JP2014223587A - Exhaust gas purification catalyst carrier, manufacturing method of exhaust gas purification catalyst carrier, exhaust gas purification catalyst, and manufacturing method of exhaust gas purification catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purification catalyst carrier and an exhaust gas purification catalyst, excellent in heat resistance and purification performance with a reduced amount of rare earth elements for use, and a manufacturing method of the exhaust gas purification catalyst carrier and the exhaust gas purification catalyst.SOLUTION: The exhaust gas purification catalyst carrier satisfies the following conditions: including an oxide 1 of perovskite type oxide and an oxide 2 having low reactivity with the perovskite type oxide which are mixed; the surfaces of a plurality of particles of the oxide 1 being sintered with each other into a secondary particle made of porous body with a porosity of 20 to 60% and an average particle diameter of 5 μm or more; the oxide 1 having an average particle diameter of 0.05 to 0.5 μm; the oxide 2 having an average particle diameter of 0.1 μm or less, mainly existing at the boundary between the oxide 1 and pores; and the oxide 2 being at least one selected from YO, LaO, CeO, and NiO, essentially including YO, with a total amount of Y, La, Ce, and Ni of 5 to 30 mol% relative to the total number of moles of Sr and A of the oxide 1.

Description

The present invention relates to an exhaust gas purification catalyst carrier for purifying carbon monoxide (CO), nitrogen oxides (NO _x ), and unburned hydrocarbons (HC) in combustion exhaust gas, a method for producing an exhaust gas purification catalyst carrier, and The present invention relates to an exhaust gas purification catalyst. In particular, an exhaust gas purification catalyst carrier that purifies carbon monoxide (CO), nitrogen oxides (NO _x ), and unburned hydrocarbons (HC) discharged from an internal combustion engine such as an automobile engine, and an exhaust gas purification catalyst carrier. The present invention relates to a manufacturing method and an exhaust gas purifying catalyst.

Gases emitted from internal combustion engines such as automobile engines contain harmful CO, NO _x , and HC, which are harmless carbon dioxide (CO ₂ ), nitrogen (N ₂ ), water (H ₂ O). In general, a catalytic technique for reducing CO, NO _x , and HC emissions is known. Such a catalyst technology is used not only for exhaust gas from an internal combustion engine but also for other combustion exhaust gas.

A three-way catalyst that simultaneously purifies CO, NO _x , and HC in automobile exhaust gas uses a combination of noble metals such as Pt, Pd, and Rh. These noble metals have active alumina (γ-alumina, ρ-alumina, χ-alumina, η-alumina, δ-alumina, κ-alumina, θ-alumina, amorphous alumina, etc.) oxide powder as a support and their surface. The catalyst powder is used as a catalyst powder, and the catalyst powder is applied and baked on a metal or ceramic honeycomb.

  The three-way catalyst works effectively near the stoichiometric air-fuel ratio, but in order to expand the range of the air-fuel ratio that works effectively, an oxygen storage material such as cerium oxide, which is a rare earth oxide, is used as a carrier, and a noble metal is used as the carrier. The catalyst performance is also improved by carrying it. For example, Patent Document 1 discloses a catalyst in which a noble metal is supported on a support obtained by adding an appropriate amount of ceria to an activated alumina oxide. The oxygen storage capacity by ceria improves the catalyst performance, but the amount of noble metals has not been reduced.

In addition, composite oxides have been studied as oxides other than ceria having oxygen storage capacity, and in particular, composite oxides having a perovskite structure containing rare earth elements have been studied as carriers. The oxide of perovskite structure is expressed as ABO _3-δ . The A part (A site) contains rare earth elements and alkaline earth metal elements, and the B part (B site) mainly contains transition elements. It can contain many elements. The reason why the perovskite oxide has a high oxygen storage capacity is that the perovskite structure can be stably maintained even when a large oxygen deficiency exists in the range of δ up to about 0.5. However, with the oxygen atoms that are the skeleton of the crystals being easy to move, the sintering of the oxide carrier proceeds at a relatively low temperature of about 1000 ° C. where the catalyst is used, and the purification characteristics deteriorate with the sintering. The problem of heat resistance has been pointed out.

In order to impart heat resistance to the perovskite oxide itself, a technique is disclosed that essentially requires a large amount of rare earth elements including La as a representative element of the A site. Patent Document 2 discloses that a noble metal element is supported on a perovskite oxide containing a rare earth element such as (La, Sr) FeO ₃ or (La, Sr) MnO _3. Over 80% of the sites are rare earth elements. Furthermore, the composition of the (La, Sr) FeO ₃ and (La, Sr) MnO ₃ and other elements are added to improve the heat resistance, but the rare earth element is 50% or more of the A site. Contains a large amount (Patent Document 3). Further, in order to improve the heat resistance of the catalytic activity of the noble metal, the noble metals Pd to Rh are incorporated into the perovskite lattice, and La (Fe, Pd) O ₃ to La (Fe, Complex oxides such as Rh) O ₃ are disclosed (Patent Documents 4 and 5). In the above technique, rare earth elements such as La are relatively expensive, and there is room for improvement in cost when they are contained in a large amount as the main component of the perovskite oxide. Recently, the destabilization of supply of so-called rare metals containing rare earth elements has become a major problem, and reduction of the amount of rare earth elements used is an important issue.

As another method for improving the heat resistance, a technique for ensuring the heat resistance of the entire catalyst carrier by allowing the perovskite complex oxide to coexist with the heat resistant oxide is disclosed. Patent Document 6 discloses a catalyst in which a heat-resistant composite oxide, a perovskite oxide that must contain a rare earth element as an A-site constituent element, and a noble metal coexist. In this publication, a perovskite-type oxide is compounded on a heat-resistant oxide. However, according to the examples, more than 50% of the A site of the perovskite-type structure ABO _3-δ contains a large amount of rare earth elements. The reduction of the amount of rare earth elements used is a problem. Patent Document 7 discloses an exhaust gas purification catalyst comprising a noble metal, a perovskite complex oxide, and a heat-resistant oxide. In this publication as well, according to an embodiment, a so-called A site 60 having a perovskite structure is disclosed. % And a large amount of rare earth elements are contained, and reduction of the amount of rare earth elements used is a problem. Moreover, it is necessary to mix a large amount of heat-resistant oxide, and the purification characteristics per catalyst weight are not sufficient.

  Patent Document 8 discloses a technique in which a composite oxide spacer is combined with a composite particle aggregate in which a noble metal is supported on a perovskite oxide to suppress sintering of the perovskite oxide. Technology for exhaust gas purification catalyst in which noble metal coexists in mixture of type oxide and heat resistant oxide, Patent Document 10 discloses a sol such as yttria in which noble metal coexists in a mixture of perovskite type oxide and heat resistant oxide Although a technology relating to an exhaust gas purifying catalyst containing a binder as a binder is disclosed, in Patent Document 8, the mixing ratio between the perovskite oxide and the spacer composite oxide is not clearly shown, but around the perovskite oxide. Perovskite-type oxide grains are separated from each other by arranging spacer oxide, so at least perovskite It is clear that to be mixed with preparative oxide and an equal volume of the spacer oxide. According to Examples of Patent Documents 9 and 10, it is clearly indicated that an equivalent amount of heat-resistant oxide is added to perovskite oxide. Both techniques require mixing a large amount of heat-resistant oxide, and the purification characteristics per catalyst weight are not sufficient.

  Patent Document 11 discloses a technique for suppressing aggregation of noble metals by mixing one or more of a rare earth oxide, aluminum oxide, iron oxide, and calcium or barium with a perovskite oxide. However, even if aggregation of the noble metal itself can be suppressed, sintering of the perovskite oxide cannot be suppressed, and it is clear that the purification characteristics deteriorate when the perovskite oxide as a support is sintered.

For the purpose of cost improvement, perovskite oxides that do not contain rare earth elements have been studied from the beginning (Patent Document 12). In this publication, A _α B _1-x B ′ _x O ₃ − _δ (A is Ba and Sr, B is Fe and Co, B ′ is one element selected from Nb, Ta, and Ti, or 2 Perovskite type oxides, which are a combination of more than one element, are disclosed, but by making the specific surface area of the perovskite type oxides less than 10 m ² / g, the change in specific surface area at high temperatures is small, resulting in the use of catalysts. It has realized a catalyst with little change in characteristics in the process and high heat resistance. However, from the inventor's experience, such a purification catalyst has a problem in purification characteristics under a low temperature condition of 400 ° C. or lower or a condition in which the response speed of the catalyst is required for a rapid time change of exhaust gas components. It turned out that there are many. In addition, since the oxide supporting the noble metal has a low specific surface area, it is found that the particle size of the noble metal is likely to become coarse in the process of using the catalyst, and there are cases where the heat resistance of the noble metal may be problematic. It was.

