Exhaust gas purifying catalyst

Abstract

The present invention is a catalyst for exhaust gas purification. A catalyst for exhaust gas purification having both catalytic performance and OSC performance under an atmosphere where the air-fuel ratio (A / F) is rich and HC poisoning is easy is provided. The present invention relates to a catalyst for exhaust gas purification which is a catalyst for exhaust gas purification having a substrate and a catalyst coating layer coated on the substrate, the catalyst coating layer having a first catalyst coating layer containing Pd and / or Pt as a catalyst metal and a second catalyst coating layer containing Rh as a catalyst metal, the first catalyst coating layer being formed from the end portion on the upstream side with respect to the exhaust gas flow direction in the catalyst for exhaust gas purification, the second catalyst coating layer containing a high specific surface area OSC material having a specific surface area exceeding 40 m 2 / g, a middle specific surface area OSC material having a specific surface area of 4 m 2 / g to 40 m 2 / g, and a low specific surface area OSC material having a specific surface area of less than 4 m 2 / g.

Description

TECHNICAL FIELD

[0001] The present application relates to an exhaust gas purification catalyst. BACKGROUND

[0002] In exhaust gas emitted from an internal combustion engine, such as a gasoline engine or a diesel engine, etc., for an automobile, etc., harmful components, such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), etc., are contained.

[0003] Thus, generally, an exhaust gas purification device for decomposing and removing these harmful components is provided to the internal combustion engine, and by an exhaust gas purification catalyst installed in the exhaust gas purification device, these harmful components are substantially rendered harmless.

[0004] For example, Patent Literature 1 discloses an exhaust gas purification catalyst which is an exhaust gas purification catalyst composed of a cell structure substrate through which exhaust gas flows and a catalyst layer formed on the cell wall surface of the substrate, the catalyst layer being composed of a lower catalyst layer formed on the surface of the substrate and an upper catalyst layer formed on the surface of the lower catalyst layer, the upper catalyst layer being formed of at least a zirconia support on which rhodium is supported and two kinds of ceria-zirconia-based composite oxides which do not support rhodium and differ in specific surface area, the lower catalyst layer being formed of an alumina support on which platinum is supported and a ceria-zirconia-based composite oxide.

[0005] Patent Literature 2 discloses an exhaust gas purification catalyst which is an exhaust gas purification catalyst disposed in an exhaust passage of an internal combustion engine and purifies exhaust gas emitted from the internal combustion engine, provided with a substrate and a catalyst coating layer formed on the surface of the substrate, the catalyst coating layer containing an OSC material having oxygen storage capacity, and the catalyst coating layer is provided with a Rh layer in which Rh as a catalyst metal is disposed as a main body, and a Pd / Pt layer in which Pd and / or Pt as a catalyst metal is disposed as a main body, and at least a part of the Pd / Pt layer among the catalyst coating layer contains a low specific surface area OSC material composed of a ceria-zirconia-based composite oxide having a specific surface area of 40 m 2 / g or more and 60 m 2 / g or less as the OSC material.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: Japanese Patent Application Publication No. 2016-175053

[0009] Patent Literature 2: Japanese Patent Application Publication No. 2022-007587 SUMMARY

[0010] The exhaust gas purification catalysts of Patent Literatures 1 and 2 have a structure in which a catalyst coating layer is coated on a substrate. The catalyst coating layer contains a noble metal as a catalyst metal.

[0011] From the viewpoint of resource risk, it is required to reduce the amount of the noble metal used in the exhaust gas purification catalyst. In order to reduce the amount of the noble metal, it is sufficient to prevent the catalyst activity of the noble metal from decreasing due to the use of the exhaust gas purification catalyst, and in order to prevent the catalyst activity of the noble metal from decreasing, for example, it is possible to cite the poisoning of the noble metal by HC in the exhaust gas (HC poisoning) which is one of the main factors of the decrease in the catalyst activity of the noble metal.

[0012] On the other hand, the catalyst coating layer can contain, in addition to the catalyst metal, a material having oxygen storage capacity (OSC material). The OSC material is a material capable of occluding and releasing oxygen, and by the OSC material, it is possible to maintain the oxygen concentration constant even in the case where the air-fuel ratio varies, and to maintain the purification performance (catalytic performance) of the exhaust gas purification catalyst.

[0013] That is, as the exhaust gas purification catalyst, it is desirable to be an exhaust gas purification catalyst which has both the catalytic performance, that is, the suppression of HC poisoning of the noble metal, and the OSC performance.

[0014] Therefore, an object of the present application is to provide an exhaust gas purification catalyst which has both the catalytic performance and the OSC performance in an atmosphere in which the air-fuel ratio (A / F) in which HC poisoning is easy is rich.

[0015] The purification of NOx under the catalyst activity is borne by the noble metal, in particular, rhodium (Rh). However, the catalyst activity of Rh is easily decreased by the influence of HC poisoning, and in particular, for example, in an atmosphere in which the A / F in which the state in which the oxygen concentration is low continues, the Rh surface can be covered with HC, and thus the decrease is more likely to occur. Therefore, for the suppression of the decrease in the catalyst activity, the suppression of the HC poisoning of Rh is effective.

[0016] On the other hand, the OSC material has the possibility of causing the delay of the state change of the noble metal and the decrease in the catalyst activity depending on the OSC performance thereof. For example, the OSC material having a large specific surface area, although having high OSC performance, is easily covered with HC in the exhaust gas, and thus can cause the decrease in the catalyst activity of the noble metal and the decrease in the OSC performance. In contrast, for example, the OSC material having a small specific surface area is difficult to be covered with HC in the exhaust gas, and thus can suppress the decrease in the catalyst activity of the noble metal, but there is a limit in the OSC performance. Therefore, in order to ensure appropriate OSC performance, it is required to select an appropriate OSC material.

[0017] Therefore, the present inventors made various studies on a means for solving the problem, and as a result, found that by providing, as a catalyst coating, a first catalyst coating containing Pd and / or Pt as a catalyst metal and a second catalyst coating containing Rh as a catalyst metal in an exhaust gas purification catalyst having a substrate and a catalyst coating applied to the substrate, forming the first catalyst coating from an end portion on an upstream side with respect to a flow direction of exhaust gas in the exhaust gas purification catalyst, and providing three kinds of OSC materials having different specific surface areas in the second catalyst coating, HC can be purified using Pd and / or Pt in the first catalyst coating, and NOx can be efficiently purified using Rh in an oxygen atmosphere adjusted using the three kinds of OSC materials in the second catalyst coating, thereby completing the present invention.

[0018] That is, the gist of the present invention is as follows.

[0019] (1) An exhaust gas purification catalyst is an exhaust gas purification catalyst having a substrate and a catalyst coating applied to the substrate,

[0020] The catalyst coating has a first catalyst coating containing Pd and / or Pt as a catalyst metal and a second catalyst coating containing Rh as a catalyst metal,

[0021] The first catalyst coating is formed from an end portion on an upstream side with respect to a flow direction of exhaust gas in the exhaust gas purification catalyst,

[0022] The second catalyst coating contains a high specific surface area OSC material having a specific surface area exceeding 40 m 2 / g, a middle specific surface area OSC material having a specific surface area of 4 m 2 / g to 40 m 2 / g, and a low specific surface area OSC material having a specific surface area of less than 4 m 2 / g.

[0023] (2) The exhaust gas purification catalyst according to (1), wherein the high specific surface area OSC material and the middle specific surface area OSC material each independently contain an alumina (AI2O3)-ceria (CeO2)-zirconia (ZrO2) based composite oxide (ACZ) or a ceria-zirconia based composite oxide (CZ), and the low specific surface area OSC material contains a ceria-zirconia based composite oxide.

[0024] (3) The exhaust gas purification catalyst according to (2), wherein the low specific surface area OSC material contains a ceria-zirconia based composite oxide having a pyrochlore structure.

[0025] (4) The exhaust gas purification catalyst according to any one of (1) to (3), the second catalyst coating layer having an upstream coating layer formed from an end portion on the upstream side with respect to a direction of exhaust gas flow in the exhaust gas purification catalyst, and a downstream coating layer formed from an end portion on the downstream side with respect to the direction of exhaust gas flow in the exhaust gas purification catalyst.

[0026] (5) The exhaust gas purification catalyst according to (4), the length of the first catalyst coating layer being 20% to 50% of the entire length of the substrate in the exhaust gas purification catalyst, the length of the upstream coating layer being 30% to 70% of the entire length of the substrate in the exhaust gas purification catalyst, and the length of the downstream coating layer being 30% to 70% of the entire length of the substrate in the exhaust gas purification catalyst.

[0027] (6) The exhaust gas purification catalyst according to (4) or (5), the first catalyst coating layer being disposed on the upstream coating layer.

[0028] (7) The exhaust gas purification catalyst according to (4) or (5), the first catalyst coating layer being disposed under the upstream coating layer.

[0029] (8) The exhaust gas purification catalyst according to any one of (4) to (7), the upstream coating layer containing a high specific surface area OSC material and a low specific surface area OSC material, and the downstream coating layer containing a medium specific surface area OSC material and a low specific surface area OSC material.

[0030] (9) The exhaust gas purification catalyst according to (8), the amount of ceria in the high specific surface area OSC material being 10% to 40% by weight with respect to the total ceria weight of the upstream coating layer and the downstream coating layer as the second catalyst coating layer, the amount of ceria in the medium specific surface area OSC material being 10% to 40% by weight with respect to the total ceria weight of the upstream coating layer and the downstream coating layer as the second catalyst coating layer, the total amount of ceria in the high specific surface area OSC material and the medium specific surface area OSC material being 60% by weight or less with respect to the total ceria weight of the upstream coating layer and the downstream coating layer as the second catalyst coating layer, and the amount of ceria in the low specific surface area OSC material being 40% to 80% by weight with respect to the total ceria weight of the upstream coating layer and the downstream coating layer as the second catalyst coating layer, where the total of the amounts of ceria in the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material is 100% by weight.

[0031] (10) The exhaust gas purification catalyst according to any one of (4) to (9), the first catalyst coating layer containing Pd as a catalyst metal.

[0032] (11) The exhaust gas purification catalyst according to any one of (4) to (10) is used as S / C in a dual catalyst system.

[0033] (12) The exhaust gas purification catalyst according to any one of (1) to (3) is formed from the end that is downstream of the exhaust gas flow direction in the exhaust gas purification catalyst.

[0034] (13) According to the exhaust gas purification catalyst described in (12), the length of the first catalyst coating is 15% to 50% of the total length of the substrate in the exhaust gas purification catalyst, and the length of the second catalyst coating is 65% to 95% of the total length of the substrate in the exhaust gas purification catalyst.

[0035] (14) The first catalyst coating of the exhaust gas purification catalyst according to (12) or (13) comprises Pt as a catalyst metal.

[0036] (15) The exhaust gas purification catalyst according to any one of (12) to (14) is used as UF / C in a dual catalyst system.

[0037] (16) A method for manufacturing an exhaust gas purification catalyst, comprising: a substrate and a catalyst coating including a first catalyst coating and a second catalyst coating coated on the substrate; the method comprising:

[0038] (i) The step of preparing a first catalyst coating slurry comprising a catalyst metal precursor and a solvent, wherein the catalyst metal precursor comprises Pd and / or Pt as catalyst metals.

[0039] (ii) Preparation of a product containing Rh precursor, solvent, and a specific surface area exceeding 40 m² 2 / g high specific surface area OSC material, specific surface area of ​​4m³ 2 / g~40m 2 / g of medium specific surface area OSC materials and specific surface area less than 4m² 2 The process of preparing a slurry for the second catalyst coating of a low specific surface area OSC material of / g, wherein the Rh precursor contains Rh as a catalyst metal;

[0040] (iii) A process of forming a first catalyst coating by applying the first catalyst coating slurry prepared in step (i) from the end upstream of the exhaust flow direction relative to the exhaust gas purification catalyst; and

[0041] (iv) The process of forming the second catalyst coating by coating the slurry for the second catalyst coating prepared in step (ii).

[0042] (17) According to the method described in (16), the high specific surface area OSC material and the medium specific surface area OSC material independently comprise an alumina-cerium dioxide-zirconia composite oxide or a cerium dioxide-zirconia composite oxide, and the low specific surface area OSC material comprises a cerium dioxide-zirconia composite oxide.

[0043] (18) According to the method described in (17), the low specific surface area OSC material comprises a cerium dioxide-zirconia composite oxide with a pyrochlore-type structure.

[0044] (19) According to any one of (16) to (18), the second catalyst coating has an upstream side coating formed from an end that is upstream of the exhaust flow direction in the exhaust gas purification catalyst and a downstream side coating formed from an end that is downstream of the exhaust flow direction in the exhaust gas purification catalyst. Step (ii) as a step of preparing a slurry for the second catalyst coating includes (ii-1) a step of preparing a slurry for the downstream side coating and (ii-2) a step of preparing a slurry for the upstream side coating. Step (iv) as a step of forming the second catalyst coating includes (iv-1) a step of coating the downstream side coating slurry prepared in step (ii-1) to form a downstream side coating and (iv-2) a step of coating the upstream side coating slurry prepared in step (ii-2) to form an upstream side coating.

[0045] (20) According to the method described in (19), in step (iii), the first catalyst coating slurry is applied to 20% to 50% of the total length of the substrate in the exhaust gas purification catalyst; in step (iv-1), the downstream coating slurry is applied to 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst; and in step (iv-2), the upstream coating slurry is applied to 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst.

[0046] (21) According to the method described in (19) or (20), step (iii) is performed after step (iv-2).

[0047] (22) According to the method described in (19) or (20), step (iii) is performed before step (iv-2).

[0048] (23) According to any one of (19) to (22), step (ii-1) is a step of preparing a downstream coating slurry containing Rh precursor, solvent, medium specific surface area OSC material and low specific surface area OSC material, and step (ii-2) is a step of preparing an upstream coating slurry containing Rh precursor, solvent, high specific surface area OSC material and low specific surface area OSC material.

[0049] (24) According to the method described in (23), adjustments are made in steps (ii-1) and (ii-2) such that the amount of cerium dioxide in the high specific surface area OSC material is 10% to 40% by weight relative to the total weight of cerium dioxide in the upstream and downstream coatings of the second catalyst coating, and the amount of cerium dioxide in the medium specific surface area OSC material is 10% to 40% by weight relative to the total weight of cerium dioxide in the upstream and downstream coatings of the second catalyst coating, and the amount of cerium dioxide in the high specific surface area OSC material and ... The total amount of cerium dioxide in the surface area OSC material is 60% by weight or less relative to the total weight of cerium dioxide in the upstream and downstream coatings that serve as the second catalyst coating. The amount of cerium dioxide in the low specific surface area OSC material is 40% to 80% by weight relative to the total weight of cerium dioxide in the upstream and downstream coatings that serve as the second catalyst coating. Here, when the amounts of cerium dioxide in the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material are all added together, the total amount is 100% by weight.

[0050] (25) According to any one of (19) to (24) the method, (i) is the process of preparing a first catalyst coating slurry containing a Pd precursor and a solvent.

[0051] (26) The exhaust gas purification catalyst is used as the S / C in a dual catalyst system according to any one of (19) to (25) of the method described.

[0052] (27) According to any one of (16) to (18), step (iv) is a step of forming a second catalyst coating by applying the slurry for the second catalyst coating prepared in step (ii) from the end that is downstream of the exhaust flow direction in the exhaust purification catalyst.

[0053] (28) According to the method described in (27), in step (iii), the first catalyst coating slurry is applied to 15% to 50% of the total length of the substrate in the exhaust gas purification catalyst, and in step (iv), the second catalyst coating slurry is applied to 65% to 95% of the total length of the substrate in the exhaust gas purification catalyst.

[0054] (29) According to the method of (27) or (28), step (i) is the step of preparing a first catalyst coating slurry containing a Pt precursor and a solvent.

[0055] (30) The method according to any one of (27) to (29) is used as UF / C in a dual catalyst system.

[0056] This invention provides an exhaust gas purification catalyst that combines catalytic performance and OSC performance in an atmosphere with a rich air-fuel ratio (A / F) where HC poisoning is likely. Attached Figure Description

[0057] Figure 1 This is a diagram schematically illustrating an example of a first embodiment of the present invention.

[0058] Figure 2 This is a diagram schematically illustrating an example of a first embodiment of the present invention.

[0059] Figure 3 This is a diagram schematically illustrating an example of a first embodiment of the present invention.

[0060] Figure 4 This is a diagram schematically illustrating an example of a first embodiment of the present invention.

[0061] Figure 5 This is a diagram schematically illustrating an example of a first embodiment of the present invention.

[0062] Figure 6 This is a diagram schematically illustrating an example of a first embodiment of the present invention.

[0063] Figure 7 This is a diagram that schematically illustrates an example of a second embodiment of the present invention.

