JP7226943B2 - Exhaust gas purification catalyst - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst, and more particularly to an exhaust gas purifying catalyst comprising a catalyst layer of laminated structure using palladium and rhodium as essential components.

Platinum group elements such as ruthenium, rhodium, palladium, osmium, iridium, and platinum in purification of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emitted from internal combustion engines such as automobiles A three-way catalyst (TWC) using (PGM: Platinum Group Metal) as a catalytically active component is widely used.

Conventionally, in order to reduce the amount of PGM, which is relatively expensive, and to ensure high catalytic activity, exhaust gas purifying catalysts with a composite particle structure, in which catalytically active components are supported on a substrate in the form of fine particles, have been widely used. used. Specifically, an exhaust gas purifying catalyst having base material particles made of a metal oxide such as alumina, zirconia or ceria and a platinum group element supported on the base material particles is exemplified.

This type of exhaust gas purifying catalyst is installed directly under the engine in order to shorten the warm-up time by supplying high-temperature exhaust gas and quickly raise the temperature to the catalyst activation temperature to exhibit highly efficient purification performance. There are many things. However, since the temperature of the exhaust gas is low, for example, at the initial stage of engine start-up, it is difficult to obtain the desired catalytic activity. In recent years, more and more vehicles frequently repeat engine stop and operation. Therefore, it is required to improve the warm-up performance of the catalyst and to improve the low-temperature purification performance. In order to improve the low-temperature purification performance of the catalyst, it is conceivable to increase the amount of catalyst precious metal supported, but there is a potential problem that it leads to an increase in cost.

Various proposals have been made to address this problem. For example, an exhaust gas purifying catalyst having a laminated catalyst layer using palladium and rhodium as essential components has been developed. Specifically, Patent Documents 1 and 2 disclose an exhaust gas purifying catalyst comprising a catalyst layer having a three-layer laminated structure having a palladium catalyst layer, a rhodium catalyst layer, and a palladium catalyst layer in this order on a honeycomb substrate. It is

Further, a zone-coated catalyst or the like has been developed in which separate catalyst layers are arranged on the honeycomb substrate on the upstream side and the downstream side in the exhaust gas flow path. For example, Patent Document 3 discloses an exhaust gas purifying catalyst provided with a catalyst layer having a palladium region and a rhodium region arranged adjacent to the palladium region on the surface of a honeycomb substrate or the like. Further, in Patent Document 4, a lower catalyst layer containing at least one of Pd and Pt formed on the surface of a honeycomb substrate or the like, and a surface of the lower catalyst layer on the upstream side in the gas flow direction of the exhaust gas are coated. and a rear upper catalyst layer containing Rh, which covers the surface of the lower catalyst layer on the downstream side of the front upper catalyst layer in the direction of gas flow. An exhaust gas purifying catalyst is disclosed in which the density, coating length, and coating amount are adjusted.

Japanese translation of PCT publication No. 2010-501337 Obtained Table 2012-525955 JP 2015-093266 A JP 2016-026112 A

Exhaust gases emitted from internal combustion engines such as automobiles contain large amounts of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) when the catalyst temperature is low, such as at the time of starting. In order to improve purification performance, it is important to quickly raise the temperature of the catalyst and improve the low-temperature purification performance of the catalyst. That is, the catalyst can be activated early by improving the temperature rising performance of the catalyst, in other words, the warm-up performance, which is the ease with which the catalyst warms up. Further, by improving the low-temperature purification performance, it is possible to purify harmful substances in the exhaust gas with high efficiency.

However, Patent Documents 1 and 2 merely disclose that the purification performance of the three-way catalyst is improved, and sufficient studies have been made on the low-temperature purification performance and warm-up characteristics of the exhaust gas emitted from internal combustion engines such as automobiles. not done.

In addition, Patent Document 3 discloses that the catalyst layer is zone-coated, and Patent Document 4 discloses that the coat length of the catalyst layer is optimized to facilitate the warming of the catalyst, which is important for the low-temperature purification performance of the catalyst. There is a disclosure to the effect that exhaust gas purification performance is improved by improving machine performance. However, even in these Patent Documents 3 and 4, sufficient examination is not made on the influence of overlapping zone coats.

The present invention has been made in view of the above problems. That is, an object of the present invention is to provide an exhaust gas purifying catalyst or the like which has improved warm-up performance and low-temperature purification performance while using a relatively small amount of precious metal.

The present inventors have made extensive studies to solve the above problems. As a result, the inventors have found that the above problems can be solved by adopting a zone-coated catalyst having a predetermined laminated structure, and have completed the present invention.

That is, the present invention provides various specific aspects shown below.
(1) A base material that partitions a gas flow path through which exhaust gas passes, and a catalyst layer that is provided directly on the base material or via another layer, and is provided upstream of the gas flow path. and an upstream catalyst layer containing Pd, provided directly on the base material or via the other layer, and separated from the upstream catalyst layer by a distance Lc on the downstream side of the gas flow path and a catalyst layer having a downstream catalyst layer that is provided and contains Rh.
Here, Lc is more than 0% and less than 15% based on the total length of the base material in a cross-sectional view in the flow direction of the exhaust gas.

(2) the upstream catalyst layer is provided so as to cover the base material or the other layer in a range of 30 to 70% of the total length of the base material in a cross-sectional view in the flow direction of the exhaust gas; The downstream catalyst layer is provided so as to cover the base material or the other layer in a range of 70 to 30% of the total length of the base material in a cross-sectional view in the flow direction of the exhaust gas. A catalyst for purifying an exhaust gas as described.
(3) The exhaust gas purifying catalyst according to (1) or (2), wherein the Rh content in the downstream catalyst layer is higher than the Rh content in the underlying catalyst layer.

(4) The method according to any one of (1) to (3), further comprising an OSC layer containing an oxygen storage/release material provided on the substrate, and an underlying catalyst layer provided on the OSC layer and containing Rh. The exhaust gas purifying catalyst according to any one of the items.
(5) The exhaust gas purifying catalyst according to (4), wherein the base catalyst layer contains at least first base material particles and first composite catalyst particles having the Rh supported on the first base material particles.
(6) The exhaust gas purifying catalyst according to (4) or (5), wherein the underlying catalyst layer further contains an oxygen storage/release material.

(7) Any one of (1) to (6), wherein the upstream catalyst layer contains at least second base material particles and second composite catalyst particles having the Pd supported on the second base material particles. 1. The exhaust gas purifying catalyst according to item 1.
(8) The exhaust gas purifying catalyst according to (7), wherein the upstream catalyst layer further contains an oxygen storage/release material.