In a conventional three-way catalyst, the raw material is dissolved in a solvent and homogenized, and then subjected to a process such as gelation and precipitation formation, followed by drying and firing to obtain an oxide, which is produced by a so-called solution method. Thus, it is common to obtain a powder with a high specific surface area and achieve high purification characteristics. For example, Patent Document 13 discloses a catalyst in which palladium is contained in a defective perovskite oxide having a specific surface area of 10 m ² / g or more as a three-way catalyst for the purpose of improving catalyst activity and heat resistance. Further, there is disclosed a catalyst characterized in that 10 to 50% of the palladium is dissolved in a defect perovskite oxide and the remaining palladium is supported on the defect perovskite oxide in a PdO or Pd state. The defect perovskite oxide is produced by a kind of coprecipitation method of the solution method. According to the experience of the present inventors, the catalyst produced by such a solution method has a relatively excellent purification activity in the initial stage, but is easily sintered at a high temperature, and the specific surface area is reduced during use. There is a problem that the catalyst activity is lowered, and it tends to be deteriorated by solid-phase reaction with another coexisting oxide, resulting in low heat resistance. In addition, production by a solution method such as a coprecipitation method is complicated in operation and disadvantageous in terms of cost.

JP 54-159391 A JP 2006-36558 A JP 2003-175337 A JP 2004-41866 A JP 2004-41867 A JP-A-1-168343 JP 2007-313500 A JP 2010-99638 A JP-A-6-210175 JP-A-5-253484 Japanese Patent Laid-Open No. 5-38448 JP 2007-160149 A Japanese Patent Laid-Open No. 62-269747

  As described above, regarding a catalyst for purifying CO, NOx, and HC in combustion exhaust gas, in a three-way catalyst using a conventional perovskite oxide, in order to effectively improve the catalyst performance and obtain heat resistance, It was practically essential to contain a relatively expensive rare earth element as a major component of the perovskite oxide. In addition, a catalyst carrier that does not contain a rare earth element as a main component of the perovskite oxide has been developed to increase the heat resistance of the catalyst carrier by not increasing the specific surface area of the catalyst carrier. However, problems remained in the purification performance at low temperatures and the response speed of the purification. The technology for improving the heat resistance by coexisting a heat-resistant oxide with the perovskite oxide requires mixing a large amount of the heat-resistant oxide, and sufficient purification characteristics are not obtained. Further, in the production of these catalyst carriers, it is common to use a solution method, but there are problems in the heat resistance of the product, the ease of production operations, the cost, and the like.

  Accordingly, the present invention solves the above-described problems of the prior art, greatly reduces the amount of rare earth elements used, and has excellent heat resistance and purification performance. Exhaust gas purification catalyst carrier, method for producing exhaust gas purification catalyst carrier, and exhaust gas purification It is an object to provide a catalyst for use.

The inventors have so far invented a catalyst support for exhaust gas purification comprising a perovskite oxide material having a specific surface area of at least 5 m ² / g after heat treatment at 900 ° C. for 5 hours in the atmosphere (Japanese Patent Application 2012- 206532). It has a perovskite oxide material is an average particle diameter of 0.2μm or less, Y ₂ O _3, La ₂ O _3, average particle size of at least one of CeO _2, NiO always be comprise choosing a Y ₂ O ₃ from the It is a mixture of oxides smaller than the perovskite oxide and 0.1 μm or less.

That is, at least one oxide particle selected from Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , and NiO by including Y ₂ O ₃ is used as another second phase that does not react with the perovskite oxide. Coexists with the perovskite oxide and suppresses the sintering of the perovskite oxide. Rare earth elements are present as a second phase separate from the perovskite oxide, rather than containing the rare earth element as a component in the perovskite oxide, and the A site of the perovskite oxide ABO _3-δ is an alkaline earth It has been found that heat resistance can be ensured by using only metal elements, and as a result, the amount of rare earth elements used can be reduced. Rare earth oxides Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , and oxides that have low reactivity and can improve the heat resistance of the catalyst support even when coexisting with the perovskite type oxide as the second phase, It was found that there was NiO as a transition metal oxide. Among these, Y ₂ O ₃ was particularly effective for improving heat resistance.

However, further studies revealed the following further issues. The above-mentioned prior invention specifies that the specific surface area after heat treatment at 900 ° C. for 5 hours in the atmosphere is at least 5 m ² / g, which is sufficient for exhaust gas purification during actual use. Even perovskite-type oxide materials that do not contain rare earth elements, once a perovskite-type oxide having a specific surface area of about 25 m ² / g is produced, by adding second phase oxide particles such as Y ₂ O ₃ , The specific surface area after heat treatment at 900 ° C. for 5 hours in the atmosphere can be at least 5 m ² / g. The reason why the specific surface area decreases from 25 m ² / g is that the perovskite oxide having a small particle size is sintered and the particle size becomes coarse, but in the prior invention, the perovskite of about 25 m ² / g is used. When adding second phase oxide particles such as Y ₂ O ₃ to the type oxide, noble metal is supported at the same time. In such a form, when the perovskite type oxide having a small particle size is sintered and the particle size becomes coarse, the noble metal is dissolved in the coarse perovskite type oxide and cannot contact the purified gas. It has been found that the surface of the noble metal is increased, thus reducing the purification performance. Accordingly, the inventors have devised a perovskite oxide support of the present invention in which perovskite oxide is sintered to a certain level in advance, and an exhaust gas purification catalyst of the present invention in which a noble metal is supported on the perovskite oxide support.

That is, the present invention has the following gist.
[1] A mixture of oxide 1 which is a perovskite complex oxide and oxide 2 having low reactivity with the perovskite oxide (i),
The surfaces of the plurality of oxide 1 grains are sintered, and secondary particles having an average particle diameter of 5 μm or more are formed of a porous body having a porosity of 20% or more and 60% or less (ii),
The average particle diameter of the oxide 1 is 0.05 μm or more and 0.5 μm or less (iii),
The oxide 2 has an average particle size of 0.1 μm or less and exists mainly at the interface between the oxide 1 and the pores (iv),
The composition of oxide 1 is represented by the following (formula 1) (v),
Oxide 2 is at least one selected from Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , and NiO, including Y ₂ O ₃ , and the total amount of Y, La, Ce, and Ni is an oxide. 1 to 30 mol% with respect to the total number of moles of Sr and A (vi),
A catalyst carrier for exhaust gas purification characterized by the above.
{Sr _(1-a) A _a } _s Fe _(1-btc) B _b Ti _t C _c O _3-δ (Formula 1)
(Here, A, B, C may not arrange elements,
When arranging A, one or more elements selected from Ba, Ca, and La,
When arranging B, one or more elements selected from Co, Cu and Ni,
When C is arranged, one or more elements selected from Nb, Ta and Mn,
1.0 ≦ s ≦ 1.1, 0 ≦ a ≦ 0.5,
0 ≦ b ≦ 0.25, 0.05 ≦ t ≦ 0.3, 0 ≦ c ≦ 0.25, 0.05 ≦ t + c ≦ 0.3,
δ is a value determined by the history of the material)

[2] In oxide 1 which is a perovskite oxide defined by (Formula 1), when A is arranged, it is selected from one or more elements selected from Ba and Ca.
The oxide 2, characterized in that selected by always contains Y ₂ O ₃ from Y ₂ O _3, NiO, a catalyst carrier for purifying an exhaust gas according to [1].
[3] In oxide 1, which is a perovskite oxide defined by (formula 1), A, B, and C are not arranged,
The catalyst support for exhaust gas purification according to [1] or [2], wherein the oxide 2 comprises only Y ₂ O ₃ .
[4] Exhaust gas, characterized in that at least one noble metal selected from Pd, Pt, and Rh is supported on the exhaust gas purification catalyst carrier according to any one of [1] to [3]. Purification catalyst.

[5] A method for producing an exhaust gas-purifying catalyst carrier according to any one of [1] to [3], wherein the average has a crystal phase of a perovskite structure represented by (Formula 1). A step of producing a precursor of oxide 1 having a particle size of 0.5 μm or less, and an S liquid containing at least one kind of Y, La, Ce, and Ni ions that must be selected to include Y. A step of heat-treating the mixture of the S liquid and the oxide 1 precursor in an atmosphere containing oxygen gas at a temperature of 700 ° C. or higher, and a secondary particle size of less than 100 μm after the heat treatment. And a crushing step. A method for producing an exhaust gas purifying catalyst carrier.
[6] The step of producing a precursor of oxide 1 having an average particle size of 0.5 μm or less having a crystal phase of the perovskite type structure is essential for the metal elements (Sr, Fe, Ti) described in (Formula 1) , A, B, C (A is one or more selected from Ba, Ca, La, B is one or more elements selected from Co, Cu, Ni, C is Nb, Ta, Mn 1) or 2 or more elements selected from: optional) a step of mixing powders selected from the group consisting of carbonates, hydroxides, and oxides, and the resulting mixed powder is 900 ° C. or higher and 1200 ° C. The exhaust gas according to [5], comprising a step of synthesizing an oxide by firing at a temperature of ℃ or less and a step of mechanically pulverizing the obtained oxide powder to make it fine. A method for producing a purification catalyst carrier.
[7] A method for producing the exhaust gas purifying catalyst according to [4], wherein the exhaust gas purifying catalyst carrier according to any one of [1] to [3] is provided with Pd, Pt, A method for producing an exhaust gas purifying catalyst, comprising impregnating a solution of at least one noble metal selected from Rh and supporting the noble metal.