[0064] Figure 8 This is a diagram that schematically illustrates an example of a second embodiment of the present invention.

[0065] Figure 9 The graphs show the NOx purification rate of the exhaust gas purification catalysts of Comparative Example 1 and Example 2 under a rich atmosphere and the OSC performance at low and high temperatures.

[0066] Figure 10 The graphs show the NOx purification rate of the exhaust gas purification catalysts of Comparative Example 3 and Example 5 under a rich atmosphere and the OSC performance at low and high temperatures.

[0067] Figure 11 This is a graph showing the relationship between the proportion of cerium dioxide in the high specific surface area OSC material in the second catalyst coating and the NOx purification rate and OSC performance under a concentrated atmosphere.

[0068] Figure 12 The graphs show the NOx purification rate and OSC performance of the exhaust gas purification catalysts of Comparative Examples 4 and 5 and Example 9 under a rich atmosphere.

[0069] Figure 13The graph shows the NOx purification rate of the exhaust gas purification catalysts of Comparative Examples 4 and 6, and Examples 8 and 10, under a rich atmosphere.

[0070] Explanation of reference numerals in the attached figures

[0071] 1: Substrate; 2: Upstream side coating; 3: Downstream side coating; 4: First catalyst coating; 5: Second catalyst coating. Detailed Implementation

[0072] The preferred embodiments of the present invention will now be described in detail.

[0073] In this specification, the features of the invention are described with appropriate reference to the accompanying drawings. In the drawings, the dimensions and shapes of the parts are exaggerated for clarity and are not accurately depicted. Therefore, the scope of the invention is not limited to the dimensions and shapes of the parts shown in these drawings. Furthermore, the exhaust gas purification catalyst of the present invention is not limited to the following embodiments and can be implemented in various ways that can be obtained by modifications and alterations that can be made by those skilled in the art without departing from the spirit of the invention.

[0074] In addition, in this specification, the terms "coating length", "total length of substrate", "overlap length", and "coating length" are all specified in the [specification / reference]. Figures 1-8 The middle refers to the length in the left-right direction.

[0075] This invention relates to an exhaust gas purification catalyst having a substrate and a catalyst coating coated on the substrate. The catalyst coating has a first catalyst coating containing Pd and / or Pt as catalyst metals and a second catalyst coating containing Rh as catalyst metal. The first catalyst coating is formed from an end upstream of the exhaust gas flow direction in the exhaust gas purification catalyst, and the second catalyst coating contains three OSC materials with different specific surface areas.

[0076] (Substrate)

[0077] As the substrate, known honeycomb-shaped substrates can be used. Specifically, integral honeycomb-shaped substrates (honeycomb filters, high-density honeycomb, etc.) are suitable. Furthermore, the material of such substrate is not particularly limited; substrates made of ceramics such as cordierite, silicon carbide (SiC), silicon dioxide (SiO2), alumina (Al2O3), and mullite, as well as substrates made of metals such as stainless steel containing chromium and aluminum, are suitable. From a cost perspective, cordierite is preferred.

[0078] (Catalyst coating)

[0079] The catalyst coating has at least a first catalyst coating containing Pd and / or Pt as catalyst metals and a second catalyst coating containing Rh as catalyst metals.

[0080] The first catalyst coating is formed from the end face (end face) on the upstream side (the side where the exhaust flows in) relative to the exhaust flow direction in the exhaust purification catalyst.

[0081] The first catalyst coating, having the above-described structure, is capable of efficiently purifying the incoming exhaust gas, especially HC in the exhaust gas.

[0082] • First Implementation

[0083] In the first embodiment of the present invention, the second catalyst coating has an upstream side coating formed from an end that is upstream of the exhaust flow direction in the exhaust purification catalyst and a downstream side coating formed from an end (end face) that is downstream of the exhaust flow direction in the exhaust purification catalyst (the side from which the exhaust flows out).

[0084] In the first embodiment of the present invention, the length of the first catalyst coating is typically 20% to 50%, preferably 20% to 35%, of the total length of the substrate in the exhaust gas purification catalyst.

[0085] In the first embodiment of the present invention, by having the length of the first catalyst coating within the aforementioned range, it is possible to suppress the aggregation of catalyst metals caused by excessively short length, such as the aggregation of Pd and Pt caused by high density of Pd and Pt, and to increase the frequency of contact between Pd and Pt and harmful components in the exhaust gas, such as HC, thereby improving exhaust gas purification performance.

[0086] In the first embodiment of the present invention, the length of the upstream coating is typically 30% to 70%, preferably 30% to 60%, of the total length of the substrate in the exhaust gas purification catalyst.

[0087] In the first embodiment of the present invention, the length of the downstream coating is typically 30% to 70%, preferably 50% to 70%, of the total length of the substrate in the exhaust gas purification catalyst.

[0088] In the first embodiment of the present invention, by using the lengths of the upstream and downstream coatings within the aforementioned range, it is possible to suppress the aggregation of catalyst metals caused by excessively short lengths, such as the aggregation of Rh caused by high density of Rh, and to increase the frequency of contact between Rh and harmful components in the exhaust gas, such as NOx, thereby improving exhaust gas purification performance.

[0089] In a first embodiment of the present invention, the first catalyst coating may be disposed on the upstream side coating.

[0090] In the first embodiment of the present invention, by disposing the first catalyst coating on the upstream side coating, it is possible to purify harmful components, especially HC, in the incoming exhaust gas using Pd and Pt contained in the first catalyst coating, and then purify harmful components, especially NOx, using Rh contained in the upstream side coating.

[0091] In the first embodiment of the present invention, the first catalyst coating may also be disposed under the upstream side coating.

[0092] In the first embodiment of the present invention, by distributing the first catalyst coating under the upstream side coating, it is possible to prevent the oxidation of ammonia (NH3) to nitrous oxide (N2O) caused by Pd and Pt during, for example, preheating operation, and to use Rh to purify NOx.

[0093] In the first embodiment of the present invention, the lengths of the first catalyst coating and the upstream coating may be the same or different. In the first embodiment of the present invention, when the lengths of the first catalyst coating and the upstream coating are different, the first catalyst coating may be longer. In the first embodiment of the present invention, when the lengths of the first catalyst coating and the upstream coating are different, the upstream coating may be longer.

[0094] In the first embodiment of the present invention, when the lengths of the first catalyst coating and the upstream side coating are different from each other, it is preferable that the upstream side coating is longer.

[0095] By making the upstream coating longer than the first catalyst coating, the activity of Rh can be improved compared with that of Pd and Pt, thus achieving more efficient Rh utilization.

[0096] In a first embodiment of the present invention, the first catalyst coating and the downstream coating may be formed together as a single layer on the entire substrate. In a first embodiment of the present invention, the first catalyst coating and the downstream coating may also overlap. In a first embodiment of the present invention, when the first catalyst coating and the downstream coating overlap, the first catalyst coating may be disposed on top of the downstream coating in the overlapping portion. In a first embodiment of the present invention, when the first catalyst coating and the downstream coating overlap, the first catalyst coating may also be disposed below the downstream coating in the overlapping portion. In a first embodiment of the present invention, when the first catalyst coating and the downstream coating overlap, the overlap length of the overlapping areas of the first catalyst coating and the downstream coating in the overlapping portion is typically 5% to 30% of the total length of the substrate in the exhaust gas purification catalyst.

[0097] In the first embodiment of the present invention, it is preferable that the first catalyst coating does not overlap with the downstream coating.

[0098] By ensuring that the first catalyst coating does not overlap with the downstream coating, it is possible to prevent Pd and / or Pt in the first catalyst coating from alloying with Rh in the downstream coating.

[0099] In the first embodiment of the present invention, the upstream side coating and the downstream side coating can be formed together as a single layer on the entire substrate.

[0100] In the first embodiment of the present invention, the upstream coating and the downstream coating may overlap. In the first embodiment of the present invention, when the upstream and downstream coatings overlap, the upstream coating may be disposed on top of the downstream coating in the overlapping portion. In the first embodiment of the present invention, when the upstream and downstream coatings overlap, the upstream coating may also be disposed below the downstream coating in the overlapping portion. In the first embodiment of the present invention, when the upstream and downstream coatings overlap, the overlap length of the overlapping areas of the upstream and downstream coatings in the overlapping portion is typically 5% to 30% of the total length of the substrate in the exhaust gas purification catalyst.

[0101] In the first embodiment of the present invention, when the upstream coating and the downstream coating overlap, the upstream coating is preferably disposed on top of the downstream coating in the overlapping portion.

[0102] By placing the upstream coating on top of the downstream coating, exhaust gas is introduced into the downstream coating after the atmosphere is softened by the upstream coating. As a result, the downstream coating can be utilized more effectively.

[0103] In a first embodiment of the present invention, when the first catalyst coating, the upstream coating, and the downstream coating overlap, in the overlapping portion, the upstream coating may be disposed on top of the first catalyst coating and below the downstream coating in a manner where the first catalyst coating and the downstream coating do not contact each other. In a first embodiment of the present invention, when the first catalyst coating, the upstream coating, and the downstream coating overlap, in the overlapping portion, the upstream coating may also be disposed below the first catalyst coating and above the downstream coating in a manner where the first catalyst coating and the downstream coating do not contact each other. In a first embodiment of the present invention, when the first catalyst coating, the upstream coating, and the downstream coating overlap, in the overlapping portion, the overlap length of the mutually overlapping areas of the first catalyst coating, the upstream coating, and the downstream coating is typically 5% to 30% of the total length of the substrate in the exhaust gas purification catalyst.

[0104] In the first embodiment of the present invention, since the first catalyst coating and the downstream coating do not contact each other due to the upstream coating, it is possible to prevent Pd and / or Pt in the first catalyst coating from alloying with Rh in the downstream coating.

[0105] In the first embodiment of the present invention, the second catalyst coating has the above-described configuration. When the exhaust purification catalyst is used in an S / C system, especially in a dual-catalyst system containing a starting catalyst (also known as an S / C, starting converter, etc.) and an underfloor catalyst (also known as an UF / C, underfloor converter, underfloor catalyst, etc.), the exhaust gas can be purified efficiently even in an atmosphere where there may be a high concentration of exhaust gas, such as during preheating operation.

[0106] exist Figures 1-6 An example of the first embodiment of the present invention is shown in the figure.

[0107] Figure 1 The exhaust gas purification catalyst of the first embodiment of the present invention shown has a substrate 1 and catalyst coatings 2 to 4 coated on the substrate 1. The catalyst coatings 2 to 4 are composed of a second catalyst coating and a first catalyst coating 4. The second catalyst coating has an upstream side coating 2 formed on the substrate 1 from an end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream side coating 3 formed on an end that is downstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the upstream side coating 2 and the downstream side coating 3 are formed together as a single layer on the entire substrate 1. The first catalyst coating 4 is disposed on the upstream side coating 2 of the second catalyst coating and is formed from an end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the length of the first catalyst coating 4 is shorter than the length of the upstream side coating 2.

[0108] exist Figure 1 In the exhaust gas purification catalyst of the first embodiment of the present invention shown, there is no overlap between the upstream coating 2 and the downstream coating 3. Therefore, in this exhaust gas purification catalyst, the most efficient utilization of Rh can be achieved. Therefore, in this exhaust gas purification catalyst, a better combination of purification performance and OSC performance can be achieved.

[0109] Figure 2The exhaust gas purification catalyst of the first embodiment of the present invention shown has a substrate 1 and catalyst coatings 2 to 4 coated on the substrate 1. The catalyst coatings 2 to 4 are composed of a second catalyst coating and a first catalyst coating 4. The second catalyst coating has an upstream side coating 2 formed on the substrate 1 from an end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream side coating 3 formed from an end that is downstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the upstream side coating 2 and the downstream side coating 3 overlap. In the overlapping part, the upstream side coating 2 is disposed below the downstream side coating 3. The first catalyst coating 4 is disposed on the upstream side coating 2 of the second catalyst coating and is formed from an end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the length of the first catalyst coating 4 is shorter than the length of the upstream side coating 2.

[0110] exist Figure 2 In the exhaust gas purification catalyst of the first embodiment of the present invention shown, there is an overlap between the upstream coating 2 and the downstream coating 3, which can reduce the effective utilization of Rh. On the other hand, this overlap ensures sufficient OSC performance. Therefore, in this exhaust gas purification catalyst, both good purification performance and OSC performance can be achieved.

[0111] Figure 3 The exhaust gas purification catalyst of the first embodiment of the present invention shown has a substrate 1 and catalyst coatings 2 to 4 coated on the substrate 1. The catalyst coatings 2 to 4 are composed of a second catalyst coating and a first catalyst coating 4. The second catalyst coating has an upstream side coating 2 formed on the substrate 1 from an end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream side coating 3 formed from an end that is downstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the upstream side coating 2 and the downstream side coating 3 overlap. In the overlapping portion, the upstream side coating 2 is disposed on the downstream side coating 3. The first catalyst coating 4 is disposed on the upstream side coating 2 of the second catalyst coating and is formed from an end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the length of the first catalyst coating 4 is shorter than the length of the upstream side coating 2.

[0112] exist Figure 3 In the exhaust gas purification catalyst of the first embodiment of the present invention shown, there is an overlapping portion between the upstream coating 2 and the downstream coating 3, which can reduce the effective utilization portion of Rh. On the other hand, this overlapping portion ensures sufficient OSC performance, and in this overlapping portion, the upstream coating 2 moderates the exhaust atmosphere, making more effective use of the downstream coating 3. Therefore, in this exhaust gas purification catalyst, it is possible to achieve both better purification performance and OSC performance.

[0113] Figure 4 The exhaust gas purification catalyst of the first embodiment of the present invention shown has a substrate 1 and catalyst coatings 2 to 4 coated on the substrate 1. The catalyst coatings 2 to 4 are composed of a second catalyst coating and a first catalyst coating 4. The second catalyst coating has an upstream side coating 2 formed on the substrate 1 from an end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream side coating 3 formed from an end that is downstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the upstream side coating 2 and the downstream side coating 3 overlap. In the overlapping portion, the upstream side coating 2 is disposed below the downstream side coating 3. The first catalyst coating 4 is disposed on the upstream side coating 2 of the second catalyst coating and is formed from an end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the length of the first catalyst coating 4 is longer than the length of the upstream side coating 2. There is an overlapping portion of the first catalyst coating 4, the upstream side coating 2 and the downstream side coating 3. In the overlapping portion, the first catalyst coating 4 is disposed on the upstream side coating 2 and the downstream side coating 3.

[0114] exist Figure 4 In the exhaust gas purification catalyst of the first embodiment of the present invention shown, since the upstream coating 2 is covered by the first catalyst coating 4 or the downstream coating 3, the frequency of contact between the exhaust gas and the upstream coating 2 is reduced, and the atmosphere tempering ability of the upstream coating 2 is reduced. On the other hand, the overlapping portion of the upstream coating 2 and the downstream coating 3 ensures sufficient OSC performance. In addition, in the overlapping portion of the first catalyst coating 4 and the downstream coating 3, the first catalyst coating 4 efficiently purifies the exhaust gas, especially HC, and suppresses Rh poisoning in the downstream coating 3. Therefore, in this exhaust gas purification catalyst, both purification performance and OSC performance can be achieved.

[0115] Figure 5 The exhaust gas purification catalyst of the first embodiment of the present invention shown has a substrate 1 and catalyst coatings 2 to 4 coated on the substrate 1. The catalyst coatings 2 to 4 are composed of a second catalyst coating and a first catalyst coating 4. The second catalyst coating has an upstream side coating 2 formed on the substrate 1 from the end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream side coating 3 formed on the end that is downstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the upstream side coating 2 and the downstream side coating 3 are formed together as a single layer on the entire substrate 1. The first catalyst coating 4 is disposed on the upstream side coating 2 of the second catalyst coating and is formed from the end that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the length of the first catalyst coating 4 is the same as the length of the upstream side coating 2.

[0116] exist Figure 5 In the exhaust gas purification catalyst of the first embodiment of the present invention shown, since the upstream side coating 2 is covered by the first catalyst coating 4, the frequency of contact between the exhaust gas and the upstream side coating 2 is reduced, and the atmosphere tempering ability of the upstream side coating 2 is reduced. On the other hand, since there is no overlap between the upstream side coating 2 and the downstream side coating 3, effective utilization of Rh can be achieved. Therefore, in this exhaust gas purification catalyst, both purification performance and OSC performance can be achieved.

[0117] Figure 6 The exhaust gas purification catalyst of the first embodiment of the present invention shown has a substrate 1 and catalyst coatings 2 to 4 coated on the substrate 1. The catalyst coatings 2 to 4 are composed of a first catalyst coating 4 and a second catalyst coating. The first catalyst coating 4 is disposed on the substrate 1 and is formed from an end that is upstream relative to the exhaust gas flow direction in the exhaust gas purification catalyst. The second catalyst coating has an upstream side coating 2 disposed on the first catalyst coating 4 and the substrate 1 and formed from an end that is upstream relative to the exhaust gas flow direction in the exhaust gas purification catalyst, and a downstream side coating 3 formed from an end that is downstream relative to the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the upstream side coating 2 and the downstream side coating 3 are formed together as a single layer on the entire substrate 1, and the length of the first catalyst coating 4 is shorter than the length of the upstream side coating 2.

