Exhaust gas control catalyst

Abstract

Exhaust gas control catalyst (2; 3), comprising: a substrate (21; 31); and a first catalyst layer (22; 32) arranged on the substrate (21; 31), characterized by the fact that the first catalyst layer (22; 32) comprises: a palladium region (23; 33) containing palladium, aluminium oxide, a cerium oxide-zirconium oxide mixed crystal and a LaFeO3-La2Zr2O 7- ZrO2 composite oxide, and a rhodium region (24; 34) which is adjacent to the palladium region (23; 33) along a plane direction of the first catalyst layer (22; 32) and contains rhodium, aluminium oxide and a cerium oxide-zirconium oxide mixed crystal.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to an exhaust gas purification or exhaust gas control catalyst. 2. Description of the state of the art

[0002] An exhaust gas purification or exhaust gas control catalyst of a car oxidizes hydrocarbons (HC) and carbon monoxide (CO) into water and carbon dioxide (CO2) and reduces nitrogen oxides (NO2). x ) in nitrogen, where the hydrocarbons (HC) are carbon monoxide (CO) and the nitrogen oxides (NOx) x ) contained in exhaust gas emitted by an internal combustion engine. A precious metal-supported catalyst is generally used as an exhaust gas control catalyst, in which a catalyst layer with particles of a catalytic precious metal such as palladium (Pd), rhodium (Rh), and platinum (Pt) is deposited on a heat-resistant metal support.

[0003] The catalyst layer, consisting of the precious metal-supported catalyst, contains, in addition to the catalytic precious metal particles described above, an oxygen storage material (hereinafter referred to simply as "OSC") that has an oxygen storage capacity. This OSC material acts as a co-catalyst. The OSC material stores oxygen and releases it to facilitate exhaust gas purification and control reactions by the catalytic precious metals. A cerium oxide (CeO₂)-zirconium oxide (ZrO₂) mixed crystal is commonly used as the OSC material, and various OSC materials have been developed to further enhance performance.

[0004] For example, Japanese patent JP 4 670 603 B describes catalyst particles that can store and release oxygen, wherein the particles comprise: an iron compound in which an element other than Fe with a valence of two is firmly dissolved in an oxide of Fe (Fe oxide) with a valence of three; and a core section formed from an Fe oxide with a valence of three as its main component, wherein the iron compound forms a layer that is formed on an outer circumferential surface of the core section.

[0005] Japanese patent JP 4 666 006 B describes an exhaust gas control catalyst in which a catalyst layer is formed on a support, the catalyst layer comprising: Ce-containing oxide particles with oxygen storage capacity; and a catalyst metal formed from at least one noble metal selected from the group consisting of Pt, Pd, and Rh. A large quantity of iron oxide particles is distributed and contained within the catalyst layer, wherein at least a portion of the iron particles are fine iron oxide particles with a particle size of 300 nm or less, the fine iron oxide particles being in contact with the Ce-containing oxide particles, and the ratio of the area of ​​the fine iron oxide particles to the total area of ​​the iron oxide particles being 30% or more when viewed under an electron microscope.

[0006] Japanese patent JP 4 525 909 B describes a catalyst for a water-gas shift reaction or water-gas conversion reaction, formed from a mixed or composite oxide. This catalyst contains calcium and aluminum as its main components and iron in an amount ranging from 0.001 mol% to 10 mol% relative to the aluminum. The catalyst has an oxygen storage capacity of 20 µmol / g to 200 µmol / g at 500°C and a BET-specific area of ​​20 m². 2 / g or more.

[0007] Finally, WO 2011 / 011565 A2 teaches an oxygen storage catalyst with a reduced cerium oxide reduction temperature.

[0008] As described above, various iron oxide-containing materials have been developed as OSC materials for use in exhaust gas purification or exhaust gas control catalysts. However, if an exhaust gas control catalyst using an iron oxide-containing material as the OSC material is used over a long period, the catalytic activity of the catalytic noble metal and / or the oxygen storage capacity of the OSC material may decrease. SUMMARY OF THE INVENTION

[0009] The invention provides an exhaust gas purification or exhaust gas control catalyst that is suitable to substantially prevent the decrease in catalytic activity and / or the decrease in oxygen storage capacity of the OSC material after use over a long period of time.

