Exhaust gas purification catalyst system

Abstract

To provide an exhaust gas purification catalyst device that reduces a HC emission amount when cold and a NOx emission amount when cold and hot.SOLUTION: An exhaust gas purification catalyst device includes a substrate, a lower catalyst coating layer on the substrate, and an upper catalyst coating layer on the lower catalyst coating layer. The lower catalyst coating layer includes a lower upstream-side catalyst coating layer disposed at an upstream side of an exhaust gas flow and containing one or two catalytic noble metals selected from Pd and Pt, and a lower downstream-side catalyst coating layer disposed at a downstream side of the exhaust gas flow and containing Rh as a catalytic noble metal. The upper catalyst coating layer is arranged from the upstream end of the substrate toward the downstream end of the exhaust gas flow. The upper catalyst coating layer contains a catalytic noble metal Rh. A total amount of the catalytic noble metals contained in the exhaust gas purification catalyst device is less than 1.88 g per 1 L of the substrate. Rh concentration in the upper catalyst coating layer is higher than the Rh concentration in the lower downstream-side catalyst coating layer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This invention relates to an exhaust gas purification catalyst device. [Background technology]

[0002] Exhaust gas from internal combustion engines such as automobile engines contains nitrogen oxides (NOx). x These exhaust gases contain 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] Regarding the three components contained in exhaust gases—CO, HC, and NOx—various countries regulate the amount of emissions per unit distance traveled by vehicles, from the perspective of mitigating air pollution.

[0004] Exhaust gas regulations are being strengthened year by year. Recent exhaust gas purification regulations tend to require reductions in HC emissions during cold conditions such as engine startup, as well as NOx emissions during both cold and hot conditions. On the other hand, CO emissions have been sufficiently purified by conventional exhaust gas purification catalyst technology, and there is still room for improvement even with strengthened exhaust gas regulations.

[0005] Incidentally, platinum group elements are used as catalytic active components in exhaust gas purification catalyst devices. For example, Patent Document 1 discloses a configuration in which a high concentration of Pd is placed upstream of the lower catalyst coating layer, a low concentration of Pd is placed downstream of the lower catalyst coating layer, and Rh is placed in the upper catalyst coating layer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-50961 [Overview of the project] [Problems that the invention aims to solve]

[0007] Platinum group elements, used in exhaust gas purification catalysts, are expensive and rare, so their reduction is being considered.

[0008] However, with conventional technology, when the amount of platinum group elements is reduced in an exhaust gas purification catalyst with the same layer configuration, once it falls below a certain threshold, the exhaust gas purification activity drops sharply, and emissions increase. Therefore, it has been difficult to realize an exhaust gas purification catalyst that is both low-cost and highly active.

[0009] The present invention has been made in view of the above circumstances. The object of the present invention is to provide an exhaust gas purification catalyst that reduces the amount of HC emissions during the cold phase, as well as the amount of NOx emissions during both the cold and hot phases, in an exhaust gas purification catalyst that uses a reduced amount of platinum group elements. [Means for solving the problem]

[0010] The present invention is as follows:

[0011] <Aspect 1> An exhaust gas purification catalyst device having a base material, a lower catalyst coating layer on the base material, and an upper catalyst coating layer on the lower catalyst coating layer, The aforementioned lower catalyst coating layer is A lower upstream catalyst coating layer is provided, located on the upstream side of the exhaust gas flow, and containing one or two catalyst noble metals selected from Pd and Pt. A lower downstream catalyst coating layer is positioned on the downstream side of the exhaust gas flow and contains Rh as a catalytic precious metal. Includes, The upper catalyst coating layer is arranged from the upstream end of the exhaust gas flow of the substrate toward the downstream side of the exhaust gas flow. The aforementioned upper catalyst coating layer contains a catalyst noble metal, which is Rh. The total amount of catalytic precious metals contained in the exhaust gas purification catalyst is less than 1.88 g / L per liter of the base material, and The Rh concentration in the upper catalyst coating layer is higher than the Rh concentration in the lower downstream catalyst coating layer. Exhaust gas purification catalyst device. <Aspect 2> The amount of Rh contained in the upper catalyst coating layer is 1.5 times or more and 4.5 times or less than the amount of Rh contained in the lower downstream catalyst coating layer. Exhaust gas purification catalyst device according to Embodiment 1. <Aspect 3> The exhaust gas purification catalyst according to aspect 1 or 2, wherein the total amount of catalytic precious metals contained in the exhaust gas purification catalyst is 1.50 g / L or less per 1 L of the base material. Appearance 4: An exhaust gas purification catalyst device according to any one of Appearances 1 to 3, wherein the amount of Rh contained in the upper catalyst coating layer is 2.0 times or more and 3.0 times or less than the amount of Rh contained in the lower downstream catalyst coating layer. <Aspect 5> An exhaust gas purification catalyst device according to any one of aspects 1 to 4, wherein the upper catalyst coating layer is arranged in a region from the upstream end of the exhaust gas flow of the substrate to 50% to 90% of the total length of the substrate. <Aspect 6> An exhaust gas purification catalyst device according to any one of aspects 1 to 5, wherein the lower upstream catalyst coating layer is arranged in a region from the upstream end of the exhaust gas flow of the substrate to 15% to 75% of the total length of the substrate. <Aspect 7> The downstream end of the lower upstream catalyst coating layer and the upstream end of the lower downstream catalyst coating layer are in contact, or The downstream end of the lower upstream catalyst coating layer and the upstream end of the lower downstream catalyst coating layer are stacked together. An exhaust gas purification catalyst device according to any one of embodiments 1 to 6. <Aspect 8> An exhaust gas purification catalyst according to any one of aspects 1 to 7, wherein the total amount of catalytic precious metals contained in the exhaust gas purification catalyst is 0.12 g / L or more per 1 L of the base material. Appearance 9: An exhaust gas purification catalyst device according to any one of Appearances 1 to 8, wherein the amount of one or two catalyst precious metals selected from Pd and Pt contained in the lower upstream catalyst coating layer is 0.10 g / L or more and 1.00 g / L or less per 1 L of the substrate volume. 《Aspect 10》The total amount of Rh contained in the lower downstream catalyst coating layer and the upper catalyst coating layer is 0.02 g / L or more and 0.25 g / L or less per liter of the volume of the substrate, and the exhaust gas purification catalyst device according to any one of Aspects 1 to 8.

