exhaust gas purification catalyst

Abstract

To provide an exhaust gas purification catalyst excellent in warming-up characteristics and capable of speedily exhibiting an effective catalyst activity even when a relatively low temperature exhaust gas is introduced.SOLUTION: In an exhaust gas purifying catalyst disclosed herein, a catalyst supporting portion (20) formed on a substrate (11) is composed of a catalyst coating portion (22) having a carrier made of inorganic compound particles and at least one kind of catalytic metal supported on the carrier, and a catalyst metal direct support portion (24) having at least one catalyst metal directly supported on the substrate without the carrier therebetween, wherein the catalyst metal direct support portion is formed in at least an upstream region with a predetermined length from an upstream end (16A) in at least an exhaust gas passage, and the catalyst coating portion is not formed in the upstream region in the exhaust gas passage and is formed only in a region on the downstream side of this region.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas purification catalyst provided in an exhaust system of an internal combustion engine of a vehicle. [Background technology]

[0002] Hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO) are extracted from exhaust gases emitted by internal combustion engines such as vehicle engines. x A so-called three-way catalyst (TWC) is used as an exhaust gas purification catalyst for removing exhaust gas components such as toluene, toluene, toluene-containing alcohols, and the like by oxidation or reduction reactions. In general, in a three-way catalyst, a catalyst coating layer is formed on a honeycomb substrate made of cordierite or the like, the catalyst coating layer including a porous carrier made of an inorganic oxide such as alumina (Al2O3) or zirconia (ZrO2) and a metal (hereinafter also referred to as "catalytic metal") such as palladium (Pd) or rhodium (Rh) that functions as an oxidation catalyst and / or reduction catalyst supported on the carrier.

[0003] Such three-way catalysts exhibit high catalytic activity under certain high-temperature conditions. Therefore, when the exhaust system is still cold, such as when the engine is started, the activity of the three-way catalyst installed in the exhaust system is lower than when the engine is running continuously for a long period of time and the temperature is high. Therefore, there is a need for technology that can effectively purify exhaust gases even under such conditions. In particular, in recent years, hybrid vehicles and so-called eco-cars equipped with idling stop and fuel cut functions have become popular. In these vehicles, the engine is frequently stopped while driving, and the exhaust system is likely to remain in a cold state, similar to when the engine is started, even after driving has begun. Therefore, there is a demand for technology that can effectively purify exhaust gases using a three-way catalyst even under such conditions. One type of exhaust gas purification catalyst that meets these demands is a so-called electrically heated (also called electrically heated) exhaust gas purification catalyst, also known as EHC, which is an exhaust gas purification catalyst that includes a carrier such as a honeycomb carrier and a catalytic metal supported on the carrier, and further includes a pair of electrodes configured to supply electricity to the pair of electrodes to heat the catalytic metal. For example, Patent Documents 1 and 2 describe conventional examples of electrically heated exhaust gas purification catalysts (EHC). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-275559 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-1704 Summary of the Invention [Problem to be solved by the invention]

[0005] However, EHC requires the installation of electrodes to actively heat the catalytic metal, which increases the installation cost of the exhaust gas purification catalyst and complicates the structure, so an exhaust gas purification catalyst with a simpler configuration that can meet the above requirements is desired. Furthermore, even when EHC is adopted, an EHC with an official configuration that can heat more effectively than conventional EHCs and quickly demonstrate high exhaust gas purification performance is desired. The present invention has been created to meet such demands, and provides an exhaust gas purification catalyst with excellent warm-up characteristics that can quickly demonstrate effective catalytic activity even when exhaust gas in a relatively low temperature range, such as when starting an engine, is introduced. [Means for solving the problem]

[0006] The inventors have studied the relationship between the heat capacity of the entire exhaust gas purification catalyst, catalytic activity, and the temperature of the exhaust gas introduced, and have discovered a configuration that improves the warm-up performance of the upstream region (also called the front (Fr) region) in the exhaust gas flow direction by making the heat capacity smaller than the heat capacity of the downstream region (also called the rear (Rr) region), while achieving sufficient exhaust gas purification performance in the downstream region, thereby completing the present invention.

[0007] That is, according to the technology disclosed herein, there is provided an exhaust gas purification catalyst that purifies exhaust gas emitted from an internal combustion engine, comprising: a substrate disposed in an exhaust pipe of the internal combustion engine, the substrate having an exhaust gas passage extending from an upstream end where exhaust gas is introduced to a downstream end where exhaust gas is discharged; a catalyst support portion formed in an exhaust gas passage of the substrate, the catalyst support portion including a catalytic metal that functions as a catalyst capable of oxidizing or reducing at least one exhaust gas component; It is equipped with The catalyst support portion is a catalyst-coated portion having a carrier made of inorganic compound particles and at least one catalytic metal supported on the carrier; a catalytic metal directly supported portion having at least one catalytic metal supported directly on the substrate without including the carrier; It is composed of wherein the catalytic metal directly supported portion is formed at least in an upstream region of the exhaust gas passage that is a predetermined length from the upstream end portion of the exhaust gas passage, The catalyst coating portion is not formed in an upstream region of the exhaust gas passage within a predetermined length from the upstream end, but is formed only in a region downstream of the upstream end, in an exhaust gas purification catalyst. Here, the "exhaust gas passage" refers to a region through which exhaust gas introduced into the exhaust gas purification catalyst can flow, and is not limited to the spaces (cells) formed inside the substrate and the surrounding wall surfaces. The inside (inside the pores) of the porous body that constitutes the substrate also constitutes part of the exhaust gas passage as long as exhaust gas can be introduced and flow through it.

