JP2017177095A - Exhaust gas purification catalyst, method for producing the same and exhaust gas purification apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel exhaust gas purification catalyst that can maintain catalytic activity of noble metal in a highly active state, to provide a method for producing the catalyst and to provide an exhaust gas purification apparatus using the catalyst.SOLUTION: An exhaust gas purification catalyst 10 comprises a first carrier particle 1, a second carrier particle 2 and a noble metal catalyst particle 3 carried each on the first and second carrier particles. In the exhaust gas purification catalyst 10, the first carrier particle 1 contains at least one kind of metal oxide selected from the group consisting of silica, alumina, ceria, zirconia and titania and a rare earth oxide other than ceria; the second carrier particle 2 contains a rare earth oxide other than ceria; the content of metal oxide in the first carrier particle 1 is higher than the content of metal oxide in the second carrier particle 2; the content of rare earth oxide in the second carrier particle 2 is higher than the content of rare earth oxide in the first carrier particle 1; and the correlation function is 85.0% or more as determined by an energy dispersive X-ray analysis using a field emission type scanning electron microscope.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a novel exhaust gas purification catalyst, a production method thereof, and an exhaust gas purification apparatus using the same.

The exhaust gas from an internal combustion engine such as an automobile engine contains nitrogen oxides (NO _x ), carbon monoxide (CO), hydrocarbons (HC) and the like. Therefore, to oxidize CO and HC, and after purification by exhaust gas purifying catalyst for reducing NO _x, which emits these exhaust gases to the atmosphere. A typical exhaust gas purification catalyst is a three-way catalyst in which a noble metal such as platinum (Pt), rhodium (Rh), palladium (Pd) is supported on a porous metal oxide carrier such as γ-alumina. Are known.

The metal oxide support can be made of various materials, but conventionally, alumina (Al ₂ O ₃ ) has been generally used to obtain a high surface area. In recent years, however, various other materials such as ceria (CeO ₂ ), zirconia (ZrO ₂ ), titania (TiO ₂ ), etc. have been combined with alumina in order to promote the purification of exhaust gas by utilizing the chemical properties of the carrier. It has also been proposed to use it in combination or not. It has also been proposed to use ceria zirconia solid solution as such a carrier.

  Regarding ceria zirconia solid solution, it is known that the heat resistance of ceria zirconia solid solution can be improved by adding an element selected from the group consisting of alkali metals, alkaline earth metals and rare earths to ceria zirconia solid solution (for example, Patent Document 1). ). Patent Document 2 discloses that good exhaust gas purification performance can be obtained by loading rhodium on rare earth-doped zirconia support particles.

  Patent Documents 3 and 4 disclose carrier particles in which a rare earth-enriched region is provided on the surface of ceria zirconia solid solution particles. The inventions described in Patent Documents 3 and 4 focus on the affinity between rare earth oxides and rhodium, suppress rhodium migration and sintering on the particle surface and prevent rhodium oxidation in the rare earth-enriched region. As a result, the catalytic activity of rhodium is maintained at a high level.

  By combining the metal oxide support with the rare earth element in this way, sintering of the catalyst noble metal can be prevented.

  By the way, conventionally, the metal oxide support as described above has been formed on a base material that does not itself have an exhaust gas purification ability, for example, a cordierite honeycomb base material. However, in recent years, an exhaust gas purification catalyst device in which a noble metal is supported on a base material composed of a metal oxide support has been proposed (Patent Document 5).

JP 2004-275919 A JP-T-2002-518171 JP 2008-018323 A JP 2008-104928 A Japanese Patent Laying-Open No. 2015-85241

  An object of the present invention is to provide a novel exhaust gas purifying catalyst, a method for producing the same, and an exhaust gas purifying apparatus using the same, which can maintain the catalytic activity of a noble metal at a higher level than conventional exhaust gas purifying catalysts. To do.

Embodiments of the present invention can include the following aspects:
<< Aspect 1 >>
An exhaust gas purifying catalyst having first carrier particles, second carrier particles, and noble metal catalyst particles carried on the first and second carrier particles,
The first carrier particles contain at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania, and a rare earth oxide other than ceria,
The second support particles may contain a rare earth oxide other than ceria, and may contain at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania. The content rate of the metal oxide in the first support particles is higher than the content rate of the metal oxide in the second support particles,
The content rate of the rare earth oxide in the second carrier particles is higher than the content rate of the rare earth oxide in the first carrier particles, and energy dispersive X-ray using a field emission scanning electron microscope When the intensity of characteristic X-rays obtained by analysis is measured, the correlation coefficient calculated by the following formula is 85.0% or more:
(Here, the spectrum intensity value of the noble metal element contained in the noble metal catalyst particle i is x _i , the spectrum intensity average value of the noble metal element is x _av, and the spectrum of rare earth elements other than cerium at the position of the noble metal catalyst particle i The intensity value is y _i and the spectral intensity average value of rare earth elements other than cerium is y _av ).
<< Aspect 2 >>
The content of the rare earth oxide in the first carrier particles is less than 20% by weight, and the content of the rare earth oxide in the second carrier particles is 20% by weight or more. Exhaust gas purification catalyst.
<< Aspect 3 >>
When the first carrier particles and the second carrier particles are observed with a field emission scanning electron microscope, the ratio of the projected area of the second carrier particles to the projected area of the first carrier particles The exhaust gas purifying catalyst according to aspect 2, wherein (the area of the second carrier particles / the area of the first carrier particles) is in the range of 0.050 or more and 0.200 or less.
<< Aspect 4 >>
The metal oxide of the first support particles and the metal oxide of the second support particles, if present, are ceria zirconia solid solutions, and the rare earth oxide and the first support particles of the first support particles. The rare earth oxide of the two support particles is an oxide of a rare earth element selected from at least one selected from the group consisting of yttrium, lanthanum, praseodymium, neodymium and samarium. Exhaust gas purification catalyst.
<< Aspect 5 >>
The first carrier particles contain 50 to 95% by weight of zirconia, 5.0 to 45% by weight of ceria, and 1.0 or more and less than 20% by weight of a rare earth oxide other than ceria, and the second The exhaust gas according to aspect 4, wherein the carrier particles contain 0.0 to 40% by weight of zirconia, 0.0 to 40% by weight of ceria, and 20 to 60% by weight of rare earth oxides other than ceria. Purification catalyst.
<< Aspect 6 >>
The average particle diameters of the first carrier particles and the second carrier particles measured by a field emission scanning electron microscope are 0.50 to 100 μm and 0.50 to 5 μm, respectively. The exhaust gas purifying catalyst according to any one of the above.
<< Aspect 7 >>
The exhaust gas purifying catalyst according to any one of aspects 1 to 6, wherein the noble metal catalyst particles include platinum particles, palladium particles, rhodium particles, or a combination thereof.
<< Aspect 8 >>
The exhaust gas purifying catalyst according to any one of aspects 1 to 7, wherein the correlation coefficient is 87.0% or more.
<< Aspect 9 >>
An exhaust gas purifying apparatus comprising the base material on which the exhaust gas purifying catalyst according to any one of aspects 1 to 8 and a catalyst layer including the catalyst are formed.
<< Aspect 10 >>
An exhaust gas purification apparatus comprising the exhaust gas purification catalyst according to any one of aspects 1 to 8 and a base material including the catalyst.
<< Aspect 11 >>
A method for producing an exhaust gas purifying catalyst comprising:
Carrier particles containing at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania and a rare earth oxide other than ceria; from yttrium, neodymium, lanthanum, and praseodymium A salt of a rare earth element selected from one or more kinds; a salt of a catalyst noble metal; and an organic carboxylic acid are mixed in an aqueous dispersion to carry the catalyst noble metal on the carrier particles, thereby forming an unfired exhaust gas purification catalyst. Obtaining an aqueous dispersion comprising:
A step of drying and calcining the aqueous dispersion containing the unfired exhaust gas-purifying catalyst;
<< Aspect 12 >>
The metal oxide of the support particles is a ceria zirconia solid solution; the rare earth oxide of the support particles is selected from at least one selected from the group consisting of yttrium, lanthanum, praseodymium, neodymium, and samarium. The method according to embodiment 10, wherein the rare earth element salt is nitrate or sulfate; and the catalyst noble metal salt is a nitrate or sulfate of platinum, palladium, rhodium, or a combination thereof.
<< Aspect 13 >>
The method according to embodiment 11 or 12, wherein the organic carboxylic acid is an organic carboxylic acid having a molecular weight of 300 or less.
<< Aspect 14 >>
Any of the aspects 11 to 13 wherein the substance amount ratio [mol / mol-Ln] of the organic carboxylic acid to the total amount of rare earth elements contained in the carrier particles is 0.5 or more and 3.5 or less. The method according to claim 1.