Advantages of the Invention

[0012] According to the present invention, there is provided an exhaust gas purification catalyst device in which the amount of platinum group elements used is reduced, while the HC emission amount during cold start and the NOx emission amounts during cold start and hot start are reduced.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram showing the configuration of the catalyst coating layer of the exhaust gas purification catalyst device obtained in the examples and comparative examples. [Figure 2] It is a graph showing the relationship between the total noble metal amount of the exhaust gas purification catalyst device obtained in the examples and comparative examples and the NMHC (non-methane hydrocarbon) emission amount. [Figure 3] It is a graph showing the relationship between the total noble metal amount of the exhaust gas purification catalyst device obtained in the examples and comparative examples and the NOx emission amount (total of cold NOx and hot NOx).

Modes for Carrying Out the Invention

[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, a lower catalyst coating layer on the substrate, and an upper catalyst coating layer on the lower catalyst coating layer, The lower catalyst coating layer is A lower upstream catalyst coating layer disposed on the upstream side of the exhaust gas flow and containing one or two catalyst noble metals selected from Pd and Pt, A lower downstream catalyst coating layer disposed on the downstream side of the exhaust gas flow and containing Rh as a catalyst noble metal and includes The upper catalyst coating layer is disposed from the upstream end of the substrate in the exhaust gas flow direction toward the downstream side of the exhaust gas flow, The upper catalyst coating layer contains the catalyst noble metal Rh, The total amount of catalytic precious metals contained in the exhaust gas purification catalyst is less than 1.88 g / L per liter of base material, and The Rh concentration in the upper catalyst coating layer is higher than the Rh concentration in the lower downstream catalyst coating layer. Exhaust gas purification catalyst system That is the case.

[0015] In other words, the exhaust gas purification catalyst device of the present invention is A lower upstream catalyst coating layer comprising one or two selected from Pd and Pt, A lower downstream catalyst coating layer containing Rh, Rh-containing upper catalyst coating layer Includes, The Rh concentration in the upper catalyst coating layer is higher than the Rh concentration in the lower downstream catalyst coating layer.

[0016] In the exhaust gas purification catalyst device of the present invention, one or two types selected from Pd and Pt are placed only on the upstream side of the catalyst coating layer, where the temperature rises rapidly, such as immediately after engine startup, to be responsible for HC purification during cold conditions.

[0017] On the other hand, Rh was placed in a high concentration upstream of the catalyst coating layer to handle NOx purification during cold conditions, and also in a low concentration downstream of the catalyst coating layer to ensure NOx purification during hot conditions.

[0018] Furthermore, the upstream catalyst coating layer, which contains a high concentration of Rh, was placed in the uppermost layer to effectively utilize Rh, which contributes to NOx purification during cold conditions.

[0019] The exhaust gas purification catalyst device of the present invention, having the layer configuration described above, reduces HC emissions during cold conditions, as well as NOx emissions during both cold and hot conditions, even when the total amount of catalytic precious metals contained in the exhaust gas purification catalyst device is low, at less than 1.88 g / L per liter of substrate volume.

[0020] <Base material> The substrate in the exhaust gas purification catalyst device of the present invention may be the same as the substrate used in exhaust gas purification catalyst devices. The substrate may be, for example, a honeycomb substrate having a plurality of exhaust gas flow paths partitioned by partition walls. The partition walls of the substrate may have pores that allow fluid communication between adjacent exhaust gas flow paths.

[0021] The constituent material of the substrate may be, for example, a refractory inorganic oxide such as cordierite. The substrate may be of the straight-flow type or the wall-flow type.

[0022] The substrate in the exhaust gas purification catalyst device of the present invention may typically be, for example, a straight-flow type monolithic honeycomb substrate made of cordierite.

[0023] <Underlayer catalyst coating layer> The exhaust gas purification catalyst device of the present invention has a lower catalyst coating layer on a substrate.

[0024] The lower catalyst coating layer is A lower upstream catalyst coating layer is provided, located on the upstream side of the exhaust gas flow, and containing one or two catalyst noble metals selected from Pd and Pt. A lower downstream catalyst coating layer is positioned on the downstream side of the exhaust gas flow and contains Rh as a catalytic precious metal. Includes.

[0025] (Lower upstream catalyst coating layer) The lower upstream catalyst coating layer is located upstream of the exhaust gas flow and contains one or two catalyst precious metals selected from Pd and Pt.

[0026] The lower upstream catalyst coating layer is positioned upstream of the catalyst coating layer, where the temperature rises rapidly, such as immediately after engine startup. It also contains one or two catalytic precious metals selected from Pd and Pt, which have an oxidative catalytic effect, thus enabling efficient oxidation and purification of HC during cold conditions.

[0027] In order to allow the temperature to rise as quickly as possible immediately after engine startup and to maximize the efficiency of HC purification when cold, the lower upstream catalyst coating layer may be arranged to extend in the longitudinal direction of the substrate from the upstream end of the exhaust gas flow of the substrate. The length of the lower upstream catalyst coating layer may be 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, or 55% or more of the total length of the substrate, and may be 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, or 45% or less of the total length of the substrate.

[0028] The lower upstream catalyst coating layer may typically be positioned in a region extending from the upstream end of the exhaust gas flow of the substrate to 15% to 75% of the total length of the substrate.

[0029] The lower upstream catalyst coating layer contains one or two catalyst noble metals selected from Pd and Pt.

[0030] The lower upstream catalyst coating layer may contain optional components in addition to the catalyst precious metal, such as inorganic oxide particles or binders.

