Method for manufacturing an exhaust gas purification catalyst and exhaust gas purification catalyst
By directly supporting Pd on a Si or SiC member within the catalyst layer, the migration of Pd is prevented, ensuring effective temperature characteristics and purification performance in high-temperature environments.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- CATALER CORP
- Filing Date
- 2021-11-04
- Publication Date
- 2026-05-29
Smart Images
Figure 0007867330000002 
Figure 0007867330000003 
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Abstract
Description
Technical Field
[0001] The present invention relates to a catalyst for purifying exhaust gas. More specifically, it relates to a method for manufacturing a catalyst for purifying exhaust gas provided with a SiC substrate and a catalyst for purifying exhaust gas obtained by the manufacturing method.
Background Art
[0002] Exhaust gas discharged from an internal combustion engine contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). An exhaust gas purification catalyst for purifying these harmful components is disposed in the exhaust passage of the internal combustion engine. A general exhaust gas purification catalyst includes a honeycomb-structured substrate in which a plurality of gas flow paths (cells) are partitioned by partition walls, and a catalyst layer formed on the surface of the partition walls of the substrate. This catalyst layer is usually formed of a catalyst material in which a noble metal catalyst is supported on a metal oxide carrier such as alumina particles.
[0003] In the exhaust gas purification catalyst having the above configuration, a substrate containing silicon carbide (SiC) (hereinafter referred to as "SiC substrate") may be used. For example, in order for the exhaust gas purification catalyst to exhibit a suitable exhaust gas purification effect, it needs to be used in a state where the temperature is raised to the activation temperature of the noble metal catalyst. Here, in a normal exhaust system, the heat for raising the temperature of the exhaust gas purification catalyst is the heat from the exhaust gas. Therefore, in a situation where the exhaust gas temperature is low, such as immediately after the engine is started, there is a possibility that a suitable exhaust gas purification effect cannot be exhibited. On the other hand, in recent years, an electrically heated catalyst (EHC) has attracted attention (see Patent Documents 1 to 4). This electrically heated catalyst includes a SiC substrate having conductivity and functioning as a resistance heating element. The electrically heated catalyst provided with this SiC substrate can easily raise the temperature inside the substrate by energization, so that a suitable purification effect can be exhibited even in a situation where the exhaust gas temperature is low. In addition, since the SiC substrate is less likely to crack in a high-temperature environment, it is also used for a diesel particulate filter (DPF) and the like.
Prior Art Documents
Patent Documents
[0004] [Patent Document 1] Patent No. 6052250 [Patent Document 2] Patent No. 6364374 [Patent Document 3] Japanese Patent Publication No. 11-230132 [Patent Document 4] Japanese Patent Publication No. 2004-351292 [Overview of the Initiative] [Problems that the invention aims to solve]
[0005] As described above, SiC substrates are widely used in the field of exhaust gas purification catalysts. However, exhaust gas purification catalysts equipped with SiC substrates have a problem in which the noble metal catalyst in the catalyst layer migrates to the partition wall side of the SiC substrate in high-temperature environments. As this migration of the noble metal catalyst progresses, the frequency of contact between the noble metal catalysts increases, promoting aggregation, which may make it difficult to achieve suitable exhaust gas purification performance (e.g., temperature characteristics).
[0006] This invention was made to solve the above-mentioned problems and aims to provide a technology that can suppress the migration of noble metal catalysts in high-temperature environments and prevent a decrease in temperature characteristics. [Means for solving the problem]
[0007] To solve the above problems, a method for manufacturing an exhaust gas purification catalyst (hereinafter also simply referred to as the "manufacturing method") is provided herein.
[0008] The manufacturing method disclosed herein comprises a substrate preparation step of preparing a SiC substrate having partitions separating a plurality of cells and containing SiC, and a catalyst layer formation step of forming a Pd catalyst layer containing at least Pd on the surface of the partitions of the SiC substrate. In the manufacturing method disclosed herein, the Pd catalyst layer is formed in the catalyst layer formation step by directly supporting Pd on a Si member containing Si or SiC.
[0009] Various experiments have confirmed that the migration of the noble metal catalyst to the SiC substrate is particularly pronounced when palladium (Pd) is used as the noble metal catalyst. The inventors hypothesized that the reason for this phenomenon is that Pd is highly reactive with elemental Si and SiC, and is easily guided toward the partition walls of the SiC substrate containing a large amount of these. The technology disclosed herein is based on this finding. In other words, in the manufacturing method disclosed herein, Pd is directly supported on a Si member containing elemental Si or SiC. By bringing the Si member and Pd into contact in this way beforehand, the migration of Pd in a high-temperature environment can be suppressed, and the deterioration of temperature characteristics due to aggregation of the noble metal catalyst (Pd) can be prevented.
[0010] In one preferred embodiment of the manufacturing method disclosed herein, a Pd catalyst layer substantially free of metal oxide supports is formed in the catalyst layer formation step. This makes it possible to more effectively prevent the migration of Pd under high-temperature conditions.
[0011] As an example of the above-mentioned metal oxide support, metal oxide particles containing at least one selected from the group consisting of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, praseodymium oxide, lanthanum oxide, niobium oxide, and yttrium oxide can be used. By forming a Pd catalyst layer that does not contain these metal oxide particles, the migration of Pd under high-temperature conditions can be more effectively prevented.
[0012] In one preferred embodiment of the manufacturing method disclosed herein, the catalyst layer formation step comprises a solution preparation step of preparing a Pd solution containing Pd, a solution application step of applying the Pd solution to the surface of the partition wall of the SiC substrate, and a calcination step of calcining the Pd solution attached to the surface of the partition wall. This makes it possible to easily form a Pd catalyst layer in which Pd is directly supported on the Si member (partition wall of the SiC substrate).
[0013] In one preferred embodiment of the manufacturing method disclosed herein, the catalyst layer formation step comprises a slurry preparation step of preparing a Pd-Si slurry by dispersing Si or SiC-containing Si particles in a Pd solution containing Pd; a slurry application step of applying the Pd-Si slurry to the surface of a partition wall of a SiC substrate; and a calcination step of calcining the Pd-Si slurry adhering to the surface of the partition wall. This makes it possible to easily form a Pd catalyst layer in which Pd is directly supported on a Si member (Si-containing particles).
