Exhaust gas purification catalyst device

Abstract

Disclosed is an exhaust gas purification catalyst device which has a base material and a catalyst coating layer disposed on the base material, wherein: the catalyst coating layer is a single layer or a multilayer body that is composed of two or more layers; the uppermost layer of the catalyst coating layer has an upper layer first zone that contains Pd, an upper layer second zone that contains Rh, and an upper layer third zone that contains Rh in this order from the upstream side of the exhaust gas flow; and the Rh concentration in the upper layer second zone is higher than the Rh concentration in the upper layer third zone.

Description

Exhaust gas purification catalyst device

[0001] The present invention relates to an exhaust gas purification catalyst device.

[0002] Nitrogen oxides (NO) are contained in exhaust gases from internal combustion engines such as automobile engines. ｘ These exhaust gases contain NOx, carbon monoxide (CO), hydrocarbons (HC), etc. These exhaust gases are purified by an exhaust gas purification catalyst that oxidizes CO and HC and reduces NOx before being released into the atmosphere.

[0003] With a view to mitigating air pollution, each country regulates the weight of components contained in exhaust gases emitted per unit distance traveled by automobiles. These exhaust gas regulations are becoming stricter every year. Currently, the United States applies LEV III regulations, Europe applies Euro 6 regulations, and China applies Country 6 regulations. However, in the near future, these countries are expected to transition to LEV IV regulations, Euro 7 regulations, and Country 7 regulations, respectively.

[0004] The Euro 7 regulations require a reduction in NOx emissions in the cold region, for example, during engine start-up. The exhaust gas atmosphere during engine start-up is in the rich to stoichiometric region. Therefore, it is difficult to reduce NOx emissions in the cold region using conventional NOx purification technologies that are based on lean-burn engines.

[0005] As a conventional technique for reducing NOx emissions, for example, Patent Document 1 describes an exhaust gas purification catalyst comprising: a lower catalyst layer containing a first composite oxide containing Ce and Zr and Pd supported on the first composite oxide; and an upper catalyst layer containing a second composite oxide containing Ce and Zr and Rh supported on the second composite oxide, wherein an alkaline earth metal selected from Ca, Sr, and Mg is solid-solved in at least one of the first composite oxide and the second composite oxide.

[0006] Furthermore, Patent Document 2 describes an oxidation-reduction catalyst in which palladium and an alkaline earth metal are supported on an oxide having oxygen storage and release capacity.

[0007] JP 2010-119994 A JP 2001-198461 A

[0008] The above-mentioned Patent Documents 1 and 2 both belong to the category of prior art exhaust gas purification catalysts, and are insufficient in reducing the amount of NOx emissions in the cold region, such as when starting the engine.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide an exhaust gas purification catalyst device that reduces both HC emissions in the cold region and NOx emissions in the cold region.

[0010] The present invention is as follows.

[0011] 1. A catalytic device for purifying exhaust gases, comprising a substrate and a catalytic coating layer on the substrate, wherein the catalytic coating layer is a single layer or a laminate of two or more layers, and wherein the uppermost layer of the catalytic coating layer has, from the upstream side of the exhaust gas flow, a first upper zone containing Pd, a second upper zone containing Rh, and a third upper zone containing Rh, in that order, and wherein the Rh concentration in the second upper zone is higher than the Rh concentration in the third upper zone. 2. A catalytic device for purifying exhaust gases according to claim 1, wherein the Rh concentration in the second upper zone is 0.20 g / L or more and 0.50 g / L or less, and the Rh concentration in the upper third zone is 0.05 g / L or more and less than 0.20 g / L. <Aspect 3> The exhaust gas purification catalyst device according to Aspect 1, wherein the Rh concentration in the upper second zone is 1.5 to 4.0 times the Rh concentration in the upper third zone. <Aspect 4> The exhaust gas purification catalyst device according to Aspect 1, wherein the Ce element concentration in the upper second zone is lower than the Ce element concentration in the upper third zone. <Aspect 5> The exhaust gas purification catalyst device according to Aspect 1, wherein the Ce element concentration in ceria equivalent in the upper second zone is 7.0 g / L or less, and the Ce element concentration in ceria equivalent in the upper third zone is 5.0 g / L or more and 15.0 g / L or less. <Aspect 6> The exhaust gas purification catalyst device according to Aspect 2, wherein the Ce element concentration in ceria equivalent in the upper second zone is 7.0 g / L or less, and the Ce element concentration in ceria equivalent in the upper third zone is 5.0 g / L or more and 15.0 g / L or less. Aspect 7: The catalytic device for purifying exhaust gases according to Aspect 3, wherein the concentration of Ce element in terms of ceria in the second upper zone is 7.0 g / L or less, and the concentration of Ce element in terms of ceria in the third upper zone is 5.0 g / L or more and 15.0 g / L or less. Aspect 8: The catalytic device for purifying exhaust gases according to any one of Aspects 1 to 7, wherein at least a portion of the Rh contained in the second upper zone is supported on inorganic oxide particles containing Ce element, and the Rh contained in the third upper zone is supported on inorganic oxide particles containing Ce element.Aspect 9: The catalytic device for purifying exhaust gas according to any one of Aspects 1 to 7, wherein at least a portion of the Rh contained in the upper second zone is supported on inorganic oxide particles that are substantially free of elemental Ce, and the Rh contained in the upper third zone is supported on inorganic oxide particles that contain elemental Ce. Aspect 10: The catalytic device for purifying exhaust gas according to any one of Aspects 1 to 7, wherein at least a portion of the Rh contained in the upper second zone is supported on inorganic oxide particles that are substantially free of elemental Ce, the upper second zone further contains inorganic oxide particles that contain elemental Ce, and the Rh contained in the upper third zone is supported on inorganic oxide particles that contain elemental Ce. <Aspect 11> The catalytic device for purifying exhaust gas according to any one of Aspects 1 to 7, wherein the catalyst coating layer is a laminate consisting of two layers, and the lower layer of the catalytic coating layer has, from the upstream side of the exhaust gas flow, a lower layer first zone containing Rh, and a lower layer second zone containing one or two elements selected from Pd and Pt, in this order. <Aspect 12> The catalytic device for purifying exhaust gas according to Aspect 11, wherein the Rh concentration in the upper layer second zone is substantially the same as the Rh concentration in the lower layer first zone. <Aspect 13> A method for purifying exhaust gas, comprising: disposing the catalytic device for purifying exhaust gas according to any one of Aspects 1 to 7 in an exhaust system of an internal combustion engine, with the upper layer first zone facing upstream in the exhaust gas flow, and purifying exhaust gas emitted from the internal combustion engine.

