Electrically heated exhaust gas purification catalyst

Abstract

The object of the present invention is to provide an electrically heated exhaust gas purification catalyst whose exhaust gas purification performance is not easily deteriorated. To achieve this object, the following electrically heated exhaust gas purification catalyst (1) is provided: the catalyst comprises a substrate (10), at least a pair of electrodes (20a, 20b) arranged on the substrate (10), an undercoat layer (30) arranged on the substrate (10) and having aluminum oxide as a main component, and a catalyst layer (40) arranged on the undercoat layer (30) and containing a precious metal element, wherein the undercoat layer (30) contains a Group II element.

Description

Technical Field

[0001] The present invention relates to an electrically heated catalyst for purifying exhaust gas. Background Art

[0002] Electrically heated catalysts (EHCs) are known as exhaust gas purification catalysts installed in the exhaust passage of internal combustion engines. In an EHC, when a voltage is applied between a pair of electrodes provided on a substrate, current flows through the substrate, generating heat due to Joule heating. Therefore, an EHC can increase the temperature of the catalyst layer provided on the substrate before and / or immediately after the internal combustion engine is started, thereby enabling full exhaust gas purification performance immediately after engine startup.

[0003] In the EHC, silicon carbide (SiC), for example, is used as a material constituting a base material (for example, Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-136577 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, conventional EHCs have a problem in that exhaust gas purification performance is easily deteriorated.

[0009] Therefore, an object of the present invention is to provide an electrically heated exhaust gas purification catalyst in which exhaust gas purification performance is less likely to deteriorate.

[0010] Solutions for solving problems

[0011] The present inventors have discovered that when a conventional EHC is exposed to high temperatures (eg, 900° C. or higher, particularly 1000° C. or higher), precious metal elements contained in the catalyst layer migrate toward the substrate, which causes deterioration in exhaust gas purification performance.

[0012] Therefore, the present inventors conducted in-depth research on means for inhibiting the movement of precious metal elements contained in the catalyst layer toward the substrate. As a result, they found that by arranging an undercoat layer with aluminum as the main component and containing Group II elements between the substrate and the catalyst layer, the movement of precious metal elements contained in the catalyst layer toward the substrate can be inhibited, thereby completing the present invention.

[0013] That is, the present invention provides an electrically heated exhaust gas purification catalyst comprising: a substrate; at least a pair of electrodes disposed on the aforementioned substrate; an undercoat layer disposed on the aforementioned substrate and having aluminum as a main component; and a catalyst layer disposed on the aforementioned undercoat layer and containing a precious metal element, wherein the aforementioned undercoat layer contains a Group II element.

[0014] Effects of the Invention

[0015] According to the present invention, it is possible to provide an electrically heated exhaust gas purification catalyst in which exhaust gas purification performance is less likely to deteriorate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a partial cross-sectional view showing a state in which an exhaust gas purification catalyst according to one embodiment of the present invention is arranged in an exhaust passage of an internal combustion engine.

[0017] Figure 2 yes Figure 1 AA line end view.

[0018] Figure 3 yes Figure 2 An enlarged view of the area indicated by symbol R in FIG.

[0019] Figure 4 yes Figure 1 BB line end view.

[0020] Figure 5 This is an end view of a modified example of the exhaust gas purification catalyst according to one embodiment of the present invention (with Figure 4 corresponding end view).

[0021] Figure 6 It is a graph explaining the linear analysis of the primer layer performed in Examples and Comparative Examples.

[0022] Figure 7 This is a diagram illustrating the measurement of the movement distance of the palladium element performed in Examples and Comparative Examples. DETAILED DESCRIPTION

[0023] The following, according to Figures 1 to 4 , an exhaust gas-purifying catalyst 1 according to one embodiment of the present invention will be described. Figure 1 is a partial cross-sectional view showing a state in which the exhaust gas purifying catalyst 1 is arranged in an exhaust passage of an internal combustion engine. Figure 2 yes Figure 1 AA line end view, Figure 3 yes Figure 2 The symbol R in the figure represents an enlarged view of the area. Figure 4 yes Figure 1 BB line end view.

[0024] like Figure 1 and Figure 2 As shown, the exhaust gas purification catalyst 1 is arranged in the exhaust passage in the exhaust pipe P of the internal combustion engine. Examples of the internal combustion engine include gasoline engines in hybrid systems (e.g., hybrid vehicles) equipped with a gasoline engine and an electric motor. Exhaust gas discharged from the internal combustion engine flows through the exhaust passage in the exhaust pipe P from one end to the other end and is purified by the exhaust gas purification catalyst 1 provided in the exhaust pipe P. In the accompanying drawings, the direction of exhaust gas flow is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas inflow side," and the downstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas outflow side."

[0025] In the exhaust passage within the exhaust pipe P, other exhaust gas purifying catalysts may be arranged in addition to the exhaust gas purifying catalyst 1. For example, the exhaust gas purifying catalyst 1 may be arranged upstream of the exhaust passage within the exhaust pipe P, while other exhaust gas purifying catalysts may be arranged downstream of the exhaust passage within the exhaust pipe P. The other exhaust gas purifying catalysts may or may not be electrically heated. Examples of other exhaust gas purifying catalysts include the later-described Modified Example 1' of the exhaust gas purifying catalyst 1.

[0026] like Figure 1 and Figure 2 As shown, an annular insulating member M is provided between the exhaust gas purifying catalyst 1 and the exhaust pipe P to insulate the exhaust gas purifying catalyst 1 from the exhaust pipe P. Examples of the material constituting the insulating member include inorganic materials with low electrical conductivity (such as alumina).

[0027] like Figures 1 to 4 As shown, the exhaust gas-purifying catalyst 1 includes: a substrate 10; a pair of electrodes 20a, 20b provided on the substrate 10; an undercoat layer 30 provided on the substrate 10; and a catalyst layer 40 provided on the undercoat layer 30. It should be noted that the pair of electrodes 20a, 20b and the undercoat layer 30 are both provided on the substrate 10, but the portion of the substrate 10 where the pair of electrodes 20a, 20b are provided is different from the portion where the undercoat layer 30 is provided. In this embodiment, as described later, the pair of electrodes 20a, 20b are provided on the outer peripheral surface of the cylindrical portion 11 of the substrate 10, and the undercoat layer 30 is provided on the partition wall portion 12 of the substrate 10.

[0028] The exhaust gas purification catalyst 1 is an electrically heated exhaust gas purification catalyst. Figure 1As shown, a power source E is electrically connected to the pair of electrodes 20a and 20b via electrode terminals T, cables C, and the like. When a voltage is applied between the pair of electrodes 20a and 20b by the power source E, a current flows through the substrate 10, causing the substrate 10 to release heat due to Joule heat. Therefore, the exhaust gas-purifying catalyst 1 can increase the temperature of the catalyst layer 40 provided on the substrate 10 before and / or immediately after the internal combustion engine is started, thereby enabling full exhaust gas purification performance to be exhibited immediately after the internal combustion engine is started.