[0008] As described above, in the exhaust gas purification catalyst disclosed herein, the catalyst support portion formed in the exhaust gas passage of the substrate is composed of the catalyst coated portion and the catalyst metal directly supported portion, and the catalyst metal directly supported portion is formed in an upstream region of a predetermined length from the upstream end, while the catalyst coated portion is not formed in the upstream region of the predetermined length from the upstream end in the exhaust gas passage, but is formed only in a region downstream of said region. In other words, the catalyst support portion in the upstream region of the predetermined length does not contain a carrier made of inorganic compound particles, and the heat capacity can be reduced accordingly. As a result, the exhaust gas purification catalyst disclosed herein has an increased temperature rise in the upstream region of a predetermined length from the upstream end (i.e., the Fr region where only the catalyst metal directly supported portion is formed as the catalyst supported portion), and can realize an improvement in the efficiency of purifying exhaust gases during so-called cold starts and cold running in a relatively low temperature range such as when starting an internal combustion engine. Furthermore, since a catalyst coated portion is provided in the region downstream of this region, sufficient exhaust gas purification performance can be maintained during hot running.

[0009] In a preferred embodiment of the exhaust gas purification catalyst disclosed herein, the catalytic metal directly supported portion is formed in a region having a length that is at least 30% or more of the entire length of the exhaust gas passage from the upstream end. The exhaust gas purification catalyst having such a configuration further increases the temperature rise property in the Fr region, and can further improve the efficiency of purifying exhaust gases during cold starts and cold running of an internal combustion engine.

[0010] In another preferred embodiment of the exhaust gas purification catalyst disclosed herein, the catalytic metal directly supported portion is formed only in an upstream region of a predetermined length from the upstream end, and is not formed in a region downstream of the upstream region where the catalyst coated portion is formed. With this configuration, the heat capacity of the upstream region can be suitably reduced, and the efficiency of purifying exhaust gases during cold starts and cold running of the internal combustion engine can be further improved.

[0011] In another preferred embodiment of the exhaust gas purification catalyst disclosed herein, the catalytic metal directly supported portion is also formed in at least a part of the region where the downstream catalyst coated portion is formed. With an exhaust gas purification catalyst of this configuration, the catalyst support portion in the downstream region is composed of both a catalyst coated portion and a catalyst metal directly supported portion, thereby making it possible to further optimize exhaust gas purification performance, for example, during hot driving.

[0012] In another preferred embodiment of the exhaust gas purification catalyst disclosed herein, the catalytic metal directly supported portion contains palladium and / or platinum as the catalytic metal, and the catalytic coated portion contains rhodium as the catalytic metal. With an exhaust gas purification catalyst having such a configuration, the catalytic metal directly supported portion in the upstream region can more optimally purify exhaust gas during cold starts and cold running, particularly purifying exhaust gas components that can be purified by oxidation, such as hydrocarbons (HC) and carbon monoxide (CO).

[0013] Another preferred embodiment of the exhaust gas purification catalyst disclosed herein is an exhaust gas purification catalyst in which the substrate is formed from a material that can be heated by passing electricity through it, and thus the catalyst is configured as an electrically heated catalyst. As described above, the exhaust gas purification catalyst disclosed herein can improve temperature rise (warm-up performance) by reducing the heat capacity of the upstream region. Such performance has been a basic performance required for conventional electrically heated exhaust gas purification catalysts (EHC). Therefore, by constructing an EHC using the exhaust gas purification catalyst disclosed herein, it is possible to provide an EHC with improved temperature rise characteristics (warm-up characteristics) compared to conventional EHCs. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view schematically showing an example of an exhaust gas purification catalyst that constitutes a three-way catalyst. [Figure 2] 1 is a perspective view schematically showing an example of an exhaust gas purification catalyst constituting an electrically heated exhaust gas purification catalyst (EHC). FIG. [Figure 3] 1 is a diagram schematically illustrating the configuration of an embodiment of an exhaust gas purification catalyst disclosed herein. [Figure 4] 1 is a diagram schematically illustrating the configuration of an embodiment of an exhaust gas purification catalyst disclosed herein. [Figure 5] 1 is a diagram schematically illustrating the configuration of one embodiment of an exhaust gas purification catalyst. [Figure 6] 1 is a diagram schematically illustrating the configuration of one embodiment of an exhaust gas purification catalyst. [Figure 7] 1 is a graph showing the warm-up characteristics in terms of HC conversion rates for four exhaust gas purification catalysts constructed using a Si—SiC substrate. [Figure 8] 1 is a graph showing warm-up characteristics in terms of HC conversion rates for two exhaust gas purification catalysts constructed using a cordierite substrate. [Figure 9] 1 is a graph showing the warm-up characteristics in terms of HC purification rate for two exhaust gas purification catalysts constructed using a metal substrate. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, some preferred embodiments of the exhaust gas purification catalyst disclosed herein will be described with appropriate reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present technology can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present technology can be implemented based on the contents disclosed in this specification and technical knowledge in the relevant field. It should be noted that, in this specification, when a numerical range is described as A to B, it means A or more and B or less.