[0012] According to the present invention, there is provided an exhaust gas purification catalyst device which reduces NOx emissions in the cold region as well as HC emissions in the cold region.

[0013] FIG. 1 is a schematic diagram showing the configuration of an exhaust gas purification catalyst device produced in Example 1. FIG. 2 is a schematic diagram showing the configuration of an exhaust gas purification catalyst device produced in Example 2. FIG. 3 is a schematic diagram showing the configuration of an exhaust gas purification catalyst device produced in Example 3. FIG. 4 is a schematic diagram showing the configuration of an exhaust gas purification catalyst device produced in Example 4. FIG. 5 is a schematic diagram showing the configuration of an exhaust gas purification catalyst device produced in Example 5. FIG. 6 is a schematic diagram showing the configuration of an exhaust gas purification catalyst device produced in Example 6. FIG. 7 is a schematic diagram showing the configuration of an exhaust gas purification catalyst device produced in Example 7. FIG. 8 is a schematic diagram showing the configuration of an exhaust gas purification catalyst device produced in Comparative Example 1.

[0014] <<Exhaust Gas Purification Catalyst Device>> The exhaust gas purification catalyst device of the present invention is an exhaust gas purification catalyst device having a substrate and a catalyst coating layer on the substrate, wherein the catalyst coating layer is a single layer or a laminate consisting of two or more layers, and the uppermost layer of the catalyst coating layer has, from the upstream side of the exhaust gas flow, a first upper layer zone containing Pd, a second upper layer zone containing Rh, and a third upper layer zone containing Rh, in this order, and the Rh concentration in the second upper layer zone is higher than the Rh concentration in the third upper layer zone.

[0015] In the exhaust gas purification catalyst device of the present invention, the uppermost layer of the catalyst coating layer has, from the upstream side of the exhaust gas flow, an upper layer first zone containing Pd, an upper layer second zone containing Rh, and an upper layer third zone containing Rh, in this order, and the Rh concentration in the upper layer second zone is set higher than the Rh concentration in the upper layer third zone.

[0016] In the exhaust gas purification catalyst device of the present invention, the first upper layer zone, which is the most upstream of the top layer, contains Pd, thereby enhancing the HC purification capacity in the cold region. Furthermore, the second upper layer zone and the third upper layer zone, which are located downstream of the first zone, contain Rh, thereby thoroughly purifying HC.

[0017] In the exhaust gas purification catalyst device of the present invention, the high concentration of Rh contained in the upper second zone enhances the NOx purification ability in the cold region. Furthermore, an upper third zone containing Rh is also disposed downstream of the upper second zone to capture and purify NOx that passes through the upper second zone in the high-speed region. Here, since most of the NOx is purified in the upper second zone, the Rh concentration in the upper third zone may be low.

[0018] In the exhaust gas purification catalyst device of the present invention, the amount of catalytic precious metal used is suppressed by the above-mentioned mechanism of action, and at the same time, NOx emissions in the cold region as well as HC emissions in the cold region are reduced.

[0019] However, the present invention is not bound by any particular theory.

[0020] In a preferred embodiment of the exhaust gas purification catalyst device of the present invention, the catalyst coating layer is a laminate consisting of two layers, and the lower layer of the catalyst coating layer may have, from the upstream side of the exhaust gas flow, a lower layer first zone containing Rh, and a lower layer second zone containing one or two species selected from Pd and Pt, in this order.

[0021] The components of the exhaust gas purification catalyst device of the present invention will be described below in order.

[0022] The substrate in the catalytic converter for exhaust gas purification of the present invention may be a substrate having a plurality of cell flow paths separated by partition walls, or may be a honeycomb substrate used in conventional catalytic converters for exhaust gas purification. The partition walls of the substrate may or may not have pores that fluidly connect adjacent exhaust gas flow paths.

[0023] The constituent material of the substrate may be, for example, a refractory inorganic oxide such as cordierite, or may be a metal. The substrate may be of either a straight flow type or a wall flow type.

[0024] The substrate in the exhaust gas purification catalyst device of the present invention may typically be, for example, a straight-flow type monolith honeycomb substrate made of cordierite, a wall-flow type monolith honeycomb substrate made of cordierite, or a metal honeycomb substrate.

[0025] The shape of the substrate may be a cylinder, an elliptical cylinder, a polygonal pillar, or the like.

[0026] The capacity of the substrate, as an apparent volume expressed as the base area x length, may be, for example, 500 mL or more, 800 mL or more, 1.0 L or more, or 1.2 L or more, and may be, for example, 5.0 L or less, 3.0 L or less, 2.0 L or less, 1.5 L or less, or 1.2 L or less.

[0027] <Catalyst Coating Layer> The exhaust gas purification catalyst device of the present invention has a catalyst coating layer on a substrate.

[0028] The catalyst coating layer in the exhaust gas purification catalyst device of the present invention may be a single layer or a laminate consisting of two or more layers.

[0029] (Top Layer) The top layer of the catalyst coating layer in the exhaust gas purification catalytic device has, from the upstream side of the exhaust gas flow, a first top layer zone containing Pd, a second top layer zone containing Rh, and a third top layer zone containing Rh, in this order.

[0030] The "top layer" of the catalyst coating layer means the single layer if the catalyst coating layer is a single layer, or means the layer that is located farthest from the cell flow path surface of the substrate and has a surface that comes into direct contact with the exhaust gas flow if the catalyst coating layer is a laminate consisting of two or more layers.

[0031] The length of the top layer may typically be the same as the length of the substrate.

[0032] - Upper First Zone - The upper first zone mainly contributes to the purification of HC, and is particularly effective in purifying cold HC.

[0033] To achieve this purpose, the upper first zone contains Pd. The upper first zone may contain inorganic oxide particles, a binder, and the like in addition to Pd.

[0034] The Pd concentration in the first upper zone may be 0.5 g / L or more, 1.0 g / L or more, 1.2 g / L or more, 1.4 g / L or more, or 1.6 g / L or more, and 5.0 g / L or less, 4.0 g / L or less, 3.0 g / L or less, or 2.0 g / L or less, in terms of the mass of Pd converted into metal per unit volume of the substrate. A Pd concentration within this range ensures good cold HC purification ability without excessively increasing the amount of Pd used.