[0029] The voltage applied between the pair of electrodes 20a and 20b can be appropriately adjusted according to the resistivity of the substrate 10. The resistivity of the substrate 10 is, for example, 0.001 Ω·cm or more and 10,000 Ω·cm or less.

[0030] like Figures 2 to 4 As shown, the substrate 10 includes a cylindrical portion 11 defining the outer shape of the substrate 10, a partition wall portion 12 provided in the cylindrical portion 11, and cells 13 partitioned by the partition wall portion 12. The substrate 10 is, for example, a honeycomb structure.

[0031] like Figure 2 As shown, the cylindrical portion 11 is cylindrical, but may be in other shapes such as an elliptical cylindrical shape or a polygonal cylindrical shape.

[0032] like Figures 2 to 4 As shown, partition walls 12 exist between adjacent cells 13, and adjacent cells 13 are partitioned by partition walls 12. Partition walls 12 are preferably porous. The thickness of partition walls 12 can be adjusted appropriately, for example, to 40 μm or more and 350 μm or less.

[0033] like Figure 4 As shown, the chamber 13 extends along the exhaust gas flow direction X and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0034] like Figure 4 As shown, both the exhaust gas inlet and outlet ends of chamber 13 are open. Therefore, exhaust gas flowing into chamber 13 from the exhaust gas inlet end (opening) flows out from the exhaust gas outlet end (opening). This configuration is called a through-flow type.

[0035] like Figure 2 and Figure 3 As shown, the end (opening) of chamber 13 on the exhaust gas inlet side is a quadrilateral in plan view, but may be other shapes such as hexagonal or octagonal. The end (opening) of chamber 13 on the exhaust gas outlet side also has the same plan view shape.

[0036] The cell density per square inch of the substrate 10 is, for example, not less than 150 cells and not more than 1500 cells. The cell density per square inch of the substrate 10 is the total number of cells 13 per square inch in a cross section of the substrate 10 obtained by cutting the substrate 10 along a plane perpendicular to the exhaust gas flow direction X.

[0037] The substrate 10 can be appropriately selected from substrates commonly used in electrically heated exhaust gas purifying catalysts, and examples thereof include metal substrates and conductive ceramic substrates. The metal constituting the metal substrate may be a single metal or an alloy.

[0038] From the viewpoint of achieving high heat release and low expansion coefficient, the substrate 10 is preferably a conductive ceramic substrate.

[0039] From the perspective of achieving high heat release and low expansion coefficient, the conductive ceramic substrate preferably contains an inorganic conductor containing silicon as the main component. Based on the mass of the conductive ceramic substrate, the amount of the inorganic conductor containing silicon (when two or more inorganic conductors containing silicon are the main components, the total amount of the two or more inorganic conductors containing silicon) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. It should be noted that the upper limit is theoretically 100% by mass, but considering the presence of unavoidable impurities, it may actually be less than 100% by mass (for example, less than 99% by mass). Unavoidable impurities are, for example, trace elements that are inevitably mixed in when the substrate is manufactured.

[0040] Examples of the inorganic conductor containing silicon include metallic silicon, silicon carbide, and silicides. Examples of silicides include tantalum silicide, chromium silicide, iron silicide, titanium silicide, molybdenum silicide, and tungsten silicide.

[0041] From the perspective of achieving high heat dissipation and a low expansion coefficient, the conductive ceramic substrate preferably contains silicon carbide as the main component, or contains silicon carbide and metallic silicon as the main components. When silicon carbide and metallic silicon are the main components, the amount of metallic silicon is preferably 10% by mass to 40% by mass, more preferably 12.5% ​​by mass to 35% by mass, and even more preferably 15% by mass to 30% by mass, based on the total mass of the silicon carbide and metallic silicon.

[0042] The conductive ceramic substrate may contain one or more components other than the inorganic conductor containing silicon (e.g., insulating ceramic). Examples of components other than the inorganic conductor containing silicon include alumina, zirconia, mullite, zircon, cordierite, aluminum titanate, silicon nitride, boron nitride, and various borosilicates.

[0043] Conductive ceramic substrates primarily composed of an inorganic conductor containing elemental silicon can be produced using conventional methods. For example, a powder of an inorganic conductor containing elemental silicon (e.g., silicon carbide powder, metallic silicon powder, etc.) is mixed with other ingredients (e.g., a binder, a surfactant, a pore-forming material, water, etc.) to prepare a forming material. This forming material is then shaped, dried, and fired to produce the desired conductive ceramic substrate.

[0044] like Figure 1 and Figure 2 As shown, the pair of electrodes 20 a and 20 b are provided on the outer peripheral surface of the cylindrical portion 11 of the substrate 10 so as to face each other with the central axis of the substrate 10 interposed therebetween and so as not to contact each other.

[0045] The electrodes 20a and 20b are, for example, layered in shape. To minimize variations in the current flowing through the substrate 10 (and, consequently, variations in the temperature distribution of the substrate 10), the electrodes 20a and 20b preferably extend along the exhaust gas flow direction X from the end of the cylindrical portion 11 of the substrate 10 on the exhaust gas inlet side, or in the vicinity thereof, to the end of the cylindrical portion 11 of the substrate 10 on the exhaust gas outlet side, or in the vicinity thereof.

[0046] The material constituting the electrodes 20a and 20b can be appropriately selected from commonly used materials, and examples thereof include metals and conductive ceramics. The metal may be a single metal or an alloy. The description of the conductive ceramics is the same as above.

[0047] The substrate 10 only needs to be provided with at least one pair of electrodes. Therefore, two or more pairs of electrodes may be provided on the outer circumferential surface of the cylindrical portion 11 of the substrate 10. For example, the substrate 10 may be provided with a pair of electrodes for dissipating heat from the exhaust gas inlet side of the substrate 10, and a pair of electrodes for dissipating heat from the exhaust gas outlet side of the substrate 10.

[0048] like Figure 4 As shown, the primer layer 30 is provided on the partition wall portion 12 of the substrate 10 .

[0049] like Figure 4 As shown, the undercoat layer 30 extends from the end of the partition wall portion 12 on the exhaust gas inlet side to the end of the partition wall portion 12 on the exhaust gas outlet side along the exhaust gas flow direction X. The undercoat layer 30 may extend from the end of the partition wall portion 12 on the exhaust gas inlet side along the exhaust gas flow direction X without reaching the end of the partition wall portion 12 on the exhaust gas outlet side, or may extend from the end of the partition wall portion 12 on the exhaust gas outlet side in a direction opposite to the exhaust gas flow direction X without reaching the end of the partition wall portion 12 on the exhaust gas inlet side.