  According to the present invention, it is possible to provide a novel exhaust gas purifying catalyst, a method for producing the same, and an exhaust gas purifying apparatus using the same, which can maintain the catalytic activity of the noble metal higher than that of the conventional exhaust gas purifying catalyst. it can.

FIG. 1 (a) is a conceptual diagram of a conventional exhaust gas purifying catalyst, and FIG. 1 (b) is a conceptual diagram of an exhaust gas purifying catalyst of the present invention. FIG. 2 is an element mapping by energy dispersive X-ray analysis using a field emission scanning electron microscope performed on the exhaust gas purifying catalysts of Reference Example 3 and Comparative Reference Example 3. FIG. 3 is an observation image at a magnification of 5000 times that of a field emission scanning electron microscope performed on the exhaust gas purifying catalyst of Reference Example 5.

<Exhaust gas purification catalyst>
The exhaust gas purifying catalyst of the present invention includes first carrier particles, second carrier particles, and noble metal catalyst particles supported on the first and second carrier particles. The first carrier particles contain at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania, and a rare earth oxide other than ceria, and the second carrier particles are And a rare earth oxide other than ceria, and at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania. The metal oxide content of the first carrier particles is higher than the metal oxide content of the second carrier particles, and the rare earth oxide content of the second carrier particles is the first carrier particles It is higher than the content of the rare earth oxide in the carrier particles.

  In the prior art, by providing a rare earth-enriched region on the surface of the metal oxide support, the movement and sintering of the noble metal catalyst particles are suppressed in the rare earth enriched region, and the oxidation of the noble metal catalyst particles is prevented. Is maintained at a high level. On the other hand, in the present invention, it was possible to give the noble metal catalyst particles even higher activity by using a second support having a high rare earth oxide content together with a normal metal oxide support. Although not bound by theory, in the present invention, the noble metal catalyst particles can be further enhanced in catalytic activity by being intensively supported on the second support having a high rare earth oxide content. It is believed that there is.

In the present invention, noble metal catalyst particles are intensively supported on a second support having a high content of rare earth oxide. In the present invention, it is obtained by energy dispersive X-ray analysis using a field emission scanning electron microscope. When the characteristic X-ray intensity measurement is performed, the correlation coefficient is 85.0% or more, 86.0% or more, 87.0% or more, 88.0% or more, 89.0% or more, or 90.0 It is preferable that the values agree with each other. The correlation coefficient may be less than 99%. Here, the correlation coefficient is calculated as follows:
(Here, the spectrum intensity value of the noble metal element contained in the noble metal catalyst particle i is x _i , the spectrum intensity average value of the noble metal element is x _av, and the spectrum of rare earth elements other than cerium at the position of the noble metal catalyst particle i The intensity value is y _i and the spectral intensity average value of rare earth elements other than cerium is y _av ).

  Such a measurement can be performed using a field emission scanning electron microscope S-4800 manufactured by Hitachi High-Technologies Corporation and an energy dispersive X-ray analyzer attached to the apparatus. Specifically, the center-of-gravity point analysis of the noble metal catalyst particle i is carried out in a plurality of images magnified 5000 times measured by this field emission scanning electron microscope, and the noble metal element of the noble metal catalyst particle i at the position of the center of gravity point And the above-mentioned calculation is performed by measuring the spectral intensity value of the rare earth element other than cerium at the position of the center of gravity. Here, when there are a plurality of rare earth elements other than the noble metal element and cerium, their strengths are added. The “spectrum intensity average value” means the average of all characteristic X-ray intensities of the noble metal elements contained in the noble metal catalyst particles visible in the same visual field and different visual fields or the rare earth elements other than cerium contained in the second support. Value. When performing the above calculation, it is preferable to use 300 or more of the second carrier and noble metal catalyst particles.

  In the present specification, “catalyst” means carrier particles carrying noble metal catalyst particles unless otherwise specified, and these may be calcined or left unfired. Also good. The correlation coefficient is usually not substantially changed before and after the calcination of the catalyst, and preferably does not change.