Catalysts that combine noble metals such as Pt, Pd, and Rh are widely used as three-way catalysts that simultaneously purify CO, NO _x , and HC in automobile exhaust gas, and it is Pt that has an exhaust gas purification action directly. , Pd, Rh and the like. In the present invention, the catalyst carrier is a particle for adhering and holding the fine particles of the noble metal on the surface (described as supported). The catalyst of the present invention is a particle in which at least one element selected from Pt, Pd, and Rh is supported on the catalyst carrier. In actual use as an exhaust gas purification catalyst, the catalyst is applied and baked on a ceramic or metal honeycomb base material to distribute the exhaust gas. In applying and baking, for example, a binder such as activated alumina is mixed with water to form a slurry, which is applied to the honeycomb substrate, and fired at a temperature of about 600 ° C. to be adhered and fixed.

The catalyst according to the present invention exhibits the following effects.
(A) In addition to the high promoter effect of the perovskite oxide, high exhaust gas purification characteristics are exhibited by maintaining a sufficient surface area for supporting the noble metal in a highly dispersed state.

As described above, noble metals such as Pt, Pd, Rh, etc. have an exhaust gas purification action directly, but ABO _3-δ (A contains rare earth elements and alkaline earth metal elements, and B transitions. The high oxygen storage ability of the perovskite oxide represented by (which can contain many elements, mainly elements) enhances the exhaust gas purification characteristics of the noble metal (this is called the promoter effect of the perovskite oxide). The composition of the perovskite oxide of the present invention is appropriately selected and exhibits a high promoter effect.

  Further, exhaust gas purification proceeds on the surface of the noble metal particles. Therefore, if the surface area of the noble metal is large, the purification characteristics are high. In order to increase the surface area for the same amount of precious metal, it is effective and economical to reduce the particle size of the precious metal. In order to reduce the particle size of the noble metal, it is effective to increase the surface area of the catalyst carrier supporting the noble metal, and the larger the surface area that can be supported, the more uniformly the noble metal particles having a smaller particle size can be held. (This is described as supporting a precious metal in a highly dispersed state). In actual use, noble metals tend to increase in particle size due to high temperature and reducing atmosphere, and purification properties deteriorate as the particle size increases (this is described as self-sintering of noble metals in actual use). However, when the surface area of the catalyst carrier supporting the noble metal is large, the distance between the noble metal particles is large, and thus self-sintering of the noble metal is suppressed. The catalyst carrier of the present invention realizes a large surface area capable of supporting a noble metal in a highly dispersed state.

  (B) During actual use, the self-sintering of the catalyst carrier itself made of a perovskite oxide is suppressed, the decrease in the effective surface area of the noble metal is suppressed, and the deterioration of the exhaust gas purification characteristics is suppressed.

  The catalyst carrier is required to be stable even in actual use as an exhaust gas purification catalyst. In actual use as an exhaust gas purification catalyst, if the surface area of the catalyst carrier becomes small due to sintering or the like (this is referred to as self-sintering of the catalyst carrier in actual use), the noble metal held on the surface of the catalyst carrier Self-sintering is promoted, or the noble metal is buried in the catalyst carrier, and the surface area of the effective noble metal that can come into contact with the exhaust gas is reduced (this is described as a reduction in the effective surface area of the noble metal in actual use). . The catalyst carrier of the present invention has a low degree of self-sintering during actual use, and a reduction in the effective surface area of the noble metal is suppressed.

  (C) During actual use, the reaction between the binder such as alumina and the perovskite oxide is suppressed, the decrease in the effective surface area of the noble metal is suppressed, and the deterioration of the exhaust gas purification characteristics is suppressed.

  Perovskite-type oxides easily react with binders such as alumina that are mixed during application and baking on honeycomb substrates, and are exposed to high temperatures together with the binder during actual use as exhaust gas purification catalysts. To change. As the perovskite oxide is reduced, the cocatalyst effect is reduced and the exhaust gas purification characteristics are deteriorated. In addition, when chemically reacting with the binder, the surface carrying the noble metal also changes, leading to a reduction in the effective surface area of the noble metal. The catalyst carrier of the present invention has low reactivity with the binder, maintains the promoter effect even during actual use, and suppresses the reduction in the effective surface area of the noble metal.

  In the present invention, due to the effects (a), (b) and (c), the amount of noble metal used can be reduced and the cost can be reduced. In addition, the cost can be reduced without using a large amount of rare earth elements in order to improve the heat resistance of the perovskite oxide.

  The invention [1] will be described in detail below, but this item relates to a catalyst carrier.

The constituent element i of the invention [1] is characterized in that the oxide 1 which is a perovskite complex oxide and the oxide _{2 made} of a rare earth oxide such as Y ₂ O ₃ are mixed. The perovskite oxide is the most basic constituent element of the present invention that acts as a co-catalyst for improving the exhaust gas purification characteristics of noble metals such as Pd, and as a result, reduces the amount of noble metal used. However, the perovskite type oxide has a high sinterability, and there is a problem that the effective reaction area of the noble metal is reduced by self-sintering, that is, the heat resistance is low. The oxide 2 of the present invention suppresses the progress of self-sintering of the catalyst support during actual use. Y ₂ O _{3 and the} like are compounds that are difficult to sinter themselves, and have low reactivity with perovskite oxides. Even if they are mixed with perovskite oxides and fired at high temperatures, they are perovskite type as the second phase. Coexists with oxides. Therefore, the oxide 2 is on the surface of the oxide 1 and suppresses the reaction between the oxides 1, that is, suppresses the increase in particle size due to the self-sintering of the oxide 1. Various oxides have been tested as oxides that have low reactivity with perovskite oxides and can suppress self-sintering of perovskite oxides. As a result, Y ₂ O ₃ , La ₂ O ₃ , and CeO of rare earth oxides were tested. ₂ and the transition metal oxide NiO were found. Among them, Y ₂ O ₃ was particularly effective for improving heat resistance. By this configuration requirement, the above-mentioned effect (b) is obtained, and deterioration of exhaust gas purification characteristics is suppressed.

  Constitutional requirement ii of the invention of the above [1] is that two surfaces having an average particle diameter of 5 μm or more composed of a porous body in which the surfaces of the plurality of oxide 1 grains are sintered and the porosity is 20% to 60%. It is characterized by comprising secondary particles. The porosity is the volume fraction of the pores.

The catalyst carrier according to the invention of [1] can be obtained by the following production method. As will be described later, the raw material (precursor) of the oxide 1 is pulverized until the specific surface area becomes at least 20 m ² / g, and then mixed with the raw material (precursor) of the oxide 2 and is 700 ° C. in the atmosphere. Heat treatment is performed at the above temperature. By performing this heat treatment, the sintered oxide 1 defined by the constituent requirements ii and iii is generated. However, macroscopically, the sintering progresses and secondary particles having a size of several millimeters are formed. In some cases, it is further pulverized to 5 μm or more and less than 100 μm with a mortar or jet mill. The secondary particle diameter can be evaluated by a particle size distribution measuring apparatus using a laser diffraction / scattering method.

By the heat treatment, the perovskite oxide is sintered in advance to the state specified in the constituent requirement ii, that is, the self-sintering of the perovskite oxide has already been advanced to a certain degree. Self-sintering of the perovskite oxide is suppressed (the above-mentioned effect (b)). Here, the specific surface area of the oxide 1 is greatly reduced from the specific surface area of the precursor of the oxide 1 by the heat treatment. Conventionally, in order to carry a noble metal in a highly dispersed state, it has been said that the larger the specific surface area of the catalyst carrier, the better. Therefore, it is possible to reduce the specific surface area by subjecting a material whose specific surface area has been increased by corner pulverization to heat treatment again. There wasn't. In addition, when the precursor of the oxide 2 is not added before the heat treatment, the sintering progresses too much and the specific surface area is significantly reduced. On the other hand, the addition of the precursor of the oxide 2 It is effective only after it has been micronized until the specific surface area becomes at least 20 m ² / g, and the present invention can be completed by repeating repeated tests including the composition and addition amount of the precursor of oxide 2. It was.

  Further, by forming secondary particles, the above effect (c) is obtained, and deterioration of exhaust gas purification characteristics is suppressed. When the catalyst carrier of the present invention and a binder such as alumina are mixed and applied to a honeycomb substrate and baked, the reaction proceeds at the interface between the perovskite oxide and the binder, and the perovskite oxide changes to another oxide. And lost. If the perovskite oxide forms secondary particles before mixing with the binder, the perovskite oxide that reacts with the binder will be outside the secondary particles unless the binder penetrates deeply into the secondary particles. It is a shell part. Therefore, the larger the size of the secondary particles, the smaller the reaction amount, and the average particle size of the secondary particles is desirably 5 μm or more. The amount of perovskite oxide lost by the reaction depends on the temperature at actual use and the composition and particle size of each oxide. It was found that the amount of perovskite oxide lost was kept within 5%. On the other hand, if the particle size of the secondary particles is too large, the dispersion into the slurry prepared by mixing with the binder and the application / baking are hindered, but although not strictly determined, it is preferably less than 100 μm.