[0050] The primer layer 30 contains aluminum as a main component and contains one or more Group 2 elements. It should be noted that the Group 2 elements are elements belonging to Group 2 of the periodic table.

[0051] When conventional EHCs are exposed to high temperatures (e.g., above 900°C, particularly above 1000°C), the precious metal elements contained in the catalyst layer migrate toward the substrate, causing deterioration in exhaust gas purification performance. When the substrate is a conductive ceramic substrate primarily composed of an inorganic conductor containing silicon, the precious metal elements contained in the catalyst layer are more likely to migrate toward the substrate. The present inventors have confirmed that when the substrate is a conductive ceramic substrate primarily composed of an inorganic conductor containing silicon (e.g., a conductive ceramic substrate primarily composed of silicon carbide, or a conductive ceramic substrate primarily composed of silicon carbide and metallic silicon), the precious metal elements contained in the catalyst layer are more likely to migrate toward the substrate, and the silicon elements contained in the substrate are more likely to migrate toward the catalyst layer. Furthermore, when the substrate is a cordierite substrate, the precious metal elements contained in the catalyst layer are less likely to migrate toward the substrate, and the silicon elements contained in the substrate are less likely to migrate toward the catalyst layer. From this, it can be considered that: when the substrate is a conductive ceramic substrate with an inorganic conductor containing silicon as the main component, the silicon contained in the substrate moves toward the catalyst layer, and the precious metal elements contained in the catalyst layer move toward the substrate with the help of the silicon elements moving into the catalyst layer.

[0052] In contrast, the presence of the undercoat layer 30 between the partition wall 12 of the substrate 10 and the catalyst layer 40 can suppress the migration of precious metal elements contained in the catalyst layer 40 toward the substrate 10, thereby suppressing deterioration in exhaust gas purification performance. This effect is also achieved when the undercoat layer, which contains aluminum as a main component and no Group II elements, is located between the partition wall 12 of the substrate 10 and the catalyst layer 40. However, this effect is more effectively achieved when the undercoat layer 30, which contains aluminum as a main component and contains Group II elements, is located between the partition wall 12 of the substrate 10 and the catalyst layer 40.

[0053] When the substrate 10 is a conductive ceramic substrate containing an inorganic conductor containing silicon as a main component, the above-mentioned effect of the undercoat layer 30 is particularly significant. When the substrate 10 is a conductive ceramic substrate containing an inorganic conductor containing silicon as a main component, the above-mentioned effect of the undercoat layer 30 is believed to be exerted through the following mechanism. It is believed that in order for the silicon element contained in the substrate 10 to move toward the catalyst layer 40, it must pass through the undercoat layer 30. However, when the silicon element contained in the substrate 10 passes through the undercoat layer 30, it is chemically reacted with the Group II element and is captured in the undercoat layer 30, thereby suppressing its movement toward the catalyst layer 40. Therefore, it is believed that the movement of the precious metal element contained in the catalyst layer 40 toward the substrate 10 by the silicon element that has moved into the catalyst layer 40 is suppressed.

[0054] The aforementioned effects of the primer layer 30 increase or decrease as the mass of the primer layer 30 per unit volume of the substrate 10 increases or decreases. This is because the effect of the primer layer 30 as a physical barrier increases or decreases as the mass of the primer layer 30 per unit volume of the substrate 10 increases or decreases. Furthermore, the aforementioned effects of the primer layer 30 increase or decrease as the amount of Group II elements contained in the primer layer 30 increases or decreases. This is because the amount of chemical reaction between the Group II elements and silicon (the amount of silicon captured by the reaction with the Group II elements) increases or decreases as the amount of Group II elements contained in the primer layer 30 increases or decreases. The contribution of the increase or decrease in the amount of Group II elements contained in the primer layer 30 to the aforementioned effects of the primer layer 30 is greater than the increase or decrease in the mass of the primer layer 30 per unit volume of the substrate 10. Therefore, if the amount of Group II elements contained in the primer layer 30 is increased, the aforementioned effects of the primer layer 30 can be maintained even if the mass of the primer layer 30 per unit volume of the substrate 10 is reduced. Furthermore, by increasing the amount of the Group II element contained in the undercoat layer 30 and reducing the mass of the undercoat layer 30 per unit volume of the substrate 10, the aforementioned effects of the undercoat layer 30 can be maintained, while the temperature of the catalyst layer 40 can be raised earlier. This is because, by reducing the mass of the undercoat layer 30 per unit volume of the substrate 10, the overall heat capacity of the exhaust gas-purifying catalyst 1 is reduced, which allows the temperature of the catalyst layer 40 to be raised earlier. Furthermore, the increase in the aforementioned effects of the undercoat layer 30 associated with the increase in the amount of the Group II element contained in the undercoat layer 30 can offset the decrease in the aforementioned effects of the undercoat layer 30 associated with the decrease in the mass of the undercoat layer 30 per unit volume of the substrate 10, thereby maintaining the aforementioned effects of the undercoat layer 30.

[0055] From the perspective of more effectively exerting the above-mentioned effects of the primer layer 30, the amount of aluminum element contained in the primer layer 30 is preferably 50 mol% or more, more preferably 55 mol% or more, and even more preferably 60 mol% or more, based on the total molar amount of all metal elements contained in the primer layer 30. The upper limit is the value obtained by subtracting the molar percentage of the Group II element contained in the primer layer 30 from 100 mol%, and is, for example, 99 mol%, 97 mol%, or 95 mol%.

[0056] In the case where the raw material composition for forming the undercoat layer 30 is known, the amount of the aluminum element contained in the undercoat layer 30 can be calculated from the raw material composition for forming the undercoat layer 30 .

[0057] The amount of aluminum contained in the undercoat layer 30 can be measured using conventional methods such as scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), X-ray fluorescence analysis (XRF), and inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, the amount can be determined as follows.

[0058] First, a test piece cut from the exhaust gas-purifying catalyst 1 is pulverized and then analyzed using XRF or ICP-AES to identify 20 metal elements with the highest content, ranked from most to least. Aluminum is included in these 20 identified metal elements. As long as the test piece includes a portion derived from the undercoat layer 30, it may also include a portion derived from the substrate 10 and / or a portion derived from the catalyst layer 40. If the test piece includes a portion derived from the substrate 10 and / or a portion derived from the catalyst layer 40, the 20 identified metal elements may include metal elements that constitute the substrate 10 and / or metal elements that constitute the catalyst layer.

[0059] Next, the undercoat layer 30 was analyzed using SEM-EDX. In SEM-EDX, the 20 metal elements identified above were analyzed, and the mol % of each metal element was analyzed for each of the 10 fields of view on the SEM, with the total mol % of the 20 metal elements being set to 100 mol %. The average mol % of aluminum in the 10 fields of view was taken as the amount of aluminum contained in the undercoat layer 30.