[0035] The upper first zone may or may not contain catalytic precious metals other than Pd. Examples of catalytic precious metals other than Pd include platinum (Pt) and rhodium (Rh). The upper first zone may be substantially free of catalytic precious metals other than Pd. The amount of catalytic precious metals other than Pd in ​​the upper first zone may be 5 mass% or less, 3 mass% or less, 1 mass% or less, 0.5 mass% or less, 0.3 mass% or less, or 0.1 mass% or less, relative to the mass of all catalytic precious metals in the upper first zone. Alternatively, the upper first zone may be completely free of catalytic precious metals other than Pd.

[0036] The upper first zone may contain inorganic oxide particles. The inorganic oxide particles in the upper first zone may be selected from, for example, alumina, silica, titania, zirconia, ceria, rare earth metal oxides other than ceria, and the like, and may be one or more selected from these. When two or more types of inorganic oxide particles are contained, they may be a mixture of multiple inorganic oxide particles, particles of a composite oxide containing two or more inorganic elements, a mixture of particles of two or more composite oxides, or a mixture of one or more inorganic oxide particles and one or more composite oxide particles.

[0037] The upper first zone may contain particles of one or more inorganic oxides selected from alumina and composite oxides containing aluminum (Al). The composite oxide containing Al may be a composite oxide containing Al and a rare earth metal element other than Ce, and in particular, may be a composite oxide containing Al and a rare earth metal element selected from lanthanum (La), praseodymium (Pr), yttrium (Y), neodymium (Nd), etc.

[0038] The upper first zone may be substantially free of inorganic oxide particles selected from a composite oxide containing ceria and Ce. That is, the upper first zone may be substantially free of Ce. By being substantially free of Ce, the oxidation catalytic activity of Pd, which contributes to HC purification, is effectively exhibited. The Ce element concentration in the upper first zone may be 1.0 g / L or less, 0.5 g / L or less, 0.3 g / L or less, or 0.1 g / L or less, in terms of ceria-equivalent mass per unit volume of the substrate, or the upper first zone may be completely free of a composite oxide containing ceria and Ce.

[0039] The particle size of the inorganic oxide particles in the upper first zone may be, for example, 3 μm or more and 8 μm or less.

[0040] The amount of inorganic oxide particles in the upper first zone may be, for example, 10 g / L or more, 15 g / L or more, 20 g / L or more, 25 g / L or more, or 30 g / L or more, in terms of the mass of inorganic oxide particles per unit volume of the substrate, and may be, for example, 100 g / L or less, 80 g / L or less, 70 g / L or less, or 60 g / L or less.

[0041] The Pd in ​​the upper first zone may be in the form of particles, and may be supported on inorganic oxide particles as Pd particles. The particle size of the Pd particles supported on the inorganic oxide particles may be, for example, 1 nm or more and 15 nm or less.

[0042] The inorganic oxide particles supporting Pd in ​​the upper first zone may be, for example, one or more types selected from alumina and composite oxides containing Al element.

[0043] The binder in the upper first zone may be, for example, a boehmite binder, an alumina sol, a silica sol, or the like.

[0044] The length of the upper first zone may be 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more of the length of the upper layer to ensure sufficiently high cold HC purification capacity, and may be 50% or less, 45% or less, 40% or less, or 35% or less of the length of the upper layer to maintain the lengths of the upper second zone and upper third zone that contribute to cold NOx purification.

[0045] - Upper Second Zone - The upper second zone mainly contributes to the purification of NOx, and is particularly effective in purifying cold NOx.

[0046] To achieve this purpose, the upper layer second zone contains Rh. The upper layer second zone may contain inorganic oxide particles, a binder, and the like in addition to Rh.

[0047] The Rh concentration in the second upper zone may be, in terms of metal mass of Rh per unit volume of the substrate, 0.05 g / L or more, 0.10 g / L or more, 0.15 g / L or more, 0.20 g / L or more, or 0.25 g / L or more, and may be 0.50 g / L or less, 0.40 g / L or less, 0.35 g / L or less, or 0.30 g / L or less. If the Rh concentration is within this range, good cold NOx purification performance can be ensured without excessively increasing the amount of Rh used.

[0048] The upper second zone may or may not contain catalytic precious metals other than Rh. Examples of catalytic precious metals other than Rh include Pt and Pd. The upper second zone may be substantially free of catalytic precious metals other than Rh. The amount of catalytic precious metals other than Rh in the upper second zone may be 5 mass% or less, 3 mass% or less, 1 mass% or less, 0.5 mass% or less, 0.3 mass% or less, or 0.1 mass% or less, based on the mass of all catalytic precious metals in the upper second zone. Alternatively, the upper second zone may be completely free of catalytic precious metals other than Rh.

[0049] The second upper zone may contain inorganic oxide particles. The inorganic oxide particles in the second upper zone may be appropriately selected from the inorganic oxide particles exemplified above for the first upper zone.

[0050] The upper second zone may contain particles of one or more inorganic oxides selected from ceria, a composite oxide containing Ce element, alumina, and a composite oxide containing Al element (except when Ce element is contained).

[0051] The composite oxide containing Ce may be a composite oxide containing Ce and one or two inorganic elements selected from zirconium (Zr) and Al, or may be a composite oxide further containing a rare earth metal element other than Ce. Specific examples of composite oxides containing Ce include Ce—Zr composite oxides, Al—Ce—Zr composite oxides, and composite oxides of these that further contain a rare earth metal element other than Ce.

[0052] Examples of composite oxides containing Al include composite oxides containing Al and Zr, and composite oxides which further contain a rare earth metal element other than Ce.

[0053] In the above, the rare earth metal element other than Ce may be selected from, for example, La, Pr, Y, Nd, and the like.

[0054] The second upper zone may contain inorganic oxide particles selected from ceria and a composite oxide containing Ce. The Ce concentration in the second upper zone may be 2.0 g / L or more, 2.5 g / L or more, 3.0 g / L or more, 3.5 g / L or more, or 4.0 g / L or more, in terms of ceria equivalent mass per unit volume of the substrate, and may be 12.0 g / L, 10.0 g / K or less, 7.0 g / L or less, 6.0 g / L or less, 5.0 g / L or less, 4.0 g / L or less, 3.0 g / L or less, 2.0 g / L or less, or 1.0 g / L or less. Alternatively, the second upper zone may not contain Ce.

[0055] The particle size of the inorganic oxide particles in the upper second zone may be, for example, 3 μm or more and 8 μm or less.

