WO2019194187A1

WO2019194187A1 - Material for exhaust gas purification catalyst, catalyst composition for exhaust gas purification, and exhaust gas purification catalyst

Info

Publication number: WO2019194187A1
Application number: PCT/JP2019/014655
Authority: WO
Inventors: 亮竹内; 慶徳遠藤; 大典岩倉; 庸裕田中; 三郎細川
Original assignee: 三井金属鉱業株式会社
Priority date: 2018-04-03
Filing date: 2019-04-02
Publication date: 2019-10-10

Abstract

This material for an exhaust gas purification catalyst comprises the complex oxide indicated by formula (I). This catalyst composition for exhaust gas purification includes said complex oxide and a catalytic activity component. Formula (I): M1MnO3 (In this formula, M1 indicates at least one type of rare earth element selected from Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). M1 in formula (I) is preferably a rare earth element selected from Er, Tm, Yb, and Lu. The crystal structure of the complex oxide indicated by formula (I) is preferably a hexagonal structure.

Description

Exhaust gas purification catalyst material, exhaust gas purification catalyst composition, and exhaust gas purification catalyst

The present invention relates to an exhaust gas purification catalyst material comprising a complex oxide containing rare earth elements and manganese, an exhaust gas purification catalyst composition containing the complex oxide, and an exhaust gas purification catalyst comprising the exhaust gas purification catalyst composition.

Hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NO _x ) are contained in exhaust gas emitted from internal combustion engines such as automobiles and motorcycles (also referred to as saddle-type vehicles) such as gasoline engines and diesel engines. Contains harmful ingredients such as. Conventionally, a three-way catalyst has been used for the purpose of purifying and detoxifying these harmful components. As such a three-way catalyst, a noble metal that causes high costs such as platinum (Pt), palladium (Pd), rhodium (Rh), and alumina, ceria, zirconia, or a composite oxide thereof is arbitrarily combined. Things are used.

Further, an exhaust purification catalyst in which YbFe _x Mn _1-x O ₃ is used as a carrier and a catalytically active component is carried on this carrier has been reported (Patent Document 1). This document describes that an exhaust gas purification catalyst using YbFe _x Mn _1-x O ₃ as a carrier has a high exhaust gas purification effect in a low temperature range even if the amount of noble metal is reduced as compared with the conventional art.
Further, an exhaust purification catalyst in which YMnO ₃ is used as a carrier and a catalytically active component is supported thereon has been reported (Patent Document 2). This document describes that an exhaust gas purification catalyst using YMnO ₃ as a carrier has a high exhaust gas purification effect in a low temperature range.

WO2016 / 148062 pamphlet JP 2011-189306 A

In recent years, in order to improve the purification efficiency, it has been increasingly demanded not only to exhibit the purification performance from the start of the engine but also to maintain it. That is, not only the exhaust gas purification catalyst activity at low temperature, that is, the light-off performance, but also high temperature durability that can maintain the exhaust gas purification catalyst activity in the low temperature range even when exposed to high temperature exhaust gas for a long time is increasingly required. In this regard, the catalyst composition in which the catalytically active component is supported on YbFe _x Mn _1-x O ₃ described in Patent Document 1 has room for improvement in terms of HC, NO _x , and CO purification performance after high-temperature durability. there were. Further, this catalyst composition has room for improvement in terms of thermal stability of OSC (oxygen storage capacity).
Further, the catalyst composition described in Patent Document 2 also has insufficient HC, NO _x , CO purification performance and OSC thermal stability after high temperature durability.

An object of the present invention is to provide an exhaust gas purification catalyst material and an exhaust gas purification catalyst composition that have high exhaust gas purification performance after high-temperature durability and are excellent in heat resistance.

As a result of intensive studies, the present inventors have surprisingly found that a specific rare earth manganese oxide not containing Fe has high exhaust gas purification performance after high temperature durability and high OSC after high temperature durability, which has been difficult to obtain conventionally. I found out.

The present invention is based on the above findings and provides an exhaust gas catalyst material comprising a composite oxide represented by the formula (I).
M ₁ MnO ₃ (I)
(In the formula, M ₁ represents a rare earth element selected from Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.)

The present invention also provides an exhaust gas purifying catalyst composition containing the composite oxide and a catalytically active component.

The present invention also provides an exhaust gas purifying catalyst composition containing the composite oxide and containing no catalytic active component.

The present invention also provides an exhaust gas purification catalyst having a base material and a layer of the composition formed on the surface of the base material.

1 is an X-ray diffraction chart of Example 3, Comparative Example 2 and Comparative Example 3 before thermal endurance. FIG. 2 is a graph showing the purification performance of Example 1, Example 2 and Comparative Example 4 when the exhaust gas temperature rises. CO and _C 3 _{H 6} (a) is the rise in temperature is a graph showing a change in the conversion rate that is converted to CO _2, (b) NO _x with respect to the increase of the temperature converted into _{N 2} It is a graph which shows transition of the conversion rate. 3 is an X-ray diffraction chart before and after thermal endurance in Example 3, Comparative Example 3 and Comparative Example 4. FIG.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The exhaust gas purifying catalyst material of the present embodiment is composed of a complex oxide represented by the formula (I). The composite oxide represented by the formula (I) has, for example, a powder form.
M ₁ MnO ₃ (I)
(In the formula, M ₁ represents a rare earth element selected from Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.)

In the present specification, the exhaust gas purification catalyst material is a material contained in the exhaust gas purification catalyst, preferably an exhaust gas comprising a porous substrate and a catalyst layer formed on the surface of the porous substrate. It is the material contained in the catalyst layer in the purification catalyst.
One aspect of the exhaust gas purifying catalyst material of the present embodiment serves as a carrier for supporting a catalytic active component described later, and exhibits exhaust gas purifying catalytic performance by supporting the catalytic active component.
Further, another aspect of the exhaust gas purifying catalyst material of the present embodiment exhibits the exhaust gas purifying catalyst performance by itself even when the catalytically active component is not contained.

