Exhaust gas purification catalyst device

Abstract

An exhaust gas purification catalyst device has an upper layer containing first carrier particles and rhodium and a lower layer containing second carrier particles, the upper layer containing cerium oxide, the content of cerium oxide in the upper layer being 7% by mass or more and 25% by mass or less when the total mass of the first carrier particles in the upper layer is taken as 100% by mass, in the upper layer, in a range (a) of 20% or more and 50% or less of the length of the upper layer from the upstream end of the exhaust gas flow, and in a range (b) of 18 μm or less in the depth direction from the uppermost surface of the upper layer, there is a rhodium-rich portion containing 50% or more and less than 100% of all the rhodium contained in the upper layer, the rhodium content of the portion other than the rhodium-rich portion in the upper layer being 0.01 g / L or more and 0.12 g / L or less in terms of the metal equivalent mass of rhodium per unit volume of the substrate, and in the rhodium-rich portion, in a range of 50% or less of the length of the rhodium-rich portion from the upstream end of the exhaust gas flow, there is rhodium that is 50% or more of the rhodium contained in the rhodium-rich portion.

Description

[0001] This application is a divisional application of the Chinese Patent Application No. 201980014175.9, filed on January 25, 2019, entitled "Exhaust Purification Catalyst Device". TECHNICAL FIELD

[0002] The present application relates to an exhaust purification catalyst device. BACKGROUND

[0003] An exhaust purification catalyst is used to purify exhaust gas from an internal combustion engine of an automobile or the like, which contains, for example, HC, CO, NOx, and the like. Such an exhaust purification catalyst typically has a substrate and a catalyst coating layer formed on the substrate, the catalyst coating layer containing an inorganic oxide and a noble metal.

[0004] In such an exhaust purification catalyst, a technique for improving catalytic performance by providing the catalyst coating layer in a two-layer structure of a lower layer containing Pd and an upper layer containing Rh has been proposed (Patent Literature 1). In addition, a technique for improving the utilization efficiency of Pd and Rh by causing Pd contained in the lower layer and Rh contained in the upper layer to exist by being biased toward the surface layer of each layer, respectively, has been proposed (Patent Literature 2).

[0005] Further, as a method of supporting a noble metal on a substrate using a noble metal solution, Patent Literature 3 is known.

[0006] However, in the past, the catalyst coating layer in the exhaust purification catalyst device described above has been formed on a substrate that does not have exhaust purification capability, such as a honeycomb substrate made of cordierite. However, in recent years, an exhaust purification catalyst in which a noble metal is supported on a substrate composed of inorganic oxide particles has been proposed (Patent Literature 4).

[0007] Prior Art Documents

[0008] Patent Literature 1: Japanese Patent Application Laid-Open No. 7-6017

[0009] Patent Literature 2: Japanese Patent Application Laid-Open No. 2011-255378

[0010] Patent Literature 3: Japanese Patent Application Laid-Open No. 2008-302304

[0011] Patent Literature 4: Japanese Patent Application Laid-Open No. 2015-85241 SUMMARY

[0012] In the exhaust purification catalyst device known in the past, it has not been possible to sufficiently satisfy the demand for improving exhaust purification capability at the time of warming up, such as at the time of engine start.

[0013] Therefore, an object of the present application is to provide an exhaust gas purification catalyst device capable of sufficiently exerting exhaust gas purification ability even at the time of warm-up such as at the time of engine start.

[0014] The present application is described below.

[0015] <Embodiment 1>

[0016] An exhaust gas purification catalyst device has an upper layer containing first support particles and rhodium, and a lower layer containing second support particles, in the upper layer, in a range from an upstream end of an exhaust gas flow to 50% or less of an upper layer length, and in a range from a top surface of the upper layer to 18 μm or less in a depth direction, a rhodium-rich portion is provided, the rhodium-rich portion contains 50% or more and less than 100% of all rhodium contained in the upper layer.

[0017] <Embodiment 2>

[0018] The exhaust gas purification catalyst device according to <Embodiment 1>, the range of the rhodium-rich portion in the exhaust gas flow direction is a range from an upstream end of an exhaust gas flow of the upper layer to 30% or less of an upper layer length.

[0019] <Embodiment 3>

[0020] The exhaust gas purification catalyst device according to <Embodiment 2>, the range of the rhodium-rich portion in the depth direction is a range from a top surface of the upper layer to 15 μm or less in a depth direction.

[0021] <Embodiment 4>

[0022] The exhaust gas purification catalyst device according to any one of <Embodiments 1> to <3>, a content rate of cerium oxide in the upper layer is more than 5 mass% and 25 mass% or less when a total mass of the first support particles in the upper layer is taken as 100 mass%.

[0023] <Embodiment 5>

[0024] The exhaust gas purification catalyst device according to <Embodiment 4>, a content rate of cerium oxide in the upper layer is 7 mass% or more and 15 mass% or less when a total mass of the first support particles in the upper layer is taken as 100 mass%.

[0025] <Embodiment 6>

[0026] The exhaust gas purification catalyst device according to any one of <Embodiments 1> to <5>, in the rhodium-rich portion, there is rhodium of 50% or more of rhodium contained in the rhodium-rich portion in a range from an upstream end of an exhaust gas flow to 50% or less of a length of the rhodium-rich portion.

[0027] <Embodiment 7>

[0028] The exhaust gas purification catalyst device according to any one of <Form 1> to <Form 6>, wherein the lower layer and the upper layer are present on a substrate.

[0029] <Form 8>

[0030] The exhaust gas purification catalyst device according to any one of <Form 1> to <Form 6>, wherein the lower layer constitutes part or all of the substrate, and the upper layer is present on the lower layer.

[0031] <Form 9>

[0032] A method of manufacturing the exhaust gas purification catalyst device according to any one of <Form 1> to <Form 8>, comprising the steps of: supplying a coating liquid containing a rhodium precursor to an exhaust gas upstream side end portion of an exhaust gas purification catalyst device precursor having an upper layer containing first support particles and rhodium and a lower layer containing second support particles, and then sucking the coating liquid from an exhaust gas downstream side end portion of the precursor.