[0056] The amount of inorganic oxide particles in the upper second zone may be, for example, 40 g / L or more, 45 g / L or more, 50 g / L or more, 55 g / L or more, or 60 g / L or more, in terms of the mass of inorganic oxide particles per unit volume of the substrate, and may be, for example, 150 g / L or less, 120 g / L or less, 100 g / L or less, or 80 g / L or less.

[0057] --Support for Rh in the Upper Second Zone-- The Rh in the upper second zone may be in the form of particles, and may be supported on inorganic oxide particles as Rh particles. The particle diameter of the Rh particles supported on the inorganic oxide particles may be, for example, 1 nm or more and 15 nm or less.

[0058] In another embodiment of the present invention, at least a portion of the Rh in the upper second zone is supported on inorganic oxide particles containing elemental Ce. The inorganic oxide particles containing elemental Ce may be, for example, ceria, a Ce—Zr composite oxide, or an Al—Ce—Zr composite oxide.

[0059] In yet another embodiment of the present invention, at least a portion of the Rh contained in the upper second zone is supported on inorganic oxide particles substantially free of Ce element. The inorganic oxide particles substantially free of Ce element may be, for example, alumina, Al-Zr composite oxide, etc.

[0060] In yet another embodiment of the present invention, at least a portion of the Rh in the upper second zone is supported on inorganic oxide particles containing element Ce, and the upper second zone further contains inorganic oxide particles substantially free of element Ce, which may not support Rh.

[0061] In yet another embodiment of the present invention, at least a portion of the Rh contained in the upper second zone is supported on inorganic oxide particles that are substantially free of Ce element, and the upper second zone further contains inorganic oxide particles containing Ce element, which may not support Rh.

[0062] The binder in the upper second zone may be, for example, a boehmite binder, an alumina sol, a silica sol, or the like.

[0063] The length of the upper second zone may be 5% or more, 7% or more, 10% or more, 12% or more, or 15% or more of the length of the upper layer in order to ensure sufficiently high cold NOx purification capacity, and may be 30% or less, 28% or less, 25% or less, 23% or less, or 20% or less of the length of the upper layer in order to maintain the lengths of the upper first zone, which contributes to cold HC purification, and the upper third zone, which contributes to the purification of NOx that cannot be completely purified in the upper second zone.

[0064] - Upper Third Zone - The upper third zone mainly contributes to the purification of NOx, and is particularly effective in purifying cold NOx that could not be completely purified in the upper second zone.

[0065] To achieve this purpose, the upper third zone contains Rh. The upper third zone may contain inorganic oxide particles, a binder, and the like in addition to Rh.

[0066] The Rh concentration in the upper third zone, expressed as the metal-equivalent Rh mass per unit volume of the substrate, may be 0.05 g / L or more, 0.07 g / L or more, 0.10 g / L or more, 0.11 g / L or more, or 0.13 g / L or more, and may be 0.50 g / L or less, 0.40 g / L or less, 0.30 g / L or less, 0.20 g / L or less, less than 0.20 g / L, or 0.15 g / L or less. If the Rh concentration is within this range, the NOx purification ability can be further improved without excessively increasing the amount of Rh used.

[0067] The Rh concentration in the upper third zone may be lower than the Rh concentration in the upper second zone. In one embodiment of the present invention, the Rh concentration in the upper second zone is 0.20 g / L or more and 0.50 g / L or less, and the Rh concentration in the upper third zone is 0.05 g / L or more and less than 0.20 g / L.

[0068] The upper third zone may or may not contain catalytic precious metals other than Rh. Examples of catalytic precious metals other than Rh include Pt and Pd. The upper third zone may be substantially free of catalytic precious metals other than Rh. The amount of catalytic precious metals other than Rh in the upper third zone may be 5 mass% or less, 3 mass% or less, 1 mass% or less, 0.5 mass% or less, 0.3 mass% or less, or 0.1 mass% or less, relative to the mass of all catalytic precious metals in the upper third zone. Alternatively, the upper third zone may be free of catalytic precious metals other than Rh.

[0069] The upper third zone may contain inorganic oxide particles. The inorganic oxide particles in the upper third zone may be appropriately selected from the inorganic oxide particles exemplified above for the upper first zone.

[0070] The upper third zone may contain particles of one or more inorganic oxides selected from ceria, a composite oxide containing Ce, alumina, and a composite oxide containing Al (excluding those containing Ce). Here, examples of the composite oxide containing Ce and the composite oxide containing Al are the same as those in the upper second zone.

[0071] The upper third zone preferably contains inorganic oxide particles selected from ceria and a composite oxide containing Ce. The Ce concentration in the upper third zone may be 5.0 g / L or more, 6.0 g / L or more, 7.0 g / L or more, or 8.0 g / L or more, and may be 15.0 g / L or less, 14.0 g / L or less, 13.0 g / L or less, 12.0 g / L or less, 11.0 g / L or less, or 10.0 g / L or less, in terms of the ceria-equivalent mass per unit volume of the substrate.

[0072] The elemental Ce concentration in the upper third zone may be higher than the elemental Ce concentration in the upper second zone. In one embodiment of the present invention, the elemental Ce concentration in terms of ceria in the upper third zone is 5.0 g / L or more and 15.0 g / L or less, the elemental Ce concentration in terms of ceria in the upper second zone is 7.0 g / L or less, and the elemental Ce concentration in the upper third zone is higher than the elemental Ce concentration in the upper second zone.

[0073] The particle size of the inorganic oxide particles in the upper third zone may be, for example, 3 μm or more and 8 μm or less.

[0074] The amount of inorganic oxide particles in the upper third zone may be, for example, 50 g / L or more, 60 g / L or more, 70 g / L or more, or 80 g / L or more, in terms of the mass of inorganic oxide particles per unit volume of the substrate, and may be, for example, 200 g / L or less, 150 g / L or less, 120 g / L or less, or 100 g / L or less.

[0075] --Support for Rh in the Upper Third Zone-- The Rh in the upper third zone may be in the form of particles, and may be supported on inorganic oxide particles as Rh particles. The particle diameter of the Rh particles supported on the inorganic oxide particles may be, for example, 1 nm or more and 15 nm or less.

[0076] In one embodiment of the present invention, at least a portion of the Rh in the upper third zone is supported on inorganic oxide particles containing element Ce.