In the present specification, the exhaust gas purifying catalyst composition is a composition constituting the exhaust gas purifying catalyst, and preferably comprises a porous substrate and a catalyst layer formed on the surface of the porous substrate. It is the composition which comprises the catalyst layer in the catalyst for exhaust gas purification containing.
One aspect of the exhaust gas purifying catalyst composition of the present embodiment includes the composite oxide represented by the formula (I) and a catalytically active component described later.
Further, another aspect of the exhaust gas purifying catalyst composition of the present embodiment is one that contains the composite oxide represented by the formula (I) but does not contain a catalytically active component described later.

Formula (I) is a composition formula, and a complex oxide composed of M ₁ and Mn is represented by M ₁ MnO ₃ .
The molar ratio of M ₁ and Mn in the composite oxide represented by the formula (I) is not strictly required to be 1: 1, and the ratio of the content (mole) of M _{1 to} the content (mole) of Mn. (M ₁ / Mn) may vary, for example, in the range of 0.8 to 1.2, and preferably in the range of 0.9 to 1.2. That is, the complex oxide represented by the formula (I) can also be represented as M _1x MnO _z . x is 0.8 or more and 1.2 or less. z is a value calculated to have a stoichiometric composition when the valence of M1 is trivalent, the valence of Mn is trivalent, and the valence of oxygen is bivalent, and (xx 3 + 3) ÷ 2.
Further, the composite oxide represented by the formula (I) is preferably a composite oxide composed only of M1 and Mn. However, in the range where the heat resistance and the exhaust gas purification performance at low temperature according to the present invention are obtained, You may contain 10 mol% or less of elements other than these with respect to the total number of moles of M1 and Mn.
The composition analysis can be performed, for example, by fluorescent X-ray analysis (XRF) or ICP emission spectroscopic analysis, and specifically by the method described in Examples described later.

As the element represented by _{M 1, Gd, Tb, Dy} , Ho, Er, Tm, at least one rare earth element selected from Yb, and Lu, may be a type, a a combination of two or more May be. Among these, from the viewpoint of providing an ionic radius in which the hexagonal crystal structure described below is particularly easy to form, Ho, Er, Tm, Yb, and Lu are preferable, and Er, Tm, Yb, and Lu are more preferable. Yes, most preferably Yb. Since Yb facilitates Mn oxidation-reduction, the composite oxide itself has an exhaust gas purification performance.

The crystal structure of the composite oxide represented by the formula (I) is preferably a hexagonal crystal structure. By supporting the catalytically active component on such a composite oxide, it has a higher OSC. Thereby, the material for exhaust gas purification catalyst and the catalyst composition for exhaust gas purification of the present invention are compared with the case of using a complex oxide represented by YbFeO ₃ whose orthorhombic crystal is a stable phase shown in Comparative Example 2 described later. OSC, especially OSC after heat endurance is excellent. It is confirmed by X-ray diffraction measurement that the complex oxide has a hexagonal crystal structure. For example, when using a Yb as _{M 1,} the X-ray diffraction measurement of the complex oxide using CuKα ray as a radiation source, 2 [Theta] = 32 ° or 34 ° or less, 28 ° or 30 ° or less, and 14 ° or 17 ° When peaks derived from the (112) plane, (110) plane, and (002) plane of hexagonal YbMnO ₃ are observed in the following ranges, the complex oxide represented by the formula (I) has a hexagonal crystal structure. It can be said that it has.

In the present invention, the composite oxide represented by the formula (I) has higher crystal structure stability to heat than the composite oxide described in Patent Document 1. Specifically, after heat endurance, the change from a hexagonal crystal to a crystal structure other than hexagonal is suppressed, and the crystal already has a hexagonal crystal structure before heat endurance. The degree of growth is relatively suppressed. Accordingly, the inventor has obtained the exhaust gas purification catalyst material of the present invention comprising the composite oxide represented by the formula (I) and the exhaust gas purification catalyst composition of the present invention containing the composite oxide after thermal endurance. Also believes that OSC is high. Further, such heat resistance is presumed to be a factor that the exhaust gas purification catalyst material and the exhaust gas purification catalyst composition of the present invention have high exhaust gas purification performance even after thermal endurance. On the other hand, as described in Comparative Example 3 to be described later, the composite oxide YbFe _x Mn _1-x O ₃ described in Patent Document 1 has a crystallinity even if it has a hexagonal crystal structure before thermal endurance. Is often low, and crystal growth tends to occur violently after thermal endurance. The inventor believes that this crystal growth causes a disadvantage in the exhaust gas purification performance because it causes a decrease in specific surface area accompanying an increase in the particle size of the composite oxide. The term “heat durability” as used herein means a treatment that is exposed to a high temperature for a long time. For example, heating in air at 950 ° C. for 10 hours is preferable.

For example, the composite oxide represented by the formula (I) is subjected to X-ray diffraction measurement using CuKα rays as a radiation source after heat durability treatment at 950 ° C. for 10 hours in air and before heat durability treatment. It is preferable that a peak pattern derived from the above hexagonal crystal is observed.
In the composite oxide represented by the formula (I), a peak pattern other than the hexagonal crystal may not be observed or may be observed after the heat durability treatment under the above conditions and before the heat durability treatment. . For example, when Yb is used as M1, a peak derived from YbMn ₂ O ₅ may be observed.
When a peak pattern other than hexagonal is observed, it is preferable that the complex oxide has a hexagonal crystal structure as a main crystal structure. Whether or not it is the main crystal structure depends on whether the maximum intensity of the peak derived from the hexagonal crystal among the peaks observed in the X-ray diffraction measurement using CuKα rays as the radiation source Judgment can be made based on whether the intensity is greater than the maximum intensity of the peak.