[0031] Inorganic oxide particles may consist of oxides of one or more elements selected from, for example, Al, Si, Ti, Zr, Ce, and rare earth elements other than Ce. When inorganic oxide particles consist of oxides of two or more elements, they may be a mixture of oxides of a single element or a composite oxide of two or more elements. They may also be a mixture of oxides of a single element and a composite oxide, or a mixture of composite oxides of two or more elements.

[0032] The inorganic oxide particles may include, for example, one or more selected from alumina and Ce-Zr composite oxides. The alumina may also contain small amounts of rare earth elements other than Ce in solid solution.

[0033] The catalyst noble metal in the lower upstream catalyst coating layer may be supported on at least a portion of the inorganic oxide particles.

[0034] The binder may be appropriately selected from, for example, alumina sol, zirconia sol, titania sol, etc.

[0035] The amount of catalyst noble metal in the lower upstream catalyst coating layer and the amount of coating in the lower upstream catalyst coating layer will be described later.

[0036] (Lower downstream catalyst coating layer) The lower downstream catalyst coating layer is located downstream of the exhaust gas flow and contains Rh as a catalytic precious metal.

[0037] The lower downstream catalytic coating layer is located downstream of the exhaust gas flow, so its temperature rise is thought to be slow, such as immediately after engine startup. Furthermore, as will be discussed later, the Rh concentration in the lower downstream catalytic coating layer is lower than that in the upper catalytic coating layer. Therefore, the lower downstream catalytic coating layer has limited NOx purification capacity in cold conditions. However, the presence of this lower downstream catalytic coating layer ensures NOx purification in hot conditions.

[0038] To efficiently purify NOx during hot conditions, the length of the lower downstream catalyst coating layer may be 30% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, or 70% or more of the total length of the substrate. On the other hand, to ensure the HC purification capacity of the lower upstream catalyst coating layer, the length of the lower downstream catalyst coating layer may be 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, or 50% or less of the total length of the substrate.

[0039] The downstream end of the lower downstream catalyst coating layer may or may not reach the downstream end of the exhaust gas flow of the substrate.

[0040] The lower downstream catalyst coating layer may typically be located in a region extending from the downstream end of the exhaust gas flow of the substrate to 30% to 90% of the total length of the substrate.

[0041] The lower downstream catalyst coating layer contains Rh as a catalytic precious metal.

[0042] The lower downstream catalyst coating layer may contain optional components in addition to the catalyst precious metal, such as inorganic oxide particles and binders. These optional components may be the same as those described above for the optional components of the lower upstream catalyst coating layer.

[0043] The catalyst noble metal in the lower downstream catalyst coating layer may be supported on at least a portion of the inorganic oxide particles.

[0044] The amount of catalyst noble metal in the lower downstream catalyst coating layer and the amount of coating in the lower downstream catalyst coating layer will be described later.

[0045] <Arrangement of the lower upstream catalyst coating layer and the lower downstream catalyst coating layer> On the substrate, the downstream end of the lower upstream catalyst coating layer and the upstream end of the lower downstream catalyst coating layer may be separated or in contact, or the downstream end of the exhaust gas flow of the lower upstream catalyst coating layer and the upstream end of the exhaust gas flow of the lower downstream catalyst coating layer may be laminated together.

[0046] However, if the downstream end of the lower upstream catalyst coating layer and the upstream end of the lower downstream catalyst coating layer are separated, a recess may be formed in the area corresponding to the isolated portion of the upper catalyst coating layer, which could prevent contact between the exhaust gas and the upper catalyst coating layer.

[0047] To avoid such a situation, the downstream end of the lower upstream catalyst coating layer and the upstream end of the lower downstream catalyst coating layer may be in contact, or the downstream end of the exhaust gas flow of the lower upstream catalyst coating layer and the upstream end of the exhaust gas flow of the lower downstream catalyst coating layer may be stacked.

[0048] When the downstream end of the lower upstream catalyst coating layer and the upstream end of the lower downstream catalyst coating layer are laminated, the length of the laminated portion may be 20% or less, 15% or less, 10% or less, or 5% or less of the total length of the substrate.

[0049] <Upper catalyst coating layer> The exhaust gas purification catalyst device of the present invention has an upper catalyst coat layer on a lower catalyst coat layer.

[0050] The upper catalyst coating layer is positioned from the upstream end of the exhaust gas flow on the substrate toward the downstream end of the exhaust gas flow and contains Rh as the catalyst precious metal.

[0051] The upper catalytic coating layer is positioned upstream of the catalytic coating layer, where the temperature rises rapidly, such as immediately after engine startup. Furthermore, it contains Rh, which has a reducing catalytic effect, as a catalytic precious metal, thus enabling efficient NOx purification during cold starts.

[0052] To allow the temperature to rise as quickly as possible immediately after engine startup and to maximize the efficiency of NOx purification when cold, the upper catalyst coating layer is positioned to extend from the upstream end of the exhaust gas flow of the substrate in the longitudinal direction of the substrate. The length of the upper catalyst coating layer may be 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, or 70% or more of the total length of the substrate, and may be 100% or less, 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, or 70% or less of the total length of the substrate.

[0053] The upper catalyst coating layer may typically be positioned in a region extending from the upstream end of the exhaust gas flow of the substrate to 50% to 90% of the total length of the substrate.

[0054] The upper catalyst coating layer contains Rh as a catalytic precious metal.

[0055] The upper catalyst coating layer may contain optional components in addition to the catalyst precious metal, such as inorganic oxide particles and binders. These optional components may be the same as those described above for the optional components of the lower upstream catalyst coating layer.

[0056] The catalyst noble metal in the upper catalyst coating layer may be supported on at least a portion of the inorganic oxide particles.

[0057] The amount of catalyst noble metal in the upper catalyst coating layer and the amount of coating in the upper catalyst coating layer will be described later.