  FIG. 1 (a) is a conceptual diagram of a conventional exhaust gas purifying catalyst, and FIG. 1 (b) is a conceptual diagram of an exhaust gas purifying catalyst of the present invention. In FIG. 1 (a), the exhaust gas purification catalyst (10) has metal oxide support particles (1) and noble metal catalyst particles (3). The metal oxide particles (1) include a rare earth enriched region (1a). ) Exists. In FIG. 1 (b), the exhaust gas purifying catalyst (10) includes a first support particle (1) of metal oxide, a second support particle (2) having a high content of rare earth oxide, and a noble metal catalyst particle (3). Most of the noble metal catalyst particles (3) are supported on the second carrier particles (2).

(Carrier particles)
In the exhaust gas purifying catalyst of the present invention, at least first carrier particles and second carrier particles are used as the carrier for the noble metal catalyst particles. Third carrier particles other than the first carrier particles and the second carrier particles can also be used.

  For example, the first carrier particle is defined as a particle having a rare earth oxide content other than ceria of less than 20% by weight, and the second carrier particle has a rare earth oxide content other than ceria of 20% by weight. % And the second carrier particles contained in the exhaust gas purifying catalyst of the present invention when the first carrier particles and the second carrier particles are observed by a field emission scanning electron microscope. The ratio of the projected area to the projected area of the first carrier particles (the area of the second carrier particles / the area of the first carrier particles) is 0.005 or more, 0.01 or more, 0.03 or more, 0 .05 or more, or 0.06 or more, or 0.30 or less, 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, or 0.08 or less. . Within such a range, the noble metal catalyst particles can be intensively supported on the second carrier particles, and sintering of the noble metal catalyst particles can be substantially prevented and the NOx purification temperature tends to be prevented from rising. is there. Even when the definitions of the first carrier particles and the second carrier particles are changed, the projected area ratio can be in the same range.

(Carrier particles—first carrier particles)
The first carrier particles used in the exhaust gas purifying catalyst of the present invention include at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania, and a rare earth oxide other than ceria. Containing. Preferably, the first carrier particle contains at least ceria and / or zirconia.

  For example, the first carrier particle is defined as a particle having a rare earth oxide content other than ceria of less than 20% by weight, and the second carrier particle has a rare earth oxide content other than ceria of 20% by weight. %, The average particle size of the first carrier particles is 0.50 μm or more, 1.0 μm or more, 3.0 μm or more, 5.0 μm or more, 8.0 μm or more, or 10.0 μm. It may be 100 μm or less, 80 μm or less, 50 μm or less, 30 μm or less, or 20 μm or less. Even when the definitions of the first carrier particles and the second carrier particles are changed, the average particle diameter of the first carrier particles can be in the same range.

  Here, the average particle diameter is measured by a field emission scanning electron microscope S-4800 manufactured by Hitachi High-Technologies Corporation and an energy dispersive X-ray analyzer attached to the apparatus. That is, the first carrier particles are found by energy dispersive X-ray analysis from particles having an equivalent diameter of 0.10 μm or more on a screen projected with a measurement magnification of 20,000 times with this apparatus. Then, the equivalent diameter of the particles is calculated from the projected area of the particles. This operation is performed on 20 arbitrary screens, and all average values thereof are recognized as the average particle diameter of the first carrier particles. Here, the equivalent diameter of the particles refers to the diameter of a perfect circle having an outer peripheral length equal to the outer peripheral length of the particles.

  The first carrier particles contain at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania, and the content thereof is based on the weight of the first carrier particles. 50 wt% or more, 55 wt% or more, 60 wt% or more, 65 wt% or more, or 70 wt% or more, 95 wt% or less, 90 wt% or less, 85 wt% or less, or 80 wt% % Or less.

  When the first carrier particles contain ceria as a metal oxide, the total content of ceria and rare earth oxides other than ceria in the first carrier particles is 5.0 with respect to the weight of the first carrier particles. % By weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more, 50% by weight or less, 45% by weight or less, 40% by weight or less, or 35% by weight or less It may be.

  When the first carrier particles include ceria as a metal oxide, the content of ceria may be 5.0% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more. It may be not more than wt%, not more than 40 wt%, not more than 35 wt%, or not more than 30 wt%. Furthermore, the content of rare earth oxides other than ceria may be 1.0% by weight or more, 3.0% by weight or more, 5.0% by weight or more, or 7.0% by weight or more, and 30% by weight. Hereinafter, it may be 25% by weight or less, 20% by weight or less, less than 20% by weight, 15% by weight or less, or 10% by weight or less.

  The first carrier particles are preferably in the form of a solid solution of the above metal oxide, and preferably contain, for example, a ceria zirconia solid solution as the above metal oxide. In this case, the content of zirconia in the first carrier particles is 40% by weight or more, 45% by weight or more, 50% by weight or more, 55% by weight or more, 60% by weight or more, 65% by weight or more, or 70% by weight or more. It may be 95% by weight or less, 90% by weight or less, 85% by weight or less, or 80% by weight or less. In this case, the content of ceria in the first carrier particles may be 5.0% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more, It may be 50% or less, 45% or less, 40% or less, or 35% or less. Here, these content rates can be obtained by calculation from elemental analysis.

  As the rare earth oxide of the first carrier particle, an element that has a young atomic number among rare earth elements and has ions in the 4f electron orbit or that has many vacancies, such as yttrium (Y), lanthanum (La), etc. And oxides of rare earth elements selected from the group consisting of praseodymium (Pr), neodymium (Nd) and samarium (Sm).

  The first carrier particles may contain components other than those described above, and may contain, for example, barium oxide.

  The first carrier particles can be produced by a known method described in the above patent documents.

(Carrier particles—second carrier particles)
The second carrier particle used in the exhaust gas purifying catalyst of the present invention contains a rare earth oxide other than ceria and at least one metal selected from the group consisting of silica, alumina, ceria, zirconia, and titania. An oxide may be contained. Here, the content rate of the metal oxide in the second support particles is lower than the content rate of the metal oxide in the first support particles, and the content rate of the rare earth oxide in the second support particles is: It is higher than the rare earth oxide content of the first carrier particles. Thereby, the noble metal catalyst particles can be intensively supported on the second carrier particles.