  In some cases, the slurry containing the binder penetrates deeply from the gaps between the secondary particles, but the penetration can be suppressed as the porosity decreases. The amount penetrating depends on the particle size of the oxide 1 and cannot be determined in general. However, if the porosity is 60% or less, the volume of the penetrating portion can be suppressed within 5% of the secondary particle volume. It was found that the effect (c) can be obtained. However, in order to obtain this effect more completely, the porosity is more preferably 50% or less. On the other hand, from the viewpoint of the effect (a), it is necessary to use the surface of the oxide 1 inside the secondary particles as an effective surface area of the catalyst carrier, that is, the noble metal particles can be easily formed inside, It is required that the exhaust gas can easily flow to the inside of the secondary particles, and for that purpose, a high porosity is desirable. Actually, it depends on the secondary particle size and the particle size of oxide 1, but if the porosity is 20% or more, in most cases, noble metal particles can be formed to the inside of the secondary particles. It is known that when the percentage is less than%, the number of cases where noble metal particles cannot be formed up to the center inside the secondary particles increases. In order to complete this effect, the porosity is more preferably 30% or more. Precious metal is supported in a liquid, but if the porosity is such that the precious metal can be uniformly formed up to the interior of the secondary particles, the exhaust gas is a gas, so it can penetrate sufficiently into the interior of the secondary particles, so exhaust gas purification. It will not hinder. The porosity can be confirmed with a transmission electron microscope or a scanning electron microscope.

  The constituent requirement iii of the invention [1] is characterized in that the average particle diameter of the oxide 1 is 0.05 μm or more and 0.5 μm or less. When the average particle diameter of the oxide 1 is 0.05 μm or more, the above effect (b) can be obtained. In general, the smaller the particle size of oxide particles, the larger the surface area per unit weight and the greater the driving force for sintering. The degree of self-sintering of oxide 1 cannot be determined unconditionally depending on the firing temperature and the composition of each oxide, but when the average particle size is 0.05 μm or less, The increase in average particle size during use exceeds 5%, and when the average particle size is 0.05 μm or more, the increase in average particle size during actual use of the exhaust gas purification catalyst can be suppressed to 5% or less. I know that. On the other hand, when the average particle size of the oxide 1 is 0.5 μm or less, the above-mentioned effect (A) is obtained. When the average particle diameter of the oxide 1 is larger than 0.5 μm, the surface area as a catalyst carrier is insufficient, the precious metal is not sufficiently dispersed, and the purification characteristics are deteriorated. Moreover, self-sintering of precious metals during actual use will also progress. The purification characteristics depend on the amount of precious metal, temperature, exhaust gas concentration, etc., but when the average particle size of the oxide 1 is 0.6 μm or more, the case where sufficient purification characteristics cannot be obtained increases. The particle size can be confirmed with a transmission electron microscope or a scanning electron microscope.

The constituent requirement iv of the invention of [1] is that the oxide 2 preferably has a particle size of 0.1 μm or less, more preferably 0.05 μm or less, and exists mainly at the interface between the oxide 1 and the pores. Features. This requirement (b) can be obtained by this requirement. As described above, the oxide 2 made of Y ₂ O ₃ or the like suppresses the progress of self-sintering of the oxide 1 during actual use. Y ₂ O _{3 and the} like are compounds that are difficult to sinter themselves, and have low reactivity with perovskite oxides. Even if they are mixed with perovskite oxides and fired at high temperatures, they are perovskite type as the second phase. In order to coexist with the oxide, the particle size increase due to self-sintering of the perovskite oxide is suppressed. Therefore, it is necessary that the oxide 2 is widely distributed so as to cover the particle surface of the oxide 1, that is, the particle size is small. The degree of self-sintering of the oxide 1 depends on the firing temperature and the composition of each of the oxide 1 and oxide 2 and cannot be determined unconditionally, but the average particle size of the oxide 2 is 0.1 μm or less. In some cases, it has been found that the increase in the average particle size of the oxide 1 during actual use of the exhaust gas purification catalyst can often be reduced to 5% or less. When the average particle size of the oxide 2 was 0.2 μm or more, the increase amount of the average particle size of the oxide 1 during actual use of the exhaust gas purification catalyst often exceeded 5%. On the other hand, it is extremely difficult to make the average particle size of the oxide 2 smaller than 0.005 μm. It can be confirmed with a transmission electron microscope, a scanning electron microscope, or the like that the oxide 2 has a particle size of 0.1 μm or less and exists mainly at the interface between the oxide 1 and the pores.

The constituent element v of the invention of [1] is that the composition of the oxide 1 is (Formula 1) described in [1], that is, {Sr _(1-a) A _a } _s Fe _(1-btc) B _b Ti _t C _c O _3-δ (Here, A, B, and C may not arrange elements, but when A is arranged, one or more elements selected from Ba, Ca, and La, B When arranging C, one or more elements selected from Co, Cu and Ni, when arranging C, one or more elements selected from Nb, Ta and Mn, 1.0 ≦ s ≦ 1.1 , 0 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.25, 0.05 ≦ t ≦ 0.3, 0 ≦ c ≦ 0.25, 0.05 ≦ t + c ≦ 0.3, δ is a value determined by the history of the material, that is, cations (Sr, A, Fe, B, Ti, C) having a perovskite structure phase represented by the sum of the valences of Fe, B, Ti, and C). .

  In oxide 1, A may not arrange an element, but when A is arranged, it is one or more elements selected from Ba, Ca, and La. From the viewpoint of the effect (b), it is better that A is larger, but from the viewpoint of the effect (b), A is better. As a result of examining the effect (b), that is, the degree of self-sintering of the oxide 1, the increase in the average particle size of the oxide 1 during actual use of the exhaust gas purification catalyst was 10% when a = 0. In many cases, the increase in the average particle size of oxide 1 could be suppressed to 5% simply by setting a = 0.1. On the other hand, as a result of examining the effect (A), when a = 0.5 is exceeded, the purification characteristics are insufficient in most cases, and when a = 0.2 is exceeded, there are 20% of cases where the purification characteristics are insufficient.

As described above, s is the ratio of the element amounts of the A portion (A site) and the B portion (B site) of the perovskite oxide generally expressed as ABO _3-δ. From the viewpoint of (A), s is 1.0 or more and 1.1 or less. The oxide 1 which is a perovskite oxide exists only in this range. When an oxide 1 having s of 0.9 and 1.2 is prepared, a composite oxide that is not a perovskite type is formed or a mixture of a perovskite type oxide and another oxide is formed. The purification characteristics are reduced by the amount generated.

  B may be omitted, but if B contains one or more elements selected from Co, Cu, and Ni, higher purification performance can be obtained, from the viewpoint of the above effect (ii). desirable. On the other hand, if the content of the element is too large, the oxide 1 is likely to be self-sintered, which is not desirable from the viewpoint of effect (b). That is, b is 0.25 or less. The degree of self-sintering of oxide 1 depends on the firing temperature and the composition of each of oxide 1 and oxide 2 and cannot be determined unconditionally, but when b is 0.3, the exhaust gas purification catalyst The increase in the average particle diameter of the oxide 1 during actual use exceeds 5%, which is not desirable. From the viewpoint of the effect (b), Cu is most preferable as the element of B.

  Since Ti is the most effective additive element from the viewpoint of effect (c), that is, reaction suppression with a binder such as alumina, t is preferably 0.05 or more, more preferably 0.1 or more. The amount of perovskite oxide lost due to the reaction cannot be determined unconditionally depending on the temperature at the time of actual use, the composition and particle size of each oxide, but is lost by the reaction if t is 0.05 or more. It was found that the amount of perovskite oxide was suppressed to 5% or less, and to 2% or less when t was 0.1 or more. On the other hand, as t is increased, the purification characteristics are degraded. Therefore, from the viewpoint of effect (A), t is 0.3 or less. In the case of t = 0.4, there were 20% of cases where the purification characteristics were insufficient.

  C may be omitted, but if C contains one or more elements selected from Nb, Ta, and Mn, the effect (b), that is, self-sintering of oxide 1 is suppressed. This is desirable. On the other hand, as t + c is larger, the purification characteristics are degraded. Therefore, from the viewpoint of effect (A), t + c is 0.3 or less. In the case of t = 0.4, there were 20% of cases where the purification characteristics were insufficient.

The configuration requirements vi invention of [1], oxide 2 is at least one kind chosen by always contains _{Y 2 O 3, La 2 O} 3, Y 2 O 3 from CeO _2, NiO, is mixed with The total amount of Y, La, Ce and Ni in the oxide 2 is 5 mol% or more and 30 mol% or less with respect to the total number of moles of Sr and A in the oxide 1. The component requirement vi suppresses the above effect (b), that is, self-sintering of the oxide 1. The ratio of the oxide 2 is preferably 5 mol% or more, and when it is 10% or more, a higher (b) effect is exhibited. The degree of self-sintering of the oxide 1 during actual use depends on the use temperature, the composition of each oxide, etc. and cannot be determined unconditionally, but when the proportion of the oxide 2 is less than 5 mol%, The increase in average particle diameter during actual use of the exhaust gas purification catalyst exceeds 5%, and when the ratio of oxide 2 is 10 mol% or more, the increase in average particle diameter during actual use of the exhaust gas purification catalyst Is suppressed to 2% or less. On the other hand, if too much oxide 2 is mixed, the purification properties are deteriorated. Therefore, from the viewpoint of effect (ii), oxide 2 is preferably 30 mol% or less. When 35 mol% was mixed, there were 20% of cases where the purification characteristics were insufficient. Among the oxides 2 of Y ₂ O _3, La ₂ O _3, CeO _2, NiO, and most preferably Y ₂ O _3, that will always select the Y ₂ O ₃ even when the selected two or more desirable. Therefore, 5 mol% or more of Y is mixed with respect to the total number of moles of Sr and A in the oxide 1.