[0014] Furthermore, another aspect of the technology disclosed herein is an exhaust gas purification catalyst. The exhaust gas purification catalyst disclosed herein comprises a SiC substrate containing SiC and having partitions separating a plurality of cells, and a Pd catalyst layer formed on the surface of the partitions of the SiC substrate and containing at least Pd. In the exhaust gas purification catalyst disclosed herein, Pd is directly supported on a Si member containing Si or SiC in the Pd catalyst layer. This suppresses the migration of Pd in high-temperature environments and prevents a decrease in temperature characteristics.
[0015] In one preferred embodiment of the exhaust gas purification catalyst disclosed herein, the Pd catalyst layer substantially does not contain a metal oxide support. This allows for more favorable prevention of Pd migration in high-temperature environments.
[0016] As an example of the above metal oxide carrier, metal oxide particles containing at least one selected from the group consisting of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, praseodymium oxide, lanthanum oxide, niobium oxide, and yttrium oxide can be mentioned. Thereby, the movement of Pd in a high-temperature environment can be more suitably prevented.
[0017] In a preferred embodiment of the exhaust gas purification catalyst disclosed herein, the Si member is a partition wall of a SiC substrate, and Pd is supported on the partition wall of the SiC substrate. Thereby, the movement of Pd in a high-temperature environment can be appropriately prevented.
[0018] In a preferred embodiment of the exhaust gas purification catalyst disclosed herein, the Si member is Si-containing particles containing Si or SiC, and Pd is supported on the Si-containing particles. Even in such an embodiment, the movement of Pd in a high-temperature environment can be appropriately prevented.
Brief Description of the Drawings
[0019] [Figure 1] It is a perspective view schematically showing an exhaust gas purification catalyst according to the first embodiment. [Figure 2] It is a cross-sectional view when the SiC substrate of the exhaust gas purification catalyst according to the first embodiment is cut along the cylinder axis direction (gas flow direction). [Figure 3] It is a cross-sectional view schematically showing the layer structure of the partition wall of the SiC substrate shown in FIG. 2. [Figure 4] It is a cross-sectional view schematically showing the layer structure of the partition wall of the SiC substrate of the exhaust gas purification catalyst according to the second embodiment. [Figure 5] It is the FE-EPMA analysis result before and after the durability test in Comparative Example 1. [Figure 6] It is the FE-EPMA analysis result before and after the durability test in Comparative Example 2. [Figure 7] It is the FE-EPMA analysis result before and after the durability test in Comparative Example 3. [Figure 8]The FE-EPMA analysis results before and after the durability test in Example 1. [Figure 9] It is a cross-sectional view schematically showing the layer structure in the partition wall of the SiC substrate of a conventional exhaust gas purification catalyst. [Figure 10] It is a cross-sectional view schematically showing the state of the exhaust gas purification catalyst shown in Fig. 9 after being exposed to a high-temperature environment.
Mode for Carrying Out the Invention
[0020] Hereinafter, preferred embodiments disclosed herein will be described with reference to the drawings. Incidentally, matters other than those particularly mentioned in this specification and matters necessary for the implementation of the technology disclosed here can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed here can be implemented based on the content disclosed in this specification and the technical knowledge in the relevant field. The drawings in this specification are schematically shown for understanding the content of the technology disclosed here, and the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships.
[0021] [First Embodiment] Hereinafter, the first embodiment of the technology disclosed here will be described. Fig. 1 is a perspective view schematically showing an exhaust gas purification catalyst according to the first embodiment. Fig. 2 is a cross-sectional view when the SiC substrate of the exhaust gas purification catalyst according to the first embodiment is cut along the cylinder axis direction (gas flow direction). Fig. 3 is a cross-sectional view schematically showing the layer structure in the partition wall of the SiC substrate shown in Fig. 2. The arrow A in Figs. 1 and 2 indicates the flow direction of the exhaust gas.
[0022] 1. Exhaust gas purification catalyst First, the structure of the exhaust gas purification catalyst according to this embodiment will be described. The exhaust gas purification catalyst 1 according to this embodiment is placed in the exhaust system (exhaust pipe) of various internal combustion engines (for example, diesel engines and gasoline engines) and purifies harmful components (HC, CO, NOx, etc.) in the exhaust gas emitted from the internal combustion engine. As shown in Figures 1 to 3, this exhaust gas purification catalyst 1 comprises a SiC substrate 10 and a Pd catalyst layer 20.
[0023] (1)SiC base material The SiC substrate 10 is a substrate containing silicon carbide (SiC). Such a SiC substrate 10 can be any conventionally known substrate for exhaust gas purification catalysts, primarily composed of silicon carbide (SiC), without any particular limitations. Because this SiC substrate is conductive and can function as a resistance heating element, it is suitable as a substrate for electrically heated catalysts. The SiC substrate 10 may contain components other than SiC, as long as they do not significantly impair the effects of the technology disclosed herein. For example, in this specification, "SiC substrate" refers to a substrate in which the SiC content is 20 wt% or more (preferably 50 wt% or more, more preferably 70 wt% or more) when the total weight of the substrate is 100 wt%. Other components that may be included in the SiC substrate include elemental Si. In the SiC substrate 10 for electrically heated catalysts as shown in this embodiment, elemental Si may be added to the SiC substrate for the purpose of adjusting the conductivity.
[0024] As shown in Figure 1, the SiC substrate 10 in this embodiment has a cylindrical shape. However, the shape of the SiC substrate 10 is not particularly limited and may be an elliptical cylinder, a polygonal cylinder, etc. Also, as shown in Figures 1 and 2, the SiC substrate 10 is a honeycomb structure substrate. That is, the SiC substrate 10 comprises a plurality of cells (gas channels) 12 and partition walls 16 that separate each cell 12. The shape of each cell is not particularly limited and may be a quadrilateral shape such as a square, parallelogram, rectangle, or trapezoid; a triangular shape, a hexagonal shape, an octagonal shape, or other polygonal shape; or a circle, etc.