[0058] <Total amount of catalyst precious metals> The total amount of catalytic precious metals contained in the exhaust gas purification catalyst is less than 1.88 g / L per liter of base material. The exhaust gas purification catalyst of the present invention can reduce HC emissions during cold conditions, as well as NOx emissions during both cold and hot conditions, even with a total amount of catalytic precious metals contained in less than 1.88 g / L.

[0059] The total amount of catalytic precious metal contained in the exhaust gas purification catalyst of the present invention may be 1.50 g / L or less, 1.20 g / L or less, 1.00 g / L or less, 0.80 g / L or less, 0.50 g / L or less, 0.30 g / L or less, or 0.25 g / L or less per liter of base material volume.

[0060] On the other hand, in order to ensure sufficient exhaust gas purification capacity of the exhaust gas purification catalyst, the total amount of catalytic precious metals in the exhaust gas purification catalyst may be 0.12 g / L or more per 1 L of the base material, and may be 0.20 g / L or more, 0.25 g / L or more, 0.30 g / L or more, 0.40 g / L or more, 0.50 g / L or more, or 0.70 g / L or more.

[0061] The total amount of catalytic precious metals contained in the exhaust gas purification catalyst of the present invention may typically be 0.12 g / L or more and 1.50 g / L or less per liter of base material volume.

[0062] (Amount of Rh) In the exhaust gas purification catalyst device of the present invention, Rh is contained in the lower downstream catalyst coating layer and the upper catalyst coating layer. Rh may be contained only in the lower downstream catalyst coating layer and the upper catalyst coating layer, and the lower upstream catalyst coating layer may substantially not contain Rh. The amount of Rh in the lower upstream catalyst coating layer may be 0.01 g / L or less, 0.005 g / L or less, 0.003 g / L or less, 0.001 g / L or less, or 0.0005 g / L or less, or the lower upstream catalyst coating layer may not contain Rh at all.

[0063] The total amount of Rh contained in the lower downstream catalyst coating layer and the upper catalyst coating layer may be 0.25 g / L or less per liter of substrate volume. The exhaust gas purification catalyst device of the present invention can reduce NOx emissions during both cold and hot conditions even with a low Rh content of 0.25 g / L or less.

[0064] The total amount of Rh contained in the lower downstream catalyst coating layer and the upper catalyst coating layer may be 0.20 g / L or less, 0.18 g / L or less, 0.16 g / L or less, 0.15 g / L or less, 0.12 g / L or less, or 0.10 g / L or less.

[0065] On the other hand, in order to ensure sufficient NOx purification capacity of the exhaust gas purification catalyst, the total amount of Rh contained in the lower downstream catalyst coating layer and the upper catalyst coating layer may be 0.02 g / L or more, 0.03 g / L or more, 0.05 g / L or more, 0.10 g / L or more, or 0.15 g / L or more per liter of the substrate volume.

[0066] The total amount of Rh contained in the exhaust gas purification catalyst of the present invention may typically be 0.12 g / L or more and 1.50 g / L or less per liter of base material.

[0067] In the exhaust gas purification catalyst device of the present invention, the amount of Rh contained in the upper catalyst coating layer is greater than the amount of Rh contained in the lower downstream catalyst coating layer.

[0068] To ensure a sufficiently high cold NOx purification capacity, the amount of Rh contained in the upper catalyst coating layer may be 1.5 times or more, 2.0 times or more, 2.5 times or more, or 3.0 times or more, the amount of Rh contained in the lower downstream catalyst coating layer. On the other hand, to ensure a hot NOx purification capacity, the amount of Rh contained in the upper catalyst coating layer may be 4.5 times or less, 4.0 times or less, 3.5 times or less, 3.0 times or less, or 2.5 times or less, the amount of Rh contained in the lower downstream catalyst coating layer.

[0069] The amount of Rh contained in the upper catalyst coating layer is typically between 1.5 and 4.5, and between 2.0 and 3.0, of the amount of Rh contained in the lower downstream catalyst coating layer.

[0070] In the exhaust gas purification catalyst device of the present invention, the Rh concentration in the upper catalyst coating layer may be higher than the Rh concentration in the lower downstream catalyst coating layer. The Rh concentrations in the upper catalyst coating layer and the lower downstream catalyst coating layer refer to the values ​​obtained by allocating the amount of Rh (g) contained in the catalyst coating layer to the substrate volume corresponding to the portion on which the catalyst coating layer is formed.

[0071] In other words, the total length of the base material is L A (mm), volume of the substrate is V (L), and length of the catalyst coating layer is L. S (mm) The amount of Rh contained in the catalyst coating layer is W Rh When (g) is the case, the Rhg concentration of the catalyst coating layer is W Rh / {V·(L S / L A It is expressed as}(g / L).

[0072] The Rh concentration in the upper catalyst coating layer may be 1.1 times or more, 1.2 times or more, 1.5 times or more, 1.7 times or more, or 2.0 times or more, and may be 3.0 times or less, 2.5 times or less, 2.2 times or less, 2.0 times or less, 1.8 times or less, or 1.5 times or less, compared to the Rh concentration in the lower downstream catalyst coating layer.

[0073] (Amount of one or two catalyst precious metals selected from Pd and Pt) In the exhaust gas purification catalyst device of the present invention, one or two catalytic precious metals selected from Pd and Pt (hereinafter also referred to as "Pd / Pt") are contained in the lower upstream catalyst coating layer. Pd / Pt may be contained only in the lower upstream catalyst coating layer, and the lower downstream catalyst coating layer and the upper catalyst coating layer may substantially not contain Pd / Pt. The total amount of Pd / Pt in the lower downstream catalyst coating layer and the upper catalyst coating layer may be 0.05 g / L or less, 0.04 g / L or less, 0.03 g / L or less, 0.02 g / L or less, or 0.01 g / L or less, or the lower downstream catalyst coating layer and the upper catalyst coating layer may not contain any Pd / Pt at all.

[0074] The amount of Pd / Pt contained in the lower upstream catalyst coating layer may be 0.10 g / L or more, 0.20 g / L or more, 0.30 g / L or more, 0.40 g / L or more, or 0.50 g / L or more per 1 L of substrate volume, and may be 1.00 g / L or less, 0.90 g / L or less, 0.80 g / L or less, 0.70 g / L or less, 0.60 g / L or less, or 0.50 g / L or less.

