Exhaust gas purification catalyst

Abstract

This provides an exhaust gas purification catalyst that effectively suppresses phosphorus poisoning, achieving both 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 material is greater than 1.0. The third catalyst layer 8 has a front portion 81 including an upstream catalyst material in which Pd is supported on an upstream support material, and a rear portion 82 including a downstream catalyst material in which Pd is supported on a downstream support material. The ratio D1 / D2 of the Pd concentration D1 in the upstream catalyst material to the Pd concentration D2 in the downstream catalyst material 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 enhanced cold-start purification capabilities, and lower costs.

[0004] One of the causes of a decrease in the purification performance of catalysts is poisoning by catalyst toxins such as phosphorus contained in engine oil and the aforementioned harmful components in exhaust gases. As one solution, the effects of poisoning are reduced and the decrease in the purification performance of catalysts is suppressed by devising the arrangement of catalyst materials within the catalyst monolith (see, for example, Patent Documents 1 and 2).

[0005] Specifically, Patent Document 1 discloses an exhaust gas purification catalyst having a carrier, an upstream first catalyst layer, a downstream second catalyst layer, and a third catalyst layer. In this catalyst, the upstream portion of the third catalyst layer is located on the first catalyst layer, the downstream portion of the third catalyst layer is located on the second catalyst layer, and the intermediate portion between the upstream and downstream portions of the third catalyst layer is located between the first and second catalyst layers. According to this configuration, a considerable amount of phosphorus compounds are deposited in the upstream portion and the intermediate portion (space) of the third catalyst layer, so the amount of phosphorus compounds deposited in the downstream portion of the third catalyst layer is reduced, which has a lower impact on the activity of the catalyst components, and the catalyst as a whole has a high purification capacity.

[0006] Furthermore, Patent Document 2 discloses an exhaust gas purification catalyst having a substrate and a catalyst coating layer coated on the substrate, wherein the catalyst coating layer has 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, and the second catalyst coating layer contains three types of OSC materials with different specific surface areas. In a preferred embodiment, an example is shown in which the second catalyst coating layer has an upstream coating layer formed from the upstream end and a downstream coating layer formed from the downstream end, and the first catalyst coating layer is arranged on top of the upstream coating layer. It is stated that with such a configuration, catalytic performance and OSC performance can be achieved in an atmosphere rich in air-fuel ratio (A / F) which is prone to HC poisoning. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2018 / 016606 [Patent Document 2] Japanese Patent Publication No. 2024-000368 [Overview of the project] [Problems that the invention aims to solve]

[0008] Incidentally, in order to achieve both improved purification performance and cost reduction, it is effective to focus on increasing the proportion of precious metals in areas with high contact with exhaust gases, such as the upstream and surface layers. This may allow for improved purification efficiency while suppressing the increase in the amount of expensive precious metals used.

[0009] On the other hand, exhaust gas purification catalysts often contain oxygen storage and release materials (OSC materials) in addition to precious metal catalysts. OSC materials absorb oxygen in a lean atmosphere where the oxygen concentration of the exhaust gas is high, and release active oxygen in a stoichiometric or rich atmosphere where the oxygen concentration of the exhaust gas is low. In particular, in three-way catalysts, the action of this OSC material creates a stoichiometric atmosphere that makes it easier to exhibit exhaust gas purification performance. In other words, even if the A / F (air-fuel ratio) of the exhaust gas fluctuates somewhat from the theoretical A / F, HC (hydrocarbons), CO (carbon monoxide), and NOx (nitrogen oxides) are efficiently purified (the A / F window is expanded). As an OSC material, for example, an oxide containing Ce is used, which absorbs oxygen from the exhaust gas and releases it as active oxygen through a reversible reaction involving a change in valence. OSC materials containing Ce absorb oxygen from the exhaust gas and release it as active oxygen through a reversible reaction involving a change in the valence of Ce.

[0010] However, oxides containing Ce tend to have reduced oxygen storage and release capacity due to the formation of Ce-P compounds upon phosphorus poisoning. P poisoning is known to occur more frequently in areas with high contact with exhaust gases, such as upstream and surface areas.

[0011] In other words, even if the proportion of precious metals is increased in areas with high contact with exhaust gas, such as the upstream or surface side, the oxygen absorption and release capacity of the OSC material may decrease due to phosphorus poisoning, potentially hindering improvements in purification performance.