As described above, the composite oxide represented by the formula (I) having a hexagonal crystal structure preferably has a crystallite diameter of the hexagonal crystal structure of 25 nm or more, reflecting the high crystallinity. More preferably, it is particularly preferably 35 nm or more. The crystallite diameter of the hexagonal crystal structure of the composite oxide represented by the formula (I) is preferably 100 nm or less from the viewpoint of increasing the specific surface area, and more preferably 50 nm or less.

The crystallite size of the hexagonal crystal structure of the composite oxide represented by the formula (I) is calculated by the Scherrer formula defined by the following formula (1) using a powder X-ray diffraction method. The measurement peak is near 2θ = 15 °.
D = k × λ / β × cos θ (1)
here,
D: Crystallite diameter (nm)
k: Constant (when the measured X-ray is CuKα and the half width is used, k = 0.94)
λ: wavelength of measured X-ray (nm)
β: Half width of the diffraction line (radians)
θ: Bragg angle of the diffraction line (radians)

X-ray diffraction measurement is preferably performed at 10 to 70 °, and the target of measurement may be a composite oxide or a composite oxide carrying a catalytically active component. X-ray diffraction measurement is performed, for example, by the method described in the examples.

The specific surface area of the composite oxide represented by the formula (I) is 3 m ² / g or more, and it is easy to obtain a desired amount of the catalytically active component, and high exhaust gas purification activity can be obtained even under high space velocity conditions. It is preferable at a point, and it is preferable that it is 20 m < ² > / g or less at the point which is hard to generate | occur | produce a rapid surface area change under severe heat conditions. The specific surface area of the composite oxide is more preferably 5 m ² / g or more and 15 m ² / g or less. As described above, the composite oxide reflects the stability of its crystal structure, and also has a high retention rate of the specific surface area after thermal durability. The specific surface area of the composite oxide is preferably within the above range even after heat durability of 950 ° C. or higher. The specific surface area of the composite oxide can be measured with the composite oxide or the composite oxide supporting a catalytically active component. The heat durability is preferably performed, for example, in an air atmosphere at 950 ° C. for 10 hours. Under these conditions, the maintenance ratio of the specific surface area of the composite oxide (= specific surface area after heat endurance / specific surface area before heat endurance × 100 (%)) is preferably 65% or more. The specific surface area is measured by the BET multipoint method, and specifically can be measured by the method of Examples described later.

The composite oxide represented by the formula (I) can be produced, for example, by a coprecipitation method. The complex oxide described in Patent Document 1 tends to generate impurities when it is produced by a coprecipitation method, and therefore, it is necessary to produce the complex oxide by a method having a complicated production process such as a solvothermal method. On the other hand, the complex oxide of the present invention has an advantage that a stable quality can be obtained by a simple coprecipitation method.

The co-precipitation method, by adding a precipitant to a solution comprising a water soluble salt and a manganese compound of a rare earth element M ₁ as the starting material, after obtaining a precipitate, which was dried, expression by calcining (I And a method of obtaining a composite oxide represented by Examples of the water-soluble salts of rare earth elements M _1, nitrates and oxalates, acetates, ammine complex, chloride and the like. Examples of manganese compounds include manganese nitrates, oxalates, acetates, ammine complex salts, and chlorides. Examples of the precipitating agent include alkaline agents such as aqueous ammonia. The solvent for the solution containing a water-soluble salt and manganese compound of a rare earth element M ₁ include water. The concentration of the water-soluble salts and manganese compounds manganese in the solution containing a water soluble salt and a manganese compound of a rare earth element M ₁ (prior to precipitation additive), respectively 0.01 mol / L or more 1 mol / L or less, particularly 0. 05 mol / L or more and 0.5 mol / L or less are preferable. A preferred addition amount of the precipitating agent is preferably 3 mol to 30 mol, and more preferably 5 mol to 15 mol with respect to 1 mol of the rare earth element M ₁ . The firing temperature is preferably 800 to 1000 ° C., more preferably 800 to 950 ° C., from the viewpoint of successfully obtaining the desired product. The firing atmosphere is preferably air.

The composite oxide represented by the formula (I) is not limited to a product produced by a specific production method, and can also be produced by a solvothermal method and a complex polymerization method. As a procedure of the solvothermal method and the complex polymerization method, the method described in Patent Document 1 may be applied.

The composite oxide represented by the formula (I) can carry a catalytically active component. When a catalytically active component is supported on the composite oxide represented by the formula (I), the supported catalytically active component is preferably at least one selected from Pd, Rh, Pt, Ru and Ir. Only one type of catalytically active component may be used, or two or more types may be used in combination. The catalytically active component may be in a metal state or an oxide state in the composite oxide. The catalytically active component is at least one selected from Pd and Rh with respect to the composite oxide represented by the formula (I) from the viewpoint of dramatically improving the purification activity of the composite oxide in a very small amount. Preferably, it is Pd.

The phrase “catalytically active component is supported on the composite oxide” means that the composite oxide is physically, chemically adsorbed, bonded or held on the outer surface or the inner surface of the pores. Specifically, it can be confirmed that the composite oxide supports the catalytically active component by measuring the particle diameter when observed with, for example, a scanning electron microscope (SEM). For example, the average particle size of the catalytically active component present on the surface of the composite oxide is preferably 10% or less, more preferably 3% or less with respect to the average particle size of the composite oxide. It is preferably 1% or less. The average particle diameter here is the average value of the particle diameters of 30 or more complex oxides and catalytic active components when observed with an SEM.