[0077] In another embodiment of the present invention, at least a portion of the Rh in the upper third zone is supported on inorganic oxide particles containing element Ce, and the upper second zone further contains inorganic oxide particles substantially free of element Ce, which may not support Rh.

[0078] The binder in the upper third zone may be, for example, a boehmite binder, an alumina sol, a silica sol, or the like.

[0079] The length of the upper third zone may be 20% or more, 30% or more, 35% or more, 40% or more, or 45% or more of the length of the upper layer to ensure sufficiently high NOx purification capacity, and may be 90% or less, 80% or less, 70% or less, or 60% or less of the length of the upper layer to maintain the lengths of the upper first zone, which contributes to cold HC purification, and the upper second zone, which contributes to cold NOx purification.

[0080] (Lower Layer) The catalyst coating layer of the exhaust gas purification catalyst device of the present invention may be a single-layer structure having only the top layer described above, or may be a two-layer laminate structure having a lower layer between the substrate and the top layer.

[0081] The lower layer of the catalyst coating layer may have, for example, from the upstream side of the exhaust gas flow, a lower layer first zone containing Rh, and a lower layer second zone containing one or two elements selected from Pd and Pt, in this order.

[0082] The length of the underlayer may typically be the same as the length of the substrate.

[0083] - Lower first zone - The lower first zone contains Rh and contributes to the purification of HC and NOx in the cold region and during warm-up. Rh has high catalytic activity in the cold region, and the temperature of the catalyst coating layer rises from the upstream side of the exhaust gas flow during warm-up. Therefore, the lower first zone containing Rh significantly contributes to the purification of HC and NOx in the cold region and during warm-up.

[0084] The composition of the lower first zone may be appropriately selected from the ranges described above for the composition of the upper second zone, or may be the same as the composition of the upper second zone.

[0085] The length of the lower first zone may be 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more of the length of the lower layer to ensure a sufficiently high HC and NOx purification effect, and may be 60% or less, 50% or less, 45% or less, 40% or less, or 30% or less of the length of the lower layer to maintain the length of the lower second zone that contributes to sweeping HC.

[0086] - Lower Second Zone - The lower second zone contains one or two elements selected from Pt and Pd. Due to the high oxidation activity of the one or two elements selected from Pt and Pd, the lower second zone contributes to purifying (sweeping) HC that could not be completely purified by the upper first zone and the lower first zone under high load.

[0087] To achieve this purpose, the first lower layer zone contains one or two selected from Pd and Pt. In addition to Pd and Pt, the first lower layer zone may contain inorganic oxide particles, a binder, etc.

[0088] The concentration of one or two elements selected from Pd and Pt in the second lower-layer zone may be 0.1 g / L or more, 0.3 g / L or more, 0.5 g / L or more, 0.6 g / L or more, or 0.8 g / L or more, and may be 3.0 g / L or less, 2.5 g / L or less, 2.0 g / L or less, 1.8 g / L or less, 1.5 g / L or less, or 1.5 g / L or less, in terms of the total mass of Pd and Pt calculated as metal per unit volume of the substrate. A concentration within this range ensures good HC purification ability without excessively increasing the amounts of Pd and Pt used.

[0089] The lower second zone may or may not contain catalytic precious metals other than Pd and Pt. Examples of catalytic precious metals other than Pd and Pt include rhodium (Rh). The lower second zone may be substantially free of catalytic precious metals other than Pd and Pt. The amount of catalytic precious metals other than Pd and Pt in the lower second zone may be 5 mass% or less, 3 mass% or less, 1 mass% or less, 0.5 mass% or less, 0.3 mass% or less, or 0.1 mass% or less, relative to the mass of all catalytic precious metals in the upper first zone. Alternatively, the upper first zone may be completely free of catalytic precious metals other than Pd and Pt.

[0090] The second lower zone may contain inorganic oxide particles. The inorganic oxide particles in the second lower zone may be appropriately selected from the inorganic oxide particles exemplified above for the first upper zone.

[0091] The lower second zone may contain particles of one or more inorganic oxides selected from alumina and composite oxides containing Al (except for those containing Ce), where the Al-containing composite oxides may be the same as those in the upper first zone.

[0092] The second lower zone may contain particles of an inorganic oxide selected from ceria and a composite oxide containing Ce. The Ce concentration in the second lower zone may be 10 g / L or more, 20 g / L or more, 30 g / L or more, or 40 g / L or more, and 100 g / L or less, 80 g / L or less, 70 g / L or less, or 60 g / L or less, in terms of the ceria-equivalent mass per unit volume of the substrate.

[0093] The particle size of the inorganic oxide particles in the lower second zone may be, for example, 3 μm or more and 8 μm or less.

[0094] The amount of inorganic oxide particles in the lower second zone may be, for example, 10 g / L or more, 20 g / L or more, or 30 g / L or more, in terms of the mass of inorganic oxide particles per unit volume of the substrate, and may be, for example, 80 g / L or less, 70 g / L or less, 60 g / L or less, or 50 g / L or less.

[0095] The Pd and Pt in the lower second zone may be in the form of particles, and may be supported on inorganic oxide particles as Pd particles and Pt particles, respectively. The particle diameters of the Pd particles and Pt particles supported on the inorganic oxide particles may be, for example, 1 nm or more and 15 nm or less.

[0096] The binder in the lower second zone may be, for example, a boehmite binder, an alumina sol, a silica sol, or the like.

[0097] The length of the lower second zone may be 40% or more, 45% or more, 50% or more, 55% or more, or 60% or more of the length of the lower layer to ensure sufficiently high HC purification capacity, and may be 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, or 60% or less of the length of the lower layer to maintain the length of the lower first zone that contributes to the purification of HC and NOx, particularly in the cold region.

[0098] (Third Layer) The catalyst coating layer of the exhaust gas purification catalyst device of the present invention may or may not have any other layers in addition to the above-mentioned top layer and bottom layer. Examples of the layers in addition to the top layer and bottom layer include layers for HC, NH ３ and a layer having a function of purifying HC, NOx, etc.

[0099] In some embodiments, the catalyst coating has no layers other than the top and bottom layers.

[0100] <Relative Component Concentration Ratios Between Layers> —Rh Concentration— The Rh concentration of the lower first zone may be substantially the same as the Rh concentration of the upper second zone. “The Rh concentration of the lower first zone is substantially the same as the Rh concentration of the upper second zone” means that the Rh concentration of the lower first zone is 0.90 times or more, 0.95 times or more, or 0.98 times or more, and 1.10 times or less, 1.05 times or less, or 1.02 times or less, of the Rh concentration of the upper second zone.