[0016] The exhaust gas purification catalyst disclosed herein is characterized in that the catalyst support portion is composed of the catalyst coated portion and the catalyst metal direct support portion, and the catalyst metal direct support portion is formed at least in an upstream region of the exhaust gas passage from the upstream end of the exhaust gas passage over a predetermined length, and the catalyst coated portion is not formed in the upstream region but only in a region downstream of the upstream region. Therefore, other configurations are not particularly limited. The exhaust gas purification catalyst disclosed herein can be disposed in an exhaust pipe connected to various internal combustion engines, particularly gasoline engines and diesel engines (here, an automotive gasoline engine) 1, by appropriately selecting the substrate (described below), the carrier (including the case where it is an OSC material) in the catalyst coated portion, the catalyst metal supported on each of the catalyst metal direct support portion and the catalyst coated portion, and forming them into a desired shape depending on the application.

[0017] <Base material> The substrate is a component that constitutes the framework of the exhaust gas purification catalyst. The substrate can be made of various materials and in various forms that have been conventionally used as substrates for exhaust gas purification catalysts. For example, ceramic substrates such as cordierite, aluminum titanate, and silicon carbide (SiC), which have high heat resistance, or metal substrates such as stainless steel can be used. The shape may also be the same as that of a conventional exhaust gas purification catalyst. As an example, the substrate 11 of the exhaust gas purification catalyst 10 shown in Fig. 1 is a substrate 11 having a cylindrical outer shape and a honeycomb structure made of, for example, cordierite, in which a plurality of cells 15, which are through-holes serving as exhaust gas passages, are provided in the longitudinal direction, and the exhaust gas can come into contact with partition walls (rib walls) 16 separating each cell 15. Alternatively, the substrate 11 may be a sponge-like porous body with irregular pores formed therein, as long as the exhaust gas can flow through the pores.

[0018] Furthermore, the substrate 11 is not limited to a so-called straight flow type in which exhaust gas introduced into the cells 15 from the upstream side in the exhaust gas flow direction (see the arrow in the figure), i.e., the upstream end where the exhaust gas is introduced, passes directly through the cells 15 and is discharged from the downstream end that is downstream in the exhaust gas flow direction. For example, the substrate may be a so-called wall-through type in which exhaust gas introduced from the upstream end of a cell that is open only at its upstream end passes through a porous partition wall, moves to an adjacent cell that is open only at its downstream end, and is discharged from the downstream end of the cell. Although not particularly limited, the capacity of the substrate 11 (volume of the cells 2) is usually 0.1 L or more (preferably 0.5 L or more), for example, 5 L or less (preferably 3 L or less, more preferably 2 L or less). The total length of the substrate 11 along the direction of exhaust gas flow can usually be about 10 mm to 500 mm (for example, 50 mm to 300 mm). The shape of the substrate 11 can be a honeycomb shape, a foam shape, a pellet shape, or the like. The outer shape of the entire substrate 11 may be an elliptical cylinder, a polygonal cylinder, or the like instead of a cylindrical shape.

[0019] The exhaust gas purification catalyst disclosed herein can be suitably used as an electrically heated exhaust gas purification catalyst. An example of an exhaust gas purification catalyst 10A used as an EHC is shown in Figure 2. There are no particular limitations on the shape of the substrate 11A, and it may be the same as that shown in Figure 1. The substrate 11A may be any material that can be heated by passing an electric current through it, and suitable ceramic materials for forming the substrate that can be heated well by passing an electric current include silicon carbide (SiC), a composite material of silicon carbide (SiC) and silicon (Si) (Si-SiC), and a composite material of silicon carbide (SiC) and molybdenum disilicide (MoSi2). Alternatively, alloy materials such as Ni-Cr and Fe-Cr-Al are also suitable as metal materials for forming the substrate, which can be heated well by passing an electric current through them.

[0020] As shown in FIG. 2, the electrically heated catalyst (EHC) 10A according to this embodiment has a pair of electrodes 40 formed facing each other with a substrate 11A in between. The electrode 40 includes an electrode layer 42 and an electrode terminal 44 provided on the outer surface of the substrate 11A. The electrode layer 42 has the function of diffusing current to the surface of the substrate 11A so as to generate heat efficiently. The outer shape and size of the electrode layer 42 may be set as appropriate. By providing such a pair of electrodes 40, there is no need to provide a separate heating element, and the electrically heated exhaust gas purification catalyst (EHC) 10A can be installed efficiently.