[0033] According to the present application, an exhaust gas purification catalyst device is provided which can exert sufficient exhaust gas purification ability even at the time of warm-up. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a schematic cross-sectional view showing a typical structure of the exhaust gas purification catalyst device of the present application. DETAILED DESCRIPTION

[0035] <Exhaust gas purification catalyst device>

[0036] Figure 1 A typical structure of the exhaust gas purification catalyst device of the present application is shown.

[0037] Figure 1 The exhaust gas purification catalyst device (100) of the present application has:

[0038] an upper layer (10) containing first support particles and rhodium, and a lower layer (20) containing second support particles,

[0039] In the upper layer (10), in a range (a) of up to 50% of the upper layer length from the upstream side end portion of the exhaust gas flow, and in a range (b) of up to 18 μm in the depth direction from the uppermost surface of the upper layer, there is a rhodium-rich portion (11) containing rhodium in an amount of 50% or more and less than 100% of the total rhodium contained in the upper layer (10).

[0040] Figure 1 The upper layer (10) of the exhaust gas purification catalyst device (100) of the present application is composed of a rhodium-rich portion (11) in the vicinity of the surface on the upstream side of the exhaust gas flow and other portions (12) of the upper layer.

[0041] The rhodium-rich portion (11) contains 50% or more and less than 100% of the rhodium contained in the upper layer (10).

[0042] By concentrating the rhodium contained in the upper layer on the upstream side of the exhaust gas flow, even when the temperature of the exhaust gas purification device is low at the time of warm-up or the like, it is possible to efficiently purify NOx using HC and CO on the rhodium-rich portion on the upstream side of the flow. Furthermore, by the reaction heat generated in the purification reaction in the rhodium-rich portion, it is also possible to promote the purification of the exhaust gas on the downstream side.

[0043] In addition, by concentrating the rhodium near the surface of the upper layer, it is possible to increase the opportunities for the exhaust gas to contact the rhodium, so it is possible to achieve efficient exhaust gas purification.

[0044] Hereinafter, the structure of the exhaust gas purification catalyst device will be described with reference to a preferred embodiment of the exhaust gas purification catalyst device of the present application (hereinafter also referred to as "the present embodiment").

[0045] <rhodium-rich portion>

[0046] The rhodium-rich portion of the exhaust gas purification catalyst device of the present embodiment is disposed in the upper layer containing the first carrier particles and rhodium, in a range of 50% or less of the length of the upper layer from the upstream end of the exhaust gas flow, and in a range of 18 μm or less in the depth direction from the surface of the upper layer.

[0047] The range of the rhodium-rich portion in the direction of the exhaust gas flow is in a range of 50% or less of the length of the upper layer from the upstream end of the exhaust gas flow. When the rhodium-rich portion is disposed in a range of 50% or less of the length of the upper layer from the upstream end of the exhaust gas flow, the degree of concentration of the rhodium becomes high enough, and thus, even at the time of warm-up, it is possible to generate reaction heat that can sufficiently heat the downstream side of the catalyst coating layer. The range of the rhodium-rich portion in the direction of the exhaust gas flow can be in a range of 45% or less, 40% or less, 35% or less, 30% or less, or 25% or less of the length of the upper layer from the upstream end of the exhaust gas flow.

[0048] On the other hand, in order to efficiently purify the exhaust gas, it is desirable that the rhodium-rich portion in which the rhodium is concentrated has a significant length. From this viewpoint, the range of the rhodium-rich portion in the direction of the exhaust gas flow can be disposed in a range of 5% or more, 10% or more, 15% or more, or 20% or more of the length of the upper layer from the upstream end of the exhaust gas flow.

[0049] The range of the catalyst coating layer of the rhodium-rich portion in the depth direction is from the uppermost surface of the upper layer to a range of 18 μm or less in the depth direction. Here, the "uppermost surface of the upper layer" refers to the surface of the upper layer on the side that contacts the exhaust gas stream, that is, the surface on the opposite side from the surface that contacts the lower layer. If the rhodium-rich portion is disposed in a range of 18 μm or less in the depth direction from the uppermost surface of the upper layer, even when the space velocity (SV) of the exhaust gas is large, the exhaust gas is able to diffuse to the entire depth direction of the rhodium-rich portion, and the rhodium is able to be effectively utilized. The range of the catalyst coating layer of the rhodium-rich portion in the depth direction can be from the uppermost surface of the upper layer to a range of 17 μm, 16 μm, 15 μm, 14 μm, or 13 μm or less in the depth direction.

[0050] The content of rhodium in the rhodium-rich portion is in a range of 50% or more and less than 100% of the total rhodium contained in the upper layer. By having the content of rhodium in the rhodium-rich portion be 50% or more of the total rhodium in the upper layer, the effect of concentrating rhodium in the rhodium-rich portion is sufficiently exhibited. On the other hand, by keeping the content of rhodium in the rhodium-rich portion less than 100%, a small amount of rhodium is also disposed in other portions of the upper layer, and thus oxygen release from the oxygen releasing material (OSC material, such as ceria) that is arbitrarily contained in the upper layer is promoted. Therefore, for example, at the time of rich conditions, the atmosphere within the catalyst coating layer easily remains near the stoichiometric air-fuel ratio, and the exhaust gas purification ability is maintained at a high level. The content of rhodium in other portions of the upper layer other than the rhodium-rich portion is described later.

[0051] As described above, in the exhaust gas purification catalyst device of the present embodiment, by concentrating rhodium on the upstream side of the exhaust gas stream in the upper layer, the catalytic efficiency at the time of warm-up is improved. By pursuing this aim, a concentration gradient is provided in the rhodium-rich portion, and relatively more rhodium is concentrated on the upstream side, and thus the catalytic efficiency at the time of warm-up is further improved.