[0012] Therefore, the objective of this disclosure is to provide an exhaust gas purification catalyst that can effectively suppress phosphorus poisoning and achieve both improved purification performance and reduced costs. [Means for solving the problem]

[0013] 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 having an upstream end and a downstream end, and a catalyst layer formed on the carrier for purifying the exhaust gas, The catalyst layer is A first catalyst layer is provided from the upstream end to the first position and is positioned on the outermost surface of the catalyst layer, A 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. The catalyst includes a third catalyst layer positioned closer to the carrier than the first catalyst layer and the second 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. The third catalyst layer is The front portion includes an upstream catalyst material provided from the upstream end to the third position, with Pd supported on the upstream support material, The rear portion includes a downstream catalyst material provided from the third position to the downstream end, on which Pd is supported on the downstream support material, When the Pd concentration in the upstream catalyst material is D1 and the Pd concentration in the downstream catalyst material is D2, the ratio of D1 to D2, D1 / D2, is greater than 1.0. It is characterized by the following:

[0014] As mentioned above, exhaust gas purification catalysts often contain Ce-containing OSC materials (Ce-based OSC materials) as oxygen storage and release materials (OSC materials), but Ce-based OSC materials tend to have reduced oxygen storage and release capacity due to phosphorus poisoning.

[0015] In this configuration, a first catalyst layer containing Ba but not Ce is disposed on the outermost surface on the upstream side of the catalyst layer where the gas contact property is the highest and the catalyst is most likely to be P-poisoned. Thereby, the contact between P of the oil-derived substance and Ce is suppressed, P is trapped in the form of a Ba-O-P compound, and the diffusion of P into the second catalyst layer is suppressed. In particular, by covering the second catalyst layer with the first catalyst layer at the overlapping portion, the P-poisoning of the second catalyst material can be effectively suppressed.

[0016] Furthermore, the inventors of the present application have found that by increasing the noble metal ratio on the upstream side and the surface layer side, it may be possible to mitigate the influence of P-poisoning. 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). In addition, the third catalyst layer is divided into a front part and a rear part, and the Pd concentration D1 in the front part is made higher than the Pd concentration D2 in the rear part (D1 / D2 exceeds 1.0). With these configurations, it is possible to improve the catalyst performance while suppressing the influence of P-poisoning and the increase in the amount of noble metal used.

[0017] Also, in this configuration, the third catalyst layer containing Pd is covered by the first catalyst layer and the second catalyst layer containing Rh. Thereby, the thermal deterioration and P-poisoning of Pd can be avoided by the barrier effect of the first catalyst layer and the second catalyst layer.

[0018] Preferably, the length from the upstream end to the first position is 55% or more and 100% or less of the total length of the carrier.

[0019] According to this configuration, while suppressing the influence of P-poisoning, it is possible to further improve the purification performance of HC, CO, and NOx (in this specification, these are also collectively referred to as "three components").

[0020] Preferably, the length from the downstream end to the second position is 55% or more and 100% or less of the total length of the carrier.

[0021] This configuration allows for the suppression of the effects of phosphorus poisoning while further improving the purification performance of the three components.

[0022] Preferably, the length of the overlapping portion is 8% to 90% of the total length of the carrier.

[0023] This configuration allows for the suppression of the effects of phosphorus poisoning while further improving the purification performance of the three components.

[0024] Preferably, the ratio D1 / D2 is 2.0 or greater.

[0025] This configuration is advantageous in obtaining superior purification performance for the three components.

[0026] Preferably, the ratio C1 / C2 is 1.2 or more and 5.0 or less.

[0027] This configuration effectively improves catalyst performance while suppressing the effects of phosphorus poisoning and the increase in precious metal usage.

[0028] Preferably, the amount of Ba supported in the first catalyst layer is 5 g / support or more and 20 g / support or less.

[0029] By incorporating Ba in the above-mentioned amount into the first catalyst layer, the diffusion of P into the second catalyst layer can be effectively suppressed.

[0030] Preferably, at least one of the upstream support material and the downstream support material is at least one selected from the group consisting of activated alumina, Ce-containing Zr-based composite oxide, and Ce-free Zr-based composite oxide.

[0031] Activated alumina contributes to long-term catalytic performance improvement and cost reduction due to its excellent heat resistance and cost-effectiveness. Furthermore, its superior heat resistance allows for improved heat resistance of the secondary catalyst material. Ce-containing Zr-based composite oxides contribute to improved catalytic performance by expanding the A / F window through oxygen storage and release capabilities. Ce-free Zr-based composite oxides contribute to improved catalytic performance by releasing reactive oxygen species through oxygen exchange reactions. By supporting Pd on these support materials, the purification performance of HC and CO, in particular, is improved.

[0032] Preferably, the Ce-based oxygen storage and release material is a Ce-containing Zr-based composite oxide.