[0021] <Catalyst support part> In the exhaust gas purification catalysts 10, 10A disclosed herein, a catalyst support portion 20 is formed in the cells 15, which are exhaust gas passages, specifically on the surfaces and / or inside the partition walls 16. As shown in Fig. 3, in the exhaust gas purification catalyst disclosed herein, the catalyst support portion 20 is composed of a catalyst metal directly supported portion 24 formed in at least an upstream region of a predetermined length from the upstream end portion 16A, and a catalyst coated portion 22 that is not formed in the upstream region of the predetermined length, but is formed only in a region further downstream than that. 3 and the later-described Figures 4 to 6 are all depicted as if the exhaust gas flows from left to right (see the arrows in the figures). Therefore, the left end of the substrate 11 (partition wall 16) in the figures is the upstream end 16A, and the right end is the downstream end 16B.

[0022] As shown in Fig. 3, in one embodiment, the catalyst metal directly supported portion 24 is formed only in an upstream region of a predetermined length from the upstream end 16A. Alternatively, in another embodiment shown in Fig. 4, the catalyst metal directly supported portion 24 is also formed in at least a portion of the region where the downstream catalyst coated portion 22 is formed (in the embodiment shown in Fig. 4, the entire region from the upstream end 16A to the downstream end 16B). However, in both embodiments, the catalyst coated portion 22 is not formed in the upstream region of the predetermined length, but is formed only in a region further downstream. 3 and 4, the heat capacity of the catalyst support portion 20 in the upstream region is reduced compared to when the catalyst-coated portion 22 is formed over the entire region from the upstream end 16A to the downstream end 16B, improving warm-up performance. In other words, the temperature rise capability of the catalyst metal directly support portion in the upstream region is improved, improving exhaust gas purification performance during cold starts and cold running. From this perspective, the embodiment shown in FIG. 3, which has a smaller heat capacity, is preferred. On the other hand, when the purification performance of the entire exhaust gas purification catalyst is taken into consideration, a configuration in which both the catalyst coated portion and the catalyst metal directly supported portion are formed in the downstream region as shown in FIG. 4 is preferable.

[0023] The catalyst coated portion 22 includes at least a catalytic metal that functions as a catalyst capable of oxidizing or reducing at least one exhaust gas component, and an inorganic carrier that supports the catalytic metal. Examples of catalytic metals include metals belonging to the platinum group such as palladium (Pd), rhodium (Rh), and platinum (Pt), as well as other metals that function as oxidation or reduction catalysts. Pd and Pt have excellent purification performance (oxidation purification ability) for carbon monoxide and hydrocarbons, while Rh has excellent oxidation purification ability for NO x These are particularly preferred catalytic metals for three-way catalysts because they have excellent purification performance (reduction purification ability). In addition to these, metals such as barium (Ba), strontium (Sr), and other alkaline earth metals, alkali metals, and transition metals may be used in combination as promoter components. The average particle diameter of the catalytic metals, as determined by electron microscope observation, is preferably 0.5 nm to 50 nm, and more preferably 1 nm to 20 nm, but is not particularly limited.

[0024] The carrier that supports the catalytic metal and constitutes the catalyst-coated portion 22 is not particularly limited as long as it can support the catalytic metal, and conventional carriers made of inorganic compound particles can be used. Examples include inorganic compound particles (so-called OSC materials) having oxygen storage capacity (OSC), such as ceria (CeO) and composite oxides containing ceria (e.g., ceria-zirconia composite oxide (CZ or ZC composite oxide)); oxide particles such as alumina (AlO), titania (TiO), zirconia (ZrO), and silica (SiO). These can be used alone or in combination of two or more. Because OSC materials can function as co-catalysts for exhaust gas purification, carriers containing OSC materials are more preferred. For example, OSC materials, such as ceria or ceria-zirconia composite oxides to which trace amounts of oxides containing yttrium (Y), lanthanum (La), niobium (Nb), praseodymium (Pr), or other rare earth elements, are preferred because of their improved heat resistance.

[0025] The catalyst coated portion 22 may further contain components other than the catalytic metal component and the carrier, such as a binder, a promoter component, and other additives. As in the conventional catalyst coating of this type, the binder may be alumina, silica, etc. The promoter component may be the above-mentioned metals such as Ba and Sr. There are no particular restrictions on the content of the catalytic metal in the catalyst coated portion 22. For example, it may be 0.01 mass % to 10 mass % relative to the total mass of the carrier contained in the catalyst coated portion 22, and preferably 0.1 mass % to 5 mass %. The catalyst coating portion 22 may have a simple single-layer structure as shown in Figures 3 and 4, or may have a multi-layer structure including two or more layers with different types of catalyst metals and / or carriers, different blending ratios, etc. The thickness and length of the catalyst coating portion 22 may be determined appropriately depending on the size of the cells 15 of the substrates 11 and 11A, the flow rate of exhaust gas introduced into the exhaust gas passage, etc. For example, the thickness of the catalyst coating portion may be 1 µm to 500 µm.