[0060] It should be noted that the amount of other metal elements (such as Group II elements, cerium, zirconium, noble metal elements, etc.) contained in the primer layer 30 can also be calculated or measured in the same manner as the amount of aluminum contained in the primer layer 30 .

[0061] From the viewpoint of more effectively exhibiting the above-mentioned effects of the primer layer 30 , the Group II element contained in the primer layer 30 is preferably selected from magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and more preferably magnesium.

[0062] From the viewpoint of more effectively exerting the above-mentioned effects of the primer layer 30, the amount of the Group II element contained in the primer layer 30 (when the primer layer 30 contains two or more Group II elements, it is the total amount of the two or more Group II elements) is preferably 1 mol% or more and 40 mol% or less, more preferably 3 mol% or more and 35 mol% or less, and even more preferably 5 mol% or more and 30 mol% or less, based on the total molar amount of all metal elements contained in the primer layer 30.

[0063] From the viewpoint of more effectively exerting the above-mentioned effects of the primer layer 30, the total amount of aluminum elements and Group II elements contained in the primer layer 30 is preferably 85 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, further preferably 95 mol% or more and 100 mol% or less, and further preferably 97 mol% or more and 100 mol% or less, based on the total molar amount of all metal elements contained in the primer layer 30.

[0064] A portion or all of the aluminum contained in the undercoat layer 30 may form aluminum oxide (alumina), or may be complexed with a portion or all of the Group II elements contained in the undercoat layer 30. Alternatively, a portion of the aluminum contained in the undercoat layer 30 may form aluminum oxide, and the remaining aluminum contained in the undercoat layer 30 may be complexed with a portion or all of the Group II elements contained in the undercoat layer 30. Aluminum oxide may form a single phase (aluminum oxide phase) exhibiting a crystalline phase or an amorphous phase. Examples of the aluminum oxide phase include an α-aluminum oxide phase and aluminum oxide phases other than the α-aluminum oxide phase (e.g., a γ-aluminum oxide phase, a θ-aluminum oxide phase, etc.).

[0065] A portion or all of the Group II elements contained in the primer layer 30 may form oxides (e.g., magnesium oxide, calcium oxide, strontium oxide, barium oxide, etc.), or may be complexed with a portion or all of the aluminum element contained in the primer layer 30. Alternatively, a portion of the Group II elements contained in the primer layer 30 may form oxides, and the remaining Group II elements contained in the primer layer 30 may be complexed with a portion or all of the aluminum element contained in the primer layer 30. The oxides of the Group II elements may form a single phase (the oxide phase of the Group II element) exhibiting a crystalline phase or an amorphous phase.

[0066] The compound formed by combining aluminum and a Group II element preferably comprises a composite oxide of aluminum and a Group II element. Examples of composite oxides comprising aluminum and a Group II element include oxides obtained by modifying the surface of aluminum oxide with a Group II element and oxides obtained by dissolving a Group II element in aluminum oxide.

[0067] The composite oxide containing aluminum and a Group II element may contain elements other than aluminum, a Group II element, and oxygen. Examples of elements other than aluminum, a Group II element, and oxygen include Zr, Hf, and rare earth elements (e.g., Y, La, Ce, Pr, and Nd).

[0068] In a composite oxide containing aluminum and a Group II element, the aluminum element may form a solid solution phase together with the Group II element and oxygen, or may form a single phase presenting a crystalline phase or an amorphous phase (e.g., an aluminum oxide phase), or may form both a solid solution phase and a single phase. Similarly, the Group II element may form a solid solution phase together with the aluminum element and oxygen, or may form a single phase presenting a crystalline phase or an amorphous phase (e.g., an oxide phase of the Group II element), or may form both a solid solution phase and a single phase. The formation of the solid solution phase may be confirmed using an X-ray diffraction apparatus (XRD).

[0069] When part or all of the aluminum elements contained in the undercoat layer 30 are compounded with part or all of the second group elements contained in the undercoat layer 30, the second group element is preferably magnesium from the viewpoint of more effectively exerting the above-mentioned effects of the undercoat layer 30 (especially the effect of inhibiting the movement of Pd contained in the catalyst layer 40 toward the substrate 10).

[0070] The compound formed by the composite of aluminum and a Group II element is preferably a composite oxide containing aluminum and a Group II element. The composite oxide containing aluminum and a Group II element has a spinel-type crystal structure. That is, the composite oxide containing aluminum and a Group II element contains a crystalline phase having a spinel-type crystal structure (hereinafter referred to as "spinel-type crystalline phase"). The spinel-type crystal structure is a crystal structure of a cubic system belonging to the space group Fd-3m.

[0071] The composite oxide comprising aluminum and a Group II element can be composed of a single phase of a spinel type crystalline phase, or can be composed of a mixed phase comprising a spinel type crystalline phase and comprising one or more other phases, preferably composed of a single phase of a spinel type crystalline phase. Other phases can be crystalline phases or amorphous phases. As other phases, for example, oxide phases (such as MgO phases) of Group II elements, α-alumina phases, alumina phases (such as γ-alumina phases, θ-alumina phases, etc.) other than the α-alumina phase, and hydrotalcite phases can be listed.

[0072] In the case where the composite oxide containing aluminum and the second group elements is composed of a mixed phase, the spinel-type crystalline phase is preferably the first phase. In addition, in the case where the α-alumina phase is the first phase, the spinel-type crystalline phase is preferably the second phase. "First phase" refers to: in the diffraction pattern obtained by using the powder X-ray diffraction method (XRD) using CuKα, the crystalline phase from which the peak (main peak) with the maximum intensity originates. "Second phase" refers to: in addition to the peak derived from the first phase, the crystalline phase from which the peak with the maximum intensity originates.

[0073] The presence of a spinel-type crystalline phase in a composite oxide containing aluminum and a Group II element can be confirmed by XRD using CuKα. XRD can be performed using a commercially available X-ray diffraction apparatus (e.g., Mini Flex600 manufactured by Rigaku Corporation). XRD can be performed under conditions such as an X-ray source: CuKα, an operating axis: 2θ / θ, a measurement method: continuous, a counting unit: cps, a starting angle: 5°, an ending angle: 85°, a sampling width: 0.02°, a scanning speed: 7° / min, a voltage: 15 kV, and a current: 100 mA.

[0074] In the diffraction pattern obtained by XRD using CuKα, the peak derived from the spinel-type crystalline phase exists at positions such as 2θ=15° to 25° (e.g., 19.0°±0.5°), 30° to 40° (e.g., 37.0°±0.5°), 40° to 50° (e.g., 45.0°±0.5°), and 55° to 70° (e.g., 65.5°±0.5°). The peak derived from the spinel-type crystalline phase preferably exists at a position of 2θ=37.0±0.5°.