[0052] From such a viewpoint, an amount of rhodium that is 50% or more of the rhodium contained in the rhodium-rich portion can be disposed in a range of 50% or less of the length of the rhodium-rich portion from the upstream end of the exhaust gas stream. The amount of rhodium contained in this range can be 51% or more, 53% or more, 55% or more, 57% or more, 58% or more, 60% or more, or 65% or more of the rhodium contained in the rhodium-rich portion.

[0053] On the other hand, in order to effectively purify the exhaust gas, it is desirable for the rhodium-rich portion to contain an effective amount of rhodium throughout its entire length. From this viewpoint, the proportion of rhodium disposed in a range of 50% or less of the length of the rhodium-rich portion from the upstream end of the exhaust gas stream can be 80% or less, 75% or less, 70% or less, 65% or less, or 60% or less of the rhodium contained in the rhodium-rich portion.

[0054] The rhodium-rich portion constitutes a part of the upper layer. Therefore, except for the rhodium content in the structure of the rhodium-rich portion, the following description for the upper layer is directly applied. For example, the rhodium contained in the rhodium-rich portion can be supported on the first support particles contained in the upper layer.

[0055] <Upper layer>

[0056] The upper layer of the exhaust purification catalyst device of the present embodiment contains the first support particles and rhodium.

[0057] (First support particles)

[0058] The first support particles can be particles of an inorganic oxide.

[0059] The inorganic oxide constituting the first support particles can be, for example, an oxide of one or more selected from the group consisting of aluminum, silicon, zirconium, titanium, rare earth elements, and the like. As the inorganic oxide, one or more selected from the group consisting of alumina, silica, silica alumina, zeolite, titania, zirconia, ceria, and oxides of rare earth elements other than ceria is preferable. As the inorganic oxide, it is particularly preferable to contain alumina and zirconia, or to contain alumina and ceria-zirconia composite oxide (CZ). The case where alumina and zirconia, or alumina and CZ, and oxides of rare earth elements other than ceria are contained is also a preferable mode of the present embodiment.

[0060] In the upper layer of the exhaust purification catalyst device of the present embodiment, the ceria content can be in the range of 25% by mass or less when the total mass of the first support particles in the upper layer is taken as 100% by mass. The ceria content in the upper layer is preferably limited for the following reasons.

[0061] The catalyst coating layer contains ceria having an oxygen storage capacity, and thus can maintain a state near the stoichiometric air-fuel ratio inside the catalyst coating layer even under rich or lean conditions. On the other hand, for example, at the time of engine warm-up, it is necessary to rapidly reduce rhodium to an active state. In this case, if the amount of ceria in the catalyst coating layer is too large, the amount of oxygen released from the ceria becomes too large, delaying the reduction of rhodium, and thus hindering early activation of the exhaust purification catalyst device. To avoid this, the ceria content of the upper layer is preferably limited to a predetermined value or less.

[0062] From the above viewpoint, the content of cerium oxide in the upper layer can be 25 mass% or less, 23 mass% or less, 20 mass% or less, 18 mass% or less, or 15 mass% or less, when the total mass of the first support particles in the upper layer is set to 100 mass%. On the other hand, from the viewpoint of maintaining the state in which the catalyst coated layer is maintained at around the stoichiometric air-fuel ratio, the upper layer can contain cerium oxide in a range in which the rapid reduction of rhodium at the time of engine start and the like is not delayed. Therefore, the content of cerium oxide in the upper layer can be an amount exceeding 5 mass%, for example, 6 mass% or more, 7 mass% or more, 8 mass% or more, or 10 mass% or more, when the total mass of the first support particles in the upper layer is set to 100 mass%. It is also a preferable mode of the present embodiment that the content of cerium oxide in the upper layer is in a range exceeding 5 mass% and being 25 mass% or less, or in a range of 7 mass% or more and 15 mass% or less, when the total mass of the first support particles in the upper layer is set to 100 mass%.

[0063] Here, the content of cerium oxide when cerium atoms are part of a complex oxide (e.g., CZ) refers to the amount of composition converted into CeO2.

[0064] The first support particles can be primary particles, or secondary particles in which primary particles are aggregated.

[0065] The average particle diameter of the first support particles can be, for example, 1 μm or more, 3 μm or more, 5 μm or more, or 10 μm or more, and can be, for example, 50 μm or less, 40 μm or less, 30 μm or less, or 20 μm or less.

[0066] (Rhodium)

[0067] The upper layer contains rhodium. This rhodium can be supported on the first support particles in the upper layer.

[0068] The content of rhodium in the upper layer, expressed in terms of the metal conversion mass of rhodium per unit volume of the substrate, can be, for example, 0.01 g / L or more, 0.05 g / L or more, 0.10 g / L or more, or 0.15 g / L or more, and can be, for example, 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.

[0069] Rhodium can be contained in the rhodium-rich portion in the upper layer and the other portions of the upper layer.

[0070] As described above, if all rhodium in the upper layer is disposed in the rhodium-rich portion, and the other part of the upper layer is completely free from rhodium, oxygen release from the OSC material optionally contained in the upper layer is difficult to occur, it is difficult to maintain the atmosphere in the catalyst coating layer at around the stoichiometric air-fuel ratio, and sometimes the exhaust gas purification ability is impaired. In order to avoid such a situation, the part of the upper layer other than the rhodium-rich portion can contain, for example, 0.01 g / L or more, 0.02 g / L or more, 0.03 g / L or more, 0.04 g / L or more, or 0.05 g / L or more of rhodium in terms of the mass of the metal per unit volume of the substrate.

[0071] On the other hand, in order to embody the effect of the present application in which rhodium is concentrated in the rhodium-rich portion to improve the exhaust gas purification ability at the time of warm-up, the rhodium content of the part of the upper layer other than the rhodium-rich portion can be, for example, 0.12 g / L or less, 0.10 g / L or less, or 0.08 g / L or less in terms of the mass of the metal per unit volume of the substrate.