[0025] Furthermore, as shown in Figure 2, the SiC substrate 10 in this embodiment is a straight-flow type substrate. That is, the SiC substrate 10 comprises a plurality of cells 12 and a partition wall 16 that separates two adjacent cells 12. Each cell 12 is equipped with a gas inlet 12a, which is an opening into which exhaust gas flows, and a gas outlet 12b, which is an opening into which exhaust gas flows out. Exhaust gas introduced into the SiC substrate 10 with this configuration passes through the cells 12 of the SiC substrate 10 and flows downstream while coming into contact with the Pd catalyst layer 20 (see Figure 3) formed on the surface of the partition wall 16.
[0026] The exhaust gas purification catalyst 1 according to this embodiment is used as an electrically heated catalyst. Specifically, in this embodiment, an electrode 40 is attached to the outer circumferential surface of the SiC substrate 10. Such electrode 40 can be any electrode that is provided in a conventionally known electrically heated catalyst without any particular limitations. Examples of such electrode 40 include metal electrodes and carbon electrodes. The electrode 40 comprises an electrode layer 42 attached along the outer circumferential surface of the SiC substrate 10 and an electrode terminal 44 that can be connected to a power supply (not shown). The current supplied from the power supply is diffused throughout the SiC substrate 10 via the electrode terminal 44 and the electrode layer 42. As a result, the SiC substrate 10, which is a resistance heating element, generates heat, so that even when the exhaust gas temperature is low, the inside of the substrate can be heated up to the activation temperature of the noble metal catalyst.
[0027] (2)Pd catalyst layer As shown in Figure 3, the Pd catalyst layer 20 is formed on the partition wall 16 of the SiC substrate 10. The Pd catalyst layer 20 is a layer containing at least palladium (Pd). This Pd has excellent oxidative purification function against carbon monoxide (CO) and hydrocarbons (HC). On the other hand, Pd is highly reactive to elemental Si and SiC, and has the characteristic of being easily induced into materials containing a large amount of elemental Si or SiC (typically the partition wall 16 of the SiC substrate 10) when exposed to a high-temperature environment. In contrast, in the exhaust gas purification catalyst disclosed herein, a Pd catalyst layer is formed in which Pd is directly supported on a Si member containing Si or SiC. Specifically, the "Si member" in the first embodiment is the partition wall 16 of the SiC substrate 10. As described above, the SiC substrate 10 has SiC as its main component and may contain elemental Si, so it can be called a "Si member containing Si or SiC". In the first embodiment, the Pd catalyst layer 20 is formed by directly supporting particulate Pd (Pd particles 22) on the partition wall 16 of the SiC substrate 10. This suppresses the movement of the noble metal catalyst (Pd particles 22) in high-temperature environments and prevents a decrease in temperature characteristics. The effects of the exhaust gas purification catalyst 1 according to this embodiment will be described below in comparison with conventional exhaust gas purification catalysts.
[0028] Figure 9 is a schematic cross-sectional view showing the layer structure of the partition wall of a SiC substrate in a conventional exhaust gas purification catalyst. On the other hand, Figure 10 is a schematic cross-sectional view showing the state of the exhaust gas purification catalyst shown in Figure 9 after being exposed to a high-temperature environment. In the exhaust gas purification catalyst shown in Figure 9, a Pd catalyst layer 120 is formed on the surface of the partition wall 116 of the SiC substrate 110. Also, reference numeral 130 in Figure 9 indicates a second catalyst layer 130 containing a noble metal catalyst other than Pd (Pt, Rh, etc.). The conventional Pd catalyst layer 120 shown in Figure 9 contains a catalyst material 125 in which Pd particles 122 are supported on a metal oxide carrier 123 such as alumina particles. When an exhaust gas purification catalyst with such a configuration is exposed to a high-temperature environment, the Pd particles 122 supported on the metal oxide support 123 move toward the partition wall 116 of the SiC substrate 110, and a Pd aggregation region 120a is formed on the lower side of the Pd catalyst layer 120 (the region in contact with the partition wall 116) where the Pd particles 122 have aggregated (see Figure 10). On the other hand, a catalyst disappearance region 120b is created on the upper side of the Pd catalyst layer 120 (the region opposite the partition wall 116) where almost no Pd particles 122 remain. When such movement of Pd particles 122 occurs, the Pd particles 122 come into contact with each other during movement, promoting aggregation, which may reduce the catalytic performance (typically temperature characteristics) of the Pd catalyst layer 120.
[0029] On the other hand, as described above, the Pd catalyst layer 20 in this embodiment is formed by directly supporting Pd particles 22 on the partition walls 16 of the SiC substrate 10. In other words, in this embodiment, since the Si member (the partition walls 16 of the SiC substrate) and the Pd particles 22 are in contact beforehand, the movement of Pd particles 22 in a high-temperature environment can be suppressed. Therefore, according to this embodiment, the aggregation of Pd particles 22 associated with movement is suppressed, and thus a decrease in temperature characteristics can be appropriately prevented.
[0030] The thickness and length of the Pd catalyst layer 20 are not limited to the technology disclosed herein and can be adjusted as needed. For example, the Pd catalyst layer 20 in this embodiment may be a thin film layer formed along the surface of the partition wall 16 of the SiC substrate 10. The thickness of the Pd catalyst layer 20 is preferably adjusted considering the dimensions of the SiC substrate 10 and the flow rate of the exhaust gas. For example, the thickness of the Pd catalyst layer 20 may be 0.5 nm to 500 nm, 1 nm to 100 nm, 1.5 nm to 50 nm, or 2 nm to 15 nm. Furthermore, the length of the Pd catalyst layer 20 in the stretching direction of the partition wall 16 is not particularly limited. For example, the Pd catalyst layer 20 may be formed over the entire length (100%) of the partition wall 16. Moreover, the length of the Pd catalyst layer 20 may be 90% or less, 80% or less, or 70% or less of the total length of the partition wall 16. On the other hand, the lower limit of the length of the Pd catalyst layer 20 may be 20% or more of the total length of the partition wall 16, 30% or more, 40% or more, 50% or more, or 60% or more.
