Exhaust gas purification catalyst

Abstract

This exhaust gas purification catalyst employs a zone coating structure while effectively suppressing phosphorus poisoning, resulting in improved purification performance and reduced costs. [Solution] The exhaust gas purification catalyst 1 comprises a carrier 2 and a catalyst layer 3. The catalyst layer 3 includes a first catalyst layer 6, a second catalyst layer 7, and a third catalyst layer. The first catalyst layer 6 contains a first catalyst material in which Rh is supported on a support material that does not contain Ce, and Ba, and does not contain Ce. The second catalyst layer 7 contains a second catalyst material in which Rh is supported on a support material that contains a Ce-based oxygen storage and release material. The ratio C1 / C2 of the Rh concentration C1 in the first catalyst material to the Rh concentration C2 in the second catalyst is greater than 1.0.

Description

[Technical Field]

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

[0002] In the exhaust passage of an automobile engine, a catalyst is placed to purify harmful components such as HC (hydrocarbons), CO, and NOx (nitrogen oxides) in the exhaust gas.

[0003] In recent years, with the tightening of exhaust gas regulations, there is a need for catalysts to achieve both improved purification performance, particularly improved cold-start purification performance during engine startup, and lower costs.

[0004] Generally, engine oil contains substances that act as catalyst poisons, such as phosphorus (P), which are known to mix with exhaust gas and contribute to a decrease in the catalytic converter's purification performance. Phosphorus poisoning of the catalyst is more likely to occur in areas with high contact with exhaust gas, such as the front of the catalytic converter (exhaust gas inlet side) and the surface of the catalyst layer. Therefore, a technology has been proposed to suppress the decrease in purification performance due to catalyst poison by providing poison capture regions in these areas (see, for example, Patent Document 1).

[0005] Specifically, the highly phosphorus-resistant catalyst for automobile exhaust gas treatment disclosed in Patent Document 1 includes a poison-retaining region on the outermost surface of the upstream end of the substrate on which the catalyst layer is supported, where the catalyst material is not applied. In this way, the catalyst is described as having excellent resistance to catalyst poison by suppressing the inactivation of the catalyst substance by phosphorus, which tends to accumulate on the outermost surface of the upstream end of the substrate. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2013-006179 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, one solution to achieve both improved purification performance and reduced costs is to devise a way to arrange the catalytic materials within the catalyst monolith. For example, by adopting a zone coating structure that concentrates the proportion of precious metals in areas with high contact with exhaust gas, such as the upstream side and the surface side, it may be possible to improve purification efficiency while suppressing the increase in the amount of expensive precious metals used.

[0008] The technology described in Patent Document 1 suppresses the degradation of catalytic performance due to phosphorus poisoning by not placing catalyst materials containing precious metals in areas with high contact with exhaust gas, such as the upstream or surface layers. However, this is difficult to apply to the aforementioned zone coating structure.

[0009] Therefore, the objective of this disclosure is to provide an exhaust gas purification catalyst that employs a zone coating structure while effectively suppressing phosphorus poisoning, thereby achieving both improved purification performance and reduced costs. [Means for solving the problem]

[0010] To solve the above problems, one embodiment of the exhaust gas purification catalyst disclosed herein is: An exhaust gas purification catalyst, which is installed in the exhaust passage of an engine and purifies the exhaust gas containing P from the engine, The device comprises a carrier and a catalyst layer formed on the carrier for purifying the exhaust gas, The catalyst layer is A first catalyst layer disposed on the outermost surface of the catalyst layer, The catalyst includes a second catalyst layer, at least a portion of which is located on the support side of the first catalyst layer, The first catalyst layer contains a first catalyst material in which Rh is supported on a support material that does not contain Ce, and Ba, and does not contain Ce. The second catalyst layer contains a second catalyst material in which Rh is supported on a support material containing a Ce-based oxygen storage and release material. When the Rh concentration in the first catalyst material is C1 and the Rh concentration in the second catalyst material is C2, the ratio of C1 to C2, C1 / C2, is greater than 1.0. It is characterized by the following:

[0011] Exhaust gas purification catalysts often contain an oxygen storage and release material (OSC material) containing Ce, which absorbs oxygen in a lean atmosphere with a high oxygen concentration in the exhaust gas and releases active oxygen in a stoichiometric or rich atmosphere with a low oxygen concentration in the exhaust gas. In three-way catalysts, the action of this OSC material creates a stoichiometric atmosphere that facilitates exhaust gas purification performance. In other words, even if the A / F (air-fuel ratio) of the exhaust gas fluctuates slightly from the theoretical A / F, HC (hydrocarbons), CO (carbon monoxide), and NOx (nitrogen oxides) are efficiently purified (the A / F window is expanded). Ce-containing OSC materials (Ce-based OSC materials) absorb oxygen from the exhaust gas and release it as active oxygen through a reversible reaction involving a change in the valence of Ce.

[0012] However, engine oil containing antioxidants and other substances is essential for engine operation, and such engine oils contain catalytic poisons such as phosphorus (P), which then mix into the exhaust gas. The aforementioned Ce-based OSC material tends to have reduced oxygen storage and release capacity due to the formation of Ce and P compounds upon phosphorus poisoning.

[0013] Generally, phosphorus (P) poisoning of catalysts is more likely to occur in areas with high contact with exhaust gas, such as the upstream or surface layers. In this configuration, a first catalyst layer containing barium (Ba) but no Ce is placed on the outermost surface of the upstream side of the catalyst layer, where gas contact is highest and P poisoning of the catalyst is most likely to occur. This suppresses contact between P from oil-derived substances and Ce, and captures P in the form of a Ba-OP compound, thereby suppressing P diffusion into the second catalyst layer. In particular, by having the first catalyst layer cover at least a portion of the second catalyst layer, P poisoning of the second catalyst material can be effectively suppressed.

[0014] Furthermore, the inventors of the present application have found that the influence of P poisoning can be alleviated by increasing the noble metal ratio on the upstream side and the surface layer side. Therefore, in this configuration, in addition to the above configuration, the Rh concentration C1 of the first catalyst material contained in the first catalyst layer disposed at a site with high exhaust gas contact property is set to be higher than the Rh concentration C2 of the second catalyst material contained in the second catalyst layer (C1 / C2 exceeds 1.0). Thereby, while suppressing the influence of P poisoning and the increase in the amount of noble metal used, the catalyst performance can be improved.

[0015] The ratio C1 / C2 is preferably 1.3 or more.

[0016] By setting the Rh concentration gradient of the catalyst materials contained in the first catalyst layer and the second catalyst layer within the above range, the purification efficiency can be effectively improved.

[0017] Preferably, C1 is 0.1% by mass or more and 6.0% by mass or less.

[0018] By setting the Rh concentration C1 of the first catalyst material contained in the first catalyst layer within the above range, the purification efficiency can be effectively improved.

[0019] Preferably, C2 is 1.0% by mass or less.

[0020] By setting the Rh concentration C2 of the second catalyst material contained in the second catalyst layer within the above range, the purification efficiency can be effectively improved.

[0021] Preferably, the Ce-based oxygen storage and release material is a Ce-containing Zr-based composite oxide.