  For example, the first carrier particle is defined as a particle having a rare earth oxide content other than ceria of less than 20% by weight, and the second carrier particle has a rare earth oxide content other than ceria of 20% by weight. %, The average particle size of the second carrier particles may be 0.50 μm or more, 1.0 μm or more, 2.0 μm or more, or 3.0 μm or more, 50 μm or less, It may be 20 μm or less, 15 μm or less, 10 μm or less, or 5.0 μm or less. Within such a range, the noble metal catalyst particles can be intensively supported on the second carrier particles, and sintering of the noble metal catalyst particles can be substantially prevented, and an increase in the NOx purification temperature tends to be prevented. is there. Even when the definitions of the first carrier particles and the second carrier particles are changed, the average particle diameter of the second carrier particles can be in the same range. This average particle diameter is measured by the same method as the average particle diameter of the first carrier particles.

  The second carrier particles contain a rare earth oxide other than ceria, and the content thereof is 10% by weight, 15% by weight, 20% by weight, 25% by weight, or 30% by weight or more. It may be 60% by weight or less, 55% by weight or less, 50% by weight or less, 45% by weight or less, or 40% by weight or less.

  The second carrier particles may or may not contain at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania. When the metal oxide is contained, the content thereof is 1.0% by weight or more, 2.0% by weight or more, 3.0% by weight or more, 5.0% by weight with respect to the weight of the second carrier particles. As described above, it may be 10% by weight or more, or 15% by weight or more, and may be 40% by weight or less, 35% by weight or less, 30% by weight or less, or 25% by weight or less.

  When the second carrier particles contain ceria and a rare earth oxide other than ceria, the total content is 60% by weight or more, 65% by weight or more, 70% by weight with respect to the weight of the second carrier particles. % Or more, 75% or more, or 80% or more, or 99% or less, 95% or less, 93% or less, or 90% or less.

  When the second carrier particles contain ceria, the content thereof may be 20% by weight or more, 25% by weight or more, or 30% by weight or more, and may be 60% by weight or less, 55% by weight or less, 50% by weight. % Or less, 45% by weight or less, or 40% by weight or less.

  As the rare earth oxide of the second carrier particles, the same kind of rare earth oxide contained in the first carrier particles can be used.

  Similar to the first carrier particles, the second carrier particles may contain a third component other than zirconia and rare earth oxide, and may contain, for example, alumina, silica, titania and the like.

  The second carrier particles can be produced by a known method described in the above patent documents. However, the second carrier particles are preferably obtained by introducing the carrier particles into an organic carboxylic acid solution and eluting from the carrier particles, as will be described in detail below.

(Precious metal catalyst particles)
Examples of the noble metal catalyst particles used in the exhaust gas purifying catalyst of the present invention include white metal particles, and more preferably platinum particles, palladium particles, rhodium particles, or a combination thereof.

  The noble metal catalyst particles are preferably fine particles having a sufficiently small particle diameter from the viewpoint of increasing the contact area with the exhaust gas. Typically, the average particle diameter of the catalyst particles may be about 1 to 20 nm as an average value of equivalent diameters obtained by TEM observation, or may be 10 nm or less, 7 nm or less, or 5 nm or less.

  The precious metal catalyst particles are 0.1 parts by mass or more, 0.3 parts by mass or more, 0.5 parts by mass or more, or 1 in total with respect to 100 parts by mass in total of the first carrier particles and the second carrier particles. It may be supported at 0.0 parts by mass or more, and may be supported at 10 parts by mass or less, 5 parts by mass or less, 3.0 parts by mass or less, or 2.0 parts by mass or less.

<Exhaust gas purification device>
The exhaust gas purification apparatus of the present invention includes the above-described exhaust gas purification catalyst and a base material including the catalyst. The exhaust gas-purifying catalyst may be contained in the catalyst layer on the base material, or may be contained in the base material. The exhaust gas purifying catalyst may be an exhaust gas purifying catalyst obtained by the following method for producing an exhaust gas purifying catalyst of the present invention.

  Examples of the substrate include a straight flow type or wall flow type honeycomb type substrate generally used in an exhaust gas purification apparatus. The material of the base material is not particularly limited, and examples thereof include base materials such as ceramic, silicon carbide, and metal. The capacity of the substrate can be set to about 1 L, for example.

  The catalyst layer in the exhaust gas purification apparatus of the present invention may be formed only from the above-described exhaust gas purification catalyst of the present invention, or may be formed of a mixture of the exhaust gas purification catalyst of the present invention and other components. . Examples of other components used here include alumina, CZ, zeolite, and the like, and mixtures thereof. A known exhaust gas-purifying catalyst having a noble metal supported thereon may be used as another component. The catalyst layer may be formed on a base material including catalyst carrier particles on the wall surface, for example, a base material described in JP-A-2015-85241.

  Production of the other components, mixing of the other components with the exhaust gas purifying catalyst of the present invention, and formation of the catalyst layer on the substrate are each performed by a known method or appropriate by those skilled in the art. It can be carried out by a modified method.

  When the exhaust gas-purifying catalyst is contained in the base material, a base material containing catalyst carrier particles on the wall surface, for example, a base material as described in JP-A-2015-85241 can be used. In this case, the exhaust gas purifying apparatus may be obtained by mixing the exhaust gas purifying catalyst with other inorganic particles used when manufacturing the base material.

  The exhaust gas purification apparatus of the present invention manufactured as described above has high exhaust gas purification activity of noble metals and can maintain it in a high state, and thus is suitable as an exhaust gas purification catalyst for automobiles, for example. Can be used.

<Method for producing exhaust gas purification catalyst>
The method of the present invention for producing an exhaust gas purifying catalyst contains at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania and a rare earth oxide other than ceria. A carrier particle; a rare earth element salt selected from one or more of yttrium, neodymium, lanthanum, and praseodymium; a salt of a noble metal; and an organic carboxylic acid mixed in an aqueous dispersion to carry the noble metal on the carrier particle; To obtain an aqueous dispersion containing an unfired exhaust gas purification catalyst; and drying and firing the aqueous dispersion containing an unfired exhaust gas purification catalyst.

  According to this method, the rare earth oxide is eluted from the carrier particles by the organic carboxylic acid to obtain the second carrier particles enriched with the rare earth oxide and the first carrier particles enriched with the metal oxide. . In this case, the noble metal is mainly supported on the second support particles enriched with the rare earth oxide, and thereby, sintering and oxidation of the noble metal as a catalyst can be prevented, so that the catalytic activity of the noble metal is high. A suitable exhaust gas purifying catalyst that can be maintained at a high temperature can be obtained. In the case where the carrier particles as the starting material contain a solid solution of a metal oxide, such an embodiment is particularly preferable because the rare earth oxide that is not in solid solution is easily eluted by the organic carboxylic acid.