[0075] By confirming that the composite oxide containing aluminum and the Group II element contains a spinel crystal phase, it can be confirmed that the aluminum element and the Group II element are composited.

[0076] A supply source of the Group II element (eg, acetate of the Group II element) contained in the slurry for forming the undercoat layer may remain in the undercoat layer 30 .

[0077] To more effectively exhibit the aforementioned effects of the undercoat layer 30, the Group II elements are preferably uniformly present in the undercoat layer 30. Specifically, when linear analysis of the undercoat layer 30 is performed using an electron beam microanalyzer and the correlation coefficient is determined according to the following formula, the positions of the Group II elements and the positions of the aluminum elements preferably coincide with each other at a correlation coefficient of 50% or greater, more preferably at a correlation coefficient of 60% or greater, even more preferably at a correlation coefficient of 70% or greater, and even more preferably at a correlation coefficient of 80% or greater. This indicates that when the positions of the Group II elements and the positions of the aluminum elements coincide with each other at a correlation coefficient of 50% or greater, the Group II elements are uniformly present in the undercoat layer 30.

[0078] [Mathematical formula 1]

[0079]

[0080] [Where x i represents the characteristic X-ray intensity of the second group element at position i, x av represents the average value of the characteristic X-ray intensity of the second group elements, y i represents the characteristic X-ray intensity of aluminum element at position i, y av Indicates the average value of the characteristic X-ray intensity of aluminum.]

[0081] The undercoat layer 30 preferably does not substantially contain the following substances: a composite oxide containing cerium (Ce) and zirconium (Zr) elements (CeO2-ZrO2 composite oxide). Since the CeO2-ZrO2 composite oxide is a component that may be contained in the catalyst layer 40, it is not necessary for the undercoat layer 30 to substantially contain the composite oxide. By substantially not containing the CeO2-ZrO2 composite oxide, the amount of aluminum element and / or Group II element contained in the undercoat layer 30 can be increased. When the undercoat layer 30 does not substantially contain the CeO2-ZrO2 composite oxide, the total amount of cerium element and zirconium element contained in the undercoat layer 30 is preferably 5 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less, based on the total molar amount of all metal elements contained in the undercoat layer 30. The lower limit is zero. It should be noted that the details of the CeO2-ZrO2 composite oxide are described later.

[0082] The undercoat layer 30 preferably does not contain substantially any precious metal elements. Since the precious metal elements are components contained in the catalyst layer 40, it is not necessary for the undercoat layer 30 to substantially contain precious metal elements. By substantially not containing precious metal elements, the amount of aluminum elements and / or Group II elements contained in the undercoat layer 30 can be increased. When the undercoat layer 30 does not contain substantially any precious metal elements, the amount of precious metal elements contained in the undercoat layer 30 (when the undercoat layer 30 contains two or more precious metal elements, it is the total amount of two or more precious metal elements) is preferably 3 mol% or less, more preferably 1 mol% or less, and even more preferably 0.5 mol% or less. The lower limit is zero. It should be noted that the details of the precious metal elements are described later.

[0083] From the perspective of more effectively exerting the aforementioned effects of the undercoat layer 30, the mass of the undercoat layer 30 per unit volume of the substrate 10 is preferably 10 g / L or more, more preferably 20 g / L or more, and even more preferably 30 g / L or more. Furthermore, from the perspective of accelerating the temperature rise of the catalyst layer 40, the mass is preferably 80 g / L or less, more preferably 60 g / L or less, and even more preferably 50 g / L or less.

[0084] like Figure 4 As shown, the catalyst layer 40 is disposed on the undercoat layer 30 .

[0085] like Figure 4 As shown, the catalyst layer 40 extends from the end of the partition wall portion 12 on the exhaust gas inlet side to the end of the partition wall portion 12 on the exhaust gas outlet side along the exhaust gas flow direction X. The catalyst layer 40 may extend from the end of the partition wall portion 12 on the exhaust gas inlet side along the exhaust gas flow direction X without reaching the end of the partition wall portion 12 on the exhaust gas outlet side, or may extend from the end of the partition wall portion 12 on the exhaust gas outlet side in a direction opposite to the exhaust gas flow direction X without reaching the end of the partition wall portion 12 on the exhaust gas inlet side.

[0086] The catalyst layer 40 contains one or more precious metal elements. The precious metal elements can be selected from, for example, platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os). From the perspective of improving exhaust gas purification performance, platinum (Pt), palladium (Pd), and rhodium (Rh) are preferably selected. In one embodiment, the precious metal element contained in the catalyst layer 40 is palladium.

[0087] The precious metal element is contained in the catalyst layer 40 in a form capable of functioning as a catalytically active component, such as a precious metal, an alloy containing the precious metal element, or a compound containing the precious metal element (e.g., an oxide of the precious metal element). From the perspective of improving exhaust gas purification performance, the catalytically active component is preferably in a particulate form.

[0088] From the perspective of balancing exhaust gas purification performance and cost, the mass of the catalyst layer 40 per unit volume of the substrate 10 is preferably 40 g / L to 250 g / L, more preferably 40 g / L to 210 g / L.

[0089] From the perspective of achieving a balance between exhaust gas purification performance and early heating of the catalyst layer 40, the total mass of the undercoat layer 30 and the catalyst layer 40 per unit volume of the substrate 10 is preferably greater than 50 g / L and less than 330 g / L, more preferably greater than 50 g / L and less than 290 g / L, and even more preferably greater than 50 g / L and less than 250 g / L.

[0090] The total mass of the undercoat layer 30 and the catalyst layer 40 per unit volume of the substrate 10 can be calculated as follows. Measure the volume and mass of the exhaust gas-purifying catalyst 1. Prepare a substrate 10 without the undercoat layer 30 and the catalyst layer 40, and measure its mass. Subtract the mass of the substrate 10 from the mass of the exhaust gas-purifying catalyst 1 to calculate the total mass of the undercoat layer 30 and the catalyst layer 40 in the exhaust gas-purifying catalyst 1. Divide the total mass of the undercoat layer 30 and the catalyst layer 40 in the exhaust gas-purifying catalyst 1 by the volume of the exhaust gas-purifying catalyst 1 to calculate the total mass of the undercoat layer 30 and the catalyst layer 40 per unit volume of the substrate 10.

[0091] From the perspective of the balance between exhaust gas purification performance and cost, the amount of precious metal elements per unit volume of the substrate 10 (when the catalyst layer 40 contains more than two precious metal elements, it is the total amount of more than two precious metal elements) is preferably greater than 0.1 g / L and less than 10 g / L, and more preferably greater than 0.1 g / L and less than 5 g / L, in terms of precious metal conversion.

[0092] The catalyst layer 40 preferably includes a carrier, and the catalytically active component is supported on the carrier.