[0031] Furthermore, the size of the Pd particles 22 is not particularly limited. The average particle diameter of the Pd particles 22 is preferably 400 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, and particularly preferably 10 nm or less. By forming such small Pd particles 22, the surface area between the exhaust gas and Pd can be increased, improving the exhaust gas purification performance. On the other hand, the lower limit of the average particle diameter of the Pd particles 22 is preferably 0.5 nm or more, more preferably 0.7 nm or more, even more preferably 1.5 nm or more, and particularly preferably 2 nm or more. By forming Pd particles 22 of a certain size or larger in this way, particle coarsening due to sintering can be suppressed. The average particle diameter of the Pd particles can be determined as the average value of the particle sizes of 100 Pd particles confirmed by an electron microscope (e.g., scanning electron microscope (SEM), transmission electron microscope (TEM), etc.).
[0032] Furthermore, the Pd catalyst layer 20 may contain other precious metal catalysts besides Pd. Examples of such other precious metal catalysts include platinum (Pt), rhodium (Rh), ruthenium (Ru), osmium (Os), and iridium (Ir). As will be described in more detail later, in an exhaust gas purification catalyst having a catalyst layer in which Pd and other precious metal catalysts are mixed, only Pd is guided to the partition wall of the SiC substrate. However, according to the technology disclosed herein, the migration of Pd in such a mixed catalyst layer can also be appropriately suppressed.
[0033] In addition, it is preferable that the Pd catalyst layer 20 in this embodiment substantially does not contain metal oxide supports. This more effectively prevents the movement of Pd particles 22 and reliably prevents a decrease in temperature characteristics. In this specification, "substantially does not contain metal oxide supports" means that metal oxide supports are not intentionally added to the Pd catalyst layer. Therefore, if a material that can be interpreted as a metal oxide support is inevitably and in trace amounts due to raw materials or manufacturing processes, etc., it is included in the concept of "substantially does not contain metal oxide supports" in this specification. For example, in the analysis of the Pd catalyst layer based on elemental mapping by FE-EPMA, if the amount of elements that can be interpreted as metal oxide supports is 1% or less (preferably 0.5% or less, more preferably 0.1% or less, even more preferably 0.05% or less, and particularly preferably 0.01% or less), it can be said that it "substantially does not contain metal oxide supports". Examples of metal oxide supports include metal oxide particles containing aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, praseodymium oxide, lanthanum oxide, niobium oxide, and yttrium oxide.
[0034] (3) Second catalyst layer Furthermore, in this embodiment, the exhaust gas purification catalyst 1 has a second catalyst layer 30 formed on the upper side (cell side) of the Pd catalyst layer 20. Although detailed illustration is omitted in Figure 3, the second catalyst layer 30 contains a catalyst material comprising a noble metal catalyst other than Pd and a carrier that supports the noble metal catalyst. Examples of noble metal catalysts other than Pd include platinum (Pt), rhodium (Rh), ruthenium (Ru), osmium (Os), and iridium (Ir). In particular, Rh has excellent reduction and purification performance and can suitably purify NOx, which is difficult to purify in the Pd catalyst layer 20, thus contributing to an improvement in the overall purification performance of the exhaust gas purification catalyst 1. The second catalyst layer 30 may also contain additives other than the noble metal catalyst and carrier. An example of this type of additive is an OSC material that has oxygen storage capacity.
[0035] Furthermore, the second catalyst layer 30 may contain a metal oxide support as a support. That is, the second catalyst layer 30 can use any metal oxide support, including aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, praseodymium oxide, lanthanum oxide, niobium oxide, yttrium oxide, etc., without particular limitation. In this case, it is preferable that the second catalyst layer 30 be a catalyst layer that is substantially free of Pd. This prevents the migration of Pd in the second catalyst layer 30. Here, "substantially free of Pd" means that Pd has not been intentionally added to the second catalyst layer. Therefore, if the element Pd is inevitably and tracely mixed into the second catalyst layer from the raw materials or manufacturing process (including diffusion from the Pd catalyst layer), etc., it is included in the concept of "substantially free of Pd" as specified herein. For example, in elemental mapping by FE-EPMA, if the amount of Pd element in the second catalyst layer is 1% or less (preferably 0.5% or less, more preferably 0.1% or less, even more preferably 0.05% or less, and particularly preferably 0.01% or less), it can be said that "a second catalyst layer substantially free of Pd has been formed."
[0036] Furthermore, the thickness and length of the second catalyst layer 30 are not limited to the technology disclosed herein and can be adjusted as needed. For example, the thickness of the second catalyst layer 30 may be 1 μm or more and 500 μm or 10 μm or more and 200 μm or less. In addition, the length of the second catalyst layer 30 in the stretching direction of the partition wall 16 is not particularly limited. For example, the second catalyst layer 30 may be formed over the entire length (100%) of the partition wall 16. Furthermore, the length of the second catalyst layer 30 may be 90% or less, 80% or less, or 70% or less of the total length of the partition wall 16. On the other hand, the lower limit of the length of the second catalyst layer 30 may be 20% or more, 30% or more, 40% or more, 50% or more, or 60% or more of the total length of the partition wall 16.
[0037] 2. Method for manufacturing a catalyst for exhaust gas purification Next, a method for manufacturing the exhaust gas purification catalyst 1 with the above configuration will be described. The manufacturing method according to this embodiment comprises a substrate preparation step and a catalyst layer formation step. Each step will be described below.
[0038] (1) Base material preparation process In this process, a SiC substrate 10 containing SiC is prepared, which has partition walls 16 separating multiple cells 12. The detailed structure and materials of the SiC substrate 10 have already been described and will be omitted here. Note that "preparation" here is a concept that includes not only the fabrication of the SiC substrate 10 using various molding methods, but also obtaining the SiC substrate 10 through purchase or transfer, etc.
[0039] (2)Catalyst layer formation process In this process, a Pd catalyst layer 20 containing at least Pd is formed on the surface of the partition wall 16 of the SiC substrate 10. As described above, in the Pd catalyst layer 20 of this embodiment, Pd particles 22 are directly supported on the partition wall 16 (Si member) of the SiC substrate 10. Such a Pd catalyst layer 20 can be easily formed by carrying out the solution preparation step, the solution application step, and the calcination step described below.