  Furthermore, it has been surprisingly found that the noble metal catalyst particles of the exhaust gas purification catalyst obtained by this method have a smaller diameter compared to the conventional method in which no organic carboxylic acid is added. Without being bound by theory, this is because the organic carboxylic acid rare earth is formed after the addition of the organic carboxylic acid, the noble metal is selectively adsorbed on the organic carboxylic acid rare earth, and the interaction between the rare earth and the noble metal after firing, This is thought to be due to the immobilization of precious metals. If the particle diameter of the noble metal catalyst particles is small, the surface area of the noble metal catalyst particles per unit weight is increased, which is very advantageous because the reaction point of the catalyst increases.

  According to the method of the present invention for producing an exhaust gas purification catalyst, the exhaust gas purification catalyst of the present invention can be produced in particular. Accordingly, the particle size of the carrier particles used in the method of the present invention, the addition amount of the rare earth oxide other than zirconia, ceria and ceria, the kind and addition amount of the rare earth oxide other than ceria, the kind of the salt of the rare earth element The addition amount, the type and addition amount of the noble metal, etc. can be selected with reference to the description of the exhaust gas purifying catalyst of the present invention.

  For example, in the step of obtaining an aqueous dispersion containing an unfired exhaust gas-purifying catalyst, the amount of reaction (reaction equivalent point) that reacts without excess or deficiency with respect to the amount of the rare-earth component not dissolved in the carrier particles. An organic carboxylic acid is dissolved in an aqueous solution. Then, a salt of a noble metal is mixed with an aqueous solution of an organic carboxylic acid, and an aqueous solution containing the organic carboxylic acid and the noble metal is mixed with a dispersion in which carrier particles are dispersed.

  The amount of the organic carboxylic acid used in the method of the present invention is the ratio of the amount of the organic carboxylic acid to be added [mol / mol-Ln to the total amount of the rare earth elements contained in the carrier particles [mol-Ln]. ]. A preferable substance amount ratio [mol / mol-Ln] is 0.5 or more, 1.0 or more, or 1.5 or more, and may be 3.5 or less, 3.0 or less, or 2.5 or less. Good. Within such a range, the metal oxide of the carrier particles is difficult to dissolve and the rare earth oxide is easily dissolved, so that the second carrier particles are easily generated.

  Further, in addition to the second carrier particles eluted by the carboxylic acid by mixing one or more salts of rare earth elements selected from yttrium, neodymium, lanthanum and praseodymium into the aqueous dispersion, Additional carrier particles can be produced. As the salt of the rare earth element, an inorganic acid salt and an organic acid salt can be mentioned, but there is no particular limitation as long as the second carrier particles can be additionally generated. Examples of inorganic acid salts include sulfate, hydrochloride, nitrate, carbonate, phosphate, sulfite, and chlorate. Examples of organic acid salts include carboxylic acids such as formic acid, oxalic acid, and acetic acid. A salt etc. can be mentioned. Of these, nitrates, acetates and the like were found to be particularly preferable. This is presumably because the salt was adsorbed on the surface of the carrier particles to improve the dispersibility of the carrier particles. For this reason, the salt of rare earth element is preferably added to the aqueous dispersion before adding the organic carboxylic acid.

The amount of the rare earth element salt used in the method of the present invention is 0.1 μmol or more, 0.3 μmol or more, 0.5 μmol or more, 1.0 μmol or more, or 2.0 μmol or more per 1 m ² of the surface area of the carrier particles. It may be 50 μmol or less, 30 μmol or less, 20 μmol or less, 10 μmol or less, 8 μmol or less, or 5 μmol or less. The amount of rare earth element salt per gram of carrier particles may be 6.65 μmol or more, 19.95 μmol or more, 33.25 μmol or more, 66.5 μmol or more, 133 μmol or more, 665 μmol or less, 532 μmol or less, 332 It may be 5 mol or less, or 332.5 μmol or less.

  Here, the carrier particles may have the same composition as the first carrier particles used in the exhaust gas purifying catalyst of the present invention.

  Examples of the noble metal salt include strong noble metal acid salts, and particularly noble metal nitrates and sulfates. Examples of noble metals include platinum, palladium, and / or rhodium.

Examples of the organic carboxylic acid include organic carboxylic acids having a molecular weight of 300 or less. For example, C _{1 to} C ₂₀ saturated fatty acid, unsaturated fatty acid, hydroxy acid, aromatic carboxylic acid, dicarboxylic acid, tricarboxylic acid, oxo A carboxylic acid etc. can be mentioned. Specific examples include formic acid, acetic acid, propionic acid, butyric acid, tartaric acid, oxalic acid, malonic acid, and succinic acid.

  The addition amount of the organic carboxylic acid is 0.50 times or more of the molar amount (reaction equivalent point) that reacts without excess or deficiency with respect to the molar amount of the rare earth component contained in the carrier particles, preferably the rare earth component that is not solid solution, It may be 1.0 times or more, or 2.0 times or more, and may be 5.0 times or less, 4.5 times or less, 4.0 times or less, or 3.5 times or less.

  After obtaining an unfired exhaust gas-purifying catalyst, the aqueous dispersion containing the catalyst is dried and fired. The drying temperature may be, for example, 150 ° C. or higher, 200 ° C. or higher, 250 ° C. or higher, 350 ° C. or lower, or 300 ° C. or lower. The drying time may be 16 hours or more, 12 hours or more, or 8 hours or more, and may be 24 hours or less or 20 hours or less. The firing temperature may be, for example, 400 ° C. or higher, 500 ° C. or higher, 550 ° C. or higher, or 600 ° C. or higher, or 1000 ° C. or lower, 800 ° C. or lower, or 700 ° C. or lower. The firing time may be 30 minutes or more, 1 hour or more, 2 hours or more, or 4 hours or more, or 12 hours or less, 10 hours or less, or 8 hours or less.

  In addition, the catalyst manufactured by the manufacturing method that does not depend on the manufacturing method of the exhaust gas purifying catalyst of the present invention described above has a correlation coefficient of 60.0% or more, 65.0% or more, or 70.0% or more. And typically less than 85% or less than 80%.

  The exhaust gas-purifying catalyst thus obtained can be further pulverized so that the particle size of the carrier particles is within the range of the particle size of the first carrier particles of the exhaust gas-purifying catalyst of the present invention.