[0118] exist Figure 6 In the exhaust gas purification catalyst of the first embodiment of the present invention shown, since the first catalyst coating 4 is covered by the upstream coating 2, the frequency of contact between the exhaust gas and the first catalyst coating 4 is reduced, and the purification performance of the first catalyst coating 4 is reduced. On the other hand, since there is no overlap between the upstream coating 2 and the downstream coating 3, effective utilization of Rh can be achieved. In addition, the improved exhaust gas atmosphere due to the upstream coating 2 ensures high OSC performance. Therefore, in this exhaust gas purification catalyst, both purification performance and OSC performance can be achieved.

[0119] • Second implementation method

[0120] In a second embodiment of the present invention, the second catalyst coating is formed from the end that is downstream of the exhaust flow direction in the exhaust purification catalyst.

[0121] In the second embodiment of the present invention, the length of the first catalyst coating is typically 15% to 50% of the total length of the substrate in the exhaust gas purification catalyst, preferably 15% to 35%.

[0122] In the second embodiment of the present invention, by having the length of the first catalyst coating within the aforementioned range, it is possible to suppress the aggregation of catalyst metals caused by excessively short length, such as the aggregation of Pd and Pt caused by high density of Pd and Pt, and to increase the frequency of contact between Pd and Pt and harmful components in the exhaust gas, such as HC, thereby improving exhaust gas purification performance.

[0123] In the second embodiment of the present invention, the length of the second catalyst coating is typically 65% ​​to 95%, preferably 80% to 95%, of the total length of the substrate in the exhaust gas purification catalyst.

[0124] In the second embodiment of the present invention, by having the length of the second catalyst coating within the aforementioned range, it is possible to suppress the aggregation of catalyst metals caused by excessively short length, such as the aggregation of Rh caused by high density of Rh, and to increase the frequency of contact between Rh and harmful components in the exhaust gas, such as NOx, thereby improving exhaust gas purification performance.

[0125] In the second embodiment of the present invention, the first catalyst coating and the second catalyst coating may also overlap.

[0126] In a second embodiment of the present invention, when the first catalyst coating and the second catalyst coating overlap, the first catalyst coating may be disposed on the second catalyst coating in the overlapping portion.

[0127] In the second embodiment of the present invention, by disposing the first catalyst coating on the second catalyst coating, it is possible to purify harmful components, especially HC, in the exhaust gas using Pd and Pt contained in the first catalyst coating, and then purify harmful components, especially NOx, using Rh contained in the second catalyst coating.

[0128] In a second embodiment of the present invention, when the first catalyst coating and the second catalyst coating overlap, the first catalyst coating may also be disposed under the second catalyst coating in the overlapping portion.

[0129] In the second embodiment of the present invention, by distributing the first catalyst coating under the second catalyst coating, it is possible to prevent the oxidation of ammonia (NH3) to nitrous oxide (N2O) caused by Pd and Pt during, for example, preheating operation, and to use Rh to purify NOx.

[0130] In the second embodiment of the present invention, when the first catalyst coating and the second catalyst coating overlap, the overlap length of the overlapping area of ​​the first catalyst coating and the second catalyst coating is typically 5% to 30%, preferably 10% to 20%, of the total length of the substrate in the exhaust gas purification catalyst.

[0131] In the second embodiment of the present invention, by making the overlap length fall within the range described above, it is possible to suppress the formation of alloys of Pd and / or Pt with Rh and to purify exhaust gas with high efficiency.

[0132] In the second embodiment of the present invention, the second catalyst coating has the above-described configuration. When the exhaust gas purification catalyst is used, especially in a dual catalyst system including S / C and UF / C, for UF / C, which has the function of purifying low-concentration exhaust gas that has not been completely purified by S / C, exhaust gas can be purified efficiently even in an atmosphere where the oxygen concentration is lower (oxygen deficient) than the atmosphere in S / C due to exhaust gas purification in S / C.

[0133] exist Figure 7 and 8 An example of the second embodiment of the present invention is shown in the figure.

[0134] Figure 7 The exhaust gas purification catalyst of the second embodiment of the present invention shown has a substrate 1 and catalyst coatings 4 and 5 coated on the substrate 1. The catalyst coatings 4 and 5 are composed of a first catalyst coating 4 formed from an end on the substrate 1 that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst and a second catalyst coating 5 formed from an end on the substrate 1 that is downstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the first catalyst coating 4 and the second catalyst coating 5 overlap, and in the overlapping portion, the first catalyst coating 4 is disposed on top of the second catalyst coating 5, and the length of the first catalyst coating 4 is shorter than the length of the second catalyst coating 5.

[0135] exist Figure 7 In the exhaust gas purification catalyst of the second embodiment of the present invention shown, since the exhaust gas has a high frequency of contact with the first catalyst coating 4, the catalytic performance can be particularly improved among the combined catalytic performance and OSC performance.

[0136] Figure 8 The exhaust gas purification catalyst of the second embodiment of the present invention shown has a substrate 1 and catalyst coatings 4 and 5 coated on the substrate 1. The catalyst coatings 4 and 5 are composed of a first catalyst coating 4 formed from an end on the substrate 1 that is upstream of the exhaust gas flow direction in the exhaust gas purification catalyst and a second catalyst coating 5 formed from an end on the substrate 1 that is downstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the first catalyst coating 4 and the second catalyst coating 5 overlap, and in the overlapping portion, the first catalyst coating 4 is disposed below the second catalyst coating 5, and the length of the first catalyst coating 4 is shorter than the length of the second catalyst coating 5.

[0137] exist Figure 8In the exhaust gas purification catalyst of the second embodiment of the present invention shown, since the exhaust gas has a high frequency of contact with the second catalyst coating 5, the OSC performance can be particularly improved among the combined catalytic performance and OSC performance.

[0138] In the first and second embodiments of the present invention, the catalyst coating, as long as the uppermost layer includes the first catalyst coating and the second catalyst coating, may consist solely of a layer composed of the first catalyst coating and the second catalyst coating, or it may have one or more layers (i.e., one, two, three, or four or more layers) below the layer composed of the first catalyst coating and the second catalyst coating (lower catalyst coating). The composition and structure of the lower catalyst coating are not limited; it may be the same as the first catalyst coating and / or the second catalyst coating, or it may be different from both. Furthermore, the lower catalyst coating need not be uniformly distributed throughout the substrate of the exhaust gas purification catalyst; it may, like the uppermost layer, have a composition and structure that differs in each region on the upstream and downstream sides relative to the exhaust gas flow direction.

[0139] By having a first catalyst coating and a second catalyst coating, it is possible to efficiently purify HC in the first catalyst coating and NOx in the second catalyst coating.

[0140] (First catalyst coating)

[0141] The first catalyst coating contains Pd and / or Pt as catalyst metals.

[0142] Pd and Pt have a high ability to purify HC and CO by combustion, and they have the same purification performance for harmful components, so they can be treated as interchangeable precious metals.

[0143] Therefore, for example, when the exhaust gas purification catalyst of the second embodiment of the present invention is used in the case where the UF / C, which has the function of purifying low-concentration exhaust gas that has not been completely purified by the S / C, is in a dual catalyst system containing S / C and UF / C, Pd and / or Pt can be used as the catalyst metal in the first catalyst coating, and Pt, which may become advantageous from the point of view, can preferably be used.

[0144] On the other hand, when good preheating performance is required in catalysts for exhaust gas purification, Pt is more prone to sintering after durability compared to Pd, which may result in reduced preheating performance. Therefore, Pd is preferred.

[0145] Therefore, for example, when the exhaust gas purification catalyst of the first embodiment of the present invention is used as the S / C in a dual catalyst system comprising S / C and UF / C for purifying high-concentration exhaust gas, Pd is preferably used as the catalyst metal in the first catalyst coating.

[0146] The total content of Pd and / or Pt, which are catalyst metals, contained in the first catalyst coating is not limited, but the content is typically 0.2 g to 10 g, preferably 0.5 g to 7.0 g, relative to the volume of 1 L of the substrate to which the first catalyst coating is applied, based on the metal conversion of the catalyst metal. Furthermore, the total content of Pd and / or Pt, which are catalyst metals, contained in the first catalyst coating depends on the amount of catalyst metal precursor added (excluding volatile components) used as a material in the manufacture of the exhaust gas purification catalyst.

[0147] By having a first catalyst coating containing Pd and / or Pt as catalyst metals, i.e., by configuring a first catalyst coating containing Pd and / or Pt on the upstream side, that is, in front of the exhaust purification catalyst, the ignition performance of the high density of Pd and Pt is improved, and the purification performance of exhaust gas, especially HC, is improved.

[0148] The first catalyst coating may also include other precious metals commonly used in the field of catalysts for exhaust purification, such as at least one selected from Rh, gold (Au), silver (Ag), iridium (Ir) and ruthenium (Ru).

[0149] The Pd and / or Pt contained in the first catalyst coating as catalyst metals, and other precious metals contained as appropriate, can function as a catalyst for exhaust gas purification even as is, but are preferably supported on carrier particles that are selectively contained in the exhaust gas purification catalyst of the present invention.

[0150] The carrier particles supporting Pd and / or Pt as catalyst metals, and other precious metals as appropriate, are not limited, but can be any metal oxide that is generally used as a carrier particle in the technical field of catalysts for exhaust gas purification.

[0151] Therefore, the first catalyst coating may also include carrier particles. Examples of carrier particles include metal oxides such as silicon dioxide, magnesium oxide (MgO), zirconium oxide, cerium dioxide, aluminum oxide, titanium dioxide (TiO2), yttrium oxide (Y2O3), neodymium oxide (Nd2O3), lanthanum oxide (La2O3), and their composite oxides, solid solutions, such as alumina-zirconia composite oxides (AZ), cerium dioxide-zirconia composite oxides (CZ), alumina-cerium dioxide-zirconia composite oxides (ACZ), and combinations of two or more thereof. Furthermore, the ratio of each oxide in the composite oxides, such as AZ, CZ, and ACZ, is not limited and can be ratios generally used in the field of exhaust gas purification catalysts. For example, the CZ and ACZ described in the section on the second catalyst coating can be used as CZ and ACZ.

[0152] For example, cerium dioxide has the OSC characteristic of absorbing oxygen in a dilute atmosphere and releasing oxygen in a rich atmosphere, thus enabling the exhaust gas purification catalyst to maintain a stoichiometric atmosphere. Alumina, zirconium oxide, and other metal oxides can be added to improve the durability of the carrier.

[0153] It should be understood that, based on the aforementioned characteristics of the carrier particles, there is a possibility that the exhaust purification performance, especially the HC purification performance, of the exhaust purification catalyst of the present invention can be improved by selecting the type, composition, combination, ratio, and / or amount of the carrier particles.

[0154] When Pd and / or Pt, as catalyst metals, and other precious metals as appropriate, are supported on the aforementioned carrier particles, the contact area between the exhaust gas and the catalyst metal can be increased due to the large specific surface area of ​​the carrier particles. This improves the performance of the catalyst for exhaust gas purification.

[0155] The method of loading Pd and / or Pt as catalyst metals, and other precious metals as appropriate, onto the support particles can be the method generally used in the field of catalysts for exhaust gas purification.

[0156] The content of carrier particles in the first catalyst coating is not limited, but the volume of the portion of the substrate coated with the first catalyst coating (1L) is typically 20g to 200g, preferably 20g to 100g, and more preferably 40g to 100g. Furthermore, the content of carrier particles contained in the first catalyst coating depends on the amount of carrier particles added as materials used in the manufacture of the exhaust gas purification catalyst.

[0157] The first catalyst coating is mainly composed of Pd and / or Pt as catalyst metals, other noble metals as appropriate, and support particles supporting Pd and / or Pt as catalyst metals and other noble metals. However, it may also contain other components without impairing the effects of the present invention. Other components include other metal oxides, additives, etc. used in catalyst coatings for this purpose, specifically including alkali metals such as potassium (K), sodium (Na), lithium (Li), and cesium (Cs), alkaline earth metals such as barium (Ba), calcium (Ca), and strontium (Sr), rare earth elements such as lanthanum (La), yttrium (Y), and cerium (Ce), transition metals such as iron (Fe), and one or more of the metal oxides listed above as support particles (i.e., metal oxides without catalyst metals, etc.). Other components may be in their original form or, like the catalyst metal, may be supported on support particles.

[0158] The content of other components in the first catalyst coating is not limited if present, but the amount is typically 10g to 100g, preferably 20g to 100g, and more preferably 40g to 100g, relative to the volume of the portion of the substrate coated with the first catalyst coating per liter. Furthermore, the content of other components that can be included in the first catalyst coating depends on the amount of other components added (excluding volatile components) used in the manufacture of the exhaust gas purification catalyst.

[0159] Porosity can also be formed in the first catalyst coating. The method for forming porosity can use techniques known in the field of exhaust gas purification catalysts and is not specifically limited.

[0160] The amount of the first catalyst coating is not limited, but the capacity of the portion of the substrate coated with the first catalyst coating is typically 40g to 200g, preferably 70g to 200g, per liter. Furthermore, the amount of the first catalyst coating depends on the total weight of the materials used in manufacturing the exhaust gas purification catalyst (excluding volatile components).

[0161] The thickness of the first catalyst coating is not limited, but on average, it is typically 5 μm to 50 μm, preferably 10 μm to 30 μm. The thickness of the first catalyst coating can be measured using, for example, scanning electron microscopy (SEM).

[0162] By ensuring that the amounts of each material in the first catalyst coating and the thickness of the first catalyst coating fall within the aforementioned ranges, a good balance can be maintained between pressure loss, catalytic performance, and durability in the catalyst for exhaust gas purification.

[0163] The structure of the first catalyst coating described above can be used in both the first and second embodiments of the present invention.

[0164] (Second catalyst coating)

[0165] • First Implementation

[0166] In a first embodiment of the present invention, the second catalyst coating has an upstream side coating formed from an end that is upstream of the exhaust flow direction in the exhaust gas purification catalyst and a downstream side coating formed from an end that is downstream of the exhaust flow direction in the exhaust gas purification catalyst. The upstream side coating includes Rh as a catalyst metal and an OSC material as detailed below, and the downstream side coating includes Rh as a catalyst metal and an OSC material as detailed below.

[0167] The content of Rh, a catalyst metal, contained in the upstream coating is not limited, but the amount is typically 0.05 g to 1.0 g, preferably 0.1 g to 0.8 g, based on the metal conversion of the catalyst metal, per 1 L of the portion of the substrate coated with the upstream coating. Furthermore, the content of Rh, a catalyst metal, contained in the upstream coating depends on the amount of Rh precursor added (excluding volatile components) used in the manufacture of the exhaust gas purification catalyst.

[0168] With the upstream coating containing Rh at the above-mentioned content, when the upstream coating is disposed below the first catalyst coating, Rh will not cause HC poisoning in an atmosphere where HC is sufficiently purified by the first catalyst coating, and can fully exert NOx purification performance. When the upstream coating is disposed above the first catalyst coating, NOx can be purified by Rh before the oxidation of ammonia (NH3) to nitrous oxide (N2O) caused by Pd and Pt during preheating operation.

[0169] The content of Rh, a catalyst metal, contained in the downstream coating is not limited, but the amount of Rh, which is typically 0.05 g to 1.0 g, preferably 0.2 g to 0.8 g, relative to the volume of the portion of the substrate coated with the downstream coating per liter, is calculated using the metal conversion of the catalyst metal. Furthermore, the content of Rh, a catalyst metal, contained in the downstream coating depends on the amount of Rh precursor added (excluding volatile components) used as a material in the manufacture of the exhaust gas purification catalyst.

[0170] With Rh contained in the downstream coating at the aforementioned concentration, and in an atmosphere where HC is adequately purified by the first catalyst coating present on the upstream side, Rh will not cause HC poisoning, thus fully exerting NOx purification performance.

[0171] The content of Rh, a catalyst metal, contained in the downstream coating is preferably higher than the content of Rh, a catalyst metal, contained in the upstream coating.

[0172] By having a higher Rh content in the downstream coating than in the upstream coating, the downstream coating, which is more likely to become colder than the upstream coating, can be utilized more effectively.

[0173] The upstream and downstream coatings may also include other precious metals commonly used in the field of catalysts for exhaust purification, such as at least one selected from Pd, Pt, gold, silver, iridium and ruthenium.

