Exhaust gas purification catalyst

Abstract

To provide an exhaust gas purification catalyst which achieves both catalytic performance and OSC performance in an atmosphere with a rich air / fuel ratio (A / F), which is prone to HC poisoning.SOLUTION: There is provided an exhaust gas purification catalyst having a base material and a catalyst coat layer coated on the base material, wherein the catalyst coat layer has a first catalyst coat layer containing Pd and / or Pt as a catalyst metal and a second catalyst coat layer containing Rh as a catalyst metal, the first catalyst coat layer is formed from the upstream end of the exhaust gas purification catalyst in the direction of exhaust gas flow, the second catalyst coat layer contains a high specific surface area OSC material having a specific surface area of more than 40 m2 / g, a medium specific surface area OSC material having a specific surface area of 4 m2 / g to 40 m2 / g, and a low specific surface area OSC material having a specific surface area of less than 4 m2 / g.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] This invention relates to a catalyst for exhaust gas purification. [Background technology]

[0002] Exhaust gases emitted from internal combustion engines for automobiles, such as gasoline engines or diesel engines, contain harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx).

[0003] For this reason, internal combustion engines are generally equipped with exhaust gas purification devices to decompose and remove these harmful components, and these harmful components are rendered almost harmless by exhaust gas purification catalysts installed within these devices.

[0004] For example, Patent Document 1 discloses an exhaust gas purification catalyst comprising a cell-structured substrate through which exhaust gas flows, and a catalyst layer formed on the cell wall surface of the substrate, wherein the catalyst layer comprises 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 is formed from at least a zirconia support on which rhodium is supported and two types of ceria-zirconia composite oxides that are not supported on rhodium and have different specific surface areas, and the lower catalyst layer is formed from an alumina support on which platinum is supported and a ceria-zirconia composite oxide.

[0005] Patent Document 2 describes an exhaust gas purification catalyst that is placed in the exhaust passage of an internal combustion engine and purifies the exhaust gas discharged from the internal combustion engine, comprising a base material and a catalyst coating layer formed on the surface of the base material, wherein the catalyst coating layer contains an OSC material having oxygen storage capacity, and further comprises an Rh layer in which Rh is mainly arranged as the catalyst metal and a Pd / Pt layer in which Pd and / or Pt are mainly arranged as the catalyst metal, wherein at least a portion of the Pd / Pt layer of the catalyst coating layer is made of a ceria-zirconia composite oxide with a specific surface area of ​​40 m² as the OSC material 2 / g or more 60m 2 The present invention discloses an exhaust gas purification catalyst containing a low specific surface area OSC material with a specific surface area of ​​less than / g. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-175053 [Patent Document 2] Japanese Patent Publication No. 2022-007587 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The exhaust gas purification catalysts described in Patent Documents 1 and 2 have a structure in which a catalyst coating layer is applied to a substrate. The catalyst coating layer contains a noble metal as a catalyst metal.

[0008] The amount of precious metals used in exhaust gas purification catalysts needs to be reduced from a resource risk perspective. To reduce the amount of precious metals, it is necessary to prevent the catalytic activity of precious metals from decreasing due to the use of exhaust gas purification catalysts. To prevent the decrease in catalytic activity of precious metals, one example is to suppress the poisoning of precious metals by HC in the exhaust gas (HC poisoning), which is one of the factors that causes a decrease in the catalytic activity of precious metals.

[0009] On the one hand, the catalyst coating layer may contain, in addition to the catalyst metal, a material (OSC material) having an oxygen storage capacity (OSC: Oxygen Storage Capacity). The OSC material is a material capable of absorbing and releasing oxygen. By the OSC material, even when the air-fuel ratio fluctuates, the oxygen concentration can be kept constant, and the purification performance (catalyst performance) of the exhaust gas purification catalyst can be maintained.

[0010] That is, as the exhaust gas purification catalyst, an exhaust gas purification catalyst that achieves both catalyst performance, that is, suppression of HC poisoning of the noble metal and OSC performance, is desirable.

[0011] Therefore, an object of the present invention is to provide an exhaust gas purification catalyst that achieves both catalyst performance and OSC performance in an atmosphere where the air-fuel ratio (A / F) that is easily HC-poisoned is rich.

Means for Solving the Problems

[0012] The purification of NOx in catalyst activity is particularly borne by rhodium (Rh) among noble metals. However, the catalytic activity of Rh is easily reduced by the influence of HC poisoning. In particular, for example, in an atmosphere where A / F is rich and a state of low oxygen concentration continues, the Rh surface can be covered with HC, so it is more easily reduced. Therefore, suppression of HC poisoning of Rh is effective in suppressing the reduction of catalytic activity.

[0013] On the other hand, the OSC material may cause a delay in the state change of the noble metal and a reduction in catalytic activity due to its OSC performance. For example, an OSC material with a large specific surface area has high OSC performance, but is easily covered by HC in the exhaust gas, so it can cause a reduction in OSC performance along with a reduction in the catalytic activity of the noble metal. On the contrary, for example, an OSC material with a small specific surface area is difficult to be covered by HC in the exhaust gas, so the reduction in the catalytic activity of the noble metal can be suppressed, but there is a limit to the OSC performance. Therefore, selection of an appropriate OSC material is required to ensure appropriate OSC performance.

[0014] Therefore, as a result of various studies on means for solving the above problems, the present inventors have found that in an exhaust gas purification catalyst having a base material and a catalyst coat layer coated on the base material, as the catalyst coat layer, a first catalyst coat layer containing Pd and / or Pt which are noble metals as catalyst metals, and a second catalyst coat layer containing Rh which is a noble metal as a catalyst metal are arranged, the first catalyst coat layer is formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, and by arranging three types of OSC materials having different specific surface areas in the second catalyst coat layer, while HC is purified by Pd and / or Pt in the first catalyst coat layer, it is possible to efficiently purify NOx by Rh in an oxygen atmosphere adjusted by the three types of OSC materials in the second catalyst coat layer, and thus the present invention has been completed.

[0015] That is, the gist of the present invention is as follows. (1) An exhaust gas purification catalyst having a base material and a catalyst coat layer coated on the base material, where the catalyst coat layer has a first catalyst coat layer containing Pd and / or Pt as catalyst metals and a second catalyst coat layer containing Rh as a catalyst metal, the first catalyst coat layer is formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, the second catalyst coat layer contains a high specific surface area OSC material having a specific surface area of more than 40 m 2 / g, a medium 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 Exhaust gas purification catalyst. (2) The exhaust gas purification catalyst according to (1), wherein the high specific surface area OSC material and the medium specific surface area OSC material each independently contain an alumina (Al2O3)-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. (3) The exhaust gas purification catalyst according to (2), wherein the low specific surface area OSC material contains a ceria-zirconia composite oxide having a pyrochlore structure. (4) The exhaust gas purification catalyst according to any one of (1) to (3), wherein the second catalyst coating layer has an upstream coating layer formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream coating layer formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst. (5) The exhaust gas purification catalyst according to (4), wherein the width of the first catalyst coating layer is 20% to 50% of the total length of the substrate in the exhaust gas purification catalyst, the width of the upstream coating layer is 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst, and the width of the downstream coating layer is 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst. (6) The exhaust gas purification catalyst according to (4) or (5), wherein the first catalyst coating layer is disposed on top of the upstream coating layer. (7) The exhaust gas purification catalyst according to (4) or (5), wherein the first catalyst coating layer is located below the upstream coating layer. (8) An exhaust gas purification catalyst according to any one of (4) to (7), wherein the upstream coating layer includes a high specific surface area OSC material and a low specific surface area OSC material, and the downstream coating layer includes a medium specific surface area OSC material and a low specific surface area OSC material. (9) The amount of ceria in the high specific surface area OSC material is 10% to 40% by weight relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer, the amount of ceria in the medium specific surface area OSC material is 10% to 40% by weight relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer, the amount of ceria in the high specific surface area OSC material and the medium specific surface area OSC material is 60% or less by weight relative to the total ceria weight of the upstream and downstream coating layers 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 relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer, wherein the sum 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, as described in (8). (10) An exhaust gas purification catalyst according to any one of (4) to (9), wherein the first catalyst coating layer contains Pd as a catalyst metal. (11) An exhaust gas purification catalyst according to any one of (4) to (10) for use as an S / C in a two-catalyst system. (12) The exhaust gas purification catalyst according to any one of (1) to (3), wherein the second catalyst coating layer is formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst. (13) The exhaust gas purification catalyst according to (12), wherein the width of the first catalyst coating layer is 15% to 50% of the total length of the substrate in the exhaust gas purification catalyst, and the width of the second catalyst coating layer is 65% to 95% of the total length of the substrate in the exhaust gas purification catalyst. (14) The exhaust gas purification catalyst according to (12) or (13), wherein the first catalyst coating layer contains Pt as a catalyst metal. (15) Exhaust gas purification catalyst according to any one of (12) to (14) for use as UF / C in a two-catalyst system. (16) A method for manufacturing an exhaust gas purification catalyst, comprising a substrate and a catalyst coating layer including a first catalyst coating layer and a second catalyst coating layer coated on the substrate, (i) Preparing a slurry for a first catalyst coat layer comprising a catalyst metal precursor containing Pd and / or Pt as a catalyst metal and a solvent; (ii) A Rh precursor containing Rh as a catalyst metal, a solvent, a high specific surface area OSC material having a specific surface area of more than 40 m 2 / g, a medium 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, and preparing a slurry for a second catalyst coat layer; (iii) Forming a first catalyst coat layer by applying the slurry for the first catalyst coat layer prepared in the step (i) from an upstream end portion with respect to the exhaust gas flow direction in the exhaust gas purification catalyst; (iv) Forming a second catalyst coat layer by applying the slurry for the second catalyst coat layer prepared in the step (ii); A method for manufacturing an exhaust gas purification catalyst, comprising: (17) The method according to (16), wherein 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. (18) The method according to (17), wherein the low specific surface area OSC material contains a ceria - zirconia - based composite oxide having a pyrochlore structure. (19) The method according to any one of (16) to (18), wherein the second catalyst coating layer has an upstream coating layer formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream coating layer formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, and step (ii) includes, as a step of preparing a slurry for the second catalyst coating layer, (ii-1) a step of preparing a slurry for the downstream coating layer and (ii-2) a step of preparing a slurry for the upstream coating layer, and step (iv) includes, as a step of forming the second catalyst coating layer, (iv-1) a step of applying the slurry for the downstream coating layer prepared in step (ii-1) to form the downstream coating layer and (iv-2) a step of applying the slurry for the upstream coating layer prepared in step (ii-2) to form the upstream coating layer. The method according to (19), wherein in step (iii) (20), the slurry for the first catalyst coating layer is applied to 20% to 50% of the total length of the substrate in the exhaust gas purification catalyst, in step (iv-1), the slurry for the downstream coating layer 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 slurry for the upstream coating layer is applied to 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst. The method according to (19) or (20), wherein step (iii) is performed after step (iv-2). The method according to (19) or (20), wherein step (iii) is performed before step (iv-2). The method according to any one of (19) to (22), wherein step (ii-1) is a step of preparing a slurry for a downstream coating layer containing a Rh precursor, a solvent, a medium specific surface area OSC material, and a low specific surface area OSC material, and step (ii-2) is a step of preparing a slurry for an upstream coating layer containing a Rh precursor, a solvent, a high specific surface area OSC material, and a low specific surface area OSC material. In steps (24)(ii-1) and (ii-2), the amount of ceria in the high specific surface area OSC material is 10% to 40% by weight relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer, and the amount of ceria in the medium specific surface area OSC material is 10% to 40% by weight relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer, and the amount of ceria in the high specific surface area OSC material and the medium specific surface area OSC material is The method according to (23), wherein the amount of ceria in the low specific surface area OSC material is 60% by weight or less of the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer, and the amount of ceria in the low specific surface area OSC material is 40% by weight to 80% by weight of the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer, and the amount of ceria in the high specific surface area OSC material, medium specific surface area OSC material, and low specific surface area OSC material is adjusted so that the sum of all the ceria amounts is 100% by weight. The method according to any one of (19) to (24), wherein step (i) is a step of preparing a slurry for a first catalyst coating layer comprising a Pd precursor and a solvent. (26) The method according to any one of (19) to (25), wherein the exhaust gas purification catalyst is used as an S / C in a two-catalyst system. The method according to any one of (16) to (18), wherein step (iv) is a step of applying the slurry for the second catalyst coating layer prepared in step (ii) to the exhaust gas purification catalyst from the downstream end with respect to the exhaust gas flow direction to form the second catalyst coating layer. The method according to (27), wherein in step (iii), a slurry for the first catalyst coating layer is applied to 15% to 50% of the total length of the substrate in the exhaust gas purification catalyst, and in step (iv), a slurry for the second catalyst coating layer is applied to 65% to 95% of the total length of the substrate in the exhaust gas purification catalyst. The method according to (27) or (28), wherein step (i) is a step of preparing a slurry for a first catalyst coating layer comprising a Pt precursor and a solvent. (30) The method according to any one of (27) to (29), wherein the exhaust gas purification catalyst is used as UF / C in a two-catalyst system. [Effects of the Invention]

[0016] The present invention provides an exhaust gas purification catalyst that achieves both catalytic performance and OSC performance in an atmosphere with a rich air-fuel ratio (A / F) that is prone to HC poisoning. [Brief explanation of the drawing]

[0017] [Figure 1] This figure schematically illustrates one example of the first embodiment of the present invention. [Figure 2] This figure schematically illustrates one example of the first embodiment of the present invention. [Figure 3] This figure schematically illustrates one example of the first embodiment of the present invention. [Figure 4] This figure schematically illustrates one example of the first embodiment of the present invention. [Figure 5] This figure schematically illustrates one example of the first embodiment of the present invention. [Figure 6] This figure schematically illustrates one example of the first embodiment of the present invention. [Figure 7] This figure schematically illustrates one example of a second embodiment of the present invention. [Figure 8] This figure schematically illustrates one example of a second embodiment of the present invention. [Figure 9] This graph shows the NOx purification rate in a rich atmosphere and the OSC performance at low and high temperatures for the exhaust gas purification catalysts of Comparative Example 1 and Example 2. [Figure 10] This graph shows the NOx purification rate in a rich atmosphere and the OSC performance at low and high temperatures of the exhaust gas purification catalysts of Comparative Example 3 and Example 5. [Figure 11] This graph shows the relationship between the proportion of ceria occupied by high specific surface area OSC material in the second catalyst coating layer, the NOx purification rate in a rich atmosphere, and the OSC performance. [Figure 12]This graph shows the NOx purification rate and OSC performance of the exhaust gas purification catalysts of Comparative Examples 4 and 5 and Example 9 in a rich atmosphere. [Figure 13] This graph shows the NOx purification rate of the exhaust gas purification catalysts of Comparative Examples 4 and 6 and Examples 8 and 10 in a rich atmosphere. [Modes for carrying out the invention]

[0018] Preferred embodiments of the present invention will be described in detail below. This specification will describe the features of the present invention with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part 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 forms with modifications, improvements, etc. that can be made by those skilled in the art without departing from the spirit of the present invention.