[0072] (Optional components of the upper layer)

[0073] The upper layer can contain the first support particles and optional components other than rhodium.

[0074] As the optional components of the upper layer, for example, noble metals other than rhodium, alkali metal compounds, alkaline earth metal compounds, transition metals, binders, and the like can be given.

[0075] The noble metal other than rhodium can be, for example, a platinum group metal other than rhodium, and specifically, for example, one or more selected from the group consisting of palladium and platinum. However, the exhaust gas purification catalyst device of the present embodiment is capable of sufficiently exerting high exhaust gas purification ability even if the upper layer does not contain a noble metal other than rhodium, and therefore a noble metal other than rhodium can not be disposed in the upper layer.

[0076] As the alkali metal compound, for example, a potassium compound, a lithium compound, and the like can be given. As the alkaline earth metal compound, for example, a calcium compound, a barium compound, a strontium compound, and the like can be given. They have the effect of improving the heat resistance of the resulting catalyst.

[0077] The binder has the function of bonding the first support particles to each other and the first support particles to the lower layer to impart mechanical strength to the catalyst coating layer. As such a binder, for example, alumina sol, zirconia sol, silica sol, titania sol, and the like can be given.

[0078] (Coating amount of the upper layer)

[0079] The coating amount of the upper layer, which is represented by the mass of the upper layer per unit volume of the substrate, can be, for example, 50 g / L or more, 60 g / L or more, 70 g / L or more, or 80 g / L or more, and for example, 300 g / L or less, 250 g / L or less, 200 g / L or less, or 150 g / L or less.

[0080] <Underlayer>

[0081] The underlayer of the exhaust gas purification catalyst device of the present embodiment contains the second support particles. The underlayer can contain, in addition to the second support particles, a noble metal and other optional components.

[0082] (Second support particles)

[0083] As the second support particles contained in the underlayer, those exemplified above as the first support particles contained in the upper layer can be appropriately selected and used.

[0084] (Noble metal)

[0085] The underlayer can contain a noble metal. These noble metals can be supported on the second support particles in the underlayer.

[0086] The noble metal of the underlayer can be a platinum group metal, for example, one or more selected from the group consisting of rhodium, palladium, and platinum. Here, in order to effectively exhibit the effects of the exhaust gas purification catalyst device of the present application, it is appropriate to concentrate the rhodium in the upper layer. From this viewpoint, when the total rhodium contained in the exhaust gas purification catalyst device of the present application is taken as 100%, the rhodium content of the underlayer can be less than 50%, and can be 30% or less, 10% or less, 5% or less, or 1% or less. The underlayer can not contain rhodium at all.

[0087] The underlayer can contain a noble metal other than rhodium, and preferably contains a noble metal other than rhodium.

[0088] The noble metal other than rhodium in the underlayer can be, for example, a platinum group metal other than rhodium, and specifically, for example, one or more selected from the group consisting of palladium and platinum. The noble metal other than rhodium content in the underlayer can be, for example, 0.1 g / L or more, 0.2 g / L or more, 0.3 g / L or more, 0.4 g / L or more, or 0.5 g / L or more, and for example, 1.0 g / L or less, 0.8 g / L or less, 0.7 g / L or less, or 0.6 g / L or less, per unit volume of the substrate.

[0089] (Optional components of the underlayer)

[0090] The underlayer can contain optional components other than the second support particles and the noble metal optionally disposed thereon.

[0091] As the optional components of the underlayer, for example, an alkali metal compound, an alkaline earth metal compound, a transition metal, a binder, and the like can be given. As for these, the same as the optional components of the upper layer is explained above.

[0092] (Coverage of the underlayer)

[0093] The underlayer can have a coating amount of, for example, 50 g / L or more, 60 g / L or more, 70 g / L or more, or 80 g / L or more, and for example, 300 g / L or less, 250 g / L or less, 200 g / L or less, or 150 g / L or less, as the mass of the underlayer per unit volume of the substrate.

[0094] <Substrate>

[0095] The exhaust gas purification catalyst device of the present embodiment can have the underlayer and the upper layer as described above sequentially present on the substrate, or the underlayer can constitute part or all of the substrate, and the upper layer can be present on the underlayer as part or all of the substrate. In any case, the capacity of the substrate can be, for example, about 1 L.

[0096] As the substrate when the underlayer and the upper layer are present on the substrate, a material that is generally used as a substrate for an exhaust gas purification catalyst device can be used. For example, it can be a monolithic honeycomb substrate composed of a material such as cordierite, SiC, stainless steel, inorganic oxide particles, and the like.

[0097] When the underlayer constitutes part or all of the substrate, the substrate is composed of inorganic oxide particles, part or all of which can be the same as the kind of the second support particles of the underlayer. The substrate in this case can also be, for example, a monolithic honeycomb substrate.

[0098] <Method for manufacturing exhaust gas purification catalyst device>

[0099] The exhaust gas purification catalyst device of the present embodiment can be manufactured, for example, by a method including: supplying a coating liquid containing a rhodium precursor to an exhaust gas upstream side end portion of an exhaust gas purification catalyst device precursor, and then sucking the coating liquid from an exhaust gas downstream side end portion of the exhaust gas purification catalyst device precursor, the exhaust gas purification catalyst device precursor having: an upper layer containing first support particles and rhodium, and an underlayer containing second support particles.

[0100] <Manufacturing of exhaust gas purification catalyst device precursor>

[0101] The exhaust gas purification catalyst device precursor can be manufactured, for example, by a method including:

[0102] a method (first method) of sequentially forming an underlayer containing second support particles, and an upper layer containing first support particles and rhodium on a substrate, or

[0103] a method (second method) including forming a substrate, and forming an upper layer containing first support particles and rhodium on the obtained substrate, part or all of the substrate being composed of an underlayer containing second support particles.