[0075] The amount of Pd / Pt contained in the lower upstream catalyst coating layer is typically 0.10 g / L or more and 1.00 g / L or less per liter of substrate volume.

[0076] (Amount of each catalyst coating layer) The coating amounts for the lower upstream catalyst coating layer, the lower downstream catalyst coating layer, and the upper catalyst coating layer may be as follows, expressed as the coating amount per unit volume of the substrate in the catalyst coating layer formation area.

[0077] The coating amount of the lower upstream catalyst coating layer may be 40 g / L or more, 50 g / L or more, 60 g / L or more, 70 g / L or more, or 80 g / L or more, as the coating amount per unit volume of the substrate in the portion where the lower upstream catalyst coating layer is formed, and may be 200 g / L or less, 180 g / L or less, 160 g / L or less, 140 g / L or less, 120 g / L or less, or 100 g / L or less.

[0078] The coating amounts of the lower downstream side catalyst coating layer and the upper catalyst coating layer may be 50 g / L or more, 60 g / L or more, 80 g / L or more, 100 g / L or more, 120 g / L or more, respectively, as the coating amount per substrate volume of the formation part of each catalyst coating layer, and may be 250 g / L or less, 220 g / L or less, 200 g / L or less, 180 g / L or less, 160 g / L or less, or 140 g / L or less.

[0079] The coating amount per substrate volume of the formation part of the catalyst coating layer means a value obtained by dividing the coating amount (g) of the catalyst coating layer by the substrate volume corresponding to the part where the catalyst coating layer is formed.

[0080] That is, when the total length of the substrate is L A (mm), the volume of the substrate is V (L), the length of the catalyst coating layer is L S (mm), and the coating amount of the catalyst coating layer is W S (g), the coating amount per substrate volume of the formation part of the catalyst coating layer is W S / {V·(L S / L A} (g / L).

[0081] 《Method for Manufacturing Exhaust Gas Purification Catalyst Device》 As long as the exhaust gas purification catalyst device of the present invention has the above-described configuration, it may be manufactured by any method.

[0082] The exhaust gas purification catalyst device of the present invention may be manufactured, for example, (A) Forming a lower upstream side catalyst coating layer on a substrate (lower upstream side catalyst coating layer forming step); (B) Forming a lower downstream side catalyst coating layer on the substrate (lower downstream side catalyst coating layer forming step); and (C) Forming an upper catalyst coating layer on the substrate on which the lower upstream side catalyst coating layer and the lower downstream side catalyst coating layer are formed (upper catalyst coating layer forming step) by a method including the above.

[0083] In the above method, the steps of (A) forming the lower upstream catalyst coating layer and (B) forming the lower downstream catalyst coating layer may be performed in any order.

[0084] <(A) Lower upstream catalyst coating layer formation process> The lower upstream catalyst coating layer formation process may be carried out, for example, by coating the substrate with a coating liquid for forming the lower upstream catalyst coating layer and then firing it. After coating and before firing, the coating layer may be dried as needed.

[0085] The coating of the coating liquid for forming the lower upstream catalyst coating layer on the substrate may be carried out over a predetermined length corresponding to the desired length of the lower upstream catalyst coating layer, starting from the upstream end of the substrate.

[0086] The substrate may be appropriately selected and used according to the desired configuration of the exhaust gas purification catalyst device. The substrate may be, for example, a straight-flow or wall-flow monolithic honeycomb substrate made of cordierite.

[0087] The coating solution for forming the lower upstream catalyst coating layer may be, for example, an aqueous dispersion containing one or two catalyst noble metal precursors selected from Pd and Pt, inorganic oxide particles, a binder, etc., depending on the desired configuration of the lower upstream catalyst coating layer. The Pd / Pt precursor may be a nitrate, sulfate, hydrochloride, acetate, complex salt, etc. of the desired noble metal.

[0088] The coating liquid for forming the lower upstream catalyst coating layer may further contain, for example, a thickener, a pH adjuster, an antifoaming agent, and the like.

[0089] The coating of the substrate with the coating liquid for forming the lower upstream catalyst coating layer, as well as the drying and firing after coating, may be carried out according to known methods.

[0090] <(B) Lower downstream catalyst coating layer formation process> The lower downstream catalyst coating layer formation process may be carried out, for example, by coating the substrate with a coating liquid for forming the lower downstream catalyst coating layer and then firing it. After coating and before firing, the coating layer may be dried as needed.

[0091] The coating of the coating liquid for forming the lower downstream catalyst coating layer on the substrate may be carried out over a predetermined length corresponding to the desired length of the lower downstream catalyst coating layer, starting from the downstream end of the substrate.

[0092] For the coating solution for forming the lower downstream catalyst coating layer, the same principles described for the coating solution for forming the lower upstream catalyst coating layer may be applied, except that the amount of one or two catalyst precious metal precursors selected from Pd and Pt is adjusted according to the desired Pd / Pt ratio in the lower downstream catalyst coating layer.

[0093] The coating of the lower downstream catalyst coating layer onto the substrate, as well as the drying and firing after coating, may be carried out according to known methods.

[0094] <(C) Upper catalyst coating layer formation process> The upper catalyst coating layer formation process may be carried out, for example, by coating a substrate on which the lower upstream catalyst coating layer and the lower downstream catalyst coating layer have been formed with a coating liquid for forming the upper catalyst coating layer and then firing it. After coating and before firing, the coating layer may be dried as needed.

[0095] The coating of the coating liquid for forming the upper catalyst coating layer onto a substrate on which the lower upstream catalyst coating layer and the lower downstream catalyst coating layer have been formed may be carried out from the upstream end of the substrate for a predetermined length corresponding to the desired length of the upper catalyst coating layer.