(9) Any one of (1) to (8), wherein the downstream catalyst layer contains at least third base material particles and second composite catalyst particles having the Rh supported on the third base material particles. 1. The exhaust gas purifying catalyst according to item 1.
(10) The exhaust gas purifying catalyst according to (9), wherein the downstream catalyst layer further contains an oxygen storage/release material.

According to the present invention, it is possible to realize an exhaust gas purifying catalyst or the like with further improved warm-up performance and low-temperature purification performance while using a relatively small amount of precious metal. Based on its composition and structure, the exhaust gas purifying catalyst and the like of the present invention can be particularly suitably used as a three-way catalyst (TWC) for reducing NOx, CO, HC, etc. in exhaust gas. It is possible to realize a three-way catalyst that has excellent purification performance at low temperature start, A/F fluctuation, warm-up, etc., and all of warm-up performance, low temperature purification performance, A / F characteristics can be expressed. In addition, the exhaust gas purifying catalyst and the like of the present invention can be installed in an engine direct type catalytic converter, a tandem arrangement direct type catalytic converter, etc., thereby reducing the canning cost.

1 is a schematic cross-sectional view showing a schematic configuration of an exhaust gas purifying catalyst of one embodiment; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Also, the dimensional ratios in the drawings are not limited to the illustrated ratios. However, the following embodiments are examples for explaining the present invention, and the present invention is not limited to these. That is, the present invention can be arbitrarily modified and implemented without departing from the gist thereof. In this specification, the expression of a numerical range such as "1 to 100" includes both the upper limit of "100" and the lower limit of "1". The same applies to the notation of other numerical ranges.

FIG. 1 is a schematic diagram showing a schematic configuration of an exhaust gas purifying catalyst 100 according to one embodiment of the present invention. This exhaust gas purifying catalyst 100 comprises a catalyst substrate 11 as a substrate for partitioning a gas flow path through which exhaust gas passes, an OSC layer 21 provided on at least one side of the catalyst substrate 11, and this OSC. It includes at least a base catalyst layer 31 provided on the upper surface side of the layer 21 and a catalyst layer 41 provided on the upper surface side of the base catalyst layer 31 . That is, in the present embodiment, a laminated structure including at least the OSC layer 21 , the base catalyst layer 31 and the catalyst layer 41 in this order is provided on the catalyst substrate 11 . The catalyst layer 41 has an upstream catalyst layer 41a provided on the upstream side of the gas flow path and a downstream catalyst layer 41b provided on the downstream side of the gas flow path. The side catalyst layers 41b are arranged in parallel with a distance Lc. In addition, the arrow in a figure shows the flow direction of waste gas. Each component will be described in detail below.

The catalyst base material 11 is a catalyst member for supporting the laminated structure (laminate) described above. By using the catalyst member as an integrated structure type catalyst member in which a catalyst layer is provided on the catalyst substrate 11, the applicability to various uses is increased, such as facilitating incorporation into an apparatus. For example, in exhaust gas purifying applications, a honeycomb structure base material or the like is used as the catalyst base material 11, and this monolithic structure type catalyst member is installed in the flow path through which the gas flow passes, and the gas flow is induced in the cells of the honeycomb structure base material. By passing through, it is possible to purify the exhaust gas with high efficiency.

As the catalyst base material 11 used here, one known in the art can be appropriately selected. Typical examples include ceramic monolith substrates such as cordierite, silicon carbide, and silicon nitride, metal honeycomb substrates such as stainless steel, wire mesh substrates such as stainless steel, and steel wool-like knit wire substrates. However, it is not particularly limited to these. Also, the shape thereof is not particularly limited, and any shape such as a prismatic shape, a cylindrical shape, a spherical shape, a honeycomb shape, a sheet shape, or the like can be selected. These can be used individually by 1 type or in combination of 2 or more types as appropriate.

Here, in this specification, "provided on at least one surface side of the catalyst base 11" means only the surface on the upper surface side (or the surface on the lower surface side) of the catalyst base 11 as shown in FIG. This means that it includes both an aspect in which a layered catalyst is provided on the upper surface of the catalyst base 11 and an aspect in which the catalyst layer 21 is provided on the upper surface side and the lower surface side of the catalyst base 11 . At this time, "provided on one side" means that the catalyst base 11 and the catalyst layer 21 are directly placed, and that the catalyst base 11 and the catalyst layer 21 are separated via any other layer. It is used in the sense of including both the mode in which the That is, any other layer (for example, a primer layer, an adhesive layer, etc.) may be interposed between the catalyst base 11 and the laminated catalyst.

The laminated structure (laminated body) described above has a laminated structure including at least the OSC layer 21, the base catalyst layer 31, and the catalyst layer 41 in this order. Here, in this specification, "at least provided in this order" means that the OSC layer 21, the underlying catalyst layer 31, and the catalyst layer 41 are arranged in this order, and as long as they are arranged in this order, Any other layer (eg, primer layer, adhesive layer, etc.) may be interposed between these layers. That is, the layered structure of the catalyst layer 21 includes an aspect in which the OSC layer 21, the underlying catalyst layer 31, and the catalyst layer 41 are directly placed (OSC layer 21/underlying catalyst layer 31/catalyst layer 41). A mode in which the catalyst layer 31 and the catalyst layer 41 are spaced apart via any other layer (for example, OSC layer 21/other layer/underlying catalyst layer 31/other layer/catalyst layer 41, OSC layer 21/other layer/underlying catalyst layer 31/catalyst layer 41 or OSC layer 21/underlying catalyst layer 31/other layer/catalyst layer 41).

In this embodiment, the OSC layer 21 is a layer containing an oxygen storage/release material. By providing the OSC layer 21 on the catalyst base material 11, the oxygen absorption/desorption capacity (hereinafter sometimes abbreviated as "OSC capacity") of the exhaust gas purification catalyst 100 can be raised, and the desired purification performance can be provided. can be made The oxygen storage/release material used here has an oxygen storage capacity. Specific examples include ceria-based oxygen storage/release materials (eg, ceria-based (composite) oxides) and zirconia-based high heat-resistant materials (eg, zirconia-based (composite) oxides), but are not particularly limited to these. The oxygen storage/release materials can be used singly or in combination of two or more.

In this specification, the term "ceria-based (composite) oxide" is used as a term encompassing both ceria-based oxides and ceria-based composite oxides, and specifically includes ceria (CeO ₂ ) or This is used as a concept including composite oxides or solid solutions doped with other elements. Similarly, the term "zirconia-based (composite) oxide" is used as _a term encompassing both zirconia-based oxides and zirconia-based composite oxides. is used as a concept including composite oxides or solid solutions doped with other elements. A cerium-zirconium-based composite oxide containing both cerium and zirconium shall be treated as corresponding to the former ceria-based composite oxide and not to the latter zirconia-based composite oxide.