In the catalyst carrier of the present invention, the oxide 1 composed of a perovskite oxide and the oxide 2 such as Y ₂ O ₃ effective for improving the heat resistance of the perovskite oxide are mixed, and the oxide 1 and the oxide The requirement that the composition of the product 2 is in a specific range is included in the requirement relating to the prior application (Japanese Patent Application No. 2012-206532). In the present invention, in addition to these requirements, the oxide 1 in which the perovskite oxide is sintered to a certain degree is formed while controlling the particle diameters of the oxide 1 and the oxide 2, respectively. The deterioration at the time of use (self-sintering of the catalyst carrier itself and reaction with a binder such as alumina) was improved and sufficient purification performance was ensured despite the small amount of rare earth elements used.

  The invention of [2] is limited to that in (Formula 1) of [1], the oxide 1 does not contain La and the oxide 2 does not contain La and Ce. Even if the oxide 1 does not contain La and the oxide 2 does not contain La and Ce, the above effects (a), (b), and (c) can be expressed sufficiently, so that expensive La and Ce are used. The manufacturing cost can be further reduced.

In the invention of [3], in order to obtain higher heat resistance, the composition of the oxide 1 described in [1] is limited to the composition represented by the following (formula 2), and the oxide 2 is converted to Y ₂ O. It is characterized by being limited to ₃ .
Sr _s Fe _(1-t) Ti _t O _3-δ (Formula 2)
(Where 1.0 ≦ s ≦ 1.1, 0.05 ≦ t <0.3, δ is a value determined by the history of the material)

  The invention [4] is characterized in that the exhaust gas purifying catalyst carrier according to any one of [1] to [3] is loaded with at least one noble metal selected from Pd, Pt, and Rh. An exhaust gas purifying catalyst. The catalyst carrier according to the inventions [1] to [3] is not a catalyst for exhaust gas purification until at least one or more elements selected from Pt, Pd, and Rh are supported as described above. Excellent performance. If the noble metal is not supported, sufficient exhaust gas purification performance cannot be obtained. The amount of the precious metal supported is desirably in the range of 0.1% or more and 2% or less by mass percent with respect to the composite oxide. If it is less than 0.1%, sufficient purification characteristics are not exhibited. When the precious metal is supported in excess of 2%, the cost of the catalyst is increased, and self-sintering of the precious metal during actual use is facilitated, and the purification characteristics corresponding to the amount of the precious metal supported are not exhibited. In addition, when the amount of the noble metal supported is smaller than the above range, the catalyst purification performance may be insufficient.

  Here, based on the detailed description disclosed above, the difference from the prior art will be supplementarily described.

In the prior art (Patent Documents 2, 3, 4, 5, 6 and 7), in order to suppress the self-sintering of the perovskite oxide and improve the heat resistance, the perovskite oxide represented as ABO _3-δ A technology that contains a rare earth element such as La in a large amount of 50 mol% or more of A in the A portion (A site) of the above [1] is represented by ABO _3-δ. The portion A (A site) of the perovskite oxide may not contain La or Ce as rare earth elements. That is, in the present invention, suppression of self-sintering by addition of rare earth elements to the perovskite type oxide itself is an auxiliary requirement, and from constituent requirement vi, that is, Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , NiO High heat resistance is imparted by mixing at least one oxide 2 that is always selected to contain Y ₂ O ₃ . At this time, the added amount of the oxide 2 is such that the total amount of Y, La, Ce, and Ni in the mixed oxide 2 is 5 mol% or more and 30 mol% with respect to the total number of moles of Sr and A in the oxide 1 In the following, as a constituent element of the oxide 2, only Y is essential, and it is not necessary to include La or Ce which are rare earth elements. In the present invention, the above effects (A), (B), and (C) are satisfied without containing a large amount of expensive and rare La and Ce. [2] to [3] are configured so as not to include La or Ce as rare earth elements.

  In the prior art (Patent Documents 6, 7, 8, 9 and 10), a technique for improving heat resistance by adding a heat resistant oxide to a perovskite oxide is disclosed. Is typically equivalent to the perovskite oxide, the proportion of the perovskite oxide in the catalyst unit weight is 50% or less, and the promoter effect of the perovskite oxide is halved. On the other hand, the amount of oxide 2, which is a heat-resistant oxide in [1], is such that the total amount of Y, La, Ce, and Ni is 5 mol% with respect to the total number of moles of Sr and A in oxide 1. The content is 30 mol% or less, less than that of oxide 1, and the addition of oxide 2 does not cause a significant decrease in the cocatalyst effect of the perovskite oxide.

  In the prior art (Patent Documents 9 and 10), Ce or Y is included in the composition of the heat-resistant oxide, but there is no description that Y is necessarily included, and it is suitable for the composition of oxide 1 in [1]. It has been clarified for the first time in the present application that Y is an essential constituent element as the heat-resistant oxide 2. The yttria sol disclosed in Patent Document 10 is used as a binder mixed with a perovskite type oxide when applied and baked on a ceramic or metal honeycomb substrate. The use is different from the functional oxide.

  Hereinafter, the method for producing the catalyst carrier disclosed in the above [5] and [6] of the present invention will be described in detail.

The invention [5] is the method for producing a catalyst carrier according to the above [1] to [3]. When a perovskite oxide having the same composition as that of oxide 1 and having a particle size of several hundred μm is obtained, the average particle size of the obtained oxide is preferably 0.5 μm or less following the process. Is pulverized by grinding until it becomes 0.2 μm or less. The specific surface area is pulverized until it reaches at least 20 m ² / g. In the present invention, this state is defined as the precursor of oxide 1. Conventionally, it has been difficult to produce such fine and high specific surface area oxide powders by a pulverization method. However, in the composite oxide of the present invention, a ceramic ball having a diameter of about 0.5 mm to 0.01 mm is used for pulverization. By using a medium stirring type pulverizer such as a bead mill, it is possible to easily make the fine powder. In the production of the precursor of oxide 1, a so-called solution method using a raw material such as alkoxide may be used. However, the manufacturing cost increases, which is not preferable.

Next, a perovskite oxide having the same composition as that of oxide 1 and having an average particle size of 0.2 μm or less, that is, a precursor of oxide 1 is dispersed in a solvent such as water or ethyl alcohol to form a slurry. The raw materials for oxide 2 are mixed. Examples of the raw material for the oxide 2 include Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , and NiO that have been adjusted to an average particle size of 0.1 μm or less in advance. Alternatively, preferably Y (NO ₃ ) ₃ , Y (CH ₃ COO) ₃ .4H ₂ O, La (NO ₃ ) ₃ , La (CH ₃ COO) ₃ .1.5H ₂ O, Ce (NO ₃ ) ₃ , Ce (CH ₃ COO) ₃ .H ₂ O, Ni (NO ₃ ) ₂ .6H ₂ O, NiCl ₂ .6H ₂ O and the like are dissolved in a solvent such as water or ethanol. Y, La, Ce Since Ni is dispersed at the atomic level, sintering of the oxide 1 is efficiently suppressed. The raw material of the oxide 2 is directly mixed with the precursor slurry of the oxide 1. Next, after the mixture is dried to remove the solvent, it is heat-treated at a temperature of 700 ° C. or higher in the atmosphere, and further pulverized to less than 100 μm by a mortar or jet mill to complete the catalyst carrier of the present invention. The secondary particle diameter can be evaluated by a general particle size distribution measuring device such as a laser method.

  It can be confirmed by the X-ray diffraction method that the oxides 1 and 2 are perovskite oxide and oxide, respectively. The average particle diameter of oxide 1 and oxide 2, the sintering ratio of adjacent oxide 1, and the porosity can be evaluated by a transmission electron microscope such as JEM-2100F manufactured by JEOL. About 100 particles of oxide 1 and oxide 2 are selected by element distribution analysis of the electron microscope, and the average particle diameter can be obtained by a line intercept method based on an electron micrograph. That is, it is possible to draw a plurality of straight lines on the photograph, calculate the average value of the lengths of the straight lines crossing each particle, and make the average particle diameter. The porosity is also obtained from the area ratio of the pore site by image processing of an electron micrograph. Although the oxide 2 is mainly present at the interface between the oxide 1 and the pores, it is also evaluated by the transmission electron microscope that the oxide 2 is particularly concentrated at the three-phase interface between the adjacent oxide 1 and the pores. be able to. The specific surface area of the catalyst carrier can be determined by the BET method using nitrogen gas adsorption.

  The invention [6] is one of the methods for producing a catalyst carrier according to the inventions [1] to [3], and has an average particle size having a crystal phase of a perovskite structure as described in [5]. It is characterized by a process for producing a precursor of oxide 1 of 0.5 μm or less.