[0093] "The catalytically active component is supported on the support" means that the catalytically active component is physically or chemically adsorbed or retained on the outer surface or inner surface of the pores of the support. For example, if the catalytically active component and the support are present in the same region in elemental mapping obtained by analyzing a cross-section of the catalyst layer using an energy dispersive spectrometer (EDS), it can be determined that the catalytically active component is supported on the support. Furthermore, particle size measurement using a scanning electron microscope (SEM) can confirm that the catalytically active component is supported on the support.

[0094] The average particle size of the catalytically active component present on the surface of the support is preferably 10% or less, more preferably 3% or less, and even more preferably 1% or less of the average particle size of the support. The average particle size referred to herein is the average of the Feret diameters of 30 or more particles observed using a SEM.

[0095] Examples of the support include inorganic oxide particles, etc. The inorganic oxide constituting the inorganic oxide particles may be an inorganic oxide having oxygen storage capacity (OSC) (hereinafter sometimes referred to as "oxygen storage component") or an inorganic oxide other than an oxygen storage component.

[0096] Examples of the oxygen storage component include cerium oxide and composite oxides containing cerium and zirconium (CeO 2 -ZrO 2 composite oxides).

[0097] In the CeO2-ZrO2 composite oxide, it is preferred that cerium oxide and zirconium oxide form a solid solution phase. Cerium oxide and zirconium oxide may form a single phase (cerium oxide phase, zirconium oxide phase) in addition to forming a solid solution phase.

[0098] The CeO2-ZrO2 composite oxide may contain one or more metal elements other than cerium and zirconium. The metal elements other than cerium and zirconium or their oxides may form a solid solution phase with cerium oxide and / or zirconium oxide, or may form a single phase. Examples of the metal elements other than cerium and zirconium include rare earth elements other than cerium, alkaline earth metals, and transition metals.

[0099] Examples of the inorganic oxide other than the oxygen storage component include alumina, silica, silica-alumina, alumina-silicate, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-lanthanum oxide, and titania.

[0100] The exhaust gas-purifying catalyst 1 can be produced by forming the undercoat layer 30 on the substrate 10 and then forming the catalyst layer 40 on the undercoat layer 30 .

[0101] The primer layer 30 can be formed by mixing a source of aluminum element (e.g., aluminum oxide powder), a source of Group II element (e.g., acetates, oxides, etc. of Group II element) with other components (e.g., binders, solvents, etc.) to prepare a primer layer forming slurry, and applying the primer layer forming slurry on the substrate 10, drying, and baking. The source of Group II element does not need to be a compound different from the source of aluminum element, and can be a compound that is the same as the source of aluminum element. For example, as the source of aluminum element and the source of Group II element, a composite oxide powder containing aluminum element and Group II element can be used. As the binder, metal oxide sols such as aluminum oxide hydrate sol (e.g., boehmite sol), titanium oxide sol, cerium oxide sol, and zirconium oxide sol can be listed. It should be noted that the aluminum oxide sol such as aluminum oxide hydrate sol used as the binder becomes the source of aluminum element contained in the primer layer 30. As the solvent, water, organic solvent, etc. can be listed. The drying temperature is, for example, 60°C to 120°C, and the drying time is, for example, 0.5 to 2 hours. The calcination temperature is, for example, 400°C to 700°C, and the calcination time is, for example, 0.5 to 3 hours. Calcination can be performed, for example, in air.

[0102] From the viewpoint of suppressing the migration of silicon elements contained in the substrate toward the catalyst layer, the median particle size D of the alumina powder is 50 and the median particle size D of the composite oxide powder containing aluminum and Group II elements50 The median particle size D of the alumina powder is preferably 0.1 μm or more and 15 μm or less, more preferably 0.3 μm or more and 12 μm or less, and still more preferably 0.5 μm or more and 10 μm or less. 50 The particle size distribution of the aluminum oxide powder measured by laser diffraction scattering particle size distribution measurement method is the particle size at which the cumulative volume reaches 50%. The median particle size D of the composite oxide powder containing aluminum and Group II elements is the particle size distribution of the aluminum oxide powder measured by laser diffraction scattering particle size distribution measurement method. 50 It refers to the particle diameter at which the cumulative volume reaches 50% in the volume-based particle size distribution of the composite oxide powder measured by laser diffraction scattering particle size distribution measurement.

[0103] Median particle size D of alumina powder 50 and the median particle size D of the composite oxide powder containing aluminum and Group II elements 50 The amount can be adjusted by, for example, pulverization using a jet mill, a ball mill, a bead mill, or the like, or classification using a sieve of a predetermined mesh size.

[0104] From the viewpoint of suppressing the migration of silicon contained in the substrate toward the catalyst layer, the alumina powder and the composite oxide powder containing aluminum and a Group II element are preferably porous. The specific surface area of ​​the alumina powder and the specific surface area of ​​the composite oxide powder containing aluminum and a Group II element are preferably 50 m 2 / g and above and 300m 2 / g or less, more preferably 80m 2 / g and above and 200m 2 The specific surface area is measured in accordance with "(3.5) Single-point method" in "6.2 Flow method" of JIS R1626 "Determination of specific surface area of ​​fine ceramic powder by gas adsorption BET method".

[0105] The catalyst layer 40 can be prepared by mixing a supply source of precious metal elements (such as precious metal salts, etc.) with other components (such as carriers, binders, solvents, etc.) to prepare a catalyst layer forming slurry, applying the catalyst layer forming slurry on the primer layer 30, drying and baking to form. As a binder, metal oxide sols such as titanium oxide sol, cerium oxide sol, zirconium oxide sol, etc. can be listed. As a solvent, water, organic solvents, etc. can be listed. The drying temperature is, for example, 60°C or more and 120°C or less, and the drying time is, for example, 0.5 hours or more and 2 hours or less. The baking temperature is, for example, 400°C or more and 700°C or less, and the baking time is, for example, 0.5 hours or more and 3 hours or less. Baking can be carried out, for example, in an atmospheric atmosphere.

[0106] The following, according to Figure 5, a modification 1' of the exhaust gas-purifying catalyst 1 will be described. Figure 5 This is an end view of a modified example 1' of the exhaust gas purifying catalyst 1 (with Figure 4 (corresponding end view). In the modified example 1' of the exhaust gas-purifying catalyst 1, the same components as those of the exhaust gas-purifying catalyst 1 are denoted by the same reference numerals as those of the exhaust gas-purifying catalyst 1. Hereinafter, except where otherwise noted, the above description relating to the exhaust gas-purifying catalyst 1 also applies to the modified example 1' of the exhaust gas-purifying catalyst 1.