[0019] The present invention relates to an exhaust gas purification catalyst having a substrate and a catalyst coating layer coated on the substrate, wherein the catalyst coating layer comprises a first catalyst coating layer containing Pd and / or Pt as catalyst metals and a second catalyst coating layer containing Rh as catalyst metals, the first catalyst coating layer is formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, and the second catalyst coating layer contains three types of OSC materials with different specific surface areas.

[0020] (base material) As the substrate, a known honeycomb-shaped substrate can be used, and specifically, a honeycomb-shaped monolithic substrate (honeycomb filter, high-density honeycomb, etc.) is preferably used. Furthermore, the material of such a substrate is not particularly limited, and substrates made of ceramics such as cordierite, silicon carbide (SiC), silica (SiO2), alumina (Al2O3), and mullite, or substrates made of metals such as stainless steel containing chromium and aluminum are preferably used. Among these, cordierite is preferred from the viewpoint of cost.

[0021] (Catalyst coating layer) The catalyst coating layer comprises at least a first catalyst coating layer containing Pd and / or Pt as catalyst metals, and a second catalyst coating layer containing Rh as a catalyst metal.

[0022] The first catalyst coating layer is formed from the upstream end (end face) of the exhaust gas purification catalyst with respect to the exhaust gas flow direction (the side into which the exhaust gas flows).

[0023] The first catalyst coating layer has the above configuration, which allows for efficient purification of exhaust gas, particularly HC, in the incoming exhaust gas.

[0024] • First embodiment In the first embodiment of the present invention, the second catalyst coating layer has an upstream coating layer formed from the upstream end of the exhaust gas purification catalyst with respect to the exhaust gas flow direction, and a downstream coating layer formed from the downstream end (end face) of the exhaust gas purification catalyst with respect to the exhaust gas flow direction (the side from which the exhaust gas flows out).

[0025] In the first embodiment of the present invention, the width of the first catalyst coating layer is typically 20% to 50%, preferably 20% to 35%, of the total length of the substrate in the exhaust gas purification catalyst.

[0026] In the first embodiment of the present invention, by having the width of the first catalyst coating layer within the aforementioned range, aggregation of catalyst metals due to a width that is too short, such as aggregation of Pd and Pt due to high density of Pd and Pt, can be suppressed, while the frequency of contact between Pd and Pt and harmful components in the exhaust gas, such as HC, can be improved, thereby improving exhaust gas purification performance.

[0027] In the first embodiment of the present invention, the width of the upstream coating layer is typically 30% to 70%, preferably 30% to 60%, of the total length of the substrate in the exhaust gas purification catalyst.

[0028] In the first embodiment of the present invention, the width of the downstream coating layer is typically 30% to 70%, preferably 50% to 70%, of the total length of the substrate in the exhaust gas purification catalyst.

[0029] In the first embodiment of the present invention, by having the widths of the upstream and downstream coating layers within the aforementioned range, aggregation of catalyst metals due to excessively short widths, such as aggregation of Rh due to increased Rh density, can be suppressed, while the frequency of contact between Rh and harmful components in the exhaust gas, such as NOx, can be improved, thereby improving exhaust gas purification performance.

[0030] In the first embodiment of the present invention, the first catalyst coating layer may be placed on top of the upstream coating layer.

[0031] In a first embodiment of the present invention, by arranging the first catalyst coating layer on top of the upstream coating layer, the Pd and Pt contained in the first catalyst coating layer can purify harmful components in the incoming exhaust gas, particularly HC, and then the Rh contained in the upstream coating layer can purify harmful components, particularly NOx.

[0032] In the first embodiment of the present invention, the first catalyst coating layer may be located below the upstream coating layer.

[0033] In the first embodiment of the present invention, the first catalyst coating layer is positioned below the upstream coating layer, thereby preventing the oxidation of ammonia (NH3) to nitrous oxide (N2O) by Pd and Pt during, for example, warm-up operation, while purifying NOx with Rh.

[0034] In the first embodiment of the present invention, the widths of the first catalyst coating layer and the upstream coating layer may be the same or different. In the first embodiment of the present invention, if the widths of the first catalyst coating layer and the upstream coating layer are different, the width of the first catalyst coating layer may be longer. In the first embodiment of the present invention, if the widths of the first catalyst coating layer and the upstream coating layer are different, the width of the upstream coating layer may be longer.

[0035] In the first embodiment of the present invention, when the widths of the first catalyst coating layer and the upstream coating layer are different, it is preferable that the width of the upstream coating layer is longer.

[0036] By making the width of the upstream coating layer longer than the width of the first catalyst coating layer, the activity of Rh can be increased compared to the activity of Pd and Pt, enabling more effective utilization of Rh.

[0037] In the first embodiment of the present invention, the first catalyst coating layer and the downstream coating layer may together form a single layer over the entire substrate. In the first embodiment of the present invention, the first catalyst coating layer and the downstream coating layer may overlap. In the first embodiment of the present invention, if the first catalyst coating layer and the downstream coating layer overlap, the first catalyst coating layer may be positioned above the downstream coating layer in the overlapping portion. In the first embodiment of the present invention, if the first catalyst coating layer and the downstream coating layer overlap, the first catalyst coating layer may be positioned below the downstream coating layer in the overlapping portion. In the first embodiment of the present invention, if the first catalyst coating layer and the downstream coating layer overlap, the overlap width of the overlapping region of the first catalyst coating layer and the downstream coating layer is typically 5% to 30% of the total length of the substrate in the exhaust gas purification catalyst.

[0038] In the first embodiment of the present invention, it is preferable that the first catalyst coating layer does not overlap with the downstream coating layer.

[0039] By preventing the first catalyst coating layer from overlapping with the downstream coating layer, alloying of Pd and / or Pt in the first catalyst coating layer with Rh in the downstream coating layer can be prevented.

[0040] In the first embodiment of the present invention, the upstream coating layer and the downstream coating layer may together form a single layer over the entire substrate.

[0041] In the first embodiment of the present invention, the upstream coating layer and the downstream coating layer may overlap. In the first embodiment of the present invention, if the upstream coating layer and the downstream coating layer overlap, the upstream coating layer may be positioned above the downstream coating layer in the overlapping portion. In the first embodiment of the present invention, if the upstream coating layer and the downstream coating layer overlap, the upstream coating layer may be positioned below the downstream coating layer in the overlapping portion. In the first embodiment of the present invention, if the upstream coating layer and the downstream coating layer overlap, the overlap width of the overlapping region of the upstream coating layer and the downstream coating layer is typically 5% to 30% of the total length of the substrate in the exhaust gas purification catalyst.

[0042] In the first embodiment of the present invention, when the upstream coat layer and the downstream coat layer overlap, it is preferable that the upstream coat layer be placed on top of the downstream coat layer in the overlapping portion.

[0043] By positioning the upstream coating layer on top of the downstream coating layer, exhaust gas is introduced into the downstream coating layer after the atmosphere has been mitigated by the upstream coating layer. As a result, the downstream coating layer can be utilized more effectively.

[0044] In the first embodiment of the present invention, when the first catalyst coating layer, the upstream coating layer, and the downstream coating layer overlap, the upstream coating layer may be positioned above the first catalyst coating layer and below the downstream coating layer in the overlapping portion such that the upstream coating layer does not come into contact with the first catalyst coating layer and the downstream coating layer. In the first embodiment of the present invention, when the first catalyst coating layer, the upstream coating layer, and the downstream coating layer overlap, the upstream coating layer may be positioned below the first catalyst coating layer and above the downstream coating layer in the overlapping portion such that the upstream coating layer does not come into contact with the first catalyst coating layer and the downstream coating layer. In the first embodiment of the present invention, when the first catalyst coating layer, the upstream coating layer, and the downstream coating layer overlap, the overlap width of the overlapping region of the first catalyst coating layer, the upstream coating layer, and the downstream coating layer is typically 5% to 30% of the total length of the substrate in the exhaust gas purification catalyst.

[0045] In the first embodiment of the present invention, the upstream coating layer prevents the first catalyst coating layer and the downstream coating layer from coming into contact, thereby preventing alloying between Pd and / or Pt in the first catalyst coating layer and Rh in the downstream coating layer.

[0046] In the first embodiment of the present invention, the second catalyst coating layer has the above configuration, and when the exhaust gas purification catalyst is used in a two-catalyst system including a startup catalyst (also called S / C, startup converter, etc.) and an underfloor catalyst (UF / C, underfloor converter, underbody catalyst, etc.), it can efficiently purify exhaust gas even in an atmosphere where high concentrations of exhaust gas may be present, such as during warm-up operation.

[0047] Figures 1 to 6 show an example of the first embodiment of the present invention.

[0048] The exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 1 comprises a base material 1 and catalyst coating layers 2 to 4 coated on the base material 1. The catalyst coating layers 2 to 4 consist of second catalyst coating layers 2 and 3, which have an upstream coating layer 2 formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream coating layer 3 formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, where the upstream coating layer 2 and the downstream coating layer 3 together form a single layer over the entire base material 1, and a first catalyst coating layer 4, which is arranged on the upstream coating layer 2 of the second catalyst coating layers 2 and 3 and is formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, where the width of the first catalyst coating layer 4 is shorter than the width of the upstream coating layer 2.

[0049] In the exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 1, there is no overlapping portion (wrap portion) between the upstream coating layer 2 and the downstream coating layer 3. Therefore, the most effective utilization of Rh can be achieved in this exhaust gas purification catalyst. Consequently, this exhaust gas purification catalyst can achieve both better purification performance and OSC performance.

[0050] The exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 2 comprises a base material 1 and catalyst coating layers 2 to 4 coated on the base material 1. The catalyst coating layers 2 to 4 consist of second catalyst coating layers 2 and 3, which have an upstream coating layer 2 formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream coating layer 3 formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, where the upstream coating layer 2 and the downstream coating layer 3 overlap, and in the overlapping portion, the upstream coating layer 2 is positioned below the downstream coating layer 3; and a first catalyst coating layer 4, which is positioned on the upstream coating layer 2 of the second catalyst coating layers 2 and 3 and is formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, where the width of the first catalyst coating layer 4 is shorter than the width of the upstream coating layer 2.

[0051] The exhaust gas purification catalyst of the first embodiment of the present invention, shown in Figure 2, has overlapping portions of the upstream coating layer 2 and the downstream coating layer 3, which can reduce the portion of Rh that is effectively utilized. On the other hand, these overlapping portions ensure sufficient OSC performance. Therefore, this exhaust gas purification catalyst can achieve both good purification performance and OSC performance.

[0052] The exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 3 comprises a base material 1 and catalyst coating layers 2 to 4 coated on the base material 1. The catalyst coating layers 2 to 4 consist of second catalyst coating layers 2 and 3, which have an upstream coating layer 2 formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream coating layer 3 formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, where the upstream coating layer 2 and the downstream coating layer 3 overlap, and in the overlapping portion, the upstream coating layer 2 is positioned on the downstream coating layer 3, and a first catalyst coating layer 4 is positioned on the upstream coating layer 2 of the second catalyst coating layers 2 and 3 and is formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, where the width of the first catalyst coating layer 4 is shorter than the width of the upstream coating layer 2.

[0053] The exhaust gas purification catalyst of the first embodiment of the present invention, shown in Figure 3, has overlapping portions of the upstream coating layer 2 and the downstream coating layer 3, which can reduce the portion of Rh that is effectively utilized. On the other hand, these overlapping portions ensure sufficient OSC performance, and furthermore, in these overlapping portions, the upstream coating layer 2 mitigates the exhaust gas atmosphere, allowing for more effective utilization of the downstream coating layer 3. Therefore, this exhaust gas purification catalyst can achieve both better purification performance and OSC performance.

[0054] The exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 4 comprises a substrate 1 and catalyst coating layers 2 to 4 coated on the substrate 1. The catalyst coating layers 2 to 4 consist of a second catalyst coating layer 2 and 3, which are arranged on a substrate 1 and have an upstream coating layer 2 formed from the upstream end with respect to the exhaust gas flow direction of the exhaust gas purification catalyst and a downstream coating layer 3 formed from the downstream end with respect to the exhaust gas flow direction of the exhaust gas purification catalyst, where the upstream coating layer 2 and the downstream coating layer 3 overlap, and in the overlapping portion, the upstream coating layer 2 is positioned below the downstream coating layer 3; and a first catalyst coating layer 4, which is positioned on the upstream coating layer 2 of the second catalyst coating layers 2 and 3 and is formed from the upstream end with respect to the exhaust gas flow direction of the exhaust gas purification catalyst, where the width of the first catalyst coating layer 4 is longer than the width of the upstream coating layer 2, and there is an overlapping portion between the first catalyst coating layer 4, the upstream coating layer 2 and the downstream coating layer 3, where the first catalyst coating layer 4 is positioned above the upstream coating layer 2 and the downstream coating layer 3.

[0055] In the exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 4, the upstream coating layer 2 is covered by the first catalyst coating layer 4 or the downstream coating layer 3. As a result, the frequency of contact between the exhaust gas and the upstream coating layer 2 decreases, and the atmospheric mitigation ability of the upstream coating layer 2 decreases. On the other hand, the overlapping portion of the upstream coating layer 2 and the downstream coating layer 3 ensures sufficient OSC performance. Furthermore, in the overlapping portion of the first catalyst coating layer 4 and the downstream coating layer 3, the first catalyst coating layer 4 efficiently purifies the exhaust gas, particularly HC, and suppresses the poisoning of Rh in the downstream coating layer 3. Therefore, this exhaust gas purification catalyst can achieve both purification performance and OSC performance.

[0056] The exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 5 comprises a substrate 1 and catalyst coating layers 2 to 4 coated on the substrate 1. The catalyst coating layers 2 to 4 consist of a second catalyst coating layer 2 and 3 having an upstream coating layer 2 formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream coating layer 3 formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, where the upstream coating layer 2 and the downstream coating layer 3 together form a single layer over the entire substrate 1, and a first catalyst coating layer 4 disposed on the upstream coating layer 2 of the second catalyst coating layers 2 and 3 and formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, where the width of the first catalyst coating layer 4 is the same as the width of the upstream coating layer 2.