The raw materials for Ba, Sr, and Ca in the composition formula (formula 1) are one or more carbonates or hydroxides selected from alkaline earth metal carbonates and alkaline earth metal hydroxides, preferably BaCO ₃ , A carbonate or hydroxide selected from SrCO ₃ , CaCO ₃ , Ba (OH) 2 .8H ₂ O, Sr (OH) 2 .8H ₂ O, Sr (OH) ₂ and Ca (OH) ₂ is La. The raw material is selected from La ₂ (CO ₃ ) ₃ · 8H ₂ O, La ₂ O ₃ , Fe ₂ O ₃ as the raw material of Fe, CoO as the raw material of Co, Cu, and Ni as B elements, Co ₃ O ₄ , CuO, NiO, etc., TiO ₂ as the raw material for Ti, and TiO ₂ , Nb ₂ O ₅ , Ta ₂ O _5, Mn ₃ O ₄ as the raw materials for the N elements Cb, Nb, Ta, and Mn Each of these oxides can be suitably used.

  As a raw material of the oxide 1, the carbonate, hydroxide, oxide, and the like are weighed, and then wet mixed with a mill such as a ball mill using water or ethyl alcohol as a dispersion medium. In some cases, dry mixing without using a dispersion medium may be used. The obtained slurry is dried and crushed (in the case of dry mixing, this step is usually not necessary), and then put in a ceramic container made of alumina or the like and baked for several hours in the atmosphere. To obtain a mixture of The firing temperature is 900 ° C. or higher and 1200 ° C. or lower. Firing is preferably performed a plurality of times at different temperatures, and it is desirable to grind powder with a mortar or the like to remove coarse particles between the firing. It is desirable that the firing temperatures of the firings that are performed a plurality of times be sequentially increased. Typically, it is possible to produce a catalyst carrier having excellent characteristics by firing at 900 ° C. for the first time and firing at 1100 ° C. for the second time. When the firing temperature exceeds 1200 ° C., pulverization in the subsequent process becomes difficult. On the other hand, when the calcination temperature is lower than 900 ° C., the formation of the perovskite structure is insufficient and the necessary catalyst characteristics cannot be obtained.

Through the steps described above, a perovskite oxide having the same composition as that of oxide 1 and a particle size of several hundred μm is obtained. Subsequent to the step, the obtained oxide is pulverized by pulverization until the average particle size becomes 0.5 μm or less, more preferably 0.2 μm or less. The specific surface area is pulverized until it reaches at least 20 m ² / g.

  Usually, a so-called solution method using a raw material such as an alkoxide is generally used as a production method used for obtaining a catalyst support of a perovskite oxide. Since the solution method is manufactured from a solution in which raw materials are uniformly dissolved, it is possible to obtain a perovskite type structure by relatively low-temperature firing, and it is easy to manufacture a catalyst carrier having a high specific surface area as an effect of low-temperature firing. Have. However, even if a catalyst carrier having a large specific surface area is obtained with a single perovskite oxide, sintering progresses at the stage of actual use as an exhaust gas purification catalyst, and the catalyst characteristics deteriorate, and the solution method alone is not necessarily excellent. It's not the way. In the present invention, the particle size of the precursor of the oxide 1 may be about 0.05 μm, and is a particle size sufficiently obtained by pulverization with a ceramic ball, and it is not necessary to use an expensive solution method.

  The invention of [7] relates to a method for supporting Pt, Pd, Rh on the catalyst carrier according to the above [1] to [3]. As raw materials for Pt, Pd, and Rh, dinitrodiammine platinum nitric acid aqueous solution, palladium nitrate aqueous solution, rhodium nitrate aqueous solution, or the like can be suitably used. These required amounts are weighed to form a mixed solution, and a predetermined amount of the mixed solution is impregnated into a predetermined amount of the mixture of oxide 1 and oxide 2 and dried using a rotary evaporator or the like. After that, heat treatment is performed in the atmosphere for several hours at a temperature of about 600 ° C. It is also possible to dissolve the noble metal salt in an alcohol such as ethanol and impregnate using an alcohol solvent.

  Finally, an exhaust gas purification catalyst member used when the catalyst of the present invention is used for exhaust gas purification will be described.

  The exhaust gas purifying catalyst member of the present invention is formed by applying and baking the above-described catalyst of the present invention on a substrate. By applying and baking to the base material, the spatial concentration of the catalyst can be optimally controlled, and the catalyst surface can be effectively used at the contact surface with the exhaust gas. Furthermore, it is possible to prevent the catalyst particles from being scattered by being bonded to the base material. In addition, it is possible to obtain an effect of reducing influences such as excessive temperature increase, heat deterioration due to heat generation in the catalytic reaction, temperature decrease due to heat absorption, and activity decrease.

  As the base material used in the exhaust gas purifying catalyst member of the present invention, a honeycomb-like member made of ceramics or metal can be preferably used. For example, cordierite is suitable as the ceramic, but the present invention is not limited to this. Moreover, as said metal, the ferritic stainless steel excellent in oxidation resistance is suitable, for example, However, This invention is not limited to this. When these ceramic or metal honeycomb-shaped members are used, the ventilation resistance of the exhaust gas is smaller, and the effective area where the catalyst of the present invention comes into contact with the exhaust gas increases.

  In order to manufacture the exhaust gas purifying catalyst member of the present invention, the particles of the catalyst of the present invention are fixed to a honeycomb member together with a binder. First, a slurry in which a catalyst, a binder, and the like are dispersed is prepared, and a ceramic or metal honeycomb member is immersed therein. Next, the excess slurry on the surface of the honeycomb-shaped member is removed by a method such as blowing off, and after drying, the honeycomb-shaped member is heat-treated in the atmosphere for several hours at a temperature of about 500 ° C. As the binder, an oxide or hydroxide having heat resistance can be used. As described above, the binder binds catalyst particles and the like, and in addition, has a function of giving high adhesion when the catalyst of the present invention is applied and baked on a substrate, and also has a high temperature. Since it exists stably even under oxidizing conditions, its performance as a binder is rarely deteriorated. Specifically, oxides and hydroxides such as alumina, activated alumina, boehmite, aluminum hydroxide, silica, silica-alumina, and zeolite are preferably used. In particular, activated alumina is more suitable because it is easily available and inexpensive.

(Example 1)
The composition of the oxide 1 of this example is Sr _1.05 Fe _0.9 Ti _0.1 O _3-δ . Granular SrCO ₃ , Fe ₂ O ₃ , and TiO ₂ were used as raw materials for Sr, Fe, and Ti, respectively. The raw materials are weighed so that the molar ratio is Sr: Fe: Ti = 1.05: 0.9: 0.1, added to ethyl alcohol (dispersion medium), and wet-mixed while pulverizing with a ball mill to obtain a slurry. It was. The slurry was separated from the slurry by a rotary evaporator and dried at approximately 120 ° C. for 1 hour. Next, the dried product thus obtained was crushed and then put into a corner or container made of MgO ceramic and baked in the electric furnace at 900 ° C. for 5 hours in the air to obtain a porous lumped baked product. The fired product was pulverized and then dry-pulverized with an automatic mortar. The powder was again put in a corner box made of MgO ceramic and fired in an electric furnace at 1100 ° C. for 5 hours in the atmosphere. The composite oxide powder was pulverized in a bead mill using ethanol as a solvent for 3 hours using zirconia beads having a diameter of 0.2 mm. The specific surface area of the obtained powder (precursor of oxide 1) was determined by a BET method by nitrogen gas adsorption using Belsorb manufactured by Nippon Bell Co., Ltd. It was 31 m ² / g.

  Next, a solution of yttrium nitrate (precursor of oxide 2) was prepared using ethanol as a solvent, mixed with the slurry (precursor of oxide 1) pulverized by the bead mill for 3 hours, and stirred well. The amount of Y was adjusted to be 10 mol% of Sr (see Table 2). After separating the solid content from the slurry after mixing with a rotary evaporator, the dried product obtained was crushed, put in a square sheath made of MgO ceramic, fired in an electric furnace at 900 ° C in the atmosphere for 5 hours, The mixture was lightly crushed with an automatic mortar to form granules of 5 μm or more and less than 100 μm (oxide 1 + oxide 2). The secondary particle size after crushing was measured with a laser diffraction particle size distribution analyzer (SALD-3100, manufactured by Shimadzu Corporation).

When the specific surface area of the obtained powder (oxide 1 + oxide 2) was determined by the BET method, it was 12 m ² / g in this example. Further, the composition of the powder (oxide 1 + oxide 2) was evaluated by chemical analysis, and was consistent with the amount of metal element in the charged compound. It was confirmed by the X-ray diffraction method that the oxides 1 and 2 were perovskite oxides and Y ₂ O _{3 made} of Sr, Fe, and Ti, respectively. The average particle diameters of oxide 1 and oxide 2, the sintering ratio of adjacent oxide 1, and the porosity were evaluated by a transmission electron microscope (JEM-2100F manufactured by JEOL). 100 or more particles of oxide 1 and oxide 2 were selected by element distribution analysis of the electron microscope, and the average particle diameter was determined by a line intercept method based on an electron micrograph. That is, a plurality of straight lines were drawn on the photograph, and the average value of the lengths of the straight line portions crossing each particle was calculated and used as the average particle diameter. As a result, the average particle diameters of oxide 1 and oxide 2 were 0.11 and 0.03 μm, respectively. As for the porosity, the electron micrograph was subjected to image processing, and the area ratio of the pore portion was defined as the porosity. As a result, it was 50%. The presence of oxide 2 mainly at the interface between oxide 1 and pores was also confirmed by the electron microscope (see Table 3).