[0026] On the other hand, the catalyst metal directly supported portion 24 is a part of the catalyst supported portion configured by supporting the catalyst directly on the substrate 11, 11A without using the above-mentioned carrier in order to have a smaller heat capacity than the catalyst coated portion 22. The type of catalytic metal used in the catalytic metal direct support portion 24 may be the same as or different from that in the catalytic coated portion 22. For example, when a three-way catalyst is configured, it is preferable that at least one of Pd, Pt, and Rh, as used in the examples described below, is supported on the catalytic metal direct support portion 24. For example, by supporting Pd and / or Pt as the catalytic metal, it is possible to improve the exhaust gas purification performance during cold starts and cold running, particularly the purification performance of exhaust gas components that are purified by oxidation, such as HC and CO. On the other hand, by supporting Rh as the catalytic metal, it is possible to improve the purification performance during cold starts and cold running, particularly NO. x Therefore, the purification performance of exhaust gas components that are reduced and purified can be improved. As long as the desired low heat capacity is maintained, components other than the catalytic metal may be contained. For example, in the case of a catalytic metal directly supported portion 22 containing Pd as used in the examples described below, alkaline earth metals such as barium (Ba) and strontium (Sr) may be contained (for example, about 1 to 20 mass % of the entire catalyst supported portion 20). This suppresses sintering of Pd and maintains the catalytic activity of Pd. The average particle size of these metal species based on electron microscope observation is preferably 0.5 nm to 50 nm, more preferably 1 nm to 20 nm, but is not particularly limited.

[0027] Although not particularly limited, the catalytic metal content per unit volume (1 L) of the entire exhaust gas purification catalyst 10, 10A is suitably about 0.1 to 5 g / L, and preferably about 0.2 to 2 g / L. If the catalytic metal content is too high, it is not preferable from the viewpoint of cost, and if it is too low, it is not preferable because the exhaust gas purification ability is low. In this specification, the term "catalyst volume 1 L" refers to a bulk volume 1 L including the volume of the voids in the cells 15 in addition to the pure volume of the substrates 11 and 11A.

[0028] The catalyst coated portion 22 and the catalyst metal directly supported portion 24 of the exhaust gas purification catalysts 10, 10A disclosed herein can be formed by the same method as that for forming the catalyst coated portion of a conventional exhaust gas purification catalyst. The catalyst coated portion 22 can be easily manufactured by a washcoat method or the like that has been conventionally used to form this type of catalyst coated portion. For example, an aqueous slurry containing a raw material compound (e.g., a water-soluble metal salt such as Pd nitrate or Rh nitrate) that will produce catalyst metal particles after firing, support particles made of ceramics such as alumina, zirconia, or an OSC material, a promoter component such as barium sulfate, and additives such as a thickener is coated onto the downstream end 16B of the substrate 11, 11A by a known washcoat method or the like. Thereafter, the catalyst coating portion 22 can be formed on the substrate 11, 11A by firing at a predetermined temperature for a predetermined time. The firing conditions for the wash-coated slurry are not particularly limited as they vary depending on the shape and size of the substrate or carrier, but the desired catalyst coating portion 22 can be formed by firing at about 400 to 1000°C for about 1 to 5 hours.

[0029] The catalyst metal directly supported portion 24 can also be formed by a washcoat method, similar to the formation of the catalyst coated portion 22. For example, an aqueous slurry containing a raw material compound (e.g., a water-soluble metal salt such as Pd nitrate or Rh nitrate) that will produce catalyst metal particles after firing, and an additive such as a thickener, is applied to the upstream end 16A of the substrate 11, 11A by a known washcoat method or the like. At this time, the thickness of the catalyst metal directly supported portion 24 formed in the thickness direction of the partition wall 16 of the substrate 11, 11A can be adjusted by appropriately adjusting the viscosity of the slurry used. For example, the viscosity of the slurry can be adjusted by using a commercially available cone-plate viscometer at a rotation speed of 1 to 100 rpm, room temperature (25°C), and a shear rate of 380 s -1The viscosity measured in this manner is suitably about 10 mPa to 1000 mPa, and preferably about 100 mPa to 800 mPa. When the catalyst metal is to be unevenly distributed in the surface layer portion of the partition walls 16 (for example, a surface layer portion that is about 20 to 30% from the partition wall surface when the entire partition wall thickness is taken as 100%), the viscosity is preferably about 200 mPa to 600 mPa. A conventionally known compound can be used as a thickener for adjusting the viscosity of this type of washcoat slurry, and examples of suitable thickeners include water-soluble polymers such as polyvinyl alcohol, ethylene glycol, and propylene glycol, cellulose derivatives such as hydroxyethyl cellulose, carboxymethyl cellulose, and methyl cellulose, and polysaccharides such as pectin and xanthan gum.

[0030] Thereafter, by firing at a predetermined temperature for a predetermined time, the catalyst metal directly supported part 24 can be formed on the substrate 11, 11A. The firing conditions for the wash-coated slurry are not particularly limited because they vary depending on the shape and size of the substrate or carrier, but typically, the desired catalyst metal directly supported part 24 can be formed by firing at about 400 to 1000°C for about 1 to 5 hours. Alternatively, the catalyst metal directly supported portion may be wash-coated with the slurry, and the catalyst coated portion may be wash-coated with the slurry, and then calcined at the same time.

[0031] In the exhaust gas purification catalyst disclosed herein, the length of the upstream region of a predetermined length (i.e., the region where the catalyst coated portion 22 is not formed) is not particularly limited as long as it achieves the desired reduction in heat capacity. From the viewpoint of improving the exhaust gas purification efficiency during cold starts and cold running, it is appropriate for the region to be formed in a length that is 20% or more, and preferably 30% or more, of the total length of the cells (exhaust gas passages) 15 of the substrates 11, 11A, taken as 100%. Furthermore, from the viewpoint of achieving sufficient exhaust gas purification performance during hot running as well as exhaust gas purification efficiency during cold running, it is appropriate for the region to be formed in a length that is 50% or less, and preferably 40% or less.