[0040] (a) Solution preparation process In this step, a Pd solution containing the element Pd is prepared. This Pd solution is a precursor for Pd particles 22, and the Pd particles 22 are precipitated in the calcination step described later. The Pd solution is not particularly limited as long as it contains the element Pd, and conventionally known solutions that can be used to form a Pd-containing catalyst layer can be used without any particular restrictions. An example of such a Pd solution is a solution obtained by dissolving a palladium salt in an aqueous medium. Examples of such palladium salts include palladium nitrate, palladium sulfate, palladium chloride, and palladium acetate. The content of the element Pd in the Pd solution can be appropriately adjusted according to the composition of the target Pd catalyst layer 20. For example, the Pd equivalent amount in the Pd solution is preferably 0.05 wt% or more, more preferably 0.1 wt% or more, and particularly preferably 0.2 wt% or more. On the other hand, the upper limit of the Pd equivalent amount in the Pd solution is preferably 5 wt% or less, more preferably 3 wt% or less, and particularly preferably 2 wt% or less.
[0041] As mentioned above, it is preferable that the Pd catalyst layer 20 in this embodiment substantially does not contain metal oxide supports. That is, it is preferable that the Pd solution does not substantially contain metal oxide particles such as aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, praseodymium oxide, lanthanum oxide, niobium oxide, or yttrium oxide. More specifically, the content of the above metal oxide particles in the Pd solution is preferably 0.1 wt% or less, more preferably 0.05 wt% or less, even more preferably 0.01 wt% or less, and particularly preferably 0 wt%.
[0042] Furthermore, the Pd solution preferably contains an organic thickener. Examples of such thickeners include water-soluble resin materials such as hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, polyvinyl alcohol, ethylene glycol, propylene glycol, pectin, and xanthan gum. By adding these thickeners, the viscosity of the Pd solution can be adjusted to appropriately apply the Pd solution to the partition walls 16 of the SiC substrate 10. Additionally, since organic thickeners are burned away during the firing process, they have the advantage of not hindering the effects of the disclosed technology. The viscosity of the Pd solution is preferably set appropriately considering the structure of the SiC substrate 10 (cell diameter, length, etc.). As an example, a viscosity of approximately 10 mPa to 1000 mPa is appropriate for the Pd solution, and preferably approximately 100 mPa to 800 mPa. The viscosity here is measured using a commercially available cone-plate viscometer with a rotation speed of 1 to 100 rpm, a temperature of 25°C, and a shear rate of 380 s. -1 This is the value when that is the case.
[0043] (b) Solution application step In this process, a Pd solution is applied to the surface of the partition wall 16 of the SiC substrate 10. One example of a specific procedure in this process is to introduce the Pd solution into the cell 12 from the gas inlet 12a and then suck the cell 12 out from the gas outlet 12b. This allows the Pd solution to adhere properly to the surface of the partition wall 16. This process is not limited to the suction method described above, as long as it can apply the Pd solution to the surface of the partition wall 16. For example, a pressurized feeding method can be used in which compressed air is supplied from the gas inlet 12a after introducing the Pd solution into the cell 12 from the gas inlet 12a.
[0044] Furthermore, in this process, a drying treatment may be performed after the Pd solution is applied to the surface of the partition wall 16. This allows the active ingredients (typically Pd element) in the Pd solution to be suitably fixed to the surface of the partition wall 16. The heating temperature in the drying treatment is preferably 50°C to 200°C, and more preferably 100°C to 150°C. The drying time is preferably 0.5 hours to 5 hours, and more preferably 1 hour to 3 hours.
[0045] (c) Firing process Next, in the production of the exhaust gas purification catalyst 1, a SiC substrate 10 into which a Pd solution is supplied is fired. In this embodiment, since the Pd solution is directly applied to the surface of the partition wall 16, a Pd catalyst layer 20 is formed in which Pd particles 22 are directly supported on the surface of the partition wall 16. In this Pd catalyst layer 20, the partition wall 16 of the SiC substrate 10 containing SiC or elemental Si and the Pd particles 22 are in contact beforehand, so aggregation of Pd particles 22 during movement can be appropriately suppressed.
[0046] The firing conditions in this process are not particularly limited and can be adjusted as appropriate depending on the structure of the SiC substrate 10 and the composition of the Pd solution. For example, the firing temperature may be 300°C or higher, 350°C or higher, 400°C or higher, or 450°C or higher. On the other hand, the upper limit of the firing temperature may be 1000°C or lower, 900°C or lower, 800°C or lower, 700°C or lower, or 600°C or lower. The firing time may be 0.5 hours or higher, 1 hour or higher, or 1.5 hours or higher. The upper limit of the firing time may be 8 hours or lower, 6 hours or lower, or 4 hours or lower.
[0047] Furthermore, in the manufacturing method according to this embodiment, a Pd solution that substantially does not contain solids (such as metal oxide particles) is used in the formation of the Pd catalyst layer 20. Since such a Pd solution is easily introduced into the tiny pores of the partition wall 16, Pd particles 22 may be formed inside the partition wall 16 of the SiC substrate 10 after firing (see Figures 3 and 8). Although not intended to limit the technology disclosed herein, according to the manufacturing method according to this embodiment, the amount of Pd inside the partition wall 16 can be 10% or more (typically 20% or more, for example, 30% or more). Here, "amount of Pd inside the partition wall" refers to the ratio (%) of Pd elements confirmed inside the partition wall to the total number of Pd elements (100%) confirmed by elemental mapping using FE-EPMA.
[0048] (3) Second catalyst layer formation step Furthermore, in the exhaust gas purification catalyst 1 according to this embodiment, a second catalyst layer 30 is formed on the upper side of the Pd catalyst layer 20. The formation of the second catalyst layer 30 can be carried out using conventionally known methods without particular limitation. For example, the second catalyst layer formation step may include the steps of: preparing a slurry for the second layer by dispersing a metal oxide support in a solution containing a noble metal element (noble metal solution); applying the slurry for the second layer to the upper surface of the Pd catalyst layer 20; and calcining the slurry for the second layer attached to the upper surface of the Pd catalyst layer 20. By carrying out these steps, the second catalyst layer 30 can be formed on the upper side of the Pd catalyst layer 20. The slurry for the second layer only needs to contain the precursor material of the second catalyst layer 30 described above, and its detailed components are not particularly limited.