[0057] In the exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 5, the upstream coating layer 2 is covered by the first catalyst coating layer 4, which reduces the frequency of contact between the exhaust gas and the upstream coating layer 2, thereby reducing the atmospheric mitigation ability of the upstream coating layer 2. On the other hand, since there is no overlapping portion between the upstream coating layer 2 and the downstream coating layer 3, effective utilization of Rh can be achieved. Therefore, this exhaust gas purification catalyst can achieve both purification performance and OSC performance.

[0058] The exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 6 comprises a substrate 1 and catalyst coating layers 2 to 4 coated on the substrate 1. The catalyst coating layers 2 to 4 consist of a first catalyst coating layer 4 formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst disposed on the substrate 1, and second catalyst coating layers 2 and 3 disposed on the first catalyst coating layer 4 and the substrate 1, and having an upstream coating layer 2 formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, and a downstream coating layer 3 formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the upstream coating layer 2 and the downstream coating layer 3 together form a single layer over the entire substrate 1, and the width of the first catalyst coating layer 4 is shorter than the width of the upstream coating layer 2.

[0059] In the exhaust gas purification catalyst of the first embodiment of the present invention shown in Figure 6, the first catalyst coating layer 4 is covered by the upstream coating layer 2, which reduces the frequency of contact between the exhaust gas and the first catalyst coating layer 4, thus reducing the purification performance of the first catalyst coating layer 4. On the other hand, since there is no overlapping portion between the upstream coating layer 2 and the downstream coating layer 3, effective utilization of Rh can be achieved. Furthermore, the improved atmospheric mitigation of the exhaust gas by the upstream coating layer 2 ensures high OSC performance. Therefore, this exhaust gas purification catalyst can achieve both purification performance and OSC performance.

[0060] • Second embodiment In a second embodiment of the present invention, the second catalyst coating layer is formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst.

[0061] In a second embodiment of the present invention, the width of the first catalyst coating layer is typically 15% to 50%, preferably 15% to 35%, of the total length of the substrate in the exhaust gas purification catalyst.

[0062] In a second embodiment of the present invention, by having the width of the first catalyst coating layer within the aforementioned range, aggregation of catalyst metals due to a width that is too short, such as aggregation of Pd and Pt due to high density of Pd and Pt, can be suppressed, while the frequency of contact between Pd and Pt and harmful components in the exhaust gas, such as HC, can be improved, thereby improving exhaust gas purification performance.

[0063] In a second embodiment of the present invention, the width of the second catalyst coating layer is typically 65% ​​to 95%, preferably 80% to 95%, of the total length of the substrate in the exhaust gas purification catalyst.

[0064] In a second embodiment of the present invention, by having the width of the second catalyst coating layer within the aforementioned range, aggregation of catalyst metals due to a width that is too short, such as aggregation of Rh due to increased Rh density, can be suppressed, while the frequency of contact between Rh and harmful components in the exhaust gas, such as NOx, can be improved, thereby improving exhaust gas purification performance.

[0065] In a second embodiment of the present invention, the first catalyst coating layer and the second catalyst coating layer may overlap.

[0066] In a second embodiment of the present invention, when the first catalyst coating layer and the second catalyst coating layer overlap, the first catalyst coating layer may be placed on top of the second catalyst coating layer in the overlapping portion.

[0067] In a second embodiment of the present invention, the first catalyst coating layer is arranged on top of the second catalyst coating layer, thereby purifying harmful components in the exhaust gas, particularly HC, with Pd and Pt contained in the first catalyst coating layer, and then purifying harmful components, particularly NOx, with Rh contained in the upstream coating layer.

[0068] In a second embodiment of the present invention, when the first catalyst coating layer and the second catalyst coating layer overlap, the first catalyst coating layer may be positioned below the second catalyst coating layer in the overlapping portion.

[0069] In a second embodiment of the present invention, the first catalyst coating layer is positioned below the second catalyst coating layer, thereby preventing the oxidation of ammonia (NH3) to nitrous oxide (N2O) by Pd and Pt during, for example, warm-up operation, while purifying NOx with Rh.

[0070] In a second embodiment of the present invention, when the first catalyst coating layer and the second catalyst coating layer overlap, the overlap width of the overlapping region of the first catalyst coating layer and the second catalyst coating layer is typically 5% to 30%, preferably 10% to 20%, of the total length of the substrate in the exhaust gas purification catalyst.

[0071] In a second embodiment of the present invention, by having the overlap width within the aforementioned range, exhaust gas can be efficiently purified while suppressing the formation of alloys between Pd and / or Pt and Rh.

[0072] In a second embodiment of the present invention, the second catalyst coating layer has the above configuration, and when the exhaust gas purification catalyst is used, particularly in a two-catalyst system including S / C and UF / C, in which the UF / C has the function of purifying low-concentration exhaust gas that cannot be completely purified by S / C, the exhaust gas can be efficiently purified even in an atmosphere where the oxygen concentration is lower (oxygen is deficient) compared to the atmosphere in S / C due to exhaust gas purification in S / C.

[0073] Figures 7 and 8 show an example of a second embodiment of the present invention.

[0074] The exhaust gas purification catalyst of the second embodiment of the present invention shown in Figure 7 comprises a substrate 1 and catalyst coating layers 4 and 5 coated on the substrate 1. The catalyst coating layers 4 and 5 consist of a first catalyst coating layer 4 formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst placed on the substrate 1, and a second catalyst coating layer 5 formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the first catalyst coating layer 4 and the second catalyst coating layer 5 overlap, and in the overlapping portion, the first catalyst coating layer 4 is positioned on top of the second catalyst coating layer 5, and the width of the first catalyst coating layer 4 is shorter than the width of the second catalyst coating layer 5.

[0075] In the exhaust gas purification catalyst of the second embodiment of the present invention shown in Figure 7, the frequency of contact of the exhaust gas with the first catalyst coating layer 4 is high, which allows for particularly improved catalyst performance among the combined catalyst performance and OSC performance.

[0076] The exhaust gas purification catalyst of the second embodiment of the present invention shown in Figure 8 comprises a substrate 1 and catalyst coating layers 4 and 5 coated on the substrate 1. The catalyst coating layers 4 and 5 consist of a first catalyst coating layer 4 formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst placed on the substrate 1, and a second catalyst coating layer 5 formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst. Here, the first catalyst coating layer 4 and the second catalyst coating layer 5 overlap, and in the overlapping portion, the first catalyst coating layer 4 is positioned below the second catalyst coating layer 5, and the width of the first catalyst coating layer 4 is shorter than the width of the second catalyst coating layer 5.

[0077] In the exhaust gas purification catalyst of the second embodiment of the present invention shown in Figure 7, the frequency of contact of the exhaust gas with the second catalyst coating layer 5 is high, which allows for improvement in OSC performance among the combined catalytic performance and OSC performance.

[0078] In the first and second embodiments of the present invention, the catalyst coating layer may consist only of a layer comprising the first catalyst coating layer and the second catalyst coating layer, as long as the uppermost layer includes the first catalyst coating layer and the second catalyst coating layer, or it may have one or more layers (one, two, three, or four or more layers) below the layer comprising the first and second catalyst coating layers. The composition and structure of the lower catalyst coating layer are not limited and may be the same as the first catalyst coating layer and / or the second catalyst coating layer, or different from both. Furthermore, the lower catalyst coating layer does not necessarily have to be uniform throughout the entire substrate of the exhaust gas purification catalyst, and may have different compositions and structures in regions upstream and downstream with respect to the exhaust gas flow direction, as with the uppermost layer.

[0079] By having a catalyst coating layer consisting of a first catalyst coating layer and a second catalyst coating layer, the purification of HC in the first catalyst coating layer and the purification of NOx in the second catalyst coating layer can be efficiently performed.

[0080] (First catalyst coating layer) The first catalyst coating layer contains Pd and / or Pt as catalyst metals.

[0081] Pd and Pt have high capabilities in burning and purifying HC and CO, and possess similar performance in purifying harmful components; therefore, they can be treated as interchangeable precious metals.

[0082] Therefore, for example, when using the exhaust gas purification catalyst of the second embodiment of the present invention as a UF / C that has the function of purifying low-concentration exhaust gas that cannot be completely purified by S / C in a two-catalyst system including S / C and UF / C, Pd and / or Pt can be used as the catalyst metal in the first catalyst coating layer, and preferably Pt can be used as it may be advantageous from a cost standpoint.

[0083] On the other hand, when good warm-up performance is required for exhaust gas purification catalysts, Pt is more prone to sintering after durability compared to Pd, which can result in a decrease in warm-up performance. Therefore, it is preferable to use Pd.

[0084] Therefore, for example, when using the exhaust gas purification catalyst of the first embodiment of the present invention as an S / C to purify high-concentration exhaust gas in a two-catalyst system including S / C and UF / C, it is preferable to use Pd as the catalyst metal in the first catalyst coating layer.

[0085] The content of Pd and / or Pt as catalytic metals in the first catalytic coating layer is not limited, but is typically 0.2g to 10g, preferably 0.5g to 7.0g, in terms of metal content of the catalytic metals per 1L of the portion of the substrate to which the first catalytic coating layer is applied. The content of Pd and / or Pt as catalytic metals in the first catalytic coating layer depends on the amount of catalytic metal precursor added as a material during the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0086] The first catalyst coating layer contains Pd and / or Pt as catalytic metals; that is, by placing the first catalyst coating layer containing Pd and / or Pt upstream, i.e., before the exhaust gas purification catalyst, the ignition performance is improved by increasing the density of Pd and Pt, thereby improving the purification performance of exhaust gas, especially HC.

[0087] The first catalyst coating layer may further contain at least one other precious metal commonly used in the field of exhaust gas purification catalysts, selected from the group consisting of Rh, gold (Au), silver (Ag), iridium (Ir), and ruthenium (Ru).

[0088] Pd and / or Pt and optionally other noble metals, which are catalytic metals contained in the first catalyst coating layer, can function as exhaust gas purification catalysts on their own, but it is preferable that they are supported on carrier particles which are optionally included in the exhaust gas purification catalyst of the present invention.

[0089] The carrier particles on which Pd and / or Pt and optionally other noble metals are supported as catalytic metals are not limited, but may be any metal oxide commonly used as carrier particles in the field of exhaust gas purification catalysts.

[0090] Therefore, the first catalyst coating layer may further contain carrier particles. Examples of carrier particles include metal oxides such as silica, magnesium oxide (MgO), zirconia, ceria, alumina, titania (TiO2), yttria (Y2O3), neodymium oxide (Nd2O3), lanthanum oxide (La2O3), and their composite oxides and solid solutions, such as alumina-zirconia composite oxides (AZ), ceria-zirconia composite oxides (CZ), alumina-ceria-zirconia composite oxides (ACZ), and combinations of two or more of these. The ratio of each oxide in the composite oxides, such as AZ, CZ, and ACZ, is not limited and may be a ratio commonly used in the field of exhaust gas purification catalysts. As for CZ and ACZ, for example, the CZ and ACZ described in the section on the second catalyst coating layer can be used.

[0091] For example, ceria has OSC properties that allow it to absorb oxygen in a lean atmosphere and release oxygen in a rich atmosphere, thus maintaining a stoichiometric atmosphere within the exhaust gas purification catalyst. Alumina, zirconia, and other metal oxides can be added to increase the durability of the support.

[0092] Based on the characteristics of the carrier particles described above, it should be understood that the exhaust gas purification performance of the exhaust gas purification catalyst of the present invention, particularly the HC purification performance, may be improved depending on the type, composition, combination and ratio of the selected carrier particles, and / or the amount.

[0093] When Pd and / or Pt and optionally other precious metals are supported on the carrier particles as catalytic metals, the large specific surface area of ​​the carrier particles allows for a larger contact surface area between the exhaust gas and the catalytic metal. This improves the performance of the exhaust gas purification catalyst.

[0094] The method for supporting Pd and / or Pt and optionally other noble metals as catalytic metals onto carrier particles can be one that is commonly used in the field of exhaust gas purification catalysts.

[0095] The content of carrier particles in the first catalyst coating layer is not limited, but is typically 20g to 200g, preferably 20g to 100g, and more preferably 40g to 100g, per 1L of the volume of the portion of the substrate to which the first catalyst coating layer is applied. The content of carrier particles in the first catalyst coating layer depends on the amount of carrier particles added as a material during the manufacture of the exhaust gas purification catalyst.

[0096] The first catalyst coating layer mainly consists of Pd and / or Pt as catalyst metals, optionally other precious metals, and carrier particles supporting the Pd and / or Pt and other precious metals as catalyst metals, but may further contain other components as long as they do not impair the effects of the present invention. Other components include one or more of the metal oxides and additives used in catalyst coating layers for this type of application, specifically 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 the metal oxides listed as carrier particles (i.e., metal oxides that do not support catalyst metals, etc.). The other components may be in their original form or, like the catalyst metals, in a form supported on carrier particles.

[0097] The content of other components in the first catalyst coating layer is not limited if present, but is typically 10g to 100g, preferably 20g to 100g, and more preferably 40g to 100g, per 1L of the portion of the substrate to which the first catalyst coating layer is applied. The content of other components that may be included in the first catalyst coating layer depends on the amount of other components added as materials during the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0098] Pores can also be formed in the first catalyst coating layer. The method for forming the voids can be any technique known in the field of exhaust gas purification catalysts, and is not specifically limited.

[0099] The amount of the first catalyst coating layer is not limited, but is typically 40g to 200g, preferably 70g to 200g, per 1L of the portion of the substrate to which the first catalyst coating layer is applied. The amount of the first catalyst coating layer depends on the total weight of the materials used in the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0100] The thickness of the first catalyst coating layer is not limited, but its average thickness is usually 5 μm to 50 μm, preferably 10 μm to 30 μm. The thickness of the first catalyst coating layer can be measured, for example, by a scanning electron microscope (SEM).

[0101] By keeping the amount of each material in the first catalyst coating layer and the thickness of the first catalyst coating layer within the aforementioned range, a good balance between pressure loss, catalytic performance, and durability can be maintained in the exhaust gas purification catalyst.

[0102] The configuration of the first catalyst coating layer described above can be used in either the first or second embodiment of the present invention.

[0103] (Second catalyst coating layer) • First embodiment In the first embodiment of the present invention, the second catalyst coating layer has an upstream coating layer formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst and a downstream coating layer formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, wherein the upstream coating layer contains Rh as a catalyst metal and an OSC material which will be described in detail below, and the downstream coating layer contains Rh as a catalyst metal and an OSC material which will be described in detail below.

[0104] The Rh content as a catalytic metal in the upstream coating layer is not limited, but is typically 0.05g to 1.0g, preferably 0.1g to 0.8g, in terms of metal content of the catalytic metal per 1L of the portion of the substrate to which the upstream coating layer is applied. The Rh content as a catalytic metal in the upstream coating layer depends on the amount of Rh precursor added as a material during the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0105] When the upstream coating layer contains Rh in the aforementioned content, if the upstream coating layer is located below the first catalyst coating layer, Rh can fully exhibit its NOx purification performance without being poisoned by HC in an atmosphere where HC has been sufficiently purified by the first catalyst coating layer. If the upstream coating layer is located above the first catalyst coating layer, NOx can be purified by Rh before the oxidation of ammonia (NH3) to nitrous oxide (N2O) by Pd and Pt during warm-up operation.