[0033] Ce-containing Zr-based composite oxides have high oxygen storage and release capabilities. Including Ce-containing Zr-based composite oxides in the second catalyst layer expands the A / F window, improving catalytic performance.

[0034] Preferably, the support material that does not contain Ce is a Ce-free Zr-based composite oxide.

[0035] 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. [Effects of the Invention]

[0036] 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. 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 to the second catalyst layer. In particular, by having the first catalyst layer cover the second catalyst layer in the overlapping portion, P poisoning of the second catalyst material can be effectively suppressed. Furthermore, in this configuration, the Rh concentration C1 of the first catalyst material contained in the first catalyst layer, which is located in a highly exhaust gas contact area, is set to be higher than the Rh concentration C2 of the second catalyst material contained in the second catalyst layer. In addition, the third catalyst layer is divided into a front section and a rear section, and the Pd concentration D1 in the front section is set to be higher than the Pd concentration D2 in the rear section. With these configurations, catalyst performance can be improved while suppressing the effects of P poisoning and the increase in the amount of precious metal used. Furthermore, since the third catalyst layer containing Pd is covered by the first and second catalyst layers containing Rh, thermal degradation of Pd and P poisoning can also be suppressed. [Brief explanation of the drawing]

[0037] [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. [Figure 3] A graph showing the relationship between the amount of catalyst metal supported and the HC light-off temperature T50. [Figure 4] A diagram showing the composition of the catalyst layer of the catalyst sample used in Experiment 1. [Figure 5] This figure shows the catalyst model and the configuration of the catalyst layer in the catalyst sample used in Experiment 2. [Figure 6]A graph showing CO emissions calculated by CAE analysis using the catalyst models from experimental examples 2-1 to 2-16. [Figure 7] A graph showing NOx emissions calculated by CAE analysis using the catalyst models from experimental examples 2-1 to 2-16. [Figure 8] Graph showing HC emissions calculated by CAE analysis using the catalyst models from experimental examples 2-1 to 2-16. [Figure 9] A graph showing the total emissions of the three components calculated by CAE analysis using the catalyst models from experimental examples 2-1 to 2-16. [Figure 10] This graph shows the relationship between the total emissions of the three components and the Pd concentration ratio D1 / D2, calculated by CAE analysis using the catalyst models in Experimental Examples 2-11, 2-17, and 2-11b to 2-11f. [Modes for carrying out the invention]

[0038] 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 its uses in any way.

[0039] <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.

[0040] 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.

[0041] 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.

[0042] 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 a third catalyst layer 8.

[0043] The first catalyst layer 6 is provided from the upstream end 2A to the first position P1 and is located on the outermost surface of the catalyst layer 3. The first catalyst layer 6 contains Rh as a catalytic metal.

[0044] The second catalyst layer 7 is provided from the downstream end 2B to the second position P2, which is upstream of the first position P1, and in the overlapping portion 31 with the first catalyst layer 6, it is positioned closer to the carrier 2 than the first catalyst layer 6. In other words, at least the upstream portion of the second catalyst layer 7 is covered by the first catalyst layer 6. The second catalyst layer 7 contains Rh as a catalytic metal.

[0045] 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 has a front portion 81 provided from the upstream end 2A to the third position P3, and a rear portion 82 provided from the third position P3 to the downstream end 2B. The third catalyst layer 8 contains Pd as a catalytic metal.

[0046] 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, a second catalyst layer 7, and a third catalyst layer 8, and 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 contain other noble metals such as Pt or other transition metals in addition to Rh and Pd as catalyst metals.

[0047] In this specification, the amount of material carried is generally expressed in "g / carrier". "g / carrier" means the amount of material carried per carrier with a capacity of 1L. That is, if a material with a carrying amount of y "g / carrier" is carried on a carrier with a capacity of x "L", then x × y "g" will be carried. Specifically, for example, if a material with a carrying amount of 20 "g / carrier" is carried on a carrier with a capacity of 2 "L", then 40 "g" of the material should be carried on that carrier.

[0048] Furthermore, in this specification, when a material is supported along the entire length of the carrier, the amount of material supported may be expressed in "g / L". In this case, "g / L" means the amount of material supported per liter of carrier.

[0049] [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.

[0050] 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.

[0051] 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.

[0052] Furthermore, a Ce-free Zr-based composite oxide is preferred as the support material.

[0053] Ce-free Zr-based composite oxides have the advantage of being less susceptible to phosphorus poisoning because they do not contain Ce.

[0054] 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.

[0055] 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.

[0056] As Ce-free Zr-based composite oxides, those containing La, Y, etc., in addition to Zr can be used.