Specific examples of ceria-based (composite) oxides include cerium (IV) oxide, cerium - rare earth element composite oxides other than cerium, cerium - transition element composite oxides, cerium - rare earth element other than cerium - transition element composite oxides. things, etc. Among these, as the ceria-based oxygen storage/release material, ceria-zirconia-based composite oxides are preferable because they have an excellent balance of oxygen storage capacity and heat resistance. system composite oxides are more preferred. As the ceria-based (composite) oxide, the mass ratio of Ce and Zr is preferably 50% by mass or more and 95% by mass or less in terms of oxides (CeO ₂ and ZrO ₂ ).

Specific examples of zirconia-based (composite) oxides include zirconium (IV) oxide, zirconium-cerium and rare earth element composite oxides other than zirconium, zirconium-transition element composite oxides, zirconium-cerium and rare earth elements other than zirconium Element-transition element composite oxides and the like are included. Among these, the zirconia-based high heat-resistant material is more preferably a zirconia-based composite oxide in which rare earth elements other than cerium and zirconium are solid-dissolved from the viewpoint of the balance of heat resistance and toughness. As the zirconia-based (composite) oxide, one having a Zr mass ratio of 50% by mass or more and 80% by mass or less in terms of oxide (ZrO ₂ ) is preferably used.

Here, ceria-based (composite) oxides and zirconia-based (composite) oxides include scandium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium and other rare earth elements other than cerium and zirconium (hereinafter sometimes referred to as "other rare earth elements"). Among these, yttrium, lanthanum, praseodymium, and neodymium are preferred. Other rare earth elements can be used singly or in appropriate combination of two or more. When other rare earth elements are included, the content ratio is not particularly limited, but the total amount of the other rare earth elements in terms of oxides (e.g., La ₂ O ₃ , Nd ₂ O ₃ , Pr ₅ O ₁₁ , etc.) is preferably 0.1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, preferably 55% by mass or less, and more preferably 50% by mass or less. Preferably, 45% by mass or less is more preferable.

In addition, the ceria-based (composite) oxide and the zirconia-based (composite) oxide may contain transition elements such as chromium, cobalt, iron, nickel, titanium, manganese and copper. A transition element can be used individually by 1 type or in combination of 2 or more types as appropriate. When a transition element is included, the content ratio is not particularly limited, but the total amount of the above-described transition element in terms of oxide (for example, the sum of Fe ₂ O ₃ , TiO _{2 ,} etc.) with respect to the total amount of the base material particles , 0.01% by mass or more is preferable, 0.1% by mass or more is more preferable, 0.5% by mass or more is more preferable, 10% by mass or less is preferable, 5% by mass or less is more preferable, and 3% by mass or less is More preferred.

In the above ceria-based (composite) oxides and zirconia-based (composite) oxides, part of cerium and zirconium are alkali metal elements such as lithium, sodium, and potassium, beryllium, magnesium, calcium, strontium, and barium. may be substituted with an alkaline earth metal element such as Here, the alkali metal elements and the alkaline earth metal elements can be used singly or in any combination and ratio of two or more. In addition, the above ceria-based (composite) oxide and zirconia-based (composite) oxide may contain hafnium (Hf), which is usually contained about 1 to 2% by mass in zirconia ore, as an unavoidable impurity. do not have.

Commercially available products of various grades can be used as the oxygen storage/release material described above. For example, base particles having the composition described above can also be produced by methods known in the art. These production methods are not particularly limited, but a coprecipitation method and an alkoxide method are preferred.

As a coprecipitation method, for example, an alkaline substance is added to an aqueous solution obtained by mixing a cerium salt and/or a zirconium salt and other rare earth metal elements, transition elements, etc., which are blended as necessary, in a predetermined stoichiometric ratio. A preferred method is to hydrolyze or co-precipitate the precursor, and then calcine the hydrolysis product or co-precipitate. The types of various salts used here are not particularly limited. Hydrochlorides, oxyhydrochlorides, nitrates, oxynitrates, carbonates, phosphates, acetates, oxalates, citrates and the like are generally preferred. Also, the type of alkaline substance is not particularly limited. Aqueous ammonia solutions are generally preferred. As the alkoxide method, for example, a mixture obtained by mixing cerium alkoxide and/or zirconium alkoxide and optionally other rare earth metal elements, transition elements, etc. in a predetermined stoichiometric ratio is hydrolyzed, and then A baking method is preferred. The type of alkoxide used here is not particularly limited. Generally, methoxide, ethoxide, propoxide, isopropoxide, butoxide, and ethylene oxide adducts thereof are preferred. Moreover, the rare earth metal element may be blended as a metal alkoxide or blended as various salts described above.

The firing conditions for the subsequent firing treatment are not particularly limited, and may be in accordance with conventional methods. The firing atmosphere may be an oxidizing atmosphere, a reducing atmosphere, or an air atmosphere. The firing temperature and treatment time vary depending on the desired composition and its stoichiometric ratio, but from the viewpoint of productivity and the like, it is generally preferably 150° C. or higher and 1300° C. or lower for 1 to 12 hours, more preferably. is 2 to 4 hours at 350° C. or higher and 800° C. or lower. Prior to high-temperature firing, it is preferable to perform drying under reduced pressure using a vacuum dryer or the like, and to perform drying treatment at 50° C. or higher and 200° C. or lower for about 1 to 48 hours.

The average particle diameter (D ₅₀ ) of the oxygen storage/release material described above can be appropriately set according to the desired performance, and is not particularly limited. from the viewpoint of increasing the number of . In this specification, the average particle diameter D ₅₀ of the oxygen storage/release material is measured by a laser diffraction particle size distribution analyzer (for example, laser diffraction particle size distribution analyzer SALD-3100 manufactured by Shimadzu Corporation). Means the median diameter.

The OSC layer 21 may contain other components as long as it contains the oxygen storage/release material described above. Other components include various additives known in the art, such as binders such as boehmite and alumina sol; dispersion stabilizers such as nonionic surfactants and anionic surfactants; pH adjusters; viscosity adjusters; Examples include platinum group elements such as Pd, Rh, and Pt, but are not particularly limited to these. Details of these various known additives will be described later in the section of each catalyst layer. The OSC layer 21 may also contain other components such as catalysts and co-catalysts known in the art.