[0104] According to the above-mentioned 1st method, an exhaust gas purification catalyst device precursor having a lower layer and an upper layer on a substrate is obtained. According to the 2nd method, an exhaust gas purification catalyst device precursor having a lower layer constituting part or all of a substrate and an upper layer on the lower layer as part or all of the substrate is obtained. Hereinafter, the above-mentioned 1st method and the 2nd method will be described in order.

[0105] <Manufacture of Exhaust Gas Purification Catalyst Device Precursor (1st Method)>

[0106] (Substrate)

[0107] In the 1st method for manufacturing an exhaust gas purification catalyst device precursor, as the substrate, a desired substrate that the exhaust gas purification catalyst device should have can be selected. For example, the monolithic honeycomb substrate composed of cordierite, inorganic oxide particles, and the like described above.

[0108] (Formation of Lower Layer)

[0109] By coating the lower layer-forming coating liquid containing the material of the lower layer or a precursor thereof on such a substrate and, if necessary, removing the solvent and then performing firing, the lower layer can be formed.

[0110] The lower layer of the exhaust gas purification catalyst device precursor of the present embodiment contains the 2nd support particles, and therefore the lower layer-forming coating liquid can also contain the 2nd support particles selected as appropriate from the above-mentioned description.

[0111] As with the lower layer of the exhaust gas purification catalyst device, the lower layer of the exhaust gas purification catalyst device precursor can also contain a noble metal, and preferably contains one or more selected from the group consisting of palladium and platinum. In this case, by including the intended noble metal precursor in the lower layer-forming coating liquid, these noble metals can be contained in the obtained lower layer. The noble metal precursor can be, for example, a halide, a nitrate, a sulfate, or the like of the intended noble metal.

[0112] The lower layer-forming coating liquid can contain the optional components of the lower layer described above in addition to the 2nd support particles and the noble metal precursor optionally used.

[0113] The solvent of the lower layer-forming coating liquid can typically be water.

[0114] By coating such a lower layer-forming coating liquid on the surface of the substrate and, if necessary, removing the solvent and then performing firing, the lower layer can be formed.

[0115] As the coating method, for example, known methods such as the dipping method, the flow-in method, and the like can be used without limitation. The coating amount is appropriately selected according to the intended amount of coating.

[0116] The firing after the coating can be performed, for example, at a temperature of 400 to 800°C, preferably 450 to 600°C, for example, for 5 minutes to 4 hours, preferably for 30 minutes to 3 hours. The surrounding atmosphere at the time of the firing can be in air.

[0117] (Formation of upper layer)

[0118] On the lower layer formed as described above, an upper layer-forming coating liquid containing a material of the upper layer or a precursor thereof is coated, the solvent is removed as necessary, and then firing is performed, whereby the lower layer can be formed.

[0119] The upper layer of the exhaust gas purification catalyst device precursor of the present embodiment contains the first support particles, and therefore the upper layer-forming coating liquid can also contain the first support particles selected as appropriate from the above description.

[0120] The upper layer of the exhaust gas purification catalyst device precursor contains rhodium, like the upper layer of the exhaust gas purification catalyst device. In this case, the obtained upper layer can contain rhodium by including a rhodium precursor in the upper layer-forming coating liquid. The rhodium precursor can be, for example, rhodium nitrate, rhodium chloride, sodium rhodium chloride, rhodium chloride pentaamine, rhodium carbonyl acetyl, or the like.

[0121] The upper layer-forming coating liquid can contain the optional components of the upper layer described above in addition to the first support particles and the rhodium precursor.

[0122] The solvent of the upper layer-forming coating liquid can typically be water.

[0123] By coating such an upper layer-forming coating liquid on the surface of the lower layer on the substrate, removing the solvent as necessary, and then performing firing, the upper layer can be formed, and the exhaust gas purification catalyst device precursor can be obtained.

[0124] The coating and the firing of the upper layer-forming coating liquid can be performed similarly to the coating and the firing of the lower layer-forming coating liquid, respectively.

[0125] <Manufacture of exhaust gas purification catalyst device precursor (second method)>

[0126] (Formation of substrate)

[0127] In the second method, a substrate is first formed. Here, part or all of the substrate is composed of a lower layer containing second support particles. When the lower layer prescribed in the present embodiment is part of the substrate, it is desirable that this lower layer constitutes the surface of the substrate.

[0128] The formation of the substrate in the second method can use the second support particles of the lower layer prescribed in the present embodiment, for example, as part or all of the inorganic oxide particles that constitute the substrate, and can be performed, for example, according to the method described in Patent Document 4.

[0129] When the lower layer constitutes the entire substrate, the substrate can be obtained by extrusion molding and drying and firing the substrate-forming composition. The substrate-forming composition can be obtained, for example, by mixing the second carrier particles of the lower layer defined in the present embodiment, as necessary, with other inorganic oxide particles, and then mixing and stirring the mixture with water and a binder.

[0130] When the intended lower layer contains a noble metal other than rhodium, the substrate-forming composition can contain a precursor of the intended noble metal, such as a halide, a nitrate, a sulfate, or the like, or a method can be employed in which a solution of a precursor of the intended noble metal is impregnated in the lower layer after the formation of the lower layer containing no noble metal, and then fired. By these methods, a substrate composed of a lower layer material containing a noble metal other than rhodium can be obtained.

[0131] (Formation of the upper layer)

[0132] On the lower layer formed as described above, an upper layer is then formed, and a exhaust purification catalyst device precursor can be obtained. The formation of the upper layer can be performed in the same manner as in the first method.

[0133] (Formation of the rhodium-rich portion)

[0134] Next, by forming a rhodium-rich portion in a predetermined range of the upper layer of the exhaust purification catalyst device precursor, the exhaust purification catalyst device defined in the present embodiment can be obtained.

[0135] The rhodium-rich portion can be formed by a method including a step of disposing a rhodium-rich portion-forming coating solution containing a rhodium precursor at an exhaust gas upstream side end portion of the exhaust purification catalyst device precursor, and then suctioning from an exhaust gas downstream side end portion of the exhaust purification catalyst device precursor.