[0022] The Ce-containing Zr-based composite oxide has a high oxygen storage and release ability. By including the Ce-containing Zr-based composite oxide in the second catalyst layer, the A / F window can be expanded and the catalyst performance can be improved.

[0023] Preferably, the support material containing no Ce is a Ce-free Zr-based composite oxide.

[0024] Ce-free Zr-based composite oxides are less susceptible to phosphorus poisoning because they do not contain Ce. Furthermore, Rh-supported Ce-free Zr-based composite oxides maintain an appropriate oxidizing or reducing state for Rh even immediately after switching the exhaust gas atmosphere, effectively purifying NOx. In addition, Rh-supported Ce-free Zr-based composite oxides exhibit high steam reforming (SR) activity, increasing the generation capacity of reducing gases such as CO and H2 in the first catalyst layer. Also, because the Rh concentration in the first catalyst material is higher than that in the second catalyst material, the first catalyst layer exhibits SR activity at a lower temperature than the second catalyst layer. The generated reducing gases make it easier for the support material in the second catalyst layer to enter a reduced state. That is, the Ce contained in the support material... 3+ This condition makes it easier to develop PO4 2- Ce is in a compound state with 2+ This makes it less likely for the following conditions to occur. Thus, in addition to the capture of P by Ba, the high steam reforming activity in the first catalyst layer more effectively suppresses CePO4 formation in the second catalyst layer.

[0025] The Rh content in the catalyst layer is preferably 1.0 g / L or more and 2.0 g / L or less.

[0026] This configuration ensures excellent catalytic performance.

[0027] Preferably, the amount of the first catalyst material and the amount of the second catalyst material supported are 20 g / L or more and 150 g / L or less.

[0028] This configuration ensures excellent catalytic performance.

[0029] The amount of Ba supported in the first catalyst layer is preferably 5 g / L or more and 20 g / L or less.

[0030] By containing Ba in the above-mentioned amount in the first catalyst layer, the diffusion of P into the second catalyst layer can be effectively suppressed.

[0031] Preferably, the catalyst layer is provided on the support side of the first catalyst layer and the second catalyst layer, and further comprises a third catalyst layer containing Pd.

[0032] This configuration further improves catalytic performance.

[0033] Preferably, the carrier comprises an upstream end and a downstream end, The first catalyst layer is provided from the upstream end to the first position, The second catalyst layer is provided from the downstream end to a second position upstream of the first position, and in the portion overlapping with the first catalyst layer, it is positioned closer to the carrier than the first catalyst layer.

[0034] In this configuration, in the overlapping portion, the upstream portion of the second catalyst layer is covered by the first catalyst layer, thus effectively suppressing phosphorus poisoning of the second catalyst material.

[0035] Preferably, the second position is the upstream end.

[0036] The catalytic performance is improved by providing a second catalyst layer along the entire length of the support.

[0037] Preferably, the length from the upstream end to the first position is 50% or more of the total length of the carrier.

[0038] By providing the first catalyst layer over more than half of the total length of the support, the effect of P poisoning in the second catalyst layer can be effectively suppressed. [Effects of the Invention]

[0039] As described above, in this disclosure, a first catalyst layer containing Ba but not Ce is placed on the upstream outermost surface of the catalyst layer, where gas contact is highest and phosphorus poisoning of the catalyst is most likely to occur. This suppresses contact between phosphorus from oil-derived substances and Ce, and captures phosphorus in the form of a Ba-OP compound, thereby suppressing phosphorus diffusion into the second catalyst layer. In particular, by having the first catalyst layer cover at least a portion of the second catalyst layer, phosphorus poisoning of the second catalyst material can be effectively suppressed. Furthermore, in addition to the above configuration, in this disclosure, the Rh concentration C1 of the first catalyst material contained in the first catalyst layer, which is located in a part with high exhaust gas contact, is set to be higher than the Rh concentration C2 of the second catalyst material contained in the second catalyst layer (C1 / C2 is greater than 1.0). This makes it possible to improve catalyst performance while suppressing the effects of phosphorus poisoning and the increase in the amount of precious metal used. [Brief explanation of the drawing]

[0040] [Figure 1] A perspective view and a partial cross-sectional view showing an example of an exhaust gas purification catalyst related to this disclosure. [Figure 2] A schematic cross-sectional view of the catalyst layer of Embodiment 1. [Figure 3] A graph showing the relationship between the amount of catalyst metal supported and the HC light-off temperature T50. [Figure 4] A schematic cross-sectional view of the catalyst layer in Embodiment 2. [Figure 5] This graph shows the relationship between HC emissions and Rh concentration C1, calculated by CAE analysis using the catalyst models in Experimental Examples 2-1 to 2-16. [Figure 6] This graph shows the relationship between NOx emissions and Rh concentration C1, calculated by CAE analysis using the catalyst models in Experimental Examples 2-1 to 2-16. [Figure 7] This graph shows the relationship between HC emissions and Rh concentration (C2), calculated by CAE analysis using the catalyst models in Experimental Examples 2-1 to 2-16. [Figure 8] This graph shows the relationship between NOx emissions and Rh concentration (C2) calculated by CAE analysis using the catalyst models from Experimental Examples 2-1 to 2-16. [Figure 9]This graph shows the relationship between HC emissions and Rh concentration ratio C1 / C2, calculated by CAE analysis using the catalyst models in Experimental Examples 2-1 to 2-16. [Figure 10] This graph shows the relationship between NOx emissions and Rh concentration ratio C1 / C2, calculated by CAE analysis using the catalyst models in Experimental Examples 2-1 to 2-16. [Figure 11] A graph showing the time course of spatial velocity used in the CAE analysis of Experiment 2. [Figure 12] A graph showing the time course of the catalyst inlet gas temperature used in the CAE analysis of Experiment 2. [Modes for carrying out the invention]

[0041] Embodiments of the present disclosure will be described in detail below with reference to the drawings. The following description of preferred embodiments is illustrative in nature and is not intended to limit the present disclosure, its applications or uses in any way.

[0042] (Embodiment 1) <Composition of exhaust gas purification catalyst> The exhaust gas purification catalyst 1 according to an embodiment of the present invention shown in Figure 1 is installed in the exhaust passage of an automobile engine and purifies HC, CO, and NOx in the exhaust gas containing P from the engine.

[0043] The exhaust gas purification catalyst 1 comprises a honeycomb structure carrier 2 (carrier) having an upstream end 2A and a downstream end 2B, and a catalyst layer 3 formed on the cell walls (exhaust gas passage walls) of the carrier 2 for purifying exhaust gas.

[0044] In Figure 1, the cell cross-sectional shape of the carrier 2 is shown as rectangular, but it is not limited to this, and may also be a hexagonal honeycomb structure, for example. The material of the carrier 2 is not particularly limited and can be a material commonly used in exhaust gas purification catalysts, such as an inorganic porous material like cordierite, SiC, Si3N4, Sialon, or AlTiO3. The capacity of the carrier 2 is also not particularly limited and can be appropriately determined according to the specifications of the automobile, etc.