[0010] The inventors have discovered that in an exhaust gas control catalyst in which iron oxide is used as the OSC material of the catalyst layer, a decrease in the catalytic activity and / or a decrease in the oxygen storage capacity of the OSC material can be essentially prevented by arranging an iron oxide-containing area and an area containing a catalytic noble metal adjacent to each other along a plane direction of the catalyst layer, which is how the invention came about.

[0011] According to one aspect of the invention, an exhaust gas purification or exhaust gas control catalyst is created, comprising: a substrate; and a first catalyst layer arranged on the substrate, the first catalyst layer comprising: a palladium region containing palladium, aluminum oxide, a cerium oxide-zirconium oxide mixed crystal (a solid solution of cerium oxide and zirconium oxide) and a LaFeO3-La2Zr2O7-ZrO2 composite oxide, and a rhodium region arranged adjacent to the palladium region along a plane direction of the first catalyst layer, containing rhodium, aluminum oxide and a cerium oxide-zirconium oxide mixed crystal (a solid solution of cerium oxide and zirconium oxide).

[0012] In the exhaust gas control catalyst, a surface area of ​​the palladium region on a top surface of the first catalyst layer can account for 20% to 40% of the total surface area of ​​the first catalyst layer.

[0013] The exhaust gas control catalyst may further comprise one or more second catalyst layer(s) arranged between the substrate and the first catalyst layer.

[0014] According to the invention, it is possible to create an exhaust gas purification or exhaust gas control catalyst that is suitable to substantially prevent a decrease in the catalytic activity and / or a decrease in the oxygen storage capacity of an OSC material after use over a long period of time. BRIEF DESCRIPTION OF THE DRAWING

[0015] The features and advantages as well as the technical and economic significance of exemplary embodiments of the invention are described below with reference to the accompanying drawing, in which the same reference numerals denote the same elements; here, the following is shown: Fig. 1 a schematic representation of the structure of an exhaust gas control catalyst from the prior art; Fig. 2A a schematic representation of the structure of an embodiment of an exhaust gas control catalyst according to the present invention; Fig. 2B a schematic representation of the structure of another embodiment of an exhaust gas control catalyst according to the present invention; Fig. 3 a graph showing the results of the evaluation of the maximum oxygen storage capacity (OSC) in the initial state and after a durability treatment with respect to each catalyst according to comparison examples 1 to 3 and example 1; Fig. 4. A scanning electron microscope image (SEM image) of the catalyst from comparison example 2 after a durability test; and Fig. 5 a graph showing a relationship between the area of ​​a palladium region on a top layer of a catalyst layer and the maximum oxygen storage capacity (OSC). DETAILED DESCRIPTION OF EXECUTION FORMS

[0016] Preferred embodiments of the invention are described in detail below.

[0017] For the sake of clarity, the dimensions and shapes of each section in the drawings are exaggerated and do not exactly correspond to their actual dimensions and shapes. Accordingly, the technical scope of the invention is not limited to the dimensions and shapes of each section shown in the drawings. <1. Exhaust gas purification or exhaust gas control catalyst >

[0018] An exhaust gas purification or exhaust gas control catalyst according to an embodiment of the invention has a substrate and a catalyst layer arranged on the substrate, wherein the catalyst layer contains a palladium region and a rhodium region arranged adjacent to the palladium region along a plane direction of the catalyst layer.

[0019] The inventors have discovered that in an exhaust gas control catalyst in which an iron oxide-containing material is used as the OSC material of a catalyst layer, a decrease in the catalytic activity and / or a decrease in the oxygen storage capacity of the OSC material after prolonged use can be essentially prevented by arranging an iron oxide-containing region and a region containing a catalytic noble metal adjacent to one another along a plane of the catalyst layer. The reason why the exhaust gas control catalyst has the properties described above can be explained as follows. The invention is not limited to the following measures and principles.

[0020] Fig. Figure 1 is a schematic representation showing the structure of a state-of-the-art exhaust gas purification or exhaust gas control catalyst. As in Fig. As shown in Figure 1, a prior art exhaust gas control catalyst 1 typically comprises a substrate 11 and a catalyst layer 12 arranged on the substrate 11. The catalyst layer 12 has a first catalyst layer 13 arranged on the substrate 11 and a second catalyst layer 14 arranged on the first catalyst layer 13 (hereinafter also referred to as a "two-layer catalyst"). The first catalyst layer 13 typically comprises particles of a catalytic noble metal such as palladium and an OSC material. The second catalyst layer 14 typically comprises particles of a different catalytic noble metal, such as rhodium, with a lower catalytic activity than the catalytic noble metal contained in the first catalyst layer, and an OSC material.The configuration chosen above is selected to prevent a decrease in catalytic activity caused by a component such as sulfur in the exhaust gas. Accordingly, if a material containing iron oxide is used as the OSC material in the first catalyst layer 13, the iron oxide diffuses into the second catalyst layer 14. As a result, the catalytic activity of the other catalytic noble metal contained in the second catalyst layer 14 decreases and / or the oxygen storage capacity of the OSC material may decrease.