[0032] Hereinafter, several examples of the exhaust gas purification catalyst disclosed herein will be described, but it is not intended that the present invention be limited to these specific examples.

[0033] <Production example> The following three types of honeycomb cylindrical straight-flow type substrates 1 to 3 were prepared as substrates. Each substrate had a length of 50 mm in the longitudinal direction (exhaust gas flow direction), a capacity of 0.551 L, a diameter of 118.4 mm, and approximately 600 square-section cells. The partition wall thickness was approximately 4 to 5 mils (1 mil is 1 / 1000 inch). ·Base material 1 Si-SiC base material Substrate 2: Cordierite substrate Substrate 3: High Al content ferritic (20Co-5Al) stainless steel substrate Then, using the above substrate, a honeycomb-shaped straight flow type exhaust gas purifying catalyst having a catalyst supporting portion 20 as schematically shown in any one of Figures 3 to 6 was produced. Specifically, the process is as follows.

[0034] <Comparative Example 1> The exhaust gas purification catalyst of Example 1 was produced using a substrate 1, with a catalytic metal directly supported portion 24 formed in an upstream region extending from the upstream end to 30% of the length of the entire length (100% in the exhaust gas flow direction (direction indicated by the arrow in the figure)), and with a catalytic coated portion 22 formed in the downstream region of the remaining 70% of the length, without forming a catalytic metal directly supported portion. Specifically, alumina support particles containing about 1 to 10 wt % of La2O3 and an alumina-based sol (binder) were added to and suspended in an aqueous solution containing palladium nitrate to prepare a catalyst coating portion forming slurry 1. The slurry 1 was then poured into the cell from the upstream end of the substrate 1, and unnecessary portions were blown away with a blower to form a Pd layer containing Pd as a catalytic metal on the wall surface (partition wall surface) of the substrate. The substrate was then placed in a dryer at 120°C for 2 hours to remove moisture, and then transferred to an electric furnace and fired at 500°C for 2 hours. Thus, a Pd-containing Fr region catalyst coating portion 21 was formed in the upstream region extending from the upstream end to 30% of the total length (100%).

[0035] Next, alumina support particles containing approximately 1 to 10 wt% La2O3, CZ compound particles with a CeO2 content of 15 to 40 wt% and the remainder ZrO2 as an OSC material, and an alumina-based sol (binder) were added and suspended in an aqueous solution containing rhodium nitrate to prepare slurry 2 for forming the catalyst coating portion. The slurry 2 was then poured into the cell from the downstream end of the substrate 1, and unnecessary portions were blown away with a blower to form an Rh layer containing Rh as a catalytic metal on the wall surface (partition wall surface) of the substrate. The substrate was then placed in a dryer at 120°C for 2 hours to remove moisture, and then transferred to an electric furnace and fired at 500°C for 2 hours. In this way, an Rr region catalyst-coated portion 22 containing Rh was formed in a downstream region extending from the downstream end to 70% of the total length (see FIG. 5 ). In this Comparative Example 1, the catalytic metal loading per 1 L of catalyst volume was approximately 2 g / L for the Pd loading in the Fr region catalyst-coated portion 21 and approximately 0.15 g / L for the Rh loading in the Rr region catalyst-coated portion 22.

[0036] <Comparative Example 2> Alumina support particles containing approximately 1 to 10 wt% La2O3, CZ compound particles containing 15 to 40 wt% CeO2 as an OSC material with the remainder being ZrO2, and an alumina-based sol (binder) were added and suspended in an aqueous solution containing both palladium nitrate and rhodium nitrate to prepare slurry 3 for forming the catalyst coating portion. The slurry 3 was then poured into the cell from the downstream end of the substrate 1, and unnecessary portions were blown away with a blower to form a Pd&Rh layer containing Pd and Rh as catalytic metals on the wall surface (partition wall surface) of the substrate. The substrate was then placed in a dryer at 120°C for 2 hours to remove moisture, and then transferred to an electric furnace and fired at 500°C for 2 hours. In this manner, an Rr region catalyst coating portion 22 containing both Pd and Rh was formed in the downstream region extending from the downstream end to 70% of the total length (see FIG. 6 ). In Comparative Example 2, no catalyst support portion was formed in the upstream region extending from the upstream end to 30% of the total length (100% of the total length in the exhaust gas flow direction). In Comparative Example 2, the Pd support amount in the Rr region catalyst coating portion 22 per 1 L of catalyst volume was approximately 2 g / L, and the Rh support amount was approximately 0.15 g / L.

