CO, HC, etc. in exhaust gas, and can be particularly effectively used in catalytic applications for purifying exhaust gas from diesel engines, gasoline engines, jet engines, boilers, gas turbines, etc. Furthermore, the exhaust gas purifying catalyst 100 of the present invention can be effectively used as a TWC such as an engine direct-downstream catalytic converter or a tandem-arranged direct-downstream catalytic converter. [Explanation of symbols]

[0103] 100 Exhaust gas purification catalyst 11. Catalyst substrate 21...1st catalyst layer 31...Second catalyst layer 41...Third catalyst layer 41a...Upstream third catalyst layer 41b... Third catalyst layer on the downstream side L: Total length of catalyst substrate La: Application length Lb: Application length Lc...distance

Claims

1. a substrate that defines a gas flow path through which exhaust gas passes; a catalyst layer provided on the substrate; the catalyst layer comprises a first catalyst layer provided on the substrate and containing Pd, a second catalyst layer provided on the first catalyst layer and containing Rh, and a third catalyst layer provided on the second catalyst layer, the third catalyst layer comprising: an upstream third catalyst layer provided upstream of the exhaust gas flow path and containing Pd and Pt; and a downstream third catalyst layer provided downstream of the exhaust gas flow path and spaced a distance Lc from the upstream third catalyst layer and containing Rh; the distance Lc is within a range of 0.5 to 15% of the total length of the substrate in a cross-sectional view in the flow direction of the exhaust gas, the Pt content (g / L) per 1 L of the substrate in the upstream-side third catalytic layer is in the range of 3% to 30% of the Pd content (g / L) per 1 L of the substrate in the upstream-side third catalytic layer; Catalyst for purifying exhaust gas.

2. the upstream-side third catalytic layer is provided so as to cover the second catalytic layer in a range of 30 to 70% of the entire length of the substrate in a cross-sectional view in the flow direction of the exhaust gas, The downstream-side third catalytic layer is provided so as to cover the second catalytic layer in a range of 70 to 30% of the total length of the substrate in a cross-sectional view in the flow direction of the exhaust gas. The exhaust gas purifying catalyst according to claim 1.

3. the Rh content (g / L) in the downstream third catalytic layer per 1 L of the substrate is greater than the Rh content (g / L) in the second catalytic layer per 1 L of the substrate; The exhaust gas purifying catalyst according to claim 1.

4. The amount of catalyst in the first catalyst layer per 1 L of the substrate is 10 to 100 (g / L). The exhaust gas purifying catalyst according to claim 1.

5. the upstream-side third catalytic layer contains fourth base particles containing Ce and Zr, Pt is supported on the fourth base material particles. The exhaust gas purifying catalyst according to claim 1.

Images