The amount of the catalytically active component supported on the composite oxide is preferably 0.01% by mass or more with respect to 100% by mass of the composite oxide from the viewpoint that the catalytic activity at a low temperature is more easily obtained. In addition, the amount of the catalytically active component is preferably 10% by mass or less with respect to 100% by mass of the composite oxide represented by the formula (I) from the viewpoint of keeping costs low. From these viewpoints, the amount of the catalytically active component is more preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.05% by mass with respect to 100% by mass of the composite oxide represented by the formula (I). The content is 2% by mass or less.

For the same reason as above, the amount of the catalytically active component in the exhaust gas purification catalyst composition is preferably 0.005% by mass or more and 8% by mass or less, and 0.01% by mass or more and 5% by mass or less. More preferably, it is 0.05 mass% or more and 2 mass% or less.

In order to support the catalytically active component on the composite oxide, it is preferable to immerse the composite oxide in the catalytically active component-containing solution, and then dry and calcinate. As the noble metal salt used for the preparation of the catalytically active component solution, for example, acetate, nitrate, ammine complex salt, chloride and the like can be used. As the solvent, water, acetone or the like can be used. Firing is preferably performed at 400 ° C. to 600 ° C. for 30 minutes to 10 hours in an air atmosphere.

The amount of the catalytically active component relative to the composite oxide is determined by the amount of noble metals such as Pt, Pd, Rh, Ru, and Ir in the solution obtained by dissolving the composite oxide material carrying the catalytically active component with an alkali or the like, and Mn. and obtained by measuring the amount of the rare earth element M ₁ by ICP emission spectrometry.

The composite oxide obtained by supporting the composite oxide represented by the formula (I) or the catalytically active component is an exhaust gas purification catalyst utilizing its excellent thermal stability such as OSC and the exhaust gas purification performance after high temperature durability. Can be suitably used. For example, in an exhaust gas purification catalyst having a base material and an exhaust gas purification catalyst layer formed on the surface of the base material, the composite oxide, particularly preferably the composite oxide carrying a catalytically active component on the exhaust gas purification catalyst layer By containing, an exhaust gas purification catalyst having excellent heat resistance and exhaust gas purification performance at a low temperature can be obtained.

The shape of the substrate is not particularly limited, but is generally a shape of a flow-through type honeycomb, a plate, a pellet, or a wall-through type honeycomb, and preferably a flow-through type honeycomb. Or a wall-through type honeycomb. Examples of the material of the base material include alumina (Al ₂ O ₃ ), mullite (3Al ₂ O ₃ -2SiO ₂ ), cordierite (2MgO-2Al ₂ O ₃ -5SiO ₂ ), and aluminum titanate. Examples thereof include ceramics such as (Al ₂ TiO ₅ ) and silicon carbide (SiC), and metal materials such as stainless steel.

The exhaust gas-purifying catalyst composition constituting the exhaust gas-purifying catalyst layer may be composed of, for example, the composite oxide represented by the formula (I) or the composite oxide carrying a catalytically active component. You may contain components other than.
Examples of the components other than the composite oxide in the exhaust gas purification catalyst composition constituting the exhaust gas purification catalyst layer include, for example, TiO ₂ , SiO ₂ , zeolite, MgO, MgAl ₂ , mainly serving as a carrier. As an inorganic porous material such as O ₄ , mainly serving as an OSC material, such as CeO ₂ , CeO ₂ —ZrO ₂ composite oxide, and the like serving as a NO _x adsorbent, Ba, Sr, Examples of the alkaline earth metal compound such as Mg and those serving as a binder include alumina sol and zirconia sol.
Also in these, it is preferable that the catalytically active component exemplified above is supported.
In the exhaust gas purification catalyst composition, the amount of the composite oxide represented by the formula (I) is not limited, but is preferably 10% by mass or more and 99.9% by mass or less, for example, 20% by mass or more and 98% by mass or less. It is more preferable that it is 40 mass% or more and 95 mass% or less.

The amount of the inorganic porous material including the composite oxide represented by the formula (I) is 10 mass% or more in the exhaust gas purification catalyst composition from the viewpoint of obtaining heat resistance and low temperature exhaust gas purification performance according to the present invention. It is preferably 9% by mass or less, more preferably 20% by mass or more and 98% by mass or less, and particularly preferably 40% by mass or more and 95% by mass or less.

Where the composite oxide represented by the formula (I) has OSC, the amount of the OSC material including the composite oxide represented by the formula (I) is OSC, heat resistance, and low temperature exhaust gas purification performance. In consideration of the balance for exhibiting the above, it is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and more preferably 40% by mass or more and 60% by mass or less in the exhaust gas purification catalyst composition. It is particularly preferable that the content is not more than mass%.

The alkaline earth metal compounds, include oxides and carbonates of alkaline earth metals, as its amount, taking into consideration the _the NO _x adsorption properties, the balance of exhaust gas purification performance in heat resistance and low temperature, the exhaust gas It is preferable that it is 10 mass% or less in the catalyst composition for purification, and it is more preferable that it is 1 mass% or more and 5 mass% or less.

Exhaust gas purification in which a catalyst layer is formed on a base material by applying a slurry having the exhaust gas purification catalyst composition containing the composite oxide represented by the formula (I) to the surface of the base material, drying, and firing. The catalyst for use can be obtained.
For example, when obtaining a layer of an exhaust gas-purifying catalyst composition having a composite oxide carrying a catalytically active component, the composite oxide represented by the above formula (I) and, if necessary, the other components described above are treated with catalytic activity. A slurry containing an exhaust gas purification catalyst composition is prepared by adding it to an aqueous solution containing a water-soluble salt of the component, and this slurry is applied to a substrate, dried and fired to form an exhaust gas purification catalyst. Also good. The solid content of the slurry is preferably 20% by mass or more and 40% by mass or less from the viewpoint of workability when forming the exhaust gas purifying catalyst. When forming an exhaust gas purifying catalyst without using a catalytically active component, a slurry may be prepared without using an aqueous solution containing the water-soluble salt of the catalytically active component described above.