[0174] The Rh catalytic metal contained in the upstream and downstream coatings, as well as other precious metals contained as appropriate, can function as a catalyst for exhaust gas purification even as is, but are preferably supported on the OSC material described in detail below, or on carrier particles selectively contained in the exhaust gas purification catalyst of the present invention.

[0175] The carrier particles supporting Rh as a catalyst metal and, where appropriate, other precious metals are not limited, but may be OSC materials as detailed below, or any metal oxides generally used as carrier particles in the technical field of catalysts for exhaust gas purification.

[0176] Therefore, the second catalyst coating, namely the upstream coating and the downstream coating, may also include carrier particles. Examples of carrier particles include metal oxides such as silicon dioxide, magnesium oxide, zirconium oxide, cerium dioxide, aluminum oxide, titanium dioxide, yttrium oxide, neodymium oxide, lanthanum oxide, and their composite oxides; solid solutions such as alumina-zirconia composite oxides (AZ); alumina-cerium dioxide-zirconia composite oxides (ACZ), cerium dioxide-zirconia composite oxides (CZ), etc., as OSC materials described in detail below; and combinations of two or more of them.

[0177] Acidic supports, such as silica, exhibit good compatibility with catalyst metals used for NOx reduction. Basic supports, such as magnesium oxide, show good compatibility with potassium and barium, which absorb NOx. Zirconia inhibits the sintering of other support particles at high temperatures, and, when combined with Rh as a catalyst metal, can generate H2 through steam reforming, thus efficiently reducing NOx. Amphoteric supports, such as alumina, have a high specific surface area, making them suitable for efficient NOx absorption and reduction. Titanium dioxide can suppress sulfur poisoning of catalyst metals. Furthermore, the addition of alumina, zirconium oxide, and other metal oxides can improve the durability of the supports.

[0178] It should be understood that, based on the aforementioned characteristics of the carrier particles, there is a possibility that the exhaust gas purification performance, especially the NOx purification performance, of the exhaust gas purification catalyst of the present invention can be improved by selecting the type, composition, combination, and ratio and / or amount of the carrier particles.

[0179] When Rh, the catalyst metal, and other precious metals, depending on the case, are supported on the aforementioned carrier particles, the contact area between the exhaust gas and the catalyst metal can be increased due to the large specific surface area of ​​the carrier particles. This improves the performance of the catalyst for exhaust gas purification.

[0180] The method of loading Rh, as a catalyst metal, and other precious metals as appropriate, onto the carrier particles can be used in the field of catalysts for exhaust gas purification.

[0181] The content of carrier particles in both the upstream and downstream coatings (excluding the content of OSC materials as detailed below) is not limited. The content of carrier particles in the upstream coating, for example, is typically 10g to 100g, preferably 15g to 80g, relative to the volume of the portion of the substrate coated with the upstream coating per liter. The content of carrier particles in the downstream coating, for example, is typically 25g to 170g, preferably 30g to 100g, relative to the volume of the portion of the substrate coated with the downstream coating per liter. Furthermore, the content of carrier particles that can be contained in the upstream or downstream coating depends on the amount of carrier particles added as materials used in the manufacture of the exhaust gas purification catalyst.

[0182] The upstream side coating contains materials selected from those with a specific surface area exceeding 40 m². 2 / g high specific surface area OSC material, specific surface area of ​​4m³ 2 / g~40m 2 / g of medium specific surface area OSC materials and specific surface area less than 4m² 2 The downstream coating comprises at least one OSC material selected from high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials. However, the upstream and downstream coatings together comprise three OSC materials: high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials.

[0183] Furthermore, high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials can each be composed of two or more OSC materials. For example, a high specific surface area OSC material can also be composed of a first high specific surface area OSC material and a second high specific surface area OSC material. Similarly, a medium specific surface area OSC material can be composed of a first medium specific surface area OSC material and a second medium specific surface area OSC material. Likewise, a low specific surface area OSC material can be composed of a first low specific surface area OSC material and a second low specific surface area OSC material.

[0184] In this invention, specific surface area refers to the specific surface area (BET specific surface area) of each material monomer as determined by the BET method.

[0185] The preferred specific surface area of ​​high specific surface area OSC material is 60 m². 2 / g~90m 2 / g.

[0186] The preferred specific surface area of ​​medium specific surface area OSC material is 30 m². 2 / g~40m 2 / g.

[0187] The preferred specific surface area of ​​low specific surface area OSC material is 0.5 m². 2 / g~2.0m 2 / g.

[0188] Examples of high specific surface area OSC materials include alumina-cerium dioxide-zirconia composite oxides (ACZ), cerium dioxide-zirconia composite oxides (CZ), and cerium dioxide-zirconia composite oxides with fluorite structure (CeZrO4).

[0189] Alumina-cerium dioxide-zirconia composite oxides are composite oxides in which cerium dioxide and zirconium oxide are dispersed in alumina, and a portion of the cerium dioxide and zirconium oxide form a cerium dioxide-zirconia solid solution. These can be observed using transmission electron microscopy (TEM). Furthermore, the formation of a cerium dioxide-zirconia solid solution can be confirmed, for example, by X-ray diffraction (XRD).

[0190] By incorporating alumina-cerium dioxide-zirconia composite oxides as high specific surface area OSC materials, the oxygen adsorption and release rates of alumina-cerium dioxide-zirconia composite oxides are faster than those of cerium dioxide-zirconia composite oxides, thus ensuring sufficient OSC performance.

[0191] The alumina-cerium dioxide-zirconia composite oxide composition of the high specific surface area OSC material typically has a Ce / Zr molar ratio of 0.6 or less, for example, 0.1 to 0.6, preferably 0.15 to 0.55, and the content of alumina (Al2O3) is typically 40% to 70% by weight relative to the total weight of the alumina-cerium dioxide-zirconia composite oxide. Furthermore, the composition of the alumina-cerium dioxide-zirconia composite oxide as the high specific surface area OSC material depends on the composition of the alumina-cerium dioxide-zirconia composite oxide used in the manufacture of the catalyst for exhaust gas purification.

[0192] By ensuring that the composition of the alumina-cerium dioxide-zirconia composite oxide, which is a high specific surface area OSC material, falls within the aforementioned range, it is possible to fully obtain the effects of alumina inhibiting particle growth (improving heat resistance and ensuring specific surface area), ensuring cerium dioxide's oxygen uptake and release performance (OSC performance), and ensuring zirconia's stabilizing effect on cerium dioxide.

[0193] The alumina-cerium dioxide-zirconia composite oxide, used as a high specific surface area OSC material, may also contain one or more rare earth elements selected from cerium. Examples of rare earth elements include scandium (Sc), yttrium, lanthanum, praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), ytterbium (Yb), and lutetium (Lu). Yttrium and lanthanum are preferred as rare earth elements. The content of rare earth elements, relative to the total weight of the alumina-cerium dioxide-zirconia composite oxide, is typically 2% to 6% by weight.

[0194] By incorporating rare earth elements into the alumina-cerium dioxide-zirconia composite oxide, which is used as a high specific surface area OSC material, the heat resistance of the alumina-cerium dioxide-zirconia composite oxide can be improved, thereby enhancing the performance of OSC.

[0195] The particle size (average particle size) of the primary particles of the alumina-cerium dioxide-zirconia composite oxide, which is a high specific surface area OSC material, is not limited as long as it has the specific surface area required for an OSC material. Although the particle size (average particle size) of the primary particles of the alumina-cerium dioxide-zirconia composite oxide, which is a high specific surface area OSC material, is not limited, it is generally 1 nm or more and less than 500 nm based on the average value measured by scanning electron microscopy (SEM) or transmission electron microscopy (TEM), and preferably 10 nm to 100 nm.

[0196] Furthermore, the crystallite diameter of the cerium dioxide-zirconia composite oxide in the alumina-cerium dioxide-zirconia composite oxide, which is a high specific surface area OSC material, is not limited. Although the crystallite diameter of the cerium dioxide-zirconia composite oxide in the alumina-cerium dioxide-zirconia composite oxide, which is a high specific surface area OSC material, is not limited, it is typically less than 10 nm, for example, 2 nm to 10 nm. Moreover, the crystallite diameter of the cerium dioxide-zirconia composite oxide can be determined, for example, using the full width at half maximum (FWHM) of XRD.

[0197] By ensuring that the average particle size of the alumina-cerium dioxide-zirconia composite oxide, which is a high specific surface area OSC material, and the crystallite diameter of the cerium dioxide-zirconia composite oxide in the alumina-cerium dioxide-zirconia composite oxide are within the above-mentioned range, the effect of cerium dioxide in ensuring the performance of OSC can be fully obtained.

[0198] Alumina-cerium dioxide-zirconia composite oxides, which are high specific surface area OSC materials, can be prepared, for example, by alkoxide method or co-precipitation method. By using alkoxide method or co-precipitation method to prepare alumina-cerium dioxide-zirconia composite oxides, it is possible to prepare composite oxides composed of uniform and fine primary particles, and it is also possible to easily prepare composite oxides containing cerium dioxide-zirconia solid solution.

[0199] In the alkoxide process, for example, by mixing all metal alkoxides of aluminum, cerium, zirconium, and, depending on the case, rare earth elements, and then calcining after hydrolysis, alumina-cerium dioxide-zirconia composite oxides can be prepared. Furthermore, even if not all of the aluminum, cerium, zirconium, and, depending on the case, rare earth elements are used in the form of metal alkoxides, as long as at least one of them is used in the form of a metal alkoxide, the remaining metal can be used in the form of a solution of nitrates, acetoacetates, etc.

[0200] The metal alkoxide can be any alkoxide such as a methanol salt, ethanol salt, or butoxide salt, but it is preferred to be a metal alkoxide with high solubility relative to the alcohol used as a solvent. Furthermore, any alcohol can be used as the solvent.

[0201] In the coprecipitation method, for example, by mixing water-soluble salts such as nitrates of aluminum, cerium, zirconium, and, depending on the case, rare earth elements, and using ammonia or similar water as hydroxides for coprecipitation, followed by calcination, an alumina-cerium dioxide-zirconia composite oxide can be prepared. Alternatively, even if aluminum, cerium, zirconium, and, depending on the case, all rare earth elements are not used in the form of water-soluble salts, as long as at least one of them is used in the form of a water-soluble salt, the remaining metals can be used in the form of solids such as metal powder or oxide powder.

[0202] The resulting alumina-cerium dioxide-zirconia composite oxide is preferably pre-heat-treated. By pre-heat-treating the alumina-cerium dioxide-zirconia composite oxide, excessive crystal growth of particles can be suppressed, and the degradation of OSC performance after durability can be further suppressed.

[0203] The specific surface area of ​​alumina-cerium dioxide-zirconia composite oxides, which are high specific surface area OSC materials, can be adjusted by the reaction conditions in alkoxide and co-precipitation methods, such as material concentration, addition rate, reaction time and temperature, calcination temperature and time, and pulverization conditions, especially calcination temperature and time and pulverization conditions. Generally, the higher the calcination temperature, the smaller the specific surface area; conversely, the longer the calcination time, the smaller the specific surface area. In the preparation of alumina-cerium dioxide-zirconia composite oxides as high specific surface area OSC materials, the calcination temperature and time are not limited, but are typically 500°C to 800°C and typically 0.5 hours to 10 hours in atmospheric conditions.

[0204] The alumina-cerium dioxide-zirconia composite oxide as a high specific surface area OSC material can also be a material known in this technical field, such as the material described in Japanese Patent Application Publication No. 10-202102, Japanese Patent Application Publication No. 2001-232199, and Japanese Patent Application Publication No. 2012-187518.

[0205] In cerium dioxide-zirconia composite oxides used as high specific surface area OSC materials, the ratio of cerium to zirconium in the cerium dioxide-zirconia composite oxide, expressed as a molar ratio ([cerium]:[zirconia]), is typically in the range of 43:57 to 48:52. Furthermore, the composition of the cerium dioxide-zirconia composite oxide used as a high specific surface area OSC material depends on the composition of the cerium dioxide-zirconia composite oxide used in the manufacture of the catalyst for exhaust gas purification.

[0206] By using the cerium-zirconia composite oxide with a cerium-zirconia content ratio within the range described above as a high specific surface area OSC material, the heat resistance is significantly enhanced, allowing it to fully exhibit excellent OSC performance even after prolonged exposure to high temperatures.

[0207] The cerium dioxide-zirconia composite oxide, used as a high specific surface area OSC material, may also contain one or more rare earth elements selected from cerium. Examples of rare earth elements include scandium, yttrium, lanthanum, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, ytterbium, and lutetium. Yttrium and lanthanum are preferred as rare earth elements. The content of rare earth elements, relative to the total weight of the cerium dioxide-zirconia composite oxide, is typically 1% to 20% by weight, preferably 3% to 7% by weight.

[0208] By incorporating rare earth elements into cerium dioxide-zirconia composite oxides, which are high specific surface area OSC materials, the heat resistance of cerium dioxide-zirconia composite oxides can be improved, thereby enhancing the performance of OSC.

[0209] The particle size (average particle size) of the primary particles of cerium dioxide-zirconia composite oxides, which are high specific surface area OSC materials, is not limited as long as they have the specific surface area required for high specific surface area OSC materials.

[0210] Furthermore, the crystallite diameter of cerium dioxide-zirconia composite oxides, which are high specific surface area OSC materials, is not limited. Moreover, the crystallite diameter of cerium dioxide-zirconia composite oxides can be determined, for example, using the full width at half maximum (FWHM) of XRD.

[0211] Cerium dioxide-zirconia composite oxides, as high specific surface area OSC materials, are materials that have been used as co-catalysts (oxygen storage materials) in exhaust gas purification catalysts, details of which are well known to those skilled in the art. Preferably, the cerium dioxide and zirconium oxide form a solid solution as high specific surface area OSC materials. Cerium dioxide-zirconia composite oxides as high specific surface area OSC materials can be prepared by alkoxide method or co-precipitation method. If the co-precipitation method is used, it can be prepared, for example, by the following steps: adding ammonia to an aqueous solution containing a cerium salt (cerium nitrate, etc.) and a zirconium salt (zirconia oxynitrate, etc.) to form a coprecipitate; drying the resulting precipitate; and then calcining it at a temperature typically 400 kgf / cm³. 2 ~3500kgf / cm 2 The pressure is applied for molding, and then reduction treatment is carried out at a temperature of 1450℃~2000℃.

[0212] The specific surface area of ​​cerium dioxide-zirconia composite oxides, which are high specific surface area OSC materials, can be adjusted by the reaction conditions in alkoxide and co-precipitation methods, such as material concentration, addition rate, reaction time and temperature, sintering temperature and time, and pulverization conditions, especially sintering temperature and time and pulverization conditions. Generally, a higher sintering temperature results in a smaller specific surface area, and a longer sintering time also results in a smaller specific surface area. In the preparation of cerium dioxide-zirconia composite oxides as high specific surface area OSC materials, the sintering temperature and time are not limited.

[0213] The cerium dioxide-zirconia composite oxide that serves as a high specific surface area OSC material can also be a material known in this technical field, such as the material described in Japanese Patent Application Publication No. 2011-219329.

[0214] Examples of medium specific surface area OSC materials include alumina-cerium dioxide-zirconia composite oxides (ACZ), cerium dioxide-zirconia composite oxides (CZ), and cerium dioxide-zirconia composite oxides with fluorite structure (CeZrO4).

[0215] Alumina-cerium-zirconia composite oxides (ACZ) and cerium-zirconia composite oxides (CZ) that can be used as medium specific surface area OSC materials have the same properties as those that can be used as high specific surface area OSC materials, except for specific surface area and properties that may vary depending on the specific surface area, such as the content of each component.

[0216] The specific surface area of ​​alumina-cerium dioxide-zirconia composite oxides and cerium dioxide-zirconia composite oxides, which are medium specific surface area OSC materials, can be adjusted by the reaction conditions in alkoxide and co-precipitation methods, such as material concentration, addition rate, reaction time and temperature, sintering temperature and time, and pulverization conditions, especially sintering temperature and time and pulverization conditions. Generally, a higher sintering temperature results in a smaller specific surface area, and a longer sintering time also results in a smaller specific surface area.

[0217] For example, the particle size (average particle size) of the primary particles of the alumina-cerium dioxide-zirconia composite oxide, which is a medium specific surface area OSC material, is not limited, but is usually 1 nm to 500 nm based on the average value measured by SEM or TEM, preferably 10 nm to 100 nm.

[0218] For example, the crystallite diameter of the alumina-cerium dioxide-zirconia composite oxide, which is used as a medium specific surface area OSC material, is not limited, but is usually below 25 nm, for example, 10 nm to 25 nm.

[0219] For example, in the case of preparing alumina-cerium dioxide-zirconia composite oxides as medium specific surface area OSC materials, the sintering temperature and time are not limited, but are usually 800°C to 1200°C and usually 0.5 hours to 10 hours in the atmosphere.