[0021] Fig. Figure 2A is a schematic representation showing the structure of an exhaust gas control catalyst according to the embodiment of the invention. As shown in Fig. As shown in Figure 2A, the exhaust gas control catalyst 2 has a substrate 21 and a catalyst layer 22 arranged on the substrate 21, wherein the catalyst layer 22 has a palladium region 23 and a rhodium region 24, which is arranged adjacent to the palladium region 23 along a plane direction of the catalyst layer 22 (hereinafter also referred to as the "zone catalyst"). With the above-described structure of the zone catalyst, the exhaust gas control catalyst according to the embodiment of the invention can essentially prevent the diffusion of the iron oxide, which is used as the OSC material of the catalyst layer, compared to the two-layer catalyst of the prior art. Accordingly, the exhaust gas control catalyst can essentially prevent a decrease in the catalytic activity and / or a decrease in the oxygen storage capacity of an OSC material after use over a long period of time.

[0022] In the exhaust gas control catalyst 2, the ratio of the surface area of ​​the palladium region 23 on the uppermost layer surface of the catalyst layer 22 to the total surface area of ​​the catalyst layer 22 is preferably in the range of 10% to 60% and particularly preferably in the range of 20% to 40%. In the invention, "the surface area on the uppermost layer of the catalyst layer" refers to the surface area of ​​a surface (that is, the uppermost layer) of the catalyst layer that is laminated onto the substrate.By controlling the surface area of ​​the palladium region in the exhaust gas control catalyst such that it lies within the area described above, the diffusion of iron oxide from the palladium region into the rhodium region can be substantially prevented, and a decrease in the catalytic activity and / or a decrease in the oxygen storage capacity of an OSC material after use over a long period of time can be substantially avoided.

[0023] In the exhaust gas control catalyst according to the embodiment, the palladium section comprises palladium, aluminum oxide, a cerium oxide-zirconium oxide mixed crystal (a solid solution of cerium oxide and zirconium oxide), and a composite oxide of lanthanum, iron, and zirconium. Furthermore, the rhodium section comprises rhodium, aluminum oxide, and a cerium oxide-zirconium oxide mixed crystal (a solid solution of cerium oxide and zirconium oxide).

[0024] In the embodiment of the invention, the "cerium oxide-zirconium oxide mixed crystal" refers to a mixed or composite oxide with cerium oxide (CeO2) and zirconium oxide (ZrO2). The cerium oxide-zirconium oxide mixed crystal (hereinafter also referred to as "CZ") and a mixed or composite oxide of lanthanum, iron, and zirconium (hereinafter also referred to as "LFZ") are used as the OSC material of the catalyst layer. The cerium oxide-zirconium oxide mixed crystal preferably comprises 10% to 70% by mass of CeO2 and 30% to 90% by mass of ZrO2 with respect to the total mass of the mixed crystal or the solid solution. The composite oxide of lanthanum, iron and zirconium preferably comprises 30% to 70% by mass of La2O3, 10% to 25% by mass of Fe2O3 and 15% to 40% by mass of ZrO2 with respect to the total mass of the composite oxide.The oxygen storage capacity of the exhaust gas control catalyst can be improved by using the cerium oxide-zirconium oxide mixed crystal (CZ) with the composition described above and the composite oxide (LFZ) of lanthanum, iron and zirconium with the composition described above.

[0025] Optionally, and preferably, the cerium oxide-zirconium oxide mixed crystal (CZ) comprises further oxides of one or more transition metals such as yttrium (Y), lanthanum (La), neodymium (Nd), and praseodymium (Pr). It is preferred that each of the transition metal oxides is Y₂O₃, La₂O₃, Pr₂O₃, or Nd₂O₃. It is preferred that the cerium oxide-zirconium oxide mixed crystal contains each of the transition metal oxides in an amount of 0.5 wt% to 10 wt% of the total mass of the mixed crystal. If the cerium oxide-zirconium oxide mixed crystal (CZ) contains the transition metal oxides, the oxygen storage capacity of the exhaust gas control catalyst can be further improved.