A. Reference test of various exhaust gas purification catalysts << Sample preparation >>
<Reference Example 1>
A total amount of rare earths other than cerium contained in the carrier particles was dissolved in ion exchange water with an amount of a substance that reacted without excess or deficiency to prepare an aqueous acetic acid solution. Next, the rhodium nitrate solution was added to the acetic acid solution so that the amount of rhodium was 0.50% by weight of the carrier particles to obtain an aqueous solution containing acetic acid and rhodium nitrate. This aqueous solution was mixed with a dispersion in which carrier particles were dispersed in ion exchange water. This was stirred, dried at 250 ° C. for 8 hours, calcined at 500 ° C. for 1 hour, and pulverized to obtain an exhaust gas purifying catalyst of Reference Example 1.

<Reference Examples 2 to 4 and Comparative Reference Examples 1 to 3>
Exhaust gas purifying catalysts of Reference Examples 2 to 4 were obtained in the same manner as Reference Example 1 except that other organic carboxylic acids were used instead of acetic acid. Further, exhaust gas purification catalysts of Comparative Reference Examples 1 and 2 were obtained in the same manner as Reference Example 1 except that another acid was used instead of the organic carboxylic acid. Further, an exhaust gas purifying catalyst of Comparative Reference Example 3 was obtained in the same manner as Reference Example 1 except that acetic acid was not used. Details of the composition of these examples are shown in Table 1.

<Reference Examples 5-6 and Comparative Reference Examples 4-5>
The types of the carrier particles and the noble metal salt were changed from Reference Example 2 to obtain exhaust gas purifying catalysts of Reference Examples 5-6. Exhaust gas purifying catalysts of Comparative Reference Examples 4 and 5 were obtained in the same manner as Reference Examples 5 and 6, respectively, except that no organic carboxylic acid was used. Details of the composition of these examples are shown in Table 2.

<Reference Examples 7 to 15>
The catalyst for exhaust gas purification of Reference Examples 7 to 15 was obtained by changing the composition of the carrier particles from Reference Example 4 and changing the addition amount of the organic carboxylic acid. Details of the composition of these examples are shown in Table 3.

<Reference Examples 16 to 19 and Comparative Reference Examples 6 to 9>
The types of carrier particles used in Reference Example 1 were changed to obtain exhaust gas purifying catalysts of Reference Examples 16 to 19 and Comparative Reference Examples 6 to 9. Details of the composition of these examples are shown in Table 4.

<Exhaust gas purification catalyst after endurance test>
The exhaust gas-purifying catalyst obtained as described above was placed in a flow-type durability test apparatus. Then, the internal temperature of the test apparatus is set to 1000 ° C., and a lean gas in which 1% of oxygen is added to nitrogen gas and a rich gas in which 2% of carbon monoxide is added to nitrogen gas are alternately cycled at a flow rate of 500 mL / min every 2 minutes. For 10 hours. The subsequent exhaust gas purification catalyst was evaluated as an exhaust gas purification catalyst after the durability test.

<Production of exhaust gas purification device>
The exhaust gas purification catalyst and alumina powder obtained as described above were mixed at a mass mixing ratio of 1: 1 and dispersed in pure water so that the solid content was 30% by weight to obtain a slurry. The slurry was coated on a monolith honeycomb substrate (volume 0.35 L) so that the amount of noble metal was 0.25 g / L. The coated monolith honeycomb substrate was dried at 250 ° C. for 10 minutes and then fired at 500 ° C. for 20 minutes to obtain an exhaust gas purification device.

<Exhaust gas purifier after durability test>
The exhaust gas purification device obtained as described above was placed in a flow-type durability test device. Then, the internal temperature of the test apparatus is set to 1000 ° C., and a lean gas in which 1% of oxygen is added to nitrogen gas and a rich gas in which 2% of carbon monoxide is added to nitrogen gas are alternately cycled at a flow rate of 500 mL / min every 2 minutes. For 10 hours. The subsequent exhaust gas purification apparatus was evaluated as an exhaust gas purification apparatus after the durability test.

"Evaluation method"
<Average particle diameter and abundance ratio of second carrier>
The average particle size of the carrier particles of the exhaust gas purifying catalyst was measured by a field emission scanning electron microscope S-4800 manufactured by Hitachi High-Technologies Corporation and an energy dispersive X-ray analyzer attached to the apparatus.

  Specifically, first, 50% by weight of zirconia is analyzed by energy dispersive X-ray analysis from particles having an equivalent diameter of 0.10 μm or more on a screen projected at a measurement magnification of 20,000 times with this apparatus. Particles containing ˜95% by weight and 5.0 to 50% by weight of ceria and a rare earth oxide other than ceria were found and identified as first carrier particles. And the equivalent diameter of those particles was calculated from the projected area of the particles. This operation was performed on 20 arbitrary screens, and the average value of all of them was defined as the average particle diameter of the first carrier particles.

  Further, from particles having an equivalent diameter of 0.10 μm or more, particles containing 1.0 to 40% by weight of zirconia and 60% to 99% by weight of rare earth oxides other than ceria and ceria are found. This was identified as the second carrier particle. And the equivalent diameter of those particles was calculated from the projected area of the particles. This operation was performed on 20 arbitrary screens, and the average value of all of them was defined as the average particle diameter of the second carrier particles.

  Further, for each exhaust gas purifying catalyst, the ratio of the projected area of the second carrier particles to the projected area of the first and second carrier particles (the area of the second carrier particles / the first and second carriers). The area of the particles) was calculated and used as the abundance ratio of the second carrier particles.

<Correlation position correlation coefficient>
Energy dispersive X-ray analysis was performed at the position of the center of gravity of the noble metal particles using a scanning electron microscope S-4800 manufactured by Hitachi High-Technologies, and the characteristic X-ray intensities of the rare earth elements and the noble metal were measured. When the characteristic X-ray intensity of the rare earth element of the carrier particles is compared with the characteristic X-ray intensity of the noble metal element, and the correlation coefficient is equal to or greater than 0.65, it is supported on the second carrier. When the correlation coefficient was less than 0.65, it was defined as not supported on the carrier.