[0045] As shown in Figure 2, the catalyst layer 3 has a three-layer structure consisting of a first catalyst layer 6, a second catalyst layer 7, and an arbitrary third catalyst layer 8.

[0046] In this embodiment, the first catalyst layer 6, the second catalyst layer 7, and the third catalyst layer 8 are all provided from the upstream end 2A to the downstream end 2B of the carrier 2.

[0047] The first catalyst layer 6 is located on the outermost surface of the catalyst layer 3. The first catalyst layer 6 contains Rh as a catalytic metal.

[0048] The second catalyst layer 7 overlaps with the first catalyst layer 6 along the entire length of the support 2 and is positioned closer to the support 2 than the first catalyst layer 6. The second catalyst layer 7 contains Rh as a catalytic metal.

[0049] The third catalyst layer 8 is provided on the surface of the cell wall of the carrier 2, extending along the entire length of the carrier 2, and is positioned closer to the carrier 2 than the first catalyst layer 6 and the second catalyst layer 7. In other words, the exhaust gas passage side surface of the third catalyst layer 8 is entirely covered by the first catalyst layer 6 and the second catalyst layer 7. The third catalyst layer 8 contains Pd as a catalytic metal.

[0050] Although the catalyst layer 3 in this example has a three-layer structure, it is not limited to this configuration as long as it includes a first catalyst layer 6 and a second catalyst layer 7. The catalyst layer 3 may also have a two-layer structure consisting of the first catalyst layer 6 and the second catalyst layer 7, or it may have a laminated structure of four or more layers. That is, other layers may be included between each layer and between the third catalyst layer 8 and the cell wall surface of the support 2. Furthermore, the catalyst layer 3 may include other noble metals such as Pt or other transition metals in addition to Rh and Pd as catalyst metals.

[0051] In this specification, the amount of material carried will, in principle, be expressed in "g / L". In this case, "g / L" means the amount carried per liter of carrier. However, when the material is carried over a portion of the length of the carrier, "g / L" means the amount of material carried per liter of carrier. That is, if a material with a carrying amount of y "g / L" is carried on a portion of a carrier with a capacity of x "L", then x × y "g" of the material will be carried on that portion. Specifically, for example, if a material with a carrying amount of 20 "g / L" is carried on a portion of a carrier with a capacity of 2 "L", then 40 "g" of the material should be carried on that portion.

[0052] [First catalyst layer] The first catalyst layer 6 contains a first catalyst material in which Rh is supported on a support material that does not contain Ce, and Ba. Furthermore, the first catalyst layer 6 does not contain Ce.

[0053] As described above, OSC materials containing Ce expand the A / F window due to the oxygen storage and release capacity associated with changes in the valence state of Ce, contributing to improved catalyst performance. However, P poisoning tends to reduce the oxygen storage and release capacity as compounds of Ce and P are formed. In this configuration, a first catalyst layer 6 containing Ba and no Ce is placed on the outermost surface upstream of catalyst layer 3, which has the highest gas contactability and is most susceptible to P poisoning, covering the second catalyst layer 7 which contains Ce. This physically suppresses direct contact between P, an oil-derived substance, and Ce contained in the second catalyst layer 7, while also capturing P in the form of a Ba-OP compound in the first catalyst layer 6 and suppressing its diffusion to the second catalyst layer 7.

[0054] Examples of support materials that do not contain Ce include metal oxides that do not contain Ce, specifically Ce-free Zr-based composite oxides and activated alumina. These support materials may be used individually or as a mixture of two or more.

[0055] Furthermore, a Ce-free Zr-based composite oxide is preferred as the support material.

[0056] Ce-free Zr-based composite oxides have the advantage of being less susceptible to phosphorus poisoning because they do not contain Ce.

[0057] Furthermore, Ce-free Zr-based composite oxides possess high ionic conductivity and, without altering the valence of metal ions, absorb oxygen from the surroundings through oxygen exchange reactions, releasing active oxygen. As a result, their oxygen release rate is more gradual compared to Ce-based OSC materials. Therefore, Rh-supported Ce-free Zr-based composite oxides maintain an appropriate (not excessive) oxidized or reduced state of Rh even immediately after the exhaust gas atmosphere switches from lean to rich, enabling effective NOx purification.

[0058] In addition, the Rh-supported Ce-free Zr-based composite oxide exhibits high steam reforming (SR) activity. This increases the ability of the first catalyst layer 6 to generate reducing gases such as CO and H2. Furthermore, as will be described later, because the Rh concentration C1 of the first catalyst material is higher than the Rh concentration C2 of the second catalyst material, the first catalyst layer 6 exhibits SR activity at a lower temperature than the second catalyst layer 7. The generated reducing gases make the support material of the second catalyst layer 7 more susceptible to reduction. In other words, the Ce contained in the support material is Ce 3+ This condition makes it easier to develop PO4 2- Ce is in a compound state with 2+ This makes it less likely for the following conditions to occur. As a result, in the first catalyst layer 6, in addition to the capture of P by Ba, the high steam reforming activity of the Rh-supported Ce-free Zr-based composite oxide more effectively suppresses the formation of CePO4 in the second catalyst layer 7.

[0059] As Ce-free Zr-based composite oxides, those containing La, Y, etc., in addition to Zr can be used.

[0060] From the viewpoint of ensuring sufficient catalytic performance, the amount of the first catalyst material supported on the carrier 2 is preferably 20 g / L or more and 150 g / L or less.

[0061] The Ba source for the Ba contained in the first catalyst layer 6 is not particularly limited and any generally known substance can be used. Specifically, for example, BaSO4, Ba3P4O 13 The following can be used. Ba may be incorporated directly into the first catalyst layer 6 as the Ba source material itself, or it may be incorporated into the first catalyst layer 6 in a form supported on a support material such as activated alumina.

[0062] From the viewpoint of effectively suppressing P diffusion to the second catalyst layer 7, the amount of Ba supported in the first catalyst layer 6 is preferably 5 g / L to 20 g / L, and more preferably 10 g / L to 15 g / L.

[0063] The first catalyst layer 6 may contain a binder as an optional component. The binder is not particularly limited, and any binder commonly used in exhaust gas purification catalysts may be used. Specifically, for example, Y-stabilized zirconia binder, Rh-doped CeZr-based composite oxide, etc., can be used as the binder. When using Rh-doped CeZr-based composite oxide as the binder, it is preferable to use one that has undergone reduction treatment. By performing reduction treatment, the amount of metallic Rh on the binder surface increases, increasing the opportunity for contact between metallic Rh and exhaust gas, and further improving the exhaust gas purification performance of the first catalyst layer 6. When using Rh-doped CeZr-based composite oxide as the binder, the Rh contained in the binder is not included in the calculation of the Rh concentration C1. The binder content in the first catalyst layer 6 is not particularly limited, and it should be an amount sufficient for layer formation (for example, 5 to 20% by mass of the first catalyst layer 6).

[0064] The first catalyst layer 6 may contain other components as optional components. Specifically, for example, other components may include Ce-free Zr-based composite oxides that do not contain catalytic metals, co-catalysts such as activated alumina, etc. The content of other components in the first catalyst layer 6 is not particularly limited and can be appropriately determined according to the purification performance, etc., and can be, for example, 30 g / L or less.