[0026] In the exhaust gas control catalyst according to the invention, the palladium region and the rhodium region can further comprise one or more additional materials. It is preferred that each of the additional materials is, for example, BaSO4 or La2O3. If the palladium region and the rhodium region contain the additional materials, the oxygen storage capacity of the exhaust gas control catalyst can be further improved.

[0027] The composition of each material contained in the palladium and rhodium regions is not particularly restricted and can be determined using a method such as: a method for dissolving each region of the catalyst layer in an acid or the like and performing inductively coupled plasma emission spectrometry (ICP-ES) of the metal components in the solution; a method for performing energy-dispersive X-ray spectrometry (EDX) or electron beam microanalysis (EPMA) of a cross-section or area of ​​the catalyst layer; or a method for performing X-ray fluorescence analysis (XRF) of a powder of the catalyst layer.

[0028] In the exhaust gas control catalyst 2, the substrate 21 preferably has the shape of a honeycomb, a pellet, or particles, and in particular the shape of a honeycomb. Furthermore, it is preferred that the substrate 21 comprises a heat-resistant inorganic material such as cordierite or metal. The use of such a substrate allows the catalytic activity of the exhaust gas control catalyst to be maintained at high temperatures.

[0029] Fig. Figure 2B is a schematic representation showing another embodiment of the exhaust gas control catalyst of the present invention. As shown in Fig. As shown in Figure 2B, an exhaust gas control catalyst 3 has one or more additional catalyst layer(s) 35, which are arranged such that they are located between the substrate 31 and the catalyst layer 32. In this embodiment, the substrate 31, the catalyst layer 32, the palladium region 33, and the rhodium region 34 each have the same properties as described above. It is preferred that the additional catalyst layer 35 is made of the same material as the palladium region 33. By having the additional catalyst layer 35 in the structure described above, the durability of the exhaust gas control catalyst can be further improved.

[0030] The exhaust gas control catalyst according to the embodiment of the invention is not particularly limited but can be formed, for example, using a method that is used in the prior art, such as a method for sequentially washing and coating the substrate with a slurry containing a metal oxide and optionally a catalytic precious metal.

[0031] As described above, in the exhaust gas control catalyst according to the embodiment of the invention, the diffusion of iron oxide, which is used as the OSC material of the catalyst layer, can be substantially prevented, thus preventing a decrease in the catalytic activity and / or a decrease in the oxygen storage capacity of the OSC material. Accordingly, by using the exhaust gas purification or exhaust gas control catalyst to clean the exhaust gas of an automobile, the exhaust gas control or exhaust gas purification performance can be achieved even after the automobile has been operated for a long period of time.

[0032] The invention is described in more detail below using examples. However, the technical scope of the invention is not limited to these examples. <1. Material>

[0033] A mixed or composite oxide with 1% by mass of La2O3 and 99% by mass of Al2O3 (hereinafter also referred to as "LA material") was used as the material for aluminium oxide.

[0034] The material for the cerium oxide-zirconium oxide mixed crystal (CZ - a solid solution of cerium oxide and zirconium oxide) was a composite oxide with 30 wt% CeO2, 60 wt% ZrO2, 5 wt% Y2O3 and 5 wt% La2O3 (hereinafter also referred to as "CZYL material").

[0035] A LaFO3-La2Zr2O7-ZrO2 composite oxide, prepared such that the atomic ratio (La:Fe:Zr) of La, Fe, and Zr was 1:2:1 (hereinafter also referred to as the "LFZ material"), was used as the material for a composite oxide (LFZ) of lanthanum, iron, and zirconium. The material used is not limited to the composition described above. For example, a material with a composition described in Japanese patent application JP 2013-241328A may be used.

[0036] The material used for a palladium catalyst was an aqueous palladium nitrate solution (produced by Cataler Corporation) with a precious metal content of 8.8% by mass (hereinafter also referred to as "Pd / precious metal material").