[0106] The Rh content as a catalytic metal in the downstream coating layer is not limited, but is typically 0.05g to 1.0g, preferably 0.2g to 0.8g, in terms of metal content of the catalytic metal per 1L of the portion of the substrate to which the downstream coating layer is applied. The Rh content as a catalytic metal in the downstream coating layer depends on the amount of Rh precursor added as a material during the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0107] By including Rh in the aforementioned content in the downstream coating layer, Rh can fully exhibit its NOx purification performance without being poisoned by HC in an atmosphere where HC has been sufficiently purified by the first catalyst coating layer located upstream.

[0108] It is preferable that the Rh content as a catalytic metal in the downstream coating layer is higher than the Rh content as a catalytic metal in the upstream coating layer.

[0109] Because the Rh content of the downstream coating layer is higher than that of the upstream coating layer, the downstream coating layer, which tends to be cooler than the upstream coating layer, can be utilized more effectively.

[0110] The upstream and downstream coating layers may each further contain at least one other precious metal commonly used in the field of exhaust gas purification catalysts, selected from the group consisting of Pd, Pt, gold, silver, iridium, and ruthenium.

[0111] Rh and, optionally, other precious metals, which are catalytic metals contained in the upstream and downstream coating layers, can function as exhaust gas purification catalysts on their own, but it is preferable that they are supported on carrier particles that are optionally included in the OSC material, which will be described in detail below, and in the exhaust gas purification catalyst of the present invention.

[0112] The carrier particles on which Rh and, optionally, other precious metals are supported as catalytic metals are not limited, but may be any metal oxide commonly used as carrier particles in the field of OSC materials, which will be described in detail below, or in the field of exhaust gas purification catalysts.

[0113] Therefore, the second catalyst coating layer, i.e., the upstream coating layer and the downstream coating layer, may each further contain carrier particles. Examples of carrier particles include metal oxides, such as silica, magnesium oxide, zirconia, ceria, alumina, titania, yttria, neodymium oxide, lanthanum oxide, and their composite oxides and solid solutions, such as alumina-zirconia composite oxide (AZ), alumina-ceria-zirconia composite oxide (ACZ) and ceria-zirconia composite oxide (CZ) as OSC materials, which will be described in detail below, as well as combinations of two or more of these.

[0114] Acidic supports, such as silica, are compatible with catalytic metals that reduce NOx. Basic supports, such as magnesium oxide, are compatible with potassium and barium, which absorb NOx. Zirconia suppresses sintering of other support particles at high temperatures where other support particles undergo sintering, and when combined with Rh as a catalytic metal, it can efficiently reduce NOx by generating H2 through a steam reforming reaction. Amphoteric supports, such as alumina, have a high specific surface area and can be used to efficiently absorb and reduce NOx. Titania can suppress sulfur poisoning of catalytic metals. In addition, alumina, zirconia, and other metal oxides can increase the durability of the support when added.

[0115] Based on the characteristics of the carrier particles described above, it should be understood that the exhaust gas purification performance of the exhaust gas purification catalyst of the present invention, particularly the NOx purification performance, may be improved depending on the type, composition, combination and ratio of the selected carrier particles, and / or the amount.

[0116] When Rh and, optionally, other precious metals are supported on the carrier particles as catalytic metals, the large specific surface area of ​​the carrier particles allows for a larger contact surface area between the exhaust gas and the catalytic metal. This improves the performance of the exhaust gas purification catalyst.

[0117] The method for supporting Rh and, optionally, other precious metals as catalytic metals onto carrier particles can be one that is generally used in the field of exhaust gas purification catalysts.

[0118] The content of carrier particles in the upstream and downstream coating layers (excluding the content of OSC material if the carrier particles include the OSC material described in detail below) is not limited. For example, the content of carrier particles in the upstream coating layer is usually 10g to 100g, preferably 15g to 80g, per 1L of the portion of the substrate to which the upstream coating layer is applied. For example, the content of carrier particles in the downstream coating layer is usually 25g to 170g, preferably 30g to 100g, per 1L of the portion of the substrate to which the downstream coating layer is applied. The content of carrier particles that may be contained in the upstream or downstream coating layer depends on the amount of carrier particles added as a material during the manufacture of the exhaust gas purification catalyst.

[0119] The upstream court layer has a specific surface area of ​​40 m². 2 High specific surface area OSC material with a specific surface area exceeding / g, 4m² 2 / g~40m 2 A medium specific surface area OSC material with a specific surface area of ​​4 m² / g, and a specific surface area of ​​4 m². 2 The downstream coating layer includes at least one OSC material selected from the group consisting of low specific surface area OSC materials with a specific surface area of ​​less than / g. The downstream coating layer includes at least one OSC material selected from the group consisting of high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials. However, the upstream and downstream coating layers together include three types of OSC materials: high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials.

[0120] Furthermore, high specific surface area OSC material, medium specific surface area OSC material, and low specific surface area OSC material may each consist of two or more types of OSC material. For example, high specific surface area OSC material may consist of a first high specific surface area OSC material and a second high specific surface area OSC material. For example, medium specific surface area OSC material may consist of a first medium specific surface area OSC material and a second medium specific surface area OSC material. For example, low specific surface area OSC material may consist of a first low specific surface area OSC material and a second low specific surface area OSC material.

[0121] In this invention, the specific surface area refers to the specific surface area of ​​each individual material measured by the BET method (BET specific surface area).

[0122] The specific surface area of ​​high specific surface area OSC material is 60 m². 2 / g~90m 2 / g is preferable.

[0123] The specific surface area of ​​medium-specific surface area OSC material is 30 m². 2 / g~40m 2 / g is preferable.

[0124] The specific surface area of ​​low specific surface area OSC material is 0.5 m². 2 / g~2.0m 2 / g is preferable.

[0125] Examples of high specific surface area OSC materials include alumina-ceria-zirconia composite oxides (ACZ), ceria-zirconia composite oxides (CZ), and ceria-zirconia composite oxides having a fluorite structure, such as CeZrO4.

[0126] Alumina-ceria-zirconia composite oxides are composite oxides in which ceria and zirconia are dispersed in alumina, and a portion of the ceria and zirconia form a ceria-zirconia solid solution. These oxides are observable using a transmission electron microscope (TEM), etc. The formation of a ceria-zirconia solid solution by ceria and zirconia can be confirmed, for example, by X-ray diffraction (XRD).

[0127] By including alumina-ceria-zirconia composite oxides as a high specific surface area OSC material, sufficient OSC performance can be ensured because the alumina-ceria-zirconia composite oxides have a faster oxygen absorption and release rate than ceria-zirconia composite oxides.

[0128] The composition of the alumina-ceria-zirconia composite oxide used as a high specific surface area OSC material is such that the Ce / Zr molar ratio is typically 0.6 or less, for example, 0.1 to 0.6, preferably 0.15 to 0.55, and the alumina (Al2O3) component content is typically 40% to 70% by weight relative to the total weight of the alumina-ceria-zirconia composite oxide. The composition of the alumina-ceria-zirconia composite oxide used as a high specific surface area OSC material depends on the composition of the alumina-ceria-zirconia composite oxide used as a material in the manufacture of exhaust gas purification catalysts.

[0129] By setting the composition of the alumina-ceria-zirconia composite oxide as a high specific surface area OSC material within the aforementioned range, it is possible to fully obtain the effects of suppressing particle growth by alumina (improving heat resistance and ensuring specific surface area), ensuring oxygen absorption and release performance by ceria (OSC performance), and ensuring the stabilizing effect of ceria by zirconia.

[0130] The alumina-ceria-zirconia composite oxide used as a high specific surface area OSC material may further contain one or more elements selected from rare earth elements other than 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 is usually 2% to 6% by weight as oxides relative to the total weight of the alumina-ceria-zirconia composite oxide.

[0131] By including rare earth elements in alumina-ceria-zirconia composite oxides, which are used as high specific surface area OSC materials, it is possible to improve the heat resistance and OSC performance of the alumina-ceria-zirconia composite oxides.

[0132] The particle size (average particle size) of primary particles of alumina-ceria-zirconia composite oxide as a high specific surface area OSC material is not limited as long as it has the specific surface area required for a high specific surface area OSC material. Although the particle size (average particle size) of primary particles of alumina-ceria-zirconia composite oxide as a high specific surface area OSC material is not limited, the average value obtained by scanning electron microscopy (SEM) or transmission electron microscopy (TEM) is usually between 1 nm and less than 500 nm, preferably between 10 nm and 100 nm.

[0133] Furthermore, the crystallite size of the ceria-zirconia composite oxide in alumina-ceria-zirconia composite oxides used as high specific surface area OSC materials is not limited. Although the crystallite size of the ceria-zirconia composite oxide in alumina-ceria-zirconia composite oxides used as high specific surface area OSC materials is not limited, it is usually less than 10 nm, for example, 2 nm to 10 nm. The crystallite size of the ceria-zirconia composite oxide can be measured, for example, by the full width at half maximum of XRD.

[0134] By setting the average grain size of the alumina-ceria-zirconia composite oxide and the crystallite size of the ceria-zirconia composite oxide in the alumina-ceria-zirconia composite oxide to the aforementioned range, the effect of ensuring OSC performance by ceria can be fully obtained.

[0135] Alumina-ceria-zirconia composite oxides, used as high specific surface area OSC materials, can be prepared, for example, by the alkoxide method or the coprecipitation method. By preparing alumina-ceria-zirconia composite oxides using the alkoxide method or the coprecipitation method, composite oxides consisting of uniform and fine primary particles can be prepared, and composite oxides containing ceria-zirconia solid solutions can be easily prepared.

[0136] In the alkoxide method, for example, alumina-ceria-zirconia composite oxides can be prepared by mixing all metal alkoxides of aluminum, cerium, zirconium, and optionally rare earth elements, followed by hydrolysis and calcination. Furthermore, even if not all of aluminum, cerium, zirconium, and optionally rare earth elements are used as metal alkoxides, at least one of them can be used as a metal alkoxide, while the remaining metals can be used as solutions such as nitrates or acetyl acetates.

[0137] The metal alkoxide can be any of the following: methoxide, ethoxide, butoxide, etc., but one with high solubility in the alcohol solvent is preferred. Any alcohol solvent can also be used.

[0138] In the coprecipitation method, for example, water-soluble salts such as nitrates of all metals, including aluminum, cerium, zirconium, and optionally rare earth elements, are mixed and coprecipitationd as hydroxides in ammonia water, and then calcined to prepare alumina-ceria-zirconia composite oxides. Furthermore, even if not all of aluminum, cerium, zirconium, and optionally rare earth elements are used as water-soluble salts, if at least one of them is used as a water-soluble salt, the remaining metals can be used as solids such as metal powders or oxide powders.

[0139] The alumina-ceria-zirconia composite oxide obtained in this manner is preferably heat-treated beforehand. By heat-treating the alumina-ceria-zirconia composite oxide beforehand, excessive crystal growth of the particles can be suppressed, while further suppressing the deterioration of OSC performance after durability.

[0140] The specific surface area of ​​alumina-ceria-zirconia composite oxides used as high specific surface area OSC materials can be adjusted by reaction conditions in the alkoxide method or coprecipitation method, such as material concentration, addition rate, reaction time and reaction temperature, calcination temperature and time, and grinding conditions, particularly the calcination temperature and time and grinding conditions. Generally, the higher the calcination temperature, the smaller the specific surface area, and the longer the calcination time, the smaller the specific surface area. When preparing alumina-ceria-zirconia composite oxides as high specific surface area OSC materials, the calcination temperature and time are not limited, but are usually 500°C to 800°C in air and usually 0.5 to 10 hours.

[0141] As the alumina-ceria-zirconia composite oxide used as a high specific surface area OSC material, it may be one that is known in the art, for example, those described in Japanese Patent Publication No. 10-202102, Japanese Patent Publication No. 2001-232199, and Japanese Patent Publication No. 2012-187518.

[0142] In ceria-zirconia composite oxides used as high-specific-surface-area OSC materials, the molar ratio of cerium to zirconium in the ceria-zirconia composite oxide is typically in the range of 43:57 to 48:52. The composition of ceria-zirconia composite oxides used as high-specific-surface-area OSC materials depends on the composition of ceria-zirconia composite oxides used as materials in the manufacture of exhaust gas purification catalysts.

[0143] By having a cerium-zirconia composite oxide with a cerium-zirconia content ratio within the aforementioned range, the heat resistance is sufficiently high, and the OSC performance can be sufficiently superior even after being exposed to high temperatures for a long period of time.

[0144] The ceria-zirconia composite oxide used as a high specific surface area OSC material may further contain one or more elements selected from rare earth elements other than 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 is usually 1% to 20% by weight, preferably 3% to 7% by weight, as oxides, relative to the total weight of the ceria-zirconia composite oxide.

[0145] By including rare earth elements in ceria-zirconia composite oxides, which are used as high-specific-surface-area OSC materials, it is possible to improve the heat resistance and OSC performance of the ceria-zirconia composite oxides.

[0146] The particle size (average particle size) of the primary particles of the ceria-zirconia composite oxide as a high specific surface area OSC material is not limited as long as it has the specific surface area required for a high specific surface area OSC material.

[0147] Furthermore, the crystallite size of ceria-zirconia composite oxides as high specific surface area OSC materials is not limited. The crystallite size of ceria-zirconia composite oxides can be measured, for example, by the full width at half maximum (FWHM) of an XRD.

[0148] Ceria-zirconia composite oxides, used as high-specific-surface-area OSC materials, are materials conventionally used as co-catalysts (oxygen storage materials) in exhaust gas purification catalysts, and their details are known to those skilled in the art. Preferably, ceria-zirconia composite oxides used as high-specific-surface-area OSC materials have a solid solution formed between ceria and zirconia. Ceria-zirconia composite oxides used as high-specific-surface-area OSC materials can be prepared by the alkoxide method or the coprecipitation method. In the coprecipitation method, for example, an aqueous solution of cerium salt (such as cerium nitrate) and zirconium salt (such as zirconium oxynitrate) is dissolved, and ammonia water is added to produce a coprecipitation. The resulting precipitate is then dried and calcined, and further subjected to a temperature of typically 400 kgf / cm². 2 ~3500 kgf / cm²2 It can be prepared by pressurizing and molding under pressure, and then performing a reduction treatment at a temperature of typically 1450°C to 2000°C.