[0220] For example, the particle size (average particle size) of the primary particles of the cerium dioxide-zirconia composite oxide, which is a medium specific surface area OSC material, is not limited, but is usually 1 nm to 500 nm based on the average value measured by SEM or TEM, preferably 10 nm to 100 nm.

[0221] For example, the crystallite diameter of cerium dioxide-zirconia composite oxides used as medium specific surface area OSC materials is not limited, but is usually below 25 nm, preferably 10 nm to 25 nm.

[0222] For example, in the case of preparing cerium dioxide-zirconia composite oxides as medium specific surface area OSC materials, the sintering temperature and time are not limited, but are usually 800°C to 1200°C and usually 0.5 hours to 10 hours in the atmosphere.

[0223] Examples of low specific surface area OSC materials include cerium dioxide-zirconia composite oxides (CZ), such as cerium dioxide-zirconia composite oxides with a pyrochlore-type structure (Ce2Zr2O7, pyrochlore-type CZ).

[0224] In cerium dioxide-zirconia composite oxides, the term "possessing a pyrochlore-type structure" means that cerium and zirconium ions constitute a crystalline phase with a regular arrangement of pyrochlore-type ions (pyrochlore-type phase). Some of the cerium and zirconium ions can also be replaced by additional elements such as praseodymium. The arrangement of the pyrochlore-type phase can be determined by the presence of peaks at 2θ angles of 14.5°, 28°, 37°, 44.5°, and 51° in an X-ray diffraction pattern using CuKα. Here, a "peak" refers to a peak with a height of 30 cps or more from the baseline to the peak apex. Furthermore, when calculating the diffraction line intensity, it is calculated by subtracting the average diffraction line intensity at 2θ = 10–12° (as a background value) from the values ​​of each diffraction line intensity.

[0225] In cerium dioxide-zirconia composite oxides with a pyrochlore-type structure, which are used as low specific surface area OSC materials, the content ratio of the regularly arranged pyrochlore-type crystalline phase, determined by the peak intensity ratio of the X-ray diffraction pattern, relative to all crystalline phases is preferably 50% or more, and particularly preferably 80% or more. Methods for preparing cerium dioxide-zirconia composite oxides with a pyrochlore-type structure as low specific surface area OSC materials are well known to those skilled in the art.

[0226] The pyrochlore phase (Ce₂Zr₂O₇) of cerium dioxide-zirconia composite oxides possesses oxygen defect sites. If an oxygen atom enters this site, the pyrochlore phase transforms into the κ phase (Ce₂Zr₂O₈). Conversely, the κ phase can transform into the pyrochlore phase by releasing oxygen atoms. The oxygen storage capacity of cerium dioxide-zirconia composite oxides is achieved through the absorption and release of oxygen via phase transitions between the pyrochlore and κ phases.

[0227] Here, it is known that the κ phase of cerium dioxide-zirconia composite oxides undergoes a phase transformation to a crystalline phase with a fluorite-type structure (CeZrO4: fluorite-type phase) through rearrangement. In dilute atmospheres, especially high-temperature dilute atmospheres, pyrochlore-type CZ easily transforms into the fluorite-type phase via the κ phase.

[0228] In the X-ray diffraction (XRD) determination of the crystalline phase of the cerium dioxide-zirconia composite oxide as a low specific surface area OSC material using CuKα, the diffraction line with 2θ = 14.5° is the diffraction line belonging to the (111) plane of the regular phase (κ phase), and the diffraction line with 2θ = 29° is the diffraction line formed by the superposition of the diffraction line belonging to the (222) plane of the regular phase and the diffraction line belonging to the (111) plane of the cerium dioxide-zirconia solid solution without the pyrochlore type phase. Therefore, the intensity ratio of the two diffraction lines, i.e., the value of I(14 / 29), can be used as an indicator of the presence rate of the regular phase. Based on the intensity ratio I(14 / 29) of the diffraction line with 2θ = 14.5° and the diffraction line with 2θ = 29° obtained by X-ray diffraction of cerium dioxide-zirconia composite oxide as a low specific surface area OSC material in the atmosphere after heating at 1100°C for 5 hours, using the X-ray diffraction pattern obtained by CuKα, a value of 0.017 or higher is preferred from the viewpoint of good maintenance of the regular phase and oxygen storage capacity after durability testing. Furthermore, based on the PDF card (PDF2: 01-070-4048) for the κ phase and the PDF card (PDF2: 01-075-2694) for the pyrochlore phase, the I(14 / 29) value for the complete κ phase can be calculated to be 0.04, and the I(14 / 29) value for the complete pyrochlore phase is 0.05. Furthermore, in the XRD analysis of the crystalline phase of the cerium dioxide-zirconia composite oxide, which is a low specific surface area OSC material, using CuKα, the diffraction line at 2θ = 28.5° is a diffraction line belonging to the (111) plane of the CeO2 monomer. Therefore, the intensity ratio of the diffraction line at 2θ = 28.5° to that at 2θ = 29°, i.e., the value of I(28 / 29), can be used as an indicator of the degree of CeO2 phase separation from the composite oxide. Based on the intensity ratio I(28 / 29) of the diffraction line at 2θ = 28.5° and that at 2θ = 29° obtained by X-ray diffraction analysis using CuKα on the cerium dioxide-zirconia composite oxide, which is a low specific surface area OSC material, after heating at 1100°C for 5 hours in the atmosphere, from the viewpoint of suppressing the phase separation of cerium dioxide and the oxygen storage capacity after the durability test, it is preferably 0.05 or less.

[0229] The cerium dioxide-zirconia composite oxide with a pyrochlore-type structure, which is a low specific surface area OSC material, has a secondary particle diameter (D50) of 3 μm to 7 μm, preferably 3 μm to 6 μm, and more preferably 3 μm to 5 μm. If the pyrochlore-type CZ, as a low specific surface area OSC material, has a secondary particle diameter (D50) within this range, it exhibits sufficient heat resistance compared to cases where the secondary particle diameter (D50) is not within this range, and significantly increases the oxygen uptake and release rate while maintaining a high oxygen storage capacity. Furthermore, in cerium dioxide-zirconia composite oxides with a fluorite-type structure, there is no such relationship between the secondary particle diameter and the oxygen uptake and release rate. Therefore, setting the secondary particle diameter (D50) within a specific range in the pyrochlore-type CZ to significantly increase the oxygen uptake and release rate is an unexpected effect specific to the pyrochlore-type CZ. In pyrochlore-type CZ, the secondary particle diameter has a significant impact due to the rapid internal oxygen diffusion characteristic unique to the pyrochlore structure. On the other hand, the heat resistance, which is a trade-off, shows a sensitivity different from the oxygen uptake and release rate relative to the secondary particle diameter. Sufficiently high heat resistance is maintained. Therefore, it is hypothesized that by setting the secondary particle diameter (D50) within a specific range in pyrochlore-type CZ, high heat resistance can be achieved, and the oxygen uptake and release rate can be significantly increased while maintaining a high oxygen storage capacity. Thus, by having a secondary particle diameter (D50) of 3μm to 7μm in pyrochlore-type CZ, sufficient heat resistance can be achieved, along with both high oxygen storage capacity and oxygen uptake and release rate, especially a significant increase in the oxygen uptake and release rate.

[0230] Here, "secondary particles" refers to particles composed of aggregates of primary particles. "Primary particles" generally refer to the smallest particles constituting the powder. Primary particles can be observed and identified using SEM or TEM. The diameter of primary particles in pyrochlore-type CZ, a low specific surface area OSC material, is usually smaller than that of secondary particles; however, it is not limited as long as the material possesses the specific surface area required for a low specific surface area OSC. The particle size (average particle size) of the primary particles in pyrochlore-type CZ, a low specific surface area OSC material, is not limited. Here, the primary particle diameter (D50) means the average primary particle diameter when the number distribution is measured. On the other hand, the secondary particle diameter (D50) means that the secondary particle diameter is the 50% cumulative particle diameter (also known as the median diameter or D50). For example, in a volume-based particle size distribution obtained by laser diffraction scattering, the secondary particle diameter is the particle diameter representing 50% of the volume in a cumulative volume distribution curve where the total volume is set to 100% (i.e., the volume-based cumulative 50% diameter).

[0231] Pyrochlore-type CZ with a specific range of secondary particle diameters (D50) as a low specific surface area OSC material is obtained, for example, through the following steps: mixing raw materials to obtain a precipitate, drying and calcining the precipitate, pulverizing it to obtain a powder, pressing the powder into shape, performing reduction treatment, and then pulverizing it to achieve the specified secondary particle diameter (D50). The pulverization of the shaped body can be performed using, for example, a ball mill, a vibratory mill, a stream mill, and a pin mill.

[0232] The specific surface area of ​​pyrochlore-type CZ, which is a low specific surface area OSC material, can be adjusted, particularly by adjusting the firing temperature, time, and pulverization conditions. Generally, a higher firing temperature results in a smaller specific surface area, and a longer firing time also results in a smaller specific surface area. In the case of preparing cerium dioxide-zirconia composite oxides as low specific surface area OSC materials, the firing temperature and time are not limited.

[0233] In pyrochlore-type CZ, used as a low specific surface area OSC material, the molar ratio (Zr / Ce) of zirconium (Zr) and cerium (Ce) is 1.13. <Zr / Ce<1.30。

[0234] Pyrochlore-type CZ, used as a low specific surface area OSC material, can also contain praseodymium; preferably, it contains praseodymium in addition to cerium and zirconium. Regarding praseodymium, since it is expressed by the formula: Pr6O 11 The reduction reaction represented by →3Pr₂O₃+O₂ has a negative ΔG (Gibbs free energy), so it can be assumed that the reduction reaction of CeO₂ represented by the formula: 2CeO₂→Ce₂O₃+0.5O₂ is more likely to cause a positive ΔG. When pyrochlore-type CZ containing praseodymium is used as a low specific surface area OSC material, the pyrochlore-type CZ preferably contains praseodymium at a concentration of 0.5 mol% to 5 mol% relative to the total cations. Furthermore, the molar ratio of Zr to (Ce+Pr) is preferably 1.13. <Zr / (Ce+Pr)<1.30。

[0235] As a low specific surface area OSC material, pyrochlore-type CZ can also include elements other than praseodymium as additional elements besides cerium and zirconium. The additional elements besides praseodymium are not limited, and examples include rare earth elements and alkaline earth metals other than cerium and praseodymium. Examples of rare earth elements other than cerium and praseodymium include scandium, yttrium, lanthanum, neodymium, samarium, gadolinium, terbium, dysprosium, ytterbium, and lutetium. Among these, lanthanum, neodymium, yttrium, and scandium are preferred from the viewpoint that they tend to have stronger interactions and greater affinity with noble metals when supported. Furthermore, examples of alkaline earth metal elements include magnesium, calcium, strontium, barium, and radium (Ra). Among these, magnesium, calcium, and barium are preferred from the viewpoint that they tend to have stronger interactions and greater affinity with noble metals when supported. The content of the added elements is usually less than 5 mol% relative to the total cation content of pyrochlore-type CZ.

[0236] The pyrochlore-type CZ as a low specific surface area OSC material can also be a material known in this technical field, such as the material described in Japanese Patent Application Publication No. 2018-038999.

[0237] For example, the primary particle size (average particle size) of pyrochlore-type CZ, which is a low specific surface area OSC material, is not limited, but is generally greater than 1 μm, preferably greater than 1 μm and less than 20 μm, based on the average value measured by SEM or TEM.

[0238] For example, the crystallite diameter of pyrochlore-type CZ, which is a low specific surface area OSC material, is not limited, but it is usually greater than 100 nm, for example, 150 nm to 500 nm.

[0239] For example, in the case of preparing pyrochlore-type CZ as a low specific surface area OSC material, the firing temperature and time are not limited, but are usually 1100℃~2000℃ and usually 0.5 hours~15 hours in the atmosphere.

[0240] The content of high specific surface area OSC material contained in the upstream coating is not limited, but the volume of the portion of the substrate coated with the upstream coating is typically 10g to 100g, preferably 10g to 80g per liter. Furthermore, the content of high specific surface area OSC material that can be contained in the upstream coating depends on the amount of high specific surface area OSC material added when it is used as a material in the manufacture of the exhaust gas purification catalyst.

[0241] The content of medium surface area OSC material contained in the upstream coating is not limited, but the volume of the portion of the substrate coated with the upstream coating (1L) is typically 0g to 45g, preferably 0g. Furthermore, the content of medium surface area OSC material that can be contained in the upstream coating depends on the amount of medium surface area OSC material added during the manufacture of the catalyst for exhaust gas purification.

[0242] The content of low specific surface area OSC material contained in the upstream coating is not limited, but the volume of the portion of the substrate coated with the upstream coating is typically 3g to 25g, preferably 5g to 20g per liter. Furthermore, the content of low specific surface area OSC material that can be contained in the upstream coating depends on the amount of low specific surface area OSC material added when it is used as a material in the manufacture of the exhaust gas purification catalyst.

[0243] The content of high specific surface area OSC material contained in the downstream coating is not limited, but the volume of the portion of the substrate coated with the downstream coating is typically 0 g to 80 g, preferably 0 g, per liter. Furthermore, the content of high specific surface area OSC material that can be contained in the downstream coating depends on the amount of high specific surface area OSC material added during the manufacture of the catalyst for exhaust gas purification.

[0244] The content of medium specific surface area OSC material contained in the downstream coating is not limited, but the volume of the portion of the substrate coated with the downstream coating per liter is typically 20g to 80g, preferably 40g to 80g. Furthermore, the content of medium specific surface area OSC material that can be contained in the downstream coating depends on the amount of medium specific surface area OSC material added when it is used as a catalyst for exhaust gas purification.

[0245] The content of low specific surface area OSC material included in the downstream coating is not limited, but the volume of the portion of the substrate coated with the downstream coating per liter is typically 5 g to 40 g, preferably 20 g to 40 g. Furthermore, the content of low specific surface area OSC material that can be included in the downstream coating depends on the amount of low specific surface area OSC material added when it is used as a material in the manufacture of the exhaust gas purification catalyst.

[0246] The upstream side coating preferably comprises high specific surface area OSC material and low specific surface area OSC material.

[0247] By including both high specific surface area OSC material and low specific surface area OSC material in the upstream side coating, when the exhaust gas purification catalyst of the first embodiment of the present invention is used as an S / C, NOx can be purified efficiently on the upstream side where the oxygen concentration is higher and HC is less likely to accumulate compared to the downstream side.

[0248] The downstream coating preferably comprises medium specific surface area OSC material and low specific surface area OSC material.

[0249] By including medium specific surface area OSC materials and low specific surface area OSC materials in the downstream coating, when the exhaust gas purification catalyst of the first embodiment of the present invention is used as an S / C, in the downstream side where the oxygen concentration is lower than that of the upstream side and HC is more likely to accumulate, the OSC material with a relatively low specific surface area can be used to prevent HC accumulation and purify NOx with high efficiency.

[0250] Therefore, by having the upstream coating contain both high and low specific surface area OSC materials, and the downstream coating contain both medium and low specific surface area OSC materials, it is possible to achieve a better balance between OSC performance and catalytic performance.

[0251] In the first embodiment of the present invention, the amount of cerium dioxide in the high specific surface area OSC material is not limited, but is typically 10% to 40% by weight, preferably 20% to 40% by weight, relative to the total weight of cerium dioxide in the second catalyst coating (i.e., the upstream coating and the downstream coating).

[0252] In the first embodiment of the present invention, the amount of cerium dioxide in the medium specific surface area OSC material is not limited, but is typically 10% to 45% by weight, preferably 10% to 40% by weight, and more preferably 20% to 40% by weight, relative to the total weight of cerium dioxide in the second catalyst coating.

[0253] In the first embodiment of the present invention, the total amount of cerium dioxide in the high specific surface area OSC material and the medium specific surface area OSC material is not limited, but it is generally 80% by weight or less, preferably 60% by weight or less, and more preferably 40% by weight or less, relative to the total weight of cerium dioxide in the second catalyst coating.

[0254] In the first embodiment of the present invention, the amount of cerium dioxide in the low specific surface area OSC material is not limited, but is typically 20% to 80% by weight, preferably 40% to 80% by weight, and more preferably 40% to 60% by weight, relative to the total weight of cerium dioxide in the second catalyst coating.

[0255] Here, in the first embodiment of the present invention, in the second catalyst coating, if no cerium dioxide-containing compounds are contained except for the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material, the total amount of cerium dioxide in the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material is added together to obtain 100% by weight.

[0256] By setting the amount of cerium dioxide in each OSC material in the second catalyst coating to the range mentioned above, it is possible to establish more comprehensive OSC performance and exhaust gas purification performance, especially NOx purification performance, at both low and high temperatures.