The content ratio of the oxygen storage/release material in the OSC layer 21 can be appropriately set according to the desired performance, and is not particularly limited, but is preferably 50% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less with respect to the total amount of the OSC layer 21. is 70% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or less, and still more preferably 90% by mass or less.

In addition, the coating amount (coating amount) of the OSC layer 21 can be appropriately set according to the desired performance, and is not particularly limited. It is preferably 10 to 100 g, more preferably 12 to 80 g, still more preferably 15 to 60 g per (1 L).

Here, in this specification, "per unit volume (1 L) of the catalyst base 11 (per 1 L of base)" means "not only the net volume of the catalyst base 11 (base), but also the inside of the base. Per 1 L of the entire bulk volume including the volume of the voids formed in the ". In addition, when cells are partitioned inside the catalyst substrate 11 (substrate), "the total volume including the volume of the cells in the net volume and the volume of the voids of the catalyst substrate 11 (substrate) Bulk volume of 1 L". Hereinafter, the coating amount (coating amount) of each component per 1 L of substrate may be expressed as this (g/L).

On the other hand, the base catalyst layer 31 is a catalyst layer containing Rh. By providing the underlying catalyst layer 31 on the OSC layer 21, the purification performance of the exhaust gas purification catalyst 100 at the time of A/F fluctuation can be raised, and the desired purification performance can be provided.

In the present embodiment, the underlying catalyst layer 31 contains at least first composite catalyst particles having first base material particles and rhodium as catalytically active particles supported at least on the first base material particles. At least rhodium is essential as the platinum group element contained in the underlying catalyst layer 31 from the viewpoint of improving purification performance during A/F fluctuations. In this embodiment, alumina is used as the first base material particles, and Rh-supported alumina is used as the first composite catalyst particles. Here, the first base particles are base particles that support catalytically active particles in a highly dispersed manner.

On the other hand, the catalyst layer 41 is a zone coat layer having an upstream catalyst layer 41a provided on the upstream side of the gas flow path and a downstream catalyst layer 41b provided on the downstream side of the upstream catalyst layer 41a. . By adopting a zone coat layer in which the Pd-containing upstream catalyst layer 41a and the Rh-containing downstream catalyst layer 41b are arranged in this manner, both warm-up performance and low-temperature purification performance are achieved at a high level. be able to.

In the present embodiment, the upstream catalyst layer 41a contains at least second composite catalyst particles having second base material particles and palladium as catalytically active particles supported at least on the second base material particles. From the viewpoint of improving warm-up performance, at least palladium is essential as the platinum group element contained in the upstream catalyst layer 41a. In this embodiment, alumina is used as the second base material particles, and Pd-supported alumina is used as the second composite catalyst particles. Here, the second base particles are base particles that support catalytically active particles in a highly dispersed manner.

Further, in the present embodiment, the downstream catalyst layer 41b contains at least third composite catalyst particles having third base material particles and rhodium as catalytically active particles at least supported on the third base material particles. . At least rhodium is essential as the platinum group element contained in the downstream side catalyst layer 41b from the viewpoint of improving low-temperature purification performance. In this embodiment, alumina is used as the third base particles, and Rh-supported alumina is used as the third composite catalyst particles. Here, the third base particles are base particles that support catalytically active particles in a highly dispersed manner.

The first to third base particles supporting the platinum group element described above can be appropriately selected from those known in the art according to the required performance, and the type thereof is not particularly limited. For example, silica; boehmite; alumina (α-Al ₂ O ₃ , δ-Al ₂ O ₃ , γ-Al ₂ O ₃ , δ-Al ₂ O ₃ , η-Al ₂ O ₃ , θ-Al ₂ O ₃ ) silica-alumina, silica-alumina-zirconia, silica-alumina-boria and other composite oxides containing alumina; lanthanum oxide, neodymium oxide, praseodymium oxide and other metal oxides or metal composite oxides; perovskite oxides; Barium compounds, anatase-type titania, zeolite, and the like may be mentioned, but are not particularly limited to these. Among these, porous particles having a large BET specific surface area are preferable as the substrate. Specific examples include alumina, silica, boehmite and silica-alumina. Examples of alumina include γ-alumina, δ-alumina, and θ-alumina. Silica includes amorphous, glassy, and colloidal silica, as well as crystalline silica having a variety of different phase modifications. Silica generally has a higher BET specific surface area than alumina and highly dispersed platinum group elements. Silica-alumina can be crystalline or amorphous. In silica-alumina, the Si/Al ratio varies and is appropriately set according to the application. Examples of titania include anatase titania. Examples of crystalline zeolites include ZSM-type zeolite and β-type zeolite. The base particles can be used singly or in combination of two or more.

The average particle diameter (D ₅₀ ) of the first to third base material particles can be appropriately set according to the desired performance, and is not particularly limited. From the viewpoint of increasing the number of sites, it is preferably 0.5 μm or more, more preferably 1 μm or more, still more preferably 3 μm or more, preferably 30 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. In this specification, the average particle diameter D ₅₀ of the first to third base particles is determined by a laser diffraction particle size distribution analyzer (for example, a laser diffraction particle size distribution analyzer SALD-3100 manufactured by Shimadzu Corporation). means the median diameter measured. Various grades of commercially available products can be used as the first to third base particles described above. For example, base particles having the composition described above can also be produced by methods known in the art.

Each of the catalyst layers 31, 41a, 41b includes, in addition to the above-described first to third base material particles, base material particles capable of supporting the above-described platinum group elements and noble metal elements (hereinafter referred to as "other base material particles" There is.) may be included. Other base material particles include, for example, silica; alumina; stabilized composite oxides containing alumina such as silica-alumina, silica-alumina-zirconia, silica-alumina-boria; zeolite; cerium oxide, zirconium oxide, lanthanum oxide , neodymium oxide, praseodymium oxide, titania, ceria-zirconia, zirconia doped with a rare earth element and/or a transition element, or a composite oxide such as ceria-zirconia, or a metal oxide or metal composite oxide, or a rare earth element in addition to these and stabilized composite oxides doped with transition elements and the like, but are not particularly limited to these. These materials can be used singly or in combination of two or more. Among these, γ-alumina having a specific surface area of 50 to 300 m ² /g, preferably 100 to 200 m ² /g is preferably used. The other base material particles may or may not support the platinum group element described above.

More specifically, in the underlying catalyst layer 31, the coating amount (coating amount) of rhodium can be appropriately set according to the desired performance, and is not particularly limited. It is preferably 0.01 to 0.4 g, more preferably 0.03 to 0.3 g, still more preferably 0.05 to 0.2 g in terms of noble metal amount.