Further, from the viewpoint of the catalytic activity of the obtained exhaust gas purification catalyst, the temperature for firing the substrate coated with the slurry is preferably 300 ° C. to 800 ° C., more preferably 400 ° C. to 600 ° C., and the firing time is 0 5 hours to 10 hours are preferred, and 1 hour to 3 hours are more preferred. Firing can be performed in an air atmosphere.

In the exhaust gas purification catalyst, the amount of the exhaust gas purification catalyst composition of the present invention is preferably 60 g / L or more from the viewpoint of obtaining heat resistance and low temperature exhaust gas purification performance according to the present invention, and 160 g / L or less. It is preferable from the point that suitable low-temperature activity can be obtained while preventing a decrease in back pressure. From these viewpoints, in the exhaust gas purification catalyst of the present invention, the amount of the exhaust gas purification catalyst composition of the present invention is more preferably from 70 g / L to 140 g / L, more preferably from 85 g / L to 120 g / L. It is particularly preferred that Here, the amount of the exhaust gas-purifying catalyst composition in the exhaust gas-purifying catalyst is an amount based on the volume of the substrate including the volume of the pores of the porous substrate. Further, the preferable amount of the composite oxide represented by the formula (I) in the exhaust gas purification catalyst may be the same amount as the preferable amount of the exhaust gas purification catalyst composition of the present invention in the exhaust gas purification catalyst. .

As described above, the exhaust gas purifying catalyst material, the exhaust gas purifying catalyst composition, and the exhaust gas purifying catalyst of the present embodiment have stable exhaust gas purifying catalyst performance even when exposed to a high temperature of, for example, about 900 ° C. to 1150 ° C. In particular, the exhaust gas purification performance at a low temperature can be shown. Such an exhaust gas purification catalyst material, an exhaust gas purification catalyst composition, and an exhaust gas purification catalyst are stable and high exhaust gas purification performance as an exhaust gas purification material of an internal combustion engine using a fossil fuel as a power source such as a gasoline engine or a diesel engine. Can be demonstrated. In particular, the exhaust gas purifying catalyst material, the exhaust gas purifying catalyst composition, and the exhaust gas purifying catalyst of the present embodiment are used for purifying exhaust gas discharged from gasoline engines such as automobiles and motorcycles because of their high heat resistance. Is preferred.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
Ytterbium nitrate n-hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) is used as the ytterbium compound, manganese nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) is used as the manganese compound, and 28% by mass ammonia water (Japanese Kogure Pharmaceutical Co., Ltd.) was used. A mixed aqueous solution containing 0.067 mol / L of ytterbium nitrate and 0.067 mol / L of manganese nitrate and a solution obtained by diluting the above aqueous ammonia to 3.3% by mass with water at room temperature (25 ° C.) under stirring conditions To add a coprecipitate. At this time, the molar ratio of Yb, Mn and ammonia was 1: 1: 10. After completion of the addition, the mixture was stirred at room temperature (25 ° C.) for about 1 hour, followed by standing aging for 1 hour, and the coprecipitate was separated by filtration. The solid content separated by filtration was washed with 400 ml of pure water, and then washed with 400 ml of methanol to replace water and methanol. The solid content after washing was dried overnight at room temperature (25 ° C.). Thereafter, it was crushed and fired at 800 ° C. for 10 hours in the air to obtain YbMnO ₃ powder. YbMnO ₃ powder thus obtained was subjected to composition analysis by XRF under the following conditions, the molar ratio of _{M 1} for Mn _(M 1 / Mn) was 1.03.

<Composition analysis by XRF>
The calibration curve method was adopted as the quantitative method.
As a measuring instrument, ZSX Primus II manufactured by Rigaku Corporation was used.
The measurement sample was prepared as follows.
The YbMnO ₃ powder was pulverized to 20 μm or less (D50) using a disk mill (Retsch RS200), and then 1 g of the pulverized powder was molded into a disk shape with a pressure molding machine and measured.

[Example 2]
To the acetone solution in which palladium acetate was dissolved, the YbMnO ₃ powder produced in Example 1 was added and stirred to obtain a slurry. After the acetone solution was evaporated to dryness, the obtained powder was calcined at 500 ° C. for 30 minutes in the air to produce YbMnO ₃ powder supporting Pd. The amount of Pd was 0.1% by mass with respect to 100% by mass of YbMnO ₃ . Hereinafter also show YbMnO ₃ which Pd is supported as Pd / YbMnO _3.

Example 3
The amount of Pd / YbMnO ₃ powder in which the amount of Pd was 1% by mass relative to 100% by mass of YbMnO ₃ was manufactured by changing the amount of palladium acetate in acetone. The production conditions other than the addition amount of palladium acetate in acetone were the same as in Example 2. FIG. 1 shows an X-ray diffraction chart measured by the X-ray diffraction measurement method under the following conditions in the as-manufactured state of this Pd / YbMnO ₃ powder. As shown in FIG. 1, the obtained Pd / YbMnO ₃ powder has a peak pattern derived from a hexagonal crystal of YbMnO ₃ . Based on the obtained X-ray diffraction measurement result, the crystallite diameter of the hexagonal crystal structure was measured by the above calculation method, and found to be 28 nm.