[0057] From the viewpoint of ensuring sufficient catalytic performance, the amount of the first catalyst material supported on the support 2 is preferably 20 g / support or more and 150 g / support or less.

[0058] 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.

[0059] 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 / support or more and 20 g / support or less, and more preferably 10 g / support or more and 15 g / support or less.

[0060] 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).

[0061] 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 catalyst 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 / support or less.

[0062] [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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] The second catalyst layer 7 may also contain Ba, similar to the first catalyst layer 6. This allows P to be captured by Ba even if it reaches the second catalyst layer 7, thereby suppressing the effects of P poisoning. The Ba source in the second catalyst layer 7 can be the same substance as in the first catalyst layer 6, and may be the same substance as the Ba source in the first catalyst layer 6 or a different substance. The amount of Ba supported in the second catalyst layer 7 is not particularly limited, but can be, for example, 20 g / support or less, preferably 1 g / support or more and 10 g / support or less.

[0071] Furthermore, the second catalyst layer 7, like the first catalyst layer 6, may contain binders or other optional components. These may have the same components as the first catalyst layer 6, or they may have different components. Specific examples of components include those exemplified for the first catalyst layer 6. Note that when using a 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 C2.

[0072] From the viewpoint of ensuring excellent catalytic performance, the amount of the second catalyst material supported on the support 2 is preferably 20 g / support or more and 150 g / support or less.

[0073] 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 / support or more and 2.0 g / support or less, from the viewpoint of ensuring the excellent catalytic performance of catalyst layer 3.

[0074] 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.

[0075] [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.

[0076] 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.

[0077] 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 between 1.2 and 5.0. This configuration makes it possible to improve catalyst performance while suppressing the effects of phosphorus poisoning and the increase in the amount of precious metal used.

[0078] 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 0.2% by mass or more and 4.0% by mass or less, and even more preferably 0.3% by mass or more and 1.0% 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.

[0079] 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.

[0080] 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 0.30% by mass or less, and even more preferably 0.10% by mass or more and 0.28% 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.

[0081] 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.

[0082] [Length of the first catalyst layer and the second catalyst layer] Referring to Figure 2, the lengths of the first catalyst layer 6 and the second catalyst layer 7 will be explained.

[0083] The first catalyst layer 6 may be provided along the entire length of the carrier 2. In this case, the first position P1 is the downstream end 2B.

[0084] Furthermore, the second catalyst layer 7 may also be provided along the entire length of the carrier 2. In this case, the second position P2 becomes the upstream end 2A.

[0085] The length of the first catalyst layer 6, that is, the length L1 from the upstream end 2A to the first position P1, is preferably 55% to 100%, preferably 55% to 90%, and more preferably 55% to 80%, of the total length LT of the carrier 2, from the viewpoint of further improving the purification performance of the three components while suppressing the effect of P poisoning.

[0086] Furthermore, the length of the second catalyst layer 7, i.e., the length L2 from the downstream end 2B to the second position P2, is 55% to 100% of the total length LT of the carrier 2, preferably 60% to 100%, more preferably 70% to 100%, and even more preferably 80% to 100%, from the viewpoint of further improving the purification performance of the three components while suppressing the effect of P poisoning.

[0087] Furthermore, the length L31 of the overlapping portion 31 is 8% to 90%, preferably 20% to 80%, of the total length LT of the carrier 2, from the viewpoint of further improving the purification performance of the three components while suppressing the effects of P poisoning.

[0088] From the viewpoint of improving the purification performance of the three components, a particularly preferred combination is one in which the length L1 of the first catalyst layer 6 is 55% to 77% of the total length LT, and the length L2 of the second catalyst layer 7 is 77% to 100% of the total length LT.

[0089] [Third catalyst layer] The front section 81 includes an upstream catalyst material in which Pd is supported on an upstream support material.

[0090] Furthermore, the rear section 82 includes a downstream catalyst material in which Pd is supported on a downstream support material.

[0091] While not intended to be limiting, it is preferable that at least one of the upstream support material and the downstream 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, particularly from the viewpoint of improving the purification performance of HC and CO.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] The upstream and downstream support materials may be of the same type or different types. Preferably, both the upstream and downstream support materials are a mixture of activated alumina and a Ce-containing Zr-based composite oxide. This improves the catalytic performance and durability of the third catalyst layer 8.

[0096] 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.

[0097] From the viewpoint of ensuring excellent catalytic performance, the amount of upstream catalyst material and downstream catalyst material supported on the support 2 is preferably 20 g / support or more and 150 g / support or less, respectively.