In addition, in the upstream catalyst layer 41a, the coating amount (coating amount) of palladium can be appropriately set according to the desired performance, and is not particularly limited. , preferably 1 to 20 g, more preferably 2 to 15 g, still more preferably 4 to 10 g.

Furthermore, in the downstream side catalyst layer 41b, the coating amount (coating amount) of rhodium can be appropriately set according to the desired performance, and is not particularly limited. , preferably 0.10 to 0.5 g, more preferably 0.13 to 0.45 g, still more preferably 0.15 to 0.40 g.

On the other hand, the total supported amount of Pd contained in the exhaust gas purifying catalyst 100 (OSC layer 21 and each catalyst layer 31, 41a, 41b) can be appropriately set according to the desired performance, and is not particularly limited. In terms of the amount of noble metal per unit volume (1 L) of , the total amount per 1 L of the substrate is preferably 1.0 to 10.0 g, more preferably 1.2 to 8 g, and still more preferably 1.5 to 5 g.

Further, the total supported amount of Rh contained in the exhaust gas purifying catalyst 100 (OSC layer 21 and each catalyst layer 31, 41a, 41b) can be appropriately set according to the desired performance, and is not particularly limited. In terms of the amount of noble metals per unit volume (1 L) of the substrate, the total amount per 1 L of the substrate is preferably 0.1 to 0.5 g, more preferably 0.15 to 0.4 g, further preferably 0.2 to 0.2 g. 3 g.

Here, the mass ratio of rhodium contained in each catalyst layer 31, 41b can be appropriately set according to the desired performance, and is not particularly limited, but the amount of platinum group elements used can be kept relatively low and high catalyst performance can be obtained. From the point of view, it is preferable that the Rh content in the downstream catalyst layer 41 b is higher than the Rh content in the underlying catalyst layer 31 . Specifically, the Rh content in the downstream catalyst layer 41b/Rh content in the underlying catalyst layer 31 is preferably more than 1 and 5 or less, more preferably 1.1 or more and 4 or less, and still more preferably 1.2 or more. 3 or less.

Each of the catalyst layers 31, 41a, 41b may contain other components as long as they contain the essential platinum group elements described above and the first to third base material particles blended as necessary. Other components include various additives known in the art, such as binders; dispersion stabilizers such as nonionic surfactants and anionic surfactants; pH adjusters; viscosity adjusters; platinum group elements other than the essential platinum group elements such as; alkali metals; alkaline earth metal elements;

Examples of binders include various sols such as boehmite, alumina sols, titania sols, silica sols, and zirconia sols. Also, soluble salts such as aluminum nitrate, aluminum acetate, titanium nitrate, titanium acetate, zirconium nitrate, zirconium acetate can be used as binders. In addition, acids such as acetic acid, nitric acid, hydrochloric acid and sulfuric acid can also be used as binders. The amount of the binder used is not particularly limited, but is preferably 0.01 to 15% by mass in total, and 0.05 to 10% by mass in total, relative to the total amount of each catalyst layer 31, 41a, 41b. is more preferable, and a total of 0.1 to 8% by mass is even more preferable. Each of the catalyst layers 31, 41a, 41b may contain catalysts, co-catalysts, and various additives known in the art in addition to the components described above.

A Ba-containing compound can also be used as an additive. Addition of a Ba-containing compound can be expected to improve heat resistance and activate catalytic performance. Examples of Ba-containing compounds include sulfates, carbonates, composite oxides, oxides, and the like, but are not particularly limited to these. More specifically, BaO, Ba(CH ₃ COO) ₂ , BaO ₂ , BaCO ₃ , BaZrO ₃ , BaAl ₂ O ₄ and the like can be mentioned. The amount of the Ba-containing compound used is not particularly limited, but is preferably 1 to 20% by mass in total, more preferably 2 to 15% by mass in total, with respect to the total amount of each catalyst layer 31, 41a, 41b. Preferably, the total is 3 to 13% by weight of each, more preferably.

Here, each catalyst layer 31, 41a, 41b contains oxygen having an oxygen storage capacity as other base material particles or as non-base material particles in addition to the first to third base material particles described above. It preferably contains an occlusion-release material. Since each catalyst layer 31, 41a, 41b contains an oxygen storage/release material, the OSC performance of the exhaust gas purification catalyst 100 can be reinforced, and the purification performance tends to be enhanced even when the A/F fluctuates. . As the oxygen storage/release material that can be used together, a ceria-based oxygen storage/release material or a zirconia-based high heat-resistant material is preferably used. Here, specific examples of the oxygen storage/release material that can be used in combination are the same as those described for the OSC layer described above, and redundant description will be omitted here.

In addition, when each catalyst layer 31, 41a, 41b contains other base material particles or non-base material particles, the content ratio of these can be appropriately set according to the desired performance, and is not particularly limited, but each catalyst layer 31 , 41a and 41b, respectively, preferably 1% by mass or more and 45% by mass or less, more preferably 3% by mass or more and 40% by mass or less, and still more preferably 5% by mass or more and 35% by mass or less.

The coating amount (coating amount) of the base catalyst layer 31 can be appropriately set according to the desired performance, and is not particularly limited. It is preferably 10 to 80 g, more preferably 20 to 70 g, and still more preferably 30 to 60 g per 1 L).

The coating amount (coating amount) of the upstream catalyst layer 41a can be appropriately set according to the desired performance, and is not particularly limited. It is preferably 20 to 100 g, more preferably 30 to 80 g, and even more preferably 40 to 60 g per (1 L).

The coating amount (coating amount) of the downstream side catalyst layer 41b can be appropriately set according to the desired performance, and is not particularly limited. It is preferably 20 to 120 g, more preferably 30 to 100 g, and even more preferably 40 to 100 g per (1 L).

In addition, the total coating amount (total coating amount) of the OSC layer 21 and each catalyst layer 31, 41a, 41b can be appropriately set according to the desired performance, and is not particularly limited. , the total amount per unit volume (1 L) of the catalyst base 11 is preferably 100 to 200 g, more preferably 120 to 180 g, and even more preferably 140 to 160 g. At this time, since the upper layer side of the laminated structure is likely to come into contact with exhaust gas components, it is preferable that the coating amount of the underlying catalyst layer 31 is larger than that of the OSC layer 21 . It is preferable that the number of catalyst layers 41 is large.