[0065] [Second catalyst layer] The second catalyst layer 7 contains a second catalyst material in which Rh is supported on a support material containing a Ce-based oxygen storage and release material.

[0066] Examples of Ce-based oxygen storage and release materials, though not intended to be limiting, include ceria, composite oxides of Ce and Zr, and Ce-containing Zr-based composite oxides which are composite oxides of Ce, Zr, and other elements.

[0067] A preferred OSC material containing Ce is a Ce-containing Zr-based composite oxide. Ce-containing Zr-based composite oxides have high oxygen storage and release capacity. By including a Ce-containing Zr-based composite oxide in the second catalyst layer 7, the A / F window is expanded, and catalytic performance can be improved. Furthermore, from the viewpoint of improving heat resistance and increasing oxygen storage and release due to increased crystal strain, the Ce-containing Zr-based composite oxide is preferably a composite oxide of Ce, Zr, and a rare earth element (Nd, La, Y, Pr, etc.). The Ce-containing Zr-based composite oxide may be one type or a mixture of multiple types. In the case of a mixture of multiple types, it may be a mixture of materials with different elemental compositions, or a mixture of materials with the same elemental composition but different mixing ratios.

[0068] Furthermore, the support material included in the second catalyst material may include support materials other than Ce-based oxygen storage and release materials. Examples of support materials other than Ce-based oxygen storage and release materials, though not intended to be limiting, include Ce-free Zr-based composite oxides and activated alumina. As for Ce-free Zr-based composite oxides, those with the same component composition as the first catalyst material described above can be used.

[0069] A preferred configuration includes a combination of a Ce-containing Zr-based composite oxide and a Ce-free Zr-based composite oxide as the support material.

[0070] As mentioned above, Ce-containing Zr-based composite oxides are based on reactions involving changes in the valence of Ce, resulting in a rapid oxygen release rate and effective absorption of A / F fluctuations. However, immediately after, for example, the exhaust gas atmosphere switches from lean to rich, oxygen release by the Ce-containing Zr-based composite oxide proceeds rapidly, making it easy for much of the Rh supported as a catalytic metal to enter an oxidized state. As a result, NOx in the exhaust gas, which begins to be generated immediately after the atmosphere change, cannot be effectively purified.

[0071] In this respect, as mentioned above, Ce-free Zr-based composite oxides have a gentler oxygen release rate than Ce-containing Zr-based composite oxides, and can effectively purify NOx even immediately after switching the exhaust gas atmosphere.

[0072] Therefore, combining Ce-containing Zr-based composite oxides and Ce-free Zr-based composite oxides as support materials is particularly advantageous for improving NOx purification performance.

[0073] The second catalyst layer 7, like the first catalyst layer 6, may contain optional components such as Ba, a binder, or other components. These components may be the same as those in the first catalyst layer 6, or they may be different. Specific examples of components include those exemplified for the first catalyst layer 6. Note that when using a Rh-doped CeZr composite oxide as the binder, the Rh contained in the binder is not included in the calculation of the Rh concentration C2.

[0074] From the viewpoint of ensuring excellent catalytic performance, the amount of the second catalyst material supported on the carrier 2 is preferably 20 g / L or more and 150 g / L or less.

[0075] Furthermore, the Rh content in catalyst layer 3, that is, the total amount of Rh supported in the first catalyst layer 6 and the second catalyst layer 7, is preferably 1.0 g / L or more and 2.0 g / L or less, from the viewpoint of ensuring excellent catalytic performance of catalyst layer 3.

[0076] Rh may be supported on the support 2 entirely contained within the first catalyst layer 6 and the second catalyst layer 7, or it may be dispersed and supported in other layers. However, from the viewpoint of improving NOx purification performance, it is preferable to support Rh on the support 2 entirely contained within the first catalyst layer 6 and the second catalyst layer 7.

[0077] [Rh concentration and Rh concentration ratio of the first and second catalyst materials] Figure 3 shows the HC light-off temperature T50 in core samples cut from the upstream section A1 (the portion from the front end to 30 mm in length of the exhaust gas purification catalyst 101) and the midstream section A2 (the portion from 30 mm to 60 mm in length of the exhaust gas purification catalyst 101) after bench aging at a catalyst temperature of 930°C for 300 hours. Specifically, the catalyst configuration consists of a monolithic support (diameter 118.4 mm × length 91 mm, capacity 1 L) on which the following Pd and Rh layers are supported in this order such that the Pd / Rh (mass ratio) = 4 / 1, with each layer being a uniform single-layer coating. Pd layer (lower layer): Pd-supported Al2O3 45g / L (Al2O3 load) Pd-supported ZrCeNd composite oxide 35g / L (amount of ZrCeNd composite oxide supported) ZrCeNd composite oxide 10g / L (ZrCeNd composite oxide load) Rh layer (upper layer): Rh-supported ZrCeNd composite oxide 90g / L (amount of ZrCeNd composite oxide supported) Rh-supported ZrLaY composite oxide 15g / L (ZrLaY composite oxide load) It has been found that the parts of the exhaust gas purification catalyst 1 most susceptible to phosphorus poisoning due to contact with exhaust gas containing phosphorus derived from engine oil are the upstream and outer (exhaust gas passage) sides. In other words, in the exhaust gas purification catalyst 1 shown in Figure 3, the amount of phosphorus poisoning is greater in the upstream section A1 than in the midstream section A2.

[0078] In the midstream section A2, when the amount of catalyst metal supported increases from 3 g / L to 5 g / L, T50 decreases by approximately 8°C. On the other hand, in the upstream section A1, when the amount of catalyst metal supported increases from 3 g / L to 5 g / L, T50 decreases by approximately 40°C. In other words, in the upstream section A1, compared to the midstream section A2, the improvement in HC purification performance is more pronounced as the amount of catalyst metal supported increases. This means that it may be possible to reduce the effects of phosphorus poisoning by increasing the concentration of precious metals in the upstream section. Furthermore, inferred from the results in Figure 3, it is thought that it may also be possible to reduce the effects of phosphorus poisoning by increasing the concentration of precious metals in the surface layer, which has high exhaust gas contactability and is susceptible to phosphorus poisoning, similar to the upstream section.

[0079] Accordingly, in the catalyst layer 3 of this disclosure, the Rh concentration C1 in the first catalyst layer 6 is higher than the Rh concentration C2 in the second catalyst layer 7, that is, the Rh concentration ratio C1 / C2 is greater than 1.0, preferably 1.3 or more, more preferably 1.5 or more, and even more preferably 2.0 or more and 50 or less. With this configuration, catalyst performance can be improved while suppressing the effects of phosphorus poisoning and the increase in the amount of precious metal used.

[0080] Furthermore, the Rh concentration C1 in the first catalyst layer 6 is preferably 0.1% by mass or more and 6.0% by mass or less, more preferably 0.3% by mass or more and 6.0% by mass or less, more preferably 0.7% by mass or more and 6.0% by mass or less, and more preferably 0.9% by mass or more and 5.5% by mass or less. By setting the Rh concentration C1 in the first catalyst layer 6 within the above range, the purification efficiency can be effectively improved.