[0096] For the coating solution for forming the upper catalyst coating layer, the description for the coating solution for forming the lower upstream catalyst coating layer may be applied, except that the catalyst precious metal precursor selected from Pd and Pt is changed to an Rh precursor. The Rh precursor may be a nitrate, sulfate, hydrochloride, acetate, etc. of the desired precious metal.

[0097] The coating of the upper catalyst coating layer onto the substrate on which the lower upstream catalyst coating layer and the lower downstream catalyst coating layer are formed, as well as the drying and firing after coating, may be carried out in accordance with known methods. [Examples]

[0098] 1. Preparation of coating solution for catalyst coating layer formation (1) Coating liquid for Rh layer formation A coating solution for Rh layer formation was prepared by adding 80 parts by mass of cerium-zirconium composite oxide (CeO2:ZrO2=20:80 (mass ratio)), 50 parts by mass of alumina, and rhodium nitrate to pure water, and then wet-grinding the resulting mixture using a bead mill.

[0099] The amount of rhodium nitrate added was varied for each catalyst coating layer in the examples and comparative examples so that the amount of Rh in terms of metal in the formed catalyst coating layer reached a predetermined value.

[0100] The median diameter D50 of oxide particles in the coating solution after wet grinding was 5.0 μm.

[0101] (2) Coating liquid for Pd layer formation A Pd layer-forming coating solution was prepared by adding 30 parts by mass of cerium-zirconium composite oxide (CeO2:ZrO2=60:40 (mass ratio)), 40 parts by mass of alumina, barium sulfate, and palladium nitrate to pure water, and then wet-grinding the resulting mixture using a bead mill.

[0102] The amount of barium sulfate added was 10 parts by mass, calculated as barium oxide. The amount of palladium nitrate added was varied for each catalyst coating layer in the examples and comparative examples so that the amount of Pd in ​​the formed catalyst coating layer, calculated as metal, reached a predetermined value.

[0103] The median diameter D50 of oxide particles in the coating solution after wet grinding was 5.0 μm.

[0104] (3) Coating liquid for forming a Pd / Pt layer A coating solution for forming a Pd / Pt layer was prepared in the same manner as the preparation of "(2) Pd layer forming coating solution" described above, except that platinum nitrate was used together with palladium nitrate. The amounts of palladium nitrate and platinum nitrate added were varied for each catalyst coating layer of each example and comparative example so that the amount of Pd and Pt in the formed catalyst coating layer, in terms of metal, reached predetermined values.

[0105] (4) Coating liquid for forming a Pt layer The coating solution for forming the Pt layer was prepared in the same manner as the preparation of "(2) Pd layer forming coating solution" described above, except that platinum nitrate was used instead of palladium nitrate. The amount of platinum nitrate added was varied for each catalyst coating layer in each example and comparative example so that the amount of Pt in the formed catalyst coating layer, in terms of metal, reached a predetermined value.

[0106] 2. Base material The base material is a cylindrical shape with a diameter of 93 mmΦ and a length of 118 mm (capacity 800 mL), with 750 cells / inch. 2 (116 cells / cm 2 A cordierite honeycomb substrate with a wall thickness of 2.5 mil (0.064 mm) was used.

[0107] 3. Manufacturing of exhaust gas purification catalysts First, a lower layer of the catalyst coating was formed on the cell wall of the substrate as follows.

[0108] After coating the substrate with a coating solution for forming the lower upstream catalyst coating layer over a predetermined length from the upstream end, the substrate was coated with the same coating solution for forming the lower downstream catalyst coating layer over a predetermined length from the downstream end. The coated substrate was then fired at 500°C for 1 hour to form the lower layer of the catalyst coating on the substrate.

[0109] Next, an upper layer of the catalyst coating layer was formed on the lower layer of the obtained catalyst coating layer in the following manner.

[0110] When the upper layer consists of an upper upstream catalyst coating layer and an upper downstream catalyst coating layer, a coating liquid for forming the upper upstream catalyst coating layer is applied to a predetermined length from the upstream end of the substrate, and then the coating liquid for forming the upper downstream catalyst coating layer is applied to a predetermined length from the downstream end of the substrate. After this, the upper layer of the catalyst coating layer is formed by firing at 500°C for 1 hour.

[0111] On the other hand, when the upper layer is a single catalyst coating layer, the upper catalyst coating layer was formed by coating the substrate with a coating liquid for forming the upper catalyst coating layer over a predetermined length from the upstream end, and then firing it at 500°C for 1 hour.

[0112] The amount of the catalyst coating layer after firing was set to 130 g / L for the Rh layer, per unit volume of the substrate in the area where the catalyst coating layer was formed. For the Pd layer, the amount of the catalyst coating layer was set to 90 g / L per unit volume of the substrate in the area where the catalyst coating layer was formed.

[0113] 4. Evaluation method for exhaust gas purification catalysts The resulting exhaust gas purification catalyst was installed in the exhaust system of a 0.7L naturally aspirated (NA) vehicle, and the durability of the catalyst was tested by repeatedly flowing exhaust gas in a stoichiometric atmosphere and a lean atmosphere at predetermined intervals for 50 hours at a catalyst bed temperature of 1,000°C.

[0114] The exhaust gas purification catalyst, after durability testing, was used while still installed in the exhaust system of a naturally aspirated vehicle, and NOx and NMHC (non-methane hydrocarbon) emissions were measured using WLTC (3-phase) driving modes. Here, the emissions during the Low phase were defined as the emissions under cold conditions, and the emissions during the Medium and High phases were defined as the emissions under hot conditions. Emissions for each driving distance were calculated and compared.

[0115] Comparative Examples 1 and 2, Examples 1-4, and Reference Example 1 In Comparative Examples 1 and 2, Examples 1 to 4, and Reference Example 1, the amounts of Pd and Rh contained in one exhaust gas purification catalyst device were set to be the same, and the effects of the ratio of Rh amounts between the Rh layer (layer B) of the lower downstream catalyst coating layer and the upper Rh layer (layer C), and the effects of the length of the Pd layer (layer A) of the lower upstream catalyst coating layer were investigated.