[0098] Furthermore, the Pd content in catalyst layer 3, i.e., the total amount of Pd supported in the third catalyst layer 8, is preferably 1.0 g / support or more and 5.0 g / support or less, from the viewpoint of ensuring the excellent catalytic performance of catalyst layer 3.

[0099] 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.

[0100] 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.

[0101] [Pd concentration and Pd concentration ratio of upstream and downstream catalyst materials] As described above, the results in Figure 3 suggest that increasing the concentration of precious metals upstream may reduce the effects of phosphorus poisoning.

[0102] In the catalyst layer 3 of this disclosure, the third catalyst layer 8 is divided into a front section 81 and a rear section 82, and the Pd concentration D1 of the upstream catalyst material in the front section 81 is made higher than the Pd concentration D2 of the downstream catalyst material in the rear section 82. Specifically, the Pd concentration ratio D1 / D2 is made greater than 1.0, preferably 2.0 or more, more preferably 8.0 to 30, and particularly preferably 9.0 to 27. This configuration makes it possible to improve catalyst performance while suppressing the effects of phosphorus poisoning and the increase in the amount of precious metal used.

[0103] Furthermore, the Pd concentration D1 of the front section 81 is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1.0% by mass or more and 7.0% by mass or less, and even more preferably 3.5% by mass or more and 6.5% by mass or less. By setting the Pd concentration D1 of the front section 81 within the above range, the purification efficiency can be effectively improved.

[0104] If the upstream support material consists of multiple types of support material, the Pd content may differ for each support material, or it may be the same for all of them. The Pd concentration D1 of the upstream catalyst material is expressed as a percentage of the ratio of the mass of Pd to the total mass of Pd contained in the upstream catalyst material and all support materials.

[0105] Furthermore, the Pd concentration D2 in the rear section 82 is preferably 0.05% by mass or more and 3.0% by mass or less, more preferably 0.1% by mass or more and 2.5% by mass or less, and even more preferably 0.15% by mass or more and 0.6% by mass or less. By setting the Pd concentration D2 in the rear section 82 within the above range, the purification efficiency can be effectively improved.

[0106] Furthermore, if the downstream support material consists of multiple types of support material, the Pd content may differ for each support material, or it may be the same for all of them. The Pd concentration D2 of the downstream catalyst material is expressed as a percentage of the ratio of the mass of Pd to the total mass of Pd contained in the downstream catalyst material and all support materials.

[0107] [Length of the front and rear sections] As shown in Figure 2, the length L81 of the front section 81 and the length L82 of the rear section 82 are not particularly limited as long as the relationship L81 + L82 = LT is satisfied.

[0108] Specifically, the length L81 of the front portion 81 is, for example, 20% to 80% of LT, preferably 30% to 70%, more preferably 40% to 60%, and particularly preferably 50%.

[0109] Furthermore, when the length L81 of the front section 81 is 50% of LT, the length L81 becomes equal to the length L82 of the rear section 82.

[0110] According to the above configuration, an appropriate length is ensured for the front section 81 and the rear section 82, which is advantageous in improving catalyst performance while suppressing the effects of phosphorus poisoning and the increase in the amount of precious metal used.

[0111] [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.

[0112] 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.

[0113] 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.

[0114] <Method for manufacturing an exhaust gas purification catalyst> [Preparation of catalyst material] For catalyst materials, commercially available products can be used.

[0115] Furthermore, catalyst materials containing the aforementioned composite oxides can be prepared using known methods such as the coprecipitation method and the evaporation to dryness method.

[0116] 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.

[0117] Catalyst materials containing other complex oxides can be prepared by a similar method.

[0118] [Preparation of catalysts for exhaust gas purification] The exhaust gas purification catalyst 1 can be prepared, for example, by the following method.

[0119] First, the catalyst material, which is the material for the front portion 81 and rear portion 82 of the third catalyst layer 8, is mixed with a solvent and a binder as needed to form a slurry. The slurry for the front portion 81 is injected from the upstream end 2A of the carrier 2 and coats the portion with a length L81 up to the third position P3. The slurry for the rear portion 82 is injected from the downstream end 2B of the carrier 2 and coats the portion with a length L82 up to the third position P3. Then, the third catalyst layer 8 is formed by drying and calcination (for example, at 450°C in air for 2 hours). Next, the second catalyst material, which is the material for the second catalyst layer 7, is mixed with a solvent and a binder as needed to form a slurry and coats the portion with a length L2 from the downstream end 2B of the carrier 2 to the second position P2. Then, the second catalyst layer 7 is formed by drying and calcination (for example, at 450°C in air for 2 hours). Furthermore, the first catalyst material, which is the material for the first catalyst layer 6, and optionally a binder, other components, etc., are mixed with a solvent to form a slurry, which 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 calcination (for example, 450°C in air for 2 hours). In this way, an exhaust gas purification catalyst 1 can be obtained.