[0257] Specifically, in the first embodiment of the present invention, by including three OSC materials with different specific surface areas while containing Rh in the second catalyst coating (upstream coating and downstream coating), it is possible to obtain an exhaust gas purification catalyst that simultaneously achieves the suppression of HC poisoning of Rh, especially under conditions of (1) rich air-fuel ratio (A / F) and (2) high intake air volume (high intake air volume or high Ga: synonymous with high space velocity or high SV) associated with low bulkiness of the exhaust gas purification catalyst, and ensures OSC performance at low and high temperatures, thereby improving catalytic performance, especially NOx purification performance.

[0258] The upstream and downstream coatings constituting the second catalyst coating are primarily composed of Rh as the catalyst metal, other noble metals as appropriate, support particles supporting Rh and other noble metals as the catalyst metal, and the aforementioned OSC material. However, other components may also be included without impairing the effects of the present invention. Examples of other components include other metal oxides and additives used in catalyst coatings for this purpose. Specifically, examples include one or more of the following: alkali metals such as potassium, sodium, lithium, and cesium; alkaline earth metals such as barium, calcium, and strontium; rare earth elements such as lanthanum, yttrium, and cerium; transition metals such as iron; and metal oxides listed above as support particles (i.e., metal oxides without Rh, etc.). Other components may be in their original form or, like Rh, may be supported on support particles.

[0259] In each of the upstream and downstream coatings constituting the second catalyst coating, the content of other components in the coating is not limited if present, but the capacity of the portion of the substrate coated with the upstream or downstream coating (1L) is typically 20g to 120g, preferably 80g to 120g. Furthermore, the content of other components that can be included in the upstream or downstream coating depends on the amount of other components added (excluding volatile components) used in the manufacture of the catalyst for exhaust gas purification.

[0260] The amount of upstream coating is not limited, but the capacity of the portion with upstream coating relative to the substrate is typically 30g to 250g per liter, preferably 50g to 250g. Furthermore, the amount of upstream coating depends on the total weight of the materials used in the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0261] The amount of downstream coating is not limited, but the capacity of the portion with downstream coating relative to the substrate is typically 50g to 250g per liter, preferably 100g to 250g. Furthermore, the amount of downstream coating depends on the total weight of the materials used in the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0262] The thickness of the upstream coating is not limited, but on average, it is typically 5 μm to 50 μm, preferably 10 μm to 30 μm. The thickness of the upstream coating can be measured using, for example, SEM.

[0263] The thickness of the downstream coating is not limited, but on average, it is typically 5 μm to 50 μm, preferably 10 μm to 30 μm. The thickness of the downstream coating can be measured using, for example, SEM.

[0264] By ensuring that the amounts of each material in the upstream and downstream coatings, as well as the thicknesses of the upstream and downstream coatings, fall within the aforementioned ranges, a good balance between pressure loss, catalytic performance, and durability in the exhaust gas purification catalyst can be maintained.

[0265] • Second implementation method

[0266] In a second embodiment of the present invention, the second catalyst coating comprises Rh as a catalyst metal and three OSC materials with different specific surface areas, as detailed below.

[0267] The content of Rh, a catalyst metal, contained in the second catalyst coating is not limited, but the content, calculated based on the metal conversion of the catalyst metal, is typically 0.05 g to 1.0 g, preferably 0.2 g to 0.8 g, relative to the volume of 1 L of the portion of the substrate coated with the second catalyst coating. Furthermore, the content of Rh, a catalyst metal, contained in the second catalyst coating depends on the amount of Rh precursor added (excluding volatile components) used in the manufacture of the exhaust gas purification catalyst.

[0268] With the second catalyst coating containing Rh at the above-mentioned content, in an atmosphere where HC has been sufficiently purified by the first catalyst coating, Rh will not cause HC poisoning, and the NOx purification performance can be fully utilized.

[0269] The second catalyst coating may also include other precious metals commonly used in the field of catalysts for exhaust purification, such as at least one selected from Pd, Pt, gold, silver, iridium and ruthenium.

[0270] The form of Rh and other precious metals contained in the second catalyst coating, and as appropriate, in each catalyst coating, can be the same as the form of Rh and other precious metals contained, as described in the first embodiment, i.e., their original form or their form supported on carrier particles. When the Rh and other precious metals contained in the second catalyst coating are supported on carrier particles, the content of carrier particles in the second catalyst coating (excluding the content of OSC materials described in the first embodiment if the carrier particles contain OSC materials) is typically 20g to 170g, preferably 50g to 140g, relative to the volume (in 1L) of the portion of the substrate coated with the second catalyst coating. Furthermore, the content of carrier particles that can be contained in the second catalyst coating depends on the amount of carrier particles added as materials used in the manufacture of the exhaust gas purification catalyst.

[0271] In the second embodiment of the present invention, the OSC material included in the second catalyst coating is composed of a high specific surface area OSC material, a medium specific surface area OSC material, and a low specific surface area OSC material. Here, the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material are as described in the aforementioned first embodiment.

[0272] In the second embodiment of the present invention, the second catalyst coating contains three OSC materials with different specific surface areas, which can combine OSC performance and exhaust gas purification performance, especially NOx purification performance.

[0273] In the second embodiment of the present invention, the content of high specific surface area OSC material included in the second catalyst coating is not limited, but the volume of the portion of the substrate coated with the second catalyst coating is typically 10g to 80g, preferably 20g to 40g, relative to 1L. Furthermore, the content of high specific surface area OSC material included in the second catalyst coating depends on the amount of high specific surface area OSC material added during the manufacture of the catalyst for exhaust gas purification.

[0274] In the second embodiment of the present invention, the content of medium specific surface area OSC material included in the second catalyst coating is not limited, but the volume of the portion of the substrate coated with the second catalyst coating is typically 10g to 40g, preferably 20g to 40g, relative to 1L. Furthermore, the content of medium specific surface area OSC material included in the second catalyst coating depends on the amount of medium specific surface area OSC material added during the manufacture of the catalyst for exhaust gas purification.

[0275] In the second embodiment of the present invention, the content of low specific surface area OSC material included in the second catalyst coating is not limited, but the volume of the portion of the substrate coated with the second catalyst coating is typically 5g to 30g, preferably 10g to 30g, relative to 1L. Furthermore, the content of low specific surface area OSC material included in the second catalyst coating depends on the amount of low specific surface area OSC material added during the manufacture of the catalyst for exhaust gas purification.

[0276] In the second embodiment of the present invention, by including three OSC materials with different specific surface areas in the aforementioned amount by the second catalyst coating, it is possible to establish more comprehensive OSC performance and exhaust gas purification performance, especially NOx purification performance at both low and high temperatures.

[0277] Specifically, in the second embodiment of the present invention, by including three OSC materials with different specific surface areas while containing Rh in the second catalyst coating, it is possible to obtain an exhaust gas purification catalyst that simultaneously achieves the suppression of HC poisoning of Rh, especially under conditions of (1) a rich air-fuel ratio (A / F) and (2) a large intake air volume (high intake air volume or high Ga: synonymous with high space velocity or high SV) during acceleration, thereby improving catalytic performance, especially NOx purification performance.

[0278] In the second embodiment of the present invention, the second catalyst coating is mainly composed of Rh as a catalyst metal, other noble metals as appropriate, support particles supporting Rh and other noble metals as the catalyst metal, and the aforementioned OSC material. However, it may also contain other components without impairing the effects of the present invention. Other components include other metal oxides, additives, etc., used in catalyst coatings for this purpose. Specifically, one or more of the following can be listed: alkali metals such as potassium, sodium, lithium, and cesium; alkaline earth metals such as barium, calcium, and strontium; rare earth elements such as lanthanum, yttrium, and cerium; transition metals such as iron; and metal oxides listed as support particles (i.e., metal oxides without Rh, etc.). Other components may be in their original form or, like Rh, may be in the form of being supported on support particles.

[0279] The content of other components in the second catalyst coating is not limited in its presence, but the volume of the portion of the substrate coated with the second catalyst coating is typically 20g to 120g, preferably 80g to 120g, per liter. Furthermore, the content of other components that can be included in the second catalyst coating depends on the amount of other components added (excluding volatile components) used as materials in the manufacture of the exhaust gas purification catalyst.

[0280] The amount of the second catalyst coating is not limited, but the capacity of the portion of the substrate coated with the second catalyst coating is typically 50g to 250g, preferably 150g to 250g, per liter. Furthermore, the amount of the second catalyst coating depends on the total weight of the materials used in manufacturing the exhaust gas purification catalyst (excluding volatile components).

[0281] The thickness of the second catalyst coating is not limited, but on average, it is typically 5 μm to 50 μm, preferably 10 μm to 30 μm. The thickness of the second catalyst coating can be measured using, for example, SEM.

[0282] By ensuring that the amounts of each material in the second catalyst coating and the thickness of the second catalyst coating fall within the aforementioned ranges, a good balance between pressure loss, catalytic performance, and durability in the exhaust gas purification catalyst can be maintained.

[0283] (Manufacturing method of catalyst for exhaust gas purification)

[0284] The exhaust gas purification catalyst of the present invention can be manufactured using known coating techniques, except for the components of the exhaust gas purification catalyst described above.

[0285] For example, the exhaust gas purification catalyst of the present invention, having a substrate and a catalyst coating comprising a first catalyst coating and a second catalyst coating coated on the substrate, can be manufactured by a method comprising: (i) a step of preparing a slurry for a first catalyst coating comprising a catalyst metal precursor and a solvent, wherein the catalyst metal precursor comprises Pd and / or Pt as catalyst metals; (ii) a step of preparing a slurry for a second catalyst coating comprising an Rh precursor, a solvent, a high specific surface area OSC material, a medium specific surface area OSC material, and a low specific surface area OSC material, wherein the Rh precursor comprises Rh as catalyst metal; (iii) a step of coating the first catalyst coating slurry prepared in step (i) from an end upstream of the exhaust gas flow direction in the exhaust gas purification catalyst, thereby forming a first catalyst coating; and (iv) a step of coating the second catalyst coating slurry prepared in step (ii) thereby forming a second catalyst coating.

[0286] Here, high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials are as described above.

[0287] • First Implementation

[0288] In manufacturing the exhaust gas purification catalyst according to the first embodiment of the present invention, step (ii) as a step for preparing a slurry for the second catalyst coating includes: (ii-1) a step for preparing a downstream coating slurry formed from the end of the exhaust gas flow direction relative to the exhaust gas flow direction in the exhaust gas purification catalyst; and (ii-2) a step for preparing an upstream coating slurry formed from the end of the exhaust gas flow direction relative to the exhaust gas flow direction in the exhaust gas purification catalyst. Furthermore, step (iv) as a step for forming the second catalyst coating includes: (iv-1) a step for coating the downstream coating slurry prepared in step (ii-1) to form a downstream coating; and (iv-2) a step for coating the upstream coating slurry prepared in step (ii-2) to form an upstream coating. Moreover, the order of steps (i) to (iv) is not limited, as long as step (iii) is performed after step (i), step (iv-1) is performed after step (ii-1), and step (iv-2) is performed after step (ii-2). For example, besides the order (i)→(ii-1)→(ii-2)→(iii)→(iv-1)→(iv-2), other possible orders include (ii-2)→(ii-1)→(iv-1)→(iv-2)→(i)→(iii), (i)→(ii-1)→(ii-2)→(iv-1)→(iii)→(iv-2), (ii-1)→(iv-1)→(ii-2)→(iv-2)→(i)→(iii), and (i)→(iii)→(ii-1)→(iv-1)→(ii-2)→(iv-2).

[0289] In manufacturing the exhaust gas purification catalyst according to the first embodiment of the present invention, in step (iii), the first catalyst coating slurry is preferably applied to 20% to 50% of the total length of the substrate in the exhaust gas purification catalyst. Furthermore, in step (iv-1), the downstream coating slurry is preferably applied to 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst. Additionally, in step (iv-2), the upstream coating slurry is preferably applied to 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst.

[0290] In manufacturing the exhaust gas purification catalyst according to the first embodiment of the present invention, step (ii-1) is preferably a step of preparing a downstream coating slurry comprising an Rh precursor, a solvent, a medium specific surface area OSC material, and a low specific surface area OSC material. Furthermore, step (ii-2) is preferably a step of preparing an upstream coating slurry comprising an Rh precursor, a solvent, a high specific surface area OSC material, and a low specific surface area OSC material.

[0291] In manufacturing the exhaust gas purification catalyst according to the first embodiment of the present invention, in steps (ii-1) and (ii-2), the amount of cerium dioxide in the high specific surface area OSC material used is preferably 10% to 40% by weight relative to the total weight of cerium dioxide in the upstream and downstream coatings of the second catalyst coating. Furthermore, the amount of cerium dioxide in the medium specific surface area OSC material used is preferably 10% to 40% by weight relative to the total weight of cerium dioxide in the upstream and downstream coatings of the second catalyst coating. Additionally, the total amount of cerium dioxide in the high and medium specific surface area OSC materials used is preferably 60% by weight or less relative to the total weight of cerium dioxide in the upstream and downstream coatings of the second catalyst coating. Furthermore, the amount of cerium dioxide in the low specific surface area OSC material used is preferably 40% to 80% by weight relative to the total weight of cerium dioxide in the upstream and downstream coatings of the second catalyst coating. Here, adjustments were made so that when the amounts of cerium dioxide in the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material are all added together, the total amount is 100 by weight.

[0292] In the case of manufacturing the exhaust gas purification catalyst of the first embodiment of the present invention, step (i) is preferably the step of preparing a first catalyst coating slurry comprising a Pd precursor and a solvent.

[0293] • Second implementation method

[0294] In the case of manufacturing the exhaust gas purification catalyst according to the second embodiment of the present invention, step (iv) is a step of forming a second catalyst coating by applying the second catalyst coating slurry prepared in step (ii) from the end downstream of the exhaust gas flow direction in the exhaust gas purification catalyst. Furthermore, the order of steps (i) to (iv) is not limited as long as step (iii) is performed after step (i) and step (iv) is performed after step (ii). For example, in addition to the order (i)→(ii)→(iii)→(iv), sequences such as (ii)→(iv)→(i)→(iii) and (i)→(iii)→(ii)→(iv) can also be used.

[0295] In manufacturing the exhaust gas purification catalyst according to the second embodiment of the present invention, in step (iii), the first catalyst coating slurry is preferably applied to 15% to 50% of the total length of the substrate in the exhaust gas purification catalyst. Furthermore, in step (iv), the second catalyst coating slurry is preferably applied to 65% to 95% of the total length of the substrate in the exhaust gas purification catalyst.

[0296] In the case of manufacturing the exhaust gas purification catalyst of the second embodiment of the present invention, step (i) is preferably the step of preparing a first catalyst coating slurry containing a Pt precursor and a solvent.

[0297] The exhaust gas purification catalyst of the present invention can be manufactured, for example, as follows.

[0298] In manufacturing the exhaust gas purification catalyst according to the first embodiment of the present invention, firstly, as step (ii-1), a catalyst coating slurry for a downstream coating is prepared. This slurry comprises materials constituting the downstream coating, namely, an Rh precursor (e.g., a salt containing Rh (e.g., a nitrate), etc.), one or more OSC materials selected from high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials (e.g., alumina-cerium dioxide-zirconia composite oxide as a medium specific surface area OSC material and cerium dioxide-zirconia composite oxide as a low specific surface area OSC material), a solvent (e.g., water, alcohol, a mixture of water and alcohol, etc.), and carrier particles (e.g., alumina-zirconia composite oxide) and additives (e.g., binders), which may be further contained as appropriate. Secondly, as step (iv-1), the slurry is coated onto a substrate in the area where the downstream coating is to be formed using a wash-coating method. After the excess slurry is blown away using a blower or the like, the solvent is removed by drying in the atmosphere at a temperature of 100°C to 150°C for 1 to 3 hours, and then calcined in the atmosphere at a temperature of 450°C to 550°C for 1 to 3 hours to form a downstream coating. Next, as step (ii-2), a catalyst coating slurry for the upstream coating is prepared. This slurry contains materials constituting the upstream coating, namely, an Rh precursor (e.g., a salt containing Rh (e.g., nitrate), one or more OSC materials selected from high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials (e.g., alumina-cerium dioxide-zirconia composite oxide as a high specific surface area OSC material and cerium dioxide-zirconia composite oxide as a low specific surface area OSC material), a solvent (e.g., water, alcohol, a mixture of water and alcohol), and carrier particles (e.g., alumina-zirconia composite oxide) and additives (e.g., binders), which may be further contained depending on the situation. Next, as step (iv-2), on the substrate where the downstream coating has been formed, the slurry is applied to the area where the upstream coating is to be formed using a wash-coating method. After the excess slurry is blown away using a blower or the like, the solvent is removed by drying in the atmosphere at a temperature of 100°C to 150°C for 1 to 3 hours, for example. Then, the substrate is fired in the atmosphere at a temperature of 450°C to 550°C for 1 to 3 hours to form the upstream coating.Next, as step (i), a catalyst coating slurry for the first catalyst coating is prepared. This slurry comprises materials constituting the first catalyst coating, namely, a precursor of Pd and / or Pt as a catalyst metal (e.g., a salt containing Pd and / or Pt (e.g., a nitrate), especially Pd nitrate), a solvent (e.g., water, alcohol, a mixture of water and alcohol), and, depending on the situation, carrier particles (e.g., alumina-cerium dioxide-zirconia composite oxide and / or cerium dioxide-zirconia composite oxide), and additives (e.g., a binder). Next, as step (iii), the slurry is coated onto the substrate on which the second catalyst coating (the downstream coating and the upstream coating) is formed, in the area where the first catalyst coating is to be formed (on the upstream coating), using a wash-coating method. After the excess slurry is blown away using a blower or the like, the solvent is removed by drying in the atmosphere at a temperature of 100°C to 150°C for 1 to 3 hours, and then calcined in the atmosphere at a temperature of 450°C to 550°C for 1 to 3 hours to form the first catalyst coating. Furthermore, in the method for manufacturing the exhaust gas purification catalyst according to the first embodiment of the present invention, as described above, the order in which the catalyst coating is formed is not limited. The catalyst coating may be formed in the following order: first catalyst coating, upstream side coating, downstream side coating; first catalyst coating, downstream side coating, upstream side coating; upstream side coating, downstream side coating; first catalyst coating; upstream side coating; first catalyst coating; downstream side coating; or downstream side coating, first catalyst coating, upstream side coating.