The exhaust gas purifying catalyst 100 of the present embodiment employs a zone-coat laminated catalyst having the above-described laminated structure, in which the uppermost layer (outermost layer) is the zone-coat layer of the upstream side catalyst layer 41a and the downstream side catalyst layer 41b. are doing. By adopting such a configuration, it is possible to realize the exhaust gas purification catalyst 100 that can exhibit warm-up performance, low-temperature purification performance, and A/F characteristics at a high level while using a relatively small amount of precious metal. there is The upstream catalyst layer 41a ensures warm-up performance for warming the catalyst early, the downstream catalyst layer 41b provides excellent low-temperature purification performance, and the underlying catalyst layer 31 improves purification performance during A/F fluctuations. It is presumed that the OSC layer 21 raises the level of the OSC performance, thereby exhibiting excellent exhaust gas purification performance.

At this time, the coating ratio of the upstream side catalyst layer 41a and the downstream side catalyst layer 41b can be appropriately set according to the desired performance, and is not particularly limited. The amount of precious metal used is kept relatively low, and the warm-up performance of the upstream side catalyst layer 41a is sufficiently exhibited, and the installation space for the downstream side catalyst layer 41b is sufficiently secured to achieve excellent low-temperature purification performance and A/F characteristics. From the viewpoint of exhibiting the above, the coating length La of the upstream catalyst layer 41a is preferably in the range of 30 to 70% of the total length L of the catalyst base 11 in a cross-sectional view in the flow direction of the exhaust gas. It is preferably from 35 to 65%, more preferably from 37 to 55%. A range of 70 to 30% is preferred, more preferably 65 to 35%, and even more preferably 63 to 45%. In the following also, the coating lengths La and Lb are sometimes described as percentages (%) with respect to the total length L of the catalyst base 11 .

Here, if the upstream catalyst layer 41a and the downstream catalyst layer 41b are formed so as to overlap each other in the thickness direction of the layers, the overlapping region becomes a protuberant portion that protrudes in the thickness direction, and the amount of catalyst locally increases. As a result, it has been found that the temperature rising property of the catalyst is lowered. In addition, if there is a portion protruding in the thickness direction between the upstream side catalyst layer 41a and the downstream side catalyst layer 41b, there also arises a problem that gas contact with the downstream side catalyst layer 41b is deteriorated. On the other hand, if the upstream side catalyst layer 41a and the downstream side catalyst layer 41b are too far apart, the length of the catalyst coating in the direction of gas flow is shortened, and the gas contact with the catalyst decreases, resulting in a decrease in purification performance. Therefore, from the viewpoint of catalyst temperature rise and gas permeation to the catalyst, the upstream catalyst layer 41a and the downstream catalyst layer 41b arranged in parallel on the base catalyst layer 31 are separated by a predetermined distance Lc. is preferably arranged. At this time, the distance Lc is preferably in the range of 0.5 to 15%, more preferably in the range of 1.0 to 14.5%, with respect to the total length L of the catalyst base 11, More preferably, it is within the range of 1.5 to 14.2%.

The state of separation between the upstream catalyst layer 41a and the downstream catalyst layer 41b and the separation distance Lc can be confirmed by, for example, a transmission type X-ray apparatus. Specifically, an image is obtained by irradiating the exhaust gas purifying catalyst 100 with X-rays from the side surface or the circumferential direction, and the separated state and the separated distance Lc can be confirmed in the image. The spaced distance Lc is the 1/4 position, 1/2 position (central axis), It was calculated as an average value of 3 points at 3/4 positions.

The exhaust gas purifying catalyst 100 having the layer structure described above can be obtained, for example, by providing the OSC layer 21 and the respective catalyst layers 31, 41a, 41b on the catalyst substrate 11 such as the above-described ceramic monolith substrate according to a conventional method. It is manufacturable. For example, the exhaust gas purifying catalyst 100 of the present embodiment can be obtained by sequentially coating (carrying) a slurry mixture of the OSC layer 21 and the catalyst layers 31, 41a, and 41b on the surface of the catalyst base 11. . The method of applying the slurry mixture to the catalyst base material 11 is not particularly limited and may be performed according to a conventional method. Various known coating methods, wash coating methods, and zone coating methods can be applied. After application of the slurry-like mixture, drying and firing can be carried out according to a conventional method.

Specific examples include, for example, the oxygen storage/release material described above, an aqueous medium, and, if necessary, a binder, a Ba-containing compound, other base material particles, other catalysts, co-catalysts, OSC materials, binders, platinum group elements, and various additions. A slurry mixture for the OSC layer 21 is prepared by mixing agents and the like in a desired mixing ratio, and for example, the first to third composite catalyst particles described above, an aqueous medium, and, if necessary, a binder and a Ba-containing compound. , other base material particles, other catalysts, co-catalysts, OSC materials, binders, various additives, etc. are mixed at a desired mixing ratio to prepare a slurry mixture for each catalyst layer 31, 41a, 41b, The OSC layer 21 can be provided on the catalyst substrate 11 by applying the obtained slurry mixture for the OSC layer 21 to the surface of the catalyst substrate 11 such as a honeycomb structure substrate, followed by drying and firing. Next, in the same manner, slurry mixtures for the catalyst layers 31, 41a, and 41b are successively applied, dried, and fired to form the OSC layer 21, the base catalyst layer 31, and the catalyst on the catalyst substrate 11. Layers 41 (upstream catalyst layer 41a and downstream catalyst layer 41b) may be provided. At this time, for example, the slurry mixture for the upstream catalyst layer 41a is applied by the coating length La from the upstream side of the gas flow path of the exhaust gas of the catalyst base 11, and the downstream side of the gas flow path of the exhaust gas of the catalyst base 11 is applied. The above-described zone coating can be performed by applying the slurry mixture for the downstream side catalyst layer 41b by the coating length Lb. Then, with respect to the total length L of the catalyst base 11, by setting the coating length La of the upstream side catalyst layer 41a + the coating length Lb of the downstream side catalyst layer 41b < the total length L of the catalyst base 11, the distance Lc described above is reduced to Can be set.

The amount of the aqueous medium used for preparing the slurry-like mixture may be such that each component can be uniformly dispersed or dissolved in the slurry. At this time, if necessary, an acid or a base can be added for adjusting the pH, or a surfactant, a dispersing resin, or the like can be added for adjusting the viscosity or improving the dispersibility of the slurry. From the viewpoint of firmly adhering or binding the first to third composite catalyst particles described above, it is preferable to use the binder described above. As a method for mixing the slurry, a known pulverizing method or mixing method such as pulverizing and mixing using a ball mill or the like can be applied.

After applying the slurry-like mixture onto the catalyst base material 11, it can be dried and calcined according to a conventional method. Although the drying temperature is not particularly limited, it is preferably 70 to 200°C, more preferably 80 to 150°C. The firing temperature is not particularly limited, but is preferably 300 to 650°C, more preferably 400 to 600°C. As for the heating means used at this time, for example, a known heating means such as an electric furnace or a gas furnace can be used.