[0037] Example 1 Hydroxyethyl cellulose was added as a thickener to an aqueous solution containing palladium nitrate to prepare a coating solution for forming a catalyst metal directly supported part. At this time, the viscosity was measured at 25°C and a shear rate of 380 s using a cone-plate type viscometer manufactured by Toki Sangyo Co., Ltd., with the rotation speed varied in the range of 1 to 100 rpm. -1 The amount of the thickener added was adjusted so that the viscosity measured at 100°C was 300 mPa. The resulting coating liquid was poured from the upstream end of the substrate 1 into an upstream region extending from the upstream end to 30% of the total length of the cell interior, and unnecessary portions were blown away with a blower to form a region in which Pd was directly deposited inside the partition walls of the substrate (here, a region extending to a depth of approximately 30% of the total thickness from the partition wall surface relative to 100% of the total thickness). The substrate was then placed in a dryer at 120°C for 2 hours to remove moisture, and then transferred to an electric furnace and fired at 500°C for 2 hours. Thus, a catalyst metal directly supported portion 24 containing Pd was formed in the upstream region extending from the upstream end to 30% of the total length (see FIG. 3). Next, the same process as in Comparative Example 1 was carried out using the above slurry 2, to form an Rr region catalyst-coated portion 22 containing Rh in a downstream region extending from the downstream end to 70% of the total length (100%) (see FIG. 3). In this Example 1, the catalytic metal loading amount per 1 L of catalyst volume was such that the Pd loading amount in the catalytic metal directly-loaded portion 24 (Fr region) was approximately 2 g / L, and the Rh loading amount in the Rr region catalyst-coated portion 22 was approximately 0.15 g / L.

[0038] <Example 2> The catalyst metal directly supported portion forming coating liquid was poured over the entire length from the upstream end to the downstream end inside the cell, and unnecessary portions were blown away with a blower to form a portion in which Pd was directly supported inside the partition walls of the substrate (here, a region up to a depth where the thickness from the partition wall surface was about 30% of the total thickness 100%). Next, the substrate was placed in a dryer at 120°C for 2 hours to remove moisture, and then transferred to an electric furnace and fired at 500°C for 2 hours. In this way, a catalyst metal directly supported portion 24 containing Pd was formed over the entire length of the cell (see Figure 4). Next, the same process as in Comparative Example 1 and Example 1 was carried out using the above slurry 2, and an Rr region catalyst-coated portion 22 containing Rh was formed in a downstream region extending from the downstream end to 70% of the total length (100%) (see FIG. 4). In Example 2, the catalytic metal loading amount per 1 L of catalyst volume was such that the Pd loading amount in the catalytic metal directly-loaded portion 24 was approximately 2 g / L, and the Rh loading amount in the Rr region catalyst-coated portion 22 was approximately 0.15 g / L.

[0039] <Comparative Example 3> By carrying out the same process using the same materials as in Comparative Example 1 except that the substrate was the substrate 2, an exhaust gas purification catalyst was prepared in which an Fr region catalyst coating portion 21 containing Pd was formed in an upstream region extending from the upstream end to 30% of the total length, and an Rr region catalyst coating portion 22 containing Rh was formed in a downstream region extending from the downstream end to 70% of the length (FIG. 5). In this Comparative Example 3, the catalytic metal loading per 1 L of catalyst volume was such that the Pd loading in the Fr region catalyst coating portion 21 was approximately 2 g / L, and the Rh loading in the Rr region catalyst coating portion 22 was approximately 0.15 g / L.

[0040] Example 3 An exhaust gas purification catalyst was prepared by using the same materials and processes as in Example 1, except that the substrate 2 was used as the substrate, in which a catalytic metal directly supported portion 24 containing Pd was formed in an upstream region extending from the upstream end to 30% of the total length, relative to 100% of the total length, and an Rr region catalyst coated portion 22 containing Rh was formed in a downstream region extending from the downstream end to 70% of the length (FIG. 3). In this Example 3, the catalytic metal loading per 1 L of catalyst volume was such that the Pd loading in the Fr region catalytic metal directly supported portion 24 was approximately 2 g / L, and the Rh loading in the Rr region catalyst coated portion 22 was approximately 0.15 g / L.

[0041] <Comparative Example 4> By using the same materials and processes as in Comparative Example 1 except that the substrate was the substrate 3, an exhaust gas purification catalyst was prepared in which an Fr region catalyst coating portion 21 containing Pd was formed in an upstream region extending from the upstream end to 30% of the total length, and an Rr region catalyst coating portion 22 containing Rh was formed in a downstream region extending from the downstream end to 70% of the length (FIG. 5). In this Comparative Example 4, the catalytic metal loading per 1 L of catalyst volume was such that the Pd loading in the Fr region catalyst coating portion 21 was approximately 2 g / L, and the Rh loading in the Rr region catalyst coating portion 22 was approximately 0.15 g / L.

[0042] Example 4 An exhaust gas purification catalyst was prepared by using the same materials and processes as in Example 1, except that the substrate 3 was used as the substrate, and the catalyst had a catalytic metal directly supported portion 24 containing Pd formed in an upstream region extending from the upstream end to 30% of the total length, and an Rr region catalytic coated portion 22 containing Rh formed in a downstream region extending from the downstream end to 70% of the length (FIG. 3). In this Example 4, the catalytic metal loading per 1 L of catalyst volume was such that the Pd loading in the Fr region catalytic metal directly supported portion 24 was approximately 2 g / L, and the Rh loading in the Rr region catalytic coated portion 22 was approximately 0.15 g / L.