[0037] An aqueous rhodium chloride solution (manufactured by Cataler Corporation) with a precious metal content of 2.8% by mass (hereinafter also referred to as "Rh / precious metal material") was used as the rhodium catalyst material. A cordierite honeycomb substrate (manufactured by Denso Corporation) with a volume of 875 cc was used as the substrate material. <2. Preparation of the catalyst>[Comparative example 1] Two-layer catalyst with a palladium layer (Pd(1,0) / CZ(50)+Al2O3(75)) and a rhodium layer (Rh(0,2) / CZ(60)+Al2O3(40))

[0038] A material (Pd / CZ) in which palladium (Pd) is supported on a cerium oxide-zirconium oxide (CZ) solid solution was prepared using an impregnation process employing the CZYL material and the Pd / precious metal material. The Pd / CZ material, the LA material, and an aluminum oxide-based binder (AS-200, manufactured by Nissan Chemical Industries Ltd.) were dissolved in distilled water under stirring to obtain a slurry. The slurry was adjusted such that the volumes of Pd, the LA material, and the CZYL material were 1 g / L, 75 g / L, and 50 g / L, respectively, with respect to the total volume of the slurry. The resulting slurry was poured into the substrate. Excess slurry was blown off by a blower. Using the process described above, the materials were layered onto a surface of an inner wall of the substrate.The substrate coated with the slurry was left to stand in a drying machine set to 120°C for 2 hours to evaporate the water in the slurry. Subsequently, the substrate was left to stand in an electric furnace set to 500°C for 2 hours to cure the substrate and the coating. The process described above resulted in the formation of a palladium layer with 50 parts per mass of CZ, on which 1 part per mass of Pd was carried, and 75 parts per mass of Al₂O₃ on the surface of the substrate's inner wall.

[0039] A material (Rh / CZ) in which rhodium (Rh) was supported on the cerium oxide-zirconium oxide solid solution (CZ) was prepared using an impregnation process employing the CZYL material and the Rh / precious metal material. The Rh / CZ material, the LA material, and an aluminum oxide-based binder (AS-200, manufactured by Nissan Chemical Industries Ltd.) were dissolved in distilled water under stirring to obtain a slurry. The slurry was adjusted such that the volumes of Rh, the LA material, and the CYZL material were 0.2 g / L, 40 g / L, and 60 g / L, respectively, with respect to the total volume of the slurry. The resulting slurry was poured into the substrate. Excess slurry was blown off by a blower. Using the process described above, the materials were layered onto a surface of an inner wall of the substrate.The substrate coated with the slurry was left to stand in a drying machine set to 120°C for 2 hours to evaporate the water in the slurry. Subsequently, the substrate was left to stand in an electric furnace set to 500°C for 2 hours to cure the substrate and the coating. The process described above resulted in the formation of a rhodium layer with 60 parts per mass of CZ, on which 0.2 parts per mass of Rh was carried, and a palladium layer with 40 parts per mass of Al₂O₃ was formed on an area of ​​the palladium layer that formed on the inner wall of the substrate.

[0040] [Comparative example 2] Two-layer catalyst with a palladium layer (Pd(1,0) / CZ(50)+Al2O3(75)+LFZ(30)) and a rhodium layer (Rh(0,2) / CZ(60)+Al2O3(40))

[0041] A two-layer catalyst of Comparative Example 2 was prepared according to the same procedure as in Comparative Example 1, except that 30 g / L of the LFZ material with respect to the total volume of the slurry was added to the slurry to form the palladium layer in Comparative Example 1.

[0042] [Comparative example 3] Zone catalyst with a catalyst layer containing a palladium region (Pd(1,0) / CZ(50)+Al2O3(75)) and a rhodium region (Rh(0,2) / CZ(60)+Al2O3(40)).

[0043] A material (Pd / CZ) in which palladium (Pd) was supported on a cerium oxide-zirconium oxide (CZ) mixed crystal was prepared using an impregnation process employing the CZYL material and the Pd / precious metal material. The Pd / CZ material, the LA material, and an aluminum oxide-based binder (AS-200, manufactured by Nissan Chemical Industries Ltd.) were dissolved in distilled water under stirring to obtain a slurry. The slurry was adjusted so that the volumes of Pd, the LA material, and the CYZL material were 1 g / L, 75 g / L, and 50 g / L, respectively, with respect to the total volume of the slurry. The resulting slurry was poured into a front section of the substrate (50% of the substrate's surface width). Excess slurry was blown off by a fan. Using the process described above, the materials were layered onto a surface of an inner wall at the front section of the substrate.The substrate coated with the slurry was left to stand in a drying machine set to 120°C for 2 hours to evaporate the water in the slurry. Subsequently, the substrate was left to stand in an electric furnace set to 500°C for 2 hours to cure the substrate and the coating. The process described above resulted in the formation of a palladium region with 50 parts per mass of CZ, supported by 1 part per mass of Pd, and 75 parts per mass of Al₂O₃ on the front portion of the substrate's inner wall surface, representing 50% of the total surface area of ​​the catalyst layer.