[0049] In the manufacturing method according to this embodiment, the Pd catalyst layer 20 and the second catalyst layer 30 are formed separately. However, this procedure is not limited to the technology disclosed herein, and the Pd catalyst layer 20 and the second catalyst layer 30 can also be formed simultaneously. Specifically, the Pd catalyst layer 20 and the second catalyst layer 30 can be formed simultaneously by applying a Pd solution to the surface of the partition wall 16 and drying it, and then applying a slurry for the second layer on top of the dried Pd solution and firing them simultaneously. However, considering the need to prevent some of the metal oxide support contained in the second catalyst layer 30 from mixing into the Pd catalyst layer 20, it is preferable to form the Pd catalyst layer 20 and the second catalyst layer 30 separately.
[0050] [Second Embodiment] The first embodiment of the technology disclosed herein has been described above. However, the technology disclosed herein is not limited to the first embodiment described above, and various forms can be adopted. The second embodiment of the technology disclosed herein will be described below. Figure 4 is a schematic cross-sectional view showing the layer structure in the partition wall of the SiC substrate of the exhaust gas purification catalyst according to the second embodiment.
[0051] As described above, in the first embodiment, the "Si member" is a partition wall 16 of the SiC substrate 10, and the Pd particles 22 are directly supported on the partition wall 16 (see Figure 3). However, the "Si member" in the technology disclosed herein may be a member containing only Si or SiC, and is not limited to a partition wall of the SiC substrate. For example, the "Si member" may be a carrier particle (Si-containing particle 24) containing only Si or SiC (see Figure 4). That is, in the second embodiment, the Pd catalyst layer 20 is formed by a Pd-Si catalyst material 26 on which Pd particles 22 are supported on Si-containing particles 24. Even when such a configuration is adopted, since the Si member (Si-containing particle 24) and the Pd particles 22 are in contact beforehand, aggregation of the Pd particles 22 due to movement can be suppressed, and a decrease in temperature characteristics can be prevented.
[0052] In this embodiment, when forming a Pd catalyst layer 20 containing a Pd-Si catalyst material 26, it is preferable to use a Pd-Si slurry in which Si-containing particles are dispersed in a Pd solution. By applying this Pd-Si slurry to the surface of the partition wall 16 and then performing a firing treatment, a Pd catalyst layer 20 in which Pd particles 22 are supported on Si-containing particles 24 can be easily formed. Furthermore, the term "Si-containing particles" used in this embodiment is a concept that encompasses both Si particles and SiC particles. In either case, the movement of Pd particles 22 in a high-temperature environment can be appropriately suppressed. In addition, a powder material containing a mixture of Si particles and SiC particles can also be used to form the Pd catalyst layer 20 in this embodiment. When the total weight of such a powder material containing Si particles is 100 wt%, the combined content of Si particles and SiC particles is preferably 10 wt% or more, more preferably 50 wt% or more, and particularly preferably 70 wt% or more.
[0053] The composition of the Pd-Si slurry is not particularly limited and can be adjusted as appropriate according to the composition of the desired Pd catalyst layer 20. For example, the content of Pd elements in the Pd-Si slurry can be set to approximately the same level as the content of Pd elements in the Pd solution in the first embodiment. On the other hand, the amount of Si-containing particles dispersed is preferably adjusted in consideration of its relationship to the content of Pd elements. For example, the mass ratio of Pd elements to Si-containing particles (Pd / Si) in the Pd-Si slurry is preferably 0.1 wt% or more, more preferably 0.5 wt% or more, and particularly preferably 1 wt% or more. This ensures that there are enough Si-containing particles 24 to adequately support the Pd particles 22. On the other hand, the Pd / Si ratio is preferably 14 wt% or less, more preferably 12 wt% or less, even more preferably 10 wt% or less, and particularly preferably 8 wt% or less. This allows for the formation of a Pd catalyst layer 20 with a sufficient amount of Pd particles 22.
[0054] The Pd-Si slurry may also contain Si-containing particles and additives other than Pd. Examples of such additives include OSC materials, metal oxide materials, and binders. Examples of OSC materials include composite oxides containing cerium oxide and zirconium oxide (CZ composite oxide). Examples of other metal oxide materials include aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, praseodymium oxide, lanthanum oxide, niobium oxide, and yttrium oxide. Examples of binders include inorganic binders such as alumina sol, titania sol, and zirconia sol. The Si-containing particles and additives other than Pd are not particularly limited as long as they do not significantly impair the effects of the technology disclosed herein, and additives commonly used to form the catalyst layer of exhaust gas purification catalysts can be used as appropriate.
[0055] [Other embodiments] The embodiments of the technology disclosed herein have been described above. It should be noted that the technology disclosed herein is not limited to the embodiments described above. For example, in the embodiments described above, a second catalyst layer 30 containing a noble metal catalyst other than Pd is formed above the Pd catalyst layer 20. However, the second catalyst layer 30 does not affect the effect of the technology disclosed herein and can be omitted as needed. That is, even in an exhaust gas purification catalyst without a second catalyst layer, if the Pd particles 22 are directly supported on a Si member (such as a SiC substrate 10 or Si-containing particles 24), the movement of Pd can be suitably suppressed. Furthermore, a third catalyst layer containing a different noble metal catalyst may be formed even further above the second catalyst layer.
[0056] Furthermore, in each of the embodiments described above, a straight-flow type SiC substrate 10 is used. However, the structure of the SiC substrate is not particularly limited, and structures other than the straight-flow type can also be adopted. Another example of a SiC substrate is a wall-flow type SiC substrate. Such a wall-flow type substrate comprises an inlet cell with an open end on the exhaust gas inlet side, an outlet cell with an open end on the exhaust gas outlet side, and a porous partition wall separating the inlet cell and the outlet cell. In an exhaust gas purification catalyst using a wall-flow type SiC substrate, the exhaust gas flowing into the inlet cell passes through the porous partition wall while in contact with the Pd catalyst layer, and is then discharged to the outside from the outlet cell. Even when this type of wall-flow type substrate is used, the effects of the technology disclosed herein can be appropriately demonstrated.
[0057] Furthermore, the embodiments described above used an exhaust gas purification catalyst used as an electrically heated catalyst as an example. However, the technology disclosed herein is not limited to electrically heated catalysts and can be applied without limitation to all exhaust gas purification catalysts using SiC substrates. For example, diesel particulate filters (DPFs) are heated at high temperatures during regeneration, so SiC substrates that are less prone to cracking due to thermal cycling are sometimes used. In addition, such SiC substrates for DPFs may also contain 10 wt% to 30 wt% (for example, about 20 wt%) of elemental Si. The technology disclosed herein is not limited to applications and can appropriately suppress Pd migration in SiC substrates in general, including SiC and elemental Si.