[0136] The rhodium-rich portion-forming coating solution contains a rhodium precursor, and can contain a tackifier, as necessary.

[0137] The rhodium precursor can be, for example, rhodium nitrate, rhodium chloride, sodium rhodium chloride, rhodium chloride pentaamine, rhodium carbonyl acetyl, or the like.

[0138] The tackifier can be appropriately selected from, for example, a cellulose-based tackifier, a water-soluble polymer, a tackifier derived from a natural product, or the like.

[0139] The cellulose-based tackifier can be selected from, for example, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl ester, and the like, and sodium salts, calcium salts, and the like thereof. A water-soluble polymer, polyvinyl alcohol, polyvinyl pyrrolidone, or the like can be selected. The tackifier derived from a natural product can be selected from, for example, xanthan gum, gelatin, and the like.

[0140] The solvent of the coating liquid for forming the rhodium-enriched portion can typically be water.

[0141] The coating liquid for forming the rhodium-enriched portion can be used with the viscosity adjusted to a range of 1,000 mPa-s or more and 7,000 mPa-s or less at a shear rate of 4 sec -1

[0142] To form the rhodium-enriched portion, the coating liquid for forming the rhodium-enriched portion containing a rhodium precursor is disposed at the exhaust gas upstream side end portion of the exhaust purification catalyst device precursor, and then the coating liquid is sucked from the exhaust gas downstream side end portion of the exhaust purification catalyst device precursor. Thereafter, firing can be performed.

[0143] Here, by changing the content of the viscosity-increasing agent in the coating liquid for forming the rhodium-enriched portion, the viscosity of the coating liquid is appropriately adjusted in the above range, whereby the range in the depth direction of the catalyst coating layer of the rhodium-enriched portion can be adjusted. That is, since the coating liquid with low viscosity penetrates more easily, the lower the viscosity of the coating liquid, the wider (deeper) the range in the depth direction of the catalyst coating layer of the rhodium-enriched portion can be, and the coating liquid with high viscosity penetrates less easily, the higher the viscosity of the coating liquid, the narrower (shallower) the range in the depth direction of the catalyst coating layer of the rhodium-enriched portion can be.

[0144] Further, by changing the amount of the solvent in the coating liquid for forming the rhodium-enriched portion to adjust the amount of the coating liquid, the range in the exhaust gas flow direction of the rhodium-enriched portion can be adjusted. That is, if the amount of the coating liquid disposed at the exhaust gas upstream side end portion of the exhaust purification catalyst device precursor is large, the coating liquid can reach a wide (long) range in the exhaust gas flow direction of the rhodium-enriched portion by suction, but if the amount of the coating liquid is small, the coating liquid is consumed in a narrow (short) range in the exhaust gas flow direction even by suction, and thus cannot reach the downstream side. With this, by changing the amount of the solvent in the coating liquid for forming the rhodium-enriched portion, the range in the exhaust gas flow direction of the rhodium-enriched portion can be adjusted.

[0145] ​Further, by disposing the rhodium-enriched portion forming coating liquid on the exhaust gas upstream side end portion of the exhaust purification catalyst device precursor, and changing the time until suction from the exhaust gas downstream side end portion, the concentration gradient of the exhaust gas flow in the rhodium-enriched portion can be adjusted. That is, in the vicinity of the upstream side end portion of the exhaust purification catalyst device precursor, a relatively large amount of the coating liquid contacts the upper layer from the time of disposition of the coating liquid until suction, and more rhodium is supported. In contrast, at a position slightly moving downstream from the upstream side end portion, a relatively small amount of the coating liquid contacts the upper layer after disposition of the coating liquid and by suction of the remaining coating liquid. Therefore, by changing the time from disposition of the coating liquid until suction, a difference in the amount of coating liquid contacting the upper layer can be provided between the vicinity of the upstream side end portion of the exhaust purification catalyst device precursor and the position slightly moving downstream from the upstream side end portion. By this, the degree of the concentration gradient of the exhaust gas flow direction in the rhodium-enriched portion can be adjusted.

[0146] Next, the optional firing can be performed, for example, at a temperature of 400 to 800°C, preferably 450 to 600°C, for example, for 5 minutes to 4 hours, preferably for 30 minutes to 3 hours. The surrounding atmosphere during firing can be in air.

[0147] By the above operation, the exhaust purification catalyst device of the present embodiment can be manufactured.

[0148] Example

[0149] In the following experimental examples, as the substrate, a cordierite honeycomb substrate having a capacity of 700 mL (cell number: 600 cpsi, cell shape: cross section hexagonal, wall thickness: 2 mil, substrate length: 84 mm) was used, and after the lower layer and the upper layer were formed on the substrate in this order by the wet coating method, a rhodium-enriched portion was formed in a part of the upper layer by the impregnation method, and the exhaust purification catalyst device was manufactured and evaluated.

[0150] (Preparation of the coating liquid for forming the lower layer)

[0151] In pure water, as the mass per unit capacity of the honeycomb substrate, palladium nitrate of 5.5 g / L, lanthanum oxide-alumina composite oxide of 50 g / L, cerium oxide-zirconium oxide composite oxide of 30 g / L, barium sulfate of 5 g / L, and alumina sol binder were put in, and stirred, whereby the coating liquid for forming the lower layer was prepared.

[0152] The lanthanum oxide content in the lanthanum oxide-alumina composite oxide used here was 5 mass% as La2O3. The cerium oxide-zirconium oxide composite oxide contained trace amounts of neodymium oxide, lanthanum oxide, and yttrium oxide, and the cerium oxide content was 12 mass% as CeO2.

[0153] (Preparation of the coating liquid for forming the upper layer)

[0154] In pure water, as the mass per unit volume of the honeycomb substrate, rhodium nitrate of 0.18 g / L in terms of rhodium metal, lanthanum oxide-alumina composite oxide of 55 g / L, cerium oxide-zirconium oxide composite oxide of 50 g / L, and alumina sol binder were put in and stirred, whereby the coating liquid for the upper layer formation was prepared.