[0107] like Figure 5 As shown, the modified example 1' of the exhaust gas-purifying catalyst 1 is different from the exhaust gas-purifying catalyst 1 in the following points:

[0108] The substrate 10 is provided with a first sealing portion 14 that seals the end portion of the exhaust gas outflow side of a portion of the chamber 13 and a second sealing portion 15 that seals the end portion of the exhaust gas inflow side of the remaining chamber 13. Thus, the substrate 10 is provided with: an inflow side chamber 13a whose end portion on the exhaust gas inflow side is open and whose end portion on the exhaust gas outflow side is blocked by the first sealing portion 14; and an outflow side chamber 13b whose end portion on the exhaust gas inflow side is blocked by the second sealing portion 15 and whose end portion on the exhaust gas outflow side is open, and

[0109] An undercoat layer 30a is provided on the inlet chamber 13a side of the partition wall portion 12 of the substrate 10, and a catalyst layer 40a is provided on the undercoat layer 30a. An undercoat layer 30b is provided on the outlet chamber 13b side of the partition wall portion 12 of the substrate 10, and a catalyst layer 40b is provided on the undercoat layer 30b.

[0110] like Figure 5 As shown, a plurality of (eg, four) outflow chambers 13b are adjacently arranged around one inflow chamber 13a, and the inflow chamber 13a and the outflow chamber 13b adjacent to the inflow chamber 13a are separated by a porous partition wall 12.

[0111] In the exhaust gas purifying catalyst 1', exhaust gas flowing in from the exhaust gas inlet-side end (opening) of the inlet-side chamber 13a passes through the porous partition wall 12 and flows out from the exhaust gas outflow-side end (opening) of the outflow-side chamber 13b. This configuration is called a wall flow type.

[0112] In the exhaust gas-purifying catalyst 1', exhaust gas flowing in from the exhaust gas inlet-side end (opening) of the inlet-side chamber 13a passes through the porous partition wall 12. Particulate matter (PM) in the exhaust gas is trapped within the pores of the partition wall 12. Therefore, the exhaust gas-purifying catalyst 1' is useful as a gasoline particulate filter or a diesel particulate filter in hybrid vehicles.

[0113] like Figure 5 As shown, the undercoat layer 30a and the catalyst layer 40a extend from the end of the partition wall portion 12 on the exhaust gas inlet side in the exhaust gas flow direction X, without reaching the end of the partition wall portion 12 on the exhaust gas outlet side. Alternatively, the undercoat layer 30a and the catalyst layer 40a may reach the end of the partition wall portion 12 on the exhaust gas outlet side. The undercoat layer 30b and the catalyst layer 40b extend from the end of the partition wall portion 12 on the exhaust gas outlet side in a direction opposite to the exhaust gas flow direction X, without reaching the end of the partition wall portion 12 on the exhaust gas inlet side. Alternatively, the undercoat layer 30b and the catalyst layer 40b may reach the end of the partition wall portion 12 on the exhaust gas inlet side.

[0114] The above description regarding the primer layer 30 also applies to the primer layers 30a and 30b. The compositions and the like of the primer layers 30a and 30b may be the same or different.

[0115] The above description regarding the catalyst layer 40 also applies to the catalyst layers 40a and 40b. The compositions and the like of the catalyst layers 40a and 40b may be the same or different.

[0116] Example

[0117] <Examples 1 to 8>

[0118] Alumina (Puralox SCFa-160 manufactured by Sasol) was pulverized with a ball mill to prepare a median particle size D 50 The surface area is 7-10 μm and the BET specific surface area is 160 m 2 / g of alumina powder. It should be noted that the median particle size D of the alumina powder 50 It refers to the particle size at which the cumulative volume reaches 50% in the volume-based particle size distribution of the aluminum oxide powder measured by laser diffraction scattering particle size distribution measurement.

[0119] Alumina powder, acetates or oxides of the Group II elements listed in Table 1, boehmite sol as a binder, and water were mixed to prepare a slurry for forming an undercoat layer. The amounts of aluminum and Group II elements in the slurry were adjusted to the amounts shown in Table 1, based on the total molar amount of all metal elements contained in the undercoat layer. The amounts of aluminum and Group II elements are calculated on a metal-equivalent basis.

[0120] Palladium nitrate and lanthanum oxide modified alumina (La2O3 modification amount: 5.0 mass%, BET specific surface area: 100m 2 / g), CeO2-ZrO2-based composite oxide, and water were mixed to prepare a catalyst layer-forming slurry. The component amounts in the catalyst layer-forming slurry were adjusted so that the ratio of palladium element mass in the calcined catalyst layer: lanthanum oxide-modified alumina mass: CeO2-ZrO2-based composite oxide mass was 1:10:10. It should be noted that the palladium element mass is the mass calculated on a metal-converted basis.

[0121] As a substrate, a Si / SiC honeycomb structure (diameter: 25.4 mm, length: 30 mm, cell density: 600 cells, partition wall thickness: 127 μm) was prepared. The Si / SiC honeycomb structure was composed of silicon carbide and metallic silicon.

[0122] The substrate was immersed in a slurry for forming a primer layer, the remaining slurry in the chamber was removed by blowing air, and after drying, it was calcined at 450°C in an atmospheric atmosphere for 1 hour to form a primer layer having a mass per unit volume of 40 g / L (Examples 1 and 4 to 8), 20 g / L (Example 2), or 60 g / L (Example 3).

[0123] The substrate with the undercoat layer was immersed in a slurry for forming a catalyst layer. The remaining slurry in the chamber was removed by blowing air. After drying, the substrate was calcined at 450°C for 1 hour in an air atmosphere to form a catalyst layer with a mass per unit volume of 95 g / L.

[0124] The catalyst produced in this manner was subjected to linear analysis of the undercoat layer using an electron beam microanalyzer (JXA-8800R, manufactured by JEOL Ltd.), and the correlation coefficient was calculated using the following formula. If the position of the Group II element and the position of the aluminum element agree with each other at a correlation coefficient of 50% or greater, it can be said that the Group II element is uniformly present in the undercoat layer. The results are shown in Table 1.

[0125] [Mathematical formula 2]

[0126]

[0127] [Where x irepresents the characteristic X-ray intensity of the second group element at position i, x av represents the average value of the characteristic X-ray intensity of the second group elements, y i represents the characteristic X-ray intensity of aluminum element at position i, y av Indicates the average value of the characteristic X-ray intensity of aluminum.]