[0299] In preparing the exhaust gas purification catalyst according to the second embodiment of the present invention, firstly, as step (ii), a catalyst coating slurry for a second catalyst coating is prepared. This slurry comprises materials constituting the second catalyst coating, namely, an Rh precursor (e.g., a salt containing Rh (e.g., nitrate), three OSC materials with different specific surface areas (e.g., alumina-cerium dioxide-zirconia composite oxide and / or cerium dioxide-zirconia composite oxide), a solvent (e.g., water, alcohol, a mixture of water and alcohol), and, depending on the circumstances, carrier particles (e.g., alumina-zirconia composite oxide) and additives (e.g., binders). Next, as step (iv), the slurry is applied to a substrate in the area where the second catalyst coating is to be formed using a wash-coating method. After the excess slurry is blown away using a blower or the like, the solvent is removed by drying in the atmosphere at a temperature of 100°C to 150°C for 1 to 3 hours, and then calcined in the atmosphere at a temperature of 450°C to 550°C for 1 to 3 hours to form the second catalyst coating. Next, as step (i), a catalyst coating slurry for the first catalyst coating is prepared. This slurry contains materials constituting the first catalyst coating, namely, a precursor of Pd and / or Pt as a catalyst metal (e.g., a salt containing Pd and / or Pt (e.g., a nitrate), a solvent (e.g., water, alcohol, a mixture of water and alcohol), and, depending on the situation, carrier particles (e.g., alumina-cerium dioxide-zirconia composite oxide and / or cerium dioxide-zirconia composite oxide), and additives (e.g., a binder). Next, as step (iii), the slurry is coated onto the substrate on which the second catalyst coating is formed, in the area where the first catalyst coating is to be formed, using a wash-coating method. After excess slurry is blown away using a blower or similar means, the solvent is removed by drying in the atmosphere at a temperature of 100°C to 150°C for 1 to 3 hours, and then calcined in the atmosphere at a temperature of 450°C to 550°C for 1 to 3 hours to form the first catalyst coating. Furthermore, in the method for manufacturing the exhaust gas purification catalyst according to the second embodiment of the present invention, as described above, the order in which the catalyst coatings are formed is not limited, and the second catalyst coating may be formed after the first catalyst coating.

[0300] (Applications of catalysts for exhaust gas purification)

[0301] The exhaust gas purification catalyst of the present invention can greatly improve the exhaust gas purification performance under rich atmosphere. It can be used as an exhaust gas purification catalyst with a high HC poisoning inhibition effect, even in environments where residual HC and other substances in rich atmospheres may adsorb onto the exhaust gas purification catalyst and poison it.

[0302] For example, the exhaust gas purification catalyst of the first embodiment of the present invention can be used as an S / C in a dual catalyst system including S / C and UF / C.

[0303] For example, the exhaust gas purification catalyst of the second embodiment of the present invention can be used as UF / C in a dual catalyst system including S / C and UF / C.

[0304] Example

[0305] The following describes several embodiments of the present invention, but it is not intended to limit the present invention to the solutions shown in such embodiments.

[0306] I. First Implementation

[0307] I-1. Materials Used

[0308] Material 1 (Al2O3)

[0309] La2O3 composites with Al2O3

[0310] (Al2O3: 99 wt%)

[0311] (La2O3: 1 wt%)

[0312] Material 2 (High specific surface area OSC material)

[0313] Al2O3-CeO2-ZrO2 composite oxide (ACZ)

[0314] (Al2O3: 30% by weight)

[0315] (CeO2: 20% by weight)

[0316] (ZrO2: 44% by weight)

[0317] (Nd2O3: 2 wt%)

[0318] (La2O3: 2 wt%)

[0319] (Y2O3: 2% by weight)

[0320] BET specific surface area: 65m² 2 / g

[0321] Material 3 (Medium Specific Surface Area OSC Material)

[0322] Al2O3-CeO2-ZrO2 composite oxide (ACZ)

[0323] (Al2O3: 30% by weight)

[0324] (CeO2: 20% by weight)

[0325] (ZrO2: 44% by weight)

[0326] (Nd2O3: 2 wt%)

[0327] (La2O3: 2 wt%)

[0328] (Y2O3: 2% by weight)

[0329] BET specific surface area: 35m² 2 / g

[0330] Material 4 (Low Specific Surface Area OSC Material)

[0331] CeO2-ZrO2 composite oxide with pyrochlore-type structure (Ce2Zr2O7) (CeO2: 51.5 wt%)

[0332] (ZrO2: 45.5% by weight)

[0333] (Pr6O 11 3% by weight

[0334] (Prepared based on Japanese Patent Application Publication No. 2018-038999)

[0335] BET specific surface area: 1.5m² 2 / g

[0336] Material 5 (AZ)

[0337] Al2O3-ZrO2 composite oxide (AZ)

[0338] (Al2O3: 30% by weight)

[0339] (ZrO2: 60% by weight)

[0340] (La2O3: 5% by weight)

[0341] (Y2O3: 5% by weight)

[0342] Material 6 (CZ)

[0343] CeO2-ZrO2 composite oxides (CZ)

[0344] (CeO2: 40% by weight)

[0345] (ZrO2: 50% by weight)

[0346] (La2O3: 5% by weight)

[0347] (Y2O3: 5% by weight)

[0348] Material 7 (Ba)

[0349] Barium sulfate

[0350] Material 8 (Rh)

[0351] Rhodium nitrate aqueous solution

[0352] Rh concentration: 2.75% by weight

[0353] Material 9 (Pd)

[0354] Palladium nitrate aqueous solution

[0355] Pd concentration: 8.4% by weight

[0356] substrate

[0357] 875cc (600-cell hexagonal, 2 mil wall thickness, 105mm total length) cordierite honeycomb substrate

[0358] I-2. Preparation of catalysts for exhaust gas purification

[0359] Comparative Example 1

[0360] First, materials 8 (Rh) and 5 (AZ) were added to distilled water while stirring. The resulting suspension was dried at 120°C for 2 hours and then calcined at 500°C for 2 hours to prepare Rh-supported AZ (Rh / AZ).

[0361] Next, while stirring, Rh / AZ, material 1 (Al2O3), material 2 (high specific surface area OSC material), material 4 (low specific surface area OSC material), material 5 (AZ), and Al2O3-based binder were added to distilled water to prepare a suspended slurry 1.

[0362] Next, by flowing the prepared slurry 1 into the substrate and blowing away the unwanted portion using a blower, a material is coated onto the substrate wall, thus preparing a precursor layer for the downstream coating. At this time, regarding each coating material, the volume 1L of the portion of the substrate to which the downstream coating is applied is as follows: material 8 is 0.40g (0.40g / L-zone) according to the metal conversion of Rh, material 1 is 40g (40g / L-zone), material 2 is 75g (75g / L-zone), material 4 is 28g (28g / L-zone), and material 5 is 40g (40g / L-zone). Furthermore, the coating length of the precursor layer for the downstream coating is adjusted so that it occupies 65% of the total length of the substrate in the exhaust gas purification catalyst, starting from the end facing downstream relative to the exhaust flow direction in the exhaust gas purification catalyst.

[0363] Finally, the downstream coating (rear part) was prepared by drying in a dryer at 120°C for 2 hours to allow the moisture to evaporate, and then firing in an electric furnace at 500°C for 2 hours.

[0364] Next, while stirring, materials 8 (Rh) and 5 (AZ) were added to distilled water. The resulting suspension was dried at 120°C for 2 hours and then calcined at 500°C for 2 hours to prepare Rh-supported AZ (Rh / AZ).

[0365] Next, while stirring, Rh / AZ, material 1 (Al2O3), material 2 (high specific surface area OSC material), material 4 (low specific surface area OSC material), and Al2O3-based binder were added to distilled water to prepare a suspended slurry 2.

[0366] Next, the prepared slurry 2 is fed into the substrate having the downstream-side coating from the end opposite to the end face where the downstream-side coating is formed, and unwanted portions are blown away using a blower. This coats the substrate wall with material, thus preparing a precursor layer for the upstream-side coating. At this time, regarding each coating material, relative to the volume 1L of the portion of the substrate coated with the upstream-side coating, material 8 is converted to 0.15g (0.15g / L-zone) according to Rh metal conversion, material 1 is 20g (20g / L-zone), material 2 is 15g (15g / L-zone), material 4 is 8g (8g / L-zone), and material 5 is 20g (20g / L-zone). Furthermore, the coating length of the upstream-side coating precursor layer is adjusted so that it occupies 55% of the total length of the substrate in the exhaust gas purification catalyst, starting from the end facing upstream relative to the exhaust flow direction in the exhaust gas purification catalyst.

[0367] Finally, after the moisture was removed by drying in a dryer at 120°C for 2 hours, the upstream side coating (front part) was prepared by firing in an electric furnace at 500°C for 2 hours.

[0368] Next, in the same manner as described above, materials 9 (Pd), 1 (Al2O3), 6 (CZ), 7 (Ba), and an Al2O3-based binder were added to distilled water while stirring to prepare a suspended slurry 3.

[0369] Next, the prepared slurry 3 is fed into the substrate on which the downstream and upstream coatings, serving as the second catalyst coating, are formed, from the same end face as the end face where the upstream coating is formed. Unwanted portions are blown away using a blower, thereby coating the substrate wall with material and preparing the precursor layer of the first catalyst coating. At this time, regarding each coating material, relative to the volume 1L of the portion of the substrate coated with the first catalyst coating, material 9 is converted to 5g (5g / L-zone) based on the metal conversion of Pd, material 1 is 25g (25g / L-zone), material 6 is 75g (75g / L-zone), and material 7 is 13g (13g / L-zone). Furthermore, the coating length of the precursor layer of the first catalyst coating is adjusted so that it occupies 30% of the total length of the substrate in the exhaust gas purification catalyst, starting from the end facing upstream relative to the exhaust flow direction in the exhaust gas purification catalyst.

[0370] Finally, after the moisture was removed by drying in a dryer at 120°C for 2 hours, the first catalyst coating (front part) was prepared by firing in an electric furnace at 500°C for 2 hours, and the catalyst for exhaust purification was finally prepared.

[0371] Comparative Example 2

[0372] Except that in Comparative Example 1, the total amount of material 2 in slurry 1 (75 g / L-zone) was changed to material 3 (medium specific surface area OSC material) (75 g / L-zone), and the total amount of material 2 in slurry 2 (15 g / L-zone) was changed to material 3 (medium specific surface area OSC material) (15 g / L-zone), an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1.

[0373] Example 1

[0374] Except for changing the total amount of material 2 in slurry 1 (75 g / L-zone) to material 3 (medium specific surface area OSC material) (75 g / L-zone), changing the amount of material 4 added to slurry 1 to adjust the total amount of material 4 in slurry 1 to 8 g / L-zone, and changing the amount of material 2 added to slurry 2 to adjust the total amount of material 2 in slurry 2 to 75 g / L-zone, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1.

[0375] Example 2

[0376] Except for changing the total amount of material 2 in slurry 1 (75 g / L-zone) to material 3 (medium specific surface area OSC material) (60 g / L-zone) in Comparative Example 1, and changing the amount of material 2 added to slurry 2 to adjust the total amount of material 2 in slurry 2 to 30 g / L-zone, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1.

[0377] Example 3

[0378] Except for Comparative Example 1, where the total amount of material 2 in slurry 1 (75 g / L-zone) was changed to material 3 (medium specific surface area OSC material) (25 g / L-zone), the amount of material 4 added to slurry 1 was changed to adjust the total amount of material 4 in slurry 1 to 33 g / L-zone, the amount of material 2 added to slurry 2 was changed to adjust the total amount of material 2 in slurry 2 to 30 g / L-zone, and the amount of material 4 added to slurry 2 was changed to adjust the total amount of material 4 in slurry 2 to 18 g / L-zone, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1.

[0379] Example 4

[0380] Except for Comparative Example 1, where the total amount of material 2 in slurry 1 (75 g / L-zone) was changed to material 3 (medium specific surface area OSC material) (25 g / L-zone), the amount of material 4 added to slurry 1 was changed to adjust the total amount of material 4 in slurry 1 to 18 g / L-zone, the amount of material 2 added to slurry 2 was changed to adjust the total amount of material 2 in slurry 2 to 75 g / L-zone, and the amount of material 4 added to slurry 2 was changed to adjust the total amount of material 4 in slurry 2 to 18 g / L-zone, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1.

[0381] Comparative Example 3

[0382] Except that the order of forming the catalyst coating was changed from (downstream side coating → upstream side coating → first catalyst coating) to (first catalyst coating → downstream side coating → upstream side coating) in Comparative Example 1, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1.

[0383] Example 5

[0384] Except for changing the order of forming the catalyst coating from (downstream side coating → upstream side coating → first catalyst coating) to (first catalyst coating → downstream side coating → upstream side coating) in Example 3, the catalyst for exhaust purification was prepared in the same manner as in Example 3.

[0385] Table 1 summarizes the composition of the OSC material in the upstream and downstream coatings of the exhaust gas purification catalysts of Comparative Examples 1-3 and Examples 1-5.

[0386] Table 1. Overview of the preparation levels of the examples and comparative examples.

[0387] The unit is g / L-zone

[0388]

[0389] Table 2 summarizes the proportion of cerium dioxide in each material relative to the total material in the exhaust gas purification catalysts of Comparative Examples 1-3 and Examples 1-5. Here, the amount (proportion) of cerium dioxide in the high specific surface area OSC material, medium specific surface area OSC material, and low specific surface area OSC material is summed to 100% by weight. However, in Table 2, since the proportion of cerium dioxide in each of the three OSC materials is expressed with three significant figures, the sum of these proportions is 100 ± 0.1% by weight.

[0390] Table 2 shows the proportion of cerium dioxide in each material relative to the overall material composition.

[0391]

[0392] I-3. Durability Test

[0393] Regarding the exhaust purification catalysts of Comparative Examples 1-3 and Examples 1-5, the following durability tests were conducted using actual engines.

[0394] By installing each exhaust purification catalyst separately in the exhaust system of a V8 engine, the exhaust gases of the theoretically proportioned and lean atmospheres are repeatedly flowed at a certain time (3:1 ratio) for 50 hours at a catalyst bed temperature of 950℃.

[0395] I-4. Performance Evaluation

[0396] Regarding the exhaust purification catalysts of Comparative Examples 1-3 and Examples 1-5, which underwent the I-3. durability test, the following performance evaluations were performed using actual engines.

[0397] I-4-1. OSC Evaluation

[0398] Each exhaust purification catalyst was installed in the exhaust system of an L-type 4-cylinder engine. A / F feedback control was implemented under conditions of Ga = 10 g / s, 500℃ (low temperature), or 750℃ (high temperature) to achieve an A / F ratio of 14.1 and 15.1, respectively. Based on the difference between the theoretical saturation point and the A / F sensor output, the excess or deficiency of oxygen was calculated using the following formula. The maximum oxygen uptake at Ga = 10 g / s, 500℃ (low temperature), or 750℃ (high temperature) was used as the OSC for evaluation.

[0399] OSC(g) = 0.23 × ΔA / F × Injected fuel quantity

[0400] I-4-2. NOx purification rate under concentrated atmosphere

[0401] Each exhaust purification catalyst was installed in the exhaust system of an L-type 4-cylinder engine, supplying exhaust gas with an air-fuel ratio (A / F) of 14.4. The NOx purification rate was measured at Ga = 30 / s and 550°C. The NOx purification rate after 3 minutes was used as the NOx purification activity under a rich atmosphere for evaluation.