[0155] The lanthanum oxide content in the lanthanum oxide-alumina composite oxide used here was 5 mass% in terms of La2O3. The cerium oxide-zirconium oxide composite oxide contained trace amounts of neodymium oxide, lanthanum oxide, and yttrium oxide, and materials with different cerium oxide contents were used in each of the examples and comparative examples to adjust the cerium oxide content of the upper layer.

[0156] (Preparation of the coating liquid for the rhodium-rich portion formation)

[0157] In pure water, as the mass per unit volume of the honeycomb substrate, rhodium nitrate of 0.74 g / L in terms of rhodium metal and a predetermined amount of a viscosity-increasing agent (hydroxyethyl cellulose, manufactured by Daicel Corporation) were put in and stirred, whereby the coating liquid for the rhodium-rich portion formation was prepared.

[0158] <Experimental Example 1>

[0159] (Manufacture of the exhaust gas purification catalyst device)

[0160] The coating liquid for the lower layer formation was flowed into the honeycomb substrate, and the unnecessary coating liquid was blown away with an air blower, and then dried in a drying machine at 120°C for 2 hours, and then fired in an electric furnace at 500°C for 2 hours, whereby the lower layer was formed on the substrate.

[0161] Next, the coating liquid for the upper layer formation was flowed into the substrate after the lower layer formation, and the unnecessary coating liquid was blown away with an air blower, and then dried in a drying machine at 120°C for 2 hours, and then fired in an electric furnace at 500°C for 2 hours, whereby the upper layer without the rhodium-rich portion was further formed on the lower layer on the substrate, and a precursor of the exhaust gas purification catalyst device was obtained.

[0162] The exhaust gas purification catalyst device of Example 1 was manufactured by flowing the coating liquid for the rhodium-rich portion formation from the exhaust gas flow upstream side end portion of the obtained exhaust gas purification catalyst device precursor, and then sucking it from the exhaust gas flow downstream side end portion, and then firing it in an electric furnace at 500°C for 2 hours. Further, the concentration of the viscosity-increasing agent in the coating liquid for the rhodium-rich portion formation used in Example 1 was set to 1 mass%.

[0163] (Analysis of the rhodium-rich portion)

[0164] (Analysis 1 - Range in the depth direction of the coating layer)

[0165] After filling the communication hole of the exhaust purification catalyst device with the resin, the broken test sample was measured for the distribution of each element using an electrolytic emission-type electron beam microanalyzer (FE-EPMA) (manufactured by JEOL Ltd., model name "JXA-8530F") under the following conditions, thereby investigating the depth direction range of the rhodium-enriched portion.

[0166] Field of view magnification: 400 times

[0167] Beam diameter: minimum

[0168] Accelerating voltage: 20 kV

[0169] Irradiation current: 100 nA

[0170] Converging time: 50 seconds

[0171] Number of pixels: 256 x 256

[0172] (Analysis 2 - Proportion of rhodium contained in the upstream side 50% of the rhodium-enriched portion)

[0173] The test sample of the portion of the upstream side 50% of the rhodium-enriched portion was completely crushed, and the amount of rhodium was quantified to calculate the proportion of the amount of rhodium contained in the portion with respect to the total amount of rhodium contained in the rhodium-enriched portion.

[0174] (Evaluation of the exhaust purification catalyst device)

[0175] By installing the obtained exhaust purification catalyst device in the exhaust system of a V-type 8-cylinder engine, the catalyst coating layer temperature was set to 950°C, and a method of alternately repeating the flow of exhaust gas in a theoretical air-fuel ratio atmosphere and a lean atmosphere for a certain time was used to perform durability for 50 hours. The repeated flow time of each exhaust gas was 8 seconds of exhaust gas in a theoretical air-fuel ratio atmosphere and 3 seconds of exhaust gas in a lean atmosphere.

[0176] The exhaust purification catalyst device after durability was installed in the exhaust system of the L4 engine, and the warm-up property of NOx purification at engine startup was evaluated. Specifically, under the condition of Ga = 10 g / sec, the exhaust gas at an exhaust mass flow rate air-fuel ratio (A / F) of 14.55 was supplied to the exhaust purification catalyst device, and the time until the NOx purification rate reached 50% (warm-up time T50) was investigated. The evaluation results are shown in Table 1.

[0177] <Experimental Examples 2 to 6>

[0178] The exhaust gas purification catalyst device was produced and evaluated in the same manner as in Experimental Example 1 except that the content of the adhesion improver in the rhodium-enriched portion-forming coating liquid, the coating liquid concentration, and the time from the flow of the rhodium-enriched portion-forming coating liquid into the exhaust gas purification catalyst device precursor until suction was appropriately changed, the length and depth of the rhodium-enriched portion, and the proportion (concentration gradient) of rhodium contained in the range of the front 50% of the rhodium-enriched portion-forming coating liquid were changed. The evaluation results are shown in Table 1.

[0179] Table 1

[0180]

[0181] Referring to Table 1, the exhaust gas purification catalyst devices of Experimental Examples 4 and 5 in which the rhodium-enriched portion existed from the upstream end of the upper layer beyond 50% of the upper layer length and / or from the surface of the upper layer beyond 18 μm, and Experimental Example 6 in which the proportion of rhodium contained in the rhodium-enriched portion was less than 50% of the total rhodium contained in the upper layer, had long warm-up times T50.

[0182] In contrast, the exhaust gas purification catalyst devices of Experimental Examples 1 to 3 in which the rhodium-enriched portion existed in the range from the upstream end of the upper layer up to 50% or less of the upper layer length and in the range from the surface of the upper layer up to 18 μm or less, and the proportion of rhodium contained in the rhodium-enriched portion was 50% or more and less than 100% of the total rhodium contained in the upper layer, had shorter warm-up times T50 than Experimental Examples 4 to 6. It is considered that the contactability of rhodium with exhaust gas was improved by concentrating the rhodium of the upper layer near the surface on the upstream side of the catalyst coating layer.