  Next, 0.4% by weight of Pd noble metal was supported on the powder (oxide 1 + oxide 2) as follows. A predetermined amount of commercially available palladium nitrate was weighed and diluted with ethanol to obtain a diluted solution having a volume of about 100 mL. The diluted solution and 100 g of the powder (oxide 1 + oxide 2) were put in a rotary evaporator, and first, defoaming was performed while rotating and stirring at room temperature and under reduced pressure. After returning to normal pressure and heating to about 50 ° C., it was dried under reduced pressure. After cooling to room temperature, the pressure was returned to normal pressure, the solid was taken out, and dried at about 120 ° C. for 5 hours. The obtained product was heat-treated in the atmosphere at 600 ° C. for 5 hours, and then crushed into granules. Through the above operation, a catalyst powder having a Pd loading of 0.4 mass% was obtained (see Table 4).

  Finally, the catalyst powder obtained above was applied and baked onto a stainless steel honeycomb member. In mass ratio, 10 parts by mass of the Pd-supported catalyst powder, 5 parts by mass of commercially available γ-alumina (activated alumina), 4 parts by mass of commercially available silica sol (trade name Snowtex C), 7 parts by mass of pure water, commercially available melcellulose solution (solid 2.5% by mass) and a suitable amount of antifoaming agent were mixed well with stirring to obtain a slurry. The stainless steel honeycomb member has a cylindrical shape with a cell hole cross-sectional size of 1 mm long × 2 mm wide and an overall shape of 25 mm in diameter and 60 mm in height. The honeycomb cylinder is held vertically, and an excessive amount of the slurry is uniformly deposited on the upper end face thereof, sucked from the lower end face of the honeycomb cylinder and applied to the inner wall of the honeycomb, and the excess slurry is removed to remove the upper end face of the honeycomb cylinder. The product was dried by air blowing. Further, the honeycomb cylinder was turned upside down, and the slurry was applied to the inner wall of the honeycomb cylinder and dried again. Thereafter, a heat treatment was performed in the atmosphere at 600 ° C. for 1 hour to obtain a stainless steel honeycomb member carrying the catalyst powder of the present invention. The catalyst amount and Pd amount fixed to the honeycomb member were 158 and 0.63 g / L-carrier, respectively.

  One of the above honeycomb members with a catalyst was subjected to a heat treatment at 900 ° C. for 5 hours in the atmosphere, and the other one was evaluated for purification characteristics (see Table 5).

In installing the catalyst-equipped honeycomb member in the evaluation apparatus, the honeycomb member was fixed inside the column by placing the outer periphery of the honeycomb cylinder wound with heat insulating wool of short alumina fibers inside the column. Next, a method for evaluating catalyst performance will be described. The evaluation device used here is a flow-type reaction device composed of stainless steel pipes. The model gas having the composition shown in Table 1 is introduced from the inlet side, and this is distributed to the exhaust gas purification reaction section, so that the outlet side To be discharged. The purification reaction part is heated by heating the model gas with an external heater and sending it to the exhaust gas purification reaction part. In the purification characteristics evaluation, first, the honeycomb member with catalyst was held at 450 to 500 ° C. for 1 hour in an atmosphere under the stoichiometric conditions shown in Table 1, and then cooled to near room temperature. Subsequently, the honeycomb member with catalyst is set in the column of the evaluation apparatus, and while raising the temperature, the gas having the stoichiometric condition shown in Table 1 is flowed, and the gas composition on the outflow side (after passing through the catalyst portion) is analyzed. , CO, HC, and by obtaining the change rate of the NO _x concentration, it was evaluated purification characteristic of each. The space velocity was 100,000 hr- ¹ . The catalytic properties were evaluated by determining the temperature (T50) at which CO, HC, and NOx each had a purification rate of 50% (see Table 5).

As for the purification characteristics of the catalyst, the case where the average value of T50 of CO, HC and NO _x after heat treatment is 240 ° C. or less is excellent (◎), and the case where it is 240 ° C. or more and 250 ° C. or less is purified. The case where the characteristic was good (◯), the case where the temperature was higher than 250 ° C. and the temperature was 260 ° C. or lower was judged as acceptable (Δ), and the case where the temperature was higher than 260 ° C. or the purification rate did not reach 50%, The requirement of the effect of the present invention is that sufficient exhaust gas purification characteristics can be obtained after the above heat treatment, but it is also an important characteristic that the exhaust gas purification characteristics are less deteriorated than before the heat treatment. The characteristic rank was also evaluated (see Table 5).

  When the exhaust gas purification performance of the honeycomb member with catalyst of Example 1 was measured, T50s of CO, THC, and NOx were 220 ° C., 229 ° C., and 250 ° C., respectively. Further, T50 of CO, THC, and NOx after the heat resistance test of the honeycomb-shaped carrier was 221 ° C, 230 ° C, and 254 ° C, respectively. The average value of T50 after these heat tests was 235 ° C., and the purification characteristics were excellent (◎). The average value of T50 before the endurance test was 233 ° C, and the increase in heat resistance test was 2 ° C, indicating that there was almost no deterioration (see Table 5).

(Comparative Example 1 and Comparative Example 2)
In Comparative Examples 1 and 2, the mixing ratio of the oxide 2 was changed with respect to Example 1. In Comparative Example 1, the amount of Y was 1 mol% of Sr and 50 mol% in Comparative Example 2. (See Table 2). The other production methods and the evaluation of the carrier are in accordance with Example 1. When the structure of the oxide was confirmed by X-ray diffraction after the catalyst support was completed, Y ₂ O ₃ of the oxide 2 was not confirmed in Comparative Example 1, and the porosity was less than 20% (see Table 3). ). In addition, in the electron micrograph of Comparative Example 2, Y ₂ O ₃ does not exist at the interface between the oxide 1 and the pores but exists so as to fill the pores, or the surface of the oxide 1 has a thickness of 0.1 μm or more. It was covered with. In both Comparative Examples 1 and 2, the catalyst purification characteristics were poor both before and after the endurance heat treatment, and the NOx purification rate did not reach 50%.

(Examples 2 and 3)
Examples 2 and 3 are cases where the type of noble metal was changed to Pt and Rh, respectively, as compared to Example 1 (see Table 4). The other production methods and the evaluation of the carrier are in accordance with Example 1. In both Examples 1 and 2, the catalyst purification characteristics were excellent both before and after the durable heat treatment (see Table 5).

(Examples 4, 5, and 6)
In Examples 4, 5 and 6, the composition of the oxide 2 is different from that of Example 1 in that Y ₂ O ₃ and NiO are mixed, Y ₂ O ₃ and CeO ₂ are mixed, Y ₂ O ₃ and La ₂ O, respectively. _This is the case of changing to ₃ mixing. The amount of oxide 2 was blended so that the amount of Y was 5 mol% of Sr and the amounts of Ni, Ce, or La were 5 mol% of Sr (see Table 2). The other production methods and the evaluation of the carrier are in accordance with Example 1. The catalyst purification characteristics of Examples 4 and 5 were good both before and after the durability heat treatment, and in Example 6, both before and after the durability heat treatment were excellent. However, the difference in purification characteristics before and after the durability heat treatment was small in all of these Examples. (See Table 5).

(Comparative Examples 3 and 4)
In Comparative Examples 3 and 4, the Sr composition of the oxide 1 was changed to 0.9 and 1.5 with respect to Example 1 (see Table 2). The other production methods and the evaluation of the carrier are in accordance with Example 1. In Comparative Example 3, the particle size of the oxide 1 increased to 1.1 μm, and the porosity was below 20% (see Table 3). It is presumed that the reactivity of Y ₂ O ₃ increases and Y ₂ O ₃ does not function sufficiently as a sintering inhibitor. As a result, the catalyst purification characteristics of Comparative Example 3 were poor both before and after the endurance heat treatment (see Table 5), and in particular, the NOx purification rate did not reach 50%. In Comparative Example 4, although not described in the table, as a result of X-ray diffraction of oxide 1, a phase other than the perovskite oxide was generated. As a result, the catalyst purification characteristics of Comparative Example 4 were acceptable both before and after the durable heat treatment (see Table 5), and the purification characteristics were low.