[0081] If the first catalyst material contains multiple types of support materials, the Rh content may differ for each support material, or it may be the same for each support material. The Rh concentration C1 of the first catalyst material is expressed as a percentage of the ratio of the mass of Rh to the total mass of Rh contained in the first catalyst material and all support materials.

[0082] The Rh concentration C2 in the second catalyst material contained in the second catalyst layer 7 is preferably 1.0% by mass or less, more preferably 0.05% by mass or more and 0.65% by mass or less, and even more preferably 0.1% by mass or more and 0.6% by mass or less. By setting the Rh concentration C2 of the second catalyst material within the above range, the purification efficiency can be effectively improved.

[0083] Furthermore, if the second catalyst material contains multiple types of support materials, the Rh content may differ for each support material, or it may be the same for all support materials. The Rh concentration C2 of the second catalyst material is expressed as a percentage of the ratio of the mass of Rh to the total mass of Rh contained in the second catalyst material and all support materials.

[0084] [Third catalyst layer] The third catalyst layer 8 preferably contains Pd from the viewpoint of improving the purification performance of HC and CO contained in exhaust gas. Furthermore, it is preferable that the Pd is included in the third catalyst layer 8 in a state supported on a support material. In other words, the third catalyst layer 8 preferably contains a third catalyst material in which Pd is supported on a support material.

[0085] The support material is not particularly limited, and any support material commonly used in exhaust gas purification catalysts can be employed. Specifically, examples include activated alumina, the aforementioned OSC material, and the aforementioned Ce-free support material.

[0086] Furthermore, from the viewpoint of particularly improving the purification performance of HC and CO, it is preferable that the support material be at least one selected from the group consisting of activated alumina, Ce-containing Zr-based composite oxides, and Ce-free Zr-based composite oxides.

[0087] Activated alumina contributes to long-term catalytic performance improvement and cost reduction due to its excellent heat resistance and cost-effectiveness. The type of activated alumina used is not particularly limited; any activated alumina commonly used in exhaust gas purification catalysts, such as La-stabilized alumina, can be employed.

[0088] Furthermore, as described above, Ce-containing Zr-based composite oxides expand the A / F window through their oxygen storage and release capacity, contributing to improved catalyst performance. The Ce-containing Zr-based composite oxide is not particularly limited; for example, one with the same elemental composition as the Ce-containing Zr-based composite oxide contained in the second catalyst layer 7 can be used.

[0089] As described above, Ce-free Zr-based composite oxides release reactive oxygen species through oxygen exchange reactions, thus contributing to improved catalytic performance. The Ce-free Zr-based composite oxide is not particularly limited; for example, one with the same elemental composition as the Ce-free Zr-based composite oxide contained in the first catalyst layer 6 can be used.

[0090] The third catalyst layer 8, like the first catalyst layer 6 and the second catalyst layer 7, may contain binders or other optional components. These components may be the same as those in the first catalyst layer 6 and the second catalyst layer 7, or they may be different. Specific examples of components include those exemplified for the first catalyst layer 6.

[0091] From the viewpoint of ensuring excellent catalytic performance, the amount of the third catalyst material supported on the carrier 2 is preferably 20 g / L or more and 150 g / L or less.

[0092] Furthermore, the Pd content in catalyst layer 3 is preferably 1.0 g / L or more and 5.0 g / L or less, from the viewpoint of ensuring excellent catalytic performance of catalyst layer 3.

[0093] Pd may be supported on the support 2 entirely contained within the third catalyst layer 8, or it may be dispersed and supported in other layers. However, from the viewpoint of suppressing thermal degradation of Pd and P poisoning, it is preferable to support Pd on the support 2 entirely contained within the third catalyst layer 8.

[0094] Furthermore, in this configuration, the third catalyst layer 8 containing Pd is covered by the first catalyst layer 6 and the second catalyst layer 7 containing Rh. This prevents thermal degradation of Pd and P poisoning through the barrier effect of the first and second catalyst layers.

[0095] Furthermore, the Pd concentration D1 in the third catalyst material contained in the third catalyst layer 8 can be, for example, 0.05% by mass or more and 6.0% by mass or less, although this is not intended to be limiting. By setting the Pd concentration D1 within the above range, the purification efficiency can be effectively improved.

[0096] Furthermore, if the support material contained in the third catalyst material consists of multiple types of support material, the Pd content may be different for each support material, or it may be the same for each support material. The Pd concentration D1 of the third catalyst material is expressed as a percentage of the ratio of the mass of Pd to the total mass of Pd contained in the third catalyst material and all support materials.

[0097] [Other configurations] The catalyst materials and co-catalysts contained in each catalyst layer can, without any limitation, be powders whose size is adjusted using a ball mill or the like as needed. Specifically, for example, they can be powders with an average particle size D50 of 0.1 μm or more and 50 μm or less.

[0098] Furthermore, although not intended to be limiting, the binder can be a powder whose size is adjusted using a ball mill or the like as needed. For example, it can be a powder with an average particle size D50 of 0.01 μm or more and 0.2 μm or less. It is preferable that the average particle size D50 of the binder is smaller than the average particle size D50 of the catalyst material and co-catalyst.

[0099] In this specification, the average particle size D50 of each material is the 50th percentile value of the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer.

[0100] <Method for manufacturing an exhaust gas purification catalyst> [Preparation of catalyst material] For catalyst materials, commercially available products can be used.

[0101] The catalyst material containing the above-mentioned complex oxide can be prepared using known methods such as the coprecipitation method and the evaporation to dryness method.

[0102] As an example of a preparation method using the coprecipitation method and the evaporation to dryness method, we will explain the preparation of Rh-supported CeZrNd composite oxide, which is obtained by supporting Rh on a CeZr-based composite oxide containing Nd. First, a coprecipitation is obtained by neutralizing a nitrate solution, which is made by mixing cerium nitrate hexahydrate, zirconium oxynitrate solution, neodymium nitrate hexahydrate, and deionized water, with an 8-fold diluted solution of 28% by mass ammonia water. The solution containing this coprecipitation is centrifuged to remove the supernatant (dehydration), and then deionized water is added and stirred (washing), and this operation is repeated the required number of times. After that, the coprecipitation is dried in the air at 150°C for 24 hours, pulverized, and then calcined in the air at 500°C for 2 hours. This gives a CeZrNd composite oxide powder. Rh is supported on this CeZrNd composite oxide powder by the evaporation to dryness method using an aqueous rhodium nitrate solution. In this way, Rh-supported CeZrNd composite oxide can be obtained.

[0103] [Preparation of catalysts for exhaust gas purification] The exhaust gas purification catalyst 1 can be prepared, for example, by the following method.