[0120] (Example of experiment) Next, I will describe specific examples of experiments that were conducted. (Experiment 1) Catalyst samples for Experimental Examples 1-1 to 1-4 were prepared. Details of the first, second, and third catalyst layers of each catalyst sample are shown in Figure 4 and Tables 1 and 2.

[0121] [Table 1]

[0122] [Table 2]

[0123] <Structure> [Experimental Example 1-1] As shown in Fig. 4, the catalyst layer of Experimental Example 1-1 has a two-layer structure composed of a first catalyst layer 6 and a third catalyst layer 8 provided over the entire length of the carrier 2.

[0124] [Experimental Example 1-2] The catalyst layer of Experimental Example 1-2 has a two-layer structure of a first catalyst layer 6 and a third catalyst layer 8. The first catalyst layer 6 has a front portion 61 provided at the front 50% length of the carrier 2 and a rear portion 62 provided at the rear 50% length. Also, the third catalyst layer 8 has a front portion 81 provided at the front 50% length of the carrier 2 and a rear portion 82 provided at the rear 50% length. In Tables 1 and 2, the front portions 61, 81 and the rear portions 62, 82 are indicated as "front" and "rear", respectively.

[0125] [Experimental Example 1-3] The catalyst layer of Experimental Example 1-3 has a three-layer structure composed of a first catalyst layer 6, a second catalyst layer 7, and a third catalyst layer 8 provided over the entire length of the carrier 2.

[0126] [Experimental Example 1-4][[ID=!17]] The catalyst layer of Experimental Example 1-4 has a three-layer structure of a first catalyst layer 6, a second catalyst layer 7, and a third catalyst layer 8. The third catalyst layer 8 has a front portion 81 provided at the front 50% length of the carrier 2 and a rear portion 82 provided at the rear 50% length. In Table 2, the front portion 81 and the rear portion 82 are indicated as "front" and "rear", respectively. The catalyst layer of this example corresponds to the case where L1 = L2 = LT in the catalyst layer 3 of the present disclosure shown in Fig. 2.

[0127] [Material] The composition of materials such as the carrier and the catalyst materials used for each catalyst layer is as follows.

[0128] [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.

[0129] [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 coprecipitation method described above) by evaporation to dryness. 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 coprecipitation method described above) by evaporation to dryness. The composition of the ZrLaY composite oxide is ZrO2:LaO2:Y2O3 = 84:6:10 (mass ratio). • BaSO4; Barium sulfate (commercially available) • Binder: Zirconia binder (commercially available, total load amount for the first and second catalyst layers: 12.2g / carrier) • Rh load (first catalyst layer + second catalyst layer): 1.0 g / carrier [Third catalyst layer] Pd / Al2O3; Pd-supported activated alumina 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 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). ZrCeNd; ZrCeNd complex oxide However, the ZrCeNd composite oxide is a powder of ZrCeNd composite oxide (average particle size D50: 3 μm) that does not contain noble metals. The composition of the ZrCeNd composite oxide is ZrO2:CeO2:Nd2O3 = 55:35:10 (mass ratio). • Binder: Zirconia binder (13.5g / carrier) • Pd load (third catalyst layer): 2.2g / carrier [Method for preparing catalyst samples] Experimental Example 1-1 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.

[0130] Next, 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 catalyst layer was formed. After drying, the first catalyst layer was formed by firing at 450°C for 2 hours in air. Experimental Example 1-2 The catalyst materials for the front and rear sections of the third catalyst layer, along with the binder and deionized water, were mixed to form a slurry. The slurry for the front section was injected from the upstream end of the support and coated the front 50% of the support's length. Similarly, the slurry for the rear section was injected from the downstream end of the support and coated the rear 50% of the support's length. After drying, the third catalyst layer was formed by firing in air at 450°C for 2 hours.

[0131] Next, the catalyst materials for the front and rear portions of the first catalyst layer, along with the binder and deionized water, were mixed to form a slurry. The slurry for the front portion was injected from the upstream end of the support and coated the front 50% of the support's length. Similarly, the slurry for the rear portion was injected from the downstream end of the support and coated the rear 50% of the support's length. After drying, the first catalyst layer was formed by firing in air at 450°C for 2 hours. Experimental Examples 1 and 3 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.

[0132] 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.