[0402] I-5. Evaluation Results

[0403] In Table 3 and Figure 9 and Figure 10 The results are shown in the figure.

[0404] Table 3: Overview of Evaluation Results

[0405]

[0406] As can be seen from Table 3 by comparing Comparative Examples 1 and 2 with Examples 1-4: In Examples 1-4, the second catalyst coating contains three OSC materials with different specific surface areas: a high specific surface area OSC material, a medium specific surface area OSC material, and a low specific surface area OSC material. More preferably, the upstream coating contains both high and low specific surface area OSC materials, and the downstream coating contains both medium and low specific surface area OSC materials. This allows for the maintenance of OSC performance at both high and low temperatures without producing insufficient performance, and achieves a high NOx purification rate in a concentrated atmosphere. In other words, it allows for a good balance of the three performance characteristics at a high level. For example, from... Figure 9 As can be seen, in Example 2, OSC was maintained at both low and high temperatures, and the NOx purification rate that was insufficient in Comparative Example 1 was improved.

[0407] Therefore, it can be seen that by including all of the high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials in the second catalyst coating, both OSC performance and NOx purification rate can be taken into account.

[0408] In addition, from Table 3 and Figure 10 By comparing Comparative Example 3 and Example 5, it can be seen that even if the configuration of the first catalyst coating and the upstream coating is interchanged, that is, even if the upstream coating is disposed on the first catalyst coating, the effect of the present invention can still be obtained.

[0409] II. Second Implementation

[0410] II-1. Materials Used

[0411] Material 1 (Al2O3)

[0412] La2O3 composites with Al2O3

[0413] (Al2O3: 99 wt%)

[0414] (La2O3: 1 wt%)

[0415] Material 2 (High specific surface area OSC material)

[0416] Al2O3-CeO2-ZrO2 composite oxide (ACZ)

[0417] (Al2O3: 30% by weight)

[0418] (CeO2: 20% by weight)

[0419] (ZrO2: 44% by weight)

[0420] (Nd2O3: 2 wt%)

[0421] (La2O3: 2 wt%)

[0422] (Y2O3: 2% by weight)

[0423] BET specific surface area: 65m² 2 / g

[0424] Material 3 (Medium Specific Surface Area OSC Material)

[0425] Al2O3-CeO2-ZrO2 composite oxide (ACZ)

[0426] (Al2O3: 30% by weight)

[0427] (CeO2: 20% by weight)

[0428] (ZrO2: 44% by weight)

[0429] (Nd2O3: 2 wt%)

[0430] (La2O3: 2 wt%)

[0431] (Y2O3: 2% by weight)

[0432] BET specific surface area: 35m² 2 / g

[0433] Material 4 (Low Specific Surface Area OSC Material)

[0434] CeO2-ZrO2 composite oxide with pyrochlore-type structure (Ce2Zr2O7) (CeO2: 51.5 wt%)

[0435] (ZrO2: 45.5% by weight)

[0436] (Pr6O 113% by weight

[0437] (Prepared based on Japanese Patent Application Publication No. 2018-038999)

[0438] BET specific surface area: 1.5m² 2 / g

[0439] Material 7 (Ba)

[0440] Barium sulfate

[0441] Material 8 (Rh)

[0442] Rhodium nitrate aqueous solution

[0443] Rh concentration: 2.75% by weight

[0444] Material 10 (High Specific Surface Area OSC Material): CeO2-ZrO2 Composite Oxide (CZ) (CeO2: 20 wt%)

[0445] (ZrO2: 70% by weight)

[0446] (La2O3: 5% by weight)

[0447] (Y2O3: 5% by weight)

[0448] BET specific surface area: 80m² 2 / g

[0449] Material 11 (medium specific surface area OSC material): CeO2-ZrO2 composite oxide (CZ) (CeO2: 20 wt%)

[0450] (ZrO2: 70% by weight)

[0451] (La2O3: 5% by weight)

[0452] (Y2O3: 5% by weight)

[0453] BET specific surface area: 35m² 2 / g

[0454] Material 12 (Pt)

[0455] Platinum nitrate aqueous solution

[0456] Pt concentration: 8.2% by weight

[0457] Material 13 (AZ)

[0458] Al2O3-ZrO2 composite oxide (AZ) (Al2O3: 30 wt%)

[0459] (ZrO2: 60% by weight)

[0460] (Nd2O3: 2 wt%)

[0461] (La2O3: 4% by weight)

[0462] (Y2O3: 4% by weight)

[0463] substrate

[0464] 875cc (600-cell hexagonal, 2 mil wall thickness, 105mm total length) cordierite honeycomb substrate

[0465] II-2. Preparation of catalysts for exhaust gas purification

[0466] Comparative Example 4

[0467] First, materials 8 (Rh) and 13 (AZ) were added to distilled water while stirring. The resulting suspension was dried at 120°C for 2 hours and then calcined at 500°C for 2 hours to prepare Rh-supported AZ (Rh / AZ).

[0468] Next, while stirring, Rh / AZ, material 1 (Al2O3), material 2 (high specific surface area OSC material), material 4 (low specific surface area OSC material), and Al2O3-based binder were added to distilled water to prepare a suspended slurry 1.

[0469] Next, the prepared slurry 1 is fed into the substrate, and unwanted portions are blown away using a blower, thereby coating the substrate wall with material to prepare the precursor layer of the second catalyst coating. At this time, regarding each coating material, the volume 1L of the portion of the substrate coated with the second catalyst coating is set as follows: material 1 is 40g (40g / L zone), material 2 is 60g (60g / L zone), material 4 is 15g (15g / L zone), material 13 is 60g (60g / L zone), and material 8 is 0.18g (0.18g / L zone) according to the Rh metal conversion. Furthermore, the coating length of the precursor layer of the second catalyst coating is adjusted so that it occupies 80% of the total length of the substrate in the exhaust gas purification catalyst, starting from the end downstream of the exhaust gas flow direction in the exhaust gas purification catalyst.

[0470] Finally, after the moisture was removed by drying in a dryer at 120°C for 2 hours, the second catalyst coating (rear part) was prepared by firing in an electric furnace at 500°C for 2 hours.

[0471] Next, as described above, while stirring, materials 12 (Pt), 1 (Al2O3), 10 (high specific surface area OSC material), 7 (Ba), and Al2O3-based binder were added to distilled water to prepare a suspended slurry 2.

[0472] Next, the prepared slurry 2 is fed into the substrate on the opposite side of the end face where the second catalyst coating is formed, and unwanted portions are blown away using a blower. This coats the substrate wall with material, thus preparing a precursor layer for the first catalyst coating. At this time, regarding each coating material, relative to the volume 1L of the portion of the substrate coated with the first catalyst coating, material 12 is converted to 0.7g (0.7g / L-zone) based on the metal conversion of Pt, material 1 is 35g (35g / L-zone), material 10 is 30g (30g / L-zone), and material 7 is 5g (5g / L-zone). Furthermore, the coating length of the precursor layer for the first catalyst coating is adjusted so that it occupies 35% of the total length of the substrate in the exhaust gas purification catalyst, starting from the end facing upstream relative to the exhaust flow direction in the exhaust gas purification catalyst.

[0473] Finally, the first catalyst coating (front part) was prepared by using a dryer maintained at 120°C for 2 hours to remove moisture, and then firing it in an electric furnace maintained at 500°C for 2 hours. The catalyst for exhaust purification was finally prepared.

[0474] Example 6

[0475] Except that in Comparative Example 4, 10 g / L of material 2 (total: 60 g / L-zone) in slurry 1 was replaced with material 3 (medium specific surface area OSC material) (total: 10 g / L-zone), an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4.

[0476] Example 7

[0477] Except for replacing 20 g / L of material 2 (total: 60 g / L-zone) in slurry 1 with material 3 (medium specific surface area OSC material) (total: 20 g / L-zone) in Comparative Example 4, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4.

[0478] Example 8

[0479] Except that in Comparative Example 4, 30 g / L of material 2 (total: 60 g / L-zone) in slurry 1 was replaced with material 3 (medium specific surface area OSC material) (total: 30 g / L-zone), an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4.

[0480] Example 9

[0481] Except that in Comparative Example 4, 40 g / L of material 2 (total: 60 g / L-zone) in slurry 1 was replaced with material 3 (medium specific surface area OSC material) (total: 40 g / L-zone), an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4.

[0482] Comparative Example 5

[0483] Except that in Comparative Example 4, the total amount of material 2 (60 g / L-zone) in slurry 1 was changed to material 3 (medium specific surface area OSC material) (total amount: 60 g / L-zone), an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4.

[0484] Comparative Example 6

[0485] Except that in Comparative Example 4, the total amount of material 2 in slurry 1 (60 g / L-zone) was changed to material 10 (high specific surface area OSC material) (total amount: 60 g / L-zone), an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4.

[0486] Example 10

[0487] Except that in Comparative Example 6, 30 g / L of material 10 (total: 60 g / L-zone) in slurry 1 was replaced with material 11 (medium specific surface area OSC material) (total: 30 g / L-zone), an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 6.

[0488] Table 4 summarizes the composition of the OSC material of the second catalyst coating in the exhaust gas purification catalysts of Comparative Examples 4-6 and Examples 6-10.

[0489] Table 4. Overview of the preparation levels of the examples and comparative examples.

[0490]

[0491] II-3. Durability Test

[0492] Regarding the exhaust purification catalysts of Comparative Examples 4-6 and Examples 6-10, the following durability tests were conducted using actual engines.

[0493] By installing each exhaust purification catalyst separately in the exhaust system of a V8 engine, the exhaust gases of the theoretically proportioned and lean atmospheres are repeatedly flowed at a certain time (3:1 ratio) for 50 hours at a catalyst bed temperature of 900℃.

[0494] II-4. Performance Evaluation

[0495] Regarding the exhaust purification catalysts of Comparative Examples 4 to 6 and Examples 6 to 10, for which the II-3 durability test was conducted, the following performance evaluations were performed using actual engines.

[0496] II-4-1. OSC Evaluation

[0497] Each exhaust purification catalyst was installed in the exhaust system of an L-type 4-cylinder engine. A / F feedback control was implemented at Ga = 10 g / s and 500 °C to achieve an A / F ratio of 14.1 and 15.1. Based on the difference between the theoretical saturation point and the A / F sensor output, the excess or deficiency of oxygen was calculated using the following formula. The maximum oxygen uptake at Ga = 10 g / s and 500 °C was used as the OSC for evaluation.

[0498] OSC(g) = 0.23 × ΔA / F × Injected fuel quantity

[0499] II-4-2. NOx purification rate under concentrated atmosphere

[0500] Each exhaust purification catalyst was installed in the exhaust system of an L-type 4-cylinder engine, supplying exhaust gas with an air-fuel ratio (A / F) of 14.4. The NOx purification rate was measured at Ga = 30 / s and 500℃. The NOx purification rate after 3 minutes was used as the NOx purification activity under a rich atmosphere for evaluation.

[0501] II-5. Evaluation Results

[0502] In Table 5 and Figures 11-13 The results are shown in the figure.

[0503] Table 5: Overview of Evaluation Results

[0504]

[0505] From Table 5 and Figure 11 Comparing Comparative Example 4 with Examples 6-9 reveals that by adding medium specific surface area OSC material in addition to high and low specific surface area OSC materials to the second catalyst coating, OSC performance can be maintained and NOx purification rate under concentrated atmosphere can be improved. This is because by replacing a portion of the high specific surface area OSC material with medium specific surface area OSC material, the amount of HC adhering to the OSC material is reduced, making it easier to maintain the activity of noble metals.

[0506] On the other hand, from Table 5 and Figure 12By comparing Comparative Example 4 or Comparative Example 5 with Example 9, it can be seen that when only high specific surface area OSC materials and low specific surface area OSC materials are used to form the OSC material in the second catalyst coating, although the OSC performance can be maintained at a high level, the NOx purification rate under a rich atmosphere will decrease. When only medium specific surface area OSC materials and low specific surface area OSC materials are used to form the OSC material, although the NOx purification rate under a rich atmosphere can be maintained at a high level, the OSC performance will decrease.

[0507] Therefore, it can be seen that by including all of the high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials in the second catalyst coating, both OSC performance and NOx purification rate can be taken into account.

[0508] In addition, from Table 5 and Figure 13 By comparing the relationship between Comparative Example 4 and Example 8 and the relationship between Comparative Example 6 and Example 10, it can be seen that: as a high specific surface area OSC material and a medium specific surface area OSC material, not only ACZ but also CZ can be used.

Claims

1. An exhaust gas purification catalyst which is an exhaust gas purification catalyst having a substrate and a catalyst coating layer coated on the substrate, the catalyst coating layer has a first catalyst coating layer containing Pd and / or Pt as a catalyst metal and a second catalyst coating layer containing Rh as a catalyst metal, the first catalyst coating layer is formed from an end portion on an upstream side with respect to a flow direction of exhaust gas in the exhaust gas purification catalyst, The 2nd catalyst coating comprises a high specific surface area OSC material with a specific surface area of more than 40 m 2 / g, a medium specific surface area OSC material with a specific surface area of 4 m 2 / g to 40 m 2 / g, and a low specific surface area OSC material with a specific surface area of 1.5 m 2 / g and less than 4 m 2 / g.

2. The exhaust gas purification catalyst according to claim 1, the high specific surface area OSC material and the medium specific surface area OSC material each independently contain an alumina-ceria-zirconia-based composite oxide or a ceria-zirconia-based composite oxide, and the low specific surface area OSC material contains a ceria-zirconia-based composite oxide.

3. The exhaust gas purification catalyst according to claim 2, the low specific surface area OSC material contains a ceria-zirconia-based composite oxide having a pyrochlore structure.

4. The exhaust gas purification catalyst according to any one of claims 1 to 3, the second catalyst coating layer has an upstream side coating layer formed from an end portion on an upstream side with respect to a flow direction of exhaust gas in the exhaust gas purification catalyst and a downstream side coating layer formed from an end portion on a downstream side with respect to the flow direction of exhaust gas in the exhaust gas purification catalyst.

5. The exhaust gas purification catalyst according to claim 4, the length of the first catalyst coating layer is 20 to 50% of the entire length of the substrate in the exhaust gas purification catalyst, the length of the upstream side coating layer is 30 to 70% of the entire length of the substrate in the exhaust gas purification catalyst, and the length of the downstream side coating layer is 30 to 70% of the entire length of the substrate in the exhaust gas purification catalyst.

6. The exhaust gas purification catalyst according to claim 4, the first catalyst coating layer is disposed on the upstream side coating layer.

7. The exhaust gas purification catalyst according to claim 4, the first catalyst coating layer is disposed under the upstream side coating layer.

8. The exhaust gas purification catalyst according to claim 4, the upstream side coating layer contains the high specific surface area OSC material and the low specific surface area OSC material, and the downstream side coating layer contains the medium specific surface area OSC material and the low specific surface area OSC material.

9. The exhaust gas purification catalyst according to claim 8, the amount of ceria in the high specific surface area OSC material is 10 to 40% by weight with respect to the total ceria weight of the upstream side coating layer and the downstream side coating layer as the second catalyst coating layer, the amount of ceria in the medium specific surface area OSC material is 10 to 40% by weight with respect to the total ceria weight of the upstream side coating layer and the downstream side coating layer as the second catalyst coating layer, the total amount of ceria in the high specific surface area OSC material and the medium specific surface area OSC material is 60% by weight or less with respect to the total ceria weight of the upstream side coating layer and the downstream side coating layer as the second catalyst coating layer, and the amount of ceria in the low specific surface area OSC material is 40 to 80% by weight with respect to the total ceria weight of the upstream side coating layer and the downstream side coating layer as the second catalyst coating layer. wherein When the amounts of ceria in the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material are all added up, they become 100% by weight.

10. The exhaust gas purification catalyst according to claim 4, wherein the first catalyst coating layer contains Pd as a catalyst metal.

11. The exhaust gas purification catalyst according to claim 4, which is used as an S / C in a dual catalyst system.

12. The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the second catalyst coating layer is formed from the end portion on the downstream side with respect to the exhaust gas flow direction in the exhaust gas purification catalyst.

13. The exhaust gas purification catalyst according to claim 12, wherein the length of the first catalyst coating layer is 15% to 50% of the entire length of the substrate in the exhaust gas purification catalyst, and the length of the second catalyst coating layer is 65% to 95% of the entire length of the substrate in the exhaust gas purification catalyst.

14. The exhaust gas purification catalyst according to claim 12, wherein the first catalyst coating layer contains Pt as a catalyst metal.

15. The exhaust gas purification catalyst according to claim 12, which is used as an UF / C in a dual catalyst system.

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