[0104] First, the catalyst material for the third catalyst layer 8, along with a binder and other components as needed, is mixed with a solvent to form a slurry. This slurry is then coated over the entire length of the honeycomb support 2, and the mixture is dried and calcined (for example, at 450°C in air for 2 hours) to form the third catalyst layer 8. Next, the catalyst material for the second catalyst layer 7, along with a binder and other components as needed, is mixed with a solvent to form a slurry. This slurry is then coated over the entire length of the honeycomb support 2, and the mixture is dried and calcined (for example, at 450°C in air for 2 hours) to form the second catalyst layer 7. Furthermore, the catalyst material for the first catalyst layer 6, along with a binder and other components as needed, is mixed with a solvent to form a slurry. This slurry is then coated over the entire length of the honeycomb support 2, and the mixture is dried and calcined (for example, at 450°C in air for 2 hours) to form the first catalyst layer 6. In this way, an exhaust gas purification catalyst 1 can be obtained.

[0105] (Embodiment 2) Other embodiments relating to this disclosure will be described in detail below. In the description of these embodiments, the same reference numerals are used for parts that are the same as in Embodiment 1, and detailed descriptions will be omitted.

[0106] In Embodiment 1, as shown in Figure 2, the first catalyst layer 6 and the second catalyst layer 7 were provided along the entire length of the carrier 2. However, the first catalyst layer 6 and the second catalyst layer 7 may be provided only in a part of the carrier 2.

[0107] Specifically, for example, as shown in Figure 4, the first catalyst layer 6 may be provided from the upstream end 2A to the first position P1, and the second catalyst layer 7 may be provided from the downstream end 2B to the second position P2, which is upstream of the first position P1.

[0108] In this configuration, in the overlapping portion 31 of the first catalyst layer 6 and the second catalyst layer 7, the second catalyst layer 7 is positioned closer to the carrier 2 than the first catalyst layer 6. In other words, at least the upstream portion (part) of the second catalyst layer 7 is covered by the first catalyst layer 6. By covering the upstream side of the second catalyst layer 7 with the first catalyst layer 6 in the overlapping portion 31, phosphorus poisoning of the second catalyst material can be effectively suppressed.

[0109] Furthermore, from the viewpoint of improving catalyst performance, it is preferable that the second catalyst layer 7 is provided along the entire length of the support 2, that is, the second position P2 is at the upstream end 2A and the length L2 of the second catalyst layer 7 is the same as LT.

[0110] Furthermore, the length from the upstream end 2A to the first position P1, i.e., the length L1 of the first catalyst layer 6, is preferably 50% or more, more preferably 55% to 90%, of the total length LT of the carrier 2. By providing the first catalyst layer 6 in a range of more than half of the total length LT of the carrier 2, the effect of P poisoning in the second catalyst layer 7 can be effectively suppressed.

[0111] In addition, the configuration shown in Figure 4 of Embodiment 2 is the configuration shown in Figure 2 of Embodiment 1, where the first position P1 is the downstream end 2B and the second position P2 is the upstream end 2A.

[0112] Furthermore, the length L31 of the overlapping portion 31 is 8% to 100% of the total length LT of the carrier 2, preferably 30% to 90%, and more preferably 50% to 80%, from the viewpoint of further improving the purification performance of the three components while suppressing the effects of P poisoning.

[0113] The exhaust gas purification catalyst 1 of Embodiment 2 can be prepared, for example, by the following method.

[0114] First, the catalyst material for the third catalyst layer 8, along with a binder and other components as needed, is mixed with a solvent to form a slurry. This slurry is then coated over the entire length of the honeycomb support 2, and the third catalyst layer 8 is formed by drying and firing (for example, at 450°C for 2 hours in air). Next, the second catalyst material for the second catalyst layer 7, along with a binder and other components as needed, is mixed with a solvent to form a slurry. This slurry is then coated over a length L2 from the downstream end 2B of the support 2 to the second position P2. The second catalyst layer 7 is then formed by drying and firing (for example, at 450°C for 2 hours in air). Furthermore, the first catalyst material for the first catalyst layer 6, along with a binder and other components as needed, is mixed with a solvent to form a slurry. This slurry is then coated over a length L1 from the upstream end 2A of the support 2 to the first position P1. The first catalyst layer 6 is then formed by drying and firing (for example, at 450°C for 2 hours in air). In this way, an exhaust gas purification catalyst 1 can be obtained.

[0115] (Example of experiment) Next, I will describe specific examples of experiments that were conducted.

[0116] (Experiment 1) Catalyst samples for Experimental Examples 1-1 to 1-7 were prepared. Details of the first and second catalyst layers of each catalyst sample are shown in Table 1. Each catalyst sample also includes a third catalyst layer, which will be described later.

[0117] [Table 1]

[0118] <Material> The compositions of the materials such as the carrier and the catalyst materials used in each catalyst layer are as follows.

[0119] [Carrier] A ceramic honeycomb carrier with a cell wall thickness of 3.5 mil (8.89×10 -2 mm), 600 cells per square inch (645.16 mm 2 ), a diameter of 118.4 mm, a length of 91 mm, and a volume of 1 L was used.

[0120] [First Catalyst Layer and Second Catalyst Layer] · Rh / ZrCeNd: Rh-supported ZrCeNd composite oxide However, the Rh-supported ZrCeNd composite oxide is a catalyst powder (average particle size D50: 3 μm) in which Rh is supported on a ZrCeNd composite oxide (prepared by the above coprecipitation method) as a support material. The composition of the ZrCeNd composite oxide is ZrO2:CeO2:Nd2O3 = 80:10:10 (mass ratio). · Rh / ZrLaY: Rh-supported ZrLaY composite oxide However, the Rh-supported ZrLaY composite oxide is a catalyst powder (average particle size D50: 3 μm) in which Rh is supported on a ZrLaY composite oxide (prepared by the above coprecipitation method) as a support material. The composition of the ZrLaY composite oxide is ZrO2:LaO2:Y2O3 = 84:6:10 (mass ratio). · BaSO4; Barium sulfate (commercial product) · Binder; Zirconia binder (commercial product, total loading amount in the first catalyst layer and the second catalyst layer: 12.2 g / L) · Rh loading amount (first catalyst layer + second catalyst layer): 1.0 g / L [Third Catalyst Layer] · Pd / Al2O3; Pd-supported activated alumina (support material loading amount: 45 g / L, Pd concentration in Pd-supported activated alumina: 4 mass%) However, the Pd-supported activated alumina is a catalyst powder (average particle size D50: 25 μm) in which Pd is supported on commercially available activated alumina. The activated alumina is La-stabilized alumina. • Pd / ZrCeNd; Pd-supported ZrCeNd composite oxide (support material load 30 g / L, Pd concentration in Pd-supported ZrCeNd composite oxide is 0.4 mass%) However, the Pd-supported ZrCeNd composite oxide is a catalyst powder (average particle size D50: 3 μm) in which Pd is supported on a ZrCeNd composite oxide as a support material by evaporation to dryness. The composition of the ZrCeNd composite oxide is ZrO2:CeO2:Nd2O3 = 55:35:10 (mass ratio). • Binder: Zirconia binder (loading capacity 13.5g / L) • Pd loading amount (third catalyst layer): 2.2 g / L [Method for preparing catalysts] Each catalyst material, binder, and deionized water for the third catalyst layer were mixed to form a slurry, and this slurry was coated over the entire length of the honeycomb support. After drying, the third catalyst layer was formed by firing at 450°C for 2 hours in air.