[0116] <Comparative Example 1> In Comparative Example 1, a Pd layer forming coating liquid was used as the coating liquid for forming the lower upstream catalyst coating layer and the lower downstream catalyst coating layer, respectively, and a Rh layer forming coating liquid was used as the coating liquid for forming the upper layer to manufacture an exhaust gas purification catalyst device.

[0117] In Comparative Example 1, the lower upstream catalyst coating layer of the exhaust gas purification catalyst device was a Pd layer (layer A) with a length of 50% of the total length of the substrate. The amount of Pd in ​​this Pd layer (layer A) in terms of metal was 0.134 g, and the concentration per unit volume of the substrate in the portion where the lower upstream catalyst coating layer was formed was 0.335 g / L. Furthermore, the lower downstream catalyst coating layer was a Pd layer (layer A') with a length of 50% of the total length of the substrate. The amount of Pd in ​​this Pd layer (layer A') in terms of metal was 0.066 g, and the Pd concentration, defined as the value obtained by allocating this amount of Pd to the substrate volume in the portion where the lower upstream catalyst coating layer was formed, was 0.165 g / L.

[0118] The upper layer was a single catalyst coating layer, the Rh layer (C layer), with the same composition from the upstream end to the downstream end of the substrate. The amount of Rh in metal equivalent contained in this Rh layer (C layer) was 0.050 g, and the Rh concentration, defined as the value obtained by allocating this Rh amount to the substrate volume of the portion where the upper catalyst coating layer is formed, was 0.063 g / L.

[0119] A schematic diagram of the catalyst coating layer configuration of this exhaust gas purification catalyst device is shown in Figure 1(a), and the evaluation results are shown in Table 2.

[0120] <Comparative Example 2> In Comparative Example 2, a Pd layer forming coating liquid was used as the coating liquid for forming the lower upstream catalyst coating layer, and a Rh layer forming coating liquid was used as the coating liquid for forming the lower downstream catalyst coating layer and the coating liquid for forming the upper layer, respectively, to manufacture an exhaust gas purification catalyst device.

[0121] In the exhaust gas purification catalyst device of Comparative Example 2, the lower upstream catalyst coating layer was a Pd layer (layer A) with a length of 50% of the total length of the substrate. The amount of Pd in ​​this Pd layer (layer A) in terms of metal was 0.200 g, and the concentration per unit volume of the substrate in the portion where the lower upstream catalyst coating layer was formed was 0.500 g / L. Furthermore, the lower downstream catalyst coating layer was a Rh layer (layer B) with a length of 50% of the total length of the substrate. The amount of Rh in this Rh layer (layer B) in terms of metal was 0.0210 g, and the Rh concentration, defined as the value obtained by allocating this Rh amount to the substrate volume in the portion where the lower upstream catalyst coating layer was formed, was 0.053 g / L.

[0122] The upper layer was defined as an Rh layer (C layer), which was a single upper catalyst coating layer extending 70% of the total length of the substrate from the upstream end of the substrate. The amount of Rh in metal equivalent contained in this Rh layer (C layer) was 0.0290 g, and the Rh concentration, defined as the value obtained by allocating this Rh amount to the substrate volume of the portion where the upper catalyst coating layer was formed, was 0.052 g / L.

[0123] A schematic diagram of the catalyst coating layer configuration of this exhaust gas purification catalyst device is shown in Figure 1(b), and the evaluation results are shown in Table 2.

[0124] <Examples 1-4 and Reference Example 1> Except for changing the lengths (ratio to the total substrate length) of the Pd layer (layer A) of the lower upstream catalyst coating layer and the Rh layer (layer B) of the lower downstream catalyst coating layer, as well as the amounts of Pd and Rh contained in each layer, as shown in Table 1, an exhaust gas purification catalyst device was manufactured and evaluated in the same manner as in Comparative Example 2.

[0125] Schematic diagrams of the catalyst coating layer configuration of the exhaust gas purification catalyst devices obtained in each example are shown in Figures 1(b) to 1(d), and the evaluation results are shown in Table 2.

[0126] [Table 1]

[0127] [Table 2]

[0128] Tables 1 and 2 show the evaluation results for Comparative Examples 1 and 2, Examples 1 to 4, and Reference Example 1, where the amount of Pd and Rh contained in one exhaust gas purification catalyst device were the same.

[0129] The exhaust gas purification catalyst device of Comparative Example 2 slightly reduces NMHC emissions compared to the exhaust gas purification catalyst device of Comparative Example 1, but the NOx emissions remain almost unchanged. In the configuration shown in Figure 1(b), the exhaust gas purification catalyst device of Comparative Example 2 has a ratio of Rh content in the upper catalyst coating layer (layer C) to Rh content in the lower downstream catalyst coating layer (layer B) of approximately 1.0.

[0130] In contrast to these, in the exhaust gas purification catalyst devices of Example 1, where the ratio of the amount of Rh in the upper catalyst coating layer (C layer) to the amount of Rh in the lower downstream catalyst coating layer (B layer) was 2.0, and Example 2, where this ratio was 3.0, the emission of NMHC and NOx was significantly suppressed.

[0131] However, in the exhaust gas purification catalyst system of Reference Example 1, where the ratio of the Rh content in the upper catalyst coating layer (C layer) to the Rh content in the lower downstream catalyst coating layer (B layer) was set to 5.0, an increase in NMHC emissions and NOx emissions was observed. In this case, although emissions during the cold phase were suppressed, the increase in emissions during the hot phase was significant, resulting in an overall increase in emissions during both the cold and hot phases.

[0132] Based on the above, it is considered that an appropriate ratio of Rh content in the upper catalyst coating layer (C layer) to Rh content in the lower downstream catalyst coating layer (B layer) is approximately 1.5 to 4.5.