<Changes in catalyst particle size>
The exhaust gas-purifying catalyst after the durability test was analyzed by an X-ray diffractometer to analyze the particle diameter of the noble metal catalyst particles. The particle size was calculated from Scherrer's equation using the half-width of the diffraction peak of rhodium 2θ = 41.1 °; palladium 2θ = 40.1 °; and platinum 2θ = 39.8 °. From these results, for Reference Examples 1 to 4 and 7 to 19 and Comparative Reference Examples 1 to 2 and 6 to 9, noble metals were added by adding an organic carboxylic acid based on Comparative Reference Example 3 to which no organic carboxylic acid was added. The percentage of particle size change was calculated. For Reference Examples 5 and 6, the percentage of change in the noble metal particle size was calculated based on Comparative Reference Examples 4 and 5, respectively. However, in Table 1, “−” means that the particle size is refined, and “+” means that the particle size is enlarged.

<50% NO _x purification temperature>
The exhaust gas purification device after the endurance test is placed in an atmospheric pressure fixed bed type flow reaction device, and silenced at a rate of 12 ° C./min from 100 ° C. to 500 ° C. while flowing a model gas equivalent to stoichiometric, NO _x during that time The purification rate was measured continuously. The temperature at which the exhaust gas was purified by 50% was examined for each sample.

<SEM-EDX image>
Regarding Reference Example 3 and Comparative Reference Example 3, elemental mapping by energy dispersive X-ray analysis using a scanning electron microscope was taken.

"result"
The results of evaluation as described above are shown in Tables 1 to 4. In addition, SEM-EDX images of Reference Example 3 and Comparative Reference Example 3 are shown in FIG. Further, FIG. 3 shows an observation image of the field emission scanning electron microscope, which was performed on the exhaust gas purifying catalyst of Reference Example 5, at a magnification of 5000 times.

  As can be understood from Table 1, when an organic carboxylic acid was used (Reference Examples 1 to 4), a second carrier having an appropriate average particle diameter was easily obtained. In Comparative Reference Examples 1 and 2, it can be seen that the second carrier particles themselves are formed, but the particle size is very small. In this case, the catalyst particles are the second particles so that the correlation coefficient can be judged. The carrier particles were not substantially supported. This is probably because the noble metal catalyst particles were supported on the first carrier particles because the second carrier particles were too small, and the noble metal catalyst particles were sintered there.

Moreover, when organic carboxylic acid is used (Reference Examples 1-4), it turns out that the diameter of the noble metal catalyst particles was reduced after durability. When benzenesulfonic acid and nitric acid were used in place of the organic carboxylic acid (Comparative Reference Examples 1 and 2), the noble metal catalyst particles were enlarged compared to the case where no acid was used (Comparative Reference Example 3). Furthermore, in the case of Reference Examples 1 to 4, the 50% NO _x purification temperature was very low.

  As can be understood from Tables 2 and 4, such a tendency was the same even when the composition of the starting support particles and the type of the noble metal were changed.

From Table 3, it can be seen that as the amount of organic carboxylic acid added increases, the particle size of the second carrier increases. However, it can be seen that noble metal catalyst particles are not reduced in diameter as the amount of organic carboxylic acid is increased. Correspondingly, the 50% NO _x purification temperature also changed.

  When the element mapping of the exhaust gas purification catalyst of Comparative Reference Example 3 in FIG. 2 is seen, it can be seen that the distribution of the abundance of each element is uniform. On the other hand, when the elemental mapping of Reference Example 3 is seen, the abundance of cerium (Ce) and neodymium (Nd) is very high at a place where the abundance of zirconium (Zr) is low, It can be seen that the location is the second carrier particle. In addition, the abundance of rhodium (Rh) is high at the position of the second support particles, and it can be seen that the noble metal catalyst particles are concentratedly supported on the second support particles.

B. Test of exhaust gas purifying catalyst of the present invention << Sample preparation >>
<Comparative example 1>
1. Preparation of catalyst A noble metal solution was prepared by dissolving rhodium nitrate in water such that the amount of Rh metal equivalent was 0.5% by mass with respect to the support particles. Carrier particles in which the composition in terms of oxide is a mass ratio of Zr: Ce: La: Nd = 70: 20: 5: 5 (particle size 10 μm, surface area 70 m ² / g) are dispersed in ion-exchanged water, and carrier particles A dispersion was prepared. The noble metal solution was added to the carrier particle dispersion and stirred. The solid was recovered, dried by heating at 110 ° C. for 8 hours, and further calcined at 500 ° C. for 1 hour, and then pulverized and classified to obtain the catalyst of Comparative Example 1.

<Example 1>
An aqueous acid solution was prepared by dissolving 2.5 times (times-eq) propionic acid in ion-exchanged water with respect to the amount (reaction equivalent point) that reacts with the rare earth element excluding cerium in the carrier particles without excess or deficiency. . A noble metal solution was prepared by adding and dissolving rhodium nitrate in an amount such that the Rh metal equivalent amount was 0.5% by mass with respect to the carrier particles.

An aqueous solution containing 0.5 μmmol of lanthanum nitrate per 1 m ² of the surface area of the carrier particles was added to the carrier particle dispersion prepared in the same manner as in Comparative Example 1, and then mixed with the noble metal solution. Subsequent operations were performed in the same manner as in Comparative Example 1, and the catalyst of Example 1 was obtained.

[Examples 2 to 16 and Comparative Examples 2 and 3]
The types and amounts (times-eq) of acids shown in Table 5 were used instead of propionic acid, and the rare earth compounds of the types and amounts (μmol / m ² ) shown in Table 5 were used instead of lanthanum nitrate. In the same manner as in Example 1, an exhaust gas purification catalyst was prepared and evaluated. The evaluation results are shown in Table 5. The noble metal particle size shown in Table 5 is a relative value (%) based on the measured value of Comparative Example 1.

"Evaluation method"
The evaluation method was the same as in Experiment A above.

The catalysts of Examples 1 to 16 having a predetermined configuration of the present invention have a 50% NO _x purification temperature lower than that of Comparative Example 1 which is a typical example of the prior art, and are excellent in NO _x purification performance. Verified. Such a catalyst can be easily produced by the predetermined production method of the present invention using an organic carboxylic acid and a rare earth compound.

In Comparative Examples 2 and 3 in which a sulfonic acid compound or an inorganic acid is used instead of the organic carboxylic acid, the particle size of the rare earth oxide particles is small and no decrease in the 50% NO _x purification temperature is seen, but the increase. As a result. This is because the particle diameter of the particles is excessively small, so that the noble metal is also supported on the ceria zirconia support. _x It is considered that the purification performance was impaired.