[0044] A material (Rh / CZ) in which rhodium (Rh) was supported on a cerium oxide-zirconium oxide mixed crystal (CZ) was prepared using the impregnation process employing the CZYL material and the Rh / precious metal material. The Rh / CZ material, the LA material, and an aluminum oxide-based binder (AS-200, manufactured by Nissan Chemical Industries Ltd.) were dissolved in distilled water under stirring to obtain a slurry. The slurry was adjusted so that the volumes of Rh, the LA material, and the CYZL material were 0.2 g / L, 40 g / L, and 60 g / L, respectively, with respect to the total volume of the slurry. The resulting slurry was poured into a rear section of the substrate (50% of the substrate's surface width). Excess slurry was blown off by a fan. Using the process described above, the materials were layered onto a surface of an inner wall at the rear section of the substrate.The substrate coated with the slurry was left to stand in a drying machine set to 120°C for 2 hours to evaporate the water in the slurry. Subsequently, the substrate was left to stand in an electric furnace set to 500°C for 2 hours to cure the substrate and the coating. The process described above resulted in the formation of a rhodium region with 60 parts per mass CZ, on which 0.2 parts per mass Rh was supported, and 40 parts per mass Al₂O₃ on the rear portion of the substrate's inner wall surface, representing 50% of the total surface area of ​​the catalyst layer.

[0045] [Example 1] Zone catalyst with a catalyst layer comprising a palladium region (Pd(1,0) / CZ(50)+Al2O3(75)+LFZ(30)) and a rhodium region (Rh(0,2) / CZ(60)+Al2O3(40)).

[0046] A zone catalyst of Example 1 was prepared using the same procedure as Comparative Example 3, except that 30 g / L of the LFZ material with respect to the total volume of the slurry was added to the slurry to form the palladium layer in Comparative Example 3.

[0047] [Example 2] Zone catalyst with a catalyst layer containing a palladium region (Pd(1,0) / CZ(50)+Al2O3(75)+LFZ(30)) and a rhodium region (Rh(0,2) / CZ(60)+Al2O3(40)).

[0048] A zone catalyst of Example 2 was prepared using the same procedure as Example 1, except that the coating width ratio of the palladium region to the rhodium region was 10:90 compared to Example 1. The process described above resulted in the formation of a palladium region with 50 parts per mass CZ, supported by 1 part per mass Pd, and 75 parts per mass Al₂O₃ on the front portion of the substrate's inner wall surface, representing 10% of the total surface area of ​​the catalyst layer.

[0049] [Example 3] Zone catalyst with a catalyst layer containing a palladium region (Pd(1,0) / CZ(50)+Al2O3(75)+LFZ(30)) and a rhodium region (Rh(0,2) / CZ(60)+Al2O3(40)).

[0050] A zone catalyst of Example 3 was prepared according to the same procedure as Example 1, except that the coating width ratio of the palladium region to the rhodium region was 20:80 compared to Example 1. By the process described above, a palladium region of 50 parts per mass CZ, on which 1 part per mass Pd was supported, and 75 parts per mass Al2O3 were formed on the front portion of the surface of the inner wall of the substrate, that is, a region corresponding to 20% of the total surface area of ​​the catalyst layer.

[0051] [Example 4] Zone catalyst with a catalyst layer containing a palladium region (Pd(1,0) / CZ(50)+Al2O3(75)+LFZ(30)) and a rhodium region (Rh(0,2) / CZ(60)+Al2O3(40)).

[0052] A zone catalyst of Example 4 was prepared according to the same procedure as Example 1, except that the coating width ratio of the palladium region and the rhodium region was 40:60 compared to Example 1. By the process described above, a palladium region of 50 parts per mass CZ, on which 1 part per mass Pd was supported, and 75 parts per mass Al2O3 were formed on the front portion of the surface of the inner wall of the substrate, that is, a region corresponding to 40% of the total surface area of ​​the catalyst layer.