The exhaust gas purifying catalyst 100 of the present embodiment can be used, for example, as a catalyst for purifying exhaust gas from diesel engines, gasoline engines, jet engines, boilers, gas turbines, etc., and can be used as a catalyst for purifying exhaust gas from internal combustion engines, particularly automobiles. is useful as a three-way catalyst for exhaust gas purification. The exhaust gas purifying catalyst 100 of the present embodiment can be arranged in the exhaust system of various engines. The number of installations and installation locations can be appropriately designed according to exhaust gas regulations. For example, if exhaust gas regulations are strict, the number of installation locations may be two or more, and the installation locations may be arranged under the floor behind the catalyst immediately below the exhaust system. Further, according to the exhaust gas purifying catalyst 100 of the present embodiment, not only during starting at a low temperature, but also in various driving specifications including high-speed driving at a high temperature, an excellent effect in the purification reaction of CO, HC, and NOx is obtained. can be demonstrated.

The features of the present invention will be described in more detail below with reference to test examples, examples and comparative examples, but the present invention is not limited to these. That is, materials, usage amounts, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. In addition, various production conditions and values of evaluation results in the following examples have the meaning of preferable upper limit values or preferable lower limit values in the embodiments of the present invention, and the preferable range is the above-described upper limit value or lower limit value and the values in the following examples or the values between the examples.

(Example 1)
First, pure water was added to ceria-zirconia composite oxide (CeO ₂ : 40% by mass) and γ-alumina powder to prepare a slurry mixture for the OSC layer of Example 1.

The obtained slurry mixture for the OSC layer was applied onto a honeycomb substrate made of cordierite at a coating amount of 40 g/L by a wash coat method and dried to prepare an OSC layer.

Next, γ-alumina powder and the ceria-zirconia-based composite oxide described above are impregnated with a rhodium (III) nitrate solution (containing 10% by mass in terms of Rh), and fired at 600 ° C. for 30 minutes. A first composite catalyst particle of Example 1 was obtained. After that, the obtained first composite catalyst particles and boehmite were mixed and diluted with pure water to prepare a slurry mixture for the base catalyst layer of Example 1.

The obtained slurry mixture for the base catalyst layer was applied onto the OSC layer of the cordierite honeycomb substrate by a wash coating method at a coating amount of 50 g/L and dried to form the base catalyst layer (Rh coating amount: 0.10 g/L).

Next, the above-mentioned γ-alumina powder and the above-mentioned ceria-zirconia-based composite oxide are impregnated with a palladium (II) nitrate solution (containing 20% by mass in terms of Pd), and baked at 600 ° C. for 30 minutes, Second composite catalyst particles of Example 1 were obtained. Thereafter, the obtained second composite catalyst particles, a Ba compound, and boehmite were mixed and diluted with pure water to prepare a slurry mixture for the upstream catalyst layer of Example 1.

The obtained slurry mixture for the upstream side catalyst layer is applied to the base catalyst layer on the exhaust gas inflow side of the cordierite honeycomb substrate by a wash coating method at a coating amount of 80 g / L, and dried. A side catalyst layer (Pd coating amount: 5.13 g/L) was prepared. Note that the coating length La of the upstream catalyst layer is 39.0% from the end face on the exhaust gas inflow side.

Next, the above-mentioned γ-alumina powder and the above-mentioned ceria-zirconia-based composite oxide are impregnated with a rhodium (III) nitrate solution (containing 10% by mass in terms of Rh), and baked at 600 ° C. for 30 minutes, A third composite catalyst particle of Example 1 was obtained. Thereafter, the obtained third composite catalyst particles and boehmite were mixed and diluted with pure water to prepare a slurry mixture for the downstream side catalyst layer of Example 1.

The obtained slurry mixture for the downstream side catalyst layer is applied onto the base catalyst layer on the exhaust gas outflow side of the cordierite honeycomb base material by a wash coat method at a coating amount of 80 g / L, and dried. A side catalyst layer (Rh coating amount: 0.25 g/L) was prepared. The coating length Lb of the downstream side catalyst layer is 59.5% from the end face on the exhaust gas inflow side.

As a result, the OSC layer 21, the base catalyst layer 31, and the catalyst layer 41 (the upstream catalyst layer 41a and the downstream catalyst layer 41b) are provided in this order on the cordierite honeycomb base material. An integrally structured laminated catalyst of Example 1 having the layer structure shown in FIG.

Next, after each of the monolithic layered catalysts thus obtained was stored in a converter, the converter was mounted downstream of the exhaust port of a gasoline engine. After that, under exhaust gas from an engine (3UZ-FE), a bed temperature of 960° C. was subjected to durability treatment for 40 hours to obtain a monolithic layered catalyst of Example 1 after durability treatment.

(Examples 2-6)
The amount of precious metal in the slurry mixture for the downstream catalyst layer is changed as shown in Table 1 so that the total amount of precious metal does not fluctuate, and then the coating length Lb of the downstream catalyst layer is changed as shown in Table 1. Except for this, monolithic layered catalysts of Examples 2 to 5 were obtained in the same manner as in Example 1 after durability treatment.

(Comparative Examples 1 to 3)
The amounts of noble metals in the slurry mixture for the upstream catalyst layer and the slurry mixture for the downstream catalyst layer were changed as shown in Table 1 so that the total amount of noble metals did not fluctuate, and then the coating length of the upstream catalyst layer was changed. Monolithic layered catalysts of Comparative Examples 1 to 3 after durability treatment were obtained in the same manner as in Example 1, except that La and the coating length Lb of the downstream catalyst layer were changed as shown in Table 1. . In the monolithic layered catalysts of Comparative Examples 1 to 3, the downstream catalyst layer was partially overlapped with the upstream catalyst layer. It means the length (distance) of the overlapping portion with the downstream side catalyst layer.

(Comparative Example 4)
The amount of precious metal in the slurry mixture for the downstream catalyst layer is changed as shown in Table 1 so that the total amount of precious metal does not fluctuate, and then the coating length Lb of the downstream catalyst layer is changed as shown in Table 1. Except for this, in the same manner as in Example 1, a monolithic layered catalyst of Comparative Example 4 after durability treatment was obtained.

<Performance evaluation>
Warm-up performance, low-temperature purification performance, A/F characteristics, and OSC performance were evaluated for each of the obtained exhaust gas purifying catalysts after durability treatment. Evaluation conditions are shown below.