[0043] <Warm-up characteristic evaluation test> A test for evaluating warm-up characteristics was carried out using the eight exhaust gas purification catalyst samples obtained above. Specifically, one of the exhaust gas purification catalysts was connected to the exhaust system (exhaust pipe) of a gasoline engine (inline 4-cylinder engine) placed on a test stand. A bypass pipe not connected to the exhaust gas purification catalyst was installed in parallel with this exhaust system, and by switching a valve, it was possible to switch whether the exhaust gas emitted from the gasoline engine would flow to the exhaust gas purification catalyst side or the bypass pipe side. The temperature of the exhaust gas introduced into the exhaust gas purification catalyst was then adjusted to meet the specified conditions. In this evaluation test, the air-fuel ratio was set to stoichiometric (14.6 in this case), exhaust gas was produced with an intake air rate of 22 g / sec, and the exhaust gas at approximately 520°C was introduced into the exhaust gas purification catalyst connected to the exhaust system for pre-heating.

[0044] After that, the valve was switched to discharge the exhaust gas from the bypass pipe, and cooling air was introduced into the exhaust gas purification catalyst, cooling the air passing through the catalyst until its temperature reached approximately 60°C. Next, the valve was switched again, and when the temperature of the exhaust gas purification catalyst reached 60°C, the introduction of exhaust gas at 500°C into the exhaust gas purification catalyst was started, and the HC purification rate was measured. The number of seconds until the HC purification rate reached 50% was then measured and used as an index for evaluating warm-up characteristics. The results are shown in the graphs of Figures 7 to 9. The results for Comparative Examples 1 and 2 and Examples 1 and 2, which used the above-mentioned substrate 1, are shown in Figure 7, the results for Comparative Example 3 and Example 3, which used the above-mentioned substrate 2, are shown in Figure 8, and the results for Comparative Example 4 and Example 4, which used the above-mentioned substrate 3, are shown in Figure 9.

[0045] As is clear from these graphs, regardless of the type of substrate, forming the catalytic metal direct-supported portion in the upstream region improved the warm-up characteristics (warm-up performance), confirming that the HC conversion rate for relatively low-temperature exhaust gas was higher. Furthermore, both Example 1 and Example 2 had improved warm-up characteristics (warm-up performance) compared to Comparative Examples 1 and 2, which were constructed using the same substrate 1. The reason for the higher HC conversion rate in Example 1 compared to Example 2 is that the amount of Pd supported in the upstream region (here, a region 30% from the upstream end of the entire length) was higher in Example 1 than in Example 2. This may also be due to the higher HC oxidation efficiency in Example 1 when the warm-up characteristics (warm-up performance) were similar. In the test results shown in Figures 7 to 9, the catalytic metal (platinum group metal) provided in the catalytic metal direct-supported portion was Pd. However, it will be understood from the technical information disclosed herein that the effect of reducing heat capacity is not limited to Pd, and is similar for other catalytic metals (Rh, Pt, etc.). [Explanation of symbols]

[0046] 10. Exhaust gas purification catalyst 10A Electrically Heated Exhaust Gas Purification Catalyst (EHC) 11,11A Base material 15 Cell (exhaust gas passage) 16 Bulkhead 20 Catalyst support part 21,22 Catalyst coating section 24 Catalyst metal direct support part 40 electrodes 42 electrode layer 44 electrode terminals

Claims

1. An exhaust gas purification catalyst that purifies exhaust gas emitted from an internal combustion engine, a substrate disposed in an exhaust pipe of the internal combustion engine, the substrate having an exhaust gas passage extending from an upstream end where exhaust gas is introduced to a downstream end where exhaust gas is discharged; a catalyst support portion formed in an exhaust gas passage of the substrate, the catalyst support portion including a catalytic metal that functions as a catalyst capable of oxidizing or reducing at least one exhaust gas component; It is equipped with The catalyst support portion is a catalyst-coated portion having a carrier made of inorganic compound particles and at least one type of catalytic metal supported on the carrier; a catalytic metal directly supported portion having at least one type of catalytic metal supported directly on the substrate without including the carrier; It is composed of wherein the catalyst-coated portion is not formed in an upstream region of the exhaust gas passage within a predetermined length from the upstream end portion, but is formed only in a region downstream of the upstream region, The catalytic metal directly supported portion is formed only in an upstream region of the exhaust gas passage that is a predetermined length from the upstream end portion of the exhaust gas passage, and is not formed in a region downstream of the upstream region where the catalytic coated portion is formed.

2. The catalytic metal directly supporting portion is formed so as to extend from the upstream end to the exhaust gas passage along at least 30% of the total length of the exhaust gas passage.

2. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is formed in a region having a length of at least 100%.

3. The catalytic metal directly supported portion contains palladium (Pd) and / or platinum (P t), and the catalytic coating portion contains rhodium (Rh) as the catalytic metal.

3. The exhaust gas purification catalyst according to claim 1 or 2.

4. the substrate is formed of a material that can be heated by passing electricity through it, The exhaust gas purification device according to any one of claims 1 to 3, which is configured as an electrically heated catalyst. catalyst.

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