[0058] [Example Test] The following describes embodiments of the technology disclosed herein. However, the following description is not intended to limit the technology disclosed herein to those shown in the embodiments.
[0059] <Fabrication of exhaust gas purification catalysts> (Comparative Example 1) In this example, a straight-flow type SiC substrate (volume 551 mL, number of cells 600 cpsi, partition wall thickness 5 mil, cell shape hexagonal, diameter 118.4 mm, substrate length 50 mm) was first prepared. Next, a Pd-Al2O3 slurry was prepared by dispersing 20 wt% alumina support, 13 wt% CZ composite oxide material, and 0.7 wt% Al2O3-based binder in a palladium nitrate solution (Pd equivalent: 0.6 wt%). Then, this Pd-Al2O3 slurry was introduced into the cells of the substrate from the gas inlet, and the slurry was adhered to the partition walls by suction from the gas outlet with a blower. After that, a drying treatment was performed at 120°C for 2 hours, followed by a calcination treatment at 500°C for 2 hours to form a Pd-Al2O3 layer on the surface of the partition walls.
[0060] Next, an Rh-Al2O3 slurry was prepared by dispersing 16 wt% alumina powder, 9.2 wt% CZ composite oxide material, and 0.15 wt% Al2O3-based binder in a rhodium nitrate solution (Rh equivalent: 0.03 wt%). The CZ composite oxide material is a composite material mainly composed of CeO2 and ZrO2, with trace amounts of Pr2O3, Nd2O3, La2O3, and Y2O3. Next, the Rh-Al2O3 slurry was introduced into the cell of the substrate from the gas inlet, and the slurry was applied to the Pd-Al2O3 layer by sucking the gas outlet with a blower. After that, a drying treatment was performed at 120°C for 2 hours, followed by a calcination treatment at 500°C for 2 hours. This produced an exhaust gas purification catalyst in which an Rh-Al2O3 layer was formed on top of a Pd-Al2O3 layer. The amount of Pd used in this exhaust gas purification catalyst is 2 g / L, and the amount of Rh used is 0.15 g / L. In addition, the Pd-Al2O3 layer and the Rh-Al2O3 layer are formed along the entire length of the partition wall of the SiC substrate, and the total coating amount of these catalyst layers is 228.8 g / L.
[0061] (Comparative Example 2) In this example, an Rh-Al2O3 slurry was applied to the surface of the partition wall to form an Rh-Al2O3 layer, and then a Pd-Al2O3 slurry was applied on top of the Rh-Al2O3 layer to form a Pd-Al2O3 layer. As a result, in Comparative Example 2, an exhaust gas purification catalyst was produced in which a Pd-Al2O3 layer was formed on top of the Rh-Al2O3 layer. The conditions were the same as in Comparative Example 1, except that the order of formation of the Rh-Al2O3 layer and the Pd-Al2O3 layer was different.
[0062] (Comparative Example 3) In this example, first, as in Comparative Example 2, an Rh-Al2O3 slurry was applied to the surface of the partition wall to form an Rh-Al2O3 layer. Next, a Pd solution was prepared by adding a thickener (hydroxyethylcellulose) to a palladium nitrate solution (Pd equivalent: 0.5 wt%). Then, this Pd solution was introduced into the cell of the substrate from the gas inlet, and the Pd solution was applied to the Rh-Al2O3 layer by sucking the gas inlet with a blower. After that, a drying treatment was performed at 120°C for 2 hours, followed by a calcination treatment at 500°C for 2 hours to produce the exhaust gas purification catalyst of Comparative Example 3. In the exhaust gas purification catalyst produced, a single catalyst layer (Pd·Rh-Al2O3 layer) containing Rh and Pd was formed (see Figure 7). This is presumed to be because the Pd solution penetrated into the interior of the Rh-Al2O3 layer.
[0063] (Example 1) In this example, a Pd solution was first applied to the surface of the partition wall to form a Pd catalyst layer, and then an Rh-Al2O3 slurry was applied on top of the Pd layer to form an Rh-Al2O3 layer. That is, in Example 1, a Pd catalyst layer was formed by directly supporting Pd particles on the partition wall of a SiC substrate, and an Rh-Al2O3 layer was formed above the Pd catalyst layer. The Pd solution and Rh-containing slurry used in Example 1 were the same as those used in Comparative Example 3.
[0064] <Evaluation Test> (High-temperature durability test) The exhaust system of a V8 gasoline engine placed on a bench was fitted with the exhaust gas purification catalysts of Example 1 and Comparative Examples 1-3, and a 50-hour durability test was conducted at a catalyst bed temperature of 1000°C under conditions including a predetermined fuel cut-off.
[0065] (Evaluation of Pd mobility) The partition walls of the exhaust gas purification catalysts in Example 1 and Comparative Examples 1-3 were cut to a predetermined size before and after the durability test, embedded in resin, and then polished. Carbon was deposited onto the cross-section, and this cross-section was analyzed using the FE-EPMA apparatus "JXA-8530F" (manufactured by JEOL). Pd mapping images before and after the durability test for each example are shown in Figures 5-8.
[0066] Next, based on the Pd mapping image obtained by FE-EPMA described above, the percentage of Pd that moved to the substrate surface (Pd migration rate) was calculated. The procedure for calculating this Pd migration rate is as follows: First, the outermost surface of the partition wall in the EPMA image was defined as position 0, the uppermost surface of the coating layer (Pd layer and Rh layer) formed on the partition wall was defined as position X, and the position 2.5 μm from position 0 toward position X was defined as position Y. The intensity distribution of the Pd element on the 0-X line from position 0 toward position X was measured, and the integrated value a of the Pd element intensity was calculated. Next, the intensity of the Pd element on the 0-X line was corrected so that the integrated value a was set to 100. Next, the intensity distribution of the Pd element on the 0-Y line from position 0 toward position Y was measured, and the integrated value b of the Pd element intensity was calculated. Then, in this test example, the value of "(integrated value b of the sample after durability) - (integrated value b of the sample before durability)" was considered as the Pd migration rate (%). The calculation results are shown in Table 1.