<X-ray diffraction measurement>
・ Device: Ultima IV (Rigaku)
-Radiation source: CuKα line-Tube voltage: 40 kV
・ Tube current: 40 mA
・ Scanning speed: 10 ° / min
・ Step: 0.02 °
・ Scanning range: 2θ = 10 ~ 70 °

Example 4
Pd / YbMnO ₃ powder having a Pd content of 2% by mass with respect to 100% by mass of YbMnO ₃ was produced by changing the amount of palladium acetate in acetone. The production conditions other than the addition amount of palladium acetate in acetone were the same as in Example 2.

[Comparative Example 1]
Yttrium nitrate n-hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) is used as the yttrium compound, manganese nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) is used as the manganese compound, and 28% by mass ammonia water (Japanese Kogure Pharmaceutical Co., Ltd.) was used. A mixed aqueous solution containing 0.067 mol / L of yttrium nitrate and 0.067 mol / L of manganese nitrate, and the above aqueous ammonia diluted to 3.3% by mass with water are stirred at room temperature (25 ° C.). To add a coprecipitate. At this time, the molar ratio of Y, Mn and ammonia was 1: 1: 10. After completion of the addition, the mixture was stirred at room temperature (25 ° C.) for about 1 hour, left to mature for 1 hour, and the coprecipitate was separated by filtration. The solid content separated by filtration was washed with 400 ml of pure water, and then washed with 400 ml of methanol to replace the water with methanol. The solid content after washing was dried overnight at room temperature (25 ° C.). Thereafter, the mixture was crushed and fired at 800 ° C. for 10 hours in the air to obtain YMnO ₃ powder.
Except for using the YMnO ₃ powder instead of YbMnO _3, the same procedure as in Example 3, Pd was obtained YMnO _₃ (Pd / YMnO ₃₎ powder carried.

[Comparative Example 2]
In the same manner as in Example 3 except that an aqueous solution of iron nitrate nonahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was used as the iron compound instead of manganese nitrate hexahydrate, YbFeO ₃ (Pd / YbFeO ₃ ) powder was obtained. This Pd / YbFeO ₃ powder, as in Example 3, are also shown the results of X-ray diffraction measurement in a state prepared to FIG. As shown in FIG. 1, YbFeO ₃ had an orthorhombic crystal structure.

[Comparative Example 3]
Ytterbium acetate tetrahydrate (Yb (OAc) ₃ .4H ₂ O, 15 mmol), trisacetylacetonatoiron (III) (Fe (acac) ₃ , 9 mmol) and trisacetylacetonatomanganese (III) (Mn (acac ₃ , 6 mmol) was ground in a mortar and then suspended in 120 ml of 1,4-butanediol (1,4-BG) using a ultrasonic wave in a plastic container. The total charge of Fe (acac) ₃ and Mn (acac) ₃ was 15 mmol (Fe 9 mmol, Mn 6 mmol). This suspension was transferred to an autoclave reaction tube, charged into an autoclave (300 mL), and 30 ml of 1,4-BG was also added to the gap. After the inside of the autoclave was purged with nitrogen, the temperature was raised from room temperature to 315 ° C. at 2.3 ° C./min and reacted for 2 hours. The product was washed with methanol and dried. Thereafter, it was crushed and fired at 500 ° C. for 30 minutes in an air atmosphere to obtain YbFe _0.6 Mn _0.4 O ₃ powder.
Next, Pd was supported on YbFe _0.6 Mn _0.4 O ₃ in the same manner as in Example 3, and the amount of Pd was 1% by mass with respect to 100% by mass of YbFe _0.6 Mn _0.4 O ₃ . A Pd / YbFe _0.6 Mn _0.4 O ₃ powder was produced.

The result of X-ray diffraction measurement of this Pd / YbFe _0.6 Mn _0.4 O _{3 in} the same state as produced in Example 3 is also shown in FIG. _YbFe 0.6 _Mn 0.4 _{O 3} in Pd _/ YbFe _{0.6 Mn} 0.4 _{O 3} had a similar hexagonal structure as in Example 3, but its crystallinity was low. Based on the obtained X-ray diffraction measurement result, the crystallite diameter of the hexagonal crystal structure was measured by the above calculation method, and found to be 22 nm.

[Comparative Example 4]
Pd-supported alumina (Pd / Al) in the same manner as in Example 3 except that γ-Al ₂ O ₃ (JRC-ALO-7), which is a reference catalyst provided by the Catalysis Society of Japan, was used instead of YbMnO _3. ₂ O ₃ ) powder was obtained.

[Comparative Example 5]
A CeO ₂ —ZrO ₂ solid solution material (CeO ₂ —ZrO ₂ material) having a CeO ₂ content of 40% by mass was prepared.
A CeO ₂ —ZrO ₂ material was added to a 1% by mass palladium nitrate aqueous solution and stirred to obtain a slurry. This slurry was fired under air at 500 ° C. for 2 hours to produce a Pd / CeO ₂ —ZrO ₂ material powder. The amount of Pd was 1% by mass with respect to 100% by mass of CeO ₂ —ZrO ₂ .

The powder obtained in Examples and Comparative Examples was subjected to the following evaluation. In the following evaluation, the powders obtained in Examples and Comparative Examples are also referred to as exhaust gas purification catalyst compositions.

<Endurance test condition 1>
The exhaust gas-purifying catalyst composition produced in Example 3 and Comparative Example 1 was subjected to durable firing at 950 ° C. for 30 minutes in an air atmosphere.