[0101] The Rh concentration (Rh mass per unit volume of the substrate) in the upper second zone may be higher than the Rh concentration (Rh mass per unit volume of the substrate) in the upper third zone. The Rh concentration in the upper second zone may be 1.5 times or more, 2.0 times or more, 2.5 times or more, or 3.0 times or more, and may be 4.0 times or less, 3.5 times or less, 3.0 times or less, or 2.5 times or less, of the Rh concentration in the upper third zone.

[0102] The amount of Rh contained in the exhaust gas purification catalyst device of the present invention may be, in terms of the total mass of Rh per unit volume of the substrate, 0.1 g / L or more, 0.2 g / L or more, 0.3 g / L or more, or 0.4 g / L or more, and may be 1.0 g / L or less, 0.8 g / L or less, 0.6 g / L or less, or 0.5 g / L or less.

[0103] - Ce Concentration - The Ce element concentration in the lower first zone may be substantially the same as the Ce element concentration in the upper second zone. "The Ce element concentration in the lower first zone is substantially the same as the Ce element concentration in the upper second zone" means that the Ce element concentration in the lower first zone is 0.90 times or more, 0.95 times or more, or 0.98 times or more, and 1.10 times or less, 1.05 times or less, or 1.02 times or less, of the Ce element concentration in the upper second zone.

[0104] The Ce element concentration in the upper second zone may be the same as or lower than the Ce element concentration in the upper third zone. By making the Ce element concentration in the upper second zone lower than the Ce element concentration in the upper third zone, the catalytic activity of Rh on the upstream side of the exhaust gas flow in the cold region can be increased, which is advantageous in terms of purifying HC and NOx in the cold region.

[0105] The Ce element concentration (ceria-equivalent mass per unit volume of the substrate) in the upper second zone may be 1.0 times or less, 0.8 times or less, 0.6 times or less, 0.5 times or less, 0.4 times or less, or 0.3 times or less of the Ce element concentration (ceria-equivalent mass per unit volume of the substrate) in the upper third zone.

[0106] In some embodiments of the present invention, the upper second zone does not contain elemental Ce, and the upper third zone contains elemental Ce.

[0107] The Ce element concentration in the lower second zone may be higher than the Ce element concentration in the upper third zone, which has the advantage of being able to maintain NOx purification performance at high loads while exhibiting effective OSC performance.

[0108] The Ce element concentration (ceria-equivalent mass per unit volume of the substrate) in the lower second zone may be 2.0 times or more, 3.0 times or more, 4.0 times or more, 5.0 times or more, or 6.0 times or more, and may be 12.0 times or less, 10.0 times or less, 8.0 times or less, or 7.0 times or less, of the Ce element concentration (ceria-equivalent mass per unit volume of the substrate) in the upper third zone.

[0109] Furthermore, as described above, the upper first zone may be substantially free of Ce. That is, the Ce element concentrations in each zone may be in the order of (upper first zone) < (lower first zone ≈ upper second zone) < (upper third zone) < (lower second zone). This concentration order means that the Ce element concentration upstream of the exhaust gas flow is lower than the Ce element concentration downstream. Therefore, in the exhaust gas purification catalytic device of the present invention, the low-temperature purification activity upstream of the catalyst coating layer is relatively high.

[0110] <<Method for Manufacturing the Exhaust Gas Purification Catalyst Device>> The exhaust gas purification catalyst device of the present invention may be manufactured by any method as long as it has the above-described configuration.

[0111] As a non-limiting example, we will explain one example of a method for manufacturing an exhaust gas purification catalyst device in which the catalyst coating layer is a two-layer laminate consisting of a top layer and a bottom layer, and the composition of the upper layer second zone and the composition of the lower layer first zone are the same.

[0112] Such an exhaust gas purification catalytic device may be manufactured, for example, by sequentially forming each zone in a predetermined length on a substrate. The zones may be formed in any of the following order, for example: lower second zone, upper third zone, lower first zone and upper second zone, and upper first zone; lower second zone, lower first zone and upper second zone, upper third zone, and upper first zone; or lower second zone, lower first zone and upper second zone, upper first zone, and upper third zone.

[0113] In the above, the lower first zone and the upper second zone may be formed simultaneously.

[0114] Each zone may be formed by applying a coating solution prepared according to the desired zone composition, drying (solvent removal) as necessary, and then baking the applied coating. Baking may be performed for each zone formed, or may be performed all at once after all zones have been coated.

[0115] The coating liquid may be a liquid composition containing the components to be contained in the desired zone or their precursors, and a solvent. The coating liquid may contain, for example, the following components: one or more inorganic oxide particles, a precious metal precursor, optional components used as needed, and a solvent (first coating liquid); or inorganic oxide particles carrying precious metal particles, other inorganic oxide particles as needed, optional components used as needed, and a solvent (second coating liquid).

[0116] When the first coating liquid contains two or more inorganic oxide particles and a precious metal precursor, it is believed that the precious metal particles will be supported on all of the two or more inorganic oxide particles. However, when the coating liquid is prepared by contacting the first inorganic oxide particles on which the precious metal particles are to be supported with the precious metal precursor in a solvent and then adding the second inorganic oxide particles, it is believed that most of the precious metal particles will be supported on the first inorganic oxide particles.

[0117] The inorganic oxide particles carrying the noble metal particles in the second coating liquid may be produced according to a known method.

[0118] The coating of the coating liquid, drying, and baking may each be carried out according to a known method.

[0119] <<Method for Purifying Exhaust Gas>> According to another aspect of the present invention, a method for purifying exhaust gas is provided.

[0120] The method for purifying exhaust gas of the present invention comprises arranging the exhaust gas purification catalyst device of the present invention in the exhaust system of an internal combustion engine with the upper layer first zone facing upstream in the exhaust gas flow, and purifying exhaust gas emitted from the internal combustion engine.

[0121] The internal combustion engine may be, for example, a gasoline engine, a diesel engine, a hybrid engine, or the like of an automobile.

[0122] Preparation of Coating Liquid for Forming Upper Layer First Zone Palladium nitrate as a PGM source in an amount equivalent to 1.745 g / L in terms of metal Pd mass, alumina as inorganic oxide particles in an amount equivalent to 80 g / L, and boehmite binder in an amount equivalent to 4 g / L were added to pure water and stirred thoroughly to prepare a coating liquid for forming the upper layer first zone.