[0149] The specific surface area of ​​ceria-zirconia composite oxides used as high specific surface area OSC materials can be adjusted by reaction conditions in the alkoxide method or coprecipitation method, such as material concentration, addition rate, reaction time and reaction temperature, calcination temperature and time, and grinding conditions, particularly the calcination temperature and time and grinding conditions. Generally, the higher the calcination temperature, the smaller the specific surface area, and the longer the calcination time, the smaller the specific surface area. When preparing ceria-zirconia composite oxides as high specific surface area OSC materials, the calcination temperature and time are not limited.

[0150] As the ceria-zirconia composite oxide used as a high specific surface area OSC material, it may be one that is known in the art, for example, one described in Japanese Patent Application Publication No. 2011-219329.

[0151] Examples of medium-specific-surface-area OSC materials include alumina-ceria-zirconia composite oxides (ACZ), ceria-zirconia composite oxides (CZ), and ceria-zirconia composite oxides having a fluorite structure, such as CeZrO4.

[0152] Alumina-ceria-zirconia composite oxides (ACZ) and ceria-zirconia composite oxides (CZ) that can be used as medium-specific surface area OSC materials may have the same properties as those used as high-specific surface area OSC materials, other than specific surface area and properties that can change with said specific surface area, such as the content of each component.

[0153] The specific surface area of ​​alumina-ceria-zirconia composite oxides and ceria-zirconia composite oxides used as medium-specific surface area OSC materials can be adjusted by reaction conditions in the alkoxide method or coprecipitation method, such as material concentration, addition rate, reaction time and reaction temperature, calcination temperature and time, and grinding conditions, particularly calcination temperature and time and grinding conditions. Generally, the higher the calcination temperature, the smaller the specific surface area, and the longer the calcination time, the smaller the specific surface area.

[0154] For example, the particle size (average particle size) of primary particles of an alumina-ceria-zirconia composite oxide used as a medium specific surface area OSC material is not limited, but is typically 1 nm to 500 nm, preferably 10 nm to 100 nm, based on the average value obtained by SEM or TEM.

[0155] For example, the crystallite size of the ceria-zirconia composite oxide in alumina-ceria-zirconia composite oxides used as medium specific surface area OSC materials is not limited, but is usually less than 25 nm, for example, 10 nm to 25 nm.

[0156] For example, when preparing an alumina-ceria-zirconia composite oxide as a medium specific surface area OSC material, the firing temperature and time are not limited, but are typically 800°C to 1200°C in air and typically 0.5 to 10 hours.

[0157] For example, the particle size (average particle size) of the primary particles of a ceria-zirconia composite oxide used as a medium specific surface area OSC material is not limited, but is typically 1 nm to 500 nm, preferably 10 nm to 100 nm, based on the average value obtained by SEM or TEM.

[0158] For example, the crystallite size of ceria-zirconia composite oxides used as medium specific surface area OSC materials is not limited, but is usually less than 25 nm, preferably 10 nm to 25 nm.

[0159] For example, when preparing a ceria-zirconia composite oxide as a medium specific surface area OSC material, the firing temperature and time are not limited, but are typically 800°C to 1200°C in air and typically 0.5 to 10 hours.

[0160] Examples of low specific surface area OSC materials include ceria-zirconia composite oxides (CZ), such as ceria-zirconia composite oxides having a pyrochlore structure (Ce2Zr2O7, pyrochlore CZ).

[0161] In ceria-zirconia composite oxides, "having a pyrochlore structure" means that a crystalline phase (pyrochlore phase) with a pyrochlore-type ordered arrangement structure of cerium ions and zirconium ions is formed. Some of the cerium ions and zirconium ions may be substituted with additional elements such as praseodymium. The arrangement structure of the pyrochlore phase can be identified by the presence of peaks at 2θ angles of 14.5°, 28°, 37°, 44.5°, and 51° in the X-ray diffraction pattern using CuKα. Here, a "peak" refers to one with a height of 30 cps or more from the baseline to the peak top. When determining the diffraction line intensity, the average diffraction line intensity with 2θ = 10 to 12° is subtracted as a background value from the value of each diffraction line intensity.

[0162] In ceria-zirconia composite oxides having a pyrochlore structure as low specific surface area OSC materials, the content ratio of regularly arranged pyrochlore-type crystalline phases to the total crystalline phase, determined by the peak intensity ratio of the X-ray diffraction pattern, is preferably 50% or more, and particularly preferably 80% or more. Methods for preparing ceria-zirconia composite oxides having a pyrochlore structure as low specific surface area OSC materials are known to those skilled in the art.

[0163] The pyrochlore phase (Ce2Zr2O7) of ceria-zirconia composite oxides has oxygen vacancy sites, and when an oxygen atom enters these sites, the pyrochlore phase undergoes a phase change to the κ phase (Ce2Zr2O8). Conversely, the κ phase can undergo a phase change to the pyrochlore phase by releasing an oxygen atom. The oxygen storage capacity of ceria-zirconia composite oxides is due to the mutual phase change between the pyrochlore phase and the κ phase, which allows for the absorption and release of oxygen.

[0164] Here, it is known that the κ phase of ceria-zirconia composite oxides undergoes a phase change to a crystalline phase with a fluorite structure (CeZrO4: fluorite-type phase) through rearrangement. Under lean conditions, especially high-temperature lean conditions, pyrochlore CZ is more likely to undergo a phase change to the fluorite-type phase via the κ phase.

[0165] In X-ray diffraction (XRD) measurements of the crystalline phase of ceria-zirconia composite oxides as low specific surface area OSC materials using CuKα, the diffraction line at 2θ=14.5° is attributed to the (111) plane of the ordered phase (κ phase), and the diffraction line at 2θ=29° is a superposition of the diffraction line attributed to the (222) plane of the ordered phase and the diffraction line attributed to the (111) plane of the ceria-zirconia solid solution that does not have a pyrochlore phase. Therefore, the intensity ratio I(14 / 29) of the two diffraction lines can be used as an indicator of the abundance of the ordered phase. In ceria-zirconia composite oxides as low specific surface area OSC materials, the intensity ratio I(14 / 29) value of the diffraction line at 2θ=14.5° and the diffraction line at 2θ=29°, obtained from the X-ray diffraction pattern using CuKα after heating in air at 1100°C for 5 hours, is preferably 0.017 or higher, from the viewpoint of maintaining a good ordered phase and oxygen storage capacity after durability testing. Based on the PDF cards for the κ phase (PDF2:01-070-4048) and the pyrochlore phase (PDF2:01-075-2694), the I(14 / 29) value for a complete κ phase can be calculated as 0.04, and the I(14 / 29) value for a complete pyrochlore phase can be calculated as 0.05. Furthermore, in XRD measurements using CuKα of the crystalline phase of ceria-zirconia composite oxides as low specific surface area OSC materials, the diffraction line at 2θ=28.5° is attributed to the (111) plane of elemental CeO2. Therefore, the I(28 / 29) value, which is the intensity ratio of the diffraction line at 2θ=28.5° to the diffraction line at 2θ=29°, can be used as an indicator of the degree to which CeO2 is separated from the composite oxide. In ceria-zirconia composite oxides as low specific surface area OSC materials, the I(28 / 29) value, which is the intensity ratio of the diffraction line at 2θ=28.5° to the diffraction line at 2θ=29° obtained from the X-ray diffraction pattern using CuKα obtained by X-ray diffraction measurement after heating in air at 1100°C for 5 hours, is preferably 0.05 or less, from the viewpoint of suppressing ceria phase separation and oxygen storage capacity after durability testing.

[0166] Ceria-zirconia composite oxides having a pyrochlore structure as low specific surface area OSC materials have 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. When pyrochlore CZ as a low specific surface area OSC material has a secondary particle diameter (D50) within this range, it can significantly improve the oxygen absorption and release rate while maintaining a high oxygen storage capacity and sufficient heat resistance, compared to materials with a secondary particle diameter (D50) outside this range. In contrast, ceria-zirconia composite oxides having a fluorite structure do not have such a relationship between secondary particle diameter and oxygen absorption and release rate. Therefore, the significant improvement in oxygen absorption and release rate by setting the secondary particle diameter (D50) within a specific range in pyrochlore CZ is an unexpected effect unique to pyrochlore CZ. In pyrochlore CZ, the rapid internal diffusion of oxygen, characteristic of the pyrochlore structure, has a very significant impact on secondary particle size. On the other hand, heat resistance, which is in a trade-off relationship with secondary particle size, shows a different sensitivity to oxygen absorption / release rate than oxygen absorption / release rate, and sufficiently high heat resistance is maintained. As a result, it is hypothesized that by setting the secondary particle size (D50) of pyrochlore CZ within a specific range, it is possible to significantly improve the oxygen absorption / release rate while maintaining high oxygen storage capacity and high heat resistance. Therefore, by having a secondary particle size (D50) of 3 μm to 7 μm in pyrochlore CZ, it is possible to achieve both sufficient heat resistance and oxygen storage capacity and oxygen absorption / release rate, and in particular, to significantly improve the oxygen absorption / release rate.

[0167] Here, "secondary particles" refer to aggregates of primary particles, while "primary particles" generally refer to the smallest particles that make up the powder. Primary particles can be observed and determined using SEM or TEM, etc. The primary particle diameter of pyrochlore CZ as a low specific surface area OSC material is usually smaller than the secondary particle diameter and is not limited as long as it has the specific surface area required for a low specific surface area OSC material. The particle size (average particle size) of the primary particles of pyrochlore CZ as a low specific surface area OSC material is not limited. Here, the primary particle diameter (D50) refers to the average primary particle diameter when the number distribution is measured. On the other hand, the secondary particle diameter (D50) refers to the secondary particle diameter being the 50% cumulative particle diameter (also called the median diameter or D50). The secondary particle diameter (D50) is, for example, the particle diameter of the volume that is 50% of the cumulative volume distribution curve, where the total volume is 100%, in a volume-based particle size distribution obtained by measurement using laser diffraction scattering (i.e., the volume-based cumulative 50% diameter).

[0168] Pyrochlore CZ having a specific range of secondary particle size (D50) as a low specific surface area OSC material can be obtained, for example, by mixing raw materials to obtain a precipitate, drying and calcining the obtained precipitate, grinding it to obtain a powder, press-molding the obtained powder, subjecting it to a reduction treatment, and then grinding it to a predetermined secondary particle size (D50). The grinding of the molded body can be carried out by, for example, a ball mill, a vibratory mill, a stream mill, and a pin mill.

[0169] The specific surface area of ​​pyrochlore CZ as a low specific surface area OSC material can be adjusted, particularly by the firing temperature and time, and the grinding conditions. Generally, the specific surface area decreases as the firing temperature increases, and also as the firing time increases. When preparing ceria-zirconia composite oxides as low specific surface area OSC materials, the firing temperature and time are not limited.

[0170] In pyrochlore CZ as a low specific surface area OSC material, the molar ratio of zirconium (Zr) to cerium (Ce) (Zr / Ce) is 1.13 <Zr / Ce<1.30である。

[0171] Pyrochlore CZ as a low specific surface area OSC material may contain praseodymium, preferably containing praseodymium in addition to cerium and zirconium. Praseodymium is given by formula: Pr6O 11 →Since the ΔG (Gibbs free energy) of the reduction reaction represented by 3Pr2O3 + O2 is negative, it is thought that the reduction reaction of CeO2 represented by equation: 2CeO2 → Ce2O3 + 0.5O2, where ΔG is positive, is more likely to occur. When pyrochlore CZ as a low specific surface area OSC material contains praseodymium, the pyrochlore CZ preferably contains 0.5 mol% to 5 mol% of praseodymium relative to the total amount of cations, and the molar ratio of Zr to (Ce + Pr) is preferably 1.13 <Zr / (Ce+Pr)<1.30である。

[0172] Pyrochlore CZ as a low specific surface area OSC material may contain elements other than praseodymium as additional elements other than cerium and zirconium. These additional elements are not limited to praseodymium and may include, for example, rare earth elements other than cerium and praseodymium, and alkaline earth metals. 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 a stronger interaction with and greater affinity to precious metals when supported. 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 a stronger interaction with and greater affinity to precious metals when supported. The content of additional elements is typically 5 mol% or less relative to the total amount of cations in pyrochlore CZ.

[0173] As the pyrochlore CZ used as the low specific surface area OSC material, it may be one that is known in the art, for example, one described in Japanese Patent Application Publication No. 2018-038999.

[0174] For example, the particle size (average particle size) of the primary particles of pyrochlore CZ as a low specific surface area OSC material is not limited, but is usually greater than 1 μm, preferably greater than 1 μm to 20 μm, as measured by SEM or TEM.

[0175] For example, the crystallite size of pyrochlore CZ as a low specific surface area OSC material is not limited, but is usually greater than 100 nm, for example, 150 nm to 500 nm.

[0176] For example, when preparing pyrochlore CZ as a low specific surface area OSC material, the firing temperature and time are not limited, but are typically 1100°C to 2000°C in air and typically 0.5 to 15 hours.

[0177] The amount of high specific surface area OSC material contained in the upstream coating layer is not limited, but is typically 10g to 100g, preferably 10g to 80g, per 1L of the volume of the portion of the substrate to which the upstream coating layer is applied. The amount of high specific surface area OSC material that may be contained in the upstream coating layer depends on the amount of high specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0178] The amount of medium-specific surface area OSC material contained in the upstream coating layer is not limited, but is usually 0g to 45g, preferably 0g, per 1L of the volume of the portion of the substrate to which the upstream coating layer is applied. The amount of medium-specific surface area OSC material that may be contained in the upstream coating layer depends on the amount of medium-specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0179] The amount of low specific surface area OSC material contained in the upstream coating layer is not limited, but is typically 3g to 25g, preferably 5g to 20g, per 1L of the volume of the portion of the substrate to which the upstream coating layer is applied. The amount of low specific surface area OSC material that may be contained in the upstream coating layer depends on the amount of low specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0180] The amount of high specific surface area OSC material contained in the downstream coating layer is not limited, but is usually 0g to 80g, preferably 0g, per 1L of the volume of the portion of the substrate to which the downstream coating layer is applied. The amount of high specific surface area OSC material that may be contained in the downstream coating layer depends on the amount of high specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0181] The amount of medium-specific surface area OSC material contained in the downstream coating layer is not limited, but is typically 20g to 80g, preferably 40g to 80g, per 1L of the volume of the portion of the substrate to which the downstream coating layer is applied. The amount of medium-specific surface area OSC material that may be contained in the downstream coating layer depends on the amount of medium-specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0182] The amount of low specific surface area OSC material contained in the downstream coating layer is not limited, but is typically 5g to 40g, preferably 20g to 40g, per 1L of the volume of the portion of the substrate to which the downstream coating layer is applied. The amount of low specific surface area OSC material that may be contained in the downstream coating layer depends on the amount of low specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0183] The upstream coating layer preferably contains both high-specific-surface-area OSC material and low-specific-surface-area OSC material.