[0128] For the catalyst that was not subjected to the heat treatment described later, the undercoat layer was subjected to linear analysis using an electron beam microanalyzer. Figure 2 and Figure 3 As shown, the catalyst 1 produced was cut using a plane perpendicular to the axial direction of the substrate 10, and an area A1 selected from the cut surface was analyzed using an electron beam microanalyzer (JXA-8800R manufactured by JEOL Ltd.) (magnification: 1000 times, acceleration voltage: 15 kV) to obtain an elemental mapping image. Figure 6 As shown, the primer layer 30 is analyzed at 400 points (measurement positions N1, N2, N3, ..., N398, N399, N400) at intervals of 0.5 μm in a direction perpendicular to the thickness direction Z of the primer layer 30, and the spectral intensity values ​​of the second group elements of the second group element particles i at each measurement position and the spectral intensity values ​​of the aluminum element at each measurement position are measured to perform the above-mentioned calculations.

[0129] The catalyst prepared in the same manner as above was heated at 1050° C. for 25 hours in air at a relative humidity of 10%.

[0130] The movement distance of the palladium element was measured for the heated catalyst. Specifically, Figure 2 and Figure 3 As shown, the heated catalyst 1 was cut using a plane perpendicular to the axial direction of the substrate 10, and an electron beam microanalyzer (JXA-8800R manufactured by JEOL Ltd.) was used to analyze an area A2 selected from the cut surface (magnification: 500 times, acceleration voltage: 15 kV) to obtain an elemental mapping image. Another area A3 selected from the cut surface was also analyzed in the same manner to obtain an elemental mapping image. Figure 7 As shown, in each element mapping image, the boundary line L1 between the region 41 where the palladium element exists and the region 42 where the palladium element does not exist in the catalyst layer 40, and the boundary line L2 between the catalyst layer 40 and the undercoat layer 30 are confirmed. Figure 7As shown, in each elemental mapping image, 20 grid lines G1 to G20 are drawn at 12 μm intervals, parallel to the thickness direction Z of the catalyst layer 40 and the undercoat layer 30. The distances between the intersections of each of the 40 grid lines with the boundary line L1 and the intersections with the boundary line L2 are measured, and the average value is defined as the "palladium element movement distance." The smaller the palladium element movement distance, the more its movement is suppressed. The results are shown in Table 1.

[0131] <Example 9>

[0132] A composite oxide containing magnesium (Mg) and aluminum (Al) was prepared. XRD using CuKα confirmed that the prepared composite oxide contained a spinel crystal phase. The XRD conditions were the same as those described above.

[0133] The prepared composite oxide was calcined at 900° C. in air atmosphere for 3 hours and then pulverized using a ball mill to prepare a composite oxide having a median particle size D 50 The surface area is 7-10 μm and the BET specific surface area is 160 m 2 / g of composite oxide powder. It should be noted that the median particle size D of the composite oxide powder 50 It refers to the particle size at which the cumulative volume reaches 50% in the volume-based particle size distribution of the composite oxide powder measured by laser diffraction scattering particle size distribution measurement.

[0134] The composite oxide powder, boehmite sol as a binder, and water were mixed to prepare a slurry for forming an undercoat layer. The amounts of aluminum and Group II elements in the slurry were adjusted based on the total molar amount of all metal elements contained in the undercoat layer so that the amounts of aluminum and Group II elements in the undercoat layer after calcination reached the amounts shown in Table 1. The amounts of aluminum and Group II elements are calculated on a metal-equivalent basis.

[0135] The catalyst was produced and evaluated in the same manner as in Example 1 except that the above-mentioned slurry for forming a primer layer was used as the slurry for forming a primer layer.

[0136] <Comparative Example 1>

[0137] The catalyst was produced and evaluated in the same manner as in Example 1, except that the primer layer was not formed. The results are shown in Table 1. It should be noted that in Comparative Example 1, instead of the boundary line L2, a boundary line L3 (not shown) between the partition wall portion 12 of the substrate 10 and the catalyst layer 40 was determined. The distances between the intersections of the 40 grid lines with the boundary line L1 and the intersections with the boundary line L3 were measured, and the average value of these distances was defined as the "movement distance of the palladium element."

[0138] <Comparative Example 2>

[0139] The catalyst was produced and evaluated in the same manner as in Example 1, except that the undercoat layer did not contain a Group II element.

[0140] [Table 1]

[0141]

[0142] The results shown in Table 1 indicate that the presence of an undercoat layer containing aluminum as a main component and a Group II element between the substrate and the catalyst layer suppresses the migration of the precious metal elements contained in the catalyst layer toward the substrate, thereby suppressing deterioration in exhaust gas purification performance.

[0143] Description of Reference Numerals

[0144] 1…Electrically heated exhaust gas purification catalyst

[0145] 10…base material

[0146] 20a, 20b…electrodes

[0147] 30…base coat

[0148] 40…catalyst layer

Claims

1. An electrically heated exhaust gas purification catalyst comprising: substrate; at least one pair of electrodes disposed on the substrate; a primer layer disposed on the substrate and containing aluminum as a main component; and a catalyst layer disposed on the undercoat layer and comprising a noble metal element, The primer layer contains a Group II element, The substrate is a conductive ceramic substrate having an inorganic conductor containing silicon as a main component. The amount of the Group II element contained in the undercoat layer is 1 mol % or more and 40 mol % or less based on the total molar amount of all metal elements contained in the undercoat layer.

2. The exhaust gas purification catalyst according to claim 1, wherein The amount of aluminum element contained in the undercoat layer is 50 mol % or more based on the total molar amount of all metal elements contained in the undercoat layer.

3. The exhaust gas purification catalyst according to claim 1 or 2, wherein The total amount of aluminum element and Group II element contained in the undercoat layer is 85 mol % or more and 100 mol % or less based on the total molar amount of all metal elements contained in the undercoat layer.

4. The exhaust gas purification catalyst according to claim 1 or 2, wherein The aluminum element contained in the primer layer is composited with the second group element contained in the primer layer.

5. The exhaust gas purification catalyst according to claim 1 or 2, wherein The second group element contained in the undercoat layer is selected from magnesium, calcium, strontium and barium.

6. The exhaust gas purification catalyst according to claim 5, wherein The second group element contained in the undercoat layer is magnesium.

7. The exhaust gas purification catalyst according to claim 1 or 2, wherein The noble metal element contained in the catalyst layer is palladium.

8. The exhaust gas purification catalyst according to claim 1 or 2, wherein When the linear analysis of the primer layer is performed using an electron beam microanalyzer and the correlation coefficient is determined according to the following formula, the position of the Group II element and the position of the aluminum element agree with each other at a correlation coefficient of 50% or more. Where x i represents the characteristic X-ray intensity of the second group element at position i, x av represents the average value of the characteristic X-ray intensity of the second group elements, y i represents the characteristic X-ray intensity of aluminum element at position i, y av Represents the average value of the characteristic X-ray intensity of aluminum.

9. The exhaust gas purification catalyst according to claim 1 or 2, wherein The undercoat layer does not substantially contain a composite oxide containing cerium and zirconium.

10. The exhaust gas purification catalyst according to claim 1 or 2, wherein The undercoat layer contains substantially no precious metal elements.

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