<Evaluation 1: NO _x , HC, CO purification performance before and after endurance test 1>
The exhaust gas purification catalyst compositions of Example 3 and Comparative Example 1 before and after firing under durability test condition 1 were evaluated for NO _x , HC and CO purification performance using an atmospheric pressure fixed bed flow type reactor. 200 mg of the exhaust gas purification catalyst composition after durability was placed in the reactor, and helium at 500 ° C. was circulated as a pretreatment gas at a flow rate of SV = 0.12 gsmL ⁻¹ . Next, a simulated exhaust gas having the following composition with A / F = 14.7 is set at a flow rate of SV = 0.12 gsmL ⁻¹ so that the catalyst composition is heated from 100 ° C. to 500 ° C. at a rate of 10 ° C./min. The amount of each component in the outlet gas component was measured. The gas temperature at the inlet of the apparatus when the conversion rate when NO _x is converted to N ₂ reaches 50%, and the conversion rate when CO and C ₃ H ₆ are converted to CO ₂ reach 50% The gas temperature at the inlet of the apparatus was examined as the light-off temperature T50. The C ₃ H ₆ , CO, CO ₂ and N ₂ concentrations were measured using GC-8AIT manufactured by Shimadzu Corporation. The results are shown in Table 1.
Simulated exhaust gas (composition is volume ratio): C ₃ H ₆ : 250 ppm, CO: 1000 ppm, CO ₂ : 0%, O ₂ : 1125 ppm, NO: 1000 ppm, H ₂ O: 0%, and He balance T50 before firing under test condition 1 (also referred to as “T50 _{500 °} C · 30 minutes” from “500 ° C. · 30 minutes” in manufacturing conditions) and T50 ₉₅₀ after firing at endurance test condition 1 at 950 ° C. for 30 minutes. T50 maintenance rate calculated on the basis of _{° C · 30 minutes} = (T50 _{500 ° C · 30 minutes} / T50 _{950 ° C · 30 minutes} ) × 100 (%) was determined.

As shown in Table 1, the exhaust gas purification catalyst composition of Example 3 has a general durability temperature required for an exhaust gas purification catalyst for gasoline vehicles, as compared with Comparative Example 1 using YMnO ₃ powder as a carrier. It can be seen that even after endurance at 950 ° C., the NO _x , HC, and CO purification performance at low temperatures is excellent.
Further, it can be seen that the exhaust gas purification catalyst composition of Example 3 hardly deteriorates due to durability compared with Comparative Example 1, and the exhaust gas purification performance after durability is very high.

<Endurance test condition 2>
The exhaust gas purifying catalyst compositions prepared in Examples 2 to 4 and Comparative Examples 2 to 4 were subjected to durable firing at 950 ° C. for 10 hours in an air atmosphere.

<Evaluation 2: NO _x , HC, CO purification performance before and after endurance test 2>
Regarding the exhaust gas purifying catalyst compositions of Examples 2 to 4 and Comparative Examples 2 to 4 before and after firing under the durability test condition 2, NO _x , HC and CO purification performance was evaluated using an atmospheric pressure fixed bed flow type reactor. . The evaluation method of T50 before and after firing is the same as in Evaluation 1.
T50 maintenance ratio calculated based on T50 (T50 _{500 °} C./30 _minutes ) before firing in durability test condition 2 and T50 _{950 °} C. · 10 hours after firing 950 ° C. · 10 hours = (T50 _{500 ° C. · 30 Min} / T50 _{950 ° C., 10 hours} ) × 100 (%).

As shown in Table 2, the exhaust gas purifying catalyst compositions of Examples 2 to 4 were compared with Comparative Examples 2 to 4 using YbFeO ₃ powder, YbFe _0.6 Mn _0.4 O ₃ powder, and alumina powder, respectively, as carriers. It can be seen that even after endurance at 950 ° C., which is a general endurance temperature required for exhaust gas purification catalysts for gasoline vehicles, it is excellent in NO _x , HC and CO purification performance at low temperatures.
In addition, it can be seen that the exhaust gas purification catalyst compositions of Examples 2 to 4 hardly deteriorate due to durability compared to Comparative Examples 2 to 4, and the exhaust gas purification performance after durability is very high.

<Evaluation 3: OSC amount after endurance>
The exhaust gas-purifying catalyst compositions obtained in Examples 2 and 3 and Comparative Example 5 were subjected to durable firing at 900 ° C. for 25 hours under the following atmosphere.
Durability test atmosphere (composition volume basis): A / F = 14.6, CO: 0.50%, H 2: 0.17%, O 2: 0.50% NO (NO x): 500ppm, C 3 H 6 (HC): 1200ppmC, CO ₂ : 14%, H ₂ O: 10%, N ₂ : balance
The OSC of the exhaust gas purification catalyst composition after the durable firing was measured by the CO pulse method. In the OSC measurement, the exhaust gas-purifying catalyst composition was put in a quartz reaction vessel, heated to 800 ° C. under He flow, and maintained at that temperature for 10 minutes. Then, after maintaining the temperature of 800 ° C. and injecting O ₂ gas into 5 pulses and performing oxidation treatment, a test gas containing CO is injected in 20 pulses, and the total amount of consumed CO gas is 800 The total amount of OSC (μmol / g) per unit mass of the composition powder at ° C. was measured by ULVAC, RG702. The test gas was prepared by diluting 25% by volume of CO gas into 75% by volume of He gas. The results are shown in Table 3.

As shown in Table 3, the exhaust gas purification catalyst composition of Example 3 using YbMnO ₃ powder has a higher OSC ability after high temperature durability than the general exhaust gas purification catalyst composition of Comparative Example 5. It can be seen that the heat resistance is high. Further, even in Example 2 in which the amount of Pd supported is 1/10 of Example 3, it can be seen that the OSC ability after high-temperature durability is high and the heat resistance is high.