[Comparative Examples 4 and 5 and Examples 17 and 18]
Aside from using Pt nitrate (Comparative Example 4 and Example 17) or Pd nitrate (Comparative Example 5 and Example 18) in place of nitrate Rh in an amount of 0.5% by mass with respect to the carrier particles, Comparative Examples 4 and 5 were prepared in the same manner as in Comparative Example 1, and Examples 17 and 18 were prepared and evaluated in the same manner as in Example 1 above. The evaluation results are shown in Table 6. The noble metal particle size of Example 17 shown in Table 6 is a relative value (%) based on the measurement value of Comparative Example 4, and the noble metal particle size of Example 18 is based on the measurement value of Comparative Example 5. Relative value (%).

  Even when Pt or Pd was used as the noble metal instead of Rh, it was verified that the catalysts of Examples 17 and 18 having the predetermined configuration of the present invention exhibited the desired effect.

[Reference Examples 20 to 27]
Exhaust gas purification catalyst was prepared and evaluated in the same manner as in Example 1 except that the amount of propionic acid used was changed to the amount shown in Table 7 (times-eq) and no lanthanum nitrate aqueous solution was used. did. The evaluation results are shown in Table 7 together with the results of Comparative Example 1. The noble metal particle size of the reference example shown in Table 7 is a relative value (%) based on the measured value of Comparative Example 1.

In the case of Reference Examples 21 to 25 in which the particle size of the rare earth oxide particles is more than 0.5 μm and not more than 5 μm, the 50% NO _x purification temperature is significant compared to Reference Example 20 which is a typical example of the prior art the low, to be excellent in _the NO _x purification performance was verified. Such a catalyst can be easily produced by a specific production method using an organic carboxylic acid.

DESCRIPTION OF SYMBOLS 1 1st support particle 1a Rare earth rich area 2 2nd support particle 3 Catalyst particle 10 Exhaust gas purification catalyst

Claims (14)

An exhaust gas purifying catalyst having first carrier particles, second carrier particles, and noble metal catalyst particles carried on the first and second carrier particles,
The first carrier particles contain at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania, and a rare earth oxide other than ceria,
The second support particles may contain a rare earth oxide other than ceria, and may contain at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania. The content rate of the metal oxide in the first support particles is higher than the content rate of the metal oxide in the second support particles,
The content rate of the rare earth oxide in the second carrier particles is higher than the content rate of the rare earth oxide in the first carrier particles, and energy dispersive X-ray using a field emission scanning electron microscope When the intensity of characteristic X-rays obtained by analysis is measured, the correlation coefficient calculated by the following formula is 85.0% or more:
(Here, the spectral intensity values of the noble metal element contained in the precious metal catalyst particles i and x _i, the spectral intensity average value of the noble metal element and x _av, the spectrum of a rare earth element other than cerium at the position of the precious metal catalyst particles i The intensity value is y _i and the spectral intensity average value of rare earth elements other than cerium is y _av ).   2. The content of the rare earth oxide in the first support particles is less than 20 wt%, and the content of the rare earth oxide in the second support particles is 20 wt% or more. Exhaust gas purification catalyst.   When the first carrier particles and the second carrier particles are observed with a field emission scanning electron microscope, the ratio of the projected area of the second carrier particles to the projected area of the first carrier particles 3. The exhaust gas purifying catalyst according to claim 2, wherein (the area of the second carrier particles / the area of the first carrier particles) is in a range of 0.050 or more and 0.200 or less. The metal oxide of the first support particles and the metal oxide of the second support particles, if present, are ceria zirconia solid solutions, and the rare earth oxide and the first support particles of the first support particles. 4. The rare earth oxide of the support particles of 2 is an oxide of a rare earth element selected from at least one selected from the group consisting of yttrium, lanthanum, praseodymium, neodymium and samarium. Exhaust gas purification catalyst. The first carrier particles contain 50 to 95% by weight of zirconia, 5.0 to 45% by weight of ceria, and 1.0 or more and less than 20% by weight of a rare earth oxide other than ceria, and the second 5. The carrier particles of claim 4 containing 0.0 to 40 wt% zirconia, 0.0 to 40 wt% ceria, and 20 to 60 wt% rare earth oxides other than ceria. Exhaust gas purification catalyst.   The average particle diameters of the first carrier particles and the second carrier particles measured by a field emission scanning electron microscope are 0.50 to 100 μm and 0.50 to 5 μm, respectively. The exhaust gas-purifying catalyst according to any one of the above.   The exhaust gas purifying catalyst according to any one of claims 1 to 6, wherein the noble metal catalyst particles include platinum particles, palladium particles, rhodium particles, or a combination thereof.   The exhaust gas-purifying catalyst according to any one of claims 1 to 7, wherein the correlation coefficient is 87.0% or more.   An exhaust gas purification apparatus comprising the base material on which the exhaust gas purification catalyst according to any one of claims 1 to 8 and a catalyst layer including the exhaust gas purification catalyst are formed.   An exhaust gas purification apparatus comprising the exhaust gas purification catalyst according to any one of claims 1 to 8 and a base material including the catalyst. A method for producing an exhaust gas purifying catalyst comprising:
Carrier particles containing at least one metal oxide selected from the group consisting of silica, alumina, ceria, zirconia, and titania and a rare earth oxide other than ceria; from yttrium, neodymium, lanthanum, and praseodymium A salt of a rare earth element selected from one or more kinds; a salt of a catalyst noble metal; and an organic carboxylic acid are mixed in an aqueous dispersion to carry the catalyst noble metal on the carrier particles, thereby forming an unfired exhaust gas purification catalyst. Obtaining an aqueous dispersion comprising:
A step of drying and calcining the aqueous dispersion containing the unfired exhaust gas-purifying catalyst;   The metal oxide of the support particles is a ceria zirconia solid solution; the rare earth oxide of the support particles is selected from at least one selected from the group consisting of yttrium, lanthanum, praseodymium, neodymium, and samarium. The method of claim 11, wherein the rare earth element salt is a nitrate or sulfate; and the catalyst noble metal salt is a nitrate or sulfate of platinum, palladium, rhodium, or a combination thereof.   The method according to claim 11 or 12, wherein the organic carboxylic acid is an organic carboxylic acid having a molecular weight of 300 or less.   The amount ratio [mol / mol-Ln] of the organic carboxylic acid to the total amount of rare earth elements contained in the carrier particles is 0.5 or more and 3.5 or less. The method according to any one of the above.