[0133] 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. Experimental Example 1-4 The catalyst materials for the front and rear sections of the third catalyst layer, along with the binder and deionized water, were mixed to form a slurry. The slurry for the front section was injected from the upstream end of the support and coated the front 50% of the support's length. Similarly, the slurry for the rear section was injected from the downstream end of the support and coated the rear 50% of the support's length. After drying, the third catalyst layer was formed by firing in air at 450°C for 2 hours.

[0134] 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.

[0135] 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.

[0136] <Evaluation of exhaust gas purification performance> [Evaluation Method] After performing the following bench aging on each catalyst in Experimental Examples 1-1 to 1-4, the HC purification performance was investigated using simulated exhaust gas. 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. • Measurement of HC purification rate 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.

[0137] 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.

[0138] [Measurement results] Table 2 shows the gas temperature T50(HC) at the catalyst inlet when the HC purification rate reaches 50%.

[0139] As shown in Table 2, in the catalyst samples of Experimental Example 1-4, which correspond to an example of the catalyst layer of this disclosure, the T50 of HC is reduced and the HC purification performance is improved compared to the catalyst samples of Experimental Examples 1-1 to 1-3.

[0140] Specifically, while the T50(HC) of the catalyst samples in Experimental Examples 1-1 to 1-3 exceeded 283°C, the T50(HC) of the catalyst sample in Experimental Example 1-4 decreased to below 283°C, demonstrating an improvement in HC purification performance.

[0141] (Experiment 2) The catalysts from Experimental Examples 2-1 to 2-17 and Experimental Examples 2-11b to 2-11f were evaluated for their HC, CO, and NOx purification performance using CAE analysis. Furthermore, catalyst samples from Experimental Examples 2-6, 2-10, 2-11, and 2-14 to 2-17 were actually prepared, and their purification performance was evaluated.

[0142] Details of the first, second, and third catalyst layers of each catalyst are shown in Figure 5 and Table 3. The evaluation results are shown in Figures 6 to 10.

[0143] [Table 3]

[0144] <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.

[0145] [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% by mass. Furthermore, the first catalyst layer consisted of BaSO4 and a zirconia binder, with a Ba support amount of 10 g / support and a binder support amount of 12.2 g / support.

[0146] [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 / support, respectively. The Rh concentration and supported amount of Rh / ZrLaY were 0.107 mass% and 15.016 g / support, respectively. The second catalyst layer also contained a zirconia binder, with a binder supported at 12.2 g / support.

[0147] [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. In Experimental Examples 2-1 to 2-16, the Pd concentration and supported amount of Pd / Al2O3 in the front section were 7.7 mass% and 24.38 g / support, respectively, and the Pd concentration and supported amount of Pd / ZrCeNd were 0.68 mass% and 17.62 g / support, respectively. Furthermore, the Pd concentration and supported amount of Pd / Al2O3 in the rear section were 0.78 mass% and 22.676 g / support, respectively, and the Pd concentration and supported amount of Pd / ZrCeNd were 0.063 mass% and 17.511 g / support, respectively. In Experimental Example 2-17, the Pd concentration and loading amount for Pd / Al2O3 were 4.4 mass% and 47.056 g / support, respectively, and the Pd concentration and loading amount for Pd / ZrCeNd were 0.37 mass% and 35.131 g / support, respectively. In Experimental Examples 2-11b to 2-11f, the Pd concentrations of Pd / Al2O3 and Pd / ZrCeNd were the same as in Experimental Example 2-11, and the mixing ratio of the two was adjusted to obtain the Pd concentrations D1 and D2 shown in Table 3.

[0148] Furthermore, the third catalyst layer was configured to include ZrCeNd and a zirconia binder, similar to Experimental Examples 1-4, with a ZrCeNd load of 20g / carrier (10g / carrier in the front section, 10g / carrier in the rear section) and a binder load of 14g / carrier (7g / carrier in the front section, 7g / carrier in the rear section).

[0149] <Analysis conditions> The analysis conditions used are as follows: • CAE analysis software: Axisuite 1D model (manufactured by Exothermia SA) • Model: Models one side of a single cell of the carrier. • First catalyst layer and second catalyst layer: A total Rh load of 0.475 g was modeled. In all experimental examples of Experiment 2, 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, as shown in Figures 2 and 5. • Third catalyst layer: A total Pd load of 2.2g was modeled. In all experimental examples of Experiment 2, the lengths of both the front and rear sections were fixed at 50% of the LT. • 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.

[0150] <Result> Figures 6 to 8 show the emissions of HC, CO, and NOx in the catalyst models for experimental examples 2-1 to 2-16, respectively. Table 3 and Figure 9 show the total emissions of the three components, which are the sum of the emissions shown in Figures 6 to 8.