[0123] Preparation of Coating Liquid for Forming Lower Second Zone Platinum nitrate as a PGM source in an amount equivalent to 1.085 g / L of metal Pt mass, alumina as inorganic oxide particles in an amount equivalent to 40 g / L, and boehmite binder in an amount equivalent to 5.0 g / L were added to pure water and stirred thoroughly to prepare a coating liquid for forming the lower second zone.

[0124] Preparation of Coating Solution (1) for Forming Lower Layer First Zone and Upper Layer Second Zone: Rhodium nitrate in an amount equivalent to 0.279 g / L of metallic Rh mass as a PGM source, and Al—Zr composite oxide (Al ２ O ３ : ZrO ２ Then, 35.0 g / L of alumina and 10.0 g / L of Al—Ce—Zr composite oxide (Al ２ O ３ : CeO ２ : ZrO ２ = 30:20:42 (mass ratio), ACZ) were added in this order, and then a boehmite binder in an amount equivalent to 3.0 g / L was added as a binder, followed by thorough stirring to prepare a coating solution (1) for forming the lower first zone and the upper second zone.

[0125] <Preparation of Coating Liquids (2) to (5) for Forming Lower Layer First Zone and Upper Layer Second Zone> The amount of rhodium nitrate and the amount of ACZ were changed to adjust the amount of metallic Rh and CeO in the coating liquid. ２ Coating solutions (2) to (5) for forming the lower first zone and the upper second zone were prepared in the same manner as in "Preparation of Coating Solution (1) for forming the lower first zone and the upper second zone" above, except that the amounts were adjusted to the values ​​shown in Table 1.

[0126] <<Preparation of Coating Liquid (6) for Forming Lower Layer First Zone and Upper Layer Second Zone>> Coating liquid (6) for forming lower layer first zone and upper layer second zone was prepared in the same manner as in the above “Preparation of Coating Liquid (1) for Forming Lower Layer First Zone and Upper Layer Second Zone” except that ACZ was not used.

[0127] Preparation of Coating Solution (7) for Forming the Lower First Zone and the Upper Second Zone: Rhodium nitrate (as a PGM source, equivalent to 0.279 g / L of metallic Rh mass) and ACZ (as an equivalent to 10.0 g / L) were added to pure water and stirred at room temperature for 30 minutes or more. Next, 35.0 g / L of alumina and 3.0 g / L of boehmite binder were added and stirred thoroughly to prepare Coating Solution (7) for forming the Lower First Zone and the Upper Second Zone.

[0128]

[0129] <<Preparation of Coating Liquid for Forming Upper Third Zone>> A coating liquid for forming an upper third zone was prepared in the same manner as in the above-mentioned "Preparation of Coating Liquid (7) for Forming Lower First Zone and Upper Second Zone", except that the amount of rhodium nitrate charged was set to an amount equivalent to 0.139 g / L in terms of metallic Rh mass, the amount of ACZ charged was set to an amount equivalent to 45.0 g / L, and the amount of alumina charged was set to an amount equivalent to 35.0 g / L.

[0130] Preparation of Coating Liquid for Forming Lower Layer First Zone for Comparative Example 1 The coating liquid for forming the lower layer first zone for Comparative Example 1 was prepared in the same manner as in the above "Preparation of Coating Liquid for Forming Lower Layer First Zone and Upper Layer Second Zone (1)", except that the amount of rhodium nitrate charged was set to an amount equivalent to 0.139 g / L in terms of metallic Rh mass.

[0131] Preparation of Coating Liquid for Forming Upper Second Zone for Comparative Example 1 The coating liquid for forming the upper second zone for Comparative Example 1 was prepared in the same manner as in the above "Preparation of Coating Liquid (7) for Forming Lower First Zone and Upper Second Zone" except that the amount of rhodium nitrate charged was set to an amount equivalent to 0.100 g / L in terms of metallic Rh mass, and the amount of ACZ charged was set to an amount equivalent to 45.0 g / L.

[0132] Each of the above coating solutions was prepared each time in an amount that would give the component concentrations in the coated area the values ​​described above when the entire amount was applied to a predetermined coating length, taking into consideration the coating width, and the entire amount was used.

[0133] Example 1 The substrate had a diameter of 127 mm, a length of 102 mm, an apparent volume of 1.29 L, and 750 cells / cm. ２ A straight-flow type substrate made of cordierite with a wall thickness of 2.5 μm was used.

[0134] The coating liquid for forming the lower second zone was coated on the substrate from the downstream side of the exhaust gas flow to a region covering 67% of the substrate length, and the substrate was baked for 1 hour at 500°C to form the lower second zone on the substrate. Next, the coating liquid for forming the upper third zone was coated on the substrate on which the lower second zone had been formed, from the downstream side to a region covering 50% of the substrate length, and the substrate was baked for 1 hour at 500°C to form the upper third zone.

[0135] Furthermore, the coating liquid (1) for forming the lower first zone and the upper second zone was coated on a region of 50% of the length of the substrate from the upstream side of the substrate on which the lower second zone and the upper third zone had been formed, and the substrate was baked for 1 hour at 500° C. The length of the formed lower first zone was 33% of the total length of the substrate, and the length of the formed upper second zone was 17% of the total length of the substrate.

[0136] Finally, the upper layer first zone-forming coating liquid was applied to a region of 33% of the length of the substrate from the upstream side of the substrate on which the lower layer first zone, lower layer second zone, upper layer second zone, and upper layer third zone had been formed, and the substrate was baked at 500°C for 1 hour to form the upper layer first zone, thereby producing the exhaust gas purification catalyst device of Example 1. Figure 1 shows an outline of the configuration of the exhaust gas purification catalyst device of Example 1.

[0137] Examples 2 to 7 Exhaust gas purification catalyst devices of Examples 2 to 7 were produced in the same manner as in Example 1, except that the lower first zone and upper second zone forming coating liquids with the numbers shown in the "Coating Liquid Type" column in Table 2 were used instead of the lower first zone and upper second zone forming coating liquid (1). Figures 2 to 7 show outlines of the configurations of these exhaust gas purification catalyst devices.

[0138] Comparative Example 1 As the substrate, a straight flow type substrate made of cordierite of the same kind as that used in Example 1 was used.