[0184] By including high specific surface area OSC material and low specific surface area OSC material in the upstream coating layer, when the exhaust gas purification catalyst of the first embodiment of the present invention is used as S / C, NOx can be efficiently purified in the upstream side, where the oxygen concentration is relatively high and HC is less likely to accumulate compared to the downstream side.

[0185] The downstream coating layer preferably contains medium-specific surface area OSC material and low-specific surface area OSC material.

[0186] By including a medium-specific surface area OSC material and a low-specific surface area OSC material in the downstream coating layer, when the exhaust gas purification catalyst of the first embodiment of the present invention is used as an S / C, NOx can be efficiently purified while preventing HC deposition in the downstream side, where the oxygen concentration is relatively lower and HC is more likely to accumulate compared to the upstream side, by using an OSC material with a relatively low specific surface area.

[0187] Therefore, by including high-specific-surface-area OSC material and low-specific-surface-area OSC material in the upstream coating layer, and medium-specific-surface-area OSC material and low-specific-surface-area OSC material in the downstream coating layer, it is possible to achieve a better balance between OSC performance and catalytic performance.

[0188] In the first embodiment of the present invention, the amount of ceria in the high specific surface area OSC material is not limited, but is usually 10% to 40% by weight, preferably 20% to 40% by weight, relative to the total ceria weight of the second catalyst coating layer (i.e., the upstream coating layer and the downstream coating layer).

[0189] In the first embodiment of the present invention, the amount of ceria 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 ceria weight of the second catalyst coating layer.

[0190] In the first embodiment of the present invention, the amount of ceria in the high specific surface area OSC material and the medium specific surface area OSC material is not limited, but is usually 80% by weight or less, preferably 60% by weight or less, and more preferably 40% by weight or less, relative to the total ceria weight of the second catalyst coating layer.

[0191] In the first embodiment of the present invention, the amount of ceria 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 ceria weight of the second catalyst coating layer.

[0192] In the first embodiment of the present invention, if the second catalyst coating layer does not contain any ceria-containing compounds other than the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material, then the sum of all the ceria amounts in the high specific surface area OSC material, the medium specific surface area OSC material, and the low specific surface area OSC material equals 100% by weight.

[0193] By ensuring that the ceria content of each OSC material in the second catalyst coating layer falls within the aforementioned range, it becomes possible to establish a more balanced combination of OSC performance at both low and high temperatures, as well as exhaust gas purification performance, particularly NOx purification performance.

[0194] Specifically, in the first embodiment of the present invention, the second catalyst coating layer (upstream coating layer and downstream coating layer) contains three types of OSC materials with different specific surface areas together with Rh, thereby suppressing HC poisoning of Rh, particularly under conditions where (1) the air-fuel ratio (A / F) is rich and (2) the intake air volume is large during acceleration due to the reduction in the size of the exhaust gas purification catalyst (equivalent to high intake air volume, high Ga: high space velocity, or high SV), and ensuring OSC performance at low and high temperatures, thereby obtaining an exhaust gas purification catalyst with improved catalyst performance, especially NOx purification performance.

[0195] The upstream and downstream coating layers constituting the second catalyst coating layer are each composed primarily of Rh as a catalyst metal, optionally other precious metals, carrier particles supporting the Rh and other precious metals, and the aforementioned OSC material, respectively. However, they may further contain other components as long as they do not impair the effects of the present invention. Examples of other components include other metal oxides and additives used in catalyst coating layers for this type of application, specifically 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 carrier particles (i.e., metal oxides that do not support Rh, etc.). The other components may be in their original form or, like Rh, etc., supported on carrier particles.

[0196] In the upstream and downstream coating layers that constitute the second catalyst coating layer, the content of other components in the coating layer is not limited if present, but is usually 20g to 120g, preferably 80g to 120g, per 1L of the volume of the portion of the substrate to which the upstream or downstream coating layer is applied. The content of other components that may be contained in the upstream or downstream coating layer depends on the amount of other components added as materials during the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0197] The amount of the upstream coating layer is not limited, but is typically 30g to 250g, preferably 50g to 250g, per 1L of the volume of the portion of the substrate to which the upstream coating layer is applied. The amount of the upstream coating layer depends on the total weight of the materials used in the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0198] The amount of the downstream coating layer is not limited, but is typically 50g to 250g, preferably 100g to 250g, per 1L of the volume of the portion of the substrate to which the downstream coating layer is applied. The amount of the downstream coating layer depends on the total weight of the materials used in the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0199] The thickness of the upstream coating layer is not limited, but its average thickness is usually 5 μm to 50 μm, preferably 10 μm to 30 μm. The thickness of the upstream coating layer can be measured, for example, by SEM.

[0200] The thickness of the downstream coating layer is not limited, but its average thickness is usually 5 μm to 50 μm, preferably 10 μm to 30 μm. The thickness of the downstream coating layer can be measured, for example, by SEM.

[0201] By ensuring that the amounts of each material in the upstream and downstream coating layers, as well as the thicknesses of the upstream and downstream coating layers, fall within the aforementioned ranges, a good balance between pressure loss, catalytic performance, and durability can be maintained in the exhaust gas purification catalyst.

[0202] • Second embodiment In a second embodiment of the present invention, the second catalyst coating layer includes Rh as a catalyst metal and three types of OSC materials with different specific surface areas, which are described in detail below.

[0203] The Rh content as a catalytic metal in the second catalytic coating layer is not limited, but is typically 0.05g to 1.0g, preferably 0.2g to 0.8g, in terms of metal content of the catalytic metal per 1L of the portion of the substrate to which the second catalytic coating layer is applied. The Rh content as a catalytic metal in the second catalytic coating layer depends on the amount of Rh precursor added as a material during the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0204] By including Rh in the aforementioned content in the second catalyst coating layer, Rh can fully exhibit its NOx purification performance without being poisoned by HC in an atmosphere where HC has been sufficiently purified by the first catalyst coating layer.

[0205] The second catalyst coating layer may further contain at least one other precious metal commonly used in the field of exhaust gas purification catalysts, selected from the group consisting of Pd, Pt, gold, silver, iridium, and ruthenium.

[0206] The form of Rh and optionally other precious metals contained in the second catalyst coating layer in each catalyst coating layer can be the same as the form of Rh and optionally other precious metals described in the first embodiment, i.e., the form as is, the form supported on carrier particles, etc. When the Rh and optionally other precious metals contained in the second catalyst coating layer are supported on carrier particles, the content of carrier particles in the second catalyst coating layer (excluding the content of OSC material if the carrier particles include the OSC material described in the first embodiment) is, for example, usually 20g to 170g, preferably 50g to 140g, per 1L of the volume of the portion of the substrate to which the second catalyst coating layer is applied. The content of carrier particles that may be contained in the second catalyst coating layer depends on the amount of carrier particles added as material during the manufacture of the exhaust gas purification catalyst.

[0207] In the second embodiment of the present invention, the OSC material contained in the second catalyst coating layer consists 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 first embodiment above.

[0208] In a second embodiment of the present invention, the second catalyst coating layer includes three types of OSC materials with different specific surface areas, thereby achieving both OSC performance and exhaust gas purification performance, particularly NOx purification performance.

[0209] In the second embodiment of the present invention, the content of the high specific surface area OSC material in the second catalyst coating layer is not limited, but is usually 10g to 80g, preferably 20g to 40g, per 1L of the volume of the portion of the substrate to which the second catalyst coating layer is applied. The content of the high specific surface area OSC material in the second catalyst coating layer depends on the amount of high specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0210] In the second embodiment of the present invention, the content of the medium specific surface area OSC material in the second catalyst coating layer is not limited, but is usually 10g to 40g, preferably 20g to 40g, per 1L of the volume of the portion of the substrate to which the second catalyst coating layer is applied. The content of the medium specific surface area OSC material in the second catalyst coating layer depends on the amount of medium specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0211] In the second embodiment of the present invention, the content of the low specific surface area OSC material in the second catalyst coating layer is not limited, but is usually 5g to 30g, preferably 10g to 30g, per 1L of the volume of the portion of the substrate to which the second catalyst coating layer is applied. The content of the low specific surface area OSC material in the second catalyst coating layer depends on the amount of low specific surface area OSC material added as a material during the manufacture of the exhaust gas purification catalyst.

[0212] In a second embodiment of the present invention, by including three types of OSC materials with different specific surface areas in the aforementioned proportions in the second catalyst coating layer, it is possible to establish a more balanced combination of OSC performance at both low and high temperatures, as well as exhaust gas purification performance, particularly NOx purification performance.

[0213] Specifically, in the second embodiment of the present invention, the second catalyst coating layer includes three types of OSC materials with different specific surface areas together with Rh, thereby suppressing HC poisoning of Rh, particularly under conditions where (1) the air-fuel ratio (A / F) is rich and (2) the intake air volume is large during acceleration due to the reduction in the size of the exhaust gas purification catalyst (equivalent to high intake air volume, high Ga: high space velocity, or high SV), and ensuring OSC performance, thereby obtaining an exhaust gas purification catalyst with improved catalyst performance, especially NOx purification performance.

[0214] In a second embodiment of the present invention, the second catalyst coating layer is mainly composed of Rh as a catalyst metal, optionally other noble metals, carrier particles supporting the Rh as a catalyst metal and other noble metals, and the OSC material, but may further contain other components as long as the effects of the present invention are not impaired. Other components include one or more of the following used in catalyst coating layers for this type of application: 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 carrier particles (i.e., metal oxides that do not support Rh, etc.). The other components may be in their original form or, like Rh, etc., supported on carrier particles.

[0215] The content of other components in the second catalyst coating layer is not limited if present, but is typically 20g to 120g, preferably 80g to 120g, per 1L of the portion of the substrate to which the second catalyst coating layer is applied. The content of other components that may be included in the second catalyst coating layer depends on the amount of other components added as materials during the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0216] The amount of the second catalyst coating layer is not limited, but is typically 50g to 250g, preferably 150g to 250g, per 1L of the portion of the substrate to which the second catalyst coating layer is applied. The amount of the second catalyst coating layer depends on the total weight of the materials used in the manufacture of the exhaust gas purification catalyst (excluding volatile components).

[0217] The thickness of the second catalyst coating layer is not limited, but its average thickness is typically 5 μm to 50 μm, preferably 10 μm to 30 μm. The thickness of the second catalyst coating layer can be measured, for example, by SEM.

[0218] By keeping the amount of each material in the second catalyst coating layer and the thickness of the second catalyst coating layer within the aforementioned range, a good balance between pressure loss, catalytic performance, and durability can be maintained in the exhaust gas purification catalyst.

[0219] (Method for manufacturing exhaust gas purification catalyst) The exhaust gas purification catalyst of the present invention can be manufactured using known coating techniques, except that it uses the components of the exhaust gas purification catalyst described above.

[0220] For example, the exhaust gas purification catalyst of the present invention, which has a substrate and a catalyst coating layer including a first catalyst coating layer and a second catalyst coating layer coated on the substrate, can be manufactured by a method comprising: (i) preparing a slurry for a first catalyst coating layer comprising a catalyst metal precursor containing Pd and / or Pt as a catalyst metal and a solvent; (ii) preparing a slurry for a second catalyst coating layer comprising a Rh precursor containing Rh as a catalyst metal, a solvent and high specific surface area OSC material, medium specific surface area OSC material and low specific surface area OSC material; (iii) applying the slurry for the first catalyst coating layer prepared in step (i) from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst to form a first catalyst coating layer; and (iv) applying the slurry for the second catalyst coating layer prepared in step (ii) to form a second catalyst coating layer.

[0221] Here, high specific surface area OSC material, medium specific surface area OSC material, and low specific surface area OSC material are as described above.

[0222] • First embodiment In manufacturing an exhaust gas purification catalyst according to the first embodiment of the present invention, step (ii) includes, as a step of preparing a slurry for a second catalyst coating layer, (ii-1) a step of preparing a slurry for a downstream coating layer formed from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst, and (ii-2) a step of preparing a slurry for an upstream coating layer formed from the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst. Furthermore, step (iv) includes, as a step of forming a second catalyst coating layer, (iv-1) a step of forming a downstream coating layer by applying the slurry for the downstream coating layer prepared in step (ii-1), and (iv-2) a step of forming an upstream coating layer by applying the slurry for the upstream coating layer prepared in step (ii-2). The order of steps (i) to (iv) is not limited to the order in which steps (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, in addition to the order (i)→(ii-1)→(ii-2)→(iii)→(iv-1)→(iv-2), other orders such as (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) can be adopted.

[0223] When manufacturing an exhaust gas purification catalyst according to the first embodiment of the present invention, in step (iii), it is preferable that the slurry for the first catalyst coating layer is applied to 20% to 50% of the total length of the substrate in the exhaust gas purification catalyst. Furthermore, in step (iv-1), it is preferable that the slurry for the downstream coating layer is applied to 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst. Also, in step (iv-2), it is preferable that the slurry for the upstream coating layer is applied to 30% to 70% of the total length of the substrate in the exhaust gas purification catalyst.

[0224] When manufacturing an exhaust gas purification catalyst according to the first embodiment of the present invention, step (ii-1) is preferably a step of preparing a slurry for the downstream coating layer containing 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 a slurry for the upstream coating layer containing an Rh precursor, a solvent, a high specific surface area OSC material, and a low specific surface area OSC material.

[0225] When 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 ceria in the high specific surface area OSC material used is preferably 10% to 40% by weight of the total ceria weight of the upstream and downstream coat layers as the second catalyst coating layer. Furthermore, the amount of ceria in the medium specific surface area OSC material used is preferably 10% to 40% by weight of the total ceria weight of the upstream and downstream coat layers as the second catalyst coating layer. In addition, the amount of ceria in the high specific surface area OSC material and the medium specific surface area OSC material used is preferably 60% by weight or less of the total ceria weight of the upstream and downstream coat layers as the second catalyst coating layer. Furthermore, the amount of ceria in the low specific surface area OSC material used is preferably 40% to 80% by weight of the total ceria weight of the upstream and downstream coat layers as the second catalyst coating layer. Here, the total amount 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 adjusted to equal 100% by weight.

[0226] When producing an exhaust gas purification catalyst according to the first embodiment of the present invention, step (i) is preferably a step of preparing a slurry for a first catalyst coating layer containing a Pd precursor and a solvent.

[0227] • Second embodiment In manufacturing the exhaust gas purification catalyst according to the second embodiment of the present invention, step (iv) is a step of forming the second catalyst coating layer by applying the slurry for the second catalyst coating layer prepared in step (ii) from the downstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst. 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), orders such as (ii)→(iv)→(i)→(iii) and (i)→(iii)→(ii)→(iv) can be adopted.