[0183] <Experimental Example 7>

[0184] The time from the flow of the rhodium-enriched portion-forming coating liquid into the exhaust gas purification catalyst device precursor until suction was appropriately changed, and the proportion (concentration gradient) of rhodium contained in the range of the front 50% of the rhodium-enriched portion was changed, and the exhaust gas purification catalyst device was produced and evaluated in the same manner as in Experimental Example 2 except for this. The evaluation results are shown together with the results of Experimental Examples 1 to 3 in Table 2.

[0185] Table 2

[0186]

[0187] In Table 2, by comparing Experimental Example 7 with Experimental Examples 1 to 3, it can be understood that in the exhaust gas purification catalyst device defined in the present application, in the case where 50% or more of the rhodium contained in the rhodium-enriched portion exists in the range from the upstream end of the exhaust gas flow in the rhodium-enriched portion up to 50% or less of the length of the rhodium-enriched portion, a short warm-up time T50 is exhibited, and the warm-up property is excellent. It is considered that this is a result of the gist of the present application, which is to concentrate the rhodium of the upper layer on the upstream side of the catalyst coating layer, being thoroughly carried out.

[0188] <Experimental Examples 8 to 13>

[0189] As the ceria-zirconia composite oxide contained in the coating liquid for forming the upper layer, a composite oxide having a predetermined ceria content was used, and the length and depth of the rhodium-rich portion, and the proportion (concentration gradient) of rhodium contained in the range of the 50% front of the rhodium-rich portion were changed by appropriately changing the tackifier content in the coating liquid for forming the rhodium-rich portion, the coating liquid concentration, and the time from the flow of the coating liquid for forming the rhodium-rich portion into the exhaust gas purification catalyst device precursor until suction, and the exhaust gas purification catalyst devices were manufactured and evaluated in the same manner as in Experimental Example 1 except for these. The evaluation results are shown in Table 3 together with the results of Experimental Examples 1 to 3.

[0190] Table 3

[0191]

[0192] Referring to Table 3, the exhaust gas purification catalyst devices of Experimental Examples 11 in which the ceria content in the upper layer was 5 mass%, and Experimental Examples 12 and 13 in which the ceria content exceeded 25 mass% had long warm-up times T50.

[0193] On the other hand, the exhaust gas purification catalyst devices of Experimental Examples 1 to 3 and 8 to 10 in which the ceria content in the upper layer exceeded 5 mass% and was 25 mass% or less had shorter warm-up times T50 than Experimental Examples 11 to 13. This is considered to be because in the exhaust gas purification catalyst device according to the present application, by containing an appropriate amount of ceria in the upper layer, the catalyst coating layer (particularly, the upper layer) is maintained in an atmosphere near the stoichiometric air-fuel ratio, and thus the exhaust gas purification efficiency is improved.

[0194] Further, the exhaust gas purification catalyst device according to the present application was confirmed to have excellent exhaust gas purification ability when the space velocity (SV) of the exhaust gas was high in addition to the warm-up properties shown above as the experimental examples.

[0195] Explanation of Reference Numerals

[0196] 10 upper layer

[0197] 11 rhodium-rich portion

[0198] 12 other part of the upper layer

[0199] 20 lower layer

[0200] 100 exhaust gas purification catalyst device

[0201] a range of the rhodium-rich portion in the exhaust gas flow direction

[0202] b range of the rhodium-rich portion in the catalyst coating layer depth direction

Claims

1. An exhaust gas purification catalyst device having: an upper layer containing first support particles and rhodium, and a lower layer containing second support particles, the upper layer contains cerium oxide, a content of the cerium oxide in the upper layer is 7 mass% or more and 25 mass% or less when a total mass of the first support particles in the upper layer is taken as 100 mass%, the upper layer has a rhodium-rich portion in a range of 20% or more and 50% or less of an upper layer length from an upstream side end portion of an exhaust gas flow and in a range of 18 μm or less in a depth direction from a top surface of the upper layer, the rhodium-rich portion contains 50% or more and less than 100% of all the rhodium contained in the upper layer, a rhodium content of a portion other than the rhodium-rich portion in the upper layer is 0.01 g / L or more and 0.12 g / L or less in terms of a metal conversion mass of rhodium per unit volume of a substrate, and the rhodium-rich portion contains 51% or more and 80% or less of the rhodium contained in the rhodium-rich portion in a range of 50% or less of a length of the rhodium-rich portion from the upstream side end portion of the exhaust gas flow.

2. The exhaust gas purification catalyst device according to claim 1, wherein a range of the rhodium-rich portion in the exhaust gas flow direction is a range of 20% or more and 30% or less of the upper layer length from the upstream side end portion of the exhaust gas flow of the upper layer.

3. The exhaust gas purification catalyst device according to claim 2, wherein a range of the rhodium-rich portion in the depth direction is a range of 15 μm or less in the depth direction from the top surface of the upper layer.

4. The exhaust gas purification catalyst device according to claim 1, wherein a content of the cerium oxide in the upper layer is 7 mass% or more and 15 mass% or less when a total mass of the first support particles in the upper layer is taken as 100 mass%.

5. The exhaust gas purification catalyst device according to any one of claims 1 to 4, wherein the lower layer and the upper layer are present on a substrate.

6. The exhaust gas purification catalyst device according to any one of claims 1 to 4, wherein the lower layer constitutes part or all of a substrate, and the upper layer is present on the lower layer.

7. A method of manufacturing the exhaust gas purification catalyst device according to any one of claims 1 to 6, comprising the following steps: a coating liquid containing a rhodium precursor is supplied to an exhaust gas upstream side end portion of an exhaust gas purification catalyst device precursor, and then the coating liquid is sucked from an exhaust gas downstream side end portion of the exhaust gas purification catalyst device precursor, the exhaust gas purification catalyst device precursor has: an upper layer containing first support particles and rhodium, and a lower layer containing second support particles, and the upper layer contains cerium oxide.

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