[0151] As shown in Table 3 and Figure 9, the total emissions of the three components were 81.4g or less in the catalyst models of Experimental Examples 2-5 to 2-16, showing an improvement in the purification performance of the three components compared to Experimental Examples 2-1 to 2-4 and Experimental Example 2-17 with a uniform coating. In particular, in the catalyst models of Experimental Examples 2-6, 2-10, 2-11, 2-14, and 2-15, indicated by the dashed-dotted circles in Figure 9, the total emissions of the three components were 81.2g or less, demonstrating superior purification performance of the three components. Although the total emissions of the three components were relatively low in the catalyst model of Experimental Example 2-5, as shown in Figure 5, the catalyst layer of this model does not have an overlapping portion between the first and second catalyst layers, and a part of the third catalyst layer is exposed. Therefore, there is a risk that thermal degradation of Pd contained in the third catalyst layer and P poisoning will progress more easily.

[0152] <Evaluation of exhaust gas purification performance> [Evaluation Method] For each catalyst sample in Experimental Examples 2-6, 2-10, 2-11, and 2-14 to 2-17, the HC purification performance was investigated using simulated exhaust gas with the same evaluation method as in Experiment 1.

[0153] [Measurement results] Table 3 shows the gas temperature T50(HC) at the catalyst inlet when the HC purification rate reaches 50%.

[0154] As shown in Table 3, in the catalyst samples of Experimental Examples 2-6, 2-10, 2-11, and 2-14 to 2-16, which correspond to examples of catalyst layers of this disclosure, the T50 of HC is reduced and the HC purification performance is improved compared to the catalyst sample of Experimental Example 2-17 (uniform coating).

[0155] Specifically, while the catalyst sample in Experimental Example 2-17 had a T50(HC) of 213°C, the catalyst samples in Experimental Examples 2-6, 2-10, 2-11, and 2-14 to 2-16 had a T50(HC) of 212°C or lower, and in particular, the catalyst samples in Experimental Examples 2-6, 2-10, and 2-11 had a T50(HC) of 210°C or lower, demonstrating an improvement in HC purification performance. [Industrial applicability]

[0156] This disclosure is extremely useful because it can provide an exhaust gas purification catalyst that effectively suppresses phosphorus poisoning and achieves both improved purification performance and cost reduction. [Explanation of Symbols]

[0157] 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 81 Front section (of the third catalyst layer) 82 Rear section (of the 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 L81 (Length of the front section of the third catalytic converter layer) L82 (Length of the rear section of the third catalytic converter layer) P1 1st position P2 2nd position P3 3rd 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 having an upstream end and a downstream end, and a catalyst layer formed on the carrier for purifying the exhaust gas, The catalyst layer is A first catalyst layer is provided from the upstream end to the first position and is positioned on the outermost surface of the catalyst layer, A 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, the second catalyst layer is positioned closer to the carrier than the first catalyst layer. The catalyst includes a third catalyst layer positioned closer to the support than the first catalyst layer and the second 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. The third catalyst layer is The front portion includes an upstream catalyst material provided from the upstream end to the third position, with Pd supported on the upstream support material, The rear portion includes a downstream catalyst material provided from the third position to the downstream end, on which Pd is supported on the downstream support material, When the Pd concentration in the upstream catalyst material is D1 and the Pd concentration in the downstream catalyst material is D2, the ratio of D1 to D2, D1 / D2, is greater than 1.

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

2. In claim 1, The length from the upstream end to the first position is 55% or more and 100% or less of the total length of the carrier. A catalyst for purifying exhaust gases characterized by the following features.

3. In claim 1 or claim 2, The length from the downstream end to the second position is 55% or more and 100% or less of the total length of the carrier. A catalyst for purifying exhaust gases characterized by the following features.

4. In claim 1 or claim 2, The length of the overlapping portion is 8% to 90% of the total length of the carrier. A catalyst for purifying exhaust gases characterized by the following features.

5. In claim 1 or claim 2, The ratio D1 / D2 is 2.0 or greater. A catalyst for purifying exhaust gases characterized by the following features.

6. In claim 1 or claim 2, The ratio C1 / C2 is between 1.2 and 5.

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

7. 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.

8. In claim 1 or claim 2, At least one of the upstream support material and the downstream support material is at least one selected from the group consisting of activated alumina, Ce-containing Zr-based composite oxide, and Ce-free Zr-based composite oxide. A catalyst for purifying exhaust gases characterized by the following features.

9. 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.

10. 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.

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