[0067] (Evaluation of temperature characteristics) A catalytic converter for exhaust gas purification was installed in the exhaust system of an engine bench, and the engine combustion state was controlled at the stoichiometric air-fuel ratio. Using a heat exchanger, the temperature of the gas flowing into the catalyst was raised from 200°C to 500°C at a heating rate of 10°C / min. The engine intake air volume was set to 25 g / second. The gas components of the gas flowing into and out of the catalyst during heating were analyzed to calculate the temperature at which 50% of the total hydrocarbons (THC) could be purified (T50-THC), and the temperature characteristics were evaluated. The measurement results are shown in Table 1.
[0068] [Table 1]
[0069] <Evaluation Results> First, as shown in Figures 5 to 7, in all of Comparative Examples 1 to 3, a catalyst disappearance region occurred after the durability test, and migration of Pd from the Pd-Al2O3 layer (or Pd·Rh-Al2O3 layer) to the SiC substrate was confirmed. Furthermore, as shown in Table 1, the Pd migration rate was 12% or more in Comparative Examples 1 to 3. On the other hand, in Example 1, a very thin Pd layer (Pd film) was observed along the auxiliary line showing the surface of the partition wall of the SiC substrate in Figure 8, and some of the Pd had penetrated into the interior of the partition wall of the SiC substrate. Furthermore, as shown in Figure 8 and Table 1, in Example 1, no significant change was observed in the distribution of Pd (Pd film on the partition wall surface and Pd that had penetrated into the interior of the partition wall) even after the durability test. From this, it was found that the migration of Pd can be suppressed by bringing Si alone or a Si member containing SiC (in this case, the partition wall of the SiC substrate) into contact with Pd in advance. Furthermore, as shown in Table 1, in Comparative Examples 1-3, where Pd migration was confirmed, a decrease in temperature characteristics (higher T50-THC temperature) was observed. This is presumed to be because the migration under high-temperature conditions caused the Pd particles to aggregate and coarseen, reducing catalytic activity. On the other hand, in Example 1, where the migration of Pd elements was suppressed, favorable temperature characteristics were maintained even after the durability test.
[0070] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. [Explanation of symbols]
[0071] 1. Catalyst for exhaust gas purification 10 Base material 12 cells 12a Gas inlet 12b Gas outlet 16 Bulkhead 20 Pd catalyst layer 22 Pd particles 24 Si-containing particles 30 Second catalyst layer 40 electrodes 42 Electrode layer 44 Electrode terminal
Claims
1. A substrate preparation step involves preparing a SiC substrate containing SiC, which has partitions separating multiple cells, A catalyst layer formation step is to form a Pd catalyst layer containing at least Pd on the surface of the partition wall of the SiC substrate. Equipped with, In the catalyst layer formation step, the Pd catalyst layer is formed by directly supporting the Pd on the surface of the partition wall of the SiC substrate. The catalyst layer formation step is, A solution preparation step for preparing a Pd solution containing the aforementioned Pd, A solution application step of applying the Pd solution to the surface of the partition wall of the SiC substrate, A firing step in which the Pd solution adhering to the surface of the partition wall is fired. It is equipped with, A method for manufacturing an exhaust gas purification catalyst, wherein the SiC substrate is a straight-flow type substrate in which each of the plurality of cells is provided with a gas inlet for exhaust gas to flow in and a gas outlet for exhaust gas to flow out.
2. A substrate preparation step of preparing a SiC substrate having partitions separating a plurality of cells and containing SiC, A catalyst layer formation step is to form a Pd catalyst layer containing at least Pd on the surface of the partition wall of the SiC substrate. Equipped with, In the catalyst layer formation step, the Pd catalyst layer is formed by directly supporting the Pd on Si-containing particles containing Si alone or SiC. The catalyst layer formation step is, A slurry preparation step involves preparing a Pd-Si slurry by dispersing the Si-containing particles in a Pd solution containing the Pd, A slurry application step of applying the Pd-Si slurry to the surface of the partition wall of the SiC substrate, A firing process for firing the Pd-Si slurry adhering to the surface of the partition wall. It is equipped with, A method for manufacturing an exhaust gas purification catalyst, wherein the SiC substrate is a straight-flow type substrate in which each of the plurality of cells is provided with a gas inlet for exhaust gas to flow in and a gas outlet for exhaust gas to flow out.
3. A method for producing an exhaust gas purification catalyst according to claim 1 or 2, wherein in the catalyst layer formation step, a Pd catalyst layer that substantially does not contain a metal oxide support is formed.
4. The method for producing an exhaust gas purification catalyst according to claim 3, wherein the metal oxide support is a metal oxide particle comprising at least one selected from the group consisting of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, praseodymium oxide, lanthanum oxide, niobium oxide, and yttrium oxide.
5. A SiC substrate containing SiC has partitions separating multiple cells, A Pd catalyst layer containing at least Pd is formed on the surface of the partition wall of the SiC substrate. Equipped with, In the Pd catalyst layer, the Pd is directly supported on the surface of the partition wall of the SiC substrate. The SiC substrate is a straight-flow type substrate in which each of the plurality of cells is provided with a gas inlet for exhaust gas to flow in and a gas outlet for exhaust gas to flow out, thereby providing a catalyst for exhaust gas purification.
6. A SiC substrate having partitions that separate a plurality of cells and containing SiC, A Pd catalyst layer containing at least Pd is formed on the surface of the partition wall of the SiC substrate. Equipped with, In the Pd catalyst layer, the Pd is directly supported on Si-containing particles containing Si alone or SiC. The SiC substrate is a straight-flow type substrate in which each of the plurality of cells is provided with a gas inlet for exhaust gas to flow in and a gas outlet for exhaust gas to flow out. The Pd catalyst layer is a layer in which the Si-containing particles and the Pd are dispersed, in an exhaust gas purification catalyst.
7. The exhaust gas purification catalyst according to claim 5 or 6, wherein the Pd catalyst layer substantially does not contain a metal oxide support.
8. The exhaust gas purification catalyst according to claim 7, wherein the metal oxide support is a metal oxide particle comprising at least one selected from the group consisting of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, praseodymium oxide, lanthanum oxide, niobium oxide, and yttrium oxide.