[0133] Furthermore, the exhaust gas purification catalyst devices of Examples 3 and 4, in which the length of the Pd layer (layer A) of the lower upstream catalyst coating layer was shortened and the length of the Rh layer (layer B) of the lower downstream catalyst coating layer was lengthened, showed further suppression of NMHC emissions while maintaining the NOx emission suppression effect compared to Example 1. In particular, the suppression effect of NMHC emissions during cold operation was significant.

[0134] From this, it was found that the length of the Pd layer (layer A) can be short as long as the exhaust gas oxidation purification function is effectively performed.

[0135] Comparative Examples 3 and 4, and Examples 5 and 6 In Comparative Examples 3 and 4, and Examples 5 and 6, the effects of replacing some or all of the Pd in ​​layer A with Pt were investigated.

[0136] Except for using a Pd / Pt layer forming coating liquid or a Pt layer forming coating liquid instead of a Pd layer forming coating liquid as the coating liquid for forming the lower upstream catalyst coating layer, the exhaust gas purification catalyst device was manufactured and evaluated in the same manner as in Comparative Example 2 or Example 1, so that the noble metal composition in the Pd layer (Layer A) was as shown in Table 3. The evaluation results, along with the results for Comparative Example 2 and Example 1, are shown in Table 3.

[0137] [Table 3]

[0138] Comparing each pair of Comparative Example 2 and Example 1, Comparative Example 3 and Example 5, and Comparative Example 4 and Example 6 shown in Table 3, it was found that even when some or all of the Pd in ​​the layer was replaced with Pt, the exhaust gas purification catalyst of the present invention suppressed both NMHC emissions and NOx emissions compared to the exhaust gas purification catalyst of the corresponding comparative example. In this case, it was confirmed that NOx emissions during cold conditions were particularly significantly suppressed.

[0139] Comparative Examples 5-12, Examples 7 and 8, and Reference Examples 2 and 3 In Comparative Examples 5-12, Examples 7 and 8, and Reference Examples 2 and 3, exhaust gas purification catalyst devices were manufactured and evaluated by varying (increasing) the total amount of precious metals as shown in Table 4, while maintaining the ratio of precious metals (Pd and Rh) in each catalyst coating layer as in Comparative Examples 1 and 2 and Example 3. The evaluation results, along with the results for Comparative Examples 1 and 2 and Example 1, are shown in Table 4 and Figures 2 and 3. The NOx emissions in Figure 3 represent the total amount of cold NOx and hot NOx.

[0140] [Table 4]

[0141] Referring to Table 4 and Figures 2 and 3, it appears that the effects of the present invention are not effectively realized when the total amount of precious metals per exhaust gas purification catalyst is 1.5 g / unit (1.88 g / L) or more. However, it is understood that the effects of the present invention are realized in the region where the total amount of precious metals is less than 1.5 g / unit (1.88 g / L), and in particular, the NOx suppression effect is remarkably observed in the region where the total amount of precious metals is 1.0 g / unit (1.250 g / L) or less.

Claims

1. An exhaust gas purification catalyst device having a base material, a lower catalyst coating layer on the base material, and an upper catalyst coating layer on the lower catalyst coating layer, The aforementioned lower catalyst coating layer is A lower upstream catalyst coating layer is provided, which is located on the upstream side of the exhaust gas flow and contains one or two catalyst noble metals selected from Pd and Pt. A lower downstream catalyst coating layer is positioned on the downstream side of the exhaust gas flow and contains Rh as a catalytic precious metal. Includes, The upper catalyst coating layer is arranged from the upstream end of the exhaust gas flow of the substrate toward the downstream end of the exhaust gas flow. The aforementioned upper catalyst coating layer contains a catalyst noble metal, which is Rh. The total amount of catalytic precious metals contained in the exhaust gas purification catalyst is less than 1.88 g / L per liter of the base material. The Rh concentration in the upper catalyst coating layer is higher than the Rh concentration in the lower downstream catalyst coating layer, and The amount of Rh contained in the upper catalyst coating layer is 1.5 times or more and 4.5 times or less than the amount of Rh contained in the lower downstream catalyst coating layer. Exhaust gas purification catalyst device.

2. The exhaust gas purification catalyst according to claim 1, wherein the total amount of catalytic precious metals contained in the exhaust gas purification catalyst is 1.50 g / L or less per liter of the volume of the base material.

3. The exhaust gas purification catalyst device according to claim 1 or 2, wherein the amount of Rh contained in the upper catalyst coating layer is 2.0 times or more and 3.0 times or less than the amount of Rh contained in the lower downstream catalyst coating layer.

4. The exhaust gas purification catalyst apparatus according to any one of claims 1 to 3, wherein the upper catalyst coating layer is arranged in a region from the upstream end of the exhaust gas flow of the substrate to 50% to 90% of the total length of the substrate.

5. The exhaust gas purification catalyst apparatus according to any one of claims 1 to 4, wherein the lower upstream catalyst coating layer is arranged in a region from the upstream end of the exhaust gas flow of the substrate to 15% to 75% of the total length of the substrate.

6. The downstream end of the lower upstream catalyst coating layer and the upstream end of the lower downstream catalyst coating layer are in contact, or The downstream end of the lower upstream catalyst coating layer and the upstream end of the lower downstream catalyst coating layer are stacked together. An exhaust gas purification catalyst device according to any one of claims 1 to 5.

7. The exhaust gas purification catalyst according to any one of claims 1 to 6, wherein the total amount of catalytic precious metals contained in the exhaust gas purification catalyst is 0.12 g / L or more per 1 L of the volume of the base material.

8. The exhaust gas purification catalyst apparatus according to any one of claims 1 to 7, wherein the amount of one or two catalyst noble metals selected from Pd and Pt contained in the lower upstream catalyst coating layer is 0.10 g / L or more and 1.00 g / L or less per 1 L of the substrate volume.

9. The exhaust gas purification catalyst device according to any one of claims 1 to 8, wherein the total amount of Rh contained in the lower downstream catalyst coating layer and the upper catalyst coating layer is 0.02 g / L or more and 0.25 g / L or less per 1 L of the substrate volume.

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