(Example 7, Comparative Examples 5 and 6)
In Example 7, Comparative Examples 5 and 6, the heat treatment temperature after changing the precursors of oxides 1 and 2 to Example 1 was changed. The other production methods and the evaluation of the carrier are in accordance with Example 1. Example 7 is 700 degreeC heat processing (refer Table 2), and is the range of this invention. The oxide 1 particle size was 0.06 μm, the porosity was 59% (see Table 3), and the purification characteristics before durable heat treatment were 228 ° C. at T50, which was extremely good even among the excellent. However, the purification characteristics after the durability heat treatment are good, and there are some problems in durability (see Table 5). Comparative Example 5 is a heat treatment at 500 ° C. (see Table 2). The structure and purification characteristics of oxide 1 are similar to those in Example 7, but the purification characteristics before durability heat treatment are very good. Because of its low purification properties, it cannot be put to practical use (see Table 5). Comparative Example 6 is a heat treatment at 1200 ° C. (see Table 2), but the particle size of the oxide 1 is as large as 1.8 μm and the porosity is as low as 7% (see Table 3). If the heat treatment temperature is too high, the function of the oxide 2 is relatively weak, and it is assumed that sintering proceeds too much. The catalyst purification characteristics of Comparative Example 6 were poor both before and after the endurance heat treatment (see Table 5), and in particular, the NOx purification rate did not reach 50%.

(Examples 8, 9, 10, 11 and Comparative Example 7)
Examples 8, 9, and 10 are cases where 10 mol% of Sr of oxide 1 was replaced with Ba, La, and Ca, respectively, as compared to Example 1 (see Table 2). The other production methods and the evaluation of the carrier are in accordance with Example 1. The particle size, porosity, and purification characteristics of the oxide 1 were slightly superior or inferior, but all exhibited excellent purification characteristics, and the difference before and after the durable heat treatment was small (see Table 5).

  Example 11 and Comparative Example 7 are the cases where 40 mol% and 60 mol% of Sr of oxide 1 were substituted with La for Example 1 (see Table 2). In any case, the particle size of the oxide 1, the porosity, the BET specific surface area of the catalyst after supporting Pd are good (see Table 3 and Table 4), and the difference in purification characteristics before and after the durable heat treatment is also small (see Table 5). The purification characteristics themselves are inferior, and in Comparative Example 7, the purification characteristics are acceptable and are not suitable for practical use.

(Examples 12, 13, and 14 and Comparative Examples 8 and 9)
Examples 12, 13, and 14 and Comparative Examples 8 and 9 are different from Example 1 in that Fe0.9 of Fe0.9 Ti0.1 of oxide 1 is Fe0.7Cu0.2, Fe0.7Co0.2, This is a case where it is replaced with Fe0.7Ni0.2, Fe0.6Cu0.3, Fe0.6Cu0.2Co0.1 (see Table 2). In Comparative Examples 8 and 9, the total of the elements B (see Formula 1) exceeds 0.25, which is outside the scope of the present invention. By substituting Fe with Cu, Co, and Ni, in these five examples, the particle diameter of the oxide 1 is larger and the porosity is lower than in the examples (see Table 3). The BET specific surface area tends to decrease (see Table 4). In Comparative Examples 8 and 9, the increase in particle size, the decrease in porosity, and the decrease in BET specific surface area are remarkable. In addition, the purification characteristics after the durability heat treatment are good in Examples 12, 13, and 14, but in the comparative example, they are poor and unsuitable for practical use (see Table 5). However, in all of the five examples, the characteristics after the heat treatment are deteriorated compared with those before the durability heat treatment, and substitution with Cu, Co, and Ni lowers the durability.

(Comparative Examples 10 and 11)
In Comparative Examples 10 and 11, the Ti ratio of Fe0.9Ti0.1 of the oxide 1 was changed from that of Example 1 and replaced with Fe0.98Ti0.02 and Fe0.5Ti0.5, respectively. This is outside the range of 0.05 ≦ t ≦ 0.3 of the present invention (see Table 2). Although the particle size and porosity of the oxide 1 and the BET specific surface area after supporting the catalyst are good (see Table 3 and Table 4), in Comparative Example 10, the purification property after the durability test is greatly deteriorated, Durability is reduced (see Table 5). In Comparative Example 11, the purification characteristics are acceptable both before and after the durability heat treatment (see Table 5), which is unsuitable for practical use.

(Examples 15, 16, and 17 and Comparative Examples 12 and 13)
Examples 15, 16, and 17 and Comparative Examples 12 and 13 are obtained by substituting Fe of oxide 1 with element C (see Formula 1) for Example 1, but Fe0.9Ti0.1 was changed. It is the case where it replaced with Fe0.8Ti0.1Nb0.1, Fe0.8Ti0.1Ta0.1, Fe0.8Ti0.1Mn0.1, Fe0.5Ti0.1Nb0.4, Fe0.5Ti0.1Nb0.2Ta0.2 respectively (Table 2). In Comparative Examples 12 and 13, the sum of Ti and element C (see Formula 1) exceeds 0.3, which is outside the scope of the present invention. By substituting Fe with an element such as Nb, Ta, or Mn, the heat resistance is improved as compared with Example 1, which reduces the particle size of oxide 1, increases the porosity, and the BET ratio after supporting the catalyst. This leads to an increase in surface area (see Tables 3 to 5). In Examples 15, 16, and 17, the purification characteristics were excellent both before and after the durable heat treatment (see Table 5). However, in Comparative Examples 12 and 13, the purification characteristics are acceptable both before and after the durability heat treatment (see Table 5), and if Fe is reduced too much, the purification characteristics are deteriorated in the first place.

Claims (7)

A mixture of oxide 1 which is a perovskite oxide and oxide 2 which has low reactivity with the perovskite oxide (i),
The surfaces of the plurality of oxide 1 grains are sintered, and secondary particles having an average particle diameter of 5 μm or more are formed of a porous body having a porosity of 20% or more and 60% or less (ii),
The average particle diameter of the oxide 1 is 0.05 μm or more and 0.5 μm or less (iii),
The oxide 2 has an average particle size of 0.1 μm or less and exists at the interface between the oxide 1 and the pores (iv),
The composition of oxide 1 is represented by the following (formula 1) (v),
Oxide 2 is at least one selected from Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , and NiO, including Y ₂ O ₃ , and the total amount of Y, La, Ce, and Ni is an oxide. 1 to 30 mol% with respect to the total number of moles of Sr and A (vi),
A catalyst carrier for exhaust gas purification characterized by the above.
{Sr _(1-a) A _a } _s Fe _(1-btc) B _b Ti _t C _c O _3-δ (Formula 1)
(Here, A, B, C may not arrange elements,
When arranging A, one or more elements selected from Ba, Ca, and La,
When arranging B, one or more elements selected from Co, Cu and Ni,
When C is arranged, one or more elements selected from Nb, Ta and Mn,
1.0 ≦ s ≦ 1.1, 0 ≦ a ≦ 0.5,
0 ≦ b ≦ 0.25, 0.05 ≦ t ≦ 0.3, 0 ≦ c ≦ 0.25, 0.05 ≦ t + c ≦ 0.3,
δ is a value determined by the history of the material) In oxide 1, which is a perovskite oxide defined by (formula 1), when A is arranged, it is selected from one or more elements selected from Ba and Ca,
Oxide 2 is selected from Y ₂ O ₃ , NiO and including Y ₂ O ₃ ,
The exhaust gas purifying catalyst carrier according to claim 1. In oxide 1, which is a perovskite oxide defined by (formula 1), A, B, and C are not arranged,
_3. The exhaust gas purifying catalyst carrier according to claim 1, wherein the oxide 2 is made of Y ₂ O ₃ .   An exhaust gas purification catalyst comprising at least one precious metal selected from Pd, Pt, and Rh supported on the exhaust gas purification catalyst carrier according to any one of claims 1 to 3. A method for producing an exhaust gas purifying catalyst carrier according to any one of claims 1 to 3,
A step of producing a precursor of oxide 1 having an average particle diameter of 0.5 μm or less having a crystal phase of a perovskite structure represented by (Formula 1);
A step of mixing an S liquid containing at least one kind of Y, La, Ce, and Ni ions, which must be selected by including Y, with the precursor of the oxide 1;
Heat-treating the mixture of the S liquid and the oxide 1 precursor in an atmosphere containing oxygen gas at a temperature of 700 ° C. or higher;
Crushing to a secondary particle size of less than 100 μm after the heat treatment;
A method for producing an exhaust gas purifying catalyst carrier, comprising: Producing a precursor of oxide 1 having an average particle size of 0.5 μm or less having a crystal phase of the perovskite structure,
Metal elements (Sr, Fe, Ti are essential in the above (Formula 1), A, B, C (A is one or more selected from Ba, Ca, La, B is Co, Cu, Ni 1 or 2 or more elements selected from C, 1 or 2 or more elements selected from Nb, Ta, and Mn) are optional) from the group consisting of carbonates, hydroxides, and oxides. Mixing the selected powder;
Baking the obtained mixed powder at a temperature of 900 ° C. or higher and 1200 ° C. or lower to synthesize an oxide;
A step of mechanically pulverizing the obtained oxide powder, and
The method for producing a catalyst carrier for exhaust gas purification according to claim 5, comprising: A method for producing the exhaust gas purifying catalyst according to claim 4,
The exhaust gas purifying catalyst carrier according to claim 1 is impregnated with a solution of at least one noble metal selected from Pd, Pt, and Rh, and the noble metal is supported. A method for producing an exhaust gas purifying catalyst.