[0228] When manufacturing an exhaust gas purification catalyst according to the second embodiment of the present invention, in step (iii), it is preferable that the slurry for the first catalyst coating layer is applied to 15% to 50% of the total length of the substrate in the exhaust gas purification catalyst. Furthermore, in step (iv), it is preferable that the slurry for the second catalyst coating layer is applied to 65% to 95% of the total length of the substrate in the exhaust gas purification catalyst.

[0229] When producing an exhaust gas purification catalyst according to a second embodiment of the present invention, step (i) is preferably a step of preparing a slurry for a first catalyst coating layer containing a Pt precursor and a solvent.

[0230] The exhaust gas purification catalyst of the present invention can be manufactured, for example, as follows.

[0231] In manufacturing the exhaust gas purification catalyst according to the first embodiment of the present invention, first, as step (ii-1), a catalyst coating layer slurry for the downstream coating layer is prepared, which includes materials constituting the downstream coating layer, namely Rh precursors (e.g., salts containing Rh (e.g., nitrates), etc.), one or more OSC materials selected from the group consisting of high specific surface area OSC materials, medium specific surface area OSC materials, and low specific surface area OSC materials (e.g., alumina-ceria-zirconia composite oxide as a medium specific surface area OSC material and ceria-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 optionally further carrier particles (e.g., alumina-zirconia composite oxide) and additives (e.g., binders). Subsequently, as step (iv-1), the slurry is coated onto the region on the substrate where the downstream coating layer is to be formed by a wash-coat method. After blowing away excess slurry with a blower or the like, the solvent is removed by drying in the air, usually at 100°C to 150°C for 1 to 3 hours, and then calcined in the air, usually at 450°C to 550°C for 1 to 3 hours to form the downstream coat layer. Subsequently, in step (ii-2), a catalyst coat layer slurry for the upstream coat layer is prepared, which includes the materials constituting the upstream coat layer, namely Rh precursors (e.g., salts containing Rh (e.g., nitrates)), one or more OSC materials selected from the group consisting of high specific surface area OSC materials, medium specific surface area OSC materials and low specific surface area OSC materials (e.g., alumina-ceria-zirconia composite oxide as a high specific surface area OSC material and ceria-zirconia composite oxide as a low specific surface area OSC material), a solvent (e.g., water, alcohol, a mixture of water and alcohol), and optionally further carrier particles (e.g., alumina-zirconia composite oxide) and additives (e.g., binders). Next, in step (iv-2), the slurry is applied to the area on the substrate on which the downstream coating layer has been formed, using a wash-coat method, to form the upstream coating layer. After blowing away any excess slurry with a blower or the like, the solvent is removed by drying in the air, usually at 100°C to 150°C for 1 to 3 hours, and then the upstream coating layer is formed by firing in the air, usually at 450°C to 550°C for 1 to 3 hours.Next, in step (i), a catalyst coating slurry for the first catalyst coating layer is prepared, which includes the materials constituting the first catalyst coating layer, 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, etc.), and optionally carrier particles (e.g., alumina-ceria-zirconia composite oxide and / or ceria-zirconia composite oxide) and additives (e.g., a binder). Then, in step (iii), the slurry is applied to the area on the substrate on which the second catalyst coating layer (downstream coating layer and upstream coating layer) is formed, specifically the area on the upstream coating layer, by a wash-coat method. After blowing away excess slurry with a blower or the like, the solvent is removed by drying in the air, usually at 100°C to 150°C for 1 to 3 hours, and then calcined in the air, usually at 450°C to 550°C for 1 to 3 hours to form the first catalyst coating layer. In the method for manufacturing an exhaust gas purification catalyst according to the first embodiment of the present invention, as described above, the order of formation of the catalyst coating layer is not limited, and the catalyst coating layers may be formed in the order of the first catalyst coating layer, upstream coating layer, downstream coating layer, upstream coating layer, upstream coating layer, upstream coating layer, downstream coating layer, first catalyst coating layer, or downstream coating layer, first catalyst coating layer, upstream coating layer.

[0232] In manufacturing an exhaust gas purification catalyst according to a second embodiment of the present invention, first, as step (ii), a catalyst coating layer slurry for the second catalyst coating layer is prepared, which includes materials constituting the second catalyst coating layer, namely Rh precursors (e.g., Rh-containing salts (e.g., nitrates), etc.), three types of OSC materials with different specific surface areas (e.g., alumina-ceria-zirconia composite oxides and / or ceria-zirconia composite oxides, etc.), a solvent (e.g., water, alcohol, a mixture of water and alcohol, etc.), and optionally further carrier particles (e.g., alumina-zirconia composite oxides) and additives (e.g., binders). Subsequently, as step (iv), the slurry is coated onto a region on the substrate where the second catalyst coating layer is to be formed by a wash-coat method. After blowing away excess slurry with a blower or the like, the solvent is removed by drying in the air, usually at 100°C to 150°C for 1 to 3 hours, and then calcined in the air, usually at 450°C to 550°C for 1 to 3 hours to form a second catalyst coating layer. Subsequently, in step (i), a catalyst coating layer slurry for the first catalyst coating layer is prepared, which contains the materials constituting the first catalyst coating layer, 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 optionally carrier particles (e.g., alumina-ceria-zirconia composite oxide and / or ceria-zirconia composite oxide) and additives (e.g., a binder). Next, in step (iii), the slurry is applied to the area on the substrate on which the second catalyst coating layer has been formed, by a wash-coat method, to which the first catalyst coating layer is to be formed. After blowing away excess slurry with a blower or the like, the solvent is removed by drying in air, usually at 100°C to 150°C for 1 to 3 hours, and then firing in air, usually at 450°C to 550°C for 1 to 3 hours, to form the first catalyst coating layer. In the method for manufacturing an exhaust gas purification catalyst according to the second embodiment of the present invention, as described above, the order of formation of the catalyst coating layers is not limited, and the first catalyst coating layer may be formed first, followed by the second catalyst coating layer.

[0233] (Applications of exhaust gas purification catalysts) The exhaust gas purification catalyst of the present invention can demonstrate a significant effect in exhaust gas purification performance in a rich atmosphere, and can be used as an exhaust gas purification catalyst that exhibits a high HC poisoning suppression effect, even in environments where excess HC and other substances in a rich atmosphere can be adsorbed onto the exhaust gas purification catalyst and poison the catalyst.

[0234] For example, the exhaust gas purification catalyst of the first embodiment of the present invention can be used as S / C in a two-catalyst system including S / C and UF / C.

[0235] For example, the exhaust gas purification catalyst of the second embodiment of the present invention can be used as a UF / C in a two-catalyst system including an S / C and an UF / C. [Examples]

[0236] The following describes some embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments.

[0237] I. First Embodiment I-1. Materials used Material 1 (Al2O3) :La2O3 composite Al2O3 (Al2O3:99% by weight) (La2O3:1% by weight) Material 2 (high specific surface area OSC material) Al2O3-CeO2-ZrO2 composite oxide (ACZ) (Al2O3: 30% by weight) (CeO2:20% by weight) (ZrO2:44% by weight) (Nd2O3:2% by weight) (La2O3:2% by weight) (Y2O3:2% by weight) BET specific surface area: 65m 2 / g Material 3 (medium specific surface area OSC material) Al2O3-CeO2-ZrO2 composite oxide (ACZ) (Al2O3: 30 wt%) (CeO2: 20 wt%) (ZrO2: 44 wt%) (Nd2O3: 2 wt%) (La2O3: 2 wt%) (Y2O3: 2 wt%) BET specific surface area: 35 m 2 / g Material 4 (low specific surface area OSC material) : CeO2-ZrO2-based composite oxide (Ce2Zr2O7) with a pyrochlore structure (CeO2: 51.5 wt%) (ZrO2: 45.5 wt%) (Pr6O 11 : 3 wt%)​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ I-2. Preparation of Catalyst for Exhaust Gas Purification Comparative Example 1 First, Material 8 (Rh) and Material 5 (AZ) were added to distilled water while stirring, and the obtained suspension was dried at 120 °C for 2 hours and further calcined at 500 °C for 2 hours to prepare Rh-supported AZ (Rh / AZ).

[0239] Next, 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 an Al2O3-based binder were added to distilled water while stirring to prepare Suspension 1.

[0240] Subsequently, the prepared Suspension 1 was poured onto the substrate, and the unnecessary components were blown off with a blower to coat the substrate wall with the material, thereby preparing a precursor layer of the downstream coating layer. At that time, for each coating material, with respect to a volume of 1 L of the portion where the downstream coating layer of the substrate is applied, Material 8 was 0.40 g in terms of metallic Rh (0.40 g / L-zone), Material 1 was 40 g (40 g / L-zone), Material 2 was 75 g (75 g / L-zone), Material 4 was 28 g (28 g / L-zone), and Material 5 was 40 g (40 g / L-zone). Also, the coating length of the precursor layer of the second catalyst coating layer was adjusted to account for 65% of the total length of the substrate in the exhaust gas purification catalyst from the downstream end in the exhaust gas flow direction of the exhaust gas purification catalyst.

[0241] Finally, after removing moisture for 2 hours in a dryer maintained at 120 °C, firing was performed for 2 hours in an electric furnace maintained at 500 °C to prepare the downstream coating layer (rear part).

[0242] Subsequently, Material 8 (Rh) and Material 5 (AZ) were added to distilled water while stirring, and the obtained suspension was dried at 120 °C for 2 hours and further calcined at 500 °C for 2 hours to prepare Rh-supported AZ (Rh / AZ).

[0243] Next, Rh / AZ, material 1 (Al2O3), material 2 (high specific surface area OSC material), material 4 (low specific surface area OSC material), and an Al2O3-based binder were added to distilled water while stirring to prepare a suspended slurry 2.

[0244] Next, the prepared slurry 2 was poured onto the substrate on which the downstream coating layer had been formed, from the end face opposite to the end face on which the downstream coating layer had been formed. Excess material was then blown away with a blower to coat the substrate wall with the material and prepare the precursor layer for the upstream coating layer. At that time, for each coating material, per 1 L of the portion of the substrate on which the upstream coating layer was applied, material 8 was 0.15 g (0.15 g / L-zone) in terms of Rh metal equivalent, material 1 was 20 g (20 g / L-zone), material 2 was 15 g (15 g / L-zone), material 4 was 8 g (8 g / L-zone), and material 5 was 20 g (20 g / L-zone). Furthermore, the coating length of the precursor layer for the upstream coating layer was adjusted so that it occupied 55% of the total length of the substrate in the exhaust gas purification catalyst, starting from the end face upstream of the exhaust gas flow direction in the exhaust gas purification catalyst.

[0245] Finally, the material was dried in a dryer maintained at 120°C for 2 hours to remove moisture, and then fired in an electric furnace maintained at 500°C for 2 hours to prepare the upstream coating layer (front section).

[0246] Next, as described above, material 9 (Pd), material 1 (Al2O3), material 6 (CZ), material 7 (Ba), and an Al2O3-based binder were added to distilled water while stirring to prepare a suspended slurry 3.

[0247] Next, the prepared slurry 3 was poured onto the substrate on which the second catalyst coating layer, consisting of a downstream coating layer and an upstream coating layer, was formed, starting from the same end face on which the upstream coating layer was formed. Excess material was then blown away with a blower to coat the substrate wall with the material, thereby preparing the precursor layer for the first catalyst coating layer. At this time, for each coating material, the amount of material 9 was adjusted so that, per 1 L of the portion of the substrate to which the first catalyst coating layer was applied, the amount of material 9 was 5 g (5 g / L-zone) in terms of Pd metal equivalent, material 1 was 25 g (25 g / L-zone), material 6 was 75 g (75 g / L-zone), and material 7 was 13 g (13 g / L-zone). Furthermore, the coating length of the precursor layer for the first catalyst coating layer was adjusted so that it occupied 30% of the total length of the substrate in the exhaust gas purification catalyst, starting from the upstream end relative to the exhaust gas flow direction in the exhaust gas purification catalyst.

[0248] Finally, after removing moisture in a dryer maintained at 120°C for 2 hours, the material was fired in an electric furnace maintained at 500°C for 2 hours to prepare the first catalyst coating layer (front part), and finally the exhaust gas purification catalyst was prepared.

[0249] Comparative Example 2 In Comparative Example 1, the exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1, except that the entire amount of material 2 (75 g / L-zone) in slurry 1 was changed to material 3 (medium specific surface area OSC material) (75 g / L-zone), and the entire amount of material 2 (15 g / L-zone) in slurry 2 was changed to material 3 (medium specific surface area OSC material) (15 g / L-zone).

[0250] Example 1 In Comparative Example 1, the exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1, except that the entire 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), the amount of material 4 added to slurry 1 was changed to adjust the total amount of material 4 in slurry 1 to 8 g / L-zone, and 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.

[0251] Example 2 In Comparative Example 1, the exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1, except that the entire amount of material 2 in slurry 1 (75 g / L-zone) was changed to material 3 (medium specific surface area OSC material) (60 g / L-zone), and 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.

[0252] Example 3 In Comparative Example 1, the exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1, except that 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.

[0253] Example 4 In Comparative Example 1, the exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1, except that the entire 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.

[0254] Comparative Example 3 In Comparative Example 1, the exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 1, except that the order in which the catalyst coating layers were formed was changed from (downstream coating layer → upstream coating layer → first catalyst coating layer) to (first catalyst coating layer → downstream coating layer → upstream coating layer).

[0255] Example 5 In Example 3, an exhaust gas purification catalyst was prepared in the same manner as in Example 3, except that the order of forming the catalyst coat layer was changed from (downstream coat layer → upstream coat layer → first catalyst coat layer) to (first catalyst coat layer → downstream coat layer → upstream coat layer).

[0256] Table 1 summarizes the catalyst configurations of the OSC materials in the upstream coat layer and the downstream coat layer of the exhaust gas purification catalysts of Comparative Examples 1 to 3 and Examples 1 to 5.

[0257] [[ID=***10]] [[ID=***11]] [Table 1]

[0258] Table 2 summarizes the ratio of ceria occupied by each material with respect to the whole material in the exhaust gas purification catalysts of Comparative Examples 1 to 3 and Examples 1 to 5. Here, the amount (ratio) 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 becomes 100% by weight when all are added together. However, in Table 2, since the ratio of ceria in each OSC material among the three OSC materials is shown with three significant figures, the ratio of the ceria becomes 100 ± 0.1% by weight when all are added together.

[0259] [Table 2]

[0260] I-3. Durability Test Regarding the exhaust gas purification catalysts of Comparative Examples 1 to 3 and Examples 1 to 5, the following durability test was carried out using an actual engine. Each exhaust gas purification catalyst was respectively mounted in the exhaust system of a V-type 8-cylinder engine, and the exhaust gas in each atmosphere of stoichiometry and lean was repeatedly flowed at a certain time (ratio of 3:1) for 50 hours at a catalyst bed temperature of 950°C.