[0053] [Example 5] Zone catalyst with a catalyst layer containing a palladium region (Pd(1,0) / CZ(50)+Al2O3(75)+LFZ(30))) and a rhodium region (Rh(0,2) / CZ(60)+Al2O3(40))

[0054] A zone catalyst of Example 5 was prepared according to the same procedure as Example 1, except that the coating width ratio of the palladium region to the rhodium region was 60:40 compared to Example 1. By the process described above, a palladium region of 50 parts per mass CZ, on which 1 part per mass Pd was supported, and 75 parts per mass Al2O3 were formed on the front portion of the surface of the inner wall of the substrate, that is, a region corresponding to 60% of the total surface area of ​​the catalyst layer. <3. Catalyst Evaluation Method>[OSC Evaluation Method]

[0055] Using a gasoline engine (2AZ-FE, manufactured by Toyota Motor Corporation), the oxygen storage capacity of the catalysts in comparison examples 1 to 3 and examples 1 to 5 was evaluated. An air-fuel ratio (A / F) was controlled to achieve an A / F of 14.1 or 15.1. Excess or lack of oxygen was calculated according to the following expression based on the difference (ΔA / F) between the theoretical air-fuel ratio and an A / F sensor output at the stoichiometric point. The maximum oxygen storage was evaluated as OSC. OSC(g)=0.23×ΔA / F×fuel injection amount [Expandment treatment]

[0056] Using a gasoline engine (1UR-FE, manufactured by Toyota Motor Corporation), an accelerated aging process was performed on the catalysts of comparison examples 1 to 3 and examples 1 to 5 under conditions of 1000°C (catalyst bed temperature) for 25 hours. By adjusting the throttle opening angle and engine load, the treatment was repeatedly performed in a constant cycle: rich, stoichiometric, and lean conditions. As a result, the aging of the catalysts was accelerated, while the composition of the exhaust gas changed. <4. Evaluation of the results of the catalysts>

[0057] For each catalyst in comparison examples 1 to 3 and example 1, the maximum oxygen storage capacity values ​​were evaluated at baseline and after the durability treatment using the procedure described above. The results are presented in Fig. 3 shown.

[0058] As in Fig. As shown in Figure 3, the maximum oxygen storage capacity of the catalyst in Comparative Example 2, although the palladium layer contained LFZ, decreased significantly after the durability treatment compared to the initial value. Surface analysis of the catalyst in Comparative Example 2 after the durability treatment, using scanning electron microscopy and electron beam microanalysis (EPMA), revealed that the iron in the LFZ contained in the palladium layer diffused to the interface between the palladium and rhodium layers. Fig. 4) In contrast, with the catalyst from Example 1, the construction of the zone catalyst noticeably prevented a decrease in the maximum oxygen storage capacity after the durability treatment compared to the value in the initial state.

[0059] For each catalyst in Examples 1 to 5, the maximum oxygen storage capacity at the initial state was evaluated according to the process described above. The results are presented in Fig. 5 shown.

[0060] As in Fig. As shown in Figure 5, the OSZ was maximal when the area of ​​the palladium region to which LFZ was added comprised 20% to 40% of the total area of ​​the catalyst layer.

Claims

[1] Exhaust gas control catalyst (2; 3), comprising: a substrate (21; 31); and a first catalyst layer (22; 32) arranged on the substrate (21; 31), characterized by , that the first catalyst layer (22; 32) comprises: a palladium region (23; 33) containing palladium, aluminium oxide, a cerium oxide-zirconium oxide mixed crystal and a LaFeO3-La2Zr2O 7- ZrO2 composite oxide, and a rhodium region (24; 34) which is adjacent to the palladium region (23; 33) along a plane direction of the first catalyst layer (22; 32) and contains rhodium, aluminium oxide and a cerium oxide-zirconium oxide mixed crystal. [2] Exhaust gas control catalyst (2; 3) according to claim 1, characterized by , that an area of ​​the palladium region (23) on a top surface of the first catalyst layer (22; 32) makes up 20% to 40% of the total area of ​​the first catalyst layer (22; 32). [3] Exhaust gas control catalyst (2; 3) according to claim 1 or 2, characterized by , that it further exhibits: one or more second catalyst layer(s) (35) arranged between the substrate (21; 31) and the first catalyst layer (22; 32).

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