[0139] The coating liquid for forming the second lower layer zone was coated on the substrate from the downstream side of the exhaust gas flow to a region covering 67% of the substrate length, and then baked for 1 hour at 500° C. to form the second lower layer zone on the substrate. Next, the coating liquid for forming the first lower layer zone for Comparative Example 1 was prepared and coated on the substrate on which the second lower layer zone had been formed to a region covering 33% of the substrate length from the upstream side, and then baked for 1 hour at 500° C. to form the first lower layer zone.

[0140] Furthermore, the upper layer second zone forming coating liquid for Comparative Example 1 was coated on a region of the substrate on which the lower layer first zone and the lower layer second zone were formed, covering 67% of the substrate length from the upstream side, and the substrate was baked at 500°C for 1 hour to form the upper layer second zone. Finally, the upper layer first zone forming coating liquid was coated on a region of the substrate on which the lower layer first zone, the lower layer second zone, and the upper layer second zone were formed, covering 33% of the substrate length from the upstream side, and the substrate was baked at 500°C for 1 hour to form the upper layer first zone, thereby producing the exhaust gas purification catalyst device of Comparative Example 1. Figure 8 shows a schematic configuration of the exhaust gas purification catalyst device of Comparative Example 1.

[0141] <Evaluation of Exhaust Gas Purification Catalyst Devices> Each of the exhaust gas purification catalyst devices manufactured above was subjected to durability testing by the following method, and then its exhaust gas purification ability was evaluated.

[0142] (1) Durability The exhaust gas purification catalyst devices obtained in the above Examples and Comparative Examples were installed in the exhaust system of a 2.7L TC (turbocharged) gasoline engine so that the upper first zone and the lower first zone were located upstream of the exhaust gas flow, and a durability test equivalent to driving 150,000 miles was conducted by repeatedly changing the exhaust gas into a stoichiometric atmosphere and a lean atmosphere at predetermined intervals.

[0143] (2) Evaluation of exhaust gas purification performance After the durability test, each exhaust gas purification catalyst device was installed in the exhaust system of a turbocharged (TC) vehicle with a 2.7L gasoline engine, with the upper first zone and the lower first zone positioned upstream of the exhaust gas flow, and the exhaust gas purification performance was evaluated using "FTP75." The evaluation results are shown in Tables 2 to 4.

[0144]

[0145]

[0146]

[0147] The inorganic oxide particles in Tables 2 to 4 are listed in the order of addition when preparing the coating liquid. The results shown in Tables 2 and 3 verify that the exhaust gas purification catalyst devices of Examples 1 to 7 according to the present invention suppress NOx emissions compared to the exhaust gas purification catalyst device of Comparative Example 1, which belongs to the prior art.

[0148] In particular, in the exhaust gas purification catalyst devices of Examples 1 to 5, in which the Ce element concentration in the upper second zone is lower than the Ce element concentration in the upper third zone, it was verified that NOx emissions were suppressed in Bag 1, which corresponds to a cold start, Bag 2, which corresponds to a transient period, and Bag 3, which corresponds to high-speed driving.

Claims

1. An exhaust gas purification catalyst device having a substrate and a catalyst coating layer on the substrate, wherein the catalyst coating layer is a single layer or a laminate consisting of two or more layers, and the uppermost layer of the catalyst coating layer has, from the upstream side of the exhaust gas flow, an upper layer first zone containing Pd, an upper layer second zone containing Rh, and an upper layer third zone containing Rh, in that order, and the Rh concentration in the upper layer second zone is higher than the Rh concentration in the upper layer third zone.

2. The exhaust gas purification catalyst device according to claim 1, wherein the Rh concentration in metal equivalent in the second upper zone is 0.20 g / L or more and 0.50 g / L or less, and the Rh concentration in metal equivalent in the third upper zone is 0.05 g / L or more and less than 0.20 g / L.

3. The exhaust gas purification catalyst device according to claim 1, wherein the Rh concentration in the second upper zone is 1.5 to 4.0 times the Rh concentration in the third upper zone.

4. The exhaust gas purification catalyst device according to claim 1, wherein the Ce element concentration in the upper second zone is lower than the Ce element concentration in the upper third zone.

5. The exhaust gas purification catalyst device according to claim 1, wherein the Ce element concentration in terms of ceria in the upper second zone is 7.0 g / L or less, and the Ce element concentration in terms of ceria in the upper third zone is 5.0 g / L or more and 15.0 g / L or less.

6. The exhaust gas purification catalyst device according to claim 2, wherein the Ce element concentration in terms of ceria in the upper second zone is 7.0 g / L or less, and the Ce element concentration in terms of ceria in the upper third zone is 5.0 g / L or more and 15.0 g / L or less.

7. The exhaust gas purification catalyst device according to claim 3, wherein the Ce element concentration in terms of ceria in the upper second zone is 7.0 g / L or less, and the Ce element concentration in terms of ceria in the upper third zone is 5.0 g / L or more and 15.0 g / L or less.

8. An exhaust gas purification catalyst device according to any one of claims 1 to 7, wherein at least a portion of the Rh contained in the upper second zone is supported on inorganic oxide particles containing Ce element, and the Rh contained in the upper third zone is supported on inorganic oxide particles containing Ce element.

9. An exhaust gas purification catalyst device according to any one of claims 1 to 7, wherein at least a portion of the Rh contained in the upper second zone is supported on inorganic oxide particles substantially free of Ce element, and the Rh contained in the upper third zone is supported on inorganic oxide particles containing Ce element.

10. An exhaust gas purification catalyst device according to any one of claims 1 to 7, wherein at least a portion of the Rh contained in the upper second zone is supported on inorganic oxide particles substantially free of Ce element, the upper second zone further contains inorganic oxide particles containing Ce element, and the Rh contained in the upper third zone is supported on inorganic oxide particles containing Ce element.

11. An exhaust gas purification catalyst device according to any one of claims 1 to 7, wherein the catalyst coating layer is a laminate consisting of two layers, and the lower layer of the catalyst coating layer has, from the upstream side of the exhaust gas flow, a lower layer first zone containing Rh, and a lower layer second zone containing one or two types selected from Pd and Pt, in this order.

12. The exhaust gas purification catalyst device according to claim 11, wherein the Rh concentration in the upper second zone is substantially the same as the Rh concentration in the lower first zone.

13. A method for purifying exhaust gas, comprising: disposing an exhaust gas purification catalyst device according to any one of claims 1 to 7 in an exhaust system of an internal combustion engine, with the upper layer first zone facing upstream in the exhaust gas flow, and purifying exhaust gas discharged from the internal combustion engine.

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