[0121] Next, the catalyst materials, binder, and deionized water of the second catalyst layer were mixed to form a slurry, and this slurry was coated over the entire length of the support on which the third catalyst layer was formed. After drying, the second catalyst layer was formed by firing at 450°C for 2 hours in air.

[0122] Then, the catalyst materials, binder, and deionized water of the first catalyst layer were mixed to form a slurry, and this slurry was coated over the entire length of the support on which the third and second catalyst layers were formed. After drying, the first catalyst layer was formed by firing at 450°C for 2 hours in air.

[0123] <Evaluation of exhaust gas purification performance> [Evaluation Method] After bench aging was performed on each catalyst in Experimental Examples 1-1 to 1-7, the HC and NOx purification performance was investigated using simulated exhaust gas. The results are shown in Table 2.

[0124] [Table 2]

[0125] -Bench aging- A bench-aging sample measuring 43 mm in diameter, 75 mm in length, and 110 mL in volume was cut from the longitudinal and radial center of each catalyst sample. Using an engine bench system, each bench-aging sample was aged by repeatedly performing the following engine operation modes: idle operation (A / F (air-fuel ratio) = 14.7) for 1 minute → acceleration operation (engine speed 3560 rpm, A / F = 13.5) for 1 minute → steady-state operation (engine speed 3300 rpm, A / F = 14.7) for 2 minutes → fuel cut operation (A / F > 20) → return to idle operation. The catalyst temperature was 900°C and the aging time was 100 hours. During this aging process, engine oil was supplied to the engine from the intake manifold at a flow rate of 30 mL / h.

[0126] -Measurement of HC and NOx purification rates- Core samples with a diameter of 38.1 mm, a length of 30 mm, and a volume of 34 mL were cut from the longitudinal and radial centers of each bench-aged sample after bench aging. These core samples were attached to a gas flow reactor, and the temperature of the simulated exhaust gas flowing into the catalyst was gradually increased from 100°C. The concentration of HC in the gas flowing out of the catalyst was detected to determine the HC purification rate.

[0127] The simulated exhaust gas had an A / F ratio of 14.7 ± 0.9 (1.0 Hz), with the following gas composition: H2O; 10.0%, C3H6 (HC); 1600 ppmC, NO; 1000 ppm, CO; 0.56%, CO2; 13.9%, O2; 0.56%, H2; 1800 ppm, and the remainder being N2. The flow rate of the simulated exhaust gas was 34.2 L / min (space velocity SV = approximately 60,000 h). -1 The simulated exhaust gas temperature was set to 100°C to 450°C, and the heating rate was set to 25°C / min.

[0128] [Measurement results] Table 2 shows the gas temperature T50(HC) at the catalyst inlet when the HC purification rate reaches 50%, and the gas temperature T50(NOx) at the catalyst inlet when the NOx purification rate reaches 50%.

[0129] As shown in Table 2, the catalyst samples in Experimental Examples 1-5 to 1-7 showed a decrease in T50 for both HC and NOx compared to the catalyst samples in Experimental Examples 1-1 to 1-4, indicating an improvement in their purification performance.

[0130] Specifically, in the catalyst samples of Experimental Examples 1-5 to 1-7, T50(HC) decreased to below 290°C and T50(NOx) decreased to below 225°C, demonstrating an improvement in purification performance.

[0131] (Experiment 2) The catalysts used in Experimental Examples 2-1 to 2-18, shown in Table 3, were evaluated for their HC and NOx purification performance using CAE analysis. The results are shown in Figures 5 to 10.

[0132] [Table 3]

[0133] <Analysis conditions> The analysis conditions used were as follows: • CAE analysis software: Axisuite 1D model (manufactured by Exothermia SA) • Carrier: Cell wall thickness 3.5 mil (8.89 × 10 -2 mm), 1 square inch (645.16 mm) 2 A ceramic honeycomb carrier with 600 cells per unit, a diameter of 118.4 mm, a length of 91 mm, and a capacity of 1 L. • Model: Models one side of a single cell of the carrier. • First and second catalyst layers: The total Rh load on the support was set to 1.0 g / L, and the amount of catalyst material (Rh + support material) was set to 147 g / L. The amount of catalyst material (Rh + support material) in the first and second catalyst layers was variable as shown in Table 3. The amount of noble metal in both layers was changed proportionally by changing the number of active sites. The composition of the support material and other materials was assumed to be the same as in Experiment 1. • Third catalyst layer: The total Pd load on the entire support was set to 2.2 g / L, and the load on the catalyst material (Pd + support material) was set to 113 g / L. The composition of the support material and other materials was assumed to be the same as in Experiment 1. • Gas composition: During time 0-194 seconds, HC=C3H6; 1600 ppm C, NO; 1000 ppm, CO; 0.56%, O2; 0.56%, H2; 1800 ppm, CO2; 13.9%, H2O; 10.0%, remaining N2. • Spatial velocity: As shown in Figure 11, it is variable with respect to time. • Catalyst inlet gas temperature: As shown in Figure 12, the temperature change for any driving mode is applied and made variable with respect to time.

[0134] <Result> The data labeled E2-9 in Figures 5-10 represent the results for the uniform coating (Rh concentration ratio C1 / C2=1) in Experimental Example 2-9 of Table 3.

[0135] As shown in Figures 5 and 6, it can be seen that as the Rh concentration C1 increases, the amount of HC and NO emitted decreases, and the purification performance improves. In particular, setting C1 to preferably 0.3% by mass or higher is advantageous from the viewpoint of HC and NO purification performance. However, due to manufacturing requirements for the catalyst, it is preferable that the upper limit of C1 be 6.0% by mass or lower.

[0136] As shown in Figures 7 and 8, it can be seen that the lower the Rh concentration C2, the lower the amount of HC and NO emitted, and the improved purification performance. In particular, setting C2 to preferably 1.0% by mass or less, and more preferably 0.6% by mass or less, is advantageous from the viewpoint of HC and NO purification performance. Furthermore, from the viewpoint of purification performance, it is preferable that the lower limit of C2 be 0.1% by mass or more.

[0137] As shown in Figures 9 and 10, it can be seen that as the Rh concentration ratio C1 / C2 increases, the amount of HC and NO emitted decreases, and the purification performance improves. In particular, setting C1 / C2 to 1.0 or higher, preferably 1.3 or higher, is advantageous from the viewpoint of HC and NO purification performance.

[0138] (Experiment 3) The catalysts in Experimental Examples 3-1 to 3-6 were evaluated for their purification performance against HC, CO, and NOx (also referred to as "three components" in this specification) by CAE analysis.

[0139] Table 4 shows the details and evaluation results of the first, second, and third catalyst layers of each catalyst.

[0140] [Table 4]

[0141] <Material> [carrier] Cell wall thickness 3.5 mil (8.89 × 10 -2 mm), 1 square inch (645.16 mm) 2 A ceramic honeycomb carrier with 600 cells per unit, a diameter of 118.4 mm, a length of 91 mm, and a capacity of 1 L was used.