[0261] I-4. Performance Evaluation Note: There seem to be some inconsistent or repeated tags in the original text which might need further clarification from the source. But I've translated it as accurately as possible based on the given rules.I-3. The exhaust gas purification catalysts of Comparative Examples 1-3 and Examples 1-5, which underwent durability testing, were evaluated using actual engines as follows.

[0262] I-4-1. OSC Evaluation Each exhaust gas purification catalyst was installed in the exhaust system of an L-type 4-cylinder engine, and A / F feedback control was performed to achieve A / F ratios of 14.1 and 15.1 under conditions of Ga=10g / s and 500℃ (low temperature) or 750℃ (high temperature). The oxygen surplus or deficiency was calculated from the difference between the stoichiometric point and the A / F sensor output using the following formula, and the maximum oxygen storage capacity at Ga=10g / s and 500℃ (low temperature) or 750℃ (high temperature) was evaluated as OSC. OSC(g)=0.23×ΔA / F×Injected fuel amount

[0263] I-4-2. NOx purification rate in a rich atmosphere Each exhaust gas purification catalyst was installed in the exhaust system of an L-type 4-cylinder engine, and exhaust gas with an air-fuel ratio (A / F) of 14.4 was supplied. The NOx purification rate was measured at Ga=30 / s and 550°C. The NOx purification rate after 3 minutes of continuous use was evaluated as the NOx purification activity in a rich atmosphere.

[0264] I-5. Evaluation Results The results are shown in Table 3 and Figures 9 and 10.

[0265] [Table 3]

[0266] Table 3 shows that by comparing Comparative Examples 1 and 2 with Examples 1 to 4, it was found that in Examples 1 to 4, the second catalyst coating layer contains three types of OSC materials with different specific surface areas, namely high specific surface area OSC material, medium specific surface area OSC material, and low specific surface area OSC material. More preferably, the upstream coating layer contains high specific surface area OSC material and low specific surface area OSC material, and the downstream coating layer contains medium specific surface area OSC material and low specific surface area OSC material. This allows for a high NOx purification rate in a rich atmosphere while maintaining OSC performance at high and low temperatures without causing performance deficiencies, i.e., maintaining all three performances in a well-balanced and high-level manner. For example, Figure 9 shows that in Example 2, the NOx purification rate, which was insufficient in Comparative Example 1, is improved while maintaining OSC performance at low and high temperatures.

[0267] Therefore, it was found that by including high specific surface area OSC material, medium specific surface area OSC material, and low specific surface area OSC material in the second catalyst coating layer, it is possible to achieve both OSC performance and NOx purification rate.

[0268] Furthermore, by comparing Comparative Example 3 and Example 5 in Table 3 and Figure 10, it was found that the effects of the present invention can be obtained even if the arrangement of the first catalyst coating layer and the upstream coating layer is reversed, that is, even if the upstream coating layer is placed on top of the first catalyst coating layer.

[0269] II. Second Embodiment II-1. Materials used Material 1 (Al2O3) :La2O3 composite Al2O3 (Al2O3:99% by weight) (La2O3:1% by weight) Material 2 (high specific surface area OSC material) Al2O3-CeO2-ZrO2 composite oxide (ACZ) (Al2O3: 30% by weight) (CeO2:20% by weight) (ZrO2:44% by weight) (Nd2O3:2% by weight) (La2O3:2% by weight) (Y2O3:2% by weight) BET specific surface area: 65m 2 / g Material 3 (medium specific surface area OSC material) Al2O3-CeO2-ZrO2 composite oxide (ACZ) (Al2O3: 30% by weight) (CeO2:20% by weight) (ZrO2:44% by weight) (Nd2O3:2% by weight) (La2O3:2% by weight) (Y2O3:2% by weight) BET specific surface area: 35m 2 / g Material 4 (Low specific surface area OSC material) : CeO2-ZrO2 composite oxide (Ce2Zr2O7) having a pyrochlore structure (CeO2:51.5% by weight) (ZrO2:45.5wt%) (Pr6O 11 :3% by weight) (Prepared based on Japanese Patent Publication No. 2018-038999) BET specific surface area: 1.5m 2 / g Material 7(Ba) : barium sulfate Material 8 (Rh) Rhodium nitrate aqueous solution Rh concentration: 2.75% by weight Material 10 (high specific surface area OSC material) CeO2-ZrO2 composite oxide (CZ) (CeO2:20% by weight) (ZrO2: 70% by weight) (La2O3:5% by weight) (Y2O3:5% by weight) BET specific surface area: 80m 2 / g Material 11 (High specific surface area OSC material) CeO2-ZrO2 composite oxide (CZ) (CeO2:20% by weight) (ZrO2: 70% by weight) (La2O3:5% by weight) (Y2O3:5% by weight) BET specific surface area: 35m 2 / g Material 12(Pt) Platinum nitrate aqueous solution Pt concentration: 8.2% by weight Material 13(AZ) Al2O3-ZrO2 composite oxide (AZ) (Al2O3: 30% by weight) (ZrO2:60% by weight) (Nd2O3:2% by weight) (La2O3:4% by weight) (Y2O3:4% by weight) Base material : 875cc (600-cell hexagonal, wall thickness 2mil, total length 105mm) cordierite honeycomb substrate

[0270] II-2. Preparation of Catalysts for Exhaust Gas Purification Comparative Example 4 First, material 8 (Rh) and material 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).

[0271] Next, Rh / AZ, material 1 (Al2O3), material 2 (high specific surface area OSC material), material 4 (low specific surface area OSC material), and an Al2O3-based binder were added to distilled water while stirring to prepare a suspended slurry 1.

[0272] Next, the prepared slurry 1 was poured onto the substrate, and excess material was blown away with a blower to coat the substrate wall with the material, thereby preparing the precursor layer for the second catalyst coating layer. At that time, for each coating material, the amount of material 1 was 40g (40g / L-zone) per 1L volume of the portion of the substrate to which the second catalyst coating layer would be applied, material 2 was 60g (60g / L-zone), material 4 was 15g (15g / L-zone), material 13 was 60g (60g / L-zone), and material 8 was 0.18g (0.18g / L-zone) in terms of Rh metal equivalent. Furthermore, the coating length of the precursor layer for the second catalyst coating layer was adjusted so that it occupied 80% of the total length of the substrate in the exhaust gas purification catalyst, starting from the downstream end relative to the exhaust gas flow direction in the exhaust gas purification catalyst.

[0273] Finally, the material was dried in a dryer maintained at 120°C for 2 hours to remove moisture, and then fired in an electric furnace maintained at 500°C for 2 hours to prepare the second catalyst coating layer (rear portion).

[0274] Next, in the same manner as described above, material 12 (Pt), material 1 (Al2O3), material 10 (high specific surface area OSC material), material 7 (Ba), and an Al2O3-based binder were added to distilled water while stirring to prepare a suspended slurry 2.

[0275] Next, the prepared slurry 2 was poured onto the substrate on which the second catalyst coating layer had been formed, from the end face opposite to the end face on which the second catalyst coating layer had been formed. Excess material was then blown away with a blower to coat the substrate wall with the material and prepare the precursor layer for the first catalyst coating layer. At that time, for each coating material, the amount of material 12 was 0.7 g (0.7 g / L-zone) in terms of Pt equivalent per 1 L of the portion of the substrate on which the first catalyst coating layer was applied, material 1 was 35 g (35 g / L-zone), material 10 was 30 g (30 g / L-zone), and material 7 was 5 g (5 g / L-zone). In addition, the coating length of the precursor layer for the first catalyst coating layer was adjusted so that it occupied 35% of the total length of the substrate in the exhaust gas purification catalyst, starting from the upstream end relative to the exhaust gas flow direction in the exhaust gas purification catalyst.

[0276] Finally, after removing moisture in a dryer maintained at 120°C for 2 hours, the material was fired in an electric furnace maintained at 500°C for 2 hours to prepare the first catalyst coating layer (front part), and finally the exhaust gas purification catalyst was prepared.

[0277] Example 6 In Comparative Example 4, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4, except that 10 g / L-zone of Material 2 (total amount: 60 g / L-zone) in Slurry 1 was replaced with Material 3 (medium specific surface area OSC material) (total amount: 10 g / L-zone).

[0278] Example 7 In Comparative Example 4, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4, except that 20 g / L-zone of Material 2 (total amount: 60 g / L-zone) in Slurry 1 was replaced with Material 3 (medium specific surface area OSC material) (total amount: 20 g / L-zone).

[0279] Example 8 In Comparative Example 4, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4, except that 30 g / L-zone of Material 2 (total amount: 60 g / L-zone) in Slurry 1 was replaced with Material 3 (medium specific surface area OSC material) (total amount: 30 g / L-zone).

[0280] Example 9 In Comparative Example 4, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4, except that 40 g / L-zone of Material 2 (total amount: 60 g / L-zone) in Slurry 1 was replaced with Material 3 (medium specific surface area OSC material) (total amount: 40 g / L-zone).

[0281] Comparative Example 5 In Comparative Example 4, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4, except that the entire 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).

[0282] Comparative Example 6 In Comparative Example 4, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 4, except that the entire amount of material 2 (60 g / L-zone) in slurry 1 was changed to material 10 (high specific surface area OSC material) (total amount: 60 g / L-zone).

[0283] Example 10 In Comparative Example 6, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 6, except that 30 g / L-zone of material 10 (total amount: 60 g / L-zone) in slurry 1 was replaced with material 11 (medium specific surface area OSC material) (total amount: 30 g / L-zone).

[0284] Table 4 summarizes the catalyst composition of the OSC material in the second catalyst coating layer of the exhaust gas purification catalysts in Comparative Examples 4-6 and Examples 6-10.

[0285] [Table 4]

[0286] II-3. Durability Test The exhaust gas purification catalysts of Comparative Examples 4-6 and Examples 6-10 were subjected to the following durability tests using an actual engine. Each exhaust gas purification catalyst was installed in the exhaust system of a V8 engine, and the procedure was carried out by repeatedly passing exhaust gases in stoichiometric and lean atmospheres for a set period of time (in a 3:1 ratio) over 50 hours at a catalyst bed temperature of 900°C.

[0287] II-4. Performance Evaluation II-3. The exhaust gas purification catalysts of Comparative Examples 4-6 and Examples 6-10, which underwent durability testing, were evaluated using actual engines as follows.

[0288] II-4-1. OSC Evaluation Each exhaust gas purification catalyst was installed in the exhaust system of an L-type 4-cylinder engine, and A / F feedback control was performed to achieve A / F ratios of 14.1 and 15.1 under conditions of Ga=10g / s and 500℃. The oxygen surplus or deficiency was calculated from the difference between the stoichiometric point and the A / F sensor output using the following formula, and the maximum oxygen storage capacity at Ga=10g / s and 500℃ was evaluated as OSC. OSC(g)=0.23×ΔA / F×Injected fuel amount

[0289] II-4-2. NOx purification rate in a rich atmosphere Each exhaust gas purification catalyst was installed in the exhaust system of an L-type 4-cylinder engine, and exhaust gas with an air-fuel ratio (A / F) of 14.4 was supplied. The NOx purification rate was measured at Ga=30 / s and 500°C. The NOx purification rate after 3 minutes of continuous use was evaluated as the NOx purification activity in a rich atmosphere.

[0290] II-5. Evaluation Results The results are shown in Table 5 and Figures 11-13.

[0291] [Table 5]

[0292] Table 5 and Figure 11 show that by comparing Comparative Example 4 with Examples 6-9, it was found that by adding a medium-surface-area OSC material in addition to the high-surface-area OSC material and the low-surface-area OSC material to the second catalyst coating layer, the NOx purification rate in a rich atmosphere can be improved while maintaining OSC performance. This is because replacing a portion of the high-surface-area OSC material with the medium-surface-area OSC material reduces the amount of HC adhering to the OSC material, making it easier to maintain the precious metal activity.

[0293] On the other hand, as shown in Table 5 and Figure 12, by comparing Comparative Example 4 or 5 with Example 9, it was found that when the second catalyst coating layer is composed only of high specific surface area OSC material and low specific surface area OSC material, the OSC performance can be maintained at a high level, but the NOx purification rate in a rich atmosphere decreases. Conversely, when the OSC material is composed only of medium specific surface area OSC material and low specific surface area OSC material, the NOx purification rate in a rich atmosphere can be maintained at a high level, but the OSC performance decreases.

[0294] Therefore, it was found that by including high specific surface area OSC material, medium specific surface area OSC material, and low specific surface area OSC material in the second catalyst coating layer, it is possible to achieve both OSC performance and NOx purification rate.

[0295] Furthermore, by comparing the relationship between Comparative Example 4 and Example 8, and between Comparative Example 6 and Example 10, as shown in Table 5 and Figure 13, it was found that not only ACZ but also CZ can be used as high specific surface area OSC material and medium specific surface area OSC material. [Explanation of Symbols]

[0296] 1: Substrate, 2: Upstream coating layer, 3: Downstream coating layer, 4: First catalyst coating layer, 5: Second catalyst coating layer

Claims

1. A catalyst for exhaust gas purification having a base material and a catalyst coating layer coated on the base material, The catalyst coating layer comprises 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 the upstream end with respect to the exhaust gas flow direction in the exhaust gas purification catalyst. The second catalyst coating layer has a specific surface area of ​​40 m². ２ High specific surface area OSC material with a specific surface area exceeding 1g / g, with a specific surface area of ​​4m² ２ / g to 40m ２ Medium specific surface area OSC material with a specific surface area of ​​4 m² / g, and a specific surface area of ​​4 m². ２ Includes low specific surface area OSC material with a specific surface area of ​​less than / g. Catalyst for exhaust gas purification.

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

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

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

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

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

7. The exhaust gas purification catalyst according to claim 4, wherein the first catalyst coating layer is located below the upstream coating layer.

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

9. The amount of ceria in the high specific surface area OSC material is 10% to 40% by weight relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer; the amount of ceria in the medium specific surface area OSC material is 10% to 40% by weight relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer; the amount of ceria in the high specific surface area OSC material and the medium specific surface area OSC material is 60% or less by weight relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer; the amount of ceria in the low specific surface area OSC material is 40% to 80% by weight relative to the total ceria weight of the upstream and downstream coating layers as the second catalyst coating layer; and the sum 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.

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, for use as an S / C in a two-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 downstream end 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 width of the first catalyst coating layer is 15% to 50% of the total length of the substrate in the exhaust gas purification catalyst, and the width of the second catalyst coating layer is 65% to 95% of the total 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, for use as UF / C in a two-catalyst system.

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