[Measurement of warm-up characteristics]
Warm-up characteristics were measured using each of the exhaust gas purifying catalysts that had been allowed to cool to room temperature after the endurance treatment. Here, using a 2L engine, under the conditions of an engine speed of 2500 rpm, a boost pressure of -380 mmHg, and an A/F rate of 14.56±0.1/2.5 Hz, a temperature sensor was attached to a portion 1 inch from the catalyst inlet end face. , an exhaust gas kept at 400°C was introduced by switching the bypass, and the measurement was performed with the temperature rising from the starting temperature of 50°C. The catalyst inlet and outlet gas compositions were analyzed to determine the HC purification rate. Then, the time required for the HC purification rate to reach 50% (HC 50% purification time) was calculated and used as the warm-up characteristic. A shorter HC 50% purification time indicates a better catalyst.

[Measurement of light-off performance]
The light-off performance was measured using each of the exhaust gas purifying catalysts that had been allowed to cool to room temperature after the endurance treatment. Here, using a 2L engine, the engine speed is 2500rpm, the boost pressure is -300mmHg, and the A/F rate is 14.56±0.4/2.5Hz. After installation, the catalyst inlet gas temperature was varied from 200 to 450° C. at a constant heating rate (10° C./min), and the catalyst inlet and outlet gas compositions were analyzed to determine the HC purification rate. Then, the temperature (light-off temperature) at which the HC purification rate reached 50% was measured and defined as the light-off performance. A lower HC 50% purification temperature indicates a better catalyst.

[Measurement of A/F characteristics]
A/F characteristics were measured using each of the exhaust gas purifying catalysts that had been allowed to cool to room temperature after the endurance treatment. Here, using a 2L engine, the engine speed is 2500 rpm, the boost pressure is -300 mmHg, the catalyst inlet gas temperature is fixed at 500 ° C. was continuously changed, and the catalyst inlet and outlet gas compositions at this time were analyzed to obtain the purification rates of CO, HC, and NOx when the average air-fuel ratio A/F ranged from 13.5 to 15.5. By plotting the CO, HC and NOx purification rates against the inlet air-fuel ratio obtained in this way on a graph, a ternary characteristic curve is created, and the purification rate at the intersection point (crossover point: COP) of the CO and NOx purification curves is calculated. A/F characteristic. The higher the COP purification rate, the better the catalyst.

[Measurement of OSC performance]
The OSC performance was measured using each of the exhaust gas purifying catalysts that had been allowed to cool to room temperature after the endurance treatment. Here, a 2L engine is used, the engine speed is 2500 rpm, the boost pressure is -300 mmHg, the catalyst inlet gas temperature is fixed at 500 ° C., and the A / F is between 14.1 and 15.1. Concentration was measured continuously. The amount of oxygen released until the air-fuel ratio reached 15.1 to 14.1 was calculated as the oxygen storage amount and used as the OSC performance. A higher oxygen storage capacity indicates a better catalyst.

Table 1 shows the formulations and configurations of the exhaust gas purifying catalysts of Examples 1 to 6 and Comparative Examples 1 to 4, and the performance evaluation results of each catalyst.

As shown in Table 1, for the monolithic laminated catalysts of Comparative Examples 1 to 3, in which the downstream catalyst layer partially overlaps the upstream catalyst layer, the upstream catalyst layer and the downstream catalyst layer It was confirmed that the monolithic layered catalysts of Examples 1 to 6, in which the . Further, it was confirmed that the monolithic layered catalysts of Examples 1 to 6 had well-balanced catalytic properties such as warm-up properties, light-off properties, A/F properties, and OSC properties. On the other hand, in Comparative Example 4 in which the distance Lc was 16.3%, it was confirmed that the purification performance remained at the same level as Comparative Examples 1-3.

The exhaust gas purifying catalyst 100 of the present invention can be widely and effectively used as a three-way catalyst for reducing NOx, CO, HC, etc. in exhaust gas. It can be used particularly effectively in catalytic applications for purifying exhaust gas from turbines and the like. Further, the exhaust gas purifying catalyst 100 of the present invention can be effectively used as a TWC such as an engine direct type catalytic converter or a tandem arrangement direct type catalytic converter.

DESCRIPTION OF SYMBOLS 100... Exhaust gas purifying catalyst 11... Catalyst base material 21... OSC layer 31... Base catalyst layer 41... Catalyst layer 41a... Upstream side catalyst layer 41b... Downstream side catalyst layer L: total length of catalyst base La: coating length Lb: coating length Lc: distance

Claims (6)

a substrate defining a gas flow path through which exhaust gas passes;
an OSC layer provided on the substrate and containing an oxygen storage/release material;
a base catalyst layer provided on the OSC layer and containing Rh;
a catalyst layer provided on the substrate via the OSC layer and the underlying catalyst layer, the upstream catalyst layer being provided on the upstream side of the gas flow path and containing Pd; and the substrate A catalyst having a downstream catalyst layer containing Rh provided thereon via the OSC layer and the underlying catalyst layer, and provided on the downstream side of the gas flow path at a distance Lc from the upstream catalyst layer. layer and
with at least
the Rh content in the downstream catalyst layer is higher than the Rh content in the underlying catalyst layer ;
Exhaust gas purification catalyst.
Here, Lc is more than 0% and less than 15% based on the total length of the base material in a cross-sectional view in the flow direction of the exhaust gas. The upstream catalyst layer is provided so as to cover the OSC layer and the base catalyst layer in a range of 30 to 70% of the total length of the base material in a cross-sectional view in the flow direction of the exhaust gas,
2. The downstream side catalyst layer is provided so as to cover the OSC layer and the underlying catalyst layer in a range of 70 to 30% of the total length of the substrate when viewed in cross section in the flow direction of the exhaust gas. 2. The exhaust gas purifying catalyst according to . The ratio of the Rh content in the downstream catalyst layer to the Rh content in the underlying catalyst layer (Rh content in the downstream catalyst layer/Rh content in the underlying catalyst layer) is more than 1 and 5 or less.
3. The exhaust gas purifying catalyst according to claim 2 . The underlying catalyst layer contains at least first base material particles and first composite catalyst particles having the Rh supported on the first base material particles.
The exhaust gas purifying catalyst according to any one of claims 1 to 3 . The upstream catalyst layer contains at least second base material particles and second composite catalyst particles having the Pd supported on the second base material particles.
The exhaust gas purifying catalyst according to any one of claims 1 to 4 . The downstream catalyst layer contains at least third base material particles and second composite catalyst particles having the Rh supported on the third base material particles.
The exhaust gas purifying catalyst according to any one of claims 1 to 5 .

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