[0142] [First catalyst layer] As the catalyst material included in the first catalyst layer, Rh / ZrLaY (Rh-supported ZrLaY composite oxide) used in Experiment 1 was employed. However, the Rh concentration was 3.67 mass%. Furthermore, the first catalyst layer consisted of BaSO4 and a zirconia binder, with a Ba support amount of 10 g / L and a binder support amount of 12.2 g / L.

[0143] [Second catalyst layer] As catalyst materials for the second catalyst layer, Rh / ZrCeNd (Rh-supported ZrCeNd composite oxide) and Rh / ZrLaY (Rh-supported ZrLaY composite oxide), which were used in Experiment 1, were employed. The Rh concentration and supported amount of Rh / ZrCeNd were 0.276 mass% and 90.249 g / L, respectively. The Rh concentration and supported amount of Rh / ZrLaY were 0.107 mass% and 15.016 g / L, respectively. The second catalyst layer also contained a zirconia binder, with a binder load of 12.2 g / L.

[0144] [Third catalyst layer] As catalyst materials included in the third catalyst layer, Pd / Al2O3 (Pd-supported activated alumina) and Pd / ZrCeNd (Pd-supported ZrCeNd composite oxide), which were used in Experiment 1, were employed. The Pd concentration and supported amount of Pd / Al2O3 were 4.4% by mass and 47.056 g / L, respectively, while the Pd concentration and supported amount of Pd / ZrCeNd were 0.37% by mass and 35.131 g / L, respectively.

[0145] Furthermore, the third catalyst layer consisted of a co-catalyst containing ZrCeNd (a ZrCeNd composite oxide (ZrO2:CeO2:Nd2O3 = 55:35:10 (mass ratio)) powder (average particle size D50:3μm)) and a zirconia binder, with a ZrCeNd load of 20 g / L and a binder load of 14 g / L.

[0146] <Analysis conditions> The analysis conditions used were as follows: • CAE analysis software: Axisuite 1D model (manufactured by Exothermia SA) • Model: Models one side of a single cell of the carrier. • First and second catalyst layers: A total Rh load of 0.475 g was modeled. In all experimental examples of Experiment 3, the Rh load and the amount of catalyst material loaded in the first and second catalyst layers were kept the same, and the lengths L1 and L2 of the first catalyst layer 6 and the second catalyst layer 7 were varied (see Figure 4). • Third catalyst layer: Modeled a total Pd load of 2.2g. • Gas composition: Time 0-720 seconds, H2O; 10%, C3H6(HC); 1600 ppmC, NO(NOx); 1000 ppm, CO; 0.56%, CO2; 13.9%, O2; 0.56%, H2; 1800 ppm, remainder N2. The gas space velocity SV was approximately 60,000 h. -1 The gas temperature was set to 100°C to 450°C, and the heating rate was 30°C / min. The emissions of HC, CO, and NOx were calculated and then added together to obtain the total emissions of the three components.

[0147] <Result> As shown in Table 4, in Experimental Example 3-6, which uses the configuration of Embodiment 1, the total discharge amount of the three components was 81.3g. In Experimental Examples 3-1 to 3-5, which use the configuration of Embodiment 2, the total discharge amount of the three components was similar, indicating good purification performance. In particular, in Experimental Examples 3-4 and 3-5, similar to Experimental Example 3-6, the total discharge amount of the three components was 81.3g or less, indicating excellent purification performance. [Industrial applicability]

[0148] This disclosure is extremely useful because it can provide an exhaust gas purification catalyst that effectively suppresses phosphorus poisoning while employing a zone coating structure, thereby achieving both improved purification performance and cost reduction. [Explanation of symbols]

[0149] 1. Catalyst for exhaust gas purification 2 carriers 2A Upstream end (of the carrier) 2B Downstream end (of the carrier) 3 Catalyst layer 31 Overlapping part 6 First catalyst layer 7 Second catalyst layer 8 Third catalyst layer Total length of LT carrier L1 Length of the first catalyst layer L2 Length of the second catalyst layer L31 Length of overlapping portion P1 1st position P2 2nd position

Claims

1. An exhaust gas purification catalyst, which is installed in the exhaust passage of an engine and purifies the exhaust gas containing P from the engine, The device comprises a carrier and a catalyst layer formed on the carrier for purifying the exhaust gas, The catalyst layer is A first catalyst layer disposed on the outermost surface of the catalyst layer, It includes a second catalyst layer, at least a portion of which is disposed on the support side than the first catalyst layer, The first catalyst layer contains a first catalyst material in which Rh is supported on a support material that does not contain Ce, and Ba, and does not contain Ce. The second catalyst layer contains a second catalyst material in which Rh is supported on a support material containing a Ce-based oxygen storage and release material. When the Rh concentration in the first catalyst material is C1 and the Rh concentration in the second catalyst material is C2, the ratio of C1 to C2, C1 / C2, is greater than 1.

0. A catalyst for purifying exhaust gases characterized by the following features.

2. In claim 1, The ratio C1 / C2 is 1.3 or greater. A catalyst for purifying exhaust gases characterized by the following features.

3. In claim 1 or claim 2, The aforementioned C1 is 0.1% by mass or more and 6.0% by mass or less. A catalyst for purifying exhaust gases characterized by the following features.

4. In claim 1 or claim 2, The amount of C2 is 1.0% by mass or less. A catalyst for purifying exhaust gases characterized by the following features.

5. In claim 1 or claim 2, The Ce-based oxygen storage and release material is a Ce-containing Zr-based composite oxide. A catalyst for purifying exhaust gases characterized by the following features.

6. In claim 1 or claim 2, The support material that does not contain Ce is a Ce-free Zr-based composite oxide. A catalyst for purifying exhaust gases characterized by the following features.

7. In claim 1 or claim 2, The Rh content in the catalyst layer is 1.0 g / L or more and 2.0 g / L or less. A catalyst for purifying exhaust gases characterized by the following features.

8. In claim 1 or claim 2, At least one of the loading amount of the first catalyst material and the loading amount of the second catalyst material is 20 g / L or more and 150 g / L or less. A catalyst for purifying exhaust gases characterized by the following features.

9. In claim 1 or claim 2, The amount of Ba supported in the first catalyst layer is 5 g / L or more and 20 g / L or less. A catalyst for purifying exhaust gases characterized by the following features.

10. In claim 1 or claim 2, The catalyst layer further comprises a third catalyst layer containing Pd, which is provided on the support side of the first and second catalyst layers. A catalyst for purifying exhaust gases characterized by the following features.

11. In claim 1 or claim 2, The carrier comprises an upstream end and a downstream end, The first catalyst layer is provided from the upstream end to the first position, The second catalyst layer is provided from the downstream end to a second position upstream of the first position, and in the portion overlapping with the first catalyst layer, it is positioned closer to the carrier than the first catalyst layer. A catalyst for purifying exhaust gases characterized by the following features.

12. In claim 11, The second position is the upstream end. A catalyst for purifying exhaust gases characterized by the following features.

13. In claim 11, The length from the upstream end to the first position is 50% or more of the total length of the carrier. A catalyst for purifying exhaust gases characterized by the following features.

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