<Evaluation 4: Influence of amount of catalytically active component>
The exhaust gas purification catalyst compositions of Example 1, Example 2 and Comparative Example 4 after firing under the above durability test condition 2 were increased from 100 ° C. to 500 ° C. at 10 ° C./min in the same manner as in the above evaluation 1. When the simulated exhaust gas is circulated at a flow rate of SV = 0.12 gsmL ⁻¹ so as to be heated, the conversion rate when NO _x is converted to N ₂ at each gas temperature at the apparatus inlet, and CO and C The conversion rate when ₃ H ₆ was converted to CO ₂ was examined. The obtained graph is shown in FIG.

As shown in FIG. 2, the exhaust gas purifying catalyst composition of Example 1 has an exhaust gas purifying catalytic activity even when it does not contain a catalytic active component, and the amount of catalytic active component is 0 as in Example 2. It can be seen that even when the amount is as small as 1% by mass, the catalyst of the exhaust gas purification catalyst activity is superior to that of the composition of Comparative Example 4 in which 1% by mass of the catalytically active component is supported. Therefore, by using the composite oxide of the present invention, it is possible to achieve both reduction in the amount of noble metal used and improvement in exhaust gas purification catalyst performance.

<Evaluation 5: Heat resistance of crystal structure>
The X-ray diffraction charts measured for the exhaust gas purifying catalyst compositions of Example 3, Comparative Example 3, and Comparative Example 4 before and after the durability test of <Durability Test Condition 2> (hereinafter also simply referred to as Durability Test 2) are shown in the figure. 3 shows. The above conditions were adopted for the X-ray diffraction measurement method. Table 4 shows the specific surface area before and after the durability test 2 and the maintenance ratio of the specific surface area (= specific surface area after durability / specific surface area before durability × 100 (%)) for each exhaust gas purifying catalyst composition.
<Method for measuring specific surface area>
The specific surface area was measured by BET multipoint method (measurement gas: nitrogen) using BEL SORP-mini II-HSP manufactured by Microtrack Bell.

As shown in FIG. 3, the Pd / YbMnO ₃ powder of Example 3 had a peak pattern derived from the hexagonal YbMnO ₃ before and after the endurance test 2, and before and after the endurance test of <endurance test condition 2>. However, there is almost no change in the peak pattern, and the crystal structure at the time of manufacture is maintained after the endurance. On the other hand, Pd / YbFe _0.6 Mn _0.4 O ₃ of Comparative Example 3 has a very sharp peak after the durability test 2 and the crystal structure is greatly changed. To confirm this, as shown in Table 4, the retention rate after endurance of the specific surface area of Example 3 was as high as 69.2%, whereas in Comparative Example 3, the retention rate after endurance of the specific surface area was 12%. It is significantly inferior at 8%.
In addition, Pd / Al ₂ O ₃ of Comparative Example 4 in which Pd is supported on Al ₂ O ₃ , which is generally said to have high heat resistance, has little change in peak pattern before and after durability test 2 and has a specific surface area durability. Although the subsequent maintenance rate is also high to some extent, it can also be seen that the maintenance rate before and after the endurance of the specific surface area of Pd / YbMnO ₃ of Example 3 exceeds that as shown in Table 4.

1 and 3, it can be seen that the peak pattern derived from the hexagonal crystal of Example 3 and the peak pattern derived from the hexagonal crystal of Comparative Example 3 are different. For example, in the peak pattern of Example 3, three peaks are observed at positions of 29 ° to 30 °, 30 ° to 31 °, and 31 ° to 32 ° in the range of 2θ = 28 ° to 32 °. On the other hand, in the peak pattern of Comparative Example 3, only two peaks are observed at positions of 28 ° to 30 ° and 30 ° to 32 °. Thus, the crystal structures of Example 3 and Comparative Example 3 are different in detail even though they are the same hexagonal crystal. Such a difference in crystal structure can also be considered to be one of the factors in which the exhaust gas purification catalyst composition of Example 3 has higher exhaust gas purification performance after endurance than Comparative Example 3.

According to the present invention, there are provided an exhaust gas purification catalyst material, an exhaust gas purification catalyst composition, and an exhaust gas purification catalyst that have high exhaust gas purification performance after endurance at high temperatures and are excellent in heat resistance.

Claims

A material for exhaust gas purification catalyst comprising a composite oxide represented by the formula (I).
M 1 MnO 3 (I)
(In the formula, M 1 represents at least one rare earth element selected from Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.)
The exhaust gas purifying catalyst material according to claim 1, wherein M 1 in the formula (I) is at least one rare earth element selected from Er, Tm, Yb and Lu.
The exhaust gas purifying catalyst material according to claim 1 or 2, wherein a crystal structure of the composite oxide represented by the formula (I) is a hexagonal crystal structure.
The exhaust gas purification catalyst material according to claim 3, wherein a crystallite diameter of a hexagonal structure of the composite oxide represented by the formula (I) is 25 nm or more and 100 nm or less.
An exhaust gas purifying catalyst composition comprising the exhaust gas purifying catalyst material according to any one of claims 1 to 4 and a catalytically active component.
The catalyst composition for exhaust gas purification according to claim 5, wherein the amount of the catalytically active component is 0.01% by mass or more and 10% by mass or less with respect to the composite oxide represented by the formula (I).
The exhaust gas purifying catalyst composition according to claim 5 or 6, which contains Pd as the catalytic active component.
An exhaust gas purifying catalyst composition containing the exhaust gas purifying catalyst material according to any one of claims 1 to 4 and containing no catalytically active component.
A substrate;
An exhaust gas purification catalyst comprising a layer of the exhaust gas purification catalyst composition according to any one of claims 5 to 8, formed on a surface of the base material.
The exhaust gas purification catalyst according to claim 9, wherein the exhaust gas purification catalyst composition is contained in an amount of 60 g / L or more and 160 g / L or less with respect to the base material.